BIOL06Y
LIBRARY
-.-
POLAEISCOPE ()J5JK( IS.
158
TuffenWeci.del
Pi M K VITI.
Edmund Kvans.
THE
MICROSCOPE:
ITS
HISTORY, CONSTRUCTION, AND APPLICATION:
A FAMILIAR INTRODUCTION TO THE USE OF THE INSTRU-
MENT, AND THE STUDY OF MICROSCOPICAL SCIENCE.
BY JABEZ HOGG, M.R.C.S., F.R.M.S,
V
CONSULTING SURGEON TO THE ROYAL WESTMINSTER OPHTHALMIC HOSPITAL ;
LATE PRESIDENT OF THE MEDICAL MICROSCOPICAL SOCIETY; LL.D. ;
HONORARY FELLOW OF THE ACADEMY OF SCIENCES, PHILADELPHIA ; OF
THE MEDICO-LEGAL SOCIETY, NEW YORK J OF THE BELGIAN MICRO-
SCOPICAL SOCIETY, ETC. J AUTHOR OF " ELEMENTS OF NATURAL PHILO-
SOPHY," "A MANUAL OF OPHTHALMOSCOPIC SURGERY," ETC.
WITH UPWARDS OF FIVE HUNDRED ENGRAVINGS, AND
COLOURED ILLUSTRATIONS BY TUFFEN WEST.
Cbifion,
LONDON:
GEORGE ROUTLEDGE AND SONS,
BROADWAY, LUDGATE HILL.
NEW YORK: 9, LAFAYETTE PLACE.
1886.
BIOLOGY
LIBRARY
PKEFACE TO THE TENTH EDITION.
WENTY- EIGHT TEARS have passed
away since the first edition of this book
on the microscope was published. It was
hailed as the pioneer of a more useful
form of literature than had heretofore
appeared on the history, construction and appli-
cation of the instrument. In this period of time,
nine large editions, exceeding in the aggregate 60,000
copies, have been sold out, and yet another edition is
called for a proof, if it were wanting, that the book
has not only maintained its ground, but its popularity.
In issuing a tenth edition, the Author, by a careful
revision of the text, and by an addition of no fewer
than fifty new woodcuts, trusts that his book has been
made more acceptable and useful to those for whom
it was originally intended. Part I. has been almost
wholly rewritten and rearranged. To Mr. Frank
Crisp the Author is indebted for Professor Abbe's
theory of microscopic vision. To the processes of
hardening, section-cutting and staining much in vogue>
and which have created a new era in physiological
studies, have been assigned the space they seem to
merit. Part II. has been carefully revised ; a chapter
added on the application of the microscope to minera-
logical and spectroscopical analysis, and the examina-
tion of potable water. That his book may for some
years to come be found a familiar introduction to the
use of the microscope, and the study of microscopical
science, is the earnest wish of the Author.
1, BEDFORD SQUARE, June, 1882.
PREFACE TO THE EIGHTH EDITION.
issuing the Eighth Edition of this Work
on the MICROSCOPE, I may say that it has
been thoroughly revised and for the most
part rewritten. Eight carefully and
beautifully executed Plates are added,
which were drawn by Mr. Tuffen West from
natural objects, engraved and printed by Mr.
Edmund Evans in his usual excellent manner.
The Author cannot but express his grateful surprise
at the extraordinary popular reception which his book
has met with : a sale of fifty thousand is an unpre-
cedented event for a work of the kind. This circum-
stance is extremely gratifying to him, because it affords
reasonable grounds for believing that his work has
been useful, and encourages renewed effort to make
the volume still more acceptable. It has been his
endeavour to bring the information contained in its
pages up to the most Decent discoveries ; although, in
a daily progressing field of science, it is almost im-
possible to keep pace with the advance of knowledge
in all its ramifications.
1, BEDFORD SQUARE,
October, 1867.
PREFACE TO THE WEST EDITION.
HE Author of this Publication entered upon
his task with some hesitation and diffidence ;
but the reasons which influenced him to
undertake it may be briefly told, and they
at once explain his motives, and plead his
justification, for the work which he now
ventures to submit to the indulgent con-
sideration of his readers.
It had been to him for some time a sub-
ject of regret, that one of the most useful
and fascinating studies that which belongs to the do-
main of microscopic observation should be, if not wholly
neglected, at best but coldly and indifferently appreciated
by the great mass of the general public ; and he formed
a strong opinion, that this apathy and inattention were
mainly attributable to the want of some concise, yet suffi-
ciently comprehensive, popular account of the Microscope,
both as regards the management and manipulation of the
instrument, and the varied wonders and hidden realms of
beauty that are disclosed and developed by its aid. He
saw around him valuable, erudite, and splendid volumes ,
which, however, being chiefly designed for circulation
unongst a special class of readers, were necessarily pub
Vlll PREFACE.
lished at a price that renders them practically unattainable
by the great bulk of the public. They are careful and
beautiful contributions to the objects of science, but they
cannot adequately bring the value and charm of micro-
scopic studies home, so to speak, to the firesides of the
people. Day after day, new and interesting discoveries,
and amplifications of truth already discerned, have been
made, but they have been either sacrificed in serials, or,
more usually, devoted to the pages of class publications ;
and thus this most important and attractive study has
been, in a great measure, the province of the few only,
who have derived from i\ a rich store of enlightenment
and gratification : the many not having, however, parti-
cipated, to any great extent, in the instruction and enter-
tainment which always follow in the train of microscopical
studies. 1
The manifold uses and advantages of the Microscope
crowd upon us in such profusion, that we can only attempt
to enumerate them in the briefest and most rapid manner
in these prefatory pages.
It is not many years since this invaluable instrument
was regarded in the light of a costly toy ; it is now the
inseparable companion of the man of science. In the
medical world, its utility and necessity are fully appre-
ciated, even by those who formerly were slow to perceive
its benefits ; now, knowledge which could not be obtained
even by the minutest dissection is acquired readily by itv
assistance, which has become as essential to the anatomist
and pathologist as are the scalpel and bedside observation.
The smallest portion of a diseased structure, placed under
a Microscope, will tell more in one minute to the ex-
perienced eye, than could be ascertained by long examina-
(1) At the time this work was written, scarcely a book of the kind had beer
published at a price within t>e reach of the working classes
PREFACE. iA
tion of the mass of disease in the ordinary method.
Microscopic agency, in thus assisting the medical man,
contributes much to the alleviation of those multiplied
" ills which flesh is heir to." So fully impressed were the
Council of the Eoyal College of Surgeons with the import-
ance of the facts brought to light in a short space of time,
that, in 1841, they determined to establish a Professorship
of Histology, and to form a collection of preparations of
the elementary tissues of both animals and vegetables,
healthy and morbid, which should illustrate the value of
microscopical investigations in physiology and medical
science. From that time, histological anatomy deservedly
became an important branch of the education of the
medical student.
In the study of Vegetable Physiology, the Microscope
is an indispensable instrument ; it enables the student to
trace the earliest forms of vegetable life, and the functions
of the different tissues and vessels in plants. Valuable
assistance is derived from its agency in the detection of
adulterations. In the examination of flour, an article of
so much importance to all, the Microscope enables us
to judge of the size and shape of the starch-grains, ther
markings, their isolation and agglomeration, and thus to
distinguish the starch-grains of one meal from those of
another. It detects these and other ingredients, invisible
to the naked eye, whether precipitated in atoms or aggre-
gated in crystals, which adulterate our food, our drink,
and our medicines. It discloses the lurking poison in
the minute crystallisations which its solutions precipitate.
" It tells the murderer that the blood which stains him is
that of his brother, and not of the other life which he
pretends to have taken ; and as a witness against the
criminal, it on one occasion appealed to the very sand on
which he trod at midnight."
JU1 PREFACE.
acknowledgments are likewise due to Mr. George Pearson,
for the great care lie has bestowed upon the engravings
which illustrate these pages.
Finally, it is the Author's hope that, "by the instru-
mentality of this volume, he may possibly assist in bring-
ing the Microscope, and its most valuable and delightful
studies, before the general public in a more familiar, com-
pendious, and economical form than has hitherto been
attempted ; and that he may thus, in these days of a
diffused taste for reading and the spread of cheap pub-
lications, supply further exercise for the intellectual
faculties, contribute to the additional amusement and
instruction of the family circle, and aid the student of
nature in investigating the wonderful and exquisite works
of the Almighty. If it shall be the good fortune rf this
work, which is now confided with great diffidence to the
consideration of the public, to succeed in however slight a
degree, in furthering this design, the Author will feel
sincerely happy, and will be fully repaid for the attention,
fcime, and labour that he has expended.
I<ONix)N, May, 1854.
PART I.
HISTORY OF THE INVENTION AND IMPROVE-
MENTS OF THE MICROSCOPE.
CHAPTER I.
HISTORY OF THE INVENTION AND IMPROVEMENTS MADE IN THH
MICROSCOPE
PAGE
1
CHAPTER II.
FORMATION OP IMAGES BY THE ORGAN OF VISION THEORY OF
MICROSCOPICAL VISION, CHROMATIC AND SPHERICAL ABERRA-
TION OF LENSES MECHANICAL AND OPTICAL PRINCIPLES
INVOLVED IN THE CONSTRUCTION OF THE MICROSCOPE LENSES
MODE OF ESTIMATING THEIR PC WER ACHROMATIC LENSES
MAGNIFYING POWER WOLLASTON's DOUBLET CODDINGTON*S
LENS SIMPLE AKD COMPOUND MICROSCOPES ROSS'S, POWELL
AND LEALAND'S, BECK'S, BAKER'S, PILLISCHER'S, LADD'S,
MURRAY'S, COLLINS'S, BROWNING'S, WATSON'S, SWIFT'S, HOW'S
MECHANICAL AND SWING STAGE EYE-PIECESOBJECTIVES
MODE OF CORRECTING APERTURE OF IMMERSION, ETC.
MICROMETERS POLARISED LIGHT CAMERA LUCIDA BINO-
CULAR PHOTOGRAPHIC-DRAWING MICROSPECTROSCOPY .
16
162
PAET n.
CHAPTKJL L
n.
CHAIYKR DL
511
O05TE5T3.
CHAPTER I
651
CHAPTER VL
APPENDIX.
. 74S
KX DESCRIPTION OP COLOURED PLATES.
of the external hairs 144. Egg of Bot-Fly ; the larva just escaping 145.
Egg of parasite of Pheasant 146. Egg of Scatophaga 147. Egg of parasite
of magpie 148. Egg of Jodisvernaria (Small Emerald Butterfly).
PLATE VII. Page 654.
V E R T E B R A T A.
Fig. 149. Toe of mouse, integuments, bone of foot, and vessels 150. Tongue of
mouse, showing erectile papillae,, muscular layer, &c. 151. Brain of rat,
showing its vascular supply 152. Tongue of cat, showing fungi-form papilla;,
with capillary loops passing into them, vessels, <fcc.; perpendicular section
153. Kidney of cat, showing Malpighian turfts and arteries 154. Small
intestine of rat, showing villi and layer of mucous membrane 155. Nose of
mouse, showing vascular supply to roots of whiskers 156. Vascular supply
to internal gill of tadpole, during one phase of its development 157. Sec-
tion through sclerotic and retina of eat's-eye, allowing vascular supply ot
choroid and other coats 158. Interior of a fully-developed tadpole, exhibiting
heart, vascular arrangement and vascular system throughout, after Whitney.
This plate is designed to show the value of injected preparations
in the delineation of animal structures. By thus artificially re-
storing the blood and distending the tissue, a much better idea is
obtained of the relative condition of parts during life, while we
receive much assistance in the elucidation of complicated and deli-
cate membranes, the appearance of erectile tissues, papillae, &c.
PLATE VIII. To face Title.
POLARISCOPE OBJECTS.
Fig. 158. New Red Sandstone 159. Quartz 160. Granite 161. Sulph. Copper
162. Saliginine 163. Sulph. Iron and Cobalt, crystallized in the way
described by Thomas 164. Borax 165. Sulph. Nickel and Potash 166.
Kreatine 167. Starch granules 168. Aspartic Acid 169. Fibro-Cells,
Orchid. 170. Equisetum cuticle 171. Spicula Holothuria, Australia 172.
Spicula, Holothuria, Port Essington 173. Deutzia Scabra ; upper and under
surface 174. Cat's tongue, process 175. Prawn shell, exuvia with crystals
of lime 176. Grayling scale 177. Scyllium caniculum scale 178. Rhi-
noceros horn, transverse section 179. Horse hoof 180. Dytiscus, elytra
with crystals of lime.
This plate is especially intended to illustrate the beautiful and
gorgeous spectacle produced by polarised light on the various objects
here grouped together. It will be seen that structures belonging
either to the animal, vegetable, or mineral kingdoms in which the
power of unequal or double refraction is suspected to be present, may
be submitted to this mode of micro-chemical investigation with advan-
tage.
PLATE IX. Woodcut. Page 498.
ASTEROIDEA ECHINIDyE CRUSTACEA, &c.
Grouped to show the animal and vegetable life of an ordinary
window salt-water aquarium.
THE MICROSCOPE.
PAKT I.
HISrORY OF THE INVENTION AND IMPROVEMENTS OF
THE MICROSCOPE.
CHAPTER I.
HISTORY OF THE MICROSCOPE.
HE instrument known as the Mi-
croscope derives its name from
two Greek words, /xtKpos, small,
and O-KOTTCW, to view; that is, to
see or view such minute objects
as without its aid would be in-
visible.
The honour of the invention
is claimed by the Italians and the
Dutch; the name of the inventor,
however, is lost. Probably the
discovery did not at first appear
sufficiently important to engage
the attention of those men who,
by their reputation in science, were able to establish an
opinion of its merit, and to hand down the name of itr
inventor to succeeding ages.
If we consider the microscope as an instrument con-
sisting of one lens only, it is not at all improbable that it
was known at a very early peri ad, nay even in a degree to
B
2 HISTORY OP THE MICROSCOPE.
the Greeks and Romans ; at any rate, it is tolerably certain
that spectacles were used as early as the thirteenth century.
Now as the glasses of these were made of different con-
vexities, and consequently of different magnifying powers,
it is natural to suppose that smaller and more convex
lenses were made, and applied to the examination of
minute objects. Many among the learned refuse to the
ancients a knowledge of magnifying lenses, and & fortiori
that of refracting telescopes, since, according to them, the
Greeks and Romans had only very imperfect notions with
respect to the fabrication of glass.
From a passage in Aristophanes it is plain that globules
of glass were sold at the shops of the grocers of Athens, in
the time of that comic author. He speaks of them as
" burning spheres."
Pliny states that the immense theatre (it was capable of
containing eighty thousand persons) erected at Rome by
Scaurus, son-in-law of Sylla, was three stories in height,
and that the second of these stories was entirely inlaid
with a mosaic of glass.
Ptolemy, in his " Optics," has inserted a table of the
refractions which light experiences under different angles
of incidence, in passing from air into glass. The values
of these angles, which differ only in a slight degree from
those obtained in the present day by means of similar ex-
periments, prove that the glass of the ancients differed
very little from that manufactured in our own times.
There is in the French Cabinet of Medals a seal, said to
have belonged to Michael Angelo, the fabrication of which,
it is believed, ascends to a very remote epoch, and upon
which fifteen figures have been engraven in a circular
space of fourteen millimetres in diameter. These figures
are not all visible to the naked eye.
Cicero makes mention of an Iliad of Homer written
upon parchment, which was comprised in a nutshell.
Pliny relates that Myrmecides, a Milesian, executed irj
ivory a square figure which a fly covered with its wings.
Unless it be maintained that the powers of vision of our
ancestors surpassed those of the most skilful modern
artists, these facts establish that the magnifying property
of lenses was known to the Greeks and Romans nearly
HISTORY OP THE MICROSCOPE. 3
two thousand years ago. We may besides advance a step
surther, and borrow from Seneca a passage whence the
same truth will emerge in a manner still more direct and
decisive. In the " Natural Questions " we read : " How-
ever small and obscure the writing may be, it appears
larger and clearer when viewed through a globule of glass
filled with water."
Dutens has seen in the Museum of Portici ancient
lenses which had a focal length of only nine millimetres.
He actually possessed one of these lenses, but of a longer
focus, which was extracted from the ruins of Hercu-
laneum.
At the meeting of the British Association, held at
Belfast in the year 1852, Sir David Brewster showed a
plate of rock-crystal worked into the form of a lens, which
was recently found among the ruins of Nineveh. Sir
David Brewster, so competent a judge in a question of this
kind, maintained that this lens had been destined for
optical purposes, and that it never was an article of dress.
It is not difficult to fix the period when the microscope
first began to be generally known, and to be used for the
purpose of examining minute objects ; for though we are
ignorant of the name of the first inventor, we are acquainted
with the names of those who introduced it to public view.
Zacharias Jansens and his son are said to have made micro-
scopes before the year 1590 : about that time the ingenious
Cornelius Drebell brought one made by them with him
to England, and showed it to William Borrell and others.
It is possible this instrument of Drebell's was not strictly
what is now called a microscope, but was rather a kind
of microscopic telescope, something similar in principle
to that lately described by M. Aepinus in a letter to the
Academy of Sciences at St. Petersburg. It was formed of
a copper tube six feet long and one inch in diameter,
supported by three brass pillars in the shape of dolphins ;
these were fixed to a base of ebony, on which the objects
to be viewed by the microscope were placed. Fontana, in j
a work which he published inl646,says that he had made
microscopes in the year 1618 : this may be perfectly true,
without derogating from the merit of the Jansens; for
we have many instanced in our own times of more than
B 2
4 HISTORY OP THE MICROSCOPE.
one person having made the same invention nearly simul-
taneously, -without any communication from one to the
other. In 1685 Stelluti published a description of the
parts of a bee, which he had examined with a microscope.
The history of the microscope, like that of nations and
arts, has had its brilliant periods, in which it shone with
uncommon splendour, and was cultivated with extraordi-
nary ardour ; and these have been succeeded by intervals
marked with no discovery, and in which the science seemed
to fade away, or at least to lie dormant, till some favour-
able circumstance the discovery of a new object, or some
new improvement in the instruments of observation
awakened the attention of the curious, and reanimated
their researches. Thus, soon after the invention of the
microscope, the field it presented to observation was culti-
vated by men of the first rank in science, who enriched
almost every branch of natural history by the discoveries
they made by means of this instrument.
The Single, or Simple Microscope. We shall first speak of
the single microscope, that having been invented and used
long before the double or compound microscope. When
the lenses of the single microscope are very convex, and
consequently the magnifying power great, the field of view
is small ; and it is so difficult to adjust with accuracy their
focal distance, that it requires some practice to render the
use of them familiar. It was with an instrument of this
kind that Leeuwenhoek and Swammerdam, Lyonet and
Ellis, examined the invisible forms of nature, and by their
example stimulated others to the same pursuit.
About the year 1665, small glass globules began to be
occasionally applied to the single microscope, instead of
convex lenses ; and by these globules an immense magni-
fying power was obtained. Their invention has been
generally attributed to M. Hartsoeker ; though it appears
that we are really indebted to the celebrated Dr. Hooke
for this discovery, for he described the manner of making
them in the preface to his Micrographia Illustrata, pub-
lished in the year 1656.
Mr. Stephen Gray 1 having observed some irregular
particles within a glass globule, and finding that they
(1) Philosophical Transactions, 1696.
HISTORY OP THE MICROSCOPE. 5
appeared distinct and prodigiously magnified when held
close to his eye, concluded, that if he placed a globule of
water in which there were any particles more opaque than
the water near his eye, he should see those particles dis-
tinctly and highly magnified. The result of this idea far
exceeded his expectation. His method was, to take on a
pin a small portion of water which he knew contained
gome minute animalcules j this he laid on the end of a
email piece of brass wire, till there was formed somewhat
more than a hemisphere of water ; on applying it then to
the eye, he found the animalcules enormously magnified ;
for those which were scarcely discernible with his glasw
globules, with this appeared as large as ordinary-sized
peas.
Dr. Hooke thus describes the method of using this
water-microscope : " If you are desirous," he says, " of
obtaining a microscope with one single refraction, and
consequently capable of procuring the greatest clearness
and brightness any one kind of microscope is susceptible
of, spread a little of the fluid you intend to examine on
a glass plate ; bring this under one of your globules, then
move it gently upwards till the fluid touches the globule,
to which it will soon adhere, and that so firmly as to bear
being moved a little backwards or forwards. By looking
through the globule, you will then have a perfect view of
the animalcules in the drop."
The construction of the single microscope is so simple,
that it is susceptible of but little improvement, and has
therefore undergone few alterations ; and these have been
chiefly confined to the mode of mounting it, or to addi-
tions to its apparatus. The greatest improvement this
instrument has received was made by Lieberkuhn, 1 about
the year 1740 : it consists in placing the small lens in the
centre of a highly-polished concave speculum of silver, by
which means a strong light is reflected upon the upper
surface of an object, which is thus examined with great
ease and pleasure. Before this contrivance, it was almost
impossible to examine small opaque objects with any
degree of exactness ; for the dark side of the object being
next the eye, and also overshadowed by the proximity of
(1) Dr. Nathaniel Lieberkuhn of Berlin.
6
HISTORY OP THE MICROSCOPE.
the instrument, ite appearance was necessarily obscure and
indistinct. Lieberkuhn adapted a separate microscope to
every object : but all this labour was
not bestowed on trifling objects ; his
were generally the most curious ana-
tomical preparations, twelve of which,
with their microscopes, are deposited in
the Museum of the Royal College of
Surgeons.
Lieberkuhn's instrument, fig. 1, is
thus described by Professor Quekett i 1 a b
represents a piece of brass tube, about an
inch long and an inch in diameter, which
is provided with a cap at each extremity ;
the one at a carries a small double -convex
lens of half an inch in focal length, whilst
the one at b carries a condensing lens three-
quarters of an inch in diameter.
A vertical section of one of these instru-
ments is seen in fig. 2 : a represents the mag-
nifier, which is lodged in a cavity formed
partly by the cap a, and by the silver cup
or speculum I. In front of the lens is the
speculum I, which is a quarter of an inch
thick at its edge, and whose focus is about
half an inch ; in front of this again there is
a disk of metal c, three-eighths of an inch in
diameter, connected by a wire with the small
F 'g- h knob d j upon this disk the injected object
is fastened, and is covered over with some
kind of varnish which has dried of a hemispherical figure.
Between this knob and the inside and
outside of the tube there are two slips of
thin brass, which act as springs to keep
the wire and disk steady. When the
knob is moved, the injected object is
carried to or from the lens, so as to be in
its focus, and to be seen distinctly, whilst
the condensing lens b serves to concen-
trate the light on the speculum. To the
Fig. 2.
IMerkuhn't Micro-
fCOft.
(1) Practical Treatise ou the Microscope, p. 16.
HISTORY OP THE MICROSCOPE. 7
lower part of the tube a handle of ebony, about three
inches in length, is attached by a brass ferrule and two
Bcrews. The use of this instrument is obvious : it la
held in the hand in such a position that the rays of light
from a lamp or white cloud may fall on the condenser b,
by which they are concentrated on the speculum I ; this,
again, further condenses them on the object and the
disk c, which object, when so illuminated, can readily be
adjusted by the little knob d, so as to be in the focus of
the small magnifier at a.
We must not omit in this place some account of Leeu-
wenhoek's microscopes, which were rendered famous
throughout all Europe, on account of the numerous dis-
coveries he had made with them. At his death he be-
queathed a part of them to the Royal Society.
The microscopes he used were all single, and fitted up in
a convenient and simple manner : each consisted of a very
small double- convex lens, let into a socket between two
plates riveted together, and pierced with a small hole ; the
object was placed on a silver point or needle, which, by
means of screws adapted for that purpose, might be turned
about, raised or depressed at pleasure, and thus be brought
nearer to, or be removed farther from the glass, as the eye
of the observer, the nature of the object, and the conve-
nient examination of its parts required.
Leeuwenhoek fixed his objects, if they were solid, to these
points with glue ; if they were fluid, he fitted them on a
little plate of talc, or thin-blown glass, which he afterwards
glued to the needle in the same manner as his other
objects. The glasses were all exceedingly clear, and of
different magnifying powers, proportioned to the nature of
the object and the parts designed to be examined. He
observed, in his letter to the Royal Society, that " from
upwards of forty years' experience, he had found the most
considerable discoveries were to be made with glasses of
moderate magnifying power, which exhibited the object
with the most perfect brightness and distinctness." Each
instrument was devoted to one or two objects ; hence he
had always some hundreds by him.
The three first compound microscopes that attract our
notice are those of Dr. Hooke, Eustachio Divini, and Philip
8 HISTORY OP THE MICROSCOPE.
Bonnani. Dr. Hooke gives us an account of his in the
preface to his Micrographia, published in the year 1667 :
it was about three inches in diameter, seven inches long,
and furnished with four draw-out tubes, by which it might
be lengthened as occasion required ; it had three glasses
a small object-glass, a middle glass, and a deep eye-glass.
Dr. Hooke used all the glasses when he wanted to take in
a considerable part of an object at once, as by the middle
glass a number of radiating pencils were conveyed to the
eye which would otherwise have been lost ; but when he
wanted to examine with accuracy the small parts of any
substance, he took out the middle glass, and only made
use of the eye and object lenses ; " for," he writes, lt the
fewer the refractions are, the clearer and brighter the
object appears."
Dr. Hooke also gave us the first and most simple method
of finding how much any compound microscope magnifies
an object. He placed an accurate scale, divided into very
minute parts of an inch, on the stage of the microscope ;
adjusted the microscope till the divisions appeared distinct,
and then observed with the other eye how many divisions
of a rule similarly divided and laid on the stage were
included in one of the magnified divisions ; " for if one
division, as seen with one eye through the microscope,
extends to thirty divisions on the rule, which is seen by
the naked eye, it is evident that the diameter of the object
is increased or magnified thirty times."
An account of Eustachio Divini's microscope was read
at the Royal Society in 1668. It consisted of an object-
lens, a middle glass, and two eye-glasses, which were plano-
convex lenses, and were placed so that they touched each
other in the centre of their convex surfaces. The tube in
which the glasses were enclosed was as large as a man's
leg, and the eye-glasses as broad as the palm of the hand.
It had four several lengths : when shut up was 1 6 inches
long, and magnified the diameter of an object 41 times,
at the second length 90, at the third length 111, and at
the fourth length 143 times. It does not appear that
Divini varied the object-glasses.
Philip Bonnani published an account of his two micro-
scopes in 1698. Both were compound. The first was
HISTORY OF THE MICROSCOPE. 9
similar to that which Mr. Martin published as new, in his
Micrographia Nova, in 1712. His second was like the
former, composed of three glasses, one for the eye, a
/niddle glass, and an object lens; they were mounted in a
cylindrical tube, which was placed in a horizontal position;
behind the stage was a small tube with a convex lens at
each end ; beyond this was a lamp ; the whole capable of
various adjustments, and regulated by a pinion and rack.
The small tube was used to condense the light on to the
object.
A short time before this, Sir Isaac Newton having dis-
covered his celebrated theory of light and colours, was led
to improve the telescope, and apply his principles most
successfully to the construction of a compound reflecting
microscope. On the 6th of February, 1672, he communi-
cated to the Royal Society his " design of a microscope by
reflection." It consisted of a concave spherical speculum
of metal, and an eye-glass which magnified the reflected
image of any object placed between them in the conjugate
focus of the speculum. He also pointed out the proper
mode of illuminating objects by artificial light, as he
describes it, "of any convenient colour not too much
compounded," mtmo-chromatic. We find other two plans
of this kind; the first that of Dr. Robert Barker, and the
second that of Dr. Smith. In the latter there were two
reflecting mirrors, one concave, and the other convex : the
image was viewed by a lens. This microscope, though far
from being executed in the best manner, performed, says
Dr. Smith, very well, so that he did not doubt it would
have excelled others, had it been properly finished.
In 1738, Lieberkuhn's invention of the solar microscope
was communicated to the public. The vast magnifying
power obtained by this instrument, the colossal grandeur
with which it exhibited the " minutiae of nature," the plea-
sure which arose from being able to display the same object
to a number of observers at the same time, by affording a
new source of rational amusement, increased the number
of microscopic observers, who were further stimulated to
the same pursuits by Mr. Trembley's famous discovery of
the polype. The discovery of the wonderful properties of
this little animal, together with the works of Mr. Trembley ;
10 HISTORY OF THE MICROSCOPE.
Mr. Baker, and Mr. Adams, combined to spread the repu-
tation of the instrument.
In 1742, Mr. Henry Baker, F.B.S., published an ad-
mirable treatise on the microscope. He also read several
papers before the Royal Society on the subject of his
microscopic discoveries. In the wood-cut (fig. 3) at the
end of this chapter we have represented an elegant scroll
" pocket microscope with a speculum/' described by him
as a new invention.
In 1770, Dr. Hill published a treatise, in which he
endeavours by means of the microscope to explain the
construction of timber, and to show the number, the
nature, and office of its several parts, their various
arrangements and proportions in the different kinds ; and
he points out a way of judging, from the structure of
trees, the uses they will best serve in the affairs of life.
M. L. F. Delabarre published an account of his micro-
scope in 1777. It does not appear that it was superior in
any respect to those that were then made in England. It
was inferior to some; for those made by Mr. Adams, in
1771, possessed all the advantages of Delabanre's in a
higher degree, except that of changing the eye-glasses.
In 1774, Mr. George Adams, the son of the above, im-
proved his father's invention, and rendered it useful fpr
viewing opaque as well as transparent objects. This in-
strument, made and described by him, 1 continued in use
up to the time of the invention of the achromatic im-
provement, proposed and made in 1815 for Amici, who
subsequently gave so much time to the investigation of
polarised light, and the adaptation of a polarising apparatus
to the microscope.
In 1812, Dr. Wollaston proposed a doublet in which
the glasses were in contact, under the name of a " Periscopic
Microscope." And he says, "with this doublet I have
seen the finest striae and serratures on the scales of the
lepisma and podura, and the scales on a gnat's wing."
In the year 1816, Frauenhofer, a celebrated optician of
Munich, constructed object-glasses for the microscope of a
single achromatic lens, in which the two glasses, although
in juxtaposition, were not cemented together : these glasses
(1) Microscopical Essays, 1787.
HISTORY OP THE MICROSCOPE. 11
were very thick, and of long focus. Although such con-
siderable improvements had taken place in the making of
achromatic object-glasses since their first discovery by
Euler in 1776, we find, even at so late a period as 1821,
M. Biot writing, "that opticians regarded as impossible
the construction of a good achromatic microscope." Dr.
Wollaston also was of the same opinion, " that the com
pound instrument would never rival the single."
In 1823, experiments were commenced in France by
M. Selligues, which were followed up by Frauenhofer in
Munich, by Amici in Modena, by M. Chevalier in Paris,
and by the late Dr. Goring and Mr. Tulley in London. To
M. Selligues we are indebted for the first plan of making
an object-glass composed of four achromatic compound
lenses, each consisting of two lenses. The focal length of
each object-glass was eighteen lines, its diameter six lines,
and its thickness in the centre six lines, tlie aperture only
one line. They could be used combined or separated.
A microscope constructed on this principle, by M. Che--
valier, was presented by M. Selligues to the Academic des
Sciences on the 5th of April, 1824. In the same year, and
without a knowledge of what had been done on the Con-
tinent, the late MrJTulley, at the suggestion of Dr. Goring,
constructed an achromatic object-glass for a compound \
microscope of nine-tenths .of an inch focal length, com-
posed of three lenses, and transmitting a pencil of
eighteen degrees ; this was the first that had been made in
England.
Sir David Brewster first pointed out in 1813, the value \)
of precious stones, the diamond, ruby, garnet, &c., for the
construction of microscopes. " The durability," he says,
" of lenses made of precious stones is one of their greatest
recommendations. Lenses of glass undergo decomposition,
and lose their polish in course of time. Mr. Baker found
the glass lenses of Leeuwenhoek utterly useless after they
became the property of the Koyal Society. The glass
articles found in Nimroud were decomposed, while the
rock crystal lens was uninjured." Mr. Pritchard at one
time made two plano-convex lenses from a very perfect
diamond, one the twentieth of an inch focus, which was
12 HISTORY OF THE MICROSCOPE.
purchased by the late Duke of Buckingham, and another
the thirtieth of an inch focus.
In March 18:25, M. Chevalier presented to the Society
for the Encouragement of the Sciences, an achromatic
lens of four lines focus, two lines in diameter, and one line
in thickness in the centre. This lens was greatly superior
to the one before noticed, which had been made by him
for M. Selligues.
In 1826, Professor Amici, of Modena, who from the
year 1815 to 1824 had abandoned his experiments on the
achromatic object-glass, was induced, after the report of
Fresnel to the Academy of Science, to resume them ; and
in 1827 he brought to this country and to Paris a hori-
zontal microscope, in which the object-glass was composed
of three lenses superposed, each having a focus of six lines
and a large aperture. This microscope had also extra eye-
pieces, by which the magnifying power could be increased.
A microscope constructed on Amici's plan by Chevalier,
during the stay of that physician in Paris, was exhibited
at the Louvre, and a silver medal was awarded to ita
maker. 1
" While these practical investigations were in progress,"
Bays Mr. Ross, "the subject of achromatism engaged the
attention of some of the most profound mathematicians in
England. Sir John Herschel, Professors Airy and Barlow,
Mr. Coddington, and others, contributed largely to tba
theoretical examination of the subject; and though the
results of their labours were not immediately applicable
to the microscope, they essentially promoted its im-
provement."
Mr. Jackson Lister, in 1829, succeeded in forming a
combination of lenses upon the theory propounded by
these gentlemen, and effected one of the greatest improve-
ments in the manufacture of object-glasses, by joining
together a plano-concave flint lens and a convex, by means
of a transparent cement, Canada balsam. This is desirable
(I) In 1855, when the Jury on Microscopes at the Paris Exposition were com-
paring the rival instruments, Professor Amici brought a compound achromatic
microscope, comparatively of small dimensions, which exhibited certain striae
in test objects better than any of the instruments under examination. This
superiority was produced by the introduction of a drop of water between the
object and the object-glass.
HISTORY OP THE MICEOSCOPE. 13
to be taken as a basis for the microscopic object-glass ; it
diminishes very nearly half the loss of light from reflec-
tion, which is considerable at the numerous surfaces of
a combination; the clearness of the field and brightness
of the picture is evidently increased by doing this; and
it prevents any dewiness or vegetation from forming
on the inner surfaces. Since this time, Mr. Ross has
been constantly employed in bringing the manufacture
of object-glasses to their greatest perfection, and at
length they have attained to their present improved
manufacture. Having applied Mr. Lister's principles
with a degree of success never anticipated, so perfect
were the corrections given to the achromatic object-
glass, so completely were the errors of sphericity and
dispersion balanced or destroyed, that the circumstance
of covering the object with a plate of the thinnest glass
or talc disturbed the corrections, if they had been
adapted to an uncovered object, and rendered an object-
glass which was perfect under one condition sensibly
defective under the other. Here was another and
unexpected difficulty to be overcome, but which was
finally accomplished ; for in a communication made to
the Society of Arts in 1837, Mr. Ross stated, that by
separating the anterior lens in the combination from
the other two, he had been completely successful. The
construction of this object-glass will be illustrated and
explained in a subsequent chapter.
The rapid improvement of the achromatic micro-
scope was greatly furthered by the spirit of liberality
evinced by the late Sir David Brewster, Dr. Goring,
Messrs. R. H. Solly, Bowerbank, and Wenham. To
Dr. Goring we are indebted for the first triplet achro-
matic object-glass, for the diamond lens, and for the ^
improved reflecting instrument of Amici by Cuthbert.
The instruments manufactured by the leading
London makers, Messrs. Ross, Powell and Lealand, and
Smith and Beck, are unsurpassed in any part of the
world.
American opticians have shown themselves quite
equal to their brethren of the old country. The im- ,
proved forms of instruments manufactured by Tolles, ""
14 HISTORY OF THE MICROSCOPE.
Zentmayer, Sidle, Spencer, and Gnndlacli, prove
worthy rivals of those of London makers. Indeed, the
Ross-Zentmayer model has been generally admired,
and its principle of construction is admittedly of the
highest order of mechanical skill. On the Continent,
Hartnach, Zeiss, Mertz, Verich, Nacliet, etc., hold
equal rank as makers of first-class instruments.
Hartnach's accurately fitted concentric stage is the
admiration of microscopists, and has consequently
"been very generally adopted. The greatest and most
important improvement the instrument has received
is that of the immersion objective. Amici, some fifty
years ago, first applied the immersion system. Pro-
fessor Scemmering, writing of its adaptation to a
microscope of Amici's, says of it, " Its magnifying
power, and the admirable precision and clearness with
which the object is s-een, seems astonishing." The
immense importance of the system was only slowly
realized in England, and when, some ten or a dozen
years ago, the Author and Mr. John Mayall, Jun., made
an attempt to bring the immersion objective to the
notice of the Microscopical Society, much opposition
was offered, especially by opticians. Its advantages are
now fully acknowledged ; it is understood to give in-
crease of light, superior definition and clearness to the
optical image, an image obtained by simpler means of
illumination, whilst a much greater working distance
between the object and the objective is secured.
Further improvements remain to be noticed ; first, that
of the adaptation of the " Homogeneous Immersion "
system, the principle of the construction of which is
also due to Professor Amici ; its realization for micro-
Jjficopy is, however, the work of Messrs. J. "W. Stephen-
son, and of the learned Professor E. Abbe, of Jena ;
secondly, that effected in the microscope stand itself,
as my pages were passing through the press " The
Universal Inclining and Rotating Microscope," devised
by Mr. Wenham, to whom the instrument is already so
much indebted. This great change in the form of the
instrument has been made with the special object of
obtaining a large range of effects of oblique light both
HISTORY OF THE MICROSCOPE.
15
in altitude and azimuth. Fig. 3a shows the instrument
inclined at about the usual position for working with
central lights ; and fig. 3& shows the section at the
lowest point in the horizontal position and with the
sub-stage removed. The principal movements of this
improved form of
B-oss-Wenham mi-
croscope were de-
scribed in the Jour-
nal of the Royal
Microscopical Soci-
ety, April, 1882, p.
255. Briefly stated,
the leading princi-
ple followed in the
construction of the
stand is that when
it is inclined back-
wards, or turned
laterally or horizon-
tally, or rotated on
the base-plate, a
pencil of light from
a fixed source will
always reach the
object, all the move-
ments, whether sep-
arate or combined,
radiating from the.
object or the pro-
longation of its axis
as a centre.
The stage rotates
completely and is
a modification of
Tolles', in which
the rectangular motions are effected by milled heads
acting on the surface and entirely within the circum-
ference. This instrument, which is mounted on the
Ross-Zentmayer system, will be the microscope of the
future.
FIG. 3&.
The Ross- Wenham Microscope.
16
THE MICROSCOPE.
CHAPTER II.
THE FORMATION OF IMAGES 'BY THE ORGAN OF VISION THEORY OF MICRO-
SCOPJCAL VISION CHROMATIC AND SPHERICAL ABERRATION OF LENSES -
MECHANICAL AND OPTICAL PRINCIPLES INVOLVED IN THE CONSTRUCTION
OF THE MICROSCOPE LENSES ACHROMATIC LENSES MAGNIFYING POWER
WOLLASTO.V'S DOUBLET CODDINGTON'S LENS EYE-PIECES
SIMPLE ANDCOMPOUND MICROSCOPES CONSTRUCTION APERTURE
IMMERSION SYSTEM, ETC.
N the construction of the modern
microscope, optical and mechanical
principles of some importance are
involved. These principles, together
with the more recent improvements
effected in the instrument generally,
I shall proceed to explain. 1
The microscope depends for its
utility and operation upon concave
and convex lenses, and the course of
rays of light passing through them.
Lenses are usually denned as pieces
of glass, or other transparent sub-
stances, having their two surfaces
so formed that the rays of light, in
passing through them, have their
direction changed, are made to converge or diverge
from their original parallelism, or to become parallel
after converging or diverging. When a ray of light
passes in an oblique direction from one transparent
medium to another of a different density, the direction
of the ray is changed both on entering and leaving ;
this influence is the result of the well-known law of
refraction, that a ray of light passing from a rare into
a dense medium is refracted towards the perpendicular,
and vice versa.
(1) For an explanation of the optical laws as applied to the microscope
see "The Microscope, in Theory and Practice," Nageli and Schwendener,
translated and published by Swan Sonnenschein and Allen, 15, Paternoster
Sauare. E.G. Also "A Treatise on Optics," by J. Parkinson.
THE ORGAN OP VISION. 17
The Organ of Vision. Before passing to the con-
sideration of the formation of images by the human
eye, let me say that owing to want of space, I am unable
to enter as fully as I could wish on the consideration of
the microscope as an optical instrument. Those of my
readers, however, who desire to become better acquainted
with the physical optics of the instrument, will do well
to consult one or more of the numerous standard works
devoted to this special branch of physics, or, what
may even be more profitable, secure a book specially
devoted to it. I can confidently recommend for profit-
able study the translation (already indicated) of
Nageli and Schwendener, " Theory and Practice of
the Microscope," by the indefatigable Secretary of the
Royal Microscopical Society, Mr. Frank Crisp.
The formation of images by the organ of vision ; the
way in which the waves of light impinge upon the
nervous tissue of the eye, and there leave behind an
impression of external objects, to be conveyed to the
sensory organ, the brain, comprises a series of vital and
physical actions of a marvellously complicated nature.
A recent philosophical writer sums up the various
operations associated with seeing as follows : " Sight
may be defined as an aggregation of colour feelings,
and muscle feelings, and the objects of sight groups of
such feelings, suggesting other feelings in all indivi-
duals. All the sensations which go along with the
sensation of sight, interpret it, just as language is
interpreted by the brain. That is, a sensation calls up
a conception, which is made up of an aggregation of
beliefs, and is a link between sensation and action."
(Clifford.) In the terser language of a sage, " The eye
sees only what it brings with it the power of seeing "
(Carlyle); and which, translated, means, that the unaided
eye sees but little, and that little imperfectly or incor-
rectly unless assisted, as students of the microscope
soon discover. The power of seeing, undoubtedly, has a
definite limit assigned to it, which differs in most indi-
viduals, and varies with increasing age, and from
functional causes. The act of seeing is partly volun-
tary, and partly muscular, consequently it is capable of
18 THE MICROSCOPE.
being increased, or rather strengthened, by the judicious
exercise, and at will, of a power termed accommodation.
The near-point of useful sight is fixed, for the normal
eye, at about ten inches from the object. It is for this
reason that English opticians have taken an arbitrary
measurement of ten inches for the length of the body
of the microscope. The most distant point of distinct
vision is placed where the image of the object falls
exactly on the most sensitive spot of the retina,
termed the far-point of vision. When the eye is
accommodated for viewing a near'object, the curvature
of the lens is slightly changed, and its front surface
approaches somewhat closer to the cornea. The range
of the field of vision is computed to be about 160
degrees on the horizontal plane, and 120 degrees in the
vertical. The eye is perfectly adjusted for parallel
rays of light, but when it has to do with divergent
rays it is frequently found unequal to the task of
uniting them. The great mobility of the eye-ball,
however, almost wholly compensates for this slight
defect; and, practically, all rays are parallel which
proceed from distant objects, that is from objects at
twenty feet or upwards.
Good visual accommodation depends upon three
causes : 1st, changes in the indices of refraction of
the media (cornea, lens, &c.) ; 2nd, displacement of the
surface of projection (the retina, analogous to the arti-
ficial production of accommodation by the adjustment
of the camera obscura) ; and 3rd, alteration in the
forms of the refracting surfaces.
Physicists assure us that the organ of vision, hereto
fore regarded as the most wonderful instance of creative
wisdom, is not perfectly achromatic ; that, in fact,
it possesses no proper provision for the correction of
its own chromatic and spherical aberrations, nor
for the correction of the chromatic aberration arising
from defects as an optical instrument, nor that arising
from the compound nature of light, the rays of which,
it is known, are refracted in different degrees and inten-
sities a defect slightly exaggerated by defective cen-
tring of the refractive surfaces of the internal eye. The
THEOEY OF MICROSCOPICAL VISION. 19
want of perfect achromatism is a fact somewhat analo-
gous to that belonging to the flint and crown-glass
construction of the lenses of optical instruments. On
the other hand, with regard to its spherical aberra-
tion straying away of the rays of light it is said
that the great mobility of the iris corrects this
defect. The iris acts somewhat as the diaphragm
does in the microscope, shuts off the circumferen-
tial rays of light those rays which, straying away,
produce distortion of images in lenses, and increase
the circles of dispersion over the retina. Luminous
rays on entering the eye are partly absorbed and partly
reflected, and on issuing once more follow the same
course as they did in the first instance. A certain por-
tion, however, of each bundle of axial rays, after
having undergone refraction, are brought to an accu-
rate focus on points of the retina, and excite a limited
number of the outer layer of rods and cones. The
sharpness with which the aerial image is seen depends
upon the magnitude of the retinal image and the diame-
ter of the visual angle. Other considerations enter into
the theory of vision, as that of the situation of the
retinal image, etc. By education and experience we
"become acquainted with the fact that objects are not
so well defined under a small visual angle, and for
seeing minute objects it is absolutely necessary to
resort to artificial means. Withal, to view the infi-
nitely little in all their beauty of form and complexity
of design, we require, for the most part, associated
with light, a difference and intensity of brightness and
of colour; for the delicacy of visual perception is
found to depend less upon the number of the retinal
elements, set in motion by the waves of light, than
upon the number of elements capable of appreciating
and separating the many delicately coloured tints,
which are embraced by the images. (Hermann.)
Theory of Microscopical Vision.
Recently, however, Professor Abbe, of Jena, a high
authority on all that relates to microscopical optics,
has propounded a theory of the formation of the images
C 2
20 THE MICROSCOPE.
of minute objects, which is the most important con-
tribution to the theory of the microscope that has yet
appeared, furnishing, as it does, an explanation of many
points which have hitherto greatly puzzled and per-
plexed microscopists, and showing that the conditions
of ordinary vision do not apply to objects of minute
size, so that microscopical vision is in this case a thing
sui generis^ in regard to which nothing can be legiti-
mately inferred from the optical phenomena connected
with objects of larger size.
The essential point in the Abbe theory is that the
images of minute objects in the microscope are not
formed, as was formerly supposed, exclusively on the
ordinary dioptric method (that is in the same way in
which they are formed in the camera or telescope), but
that they are very largely affected by the peculiar
manner in which the minute constitution of the object
breaks up the incident rays, giving rise to diffraction.
The phenomena of diffraction in general may be
observed experimentally by plates of glass ruled with
fine lines. Fig. 4 shows the appearance presented by
a single candle-flame seen through such a plate, an
uncoloured image of the flame occupying the centre,
flanked on either side by a row of coloured spectra of
the flame, which become
dimmer as they recede
from the centre. A simi-
lar phenomenon may be
produced by dust scat-
tered over a glass plate,
and by other objects whose structure contains very
minute particles, the rays suffering a characteristic
change in passing through such objects ; that change
consisting in the breaking up of a parallel beam of
light into a group of rays, diverging with wide angle
and forming a regular series of maxima and minima
of intensity of light, due to difference of phase of
vibration.
In the same way, in the microscope, the diffraction
pencil originating from a beam incident upon, for in-
stance, a diatom, appears as a fan of isolated rays,
THEORY OF MICROSCOPICAL VISION.
21
decreasing in intensity as they are further removed
from the direction of the incident beam transmitted
through the structure, the interference of the primary
waves giving a number of successive maxima of light
with dark interspaces.
When a diaphragm opening is interposed between the
mirror, and a plate of ruled lines placed upon the stage
such as fig. 5, the appearance shown in fig. 5a, will be
observed at the back of the objective on removing the
eye-piece and looking down the tube of the microscope.
The centre circles are the images of the diaphragm
opening produced by the direct rays, while those on
the other side (always at right angles to the direction
of the lines) are the diffraction images produced by
the rays which are bent off from the incident pencil.
Fro. 5.
FIG. 5a.
In homogeneous light the central and lateral images
agree in size and form, but in white light the diffrac-
tion images are radially drawn out, with the outer
edges red and the inner blue (the reverse of the ordi-
nary spectrum), forming, in fact, regular spectra, the
distance separating each of which varies inversely as
the closeness of the lines, being, for instance, with the
same objective, twice as far apart when the lines are
twice as close.
The influence of these diffraction spectra may be
demonstrated by some very striking experiments, which
show that they are not by any means accidental pheno-
mena, but are directly connected with tne image which
is seen by the eye.
The first experiment shows that with, for instance,
tlie central beam, or any one of the spectral beams
22 THE MICROSCOPE.
alone, only the contour of the object is seen, the addi-
tion of at least one diffraction spectrum being essential
to the visibility of the structure.
When by a diaphragm placed at the back of the objec-
tive, as in fig. 6, we cover up all the diffraction spectra of
fig. 5,and allow only the central rays to reach the image,
the object will appear to be wholly deprived of fine
FIG. 6.
FIG. 6a.
details, the outline alone will remain, and every deline-
ation of minute structure will disappear, just as if the
microscope had suddenly lost its optical power, as in
fig. 60.
This experiment illustrates a case of the obliteration
of structure by obstructing the passage of t^e diffrac-
tion spectra to the eye-piece. The next experiment
shows how the appearance of fine structure may bo
created by manipulating the spectra.
Fio. 7.
FIG. 7o.
When a diaphragm such as that shown in fig. 7 is
placed at the back of the objective, so as to cut off
each alternate one of the upper row of spectra in
fig. 5, that row will obviously become identical with
the lower one, and if the theory holds good, we
THEORY OF MICROSCOPICAL VISION. 23
should find the image of the upper lines identical with
that of the lower. On replacing the eye-piece, we see
that it is BO, the upper set of lines are doubled in
number, a new line appearing in the centre of the
space between each of the old (upper) ones, and upper
and lower set having become to all appearance identi-
cal, as seen in fig. 7 a.
In the same way, if we stop off all but the outer
^
Pio. 8.
Fia. So.
spectra, as in fig. 8, the lines are apparently again
doubled, as seen in fig. 80.
A case of apparent creation of structure, similar in
principle to the foregoing, though more striking, is
afforded by a network of squares, as in fig. 9,
having sides parallel to this page, which gives the
Fio. 9.
Fio.
spectra shown in fig. 90, consisting of vertical rows
for the horizontal lines and horizontal rows for the
vertical ones. But it is readily seen that two diagonal
rows of spectra exist at right angles to the two diago-
nals of the squares, just as would arise from sets of
lines in the direction of the diagonals, so that if the
theory holds good we ought to find, on obstructing all
24 THE MICROSCOPE.
the other spectra and allowing only the diagonal ones
to pass to the eye-piece, that the vertical and horizontal
lines have disappeared and are replaced by two new
sets of lines at right angles to the diagonals.
On inserting the diaphragm, fig. 10, and replacing
the eye-piece, we find in the place of the old network
the one shown in fig. 16, the squares being, however,
FIG. 10.
FIG. 10a.
smaller in the proportion of 1 : \/ 2, as they should be
in exact accordance with theory.
An object such as Pleurosigma angulatum, which
gives six diffraction spectra arranged as in fig. 11
should, according to theory, show markings in a
hexagonal arrangement. For there will be one set of
lines at right angles to 6, a, e, another set at right
angles to c, a, f, and a third at right angles to g, a, d.
/X X X XT\
x x x x X'
IX X X X X X
\ X X X X
FIG. 11.
X XA X X/
FIG. lla.
These three sets of lines will obviously produce tho
appearance shown in fig. 110.
A great variety of appearances may be produced
with the same arrangement of spectra. Any two
adjacent spectra with the central beam (as b, c, a)
will form equilateral triangles and give hexagonal
THEORY OF MICROSCOPICAL VISION. 25
markings. Or by stopping off all but g, c, e (or b, d,f),
we again have the spectra in the form of equilateral
triangles ; but as they are now further apart, the sides
of the triangles in the two cases being as \/ 3:1, the
hexagons will be smaller and three times as numerous.
Their sides will also be arranged at a different angle
to those of the first set. The hexagons may be
entirely obliterated by admitting only the spectra g, c,
or g,f, or &, /, etc., when new lines will appear at right
angles, or obliquely inclined, to the median line. By
varying the combinations of the spectra, therefore,
different figures of varying size and positions are pro-
duced, all of which cannot, of course, represent the
true structure. Not only, however, may the appear-
ance of particular structure be obliterated or created,
but it may even be predicted before it has been actually
seen under the microscope. If the position and relative
intensity of the spectra in any particular case are
given, the character of the re-
sultant image may be worked
out by mathematical calcula-
tions solely. A remarkable in-
stance of such a prediction is to
be found in the case recorded
by Mr. Stephenson, where a
mathematical student who had
never seen 'a diatom, worked
out the purely mathematical
result of the interference of the p^ 12>
six spectra & g of fig. 11 (iden-
tical with P. angulatum), giving the drawing copied in
fig. 12. The special feature was the small markings
between the hexagons, which had not before been
noticed on P. angulatum. On more closely scruti-
nizing a valve, stopping out the central beam and
allowing the six spectra only to pass^, the small mark,
ings were found actually to exist, though they were
so faint that they had escaped observation until the
result of the mathematical deduction had shown that
they ought to be seen.
These experiments prove that diffraction plays a
26 THE MICROSCOPE.
most important part in the formation of microscopical
images, since dissimilar structures give identical images
when the difference of their diffractive effect is re-
moved, and conversely similar structures may give dis-
similar images when their diffractive images are made
dissimilar. Whilst a purely dioptric image answers
point for point to the object on the stage, and enables
a safe inference to be drawn as to the actual nature
of that object, the visible indications of minute struc-
ture in a microscopical image are not always or neces-
sarily conformable to the real nature of the object
examined, so that nothing more can safely be inferred
from the image as presented to the eye, than the
presence in the object of such structural peculiarities
as will produce the particular diffraction phenomena
on which these images depend.
It should be carefully noted that diffraction is not
limited to lined objects, it applies to structures of all
kinds. But lined objects give brighter and more dis-
tinct diffraction spectra, and are best suited for experi-
mental illustration. Nor, again, is diffraction limited to
transparent or semi-transparent objects viewed by trans-
mitted light. It equally applies to opaque objects, and
is, in fact, universal whenever the strictly uniform
propagation of the luminous waves is disturbed by the
interposition either of opaque or semi-opaque elements,
or of transparent elements of unequal refraction, which
give rise to unequal retardations of the waves.
The Simple Microscope.
A single lens, or a sphere of glass or water, forms a
simple microscope, or, as it is more familiarly called, a
magnifying glass. Lenses are ground of various forms,
as represented in fig. 13 ; a is a plane glass of equal
thickness throughout ; &, a meniscus, concave on one
side, convex on the other ; c, a double-concave : d, a
plano-concave ; e, a double-convex ; /, a plano-convex.
By a proper combination of certain forms of lenses,
we unite on the same sensible point a number of rays,
proceeding from the same point of an object, each
THE SIMPLE MICROSCOPE. 27
ray carrying with, it the image of the point from
whence it proceeds, and as all the rays unite to form
an image of the object from whence they were emitted,
this image is brighter in proportion as there are more
rays united, and more distinct in proportion as the
order in which they have proceeded is perfectly pre-
served and in perfect union. The point at which
parallel rays meet, after passing through a lens, is
known as its principal focus, and its distance from the
middle of the lens, the focal length. The radiant
point and its image after refraction are known as the
conjugate foci. In every lens the right line perpendi-
cular to the two surfaces is the axis of the lens. This
is indicated by the line drawn through the several
lenses, as seen in the diagram. The point where the
axis cuts the surface of the lens is termed the vertex.
Parallel rays falling on a double-convex lens are
brought to a focus in the centre of its diameter ; con-
versely, rays diverging from that point are rendered
parallel. Hence the focus of a double-convex lens will
be at just half the distance, or half the length, of the
focus of a plano-convex lens having the same curvature
on one side. The distance of the focus from the lens
will depend as much on the degree of curvature as
upon the refracting power (called the index of refrac-
tion) of the glass of which it may be formed. A lens
of crown-glass will have a longer focus than a similar
one of flint-glass ; since the latter has a greater refract-
ing power than the former. For all ordinary practical
purposes, we may consider the principal focus as the
28 THE MICROSCOPE.
focns for parallel rays is termed of a double-convex
lens to be at the distance of its radius, that is, in its
centre of curvature ; and that of a plano-convex lens
to be at the distance of twice its radius, that is, at the
other end of the diameter of its sphere of curvature.
The converse of all this occurs when divergent rays
are made to fall on a convex lens. Kays already con-
verging are brought together at a point nearer than the
principal focus ; whereas rays diverging from a point
within the principal focus are rendered still more
diverging, though in a diminished degree. Bays
diverging from points more distant than the principal
focus on either side, are brought to a focus beyond it :
if the point of divergence be within the circle of curva-
ture, the focus of convergence will be beyond it ; and
vice versa. The same principles apply equally to a
plano-convex lens ; allowance being made for the double
distance of its principal focus. They also apply to a
lens whose surfaces have different curvatures ; the
principal focus of such a lens is found by multiplying
the radius of one surface by the radius of the other,
and dividing this product by half the sum of the radii.
The refracting influence of concave lenses will be
precisely the opposite of that of convex. Bays which
fall upon them in a parallel direction, will be made to
diverge as if from the principal focus, which is here
called the negative focus. This will be, for a piano-
concave lens, at the distance of the diameter of the
sphere of curvature ; and for a double-concave, in the
centre of that sphere. A lens convex on one side and
concave on the other, is known as a meniscus.
In the construction of the microscope, either simple
or compound, the curvature of the lenses employed is
spherical. Convergent lenses, however, with spherical
curvatures, have the defect of not bringing all the
rays of light which pass through them to one and
the same focus. Each circle of rays from the axis
of the lens to its circumference has a different focus,
as shown in fig. 14. The rays a a, which pass
through the lens near its circumference, is seen to bo
more refracted, or come to a focus at a shorter distance
SIMPLE MICROSCOPICAL LENSES.
29
behind it than the rays b b, which pass through near
its centre or axis, and are less refracted. The conse-
quence of this defect of lenses with spherical curva-
tures, which is called spherical aberration, is that a
well-defined image or picture is not formed by them,
for when the object is focussed, for the circumferential
rays, the picture projected to the eye is rendered indis-
Fio. 14.
tinct by a halo or confusion produced by the central
rays falling in a circle of dissipation, before they have
come to a focus. On the other hand, when placed in
the focus of the central rays, the picture formed by
them is rendered indistinct by the halo produced by
the circumferential rays, which have already come to
a focus and crossed, and now fall in a state of diver-
gence, forming a circle of dissipation. The grosser
defects of spherical aberration are corrected by
cutting off the passage of the rays a a, through the
circumferences of the lens, by means of a stop dia-
phragm, so that the central rays, b b, only are con-
cerned in the formation of the picture. This defect is
reduced to a minimum, by using the meniscus form of
lens, which is the segment of an ellipsoid instead of a
sphere.
The ellipse and the hyperbola are forms of lenses in
which the curvature diminishes from the central ray,
or axis, to the circumference b ; and mathematicians
have shown that spherical aberration may be practi-
cally got rid of by employing lenses whose sections are
ellipses or hyperbolas. The remarkable discovery of
30
THE MICROSCOPE.
this fact was made by Descartes, who mathematically
demonstrated it.
If a I, a I', for example, fig. 15, be part of an ellipse
whose greater axis is to the distance between its foci
ff as the index of refraction is to unity, then parallel
rays r I', r" I incident upon the elliptical surface V a I,
will be refracted by the single action of that surface
into lines which would meet exactly in the farther
focus /, if there were no second surface intervening
between I a I' and /. But as every useful lens must
have two surfaces, we have only to describe a circle
I of I' round f as a centre, for the second surface of the
lens V I.
As all the rays refracted at the surface I a V converge
PIG. 15.
accurately to /, and as the circular surface I of I' is
perpendicular to every one of the refracted rays, all
these rays will go on to / without suffering any refrac-
tion at the circular surface. Hence it should follow,
that a meniscus whose convex surface is part of an
ellipsoid, and whose convex surface is part of any
spherical surface whose centre is in the farther focus,
will have no appreciable spherical aberration, and will
refract parallel rays incident on its convex surface to
the farther focus.
It is almost impossible to give microscopical lenses
other than the spherical form. The best made convex
single lenses do not bring rays of light to an exact
focus. If a true elliptical or hyperbolic curve could be
SIMPLE MICROSCOPICAL LEN323.
31
got, lenses would not only be very nearly perfect, but
spherical aberration would be nearly overcome. But
even this serious defect can be considerably reduced in
practice by observing a certain ratio between the radii
of the anterior and posterior surfaces of lenses ; thus
the spherical aberration of a lens, the radius of one
FIG. 16.
surface of which is six or seven times greater than
that of the other, as in fig. 16, will be much reduced
when its more convex surface is turned forward to
receive parallel rays, than when its less convex surface
is turned forwards. 1
Two forms of lenses may be so combined, that their
opposite aberrations shall neutralize each
other, and magnifying power be gained. The
aberration of a concave lens is exactly the
opposite of that of a convex lens, so that
the aberration of a convex lens placed in
its most favourable position may be cor-
rected by a concave lens of much less power
in its most favourable position. This prin-
ciple of a combination was proposed by Sir
John F. W. Herschel; his "aplanatic doublet," fig. 17,
consists of a double-convex lens and a meniscus. A
doublet of this kind is an extremely useful and avail-
able one for microscopic purposes. By a skilful com-
bination of crown and flint glass lenses with spherical
curves assisted by the Lister adjusting collar, or,
what is even more efficient, the homogeneous immersion
(1) It must be borne in mind that in lenses having curvatures of the kind
the object would only be correctly seen in focus at one point the mathe-
matical or geometrical axis of the lens.
32 THE MICROSCOPE.
system theoretical and practical difficulties have been
overcome in the construction of the modern microscope,
and which, until quite lately, were thought to be insur-
mountable, thus greatly adding to the value of the
instrument as a means of scientific research.
Chromatic Aberration. A far greater difficulty arises
from the unequal ref rangibility of the different coloured
rays which together make up white light. It is this
difference in refrangibility that produces a complete
separation of rays by the prism, forming the spectrum.
The correction of chromatic and spherical aberration
is effected in a very ingenious manner, by combining a
convex lens made of crown-glass, and a concave lens of
flint-glass. If we examine closely the image projected
on the table of a camera obscura provided with a com-
mon lens, we see that it is fringed with the colours of
the rainbow ; again, if we look through a common mag-
FJG. 18.
nifying-glass at the letters on the title-page of a book,
we see them slightly coloured at their edges in a similar
manner. The cause of this iridescent border is that
the primitive rays red, yellow, and blue, of which a
colourless ray of light is composed, are not equally re-
frangible. Hence they are not simultaneously brought to
one point or focus; the blue rays being the most refran-
gible, come to a focus nearer the lens than the yellow,
which are less refrangible, and the yellow rays than
the red, which are the least refrangible. It is seen,
in fig. 18, chromatic aberration proves still more detri-
mental to the distinct definition of images formed by
a lens, than spherical aberration. This arises more
CHROMATIC ABERRATION.
33
from the sizes of the circles of dissipation, than from
the iridescent border, and it may still exist, although
the spherical aberration of the lens is quite corrected.
Chromatic aberration is, as before stated, corrected by
combining, in the construction of lenses, two media
of opposite forms, differing from each other in the
proportion in which they respectively refract and dis-
perse the rays of light ; so that the one medium may,
by equal and contrary dispersion, neutralize the disper-
sion caused by the other, without, at the same time,
wholly neutralizing its refraction. .It is a remarkable
fact that the media found most valuable for the purpose
should be a combination of pieces of crown and flint
glass, of crown-glass whose index of refraction is T519,
and dispersive power O036, and of flint-glass whose
index of refraction is 1*589, and dispersive power
FIG. 19.
The focal length of the convex crown-glass
lens must be 4J inches, and that of the concave flint-glass
lens 7f inches, the combined focal length of which is
10 inches. The diagram, fig. 19, shows how rays of light
are brought to a focus, free from colour.
In this diagram, L L is a convex lens of crown-glass,
and I I a concave one of flint-glass. A convex lens will!
refract a ray of light (s) falling at P on it exactly in
the same manner as the prism A B c, whose faces touch
the two services of the lens at the points where the ray
enters, and quits. The ray S F, thus refracted by the
lens L L, or prism ABC, would have formed a spectrum
(i j T) on a screen or wall, had there been no other lens,
tmmtmg Item & aw mtioM of tike cm 0! fidbt
- ^ - - *
;
:,;; .?
.---.- - ,
diwqp-ffcw.tfce
ItMU *fce*e
we shall proceed to applj them to its
T%# Jfer&K^.--A Mienwcope. as I
said, ma j be either a. JM^C, or JHM
C
00 THE MICROSCOPE.
instrument. The simple microscope may consist of one,
as seen in fig. 21, or of two or three lenses; if the
latter, then so arranged as to have the effect only of a
single lens. In the compound microscope, not less
than two lenses can be employed : one to form an in-
verted image of the object, which, being the nearest to-
the object, is called the object-glass ; the other to mag-
nify this image, and from being near the eye of the
observer, is called the eye-glass.
I have so far considered a lens simply with reference
to its enlargement of the object, the increase of the
angle under which the object is seen. A further
and equally important consideration is that of the
number of rays or quantity of light by which every
point of the object is rendered visible ; and much may
be accomplished, as I have already pointed out, by the
combination of two or more lenses, which w r ill at once
reduce the angles of incidence and refraction. The
first satisfactory combination for the purpose was
the invention of the celebrated Dr. Wollaston. His
doublet (fig. 22) consists of two plano-convex lenses
having their focal lengths in the proportion of one to
three, or nearly so, and mounted at a distance which
is readily ascertained by experiment. The plane sides
of the lenses should be towards the object, and the
lens of shortest focal length next the object.
It appears that Dr. Wollaston was led to this inven-
tion by considering that the achromatic Huyghenian
eye-piece, presently to be described, would, if reversed,
possess a power equal to that of the simple microscope.
But it will be evident, when the eye-piece is under-
stood, that the circumstances which render it achro-
matic are very imperfectly applicable to the simple
microscope, and that the doublet, without a nice
adjustment or a stop, would be valueless.
The nature of the corrections which take place in
the doublet is explained in the annexed diagram, where
1 o V is the object, p a portion of the cornea of the
eye, and d d the stop, or limiting aperture (fig. 22).
Now it will be observed that each pencil of
light proceeding from I I' of the object is rendered
THE DOUBLET. 37
excentrical by the diaphragm d, d ; consequently, they
pass through the lenses on opposite sides of their
common axis o p; thus each becomes affected by
opposite errors, which to some extent balance and
correct each other. To take the pencil Z, for instance,
which enters the eye at r b, r I : it is bent to the right
at the first lens, and to the left at the second ; and
as each bending alters the direction of the blue ray
more than the red, and, moreover, as the blue ray
falls nearer the margin of the second lens, where the
refraction being more powerful than nearer the centre,
compensates in some degree for the greater focal length
of the second lens, the blue rays will emerge very
38 THE MICROSCOPE.
nearly parallel, and of consequence colourless to the
eye. At the same time the spherical aberration has
much diminished, "because the side of the pencil as it
proceeds through one lens passes nearest the axis and in
the other nearest the margin.
This explanation applies to pencils farthest from
the centre of the object. The central pencils, it is
obvious, would pass both lenses symmetrically, tho
same portions of rays occupying nearly the same
relative places in both lenses. The blue ray would
enter the second lens nearer to its axis than the red ;
and being thus less refracted than the red by the
second lens, a small amount of compensation would
take place, quite different in principle, and inferior
in degree, to that which is produced in the excentrical
pencils. In the intermediate spaces the corrections are
still more imperfect and uncertain ; and this explains
the cause of the aberrations which must of necessity
exist even in the best-made doublet. It is, however,
infinitely superior to a single lens, and will transmit
a pencil of an angle of from 35 to 50.
The next step towards improving the simple micro-
scope was in relation to the eye-piece ; this was effected
by Mr. Holland. It consists in substituting two lenses
for the first in the doublet, and placing a stop between
them and the third. The first bending of the pencils
of light being effected by two lenses instead of one,
produces less aberration, and this is more completely
balanced or corrected at the second bending, and in
the opposite direction, by the third lens.
A useful form of pocket lens was proposed by Dr.
Wollaston, named by him " Periscopic." This combi-
nation consists of two hemispherical lenses cemented
together by their plane faces, with a stop between
them to limit the aperture. A similar proposal, made
by Sir David Brewster in 1820, is well known as the
Coddington lens, 1 shown at fig. 23 : this gives a
(1) The late Mr. Coddington, of Cambridge, who had a high opinion of the
value of this lens, had one of these grooved spheres executed by Mr. Carey,
who gave it the name of the Coddington Lens, supposing that it was invented
by the person who employed him, whereas Mr. Coddington never laid claim
to it, and the circumstance of his having one made was not until nine years
after it was described by Sir David Brewster in the " Edinburgh Journal."
THE CODDINGTON LENS.
39
larger field of view, and is equally good in all
directions, as it is evident that the pencils a b and & a
pass through under precisely the same circumstances.
Its spherical form has the further advantage of render-
ing the position in which it is held of comparatively
little consequence. It is very generally used as a hand
magnifier ; but its definition is certainly not so good as
that of a well-made doublet or achromatic lens. It is
usually set in a folding case, as represented in the
figure, and so contrived as to be admirably adapted
for the waistcoat-pocket. It is sold with the small
holder, fig. 23#, for holding and securing small. objects
Fio. 23.
FIG. 23a.
during examination. Browning's Platyscopic Pocket
Lens is a useful form for botanists and mineralogists.
Its focus is about three times farther from the object
than the Coddington, and allows of opaque objects
being easily examined ; it has also three degrees of
magnifying power of 15, 20, and 30 diameters^
When the magnifying power of a lens is consider,
able, or when its focal length is short, and its proper
distance from the object equally short, it then becomes
necessary to be placed at a proper distance with great
precision; it cannot therefore be held with sufficient
40
THE MICROSCOPE.
accuracy and steadiness bj the unassisted hand, bnt
must be mounted in a frame, having a rack or screw
to move it towards or from another frame or stage
which holds the object. It is then called a micro-
scope ; and it is furnished, according to circumstances,
with lenses and mirrors to collect and reflect the light
upon the object, with other conveniences.
The best of the kind, contrived by the late Mr. Boss,
|g represented in fig. 24; and consists of a circular
foot e, from which
rises a short tubular
stem d, into which
slides another short
tube c, carrying at
its top a joint /; to
this joint is fixed a
square tube a, through
which a rod b slides ;
this rod has at one
end another but
smaller joint g, to
which is attached a
collar h, for receiving
the lens i. By means
of the joint at /, the
square rod can be
moved up or down, so as to bring the lens close to
the object ; and by the rod sliding through the square
tube a, the distance between the stand and the lens
may be either increased or diminished : the joint g,
at the end of the rod, is for the purpose of allow-
ing the lens to be brought either horizontally or
at an angle to the subject to be investigated. By
means of the sliding arm the distance between the
table and the jointed arm can be increased or dimin-
ished. This microscope is provided with lenses of
one-inch and half-inch focal length, and is thereby
most useful for the examination and dissection of
objects. It is readily unscrewed and taken to
pieces, and may be packed in a small case for the
pocket.
FIG. 24. Boss's Simple Microscope.
THE COMPOUND MICROSCOPE. 41
THE COMPOUND MICROSCOPE. The compound micro-
scope consists of two essential parts, the stanc
optical arrangement ; the first image being further
magnified by one or more lenses forming tHe eye-
piece. The mechanical principles involved in tte con-
struction of the compound instrument are feW and
simple. The more finished form of microscope has
assumed a degree of solidity and luxurious elegknce
heretofore unknown, whilst its accessories have multi.
plied to an almost unlimited extent. This has resulted
from a desire to save time or overcome difficulties, as
the practical skill and experience of the microscopisf
or optician may have suggested, so that whilst the-
wants of the amateur have been duly considered, tht-
more modest demands of the student have in no wa^
been overlooked or forgotten.
Fortunately for the student, no large and expensive
form of instrument is absolutely necessary for the
pursuit of microscopical science. A small and simple
microscope is as well adapted to his wants indeed is
all that he requires for the work he has to perform.
And as for his cabinet of objects, these will grow day
by day, and by the labour of his hands. It was with
a very unpretending form of microscope that John
Quekett worked ; that John Ralfs studied the " British
DesmidiaceaD ; " John Denny the " Anoplura ; " Wil-
liam Smith the " British Diatomaceee ; " George John-
son the " British Zoophytes ; " and Dr. Bowerbank the
" British Spongiidee." The microscope has its place
in the educational movement of the age, and it is the
more incumbent on opticians to manufacture an econo-
mic form of instrument, adapted to the wants of a large
and increasing class. In the selection of an instrument,
it must be borne in mind that a firm stand and a well
corrected object-glass are indispensably necessary. It
may be of some advantage to those who are about
to purchase an instrument if I were to shortly de-
scribe its several parts the stand, body, stage, sub-
stage, mirror, eye-piece and objective, seriatim. The
etand, the bearings upon which the superstructure of
the microscope rests, should be solid; and the foot
42 THE MICROSCOPE.
or claw horseshoe shaped, that it may steadily grasp
the table and assist in maintaining the centre of gravity
in any position the instrument may be placed. To
the foot should be attached two upright pillars, with
trunnions, for making the attachments and securing
the sliding bar which carries the tubular body and
stage.
The tubular body should be about eight or ten
inches in length, with a second or inner tube, "the
draw-tube," of five or six inches in length, sliding with-
in it. The "draw-tube" assists in the magnification
of the image, and is usually engraved with a scale of
inches and parts of an inch, for measuring the dis-
tance between the eye-piece and the front of the
object-glass. The eye-piece surmounts the body, while
to the other extremity is attached or screwed the
object-glass. The focus is obtained by either a sliding
or rack-and-pinioii motion, termed the " coarse-ad-
justment," the fine-adjustment being obtained by a
milled-head screw acting upon the long end of a lever,
or by other mechanical means. Whatever the kind of
motion adopted, neither jumping nor lateral movement
of the body should take place, otherwise the object,
when placed on the stage, will appear to change its
position either to the right or left. A fine-adjustment
is very necessary, as without it the highest magnifying
powers can hardly be used without risk of damage
being done either to the object or the objective.
Pig. 25 represents the body of an ordinary com-
pound microscope with triple object-glass ; o is an
object, above it is seen the triple achromatic object-
glass, in connection with the eye-piece e e, ff the plano-
convex lens ; e e being the eye-glass, and // the field-
glass, and between them, at b &, a dark spot or dia-
phragm. The course of the light is shown by three
rays drawn from the centre, and three from each end
of the object o ; these rays, if not prevented by the
lens / /, or the diaphragm at b &, would form an image
at a a ; but as they meet with the lens f f in their
passage, they are converged by it, and meeting at b b,
where a diaphragm is placed to intercept all extraneous
THE COMPOUND MICROSCOPE.
43
light, excepting that required for the formation of the
image ; a further magnification of the image is effected
by the eye-lens e e, and precisely as if it were an
original object.
The Stage. The stage of the
microscope should be perfectly flat
and rigid, without flexure, and as
thin as may be consistent with
these essential qualities. It should
rotate on its axis, as a revolving
stage possesses great advantages.
It enables the observer to keep a
diatom in view, while it is pre-
sented in succession to rays of
greater or less obliquity, and thus
a better insight is obtained into
structure. Supposing fig. 26 were
an object marked by longitudi-
nal strise, but too faint to be
seen by ordinary direct light, the
light most useful for bringing
these into view will be that pro-
ceeding obliquely in either of the
directions C and D ; whilst rays of
light falling upon it in the direc-
tions A and B would tend to ob-
scure the strias rather than disclose
them. If the markings, however,
are due to furrows or prominences
having one side inclined and the
other side abrupt, they will not be
brought into view indifferently by
light from C, or from D, but will be
seen best by that which produces
the strongest shadow ; hence, if
there be a projecting ridge, with
an abrupt side looking towards c,
they will be best seen by light from D ; if, however, there
be a furrow with a steep bank on the side of c, they
will be seen by light from the same side. It not
unfrequently happens that longitudinal strise, or lines,
44 THE MICROSCOPE.
are crossed by others, and then these transverse strise
will be better seen by an illuminating pencil less
favourable for longitudinal, so that, in
order to bring them into distinct view,
either the illuminating pencil or the
object must be moved or rotated a
quarter round.
Swinging Sul-stage, or Tailpiece.
The swinging sub- stage, although a
revival of an invention contrived by
Mr. T. Grubb some twenty years ago,
has been very generally adopted, since
it is thought by manufacturers to be an important and
FIG. 27.
THE MECHANICAL STAGE. 45
useful addition to the more perfected forms of instru-
ments. This tailpiece, represented in sectional elevation
fig. 27, consists of s, the limb carrying the body, with
coarse and fine adjustments ; A, the stem carrying the
sub-stage, B, and mirror. A is attached to s by the sleeve
or socket I, clamped by the nut j, and on I A may be
swung sideways in either direction to the right or left,
either below or above the stage, the axis of revolution
of which is the line x T ; that is, a line in the plane of
the object to be viewed on the stage c, intersected by
the optical axis of the instrument ; that is, the line N o,
passing through the centre of the body and the object-
glass of the microscope. The stage c is also attached
to s by the pin C 1 , terminated by the screen C 2 , which
pin passes through the centre of the socket I, and
moves therein so that the stage C may readily turn in
either direction in conjunction with or independent of
A, the axis of its revolution being also the line x T.
By this kind of arrangement the stage C and the stem
A can be set at any angle to the axis of the microscope,
either below or above x Y, intersecting the plane of the
object to be viewed, and relatively to each other, and
when so set the stage C can be clamped at the desired
angle by the nut D on the screw C 2 acting on s and the
collar K.
A mechanical stage is one consisting of two or more
plates, the rectangular motions of which are obtained
by rack and pinion. It is considered a necessary
appendage to the more finished instruments. The
cheaper kinds are provided with a simple form of
sliding plate, the lower part of which is a raised edge
for the objects to rest against. It is often found con-
venient to have a means of watching growing and
other processes, which are either promoted or assisted
by maintaining the object for a time at a certain tem-
perature. For this purpose many forms of apparatus
have been contrived. A very inexpensive form is that
of Mr. Bartley's, fig. 28.
The vessel E, three parts filled with water, and sup-
ported on a ring-stand, is kept at any temperature by
the spirit lamp c, a syphon-tube d conveys the Jbot
46 THE MICROSCOPE.
water along /and through the bent tubing which sur-
FIG. 28.Eartl#y's Warm Stage.
rounds the object on the stage D, and passing off through
the open end c into the receptacle B, placed to receive
the overflow.
Mr. Stephenson's safety-stage is one of those happy
FIG. 29. Stephenson's Safety-Stage.
contrivances by means of which an accident to either
THE MIRROR, AND EYE-PIECE. 47
the object or objective will be prevented. When
about to be used it is simply necessary to place it on
the fixed stage of the microscope. The object about to
be examined is supported and kept in place by a couple
of clips or projecting springs. Should a tyro in the
use of the instrument hastily rack down the body, all
undue force is broken by the elasticity of the springs.
Messrs. Watson and Son, of Holborn, manufacture a
light and elegant form in ebonite of this accessory
safety-stage.
The Mirror. The mode in which an object is illu-
minated is, in the words of Andrew Ross, " second only
in importance to the excellence of the glass through
which it is seen." To ensure good illumination the
mirror should be in direct co-ordination with the
objective and eye-piece; it must be regarded as a
part of the same instrument, and tending by a com-
bined series of acts to a common result. Illumination
is spoken of as of three kinds or qualities reflected,
transmitted, and refracted light. For the illumination
of transparent objects, transmitted light is brought
into use ; for opaque objects, reflected. The trans-
mitted illuminating pencil should be as large as can
well be received by the lens, and no larger. Any
light beyond this is liable to produce confusion of
image. In using the mirror the reflected light can be
made brighter, more concentrated, by employing a
bull's-eye condensing lens.
The Eye-piece. The eye-piece of the compound
microscope consists of two plano-convex lenses; that
furthest from the eye, as I have already explained, is
the field-glass, and that nearest the eye is the eye-
glass. The former increases the field of vision,
the latter magnifies, the enlarged inverted image.
Combined together, the two materially assist in cor-
recting residual imperfections of the objective. The
magnifying power of the microscope depends in a
measure, then, upon the eye-piece, but the limit of
usefulness in this direction is soon reached, for,
although the size of the image is thereby increased,
this increase is achieved at the expense of per-
48 THE MICROSCOPE.
feet definition; and it should be observed that only
objectives of the finest construction will bear the
deeper eye-pieces. Opticians furnish with most of
their instruments two, three, or more oculars : A, B,
and C ; these, together with a Kellner or orthoscopic
eye-piece, D, the field-lens of which is bi-convex, and
therefore gives a larger field, are all the microscopist
will require. The Huyghenian eye-piece, which is
still in use, consists of two plano-convex lenses, with
their plane sides turned towards the eye, and at a
distance apart equal to half the sum of their focal
lengths, and having a stop or diaphragm midway
between the lenses. Huyghens was not aware of the
value of his eye-piece ; it was reserved for Boscovicli
D c A a
IG. 30. Eye-pieces.
to point out that, by this important arrangement, he
had accidentally corrected a portion of the chro-
matic aberration incidental to the earlier forms. Let
fig. 31 represent the Huyghenian eye-piece of a micro-
scope, f f being the field glass, and e e the eye-glass,
and I m n the two extreme rays of each of the three
pencils emanating from the centre and ends of the
object, of which, but for the field-glass, a series of
coloured images would be formed from r r to b b ;
those near r r being red, those near b b blue, and the
intermediate ones green, yellow, and so on, correspond-
ing with the colours of the prismatic spectrum. This
order of colours is the reverse of that of the common
compound microscope, in which the single object-glass
projects the red image beyond the blue.
HUYGHENIAN EYE-PIECE.
49
The effect just described, of projecting the blue
image beyond the red, is purposely produced for
reasons presently to be given, and is called over-
correcting the object-glass as to colour. It is to be
observed, also, that the images b b and r r are curved
in the wrong direction to be distinctly seen by a
convex eye -lens, and this is a further defect of the
compound microscope of two lenses. But the field-
glass, at the same time that it bends the rays and
converges them to foci at &' V and r f /, also reverses
the curvature of the images as here shown, giving
E
50 THE MICROSCOPE.
them the form best adapted for distinct vision by the
eye-glass e e. The field-glass has at the same time
brought the blue and red images closer together, so
that they are adapted to pass uncoloured through the
eye-glass. To render this important point more intel-
ligible, let it be supposed that the object-glass had
not been over-corrected, that it had been perfectly
achromatic ; the rays would then have become coloured
as soon as they had passed the field-glass; the blue
rays, to take the central pencil, for example, would
converge at &", and the red rays at /', which is just
the reverse of what the eye-lens requires ; for as its-
blue focus is also shorter than its red, it would demand
rather that the blue image should be at r", and the
red at W. This effect has already been referred to as
due to over- correction of the object-glass, which re-
moves the blue foci b 6 as much beyond the red foci
r r as the sum of the distances between the red and
the blue foci of the field-lens and eye-lens ; so that
the separation b r is exactly taken up in passing
through those two lenses, and the several colours
coincide, so far as focal distance is concerned, as the
rays pass the eye-lens. But while they coincide as to
distance, they differ in another respect, the blue
images are rendered smaller than the red by the
greater refractive power of the field-glass upon the
blue rays. In tracing the pencil Z, for instance, it
will be noticed that, after passing the field-glass, two
sets of lines are drawn, one whole and one dotted, the
former representing the red, and the latter the blue
rays. This is the accidental effect in the Huyghenian
eye-piece pointed out by Boscovich. The separation
into colours of the field-glass is like the over-cor-
rection of the object-glass, and leads to subsequent
complete correction. For if the differently coloured
rays were kept together till they reached the eye-glass,
they would then become coloured, and present coloured
images to the eye; but fortunately, and most use-
fully, the separation effected by the field-glass causes
the blue rays to fall so much nearer the centre of the
eye-glass, where, owing to the spherical figure, the
THE RAMSDEN EYE-PIECE.
51
FIG. 32.
refractive power is less than at the margin, so that
spherical error of the eye-lens constitutes a nearly
perfect balance to the chromatic dispersion of the
field-lens, and the blue and red rays V and I" emerge
sensibly parallel, presenting, in consequence, the perfect
definition of a single point to the eye. The same reason-
ing is true of the intermediate colours and of the other
pencils. The eye-glass thus constructed not only brings
together the images b' b', r r r', but it likewise has the
most important effect of rendering them flat, and at once
correcting both chromatic and spherical aberrations.
The Huyghenian eye-piece described, has served
the purpose of illustrating the optical
effects of this part of the instrument ;
but when it is required to measure the
magnified image, we use the eye-piece
invented by Bamsden, and called by
him the micrometer eye-piece. The
arrangement will be readily understood
upon reference to fig. 32. The field-
glass having its plane face turned to-
wards the object, so that the rays from the object are
made to converge immediately in front of the field-glass;
and here is placed a plane-glass, on which is engraved
divisions of l-100th of an inch or more. The markings
of these divisions come
into focus, therefore, at the
same time as the image of
the object, both being dis-
tinctly seen together. The
glass with its divisions is
shown in fig. 33, on which,
at A, are seen some magni-
fied grains of starch. Thus
the measure of the magni-
fied image is given by mere
inspection ; and the value
of such measurements, in
reference to the real object, when once obtained, is
constant for the same object-glass. 1
(1) It was affirmed by Ross, that if the achromatic principle were applied
E 2
FIG. 33.
52 THE MICROSCOPE.
Mr. Lister proposed to place on the stage of tlie
microscope a divided scale, of a certain value ; viewing
the scale as a microscopic object, he observed how many
of the divisions on the scale attached to the eye-pie.ce
corresponded with one or more of a magnified image.
If, for instance, ten of those in the eye-piece correspond
with one of those in the image, and if the divisions
are known to be equal, then the image is ten times
larger than the object, and the dimensions of the object
ten times less than that indicated by the micrometer.
If the divisions on the micrometer and on the magnified
scale are not equal, it becomes a mere rule-of-three
sum ; but in general this trouble is taken by the maker
of the instrument, who furnishes a table showing the
value of each division of the micrometer for every
object-glass with which it may be employed.
Mr. Jackson invented the simple and cheap form of
micrometer, represented in fig. 34, which he described
in the Microscopical Society's Transactions, 1840. It
consists of a slip of glass placed in the focus of the
eye-glass, with the divisions sufficiently fine to have
the value of the ten-thousandth of an inch with the
quarter-inch object-glass, and the twenty-thousandth
with the eighth ; at the same time the half, or even
the quarter of a division may be estimated, thus afford-
ing the means of attaining all the accuracy that is
really available. It may therefore entirely supersede
the more complicated and expensive screw-micrometer,
being much handier to use, and not liable to derange.
iDent in inexperienced hands.
The positive eye-piece gives the best view of the
micrometer, the negative of the object. The former is
quite free from distortion, even to the edges of the
field ; but the object is slightly coloured. The latter
is free from colour, but is slightly distorted at the
edges. In the centre of the field, however, to the
to the construction of eye-pieces, the Ramsden is the form by which greater
perfection should be obtained. That such an adaptation might be produc-
tive of valuable results, appears from Mr. Brooke's statement, that he hai
employed as an eye-piece, a triplet objective of one-inch focus, the definition
obtained by it being superior to that afforded by the ordinary Hu\ghet,ian
eye-piece. An inch or half-inch achromatic object-glass answers extremely
well as an eye-piece.
MICROMETER EYE-PIECE.
53
extent of half its diameter, there is no perceptible
distortion ; and the clearness of the definition gives a
precision to the measurement which is very satisfactory.
Short bold lines are ruled on a piece of glass, a, fig.
34; to facilitate counting, the fifth is drawn longer,
and the tenth still longer, as in the common rule. Very
finely levigated plumbago is rubbed into the lines to
render them visible ; and they are covered with a piece
of thin glass, cemented by Canada balsam, to prevent
the plumbago from being wiped out. The slip of glasf
thus prepared is secured in a thin brass frame, so thai
FIG. 34. Jackson's Micrometer Eye-piece.
it may slide freely ; it is acted on at one end by a
pushing screw, and at the other by a slight spring.
Slips are cut in the negative eye-piece on each side,
#, so that the brass frame may be pressed across the
field in the focus of the eye-glass, as at m ; the cell of
which should have a longer screw than usual, to admit
of adjustment for different eyes. The brass frame is
retained in its place by a spring within the tube of the
eye-piece ; and in using it the object is brought to the
centre of the field by the stage movements ; and the
coincidence between one side of it and one of the long
lines is made with great accuracy by means of the
54 THE MICROSCOPE.
small screw acting upon the slip of glass. The divi-
sions are then read off as easily as the inches and
tenths on a common rule. The operation, indeed, is
nothing more than the laying a rule across the body to
be measured ; and it matters not whether the object be
transparent or opaque, mounted or not mounted, if its
edges can be distinctly seen, its diameter can be taken.
Previously, however, to using the micrometer, the
value of its divisions should be ascertained with each
object-glass ; the method of doing this is as follows :
Lay a slip of ruled glass on the stage ; and having
turned the eye-piece so that the lines on the two glasses
are parallel, read off the numbrr of divisions in the
eye-piece which cover one on tho stage. Repeat this
process with different portions of the stage-micrometer,
and if there be any difference, take the mean. Sup-
pose the hundredth of an inch on the stage requires
eighteen divisions in the eye-piece to cover it ; it is
quite plain that an inch would require eighteen hun-
dred, and an object which occupied nine of these
divisions would measure the two-hundredth of an
inch. Take the instance supposed, and let the micro-
scope be furnished with a draw-tube, marked on the side
with inches and tenths. By drawing this out a short
distance, the image of the stage micrometer may be
expanded until one division is covered by twenty in
the eye-piece. These will then have the value of two-
thousandths of an inch, and the object which before
measured nine will then measure ten ; which, divided
by 2,000, gives the decimal fraction '005.
Enter in a table the length to which the tube is
drawn out, and the number of divisions on the eye-
piece micrometer equivalent to an inch on the stage ;
and any measurements afterwards taken with that
micrometer and object-glass may, by a short process
of mental arithmetic, be reduced to the decimal parts
of an inch, if not actually observed in them. In
ascertaining the value of the micrometer with a
deep object-glass, if the hundredth of an inch on the
stage occupies too much of the field, then the two-
hundredth or five-hundredth should be used, and
NOBERT'S LINES. 55
the number of divisions corresponding to that quantity
"be multiplied by two hundred or five hundred, as the
case may be.
The micrometer should not be fitted into too deep
an eye-piece, for it is essential to preserve clear defini-
tion. A middle power or Kellner eye-piece is the
best, provided the object-glass be of the first quality ;
otherwise, use the eye-piece of lowest power. The
lens above the micrometer should not be of shorter
focus than three-quarters of an inch, even with the
best object-glasses ; and the slit cut in the tube can
be closed at any time by a small sliding bar, placed at
Z, m, fig. 34.
The wonderful tracings on glass executed by the late
M. Nobert, of Earth, deserve attention. The plan
adopted by him was to trace on glass ten or more
separate bands at equal distances from each other,
each band being composed of parallel lines of a frac-
tional part of a Prussian inch apart ; in some they are
l-1000th, and in others only 1 -4000th of a Prussian
inch separated. The distance of these parallel lines
forms part of a geometric series :
O'OOIOOO lines. 0'000463 lines.
0-000857 C'000397
0-000735 0-000340
C'000630 0/000292
0-000540 0-000225
To see these lines at all, it is requisite to use a micro-
scope with a magnifying power of 100 diameters ; the
bands containing the fewest number of lines will then
be visible. To distinguish the finer lines, it will be
necessary to use a magnifying power of 300, and then
the lines which are only 1 -4700th of an inch (Prussian)
apart will be seen perfectly traced. Of all the tests
yet found for object-glasses of high power, these
would seem the most valuable. Robert's tracings have
tended to confirm the undulating theory of light, the
different colours of the spectrum being exhibited in the
ruled spaces varying with the separation of the lines;
in those cases where the distances between the lines are
smaller- than the length of the violet-coloured waves,
*io colour is perceived ; while, on the other hand, if
56 THE MICROSCOPE.
Inequalities amounting to '000002 line occnr, stripes of
another colour appear in them.
Schmidt's goniometer positive eye-piece, for mea-
suring the angles of crystals, is so arranged as to be
easily rotated within a large and accurately graduated
circle. In the focus of the eye-piece a single cobweb
is drawn across, and to the upper part is attached a
vernier. The crystals being placed in the field of the
microscope, care being taken that they lie perfectly,
fat, the vernier is brought to zero, and then the whole
apparatus turned until the line is parallel with one face
of the crystal; the frame- work bearing the cobweb,
with the vernier, is now rotated until the cobweb
becomes parallel with the next face of the crystal, and
the number of degrees which it has traversed may then
be accurately read off.
Erector eye-pieces and erecting prisms are employed
for the purpose of making the image presented to the
eye correspond with the position of the object. They
are most useful for minute dissections, but the loss
of light occasioned by sending it through two addi-
tional surfaces is a drawback impairs the sharpness
of the image. Nachet designed an extremely ingenious
arrangement whereby the inverted image became erect;
he adapted a simple rectangular prism to the eye-
piece. The obliquity which a prism gives to the
visual rays, when the microscope is used in the erect
position, as for dissecting, is an advantage, as it brings
the image to the eye at an angle very nearly correspond-
ing to the inclined position in which the microscope is
ordinarily used.
The Value of Eye-pieces. The magnifying power of
Ross's lowest eye-piece A is about 5; that of B, 8 to 10;,
C, 15; D, 20; and E, 25.
For viewing thin sections of recent or fossil woods,,
coal, the fructification of ferns and mosses, fossil-shells,
seeds, small insects, or parts of larger ones ; molluscs,
the circulation in the frog, etc., the A eye-piece is best
adapted.
For the examination of details of minuter objects,
the B eye-piece is preferred; the pollen of flowers^
THE VALUE OF EYE-PIECES.
57
dissected insects, the vascular and cellular tissues of
plants, the Haversian canals, the lacunas of bone, and
the serrated laminaa of the crystalline lens of the eyes
of birds and fishes require the B eye-piece.
The C eye-piece is brought into use when it is neces-
sary to investigate the structure of very delicate tissues ;
and in observations upon minute diatoms and desmids,
scales of moths, gnats, raphides, etc. The employment
of a deep eye-piece sometimes obviates the necessity of
using a deeper object-glass, and which always occasions
a re-arrangement of the illumination generally. It
must be borne in mind, that the more powerful the
eye-piece, the more palpable will the imperfections of
the object-glass become ; hence less confidence should
be placed in observations made with a powerful eye-
piece than when amplification is obtained with a
shallow one and a deeper object-glass. 1
The Draw-tiibe is an intermediate tube, which when
(1) AMPLIFICATION OF OBJECTIVES AND EYE-PIECES.
OBJECTIVES.
EYE-PIECES AND OBJECTIVES COMBINED.
Focal
Length.
Magni-
fying
Power.
With
Beck's i,
Powell's
i,
Boss's A.
With
Beck's 2,
Powell's
Boss's B.
With
Powell's
3-
With
Boss's C.
With
Beck's 3.
With
Beck's 4,
Powell '34,
Boss's B.
With
Beck's 5,
Boss's E.
Ins
5
2
10
15
20
25
30 40
50
4
2*
12*
18|
25
31J
37* 50
62*
3
3*
16
25
33*
4l|
50
66g
83*
4)
5
25
37*
50
62
75
100
125
1*
6
33*
50
66|
83*
100
133*
166
1
10
50
75
100
125
150
200
250
* *
13
62*
66
93|
100
125
133*
166|
187*
200
250
266
312* i
333*
i
15
75
112*
150
187*
225
300
375
i
20
100
150
200
250
300
400
500
&
25
125
187*'
250
312*
375
500
625
*
30
150
225
300
375
450
600
750
TO
33*
160
250
333*
416-3-
500
666
833*
1
40
200
300
400
500
600
800
10CO
i
50
250
375
500
625
750
1000
1250
\
60
300
450
600
750
900
1200
1500
i
70
350
525
700
875
1050
1400
1750
|
80
400
600
800
1000
1200
1600
2000
1
g
90
450
675
900
1125
1350
1800
2250
T5
100
500
750
1000
1250
1500
2000
2500
Reduced from a comprehensive table of the magnifying power of eye-
pieces, and the amplification of objectives and eye-pieces combined, issued
in a separate form with the Journal of the Royal Microscopical Society.
58 THE MICROSCOPE.
drawn out increases the magnification of the image,
without having to change the eye-piece. When using
the micrometer eye-piece, we are enabled by the aid of
the draw-tube to fill the whole field of view and make
a precise comparison between the divisions of the eye-
piece and the stage micrometer. In Messrs. Beck's
microscopes, the draw-tube is furnished with a rack-
and- pinion movement for the purpose of facilitating
adjustment.
The Object-glass. The microscope depends so much
for its effectiveness and general utility upon the perfec-
tion of the object-glass or objective, that it is absolutely
necessary for any one about to use the instrument to
make himself perfectly familiar with its relative quali-
ties. It will scarcely be possible to form any just
estimate of the value of this or that maker's objective
by a comparison of magnification ; indeed the propor-
tional amplification of the object-glasses of the most
conscientious opticians will on comparison be found to
differ materially.
To arrive at a literally correct judgment of the value
of an objective to the microscopist, there are special
qualifications by which it should be judged. These,
for the sake of convenience, may be divided into :
Its defining power; its penetrating power, or focal
depth ; its resolving power ; its working distance and
its flatness of field : all of which are qualifications of
the greatest importance, especially when an objective
is about to be employed in scientific researche.
The Defining Power of the objective depends upon
the perfection with which the corrections of its chro-
matic and spherical aberrations are made. When these
are nicely balanced, the image will be sharp, and the
minutest details of an object seen with greater clear-
ness. Whatever other qualities may be absent in the
object-glass, fine definition must be secured. This
quality may be tested by taking a known test-object,
as it is termed, a blood corpuscle, a diatom mounted
in balsam, or a Podura-scale, and comparing the sharp-
ness and perfection of the image produced by one
objective, against that of another.
Penetrating Power, or focal depth, is a quality
THE OBJECTIVE. 59
which affords the observer a deeper insight into struc-
ture. The objective having the longest working dis-
tance, as a rule, possesses the greatest amount of pene-
tration. Theoretically, according to Professor Abbe, the
penetration of an objective decreases as the square of
the angular aperture increases. The botanist or phy-
siologist, studying the minute anatomy of plant or
animal, would gain a very imperfect idea of the
structural elements entering into either, unless
the objective possessed good penetration. It is, how-
ever, somewhat unusual to find good penetrating or
separating power combined with equally good definition
in any objective. The latter quality is compatible only
with the highest attainable aperture.
Fio. 35. Wenham's Binocular Objective.
Penetration is an indispensable quality for the bino-
cular microscope, consequently opticians have been
induced to furnish special forms of object-glasses for
use with this form of instrument. Mr. Wenham carried
a kind of speciality into the construction of high-power
objectives for the binocular, by mounting a prism in a
separate tube, and slipping it down the objective,
and letting it almost touch the back lens. Fig. 35
represents a fth objective of the kind, full size,
with correcting adjustment. D being the objective
complete, and the tube with prism fixed in its place.
The objective, it will be seen, is shorter than an ordinary
Jth, and can be made to answer a double purpose. ^ It
becomes more effective as a homogeneous-immersion
60 THE MICROSCOPE.
objective, and if intended to be so used, the correcting
adjustment will be unnecessary, since the body part
can be made shorter, and the back lens brought into
close contact with the binocular prism.
Messrs. Swift have also constructed a series of
object-glasses for a similar purpose. The taper front
objectives (fig. 36) are for use with their erecting
Stephenson's binocular instrument, and for the better
illumination of opaque objects. From their peculiar
construction, the illuminating rays from the bull's-eye
condenser are made to impinge somewhat more verti-
cally upon the object, thus avoiding deep shadows,
which often give rise to false appearances when the
light is thrown too obliquely on the object.
FIG. 36. Swift's Taper Object-glasses.
With regard to the binocular microscope, it should
be understood, writes Professor Abbe, that fairly satis-
factory stereoscopic observation cannot be extended
beyond moderate amplification, not even when the
binocular arrangement allows of the use of high
powers. In fact, as soon as the use of higher powers
is resorted to, stereoscopic vision is limited to objects
of so little depth that a merely plastic view of them
can hardly be productive of any scientific advantage,
although effective images may still be obtained.
Resolving Power is the power or capacity of the-
objective to resolve the finest lines, striae or dots ; that
is, separate and define them distinctly. Resolution
increases with width of aperture, and may therefore be
regarded as another expression for definition. The
THE OBJECTIVE. 61
maximum attainable resolving power of an objective of
180 aperture,, according to Professor Abbe, is tlie sepa-
ration or resolution of fine lines ruled 118000th of an
inch apart. Resolution depends more or less upon the
quality and quantity of the light admitted, the power
of collecting the greatest number of rays, and the per-
fection of centring. In other words, upon the co-ordi-
nation of the illuminating system of the microscope
mirror, achromatic condenser, objective and eye-piece.
If diatoms are employed as test- objects, it should be
borne in mind that there are great differences even in
the same species, and in the distances their lines are
apart. For this reason ruled lines of known value, as
Robert's lines, are much to be preferred. The follow-
ing example may be taken as a test of the value of a dry
Jth objective of 120 in defining the rulings of a 19-band
plate, which is equivalent to the l-67000th of an inch.
This objective, with careful illumination, showed them
all ; but when cut down by a diaphragm to 110, the
eighteenth line was not separable ; further cut down to
100 the seventeenth was the limit, to 80 the four-
teenth, and to 60 the tenth barely reached.
Flatness of Field is a quality of some importance,
and must be included in the general practical value of
the objective, denoting its capacity to exhibit the peri-
pheral portions of the field with the same degree of
sharpness as the central. Flatness of field is much
enhanced by the width of the opening or angular aper-
ture. In all high -angled objectives the image should
be sharp and quite free from colour to the very mar-
ginal portions of the field. In experimenting on the
comparative merits of two object-glasses as to flatness
of field, an eye-piece of large aperture should be used.
For testing flatness of field, Cole's exquisitely prepared
double-stained sections of woods will be found in every
way suitable objects. The proboscis of the fly is also
recommended, and if its details have not been de-
stroyed by being mounted in balsam, it is a good test.
Glycerine is the proper medium for displaying its
several structures. The cover-glass of the object, it must
be remembered, as Amici pointed out, is not an nnimpor
62
THE MICROSCOPE.
tant factor in the production of the image. An object
viewed without a cover-glass is more clearly defined
than one with. The late Andrew Ross explained the
cause of this difference in a paper published in the
" Transactions of the Society of Arts," vol. 41.
Perfect definition is the quality most sought after by
those engaged in histological pursuits ; whilst perfect
resolution is more highly esteemed by those who take
especial interest in the finest diatoms and test objects
of a similar nature. Various modifications have taken
place in the construction of the object-glass of the
FIG. 37. Forms of Object-glasses.
A, Double-convex lens ; B, Plano-concave ; C, Bi-convex and plano-concave
united ; shown in their various combinations, as at D, form the 3-in.,
2-in. or IJ-in. ; at E, 1-in. and jj-in. ; and at F, the -in. -in. J-in. and
5 i 3 -in. objectives.
microscope : opticians, however, are quite agreed that
the highest theoretical perfection will be obtained by
an increase rather than a decrease in the number of
lenses entering into its combination. Both at home
and abroad first-class makers, such as Ross, Powell
and Lealand, Beck, Dallmeyer, Tolles, Wales, Zeiss,
&c., have been working on this principle. To a well-
considered combination formula they have added a
single front plano-convex lens of crown-glass, which
gives increase of power with a longer working distance
to the objective.
THE OBJECTIVE. 63
The accompanying diagram is intended to show the
several lenses that enter into the construction of the
ordinary achromatic object-glass. A double convex
lens and plano-convex lens of crown-glass, and a piano
and donble concave lens and a miniscns lens of flint-
glass, are ingeniously cemented with Canada balsam
into a solid mass. Each objective, from the -|-inch to
the -jL-inch and upwards, is thus made up of at least
eight original lenses, the back combination of each
being a triplet formed of two double convex lenses of
crown-glass, with an intermediate double ccncave lens
of flint-glass.
I cannot bring these brief observations on the object-
glass to a close without referring more directly to the
great improvement effected in balancing its aberrations
by the late Mr. Lister. This gentleman devised the
very important screw-collar adjustment, by means of
which the front lens of the objective is brought nearer
to the back lens; this at once compensates for the
disturbance produced by rays of light being made to
pass through different thicknesses of glass covers.
When an objective has its aberrations balanced for
viewing an opaque object, and it is required to examine
that object by transmitted light, the correction will
remain ; but if it is necessary to immerse the object
in a fluid, or to cover it with glass, an aberration arises
from either circumstance which will disturb the pre-
vious correction, and deteriorate the definition ; and
this defect will be more obvious from the increase of
distance between the object and objective.
How this very important correction is effected may
be further explained. If an object-glass be constructed
as represented in fig. 38, where the posterior combina-
tion p and the middle m have together an excess of
negative aberration, and if this be corrected by the-
anterior combination a having an excess of positive
aberration, then this latter combination can be made
to act more or less powerfully upon p and w, by
making it approach to or recede from them ; for when
the three act in close contact, the distance of the
object from the object-glass is greatest, and conse-
64 THE MICROSCOPE.
quently the rays from the object arc diverging from a
point at a greater distance than when the combina-
tions are separated ; and as a lens bends the rays more,
or acts with greater effect, the more distant the object
is from which the rays diverge, the effect of the
anterior combination a upon the other two, p and m,
will vary with its distance from thence.
When, therefore, the correc-
tion of the whole is effected for
an opaque object, with a certain
distance between the anterior
and middle combination, if they
are then put in contact, the dis-
tance between the object and
object-glass will be increased ;
consequently, the anterior com-
bination w r ill act more power-
fully, and the whole will have
an excess of positive aberration.
Now the effect of the aberra-
tion produced by a piece of flat
and parallel glass being of a negative character, it
is obvious that the above considerations suggest the
means of correction, by moving the lenses nearer to-
gether, and the positive aberration is made to balance
the negative aberration caused by the medium.
The preceding refers only to "the spherical aberra-
tion ; but the effect of the chromatic is also seen when
an object is covered with a piece of glass : it pro-
duces chromatic thickening of the outline of Podura
and other delicate scales ; and if diverging rays near
the axis and at the margin are projected through a
piece of flat parallel glass, with the various indices of
refraction for the different colours, it will be seen that
each ray will emerge, separated, into a beam con-
sisting of the component colours of the ray, and that
each beam is widely different in form. This difference,
being magnified by the objective of the microscope,
readily accounts for the chromatic thickening of the
outline just mentioned. Therefore, to obtain the finest
definition of extremely delicate and minute objects,
THE CORRECTION OF THE OBJECTIVE.
65
they should be viewed without a covering ; if it be
desirable to immerse them in a fluid, they should be
covered with the thinnest possible film of talc, as,
from the character of the chromatic aberration, it will
be seen that varying the distances of the combinations
will not sensibly affect the correction ; though object-
lenses may be made to include a given fluid, or solid
medium, in their correction for colour.
The mechanism for applying these principles to the
correction of an object-glass under the various circum-
stances, is represented in fig. 39, where the anterior
lens is set in the end of a tube
a, which slides on the cylinder
b, containing the remainder of
the combination ; the tube a,
holding the lens nearest the
object, may then be moved
upon the cylinder &, for the
purpose of varying the dis-
tance, according to the thick-
ness of the glass covering the
object, by turning the screwed
ring c, or more simply by
sliding the one on the other,
and clamping them together
when adjusted. An aperture
is made in the tube a, within
which is seen a mark engraved
on the cylinder ; and on the edge of which are two
marks, a longer and a shorter, engraved upon the tube.
When the mark on the cylinder coincides with the
longer mark on the tube, the adjustment is perfect for
an uncovered object ; and when the coincidence is with
the short mark, the proper distance is obtained to
balance the aberrations produced by glass the hun-
dredth of an inch thick, and such glass can be readily
supplied. This adjustment should be tested experi-
mentally by moving the milled edge, so as to separate
or close together the combinations, and then bringing
the object to distinct vision by the screw adjustment
of the microscope. In this process the milled edge of
FIG. 39.
66 THE MICROSCOPE.
the object-glass will be employed to adjust for charac-
ter of definition, and the fine screw movement of the
microscope for correct focus.
The graduations on the correction-collar are merely
for convenience of registering the point of " best cor-
rection " for particular objects, so that the objective
may be set at the same correction if the observation
has to be repeated. It is usual with amateurs, who
have not practised themselves thoroughly in rapidly
adjusting their objectives by inspection of the image,
to note on their slides the best point of adjustment as
well as the position of the object, either with reference
to stage graduations or to Maltwood's finder. The
registration of the position may save time in re-
peating an observation ; but the registration of the
best point of adjustment should, generally speaking,
be regarded as an approximative process only, for the
adjusting collar is seldom made so accurately that
absolute reliance can be placed on the index. To
obtain fine definition test the correction in both direc-
tions, and take care to follow the image with the fine
adjustment. With objectives of large aperture this
process is of much importance, as the exact " distanc-
ing " makes or mars the definition.
Mr. Wenham recommends the following method of
securing the most efficient performance of an object-
glass. Select any dark speck or opaque portion of
the object, and bring the outline into perfect focus ;
then lay the finger on the milled head of the fine ad-
justment, and move it briskly backwards and forwards
in both directions from the first position. Observe the
expansion of the dark outline of the object, both when
within and when without- the focus. If the greater
expansion, or coma, be when the object is without the
focus, or farther from the objective, the lenses must
be placed farther asunder, or towards the mark " un-
covered." If the greater coma be when the object is
within the focus, or nearer to the objective, the lenses
must be brought closer together, or towards the mark
"covered." When the object-glass is in proper ad-
justment, the expansion of the outline is exactly the
t
TESTING THE OBJECTIVE. 67
same both within and without the focus. A different
indication, however, is afforded by such test-objects as
present (like the Podura-scale, the Diatoms, &c.) a
set of distinct dots or other markings. If the dots
have a tendency to run into lines when the object is
without the focus, the glasses should be brought closer
together; on the contrary, if the lines appear when
the object is within the focal point, the glasses must
be farther separated.
The Podura-scale is an excellent test-object. The
structure consists of a delicate transparent lamina or
membrane, covered with an imbricated arrangement of
epithelial plates, the length of which is six or eight
times their breadth, and arranged like the tiles on
a roof, or the long pile of some kinds of plush. The
scales may be readily obtained by putting a live
Podura into a small test-tube, and inverting it on a
glass-slide; the insect should then be allowed for a
time to leap and run about in the confined space. By
this means the scales will be freely deposited on the
glass ; and being subsequently trodden on by the insect,
several will be found from which the epithelial plates
have been partially rubbed off, and at the margin of
the undisturbed portion the form and position of the
plates may be readily recognized. Their structure ap-
pears to be rendered more palpable by mounting the
scales thus obtained in Canada balsam, and illuminating
them by means of Wenham's parabolic reflector. The
structure may also be very clearly recognized when the
scale is seen as an opaque object under a Boss's -^ (spe-
cially adjusted for uncovered objects), illuminated by
a combination of the parabola and a flat Lieberkuhn.
The under-side of the scale appears as a smooth glis-
tening surface, with very slight markings, correspond-
ing, probably, to the points of insertion of the plates on
the contrary side. The minuteness and close proximity
of the epithelial plates may account for their being
found a erood test of definition, while their prominence
renders them independent of the separating power due
to larger aperture.
The structure of another class of test-objects, the
F 2
68 THE MICROSCOPE.
diatomacene, differs entirely from that above described ;
it will suffice for my present purpose to notice the
valves of three species only of the genus Pleurosigma ;
these, arranged in the order of easy visibility, are,
P. formosum, P. hippocampus, P. angulatum. All
appear to consist of laminae of homogeneous trans-
parent silex, studded with dots, or rather protuberances,
which in P. formosum and P. angulatum have a trian-
gular arrangement, and in hippocampus a quadrangular.
The " dots " have been described as depressions ; but
if the frustule be broken the fracture is invariably
observed to take place between the rows of dots, and
not through them, as would naturally occur if the dots
were depressions, for the substance is thinner there
than elsewhere.
This, in fact, is always observed to take place in the
siliceous loricse of some of the border tribes that occupy
a sort of neutral, and yet not undisputed, ground
between the confines of the animal and vegetable king-
doms ; as, for example, the Isthmia, which possess a
reticulated structure, with depressions between the
meshes, somewhat analogous to that which would
result from pasting together bobbin-net and tissue-
paper. The valves of P. angulatum, and similar objects,
have been by some investigators supposed to be made
up of two substances possessing different degrees of
refractive power ; but this hypothesis is purely specula-
tive, since the observed phenomena will naturally result
from a series of rounded or lenticular protuberances of
one homogeneous substance. Moreover, if the centres
of the markings were centres of greatest density, if, in
fact, the structure were at all analogous to that of the
crystalline lens of the eye, it is difficult to conceive why
oblique rays only should be visibly affected. When P.
hippocampus or P. formosum is illuminated by a proper
condenser, with a central stop placed under the lenses,
and viewed by a quarter-inch object-glass of 70 aper-
ture, both being accurately adjusted, we may observe
in succession, as the object-glass approaches the object,
first a series of well-defined bright dots ; secondly, a
scries of dark dots replacing these ; and thirdly, the
THE APEKTCRE OF THE OBJECTIVE. 60
latter again replaced by bright dots, not, however, so
well defined as the first series. A similar succession of
bright and dark points may be observed in the centre
of the markings of some species of Coscinodiscus from
Bermuda when viewed by transmitted light.
These appearances would result if a thin plate of
glass were studded with minute, equal, and equidistant
plano-convex lenses, the foci of which would necessarily
lie in the same plane. If the focal surface, or plane of
vision, of the object-glass be made to coincide with this
plane, a series of bright points would result from the
accumulation of the light falling on each lens. If the
plane of vision be next made to coincide with the sur-
faces of the lenses, these points would appear dark, in
consequence of the rays being refracted towards points
now out of focus. Lastly, if the plane of vision be
made to coincide with the plane beneath the lenses that
contain their several foci, so that each lens may be, as
it were, combined with the object-glass, then a second
series of bright points will result from the accumula-
tion of the rays transmitted at those points. Moreover,
as all rays capable of entering the object-glass are con-
cerned in the formation of the second series of bright
focal points, whereas the first series being formed by the
rays of a conical shell of light only, it is evident that
the circle of least confusion must be much less, and
therefore the bright points better defined in the first
than in the last series.
The Aperture of the Object-glass. The aperture of
an objective has been, down to a comparatively recent
period, the occasion of much controversy. It was
contended that the aperture of a dry objective of 180
angle represented the largest aperture possible, that
this could not be exceeded by any immersion objectives,
the advantages of the latter resting solely upon the
increase in light, through the absence of reflection at
the surface of the front lens, and their greater working
distance.
The confusion into which the aperture question was
brought by this contention, arose almost entirely from
the fact that its supporters had not appreciated the
70 THE MICROSCOPE.
proper definition of the term " aperture," bat had
assumed it to be synonymous with what was known as
" angular aperture." The angles of the pencils admit-
ted by objectives cannot however serve as a measure of
their apertures. When the medium in which they
work is the same, as air, it is not the angles but the
sines of those angles which enable the proper com-
parison to be made, thus : if two dry objectives admit
pencils of 60 and 180, their real apertures are not as
1 : 3, but as 1 : 2 only. When the media are different,
as air, water and oil, the angles are still more misleading,
as there may be three angles all with the same number
of degrees, and yet representing entirely different aper
tures.
Whilst, however, those who insisted upon the increase
of the apertures of objectives with the increase in the
refractive index of the immersion fluid, were right in
their contention, a somewhat similar lack of proper
definition of the term aperture prevented the question
being at that time effectually disposed of. The whole
matter was, however, recently exhaustively dealt with
in the course of a renewal of the " aperture question,"
before the Royal Microscopical Society, and in the
papers of Professor Abbe (of Jena), and Mr. Crisp
(Sec. R<. Micr. Soc.), printed in the journal of that
society, 1 the subject of aperture will be found to be
at last placed on a scientific basis. To follow the
question in all its details, reference must be made to
these papers, but a brief resume of the leading points
will be found instructive and useful.
The first essential step in the consideration of aper-
ture is, as I have said, to understand clearly what is
meant by the term. It will be at once recognized that
its definition must necessarily refer to its primary
meaning of " opening," and must, in the case of an
optical instrument, define its capacity for receiving
rays from the object, and transmitting them to the
image.
In the case of the telescope-objective, its capacity
for receiving and transmitting rays is necessarily mea-
(1) Journ. R. Micr. Soc., I. (1881), pp. 303-60 and pp. 388-123.
THE APEKTUHE OF THE OBJECTIVE. 7]
Eured by the expression of its absolute diameter or
" opening." No such absolute measure can be applied
in the case of microscope-objectives, the largest lenses
having by no means the largest apertures, but being,
in fact, found with the low powers, whose apertures
are but small. The capacity of a microscope- objective
for receiving and transmitting rays is, however, as will
be seen, estimated by its relative opening, that is, its
opening in relation to its focal length. When this
relative opening has been ascertained, it may be
regarded as synonymous with that denoted in the
telescope by absolute opening. That this is so will be
better appreciated by the following consideration :
In a single lens, the rays admitted within one meri-
dional plane evidently increase as the diameter of the
lens (all other circumstances remaining the same), for
in the microscope we have, at the back of the lens, the
same circumstances as are in front in the case of the
telescope. The larger or smaller number of emergent
rays will therefore be measured by the clear diameter,
and as no rays can emerge that have not first been
admitted, this must also give the measure of the admit-
ted rays.
If the lenses compared have different focal lengths
but the same clear " openings," they will transmit the
same number of rays to equal areas of an image at a
definite distance, because they would admit the same
number if an object were substituted for the image ;
that is, if the lens were used as a telescope-objective.
But as the focal lengths are different, the amplification
of the images is different also, and equal areas of these
images correspond to different areas of the object from
which the rays are collected. Therefore, the higher
power lens with the same opening as the lower power,
will admit a greater number of rays in all from the same
object, because it admits the same number as the latter
from a smaller portion of the object. Thus, if the focal
lengths of two lenses are as 2 : 1, and the first ampli-
fies N diameters, the second will amplify 2 N with the
same distance of the image, so that the rays which are
collected to a given field of I mm. diameter of the
72 THE MICROSCOPE.
image are admitted from a field of N nim. in the first
case, and of ^ mm. in the second. As the " opening "
of the objective is estimated by the diameter (and not
by the area) the higher power lens admits twice as
many rays as the lower power, because it admits the
same number from a field of half the diameter, and, in
general, the admission of rays by the same opening,
but different powers, must be in the inverse ratio of
the focal lengths.
In the case of the single lens, therefore, its aperture
is determined by the ratio between the clear opening
and the focal length. The same considerations apply to
the case of a compound objective, substituting, however,
for the clear opening of the single lens the diameter of
the pencil at its emergence from the objective, that is,
the clear utilized diameter of the back lens.
All equally holds good whether the medium in which
the objective is placed is the same in the case of the
two objectives or different, as an alteration of the
medium makes no difference in the power.
Thus we arrive at a general proposition for all kinds
of objectives: 1st, when the power is the same, the
admission of rays (or aperture) varies with the diame-
ter of the pencil at its emergence; 2nd, when the
powers are different, the same aperture requires differ-
ent openings in the ratio of the focal lengths, or
conversely with the same opening the aperture is in
inverse ratio to the focal lengths. We see, therefore,
that just as in the telescope the absolute diameter of
the object-glass defines its aperture, so in the micro-
scope the ratio between the utilized diameter of the back
lens and the focal length of the objective defines its
aperture also, and this is clearly a definition of aperture
in its primary and only legitimate meaning as " open-
ing ; " that is, the capacity of the objective for admit-
ting ravs from the object and transmitting them to the
image.
If, by way of illustration, we compare a series
of dry and oil-immersion objectives, and commencing
with small air angles, progress up to 180 air angle,
and then take an oil -immersion of 82 and progress
180 Oil Angle.
(Numerical Aperture T52.)
NUMERICAL APERTURE. 73
again to 180 oil angle, the ratio of opening to power
progresses also, and attains its maximum, not in the
case of the air angle of 180 (when it is exactly equiva-
lent to the oil angle of only 82), but is greatest at
the oil angle of 180. If we assume the objectives to
have the same
power through-
out we get rid of
one of the factors
of the ratio, and
we have only to
compare the dia-
meters of the
emergent beams,
and can represent
their relations by
diagrams.
Fig. 40 illus-
trates five cases
of different aper-
tures of J - in.
objectives, viz. :
those of dry ob-
jectives of 60,
97, and 180 air
angle, a water-
immersion of 180
water angle, and
an oil-immersion
of 180 oil angle.
The inner dotted
circles in the two
latter cases are of
the same size as
,i , j of various dry and mmerson
that correspond- game power ( |. in-) from an air angi* of 60 to an
ing to the 180 oil angle of 180.
air angle.
A dry objective of the maximum air angle of 180
is only able to utilize a diameter of back lens equal to
twice the focal length, while an immersion lens of even
only 100 utilizes a larger diameter, i.e., it is able to
O
180 Water Anglo.
(Numerical Aperture T33.)
180 Air Angle.
96 Water Angle.
82 Oil Angle.
(Numerical Aperture I'OO.)
97 Air Angle.
(Numerical Aperture 75.)
60 Air Angle.
(Numerical Aperture '50.)
FIG. 40.
Relative diameters of the (utilized) back lenses
of various dry and immersion objectives of the
74 THE MICROSCOPE.
transmit more rays from the object to the image than
any dry objective is capable of transmitting. When-
ever the angle of an immersion lens exceeds twice the
critical angle for the immersion fluid, i.e., 96 for water
or 82 for oil, its aperture is in excess of that of a dry
objective of 180.
This excess will be seen if we take an oil-immersion
objective of, say 122 balsam-angle, illuminating it so
that the whole field is filled with the incident rays, and
use it first on an object not mounted in balsam, but dry.
We then have a dry objective of nearly 180 angular aper-
ture, for, as will be seen by reference to fig. 41, the
cover-glass is virtually the first surface of the objective,
as the front lens, the immersion fluid, and the cover-
glass are all approximately of the same index, and
FRONTLENS
____^__ IMMERSION FLUID
DBJUCTINMR __r^jr^ni COVE* CLASS
SLIDE
FIG. 41.
form, therefore, a front lens of extra thickness. When
the object is close to the cover-glass the pencil radiating
from it will be very nearly 180, and the emergent
pencil (observed by removing the eye-piece) will be seen
to utilize as much of the back lens of the objective as
is equal to twice the focal length, that is the inner of
the two circles at the head of fig. 40.
If now balsam is run in beneath the cover-glass so
that the angle of the pencil taken up by the objective
is no longer 180, but 122 only (that is, smaller), the
diameter of the emergent pencil is larger than it was
before, when the angle of the pencil was 180 in air,
and will be approximately represented by the outer
circle of fig. 40. . As the power remains the same in
both cases, the larger diameter denotes the greater
NUMERICAL APERTURE. 75
aperture of the immersion objective over a dry objective
of even 180 angle, and the excess of aperture is made
plainly visible.
Having settled the principle, it is still necessary,
however, to find a proper notation for comparing
apertures. The astronomer can compare the apertures
of his various objectives by simply expressing them in
inches, but this is obviously not available to the micro-
scopist, who has to deal with the ratio of two varying
quantities.
In consequence of a discovery made by Professor
Abbe in 1873, that a general relation existed between
the pencil admitted into the front of the objective,
and that emerging from the back of the objective, he
was able to show that the ratio of the semi -diameter
of the emergent pencil to the focal length of the
objective could be expressed by the formula n sin u>
i.e., by the sine of half the angle of aperture (u)
multiplied by the refractive index of the medium (n)
in front of the objective (n being I'O for air, 1'33 for
water, and 1*52 for oil or balsam).
When, then, the values in any given cases of the
expression n sin u (which is known as the " numerical
aperture") has been ascertained, the objectives are
instantly compared as regards their aperture, and,
moreover, as 180 in air is equal to I'O (since %=1'0
and the sine of half 180=1'0) we see, with equal
readiness, whether the aperture is smaller or larger
than that corresponding to 180 in air. Thus, sup-
pose we desire to compare the apertures of threo
objectives, one a dry objective, the second a water
immersion, and the third an oil immersion; these
would be compared on the angular aperture view as,
say 74 air angle, 85 water angle, and 118 oil
angle, so that a calculation must be worked out to
arrive at the actual relation between them. Applying,
however, the " numerical " notation, which gives '60
for the dry objective, '90 for the water immersion, and
1'30 for the oil immersion, their relative apertures are
immediately recognized, and it is seen, for instance,
that the aperture of the water immersion is some-
'O TEE MICROSCOPE.
what less than that of a dry objective of 180*, and
that the aperture of the oil immersion exceeds thau
of the latter by 30%
The advantage of immersion, in comparison with
dry objectives, is also at once apparent. Instead of
consisting merely in a diminution of the loss of light
by reflection or increased working distance, it is seen
that a wide-angled immersion objective has a larger
aperture than a dry objective of maximum angle, so
that for any of the purposes for which aperture is
essential an immersion must necessarily be preferred to
a dry objective.
That pencils of identical angular extension but in
different media are different physically, will cease to
appear in any way paradoxical if we recall the simple
optical fact that rays, which in air are spread out
over the whole hemisphere, are in a medium of higher
refractive index such as oil compressed into a cone of
82 round the perpendicular, i.e., twice the critical
angle. A cone exceeding twice the critical angle of
the medium will therefore embrace a surplus of rays
which do not exist even in the hemisphere when the
object is in air.
The whole aperture question, notwithstanding the in-
numerable perplexities with which it has hitherto been
surrounded, is in reality completely solved by these
two simple considerations : First, that " aperture " is
to be applied in its ordinary meaning as representing
the greater or less capacity of the objective for
receiving and transmitting rays ; and second, that
when so applied the aperture of an objective is
determined by the ratio between its opening and its
focal length ; the objective that utilizes the larger
back lens (or opening) relatively to its focal length
having necessarily the larger aperture. It would
hardly, therefore, serve any useful purpose if we were
here to discuss the various erroneous ideas that gave
rise to the contention that 180 in air must be the
maximum aperture. Amongst these was the sugges-
tion that the larger emergent beams of immersion
objectives were due to the fact that the immersion
THE IMMERSION APERTURE. 77
fluid abolished the refractive action of the first plane
surface which, in the case of air, prevented there being
any pencil exceeding 82 within the glass. Also the very
curious mistake which arose from the assumption that
a hemisphere did not magnify an object at its centre
because the rays passed through without refraction.
A further erroneous view has, however, been so wide-
spread that it will be desirable to devote a few lines
to it, especially as it always seems at first sight to be
both simple and conclusive.
If a dry objective is used upon an object in air as
in fig. 42, the angle may approach 180, but when the
object is mounted in balsam as in fig. 420, the angle
at the object cannot exceed 82, all rays outside that
limit (shown by dotted lines) being reflected back at
the cover-glass and not emerging into air. On using
an immersion objective, however, the immersion fluid
which replaces the air
above the cover-glass
allows the rays former-
ly reflected back to pass
through to the objec-
tive so that the angle
at the object may again
be nearly 180 as with the dry lens. The action of the
immersion objective was, therefore, supposed to be
simply that it repaired the loss in angle which was
occasioned when the object was transferred from air to
balsam, and merely restored the conditions existing in
fig. 430 with the dry objective on a dry object.
As the result of this erroneous supposition, it fol-
lowed that an immersion objective could have no
advantage over a dry objective, except in the case of
the latter being used upon a balsam-mounted object,
its aperture then being (as was supposed) " cut down."
The error lies simply in overlooking the fact that the
rays which are reflected back when the object is mounted
in balsam (fig. 420) are not rays which are found when
the object is in air (fig. 42), but are additional and
different rays which do not exist in air, as they cannot
be emitted in a substance of so low a refractive index.
78 THE MICROSCOPE.
Lastly, it should also be noted that it is numerical
and not angular aperture which measures the quantity
of light admitted to the objective by different pencils.
First take the case of the medium being the same.
The popular notion of a pencil of light may be illus-
trated by fig. 43, which assumes that there is equal
intensity of emission in all directions, so that the
quantity of light contained in any given pencils may
be compared by simply comparing the contents of the
solid cones. The Bouguer-Lambert law, however,
shows that the quantity of light emitted by any
bright point varies with the obliquity of the direction
of emission, being greater in a perpendicular than in
an oblique direction. The rays are less intense in
proportion as they are more inclined to the surface
FIG. 43. FIG. 43a.
which emits them, so that a pencil is not correctly
represented by fig. 43, but by fig. 43, the density of
the rays decreasing continuously from the vertical to
the horizontal, and the squares of the sines of the
semi-angles (i.e., of the numerical aperture) constitut-
ing the true measure of the quantity of light con-
tained in any solid pencil.
If, again, the media are of different refractive indices,
as air (TO), water (T33), and oil (1'52), the total
amount of light emitted over the whole 180 from
radiant points in these media under a given illumination
is not the same, but is greater in the case of the media
of greater refractive indices in the ratio of the squares
of those indices (i.e., as TO, 177 and 2'25). The quan-
tity of light in pencils of different angle and in different
media must therefore be compared by squaring the
THE IMMERSION APERTURE. 79
product of the sines and the refractive indices, i.e.
(n Sin w 2 ), for the square of the numerical aperture.
The fact is therefore established that the aperture o{
a dry objective of 180 does not represent, as was sup.
posed, a maximum, but that aperture increases with the
increase in the refractive index of the immersion fluid ;
and it should be borne in mind that this result has
been arrived at in strict accordance with the ordinary
propositions of geometrical optics, and without any
reference to or deductions from the diffraction theory
of Prof. Abbe.
We have, however, still to determine the proper
function of aperture, immersion objectives of large
aperture excelling, as is well known, any dry objective
in the delineation of minute structures.
The old explanation of the increased power of vision
obtained by increase of aperture was, that by the
greater obliquity of the rays to the object " shadow
effects " were produced, a view which overlooked the
fact, first, that the utilization of increased aperture
depends not on the obliquity of the rays to the object,
but to bhe axis of the microscope ; and secondly, that just
as there is no acoustic shadow produced by an obstacle,
which is only a few multiples of the length of the
sound waves, so there can be no shadow produced by
minute objects which are only a few multiples of the
light waves, the latter then passing completely round
the object. The Abbe diffraction theory, however,
supplies the true explanation, and shows that the
increased performance of immersion objectives of
large aperture is directly connected (as might havt
been anticipated) with the larger "openings " in the
proper sense of the term, which, as we have just
seen, such objectives necessarily possess. It has also
been shown, then, in order that the image should exactly
correspond with the object, all the diffracted rays
must be gathered up by the objective. If any ar^ lost
we then get not an image of the real object but a
spurious one. Now, if we have a coarse object, the
diffracted rays are all comprised within a narrow cone
round the direct beam, and an objective of small
80 THE MICROSCOPE.
aperture will transmit them all. With a minute
object, however, the diffracted rays are widely spread
out so that a small aperture can admit only a fractional
part to admit the whole or a very large part, and
consequently to see the minute structure of the object,
or to see it truly, a large aperture is necessary, and in
this lies the value of aperture and of a wide-angled
immersion-objective for the observation of minute
structures.
Object-glasses. With regard to the selection of
object-glasses, this will depend on the work in which we
may be about to engage. The amateur or student will
be well advised to commence with moderate or even
low powers, as a 3-inch, a 2-inch, a 1-inch, and a
f -inch focus. These powers used with the A eye-piece
will give a range of magnification of from 20 to 70
diameters ; and with the B eye-piece will be increased
to 120 diameters. Zeiss, of Jena, has lately constructed
a very useful adjustable objective; by an ingenious
screw-collar arrangement the relative position of the
front lens is changed, and a range of power, varying
from 12 to 24, or 30 diameters, is obtained. This
object-glass consists of a convex back lens and a con-
cave front lens (both achromatic), the distance of
which is changed by means of a screw acting in the
manner of a correcting collar of wide range. When
the collar is put to 10, the objective has its minimum
focal length or maximum power, approximately corre-
sponding to that of a single 2-inch lens. By closing
the collar the equivalent focal length increases, the
back lens is made to approach nearer the eye-piece,
and the magnifying power is varied, so that when the
collar is put to the actual power of the objective
corresponds to that of a 4-inch lens. By a judicious
use of the draw-tube of the microscope a further mag-
nification of the image can be obtained, which is of
value if botanical sections, opaque objects, and whole
insects are under examination. With an erecting eye-
piece the lower powers above mentioned are most useful
for dissection purposes.
Objectives of medium power are the |-inch, 4-10ths,
THE SELECTION OF OBJECT-GLASSES. 81
J and Jth, with a magnification ranging from about 125
to 250 diameters with the A eye-piece, and increasing
with the b eye-piece to 375 diameters. I have in
my possession a fine J made for me by Dallmeyer,
with an aperture of 120. It bears an extra deep
eye-piece, and will then give a magnification of 1,000
diameters in every way satisfactory. It also works
through almost any thickness of cover-glass ; its
aberrations being equally well balanced for uncovered
objects, no mean test of a good objective. These
several points prove that its working aperture has been
brought to the maximum of utility. On the whole,
the power is one of considerable value for the investi-
gation of organized structure and for viewing living
action. Every one aiming at original observations upon
the morphology of living creatures should become
skilled in the use of high magnifying powers, as the -J,
7*05 T 1 2 > "iV an ^ "sV- -^ nave > however, always pointed to
the futility of constructing higher power object-glasses,
except with a proportionately increased width of aper-
ture. As the maximum angle appears to be 180, or
160, for the odd 20 are not worth the having (compare
the chords of 180 and 160 there is hardly any differ-
ence), and as a T ^ can be made to transmit an angle of
160, I maintain that it will possess as much resolving
power as any dry -fa or -g^th. 1 This is seen in the series
of wonderful photographs of muscular tissue, blood
corpuscles, etc., taken by Dr. Woodward, of Washington,
U.S., and which certainly prove that the photographic
eye sees after making every allowance for what is
due to the nature and undulations of light what the
human eye cannot see.
The Immersion System. About fifty years ago
Amici demonstrated the value of a drop of water in-
serted as an adjustable film between the object and
the objective, and showed that it materially assisted in
(1) Professor Abbe has shown that no objective can possess at the same
lime penetrating power and perfect definition. The practical outcome of
this observation is, that neither penetrating objectives nor defining objectives
Rie aloi.e sufficient for every kind of microscopical work. Both are neces-
sary. If, however, the student is limited in the number of his objectives,
then he should at least provide himself with a low-power defining lens,
|-inch Ross, and high-power penetrating immersion.
G
82 THE MICROSCOPE.
balancing certain uncorrected aberrations. Soem-
mering, writing of one of Arnici's microscopes, ob-
serves : " The magnifying power, admirable precision,
and clearness with which the object is seen, seems to
me quite astonishing." It is not difficult to perceive
that, this optician's method of connecting the objective
with the cover-glass of the object by means of a drop
of water should diminish the reflection which takes
place in the incidence of oblique light when the dry
objective is used. The limiting angle of refraction
of water being nearly 48, it follows that whatever
the degree of obliquity in the incident light falling on
the object, the immersion lens can never have to deal
with rays of greater obliquity than 48. To this
circumstance, as well as to the greater number of
parallel rays brought to a focus, and to the increased
angle of aperture is due the greater clearness and pre-
cision and sharpness of the image. The film of water
not only furnishes increased angle of aperture, but it
also collects the straying away peripheral rays of light,
and sends them on to the eye-piece, to assist in render-
ing the image more perfect ; becomes, indeed, an in-
tegral part of the optical system, and very materially
aids in the removal of residuary secondary aberrations.
The water-immersion system was warmly advocated
and fully developed by continental makers Hartnack,
Merz, Nachet, and others long before English opticians
could be persuaded to acknowledge its advantages.
Messrs. Powell and Lealand were the first opticians
who made a ^-inch and a |-th objective, which, by a
mere change of the front lens, could be used either
as a wet or dry lens.
The immersion principle has recently been still
further developed. The substitution of oil for water
was first proposed by Amici, in 1844, who abandoned it
as it seemed unmanageable and without correspond-
ing advantages as compared with water, an opinion
shared by Oberhauser and Wenham. At this time,
however, it was supposed that the chief gain of the
immersion consisted in a diminished loss by reflection
at the front lens and an increase of working distance ;
THE IMMERSION SYSTEM. 83
it was not recognized that additional aperture was also
obtained. In 1877 Mr. J. W. Stephenson demonstrated
that as the aperture of an objective increased with
the increase in the refractive index of the immer-
sion fluid great practical advantage would result
from using instead of water a homogeneous fluid;
that is, one not merely of the same refractive index,
but also of the same dispersive power as the glass
of the front lens of the objective. This sugges-
tion was immediately acted upon by Professor Abbe,
and in December, 1877, the, first objective on the new
system was issued from Zeiss's workshop, giving an in-
crease in aperture of upwards of 50 per cent, over a dry
objective of equal angle. In addition to increase of
aperture, the use of a homogeneous fluid gives a pre-
viously unlooked-for advantage that it is possible to
correct a "homogeneous immersion" objective with
more facility than one which works in such media as air
and water, both of which differ considerably in refrac-
tive and dispersive power from the glass of the lenses.
With air, or even water objectives, there is a large
amount of aberration affecting the pencils on their
passage from the radiant to the medium of the front
lens, which bears a considerable ratio to the total
spherical aberration within the objective, and in the
case of wide angles increases disproportionately from
the axis outwards. This can only be corrected by a
rough method of balancing, that is, by introducing an
excess of opposite aberration at the posterior lenses.
An uncorrected residuum, rapidly increasing with larger
apertures, is then left, and this appears in the image
amplified by the total power of the objective, so that
with a non-homogeneous medium there is a maximum
angular aperture which cannot be surpassed without
undergoing a perceptible loss of definition, provided
working distance is required. If we abolish the an-
terior aberration for all colours, by an immersion fluid
which is equal to crown-glass in refractive and dis-
persive power, the difficulty will be at once overcome.
If, for instance, we have an objective of 140 in glass
(= 1*25 N.A.) and water as the immersion fluid, the
G 2
84 THE MICROSCOPE.
aberration in front would affect a pencil of 140*. Sub.
stituting a homogeneous medium, the same pencil,
contracted to the equivalent angle in that medium of
112, will be admitted to the front lens without any
aberration, and may be made to emerge from the curved
surface also without any detrimental aberration, but
contracted to an angle varying from 70 to 90. The first
considerable spherical aberration of the pencil then
occurs at the anterior surface of the second lens, where
the maximum obliquity of the rays is already con-
siderably diminished.
Figs. 44 and 44# will serve to further elucidate this.
If the objective of 140 works with water (fig. 44),
there would be a cone of rays extending up to 70 on
FIG. 44. FIG. 44a.
both sides of the axis, and this large cone would be
submitted to spherical aberration at the front surface a.
But with homogeneous immersion (fig. 440) the whole
cone of 112 is admitted to the front lens without any
aberration, there being no refraction at the plane sur-
face ; and as the spherical surface of the front lens is
without notable spherical aberration, the incident pencil
is brought from the focus P to the conjugate focus /,
and contracted to an angle of divergence of 70 90
without having undergone any spherical aberration
at all.
Thus the problem of correcting a very wide-angled
objective is reduced by the homogeneous- immersion
THE IMMERSION SYSTEM. 85
system, both in theory and in practice, to the prob-
lem of correcting an objective having a moderate air
angle. 1
The adoption of the Homogeneons-immersion system
is at present warmly advocated by all opticians.
Messrs. Powell and Lealand take the lead with their
new formula |, which, illuminated by their oil immer-
sion-illuminator, will resolve the most difficult test-
objects. This objective has an aperture, measured in
crown-glass, of 150,= 1*47 N.A. "the widest aperture
yet produced." The same firm have constructed a -^ 5
and a -fj on the homogeneous system, but the apertures
are not so high as the ^th. " By the homogeneous-
immersion formula adopted by Powell and Lealand 2
the focal distance is practically a constant quantity,
and it follows that reduction of aperture by making
the front lens thinner ensures a much greater working
distance without affecting the aberrations ; for as the
first refraction takes place at the posterior or curved
surface of the front lens, the removal of any portion of
thickness at the anterior or plane surface simply cuts
off zones of peripheral rays without altering the dis-
tance any space being filled up by the homogeneous-
immersion fluid, or by an extra thickness of cover-
glass.
" By applying an extra front lens to the back construc-
tion of such a -j^ th, the observer is enabled to view an
object through a cover-glass that would be practically
a maximum thickness for a -Jth (aperture =90) con-
structed on the usual formula where the setting en-
croaches on the active spherical refracting surfaces. A
second front might give a high average aperture for a
-j^- (115), while the thickest front representing the
maximum aperture of the whole construction (142)
would enable the observer to view an object with a
greater aperture than has hitherto been obtained with
any T V* n > owing to difficulties of construction, and
through a thicker cover-glass than a y^th of the same
(1) See Prof. Abbe " On Stephenson's System of Homogeneous Immersion
for Microscope Objectives," Journ. R. Micr. Soc., II. (1S79), p. 256, and on
'The Essence of Homogeneous Immersion ." Ibid., I. (1881), p. 13L,
(2) Jovial of the R. M. S., Vol. III., p. 1050 (1880;.
86 THE MICROSCOPE.
aperture will admit of ; x hence three different fronts
would give a great range of aperture with a correspond-
ing working distance, which is practically what is
sought by having objectives constructed of the threa
different foci, |, T V, and -5^-."
" There can be no doubt," adds the writer, " English
Mechanic," "that the development of the homogeneous-
immersion system, is the problem of the future as
regards attaining the limit of resolution with the micro-
scope." But to ensure the fullest advantages the system
is capable of, a fluid is wanted which will meet all its
requirements. Professor Abbe, Mr. Stephenson and others
have experimented on various substances, and the con-
clusion come to is that the essential oils of cedar wood,
or fennel, which so nearly correspond to glass in their
refractive and dispersive power, will be found to afford
the best results. Oil of aniseed, chloral hydrate and
glycerine, various turpentines, and lead solutions have
been tried and ultimately abandoned. One precaution
is required with regard to all essential oils, they can only
be used with objectives having their fronts specially
cemented. Very fine objectives constructed on the
homogeneous immersion system by Zeiss, and requiring
no adjusting collar, may be had of Baker, Holborn, the
London agent of this optician.
THE CONSTRUCTION OF THE MICROSCOPE. THE MICRO-
SCOPE STAND.
The Principal Forms of Microscopes. Having duly
considered the essential parts of the compound achro-
matic microscope, I shall proceed to offer a few re-
marks on typical forms of English manufacture. I
must not attempt a critical examination of the very
numerous stands known to practical microscopists.
This would be impossible in a limited space. Neither
shall I attempt to institute invidious comparisons, as,
in my opinion, most forms of instruments brought
to notice possess some feature of a useful and praise-
(1) Powell and Lealand have also constructed a V and 53 on the homo
gcncons system, but the apertures are nots/> high as in the $ just mentioned
THE ROSS-ZENTMAYER STAND.
87
FIG. 45. The Improved Ross-Zentmai/er Model.
00 THE MICROSCOPE.
worthy character. My observations will therefore be
almost exclusively confined to points of excellence in
workmanship, to mechanical difficulties successfully
overcome, and new forms introduced since the publica-
tion of my ninth edition.
The Improved Koss-Zentmayer Microscope is a
thoroughly substantial and practical instrument, com-
bining elegance of appearance with facility in the
attainment of everything the microscope can at present
be expected to accomplish.
The stand is on the well-known Jackson model, with
extra wide slides for the rack-and-pinion movement.
The slow movement is obtained by a second slide
close behind the first, but to avoid the friction of rub-
bing surfaces, hardened steel rollers are inserted between
them, which gives a frictionless fine motion, amenable
to the slightest touch of the milled-head screw, situated
conveniently at the back of the limb, through which
a steel lever passes which actuates the slow motion
slide. The body of the instrument is therefore not
touched during the fine focussing, so that all lateral
movement is avoided. The mechanical stage is made to
rotate axially, and the outer edge of the lower plat?
is divided into degrees, in order to register the angles,
and a simple mode of adjustment is provided, for
setting the centre of rotation exactly coincident with
the focal point of the object-glass. As the plates of
the stage have no screw or rack work between them
(these being placed externally), they are brought close
together, giving the advantage of a very thin sub-
stantial stage, and ensuring rigidity where required ;
phosphor bronze being used in its construction. The
stage is attached to the limb by a conical stem, with a
screw and clamp nut at the back, so that it can
be easily removed for the substitution of a simple
plate, or other stage, and by turning the stem in the
socket the stage may be tilted sideways at any angle
required. One special feature in the Ross-Zentmayer
stand is a swinging sub- stage and bar, carrying the
mirror, having its axis of rotation situated from an
axial point in the plane of the object, which conse-
THE ROSS-ZENTMAYER STAND. 89
quently receives the light without requiring altera-
tion of focus in any position of the bar ; by this means
facilities are afforded for the resolution of objects
requiring oblique light and for the development of their
structure. Rays are thus obtained in the readiest
manner possible from any angle, which is indicated by
a graduated circle round the eye or top of the swing-
bar, and many troublesome and expensive pieces of
sub-stage apparatus, before
used as specialities for ob-
taining oblique illumina-
tion, are dispensed with.
The value of this arrange-
ment was recognized, as I
have already stated, in
Grubb's "Sector Stand,"
the movement of which
was obtained in a far less
efficient manner. Costly
high - angled condensers
may be dispensed with in
Ross's microscope, and
simple arrangements used
in their place, as Wen-
ham's immersion disc, or
the hemispheric lens. A
1^-inch or 2-inch object-
glass will generally suffice
for a condenser. This and other lenses can also be
used for opaque objects, by bringing the swing arm
and holder round above the stage, which it clears in
rotation.
The base or stand of the Ross-Zentmayer instrument
is sometimes made in one piece, but preference will, I
believe, be given to the double pillar support, as this is
very firm, and allows the sub-stage to swing free, while
the microscope is in a vertical position, as in working
with fluid preparations. The rim of the sub-stage is
provided with set screws for centring the lenses used,
and, when determined, can be secured by a clamping
screw.
FIG. 46. The Ross-Zentmayer
Student's Microscope.
-90 THE MICROSCOPE.
The sub-stage, with its apparatus in place, can be
instantly removed, by being drawn out sideways, so as
to use the mirror alone, which is a great convenience.
The mechanical movements of this instrument are
perfect, and well adapted to their purpose, and the
excellence of the workmanship is such as might have
been expected from the long-established reputation of
the house of Ross.
The Ross-Zentmayer Student's Stand (fig. 46) is a useful
instrument on a small scale, possessing all the advan-
tages of a larger microscope. It has an excellent fine
adjustment, the milled-head for working which is in
as convenient a place as that of more expensive stands.
It is not so costly as more pretentious instruments,
.a consideration often of importance to the student of
the collateral sciences. Messrs. Ross make a very good
and cheap series of object-glasses for histological work,
especially adapted for use with this instrument.
The general plan of Powell and Lealand's Compound
Microscope is represented in fig. 47. The tripod-stand
gives a firm support to the trunnions that carry the
tube to which the stage is attached, and from which a
triangular stem is raised by the rack-and- pinion move-
ment set in action by the double- milled head, whereby
the coarse adjustment of the focus is obtained. To
the upper part of the triangular bar a broad arm is
fixed, bearing the compound body ; this arm is hollow,
and contains the mechanism for the fine adjustment,
which is effected by turning the small milled-head.
The arm is connected with the triangular bar by a
strong conical pin, on which it turns, so that the
compound body may be moved aside from the stage
when necessary ; by a mechanical arrangement it
.stops when central. The stage has been improved in
construction, having vertical, horizontal, and circular
movements, and graduated for the purpose of register-
ing objects so as to be found at pleasure ; and in order
to do this effectually a clamping piece is provided
against which the object slide rests, and the circular
motion of the stage is stopped. It is an exceedingly
effectual method of finding a favourite object. The
POWELL AND LEALAND'S STAND. 91
stage is firm and strong, and at the same time so
thin, that the utmost obliquity of illumination is
attainable, the under portion being entirely turned
out ; it has a dove-tailed sliding bar movable by rack
and pinion ; into this bar slides the sub-stage, having
vertical and horizontal motions for centring, and also
a circular motion ; the sub- stage carries the various
FIG. 47. Powell and LealancVs Microscope, with Amid prism arranged for
oblique illumination.
appliances for underneath illumination, removed in the
woodcut. The achromatic condenser is seen detached.
Powell and Lealand have another pattern, larger
and more massive in its general arrangements. The
construction of the stage and sub-stage differ some-
what ; both resting on a large solid brass ring, firmly
attached to the stem of the instrument. The upper
side of this ring bears a sort of carriage that supports
92
THE MICROSCOPE.
the stage, and to this carriage a rotatory motion is
given by a milled-head, the amount of the movement,
which may be carried through an entire revolution,
being exactly measured by the graduation of a circle
of gun metal, which is borne on the upper surface
of the ring. The rotatory action of the stage being
effected beneath the traversing movement, the centring
of an object brought into the axis of the microscope is
not disturbed by it ; and the workmanship is so accu-
FIG. 48. Poicell and Zealand's Microscope arranged for direct illumination.
A. Secondary Stage racked up to bring the Achromatic Condenser close to
the object.
rate that the stage may be driven through its whole
revolution without throwing out of the field an object
viewed with the T Vth objective. The stage withal is
made thin enough to admit of the most oblique light
being thrown on the object. This instrument combines
remarkable steadiness with great solidity, and is so
well balanced on its horizontal axis that it requires no
clamping in whatever position it may be placed.
Cheaper instruments are furnished by Powell and
Lealand ; a student's microscope, with |^-inch stage
BECK'S POPULAR STAND. 93
movement, coarse and fine adjustments to body, plane
and concave mirrors, revolving diaphragm, Lister's
dark-wells, and two eye-pieces, for 8.
An increasing demand for good, useful, and moder-
ately priced instruments for students and general use,
has had the effect of inducing makers to vie with each
other in their endeavours to give a better class micro-
scope for a small sum. Among those manufacturers,
and to whom the microscope owes very many improve-
ments, I may mention the firm of R. and J. Beck.
Their Popular Microscope, fig. 49, is a fair example of
their excellent workmanship.
The body, A (in the illustration shown as binocular),
is carried by a strong arm, B ; and this is attached to a
square bar, c, which may be moved up or down by a
rack- work and pinion in the lower part of the stand,
where the stage, D, and the mirror, E, are attached.
The base, F, is triangular ; and it is connected with
the parts of the instrument already described by a
broad stay, G, which moves on centres at the top and
bottom, so as to allow the end of the tube, H, to fit by
its projecting pin into various holes along the medial
line of the base. With this arrangement, if the body
of the microscope be required in a more or less inclined
position as in the figure, four holes are provided near
the extremity of the base for the pin of the tube to fit
into. A hole near the stout pin, L, is used when a
vertical position is wanted ; while to obtain the hori-
zontal position, the pin of the tube is placed in a hole
in the stud, K, the inner surface of the stay, G, resting
at the same time on the top of the stout pin, L. This
form of construction is novel, and possesses the fol-
lowing advantages ; it is strong, firm, and yet light ;
the instrument cannot alter from any particular incli-
nation it is put into, which is not unfrequently the case
when the ordinary joint works loose; and in every
position the heavier part of the stand is brought over
the centre of the base, to ensure an equality of balance.
To adjust the focus of the object-glass, turn the
milled-heads for a quick movement, or the milled-
head p for a slow one.
94 THE MICROSCOPE.
The stage, D, is circular, and upon it fits a plate, T ;
FIG. 49.- Beck's Popular Microscope.
this again carries the object-holder, u, which is pro-
BECK'S " IDEAL" STAND. 95
vided with a ledge, v, and a light spring, w ; it is held
on the plate T by a spring underneath, so that it can
be moved about easily and smoothly by one or by both.
FIG. 50. Beck's "Ideal" Microscope.
hands. Messrs. Beck's latest improvement consists in
a glass friction stage, and this is adapted to all their
Students' microscopes. A polished glass plate is firmly
embedded in the brass stage-plate, and there held in
96
THE MICROSCOPE.
contact by a strong wire ring. A piece of velvet
cemented to the under sur-
face renders the stage move-
ments extremely smooth and
easy. The mirror, E, besides
swinging in a rotating semi-
circle, will slide up or down
the tube, H, or it will turn on
either side for oblique illumi-
nation.
Beck's "Ideal" Microscope. In this excellent and
novel instrument (shown as a monocular in fig. 50)
. 51. Beck's Double Nose-piece.
FIG. 52. Baker's Student's Microscope.
the stage is of very thin and stiff brass, with a large
BAKER'S STUDENT'S STAND.
97
opening, and provided with reversible spring clips so
as to attach an object to the underside if required.
To the stage can be adapted either a circular stage-
plate of thin sheet-brass revolving concentrically, or
the glass stage-plate shown detached, with brass
object-carrier, and allowing one inch of movement
in all directions. The mirror and sub-stage slide
FIG. 53. Baker's Model Histological Microscope,
upon a swinging tailpiece, the latter being attached
to a graduated circle, and allowing a wide range of
motion above and below the stage. The body draws out
to the standard length (10 inches), and takes a full-
sized eye-piece. It has an adapter for the broad-gauge
screw. When fully extended it is 15 inches in height,
or can be reduced to 10 inches.
9b THE MICROSCOPE.
The working microscopist will find Beck's double or
triple nose-piece (fig. 51) a useful addition and an econo-
mizer of time, as enabling him to find a minute object,
which he may wish to submit to a more thorough
examination under a high power.
Mr. Baker (Holborn) has kept pace with most opti-
cians, and his first-class microscopes are not inferior to
those of any other manufacturer. One of his best, the
FIG. 54. Baker's Stephenson's Binocular Dissecting Microscope.
old Ross form, combines good workmanship with soli-
dity and completeness in most of its details.
The Student's Microscope (fig. 52) is a well-finished in-
strument, with quick and slow motions, circular rotat-
ing stage, live-box, stage and dissecting forceps, packed
in mahogany case. It has a universal sub-stage fitting,
capable of receiving all accessories, and being provided
with good object-glasses and other apparatus, is cer-
tainly a very complete and useful microscope.
Baker's Model Histological Microscope (fig. 53), a
highly-finished instrument, having sliding body, micro-
BROWNING'S ROTATING STAND.
99
meter screw fine-adjustment, glass concentric rotating
stage, double mirror, universal sub-stage fitting to carry
FIG. 55. Broicning's Improved Rotating Microscope.
all apparatus, and one eye-piece, packed in mahogany
case, for the small price of 3 10s.
An excellent form of binocular, in which the lowest
H 2
100 THE MICROSCOPE.
and the highest objective can be used with equal
advantage, has been adapted by Mr. Baker to a micro-
scope stand (fig. 54), well suited for laboratory use, and
for many practical purposes. It is superior to the
ordinary dissecting microscope; the erecting principle
renders it generally serviceable, as, for example, in
selecting and arranging shells, and in the proper dis-
position of specimens in the process of mounting.
The double bodies are attached by an arm to a rack-
work of unusual length, suspended, as it were, over a
stage 6 in. X 3 in. in the horizontal position ; it has the
usual double mirror of large size, the whole being sup-
ported by three solid uprights to a heavy base. The
figure scarcely does the instrument justice ; it fails to
show the second body.
Browning's (63, Strand) Rotating Microscope (fig. 55)
is well adapted for pathological work. It has a circu-
lar glass sunk in to the stage, and is consequently not
likely to be damaged by moist preparations. The utility
of a turning-stage, as already explained, gives the com-
mand of varying the position and illumination of the
object to be examined. In the construction of this in-
strument this fact has been kept in view; the stage and
the eye-piece revolving together on thp same axis ; and
the image remaining in the field of vision during the
whole revolution. The microscope stand aims at com-
bining, in the simplest and least expensive form, the
high qualities of the best English models.
Browning's Complete Binocular has a well-finished
stand, with the latest improvements, mechanical mo-
tions to stage, secondary stage, with removable fittings,
etc., and is, in every respect, a complete instrument.
Watson's Microscope Stand (fig. 56) presents points of
novelty, the most notable among which is the inclining
motion of the limb, carrying the optical body and stage
on an axis in a line with the object on the stage. By
the simple inclination of the limb, varying effects of
oblique illumination can be obtained direct from the
mirror, which can be attached for this purpose to the
centre of the base, and is then independent ot the
inclination of the limb.
WATSON'S NEW STAND. 101
The base of the stand is circular, with three project-
ing claws ; on this base a disc of metal, carrying the
pillar-support (of the limb, stage, etc.), is made to
FIG. 56. Watson and Son's New Microscope Stand.
rotate on the perpendicular optic axis ; a graduated
zone shows the angle of rotation.
In the centre of the base a smaller disc (projecting
slightly above the general plane) is made to rotate ;
this disc has a groove into which the mirror-fitting
102 THE MICROSCOPE.
slides, and a spring-notch shows the axial position.
The sliding fitting allows the mirror to be placed some
distance out of the axis radially, and then the rotation
of the circular moving base plate gives a considerable
range of obliquity of light in azimuth ; the light from
the mirror remaining constantly directed upon the
object, this facility obtains with all inclinations of the
limb and stage, because the object itself forms the centre
both of the azimuthal rotation and of the inclination
in altitude. The limb is mounted in a " cradle " joint,
at the top of the pillar, permitting inclination from the
perpendicular.
The angle of inclination is registered upon a gradu-
ated ring against the clamping screw. The optical
body is mounted, not as usual on the front of the
" Jackson " limb, but on the side of it; thus converting
the side of the limb into the front.
The coarse-adjustment is by the ordinary rack and
pinion ; the fine- adjustment lifts the optical body in a
separate slide-fitting by means of a wedge-shaped block
acted upon by the conical end of a fine micrometer-
screw. The focal distance can be measured by the
scale engraved on the slide-fitting.
The stage is of the newest construction, and beneath
which is the sub-stage arm, carrying the usual screw-
centring and rack-adjusting sub-stage, so attached to a
sector in the rear of the stage in which it traverses
concentric with the object. The sub-stage bar also
carries the usual centring fitting for condenser, etc.,
and swings forwards or backwards concentric with
the object on the main stage, and the obliquity of the
swing can be registered on a graduated ring imme-
diately behind the stage. The construction is similar
to that of the Ross-Zentmayer. An extra swinging
bar is attached behind, into which the mirror can be
slid for use in combination with the condenser, etc. It
should be noticed that there is a third divided circle
on the sub- stage sector giving the inclination of the
sub-stage to the axis of the body. A strong clamp ou
the other side of the cradle joint holds the body firmly
at any inclination, and a graduation on the slide of
WATSON'S COLLEGE STAND.
103
the coarse-adjustment enables the working distance of
objectives to be measured and compared.
Watson's Medical or College Microscope (fig. 57) i s
an economical form of instrument, having a sliding
body for coarse- adjustment, fine-adjustment, draw-tube*,
wheel of diaphragms, tube -fitting for under-stage appa-
ratus, plane and concave mirrors, with one eye-piece,
FIG. 57. Watson's Medical or College Microscope.
J-inch and 1-inch objectives, and stand condenser. It
is well adapted for class or laboratory use. The maker
strongly recommends it for the use of the brewer, and
amateur, as a cheap and useful instrument.
Mr. Pillischer (New Bond Street) is favourably
known for the excellency of his instruments. His
No. 1 Microscope (fig. 58) is of good workmanship, and
104 THE MICROSCOPE.
somewhat novel in design. It is constructed on a plan
Fio. 5S.PiUischer's Binocular Microscope.
which may be described as intermediate between that
of Smith and Beck and Ross's well-known pattern, and
COLLINS'S STUDENT'S STAND. 105
in point of finish, is equal to the students' micro,
scopes of first-class manufacturers. The semicircular
form given to the arm carrying the body increases the
strength and solidity of the instrument, although it is
doubtful whether it adds to its steadiness when placed
in the horizontal position. The straight body rests
for a great part of its length upon a parallel bar of
solid brass, ploughed into which is a groove for the
reception of the rack attached to the body, the groove
being of such a form that the rack is held firmly while
the pinion glides smoothly through it. A steady uni-
form motion is thus obtained, and which almost renders
the fine-adjustment unnecessary. The fine-adjust-
ment screw is removed from the usual position and
placed in front of the body, just above and in front of
the Wenham prism. The binocular bodies are inclined
at a smaller angle to one another than in most instru-
ments ; nevertheless, the range of motion given to the
eye-pieces by the rack and pinion, enables those whose
eyes are widely separated to use the instrument with
comfort. The prism is so well set that it illuminates
both fields with equal intensity. The stage is provided
with rectangular traversing movements to the extent
of an inch and a quarter in each direction. The milled-
heads which effect these are placed on the same axis,
instead of side by side, one of them the vertical one
being repeated on the left of the stage, so that the
movements may be communicated either by the right
hand alone or by both hands acting in concert. The
stage-plate has the ordinary vertical and rotatory motions,
but to a much greater extent than usual ; and the plat-
form which carries the object is provided with a spring
clip to secure the object when the stage is placed in
the vertical position. A regularly fitted sub-stage with
centring screws is made in the usual way to carry an
achromatic condenser, diaphragm, polarising and other
apparatus.
Collins's Student's Microscope (fig. 59) has a 10-inch
body and a draw- tube for increasing its length. The
diameter of the tube is of full English size ; the field
is consequently large. The fittings for objectives and
106 THE MICROSCOPE.
accessory apparatus are all of standard size, and can,
therefore, be applied to any of the larger and more
elaborate instruments of English model. The fine-
adjustment is ingeniously modified, very delicate, and
quite free from lateral motion. Not only is the field of
all the objectives supplied with it excellent, but their
FIG. 59 Collins's Histological or Student's Microscope.
penetration is of a high standard. The stand alone
can be had at a lower price with eye-piece and case.
On the whole, the instrument is of excellent workman-
ship, and possesses all the advantages and conveniences
which belong to students' microscopes.
Collins's Binocular Microscope Stand (fig. 60), on the
"Jackson" principle, is extremely steady and solid.
COLLINS'S BINOCULAR STAND.
107
The limb that carries the body, stage, sub-stage, and
mirror, is in one piece, with a machine-planed groove
from end to end, thus ensuring considerable accuracy.
A rack-work movement of 6 in. is given to the body,
FIG. 60. Coliins's Binocular Microscope.
allowing the use of low-power objectives, so much
appreciated in binocular microscopes. The Wenham
prism box is made on the Harleyplan, enabling the
polariscope to be brought into action without removal
of the objectives or putting the same out of focus.
108
THE MICROSCOPE.
The stao^e is circular in form, with concentric rota-
tion, horizontal and vertical mechanical movements,
and top slide for holding the objects, trough, etc., while
under examination. It has a clear aperture underneath
of 3 in. when the apparatus plate is removed, and, in
consequence of the improved plan of mounting the
mirrors from the back, a great obliquity of illumination
can be obtained as well as a considerable range of
movement when a sub- stage is fitted.
Collins's Dissecting Microscope, for plant or insect
dissection (fig. 61), has a firm metal stand, sliding
adjustment for focuss-
ing, two simple lenses,
to be used together or
separate, with mirror
for illuminating.
Swift's Challenge
Microscope (fig. 62),
of the Jackson- Lister
form, which experi-
enced microscopists still
believe, for many rea-
sons, to be one of the
best, is well finished in
'Microscope, on ^^ ^^ fa Q coarge .
adjustment is sensi-
tive; the focussing can be accurately done by it
alone, whilst the fine-adjustment is so conveniently
placed as to be within easy reach of one of the fingers
of the hand which works the rack. By a somewhat
novel arrangement, Messrs. Swift have succeeded in
mounting the analyzer above the Weiiham's prism
within the binocular body, so that it can be easily
brought into use by pushing it into the optic axis of
the instrument, without any screwing or unscrewing
of the objective. To those in the habit of frequently
employing the polariscope, this simple arrangement
must commend itself, as the definition of the object-
glass is much less interfered with by this method of
mounting the analyzer than where the Wenharn prism
intervenes between it and the eye-piece. The instru
FIG. 61. Collins's Diasecti
Prof. Henslow's
SWIFT'S CHALLENGE STAND. 109
ment is furnished either with a simple rotating and
FIG. 62. Swift's New Challenge Microscope.
universal movement stage, or a very thin mechanical
stage with rectangular as well as rotatory adjustments,
110
THE MICROSCOPE.
and also with, a centring and focussing sub-stage,
for the adaptation of the achromatic condenser,
paraboloid, polariscope, etc. The mirror moves by a
double elbow joint, and is arranged to be used at any
angle.
Swift's College or Student's Microscope is a solid,
FIG. 63. Crouch's New Fine-Adjustment.
well-made, handy instrument, designed for class use,
and it may be expected to take the place of the con-
tinental microscope hitherto much employed in our
colleges and schools of medicine.
Crouch's Microscope possesses certain advantages as
a cheap microscope, since it combines perfect perform-
CROUCH, AND HOw's STAND. 11]
ance witli good workmanship in the construction of the
stand.
The chief point of novelty is the fine-adjustment,
shown in detail in fig. 63. The solid bar A, carrying
the optical body B, is suspended on the front ends of
the two broad, flat, parallel tempered-steel springs c c,
the other ends of which are attached to the limb D.
The pressure of the focussing screw E, by the point at
F on the solid bar, forces down this bar, the springs
bending sufficiently to allow about J-in. range of motion
Downwards from the normal position. The actual motion
of focussing displaces the optic axis slightly ; but this
displacement is attended with no inconvenience, except
where the microscope is provided with a rotating stage.
This mode of focussing must be regarded as practically
free from friction, as there are no metal surfaces in
contact ; the only friction is between the point of the
screw at F, where it acts on the bar by pressure. The
suspension of the optical body is strictly on the two
springs c C. 1
How's (Farringdon Street) Student's instrument (fig.
64) is deserving of a place among microscopes designed
for general use. The stand is of brass, firm and well
finished ; the body is fitted with coarse and fine adjust-
ments for focussing; and a draw- tube for increasing
the magnifying power of the eye-piece. The stage
has an arrangement, simple but novel in construction,
by which a near approach to a universal movement is
obtained. The movable, or upper plate, is held to the
fixed lower plate with springs, and, although offering
a convenient resistance, allows of a smoothness of
motion quite remarkable. It resembles the magnetic
stage, but is far more reliable, and can be moved up-
wards, downwards, laterally, or in a slanting direction,
thus enabling the microscopist to follow living objects
with great facility, superseding to some extent the
more expensive mechanical stage. A dividing set of
object-glasses is supplied with the B eye-piece, thus
giving a range of power varying from 40 to about 200
diameters.
(1) Journal R. M. S , p. Ill 1S61.
112 THE MICROSCOPE.
Murray and Heath's Student's Microscope (fig. 65)
is a good solid form of instrument with a bent tripod-
stand. The stand is remarkably firm, and, being
FlG. 64. How's Student's Microscope.
bronzed over, is well adapted for daily nse in the
class-room or laboratory. The adjustment is effected
by a chain-movement, which gives sufficient delicacy
for powers up to the J-inch. The stage is perfectly
MURRAY AND HEATH's STAND. 113
flat, and the slide-rest moves smoothly and freely over
it. If the instrument is intended for use in the
laboratory, a glass stage is made to replace the brass
one. The objectives furnished with this microscope
FIG. 65. Murray and Heath's Student's Microscope.
are a -inch of 75 angular aperture, and a 1-inch of
15, both of excellent quality.
Murray and Heath's Class Microscope, represented
in fig. 66, is especially intended for the use of teachers
in the demonstration of objects to a class of students.
The instrument consists of the usual microscope body
i
114
THE MICROSCOPE.
(A), which can be inclined at any angle, with a mirror
(c) on a ball-and-socket joint ; and a stage-plate with
universal movement. When about to be used as a
class microscope, the slide is placed in a shallow box,
into which it is locked by means of a key. The same
key locks this box firmly on the stage -plate. When
the object has been found, this latter can be secured
firmly on the stage in the same manner. After focus-
sing, the body is also locked in its place with the same
key, which is seen at D, the final adjustment being
made with the eye-piece. The body is then placed in
the horizontal position, and fastened with a screw.
The instrument can now be passed round a class-room
FIG. 66. Murray and Heath's Class Microscope.
without possibility of injury either to object or object-
glass. The illumination is obtained either by direct,
ing the instrument towards the window, or by means
of a small lamp (B), similar to that employed by Dr.
Beale, and which can be so adjusted as to be used
either for opaque or transparent objects.
In Mr. Ladd's student instrument, such as that repre-
sented in fig. 67, he has taken great care to obtain
a perfect balance in any position, even when placed
in the horizontal axis ; no instrument can be better
adapted than this to the wants of the microscopist j
it is certainly one combining many of the advantages
of the more expensive forms.
LADD'S TRIPOD STAND. 115
Nachet and Hartnack of Paris, and Merz of Munich,
hold an almost equal rank as makers of first-class
FIG. 67. Ladd's Student's Microscope.
microscopes, and in point of excellence of workman-
ship fairly rival those of English makers.
FIG. 68. Nacliefs Portable Demonstrating Microscope.
i 2
116 THE MICROSCOPE.
APPLICATION OF BINOCULARITY TO THE MICROSCOPE.
The application of this principle to microscopic pur-
poses seems to have been tried as early as 1677, by a
French philosopher, le Pere Cherubin, of Orleans, a Capu-
chin friar. The following is an extract from the description
given by him of his instrument : " Some years f igo I
resolved to effect what I had long before premeditated, to
make a microscope to see the smallest objects with the
two eyes conjointly; and this project has succeeded even
beyond my expectation, with advantages above the single
instrument so extraordinary and so surprising, that every
intelligent person to whom I have shown the effect, has
assured me that inquiring philosophers will be highly
pleased with the communication."
This communication long slumbered and was forgotten,
and nothing more was heard of the subject until Professor
Wheatstone's very surprising invention of the stereoscope,
which he evidently expected to apply to the microscope,
for he applied to both Ross and Powell to make him
a binocular microscope. But this was not done; and
during the year 1853 a notice appeared in Sillimari*
American Journal of a binocular instrument constructed
by Professor Eiddel of America, who contrived a binocular
microscope in 1851, with the view " of rendering both eyes
serviceable in microscopic observations." " Behind the ob-
jective," he says, " and as near thereto as possible, the light
is equally divided and bent at right angles, and made to
travel in opposite directions, by means of two rectangular
prisms, which are in contact by their edges somewhat
ground away, the reflected rays are received, at a proper
distance for binocular vision, upon two other rectangular
prisms, and again bent at right angles, being thus either
completely inverted for an inverted microscope, or restored
to their n'rst direction for the direct microscope." M.
Nachet also constructed a binocular microscope, upon the
same principle as his double microscope, with the tubes
placed vertically and 2J inches distant. This had many
disadvantages and inconveniences, which Mr. F. H. Wenham
ingeniously succeeded in modifying and improving.
THE BINOCULAR MICROSCOPE. 1 J /
111 describing his improvements, he observes : " That in
obtaining binocularity with the compound achromatic mi-
croscope, in its complete acting state, there are far greater
practical difficulties to contend against, and which it is
highly important to overcome, in order to correct some of
the false appearances arising from what is considered the
very perfection of the instrument.
" All the object-glasses, from the one-inch upwards, are
possessed of considerable angular aperture ; consequently,
images of the object are obtained from a different point of
view, with the two opposite extremes of the margin of the
cone of rays; and the resulting effect is, that there are a
number of dissimilar perspectives of the object all blended
together upon the single retina at once. For this reason,
if the object has any considerable bulk, we shall have a
more accurate notion of its form by reducing the aperture
of the object-glass.
" Select any object lying in an inclined position, and
place it in the centre of the field of view of the micro-
scope; then, with a card held close to the object-glass,
stop off alternately the right or left hand portion of the
front lens : it will be seen that during each alternate
change certain parts of the object will alter in their rela-
tive position.
" To illustrate this, fig. 69 , b
are enlarged drawings of a portion
of the egg of the common bed-bug
i {Cimex lecticularis), the operculum
which covers the orifice having
been forced off at the time the
young was hatched. The figures
exactly represent the two positions
that the inclined orifice will oc-
Flg< 69 - cupy when the right and left hand
portions of the object-glass are stopped off. It was illumi-
nated as an opaque object, and drawn under a two-thirds
object-glass of about 28 of aperture. If this experiment
is repeated, by holding the card over the eye-piece, and
stopping off alternately the right and left half of the
ultimate emergent pencil, exactly the same changes and
appearances will be observed in the object under view
118
THE MICROSCOPE
The two different images just produced are such as are
required for obtaining stereoscopic vision. It is therefore
evident that if, instead of bringing them confusedly toge-
ther into one eye, we can separate them so as to bring fig.
96 a b into the left and right eye, in the combined effect
of the two projections, we shall obtain all that is necessary
to enable us to form a correct judgment of the solidity
and distances of the various parts of the object.
" Diagram 3, fig. 70, represents the methods that I have
contrived for obtaining the effect of bringing the two eyes
sufficiently close to each other to enable them both to see
through the same eye-piece together, a a a are rays con-
verging from the field lens of the eye-piece ; after passing
the eye-lens 6, if not intercepted, they would come to a
focus at c ; but they are arrested by the inclined surfaces,
d d, of two solid glass prisms. From the refraction of the
under incident surface of the prisms, the focus of the eye-
piece becomes elongated, and falls within the substance of
the glass at e. The rays then diverge, and after being
reflected by the second inclined surface f t emerge from the
upper side of the prism, when their course is rendered
still more divergent, as shown by the figure. The reflecting
angle that I have given to the prisms is 47. I also find
it is requisite to grind away the contact edges of the
prisms, as represented, as it prevents the extreme margins.
ABBE'S STEREOSCOPIC EYE-PIECE.
of the reflecting surfaces from coming into operation,
\vhich can seldom be made very perfect.
The purpose of the binocular microscope is to give
a stereoscopic view of objects, whereby the form,
distance and position of their various parts are simul-
taneously seen ; the result is often as striking as if the
minute object were placed in the hand as a model.
To produce a stereoscopic effect there must be an
equal division of the rays after they have passed
through the object-glass, so that each eye may be
furnished with an appropriate one-sided view of the
object ; but the methods hitherto contrived to effect
this not only materially injure the definition of the
object-glasses, but also require expensive alterations in
their adaptation, or, more frequently still, a separate
stand ; whereas the arrangement contrived by Mr.
Wenham is no obstacle to the use of the monocular
instrument, and the definition even of the highest
powers is scarcely impaired. Nachet of Paris has
throughout endeavoured to vie with Wenham, and
he substituted a double eye-piece for the binocular
body. This idea was improved upon by Tolles, of
Boston, U.S., and more recently it has received some
improvement from Professor Abbe. Fig. 71 presents
a sectional view of Abbe's stereoscopic eye-piece, and
which consists of three prisms of crown glass, a t b and
5', placed below the field-glass of the two eye-pieces ;
the tube C is slipped into the tube or body like an
ordinary eye-piece. The two prisms a and b are united
so as to form a thick plate with parallel sides, inclined
to the axis at an angle of 38'5. The cone of rays
from the objective is thus divided into two parts, one
being transmitted and the other reflected ; that trans-
mitted passing through a b and forming an image of
the object in the axial eye-piece B. Adjustment for
different distances between the eyes is effected by the
screw placed to the right-hand side of the figure, which
moves the eye-piece B', together with the prism &', in
a parallel direction. The tubes can also be drawn out,
if greater separation is required. The special feature
of the instrument is an ingenious arrangement for
120
THE MICROSCOPE.
halving the cones of rays above the eye-pieces, where,
by simply turning the caps with the diaphragms,
orthoscopic or pseudoscopic effects can be instanta-
neously produced. This arrangement is particularly
suitable for the cheaper forms of microscopes, and for
those of foreign manufacture, which are usually shorter
in the body than English -made instruments.
FIG. 71. Professor Abbe's Stereoscopic Eye-pieces.
The most important improvement effected by Wen-
ham consists in splitting up or dividing the pencil of
rays proceeding from the objective by the interposition
of a prism of the form shown in fig. 72. This is placed
in the body or tube of the microscope (fig. 72&, a) so as
to interrupt only one-half (a. c) of the pencil, the other
half (a &) going on continuously to the field-glass, eye-
piece, of the principal body. The interrupted half of
the pencil, on its entrance into the prism, is subjected
to very slight refraction, since its axial ray is perpen-
WENHAM S BINOCULAR PRISM.
121
dicular to the surface it meets. Within the prism it is
subjected to two reflections at b and c, which send it
forth again obliquely on the line b towards the eye-
piece of the secondary body, to the left-hand side of
the figure ; and since at its emergence its axial ray is
again perpendicular to the surface of the glass, it-
suffers no more refraction on passing out of the prism
than on entering it. By this arrangement, the image
FIG. 72.
received by the right eye is formed
by the rays which have passed
through the left half of the objec-
tive; whilst the image received by
the left eye is formed by the rays
which have passed through the right
half, and which have been subjec-
tive to two reflections within the
prism, passing through only two FlG< 72a
surfaces of glass. The prism is
held by the ends only on the sides of a small brass
drawer, so that all the four polished surfaces are
accessible, and should slide in so far that its edge may
just reach the central line of the objective, and be
drawn back against a stop, so as to clear the aperture
of the same. In this case the straight tube acts as a
single microscope.
The binocular constructed as we have described
performs satisfactorily up to the Jth inch; but for
122 THE MICROSCOPE.
powers above this a special arrangement is needed for
the prism, which must be set close behind the lens of
the -|th or y^th inch, in order to obtain an entire field
of view in each eye.
A strong light should be avoided for the illumina-
tion of objects observed with the binocular microscope,
as direct rays tend to destroy the stereoscopic effect.
The illuminator that has been found to give an excel-
lent effect consists of three plano-convex lenses, so
combined as to give a very large area of light, as well
as great intensity.
The improvement effected in Nachet's binocular eye-
piece by Mr. Tolles, optician, of Boston, U.S., consists in
mounting the prisms in a light material, vulcanite,
which are made to fit into the monocular microscope
body, taking the place of the ordinary eye-piece. The
image transmitted by the objective is brought to a focus
on the face of the first equilateral triangular prism by
the intervention of an erector eye-piece inserted beneath
it. The second set of prisms are by a rack-and-pinion
movement adjusted to suit any visual angle ; thus the
illumination of both fields is of nearly equal brightness.
Spectro-Microscopy*
The application of the spectroscope to the microscope
is one of the most beautiful additions the instrument
has ever received. The honour of the invention
appears to belong to H. C. Sorby, F.R.S., whose first
experiments were made with a simple triangular
prism, arranged and fixed below the stage, so that a
minute spectrum of any transparent object might be
readily examined, when placed in position imme-
diately before the slit. Shortly after the publication
of Mr. Sorby's paper, Mr. Huggins proposed to adapt
a direct vision spectroscope to the eye-piece, for the
purpose of viewing the spectra of opaque as well as
transparent objects. The exact form since adopted
is the Sorby-Browning Spectroscope.
The first spectroscope made byMr.Browning(63 Strand)
is represented in fig. 73. A prism is placed at P, which is
enclosed in a box, so as to give a black field, by excluding
THE BROWNING MICRO-SPECTROSCOPE.
123
extraneous light. The rays of light, after passing between
the knife-edges at K, are rendered parallel by means of
the lens at L. Then passing through the prism and con-
denser (c), they reach the object at o. The light is placed
at w, and if it be proposed to examine a liquid, it can be
placed in a small tube (T), closed at one end ; or a trans-
parent object may be placed on the stage in the usual
3. Sectional uiuw uj tii,e JJrowuiug Spectroscope.
manner. By the addition of a small telescope, instead of
a condenser, this contrivance can be applied to a micro-
scope in place of the eye-piece, and it can then be used for
the examination of opaque objects.
The great objection to this form is its limited range,
and the constant shifting of parts it requires for finding
and focussing the object, and the awkward position of the
microscope, whether it be used under the stage or as an
eye-piece.
Fig. 74. The Browning Huggin* Micro-spectroscope.
The apparatus used bv Mr. Huggins (fig. 74) was a star
THE MICROSCOPE.
spectroscope, of which the collimativc-tube was inserted
in the body of the microscope, instead of an eye-pieco.
With this apparatus he has succeeded in obtaining a
spectrum showing the absorption-bands from a mere frag-
ment of single blood-disc, when mounted as a transparent
object. In fig. 74. K represents the knife-edges, c the tube
containing the collimating-lens, P the prisms, T the teles-
cope, and M the micrometer ; the object is placed on the
stages at o, and must be illuminated from below if trans-
parent, or, if opaque, from above by any kind of con-
denser.
Mr. Sorby suggested that a prism might be made of
dense flint-glass, of such a form, that it could be used in
two different positions, and that in one it should give
twice the dispersion that it would in the other, but that
the angle made by the incident and emergent rays should
be the same in both positions.
Fig. 75. Kg. ira.
Figs. 75 and 75 a represent prisms of the kind made by
Mr. Browning, used in two different positions, i and i 1
being the same angle as I and i'.
For most absorption-bands, particularly if faint, the
prism would be used in the first position, in which it
gives the least dispersion ; but when greater dispersion
is required, so as to separate some particular lines more
widely, or to ^show the spectra of the metals, or Friiun-
hofer's lines in the solar spectrum, then the prism must
be used as in fig 75 a . This answers well for liquids 01
transparent objects, but it is, of course, not applicable to
opaque objects.
THE DIRECT SPECTROSCOPE.
125
To combine both purposes, some form of direct vision-
prisms which can be applied to the body of the micro-
scope is required. Fig. 76 represents the arrangement of
direct vision-prisms, invented by A. Herschel. The line
B R' shows the path of a ray of light through the prisms,
where it would be seen that the emergent ray R' is parallel
.\nd coincident with the incident ray R.
Kg. 7(3.
Fig. 7<3.
Another very compact combination is shown in fig. 76a.
Any number of these prisms (P p P) may be used, accord-
ing to the amount of dispersion required. They are
mounted in a similar way to a Nicols' prism, and are
applied directly over the eye-piece of the microscope.
The slit s s is placed in the focus of the first glass (P) if
a negative, or below the second glass if a positive eye-
piece be employed. One edge of the slit is moveable,
and, in using the instrument, the slit is first opened wide,
so that a clear view of the object is obtained. The part
of the object of which the spectrum is to be examined
is then made to coincide with the fixed edge of the slit,
and the moveable edge is screwed up, until a brilliant
coloured spectrum is produced. The absorption-bands
wilJ then be readily found by slightly altering the focus.
This contrivance answers perfectly for opaque objects,
126 THE MICROSCOPE.
without any preparation ; and, when desirable, the sam<
prism can be placed below the stage, and a micrometer
used in the eye-piece of the microscope, thus avoiding a
multiplication of apparatus.
The latest improvement is that shown in fig. 77, also
effected by Mr. Browning, who deserves great credit for
the skill displayed in the invention and construction of
this new and elegant micro-spectroscope.
Fig. 17. The Sorby-Browning Micro-spectroscope.
The prism is contained in a small tube, which can be.
removed at pleasure. Mow the prism is an achromatic
eye-piece, having an adjustable slit between the two
lenses, the upper lens being furnished with a screw
motion to focus the slit. A side slit, capable of adjust-
ment, admits, when required, a second beam of light from
any object whose spectrum it is desired to compare with
that of the object placed on the stage of the microscope.
This second beam of light strikes against a very small
prism, suitably placed inside the apparatus, and is reflected
up through the compound prism, forming a spectrum in
the same field with that obtained from the object on tht
stage.
A is a brass tube, carrying the compound direct vision
prism. B, a milled head, with screw motion to adjust the
focus of the achromatic eye lens, c, milled head, with
screw motion to open or shut the slit vertically. Anothej
THE MICRO-SPECTROSCOPE. 127
screw at right angles to c, but which from its position
could not be shown in the cut, regulates the slit hori-
zontally. This screw has a larger head, and when once
recognised cannot be mistaken for the other. D D is an appa-
ratus for holding a small tube, that the spectrum given
by its contents may be compared with that from an object
on the stage. E is a square-headed screw, opening and shut-
ting a slit to admit the quantity of light required to form
the second spectrum. A light entering the round hole
near E, strikes against the right-angled prism, which we
have mentioned as being placed inside the apparatus, and
is reflected up through the slit belonging to the compound
prism. If any incandescent object be placed in a suitable
position with reference to the round hole, its spectrum
will be obtained. F shows the position of the field lens of
the eye-piece. G is a tube made to fit the microscope to
which the instrument is applied. To use this instrument
insert G, like an eye-piece in the microscope tube, taking
care that the slit at the top of the eye-piece is in the same
direction as the slit below the prism. Screw on to the
microscope the object-glass required, and place the object
whose spectrum is to be viewed on the stage. Illuminate
with the stage mirror if it be transparent; with mirror^
Lieberkiihn, and dark well, by side reflector, or bull's-eye
condenser if opaque. Remove A, and open the slit by
means of the niilled-head, not shown in cut, but' which ia
at right angles to D D. When the slit is sufficiently open
the rest of the apparatus acts like an ordinary eye-piece,
and any object can be focussed in the usual way. Having
focussed the object, replace A, and gradually close the slit
till a good spectrum is obtained. The spectrum will be
much improved by throwing the object a little out of
focus.
Every part of the spectrum differs a little from adjacent
parts in refrangibility, and delicate bands or lines can only
be brought out by accurately focussing that particular part
of the spectrum. This can be done by the milled head B.
Disappointment will occur in any attempt at delicate in-
vestigation if this direction be not carefully attended to.
At B a small mirror is attached, which is omitted in the
diagram to prevent confusion. It is like the mirror belov
1?3 THE MICROSCOPE.
the stage of a microscope, and is mounted in a similar
manner. By means of this mirror light may be reflected
into the eye-piece, and in this way two spectra may be
procured from one lamp.
For observing the spectra of liquids in cells or tubes
of considerable diameter, say not less than j^th of an
inch, powers from 2 inch to 1 inch will be the most
suitable, and of course low powers only can be used to
investigate the spectra of opaque objects ; but when the
spectra of very minute objects are to be viewed, powers of
from half an inch to one-twentieth, or even higher, may
be employed.
Blood, madder, aniline red, permanganate of potash, in
crystals or solution, are convenient substances to begin
experiments with. Solutions when made too strong pro-
duce dark clouds instead of absorption bands. Professor
Church has recently pointed out that zircon, an almost
colourless stone, gives well-defined absorption-bands.
Mr. Sorby says of the correct performance of a spectrum
adaptation, " The best tests are, first, that the absorption-
bands in blood can be seen when they are very faint ;
second, to well divide the bands in permanganate of
potash; and, third, to see distinctly the very fine line
given in the red by a solution of chloride of cobalt dis-
solved in a concentrated cold solution of chloride of calcium :
there is a line so fine that it looks like a Fraunhofer'a
line. An instrument that shows all these well is all that
can be desired.
" The objects most easily obtained, and which furnish
as 'with the greatest variety of spectra, are coloured
crystals, coloured solutions, and coloured glasses. The
spectrum microscope enables us to examine the spectra of
very minute crystals, of very small quantities of material
in solution, and of small blow-pipe beads. As previously
named, the thickness of the object makes a very great
difference in the spectrum. For example, an extremely
thin crystal of ferricyanide of potassium cuts off all the
blue rays, and leaves merely red, orange, yellow, and more
or less green ; but on increasing the thickness, the green
and yellow disappear ; and when very much thicker, little
else but a bright red light is transmitted. In all such
TUB MICRO-SPECTROSCOPE. 129
cases, the apparent magnitude of the effect of an increase
in thickness is far greater when the object is thin than
when thick, and past a certain thickness the change is
comparatively very slight. If only small crystals can bs
obtained, it is well to mount a number of different thick-
nesses ; but when it is possible to obtain crystals of suf-
ficient size, it is far better to make them into wedge-
shaped objects, since then the effect of gradual change in
thickness can easily be observed. Different kinds of
crystals require different treatment, but, as a general rule,
I find that it is best to grind them on moderately soft
Water-of-Ayr stone with a small quantity of water, which
soon becomes a saturated solution, and then to polish
them with a little rouge spread on paper laid over a flat
surface ; or else, in some cases, to dissolve off a thin layer
by carefully rubbing the crystal on moist blotting-paper
until the scratches are removed. Then, whenever it is
admissible, I mount the crystal on a glass, and also cover
it with a piece of thin glass with Canada balsam. Strongly
coloured solutions may be examined in test-tubes, or may
be kept sealed up in small bottles made out of glass tubes,
the light then examined being that which passes through
the centre of the tube from side to side. (Most of these
solutions require the addition of a little gum Arabic to
make them keep.) Such tubes may be laid on the ordinary
stage, or laid on the stage attached to the eye-piece.
Smaller quantities may be examined in cells cut out of
thick glass tubes, one side being fixed on the ordinary
glass with Canada balsam, like a microscopic object, and
the other covered with thin glass, which readily holds on
by capillary attraction, or may be cemented fast with gold
size or Canada balsam, if it be desirable to keep it as a
permanent object. Such tubes may be made of any length
that may be required for very slightly-coloured solutions.
Cells made out of spirit thermometer tubes, so as to be
about ^th of an inch in diameter, and an i ncn l n o>
are very suitable for the examination of very small quan-
tities ; but where plenty of material can be obtained, it
IB far better to use cells cut out of strong tubes, having
an interior diameter of about |-ths of an inch, cut wedge-
ehape, so that the thickness of the solution may be JtJi
130 THE MICROSCOPE.
of an inch, or more, on one side, and not above - 4 \jth on
the other ; and then the effect of different thicknesses can
easily be ascertained.
" Fortunately, the various modifications of the colouring
matter of blood yield such well-marked and characteristic
spectra, that there are few subjects to which the spectrum-
microscope can be applied with greater advantage than the
detection of blood-stains, even when perfectly dry. For
this purpose condensed light may be used, provided a
sufficiently bright light be thrown on the object by means
of a parabolic reflector or bulTs-ej condenser. A speck
of blood on white paper shows th spectrum very well,
provided it be fresh, and the colour 'fee neither too dark
nor too light, and the thickness of the colouring matter
neither too great nor too little. A mere atom, invisible to
the naked eye, which would not weigh above the icoioooth
of a grain, is then sufficient to show the characteristic
absorption-bands. They are, however, far better seen in
solution. About T&yth of a grain of liquid blood, in a cell
of -^fth of an inch in diameter, and J an inch long, gives
a spectrum as well marked as could be desired. In
exhibiting the instrument to a number of persons at a
meeting, I have found that no object is more convenient,
or excites more attention, than one in which a number of
cells are fixed in a line, side by side, containing a solution
of various red-colouring matters. In one I mount blood,
which gives two well-marked absorption-bands in the
green ; in another magenta, which gives only one distinct
band in the green; and in another I place the juice of
some red-coloured fruit, which shows no well-defined
absorption-band. Keeping a larger cell containing blood
on the stage attached to the eye-piece, these three objects
can be passed one after another in front of the object-glass,
and the total difference between the spectrum of blood and
that of either fruit-juice or magenta, and the perfect iden-
tity of the spectra when both are blood, can be seen at
a glance. By holding coloured glasses, which cut off the
red, but allow the green rays to pass, we can readily, show
how the presence of any foreign colouring-matter, which
entirely alters the general colour, might not in any degree
disguise the characteristic part of the spectrum; and by
ABSORPTION-BANDS OF BLOOD.
131
changing tho cell held on the eye-piece for a tube con-
taining an amnioniacal solution of cochineal, it is easy to
show that, though it yields a spectrum with two absorp-
tion-bands, more like those due to blood than I have seen
in any other substance, they differ so much in relation,
size, and position, that thero is no chance of their being
confounded when compared together side by side." l
We have been usually taught that the red-blood corpuscles consisted of two
substances, haematin and globulin; but later researches lead to the belief
that they consist of one crystalline substance, termed globulin or luemato-globu-
lin. A solution of this substance, as well as of certain products of its decom-
position, produces the absorption-bands referred to. Hoppe was the first to
demonstrate this fact : he found that a very dilute solution of blood was suffi-
cient for the purpose. Professor Stokes proved that this colouring-matter is
capable of existing in two
states of oxidation,and that
" ' a very different spectrum
is produced according a*
the substance, which he
has termed cruorine, is in
a more or less oxidise!
condition, 2 Proto-sulphate
of iron, or proto-chloride
of tin, causes the reduction
of the colouring-matter,
and, by exposure to air,
oxygen is absorbed, and
the solution again exhibits
the spectrum character-
istic of the more oxidised
state. The different sub-
stances obtained from
blood colouring - matter
produce different bands.
Thus, hcematin gives rise
to a band in the red spec-
trum ; hcemato - globulin
produces two bands, the
second twice the breadth
of the first in the yellow
portion of the spectrum
between the lines D and E,
No. 1. The absorption-
bands differ according to
the strength of the solu-
tion employed, and the
medium in which the blood-
salt is dissolved ; but an
exceedingly minute pro-
portion dissolved in water
is sufficient to bring out
very distinct bands.
No. 1. Arterial Blood, Scarlet Cruorine.
No. 2. Venous Blood, Purple Cruorine.
No. 3. Blood treated with Acetic Acid.
No. 4. Solution of Hcematin.
ABSORPTION-BANDS, AFTER STOKES.
(1) Popular Science Review, January, 1866.
(2) Professor Stokes, " On the Reduction and Oxidation of the Colouring-
snatter of the Blood" (Proceed. Royal Soc. vol. xiii. p. 355). The oxidising
solution is made as follows : To a solution of proto-sulphate of iron, enough
tartaric acid is added to prevent precipitation by alkalies. A small quantity of
this solution, made slightly alkaline by ammonia or carbonate of soda, is to be
added to the weak solution of blood in water.
132
THE MICROSCOPE.
The Camera Lucida.
The main point to be observed when using the
Camera Lucida is that the microscope shall be placed
in the horizontal position, and the object well lighted.
The Ross-Wollaston Neutral Tint Camera Lucida con-
sists of a metallic cylinder, cut at an angle of 45 to its
axis, thus producing an elliptical opening, into which
FIG. 78. The Ross-JFollaston Camera Lucida.
a plate of neutral tint glass is fitted. Opposite to this
is an opening about half an inch in diameter, through
which the student may view, and trace or measure the
object on drawing-paper, the microscope with the
camera attached to the eye-piece having been previously
brought into a horizontal position.
MICEOSCOPICAL DRAWING. 133
Microscopical Drawing. The proper method of draw-
ing microscopic objects is acquired by looking down
the tube of the microscope with one eye (preferably
the left) , and at the paper on which the drawing is to
be made with the other. Place the microscope in the
horizontal position, having first secured the object to be
copied to the stage, focus it carefully, and take care not
to place it too centrally, but as far towards the right as
it will go without taking it out of the field of view. If
the right eye is now opened, while the other is looking
down the tube, the object will be seen projected on the
paper, and can thus be easily traced in all its details.
The Polarisation of Light.
Common light moves in two planes at right angles to
each other, polarised light moves only in one plane.
Common light may be turned into polarised light either
by transmission or reflection ; in the first instance, one of
the planes of common light is got rid of by reflection, in
the other, by absorption. Huyghens was among the first
to notice that a ray of light has not the same properties
in every part of its circumference, and he compared it to
a magnet or a collection of magnets ; and supposed that
the minute particles of -which it was said to be composed
had different poles, which, when acted on in certain ways,
arranged themselves in particular positions; and thence
the term polarisation, a term having neither reference to
cause nor effect. It is to Malus, however, who, in 1808,
discovered polarisation by reflection, that we are indebted
for the series of splendid phenomena which have since that
period been developed ; phenomena of such surpassing
beauty as far to exceed, all ordinary objects presented
to our eyes under the microscope. It has been truly
observed by Sir David Brewster, that " the application of
the principles of double refraction to the examination of
structures is of the highest value. The chemist may per-
form the most dexterous analysis ; the crystallographer
may examine crystals by the nicest determination of their
forms and cleavage ; the anatomist or botanist may use
the dissecting knife and microscope with the most exqui-
site skill ; but there are still structures in the mineral,
134
THE MICEOSCOPE.
vegetable, and animal kingdoms, which defy all such modes
of examination, and which will yield only to the magical
analysis of polarised light. A body which is quite trans-
parent to the eye, and which might be judged as mono-
tonous in structure as it is in aspect, will yet exhibit,
under polarised light, the most exquisite organisation, a,nd
will display the result of new laws of combination which
the imagination even could scarcely have conceived. In
evidence of the utility of this agent in exploring mineral,
vegetable, and animal structures, the extraordinary organi-
sation of Apophyllite and Analcime may be referred to ',
also the symmetrical and figurate depositions of siliceous
crystals in the epidermis of equisetaceous plants, and the
wonderful variations of density in the crystalline lenses of
the eyes of animals.
Oo
If we transmit a beam of the sun's light through a cir-
cular aperture into a darkened room, and if we reflect it
from any crystallised or uncrystallised body, or transmit
it through a thin plate of either of them, it will be reflcted
and transmitted in the very same manner, and with the
same intensity, whether the surface of the body is held
above or below the beam, or on the right side or left, pro-
vided that in all cases it falls upon the surface in the same
manner ; or, what amounts to the same thing, the beam of
solar light has the same properties on all its sides; and
this is true, whether it is white light as directly emitted
from the sun, or from a candle or any burning or self-
luminous body; and all such light is called common light.
A section of such a beam of light will be a circle, like a b
c d, fig. 79 ; and we shall distinguish the section of a beam
POLAEISATION OF LIGHT. 13^
of common light by a circle with two diameters a 6, c d t at
right angles to each other.
If we now allow the same beam of light to fall upon a
rhomb of Iceland spar, and examine the two circular
beams, o E e, formed by double refraction, we shall 'find,
1st, that the beams o E e have different properties on
different sides, so that each of them differs in this respect
from the beam of common light.
2d. That the beam o differs from E e in nothing ex-
ceptiug that the former has the same properties at the
sides a b' that the latter has at the sides c' and d' ; or in
general that the diameters of the beam, at the extremities
of which the beam has similar properties, are at right
angles to each other, as a' b' and c' d' for examplo
Thesa two beams, o, E e, are therefore said to be
polarised, or to be beams of polarised light, because they
have sides or poles of different properties and planes passing
through the lines a b } c d ; or a' b', c' d', are said to be the
planes of polarisation of each beam, because they have the
same property, and one which no other plane passing
through the beam possesses.
Now it is a curious fact, that if we cause the two
polarised beams o, E e to be united into one, or if we
produce them by a thin plate of Iceland spar, which is not
capable of separating them, we obtain a beam which has
exactly the same properties as the beam a b c d of common
light. Hence we infer that a beam of common light, a b
c d, consists of two beams of polarised light, whose plane
of polarisation, or whose diameters of similar properties,
are at right angles to one another. If o be laid above
E e, it will produce a figure like a b c d ; and we shall
therefore represent polarised light by such figures. If we
were to place o above E e, so that the planes of polarisa-
tion a' b' and c' d- coincide, then we should have a beam of
polarised light twice as luminous as either o or E e, and
possessing exactly the same properties; for the lines of
similar property in the one beam coincide with the lines of
similar property in the other. Hence it follows that there
are three ways of converting a beam of common light, a b
c d, into a beam or beams of polarised light.
1st. We may separate the beam of common light, a & c d,
136
THE MICROSCOPE.
component parts o and E e. 2d. We may turn round
the planes of polarisation, abed, till they coincide or are
parallel to each other. 3d. We may absorb or stop one of
the beams, and leave the other, which will consequently
be in a state of polarisation." 1
The first of these methods of producing polarised light
is that in which we employ a doubly refracting crystal,
and was first discovered to exist in a transparent mineral
substance called Iceland spar, calcareous spar, or carbonate
of lime. This substance is admirably adapted for exhibit-
ing this phenomenon, and is the one generally used by
microscopists. Iceland spar is composed of fifty-six parts
of lime and forty-four parts of carbonic acid ; it is found
in various shapes in almost all
countries; but whether found in
crystals or in masses, we can always
cleave it or split it into shapes re-
presented by fig. 80, which is called
a rhomb of Iceland spar, a solid
bounded by six equal and similar
rhomboidal surfaces, whose sides
are parallel, and whose angles b a c,
a c d, are 101 55' and 78 5'. The
line a x, called the axis of the rhomb, or of the crystal, is
equally inclined to each of the six faces at an angle of
45 23.' It is very transparent, and generally colourless. Its
natural faces when it is split are commonly even and per-
fectly polished ; but when they are not so, we may, by a
new clevage, replace the imperfect face by a better one,
or we may grind and polish an imperfect face.
It is found that in all bodies where there seems to be
an irregularity of structure, as salts, crystallised minerals,
&c., on light passing through them, it is divided into two
distinct pencils. If we take a crystal of Iceland spar, and
look at a black line or dot on a sheet of paper, there will
appear to be two lines or dots; and on turning the spar
round, these objects will seem to turn round also; and
twice in the revolution they will fall upon each other,
which occurs when the two positions of the spar are exactly
opposite, that is, when turned one-half from the position
(1) Brewster's " Optics "
POLARISATION OF LIGHT. 137
where it is first observed. In the accompanying diagram,
fig. 81, the line appears double, as a b and c d, or the dot,
as e and /. Or allow a ray of light, g h y to fall thus on the
crystal, it will in its passage through be separated into two
rays, hf, he; and on coming to the opposite surface of the
crystal, they will pass out at ef in the direction of i k,
parallel to g h. The plane I m n o is designated the prin-
cipal section of the crystal, and the line drawn from the
solid angle I to the angle o is where the axis of the crystal
is contained; it is also the optic axis of the mineral. Now
when a ray of light passes along this axis, it is undivided,
and there is only one image; but in all other directions
there are two.
If two crystals of Iceland spar be used, the only differ-
ence will be, that the objects seem farther apart, from the
increased thickness. But if two crystals be placed with
their principal sections at right angles to each other, the
ordinary ray refracted in the first will be the extraordinary
m the second, and so on vice versd. At the intermediate
position of the two crystals there is a subdivision of each
ray, and therefore four images are seen ; when the crystals
are at an angle of 45 to each other, then the images are
all seen of equal intensity.
Mr. Nicol first succeeded in making rhombs of Iceland
Bpar into single-image prisms, by dividing one into two
equal portions. His mode of proceeding is thus described
in the Edinburgh Philosophical Journal (vol. vi. p. 83) :
138
THE MICROSCOPE.
"A rhomb of Iceland spar of one-fourth of an inch in
length, and about four-eighths of an inch in breadth and
thickness, is divided into two equal portions in a plane,
passing through the acute lateral angle, and nearly touching
the obtuse solid angle. The sectional plane of each of
these halves must be carefully polished, and the portions
cemented firmly with Canada balsam, so as to form a
rhomb similar to what it was before its division ; by this
management the ordinary and extraordinary rays are so
separated that only one of them is transmitted : the cause
of this great divergence of the rays is considered to be
owing to the action of the Canada balsam, the refractive
index of which (1-549) is that between the ordinary
(1:6543) and the extraordinary (1-4833) refraction of
calcareous spar, and which will change the direction of
both rays in an opposite manner before they enter the
posterior half of the combination." The direction of rays
Fig. 82.
passing through such a prism is indicated . by the arrow,
fig. 82, and the combination is shown mounted, one for
Fig. 83.
Fig. 83.
use under the stage of the microscope, fig. 83, termed the
polariser; another, fig. 83ar. screwed on to and above the
POLARISATION OF LIGHT.
139
object-glasses, is called the analyser. The definition is
better if the analyser be placed at top of the A eye-piece,
and it is more easily rotated than the polariser.
Method of using the polarising Prism, fig. 83. After
having adapted it to slide into a groove on the under-surface
of the stage, it is held in its place by turning the small
milled-head screw at one end : the other prism, fig. 83#. is
screwed on above the object-glasses, and made to pass into
the body of the microscope itself. The light having been
reflected through them by the mirror, it becomes necessary
to make the axes of the two prisms coincide ; this is done
by regulating the milled-head screw, until by revolving the
polarising prism, the field of view is entirely darkened twice
during one revolution. This should be
ascertained, and carefully corrected by
the maker and adapter of the apparatus,
If very minute salts or crystals are to be
viewed, it is preferable to place the ana-
lyser above the eye-piece; it will then
require to be mounted as in fig. 84. Thus
the polariscope consists of two parts ; one
for polarising, the other for analysing
or testing the light. There is no essen-
tial difference between the two parts,
except what convenience or economy may
lead us to adopt ; and either part, there-
fore, may be used as polariser or analyser ;
but whichever we use as the polariser, the
other becomes the analyser.
The tourmaline, a precious stone of a neutral or bluish
tint, forms an excellent analyser; it should be cut about
2\,th of an inch thick, and parallel to its axis. The great
objection to it is, that the transmitted polarised beam is
more or less coloured. The best tourmaline to choose is
the one that stops the most light when its axis is at right
angles to that of the polariser, and yet admits the most
when in the same plane. It is necessary to choose the
etone as perfect as possible, the size is of no importance
when used with the microscope.
In the illumination of objects by polarised light, when
under view with high powers, for the purpose of obtaining
Fig. 84.
140
THE MICROSCOPE.
the maximum effect, it is also requisite that the angle of
aperture of the polariser should be the same a.s the object-
glass, each ray of which should be directly opposed by a
ray of polarised light. The Polarising Condenser is merely
an ordinary achromatic condenser of large aperture, close
under the bottom lens of which is placed a plate of tour-
maline, used in combination with a superposed film of
Belenite or not, as required. The effect of this arrangement
on some objects is very remarkable, bringing out strongly
colours which are almost invisible by the usual mode.
The production of colour by polarised light has been
thus most clearly and comprehensively explained by Mr.
Woodward, in his t( Introduction to the Study of Polarised
Light." 1
Fig. 85.
h
abed represent the rectangular vibrations by which
a ray of common light is supposed to be propagated.
e, a plate of tourmaline, called in this situation the
polariser, and so turned that a b may vibrate in the piano
of its crystallographical axis.
(U Mr Woodward constructed a very available form of polariscope for most
yurposes'; the instrument is described in Elements of Natural Philosophy, by
Jabez Hogg.
POLARISATION OF LIGHT. Kl
jr; light polarised by e, by stopping the vibrations c d,
and transmitting those of a b.
g, a piece of selenite of such a thickness as to produce
red light, and its complementary colour green.
h, the polarised light / bifurcated, or divided into ordi-
nary and extraordinary rays, and thus said to be de-
polarised by the double refractor g, and forming two planes
of polarised light, o and e, vibrating at right angles to
each other.
i, a second plate of tourmaline, here called the analyser,
with its axis in the same direction as that of e, through
which the several systems of waves of the ordinary and
extraordinary rays h, not being inclined at a greater
angle to the axis of the analyser than that of 45 degrees,
are transmitted and brought together under conditions
that may produce interferences.
kj the waves R o and R e, for red light of the ordinary
and extraordinary systems meeting in the same state of
vibration, occasioned by a difference of an even number
of half undulations, and thus forming a wave of doubled
intensity for red light.
I m, the waves Y o and Y e and B o and B e for yellow and
blue of the ordinary and extraordinary systems respec-
tively meeting together, with a difference of an odd
number of half undulations, and thus neutralising each
other by interferences.
n, red light, the result of the coincidence of the waves
for red light, and the neutralisation by interferences of
those for yellow and blue respectively.
h, fig. 85#, depolarised light, as fig. 85.
i, the analyser turned one quarter of a circle, its axis
being at right angles to that of i in fig. 85.
k, the waves R o R e, for red light of the ordinary and
extraordinary systems meeting together with a difference
of an odd number of half undulations, and thus neutral-
ising each other by interference.
I m, the waves Y o Y e and B o B e, for yellow and blue of
the two systems severally meeting together in the same
state of vibration, occasioned by the difference of an even
number of half undulations, and forming by their coin-
cidences waves of doubled intensity for yellow and blue
light.
142 THE MICROSCOPE.
n, green light, the result of the coincidences of the
waves for yellow and blue light respectively, and the
neutralisation by interference of those for red light.
By substituting Nicol's prisms for the two plates of
tourmaline, and by the addition of the object-glass and
eye-piece, the diagrams would then represent the passage
of polarised light through a microscope.
For showing objects by polarised light under the micro-
scope that are not in themselves doubly refractive, put
upon the stage a film of selenite, which exhibits, under
ordinary circumstances, the red ray in one position of the
polarising prism, and the green ray in another, using a
double-image prism over the eye-piece ; each arc will
assume one of these complementary colours, whilst the
centre of the field will remain colourless. Into this field
introduce any microscopic object which in the usual
arrangement of the polariscope undergoes no change in
colour, when it will immediately display the most brilliant
effects. Sections of wood, feathers, algse, and scales, are
among the objects best suited for this kind of exhibition.
The power suited for the purpose is a two-inch object-
glass, the intensity of colour, as well as the separating
power of the prism, being impaired under much higher
amplification; although in some few instances, such as in
viewing animalcules, the one-inch object-glass is perhaps
to be preferred.
Selenite is the native crystallised hydrated sulphate of
lime. A beautiful fibrous variety called satin gypsum is
found in Derbyshire. It is found also at Shotover Hill,
near Oxford, where the labourers call it quarry '-glass. Very
large crystals of it are found at Montmartre, near Paris.
The form of the crystal most frequently met with is that
of an oblique rectangular prism, with ten rhomboidal
faces, two of which are much larger than the rest. It is
usually slit into thin laminse parallel to these large
lateral faces; the film having a thickness of from one-
twentieth to the one-sixtieth of an inch. In the two rec-
tangular directions they allow perpendicular rays of pola-
rised light to traverse them unchanged; these directions
are called the neutral axes. In two other directions,
however, which form respectively angles of 45 with the
HEEAPATHITE. 143
neutral axes, these films have the property of double
refraction. These directions are known as the depolarising
axes.
The thickness of the film of selenite determines the
particular tint. If, therefore, we use a film of irregular
thickness, different colours are presented by the different
thicknesses. These facts admit of very curious and beau-
tiful illustration, when used under the object placed on the
stage of the microscope. The films employed should be
mounted between two glasses for protection. Some persons
employ a large film mounted in this way between plates of
glass, with a raised edge, to act as a stage for supporting
the object, it is then called the " selenite stage." The best
film for the microscope is that which gives blue, and its
complementary colour yellow. Mr. Darker has constructed
a very neat stage of brass for this purpose, producing a
mixture of all the colours by superimposing three films,
one on the other ; by a slight variation in their positions,
produced by means of an endless-screw motion, all the
colours of the spectrum are shown. When objects are
thus exhibited, we must bear in mind that all the negative
tints, as we term them, are diminished, and all the
positive ones increased ; the effect of this plate is to mask
the true character of the phenomena. Polarised structures
should therefore never be drawn and coloured under such
conditions.
Dr. Herapath, of Bristol, described a salt of quinine,
which is remarkable for its polarising properties. The salt
was first accidentally observed by Mr. Phelps, a pupil of
Dr. Herapath's, in a bottle which contained a solution of
disulphate of quinine: the salt is formed by dissolving
disulphate of quinine in concentrated acetic acid, then
warming the solution, and dropping into it carefully, and
by small quantities at a time, a spirituous solution of
iodine. On placing this mixture aside for some hours,
brilliant plates of the new salt will be formed. The crystals
of this salt, when examined by reflected light, have a
brilliant emerald-green colour, with almost a metallio
lustre ; they appear like portions of the ely trss of cantha-
rides, and are also very similar to murexide in appearance.
When examined by transmitted light, they scarcely possess
144 THE MICROSCOPE.
any colour, there is only a slightly olive-green tinge ;
but if two crystals, crossing at right angles, be
examined, the spot where they intersect appears per-
fectly black, even if the crystals are not one five-
hundredth of an inch in thickness. If the light be in
the slightest degree polarised as by reflection from a
cloud, or by the blue sky, or from the glass surface of
the mirror of the microscope placed at the polarising
angle 56 45' these little prisms immediately assume
complementary colours : one appears green, and the
other pink, and the part at which they cross is a cho-
colate or deep chestnut-brown, instead of black. As
the result of a series of very elaborate experiments, Dr.
Herapath finds that this salt possesses the properties
of tourmaline in a very exalted degree, as well as of a
plate of selenite ; so that it combines the properties of
polarising a ray and of depolarising it. Dr. Herapath
has succeeded in making artificial tourmalines large
enough to surmount the eye-piece of the microscope ; so
that all experiments with those crystals upon polarised
light may be made without the tourmaline or Nicol's
prism. The brilliancy of the colours is much more
intense with the artificial crystal than when employing
the natural tourmaline. As an analyser above the eye-
piece, it offers some advantages over the Nicol's prism
in the same position, as it gives a perfectly uniform tint
of colour over a much more extensive field than can be
had with the prism. 1 These crystals are liable to be
injured by damp.
" The following experiments, if carefully performed,
will illustrate the most striking phenomena of double
refraction, and form a useful introduction to the prac-
tical application of this principle.
(1) Dr. Herapath subsequently furnished a better process for the manu-
facture of these artificial tourmalines, see Quarterly Journal of Microscopical
Science for January, 1854. " These beautiful rosette crystals are made as
follows : Take a moderately strong solution of Cinchonidine in Herapath's
test-fluid (as already described). A little of this is dropped on the centre of
ft slide and laid down for a time, until the first crystals are observed to be
formed near the margin. The slide should now be placed upon the stage of
the microscope, and the progress of formation of the crystals closely watched.
When these are seen to be large enough, and it is deemed necessary to stop
their further development, the slide must be quickly transferred to the palm
of the hand, the warmth of which will be found sufficient to stop further
trystallization,"
POLARISATION OF LIGHT. 145
" A plate of brass, fig. 86, three inches by one, perforated
with a series of holes from about one-sixteenth to one-
Fig. S3. Red is represented by perpendicular lines ; Green by oblique.
fourth of an inch in diameter; the size of the smallest
should be in accordance with the power of the object-glass,
and the separating power of the double refraction.
" Experiment 1. Place the brass plate so that the smallest
hole shall be in the centre of the stage of the instrument ;
employ a low power (1^ or 2 inch) object-glass, and adjust
the focus as for an ordinary microscopic object; place the
double image prism over the eye-piece, and there will
appear two distinct images; then, by revolving the prism,
these will describe a circle, the circumference of which
cuts the centre of the field of view ; the one is called the
ordinary, the other the extraordinary ray. By passing the
slide along, that the larger orifices may appear in the field,
the images will not be completely separated, but will
overlap, as represented in the figure.
" Experiment 2. Screw the Nicol's prism into its place
under the stage, still retaining the double image prism
over the eye-piece ; then, by examining the object, there
will appear in some positions two, but in others only one
image; and it will be observed, that at 90 from the latter
position this ray will be cut off, and that which was first
observed will become visible; at 180, or one-half the
circle, an alternate change will take place; at 270, another
change; and at 360, or the completion of the circle, the
original appearance.
" Before proceeding to the next experiment, it will be as
well to observe the position of the Nicol's prism, which
should be adjusted with its angles parallel to the square
parts of the stage. In order to secure the greatest
brilliancy in the experiment, the proper relative position
of the selenite may be determined by noticing the natural
146 THE MICROSCOPE.
flaws in the film, which will be observed to run parallel
with each other; these flaws should be adjusted at about
46 from the square parts of the stage, to obtain the
greatest amount of depolarisation.
"Experiment 3. If we now take the plate of selenite thus
prepared, and place it under the piece of brass on the
stage, we shall see, instead of the alternate black and
white images, two coloured images composed of the con-
stituents of white light, which will alternately change by
revolving the eye-piece at every quarter of the circle ; then,
by passing along the brass, the images will overlap ; and
at the point at which they do so, white light will be pro-
duced. If, by accident, the prism be placed at an angle of
45 from the square part of the stage, no particular colour
will be perceived; and it will then illustrate the phenomena,
of the neutral axis of the selenite, because when placed in
that relative position no depolarisation takes place. The
phenomena of polarised light may be further illustrated
by the addition of a second double image prism, and a
film of selenite adapted between the two. The systems
of coloured rings in crystals cut perpendicularly to the
principal axis of the crystal are best seen by employing the
lowest object-glass."
To show the phenomena of the rings round the optic
axes of the crystals, the following plan, which is by far
the best, must be followed, and the rings will appear .in
perfection :
1. The B eye-piece without a diaphragm, and the lenses
so adjusted that the field-lens may be brought nearer to,
or farther from the eye-lens as occasion may require ; thus
giving different powers, and different fields, and when
adjusted for the largest field it will be full 15 inches, and
take in the widest separation of the axis of the aragonite.
2. A crystal stage to receive the crystals, and to be
placed over the eye-piece, so constructed as to receive a
tourmaline, and that to turn round.
3. A tourmaline of a blue tint.
4. A large Nicol's prism as a polariser.
5. A common two-inch lens, not achromatic; which,
must be set in a brass tube long enough when screwed into
POLAEISING CKYSTALS. 147
the microscope to reach the polariser, that all extraneous
light may be excluded.
The concave mirror should be used with a bull's-eye
condenser by lamplight. The condenser may be dispensed
with by daylight. The above apparatus is furnished by
Messrs. Powell and Lealand.
The crystals best adapted to show the phenomena of
rings round the optic axes, are :
Quartz. A uniaxial crystal, one system of rings, no
entire cross of black, only the ends of it, the centre being
coloured, and as the tourmaline is revolved, the colour
gradually changing into all the colours of the spectrum,
one colour only displayed at once.
Quartz. Cut so as to exhibit right-handed polarisation.
Quartz. Cut so as to exhibit left-handed polarisation ;
that is, the one shows the same phenomena when the
tourmaline is turned to the right, as the other does when
turned to the left.
Quartz. Cut so as to exhibit straight lines.
Gale Spar. A uniaxial crystal, one system of rings, and
a black cross, which changes into a white cross on revolving
the tourmaline, and the colours of the rings into their
complementary colours,
Topaz. A biaxial crystal, although it has two axes, only
exhibits one system of rings with one fringe, owing to the
wide separation of the axes. The fringe and colours
change on revolving the tourmaline ; this is the case in all
the crystals.
Borax. A biaxial crystal; the colours more intense
than in topaz, but the rings not so complete, only one
set of rings taken in, from the same cause as topaz.
Rochelle Salt. A biaxial crystal; the colours more
widely spread. Very beautiful. Only one set of rings
taken in.
Carbonate of Lead. A biaxial crystal, axes not much
separated, both systems of rings exhibited, far more widely
spread than those of nitre.
Aragonite. A biaxial crystal, axes widely separated ; but
both systems of rings exhibited, and decidedly the best
crystal for displaying the phenomena of biaxial crystals.
The field-lens of the eye-piece requires to be brought as
L 2
148
THE MICROSCOPE.
close as possible to the eye-lens, to see properly the
phenomena in quartz and aragonite ; it must be placed
at an intermediate distance for viewing topaz, borax,
Rochelle salt, and carbonate of lead ; it must be drawn
out to its full extent to view nitre and calc spar.
It was long believed that all crystals had only one
axis of double refraction ; but Brewster found that the
great body of crystals, which are either formed by art,
or which occur in the mineral kingdom, have two axes
of double refraction, or rather axes around which the
double refraction takes place ; in the axes themselves
there is no double refraction.
Nitre crystallises in six-sided prisms with angles of
oj|!!' 'iiii'i. .; i|i " ~ ~ r ~~ ~ :
FIG. 87. Darter's Selcnite Films and Stage.
about 120. It has two axes of double refraction, along-
which a ray of light is not divided into two. These
axes are each inclined about 2 to the axes of the
prism, and 5 to each other. If, therefore, we cut off
a piece from a prism of nitre with a knife driven by a
smart blow of a hammer, and polish the two surfaces
perpendicular to the axes of the prism, so as to leave
the thickness of the sixth or eighth of an inch, and
then transmit a ray of polarised light along the axes
of the prism, we shall see the double system of rings
shown in figs. 88 and S8a.
When the line connecting the two axes of the crystal is
inclined 45 to the plane of primitive polarisation, a cross
is seen as at fig. 88 ; on revolving the nitre, it gradually
POLARISING CRYSTALS.
149
assumes the form of the two hyperbolic curves, fig 88a. But
if the tourmaline be revolved, the black crossed lines will
Fig. SSa.
be replaced by white spaces, and the red rings by green,
the yellow by indigo, and so on. These systems of rings
have, generally speaking, the same colours as those of
thin plates, or as those of a system of rings round one
axis. The orders of the colours commence at the centres
of each system; but at a certain distance, which corre-
sponds to the sixth ring, the rings, instead of returning
and encircling each pole, encircle the two poles as an
ellipse does its two foci. When we diminish or increase
the thickness of the plate of nitre, the rings are diminished
or increased accordingly.
Small specimens of salts may also be crystallised and
mounted in Canada balsam for viewing under the stage of
the microscope ; by arresting the crystallisation at certain
stages, a greater variety of forms and colours will be
obtained : we may enumerate salicine, asparagine, acetate
of copper, phospho-borate of soda, sugar, carbonate of
lime, chlorate of potassa, oxalic acid, and all the oxalates
found in urine, with the other salts from the same fluid, a
few of which are shown at fig. 89.
Dr. W. B. Herapath contributed an interesting addi-
tion to the uses of polarised light, by applying it to discover
the salts of alkaloids, quinine, &c. in the urine of patients.
150
THE MICROSCOPE.
He says : " It has long been a favourita subject of inquiry
with the professional man to trace the course of remedies
Fig. 89. Urinary Salts.
a, Uric acid; b, Oxalate of lime, octahedral crystals of; c, Oxalate of lime
allowed to dry, forming a black cube; d, Oxalate of lime, as it occasionally
appears, termed the dumb-bell crystal.
in the system of the patient under his care, and to know
what has become of the various substances which he might
have administered during the treatment of the disease.
" Having been struck with the facility of application,
and the extreme delicacy of the reaction of polarised light,
when going through the series of experiments upon the
sulphate of iodo-quinine, I determined upon attempting
to bring this method practically into use for the detection
of minute quantities of quinine in organic fluids ; and after
more or less success by different methods of experimenting.
I have at length discovered a process by which it is possible
to obtain demonstrative evidence of the presence of quinine,
even if in quantities not exceeding the one-millionth part
of a grain ; in fact, in quantities so exceedingly minute, that
all other methods would fail in recognising its existence.
Take for test-fluid a mixture of three drachms of pure
acetic acid, with one fluid-drachm of rectified spirits-of-
wine, to which add six drops of diluted sulphuric acidL
" One drop of this test-fluid placed on a glass-slide,
and the merest atom of the alkaloid added, in a short time
POLARISING CEYSTALS.
151
solution will take place ; then, upon the tip of a very fine
glass-rod let an extremely minute drop of the alcoholic
solution of iodine be added. The first effect is the produc-
tion of the yellow or cinnamon-coloured compound of iodine
and quinine, which forms as a small circular spot; tho
alcohol separates in little drops, which by a sort of repul-
sive movement, drive the fluid away ; after a time, the acid
liquid again flows over the spot, and the polarising crystals
of sulphate of iodo-quinine are slowly produced in beautiful
rosettes. This succeeds best without the aid of heat.
" To render these crystals evident, it merely remains to
bring the glass-slide upon the field of the microscope, with
the selenite stage and single tourmaline, or Nicol's prism,
beneath it ; instantly the crystals assume the two comple-
mentary colours of the stage ; red and green, supposing
that the pink stage is employed, or blue and yellow, pro-
vided the blue selenite is made use of. All those crystals
at right angles to the plane of the tourmaline, producing
Fig. 90. In this figure heraldic lines are adopted to denote colour. The
dotted parts indicate yellow, the straight lines red, the horizontal lines blue,
and the diagonal,-or oblique lines, green. The arrows show the plane of the
tourmaline, a, blue stage ; 6, red stage of selenite employed.
that tint which an analysing-plate of tourmaline would
produce when at right angles to the polarising-plate ;
152
THE MICROSCOPE.
whilst those at 90 to these educe the complementary tint,
as the analysing-plate would also have done if revolved
through an arc of 90.
"This test is so ready of application, and so delicate,
that it must become the test, par excellence, for quinine :
fig. 90, a and b. Not only do these peculiar crystals act
in the way just related, but they may be easily proved to
possess the whole of the optical properties of that remark-
able salt of quinine, the sulphate of iodo-quinine.
" To test for quinidine, it is merely necessary to allow
the drop of acid solution to evaporate to dryness upon the
slide, and to examine the crystalline mass by two tourma-
lines, crossed at right angles, and without the stage.
Immediately little circular discs of white, with a well-
defined black cross very vividly shown, start into existence,
should quinidine be present even in very minute traces.
These crystals are represented in fig. 91.
Fig. 91.
' If we employ the selenite stage in the examination of
this object, we obtain one of the most gorgeous appear-
ances in the whole domain of the polarising-microscopo :
the black cross at once disappears, and is replaced by one
which consists of two colours, being divided into a cross
SNOW CRYSTALS.
153
Flff. 92. Sntic CryttaU.
154 THE MICROSCOPE.
having a red and green fringe, whilst the four intermediate
sectors are of a gorgeous orange-yellow. These appear-
ances alter upon the revolution of the analysing-plate of
tourmaline ; when the blue stage is employed, the cross
will assume a blue or yellow tint, according to the position
of the aualysing-plate. These phenomena are analogous
to those exhibited by certain circular crystals of boracic
acid, and to those circular discs of salicine (prepared by
fusion) ; the difference being, that the salts of quinidine
have more intense depolarising powers than either of the
other substances ; besides which, the mode of preparation
effectually excludes these from consideration. Quinine
prepared in the same manner as quinidine has a very
different mode of crystallisation ; but it occasionally pre-
sents circular corneous plates, also exhibiting the black
cross and white sectors, but not with one-tenth part of the
brilliancy, which of course enables us readily to discrimi-
nate the two."
Ice doubly refracts, while water singly refracts. Ice
takes the rhomboidic form ; and snow in its crystalline
form may be regarded as the skeleton crystals of this
system. A sheet of clear ice, of about one inch thick, and
slowly formed in still weather, will show the circular rings
and cross if viewed by polarised light.
It is probable that the conditions of snow formation are
more complex than might be imagined, familiar as we are
with the conditions relating to the crystallisation of water
on the earth's surface. Dr. Smallwood, of Isle Jesus,
Canada East, has traced an apparent connection between
the form of the compound varieties of snow crystals and
the electrical condition of the atmosphere, whether nega-
tive or positive ; and is instituting experiments for hia
better information on the subject.
A great variety of animal, vegetable, and other sub-
stances possess a doubly refracting or depolarising struc-
ture, as : a quill cut and laid out flat on glass ; the cornea
of a sheep's eye ; skin, hair, a thin section of a finger-nail ;
sections of bone, teeth, horn, silk, cotton, whalebone ;
Btems of plants containing silica or flint ; barley, wheat, &c.
The larger-grained starches form splendid objects; tous-
Its-mois, being the largest, may be taken as a type of al]
POTATOE STARCH. 155
the others. It presents a black cross, the arms of which
meet at the hilum. On rotating the analyser, the
black cross disappears, and
at 90 is replaced by a white
cross ; another, but much
fainter black cross being per-
ceived between the arms of
the white cross. Hitherto,
however, no colcur is percep-
tible. But if a thin plate of
selenite be interposed between
Flg> 93 ' the starch-grains and the po-
Potato Starch, seen under polarised , , , -.., * <*
light. lariser, most splendid and
delicate colours appear. All
the colours change by revolving the analyser, and become
complementary at every quadrant of the circle. West and
East India arrow-root, sago, tapioca, and many other
starch-grains, present a similar appearance ; but in pro-
portion as the grains are smaller, so are their markings
and colourings less distinct.
" The application of this modification of light to the
illumination of very minute structures has not yet been
fully carried out ; but still there is no test of differences
in density between any two or more parts of the same
substance that can at all approach it in delicacy. All
structures, therefore, belonging either, to the animal, vege-
table, or mineral kingdom, in which the power of unequal
or double refraction is suspected to be present, are those
that should especially be investigated by polarized light.
Some of the most delicate of the elementary tissues of
animal, such as the tubes of nerves, the ultimate fibrillse
of muscles, &c., are amongst the most striking subjects that
may be studied with advantage under this method of illu-
mination. Every structure that the microscopist is
investigating should be examined by this light, as well
as by that either transmitted or reflected. Objects
mounted in Canada balsam, that are far too delicate to
exhibit any structure under transmitted, will often be
well seen under polarised light ; its uses, therefore, are
manifold." 1
(1) Quekett's Practical Treatiteon the Use of the Microscope.
156 THE MICROSCOPE.
Molecular Rotation. For the purpose of studying
the various interesting phenomena of molecular rotation,
a few necessary pieces of apparatus must be added to
the microscope. First, an ordinary iron three-armed
retort stand, to the lower arm of which must be
attached either a polarising prism or a bundle of glass
plates inclined at the polarising angle. In the upper
an analysing prism. The fluid to be examined should be
contained in a narrow glass tube about eight inches iii
height, and this must be attached to the middle arm.
If the prisms be crossed before inserting a fluid,
possessing rotatory power, the light passing through
the analyser will be coloured. If a solution of sugar
be employed, and the light which passes through the
second prism is seen to be red, but on rotating the ana-
lyser towards the right, the colour changes to yellow,
and passes through green to violet, it maybe concluded
that the rotation is right-handed. If, on the contrary,
the analyser requires to be turned towards the left
hand, we conclude that the polarisation is left-handed.
These phenomena are wholly distinct from those
accompanying the action of doubly refracting sub-
stances upon plane polarised light. It is not easy to
explain in a limited space the course to be followed in
ascertaining the amount of rotation produced by
different substances. Monochromatic light should be
used. If we are about to examine a sugar solution with
the prisms crossed, the index attached to the analyser
must first be made to point to zero. The sugar is
then introduced, when it will be necessary to rotate
the analyser 23 to the right, in order that the light
may be extinguished. This is the amount of rotation
for that particular fluid at a given density and that
height of column. As the arc varies with increase
or decrease of density and height of the fluid, it is
needful to reduce it to a unit of height and density.
The following formula is that given by Biot: P=
quantity of matter in a unit of solution ; d = sp. gr. ;
I = length of column ; a = arc of rotation ; m = mole-
cular rotation. Then m = -= -,
l d
APPLICATION OF PHOTOGRAPHY. 15?
A fine effect may be obtained by using Furze's spotted
lens, with a Herapathite polariser; see Mic. Soc. Trans.
2d series, vol. iii. p. 63.
APPLICATION OF PHOTOGRAPHY TO THE MICROSCOPE!.
At the time this book was projected, it was thought that
if the objects so beautifully exhibited under the microscope
could be drawn by light on the page of the book, or on
the wood-blocks, so that the engraver might work directly
from the drawings thus made, truthfulness would be in-
sured, and we should present to the reader a valuable
record of microscopic research never before seen or
attempted. But in this we were doomed to disappoint-
ment by the existence of a patent, which presented ob-
stacles too great to be surmounted ; and the idea waa
abandoned, with the exception of a few drawings then
prepared, and ready to hand : the patent restrictions having
been since removed, we have embodied them in our pages.
The eye and feet of fly, antenna of moth, paddles of whirli-
gig, with a few others, were first taken on a film of collo-
dion, then floated off the glass on to the surface of a block
of wood, the wood having been previously and lightly
inked with printer's ink or amber-varnish, and the film
gently rubbed or smoothed down to an even surface, at
the same time carefully pressing out all bubbles of air or
fluid.
For the purposes of photography the only necessary
addition to the ordinary microscope is that of a dark
chamber ; it should indeed form a camera obscura, having
at one end an' aperture for the insertion of the eye-piece
end of the microscopic tube, and at the other a groove for
carrying the crown-glass for focussing. This dark chamber
must not exceed eighteen inches in length ; for if longer,
the pencil of light transmitted by the object-glass is dif-
fused over too large a surface, and a faint and unsatis-
factory picture results therefrom. Another advantage is,
that pictures at this distance are in size very nearly equal
to the object seen in the microscope. In some instances,
better pictures are produced by taking away the eye-pieoe
158 THE MICROSCOPE.
of the microscope altogether. The time of producing the
picture varies from five to twenty seconds, with the strength
of the daylight. A camphine lamp, light Cannel coal-gas,
or the lime-light, will enable a good manipulator to pro-
duce pictures nearly equal to those produced by sun-light.
Collodion offers the best medium, as a strong negative can
be made to produce any number of printed positives.
The light is transmitted from the mirror through the
object and lenses, and brought to a focus on the ground-
glass, or prepared surface of collodion, in the usual manner.
Care must be taken not to use the burning focus of the
lenses. The gas microscope may be used to make an
enlarged copy of an object, it is only necessary to pin up
against the screen a piece of prepared calotype paper to
receive the reflected image. Mr. Wenham gives direc-
tions for improving "microscopic photography " in the
Quarterly Journal of Microscopical Science for January,
1855. In this paper he has shovn how to insure quick
and accurate focussing ; or, in other words, the making of
the actinic and visual foci of the objective coincident. The
simplest and cheapest way of producing coincidence is to
screw a biconvex lens into the place of the back-stop of
the object-glass, which thus acts as part of its optical com-
bination. An ordinary spectacle lens, carefully centred
and turned down to the required size, answers the purpose
exceedingly well.
An excellent method has been proposed and adopted by
Mr. Wenham, for exhibiting the form of certain very
minute markings upon objects. A negative photographic
impression of the object is first taken on collodion, in the
ordinary way, with the highest power of the microscope
that can be used. After this has been properly fixed, it is
placed in the sliding frame of an ordinary camera, and the
frame end of the latter adjusted into an opening cut in
the shutter of a perfectly dark room. Parallel rays of
sunlight are then thrown through the picture by means
of a flat piece of looking-glass fixed outside the shutter at
euch an angle as to catch and reflect the rays through the
camera. A screen standing in the room, opposite the lens
of the camera, will now receive an image, exactly as from
* magic lantern, and the size of the image will be proper,
APPLICATION OP PHOTOGRAPHY, 139
tionate to the distance. On this screen is placed a sheet
of photogenic paper intended to receive the magnified
picture. We ought to add, however, that it requires con-
siderable practice to avoid the distortion and error of
definition occasioned by a want of coincidence in the
chemical and visual foci. Imperfections are much in-
creased when the highest powers of the microscope are
employed ; false notions of structure are also given,
which is the case in Mr. Wenham's photograph of P. An-
gulatum.
Mr. S. Highley has a mode of adapting an object-glass to
the ordinary camera, for the purpose of taking microscopic
objects on collodion and other surfaces, fig. 94; a sec-
tional view of his arrangement is here given, which is
Fig. 94. HigMey's Camera.
very compact, steady, and ever ready for immediate use.
The tube A screws into the flange of a camera which has
a range of twenty-four inches; the front of this tube is
closed, and into it screws the object-glass B. Over A slides
another tube c ; this is closed by a plate, D, which extends
beyond the upper and lower circumference of c, and carries
a small tube, E, on which the mirror p is adjusted. To the
upper part of D the fine adjustment G is attached ; this
consists of a spring-wire coil acting on an inner tube, to
which the stage-plate H is fixed, and is regulated by a gra-
duated head, K, acting on a fine screw, likewise attached to
160 THE MICROSCOPE.
the stage-plate, after the manner of Oberhauser's micro-
scopes. An index L is affixed opposite the graduated head
K. The stage and clamp slides vertically on H ; and by
sliding this up or down, and the glass object-slide hori-
zontally, the requisite amount of movement is obtained to
bring the object into the field. The object being brought
into view, the image is roughly adjusted on the focussing-
glass by sliding c on A ; the focussing is completed by aid
of the fine adjustments G K, and allowance then made for
the amount of non-coincidence between the chemical and
visual foci of the object-glass. The difference in each glass
employed should be ascertained by experiment in the first
instance, and then noted. By employing a finely-ground
focussing-glass greased with oil, this arrangement forms an
agreeable method of viewing microscopical objects with
both eyes, and is less fatiguing. As a very large field is
presented to the observer, this arrangement might be
advantageously employed for class demonstration.
Fig. 95.Highley's Photo-micrographic Arrangement.
This arrangement combines the most recent improve-
ments of Dr. Maddox, and consists of a lens-carrier with
ordinary adjustments; stage with gymbal motions so as
to bring any object parallel to the surface of the object-
glass ; bright ground illuminator, graduating diaphragm ;
and a speculum reflector for giving the light from a
single surface.
MICROPHOTOGRAPHIC APPARATUS.
161
Professor Draper employed the following form of
lantern for microphotography : a is a zirconia light
rendered incandescent by the mixed gases ; b b a very
short condensing lens ; c the stage or support carrying
the object to be photographed ; d the projecting lens,
formed of three sets of lenses, and giving a flat recti-
linear field ; a, c, d are mounted on a base board, e, f,
to the end of which the lantern box a b is attached, and
which is freely opened above and below for perfect
ventilation. The lateral grooves a, c, d slide and allow
of an adjusting movement by the screw r, and by
means of which the change of distance between a and
c admits of a correct focus being obtained. By means
of the hinge at Ji the whole can be adjusted at any
angle.
FIG. 95a. Draper's Microphotographic Apparatus.
162
THE MICROSCOPE.
CHAPTER III.
RELIMINART DIRECTIONS ILLUMINATION ACCESSORY APPARATUS GILLETT'S,
ROSS'S, BECK'S, POWELL AND LEALAND'S, AND OTHER CONDENSERS THE
LIEBERKUHN SIDE REFLECTOR LAMP-
OBJECT FINDER COLLECTING STICK
ANIMALCULE CAGE SECTION CUTTER
PREPARING AND MOUNTING OBJECTS
DOUBLE STARRING, ETC.
AVINGr selected an apartment
with a northern aspect, and, if
possible,with only one window,
and that not overshadowed by
trees or buildings in such a
room, on a firm, steady table,
keep your instruments and ap-
paratus open, and at all times
ready for observation. A large
bell-glass will be found most
convenient for keeping dust
from the microscope when set
up for use. In winter it will be
proper to slightly warm the
instrument before using it,
otherwise the perspiration from the eye will condense
on the eye-glass, and obscure vision.
Management of the Microscope. Should the micro-
scope not have been used for some time, dust and
moisture will in all probability collect and settle on
the eye-piece. The foggy atmosphere of large towns
may insinuate itself into the interior of the objective.
In such cases, dust and moisture can only be removed
by gently wiping the glasses with a piece of soft,
well-used chamois leather. When necessary to clean
the eye-piece, unscrew one glass at a time and replace
it before removing another. The objective can only
ITS MANAGEMENT. 163
be unscrewed, or tampered with, at the risk of
damaging the cement which binds the lenses together.
If the objective be an immersion, carefully wipe off
the fluid from the front lens as soon as it is done with,
for even distilled water will leave a stain behind.
When looking through the eye-piece be sure to
place the eye close to the lens, otherwise the whole
field will not be perfectly visible ; it should appear as
an equally well-illuminated circular disc. The position
of the observer should be easy and comfortable, and
the microscope inclined to an agreeable working angle
This will prevent fatigue and congestion of the eyes,
the first indication of which is small bodies moving
about or floating before them. If the eyelashes are
reflected from the eye-glass, the observer is looking
upon the eye-piece, and not through it. Eor the
examination of transparent mounted objects, it is
simply necessary to place them upon the stage of the
microscope, and throw light from the concave mirror
through them. The distance at which the mirror
should be set depends upon the source whence the
illumination is derived, and whether it be daylight or
lamp-light. The stem which carries the mirror is
generally so arranged as to be capable of elongation.
The working focal distance of the mirror is that which
brings the images of the window bars sharply out upon
the glass slip or object resting upon the stage. In
other words, the focus of the mirror is that which
brings parallel rays to a correct focus on the object-
glass. If employing artificial light, then the flame
of the lamp should be distinguishable ; a slight change
in the inclination of the mirror will be required to
throw the image of the lamp-flame out of the field.
A good illumination having been obtained, the
diaphragm must be brought into use to regulate the
amount of light. The more transparent the object,
the less light will it require to display it properly.
Some microscopists carefully tone down the light, by
interposing a piece of monochromatic glass, or a fluid
medium, a weak solution of sulphate of copper, between
the light and the object. The best artificial source
16-4
THE MICROSCOPE.
of illumination is the steady flame of a paraffin lamp,
with a flat wick (fig. 96). Collins's Bocket Lamp, with
bull's-eye condenser mounted on a stem, so as to be
adjustable at any height, is a suitable form of lamp.
Whatever be the source of light, the objects hould on
no account be over-illuminated : a flood of light mars
the image, and spoils the performance of the object-
glass.
For viewing opaque objects, or whole insects, the
eletra of a beetle, etc., the light must be thrown down
or condensed upon it, by
the condensing or bull's-
eye lens ; or by Beck's
parabolic side- silver re-
flector, placed at a pro-
per angle to the source
of illumination.
For examining par-
tially opaque minute ob-
jects, as the Podura-scale,
under high-power mag-
nification, the vertical
illuminator is useful. If
the object is a small por-
tion of a dissected animal
or plant, or a patholo-
gical specimen in a fluid
medium, the microscope
should be employed in
the vertical or upright
position. The object
should be covered with a thin cover-glass, to prevent
the escape of the fluid, which, should it run over, might
damage the stage and its mechanical movements.
Test for Illumination. Dr. C. Seiler recommends the
human blood corpuscle as the best test of good illumina-
tion. He prepares the object in the following manner :
Take for the purpose a clean glass slide of the ordinary
kind, and place near its extreme edge a drop of fresh
blood drawn by pricking the finger with a needle.
Then take another slide of the same size, with
FIG. 96. Collins's Bocket Lamp.
ERRORS OF INTERPRETATION. 165
ground edges, and bring one end in contact with the
drop of blood, as shown in fig. 97, at an angle of
45 ; then draw it evenly and quickly across the uiider-
slide, and the result will be to spread out the corpus-
cles evenly throughout. The blood discs being lenti-
cular bodies, with depressed centres, act like so many
little glass-lenses, and show diffraction rings if the
light is not properly adjusted. In the Journal of the
Royal Microscopical Society, page 542, vol. iv., Dr. Seiler
fully describes the arrangement of the lamp, condenser,
and mirror.
Errors of Interpretation. To be in a position to
draw accurate conclusions of the nature and properties
of the object under examination is a matter of the
greatest importance to the microscopist. The viewing
of objects by
transmitted light
is quite of an ex-
ceptional charac-
ter, much calcu-
lated to mislead
the judgment as
well as the eye.
It requires, there- FlG . ^.-Seller's
lore, an unusual
amount of care to avoid falling into errors of inter-
pretation. There are perhaps no set of objects with
which I have become acquainted, and which have given
rise to more discussion as to the precise nature of their
structural elements than those of certain of the diato-
maceee. The minute scales of the Podura (Lepidocyr-
tus cervicollis') and their congeners Lepisma saccharin
are equally debatable. Mr. E. Beck, in an instructive
paper published in the Transactions of the Royal
Microscopical Society, says that the scales of the latter
can be made to put on an appearance which bears
little resemblance to their actual structure.
On the more abundant kind of scales the prominent
markings appear as a series of double lines, these run
parallel and at considerable intervals from end to end
of the scale, whilst other lines, generally much fainter,
166
THE MICROSCOPE.
radiate from the quill, and take the same direction as
the outline of the scale when near the fixed or quill
end ; but there is, in addition, an interrupted appear-
ance at the sides of the scale which is very different
from the mere union, or ' cross-hatchings,' of the two
sets of lines. (Fig, 98, Nos. 1 and 2, the upper
portions.)
The scales themselves are formed of some truly
transparent substance, for water instantly and almost
entirely obliterates their markings, but they reappear
FIG. 98. Portions of Scales of Lepisma, after Beck.
unaltered as the moisture leaves them ; therefore the
fact of their being visible at all, under any circum-
stances, is due to the refraction of light by superficial
irregularities, and the following experiment establishes
this fact, whilst it determines at the same time the
structure of each side of the scale, a matter which it
is impossible to do from the appearance of the mark-
ings in their unaltered state :
" Remove some of the scales by pressing a clean and
dry slide against the body of the insect, and cover
them with a piece of thin glass, which may be pre-
IEPISMA SCALES. 167
vented from moving by a little paste at each corner.
No. 3 may then be taken as an exaggerated section of
the various parts. A B is the glass slide, with a scale,
C, closely adherent to it, and D the thin glass-cover.
If a very small drop of water be placed at the edge of
the thin glass, it will run under by capillary attraction ;
but when it reaches the scale, C, it will run first
between it and the glass slide A B, because the attrac-
tion there will be greater, and consequently the mark-
ings on that side of the scale which is in contact with
the slide will be obliterated, while those on the other
side will, for some time at least, remain unaltered :
when such is the case, the strongly marked vertical
lines disappear, and the radiating ones become con-
tinuous. (See No. 1, the lower left-hand portion.)
To try the same experiment with the other, or inner
surface of the scales, it is only requisite to transfer
them, by pressing the first piece of glass, by which
they were taken from the insect, upon another piece,
and then the same process as before may be repeated
with the scales that have adhered to the second slide ;
the radiating lines will now disappear, and the vertical
ones become continuous. (See No. 2, left portion.)
These results, therefore, show that the interrupted
appearance is produced by two sets of uninterrupted
lines on different surfaces, the lines in each instance
being caused by corrugations or folds on the external
surfaces of the scales. Nos. 1 and 2 are parts of a
camera lucida drawing of a scale which happened to
have the opposite surfaces obliterated in different
parts. No. 4 shows parts of a small scale in a dry and
natural state ; at the upper part the interrupted appear-
ance is not much unlike that seen at the sides of the
larger scales, but lower down, where lines of equal
strength cross nearly at right angles, the lines are
entirely lost in a series of dots, and exactly the same
appearance is shown in No. 5 to be produced by two
scales at a part where they overlie each other, although
each one separately shows only parallel vertical lines."
Another very characteristic fallacy resulting from
configuration is furnished in the supposed tubular
168 THE MICROSCOPE.
structure of human hair. "When we view this object
by transmitted light, it presents the appearance of a
flattened band with a darkish centre ; this, however,
is entirely due to the convergence of the rays of light
produced by the convexity of the surface of the hair.
That it is a solid structure is proved by making a
transverse section of the hair-shaft, when it is seen
quite filled by medullary substance, with the centre
somewhat darker than the other part. It is, in fact, a
spiral outgrowth of epithelial scales, overlapping each
other like tiles on a house-top, which impart a striated
appearance to the surface. A cylindrical thread of
glass in balsam appears as a flattened, band-like streak,
of little brilliancy. Another instance of fallacy arising
from diversity in the refractive power of the internal
parts of an object, is furnished by the mistakes for-
merly made with regard to the true character of the
lacunae and canaliculi of bone structure, which were
long supposed to be solid corpuscles, with radiating
opaque filaments proceeding from a dense centre ; on
the contrary, they are minute chambers, with diverging
passages, excavations in the solid osseous substance.
That such is the case, is shown by the effects of Canada
balsam, which infiltrates the osseous substance.
The molecular movements of finely divided particles,
seen in nearly all cases when certain objects are first
suspended in water, or other fluids, is another source of
embarrassment to beginners. If a minute portion of
indigo or carmine be rubbed up with a little water,
and a drop placed on a glass slide under the micro-
scope, it will at once exhibit a peculiar perpetual motion
appearance. This movement was first observed in
the granular particles seen among pollen grains of
plants, known as fovilla, and which are set free when
the pollen is crushed. Important vital endowments
were formerly attributed to these particles, but Dr.
Robert Brown showed that such granules were com-
mon enough both in organic and inorganic substances,
and were in no way " indicative of life."
Accessory Apparatus. In the more perfectly furnished
instruments, a number of accessory pieces of apparatus
THE DIAPHRAGM. 169
are usually included, many of which are essentially
necessary for the prosecution of microscopical pursuits
and for the perfect examination of most objects.
The Diaphragm, fig. 99, is a circular plate with a
series of circular apertures cut in it. In fact, there
FIG. 99. The Diaphragm.
are two plates of brass, one being perforated with four
or five holes of different sizes, and arranged to revolve
upon another plate by a central pin or axis, the last
being also provided with a hole as large as the
largest in the diaphragm-plate, and corresponding in
situation to the axis of the compound body. The holes
FIG. 100. Dr. Anthony's Stage Diaphragm.
in the diaphragm-plate are centred and retained by
a bent spring that fits into the second plate, which
rubs against the edge of the diaphragm-plate and
catches in a notch. The blank space shuts off the light
from the mirror when condensed light is used. It is
impossible to dispense with the use of the diaphragm,
170 THE MICROSCOPE.
as without it the transmitted rays would in many cases
produce confusion of the image. Dr. Anthony advo-
cates the use of a stage- diaphragm, and which consists,
as seen in fig. 100, of three slips of smooth blackened
cardboard or vellum with perforations, any of which
can be brought into the centre and clamped, and re-
tained in its place under the glass slip. The larger
perforated discs form an additional slide ; while various
other forms, slits, slots, cat's-eyes, bars, &c., may be
added at pleasure.
The Iris Diaphragm, fig. 101, is an inexpensive and
ingenious form of iris diaphragm designed by Wale, of
America, for use with his "Working, or Student's,"
microscope. It consists of a piece of very thin cylindrical
tube, A, about f of an inch in length and | of an inch in
FIG. 101. Wale's Iris Diaphragm.
diameter, the circumference of which is cut throughout
with shears to nearly the whole length, and at intervals
of about of an inch; by means of a screw collar
B attached below, this cut tube is forced into a
parabolic metal shsll, contained within c, whose
apex is truncated to an aperture of about -| of an inch;
the pressure of the screw causes the thin metal tongues
to turn and to overlap in a spiral, which gradually dimin-
ishes the aperture to the size of a pin-hole. On unscrew-
ing the collar B, the spiral overlapping of the tongues
is released, and by their elasticity causing the aperture
gradually to expand. The whole device is fitted into the
opening of the stage from beneath, so as to be flush with
the upper surface, with one turn of a coarse screw on
the edge of c.
IRIS DIAPHRAGMS.
171
Beck's Iris Diaphragm (fig. 102) is very simple, and
on that account preferred. By pressing the lever
handle placed at the side of the brass box the aperture
is gradually made to close up, and without for a
moment losing sight of the object.
FlG. 102. Beck-Brown's
Iris Diaphragm,
FIG. 102a. Collins- Davis' s Iris Nose-
piece Diaphragm.
Collins's Limiting Diaphragm, or Aperture Shutter.
Fig. 102 shows the instrument as a nose-piece for screw-
ing on to the lower end of the microscope tube. This
form of aperture shutter enables the observer to adjust
his objective to any aperture he wishes, and the closing
of the shutter does not contract the absolute size of
the field, but limits its brightness ; in this way the
true value of penetration is observed without moving
the eye from the tube.
Mr. Nelson suggests the application of a series
of diaphragms in connection with an ingenious cen-
tring nose-piece devised
likewise as a sub-stage.
This piece of apparatus
is recommended as a use-
ful addition, and as a
convenient and inexpen-
sive centring sub- stage
for small instruments.
The optical part of a T 4 o
objective forming the
condenser, and which for
the purpose should be
fitted with the shortest
possible adapter, so that the diaphragms may be brought
close to the back lens. The sub-stage is seen in fig. 103.
FIG. 103. Nelson's Sub-stage Condenser.
172
THE MICROSCOPE.
Mr. Nelson recommends as the most useful of his
diaphragms those represented in fig. 104, in which a
may be regarded as a type shape for one pencil of light,
and b for two, at right angles. The superposition of
stops c will cut off more or less of the central light,
d will stop out more or less of the peripheral zone ;
while e is a combination intended to utilize the most
FIG. 104. Nelson's Diaphragms.
oblique pencil required for the resolution of fine lined
objects. A variety of discs of the forms c and d may
be used ; any of which, dropped into a metal holder
with an inner ring made deep enough to receive two or
three, which when in place can be rotated by a milled
edge, or moved out of the axis by the handle. 1
Dark Field Illuminators. To Mr. F. H. Wenham's
the microscope is deeply indebted for many valuable
improvements ; not the least important being the dark-
field or parabolic illuminator, invented
in 1851. The operation of the para-
bolic condenser (fig. 105) depends for
its action on rays thrown on the object
at an angle extending beyond that
known as the aperture of the object-
glass, and which otherwise would be
lost ; consequently, as the source from
which the light comes is without the
range of the pencil of rays of the ob-
jective, the field must be dark ; but if
an object possessing a partial opacity is
placed exactly in focus, it becomes brilliantly luminous
by means of these rays. Dark-ground illumination is
not suitable for very transparent objects that is, unless
there is a considerable difference in their refraction, or
they are pervaded by air-cells.
One very remarkable example of this fact may be
(1) Journal of the Royal Microscopical Society, Vol. IV., p. 126 (1881).
THE PARABOLIC ILLUMINATOR.
173
seen in the tracheal system of insects. If any of the
transparent larvae of the various kinds of gnat found
about ponds in spring-time, be mounted in the elastic
gelatine and glycerine jelly (which must be warmed
only enough to run, and not kill the insect at the
time), on about the third day afterwards all the water
is absorbed from the tubes, and they become filled with
air. Illuminated by the parabolic condenser, and
viewed with the binocular microscope, and a low
power, the gnat-larva is a superb object. The body of
the insect is but faintly visible, but, in its place, is dis-
played a marvellous tracheal skeleton, with each tube
FIG. 106. A sectional vieio of Wenham's Parabolic Illuminator.
standing out in perspective, shining brilliantly, like
a structure of burnished silver. Unfortunately, such
objects are not permanent, for when the whole of the
free w r ater dries up, the tracheal tubes either collapse
or become refilled with fluid.
As the blackness of field, and luminosity of the
object, depends upon the excess of light from the
paraboloid received beyond the angle of aperture of
the object-glass, it is found in practice that more and
more of the inner annulus of rays from the paraboloid
has to be stopped off, until, at last, with high-angled
objectives, it is scarcely possible to obtain a black field.
V
174 THE MICROSCOPE.
The parabola answers quite well for objects in balsam
or mounted dry, but its application scarcely extends
to object-glasses higher than l-5th, unless of large
aperture. 1
Wenham's parabolic reflector, seen in section, fig.
106, a a, of a tenth of an inch focus, has a polished
silver surface, the apex of which is cut away so as
to bring the focal point at a proper distance above the
top of the apparatus (which is closed with a screw-
cap when not in use), thus allowing the pencil ot
light to pass through the thickest glass cover used for
mounting. At the base of the parabola is a disc of
thin glass b &, in the centre of which is cemented
a dark well, with a flange equal in diameter to the
aperture at the top of the reflector, for the purpose of
stopping all direct rays from passing.
The reflector is moved to and from the object by
means of the rack and pinion c, with a similar adjust-
ment for centring, and is either fixed under the stage
of the microscope or made to slide into the sub-stage ;
in addition, there is a revolving diaphragm d, with two
apertures e e, placed diametrically, for the purpose of
obtaining two pencils of oblique light in opposite
directions.
In using the paraboloid, the plane mirror is so ad-
justed that parallel rays enter it and impinge on the
rabolic sides of the reflector, in such a manner as to
totally reflected without suffering refraction, and
meet in the centre of a spherical hollow made in the
top of the paraboloid. The adjustable stop being
either raised or lowered, will effectually arrest all
superfluous rays.
The light most suitable for this method of illumina-
tion is lamp, the rays of which should in all cases be
rendered more parallel by means of a large plano-convex
lens, or condenser.
The Immersion Illuminator. Mr. Wenham, in the
year 1856, described various forms of oblique illumina-
tors, one of which was an immersion ; a simple right-
(1) See an excellent summary of the value of parabolic illumination and
immersion illuminators by Mr. J. Mayall, junr., Vol. II., p. 27, Journal of
the Royal Microscopical Society (1879).
THE IMMERSION ILLUMINATOR, 175
angled prism, connected by a fluid medium of oil of
turpentine, or oil of cloves. This, however, was aban-
doned for a nearly hemispherical
lens, connected with the slide,
and which, although a great im-
provement, did not reach the
point of excellence Mr. Wenham
was looking for. Ultimately he FIG. 107. FIG. io7a.
adopted a semicircular disc of
glass of the exact form and size represented in the
drawing, fig. 107, being a side view, and fig. 10 7a,
an edge view of the same, and having a quarter-
inch radius, with a well-polished rounded edge, the
sides being grasped by a simple kind of open clip
attached to the sub-stage. The fluid medium used for
Connecting the upper surface with the slide being
either water, glycerine, or oil ; a certain increase of
obliquity being obtained by swinging the ordinary
mirror sideways. By means of an illuminator of the
kind difficult objects mounted in balsam were resolyed.
This simple piece of glass, in appearance somewhat
resembling the half of a broken button half an inch
in diameter, collects and concentrates light in a sur-
prising way, and is by no means a bad substitute for
the more costly forms of achromatic condenser. It
can be used either in fluid contact with the slide, or
dry, as an ordinary condenser.
Mr. Wenham subsequently contrived a small trun-
cated glass paraboloid, for use in fluid contact with the
slide ; water, glycerine, gum, oil, or other substance
being employed as a contact medium. The rays of light
in this illuminator being internally reflected from a
convex surface of glass, impinge very obliquely on
the under surface of the slide, and are transmitted by
the fluid uniting medium, and internally reflected from
the upper surface of the cover-glass to the objective.
To use the reflex illuminator efficiently it must be
racked up to a level with the stage. The centre of
rotation is then set true by a dot on the fitting, seen
with a low power, a drop of water is then placed on
the top, and upon this the slide is laid. Minute objects
176 THE MICROSCOPE.
on the slide, found by the aid of a low power, and
distinguished by their brilliancy, or by rotating the
illuminator ; the effect on the Podura is superb, the
whole scale appearing dotted with bright blue spots
in a zig-zag direction. Objects for this illuminator
should be specially selected or mounted on the slide.
Mr. J. May all, Jun.'s, semi- cylinder or prism for
oblique illumination (fig. 108) is a convenient form,
as it permits of the semi-cylinder
being tilted and placed excentrically ;
in this manner, without immersion
contact, and by suitable adjustment,
a dry object can be viewed with
any colour of monochromatic light.
If placed in immersion contact with
the slide, the utmost obliquity of in-
cident light can be obtained. Objects
in fluid may be placed on the plane-
surface of the semi-cylinder, and
illuminated by ordinary transmitted
light, or rendered " self-luminous "
in a dark field, as with the hemi-
spherical illuminator or Wenham's
immersion paraboloid. A concave
mirror with a double arm is quite
sufficient to direct the illuminating pencil. This semi-
cylinder was originally made by Tolles, of Boston, for
measuring apertures, but, at Mr. Mayall's suggestion,
Messrs. Ross mounted it as an illuminator.
The Achromatic Condenser.
The aim of the microscopists in bringing the achro-
matic condenser into use, is to secure a pencil of light
that shall approximately fill the aperture of the objec-
tive, and by the intervention of central stops, or slots,
the various portions of the cone of condensed light,
according to the kind of object under examination, shall
fully utilize the same.
The peculiar advantages of employing an achromatic
condenser for the purpose indicated, were first pointed
out by Dujardin, since which time an object-glass
FIG. 108. Mayall's
Semi-Cylinder
Illuminator.
GILLETT S ACHROMATIC CONDENSER.
177
has been frequently but inconveniently employed ; and
more recently much, attention has been bestowed upon
achromatic illuminators by most of our instrument
makers. It is now some years since Mr. Gillett was
led by observation to appreciate the importance of
controlling and condensing the quantity of light by
a diaphragm placed anywhere between the source of
light and the object. This he found more fully effected
by a diaphragm placed immediately behind the achro-
matic illuminating combination. Such a diaphragm is
represented in fig. 109, Ross's original Gillett. It con-
sists of an achromatic illuminating lens c, which is about
d.
FIG. 109. The original form ofGrilletfs Achromatic Condenser.
equal to an object-glass of one-quarter of an inch focal
length, with an angular aperture of 80. This lens
is screwed on to the top of a brass tube, and intersect-
ing which, at an angle of about 25, is a circular rotat-
ing brass plate a b, provided with a conical diaphragm,
having a series of circular apertures of different sizes
h g, each of which in succession, as the diaphragm
is rotated, proportionally limits the light transmitted
through the illuminating lens. The circular plate in
which the conical diaphragm is fixed is provided with a
spring and catch ef. the latter indicating when an aper-
ture is central with the illuminating lens, also the num-
178 THE MICROSCOPE.
ber of the aperture as marked on the graduated circular
plate. Three of these apertures have central discs, for
circularly oblique illumination, allowing only the pas-
sage of a hollow cone of light to illuminate the object.
The illuminator above described is placed in the second-
ary stage i i, which is situated below the general stage
of the microscope, and consists of a cylindrical tube
having a rotatory motion, also a rectangular adjust-
ment, which is effected by means of two screws I m,
one in front, and the other on the left side of its frame.
This tube receives and supports all the various illumi-
nating and polarising apparatus, and other auxiliaries.
Very many modifications
of Gillett's condenser are
known to microscopists, by
far too numerous to de-
scribe in detail. Boss's im-
proved form is made to slip
into the sub-stage in the
same way as his Improved
Achromatic Condenser (fig.
110), and when arranged
for oblique illumination, is
an extremely efficient instru-
ment. The optical part is
FIG. no. Ross's improved Achro- similar to a T 4 oths object-
matic Gillett Condenser. glass. It has two Sets of
revolving diaphragms with apertures and stops, for
showing surface markings in a brilliant manner.
Directions for Using Gillett's Condenser. In the ad-
justment of the compound body of the microscope for
using with Gillett's illuminator, one or two important
points should be observed first, centricity, and second-
ly, the fittest conpensation of the light to be employed.
With regard to the first, place the illuminator in the
cylindrical tube, and press upwards the sliding bar k in
its place, until checked by the stop; move the microscope
body either vertically or inclined for convenient use ;
and with the rack and pinion which regulates the slid-
ing bar, bring the illuminating lens to a level with
the upper surface of the object-stage ; then move the
179
arm which, holds the microscope body to the right,
until it meets the stop, whereby its central position is
attained ; adjust the reflecting mirror so as to throw
light up the illuminator, and place upon the mirror
a piece of clean white paper to obtain a uniform disc
of light. Then put on the low eye-piece, and a low
power (the half -inch), as more convenient for the mere
adjustment of the instrument ; place a transparent
object on the stage, adjust the microscope-tube, until
vision is obtained of the object ; then remove the ob-
ject, and take off the cap of the eye-piece, and in its
place fix on the eye-glass called the " centring eye-
glass," described below, which will be found greatly to
FIG. 111. Beck's New Achromatic FIG. Ilia. Beck's Dry Achromatic
Condenser. Condenser.
facilitate the adjustment now under consideration,
namely, the centring of the compound body of the
microscope with the illuminating apparatus of what-
ever description. The centring-glass, being thus
affixed to the top of the eye-piece, is then to be adjusted
by its sliding- tube (without disturbing the microscope-
tube) until the images of the diaphragms in the object-
glass and centring lens are distinctly seen. The illu-
minator should now be moved by means of the left-hand
screw on the secondary stage, while looking through
the microscope, to enable the observer to recognize the
diaphragm belonging to the illuminator, and by means
of the two adjusting screws, to place this diaphragm
N 2
180
THE MICEOSCOPE.
central with the others : thus, the first condition, that
of centricity, will be accomplished. Remove the white
paper from the mirror, and also the centring-glass,
and replace the cap on the eye-piece, also the object
on the stage, of which distinct vision should then be
obtained by the rack and pinion, or fine screw adjust-
ment, should it have become deranged.
Beck's New "Wet and Dry" Condenser (fig. 111).
In an earlier form of dry condenser (fig. Ilia) Messrs.
teck made use of a revolving front, with the intention
FIG. 112. Powell and Zealand's Condenser.
of obtaining large angular aperture, and of rotating a
series of lenses. They have more recently introduced
a new form, and the advantages to be gained are First,
That it is available for either dry or immersion object-
glasses up to 1'3 numerical aperture on diatoms, &c., or
dry ones on histological objects. Secondly, That the
spherical form of the front, worked by a milled head,
enables a series of lenses to be used, and yet avoids the
inconvenience of having the connecting fluid drawn
away from the one in use by capillary attraction, as
POWELL AXD LEALAND'S IMMERSION. 181
would be the case if they were mounted on a flat
surface. It also interferes less than the old form with
the movements of the stage.
Powell and Lealand's Immersion Condenser, or non-
achromatic condenser (fig. 112), is constructed on a
somewhat novel plan. It admits of a very large angle
of light, about 130 degrees, and allows of the use of
either central light, or one or two oblique pencils of
00 degrees apart. Two diaphragm slots (shown in the
woodcut apart from the condenser), fit in at A and B ;
FIG. 113. Swift's Achromatic Condenser.
by means of which two beams of light at right angles
can be used. The movement of these diaphragms is
effected by means of an outer sliding tube b with a slot
at the top, and into which the arm A fits; whilst another
at B gives a ready command of the rotation of the two,
either together or separately, thus producing consider-
able modifications of light.
Swift and Son's Achromatic Condenser is conveni-
ently arranged to supply the place of a compound sub-
stage, and to receive accessory diaphragms. The optical
182
THE MICROSCOPE.
combination A is computed to be used as an effective
spot-lens from a 3-inch objective up to a sixth, c C are
two small milled heads by means of which the optical
combination A is centred to the axis of the objective.
The revolving diaphragm E has four apertures for the
purpose of receiving central stops, oblique light discs,
and selenite films. D is a frame carrying two revolv-
ing cells, into one of which a mica film is placed, which
can be revolved with ease over either of the selenites
below, whereby changes of colour can be obtained in
experimenting with polarised light. The darts and
p A'S indicate the position of the positive axis of the
mica and selenic films, and by this means results can
be recorded, &c. Either of the revolving cells can be
FIG. 114. Swift's Diaphragms and Central Stops.
thrown into the centre of the condenser, and there
stopped by means of a spring catch ; when so arranged
the mica film, &c., may be revolved in its place by
turning the cell D, asboth cells are geared together
with fine racked teeth. F is a polarising prism mounted
on an eccentric arm, rendered central when in use, or
thrown out, as seen when out of use. G is the rack dove-
tail slide for indicating focussing the condenser on
the object. The advantages of this condenser consist
in having the polarising prism, selenite films, dark
ground and oblique light stops, so that they may be
brought close under the optical combination.
Collins's Webster's Universal Achromatic Condenser
(fig. 115) is a mechanical contrivance provided with
COLLINS'S UNIVERSAL CONDENSER.
183
a shutter diaphragm. This addition to the microscope
can be used with any instrument and without a sub-
stage, and is on this account easily adapted to the
FIG. 115. Collinses Webster's Universal
Condenser.
Shutter Diaphragm seen separately.
cheaper forms of microscopes. Its advantages are,
that it is moderately cheap, is at once an achromatic
condenser, parabolic illuminator, and graduating dia-
phragm and polariser. By means of a lever, the
central aperture can be gradually closed, and, pro-
vided the object-glass has sufficient "resolving power,"
it facilitates the resolution of the
more difficult test-objects. With a
" spot-lens stop" the object is illu-
minated on a dark ground, and
when high powers are used in con-
nection with the polariscope, the
advantage derived by such an ad-
dition to the ordinary mode of
illumination is considerable.
Mr. Hyde's " Condenser " is con-
structed for use with immersion
objectives, having apertures greater
than correspond to 180 in air. The
lens is a right-angled prism, having
a plano-convex lens fitted in an up-
right, and mounted in brass to slip into the sub- stage
(fig. 116), will condense parallel rays to a focus on a
balsam-mounted object, through a slide of average
FIG. 116. Hyde's Illu-
minator.
184
THE MICROSCOPE.
thickness, \/hen the illuminator is brought into immer-
sion contact. Its action is diagramatically shown in
fig. 117. A is the first lens of an immersive objective
in fluid contact with the cover-glass ; o the object in
balsam ; p a right-angled prism in immersion contact
with the base of the slide ; L a lens designed to focus
FIG. 117.
the illuminating rays on the object o. For oblique
illumination, as seen in the figure, the apparatus must
be thrown out of the axis of the microscope, and in
this way and with any objective of less aperture than
90 in glass would give a dark field. If brought nearer
the axial line it is evident that less oblique rays could
be used.
Mr. John Mayall devised a set of spiral diaphragms
as a convenient mode
of obtaining oblique
illumination in con-
nection with high-an-
gled condensers. If a
slot diaphragm, fig.
118, be fixed close be-
Fio. 118. Mayall's Spiral Diaphragm. neath the larger lens,
such as those of Powell
.and Lealand, Zeiss and other makers, the rotation
under it of a diaphragm having a spiral opening,
CATOPTRIC ILLUMINATOR. 185
will give a pencil of light at varying degrees of ob-
liquity throughout the range of the aperture of the
condenser. The azimuthal direction of the incident
pencil will be controlled either by rotating the object
or the condenser carrying the diaphragms ; whilst the
rotation of the spiral in the fixed slot will not change
the direction in the azimuth but in altitude, so far as
the aperture of the condenser will permit.
Mr. J. W. Stephenson's " Catoptric Immersion Illumi-
nator " attains its object in a simple way. Fig. 119
represents the form and size of the little piece of
apparatus. It is a plano-convex
lens worked on a 1-inch tool, and
having a diameter of 1*2 inches,
which is then edged down to 1
inch, as being more convenient in
size, and as giving an aperture
sufficient for the purpose. The
upper or convex side of the lens is
cut down or flattened, so as to
give a surface of -A- of an inch in FIG. 119. catoptric im-
diameter, with which the slide is
to be brought into contact, by a drop of oil, glycerine,
or water. The upper curved surface is silvered ; be-
neath the lens a flat silvered plate gV of an inch thick,
and corresponding in size and position with the upper
flattened surface, is balsamed. The incident ray is
thus rendered normal to the under surface, and is
thrown back on the plane or under surface of the
lens, whence the more oblique rays falling beyond the
central angle are totally reflected and conveyed to a
focus. A stop is placed about an -Jth of an inch or less
below the condenser, and the opening used is of a lens-
shaped form, which admits a broad beam of light with-
out appreciable spherical aberration. The Iris dia-
phragm greatly improves this illuminator. 1
The Oil Immersion Condenser. In this is combined
the latest improvement in immersion condensers. In
operation, an oil-medium possesses superior advantages
in connection with high-angled objectives. The oil
(1) Journal ofR. M. S., Vol. II., p. 36, 1879.
186 THE MICROSCOPE.
immersion condenser of Powell and Lealand is an im-
proved form, consisting of the truncation of the vertex
of the upper lens of the condenser, and admits of
the lower lens being brought into closer proximity,
when the marginal rays become more effective. Its
speciality is the conversion of axial light into con-
densed obliquely incident light by the refraction of
the condenser.
For the illumination of opaque objects under high
powers, Tolles of Boston, U.S.A., introduced a verti-
cal illuminator into the body of the microscope close
to and above the objective.
The Vertical Illuminator consists of a small silver
speculum (Professor Smith), or a movable disc of thin
glass (Beck), or a small piece of parallel glass, placed
at an angle of 45 (Powell and Lealand), and fixed in a
short tube, with a side aperture, interposed between
the objective and the body of the microscope ; by
which means a pencil of light entering at the aperture,
and striking against the speculum or inclined surface
of the disc, is reflected downwards through the objec-
tive and upon the object placed on the stage of the
microscope. The object-glass is thus made its own
achromatic condenser. When this form of illuminator
was introduced, it was soon discarded on account of the
halo or fog which surrounded the image, and which
was caused, as Mr. Stephenson explained, by the reflec-
tion, at the upper surface of the cover-glass, of the
rays transmitted through the objective. With the
introduction of the oil-immersion objective all this
fogging disappeared ; the front lens of the objective,
the intervening stratum of oil, and the cover-glass of
the object all become optically continuous, so that the
upper surface of the cover-glass virtually ceases to
exist, the only reflection being from its under surface,
when dry objects are used. " The explanation is that
if the vertical illuminator be adjusted, and used with
an immersion objective, having a numerical aperture
greater than I'O, focussed on a plane glass slip, it is
evident that (practically) all that part of the pencil
comprised within the numerical aperture I'O will
THE AMICI PEISM. 187
emerge at the plane base of the slip, and be lost to
view ; but the peripheral zone of the pencil beyond the
numerical aperture I'O will not emerge, but is totally-
reflected at the internal surface of the base of the slip,
and is seen as a luminous zone surrounding a nearly
dark field (the field is not absolutely dark, because of
the ordinary reflection of light that takes place before
the emergence of the central pencil)." 1
Method of Using Condensers. Whatever the special
form of apparatus, it should always subserve the pur-
pose of condensing the light reflected by the mirror to
a correct focus upon the object. The light reflected
from either the plane or concave mirror should pass
through the axis of the condenser, moving at the same
time in all directions, and in the axis of the objective,
body, and eye-piece of the microscope. The secondary
stage should be made to
admit of perfect centring
and be provided with a
racking adjustment. Upon
changing the objective,
Ross's centring eye-glass
must be brought into use
to ensure the centricity of
the condenser and the
body of the microscope. 3
I he Amici .Prism was
originally designed for oblique illumination. It con-
sists of a flattened triangular glass prism, the two
narrower sides of which are slightly convex, while the
third or broadest side forms the reflecting surface.
When properly used, it is capable of transmitting a
very oblique pencil of light. The prism is usually
mounted, as in fig. 120, for slipping into the sub-
stage.
The LieberJcuhn. The concave speculum termed a
(1) English Mechanic.
(2) This centring-glass consists of a tubular cap with a minute aperture,
containing two plano-convex lenses, so adjusted that the image of the aper-
ture in the object-glass, and the images of the apertures of the lenses and
the diaphragms contained in the tube which holds the illuminating com-
bination, may all be in focus at the same time, so that by the same adjust-
ment they may be brought sufficiently near to recognize their centricity.
IS?
THE MICKOSC01T.
"Lieberkuhn," from its celebrated inventor, -was for-
merly much in use as a re-
tleetor, but is uow almost
abandoned, or rather replaced
by other and better contriv-
ances. The Uoberkiilm is
generally attached to the
object -class, in the manner
represented at tig. 1'Jl. Nvhoro
a exhibits the lowor part of
the compound body, /, the
object-glass, over whieh is
slid a tube and the Lieber-
kiilin, ( \ attached to it ; the
ra\ s of lii^-ht retleetevl fi'oin
the mirror are brought to a
focus upon an object </,
the mirror. The object may
a slip of Lrlass. or else held
en very small, or \\hen trans-
gum it to the dark \\ell, ,
.'s opaqne disc-revolver (tig-.
placed between it and
either be mounted on
by the forceps,/; NN ;
parent, it is better to
or mount it on Becl
Beck eiVectcd a considerable
improvement upon the
Liebcrkiihn by
the introduction
of the silver side-
retlector(fig.rJo),
\\hich causes the
shadows to fall on
the proper >ide,
and is employed on this account. This is ei:
into the stage of the microscope or used on a separate
Maud, so that it may be turned in any direction
towards the source of light The parabolic side-
reflector (fig. 123<i) is adapted for use with high
powers.
^Sorby, while experiment imr with a reflector of the
kind, discovered the value of observing the peculiari-
ties of objects under every kind of illumination ; for, on
viewing specimens of iron and steel with this reflector,
THE SILVER SIDE- REFLECTOR.
189
he found that, owing to the obliquity of illumination,
the more brilliantly polished parts
reflected the light beyond the aper-
ture of the objective, and he could
not therefore distinguish them from
those parts which merely absorbed
the light. To throw the illumination
more perpendicularly upon the speci-
men, he was obliged to place a small
flat mirror immediately in front of
the objective, and cover half its aper-
ture, and at the same time stop-off,
by means of a semi -cylindrical tube,
the light from the parabolic reflector.
J>y such an arrangement, the light
produces the reverse appearances of
the former mode of illumination, and
is a valuable aid in determining the
true condition of the object.
The Bull's-eye Condenser. The
Fio. 123. Beck's Silver
FIG. 123a. Beck's Pmraljolic Reflector.
bull's-eye condensing lens (fig. 124) is used for con-
verging rays from a lamp upon the mirror; or for
reducing the diverging rays of the lamp to parallelism,
for use either with the parabolic illuminator, or silver
side-reflector. A plano-convex lens of about three
inches focal length, is the form generally adopted ; it
is borne upon a swivel-joint, which allows of its being
turned in any direction, and placed at any angle ; the
tube is double, and thus admits of being lengthened or
shortened. When used by daylight, its plane side
should be turned towards the object, and the same
position should be given when used for converging the
rays from a lamp ; but when used with the parabolic
190
THE MICROSCOPE.
or side-reflector, the plane side must be turned towards
the lamp.
FIG. 124. -Bull's-eye Condensing Lens.
The Microscope Lamp. The
introduction of paraffin into
household use has somewhat
modified our views with regard
to the most suitable artificial
source of illumination. Paraffin
burns with a whiter and purer
flame than either oil or gas, and
consequently is less liable to pro-
duce fatigue or injury to the
eyes. The first cost of the lamp
is trifling ; for a moderate sum a
handy form of lamp can be pro-
cured, mounted on an adjustable
sliding-ring stand, and with a
porcelain, metal, or paper shade,
to protect the eyes from scat-
tered rays of light (fig. 125).
To give the increased effect of
whiteness to the light ("white FIG. 125. Beck's Microscope
cloud illumination" as it is
Lamp.
termed), take a piece of tissue paper, dip it into a hot
FINDERS AND INDICATORS. 191
"bath of spermaceti, and, when nearly cold, cut out a
circular piece and secure it over the largest opening in
the diaphragm plate. This will materially moderate
and soften the light.
Finders and Indicators. A finder, as applied to the
microscope, is the means of registering the position of
any particular object in a slide : as, for instance, some
particularly good specimen of a diatom, so that it may
be referred to at a future time. The subject will be
found fully discussed in the pages of the Journal of the
Royal Microscopical Society. The traversing stage of
FIG. 126. Amyot's Object finder.
the microscope admits of such finders as those of Mr.
Okeden, Mr. Tyrrell, Mr. Amyot (fig. 126), &c., being
used. The first named . (Mr. Okeden's) finder consists
of two graduated scales, one of them vertical, attached
to the fixed stage-plate, and the other horizontal,
attached to an arm carried by the intermediate plate ;
the first of these scales enables the observer to " set "
the vertically- sliding plate to any determinate position
in relation to the fixed plate, while the second gives
him the like power of setting the horizontally-sliding
plate by the intermediate.
For those microscopists whose instruments are with-
192 THE MICROSCOPE.
out a traversing stage " Maltwood's finder " will be
found an efficient substitute. It consists of a glass
slide, 3 x 1^ inches, on which is photographed a scale
occupying a square inch ; this is divided by horizontal
and vertical lines into 2,500 squares, each of which
contains two numbers marking its " latitude," or place
in the vertical series, and its " longitude," or place in
FIG, 127. -Dipping-tubes. FIG. 127a. Stock-bottle.
the horizontal series. The scale is in each instance an
exact distance from the bottom and left-hand end of
the glass slide ; and the slide when in use should rest
upon the ledge of the stage of the microscope, and be
made to abut against a stop, a simple pin, about an
inch and a half from the centre of the stage. Messrs.
Beck supply this finder with their microscopes.
Dipping-tubes are tubes of glass (tig. 127) about nine
COLLECTING- STICK.
193
inches in length, open at both ends, and from one-
eighth to one-fourth of an inch in diameter. The ends
must be nicely rounded off in the flame of a blow-pipe;
some of them should be made perfectly straight, whiJe
others should be bent or drawn out to a fine point, and
made either of the shapes represented.
FIG. 128.
A. Trough for showing Circulation in Fisli-tail.
B. Collecting-bottle and Stick.
Fig. 128, at B, is represented a convenient and port-
able " Collecting-bottle and Stick ;" an ordinary cane
divided by a screw, or socket-joint, into two parts for
the convenience of packing, and terminated by a brass
ring, which is adapted to receive a wide-mouthed
bottle. A small fine-gauze net and a hook can be
screwed into the same stock, and the whole packed into
a small compass.
Fio. 129. Net for collecting Minute Animals.
Compressorium. The purpose of this accessory is to
apply a gradual pressure to objects whose structure can
only be made out when they are pressed or thinned out
by extension. The general plan of the compressorium
is shown in fig. 130.
Boss's Compressorium consists of a stout plate of
brass A, about three inches long, having in its centre a
194
THE MICROSCOPE.
piece of glass like the bottom of a live-box. This piece
of glass is set in a frame B, which slides in and out so
that it can be removed for the convenience of preparing
any object upon it
under water if de-
sirable. The upper
movable part I) is
attached to a screw-
motion at C ; and at
one end of the brass
plate A, which forms
the bed of the in-
strument, is an up-
right piece of brass C, grooved so as to receive a ver-
tical plate, to which a downward motion is giyen by a
FIG. 130. Ross's Compressorium.
FIG. 131. Beck's Parallel-plate Compressor.
single fine screw, surrounded by a spiral spring, which
elevates the plate as soon as the screw-pressure is re-
moved.
Beck's Parallel-plate Compressor, fig. 131, affords a
FIG. 132. Botterill's Live-trough.
more exact means of regulating the pressure, and can be
used for a variety of purposes. It is also easily cleaned.
Lire-troughs are made to partake of a variety of
GLASS TROUGHS AND CELL?. 195
forms and shapes. Botterill's (fig. 132) consists of
two brass plates, screwed together by binding screws,
and holding between them two plates of thin glass,
and which, are maintained at a proper dis-
tance by inserting half of a circular flat disc
of india-rubber.
Beck's glass trough, for chara and polypes,
a sectional view of which is shown at fig. 133,
is made of three pieces of glass, the bottom
being a thick strip, and the front a of
thinner glass than the back & ; the whole is
cemented together with Jeffery's marine-
glue. The method adopted for confining
objects near to the front glass varies ac-
cording to circumstances. One of the most
convenient plans is to place in the trough a
piece of glass that will stand across it
diagonally, as at c ; then if the object be PIG 13
heavier than water, it will sink, until stopped
by this plate of glass. At other times, when used to
view chara, the diagonal plate may be made to press it
close to the front by means of thin strips of glass, a
wedge of glass or cork, or even a folded spring.
When using the trough, the microscope should be
placed in a nearly horizontal position.
Growing. cells. Considerable attention has been given
FIG. 134. Weber's Slip with Convex FIG. 134a. Seek * Current-slide Live-
Cell for use as a Live-trough. cell.
to various forms of growing-cells for maintaining a con-
tinuous supply of fresh water to objects under observa-
tion, and for the purpose of sustaining their vital
energy for a long period. The employment of live-cells
is strongly commended to microscopists, as there is yet
much to be discovered concerning the metamorphoses
which some of the lower microscopic forms of plant
o 2
196
THE MICROSCOPE.
and animal life pass through ; a patient investigation
will probably show that many which are now classed
as distinct species are merely different phases of the
same type, which alternate according to the varied
Fro. 135. Holman's Life Slide. Full size.
conditions of temperature and nutrition under which
they are placed.
Holman's life slide consists of a 3 x 1 inch glass
slide, with a deep oval cavity in the middle to receive
the material for observation. A shallow oval is ground
and polished around the deep cavity, forming a bevel.
FIG. 136. Holman's Moist Chamber.
From this bevel a fine cut extends, to furnish fresh air
to the living low forms of life which invariably seek
the bevelled edge of the cavity, thus bringing them
within the reach of the highest powers.
Mr. Holman contrived a form of " moist chamber,''
HOLMAN'S SYPHON SLIDE. 197
or animalcule-cage, fig. 136, for the purpose of study-
ing the growth of fungi and other delicate organisms,
without in any way disturbing them for a lengthened
period. This will also be found useful as a dry
chamber for holding minute insects, and preserving
them in a living condition for observation.
Zentmayer's Holman Syphon Slide (fig. 137) is used
either as a hot or cold water cell. It should be deep
enough to hold a small fish or newt, and retain it with-
out any undue pressure. When in use it is only necessary
FIG. 137. Hotmail's Syphon Slide.
to place the animal into the groove with some water,
cover it with the glass cover, and immerse one of the
rubber tubes in a jar of water, the other receiving it as
it passes away. When the slide is on the stage of the
microscope the jars should stand on a lower level, so
that the slide be made the highest part of the syphon.
The pressure of the atmosphere is sufficient to keep
the cover-glass in its place. This apparatus is also
adapted for the gas microscope.
The examination of various kinds of infusorial life
be greatly facilitated by the addition of the small-
198 THE MICROSCOPE.
est particle of colouring matter, either carmine OP
indigo. Mr. Thomas Bolton 1 directs a small quantity
of either of these colours to be rubbed up in a little
water in a watch-glass, and a portion taken up on the
point of a brush, and the brush run along the top
of the water in a trough; sufficient will be left
behind to barely tinge the water with the colour, but
this will gradually subside over the rotifers. Under
the microscope this minute quantity will be seen like
a rising cloud of dust, which as soon as it comes
near a rotifer is whirled round in definite curves,
showing at once the action of its wonderful coronary
cilia. This colouring matter is greedily devoured by
these creatures, and may be followed from the mouth
to the digestive canal. If rotifers or infusoria are
already in a cell and under a thin cover, a drop of the
mixed colour may be placed at the edge of the cover-
glass, and a piece of blotting paper touched at the other
side will draw a current through the cell. The cilia
and fine flagella on many of the small protophytes and
infusoria, which are very difficult to see while they are
in full activity, are easily seen when dying or after
death from a drop of iodine. The effect of colour-
ing matter on Volvox globator, Euglena viridis, and
Protococcus pluvialis is very interesting ; besides show-
ing the cilia, it brings out many histological specialities,
which are otherwise invisible. Aniline dyes are occa-
sionally useful for colouring. Osmic acid is used for
killing infusoria quickly in their expanded condition,
and they may afterwards be stained advantageously
with picrate of carmine. The most useful aquaria for
preserving and breeding minute organisms is the
ordinary confectionery cake-glass inverted. A square
block of wood (8 in. square) with a hollow turned
in the centre is required to receive the knob. It
should be covered with a round glass to exclude the
dust.
For finding or selecting minute animals, or dis-
secting botanical specimens, the Houston-Browning
(1) Mr. T. Bolton, of 57, Newhall Street, Birmingham, furnishes interest-
ing tubes of living specimens for the microscope at a trifling wst to hi
torrespondents.
DISSECTING SPECIMENS. 199
Dissecting Microscope will be found a handy and use-
ful form, fig. 138.
This instrument consists of a duplex lens of three
powers, magnifying 4, 6, and 10 diameters, screwed to
the end of a brass focussing tube, and moving upon a
brass pillar attached to a sliding bar at the bottom
of the box. The dissecting stage is a cork slide, plain
on one side for general work, and a shallow cell on the
other, for the dissection of such objects as small glossy
seeds which "fly" under the needles, whilst a pitted
glass slide, for carrying on dissections under water,
is also provided.
Microscopic Dissection. The mode of using needles
for teasing out tissue is very simple. With a pair
FIG. 138. Browning's Houston Botanical Dissecting Microscope.
of the small needles held firmly between the fore-
finger and thumb, as shown in fig. 139, the structure
must be teased out ; an operation which requires some
care. All substances should be carefully separated
from dust and other impurities which render their
structure indistinct or confusing. With delicate mem-
branes, those of the nervous system of the smaller
animals, insects, etc., it is necessary to make the dissec-
tion under water, or in fluid of some kind. For this
purpose take a glass cell, and then throw a strong light
down upon it by the aid of condensing lens, as repre-
sented in fig. 140. Delicate structures will be better
teased out in a dilute solution of sugar or common salt,
to prevent change from endosmose. Should the object
200
THE MICROSCOPE.
be a portion of an injected animal, it is better to pin it
out on a leaded cork, covered with white wax, and im-
mersed in a water-trough, as in fig. 140. The dissec-
tion of delicate vegetable structures is better carried
on under water.
Dissecting Needles, Knives, and Scissors. In addition
FIG. 139. Baker's Student's Dissecting Microscope.
to forceps, needles, and knives, scissors are necessary
for purposes of dissection. The most useful, straight
and curved, are shown in fig. 141. In dissections
under the microscope, the curved-pointed pair / will be
convenient. In all the points should fit accurately
together.
SECTION CUTTING. 201
Section-cutting Instruments. Solid tissues are, as a
rule, much too hard to admit of being cut either by
FIG. 140. Dissecting in, a fluid Medium.
scissors or Valentin's knife. As important information
will be gained respecting the structure of such sub-
Fio. 141.. "Dissecting Scissors and Forceps.
stances as stems and roots of plants, horns, hoofs, car-
tilages, and other firm parts of animals, by cutting
202
THE MICROSCOPE.
thin sections, it would be quite impossible for the
microscopist to get on without a section-cutting
instrument.
Hailes' Section- cutting Machine. A is a short tube
of about 1J inches in diameter, provided with flanges
B, B, at each end. The upper one of these flanges
serves as a cutting bed or table. Inside the tube A is
fitted, so as to slide freely up and down, a second tube
c, in which is placed the material intended to be cut.
This inner tube is provided with two clamping screws
d, d, topped into a block which passes through a slot
formed in the outer tube A, thereby preventing any
PIG. 142. Dissecting Knives.
FIG. 142a. Needles for teasing out Tissue.
rotary movement of the inner tube. Inside the tube
c, and at its lower end, is secured the nut or boss D,
through which passes the micrometer screw E, pro-
vided with a milled head e, and a divided collar /.
This screw is carefully shouldered into a cock or
bracket r, forming part of the lower flange B. In order
to secure the machine firmly to the table, the upper
flange B, is screwed to a transverse bar of wood G,
which in its turn is secured to the table by the clamp
H, thus avoiding all strain upon the machine itself.
The material it is intended to cut may be packed in any
convenient manner in the inner tube C, and secured by
the clamping screws d, d. It will now be clearly seen
HAILES' SECTION CUTTEE.
203
that by turning the micrometer screw E the inner tube C
will be carried steadily upwards, and with it the mate-
rial to be cut, without compression, and consequently
without any jerking. The sections, however, may be
cut with a chisel or with a
razor in the usual manner.
The upper flange B of the
machine, which serves as a
cutting table, is provided
with two strips of hardened
and polished steel a. These
form convenient surfaces over
which the cutting tool may
be passed, when cutting wood
or softer sections, and they
also serve another important
purpose. At the back of the
cutting table is secured, by
means of a spring and screw
and steady-pins, a metal block
fc. This block carries, fixed
in it, two hard steel rods c,
which overlie the strips a.
By passing the blade of a fine
saw between the rods c and the strips a, sections of
bone or other material too hard to be cut with a knife,
may be sawn off as thin as the nature of the material
will permit, in some cases sufficiently thin to permit of
their being at once mounted. The rods c and strips
a, being of the hardest steel, receive no injury from
the teeth of the saw. The machine is made by Baker,
144, Holborn.
Method of making Sections. If the wood be green, it
should be cut to the required length, and be immersed
for a few days in strong alcohol, to get rid of all
resinous matters. When this is accomplished, it may
be soaked in water for a week or ten days; it will
then be ready for cutting. If the wood be dry, it
should be first soaked in water and afterwards immersed
in spirit, and before cutting placed in water again, as in
the case of the green wood.
FIG. 143. Hailes' Improved
Stction-cutting Machine.
204
THE MICROSCOPE.
With a little practice tlie finest and thinnest possible
slices will be cut. It is usual to first slice off a few
thicker slices to give a smooth and even surface to the
specimen. Then turn the screw to raise it a little,
sprinkle the surface with spirit and water, and cut
with a light hand. Remove the cut sections with a
fine camel's-hair brush or blotting-paper to a small
vessel containing water, when the thinnest sections
will float on the surface, and are more easily selected
and removed to a bottle of spirit and water, where
they should remain until they can be mounted. Sec-
tions of hard woods, and of those containing gum,
resin, and other insoluble materials, must first be soaked
in alcohol or ether and then transferred to oil of cloves,
to render them sufficiently transparent for mounting.
I
FIG. 143a. Sections of Wood.
If the entire structure of any exogenous wood is
required to be examined, the sections must be made in
at least three different ways : these may be termed the
transverse, the longitudinal, and the oblique, or, as
they are sometimes called, the horizontal, vertical,
and tangental : each of these will exhibit different
appearances, as may be seen upon reference to fig. 143# :
6 is a vertical section through the pith of a coniferous
plant : this exhibits the medullary rays, which are known
PREPARATION OF HARD TISSUES. 205
to the cabinet-maker as the silver grain; and at e is a
magnified view of a part of the same: the woody fibres
are seen with their dots I, and the horizontal lines k indi-
cating the medullary rays cut lengthwise ; whilst at c is a
tangental section, and fa, portion of the same magnified:
the openings of the medullary rays mm, and the woody
fibres with vertical slices of the dots, are seen. Very
instructive preparations may be made by cutting oblique
sections of the stem, especially when large vessels are
present, as then the internal structure of the walls of some
of them may oftentimes be examined. The diagram above
given refers only to sections of a pine ; all exogenous stems,
however, will exhibit three different appearances, according
to the direction in which the cut is made ; but in order to
arrive at a true understanding of the arrangement of the
woody and vascular bundles in endogens, horizontal and
vertical sections only will be required. Specimens of
wood that are very hard and brittle should be first
softened by boiling in water ; and as the cutting-machine-
will answer for other structures besides wood, it should
be understood, that horny tissues will also be softened
by boiling, and can then be cut very readily.
Preparation of Hard Tissues. All sections of recent and
greasy bones should be soaked in ether for some time, and
afterwards dried in the air, before they are fit for the saw,
file, and hone ; by dissolving out the grease, the lacunas
and canaliculi show up very much better. When it is
wished to examine the bone-cells of fossil bone, chippings
only are required ; these may be procured by striking the
bone with the sharp edge of a small mineralogical-hammer:
carefully select the thinnest of the chips, and mount them
at once, without grinding, in Canada balsam. If desirable
to compare bone structures, it must be borne in mind that
the specimens for comparison should be cut in one and the
same direction ; as the bone-cells, on which we rely for our
determination, are always longest in the direction of the
shaft of the bone, it follows that if one section were trans-
verse, and the other longitudinal, there must be a vast
difference in the measurement of the bone- cells, in conse-
quence of their long diameter being seen in the one case,
206
THE MICROSCOPE.
and their short diameter in the other. In all doubtful
cases, the better plan is to examine a number of fragments,
both transverse and longitudinal, taken from the same
bone, and to form an opinion from the shape of bone-cell
which most commonly prevails.
The Teeth. The best mode of examining teeth is by
making fine sections. Specimens should be taken, both
from young and old teeth, to note
the changes. A longitudinal or
transverse slice should be first
taken off; a circular saw. fitted to
the lathe, fig. 143. cuts sections
very quickly then rub down, first
by the aid of the corundum-wheel,
which should also be fitted to
the head-stock of the lathe, then
finish them off between two
pieces of water-of-Ayr stone, and
finally clean and polish between
plates of glass, or on a polishing
strap with putty powder. The
section requires to be washed in
ether, to remove all dirt and im-
purities j when well polished and
dried, it may be preserved under
thin glass, and cemented down
with gold-size or varnish.
Such polished sections are preferable to many others
which, on account of their irregular surface, require to be
covered with fluids, as Canada-balsam, turpentine, &c., in
order to fit them for examination with high powers. It
almost always happens, that some portion of these fluids
enters the dentine, which then becomes indistinct, and
almost invisible in its ramifications.
Two sections made perpendicularly to one another
through the middle of the crown and fang of a tooth,
from before backwards, and from right to left, are suffi-
cient to exhibit the more important features of the teeth ;
but sections ought also to be prepared, showing the surface
of the pulp cavity and that of the enamel ; and likewise
various ohlkiue and transverse sections through the dentine
Fig 1436 Small Lathe for
polishing.
MAKING SECTIONS OP TEETH. 20?
in the fangs, to exhibit the anastomoses of their branches.
The dental cartilage is easily shown by maceration in
hydrochloric-acid, a process which requires a longer or
shorter time, according to the concentration of the acid.
It is very instructive also to macerate thin sections in
acid, and to examine them upon a slip of glass, at
intervals, until they entirely break up. The enamel
prisms are readily isolated in developing enamel in this
way, and the transverse lines readily seen when the section
is moistened with hydrochloric acid. The early develop-
ment may be studied in embryos of two, three, or four
months with the simple microscope ; and in transverse
sections of parts hardened in spirits of wine. The pulp of
mature teeth is obtained by breaking them in a vice, and
the nerves can be made out without difficulty on the addi-
tion of a dilute solution of caustic soda.
To cut through the enamel of the tooth, it will be
necessary to lessen the friction, by dropping water upon
the saw as it is made to revolve. The section is after-
wards very quickly ground down by holding it against
the flat side of the corundum- wheel. 1 A small handle,
mounted with shell-lac, to fix the section in, forms a ready
holder : polish, as before directed, between two pieces of
the water-of-Ayr stone, or on a hone of Turkey-stone kept
wet with water. As the flatness of the polished surface is
a matter of the first importance, that of the stones them-
selves should be tested from time to time ; and whenever
they are found to have been rubbed down on one part
more than another, they should be flattened on a paving
stone with fine sand, or on a lead plate with emery. When
this has been sufficiently accomplished, the section is to be
secured, with Canada balsam, to a slip of thick well-
annealed glass, in the following manner : Some Canada
balsam, previously rendered somewhat stiff by evaporation
of part of its turpentine, is to be melted on the glass-slip,
so as to form a thick drop, covering a space somewhat
larger than the size of the section, and it should then be
set aside to cool ; during which process, the bubbles that
may have formed in it will usually burst. When cold, its
(1) Corundum is a species of emery composition ; alumina, red oxide of iron*
Uld lime ; it is much used by dentists M & polishing material.
208 THE MICROSCOPE.
hardness should be tested with the edge of the thumb
nail, for it should be with difficulty indented by pressure,
and yet should not be so resinous as to be brittle. If it
be too soft, as indicated by its too ready yielding to the
thumb-nail, it should be boiled a little more ; if too hard,
which will be shown by its chipping, it should be re-melted
and diluted with more fluid balsam, and then set aside to
cool as before. When of the right consistence, the section
should be laid upon its surface, with the polished side
downwards ; the slip of glass is next to be gradually
warmed until the balsam is softened, care being taken to
avoid the formation of bubbles, and the section is then to
be gently pressed down upon the liquefied balsam in a sort
of wave towards the side, and an equable pressure being
finally made over the whole. When the section has been
thus secured to the glass, it may be readily reduced in
thickness by grinding. When the thinness of the section
is such as to cause the water to spread around it between
the glass and the stone, an excess of thickness on either
side may often be detected by noticing the smaller distance
to which the liquid extends. In proportion as the section
attached to the glass is ground away, the superfluous
balsam which may have exuded around it will be brought
into contact with the stone ; and this should be removed
with a knife, care being taken that a margin be still left
round the edge of the section. As the section approaches
the degree of thinness which is most suitable for the
display of its organization, great care must be taken that
the grinding process is not carried too far ; and frequent
recourse should be had to the microscope to examine it.
The final polish must be given upon a leathern strap, or
upon the surface of a board covered with buff-leather,
sprinkled with putty-powder and water, until all marks
and scratches have been rubbed out of the section.
In mounting sections of bone, or teeth, it is important
to avoid the penetration of the Canada balsam into the
interior of the lacunce and canaliculi; since, when these
are filled by it, they become almost invisible. The benefit
which is derived from covering the surfaces of the
specimen with Canada balsam, may be obtained, without
the injury resulting from the penetration of the balsam
CIRCULAR DISC. 209
into its interior, by adopting the following method :
A small quantity of balsam, proportioned to the size of
the specimen, is to be spread upon a slip of glass, and to
be rendered stiff er by boiling, until it becomes nearly
solid when cold ; the same is to be done to the thin glass
cover ; next, the specimen being placed on the balsamed
surface, and being overlaid by the balsamed cover, such
a degree of warmth is to be applied as will suffice to
liquefy the balsam, without causing it to flow freely;
and the glass cover is then to be quickly pressed down,
and the slide to be rapidly cooled, so as to give as little
time as possible for the penetration of the liquefied
balsam.
Circular Disc. For the purpose of cutting glass covers
or making shallow cells with japanners' gold-size for
mounting objects, Beck's Walmsley's turn-table (fig.
143c) is most useful.
Fia. 143c. Beck's Walmsley's Cell-making Instrument.
For making cells, take a camel's-hair pencil, pre-
viously dipped in japanners' gold-size, hold it firmly
between the finger and thumb, and set the wheel in
motion, when a perfect circle will be rapidly formed ;
it must be put aside to dry. To cut cover-glasses
secure a sheet of thin glass under the brass springs,
and substituting for the pencil a cutting diamond,
a circular cover may be readily cut out. A cutting
diamond is not only useful to the microscopist for
the above purpose, but also for writing the names of
mounted objects on the ends of the glass slides.
p
210
THE MICROSCOPE.
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DIRECTIONS FOE MOUNTING. 211
The various accessory pieces of apparatus represented
on the opposite page will facilitate the process of mount-
ing specimens.
By the aid of the Universal Spring-Clip (fig. 143e)
objects of great delicacy when mounted may he left to
dry and harden for any length of time.
FIG. 143e. The Universal Spring-clip for Mounting.
General Directions for the ^Preparation and Mounting
Objects. Objects exhibited under the microscope are
either opaque or transparent. The former, in the majority
of instances, require little or no preparation beyond placing
them in such a position as to show their external surface
by reflected or condensed light, and covering with thin glass to
exclude dust. Those objects, however, which it is intended
to examine by transmitted light require, in most cases, to
be prepared previously to mounting them, in whatever
vehicle may be found most suitable for exhibiting theh
structure. The medium most used for mounting trans
parent objects is Canada balsam. The pure balsam is,
however, too thick for use, and it requires to be diluted
with spirit of turpentine to render it sufficiently fluid to
permeate the structure to be exhibited. As a general rule,
it should be just fluid enough to drop readily from the
point of a needle. Those who desire to avoid the trouble
of mixing their own mounting medium, can procure it
ready for use from any of the microscope makers. There
are some few objects whose structure is so transparent
that they must be mounted dry. Scales from the wings
of butterflies and moths, of the podura and lepisma sac-
charina, and some of the diatomacess are of this class. All
that is necessary in preparing objects for dry mounting,
is to take care that they are free from extraneous matter,
and to fix them permanently in that position in which
their structure will show to the host advantage. Care
p 2
212 THE MICROSCOPE.
should be taken to have no draught of air through the
room while handling very delicate objects ; many a beauti-
ful object has been wafted from under the hand of the
microscopist in this way, sometimes, even by his own
breath.
The preparation of very minute objects which require
particular chemical treatment before mounting, will bo
more fully described hereafter. To this class belong the
diatomaceae, whose delicate structure forms one of the most
beautiful objects which can be exhibited. In mounting
entomological specimens, the first thing, of course, is the
dissection of the insect. This is best accomplished by
the aid of Collins's Dissecting Microscope, a pair of small
brass forceps, and very finely-pointed scissors ; the parts
to be prepared and mounted should first be carefully
detached from the insect with the scissors, then immersed
in a solution of caustic alkali (Liquor Potass^) for a few
days, to soften and dissolve out the fat and soft parts : the
length of time it is necessary to immerse them can only be
ascertained by experience, but, as a general rule, the objects
assume a certain amount of transparency when they have
been long enough in the alkali ; when this is ascertained
to be the case, the object is to be placed in a flat receptacle
(a shallow pomatum pot is as good a thing as can be used),
and put to soak for two or three hours in soft or distilled
water. It is then to be placed between two slips of glass,
and gently pressed till the softer parts, &c. are removed.
These will frequently adhere to the edge of the object ; it
will, therefore, be necessary to wash the latter carefully
in water to get rid of the superfluous matter, a process
which will be much aided by delicate touches of a camel's-
hair brush. Place the object now and then under the
microscope to see that all extraneous matter is removed,
and when this is accomplished take the specimen up care-
fully with the camel's-hair brush, and lay it on a piece of
<very smooth paper (thick ivory note is very' good for
the purpose), arrange it, if necessary, to its natural appear-
ance with the brush and a finely-pointed needle, place a
second piece of paper over it, and press it flat between
two slips of glass, and compress it by one of the American
clips which may be bought for a few pence per dozen.
PREPARING AND MOUNTING. 213
When thoroughly dry (which it will prohably he in ahout
twenty-four hours, if in a warm room), separate the
glasses, and gently unfold the paper ; then, with a little
careful manipulation, the object may he readily detached,
and should he at once placed in a little spirit of turpentine,
where it should remain for a few days till it is rendered
transparent and fit for mounting. The time daring which
it should remain in this liquid will depend on the struc-
ture ; some objects, such as wings of flies, will be quickly
permeated, while horny and dense objects require an
immersion of a fortnight or even longer. A pomatum pcd
with a concave bottom and well-fitting lid will be found
to answer admirably for the soaking process, and it is
well, in preparing several specimens at a time, to have two
pots, one for large and medium, the other for very small
objects, or the smaller ones will be found often to adhere
to the larger.
The glasses on which objects are mounted are usually
slips of flatted crown or sheet glass cut to a size of three
inches by one, and ground at the edges. The mode ol
mounting the object is as follows : Having chosen a glass
slide, clean and polish it with a piece of chamois leather,
ascertain the centre of the slide by means of a piece of
paper or card of exactly the same size as itself, and in
which a hole has been cut exactly in the centre,
place the piece of paper under the slide, and, having
removed the object to be mounted from the turpentine in
Fig 143/. Showing the mode cf placing Glass Cover on the Object.
which it has been soaked, lay it on the slide on the spot
corresponding to the hole in the card underneath ; then
tak'5 up a small quantity of the prepared Canada balsam
>n the point of a large needle or pointed pen-knife, and
214 THE MICROSCOPE.
drop ifc immediately over the object, slightly warm the
under part of the slide over a spirit-lamp to diffuse the
balsam and cause it thoroughly to penetrate the object,
and immediately cover the latter with one of the small
circles of thin glass, sold by opticians for the purpose.
In laying the glass cover on theJ object, care should be
taken to bring the edge of the circle down first, and let
the other fall slowly on the object (see fig. 143/*), to
prevent the formation of bubbles from the sudden dis-
placement of the air. It requires some little practice
to keep the object in the centre of the circle.
Notwithstanding very great care in manipulation, air-
bubbles will appear. These may, however, be removed
by gently warming the under part of the slide over
the spirit-lamp, when the bubbles will usually leave the
object, and travel towards the edge of the circle. In most
cases they will entirely disappear as the balsam becomes
firmer and drier. If it be desired to dry the balsam
quickly, the slide may be placed in some warm situation
where the heat does not much exceed 100, and it must
^)e maintained in a perfectly horizontal position, to prevent
displacement, until the balsam has become dry. When
this has been ascertained . to be the case, the superfluous
balsam which surrounds the edge of the circle may be
scraped off by the point of a penknife ; and when the
major part has been removed in this way, the remainder
may be got rid of, and the edges of balsam rendered smooth
by rubbing gently with an old silk handkerchief moistened
with spirit of turpentine. The edge of the circle of balsam
will probably appear white and dull, but it may be rendered
transparent by gently warming the under part of the slide
over a spirit-lamp, and again placing the object in a warm
room till the balsam has a second time become hard and
dry ; after which the name of the object should be written
with a small writing diamond at one end of the slide.
Some microscopists prefer to cover the slide with orna-
mental paper, which may be procured very cheaply.
In covering the slides with paper, their edges need not
be ground, but may be rubbed with a fine file, which will
prevent the sharp glass from damaging the paper cover,
and cutting the fingers of the operator. The foregoing ia
PREPARING AND MOUNTING. 215
the method by which objects are mounted in balsam ;
there are, however, some specimens, the mounting of
which, in balsam, would render them almost invisible, in
which case if not suitable for dry-mounting they should
be placed in fluid in cells, the size and depth of which
must be regulated by the proportions of the object. If
it be the scale of a fish, or the pollen of a flower, a very
shallow cell will suffice, and it may be formed of " Bruns-
wick black" in the manner already described. When the
cell is quite dry, take the object (which should have been
some time previously soaked in the fluid in which it is to
be mounted to dispel the air from its substance), place it in
the middle of the circle, fill the space quite full of the
mounting fluid, and cover it with a glass circle ; place the
edge down first, and bring the whole surface of the circle
very gradually upon the cell as pointed out in the former
case. Some of the fluid will immediately escape under the
edge ; this may be absorbed by a piece of filtering paper.
Should too much escape, a bubble will make its appearance
in the cell; in this case the process must be repeated.
When this has been performed successfully, secure the glass
circle in its place with a small spring-clip ; then take a
camel' s-hair brush, charged with varnish, and carry it
round, and slightly over the edge of the cover. Allow the
first layer to dry before another is added, and continue to
add more gradually until the cell is made perfectly air-tight.
Glass or metal cells must be employed- -for those objects
whose bulk renders the method just described inadmissible.
Glass-cells may be fastened to the glass-slide either by
Canada balsam, by Jeflerey's marine glue, or Brunswick
black ; the latter will be rendered very durable by mixing
it with a small quantity of India-rubber varnish (made by
dissolving small strips of caoutchouc in gas-tar). The pro-
cess of mounting in glass-cells is similar to that employed
in making varnish-cells, except that a somewhat larger
quantity of cementing medium is required on account of
the greater weight of the cell. Objects mounted In this
way should always be kept in the horizontal position, and
a little fresh varnish applied now and then, if the cement
show any tendency to crack.
In mounting objects in balsam, great care should be
216 THE MICROSCOPE.
taken to have the specimens quite dry before soaking them
in turpentine. Objects mounted in cells, on the contrary
should have become perfectly saturated with the mounting
fluid before being finally secured.
It is preferable to riount and preserve specimens o'f aiihnal
tissues In shallow cells, to avoid undue pressure on the
preparation. Cells intended to contain preparations im-
mersed in fluid must be made of a substance impervious
to the fluid used; on the whole, the
most useful are those made with
circles of thin glass, cemented to
the glass-slide with marine glue,
such as we have here represented
(fig. 143<7). The surface of the glass
shoul(i be slightly roughened before
applying the cement.
Different modes of mounting may be employed with
advantage, to show different structures ; entomological
specimens, such as legs, wings, spiracles, trachea, ovi-
positors, stings, tongues, palates, cornece, &c. show best
in balsam : the trachea of the house-cricket, however
should be mounted dry. Sections of bone show bes".
when mounted dry, or in a cell with fluid. Scales of
butterflies, moths, &c. should be mounted dry. Other
objects, as sections of wood and stones of fruit, exhibit
their structure best in a cell with fluid.
There are some objects much more difficult to prepare
than others, and which tax the patience of the beginner
in a manner which can hardly be imagined by any one
who has never made the attempt. The structure of many
creatures is so delicate, as to require the very greatest care to
prevent mutilation, and consequent spoliation of the spe-
cimen. The beginner, therefore, must not be discouraged
by a few failures in commencing, but should persevere
in his attempts, and constant practice will soon teach him
the best way of managing intricate and difficult objects.
The room in which he operates should be free from dust,
smoke, and intrusion, and everything used should be kept
scrupulously clean, since a very small speck of dirt, which
may be almost invisible by the naked eye, will assume
onpleasant proportions under the microscope, and not only
MOUNTING AND PRESERVING OBJECTS. 217
mar the beauty, but posssiblj interrupt a clear view of
a, very splendid and delicate object. Then, again, if
the microscopist prefers to cut and grind his own glass
slips, he should be very careful that there are no sand-
specks or air-bubbles in the centre of the slide, or of
the glass cover : many a good object has been spoiled
from neglect of this precaution. A good light by which
to work is also highly important. In using the ordinary
microscope, the microscopist should keep both eyes open,
the practice of closing the eye not in use being
injurious to the sight of both. The beginner who is
about to purchase a microscope, will do well to procure
a binocular, the price of which has been reduced so
much as to bring it within the reach of those of even
moderate means.
In mounting objects in fluid, the glass cover should
come nearly, but not quite, to the edge of the cell ; a
slight margin being left for the cement, which ought
to project slightly over the edge of the cover, in order
to unite it securely to the cell.
To preserve and mount diatomaceas in as nearly as
possible a natural condition, they should be first
well washed in distilled water and mounted in a
medium composed of one part of spirits of wine to
seven parts of distilled water. The siliceous coverings
of the diatoms, however, which show various beautiful
forms under the higher powers of the microscope,
require more care in preparation. The guano, or in-
fusorial earth containing them, should first be washed
several times in water till the water is colourless,
allowing sufficient time for precipitation between each
washing. The deposit must then be put into nitro-
hydrochloric acid (equal parts of nitric and hydro-
chloric acids), when a violent effervescence will take
place. When this has subsided, the whole should be
subjected to heat, brought nearly up to the boiling-
point, for six or eight hours. The acid must now be
carefully poured off, and the precipitate washed in a
large quantity of water, allowing some three or four
hours between each washing, for the subsidence of
Borne of the lighter forms. The sediment must be
218 THE MICROSCOPE.
examined under the microscope with an inch object-
glass, and the siliceous valves of the diatoms picked
out with a coarse hair or bristle.
Dr. Rezner's Mechanical Finger (fig. 143/fc) for select-
ing and arranging diatoms, adaptable to any micro-
scope, is made to slip on to the objective far enough to
have a firm bearing, and so that the bristle point can
be brought into focus when depressed to its limit. It
is clamped in its place by a small thumb-screw. The
bristle holder slides into its place so that it can be
brought into the centre of the field. When using the
finger, the bristle is first raised by means of the micro-
meter screw till so far within focus as to be nearly or
quite invisible, then the objective is focussed on to the
FIG. 1437t. Rentier's Mechanical Finger.
slide, and the desired object sought for and brought
into the centre of the field ; the bristle point is then
lowered by the screw until it reaches the object, which
usually adheres to it at once, and can then be exam-
ined by rotating the bristle wire by means of the
milled head. Professor H. L. Smith offers some useful
hints which will facilitate the use of this finger. 1
The medium used for mounting diatomaceos is of
very considerable importance, inasmuch as their visi'
bility is either diminished or much increased there-
by. Professor Abbe, experimenting with the more
minute test-objects, diatoms, &c., found monobro-
mide of naphthaline gave increased definition to most
of them. This liquid is colourless, somewhat of an
Journal of the Royal Microscopical Society, Vol. II., 1879, pp. 952-3.
MOUNTING DIATOMS. 219
oleaginous nature, and is soluble in alcohol. Its
density is 1*555, and refractive index 1'6. Its index
of visibility is about twice that of Canada balsam.
Mr. Stephenson, who first directed special attention to
the subject, came to the conclusion that the visibility
of lined objects depends upon the difference of the
refractive indices of the object observed and the medium
in which it is placed.
Taking the refractive index of air as 1*0, and diato-
maceous silex as 1'43, the visibility may be .expressed
by the difference *43.
The following table may be constructed :
Refractive indices Visibility of sile.it
(taken approximately). (Refr. index = T43).
Water = 1'33 ... 10
Canada balsam = 1'54 ... 11
Bisulphide of carbon = 1'CS ... 25
Sol. of sulphur in bisulph. ... = 1'75 ... 32
phosphorus ,, ... = 2'11 ... 67
These data relating to visibility must be taken in
connection with the numerical aperture 1 of the objec-
tives and of the illuminating pencil. The effect pro-
duced on diatoms is very remarkable, the markings on
their siliceous frustules being visible under much lower
powers.
So that the visibility of the diatom mounted in
phosphorus as compared with balsam is as sixty-seven
to eleven ; in other words, the image is six times more
visible. Mr. Stephenson's phosphorus medium is
composed of a solution of solid or stick phosphorus
dissolved in bisulphide of carbon. Great care is re-
quired in preparing the solution owing to the very
inflammable nature of the materials. So small a
quantity of the bisulphide of carbon is required to
dissolve the phosphorus that the diatom may be said
to be mounted in nearly pure phosphorus. Remark-
able enough, this medium has the reverse effect upon
some other test-objects, as Podura and Lepisma scales,
which lose their characteristic markings.
F. M. Rimmington's Glycerine Jelly is especially
(1) Professor Abbe introduced a new expression for apertnre (i.e., "numer-
ical aperture"), by which the relative resolving power cf different objec-
tives is se*n by the reading of their numerical apertures.
220 THE MICROSvOPE.
adapted for mounting algse, fungi, vegetable and animal
tissues, urinary deposits, casts, epithelium, crystals,
starch granules, diatomaceas, &c. For certain delicate
organisms, as the desmidiaceee, whose plasma may be-
affected by too dense a medium, the jelly may be diluted
one-quarter or one-third with camphor- water.
Dr. E. Kaiser describes a process for preparing a
pure glycerized gelatine : Take one part by weight of
the finest French gelatine, steep for about two hours
in six parts by weight of distilled water, and add
seven parts of pure glycerine. Then to every 100
grams of the mixture 1 gram of concentrated carbolic
acid. The whole must be warmed for ten or fifteen
minutes, stirring all the while until the flakes produced
by the carbolic acid have disappeared. Then filter
while still warm through the finest spun glass, pre-
viously washed in distilled water. When cold the
preparation can be used like Canada balsam. This
medium is also an excellent embedding substance for
section-making. For this purpose the objects must bo
placed in the glycerine-gelatine after again warming.
When sections of objects have to be made so delicate
that there is danger of their falling to pieces after cut-
ting, the object must be left in the warmed glycerine-
gelatine until it is thoroughly penetrated by the latter.
The gelatine may be removed from the tissues by a
fine jet of warm water after the section is made and
placed on the slide. For imbedding hard tissues
glycerine-gelatine is an excellent medium, for after it
is set, any degree of hardness may be imparted to them
by treating with absolute alcohol, the time required
for this being from ten to thirty minutes. One special
recommendation of this substance for imbedding is its-
transparency, which enables the operator to see the
precise position of the object.
For mounting numerous minute objects, Half's
Carbolic Acid Fluid is a very useful medium; it is
more simple, cleanly and rapid than turpentine for
insects, small crustaceans, moluscs, &c. The purest
crystals of carbolic acid, with just sufficient water
added to render them fluid, produces the best
CEMENTING. 221
results. No more should be dissolved than can be
used up, as after solution the light spoils it, and gives
it colour. Vegetable tissues, foraminifera, the palates
of moluscs (the latter, after boiling in liquid potash,
and washing in water to remove all traces of alkali),
may be immersed in carbolic acid. If it be wished to
mount them foi-thwith, then place the specimen, after
washing in a glass slip, and drop one or two drops of
acid upon it. Should it appear to be thick or cloudy,
warm the slide over a spirit lamp ; set it aside to get cool,
and drain away the acid, or remove it with blotting-
paper. If not perfectly clear add another drop or two
of fresh carbolic acid and again warm it ; place a cover-
glass over it, remove as much of the acid as possible,
and then let a drop of fluid Canada balsam run under
the cover to take the place of the acid. Gently
warming the slide will facilitate this operation. A
number of specimens may be put into a test tube with
the carbolic acid solution and boiled for a few minutes,
corked up tightly, and put aside for mounting at leisure,
either in balsam or dammar. When the balsam becomes
too thick, it can be rendered fluid by adding either
benzoline or chloroform.
Dammar varnish for cementing the cover-glass is
prepared as follows :
Take of gum dammar, 1 oz. ; spirits of turpentine,
1 oz. ; dissolve by gentle heat : then take gum mastic,
1 oz. ; chloroform, 2 oz. ; dissolve without heat, and,
having filtered out all impurities, mix the two solutions
together by shaking.
Method of Cementing. After many years' experience,
I have arrived at the conclusion that for cementing
down the cover-glass, there is nothing better than either
gold size or gum dammar varnish. The latter, for
some preparations, will be improved by the addition
of a small proportion of india-rubber dissolved in
naphtha. Whichever is used, it should be applied
with care and some skill. The brush should be held
nearly in the upright position, and the turn-table spun
round rapidly, so that the gold size may form a warm
ring round the outside of the cover-glass. After the
222 THE MICROSCOPE.
gold size has become dry and the slide cleaned off, it
may be coloured by aniline mixed in a little cement,
or by a coating of water- colour, over which a final
thin coating of gold size should be applied.
A good ringing medium for balsam mounts is
dammar dissolved in chloroform, because if it is in-
clined to run under the cover it will readily mix with
the mounting material without leaving a visible trace
behind. It is better to apply the brush to the edge of
the cover almost dry, the slide on the turn-table being
made to spin rapidly round, so as to create a track in
which the dammar solution will readily flow. The second
application is made immediately to follow the first,
with the brush full, so that there will be a small drop
of solution on the end, and this is allowed to touch the
edge of the cover without letting the brush itself come
in contact with the glass. This process must be
repeated until the ring is built up to the proper size.
In drying, however, the ring of dammar will shrink
considerably, and thus it is necessary to make a subse-
quent application in a few hours' time.
Wash away all surplus glycerine by syringing, then
apply a ring of a waterproof cement around the cover.
Such a cement may be bought under the name of Bell's
cement. A better and less expensive cement may,
however, be made by dissolving 10 grs. of gum-ammo-
niac in 1 oz. of acetic acid (No. 8) ; then add to this
solution 2 drachms of Cox's gelatine. This liquid
flows easily from the brush and is waterproof, rendered
more so if subsequently brushed over with a solution
of 10 grs. of bichromate of potash in 1 oz. of water.
But what especially recommends this cement is its
adhesive power to glass, even should there be a little
glycerine left behind on the cover. After the gelatine
ring is dry any kind of cement may be employed.
When a considerable number of different objects are
being prepared at the same time, write the name of
each with pen and ink upon the glass slide. 1
.. Mounting Polyzoa. Mr. Morris, of Bath, has suc-
[ ceeded in obtaining beautiful specimens of polyzoa and
Mr. C. Seller, Microscopical Jourm.*
PRESERVATIVE FLUIDS. 223
hydroid zoophytes, with, tentacles expanded, by adding \ /
spirit of wine, drop by drop, to the salt-water cell in
which they are confined. Animals should be killed
in this way as soon as possible after capture.
A plan of mounting objects in a mixture of balsam
md chloroform is described by Mr. Wm. Henry Heys
in the Microscopical Journal : Take a quantity of
the oldest balsam procurable, and place it in an open
^lass cup, and mix with it as much chloroform as
will make the whole quite fluid, so that a very small
quantity will drop from the lip of the containing
vessel. Then put this prepared balsam into long thin
half-ounce phials, and cork and set them aside for at
least a month. The advantage of having the medium
^eady-made is, that there is no waste, and none of the
usual and troublesome preparation required for putting
up objects in Canada balsam; if it has stood for
some time, it loses the yellow tinge which is observable
ji most samples when first mixed, and, moreover, air-
3ubbles escape more readily.
Groadby's fluids are cheap and efficient for preserving
ind mounting animal structures. The following are
lis formulae :
Take for No. 1 solution, bay salt, 4 oz. ; alum, 2 oz. ;
;orrosive sublimate, 2 grains ; boiling water, 1 quart :
nix. For No. 2 solution, bay salt, 4 oz. ; alum, 2 oz. ;
corrosive sublimate, 4 grs. ; boiling-water, 2 quarts :
nix.
The No. 1 is too strong for most purposes, and should
mly be employed where great astringency is needed to
*ive form and support to very delicate structures,
^o. 2 is best adapted for permanent preparation ; but
leither should be used in the preservation of animals
containing carbonate of lime (the mollusca), as the
ilum becomes decomposed, and sulphate of lime pre-
cipitated. For the preservation of crustaceans use the
;ollowing :
Bay salt, 8 oz. ; corrosive sublimate, 2 grs. ; water,
L quart : mix.
The corrosive sublimate is used to prevent the
jroTvth of vegetation in the fluid; but it also pos-
224 THE MICEOSCOPE.
sesses the property of coagulating albumen, and there-
fore cannot be used iii the preservation of ova, cellular
tissue, the white corpuscles of the blood, &c.
Goadby's method of preparing -marine-glue for
cementing cells is as follows : dissolve separately equal
parts of shell-lac and india-rubber in coal or mineral
naphtha, and afterwards mix the solutions carefully by
the application cf heat. It may be rendered thinner
by the addition of more naphtha, and redissolved,
when hard or dry, by adding naphtha, ether, or liquid
potash.
Multiple Sfaining, Animal and Vegetable.
"Within a short period of time the staining of
animal and vegetable tissues for microscopical exami-
nation may be said to have almost superseded injec-
tions. The results obtained lent a charm to the stain-
ing process, and it was soon seen that other and far
more important advantages could be gained by its
adoption and further development. Formative tissue
and structural differences, heretofore difficult to differ-
entiate, were by a method of double staining, that is
dying the tissues of two or more colours, made instruc-
tive and palpable even by the aid of only moderate
powers of the microscope.
Various methods, mostly differing in details, have
"been from time to time proposed for the combi-
nation of colours and producing striking and perma-
nent results. One of the most useful manuals of
reference on the subject is Dr. Thin's, 1 whose experi-
ence is founded on methods adopted by continental
schools, and that of Ranvier's in particular. The
student is recommended to provide himself for ordinary
histological work, and which he should as far as possible
become proficient in before he can expect to succeed in
staining and preparing tissues, the following instru-
ments : Two needles fixed in handles ; strong and fine
scissors ; a scalpel ; a razor ; flat 011 the under surface
and slightly grooved on the upper ; a section-lifter or
(1) An Introduction to Practical Histology, by George Thin, M.D. Bail
Iftre, Tindall <fe Cox, King William Street, Strand.
PREPARATION OF TISSUES. 225
pud for removing sections from one fluid to another ;
sveral glass-rods or pipettes ; a dozen glass phial bottles
>r containing reagents and staining fluids ; glycerine ;
cetic acid,osmic acid, alcohol, methylated spirit, distilled
ater, &c. ; and lastly, a few camel's- hair brushes, watch-
lasses, and two or three porcelain capsules. All spirits
iould be kept in well-stoppered bottles. For dissec-
ions and the examination of small animals, or portions
f larger, and of tissues in general, a dissecting micro-
30pe fitted with two or three powers will be found
lost convenient. The method of teasing out with
eedles is shown in the annexed fig. 143^.
All animal tissues should be examined in as fresh a
iate as possible, and kept in blood serum, white of
2fg, or a very weak solution (1 part of salt in 200
FIG. 143i. Microscopic Dissection. Teasing out with Needles.
arts of water) of salt. For hardening tissues, sec-
ons, or organs, use the following reagents : Absolute
Icohol, methylated spirit, solutions of chromic acid
;ome prefer a mixture of the latter and alcohol),
E bichromate of potash, picric acid, chloride of palla-
ium, and M tiller's fluid. All solutions of corrosive
g^ents should be used weak. Chromic acid, a quarter or
t most a 1 per cent, solution ; of bichromate of potash,
or 2 per cent., picric acid, a saturated solution ;
bloride of palladium a one-tenth per cent., with a few
rops of hydrochloric acid added to prevent change,
liiller's fluid is made by adding together equal parts
f a 2 per cent, solution of bichromate of potash and
1 per cent, solution of sulphate of soda. A short
mmersion in either of these solutions prepares tissues
Q
226 THE MICROSCOPE.
for teasing out ; for hardening they require to be kepi
in either Miiller's fluid or chromic acid for a few days,
and to complete the process by transferring to alcoho"
or methylated spirit for from 12 to 24 hours. Wher
employing chromic acid, bichromate of potash o]
picric acid, immerse only a small portion of tissue in t
large quantity of either fluid, always changing ii
in 12 or 24 hours. Osmic acid not only hardens
but stains tissues, and sections can be cut without sub.
sequent immersion in alcohol. Sections of skin, anc"
cornea, can also be made after reduction by th(
chloride of gold in acidulated water ; a half per cent
of either chloride of gold or of nitrate of silver wil
be found strong enough for most purposes. A ]
or a 1-|- per cent, of chloride of gold is recommendec
for very special specimens. The most commonly usec
colour stains are carmine, logwood, picro-carminatc
of ammonia (which combines the action of picric anc
carmine), hsematoxyline and the aniline colours, a$
magenta, commercially known as roseine or acetate o:
rosaline, aniline red, eosin, aniline blue, violet, anc
methyl - aniline. Purpurine, a dye extracted fron
madder, is also highly spoken of as a stain by Banvier
Dr. Thin strongly recommends it. It is prepared foi
use as follows: "A solution of 1 part of alum in 20(
parts of distilled w r ater is brought to the boiling poin
in a porcelain capsule, and a small quantity of solic
purpurine rubbed up in a little distilled water is addec
to it. The purpurine quickly dissolves, but ther<
should remain a small quantity undissolved, which in-
dicates that the solution is concentrated. It must b<
filtered whilst hot into rectified spirit. The alcoho
should constitute a fourth part of the total volume o:
the mixture. The fluid obtained is of a beautifu
orange red by transmitted light : it is, in fact, fluores-
cent. At the end of a month a slight precipitate ii
observed, and it begins to lose some of its colouring
matter. Tissues should remain in it from twenty-foul
to forty-eight hours. Aniline blue-black is strongly
recommended for staining the nerve-cells of the braii
and spinal cord.
STAINING FLUIDS. 227
To produce a third stain, Schwarz proposed picric
acid in combination. A mixture of picro-carmine, he
tells us, is a preferable stain for the unstriped muscle
of the intestines, &c. Ranvier also employs a picro-
carminate ; he discovered that a good green stain could
be obtained by dissolving picric acid in glycerine, dilut-
ing it with a decoction of logwood, and adding a small
quantity of a solution of chromate of potash in the
proportion of 1 part to 1,000. The solutions must be
mixed together just before they are wanted for use, as
they rapidly spoil.
Dr. W. Stirling 1 f urnishes a brief but useful account
of the methods he has employed with success for some
time for double and treble staining.
Osmic Acid and Picro-carmine. Mix on a glass
slide a drop of the blood of newt or frog and a drop of
a 1 per cent, aqueous solution of osmic acid, and allow
the slide to stand by. This will fix the corpuscles with-
out altering their shape. At the end of five minutes
remove any excess of acid with blotting-paper, add a
drop of a solution of picro-carmine, and a trace of
glycerine to prevent evaporation, and set aside for three
or four hours to see that no overstaming takes place.
At the end of this time the nucleus will be found to
be stained red, and the perinuclear part yellow.
Picric Acid and Picro-carmine. Place a drop of the
blood of a frog or newt on a glass slide, and add a drop
of a saturated solution of picric acid : put the slide aside
and allow it to remain for five minutes ; at the end
of that time, when the acid has fixed the corpuscles
(that is coagulated their contents), any excess of acid
should be removed as before. A drop of a solution of
picro-carmine should now be added, and a trace of
glycerine, and the preparation set aside for an hour.
At the end of that time remove the picro-carmine
solution by means of a narrow slip of blotting-paper,
and add a drop of Farrant's solution or glycerine and
apply glass-cover. The perinuclear part of the cor-
puscles will be seen to be highly granular and of a
deep orange colour, whilst the nucleus is stained red.
(1) Journal of Anat. and Physiol., xx. 1881, p. 349.
Q 2
228 THE MICROSCOPE.
Some of the corpuscles will appear of a delicate yellow
colour, and threads are seen extending from the nucleus
to the envelopes. The preparation should be preserved
and mounted in glycerine.
Picro-carmine and Aniline Dye. For glandular tissue,
none of the aniline dyes answer so well as iodine green,
used in the form of a 1 per cent, watery solution.
Stain the tissue in picro-carmine, wash it in distilled
water, acidulated with acetic acid, and stain it in a
solution of iodine green. As it acts rapidly, care must
be taken not to overstain. Wash the section in w r ater,
and then transfer it to alcohol ; finally clear with oil
of cloves. The washing should be done rapidly, as
the spirit dissolves out the green dye. All prepara-
tions stained with iodine green must be mounted in
dammar.
Picro-carmine and Iodine Green. Stain a section of
the cancellated head of a very young bone (foetal bone)
in picro-carmine, wash it in distilled water, and stain
it with iodine green and mount in dammar. All newly-
formed bone is stained red; that in the centre of
the osseous trabeculse, the residue of the calcified car-
tilage in which the bone is deposited, is stained green.
Many of the bone corpuscles are also stained green.
Ossifying cartilage, the back part of the tongue,
Peyer's Patch, solitary-glands, trachea, and bronchus,
may all be treated in the same way. In preparing the
skin, take a vertical section from the sole of the foot
of a foetus. The cuticle and superficial layers of the
epithelium are dyed yellow, the rete Malpighii green,
and the continuation of these cells can be traced into
the ducts of the sweat-glands, which are green, and form
a marked contrast to the red stained connective tissue
of the cutis vera ; through which they have to ascend
to reach the surface. The outer layer of the grey
matter of the cerebellum with Purkinge's cells is,
whon double stained, red, while the inner or granular
I'ayer is green. Logwood and iodine green stains the
mucous glands of the tongue (green), and the serous
glands, lilac logwood stain.
Eosin and Iodine Green. Eosin is used as the ground
STAINING FLUIDS. 229
colour. Stain the tissue in an alcoholic solution of
eosin, which will colour it very rapidly, usually in a few
seconds. Wash the section thoroughly in water acidu-
lated with acetic or hydrochloric acid, a 1 per cent, solu-
tion, and stain with iodine green. This will double stain
bone and cerebellum ; but if logwood is substituted
for the latter, the cerebrum and general substance
become stained by the eosin, while the logwood
colours the nerve-cells a lilac.
Gold Chloride and Aniline Dyes. The tissue must
be impregnated with chloride of gold, and then stained
with either aniline blue, iodine green, or rosein. The
tail of a young rat, containing as it does so many dif-
ferent structures, is an excellent material for experi-
menting upon. Remove the skin from the tail, and
place pieces half an inch long into the juice of a fresh
lemon for five minutes, wash it to get rid of the acid.
The fine tendons swell up under the action of the lemon
acid, and permit of the more ready action of the
chloride of gold solution. Place the piece for an hour
or more in a 1 per cent, solution of gold, remove it
and wash it thoroughly, and then place it in a 25 per
cent, solution of formic acid for twenty-four hours.
This reduces the gold : during the process of reduction
the preparation must be kept in the dark. The osseous
portion has then to be decalcified in the ordinary way,
with a mixture of chromic and nitric acid. After
decalcification preserve the whole in alcohol. Transverse
sections of the decalcified tail are made, and may be
stained with a red dye, as rosein, and afterwards with a
watery solution of iodine green. Mounted in dammar.
Dr. Taffani found that solutions of aniline blue
and picric acid produce beautiful green- coloured
preparations of the lymphatics, spinal cord, &c.
The action of picric acid is not like that of chromic
acid, which enters into combination with the sub-
stances upon which it reacts, and which, after being
hardened, will often part with all colour by repeated
washings. The action of picric acid is decidedly less
detrimental to most tissues than chromic acid.
Dr. Seiler uses by preference the simple carmine
230 THE MICROSCOPE.
solution of Dr. J. J. Woodward, made as follows :
Best carmine, 15 grains ; borax, 1 drachm ; water, 5--
ounces; alcohol (95 per cent.), 11 ounces: mix and
filter. Sections placed in this fluid will be stained
evenly, in a few seconds, of a violet-red colour.
Remove quickly and immerse them in a solution of
hydrochloric acid 1 part, alcohol 4 parts. Let them
remain until they assume a bright rose colour this
will be accomplished in a few seconds. Wash the
sections in distilled water and then transfer them to
alcohol and finish off in the usual way. Specimens
thus treated will have their nuclei and granules
stained, while the cell contents and fibrous tissue
remain uncoloured.
The second solution is one composed of carmine and
indigo. The sections stained with the carmine solu-
tion must be immersed in a weak solution, 2 drops of
sulphin-digotate of soda in one ounce of a 95 per cent,
alcoholic solution, which should be filtered before using,
and there left from 6 to 18 hours, according to the
rapidity with which the elements take up the indigo.
When sufficiently stained, the sections are immersed in
strong alcohol ; they are then ready for mounting. The
sulphin-digotate of soda as prepared by Bullock makes
a solution of a deep greenish-blue colour, and the effect
of the paint upon the section is to leave the nuclei
bright red, while the fully- formed material of the cell
is slightly tinged blue. The connective tissue fibres
become stained deep blue, and the blood vessels are
purplish and mapped out with distinctness. Epithe-
lium cells and hair take the stain in a distinctive
manner, thus affording a means of differentiation in
epithelioma, the so-called pearls being brought out of a
different colour from the rest of the cells.
Mr. J. W. Groves, 1 in an instructive paper on stained
sections of animal tissues, says the rule of almost uni-
versal application is that the fluid should be weak
and the quantity large in proportion to the number of
sections, or to the mass. ,A section placed in a solution
BO weak that 24 or 48 hours or more is required to give
(1) Journal of the Quekett Microscopical Club, Nov., 1S79, p. 231.
STAINING FLUIDS. 231
it the requisite tint is always better stained than one
which has been a much shorter time, because the sur-
face becomes stained before the colour has reached the
deeper parts. The sections, for the same reason, should
be as thin as possible, as they take the stain more per-
fectly, and then the deeper portions are seen under the
microscope as distinctly as the more superficial. Pro-
vided the staining is perfect and sufficient to show
all details, the paler it is the better, as it requires
less light, and is less likely to fatigue the eye. The
tints to be preferred are those that convey a cool and
pleasant sensation to the eye. Intense reds and yellows
are not nearly so pleasant as lilacs and pale blues.
Stains which impart only a body-colour are of no value
in differentiating structure. Distilled water should
always be used for washing and all staining purposes.
A five per cent, neutral aqueous solution of molybdate
of ammonia produces a cool blue-grey stain in 24 hours.
Eosin is a selective body-stain, which may be used
either before or after the sections have been coloured
with logwood. One part of eosin dissolved in a 1,000
parts of water is quite strong enough. But there
is no more useful selective stain, or one more plea-
Bant to work with, in Mr. Grroves's opinion, than log-
wood.
Kleinenburg's solution of logwood, modified by
Oolding Bird, is prepared as follows :
1. Make saturated solutions of alum and calcium
chloride, in proof spirit. 2. Mix in the proportions of
eight of the former to one of the latter. 3. Pound a
small piece of ext. hcematoxyli (the older the better) ;
add it to the mixed solution, and agitate. After it
has been allowed to stand two days, filter for use.
A watch-glass should be filled with water, and a few
drops of the mixed solutions added, till the fluid
acquires a mauve tint. Into this the sections hould
be placed, and allowed to remain for twenty-four
hours or more.
Another stain. S chafer's acid logwood solution
is especially useful for certain structures, as ten-
don, cells, &c. It is thus prepared : A one per cent.
232 THE MICROSCOPE.
solution of acetic acid is coloured by the addition o
1*3 of its volume of logwood solution.
The aniline dyes, whether in aqueous or alcoholic
Solutions, give good results, and are prepared as follows r
B/oseanilin or magenta (Igr. to loz. of alcohol), red ;
Acetate of mauvein (4gr., alcohol loz., acid nitric 2
drops), blue; aniline black (2gr., water loz.), grey-
black; Nicholson's soluble blue (l-6gr., alcohol loz~
and nitric 2m.), blue.
These stains should be used weak; and specially
observe that after sections are stained they should be
passed through alcohol and oil of cloves as rapidly a&
possible ; otherwise, the colour will dissolve out before-
they can be mounted in balsam.
Heidenhain, speaking of the use of aniline dyes r
gays : " The sections, upon removal from alcohol,
should remain for a day in a four per cent, neutral
aqueous solution, in a moist place, and then be imme-
diately mounted in glycerine and cemented."
Some aniline dyes are but sparingly soluble in alco-
hol, whereas they dissolve readily in water. Their
colour is increased by acetic acid, and removed by am-
monia. There are, however, exceptions. Use benzole-
for clearing instead of clove oil ; this fixes the colours;
better, but it has a tendency to produce shrinking in
certain structures.
The indigo carmine solution of Tiersch is a good
and useful blue stain for sections of brain and spinal
cord after they have been hardened in chromic acid;
it possesses one convenient quality viz., that if the
sections are too deeply stained, any excess of colour
may be removed by the action of a saturated solution-
of oxalic acid in alcohol. This reducing process should!
be used with caution. Tiersch's fluid consists of:
Oxalic acid, 1 part ; distilled water, 22 to 30 parts ;
indigo carmine, as much as the solution will take up.
A further dilution with alcohol may be necessary ; the
sections should be immersed in it from 12 to 48 hours j
the colour will determine the time.
Beale's fluid is thus prepared : Carmine, lOgr. ;
liq. amm. fort., 30m. ; glycerine, 2oz. ; distilled water,.
STAINING FLUIDS. 233
2oz. ; Sp. vim rect., |oz. Dissolve the carmine in the
ammonia, boil for a few seconds, add the water, filter, and
finally add the glycerine and spirit, and keep in a stop-
pered bottle. Beale says : " Let the excess of ammonia
pass off ; " but this is unnecessary, as the excess is very
slight. This solution reduced, with eleven times its
bulk of water, produces good results in from 12 to 48
hours.
Borax carmine, as follows : (1) carmine, |dr. ; (2)
borax, 2dr. ; (3) distilled water, 4oz. Bub 1 and 2
together in a mortar and gradually add the water;
let them stand in a warm place for 24 hours, after
which pour off the supernatant fluid, and the solution
is ready for use.
There are stains which, being acted upon by light,
get rapidly darker, and become opaque, and reach a
stage when they are utterly useless.
Nitrate of silver darkens by exposure ; it is used
in a half per cent, watery solution. Specimens to
be acted upon should be washed in distilled water to
remove every trace of sodium chloride, and then steeped
in the silver solution for some two or three minutes r
after which they should be again washed until
they cease to turn milky; then place them in gly-
cerine and expose them to the action of light until they
assume a dark brown colour, when they should be
mounted in glycerine or glycerine jelly.
By means of this stain the endothelial cells of the
lymphatics, blood-vessels, &c., and the nodes of Ban-
vier, in medullary nerves, are rendered visible. Sec-
tions of any of these may subsequently be stained by
logwood or carmine.
Several methods have been adopted for staining with
gold chloride. Dr. Klein's and Mr. Schafer's are among
the best.
1. Dr. Klein's method of showing the nerves of the
cornea is as follows ; Bemove the cornea within fifteen
minutes of death ; place it in a half per cent, chloride
of gold solution for half an hour or an hour ; wash in
distilled water, and expose to the light for a few days ;
in the meantime occasionally change the water. Then
234 THE MICROSCOPE.
immerse it in glycerine and distilled water, in the
proportion of one to two ; lastly, place it in water,
and brush gently with a sable pencil to remove
any precipitate, when it will be fit for mounting in
glycerine. The colour of the cornea should be grey
Tiolet.
Mr. Schafer adopts another method a double chlo-
ride of gold and potassium solution.
Osmic acid, first used by Schultze, is useful for the
demonstration of fatty matters, all of which it colours
black ; it is also valuable for certain nerve preparations.
Specimens should be allowed to remain in a 1-2 per
cent, aqueous solution of the acid from a quarter to
twenty-four hours, when the staining will be completed ;
but if it is desired to harden specimens at the same
time, they should remain in it for some few days. Osmic
acid does not penetrate very deeply, therefore small
portions should be selected for its action.
Chloride of palladium, another of Schultze's staining
fluids, is nsed to stain and harden the retina, crystalline
lens, and other tissues of the eye ; the cornified fat and
connective tissues remaining uncoloured. The solu-
tion should be used very weak : Chloride of palladium,
1 part ; distilled water, 1,000 parts. Specimens should
be mounted in glycerine at once, or further stained
with carmine.
Schafer also employs a silver nitrate and gelatine
solution for demonstrating lung epithelium ; this is
made as follows : Take of gelatine 10 grin., soak in
cold water, dissolve, and add warm water to lOOc.c.
Dissolve a decigramme of nitrate of silver in a little
distilled water, and add to the gelatine solution. Inject
this with a glass syringe into the lung until distension
is pretty complete. Leave it to rest in a cool place
until the gelatine has set ; then cut sections as thin as
possible, place them on a slide with glycerine, and
expose to light nntil ready for mounting.
Of the double stains Mr. Groves refers only to those
where the double colour is produced by a single pro-
cess. Those in which one colour is first employed, and
then another. Those used as a single fluid are Picro
STAINING FLUIDS. 235
carmine, carmine and indigo carmine, aniline bine and
aniline red.
Picro-carmine is specially useful for staining sections
hardened in picric acid. It is prepared in several
ways :
1. Add to a saturated solution of picric acid in water
a strong solution of carmine in ammonia to saturation.
2. Evaporate the mixture to one-fifth its bulk over a
water bath, allow it to cool, filter from deposit, and
evaporate to dryness, when picro-carmine is left as a
crystalline powder of red-ochre colour.
Sections can be stained in a 1 per cent, aqueous
solution, requiring only ten minutes for the process ;
wash well in distilled water, and transfer them to
methylated alcohol, then to absolute alcohol, after
which they can be made transparent by immersing in
oil of cloves or benzole, before mounting in balsam or
dammar. 1
The carmine and indigo fluids adopted by Merbel
give a blue and a red stain, and are very selective.
To prepare the red fluid, take Carmine, 2 dr. ; borax,
2dr. ; distilled water, 4oz. For the blue fluid, take
Indigo carmine, 2dr. ; borax, 2dr. ; distilled water, 4oz.
Mix each in a mortar, and allow it to stand, then
pour off the supernatant fluid. If the sections have
been hardened in chromic acid, picric acid, or a bichro-
mate, they must be washed in water till no tinge
appears. Place them in alcohol for fifteen or twenty
minutes, then in the two fluids mixed in equal propor-
tions, after which wash them in a saturated aqueous
eolation of oxalic acid, where they should remain a
rather shorter time than in the staining fluids. "When
sufficiently bleached, wash them in water, to get rid
of the acid, then pass them through spirit and oil of
cloves, and mount in balsam or dammar.
To summarize Mr. Groves' recommendations:
1. Let the material be quite fresh.
2. a. Take care that the hardening or softening fluid
(1) See Rutherford, " Outlines of Practical Histology." Most of the stain-
Ing agents mentioned may be obtained of W. Martindale. chemist .10, New
W.
236 THE MICROSCOPE.
is not too strong, b. Use a large bulk of fluid in
portion to the material, c. Change the fluid frequently.
d. If freezing be employed, take care that the speci-
men is thoroughly frozen.
3. a. Always use a sharp razor, b. Take it with one
diagonal sweep through the material, c. Make the
sections as thin as possible ; and d. Remove each one as
soon as cut, for if sections accumulate on the knife or
razor they are sure to get torn.
4. a. Do not be in a hurry to stain, but b. Re-
member that a weak colouring solution permeates the
section better, and produces the best results; and
c. That the thinner the section the better it will take
the stains.
5. a. Always use glass slips and covers free from
scratches and bubbles, and chemically clean, b. Never
use any but extra thin circular covers, so that the speci-
mens may be used with high powers, c. Always use
cold preservatives, except in the case of glycerine jelly,
and never use warmth to hasten the drying of balsam
or dammar, but ran a ring of cement round the cover.
6. Label specimens correctly, keep them in a flat
tray and in the dark.
Dr. Cook pointed out that the results obtained by
logwood were often unsatisfactory, and not fairly stable,
because it must be understood that its colouring material
consists of two substances, hsematoxylin and hoema-
tein, differing from each other by two equivalents of
hydrogen. The first named, containing the larger
amount of hydrogen, is soluble in alum solution, while
the latter, the heematein, is only slightly so, and is of
no use for the colouring of animal tissues. Haematoxy-
lin forms compounds with various metallic oxides ; and
a solution of hoematoxylin, alum, and a metallic oxide,
has a clear purple colour, becoming red on the addition
of an acid. If an alkaline earth, hydrated earthy
phosphate, be suspended in it, it will absorb the
colour, and the solution w r ill become purple. If the
solution be treated with a very small percentage of a
chromate, the purple will be gradually replaced by a
yellowish-brown colour; or if a tissue, stained with
STAINING AND HARDENING. 237
itlum logwood, be immersed in an exceedingly dilute
bichromate solution, the purple will be replaced by a
yellow tint. It therefore follows that sections har-
dened in chromic acid solutions, will not colour nearly
so readily as if immersed in the fresh state. But it
has been found that this objection may be overcome if
the sections are well washed and immersed in a modi-
fied solution of logwood. The most practical form is
made as follows : Take of logwood extract 6 parts ;
alum, 6 parts ; sulphate of copper, 1 part ; water,
40 parts. All ingredients must be free from iron.
Grind up the powders together in a mortar, and
when powdered add water sufficient to form a thin
paste ; put them by and leave them for a day or two
in this state, then add the rest of the water and filter
the solution. The hoematein will be separated and left
behind in the filter ; and a crystal of thymol may
be added to preserve the solution from moulding. For
chromic hardened tissues, dilute 8 drops of the fluid
with 120 of water, and add one drop of a one-tenth
per cent, solution of bichromate of potash just before
using the solution. Wash the stained tissues as usual
in water, and mount in glycerine, Warrant's solution,
or dammar. In the former they keep best, in the last
they are apt to fade, unless the sections be thoroughly
freed from water by being immersed in absolute alcohol,
before being brought into contact with oil of cloves. If
any moisture be left behind, the preparations will be
sure to spoil.
A modified Warrant's solution may be prepared as
follows : Take of gum arabic 5 parts ; water, 5 parts ;
when the gum is fairly dissolved add 10 parts of a five
per cent, solution of carbolic acid.
Hardening, Preserving, and Section-cutting. What-
ever be the hardening or softening fluid employed (for
this is necessary when bone is the structure about to
be examined), its bulk should be large in proportion
to the size ; half a pint of fluid for a piece of about
one cubic inch. The strength of the fluid must be
made to suit the tissue about to be acted upon, and
the fluid should be changed frequently, even though it
238 THE MICROSCOPE.
be alcohol that is employed. It is better that any and
every solution should be too iveak than too strong;
for in the latter case the tissue is liable to become
friable and break down under the cutting knife or
razor, and the sections will not take the stain evenly.
To recapitulate and enforce one or two points of impor-
tance, note that the most useful strength for chromic
acid is a | or i per cent, solution ; for the bichromate-
of potash or ammonia 1% or 2 per cent, solution. When
either of the latter solutions are used the material
must be removed to an alcoholic solution in a week, or
ten days at most, or it will become very brittle. Alco-
hol is one of the best fluids for those to use who have
not much time to devote to the subject ; tissues har-
dened in alcohol afford, as a rule, the best staining
results. The price of alcohol is much against its use,,
but it may be used weak at first, and gradually increased
in strength until the material is found hard enough to
fcut with a knife. For cutting sections by hand the
best substance for embedding is a mixture of equal
/ parts of olive oil and white wax ; or Cacao butter, or
( even soap dissolved in alcohol (Micros. Journal, vol. ii.
\ p. 940, 1879) ; while in section-cutting machines with
"hollow cylinders, either the pith of elder, carrot, or
some other soft substance may be employed. If a razor
is used, its surface must be kept moist with water when
the freezing process is adopted, or with spirit w r hen
the hardening process without freezing is used. By
the freezing method we are enabled to cut and finish
off specimens sooner and more expeditiously than by
any other process. The material about to be frozen
must be removed from the hardening; fluid and well
washed in clean water before it is transferred to the
machine. Zeiss's microtome, with its surface of glass,
a practical and useful cutting and freezing machine,
can be obtained at a moderate price, of Baker,
Holborn.
Swift's freezing microtome has the advantange of
preserving the preparation for some hours unchanged
in the frozen state. The method of using it is aa
follows : Remove the lid of the box and fill the cham-
SECTION-CUTTING MACHINE.
239
her ^ith equal parts of pulverized ice and salt, care
being taken not to allow the mixture to touch the under
side of the cover, which, when replaced, must be firmly-
secured by the clamp screw. The substance to be cut
must be placed on the surface of the central circular
brass piece (there are three additional ones supplied with
the instrument) and surrounded with a little common
gum water, which readily congeals, and, as shown in the
FIG. 143. Sioift's Micr.otome and Section-cutting Machine.
woodcut, holds the specimen firmly in position, until
solidified and frozen. The edge of the razor or knife
must be raised by the three screws supporting the
frame to the required height for cutting sections.
After the first cut, each end of the razor must be again
presented to the surface of the specimen, when either
end of the blade must be adjusted by one of the back
screws until its entire length is level. By turning the
large screw in the frame it can also be lowered for each
240 THE MICROSCOPE.
successive section required. One entire revolution of
it produces a section T ^ of an inch in thickness, the
screw-head being divided into sixths ; thus one division
gives a section of ^-^ of an inch, but even thinner sec-
tions can be cut by turning the screw. Substances
that have been previously prepared in spirit or chromic
acid should be steeped in syrup for 24 hours, otherwise
they will not readily congeal. It is advisable to cover
the apparatus with baize, to facilitate the freezing
process. The brass cup (shown in the engraving) is
used for holding substances embedded in cocoa-butter,
or paraffin ; it also serves for securing hard wood, &c.,
when cements or sealing-wax are used.
Vegetable Tissues. Sections of wood and vegetable
tissues are susceptible of very fine double and even triple
.staining dyes ; the best are atlas-scarlet, soluble blue,
iodine, and malachite-green. Mr. Richardson secured
success by steeping sections in spirits of wine for
about a fortnight, and when not required for immediate
investigation, storing them away in Price's glycerine for
at least a couple of months. This renders them less
liable to fold or break than when the staining is done
immediately after the sections are cut. His method
may be gathered from the following directions for pre-
paring and staining sections of palm stem. After the
sections are cut they should be bottled up in a toler-
ably dark solution of atlas-scarlet and spirit of wine.
Leave them in this solution, corked up tightly until
they become of a uniform scarlet tint. Like sections
of animal tissues, however, they may remain in the
solution for many weeks without risk of spoiling or
counteracting the energy of the green dyes. It is on
the whole better to complete the process when the sec-
tions seein to be of a deep scarlet colour. Remove
them and wash them well in filtered water, repeatedly
change the water until it ceases to be in the slightest
degree coloured by the sections. Then transfer them
to a white porcelain water, containing a solution of
spirit of wine, coloured bluish-green by adding a couple
of drops of an aqueous saturated solution of the green
dyes ; a drop of each will be found sufficient. When
STAINING VEGETABLE TISSUES. 241
the sections appear sufficiently coloured a dark blue,
transfer them once more to a saucer of water to which a
drop of an aqueous saturated solution of arsenious acid,
or of oxalic acid (in the proportion of one grain of oxalic
acid to the ounce of water) or glacial acetic acid has
been added. Wash by rotating the saucer, then pour
off the water and place the sections in a stoppered
bottle containing absolute alcohol ; which should like-
wise contain a drop of either of the before-mentioned
acids. When all the water has been abstracted from
the sections by the alcohol (which will be in about ten
minutes) clear with oil of cloves, they are then quite
readv for mounting in Klein's' or dammar solution.
Clematis and other open sections take a very fine treble
stain by this method. Buckthorn and sycamore seem
to have a great affinity for the green stains, two minutes
in staining fluids being usually sufficient to colour the
walls of the central cells green and their contents of a
light scarlet. The staining of thin sections of potato
are equally effective, the starch granules being green,
the loculi scarlet, the depth of colour depending upon
the length of exposure to the atlas- scarlet, and mixed
green dyes; always allowing the malachite to be in
excess. 1
For double-stained vegetable tissues Mr. Barrett
prefers some of the cheaper dyes. The sections must
be first immersed in an aqueous one per cent, solution
of Crawshaw's aniline blue; then removed into a
strong acetic acid solution, which fixes the colour in
certain tissues, and removes it from others, while it
prepares the unstained portion for the reception of
another colouring material. It must again be removed
into a weak solution of magenta (Judson's dye), acidu-
lated with acetic acid : then washed and mounted in
glycerine jelly. By this process sections of burdock are
stained, the pith, very pale magenta colour; cellular
tissue, deep magenta ; spiral vessels of medullary sheath,
deep blue ; pitted vessels, blue ; cambium, deep blue ;
liber cells, dark magenta ; lactiferous vessels, deep
blue ; cuticle, parenchyma, pale blue ; epidermis, deep
(1) Transactio-M of the Uoral Microscopical Soe., page 870, 1881.
242 THE MICROSCOPE.
blue ; Lairs, pale magenta. It is almost needless to
add that both time and patience are required to attain
perfection in double staining.
Those, however, who, from want of time, cannot
follow out the details of the several processes should
pay a visit to the laboratory of the Messrs. Cole. 1
There they will find a large and choice selection of
specimens of animal and vegetable tissues, and which,
for perfection in staining, cutting and mounting, can-
not be surpassed.
The staining of vegetable tissues will give increased
interest to the study of botanical histology ; the student
in this way will obtain an insight into structure such
as can be secured by no other means.
The staining fluids most successfully employed by
Mr. Gilburt 3 for staining sections of woods and plants
blue and red by the aniline dyes are prepared as fol-
lows :
Magenta crystals . gr. J in ") -^ j
Alcohol ... loz. )
Then Nicholson's soluble ~)
pure blue . . . gr. in /
Alcohol . . 1 oz., to f L
which has been added acid nitric 4 drops )
Both solutions should be filtered.
For use take 2 parts of the blue and add it to 7 parts
of the magenta, and thoroughly mix.
Place the section in the mixture for about a minute,
then remove it to absolute alcohol, from that to oil of
cloves or benzole, and finally mount in balsam and
benzole.
To fix the magenta it is necessary to pass the sections
through benzole.
As a preparation for staining, all tissues should be
"bleached. This is effected in the case of soft vege-
table stems in alcohol; the use of which, although
(1) Arthur Cole and Son, 53, Oxford Gardens, Netting Hill, TV., are
engaged in the publication of " Studies in Microscopical Science," that is,
prepared specimens of typical objects beautifully stained, and drawings of
the samfl, with directions for staining and preparing sections for the micro-
scope. T commend these Studies to the notice of students and teachers.
<2) Journal of the Quekett Microscopical Club.
BLEACHING SECTIONS. 243
it discharges the natural colour, considerably abridges
the process. It has a further advantage, as the cell-
contents, starch, chlorophyll granules, &c., are pre-
served intact, and the nucleus, when it exists, is ren-
dered more palpable by staining.
When the stem is hard and brown, a solution of
chloride of lime should be used. A quarter of an
ounce of chloride dissolved in a pint of water, well
shaken and stood by to settle down, then pour off the
clear fluid for use. For hard tissues this solution
answers well, but it is not suitable for leaves, as they
require not only bleaching, but the cell-contents should
be dissolved out to render them transparent. A solu-
tion of chlorinated soda answers well for both stems
and leaves. It is prepared as follows :
To one pint of water add two ounces of fresh
chloride of lime, shake or stir it well two or three
times, then allow it to stand till the lime has settled.
Prepare meanwhile a saturated solution of carbonate
of soda common washing soda. Now pour off the
clear supernatant fluid from the chloride of lime, and
add to it, by degrees, the soda solution, when a preci-
pitate of carbonate of lime will be thrown down ; con-
tinue to add the soda solution till no further precipitate
is formed. Filter the solution, and keep it in a well-
stoppered bottle in the dark, otherwise it speedily
spoils.
Sections bleached in chlorinated soda must, when
white enough, be washed in distilled water and allowed
to remain in it for twenty-four hours, changing the
water four or five times, and adding a few drops of
nitric acid, or at the rate of eight or ten drops to the
half-pint, to the w r ater employed before the final wash-
ing takes place. From water transfer them to alcohol,
in which they must remain for an hour or more.
Sections may be stained in two colours, either by
alternate or single immersions.
The first process is as follows : Transfer the section
from alcohol to magenta dye for about twenty minutes,
then remove and soak in alcohol till the colour is re-
moved from the parenchyma ; next place it about a
B 2
244 THE MICROSCOPE.
minute in the blue dye, transfer it to alcohol for a few
seconds, and to absolute alcohol for a few seconds ;
remove it to oil of cloves, in which it should remain till
quite clear. It is now ready for mounting in benzole
balsam.
For staining by a single immersion, add twelve drops
of the blue dye to seven of the magenta, and thoroughly
mix. Into this purple stain place the sections for about
a minute, then remove them to alcohol ; shake well for
a few seconds, and proceed as by the former method.
The magenta dye stains the woody fibre and vascular
tissue; the blue the parenchyma, cambium layer, and
medullary rays; while the pith and bark remain neu-
tral, or partake of both.
In deciding upon which colour should be first em-
ployed, this will depend upon the particular structure
it is wished to bring out more forcibly than another.
To show the structure of the lamina use the blue
stain, because it displays the cell -walls far more dis-
tinctly than magenta. There is some difficulty in
fixing magenta, unless it is passed through benzole
and not oil of cloves ; benzole may, however, produce
an injurious effect upon the tissue.
In using blue dye, no fixed time can be laid down
for immersion, this so much depending upon the
density or permeability of the tissue. Dr. Beatty
recommends that two solutions should be prepared a-
quarter and a half-grain solution, and that the leaf
should be transferred to the stronger if the staining is
not completed in the weaker in half an hour. There
is, however, one objection to this, that far too much
colour may be taken up in parts, and giving the
sections a very mottled appearance. Experience proves
that far better results are usually obtained by the
use of weaker dyes, although a longer time may be
required.
As a general rule, sections should be left in the dye
till equally stained throughout, then remove them into
alcohol, brush the surfaces well with a camel-hair
pencil, and transfer them to absolute alcohol for a few
minutes, thence into oil of cloves till quite clear, and
STAINING BACTERIA. 245
finally into clean oil of cloves, where they must remain
ten or fifteen minutes before mounting in balsam and
benzole. Preparations stained blue may be left in oil
of cloves for a week or more without doing them any
injury.
The staining process has greatly facilitated the study
of the minuter forms of life. For staining Bacilli employ
the aniline reds as follows : Fuchsia in crystals, one
centigram ; alcohol, from twenty to twenty-five drops ;
distilled water, fifteen cubit centimetres : mix. The
colour stain taken by the bacilli is less intense than
that taken by the micrococci, and this serves to dis-
tinguish the one from the other. The minute size of
the bacilli renders their life history and study of their
growth under artificial cultivation a work of great
difficulty. Considerable importance, however, attaches
to these organisms obtained by cultivation, from the
fact that the resulting forms can be compared with
those found in connection with disease. Blood cor-
puscles are better studied under osmic acid staining
fluid, and which shows that most of the white corpuscle
may be divided into two or more kinds and forms.
One set is stained black by osmic acid, and another,
which contains granulous matter not fatty, is stained
red by an eosine solution. The best mode of showing
the three forms of corpuscles is to fix the blood in the
network of the smaller blood vessels ; for instance, in
the'choroid coat of the eye, by cutting the eye of the
frog into two parts, subjecting the section to the
vapour of osmic acid for twelve hours, then wash the
segment in distilled water, and detach the capillary
layer from the retina, spread it out on a glass slide and
stain it with ha3matoxylate of eosine. The corpuscles
will by this process be seen to be of three kinds the
ordinary, granular, and fatty. Care must be taken, as
the vapour of osmic acid is of a corrosive nature.
M. Brandt finds hoematoxylin and Bismarck-brown
suitable colours for staining living unicellular organ-
isms. For amoebae and similar delicate bodies a
dilute solution of hcematoxylin must be allowed to act
for only a short time, not more than an hour, when
246 THE MICEOSCOPE.
they must be transferred to pure water. The nuclei
will be seen stained pale violet ; although at first no
visible change is produced in the contractile vacuole,
later on it assumes a yellowish tint, and finally becomes
brown. Double staining may likewise be effected by
first using Bismarck-brown for an hour, and then
liEematoxylin for a shorter time ; the protoplasm alone
remains uncoloured : the difference in colour showing
which of the granules are fatty and which are nuclein.
The strength of the Bismarck-brown stain should not
exceed one in 3,000 or 5,000. A solution of safranine,
one of the red aniline dyes, one or two grains to the
ounce of water, is an excellent stain and test for amy-
loid, starchy matters in unicellular plants. The starch
is stained of a fine orange colour, and other portions of
a rose colour.
For bleaching sections before staining Mr. Marsh
resorts to the direct action of free chlorine, generated
in a pair of Woolf-bottles.
Fill one of the bottles about two-thirds full of filtered
water, and into this place the sections to be bleached.
Into the other bottle put a sufficient quantity of crys-
tals of chlorate of potash to slightly cover the bottom,
and pour upon them a drachm or two of strong hydro-
chloric acid. Connect the bottles by the glass tubes,
and the yellow vapour of chlorine will be observed to
pass into the water contained in the first bottle, and
effectually and safely bleach the sections. The time
required for bleaching will vary with the nature of
the sections operated upon. Decoloration having been
effected, the sections must be removed and thoroughly
washed to eliminate all trace of chlorine before employ-
ing a staining agent.
Cementing. The following cements are recommended
by Mr. Groves for mounting stained preparations :
Cements. For balsam or glycerine jelly mounts al-
most any varnish will do, but for fluids, glycerine, &c.,
it is necessary to have one tough and which will prevent
leakage. The following will be found most efficient :
]. Mastic and Bismuth. Dissolve gum mastic in
chloroform, and thicken with nitrate of bismuth.
CEMENTING. 247
The solution of mastic should be nearly saturated.
2. Oxide of Zinc, Dammar, and Drying Oil. Bub up
well-ground oxide of zinc, 2oz., with drying oil, to the
consistence of thick paint. Then add an equal quantity
of gum dammar, previously dissolved in benzoline, and
of the thickness of syrup. Strain through close-meshed
muslin. Keep in well-corked bottle, and, if necessary,
thin with benzoline.
3. Kitton's Cement is made of white lead and red
lead in powder and litharge powder in equal parts.
Grind together with a little turpentine, until tho-
roughly incorporated, and then mix with gold size.
The mixture should be thin enough to use with a
brush; in- using one coat should be allowed to dry
before applying another ; no more cement should be
mixed with the gold size than is required for imme-
diate use, as it sets quickly, and becomes unworkable.
Certain precautions are necessary to be observed in
using varnishing fluid or glycerine preparations :
1. Use no more glycerine or fluid than is just neces-
sary to fill up the space beneath the cover.
2. If the medium should escape beyond the cover-
glass, soak it up with a piece of blotting-paper, and ba
careful not to press the cover, or the cement will run
into the cell.
Of preservative mounting media, the most useful
are balsam, glycerine, and glycerine jelly.
Canada balsam should be exposed to heat until it
becomes quite brittle when allowed to cool, then it
should be dissolved in benzole till as thin as glycerine,
and should always be used cold.
Glycerine. Specimens which have been hardened
in chromic acid or bichromates may be mounted in
pure glycerine alone, but if they have been hardened
in spirit, glycerine and carbolic acid, in the propor-
tion of glycerine fifteen parts to carbolic acid one
part, is better, as it is less refractive, and prevents tho
sections becoming granular. For carmine stained
preparations it is well to add a trace of acetic acid
to the glycerine (2m., loz.). Glycerine jelly is a good
medium, as it offers the advantages of glycerine with-
248
THE MICROSCOPE.
out the chance of leaking, but it is rather difficult
to prepare, and, therefore, had better be bought.
A jelly composed of glycerine and gelatine equal
parts is very useful ; the glycerine
should be warmed, and the gelatine
(Nelson's) be allowed to dissolve
in it.
Acetate of potash in a saturated
solution is used for some prepara-
tions, but is liable to leak.
Injecting Small Animal Bodies.
For making injections it is essential
to have a proper syringe. One of
brass is the best, and of such a size
that the top of the thumb may
cover the button at the top of the
piston-rod when drawn out, while
the body is supported between the
two fingers. Fig. 143Z represents
the syringe, a is the body, with a
screw at the top for the purpose
of firmly screwing down the cover I after the piston c
FIG. 143L Injecting
Syringe.
FIG. 143;)i. Melting Vessel.
is replaced ; e is a stop-cock, to the end of which either
of the smaller pipes g can be fixed. The transverse
INJECTING APPARATUS. 249
wires are for securing them tightly with thread to the
vessels, into which they may be inserted. In addition
to the syringe, two or three tinned vessels, to contain
size, injecting fluid, and hot water, are necessary.
The size must be kept hot by the aid of a water bath ;
if a naked fire be used, there is danger of burning it.
A convenient form of apparatus for melting the size,
and afterwards keeping it at a proper temperature, is
shown in fig. 143?;?..
A pair of strong forceps, for seizing the vessel, and
a small needle, fig. 143#, is also necessary for passing
the thread round the vessel into which the injecting
pipe has been inserted, completes the list of apparatus.
To prepare the material for opaque injections : Take of
the finest and most transparent glue one pound, break
it into small pieces, put it into an earthen pot, and
pour on it three pints of cold water ; let it stand
twenty-four hours, stirring it now and then with a
FIG. 143n,. Artery Needle.
stick ; set it over a slow fire for half an hour, or until
all the pieces are perfectly dissolved ; skim off the
froth from the surface, and strain through a flannel
for use. Isinglass and cuttings of parchment make
an excellent size, and are preferable for particular
injections. If gelatine be employed an ounce to a pint
of water will be sufficiently strong, but in very hot
weather it is necessary to add a little more gelatine.
It must be first soaked in part of the cold water until
it swells up and becomes soft, when the rest of the
water, made hot, is to be added. The size thus prepared
may be mixed with finely levigated vermilion, chrome-
yellow, blue smalts, or flake white.
To prepare the subject, the principal points to be
aimed at are, to dissolve the fluids, empty the vessels
of them, relax the solids, and prevent the injection
from coagulating too soon. For this purpose it is
necessary to place the animal, or part to be injected, in
U50 THE MICROSCOPE.
warm water, as hot as the operator's hand will bear.
This should be kept at nearly the same temperature
for some time by occasionally adding hot water. The
length of time required is in proportion to the size of
the part and the amount of its rigidity.
Cold Injection-mass. A. Wikozemski describes a
modification of Panseh's method. Thirty parts by
weight of flour, and one of vermilion, are mixed while
dry, and then added to fifteen parts by weight of
glycerine, and subjected to a continuous stirring until
of a homogeneous viscous consistency ; then two
parts of carbolic acid (dissolved in a little spirit) are
added to it, and finally thirty to forty parts of water.
This injection-mass is specially adapted for subjects
already injected with carbolic acid (in the proportion
of one and a half part by weight each of carbolic acid,
spirit, and glycerine, to twenty of water) : twenty-four
hours are allowed to elapse between the two injections.
Of Injecting Different Systems of Vessels witJi
Different Colours. It is often desirable to inject
different systems of vessels distributed to a part with
different colours, in order to ascertain the arrange-
ment of each set of vessels and their relation to each
other. A portion of the gall-bladder in which the
veins have been injected with white lead, and the
arteries with vermilion, forms a beautiful preparation.
Each artery, even to its smallest branches, is seen to
be accompanied by two small veins, one lying on
either side of it. In this injection of the liver, four
sets of tubes have been injected as follows : The
artery with vermilion, the portal vein with white lead,
the duct with Prussian blue, and the hepatic vein
with lake. There are many opaque colouring matters
which may be employed for double injections.
The structure of the kidney may be demonstrated as
follows : Inject into the jugular vein of an animal, as
soon as killed, say of a rabbit, a sufficient quantity of a
one per cent, solution of the yellow prussiate of potash,
and immediately afterwards inject through the renal
artery a sufficient quantity of a weak solution of per-
chloride of iron, to distend the capillaries of the kidney.
INJECTING THE LOWER ANIMALS. 251
After the second injection has been made, pieces of kid-
ney which have become of a bluish colour are cut off with
a razor, and steeped in a one per cent, of osmic acid, in
which the pieces must be left to harden from twelve to
twenty-four hours. They should be small enough to
allow the osmic acid to penetrate freely. After they
are removed from the acid, they must be thrown into
distilled water for half an hour, and finally kept for
examination in alcohol. This method imparts a bluish
tint, with a tinge of violet, to the protoplasm and
nucleus, whilst the cells of the straight tubules receive
no coloration.
Injecting the Lower Animals. The vessels of fishes
are exceedingly tender, and require great caution in
filling them. It is often difficult or quite impossible
to tie the pipe in the vessel of a fish, and it will
generally be found a much easier process to cut off
the tail of the fish, and put the pipe into the divided
vessel which lies immediately beneath the spinal
column. In this simple manner beautiful injections of
fish may be made.
Mollusca. (Slug, snail, oyster, &c.) The tenuity of
the vessels of the mollusc often renders it impossible
to tie the pipe in the usual manner. The capillaries
are, however, usually very large, so that the injection
runs very readily. In different parts of the bodies of
these animals are numerous lacunas or spaces, which
communicate directly with the vessels. Now, if an
opening be made through the integument of the
muscular foot of the animal, a pipe may be inserted,
and thus the vessels may be injected from these lacunae
with comparative facility.
Insects. Injections of insects nid,y be made by
forcing the injection into the general abdominal
cavity, when it passes into the dorsal vessel and is after-
wards distributed to the system. The superfluous
injection is then washed away, and such parts of the
body as may be required, removed for examination.
Injection of Invertebrate Animals. Gr. Joseph uses
filtered white of egg, diluted with 1 to 5 per cent, of
carmine solution, for cold injections. This coagulates
252 THE MICROSCOPE.
when immersed in dilute nitric, chromic or osmie
acids, but remains transparent, and is sufficiently indif-
ferent to reagents. A mass of similar properties is
made of glue liquid when cold, coloured with the
violet extract of logwood reduced with alum. Injec-
tion is effected in the case of worms (leech and earth-
worm) by way of the ventral or dorsal vessel, with
large Crustaceans by the heart or the ventral vessel
which lies in the sternal canal. In many cases,
especially when lacunar spaces have to be filJed, use-
ful preparations are obtained by natural injection
(auto-injection, or autoplerosia). Natural injection of
Medusa3 is effected without injuring the vessels ; in
the case of Crustaceans, Insects, and Mollusca, through
a slit with an opening at the side remote from it.
Medusa3 are laid in a glass vessel, with the bell down-
wards, and a bell- jar ending in a narrow tube above
is placed over it and made air-tight; after the Medusa
is covered with the injection-mass, the air in the glass
is exhausted, and as the sea- water runs out by slits
in the lower side of the annular canal, the coloured
fluid runs in. In the case of leeches and large
species of earthworms, the natural injection is made
from the ventral sinus. In all cases a glass tube is
nsed, with a finely drawn-out point. The injection
is complete when the injection issues from the counter-
opening. Animals to be injected alive are kept quiet
by cold (upon ice). Besides the animals mentioned,
large caterpillars, beetles, Libellulidse, Iarva3, locusts,
&c., all serve as objects for injection ; the glass can-
nula being introduced into the posterior end of the
dorsal vessel, and the counter-opening made in the
ventral vessel, and vice versa.
Staining Living Protoplasm with Bismarck Drown.
L. !\ Henneguy having treated Paramoecium aurelia,
with an aqueous solution of aniline brown (known as
" Bismarck Brown "), found that they assumed an
intense yellow-brown colour. The colour first appears
in the vacuoles of the protoplasm, and then in the
protoplasm itself, the nucleus generally remaining
colourless, and thus becoming more visible than in the
STAINING LIYING BODIES. 253
normal state. Infusoria thus coloured were kept for
nearly fifteen days. If a yellow-tinted Paramoecium is
wounded or compressed so as to cause a small quantity
of the protoplasm to exude, it is seen that it is really
the protoplasmic substance which is coloured. All
Infusoria may be equally stained with Bismarck
brown, but no other aniline colours employed exhibit
the same property they only stain the Infusoria after
death, and some of them are in fact poisonous. As it
is generally admitted that living protoplasm does not
absorb colouring matters, and that Infusoria are essen-
tially composed of protoplasm, an attempt has been
made to ascertain whether protoplasm in general, of
animal or vegetable origin, behaved in the same way
in the presence of aniline brown. A tolerably strong-
dose of Bismarck brown was injected under the skin of
the back of several frogs. After some hours the tissues
were uniformly tinted a deep yellow; the muscular
substance especially had a very marked yellow tint.
The frogs did not appear in the least incommoded.
Small fry of trout placed in a solution stained rapidly
and continued to swim about. Finally, a guinea-pig,
under whose skin some powder of Bismarck brown had
been introduced, soon presented a yellow staining of
the buccal and anal mucous membranes and of the skin.
Seeds of cress sown on cotton soaked with a concen-
trated solution of the Bismarck brown sprouted, and
the young plants were strongly stained brown; but on
crushing the tissues and examining them under the
microscope, it was ascertained that the protoplasm of
the cells was very feebly coloured ; the vessels, on the
contrary, showed a very deep brown staining up to
their termination in the leaves. The mycelium of a
mould which had been developed in a solution of
Bismarck brown, was clearly stained after having been
washed in water, whilst it is known that the mycelium,
which frequently forms in coloured solutions, picro-
carmine, haematoxylin, &c., remains perfectly colour-
less. Other aniline colours injected under the skin of
frogs stained the fundamental substance of the con-
nective tissue as deeply as did the Bismarck brown ;
254
THE MICROSCOPE.
but the cells of the muscular substance remained
perfectly colourless. The author concludes, therefore,
that Bismarck brown possesses the property of colouring
living protoplasm both in plants and animals.
Mr. Collins has introduced a very complete Mounting-
Case, which will prove useful to microscopists, especially
so to those who devote a good deal of attention to the
preparation of specimens. A place is here found for
everything: the little box contains: Shadbolt's turn-
table, brass table, spirit-lamp, pipettes, spring clips,
wooden clips, tweezers, tin cells, balsam, marine glue,
asphalte, turps, gold size, thin glass covers, glass slips, and
five extra bottles. The price of this neat and convenient
case is 30s. Another box, more particularly adapted for
anatomical purposes, includes a neat injecting apparatus.
Fig. 14S0 Collins' Mounting Callnet.
FUNGI, ALG.-K, LICIIKNS. ETC.
8 * : '*
TuflVn West, del
PART II.
E VEGETABLE KINGDOM VITAL CHARACTERISTICS OF CELLS THE PRO-
TOCOCCITS PLUVIALIS OSCILLATOR!^ FUNGI ALGJE DESMIDACE^E
MOSSES FERNS STRUCTUEE OF PLANTS STABCH ADULTERATION OV
ARTICLES USED FOR FOOD PREPARATION OF VEGETABLE STRUCTURE?-.
ETC.
I.NCE the introduction of the achro-
matic microscope, we have obtained
nearly the whole of the valuablo
information we possess of the mi-
nute structure of plants. Indeed
in no department of nature has
microscopic investigation been more
fertile of results than in that of
the vegetable kingdom. The hum-
blest tribes of plants have had
for microscopists an attraction,
unequalled by that of any other
department of nature, from the
time of our countryman Eobert
Brown, down to the present day.
Although Brown had observed and
recorded certain facts in the phy-
siology of vegetable life, it was
Professor Schleiden's labours that
brought to light the great truth,
"that the life-history of the individual cell is the first
important and indispensable basis whereon to found a
true physiology of the life-history of plants, as well aa
that of the higher orders of creation."
256 THE MICROSCOPE.
Mirbel had shown that all the different forms of vege-
table tissue are developed from cells which enter into the
formation of the embryo plant. Schleiden followed Mir-
bel in tracing out the development of the tissues of the
fully formed plant from the nucleated cells composing
the embryo ; and he also studied the mode of formation
of the nucleated cell itself. On this point Schleiden
came to the conclusion that the nucleus is the germ of the
plant-cell, hence he named it the " cytoblast." Miiller
subsequently contended that the spinal chord is com-
posed of cells, resembling vegetable cells ; Schwann dis-
covered a nucleus in these cells, and observed that
the various forms of cells in animal structures is
similar in every respect to those of plants. From
his investigations he was led to the philosophical
generalization, that the tissues of the animal body
and those of plants were formed from cells. The
various tissues, although formed from cells in
different stages of their development, and not neces-
sarily the formative element of all cells in their fully
formed stage, for cells, when fully formed, in some cases
do not undergo further development ; for example, in
the parenchyma of glands when they break up, and
are resolved into the secretive matter.
The prevailing opinion now is and of which neither
Schleiden nor Schwann appear to have had a true
notion that nuclei and cells are propagated by the sub-
division of pre-existing nuclei and cells. As to the
particular endowments and potentialities of the dif-
ferent kinds of cells whereby each is developed and
converted into its own special tissue, and indifferently
into any kind of tissue, I must refrain from discussing,
as it would lead me into a region of speculation.
" If nature," writes Humboldt, " had endowed us
with microscopic powers of sight, and if the integu-
ments of plants were transparent, the vegetable king-
dom would by no means present that aspect of
immobility and repose under which it appears to our
senses." And so with regard to the instruments of
motion in the higher classes of creation, the muscles
of animals very soon disappear as we descend in the
CHARACTERISTICS OF CELLS. 257
scale to tlie simplest forms of life ; nevertheless, we
cannot deny animality to those minute creatures as
the Amoeba in which we are quite unable to dis-
tinguish either muscle, or any other distinct organ.
Hence there is danger of believing that to be simple
which in reality only seems to be so.
Plants and animals, if seen at the earliest stage of
existence, present themselves to our eyes as an aggregation
of transparent cells. Everything prior to the appearance
of the cell may, in the actual state of our microscopical
knowledge, be considered as not fully and certainly demon-
strated ; and therefore it is incumbent upon us to take our
starting-point from the simple cell, which is the same, in re-
spect to its principal characters, in animals and vegetables.
The external coating of a cell is nearly or quite solid and
transparent, and with no indication of structure; while
in its interior is found a liquid or solid substance, with a
nucleus either adhering to its wall or within its cavity.
A nucleolus can sometimes be demonstrated within the
nucleus ; and (a state common to all living cells) an in-
cessant mutual interchange of materials is going on between
the fluid contents and matter external to the cell, by
a process termed osmose, or diffusion, which causes a per-
petual variation in its relative condition. Chemical reagents
give a manifestly different result in the animal and vege-
table cell, hence we may conclude that there is an important
difference in their chemical composition. The vegetable
cell has an extremely fine delicate membrane lining the
inner wall, to perceive which we must have recourse
to reagents, and then we find the apparently simple cell-
wall made up of two layers, each differing in composition
and properties. t The inner layer has received the name of
primordial utricle, and ; ts composition has been shown
to be albuminous ; agreeing in this respect with the form-
ative substance of animal tissues. The external layer is
regarded as the cell-wall, although it takes no part, essen-
tially, in the formation of the cell ; it is composed of cellu-
lin y a material allied to the cellulose of vegetable tissues.
The contents are more or less coloured : the internal
colouring substance is termed endochrome ; when green it
is called chlorophyll.
258 THF MICROSCOPE.
The successive changes in the cell contents furnish
other very important characteristics, such as the dis-
appearance and re-absorption of the nucleus ; this occurs
in every cell at some period of its existence ; in the cells
of the higher plants, the inner membrane, or primordial
utricle, entirely disappears. The Algae, and some few
unicellular plants, form an exception to the rule. In the
animal, the enlargement of the cell-wall takes place in a
uniform manner, whereas in the plant this is effected by
a deposition of successive layers on its inner surface, in the
shape of continuous rings, spiral bands, or other inter-
mediate forms. Then the wall not only increases in size,
but appears to possess a power of separating and appro-
priating certain substances, as lime, silica, lignine, &c.,
which form the so-called cuticle. In animals as well as
in plants, new cells are formed within the old cells ; but
in the former, this process of a new formation begins in
the extracellular fluid, while in the latter it is mostly
endogenous. Multiplication of vegetable cells is effected
by three different modes : 1st, Many nuclei appear in the
maternal cell floating together with granular matter;
around each collects a minute vesicle, this gradually
increasing fills the maternal cell, which is eventually
absorbed. 2d, The internal substance of the cell divides
into two or more portions, each being furnished with a
nucleus. 3d, In the third mode of multiplication, the
wall itself of the maternal cell becomes gradually con-
stricted, and divides into two portions.*
* "In most cells, especially when young, a minute, rounded, colourless
body may be seen, either.in the middle or on one side, called the nucleus. This is
very distinct in a cell of the pulp of an apple ; and within this nucleus is often
to be seen another smaller body, frequently appearing as a mere dot, called the
nucleolus.
" The nucleus is imbedded in a soft substance, which fills up the entire cell ;
this 18 the protoplasm (protos, first, plasma, formative substance). As it is very
transparent, it is readily overlooked ; but it may usually be shown distinctly
by adding a little glycerine to the edge of the cover with a glass rod, when it
contracts and separates from the cell-walls. The protoplasm in some cells is
semi-solid, and of uniform consistence, while in others it is liquid in the centre,
the outer portion being somewhat firmer, and immediately in contact with the
cell-wall. In the latter case it forms an inner cell to the cell-wall, and is called
the primordial utricle. The terms ' protoplasm ' and ' primordial utricle ' are
however used by some authors synonymously.
"The protoplasm is the essential portion of the cell, and it forms or secretes
the cell-wall upon its outer surface in the process of formation of the cell, con-
sidered as a whole. It is also of different chemical composition, from the cell
wall being allied in this respect to animal matter." Griffiths.
CELL-DEVELOPMENT. 259
Taking for our examination the more simple organisms
among vegetables, we shall find numbers which present, in
their earliest as well as in their permanent state, the cell
in its simplest condition, and its reproduction a bare re-
petition of the same thing. Unicellular plants, then, in
the strictest sense, are represented only by those in which
the whole cycle of life is completely shut up in the one
cell ; the first reconstruction or division being at once the
commencement of a new cycle, in which, consequently,
the whole vegetative life is run through in the same cell
where the propagation also appears.
Fig. 144. Cell Development. (Protococcus pluvialis.)
Protococcus plnvialis, Kiitzing. Hcematococcus pluvialis, Flotow. Chlamido-
coccus versatilis, A Braun. CJilamidococcus pluvialis. Flotow and Braun.
A, division of a simple cell Into two, each primordial vesicle having developed a
cellulin envelope around itself; B, Zoospores, after their escape from the
cells ; c, division of an encysted cell into segments ; D, division of another
cell, with vibratile filaments projecting from cell- wall ; E, an encysted cell ;
., division of an encysted cell into four, with vibratile filaments projecting ;
O, division of a young cell into two.
The most widely distributed of these single-cell plants
is the Palmoglcecb macrococca, of Kiitzing, which spreads
itself as a green slime over damp stones, walls, &c. If a
email portion be scraped off and placed on a slip of glass,
and examined with a half or quarter-inch power, it will be
Been to consist of a number of ovoid cells, having a trans-
parent structureless envelope, nearly filled by a granular
matter of a greenish colour. At certain periods this mass
divides into two parts, and ultimately the cell becomes two.
Sometimes the cells are united end to end, just as we see
260 THE MICROSCOPE.
them united in the actively-growing yeast plant ; but in
this case the growth is accelerated, apparently, by cold and
damp. Another plant belonging to the same species, the
Protococcus pluvialis, is found in every pool of water, the
spores of which must be always floating in the air, since
it appears after every shower of rain.
Unicellular plants occur in the series of Fungi and
Algce, which have many and very varied correspondence in
morphological respects. The unicellular Algae that is to
say, Algae, the contents of which, containing already
organized particles, are inclosed in a single, semifluid
envelope, and this again in a cell-membrane, often
consisting of several layers of different kinds ; and many,
moreover, possess the power of dividing into several
secondary cells, for the most part equivalent to the primary
cell. To this species of unicellular plant belongs Protococcus
pluvialis. That this is the case is clearly seen in the still
form of this plant, which is most distinctly characterised
by its cell-membrane, a more or less thick though always
colourless envelope. It never, however, secretes true
thickening layers on the surface. Although this cell-
membrane exhibits all the optical characters of one com-
posed of cellulose, it is impossible to demonstrate the
presence of that principle by means of iodine and sulphuric
acid ; it is not coloured by those reagents even after the
contents of the cell have been expressed.
The contents vary much in consistence, colour, solid
and fluid constituents ; the red and green portions of
which appear to be of equal physiological importance.
The green colour is removed by ether, on the evaporation
of which solvent there remain green as well as colourless
drops. Dilute sulphuric acid at first renders the colour
paler; but its prolonged action produces a bright green
hue, which gradually becomes more and more intense, and
often almost a blue-green. Hydrochloric acid has a simi-
lar effect ; a tinge of brown is produced by nitric acid.
Carbonate of potash scarcely affects the green colour ; it
is gradually but totally destroyed by caustic potash, the
contents at the same time swelling and becoming
transparent.
The change of colour from green to red in Eugkna,
UNICELLULAR PLANTS. 2G1
appears to "be a process very nearly allied to that which
takes place in Protococcus, if it be not identical with it.
The red substance of Prot. pluvialis is not always of an
oily aspect; it only becomes so in more advanced age.
And according to Cohn's researches, this oily material >u
much more generally distributed than has been supposed,
among the lower Algae; occurring in many true brown
ipores, such as of (Edogonium, Spirogyra, VaucJieria, &c.
When still or motile cells of Protococcus are brought in
contact with a very weak solution of iodine, they become
internally, in most parts, of an intense violet or blue colour.
"With respect to the solid constituents of the Protococcus
cell contents, they may be distinguished into chlorophyll
vesicles, colourless or green particles, amylaceous granules,
and nucleus. The motile form of Protococcus consists,
as it were, of two cells, one within the other, both of which,
however, differ essentially from the common vegetable cell :
the external having a true cell-membrane and fluid con-
tents ; the other, or internal one, with denser, muco-gela-
tinous coloured contents, but without a true cell-wall.
Cohn called the external transparent vesicle the " enve-
loping " cell," and the internal coloured one the " primor-
dial cell." The term "primordial sac, or utricle," can
only be applied to its peripheral layer, and not to that
together with the contents.
The form of Protococcus (fig. 144) presents a perfect
analogy between the primordial cell and the nucleus of
the common plant-cell. The filaments which proceed
from the central mass to the peripheric cell-wall, are
tubular, giving passage to the red molecules from the
central mass. These filaments, however, which proceed
from the outer wall of the primordial cell towards the
inner surface of the enveloping cell, correspond morpho-
logically to the so-termed mucous filaments by which the
cytoblasts are commonly retained in the centre of their
cells. That they also correspond chemically with these,
is proved by the fact that they are rendered more distinct
by iodine, and that they can be made to retract by means
of reagents; and in fact they exhibit, in the course
of development, peculiarities which characterise them as
consisting of protoplasm.
262 THE MICROSCOPE.
The existence of delicate threads passing from the
central mass to the enveloping cells, and the appearance
occasionally of little particles having molecular motion,
serve to show that the contents .of the enveloping cell are
less of a gelatinous consistence, than of a fluid nature.
And the continuity of the primordial cell-wall with the
filaments proves it is surrounded only with a layer of
protoplasm, and is not inclosed in a dense membrane
of cellulose. The most distinctive characteristic of the
primordial cell, and what appears to constitute its most
essential importance in the life of the cell in general, but
particularly in that of the zoospore, consists in its being
the contractile element of the vegetable organism that
is to say, that from an intrinsic activity it possesses the
faculty of altering its figure, without any corresponding
change in volume.
The Protococcus pluvialis has true motile organs,
namely, two long vibratile flagella arising from the pri-
mordial cell (fig. 144, B, a), which, passing through two
openings in the enveloping cell, move about in the water.
These organs, during the life of the cell, move so
rapidly, that it is then difficult to perceive them ; they
are recognized by the currents produced in the water ;
as death approaches motion slackens and they become
evident enough. They are also rendered very distinct by
iodine. They are always protruded about the extreme
point of the conical elongation, at the anterior end of the
primordial cell, and in such a manner as to appear to be
mere continuations of its substance. Since these pro-
cesses consist of protoplasm, it is evident that the flag-
ella must be regarded as composed of the same sub-
stance. They resemble, in some respects, the so-called
proboscis of certain Infusoria, such as Euglena and Ifo-
nads, and do not differ very materially from the non-
vibratile, retractile filaments of Acineta and Actinophrys.
It Is only that portion of the vibratile filaments beyond
the enveloping cell that exhibits any motion, the portion
within the outer cell being always motionless, and in that
part of their course the filaments appear to be surrounded
with a sheath. This seems to be the case, not only from.
the greater thickness at that part, but also from the cir-
UNICELLULAR PLANTS. 263
cumstance that when, passing from the cell form into
the still condition, the flagella disappear, the V-shaped,
or forked internal portions remain visible. And it is
then, also, that the openings through the enveloping
cell-wall become, for the first time, visible.
Perhaps the most remarkable of all the numerous
aspects presented by Protococcus pluvialis, is the form of
naked zoospores named by Flotow Hcematococcus porphyro-
cephalus. These are extraordinarily minute globules, con-
sisting of a green, red, and colourless substance in unequal
proportions. The colourless protoplasm in them, as in all
primordial cells, constitutes the outermost delicate boun-
dary; the red substance is for the most part collected
towards the anterior end in minute spherules ; the granular
green substance occupies more the under part, while the
middle is usually colourless.
Piopagation depends upon a division of the cell
contents, particularly of the colourless or coloured proto-
plasm, or of the primordial sac. This body, without any
demonstrable influence of a nucleus, is capable of sub-
division into a determinate number of portions. Each of
these acquires a globular figure, and in the next place
surrounds itself with an envelope of protoplasm, and then
represents a visible organism, which after the reabsorption
of the parent cell-membrane, is capable of existence as an
independent reproductive individual. Besides these, which,
are the most usual modes of propagation viz. that of the
still-colls into two, and of the motile into four, secondary
cells there are a number of others which may be con-
sidered as irregular, and in which forms are produced
which do not re-enter the usual cycle until they have
gone through a series of generations. Sometimes, under
certain circumstances, the cell-contents of the still form
separate into eight or more portions, which become naked
zoospores of small size (fig. 144 B.) It is not quite
clear what becomes of this form of motile zoospores, but
there seems reason for believing that they occasionally
develop an enveloping cyst, and thus become encysted
zoospores, and at other times secrete a cellulose tissue,
and become still-cells; but most of them probably
perish without any further change. They would thus
264 THE MICROSCOPE.
correspond with the smaller motile spores observed by
Thuret and A. Braun in other Algae (the Fucoid, &c.),
associated with the larger germinating spores, them-
selves deprived of the germinative faculty.
It appears that both longitudinal and transverse
division of the primordial cell may take place ; but that
the vibratile filaments of the parent cell retain almost to
the last moment their function and their motion after
the primordial cell inclosed by it has long been detached
as a whole, and become transformed into the indepen-
dent secondary cells (fig. 144, G).
The most striking of the vital phenomena presented by
this organism is that of periodicity. Certain forms for
instance, encysted zoospores, of a certain colour, appear in
a given infusion, at first exclusively, then they gradually
diminish, become more and more rare, and finally dia-
appear altogether. After some time their number again
increases, and reaches as before to an incredible extent ;
and this proceeding may be repeated several times.
Thus, a glass which at one time presented only still
forms, contained at another nothing but motile ones. The
same thing may be observed with respect to segmen-
tation. If a number of motile cells be transferred
from a larger glass into a small vessel, it will bo found,
after the lapse of a few hours, that most of them have
subsided to the bottom, and in the course of the day they
will all be observed to be on the point of subdivision. On
the following morning the provisional generation will
have become free ; on the next, the bottom of the vessel
will be found covered with a new generation of self-divid-
ing cells, which again proceed to the formation of a new
generation, and so on. This regularity, however, is not
always observed. The influence of every change in the
external conditions of life upon propagation is very re-
markable. It is only necessary to pour water from a
smaller into a larger and shallower vessel, or one of a dif-
ferent kind, to at once induce the commencement of seg-
mentation in numerous cells. The same thing occurs in
other Algae ; thus the Vaucheria almost always develop
zoospores, at whatever time of year they may be brought
from their natural habitat into a room. Light is con.-
FRESH-WA/ER ALGJS. 265
ducive to tlie manifestation of vital action in the motile
zoospores, and they always seek it, collecting themselves
at the surface of the water, and at the edge of the vessel.
But in the act of propagation, on the contrary, and whea
about to pass into the still condition, the motile Pro-
tococcus cell seems to shun tne light; at all events it
then seeks the bottom of the vessel, or that part of the
drop of water in which it may be placed, furthest from
the light. Too strong sunlight, as when it is concentrated
by a lens, at once kills the zoospores. A temperature of
undue elevation is injurious to the development of the
more vigorous vital activity, that is to say, for the forma-
tion of the zoospores ; whilst a more moderate warmth,
particularly that of the vernal sun, is singularly favour-
able to it. Frost destroys the motile, but not the still
zoospores.*
StephanospJwera pluvialis is another variety of fresh-
water alga3, first observed by Cohn. It consists of a
hyaline globe, containing eight green primordial cells,
arranged in a circle (see Plate 1, No. 24 d). The globe
rotates, somewhat in the same manner as the volvox, by
the aid of projecting nagella, two of which are seen to pro-
ceed from each cell and pierce the transparent envelope.
Every cell divides first into two, then four, and lastly eight
young cells, each of which divides into a great number
of microgonidia, and are seen to have a motion within the
globe, and ultimately escape from it. Under certain cir-
cumstances each of the eight cells is observed to move
about in the interior of the mother- cell ; eventually they
escape, lose their flagella, form a thicker membrane as at
5, for a time become motionless, and sink to the bottom of
the vessel. If tlie vessel be permitted to become thorough-
ly dry, and again water is poured into it, motile Stephan-
osphsera reappear : from which circumstances it is proba-
ble that the green globes are the resting spores of the
plant. When in its condition of greatest activity its divi-
sion into eight is perfected during the night, and early in
the morning the young family escapes from the cell, soon
to pass through similar changes. It is calculated that in
On the "Natural History of Protococcus pluvialis," by F. Conn, translated
ly . Buk, F.R.S. for the Ray Society
Zbb THE MICKOSCOPE.
eight days, under favourable circumstances, 16,777,216
families may be formed from one resting-cell of Stephano-
sphaera, In certain of the cells, and at particular periods,
the remarkable amaboid bodies (Plate 1, No. 24 c), have
been noticed. There is a marked difference between
Stephanosphsera and Chlamydococcus, " for, while in the
latter the individual portions of a primordial cell separate
entirely from one another, each developing its own enve-
loping membrane, and ultimately escaping as a unicellular
individual j in the former, on the other hand, the eight
portions remain for a time united as a family." *
The simplest forms of vegetable life are met with in the
Confervoids, which are as interesting as they are in-
structive to the microscopist. The confervae consist of
tmbranched filamentous delicate cylindrical cells, placed
end to end ; their reproductive process is carried on by
zoospores produced from the cell contents. The fresh-
water genera are principally of a yellowish green colour ;
Bometimes presenting a striated appearance, which has
given rise to a supposition that confervoid filaments are
spiral. They are indeed plentifully distributed both in
fresh and salt-water.
Oscillatoriacece. The study of the structure of the
Oscillatorice is particularly interesting, from the fact that
we may not unreasonably expect to find in it a key to
the motive power from which they received their generic
name, and which now, for more than a century, has
formed an object of curiosity and interest to the micro-
scopist, without having received anything like a satis-
factory explanation.
The following different tissues are observable in the true
Oscillatorice: 1, An outer inclosing sheath ; 2, A special
cell-membrane, with its contents ; and 3, The axis, or pith,
of the filament.
The filaments of certain species are inclosed in sheaths
or continuous tubes, never showing any cross-markings
corresponding to the striae of the filament ; they are clearly
composed of a kind of cellulose, although they remain
unaffected by iodine. In other species, these tubes are
* See an interesting paper by P. Currey, F.K.S. Journal of Microscopiccfl
Science, vol. vi. 1858, p. 131 ; also by Mr. Wm. Archer, vol. v. 1865, p. 116
OONPBRVOID ALG2E. 267
absent, or have not yet been observed ; when present,
they will be found projecting on one or both sides of
Fig. U5. Conferva:.
I, Volvox globator. 2, A section of volvox, showing the flagellate margin of
the cell. 3, A portion more highly magnified, to show the young volvo-
eina, with their nuclei and thread-like attachments. 4, Spirogyra, near
which are spores in different stages of development. 5, Conferva flocossa.
6, Stigeoclonium protensum, jointed filaments and single zoospores. . 7,
Staurocarpus grnnlis, conjugating filaments and spores.
the filament, being somewhat longer than the latter.
Filaments inclosed in sheaths never, or but slightly, ex-
hibit their peculiar motion, although they may be seen
sliding in them, backwards and forwards, or leaving
them altogether.
The filaments themselves have been supposed to con-
sist wholly of protoplasm ; this view, however, is scarcely
correct, since the protoplasm is enclosed in a cell- mem-
brane. The cellulose always shows cross-markings
corresponding to the strise when such are observable
268
THE MICROSCOPE.
in the filament, and which divide it into distinct joints
or cells.
The presence of this cell-membrane may be best de-
monstrated by breaking up the filaments, either by moving
the thin glass cover, or by cutting through a mass of them
in all directions with a fine dissecting knife. On now
examining the slide, in most in-
stances many detached empty
pieces of this cell-membrane, with
its striae, will be found, as well
as filaments partly deprived of
the protoplasm, showing in those
places the empty, striated cel-
lulin coat. On the application
of iodine all these appearances
become unmistakably evident ;
the greater portions of the fila-
ment turning brown or red, while
the empty cells, with their striae,
remain either unaffected, or at
Fig. 146. Mesogiiavermicujaris, most present a slight yellowish
tint, as is frequently the case
with cellulose when old.
With regard to the contents of the cell, the protoplasm
(or endochrome) is coloured in the Oscillatorice, and is de-
posited within it in the form of circular bands or rings
around the axis of the cylindrical filament ; iodine stains
them brown or red, and syrup and dilute sulphuric acid
produce a beautiful rose colour. As to their mode of pro-
pagation, nothing positive is known. If kept for some
time they gradually lose their green colour those exposed
to the sun, much sooner than those less exposed ; a
stratum eventually becoming brown, sinks to the bottom
of the vessel, and presents a granular layer, embodying
great numbers of filaments in all stages of decay.*
The movements of the Oscillatorice are indeed very sin-
gular, so much so that it is in vain to attempt to explain
them as altogether dependent on physical causes, and
equally so to show that they are due to a sarcode or animal
* Dr. F. d'Alquen, "On the Structure of the Oscillatorise," Journal of
Microscopical Scioice, voL iv. p. 245. 1856.
composed of strings of cells co-
hering end to end.
MARINE ALG.E. 269
membrane. Their motion is not less lively than that of
the Bacteria,, which Dujardin and Ehrenberg placed among
infusional animalcules. To observe the movements of the
filaments, the very uppermost surface ought to be brought
into focus, leaving the margins rather undefined, bearing in
mind that the filament is not a flat but a cylindrical body.
Certainly, with regard to the movement, or the mechan-
ism by which it is effected, nothing positive is known.
The Bacillaria paradoxa is by far the most interesting
specimen of the genus ; the movements of which are very
remarkable, and so little understood, that it is rightly
called paradoxical.
The Marine Confervoid Alga3 present a general appear-
ance which might at first sight be mistaken for plants
very much higher in the scale of organization. In the
Ulvacea?, the frond has no longer the form of a filament,
but assumes that of a membranous expansion of the cell.
These cells, in which zoospores are found, have an in.
creased quantity of green protoplasm
accumulated towards one point of the
cell-wall; and the zoospores are ob-
served to converge with their apices
towards the same point. In, some
genera, which seem to be closely re-
lated in form and structure to the
Bryopsidece, we notice this important
difference, that the zoospores are de-
veloped in an organ specially destined
to this purpose, which presents pecu-
liarities of form, distinguishing it from
every other part of the branching
tubular frond. In the genus Derbesia,
distinct spore cases are seen, a young
branch of which, when destined to be- Fig 147 _
come a sporecase, instead of elongating drrhosa, with spores'
' i ! -j. 1 -L j> i j borne at the sides of tin
indenmtely, begins, after having arrived irancuuts.
at a certain length, to swell out into
an ovoid -vesicle, in the cavity of which a rapid accumu-
lation of protoplasma takes place. This is then separated
from the rest of the plant, and becomes an opaque mass,
surrounded by a distinct membrane. After a time a
270 THE MICROSCOPE.
division of the mass takes place, and a number of pyriform
zoospores, each of which is furnished with a crown of ciliae,
are set free.
In many families of the olive-coloured Alg, reproduc-
tion by zoospores is the general rule ; they differ, however,
in the arrangement of their flagella. These organs,
always two in number, are usually of unequal length,
and emanate not from the beak, but from a reddish-
coloured point in its neighbourhood. The shortest is
directed backwards, and seems to serve during the motion
of the spoje as a rudder. The longest, directed forwards, is
closely applied to the colourless beak. JEctocarpus is one
of the simplest formj of olive-coloured Algae, consisting
of branching filaments, the extremity of any of which is
liable to become converted into a sporangium, by the ab-
sorption of the septa of the terminal cells. The zoospores
are arranged in regular horizontal layers. In many genera
a peculiarity exists, the signification of which is not yet
completely understood namely, that of a double fructifi-
cation. The ovoidal sporangia contain numerous zoospores.
In the genus Cutleria (fig. 150), there is seen another feature
of interest : the appearance of two kinds of organs, which
seem to be opposed to each other as regards their repro-
ductive functions. The sporangia not only differ from
those of other genera, but the frond consists of olive-
coloured irregularly-divided flabelli, on each side of which
tufts (sori) consisting of the reproductive organs, inter-
mixed with hair-like bodies, are scattered. The zoospores
are divided by transverse partitions into four cavities, each
of which is again bisected by a longitudinal median
septum. When first thrown off they are in appearance so
much like the spores of Puccinia, that the}- may be mis-
taken for them ; they are, however, about three times larger
than those of the other olive-coloured algae.
The fruit of most olive-green Sea-weeds is enclosed
in spherical cavities under the epidermis of the frond,
termed conceptacles, and may be either male or female.
The zoids are bottle-shaped, each possessing a pair of cilia ;
the transparent vesicle in which they are contained is
itself inclosed in a second of similar form, and we have
no certain evidence of the function performed by the
MARINE ALGJE.
271
antheridia. In monoecious and dioecious Fuel, the female
conceptacles are distinguished from the male by their olive
colour. The spores are developed in each in the interior of
a perispore, which is borne on a pedicle emanating from the
inner wall of the conceptacle. They rupture the perispore
at the apex j at first the spore appears simple, but soon after
a series of changes take
place, consisting in a
splitting of the endo-
chrome into six or eight
masses, which become
spheroidal sporules. A
budding-out occurs in a
few hours' time, and ulti-
mately elongates into a
cylindrical tube. The
Vaucherice present a dou-
ble mode of reproduction,
and their fronds consist
of branched tubes, much
resembling in general
character that of the
ryopsidece, from which
indeed they differ only in respect of the arrangement of
their contents, chlorophyll. In that most remarkable
plant Saprolegnia ferox, which is structually so closely
allied to Vaucherice, though separated from them by the
absence of green colouring matter, we find a correspond-
ing analogy in the processes of its development. In the
process of the formation of its zoospores, we have an
intermediate step between that of the Algae and a class of
plants usually placed among Fungi. Cohn has shown us
that Pilobolus is structually more closely allied to the
former class than to that of the latter. Pilobolus has
a somewhat remarkable ephemeral existence ; the spore
germinates about mid-day, the plant grows till evening,
re-opens during the night, and in the morning the spore-case
bursts and the whole disappears, leaving behind scarcely
a trace of its former existence.
Red Sea-weeds, Floridece, present great varieties of struc-
ture, although comparatively little is known of their re-
Fig. 148. Development of Ulvce.
A, isolated cells of spores. B and c, clus-
tering of the same. D, cells in the fila-
mentous stage.
272 THE MICROSCOPE.
productive processes ; it will, however, be sufficient for our
purpose to notice the three leading forms. The first form,
to which the term polyspore has been applied, is that of
a gelatinous or membranous pericarp or conceptacle, in
which an indefinite number of sporidia are contained.
This organ may be either at the summit or base of a
branch, or it may be concealed in or below the cortical
layer of the stem. In some cases a number of sporidiuni-
bearing filaments emanate from a kind of membrane
at the base of a spheroidal cellular -perisporangium, by
the rupture of which the sporidia formed from the
endochrome of the filaments make their escape. Other
changes have been observed ; however, they all agree in
one particular, namely, that the sporidium is developed
in the interior of a cell, the wall of which forms its
perispore, and the internal protoplasmic membrane en-
dochrome, the sporidium itself, for
the escape of which the perispore rup-
tures at its apex.
The second form is more simple,
and consists of a globular or ovoid
cell, containing a central granular
mass, which ultimately divides into
four quadrate-shaped spores, which
when at maturity escape by rupture
of the cell- wall. This organ, called
a tetraspore, takes its origin in tho
cortical layer. The tetraspores are
arranged either in an isolated manner
along the branches, or in numbers to-
gether ; in some instances the branches
which contain them are so modified in
form that they look like special or-
gans, and have been called stichidia ;
as, for example, in Dasya (fig. 149).
Of the third kind of reproductive OP-
and two rows of tetm- gan a difference of opinion exists as to
S e eters Magni ' the signification of their antheridia;
although always produced in precisely
the same situations as the tetraspores and polyspores,
they are "agglomerations of little colourless cells, either
MARINE ALG^!.
273
united in a bunch as in Grijfithsia, or enclosed in a trans-
parent cylinder, as in Polysiphonia, or covering a kind of ex-
panded disc of peculiar form, as in Laurencia." According
to competent observers, these cellules contain spermatozoids.
Nageli describes the spermatozoid as a spiral fibre, which, as
it escapes, lengthens itself in the form of a screw. Thuret
does not coincide in this view ; on the contrary, he says
that the contents are granular, and offer no trace of a
epiral filament, but are expelled from the cells by a slow
motion. The antheridia appear in their most simple form
in Callithamnion, being reduced to a mass of cells com-
posed of numerous little bunches which are sessile 011 the
bifurcations of the terminal branches. Are not these spiral
filaments closely allied to Oscillatoriacece ? The spores are
simpler structures than the tetraspores, and mostly occupy
a more important posi-
tion. They are not scat-
tered through the frond,
but grouped in definite
masses, and generally
enclosed in a special
capsule or conceptacle,
which may be mistaken
for a tetraspore case.
The simplest form of
the spore fruit consists
of spherical masses of
spores attached to the
wall of the frond, or
imbedded in its sub-
stance, without a prope T
conceptacle ; such a fruit
is called a favellidium,
and occurs in Haly-
menia; the same name Flg - i50.-cflerio diploma. Section of
is applied to the fruits
oi similar structures not
perfectly immersed,, as
those of Gigartina, Gelidium, &c., where they form tuber-
cular swellings on the lobes. In some, the tubercles pre-
sent a pore at the summit, through which the spores find
T
lacinia of a frond, showing the stalked ijrW
chambered oosporangeff, growing on tufts
with intercalated filaments. Magnified 50
diameters.
274 THE MICROSCOPE.
exit; when such a fruit is wholly external, as in Cera-
mium (see Plate II. Nos. 27 and 37) and Callithamnion,
it is called a favella. The characteristic of Delesseria,
No. 39, the coccidium, either occurs on lateral branches, or
is sessile on the face of the frond, and consists of a case
of angular spores attached to a central wall. The cera-
midiuni is the most complete form of the conceptacular
fruit : this is enclosed in an ovate case, with an apical
spore, containing a tuft of pear-shaped spores arising from
the base of the cavity.
The general external appearance of the Red Sea- weeds
is very varied. They are exquisite objects for the Micro-
scope ; I have figured several interesting varieties in
Plate II. , each showing peculiarities of fructification. Their
beautiful leaf-like fronds are either simple, lobed, or
curiously pinnate or feathered. The Florideae of warmer
climates exhibit most elegantly formed reticulated fronds,
as may be seen on reference to the late Dr. Harvey's last
great work, " Phycologia Austr'alica"
In the plant which results from the germination of the
aggregate zoospores of Vaucheria, a genus of Siphortaceae
(Plate I. fig. 23), Kaisten has observed that on those
filaments which come in contact with the atmosphere,
are formed organs of a peculiar structure, which have
the appearance of nipple or egg-shaped buddings-out
of the cell-wall, distributed in pairs along the whole
course of the older filaments ; one elongates and curves
round to meet its fellow, which is seen to swell out
into a globular forjji; finally conjugation takes place,
preceded, however, by the conversion of the green con-
tents of the tubular organ into oil globules. If the fila-
ments be gathered at a favourable period, and cultivated
in a vessel of water well exposed to the light, the blind
ends, or ramifications of the filaments, are found densely
filled with green contents, appearing to be almost black ;
if these ends be watched early in the morning, a remark-
able series of changes is seen to occur in them when
about to produce gonidia, and, ultimately, they escape
in a peculiar way from the filament. The admirable essays
of Unger, Nageli, and Pringsheim on the process of their
reproduction may be consulted with advantage.
DESMIDTACB/K, DIATOMAC, ALGJK.
Tuffen Weit, del.
1'LATK II.
Edmund Kvar
YOLVOX GLOBATOR.
275
A fresh- water alga of singular beauty and interest to
fclie microscopist is the Volvox globator. This little cell
BO well known to the older observers as the globe-
animalcule, or revolving-cell, is represented in fig. 145,
ISTos. 1, 2, 3, and Plate I. No. 15. These revolving globular
bodies can be kept a long time alive if exposed in a
.glass bottle to a rain-drip from a roof. In this way
they maintain their activity and produce antheridia,
which are distinguishable by their orange colour.
Leeuwenhoek first perceived the motion of what he
termed globes, "not more than the 30th of an inch in
diameter, rolling through
water; and judged them to
be animated." These globes
are studded with innumerable
minute green spots, each of
which is seen to be a perfect
cell, about the 3,500th part of
an inch in size, with a.nuclens
and two flagella attached.
The whoje bound together
by threads forming a beautiful
net-work. Within the globe
busy active nature is at work
carefully providing a continu-
ance of the species ; and from
six to twenty little bright-
green spheres have been found
enclosed in the larger trans-
parent case. As each little
cell arrives at maturity, the
parent cell enlarges, and
, just before'the young burst ultimately bursts asunder,
atMRSSBWfi: "^S *& its offspring
tertum. 3, Doddium ciavatum. 4, to seek an independent exis-
Staurastrum gracilis.
Fig. 151.
younger spheres possess openings through which the water
freely flows, affording food and air to the wonderfully
constructed little being.
Dr. Carpenter believes, "The Volvocinece, whose vegetable
nature has been made known to us by observation of cer-
276 THE MICROSCOPE.
tain stages in the history of their lives, are but the motiU
forms (Zoospores) of some other plants, whose relation to
them is at present unknown." Professor Williamson,
having carefully examined the Volvox globator, says :
" That the increase of its internal cells is carried on in a
manner precisely analogous to that of the algae; that
between the outer integument and the primordial cell- wall
of each cell, a hyaline membrane is secreted, causing the
outer integument to expand; and as the primordial cell-
wall is attached to it at various points, it causes the inter-
nal colouring- matter, or endochrome, to assume a stellate
form (see Plate I. No. 15), the points of one cell being in
contact with those of the neighbouring cell, these points
forming at a subsequent period the lines of communication
between the green spots generally seen within the full-
grown Volvox." Flagella can be distinctly seen on the
outer edge of the adult Yolvox ; by compressing and rup-
turing one they may even be counted. Professor Busk has
been able to satisfy himself, by the addition of the chemical
test iodine, of the presence of a very minute quantitv of
starch in the interior of the Volvox, which he considers
as conclusive of their vegetable character. A singular
provision is made in the structure of the gemmules, con-
sisting of a slender elastic filament, by which each is at-
tached to the parent cell- wall : at times it appears to thrust
itself out, as if in search of food ; it is then seen quickly to
recover its former nestling-place by contracting the tether.
It is impossible not to recognize the great similarity
between the structure of Volvox, and that of the motile
cell of Protococcus pluvialis. The influence of re-agents
will sometimes cause the connecting processes of the young
cells as in Protococcus, to be drawn back into the central
mass, and the connecting threads are sometimes seen as
double lines, which seem like tubular prolongations of a
consistent membrane. At other times they appear to be con
nected by star-like prolongations to the parent cell, Plate I.
No. 15, presenting an almost identical appearance with
Pediastrum perticsum. Mr. Busk says that the body
designated by Ehrenberg Splwerosira volvox is an ordinary
volvox in a different phase of development; its only
marked feature of dissimilarity being that a large proper-
VOLVOCINE.fi. 277
tion of the green cells, instead of being single, are very
commonly double or quadruple; and the groups of flagel-
lated cells thus produced, form by their aggregation dis-
coid bodies, each furnished with a single cilium. These
clusters separate themselves from the primary sphere, and
swim forth freely from under the forms which have been
designated Uvella and Sfywcr^tabyEhrenberg. Accord-
ing to Mr. Carter, however, Sphcerosira is the male or
spermatic form of Volvox globator. Dr. Braxton Hicks
believes that he has seen the young volvox pass into an
amoeboid state ; he observes : " Towards the end of au-
tumn the endochrome mass of the volvox increases to
nearly double its ordinary size, but instead of undergoing
the usual subdivision, so as to produce a macro-gonidium,
it loses its colour and regularity of form, and becomes
an irregular mass of colourless protoplasm, containing
a number of brownish granules." (Plate I. No. 16.)
The final change and ultimate destination of these
curious amoeboid bodies have not as yet been made out ;
but from Dr. Hick's previous observation, made on similar
bodies developed from the protoplasmic contents of the
cells of the roots of mosses, " which in the course of two
hours become changed into ciliated bodies," he thinks it
very probable that this is designedly the way in which
these fragile structures are enabled to retain life, and to
resist all the varied external conditions, such as damp,
dryness, and rapid alternations of heat and cold. 1
(1) "We have had volvox under the microscope for several months, towards the
end of summer and throughout the autumn, and made more than a hundred
^examinations, without having once seen the remarkable change- described by
Dr. Hicks in the Quarterly Jour. Micros. Science, vol. viii. p. 96, 1862. Never-
theless, as Mr. Archer observes: "If this reasoning be correct, then contrac-
tility, amaiboid contractility for I can find no more comprehensive and expressive
single adjective must be accepted as an inherent quality or characteristic,
occasionally more or less vividly evinced, of the vegetable cell-contents, and
this in common with the animal ; in other words, that the nature of the proto-
plasm in each is similar, as has indeed, as is well known, been urged befoie on
grounds not so strong; thus reserving Siebold's doctrine, that this very con-
tractility formed the strongest distinction between animals and plants, as he
assumed it to be present in the former and absent in the latter of the two
kingdoms of the org^iic world. Therefore, an organism whose known structural
affinities, and whose mode of growth and of ultimate fructification point it out
as truly a plant, but of which, however, certain cells may for a time assume a
contractile, even a locomotive, quasi-rhizopodous state, must not by any means
on thia latter account alone be assumed as even temporarily belonging to the
animal kingdom, or as tending towards a mutation of its vegetable nature.
And from this it of course follows that an organism whose structural affinities
tnd reproduction are unknown, but which may possibly present an active!?'
278 THE MICROSCOPE.
Desmidiacece. A remarkably beautiful family of confer-
void algse, the most distinctive characteristics of the species
being their bilateral symmetry. Each frustule is, however,
a perfect unicellular plant, with a homogeneous structureless
membrane, enclosing a cellular skeleton filled with chloro-
phyll. Four modes of reproduction have been observed in
the desmids, and many points still remain to be cleared
up. Braun remarks of the products of conjugation, " that
they do not pass, like the swarming-cells of the Palmellacece
and the reproductive cells of the Diatomacese, directly and
"by uninterrupted growth into the primary generation of
the new vegetative series, but persist for a long time in a
condition of rest, during which, excepting as regards im-
perceptible internal processes, they remain wholly un-
changed. To distinguish these from the germ-cell (gonidia)
I shall call them seed-cells (spores). Certain early condi-
tions observed in Closterium and Euastrum, namely, families
of unusually small individuals, enclosed in transparent,
colourless vesicles, render it even probable that in certain
genera of this family a number of individuals are produced
from one spore, by a formation of transitory generations
occurring already within the spore." 1
contractile, even locomotive power, need not on this latter account be assumed
as therefore necessarily an animal. In the former category fall the Volvocinacese
and Rhisidium ; in the latter category Euglena and its allies, the so-called
Astasisean Infusoria, suggest themselves ; and these must of course wait until
their reproduction and history are better known before we can feel satisfied a&
to their true position : yet it seems highly probable that these will presently, if
they do not even now, take their place amongst admitted plants.
"Several writers have, indeed, from time to time, put forward th& (now, I
think, generally accepted) view that the protoplasm of the vegatable and the
sarcode of the animal cell are identical in nature ; and, in seeking for analogies
as 'regards contractility in the vegetable protoplasm as compared with the
animal, and as demonstrative thereof, special attention has been directed to
several of the now familiar phenomena displayed by certain vegetable cells.
Such are the vibratory movements of cilise, and drawing in of these, the circula-
tory movements of the cell contents, as in the hairs of the Tradescantia, <fec., the
contractile vacuole in Gonium, Volvox, &c. , and so forth. But while these are,
I think, unquestionably to a considerable, but more limited extent, manifesta-
tions of the same phenomenon, it seems to me that none of these cases present
BO exact an analogy, strongly as they may indicate it, with the rhizopodous con-
tractility as do the amreboid bodies of Stephanosphsera, of Volvox, of the
Moss-radicles, and of Rhisidium. The amoeboid bodies of Stephanosphsera seem
to display this rhizopodous contractility in greatly the most marked or ex-
aggerated degree, as their vigorous and energetic power of locomotion indicate :
In them, and indeed in those of Volvox, the Moss, and Rhisidium, the pseudo-
podal processes and their mode of protrusion and withdrawal, the flow of the
granules, and the locomotion of the whole body, were in all respects analogous
to the similar phenomena evinced by a true amoeba." Wm. Archer, Quarterly
T ourn. Micros. Science, vol. v. p. 185.
(1) " The Phenomenon of Rejuvenescence in Nature."
DESMIDIACB^E. 279
Reproduction both by conjugation and subdivision
variously modified, is common to all the families of
Desmidiacese ; and in the Zygnemaceae, which have a
close relation to them, the phenomena of conjugation are
very well known. In Staurocarpus we have those re-
markable quadrate spores formed in the cross branch,
produced by conjugation. In Spirogyra the union of two
cells belonging to the opposite filaments takes place by the
expansion of one side of each, so as to form a papilla or
short rounded-off tube (see fig. 145). The ends of the two
projections then come into contact, become slightly flattened,
then pressed together, and finally united. The double wall
formed by their union dissolves, or is broken through, so
that a free passage is established between the two cells.
Upon this, the whole of the chlorophyll, previously
arranged round the inside of each of tLe cells, becomes a
confused mass, which soon forms itself either in the cavity
of one of them, or in the connecting canal, into a globular
or oval spore invested with the colourless cellulose mem-
brane shown in one of our drawings of Penium (Fig. 155).
In Closterium conjugation takes place in a somewhat
similar manner, represented at No. 25, although it is
quite clear that if the formation of germs by conjugation
were the only provision for the reproduction of a species,
all must disappear, inasmuch as the conjugation and
consequent destruction of a pair of Closteria for the
formation of one new plant will ultimately destroy the
species. 1 Another mode, however, that of subdivision,
appears to be designed as an effectual safeguard against
such a possible extinction. Mr. Lobb has observed this
process take place in Micrasterias denticulata (Plate II.
fig. 30), in the course of three hours and a half. The small
hyaline hemisphere, put forth in the first instance from each
frustule, enlarges with the flowing in of the endochrome ; it
then undergoes progressive subdivision at its edges, first
into three lobes, then into five, then into seven, then into
thirteen, and finally at the time of its separation, acquires
the characteristic notched outline of its type, being only
distinguishable fron?. the older half by its smaller size. 2
(1) In certain species of Closterium the act of conjugation gives origin to two
porangise. (2) E. G. Lobb, Trans. Micros. Soc. N.S. vol. i., 1861.
280
THE MICROSCOPE
Desmidiacece. The once disputed question relating to
the vegetable nature of these cells received much valuable
elucidation from Mr. Balfs, who gave to the world the
Fig. 152.
I, Euastrum oblongum. 2, Micraxterias rotata. 3, Desmidium quadrangulatun.
4, Didymoprium Grevillii.
results of his laborious researches in his excellent work on
The British Desmidiece, published in 1848; and the con-
clusions arrived at by this painstaking author have been
generally accepted by men of science. The interest which
has so long attached to this topic will warrant us in
devoting some space to its consideration ; and we avail our-
selves for that purpose of Mr. Ralfs' labours, with a
recommendation to those of our readers who would
wish to familiarise themselves more completely with thi&
peculiar species, to consult the pages of the book above
referred to.
Desmidiacece are grass-green in colour, surrounded by a
transparent structureless membrane, a few only having
their integuments coloured ; they are all inhabitants of
fresh water. Their most obvious peculiarities are the
beauty and variety of their forms and their external mark-
ings and appendages ; but their most distinctive character
is their evident division into two or more segments. Each
cell or joint in the Desmidiacece generally consist of two
symmetrical valves or segments ; and the suture or line of
junction is in general well marked. The multiplication of
the 06 '.Is by repeated transverse division is full of interest,
DESMIDIACEJJ.
281
both on account of the remarkable manner in which it
takes place, and because it unfolds the nature of the pro-
cess in other families, and furnishes a valuable addition to
our knowledge of their structure and physiology.
' Pig. 153.
5, Micrasterias, sporangium of. 6, Didymoprium Borreri. 7, CosTnarium RalS$ii>
8, Staurtutrum hirsutum.
The compressed and deeply-constricted
offer most favourable opportunities for ascertaining the
manner of their division ; for although the frond is really
a single cell, yet this cell in all its stages appears like two,
the segments being always distinct, even from the com-
mencement. As the connecting portion is so small, and
necessarily produces the new segments, which cannot arise
from a broader base than its opening, these are at first
very minute ;' though they rapidly increase in size. The
segments are separated by the elongation of the connecting
tube, which is converted into two roundish hyaline lobules.
These lobules increase in size, acquire colour, and gradually
put on the appearance of the old portions. Of course, as
they increase, the original segments are pushed further
asunder, and at length are disconnected, each taking with
it a new segment to supply the place of that from which
it has separated.
It is curious t? trace the progressive development of
tLe new portions. At first they are devoid of colour, and
282
THE MICROSCOPE.
have much the appearance of condensed gelatine ; but as
they increase in size, the internal fluid acquires a green
tint, which is at first very faint, but soon becomes darker ;
Fig. 154.
7, Sphcerozosma vertebratum. 8, 9, XantMdiue. 10, X. armatum. 11, Cosmo-
im crenatum. 13, 17, Sporangia of Cosmarium. 14, X. fasiculatum. 1,
Arthrodcsmus convergens. 15, Sto-urastrumtumidum. IGfStaurastrumdilitatum.
at length it assumes a granular state. At the same time
the new segments increase in size, and obtain their normal
figure ] the covering in some species shows the presence
of puncta or granules. In Xanthidiwm and Staurastrum
the spines and processes make their appearance last,
beginning as mere tubercles, and then lengthening until
they attain their perfect form and size, armed with seta3 ;
but complete separation frequently occurs before the whole
process is completed. This singular process is repeated
again and again, so that the older segments are united
successively, as it were, with many generations. When
the cells approach maturity, molecular movements may
be at times noticed in their contents, precisely similar to
what has been described by Agardh and others as occurring
in Confervce. This movement has been aptly termed a
swarming. All the Desmidiacece are semi-gelatinous. In
some the mucus is condensed into a distinct and well-defined
DESMIDIACE^E.
286
hyaline sheath or covering, as in Didymoprium Grevillii
and Staurastrum tumidum ; in others it is more attenu-
ated, and the fact that it forms a covering is discerned
Fig. 155.
21, Penium. 24, Pediastrum biradiatum. 25, Closterium, showing conjugation
or self-division. 27, Penium Jenneri. 28, Aptogonum desmidium. 29, Pedias-
trum pecticum. 30, AnTcistrodesmus falcatus. 33, Conjugation of Peniurr
margaritaceum. 34. Spirotcemia. 35, Closterium.
only by its preventing the contact of the coloured cells.
In general its quantity is merely sufficient to hold the
fronds together in a kind of filmy cloud, which is dispersed
by the slightest touch. When they are left exposed by
the evaporation of the water, this mucus becomes denser,
and is apparently secreted in larger quantities, to protect
them from the effects of drought. Meyen states, " that the
large and small granules contain starch, and were some-
times even entirely composed of it ; " and " in the month
of May he observed many specimens of Closterium in
which the whole interior was granulated; these grains gave
with iodine the beautiful blue colour, indicative of the
presence of starch." 1
(1) The test for starch can be easily applied, and so remove any doubt that
nay exist. It is snly necessary to bear in mind that unless granular matter
284 THE MICROSCOPE
" Did we trust solely to the eye, we should indeed be
very liable to pronounce these variable and beautiful forms
as belonging to animals rather than vegetables. All
favours this supposition. Their symmetrical division into
parts; the exquisite disc-form, finely cut and toothed
Micrasterias ; the lobed Euastrum; the Cosmarium, glit-
tering as it were with gems ; the Xanlhidium, armed with
spines ; the scimitar-shaped Closterium, embellished with
striae ; the Desmidium, resembling a tape- worm ; and the
strangely insect-like Staurastrum, sometimes furnished
with arms, as if for the purpose of seizing its prey ; all
these characteristics appear to a superficial observer to
belong rather to the lowest forms of animal, than vege-
table life." Another indication Dr. Bailey adduced, by
rendering apparent their power of motion; taking a por-
tion of mud covered with Closteria, and placing it in
water exposed to light ; after a time, it will be seen tha*
if the Closteria are buried in the mud, they work their
way to the surface, and cover it with a green stratum :
this is no doubt owing to the stimulus light exerts upon
all matter, although at first appearing very like a volun-
tary effort. Another is afforded by their retiring beneath
the surface when the pools dry up. Mr. Ealfs states that
he has taken advantage of this circumstance to obtain
specimens less mingled with foreign matter than they
would otherwise have been.
During the summmer of 1854 the Eev. Lord S. G.
Osborne drew my attention to the economy of an interest-
ing specimen of this family, the Closterium Lunula; after
many careful investigations he came to the conclusion
that the membrane of the endochrome, both on its inner
and outer surface, is ciliated.
In the Closterium Lunula, we have ascertained that the
best view of its circulation is obtained by the use of
strong daylight, or sunlight transmitted through coloured
glass, or such a combination of tinted glass as that
be seen in the interior of the cell, starch cannot be present. A small quantity ct
diluted tincture of iodine may be applied, removing the free iodine by the aid of
beat, occasionally adding a little water to facilitate its removal. This also will
assist in the removal of the brownish stain which at first obscures the charac-
teristic purple tint ; and then, by applying the highest power of the microscope,
the peculiar colour of the purple iodide of starch will in general be perceived.
DESMIDIACEJ2.
285
proposed by Mr. Rainey, and adapted to a l-4th achro-
matic condenser ; with which must be used a 1-Sth ob-
ject-glass. The Gillett's condenser, or parabolic reflector,
will do equally well if used with a l-8th objective. In
diagram A, fig. 156, a specimen of the C. Lunula, as seen
Fig. 156.Closteria Lunula.
with the above arrangement of microscopic power, and a
deep eye-piece, the cilia are in full action along the edge of
the membrane which encloses the endochrome ; and also,
but not so distinctly, along the inside of the edges of the
frond itself. Their action is precisely the same as that
in the branchiae of the mussel : there is the same wavy
motion; and as the water dries up between the glasses
in which the specimen is enclosed, the circulation becomes
fainter, and the cilia are seen with more distinctness.
In diagram A, a line is drawn at b to a small oval mark;
these exist at intervals, and more or less in number over
the surface of the endochrome itself, beneath the mem-
brane which invests it. These seem to be attached by
small pedicles, and are usually seen in motion on the spot
lo which they are thus fastened ; from time to time they
286
THE MICROSCOPE.
break a way, and are carried by the circulation of the fluid,
which works all over the endochrome, to the chambers at
the extremities ; there they join a crowd of similar bodies,
each in action within those chambers, when the specimen
is a healthy one.
The circulation, when made out over the centre of the
frond, for instance at a, is in appearance of a wholly
different nature from that seen at the edges. In the
latter, the matter circulated is in globules, passing each
other, in distinct lines, in opposite directions ; in the cir-
culation as seen at a, the streams are broad, tortuous, of
far greater body, and passing with much less rapidity. To
see the centre circulation, use a Gillett's illuminator and
the 1-Sth power; work the fine adjustment so as to bring
the centre of the frond into focus, then almost lose it by
raising the objective ; after this, with great care, work the
milled head till the dark body of the endochrome is made
out ; a hair's-breadth more adjustment gives this circula-
tion with the utmost distinctness, if it is a good specimen.
It will be clearly seen, by the same means, at all the
points where the spaces are put ; and from them may be
traced, with care, down to both extremities.
The endochrome itself is evidently so constructed as to
admit of contraction and expansion in every direction. At
times the edges are in semi-lunar curves, leaving uninter-
rupted clear spaces visible between the green matter and
the investing membrane ; at other times, the endochrome
is seen with a straight margin, but so contracted as to
leave a well-defined transparent space along its whole edge,
between itself and the exterior case. It is interesting to
keep changing the focus, that at one moment we may see
the globular circulation between the outer and inner case,
and again the mere sluggish movement between the inner
case and the endochrome.
At B is given an enlarged sketch of one extremity of
a G. Lunula. The arrows within the chamber pointing to
b, denote the direction of a very strong current of fluid,
which can be detected, and occasionally traced, most dis-
tinctly ; it is acted upon by cilia at the edges of the
chamber, but its chief force appears to come from some
impulse given from the very centre of the endochromeu
DESMIDIACEA 287
The fluid is here acting in positive jets, that is, with an
almost arterial action ; and according to the strength with
which it is acting at the time, the loose floating bodies are
propelled to a greater or less distance from the end of the
endochrome ; the fluid thus impelled from a centre, and
kept in activity by the lateral flagella, causes strong eddies,
which give a twisting motion to the free bodies. The
line , in this diagram, denotes the outline of the mem-
brane which encloses the endochrome ; on both sides of
this flagella can be seen. The circulation exterior to it
passes and repasses it in opposite directions, in three or
four distinct courses of globules ; these, when they arrive
at c, seem to encounter the fluid jetted through an
aperture at the apex of the chamber ; which disperses them
so much, that they appear to be driven, for the most part,
back again on the precise course by which they had
arrived. Some, however, do enter the chamber ; occasion-
ally, but very rarely, one of the loose bodies may be seen
to escape from within, and get into the outer current, it is
then carried about until it becomes adherent to the side of
the frond.
With regard to the propagation of the C. Lunula, we
have never seen anything like conjugation; but we have
repeatedly seen what the reverend gentleman has so well
described increase by self-division.
Observe the diagram D ; but for the moment suppose
the two halves of the frond, represented as separate,
to just overlap each other. Having watched for some
time, the one half may be seen to remain passive ; the
other has a motion from side to side, as if moving on an
axis at the point of juncture : the separation then becomes
more and more evident, the motion more active, until at
last with a jerk one segment leaves the other, and they
are seen as drawn. It will be observed, that in each
segment the endochrome has already a waist ; but there
is only one chamber, which is the one belonging to the
one extremity of the original entire frond. The globular
circulation, for some hours previous to subdivision, and for
some few hours afterwards, runs quite round the obtuse
end of the endochrome a, by almost imperceptible
degrees; from the end of the endochrome symptoms of
288 THE MICROSCOPE.
an elongation of the membranous sac appear, giving a
semi-lunar sort of chamber; this, as the endochrome
elongates, becomes more denned, until it has the form and
outline of the chamber at the perfect extremity. The
obtuse end b of the frond is at the same time elongat-
ing and contracting ; these processes go on ; in about five
hours from the division of the one segment from the other,
the appearance of each half is that of a nearly perfect
specimen, the chamber at the new end is complete, tht
globular circulation exterior to it becomes affected by the cir-
culation from within the said chamber; and, in a few hours
more, some of the free bodies descend, become exposed to,
and tossed about in the eddies of the chamber, and the
frond, under a l-6th power, shows itself in all its beau-
tiful construction. E is a diagram, of one end of a C. didy-
motocum, in which the same process was noticed.
The Euastrum Didelta is well worthy
of attention, as well as many other species,
the Xanthidium Penium, Doddium, &c.
The Arthrodesmus Incus has a very
beautiful hyaline membrane stretching
from point to point, cut at the edges,
Flg * l something like the Micrasterias. This is
represented at fig. 157.
The Mode of finding and Taking Desmidiacece. As
the difficulty of obtaining specimens is very great, it will
materially assist the efforts of the microscopist to know
the method adopted by Mr. Ralfs, Mr. Jeriner, and Mr.
Thwaites. " In the water the filamentous species resemble
the Zygnemata ; but their green colour is generally paler
and more opaque. When they are much diffused in the
water, take a piece of linen, about the size of a pocket
handkerchief, lay it on the ground in the form of a bag,
and then, by the aid of a tin box, scoop up the water
and strain it through the bag, repeating the process as
often as may be required. The larger species, Euastrum,
Micrasterias, Closterium, &c., are generally situated at the
bottom of the pool, either spread out as a thin gelatinous
stratum, or collected into fiuger-lik<> tufts. If the finger
be gently passed beneath them, they will rise to the sur-
face in little masses, and with care may be removed and
DESMIDIACE^. 289
strained through the linen as above described. At first
nothing appears on the linen except a mere stain or a little
dirt ; but by repeated fillings-up and strainings a consi-
derable quantity will be obtained. If not very gelatinous,
the water passes freely through the linen, from which the
specimen can be scraped with a knife, and transferred to a
smaller piece ; but in many species the fluid at length
does not admit of being strained off without the employ-
ment of such force as would cause the fronds also to pass
through, and in this case it should be poured into bottles
until they are quite full. But many species of Stauras-
trum, Pediastrum, &c., usually form a greenish or dirty
cloud upon the stems and leaves of the filiform aquatic
plants; and to collect them requires more care than is
necessary in the former instances. In this state the
slightest touch will break up the whole mass, and disperse
it through the water : for securing them, let the hand be
passed very gently into the water and beneath the cloud,
the palm upwards and the fingers apart, so that the leaves
or stem of the inverted plant may lie between thera, and
as near the palm as possible ; then close the fingers, and
keeping the hand in the same position, but concave, draw
it cautiously towards the surface ; when, if the plant has
been allowed to slip easily and equably through the fingers,
the Desmidiacece, in this way brushed off, will be found
lying in the palm. The greatest difficulty is in withdraw-
ing the hand from the surface of the water, and probably
but little will be retained at first ; practice, however, will
soon render the operation easy and successful. The con-
tents of the hand should be at once transferred either to a
bottle, or, in case much water has been taken up, into the
box, which must be close at hand ; and when this is full,
it can be emptied on the linen as before. But in this case
the linen should be pressed gently, and a portion only of
the water expelled, the remainder being poured into the
bottle, and the process repeated as often as necessary."
When carried home, the bottles will apparently contain
only foul water ; if they remain undisturbed for a few
hours, the Desmidiacece will sink to the bottom, and most
of the water may then be poured off. If a little filtered
pain-water be added occasionally, to replace what has been
290 THE MICROSCOPE.
drawn off, and the bottle exposed to the light of the
suj), the Desmidiacece will survive for a long time.
Fungi. =-This interesting class of cellular nowerlesa
plants are chiefly microscopic, many requiring a high magni-
fying power to determine their peculiarities of structure,
They abound in damp places, among decaying and decayed
vegetable and animal matters, everywhere, and in almost
every place. The structure of all Fungi exhibits a well de-
fined separation into two parts, a mycelium (thallus) jointed
and branched, forming a kind of cottony filamentous mass,
and a reproductive spore or fruit, which, although exceed-
ingly minute, differs somewhat in appearance under the
microscope. The "spawn" used for planting mushroom
beds is composed of mycelium, and may be readily obtained
for examination (fig. 188, No. 19). The dust- like powder
of any of the moulds or mildew when sprinkled on a slip
of glass and kept under a bell glass over water, will soon
throw out filaments and spores in all directions.
De Bary's observations show that resting-spores are not
peculiar to the algas ; for he found them in two genera ot
fungi, and Tulasne ascertained their production in Per&no-
sporce, many of which are parasitic, as P. parasitica, a
species found on the cabbage and turnip leaf, as well as
on the shepherd's-purse, Capsella bursapastoris. For the
growth of P. infestans, the potato mould, the exclusion
of light seems to be needful, and it is easy to conceive
how the spores, washed down to the tuber during heavy
rains, throw out germinating threads, which easily pene-
trate the thick cuticle of the potato, and quickly produce a
murrain.
The Eev. M. J. Berkeley, the English authority on
Fungi, says : " The genus Cystoptis comprises those para-
sitic fungi amongst the Uredines which are remarkable for
their white spores. Till the resting-spores of the different
species were ascertained, it was almost impossible to find
good distinctive characters : one species at least, Cystopus
candidus, is to be found everywhere on the common
shepherd's-purse, and often accompanied by Peronospora
parasitica. It is also frequent on the crucifera : the aero-
spores, or gonidia, which spring from the swollen threads
of the mycelium, form necklaces, as in oidium, the joints
PARASITIC FUNGI. 291
of which, give rise to zoospores, as first observed "by Pre-
vost, in 1807. Like those of Peronospora, they move
about in water by means of two lash-like appendages, and
there germinate. When resting on the leaves of a plant,
they make their way by means of a germinating thread
into its subjacent tissues, and throw out little suckers.
The branched mycelium gives off sporangia and antheridia,
exactly as in Peronospora ; when ripe, the sporangia are
strongly warted. They fall, doubtless, with the leaves to
the ground, where they remain till a fitting season arrives
for their development. The provision made for the rapid
development of these parasites and for the preservation of
their species is truly marvellous, and sufficiently accounts
for the difficulty of extermination and their apparently
sudden dispersion, especially in wet weather."
De Bary's observations on the germination of Uromyces
appendiculatus are interesting, inasmuch as they show that
the sporidia produce a mycelium, from which springs in
succession 1st, spermogonia; 2dly, peridia, producing
chains of orange-coloured fruit, or, in other words, an
JScidium ; and 3dly, the original fruit of Uromyces, ac-
companied by the more simple fruit commonly called
uredo, and now called wredo-stylospores. The germination
of the fruit produced by the peridia, as well as that of
the wredo-stylospores, produces, according to De Bary,
1st, 7rec?o-stylospores, and 2d, the original Uromyces-
spores. Thus we see the Uromyces-spoies passing through
the generations of promycelium, sporidia, and mycelium
the latter producing successively the two different products,
spermogonia and secidia, and ultimately the original fruit
of Uromyces, accompanied by the Uredo. The sperrnatia,
or contents of the spermogonia, never germinate ; but we
find the fruit of the secidia, and also of the Uredo, repro-
ducing first the Uredo itself, and subsequently the original
fruit of Uromyces. Other interesting points, noticed by
the same author, are, " that not only has each species a
liking for certain special nutrient plants, but that in
certain Uredines with multiple fruit and alternate
generations each sort of reproductive organ buries its
germ in a different nutrient plant ; and that the vegeta-
tion of the parasite is the cause of the disease."
THE MICROSCOPE.
I)e Bary has also carried out a series of experiments
which go far to satisfy him that the sporidia of Puccinia
qraminis germinate on tha leaves of Herberts, and that the
jEcidium of the Berberis (Plate I. No. 22) is a stage in the
cycle of development of Puccinia. Thus, whilst in most
Uredines the entire development is carried out upon one
and the same nutrient plant, the alternate generations in
Puccinia graminis require a change of host. This is a
state of things well understood now in the animal kingdom
in the Tsenise and Trematoda, but Puccinia graminis is,
we believe, the first of the parasitic fungi in which it has
%een particularly ascertained. Another point of interest
is a confirmation of the supposed injurious effect of the
proximity of Berberis to corn, which has been denied.
De Bary further shows that Mucor mucedo (the common
mould) has three, if not four, different forms of fruit; and
"that the mould called Thamnidium by Link, or Ascophora
elegans by Corda, and the mould described by Berkeley as
Botrytis Jonesii, and made into a new genus by Fresenius,
under the name of Chcetocladium, are only varieties of the
'fruit of Mucor mucedo. Also that yeast, Achy la, Sapro-
-flegnia, and Entomophthora or Empusa, are identically the
ame as Mucor mucedo, consequently that a large reduction
is needed in the genera of the mucorini.
The main interest, however, of De Bary's paper on the
fructification of the Ascomycetes, consists in observations
en Erysiphe Cichoracearum, &c., in which the author
traces the origin of the perithecium, from its earliest state
sip to the formation of the single ascus and spores. He
notices two cells as being always present and visible from
the earliest period, one of which he conjectures may be
the female, and the other the antheridium or male organ.
He says that the cell, by the division of which the ascus
end its coating are formed, only develops itself when it
iias been in contact with the antheridium ; and he con-
eiders it very probable that impregration is effected by
cuch contact, and that the perithecium of Erysiphe (ex-
cepting the outer wall) is the product of such impreg
mtion.
De Bary's paper on parasitic -fungi was, it appears,
asixlcrtakeu with a view to contribute to the solution of
PARASITIC FUNGL
the question as to their origin ; and he concludes that
endophytes are not produced from the metamorphosed
substance of diseased plants, but that they originate from
germs which penetrate healthy plants and develop a
mycelium. In the course of his investigations he notices-
the occurrence in the genus Cystopus of organs similar to
those long since discovered by Tulasne in Peronospora^
which have been called OogonicC. He observes that rami-
fications perform the functions of antheridia, or male?
organs; and he proceeds to describe the production by th
oospores (or impregnated contents of the oogonia) of active
zoospores, similar to those produced by the ordinary spores
of Cystopus. Dr. De Bary states that these zoospores, after
remaining active for three or four hours, lose their cilia and
power of motion, assume a cellulose covering, and ger-
minate. He adds that the germ-filaments enter readily
by the stomates and leaves of the nutrient plant, but tha
those filaments only become developed which enter ths
stomates of cotyledons. In Peronospora the development
of the antheridia, oogonia, and oospores is said by De Bary
to be the same as in Cystopus; and he gives particulars of
the mode of germination of the conidia, and remarks on.
the growth of the parasite, which may be profitably
studied in the paper itself.
Parasitic fungi, vegetable blights as they are commonly,
called, have of late years become objects of earnest atten-
tion, on account both of the enormous damage done to our
growing crops, and also of the many curious facts in their:
history which have been brought to light. Corn-blights
consist chiefly of mildew, Puccinia, smut, bunt, rust, 03?
red-robin, Uredo. Oidium is a common mildew ; Bo-
trytis another; jEcidiurn, forms a kind of rust infecting
pear-trees, the peridia of which form a very pretty object
for the microscope. (Plate I. No. 22, jEcidium Herberidis.)-
In the full-grown condition they appear as little cups filled
with reddish-brown powder (spores), and may be detected in
their earliest stages by the deformities they produce hi the
structure of the plants infested, or by pale or reddish spots
on the green surface, arising from the presence of the
fungus beneath. They are common on the coltsfoot, the
berberry, gooseberry, buckthorn, nettle, &c. Plate I. No. 19^.
294 THE MICB080CPX.
represents a vertical section of a leaf of black-currant, in-
fested with JEcidium grossularice ; its sperm ogonia are
seen on the surface, and the perithecia below. The family
Sphceriacei (No. 3, Plate I.), common enough on most
herbaceous stems, first seem to be little black spots, a;
when examined more closely are found to resemble little
brownish bottles, b, filled with rows of spores. Other in-
structive specimens are *
Cystopus candidws (Uredo olim), Crucifer White-rust;
conidia equal, globose ; membrane equal, ochraceous ;
oospores sub-globose, epispore yellowish-brown, with irre-
gular obtuse warts : warts solid. On shepherd's purse,
cabbage, and other Cruciferse : receptacle consisting of
thick branched threads ; conidia concatenate, at length
separating ; oospores deeply seated on the mycelium.
Phyllactinia guttata (Olim Erysiphe). Plate I. No. 9.
Hazel Blight ; amphigenous ; mycelium web-like, often
evanescent; conceptacles large, scattered, hemispherical,
at length depressed; appendages hyaline, rigid, simple;
sporangia 4-20, containing 2-4 spores. On leaves of haw-
thorn, hazel, ash, elm, &c. Aregma (Phragmidium) bul-
bosum. Plate I. No. 20. Bramble Brand; hypogynous,
with a dull red stain on the upper surface; spores in
large tufts, 4-septate, terminal joint apiculate; peduncles
incrassated, and bulbous at the base. Puccinia variabilis,
Variable Brand ; sori amphigenous, minute, roundish, sur-
rounded by the ruptured epidermis, nearly black ; spores
variable, obtuse, cells often subdivided ; peduncle very
short. On leaves of dandelion. Puccinia buxi, Box Brand.
Plate I. No. 17. Sori sub-rotund, convex, and scattered;
spores brown, oblong, rather strongly constricted, lower
cell slightly attenuated; peduncle very long. On both
surfaces of box leaves : spores uniseptate, supported on a
distinct peduncle. Plate I. No. 18. Trichobasis (Uredo
olim) senecionis, Groundsel-rust ; spots obliterated ; sori
solitary or regularly crowded ; sub-rotund and oval, on the
under surface, surrounded by the ruptured epidermis;
spores sub-globose, orange. On various species of groundsel :
spores free ; attached at first to a short peduncle, which
at length falls away.
It appears that at particular periods of the year the
PARASITIC FUNGI. 295
atmosphere is, so to speak, more fully charged wiih the
various spores of fungi than it is at others. The spores of
the moulds aspcrgilbts, penicillium, and puccinia are per-
haps the most widely distributed bodies, and towards the
end of the hot weather, or about autumn time, they are
very abundant. Among those who have taken them at this
period of the year, we must ever associate the name of the
Rev. Lord Godolphin Osborne, who first experimented in
this direction during the cholera visitation of 1854. He
exposed prepared slips of glass, slightly moistened with
glycerine, over cesspools, gully-holes, &c., near the dwell-
ings of those where the disease appeared, and caught
what he termed aerozoa chiefly minute germs and spores
of fungi. A drawing made from one of these glasses
(Plate I. No. 13), exhibits spores almost identical with
those found on the human skin, and eteewhere.
From the year 1854 to the present time we have amused
ourselves by catching these floating atoms, and, so far as
we can judge, they are found everywhere, and in and on
every conceivable thing, if we only look close enough for
them. Even the open mouth is an excellent trap ; of
this there is ample evidence, since we find on the delicate
membrane lining the mouth of the sucking, crying infant,
and on the diphtheritic sore throat of the adult, the de-
structive plant Oidium albicans. The human or animal
stomach is invaded, and in a certain deranged condition we
find the Sarcina ventriculi, with its remarkable-looking
quaternate spores, its torulae, &c., seriously interfering with
the functions of this organ. 1 Torula diabetica is another
3f these destructive products found in the human bladder.
Fig. 153. Sarcina ventriculi.
(1) What part do tne fungi, or bacteria, play in the production of that fearful
scourge of the human i - ace, cancer? is a question not unfrequently asked since
296 THE MICROSCOPE
It is now more than a quarter of a century since Pro
fessor Owen first pointed out the vegetable nature of a
diseased growth found in the lungs of a Flamingo he
was dissecting. Soon after, Bassi discovered the vege-
table character of a disease which caused great devas-
tation among silkworms ; and, about the same time,
Schonlein, of Berlin, was led to the detection of certain
cryptogamic vegetable formations in connexion with skin?
diseases.
The Favus fungus is perhaps best known from its
having been the first to attract the attention of Schonlein.
It is commonly called cupped ringworm, or honeycomb
scall, but it is very rarely seen in this metropolis. The
crust is of a dingy yellow colour, and almost entirely
composed of the Aclwrion, mixed with epithelial scales
and broken hairs. When the fungus once establishes
itself, so fearful are its ravages, that in a very short space
of time the whole of the cutaneous surface, with the ex-
ception of the palms of the hands and soles of the feet,
becomes covered with it. As the spores penetrate the
hair-follicles they destroy the sheaths of the hairs, which
shrivel up and lose their colouring matter, and then break
off, leaving the surface bald.
Upon comparing the fermentation of the achorion
fungus with that of good healthy yeast, it will be seen to
be almost identical. In the first place, it is as actively
in the first edition of this book % (1854) I expressed a belief in "the fungoid
origin of cancer." Subsequent examinations of diseased structure more or loss
tend to confirm this view ; it appears that in this disease we have superadded to
a fungoid growth " degraded germinal matter" which, by its eiirance into th
circulation, produces a ferment and blood poisoning. The circular animal cell
degenerates, is converted into the ovoid or elongated vegetable cell, and ulti-
mately the structure, or some organ it may be, is changed into that remarkable-
looking caudate body, the typical cancer cell. This in some respects bears the
most perfect resemblance to certain spores of fungi, and to the yeast torulse.
As might be expected, its form is modified and its character more or less
changed by the peculiar kind of nourishment and condensed tissue in which it
is deposited and grows ; its powers of growth are, so to speak, perverted and
degraded, and then, as we see in other instances, it soon obtains a power of in-
definite multiplication, and destroys, not only the vitality of the organ, but the
individual. M. Davaiue believes he has traced splenic disease in sheep to the
entrance into the blood of bacterium-like bodies, and fungi ; a zymotic disease
is caused by the ferment, and by the rapid growth of the fungi the life of the
animal is quickly sacrificed to the destroyer.
To mount specimens of fungi, separate them, and add a drop or two of spirit :
when this has evaporated, add a drop of glycerine solution, or balsam dissolved
in chloroform, and put on a glass cover. If the balsam renders the asci tea
transparent, use gelatine : no cells are required.
YEAST DEVELOPMENT. 297
carried on by the former as by the latter. There is, how-
ever, just a slight difference in the size of the spores or
cells (Plate I. Nos. 7, 8, 11), those from yeast being the
larger and more clearly spherical, with a greater number
of reproductive spores, that is, cells with a single, clear,
nucleated cell in their interior, while others are filled
with a darker granular matter, having only a slight ten-
dency to coalesce or become filamentous; those from
achorion are for the most part ovoid, and very prone to
coalesce and produce elongated cells or torulae. With re
ference to the slight difference in size, -we must look upon
this as a matter of very little importance ; for to the pre-
sence of light in the one case, and its almost total exclu-
sion in the other, this difference, no doubt, is almost en-
tirely due. It would be more trustworthy if comparisons
of this kind could be made at the same stage of develop-
ment ; for be it remembered that yeast obtained from a
brewery is in a more favourable state, inasmuch as it is
stopped at a certain stage of growth or development, and
then set to begin its fermentation over again in fresh sup-
plies of a new pabulum, which give increased health an-
vigour to the plant ; while, on the other hand, the
achorion, or Favus fungus, is obtained and used in an ex-
hausted state from an already ill-nourished or stai led-out
soil. Neither can we attach much importance to differ-
ences in size and form of the spores, for even this occurs
in yeast ferment ; and although the ovoid is moet fre-
quently seen in achorion, it is equally common to yeast
when exhausted. This is strikingly exhibited in Plate
I. No. 8, a drawing made from a drop of exhausted yeast
taken from porter ; here we have oval and elongated cells
with torulse. To ensure success in these and similar ex-
periments., the fungus or yeast should be left floating on
the surface of liquids ; the process is either carried on very
slowly, or is entirely arrested by submersion.
Turpin and others, in their experiments on yeast, noticed
that the cells become oval and bud out in about an hour after
being added to the wort (fig. 159) ; but this change depends
as much upon temperature and density of the solution as
upon the quality of the yeast. It is a well-ascertained
fact that when yeast is added to distillery wa?h, which is
298 THE MICROSCOPE.
worked at a higher temperature than brewers' wort, fer-
mentation commences earlier, and the yeast-cell grows. to a
much larger size. It is, indeed, forced in this way much
as a plant in a hothouse is, and then obtains to greater
perfection in a shorter time. It will, however, be seen
that it sooner becomes exhausted ; and now, if we take a
portion of this yeast and add it to barley wort, and at the
same time keep it in a temperature of from 60 to 65
Fahr., it ferments languidly, and small yeast-cells are the
product. If the yeast is allowed to stand in a warm
place for a few days, it partially recovers its activity, but
never quite. With such a yeast there is always a good
deal of tomla3 mixed up with the degenerated cells, and
sometimes a filamentous mass, which falls to the bottom of
the vessel ; from this stage it readily passes to that of
must and mildew, and then becomes a wasteful feeder or
destroyer.
With yeast already in a state of exhaustion, we have
seen a crop of fungus produced in the head of a strumous
boy, seven years of age, who was much out of health, and
had suffered from eczema of the eyelids, with impetigo.
On placing portions of the broken hairs on a glass slip,
and moistening with a drop of liquor potassaB, spores and
torulaB were seen in abundance; represented in Plate I,
'No. 14.
In another experiment we took portions of penicillium
and aspergillus moulds, and added these to sweetwort,
and stood them by in a warm room. On the second
day afterwards in one of the solutions, and the third in
the other, fermentation had fairly set in ; the surface of
the solution was covered with a film, which proved to be
well-developed ovoid spores, filled with smaller granular
spores (conidia) : Plate I. No. 8. On the sixth day the
cells changed in form and were more spherical. Again
removing these to another supply of fresh wort, the results
obtained were quite characteristic of exhausted yeast
ferment.
Extreme simplicity of structure characterises all moulds
or milojBws. Their reproductive organs are somewhat
more complex, and both in penicillium and aspergillus the
mycelium terminates in a club-shaped head, bearing upon
YEAST PLANT.
299
it smaller filaments with small bead-like bodies upon the
apex, piled one upon the other, or, more properly speak-
ing, strung together; these, again, are surmounted by
larger spores of a discoid shape filled with granular
matter, and others which are quite empty. Those of the
aspergillus are apparently without granular matter or
nuclei, and are more highly refractive. - The puccinia are
club-shaped, the very rapid growth of the spores and
spawn of which appears to exert a specific and peculiarly
exhaustive action over the tissues of the plant on which it
feeds. Plate I. No. 12, represents a portion of the mould
taken from a saccharine solution.
The yeast plant, in its most perfect condition, is chiefly
made up of globular vesicles, measuring, when fully
grown, about the jj^nrth. of an inch in diameter. The
older cells are filled with granular or nucleated matter ;
the nucleus rapidly increases, and nearly fills up </he parent
cell, which then becomes ovoid, and ultimately the young
cell buds out and is separated from the parent. Some-
Fig. 159. A diagrammatic representation of the development of the Yeast PUnL
So. 1, Fresh Yeast: No: 2, one hour after adding it to wort; No. 3, three
hours ; No. 4, eight hours ; No. 5, third day, after which jointed filaments
are produced.
times other and smaller ceils are formed within the young
'one before it leaves the parent globule. This process goei
300
THE MICROSCOPE.
on most rapidly until the supply of food becomes ox
hausted ; the vesicles, it would appear, derive their
nourishment by the process of osmose, sucking in, as it
were, certain portions of the organic fluid and chemically
decomposing it, appropriating a part of its nitrogen and
throwing off the carbonic acid. If, however, it be placed
G Q o ?
Fig. 160. Fungoid growths.
I, Section from a Tomata, showing sporangise growing from cuticle. 2, A por-
tion of same, detached, to show the mode of budding out from the upper part
of a branch. 3, Vertical and lateral views of spores with oospores turned out
6, 7, and 8, Different stages of growth of Mycoderma cerevisice. 9, Torula
dialietica.
in any adverse condition, it becomes surrounded by layers
of condensed material, resulting from the death of the
MOULDS, ETC.
301
germinal matter ; ultimately a mere trace of life remains,
which, taking the form of an impalpable powder, is free to
be driven hither and thither with every breath of air.
From these facts we may conclude that it matters little
whether we take yeast, achorion, or penicillium spores;
the resultant is the same, and depends much more on the
food or nourishment supplied, whether the pabulum con-
tains more or less of a saccharine, albuminous, or nitro-
genous material, lactic acid, &c., together with light and
temperature ; whether we have a mould (green or blue),
an achorion, or yeast fungus produced. Diversity of form
in the cells, as well as quality and quantity of their
material contents, are certainly due to, and in a manner
regulated and controlled by that beautiful law of diffusion,
which admits, separates, sifts, and refines the coarser from
Fig. 161. Fungi. (Magnified 200 diameters.)
1, Brachycladium penicillatum, growing on the stem of a plant. 2, Aspergillus
glaucws, growing on cheese, &c. 3, Botrytis ; the common form of mould on
decaying vegetable substances. 4, Sphceria, fungi caught ever a sewer (foul
air). 5, Fungi growing on a pumpkin, 6, Fungi caught in the air at th
time of the cholera visitation, 1854.
the finer, the lighter from the denser particles, through
the porous structure of the cell-wall.
302 THE MICROSCOPE.
We cannot conclude this brief notice of the fungi with*
out adding a few words upon that curious group of subter-
ranean plants, which instead of producing their spores at
the summit of a basidium, or extremity of a simple filament,
produces them in the interior of a vesicle or pouch, called
a theca or ascus. Of this species the best known example
is the truffle (Tuber cibarium).
It is, perhaps, not very generally known that the
curiously formed, irregular mass, so much esteemed for its
delicious taste, and sought after as a luxury, the truffle, is
in truth a species of mushroom ; more properly speaking, a
subterranean puff-ball, or fungus. Its existence, entirely
removed from the action of light, is an anomaly even
among plants of the fungus kind ; for light, although not
in a large degree necessary to the fungus, is almost
always indispensable to its full development. It would,
therefore, be most difficult to discover, if it were not for
a peculiar and penetrating odour, which dogs are taught
to recognise ; and by the aid of these useful animals its
presence is detected hidden beneath the soil.
Tulasne and others have pointed out that these fungi
present two essentially different types. In the one, Hy-
menogastrece, the internal fleshy mass presents a number of
irregular cavities, lined by a membrane analogous to that
which clothes the gills of the Agaric, and the superficial
cells produce at their free extremities three or four spores,
or seeds, which become detached, and eventually fill up
the cavities. The other type, JSlaphemycce, Tuberacece,
comprising those of the truffle kind, and as may be sur-
mised by the scientific name assigned to them Tuber
aibarium, are plants characterised from the underground
root presenting a fleshy mass, the outer surface of which
constitutes the common envelope, peridium, while the
numerous narrow sinuous cavities are lined and in part
filled up by filamentous tissue, mingled with cells of a
peculiar form, and terminating in spores.
A section from the fleshy-looking mass cut very thin
(Plate I. No. 2), and viewed under a power of 250
diameters, is found to be chiefly composed of cellular
substance, the interspaces of which are tilled up by
jointed filaments, homologous to th mycelium or spawn
TRUFFLES. 303
of other fungi, in the mushroom, as an example, it is the
mushroom spawn, while the veins, the reproductive
parts, contain in their cellular tissue minute ovoid capsules,
with two or more globular yellowish seeds ; this curious
structure having all the parts of nutrition and reproduction
enclosed internally, instead of externally, as in other fungi.
Truffles are produced in this way : the mycelium quickly
decays and allows the fungoid "body to grow on in an
isolated condition. About September the ground becomes
covered with numerous white cylindrical articulated fila-
ments, not visible singly to the unassisted eye, but by
their immense numbers and rapid growth readily seen,
and found traversing the soil in every direction. These
white flaxen threads are continuous with other flocculent
filaments of the same nature. In the young truffles the
external layer is gradually consolidated, and in a short
time the destruction of the flocculent filaments are com-
plete and lost in the young plant, which is soon isolated
in the soil, and then the outer or cortical coat hardens,
and ultimately has the appearance of a small nut. Thus,
like other fungi, truffles are reproduced by spores, which
give origin to filamentous mycelium and seed-vessels, the
source of numerous offspring. Groups of spores are pretty
objects ; their stellate appearance reminds one of the
Xanthidise ; the mass of the full-grown plant at particular
seasons is almost wholly made up of these bodies, which
are of a yellowish-brown colour.
In these plants we have a double system of laminated
filaments ; one set arising from the cortical tissue absorb-
ing the surrounding moisture and serving to transmit this
to the cells in which the spores are formed, being there-
fore the organs of nutrition ; the others white and opaque,
terminating externally also, but conveying air to all parts
of the body, and bringing the whole into contact with
sporigenous cells.
The spores are developed freely in the vesicular cells
destined to produce them. They are limited in number
in each vesicle; less than two is never seen in one vesicle;
the hexagonal basket-work arrangement of each seed ap-
pears to close with a lid, and ten or twelve short spinea
project out from every point.
304 THE MICROSCOPE
Beneath the external dark-coloured reticulated mem-
brane is a second integument, smooth and transparent,
oasily separated by maceration, although it resists the
action of chemical agents, and is not coloured by iodine.
The simple cavity of the internal spore is filled with
minute granular particles and fatty globules, suspended
in a fluid probably albuminous, as well as the various
chemical salts found by Biegel, and upon which its peculiar
flavour depends.
"Two new British fungi" are figured and described by
the Rev. M. J. Berkeley, in vol. xxv. p. 431, Linnean
Soc. Trans. Peziza pygmcea, Plate I. No. 4, is a remark-
ably interesting specimen of a genus which presents much
variety in form. The description given of it is, " that it is
about J inch high, the stem often splitting or branching
out into several divisions, each of which is terminated by
a minute cup, giving the plant the appearance of a Ditiola,
or a Tympanis. Each cup produces other smaller cups on
its surface ; the branched and young cups resemble the
genus Solenia : in a specimen found at Wimbledon, the
mass of secondary cups gave, the plant almost the ap-
pearance of a small Gyr&mitra" The proliferous form is
shown at Plate I. No. 5. The colour of the mature plant
is a bright apricot, whitish and tormentose at the base of
the stem. Found in swampy places, rotten gorse, &c. at
Ascot, Wimbledon, &c. Peziza belongs to the Ascomycetoua
fungi ; the genus contains numerous species, and many of
them are brightly coloured, as in the very pretty P. bicolor,
Plate I. No. 1. Tulasne says that some of them have a
secondary fructification, consisting of stylospores. They
are mostly found growing on trunks of trees, dead
wood, &c.
We now pass to the examination of Lichens ; in these
plants, as in the Fungi, the germination of the spore
consists in the emission of a hollow filament from some
part of its surface. This filament, which is simply an
extension of the spore-membrane, branches repeatedly,
and spreads over the surface on which the spore has been
sown ; at the same time it divides by numerous septa
which occur at irregular intervals. By the intertwining
of the resultant ramifications, a stroma is formed, to which
LICHENS.
the term hypothallus is applied, and which constitutes the
vegetative system of the future lichen. So far the develop-
ment is the same as that of the fungi ; but at a longer or
shorter period after the formation of the hypothallus, wo
may observe upon its surface a whitish layer of spheroidal-
cellules, intimately united with each other as well as with?
the filaments from which they take their origin. This 1
layer is the groundwork for a second formation of globular
cells, and these are only to be distinguished from the
first by the chlorophyll which they contain. They are-
called gonidia, and are peculiar to Lichens. Such is the
formation of the most simply organized of the class, as the
Verrucarice, the receptacles (apothecia) of which closely
resemble those of a SpJiceria, and are found npon the sur-
face of the hypothallus. In the more complicated foliaceous
Lichens,as Parinelia^ihe mature thall us is made up of two<
kinds of tissues, the medullary and corticated. The cor-
ticular portion forms the layers, an inferior and superior,
and consists of thick-walled cells, closely adherent to
each other ; from the surface of the inferior layer are given
off numerous root-like appendages, on either side of which^
or rather embedded in its cortical substance, are the gonidia^
which form a green tissue. Of the spore-like organs^
spermatia and stylospores, there are three varieties, to
which the terms apothecia, spermogonia, and pyenides
have been applied. The most common form of the apo^
thecium is that of the disc, which may be plane, convex,,
or cup-shaped. This form is that which characterises the-
Gymnocarpous Lichens. In the Angiocarpece the organ is
closed upwards, its superior surface becoming internal, s*>
as to form a conceptacle like that of the Pyrenomy-
oetes ; the form, however, of which is subject to mucK-
variation.
The reproductive organs of Lichens, as in Fungi, are of 4
five kinds . 1, Sporules, which are formed by the con-
struction and subsequent separation of the extremity of a*
simple cylindrical filament ; 2, Spermatia with their sup*
porting pedicles ; 3, Stylospores with their styles ; 4 y
Theca? or asci ; 5, Basidia with their basidiospores. As
regards the complexity of their form and structure they,
may be taken in the order in which they are here placecV;
x
306 THE MICROSCOPE.
but, of the last-mentioned, it should be stated that they are
almost solely found in Fungi, which have really no other
reproductive organ. The spores present many points of dif-
fero.Dce, both in number and character, in different genera
and species, and for this reason are most interesting micro-
scopic objects. We would direct the reader's attention to
an interesting and valuable paper, from the pen of Dr.
Lauder Lindsay, in the Linmean Soc. Trans., vol. xxv.
p. 493, " On the Lichens of New Zealand" (the country
par excellence of certain Lichens). The paper is very
beautifully illustrated, showing chiefly the minute or
microscopic anatomy of the reproductive organs of the
species examined, and more especially the character of
their spores.
A vertical section of Parmelia stellala is given in
Plate I. No. 26: it belongs to an extensive genus of
Gymnocarpous open-fruited Lichens, found growing upon
trees, palings, stones, walls, &c. The emission of the ripe
spores of the Lichens is a curious process, and not unlike
that which is seen to take place in some of the Fungi, as
in Pezizce, Sphcerice, &c. If a portion of the thallus be
moistened and placed in a common phial, with the apothecia
turned toward one side, in a few hours the opposite sur-
face of the glass will be found covered with patches of
spores, easily perceptible by their colour ; or if placed on
a moistened surface, and one of the usual glass slips laid
over it, the latter will be covered in a short time. As to
the powers of dissemination of these lowly organized
plants, Dr. Hicks's observations lead to the conclusion
that the gonidia of Lichens have greater powers in this
direction than has been generally supposed. He found
by placing a clean sheet of glass in the open air during a
fall of snow, and receiving the melting water in a tube or
bottle, that he obtained large quantities of what has been
looked upon as a " unicellular plant, commonly called
' ClilorococcusJ the cells of which may remain in a dor-
mant condition for a long time during cold weather,
but upon the return of warmth and moisture they begin
to increase by a process of subdivision, into two, four
or eight portions, which soon assume a rounded form and
burst the parent cell-wall open; these secondary cells
L10HEXS. 307
soon begin to divide and subdivide again, and tiis process
may go on without much variation even for years. The
phenomena described may also be watched by taking a
portion of the bark of a tree on which the Chlorococcus
has been deposited, and placing it under a glass to keep it
in a moderately moist atmosphere ; the only difference
being a change in colour, which is caused by the growth of
the fibres, as may be seen on microscopical examination.
And this," Dr. Hicks says, " is an instructive point, be-
cause it will be found that the colour varies notably accord-
ing to the Lichen prevalent in its neighbourhood." 1 He
thinks there can be no doubt that what has been
called Chlorococcus, is nothing more than the gonidia of
some Lichen ; and that under suitable conditions, chiefly
drought and warmth, the gonidium often throws out from
its external envelope, a small fibre, which, adhering and
branching, ultimately encases it and forms a " soridium."
' The soridia also remain dormant for a very long time,
and do not develop into thalli unless in a favourable
situation ; in some cases it may be for years. It will be
easily perceived that the soridium contains all the elements
of a thallus in miniature ; in fact, a thallus does frequently
arise from one alone, yet, generally, the fibres of neigh
bouring soridia interlace, and thus a thallus is matured
more rapidly. This is one of the causes of the variation
of appearance, so common in many species of Lichens, and
is more readily seen towards the centre of the parent
thallus. "When the gonidia remain attached to the parent
thallus, the circumstances are, of course, generally very
favourable, and then they develop into secondary thalli,
attached more or less to the older one, which, in many
instances, decays beneath them. This process being con-
tinued year after year, gives an apparent thickness and
spongy appearance to the Lichen, and is the principal
cause of the various modifications in the external aspect
of the Lichens which caused them formerly to be mis-
classified." 2
(1) "For instance, where the yellow Parmelia is found, the Chlorococcu* will
assumes yellow tinge in its soridial stage. Viewed by transmitted light, they
are also opaque balls, with irregular outline."
(2) " Contributions to the Knowledge of the Development of the Gonidia of
Lichens." By J. Braxton Hicks, M.D. &c., Quarterly Journal of Micrcscopicai
Science, vol. viii. 860, p. 239.
x 2
308
THE MICROSCOPE.
The little group of Ilepaticce or Liverworts, which if
intermediate between Lichens and Mosses, presents nume-
rous objects of interest for the microscopist. These
plants are produced by dust-like grains called spores, and
minute cellular nodules called gemmce or buds. The
gemmae of Marchantia polymorphic^ are produced in
elegant membranous cups, with a toothed margin growing
on the upper surface of the frond, especially in very damp
court yards between the stones, or near running water,
where its lobed fronds are found covering extensive
surfaces of moist soil. At the period of fructification,
these fronds send up stalks, which carry at their summit
round shield-like or radiating discs. Besides which, it
generally bears upon its surface a number of little open
basket-shaped " conceptacles " -which are borne upon the
surface of the frond, as in fig. 162, and may be found
in all stages of develop-
ment. When mature
it contains a number of
little green round or ob-
long discs, each com-
posed of two or more
layers of cells; the wall
is surmounted by a glis-
tening fringe of teeth,
whose edges are them-
selves regularly fringed
with minute outgrowths.
The cup seems to be
formed by a develop-
ment of the superior
epidermis, which is raised up and finally bursts and
spreads out, laying bare the seeds. The development of
this structure presents much analogy to that of the sori of
Ferns.
Muscacece, Mosses, are an interesting form of vegetable
life, Linnaeus called them servi, servants, or workmen,
as they seem to labour to produce vegetation in newly-
formed countries, where soil is not yet formed. They also
fill and consolidate bogs, and form rich mould for the
growth of larger plants, which they protect from the
Fig. l62.Gemmiparous Conceptacle of Mar-
chantia polymorphia, expanding and rising
from the surface of a frond.
MOSSES.
309
winter's cold. The common, or Wall Screw-moss, fig.
163, growing almost every where on old walls and other
brick- work, if examined closely, will be found to have
springing from its base numerous very slender stems, each
Fig. 163. Screw Moss.
of wh.ch terminates in a dark brown case, which encloses
its fruit. If a patch of the moss is gathered when in
this state, and the green part of the base is put into water,
the threads of the fringe will uncoil and disentangle them-
selves in a most curious and beautiful manner ; frcm
this circumstance the plant takes its popular name of
Screw-moss. The leaf usually consists of either a single or
a double layer of cells, having flattened sides, by which
they adhere one to another. The
leaf-cells of the Sphagnum bog-
moss, tig. 179, exhibit a very curi-
ous departure from the ordinary
type ; for instead of being small and
polygonal, they are large and elon-
gated, and contain spiral fibres
loosely coiled in their interior. Mr.
Huxley pointed out, that the young
leaf does not differ from the older,
and that both are evolved by a
gradual process of" differentiation"
Mosses, like liverworts, possess
bothantheridiaand pistillida, which
are engaged in the process of fruo-
tification. The fertilized cell b&-
eonies gradually developed into a conical body elevated
310 THE MICBOSCOPE.
upon a foot stalk ; and this at length tears across the
walls cf the flask-shaped body, carrying the higher
part upwards as a calyptra or hood upon its summit,
whila the lower part remains to form a kind of collar
round the base. These spore-capsules are closed on their
summit by opercula or lids, and their mouths when
laid open are surrounded by a beautiful toothed fringe,
termed the peristome. This fringe is shown in fig. 164
in centre of capsule of Funaria, with its peristome
in situ. The fringes of teeth are variously constructed,
and are of great service in discrimi-
nating the genera. In Neckera anti-
pyretica. fig. 165, the peristome is
double, the inner being composed of
teeth united by cross bars, forming
a very pretty trellis. The seed spores
are contained in the upper part of
the capsule, where they are clus-
tered round a central pillar, which
Fig. lea. Double Peristome of is termed the columella ; and at the
Neckera Antip.rctica. timQ Qf maturityj the int erior of the
capsule is almost entirely occupied by spores.
It may here be mentioned, that all mosses and lichens
are more easily detached from the rocks and walls on
which they grow in frosty weather than at any other
period, and consequently
they are best studied in-
winter. One of the com-
monest, Scale-moss, fig.
166 (Jungermannia biden-
tata), grows in patches,
in moist, shady situa-
tions, near the roots of
trees; see Plate II. Xos.
Fig. iw.-Scaie.Mos,. 35 aa( j 36. The seed-
vessels are little oval bodies, which if gathered when
unexpanded, and brought into a warm room, burst
under the eye with violence the moment a drop ot
water is applied to them, the valves of the vessel taking
the shape of a cross, and the seeds distending in a cloud
of brown dust. If this dust be examined with the
EQUISETACE^E.
31]
microscope, a number of curious little chains, looking
something like the spring of a watch, will be found
among it, their use being to scatter the seeds ; and if the
seed-vessel be examined while in
the act of bursting, these little
springs will be found twisting
and writhing about like a nest
of serpents. The undulating
Hair-moss (Polytrichum undu-
latum), fig. 167, is found on
moist shady banks, and in
woods and thickets. The seed-
vessel has a curious shaggy cap ;
but in its construction it is very
similar to that of the Screw-
moss, except that the fringe
around its opening is not twisted.
Hquisetacece. The history of
the development of the Equise-
tacese (horse-tails) corresponds in
some respects with that of Ferns.
The spore-case of this solitary
genus is a most interesting object
under the microscope ; they have
apparently only one coat, for the
outer coat splits up into four
thread-like processes (elaters),
clubbed at their free ends.
While the spore remains on the
sporange, these fibres are rolled round the spore, as
in fig. 170, G; but by gently shaking the fruit spike, the
spores are discharged, the coiled fibres immediately unroll,
as at F, their elasticity causing them to spring about in a
most curious manner. In a few minutes this motion appa-
rently ceases, but if breathed upon they again unroll and
.dart about with wonderful elasticity.
Ferns. In the Ferns we have an intermediate state,
somewhat between mosses and flowering plants; this
would, not apply to the reproductive apparatus, which is
formed upon the same type as that of Mosses ; and,
furthermore, it is to be observed, that Ferns do not form
Fig. 167. Hair-Moss in Fruit.
THE MICROSCOPE.
buds like other plants, but that their leaves, or fronds as
they are properly called, when they first appear, are rolled
*ip in a circinate form, and gradually unfold, as in fig. 168.
Fig. 16S. Male Fern. A portion ol leal with BorL
fi'erns have no visible flowers; and their seeds are produced
in clusters, called sort, on the backs of the leaves. Each
sorus contains numerous thecse, and each theca encloses
^almost innumerable sporanges, with spores or seeds.
There are numerous kinds of ferns, all remarkable for some
interesting peculiarity ; but it is their spores which are
chiefly sought for by the microscopist.
The first account of the true mode of development of
.Ferns from their spores was published in 1844, by Nagoli,
ia a memoir entitled Moving Spiral Filaments (spermatic
filaments) in Ferns, wherein he announced the existence of
the bodies now called antheridia; but, mistaking the
archegonia for modified forms of the antheridia, he was
led away from a minute investigation of them. If he had
followed the development of the prothallia further, he
would have detected the relations of the nascent embryo,
which would probably have put him on the right track.
As it was, the remarkable discovery of the moving spiral
filaments occupied all his attention, and caused him to fall
FERNS.
313
into an error in certain important respects ; for example,
he has represented what is undoubtedly an archcgonium
filled with cellules, sperm-cells, which, he states, " emerged
from it as from the antheridia" This description is not
quite correct.
The reproduction of ferns had, until within. the last few
years, been a vexed question among botanists. The riddle
was at length solved by the labours of Count Suminski,
who discovered that it is in the structures developed from
the spores in germination that the pistillidia and autheridia
of ferns are to be sought. The nature of the phenomena
by which the propagation of ferns is effected, is as follows.
In all the different species of ferns, the spores are contained
in brown dots, on lines collected on the under surfaces, or
along the edges of the fronds. Each of the spore-cases
is surrounded by an elastic
ring, which when the time
arrives for the spores to be
set free, makes an effort
to straighten itself, and in
so doing causes the spore-
case to which it is attached
to split open, and the spore
dust to be dispersed. Very
soon after these spores
have begun to germinate, ^^
a flat plate-like expansion, p .
, r . . * ig- 169. Sorus of Depana prohfera.
somewhat resembling a
heart in form, shows itself. This expansion gradually
thickens, the tube from which it had sprung withering
away. So far, observes Mr. Henfrey, there is nothing very
remarkable in the development of these plants from their
spores, but the succeeding phenomena are exceedingly
curious. The main particulars are thus described by him :
" At an early period of the expanding growth of the leaf-
like product of the spore, termed the prothallium or
-germ-frond, a number of little cellular bodies are found
projecting from the lower surface, which, if placed in
water when ripe, burst and discharge a quantity of micro-
scopic filaments, curled like a corkscrew, and furnished
with vibrating hair-like appendages, by the motion of
3ii THE MICROSCOPE.
which they are rapidly propelled through the water. The
cellular bodies from which these are discharged are termed
the antheridia of the ferns, and are in their physiological
nature the representatives of the pollen of the flowering
plants. At a somewhat later period other cellular bodies
of larger size and more complex structure are found in
small numbers about the central part of the lower surface
of the prothallium on the thickened portion, situated
between the notch and the part where the radical filaments
arise. These, the pistillidia or archegonia of the ferns, are
analogous to the ovules or nascent seeds of flowering
plants, and contain, like them, a germinal vesicle, which
becomes fertilized through the agency of the spiral fila-
ments mentioned above, and is then gradually developed
into an embryo plant possessing a terminal bud. This
bud begins at once to unfold and push out leaves with a
circulate vernation, which are of a very simple form at
first, and rise up to view beneath the prothallium, coming
out at the notch; single fibrous roots are at the same
time sent down into the earth, the delicate expanded pro-
thallium withers away, and the foundation of the perfect
fern plant is laid. As the bud unfolds new leaves, the
root stock gradually acquires size and strength, and the
leaves become larger and more developed ; but it is a long
time before they assume the complete form characteristic
of the species."
These observations on Ferns have acquired vastly-
increased interest from the subsequent investigations of
Hoffmeister, Mettenius, and Suminski, on the allied Cryp-
togams, and, above all, from Hoffmeister's observations on
the processes occurring in the impregnation of the Coni-
fers, Not only have these investigations given us a satis-
factory interpretation of the archegonia and antheridia of
the Mosses and Liverworts, but they have made known
and co-ordinated the existence of analogous phenomena
in the Equisetacece, Lycopodiacece, and RhizocArpece, and
shown, moreover, that the bodies described by Mr. Brown
in the Conifers, under the name of " corpuscles," are
analogous to the archegonia of the Cryptogams ; so that a
link is hereby formed between these groups and the higher
flowering plants.
CHARA. 315
The fruits, cr sori, of Ferns afford a very beautiful
variety of objects for the microscopist, and they possess an
advantage in requiring little or no preparation nothing
more being necessary than that of taking a portion of a
frond, place it on a glass-slip under the microscope, and
throwing a condensed light upon it by the aid of the side
reflector. Even germination may be watched by simply
employing gentle heat and moisture. Take, as Hoff-
meister directs, a frond of a Fern whose fructification is
mature, lay it upon a piece of glass covered with fine
paper, and place the spore-bearing surface downwards
upon this ; in the course of a day or two this paper will
be found to be covered with a fine brownish dust, which
consists of the liberated spores. These must be carefully
collected, and spread out upon the surface of a smooth
fragment of porous sandstone, and then- placed in a saucer,
the bottom of which is before covered with water ; a glass
tumbler being inverted over it to ensure the requisite supply
of moisture, and prevent rapid evaporization. Some of the
prothallia soon germinate ; if the cup be kept only slightly
moist for some time, and then suddenly watered, a large
number of antheridia and archegonia quickly open, and in a
few hours the surface of the larger prothallia will be covered
with moving antherozoids. If sections of fhese be made,
that is, the canals laid open, with a power of 200 or 300
diameters we may occasionally see antherozoids in motion,
CHARACE.E. Ghara vulgaris is the plant in which the
important fact of vegetable circulation was discovered ;
Fig. 170, No. 1, is a portion of the plant of the natural
size. Every knot or joint may produce roots ; but it is
somewhat remarkable, that they always proceed from the
upper surface of the knot, and then turn downwards ; so
that it is not peculiar that the first roots also should rise
upwards with- the plant, come out of the base of the
branch, and then turn downwards.
Mr. Varley noticed : " The ripe globules spontaneously
open; the filaments expand and separate into clusters."
"These tube-like filaments are divided into numerous
compartments, in which are produced the most extra-
ordinary objects ever observed of vegetable origin, Fig.
170 A. At first they are seen agitating and moving- in their
316 THE MICROSCOPE.
cells, where they are coiled up in their confined spaces,
every cell holding one. They gradually escape from their
Fig. 170.
1, Branch of Chora vulgari*. 2, Magnified view : the arrows indicate the course
taken by the granules in the tubes. 3, A limb of ditto, with buds at joints.
4. Portion of a leaf of ValHtneria tpiralii, with cells and granules.
CHARA.
317
cells, and the whole field soon appears filled with life.
They are generally spirals of two or three coils, and
never become straight, though their agitated motion alters
their shape in some degree. At their foremost end is a
filament so fine as only to be seen by its motion, which is
very rapid and vibratory, running along it in waves . and
of a globule be forcibly opened before it is ripe, the fila-
ments will give little or no indication of life."
They swim about freely for a time, but gradually getting
slower and slower ; in about an hour they become quite
motionless. Unger described these moving filaments in
Sphagnum (bog-moss) as Infusoria, under the name of
Fig. 171. Anther idia of Chara fragilis, %c.
A, Portion of filament dividing into Phytozoa, " anther aids." B, A valve, with
its group of antheridial filaments, composed of a series of cells, within each of
which an antherozoid is formed, c, The escape of the mature antherozoidt is
shown. D, Antheridium, or globule, developed at the base of nucule. E, Nu-
cule enlarged, and globule laid open by the separation of its valves. F, Spores
and elatets of JZquisetum. G, Spores surrounded by elaters of Equlsetum.
Spirillum ; and consequently they have been the cause of
much controversy. Schleideri, very properly denying their
animal nature, says : " They are nothing more than fibre
318 THE MICROSCOPE.
in an early stage of development." The Characeoe are all
aquatic plants of filamentous structure. Some authors
have divided the species into two genera, Nitella (simple
tubes) and Chara (cortical tubes). The circulation in
the ordinary tubes or cells consists in the movement
of the gelatinous protoplasmic sac, seen, as one mass, slowly
passing up one side, across the ends, and down the
opposite side, not perpendicularly, but in an oblique or
spiral course, as indicated in the figure. The Characcoe
multiply by gemmas, produced at the articulations of
their stems.
Mr. H. J. Carter, in a paper of great interest, published
January, 1857, on the "Development of the Boot-cell and
its Nucleus, in Chara Verticillata? describes a structureless
cell-wall, and a protoplasm composed of many organs.
" This," he says, " is surrounded by a cell, the l proto-
plasmic sac,' which is divided into a fixed and rotatory
portion ; these again respectively enclose the nucleus
' granules,' and axial fluid ; while small portions of irre-
gular shaped granular bodies are common to both. If
we take the simple root-cell about the eighteenth hour
after germination, when it will be about half-an-inch long,
and l-600th of an inch broad, and place it in water between
two slips of glass for microscopic observation, under a
magnifying power of about four hundred diameters, we
shall find, if the circulation be active and the cell-wall
strong and healthy, that the nucleus, which is globular,
gradually becomes somewhat flattened, having several
hyaline vacuoles of different sizes ; the change goes on
gradually until it appears of more elongated form, growing
fainter on its outline, and then entirely disappears, leaving
a white space corresponding to its capsule or cell-wall,
with a faint remnant of some structure on the centre.
Subsequently, this space becomes filled up with the fixed
protoplasm, and after an hour or two the nucleus re-
appears a little behind its former situation, but now
reduced in size, and with its nucleolus double, instead of
single as before ; each nucleolus being about one-fourth
part as large as the old nucleolus, and hardly perceptible.
Meanwhile a faint septum is seen obliquely extending
across the fixed protoplasm, a little beyond the nucleus ;
DEVELOPMENT OF CHAEA. 31 V
and if iodine be applied afc this time, the division is seen
to be confined to the protoplasm, as the latter, from ccn-
traction, withdraws itself from each side of the line
where the septum appeared, ar>d leaves a free space which
is bounded laterally by an uninterrupted continuation of
the protoplasmic sac. In this way changes go on until its
shape is altered and it becomes converted into a bunch
of rootlets. Thus the new cells are never entirely with-
out a nucleus, which would appear to exert some influ-
ence upon their development, for as soon as the only two
new- cells which the root-cell gives off are formed, the old
nucleus becomes effete.
" Now as to the office of the nucleus, nothing more is
revealed to us in the developmejit of the roots of Chara,
than that, so long as new cells are to be budded forth,
the nucleus continues in active operation, but when this
ceases it becomes effete ; while the rotation of the pro-
toplasm and subsequent enlargement of the cell, &c.,
which are much better exemplified in the plant-stem than
in the root-cell, go on after the nucleus ceases to exist.
Hence the development of the root-cells of Chara affords us
nothing positive respecting the functions of this organ ;
and therefore, if we wish to assign to it any uses in par-
ticular, they must be derived from analogy with some
organism in which there is a similar nucleus whose office is
known. If for this purpose we may be allowed to
compare the nucleus of Chara with that of the rhizo-
podous cell, which inhabits its protoplasm, we shall
find the two identical in elementary composition j that
is, both consist at first of a ' nuclear utricle,' respec-
tively enclosing a structureless homogeneous nucleolus ;
the latter, too, in both, is endowed with a low degree of
movement.
" After this, however, the nucleolus of the Rliizopod cell
becomes granular and opaque ; and when, under circum-
stances favourable for propagation, a new cell-wall is
formed around the nuclear utricle, or this may be an
enlargement of the nuclear utricle itself, I do not know
which ; the granular substance of the nucleolus becomes
circumscribed, and shows that it is surrounded by a sphe-
rical, capsular cell ; the granules enlarge, separate, pass
320 THE MICROSCOPE.
through the spherical capsule into the cavity of the
nuclear utricle ; a mass of protoplasm makes its appearance,
and this divides up into monads, or, as I first called them,
* gonidia.' 1
"The movement of the rotating protoplasm in the
Characece is also very slow ; for, when it is viewed in the
long internodes of Nitella with a very low power, or even
with the naked eye, it seems hardly to move faster thaJ*
the foot of a Gasteropod ; still there is no positive evidence
that it moves round the cell after the manner of the latter,
although it would appear to possess the power of move-
ment per sc. Hence the question remains undecided, viz.
whether it moves round the cell hy itself, or by the aid of
cilia disposed on the inner surface of the protoplasmic sac,
in like manner to those which appear to exist in the
abdominal cavity of Vaginicola crystallina, and which have
been seen in Closterium lunula." 2
The stems and arms of Chara are tubular, and entirely
covered with smaller tubes, the circulation can mostly be
observed in these, as shown at Fig. 170. Any ordinary cut-
ting to obtain sections would squeeze the tube flat, and spoil
it and the lining ; it is, therefore, better to avoid this, by
laying the Chara on smooth wood, just covered with
water; then, with a sharp knife, make suddenly a num-
ber of quick cuts across it, and w> obtain the various
sections required. Wet a slip of glass, and turn the wood
over so as just to touch the water, and the sections
will fall from the wood on to the glass, ready for the
microscope.
"The Chara tribe is most abundant in still waters or
ponds that never become quite dry ; if found in running
water, it is mostly met with out of the current, in holes or
side bays, where the stream has little effect, and never on
any prominence exposed to the current. If the CJiara
could bear a current, its fruit would mostly be carried on
and be deposited in whorls ; but it sends out from its
variouo joints very long roots into the water, and these
would "by agitation be destroyed, and then the plant
(1) Ann. and Mag. Nat. Hist. vol. xvii. 1856.
(2) In Plate I. No. 27, is represented the Moss gonida, assuming the amoeboid
loru as depcribed by Dr. HicKs iu the Linnean Tram. 1882.
CHARA.
321
decays; for although it may grow long before roots ara
formed, yet when they are produced their destruction
involves the death of the plant. In order, therefore, to
preserve Chara, every care must be taken to imitate the
stillness of the water by never shaking or suddenly turning
the vessel. It is also important that the Chara should be
disturbed as little as possible ; and if requisite, it must
be done in the most gentle manner, as, for instance, in
cutting off a specimen, or causing it to descend in order
to keep the summit of the plant below the surface of the
water.
Similar care is requisite forVallisneria; but the warmest
and most equal temperature is better suited to this plant.
It should be planted in the middle of the jar in about
two inches deep of mould, which has been closely
presse^ ; over this place two or three handfuls of leaves,
then gently fill the jar with water. When the water
requires to be changed, a small portion is sufficient to
change at a time. It appears to thrive in proportion to
the frequency of the changing of the water, taking care
that the water added rather increases the temperature
than lowers it.
The natural habitat of the Frog-bit, another water-
plant of great interest, is on the surface of ponds and
ditches ; in the autumn its seeds fall, and become buried
in the mud at the bottom during the winter; in the
spring these plants rise to the surface, produce flowers,
and grow to their full size during summer. Chara may be
found in many places around London, the Isle of Dogs,
and in ditches near the Thames bank.
Anacharis alsinaslrum. This remarkable plant is so
unlike any other water-plant, that it may be at once
recognised by its leaves growing in threes round a slender
stringy stem. The watermen on the river have already
named it " Water-thyme," from a faint general resemblance
which it bears to that plant. In 1851 the Anacharis
was noticed by Mr. Marshall and others in the river
at Ely, but not in great quantities. Next year it had
increased so much, that the river might be said to be full
of it.
The colour of the plant is deep green ; the leaves are
y
322 THE MICROSCOPE.
nearly half an inch long, by an eighth wide, egg-shaped at
the point, and beset with minute teeth, which cause them to
cling. The stems are very brittle, so that whenever the
plant is disturbed, fragments are broken off. Its powers
of increase are prodigious, as every fragment is capable of
becoming an independent plant, producing roots .and
stems, and extending itself indefinitely in every direction.
Most of our water-plants require, in order to their increase,
to be rooted in the bottom or sides of the river or drain
i which they are found ; but this is independent altogether
of that condition, and actually grows as it travels slowly
down the stream after being cut. The specific gravity of
it is so nearly that of water, that it is more disposed to sink
than float. A small branch of the plant is represented,
with a Hydra attached to it, in a subsequent chapter.
Mr. Lawson pointed out the particular cells in which
the current or circulation will be most readily seen
viz. the elongated cells around the margin of the leaf
and those of the midrib. On examining the leaf with
polarised light, these cells, and these alone, are found to
contain a large proportion of silica, and present a very
interesting appearance. A bright band of light encircles
the leaf, and traverses its centre. In fact, the leaf is set,
as it were, in a framework of silica. By boiling the leaf
for a short time in equal parts of nitric acid and water,
a portion of the vegetable tissue is destroyed, and the
silica rendered more distinct, without changing the form
of the leaf. 1
It is necessary to make a thin section or strip from the
leaf of VaUisneria, for the purpose of exhibiting the circu-
lation in the cells, as shown in fig. 170, No. 4. Among the
cells granules, a few of a more transparent character than
the rest, may be seen, having a nucleolus within.
The phenomenon of cell rotation is seen in other plants
besides those growing in water. The leaf of the common
plantain or dock, Plantago, furnishes a good example ; the
movement being seen both in the cells of the plant, and
hairs of the cuticle torn from the midribs. The Spider-
wort will be noticed further on.
(1) See also a paper in Vol. IV. Microscopical Journal of Science, on the Ck
culation in the Leaf of Anacharis, by Mr F H. WeUiaro
STRUCTURE OP PLANTS. 323
Structure of Plants. The development of cells in plants
takes place in all cases in essentially the same "way,
but the form of the result is subject to a number of im-
portant modifications. Most elementary works on Botany
enter so fully into this interesting question, that it is quite
unnecessary to do more than refer very briefly to the
more important structural peculiarities of plants. Cell-
division, as we have seen, is the universal formative pro-
cess by which vegetative growth is effected, and free-cell-
formation occurs only in the production of cells connected
with reproduction. In the lower classes of plants, espe-
cially in aquatic genera, we can observe the process of cell-
division in all its details ; but in the higher, knowledge
of this kind is only accessible by dissection.
As long as the cell retains its primordial utricle, it is
capable of producing new cells, and organized forms of
assimilated matter, like starch, chlorophyll, &c. in its con-
tents. This is the case in all nascent tissues, but it ceases
to be so at various periods in different parts of the vege-
table organization. In all woody tissues, in all pitted and
spiral-fibrous cells it disappears early ; the secondary de-
posits of the ligneous character being formed apparently
from the watery cell-sap. In herbaceous organs, such, as
leaves, in the cells of the cellular plants generally, the
primordial utricle remains. " This explains why the
power to form adventitious buds exists not only in the
cambrium layer of the higher plants, but, under certain
conditions, even in the leaves, and why germination or
propagation by little cellular bulbels, or isolated cells
detached from the vegetative organs, is so common among
the cellular plants, and in the Mosses and Liverworts,
where parenchymatous tissues so greatly predominate."
(Renfrey.)
The tissues of plants, properly so called, copsist of col-
lections of cells of uniform character, permanently combined
together by more or less complete union of their outer sur-
faces. Tissues are of many kinds, according to the form
of the cells, the character of the cell-membrane, and the
manner in which the cells are connected together. Th*
milk- vessels found in connexion with certain cells appear
to be formed out of the intercellular passages, and not by
Y2
824 THE MICROSCOPE.
fusion of celis ; hence they do not constitute a true cellulai
tissue.
Vascular tissue is formed by the fusion of perpendicular
TOWS of cells ; by the absorption of their contiguous walla
they become converted into continuous tubes of more or
less considerable length. Then we have a combination of
tissues destined for particular purposes in the economy of
the plant, divided into three primary systems the Cellular,
the Fibro-vascular, and Cortical. The 1st, Cellular, forms
the great mass of the living structure of plants ; and it is
in this system that the vital processes of vegetation are
chiefly carried on. The 2d, Eibro-vascular, forms all the
woody structures, which in all cases are composed of a
quantity of conjoined portions of cellular and vascular
tissue arranged in a peculiar manner ; differing in their
modes of growth in different classes of plants, and which
in consequence present considerable differences in the
structure of their mature stems. The 3d, Cortical, also
termed the epidermal, exists in the form of a simple flat
layer of cells united firmly together by their sides, and
forming a continuous coat over the surface of a plant.
Such a layer clothes all the organs of plants above the
Mosses, and, as stems grow older, the epidermal layer
gives place to the bark or rind. Stomata are orifices
between the meeting angles of the epidermal cells ; most
abundant usually on the lower surface of leaves, often
wanting on the upper surface. On the leaves of aquatic
plants they are only found on the upper surface, and are
absent where the leaf touches the water.
Hairs and scales of all kind depend on the development
of the epidermal cells. Simple hairs are merely single
epidermal cells produced in a tubular filament, and when
cell-multiplication occurs in them they present a number
of joints ; see hairs of nettle, fig. 188, No. 2. Thorns, such
as those of the rose, are aborted branches, in which the
cells become thickened by woody secondary deposits. In
leathery or hard leaves, and in the thick tough leaves of
succulent plants, such as the aloes, the secondary layers
acquire great thickness. The aerial roots of the Orchi-
daceaa exhibit a curious structure, the growing extremities
being clothed by a whitish cellular tissue composed o^ several
FORMATION OF WOODY FIBRE. 325
layers of cells with a delicate spiral fibrous deposit on
their walls. This layer forms a kind of coat over the real
epidermis of the root, and is known by the name of the
Vela-men radicum. The young shoots of Dicotyledonous
trees and shrubs are clothed with epidermis-like herbaceous
plants ; but, before the close of the past season of growth,
in most cases the green colour gives place to brown, which
is owing to the formation of a layer of cork from the outer
layers of cortical parenchyma. Cork is composed of
tubular thin-walled cells containing only air ; and some-
times these intercellular passages occupy a considerable
space, and communicate in all directions, forming a system
of air-spaces in the tissue. In addition there is the secre-
tory system, consisting of glands, simple and compound,
milk-vessels, and canals filled with resins, oils, &c.
Much of the physiological history of plant life has yet
to be made out : the mode in which the circulation and
the formation of wood are carried on is by no means a
settled question. Mr. Herbert Spencer observes i 1 "That
the supposition that certain vessels and strings of partially
united cells, lined with spiral, annular, reticulated, or
other frameworks, are carriers of the plant juices, is
objected to on the ground that they often contain air ;
as the pressure of air arrests the movements of blood
through arteries and veins, its presence on the ducts of
stems and patioles is assumed to unfit them as channels
for sap. On the other hand, that these structures have
a respiratory office, as some have thought, is certainly
not more tenable, since the presence of air in them
negatives the belief that their function is to distribute
liquid. The presence of liquid in them equally nega-
tives the belief that their function is to distribute air.
!Nor can any better defence be made for the hypothesis
which I find propounded, that these parts serve 'to
give strength to the parenchyma.' In the absence of any
feasible alternative, the hypothesis that these vessels are
distributors of sap claims reconsideration." To obtain data
for an opinion on this vexed question, Mr. Spencer insti-
tuted a series of experiments on the absorption of dyes by
plants. His first experiments were failures, and it was only
(]) LinneanSoc. Trans, vol. xxv. pape 405,
326 THE MICROSCOPE.
after trying experiments with leaves of different ages and
different characters, and with undeveloped axes, as well as
with axes of special kinds, that it became manifest that
the appearances presented by ordinary stems, when thus
tested, are in a great degree misleading. " If an adult shoot
of a tree or shrub be cut off, and have its lower end placed
in an alumed decoction of logwood, or a dilute solution
of magenta, 1 the dye will, in the course of a few hours,
ascend to a distance, varying according to the rate of eva-
poration from the leaves. On making longitudinal
sections of the part traversed by it, the dye is found to
have penetrated extensive tracts of the woody tissue ; and,
on making transverse sections, the openings of the ducts
appear as empty spaces in the midst of a deeply-coloured
prosenchyma. It would thus seem that the liquid is carried
up the denser parts of the vascular bundles, neglecting the
cambium layer, the central pith, aud the spiral vessels of
the medullary sheath." This, however, is found to be only
partially true. " There are indications that while the layer
of pitted cells next the cambium has served as a channel
for part of the liquid, the rest has ascended the pitted
ducts, and oozed out of these into the prosenchyma around.
This is seen, if, instead of allowing the dye time for oozing
through the prosenchyma, the end of the shoot be just
dipped into the dye and taken out again, we find that,
although it has become diffused to some distance round
the ducts, it has left tracts of wood between the ducts
mentioned. Again, if we use one dye after another, a
shoot that has absorbed magenta for an hour and then
placed for five minutes in the logwood decoction, transverse
sections taken at a short distance from the end of the shoot,
show the mouths of the ducts surrounded by dark stains
in the midst of the much wider red stains. The behaviour
of these corresponds perfectly with the expectation that a
liquid will ascend capillary tubes in preference to simple
cellular tissue, or tissue not differentiated into continuous
(1) "These two dyes have affinities for different components of the tissues, and
may be advantageously used in different cases. Magenta is rapidly taken up by
woody Tnatter and secondary deposits, while logwood colours the cell-membranes,
and takes but reluctantly to the substances seized by magenta. By trying both
of them on the same structure, we may guard ourselves against any error arising
froaj relative combination."
STRUCTURE OP PLANTS.
327
canals. Experiments with leaves bring out parallel facts ;
and this, then, is confirmed, that in ordinary stems the
staining of the wood by an. ascending coloured liquid is
due, not to the passage of the coloured liquid up the sub-
Fig. 172. Termination of Vascular System (after Spencer).
1. Absorbent organ from the leaf of Euphorbia neriifolia. The cluster of
fibrous cells forming one of the terminations of the vascular system is here
embedded in a solid parenchyma.
2. A structure of analogous kind from the leaf of Ficus elastica. Here the
expanded terminations of the vessels are embedded in the network paren-
chyma, the cells of which unite to form envelopes for them.
3. End view of an absorbent organ from the root of a turnip. It is taken
from the outermost layer of vessels. Its funnel-shaped interior is drawn as it
presents itself when looked at from the outside of this layer, its narrow end
being directed towards the centre of the turnip.
4. Shows on a larger scale one of these absorbents from the leaf of Panax
Lessonii. In this figure is clearly seen the way in which the cells of the net-
work parenchyma unite into a closely-fitting case for the spiral cells.
5. A less-developed absorbent, showing its approximate connexion with a
duct. In their simplest forms, these structures consist of only two fenestratod
cells, with their ends bent round so as to meet. Such types occur in the cen-
328 THE MICROSCOPE.
tral mass of the turnip, where the vascular system is relatively imperfect
Besides the comparatively regular forms of these absorbents, there are forma
composed of amorphous masses of fenestrated cells. It should be added that
both the regular and irregular kinds are very variable in their numbers : in
some turnips they are abundant, and in others scarcely to be found. Possibly
their presence depends on the age of the turnip.
6. Represents a much more massive absorbent from the same leaf, the sur-
rounding tissues being omitted,
7. Similarly represents, without its sheath, an absorbent from the leaf of
Clusia fiava.
8. A longitudinal section through the axis of another such organ, showing its
annuli of reticulated cells when cut through. The cellular tissue which fill*
the interior is supposed to be removed.
stance of the wood, but to the permeability of its duct&
and such of its pitted cells as are united into regular
canals ; and the facts showing this at the same time in-
dicate with tolerable clearness the process by which wood
is formed, for what in these cases is seen to take place
with dye may be fairly presumed to take place with sap."
Taking it, then, as a fact that the vessels and ducts are
the channels through which the sap is distributed, the-
varying permeability of their Avails, and consequent for-
mation of wood, is due to the exposure of the plant
to intermittent mechanical strains, actual or potential, or
both, in this way. "If a trunk, a bough, shoot, or a
petule is bent by a gust of wind, the substance of its
convex side is subject to longitudinal tension, the substance
of its concave side being at the same time compressed.
This is the primary mechanical effect. The secondary is
when the fesues of the convex side are stretched, they
also produce lateral compression of them. In short, that
" the formation of wood is due to intermittent transverse
strains, such as are produced in the aerial parts of upright
plants by the action of the wind." Thus the subject is
most ingeniously worked out, and the results of many
very interesting and instructive experiments are recorded
by the author of the paper.
" In the course of experiments on the absorption of
dyes by leaves, it happened that, in making sections
parallel to the plane of a leaf, with the view of separating
its middle layer, containing the vessels, I came upon some
structures that were new to me. These structures, where
they are present, form the terminations of the vascular
ey stem. They are masses of irregular and imperfectly
united fibrous cells, such as those out cf vrhich vessels
STRUCTURE OF PLANTS. 329
are developed ; and they are sometimes slender, sometimes
bulky usually, however, being more or less club-shaped.
In transverse sections of leaves, their distinctive characters
are not shown ; they are taken for the smaller veins. It
is only by carefully slicing away the surface of a leaf,
until we come down to that part which contains them,
that we get any idea of their nature. Fig. 172, ISTo. 1, repre-
sents a specimen taken from a leaf of Euphorbia neriifolia.
Occupying one of the interspaces of the ultimate venous
network, it consists of a spirally-lined duct or set of
ducts, which connects with the neighbouring vein a
cluster of half-reticulated, half-scalariform cells. These
cells have projections, many of them tapering, which insert
themselves into the adjacent intercellular spaces, thus
producing an extensive surface of contact between the
organ and the embedding tissues. A further trait is, that
the ensheathing prosenchyma is either but little developed
or wholly absent ; and consequently this expanded vascular
structure, especially at its end, comes immediately in con-
tact with the tissues concerned in assimilation. The leaf
of Euphorbia neriifolia is a very fleshy one ; and in it
these organs are distributed through a compact, though
watery, cellular mass. But in any leaf, of the ordinary
type, which possesses them, they lie in the network of
parenchyma, composing its lower layer ; and wherever they
occur in this layer its cells unite to enclose them. This
arrangement is shown in No. 2, representing a sample
from the Caoutchouc-leaf as seen with the upper part of
its envelope removed ; and it is shown still more clearly
in a sample from the leaf of Panax Lessonii, No. 4.
]S~os. 6 and 7 represent, without their sheaths, other such
organs from the leaves of Panax Lessonii and Clusia
flava. Some relation seems to exist between their forms
and the thicknesses of the layers in which they lie.
Certain very thick leaves, such as those of Clusia flava,
have them less abundantly distributed than is usual, but
more massive. When the parenchyma is developed not
to so great an extreme, though still largely, as in the
leaves of Holly, Aucuba, Camellia , they are not so bulky ;
and in thinner leaves, like those of Privet, Elder, &c.
they become longer and less conspicuously club-shaped.
330 THE MICROSCOPE.
" Some adaptations to their respective positions seem
implied by these modifications ; and we may naturally
expect that in many thin leaves these free ends, becoming
still narrower, lose the distinctive and suggestive characters
possessed by those shown in the drawings. Eelations of
this kind are not regular, however. In various other
genera, members of which I have examined, as JRhus,
Viburnum, Griselinia, JBrexia, Botryodendron, Pereskia,
the variations in the bulk and form of these structures are
not directly determined by the spaces which the leaves
allow; obviously there are other modifying causes. It
should be added that while these expanded free extre-
mities graduate into tapering free extremities, not differing
from ordinary vessels, they also pass insensibly into the
ordinary inosculations. Occasionally, along with numerous
free endings, there occur loops ; and from such loops there
are transitions to the ultimate meshes of the veins.
" These organs are by no means common to all leaves.
In many that afford ample spaces for them they are not to
be found. So far as I have observed, they are absent from
the thick leaves of plants which form very little wood.
In Sempervivum, in Echeveria, in Bryophyllum they do not
appear to exist ; and I have been unable to discern them
in Kalanchoe rotundifolia, in Kleinia ante-eupliorbium, and
ficoides, in the several species of Crassula, and in other suc-
culent plants. It may be added that they are not absolutely
confined to leaves, but occur in stems that have assumed
the functions of leaves. At least I have found, in the
green parenchyma of Opuntia, organs that are analogous,
though much more rudely and irregularly formed. In
other parts, too, that have usurped the leaf-function, they
occur, as' in the phyllodes of the Australian acacias.
These have them abundantly developed ; and it is interest-
ing to observe that here, where the two vertically-placed
surfaces of the flattened-out petiole are equally adapted to
the assimilative function, there exist two layers of these
expanded vascular terminations, one applied to the inner
surface of each layer of parenchyma.
" Considering the structures and positions of these organs,
as well as the natures of the plants possessing them, may
we not form a shrewd suspicion respecting their function]
STRUCTURE OF PLANTS. 331
Is- it not probable that they facilitate absorption of the juices
carried back from the leaf for the nutrition of the stem.
and roots ? They are admirably adapted for performing
this office. Their component fibrous cells, having angles
insinuated between the cells of the parenchyma, are shaped
, just as they should be for taking up its contents, and the
absence of sheathing tissue between them and the paren-
chyma facilitates the passage of the elaborated liquids.
Moreover, there is the fact that they are allied to organs
which obviously have absorbent functions. I am indebted
to Dr. Hooker for pointing out the figures of two such
organs in the Icones Anatomicce of Link. One of them
is from the end of a dicotyledonous root-fibre, and the other
is from the prothallus of a young fern. In each case a
cluster of fibrous cells, seated at a place from which liquid
has to be drawn, is connected by vessels with the parts to
which liquid has been carried. I have met with another
such organ, more elaborately constructed, evidently adapted
to the same office, in the common turnip-root. As shown by
the end view and longitudinal section in Nos. 3, 5, and 8,
this organ consists of rings of fenestrated cells, arranged
with varying degrees of regularity into a funnel, ordinarily
having its apex directed towards the central mass of the
turnip, with which it has, in some cases at least, a traceable
connexion by a canal. Presenting as it does an external
porous surface terminating one of the branches of the vas-
cular system, each of these organs is well fitted for taking
up with rapidity the nutriment laid by in the turnip-root,
and used by the plant when it sends up its flower-stalk.
The cotyledons of young beans furnish other examples
of such structures, exactly in the places where, if they be
absorbents, we may expect to find them. Amid the
branchings and inosculations of the vascular layer running
through the mass of nutriment deposited in each coty-
ledon, there are found conspicuous free terminations that
are club-shaped^ and which prove to be composed, like
those in leaves, of irregularly-formed and clustered fibrous
cells, some of them diverging from the plane of the vascular
layer, dipping down into the mass of starch and albumen
which the young plant has to utilize, and which these
structures can have no other function but to take up."
332
THE MICROSCOPE.
To return to cell- development ; we found the cell chang-
ing in its outward form, the transparent membranous cell
wall becoming thickened, and spontaneous fissure taking
place; and thus is formed a series of connected cells
variously modified and arranged, according to the conditions
under which they are developed and the functions which
they are destined to exercise. The typical form, as we have
Fig 173. o, elementary cells ; 6, branched cellular tissue.
before observed, of the vegetable cell is spheroidal ; but
when developed under pressure within walls, or denser
tissues, it takes other shapes ;
as the oblong, lobed, square,
prismatical, cylindrical, fusi-
form, muriform, stellate, fila-
mentous, &c. : and is then
termed Parenchyma, and the
cells woven together are called
cellular tissue. In pulpy fruits
the cells may be easily separated
one from the other : a thin trans-
verse section of a strawberry is
represented at fig. 188, No. 15 :
within the cells are smaller
cells, commonly known as the
pulp. Fig. 173, a, is the ele-
mentary form of oval cells or
I, A transverse section of stom^of vesic l eS) passing on to the for-
" mation of branched cellular
tissue, b. Remarkable speci-
mens of the filamentous tissue may be seen in fig. 188,
No. 19, the circular elongated cells from the Mushroom;
only another and more closely connected giowth of inuce-
dinous fungi, commonly called mushroom spawn.
Equisetum, showing
nal shape of cells. 2, A vertical
section of elongated cell.
CELLULAR TISSUES.
333
Fig. 176. Stellate tisui,from ttem
of a Rush.
Fig. 175, in the stellate tissue cut from the stem of a
rush, we have the forma-
tive network dividing into
ducts for the purpose of
giving strength and light-
ness to the stem of the plant.
These ducts may undergo
other transformations; the
cell itself become gra-
dually changed into a
spiral continuous tube or
duct, as seen in fig. 198 ;
these are sometimes formed by the breaking down of the
partitions ; in the centre of which we may have a com-
pound spiral duct, resembling portions of trachese from
the silkworm.
Another important change occurs in the original cell,
it is that of its conversion into woody fibre. Common
woody fibre (Pleurenchyma)
has its sides free from de-
finite markings. In the
coniferous plants, the tubes
are furnished with circular
discs ; these discs are
thought to be contrivances
to enable the tubules of
the WOOdy tissues tO dis- Fig. 176. A section of stem of Clematis,
i j> . r> vnlh pores, highly magnified, to shot*
Charge their Contents from the line which passes round Mem.
one to the other, or into the
Cellular spaces. Plants having aromatic secretions are
furnished with glands ; these form a series of interesting
objects, and such as the sage-leaf should be mounted as
opaque specimens. A large central gland is seen in a section
of a leaf from Ficus elastica, India-rubber-tree, fig. 177, No. 2.
Professor Quekett observes, " The nature of the pores, or
discs, in conifers, has long been a subject for controversy ;
it is now certain that the bordered pores are not peculiar to
one fibre, but are formed between two contiguous to each
other, and always exist in greatest numbers on those sides
of the woody fibres parallel to the medullary rays. They
are hollow ; their shape biconvex ; and in their centre ia
334
THE MICROSCOPE.
a small circular or oval spot, fig. 176 : the latter may
occur singly, or be crossed by another at right angles,
Fig. ITT.
1, Vertical section of root of Alder, with outer wall. 2, A vertical section of a
leaf of the India-rubber tree, exhibiting a central gland.
which gives the appearance of a cross, as in fig. 204, Nos. 3,
4, a vertical section of fossil wood, remarkable for having
three or four rows of woody tissue occupied by large pores
without central markings."
We now pass to the milk, lacticiferous ducts or tissue,
the proper vessels of the old
writers. These ducts con-
vey a peculiar fluid, some-
times called latex, usually
turbid, and coloured red,
white, or yellow ; often,
however, colourless. It is
supposed they carry latex
to all the newly-formed
organs, which are nourished
by it. The fluid becomes
darker after being mounted for specimens to be viewed
under the microscope. This tissue is remarkable from its
resemblance to the earliest aggregation of cells, the yeast-
plant, and therefore has some claim to being considered
the stage of development preceding that of the reticu-
Fig. 178. Lact'iciferous tissue,
CELLULAR TISSUES.
335
lated ducts seen in fig. 178. In a section from tho
India-rubber-tree, fig. 177, No. 2, a network of these lac-
tiferous tubes will be found filled with a brownish or
Fig.l7.
1, A portion of the leaf of Sphagnum, showing ducts, vascular tissue, and spira
fibre in the interior of its cells. 2, Porous cells, from the testa of GOUK
seed, communicating with each other, and resembling ducts.
granular matter ; that in fig. 178 is an enlarged view of
this tissue from the wood of an exogen, taken near the
root.
TBittitiutaku'iriiTinwiWLuVi
1, Reticulated ducts.
Fig. 180.
2, A vertical section of Fern-root.
In many plants external to the cuticle, there exists a
very delicate transparent pellicle, without any decided
traces of organisation, though occasionally somewhat gra-
nular in appearance, and marked by lines that seem to
be impressions of the junction of the cells in contact with
each other. In nearly all plants, the cuticle is perforated
336
THE MICROSCOPE.
by minute openings termed Stomata, which are bordered by
cells of a peculiar form, distinct from those of the cuticle.
In Iris germanica, fig. 181, each surface has nearly 12,000
fl*tt
1. Fig. 181. 2.
1, Portion of a vertical section of the Leaf of the Iris: a, a, elongated cells of
the epidermii ; b, stomata cut through longitudinally; c, c, cells of the
parenchyma; d, d, colourless tissue of the interior of the leaf. 2, Portion of
leaf of Iris germanica, torn from its surface; a, elongated cells of the cuticle;
b, cells of the stomata; c, cells of the parenchyma: d, impressions on the epi-
dermic cells ; e, lacunae in the parenchyma,
stomata in every square inch ; and in Yucca each surface
has about 40,000.
The structure of the leaf of the common Iris shows
a central portion, formed by thick-walled colourless tissue,
very different from ordinary leaf-cells or from woody fibre.
rtg. 182. A portion of the epidermii of the Sugar-cane, showing the two kinds a/
cells of tnhitk ii is composed, ( Magnified 200 diameters.)
CELLULAR TISSUE. 337
Variously-cut sections of leaves should be made, and slices
taken parallel to the surfaces at different distances, for the
purpose of microscopic examination.
Among the cell-contents of some plants, are beautiful
crystals called Raphides : the term is derived from pa^i?
a needle, from the resemblance of the crystal to a needle.
They are composed of the phosphate and oxalate of lime ;
there is a difference of opinion as to their use in the
economy of the plant.
Mr. Gulliver has insisted upon the value of Raphides
as characteristic points in many families of plants.
He observes that doubts as to the value of raphides as
natural characters and as to their importance in the vege-
table economy at all will be entertained by those who do
not clearly distinguish between raphides and sphaeraphides.
Schleiden asserts that the "needle-formed crystals, in
bundles of from twenty to thirty in a cell, are present in
almost all plants," and " that inorganic crystals are rarely
met with in cells in a full state of vitality."
He further states that so really practical is the presence
or absence of raphides, that by noticing them he has been
able to pick out pots of seedling OnagraceaB, which had
been accidentally mixed with pots of other seedlings of
the same age, and at that period of growth when no
botanical character before in use would have been so
readily sufficient for the diagnosis.
If we examine a portion of the layers of an onion, fig.
183, No. 1, or a thin section of the stem or root of the
garden rhubarb, fig. 183, No. 4, we shall find many cells.
in which, either bundles of needle-shaped crystals, or
masses of a stellate form occur, not strictly raphides.
Raphides were first noticed by Malpighi in Opuntia.
and subsequently described by Juriue and Raspail.
According to the latter observer, the needle-shape or
acicular are composed of phosphate, and the stellate of
oxalate of lime. There are others having lime as a basis,
in combination with tartaric, malic, or citric acid. These
are easily destroyed by acetic acid, and are also very soluble
in many of the fluids employed in the conservation of ob-
jects; some of them are as large as the l-40th of an inch,
others are as small as the 1 -1000th. They occur in all
2
338
THE MICROSCOPE.
parts of the plant ; in the stem, bark, leaves, stipules,
petals, fruit, root, and even in the pollen, with some
exceptions. They are always situated in the interior
of cells, and not, as stated by Raspail and others, in the
Fig. 183.
I, A section from the outer layer of the bulb of an Onion, showing crystals of
carbonate of lime. 3, Cells of the Pear, showing Sclerogen, or gritty tissue.
4, Cells of garden Rhubarb, filled with raphides. 5, Cells from same, filled
with starch-grains.
intercellular passages. 1 Some of the containing cells be-
come much elongated ; but still the cell- wall can be readily
traced. In some species of Aloe, as, for instance, Aloe
verrucosa, with the naked eye we are able to discern small
silky filaments: when magnified, they are found to be
bundles of the acicular form of raphides, which no doubt
act the part of a stay or prop to the internal soft pulp.
In portions of the cuticle of the medicinal squill
SciUa maritima several large cells may be observed, full
of bundles of needle-shaped crystal. These cells, however,
do not lie in the same plane as the smaller ones belonging
to the cuticle. In the cuticle of an onion every cell is oc-
cupied either by an octahedral or a prismatic crystal of
oxalate of lime : in some specimens the octahedral form
predominates ; but in others from the same plant the
(I) "As an exception, many years ago they were discovered in the interior of
the spiral vessels in the stem of the grape-vine ; but with some botanists this
vould not he considered as an exceptional case, the vessels being regarded as
elongated cells." Quekett.
CEYSTALS IN PLANTS.
339
yabra.
crystals will be principally prismatic, and are arranged aa
if they were beginning to assume a stellate form. Some
plants, as many of the cactus
tribe, are made up almost
entirely of raphides. In
some instances every cell of
the cuticle contains a stel-
late mass of crystals ; in
others the whole interior is
full of them, rendering the
plant so exceedingly brittle,
that the least touch will
occasion a fracture; so much
so, that some specimens of
Cactus senilis, said to be a
thousand years old, which
were sent a few years since
to Kew from South America,
were obliged to be packed
-^.i n .1 Fig. 184 Siliceous cuticle from
in COtton, With all the Care surface of leaf of Deutzia scab
of the most delicate jewel-
lery, to preserve them during transport.
Raphides, of peculiar figure, are common in the bark of
many trees. In the Hiccory
(Carya alba) may be ob-
served masses of flattened
prisms having both extre-
mities pointed. In vertical
sections from the stem of
Elceagnus angustifolia, nu-
merous raphides of large size
are embedded in the pith.
Raphides are also found in
the bark of the apple-tree,
and in the testa of the seeds
of the elm ; every cell con-
tains two or more very
minute crystals.
In figs. 184 and 185 we
have other representations
of the crystalline structure
z 2
. 185. Siliceous cuticl", of Qrtut
(Pharus cristatut),
340
THE MICROSCOPE.
of plants, in sections taken from grass, and the leaf of
Deutzia scabra. This insoluble material is called silica,
and is abundantly distributed throughout certain orders
of plants, leaving a skeleton after the soft vegetable
matters have been destroyed : masses of it, having the
appearance of irregularly-formed blackened glass, will
always be found after the burning of hay or straw ; which
is caused by the fusion of the silica contained in the
cuticle combining with the potash in the vegetable tissue,
thus forming a silicate of potash (glass). To display this
siliceous structure, it is necessary to cut very thin slices
from the cuticle, and mount them in fluid or Canada
balsam.
In the Oraminacece, especially the canes ; in the Equi-
setum hyemale, or Dutch rush ; in the husk of the rice,
wheat, and other grains,
silica is abundantly found.
In the Pharus cristatus,
an exotic grass, fig. 185,
we have beautifully-ar-
ranged masses of silica with
raphides. The leaves of
Deutzia, fig. 184 are re-
markable for their stel-
late hairs developed from
the cuticle, of both their
upper and under surfaces ;
forming most interesting
arid attractive objects when
examined under the micro-
scope with polarised light.
See Plate VIII. No. 173.
Silica is found in all Ru-
liacece; both in the stem
ft,nd leaves, and if present in sufficient thickness, depolarises
light. This is especially the case in the prickles, which
all these plants have on the margin of the leaves and the
angles of the stem. One of the order Compositce, a plant
popularly known as the "sneezewort," (Archillce ptarmica)
has a large amount of silica in the hairs found on the
double serratures of its leaves ; commonly said to be tho
Fig. 186. -Portion of the husk of Wheat,
showing siliceous crystals.
CELL-CONTENTS . STARCH.
341
cause of its errhine properties when powdered and used as
snuff. It is in the underlying or true epidermis, that the
silica occurs. This membrane is permeable by fluids, not
by means of pores, but by endosmotic force.
The most generally -distributed and conspicuous of the
^ell-contents is Starch; at
the same time it is one of
great value and interest, per-
forming a similar office in
the economy of plants as that
of fat in animals. It occurs
in all plants at some period of
their existence, and is the
chief and great mark of dis-
tinction between the vege-
table and animal kingdoms.
Its presence is detected by
testing with a solution of.
iodine, which changes it to
a characteristic blue or violet
colour. 1 Being insoluble in
COld Water, it Can be readily Fig- 187. Section of a Cnne; with ;ell-
washed away and separated j$f e % wmgrTnu^mauJr!^ P T<
from other matters contained
in the cellular parts of full-grown plants. It is often
found in small granular masses in the interior of cells,
shown in fig. 183 from the garden-rhubarb. Starch-grains
are variable in size: the tous-les-mois, fig. 188, No. 5, are
very large ; in the potato, No. 14, they are smaller ; and
in rice, No. 6, they are very small indeed. Nearly all pre-
sent the appearance of concentric irregular circles; and most
of the granules have a circular spot, termed the hilum,
around which a large number of curved lines arrange them-
selves : better seen under polarised light. Plate VIII. No. 1 67,
Leeuwenhoek, to whom we are indebted for the earliest
notice of starch-granules, enters with considerable minute-
ness into a description of those of several plants such as
wheat, barley, rye, oats, peas, beans, kidney-beans, buck-
wheat, maize, and rice ; and very carefully describes
experiments made by him in order to investigate the
structure of starch-granules. Dr. Reissek regards tha
(1) This is not a test for starch when combined with albuminous matters.
342 THE MICROSCOPE.
granule as a perfect cell, from the phenomena presented
during its decay or dissolution, when left for some time in
water. Schleiden and others, after examining its expan-
sion and alteration under the influence of heat and of
sulphuric acid, considered it to be a solid homogeneous
structure.
Professor Busk agrees with M. Martin in believing the
primary form of the starch-granule to be " a spherical or
ovate vesicle, the appearance of which under the micro-
scope, when submitted to the action of strong sulphuric-
acid, conveys the idea of an unfolding of plaits or rugffi,
which have, as it were, been tucked in towards the centre
of the starch-grain." 1 The mode of applying the concen-
trated sulphuric acid is thus described by Mr. Busk : " A
small quantity of the starch to be examined is placed
upon a slip of glass, and covered with five or six drops of
water, in which it is well stirred about ; then with the
point of a slender glass-rod the smallest possible quantity
of solution of iodine is applied, which requires to be
quickly and well mixed with the starch and water; as
much of the latter as will must be allowed to drain on\
leaving the moistened starch behind, or a portion of it
may be removed by an inclination of the glass, before it is
covered with a piece of thin glass. The object must be
placed on the field of the microscope, and the J-inch
object-glass brought to a focus close to the upper edge of
the thin glass. With a slender glass-rod a small drop of
strong sulphuric acid must be carefully placed immediately
upon, or rather above the edge of the cover, great care
being necessary to prevent its running over. The acid
quickly insinuates itself between the glasses, and its course
may be traced by the rapid change in the appearance of
the starch-granules as it comes in contact with them.
The course of the acid is to be followed by moving the
object gently upwards ; and when, from its diffusion, the
re-agent begins to act slowly, the peculiar changes in the
starch- granules can be more readily witnessed. In pressing
or moving the glasses, the starch disc becomes torn, and
is then distinctly seen, especially in those coloured blue, to
(1) Professor G. Busk, F.R.S., on the Structure of the Starch-granule; Quar-
terly Journal of Microtcoyical Science, April, 1853.
CELL-CONTENTS STARCH.
343
consist of two layers, an upper and a lower one ; and the
collapsed vesicular bodies of an extremely fine but strong
and elastic membrane." Mr. Busk believes the hilum
to be a central opening into the interior of the ovate
vesicle.
Fig. 188.
1, Nucleated Cells. 2, Stinging-nettle Hairs, Urtica Dioica. 3, Ciliated spores
of Conferva;. 4, Starch grains, broken by the application of heat. 5, Starch
from Toits-les-mois. 0. Starch from Rice. 7, Starch from Sago. 8, Imita-
tion Sago-starch. 9, Wheat-starch. 10, Rhubarb-starch, in isolated
cells. 11, Maize-starch. 12, Oat-starch. 13, Barley-starch. 14, Potato-
starch. 15, Section of Strawberry, cells ovoid, containing granular matter.
16, Section of Potato, with starch destroyed by fungoid disease. 17, Potato,
with nearly all starch-grains absent. 18, Section of Potato, cells filled with
healthy starch. (These starches are grouped for comparison.) 19, Mushroom
spawn, elongated cells.
Nitric acid communicates to wheat-starch a fine orange-
yellow colour; and recently-prepared tincture of guaiacum
gives a blue colour to the starch of good wheat-flour.
344 THE MICROSCOPE.
Pure wheat-flour is almost entirely dissolved in a strong
solution of potash, containing twelve per cent, of the alkali ;
but mineral substances used for the purpose of adultera-
tion remain undissolved.
Wheat-flour is frequently adulterated with various sub-
stances ; and in the detection of these adulterations, the
microscope, together with a slight knowledge of the action
of chemical re-agents, lends important assistance. It
enables us to judge of the size, shape, and markings on the
starch grains, and thereby to distinguish the granules of
Pig. 189. Wheat-Flour Starch-granules, with a small portion of Us cellulose.
(Magnified 420 diameters.)
one meal from that of another. In some cases the micro-
scopic examination is aided by an application of a solu-
tion of potash. Thus we may readily detect the mixture
of wheat-flour with either potato-starch, meal of the
pea or bean, by the addition of a little water to a small
quantity of the flour, then, by adding a few drops of
a solution of potash (made of the strength one part liquid
potash to three parts of water), the granules of the potato-
ADULTERATION OF WHEAT-FLOUR. 345
starch will immediately swell up, and acquire three 01 four
times their natural size ; while those of the wheat-starch
are scarcely affected by it ; if adulterated with pea or bean
meal, the hexagonal tissue of the seed is at the same time
rendered very obvious under the microscope. Polarised
light will be of use as an additional aid ; wheat-starch
presents a faint black cross proceeding from the central
hilum, whereas the starch of the oat shows nothing of
the kind.
Fig. 190. Potato Starch-granules, sold under the name of British Arrow-root,
used to adulterate flour and bread, (Magnified 240 diameters.)
The diseases of wheat and corn are readily detected
under the microscope ; some of which will be seen to be
produced by a parasitic fungus, and by an animalcule re-
presented in another place : all are more or less dangerous
when mixed with articles of food.
Adulteration of bread with boiled and mashed potatoes,
next to that by alum, is, perhaps, the one which is most
commonly resorted to. The great objection to the use of
potatoes in bread, is, that they are made to take the place
346 THE MICROSCOPE.
of an article very much more nutritious. This ad alteration
can be instantly detected by means of the microscope.
The cells which contain the starch-corpuscles are, in the
potato, very large, fig. 190 ; in the raw potato they are
adherent to each other, and form a reticulated structure,
in the meshes of which the well-defined starch-granules
are clearly seen ; in the boiled potato, however, the cells
separate readily from each other, each forming a distinct
article : the starch-corpuscles are less distinct and of an
altered form.
Fig. 181. Adulterated Cocoa, sold under the name of Homoeopathic Cocoa.
(After Hassall.)
a a a, granules and cells of cocoa; bbb, granules of Canna-starch, or Tous-lt*-
mois; c, granules of Tapioca-starch.
Adulteration with alum and "stuff." This adulteration
is practised with a twofold object : first to render flour of
a bad colour and inferior quality white and equal, in
appearance only, to flour of superior quality ; and secondly
to enable the flour to retain a larger proportion of water,
ADULTERATION OF FOOD.
347
by which the loaf is made to weigh heavier. By dissolving
out the alum in water and then re-crystallising it under
the microscope, this adulteration is readily detected.
Before leaving the subject of starch, allusion may be
made to the prevalent and destructive epidemic amongst
potatoes, which is a disease of the tuber, not of the haulm
or leaves. " Examined in an early stage, such potatoes
are found to be composed of cells of the usual size ; but
they contain little or no starch : this will be seen upon
reference to Nos. 16 and 17, fig. 188. Hence it may be
Fig. 192. Structure and Character of genuine Ground Coffee. {After Hassall.)
inferred, that the natural nutriment of the plant being
deficient, the haulm dies, the cells of the tuber soon turn
black and decompose; and fungi developed as in most
other decaying vegetable substances.
"This will undoubtedly explain the most prominent
symptom of the potato-disease, the tendency to decom-
position ; and is a point in which the microscope confirms
the result of chemical experiment : for it has been found
348
THE MIQROSCOPE.
that the diseased potatoes contain a larger proportion of
water than those that are healthy. A want of organizing
power is evidently the cause of this deficiency of starch ;
but we fear the microscope will never tell us in what the
want of this organising force consists." l
The adulteration of articles of food and drink has long
been a matter of uneasy interest, and of strong, though
vague, misgiving. Accum's Death, in the Pot, between
thirty and forty years ago, awoke attention to the subject;
which has since been more or less accurately explored by
Fig. 193. Sample of Coffee, adulterated with both Chicory and Roasted
Wheat. (After Hassall.)
< a a, small fragments of coffee ; b b b, portions of chicory ; ccc starcri-grai/uiea
of wheat.
Mitchell, Normandy, Chevalier, Jules Garnier, and Harel;
and has at length derived a singularly lucid exposi-
tion from Dr. Hassall's researches, whose report of these
inquiries fills between 600 and 700 closely printed pages
(I) Professor Quekett's Histology of Vegetables. We would refer the reader
to a curious work on Fungi, by Arimini, an Italian botanist, 1759.
ADULTERATION OP FOOD. 349
of a large octavo, replete with details of the fraudulent
contaminations commonly practised by the people's pur-
veyors, at the people's expense of health and pocket. 1
" In iiearly all articles," said Dr. Hassall, before a com-
mittee appointed by the House of Commons to inquire
into these adulterations, " whether food, drink, or drugs,
my opinion is that adulteration prevails. And many of
the substances employed in the adulterating process were
not only injurious to health, but even poisonous." The
microscope was the effective instrument in the work of
Fig. 194. Tea adulterated with foreign leaves. (After Hassall.)
a, upper surface of leaf ; b, lower surface, showing cells; c, chlorophyll cells;
d, elongated cells found on the upper surface of the leaf in the course of the
veins ; e, spiral vessel ; /, cell of turmeric ; g, fragment of Prussian blue ; /.
particles of white powder, probably China clay.
-detection. Less than five years ago, it would, we are told,
have been impossible to detect the presence of chicory in
coffee : in fact, the opinion of three distinguished chemists
was actually quoted in the House of Commons to that effect ;
(1) Food and Us Adulterations ; comprising the Reports of the Analytical Sani-
tary Commission of the Lancet, for the years 1851 to 1854 inclusive. By Arthui
dill Hassall, M.D.
360 THE MICROSCOPE.
whereas by the use of the microscope the differences of
structure in these two substances, as in many other cases,
can be promptly discerned. Out of thirty-four samples of
coffee purchased, chicory was discovered in thirty-one ;
chicory itself being also adulterated with all manner of
compounds. There is no falling back either upon tea or
chocolate ; for these seem rather worse used' than coffee.
Tea is adulterated, not only here, but still more in China ;
while as to chocolate, the processes employed in corrupting
the manufacture are described as " diabolical." " It is
2
Fig. 195.
I, Radiating cells from the outer shell of the Ivory Nut. 2, Section of a Nut,
* showing cells with small radiating pores.
often mixed with brick-dust to the amount of ten per
cent., ochre twelve per cent., and peroxide of iron twenty-
two per cent*., and animal fats of the worst description. In
this country, cocoa is sold under the names of flake, rock,
granulated, soluble, dietetic, homoeopathic cocoa, <kc., fig.
191. Such names are evidently employed to disguise the
fact that they are compounded of sugar, starch, and other
substances.
To return to the subject more immediately before us
Some of the plants belonging to the Orchidese Com-
melinece particularly Tradescantia virginica (Spiderwort),
portions of the epidermis, and the jointed hairs of
the filament, form interesting microscopic objects. The
surface of the latter is marked with extremely fine longi-
tudinal parallel equidistant lines or stria}, whose intervals
are equal, from about 18 ^ 00 to ^ ^ 60 of an inch. It
might therefore in some cases be used as a micrometer or
test object. The nucleus of the joint or cell is very dis-
tinct as well as regular in form ; and by gentle pressure
CIRCULATION OF SAP IN PLANTS. 351
Is easily separated entire from the joint. It then appears
to be exactly round, nearly lenticular, and its granular
matter is either held together by a coagulated pulp not
visibly granular, or, which may be considered equally pro-
bable, by an enveloping membrane. The analogy of this
nucleus to that existing in the various stages of develop-
ment of the colls in which the grains of pollen are formed
in the same species, is sufficiently obvious.
In the joint of the same, when immersed in water,
being at the same time freed from air, and consequently
made more transparent, a circulation of very minute
granular matter is visible. This requires at least a J power
to show it well. The motion of the granular fluid is
seldom in one uniform circle, but in several apparently
independent currents : and these again, though often
exactly longitudinal, and consequently in the direction of
the striae of the membrane, are not unfrequently observed
forming various angles with these striae. The smallest of
the currents appear to consist of a single series of granules.
The course of these currents seems often in some degree
affected by the nucleus, towards or from which many of
them occasionally tend or appear to proceed. They can
hardly, however, be said to be impeded by the nucleus,
for they are occasionally observed passing between its
surface and that of the cell ; a proof that this body does
not adhere to both sides of the cavity, and also that the
number and various directions of the currents cannot be
owing to partial obstructions arising from the unequal
compression of the cell.
Flower-buds. "In the very early stage of the flower-
bud, while the anthera are yet colourless, their loculi
are filled with minute lenticular grains, having a trans-
parent flat limb, with a slightly convex and minutely
granular semi-opaque disc. This disc is the nucleus of
the cell, which probably loses its membrane or limb, and,
gradually enlarging, forms in the next stage a grain also
lenticular, and which is marked either with only one
transparent line dividing it into two equal parts, or with
two lines crossing at right angles, and dividing it into four
equal parts. In each of the quadratures a small nucleus
is visible ; and, even where one transparent line is only dis-
352 THE MICROSCOPE.
tinguishable, two nuclei may frequently be found in each
semicircular division. These nuclei may be readily ex-
tracted from the containing grain by pressure, and after
separation retain their original form. In the next stage,
the greater number of grains consist of the semicircular
divisions, naturally separated, but now containing only
one nucleus, which has gradually increased in size. In
the succeeding stage the grain apparently consists of the
nucleus of the former stage, but considerably enlarged,
and having an oval form, and a somewhat granular surface.
This oval grain, continuing to increase in size, and in the
thickening of its membrane, acquires a pale yellow colour;
and is now the perfect grain pollen."
In the whole tribe of Orchidese an abundance of raphides
may be found in almost every part of the cellular tissue.
The crystals are usually cylindrical in form, and so arranged
as to disguise their true character, often causing them to
be overlooked : by making use of a dark-ground illumina-
tor, or polarised light, this is not likely to occur. The
cause of the disease known as " spot " in Orchids, of
which several kinds have been noticed by cultivators, has
been traced by Mr. Berkeley, in one instance, to the oc-
currence of a minute parasitic fungus, belonging to the
genus Leptothyrium. A description of the disease, with
illustrations, giving the general appearance of the diseased
leaves, and a magnified figure of the parasite, appears in
the 1st part of the new series of the Journal of tJie Horti-
cultural Society.
Tlie Colouring matter of Flowers. M. F. Hildebrands,
having carefully investigated the colouring matters of
flowers, has arrived at the following conclusion respecting
them, and their distribution in the tissue of the several
organs.
1. That the colour of flowers is in constant connexion
with the cell contents, never with the walls of cells.
2. Blue, violet, rose, and (if there be no yellow in the
flower) deep red are due, with little exception, to a cell-
fluid of corresponding colour.
3. Yellow, orange, and green, are usually associated
with solid, granular, or vesicular substances in the
cells.
WOODY TISSUE.
353
4. Brown or gray, and in many cases bright red and
orange (apparen tly uniform to the naked eye), are found
to be compounded of other colours, as yellow, green, or
orange -with violet, or green and red; bright red and orange
in like manner of blue-red with yellow or orange.
5. Black, excepting in the bean, is due to a very deeply-
coloured cell-fluid.
6. All the cells of an organ are rarely uniformly
coloured.
7. The colour usually resides in one or in a few of the
outer layers of cells.
8. The coloured cells are but exceptionally covered by
a layer of uncoloured ones.
9. Combinations of colour are occasioned by diversely-
coloured matters in the same or in adjacent cells.
The Woody tissue of plants is not without its interest,
it consists of elongated transparent tubes of considerable
strength : some are almost entirely made up of this
tissue. It is by far the most useful, and supplier
material for our linen, cordage, paper, and many
other important articles in every
branch of art. This tissue, re-
markable for its toughness, is
termed fibre, the outer membrane
of which is usually structureless.
In Flax and Hemp, in which the
fibres are of great length, there
are traces of transverse markings,
and tubercles at short intervals.
In the rough condition, in which
it is imported into this country,
the fibres have been separated, to
a certain extent, by a process
termed hackling. It is once
more subjected to a repetition of
hackling, maceration, and bleach-
ing, before it can be reduced to the
white silky condition required by the spinner and weaver
when it has the appearance of structureless tubes, fig. 197 B.
China-grass, New Zealand flax, and some other plants, pro-
duce a similar ntviterial, but are not so strong, in conse
Fibres $ gJ t - on B Fibre "
354
THE MICROSCOPE.
quence of the outer membrane containing more lignine.
It is important to the manufacturer that he should be
able to determine the true character of some of the textures
of articles of clothing, and this he may readily do with the
microscope. In linen we find each component thread made
up of the longitudinal, roundel, unmarked fibres of flax ; but
if cotton has been mixed, we recognise a flattened, more or
less twisted band, as in fig. 1966, having a very striking
resemblance to hair, which, in
reality, it is ; since, in the condi-
tion of elongated cells, it lines the
inner surface of the pod. These,
again, should be contrasted with
the filaments of silk, fig. 196 A, and
also of wool, fig. 197 A. The latter
may be at once recognised by the
zigzag transverse markings on its
fibres. The surface of wool is
covered with these furrowed and
twisted fine cross lines, of which
there are from 2,000 to 4,000 in
an inch. On this structure de-
pends its felting property. In
or58. B ' ' a judging of fleeces, attention should
be paid to the fineness and elasti-
city of the fibre, the furrowed and scaly surface, as shown
by the microscope, the quantity of fibre in a given surface,
the purity of the fleece, upon which depend the success of
the scouring and subsequent operations.
In the mummy-cloths of the Egyptians, flax only was
used, whereas the Peruvians used cotton alone. By recent
improvements introduced into the manufacturing pro-
cesses, flax has been reduced to the fineness and texture of
silk, and made to resemble other materials.
Silk is secreted from a pair of long tubes ending in
a pore of the under-lip of the silkworm. Each thread is
made of two filaments coming from these, and they are
glued together by a secretion from a small gland near.
The quality of the silk depends on the character and
difference of the two secretions.
All woody fibre is made up of elongated cells, generally
Fig. 197.
A, Wool of Sheei
ments
VASCULAR TISSUE. 355
more or less pointed at both extremities, and having their
walls strengthened by internal deposits. Occasionally,
however, the fibre is short, as in the Clematis, Elder, &c. j
it is marked with pores or dots, from a deficiency of &e
internal deposits at these points.
Vascular tissue consists of
^ells, more or less elongated,
joined end to end, or over-
lapping each other, in which
either a spiral fibre, or a mo-
dification of the same, has
been deposited ; hence, if the
spiral be perfect, it is called
a true spiral vessel ; if inter-
rupted, or the fibre breaks up
into rings, it is termed annu-
lar; if the rings are connected
together by branching fibres,
so that a network, is pro-
duced, the vessel is called
reticulated; if the vertical
fibres are short, and equidis-
tant, the vessel is said to be
scalariform, from its resemblance to a ladder. Spiral
vessels have been also termed tracheae, from their resem-
blance to the air-tubes of insects, as in fig. 198.
Under this head other membranaceous tubes are included.
in which the arrangement of the fibre has been consider-
ably modified in its deposition. Elongated tubes or ducts,
with porous walls, come under the head of vascular tissue ;
they somewhat differ from the spiral varieties, inasmuch
as they cannot be unroiled without breaking. It is a
curious fact, that mostly the spiral coils from right to
left ; and it has been suggested that the direction of the
fibre may determine that in which the plant coils round
an upright pole. The Hop has left-handed spirals, and is
a left-handed climber, which would therefore appear to
support this theory. The nature of the fibre, and the
development of the tissue, have been frequently the subject
of dispute between botanists.
The late Mr. Edwin Quekett gave much attention to this
A A 2
Pig. 198. Simple and compound
spiral vessels.
356 THE M1CEOSCOPE.
subject; and published an excellent paper in the Micro-
scopical Society's Transactions, 1840 ; the results of has
observations on the development of vascular tissue.
1 Fig. 189.
1, Interior cast of the siliceous portion of spiral tubes of the Opuntia. 2, Vertical
section of Elm, showing spiral fibre.
In order to watch the development of the membranous
tnbes of plants, no better example can be chosen than the
Fig. CO.
A transverse section of Taxus baceata (Yew), showing the woody fibra
J, Vertical section of tbe Yew, exhibiting pores and spira) fibres.
VASCULAR TISSUE. 357
young flower-stalk of the long-leek (Allium porrum), in
the state in which this vegetable is usually sent to market;
it is then most frequently found to be about an inch or
Pig. 201.
1 , Portion ot transverse section of stem of Cedar, showing pith, wood, and bark.
2, Portion of transverse section of stem of Clematis, showing medullary rays.
more in length, and from a quarter to half an inch in
diameter. This membrane occurs very low down amidst the
sheathing bases of the leaves; and from having to lengthen
to two or three feet, and containing large vessels, it forms
a very fit subject for ascertaining the early appearances of
the vascular tissue.
To examine the development of vessels, it is necessary
to be very careful in making dissections of the recent
plant ; and it will be found useful to macerate the specimen
for a time in boiling water, which will render the tissues
more easily separable. When the examination is directed
in search of the larger vessels, it will be found that at this
early stage they present merely the form of very elongated
cells, arranged in distinct lines; amongst which some
vessels, especially the annular, will be found matured
even before the cytoblasts have disappeared from the cells
of the surrounding tissue.
As development proceeds, the vessels rapidly increase
in length, till they arrive at perfection. No increase in
diameter is perceptible after their first formation. At
this period, in the living plant the young vessels appear
full of fluid, which is apparently, as remarked by Schleiden,
of a thick character, and which he has designated vege-
table jelly ; by boiling which, or by the addition of alcohol,
the contents, or at least the albuminous portion, become
coagulated. From this circumstance, every cell appears
358 THE MICROSCOPE.
to enclose another in a shrivelled condition ; this state is
sometimes so far extended, that a thick granular cord is
all that can be seen of the contents.
The period of growth at which the laying dojvn of
fibre commences, determines the distance between the
several coils; for instance, when it is
first formed, the coils are quite close,
scarcely any perceptible trace of mem-
brane existing between them. In the
annular vessel, the development of
the cell and the adherence of the
granules to each other ave conducted
in the same manner ; the deposit
showing a tendency towards the spiral
direction, by the presence of a spire
connecting two rings, or by a ring
being developed in the middle of a
spiral fibre. The annular vessel is
the first observed in the youngest
parts of plants, and when found alone
Fig. 202.-^ section from indicates a low degree of organisation ;
the stem of a coniferous as sllOWll by its Occurrence 111 Sp/lO-
?S^a^SSS^^, JKquisetum, and lycopodium,
the zones of annual w hich plants, in the ascending scale of
growth, annual rings. *. , ,, ? , , , .
vegetation, are almost the first that
possess vascular tissue.
It will be found that spiral fibre occurring with rings
marks a higher step in the scale of organising power; the
true spiral more so; and the reticulated and dotted mark
the highest ; this being the order in which these several
vessels are placed in herbaceous exogens proceeding from
within outwards, the differences of structure of the several
vessels being indices of the vital energy of the plant at
the several periods of its development. In those vessels
in which the annular or spiral character of the fibre is
departed from, some curious modifications of the above
process are to be observed, as in the reticulated vessels
met with in the common balsam (Balsamina hortensis).
The primary formation of fibre in these vessels :s marked
by the tendency of the granules to take a spiral course,
when it happens that some one of the granules becomes
VASCULAR TISSUE. 35<)
enlarged by the deposition of new matter around it. This
becomes a point originating another fibre or branch, which
becomes developed by the successive attraction of granules
into bead-like strings, taking a contrary direction to the
original fibre, forming a cross-bar, or ramifying, thereby
causing the appearance by which the vessel is recognised.
Jn the exogenic vessel, the development of fibre proceeds
in the same manner as in the last example ; but the vessels
will be seen to be dotted with a central mark, usually of a
red colour, which, when viewed under high power, may be
thought to resemble a minute garnet set in the centre of
each dot. This red colour is owing to the dot being
somewhat hollowed or cupped, and the centre only thin
membrane. These vessels are 'best seen in the young
shoots of the Willow. In the endogenic vessel the con-
necting branches are given off beneath each other, so that
the dots, which are rounded, are arranged in longitudinal
rows ; but in the acrogenic, or scalariform, in which the
vessels are generally angular, and present distinct facets,
the branches come off in the same line, corresponding
generally to the angles of the vessel ; the spaces left
between are linear instead of round.
Mr. E. Quekett affirms, in opposition to the views enter-
tained by Mirbel, Richard, and Bischoff, "that the dots
left in these several vessels are not holes, neither do they
consist of broken-up fibre, but are the membranous tubes,
unsupported by internal deposit ; and on account of the
extreme tenuity of the tissue, and the minute space between
the fibres, the light in its transmission becomes decomposed,
and appears of a greenish-red hue. The structure of the
dot is best seen by examining the broken edge of any such
vessels, when it will be found that the fracture has been
caused by the vessel giving way from one dot to another,,
so that the torn edge of the membrane can be observed in
each dot."
PREPARATION OF VEGETABLE TISSUES.
The proper mode of preparing and preserving vegetable
tissues is a matter of some importance to the microscopist;
we therefore propose to add a few general directions for
the student's guidance.
360 THE MICROSCOPE.
Vegetable tissues are best prepared for the microscope
by making thin sections, either by maceration, by tearing be-
tween the thumb and the blade of a knife, or by dissection.
Th3 spiral and other vessels of plants require to be
dissected out under a simple magnify ing-glass. Take, for
instance, a piece of asparagus, and separate with the
needle-points the vessels, which require to be finished
under a magnifying-glass, in a single drop of distilled
water. When properly done, keep in spirits of wine and
Tater until mounted.
Vascular tissue requires both maceration and dissection
for its separation. The cuticle or external covering of
plants is an interesting structure; but the beauty of all
vegetable tissues is greatly enhanced by staining a?
directed in a previous chapter.
Cellular tissue maybe studied in fine sections from the
pith of elder, pulp of peach, pear, &c. The petals of flowers
are mostly composed of cellular tissue; their brilliant co-
louring arises from the action of light upon the fluid con-
tents of the cells. In the petal of the anagallis, or scarlet
chickweed, the spiral vessels diverging from the base, and
the singular cellules which fringe the edge, are interest-
ing objects ; the petal of the geranium being one of the
most beautiful for microscopic examination. The usual
way of preparing it is by immersing the leaf in sulphuric
ether for a few seconds, allowing the fluid to e vaporate,and
then mounting it dry. Dr. Inman of Liverpool suggests the
following method : " First peel off the epidermis from the
petal, which may be done by making an incision through
it at the end of the leaf, and then tear it forwards by
the forceps. This is then arranged on a slip of glass, and
allowed to dry ; when dry, it adheres to the glass. Place
on it a little Canada balsam diluted with turpentine, and
boil it for an Instant over the spirit-lamp ; this blisters it
but does not remove the colour ; then cover it with a thin
slip of glass, to preserve it. Many cells will be found
showing the mamilla very distinctly, and the hairs sur-
rounding its base, each being slightly curved and pointed
towards the apex of the mamilla. It is these hairs and the
tuamilla which give the velvety appearance to the petal/'
Fibro- cellular tissue is found readily in Sphagnum or
PREPARATION OP TISSUES. 361
bog-moss, and in the elegant creeper Cobcea tcandens. In
some orchidaceous plants the leaves are almost entirely
composed of it. A modification of this form of tissue is
found in the testa of some seeds, as in those of Sdlvia,,.
Collomia grandiflora, &c.
The curious and interesting sporules of ferns, when
ripe, burst, and are dispersed to a distance; so that they
should be gathered before they come to maturity, and
mounted as opaque objects. The development of ferns
may be observed by placing the seeds in moistened flannel,
and keeping them at a warm temperature. At first a
single cellule is produced, then a second ; after this the
first divides into two, and then others follow ; by which a
lateral increase takes place.
The pollen-grains of most flowers are very interesting
objects ; the darker kinds show best when mounted in
dark cells, and viewed as opaque objects ; the more trans -
Fig. 203. Pollen grains and seeds.
A, Seed of Clove-pink. B, Poppy seed. c. Pollen of Passion flower (Pastiflora
ccerulea). D, Pollen of Cobcea scandens.
parent should be mounted in fluid, to show internal
structure. The prettiest and most delicate forms are found
in Amarantacece, Cucurbitacece, Malvaceae, and Passiflorece ;
others are furnished from the Convolvulus, Geranium,
Campanula, Hollyhock, and some other plants. Re-
markable forms of pollen-grains are shown in fig. 203.
362
THE MICROSCOPE.
Many of the smaller kinds of seeds will reward the
microscopist ; use only a low power ; that of Caryo-
phyllum (clove-pink), is regularly covered with curiously-
jagged divisions; every one of which has a small bright,
black hemispherical knob in its middle, represented in
fig. 160, A.
The seeds of the carrot are remarkably formed,
having some resemblance to a star-iish, with its long
radiating processes. The seeds of umbelliferous plants
have peculiar receptacles for essential oil, in their coats,
termed vittce; various points of interest may be noted
as occurring in the testae, envelopes of seeds, such as
the fibre-cells of Cobcea, and the stellate cells of the
Star-anise.
All plants are provided with hairs ; and a few, like
insects, with hairs of a defensive character. Those in
the Urtica dioica, commonly called the Stinging-nettle, are
elongated hairs, developed from the cuticle, usually of a
conical figure, and containing an irritating fluid ; in some
of them a circulation is visible : when examined under the
microscope, with a power of 100 diameters, they present
the appearance seen at fig. 188, No. 2. At No. 3, same
figure, are represented a few interesting ciliated spores
from Confervce.
The circulation of the fluid-contents of vegetable cells
may be examined at the same time with the Chlorophyll
globules, by selecting for the purpose the transparent
water-plants Chara, Nitella, Anacharis, and Vallisneria,
or the hairs of Groundsel and Tradescantia. The circula-
tion of the sap in plants growing in water is termed by
botanists Gyclosis.
Fossil plants. We detect in some of the primordial
fossils a noticeable likeness to families familiar to the
modern algseologist. The cord-like plant, Chorda filium,
known as ' dead men's ropes,' from its proving fatal at
times to the too adventurous swimmer who gets entangled
in its thick wreaths, had a Lower Silurian representative,
known to the palaeontologist as the Palceochorda, or
ancient chorda, which existed, apparently, in two species,
a larger and a smaller. The still better known Chondrus
crispus, the Irish moss, or Carrageen moss, has, likewise,
FOSSIL PLANTS. 363
its apparent, though more distant representative, in Clion-
dritis, a Lower Silurian alga, of which there seems to
exist at least three species. The fucoids, or kelp-
weeds, appear to have also
their representatives in such
plants as Fucoides gradlis.
of the Lower Silurians of
the Malverns ; in short, the
Thcdlogens of the first ages
of vegetable life, seem to
have resembled, in the group,
and in at least their more
prominent features, the Algcc
of the existing time. And
with the first indications of
land we pass direct from the
Thallogens to the Acrogens,
from the sea-weeds to the
fern - allies. The Lycopo-
diacece, or club-mosses, bear
in the axils of their leaves
minute circular cases, which
form the receptacles of their
spore-like seeds. And when,
high in the Upper Silurian
system, and just when pre-
paring to quit it for the
Lower Old Red Sandstone,
we detect our earliest ter-
restrial organisms, we find that they are composed exclu-
sively of those little spore-receptacles.
" The existing plants whence we derive our analogies in
dealing with the vegetation of this early period, contribute
but little, if at all, to the support of animal life. The
fenis and their allies remain untouched by the grazing
animals. Our native club-mosses, though once used in
medicine, are positively deleterious ; horsetails (Equise-
tactce), though harmless, so abound in silex, which wrap
them round with a cuticle of stone, that they are rarely
cropped by cattle ; while the thickets of fern which cover
our hill and dell, and seem so temptingly rich and green
Fig. 204.
Woody fibre from the root of the
Elder, exhibiting small pores. 2,
Woody fibre of fossil wood, showing
large pores. 3, Woody fibre of fossil
wood, bordered with pores and spirai
fibres. 4, Fossil wood taken from coal,
364
THE MICROSCOPE.
in their season, scarce support the existence of a single
creature, and remain untouched, in stem and leaf, from
their first appearance in spring, until they droop and
wither under the frosts of early winter.
" It is not until we enter into the earlier Tertiaries that
we succeed in detecting a true dicotyledonous tree ; on such
an amount of observation is this order determined, that
when Dr. John Wilson, the Parsee Missionary, submitted
to me specimens of fossil woods which he had picked up
in the Egyptian Desert, in order that, if possible, I might
determine their age, I told him that if they exhibited the
coniferous structure, they might belong to any geologic
period from the times of the Lower Old Red Sandstone
downwards; but if they manifested in their tissue the
dicotyledonous character, they could not be older than the
times of the Tertiary. On submitting them in thin slices
to the microscope, they were found to exhibit the peculiar
dicotyledonous structure as strongly as the oak or chest-
nut. And Lieutenant Newbold's researches in the deposit
in which they occur has since demonstrated, on strati-
graphical evidence, that it belongs to the comparatively
modern formations of the Tertiary.
" The flora of the coal measures was the richest and most
luxuriant, in at least individual productions, with which
the fossil botanist has formed any acquaintance. Never
before or since did our planet bear so rank a vegetation as
that of which the numerous coal seams and inflammable
shales of the carboniferous period form but a portion of
the remains, the portion spared, in the first instance, by
dissipation and decay, and in the second by the denuding
agencies. Almost all our coal, the stored-up fuel of a
world, forms but a comparatively small part of the pro-
duce of this wonderful flora. Yet, with all this singularly
profuse vegetation of the coal measures, it was a flora un-
fitted, apparently, for the support of either graminivorous
bird or herbivorous quadruped. Nor floes the flora of the
Oolite seem to have been in the least suited for the pur-
poses of the shepherd or herdsman. Not until we enter
on the Tertiary periods do we find floras amid which man
might have profitably laboured : nay, there are whole orders
and families of plants, of the very first importance to man,
FOSSIL PLANTS. 365
which do not appear until late in even the Tertiary ages.
The true grasses scarce appear in the fossil state at all.
For the first time, amid the remains of a flora that seems
to have had its few flowers, the Oolitic ages, do we
detect, in a few broken fragments of the wings of butter-
flies, decided traces of the flower-sucking insects. Not,
however, until we enter into the great Tertiary division do
these become numerous. The first bee makes its appear-
ance in the amber of the Eocene, locked up hermetically
in its gem-like tomb, an embalmed corpse in a crystal
coffin, along with fragments of flower-bearing herbs and
trees. Her tomb remains to testify to the gradual fitting
up of our earth as a place of habitation for a creature
destined to seek delight for the mind and eye, as certainly
as for the proper senses, and in especial marks the intro-
ductiDn of the stately forest trees, and the arrival of the
delicious flowers." 1
"Sweet flowers ! what living eye hath viewed
Their myriads ? endlessly renewed ;
Wherever strikes the sun's glad ray,
Where'er the subtile waters stray,
Wherever sportive zephyrs bend
Their course, or genial showers descend. *
(1) Hugh Miller's Testimony of the Rocks.
CHAPTER li.
DIVISION OP ANIMAL KINGDOM.
BHIZOPODA POLYCYSTINA DIATOMACEJE FO8SH.
INFUSORIA, SPONGID,E, HYDROZOA, VO RTIGELIuB,
ACTINOZOA, BOTIFEB^:, POLYZOA. frc.
'INGE our very limited space forbade
more than a cursory glance at
the many and varied points of
beauty and arrangement dis-
played in every part of the vege-
table kingdom; so in the pre-
sent division is it necessary
to be equally brief in noticing
the wonders displayed by the
help of the microscope, in the
world of animal life. In the
course of remarks made upon
the early condition of vegetable
life, we drew attention to the difficulties presented in all
attempts to mark out the boundary line between vege-
tables and animals, and to define where the one ends,
and the other begins.
Upon reviewing the different characters by which
:t has been attempted to distinguish the special subjects
of the botanist and zoologist, we find that animals and
plants are not two natural divisions, but are specialised
members of one and the same group of organised beings.
When a certain number of characters concur in the same
organism, its title to be regarded as a " plant," or an
" animal," may be readily recognised ; but there are very
numerc is living beings, especially those that retain the
DIVISION OF ANIMAL KINGDOM. 367
form ot nucleated ceils, which manifest the common or-
ganic characters, but are without the true distinctive
superadditions of either kingdom.
The animal kingdom is conveniently arranged under the
following primary groups, sub-kingdoms, or departments :
PROTOZOA, COSLENTERATA, ANNULOSA, MOLLUSCA, and
VERTEBRATA. These are again divided into classes, classes
into orders, orders into families, families into genera, and
genera into species. In the first-named department, the
Protozoa, is included a vast number of creatures of the
simplest organisation, classified as follows : 1. Gregarinidse,
2. Rhizopoda, 3. Polycystina, 4. Thalassicollid^e, 5. Spongidae,
6. Infusoria. It is not unusual to place Ehizopoda and
its typical form, Amoeba, in the front rank; and as the
presence of a mouth characterises the Infusoria, the re-
maining part of the Protozoa are frequently designated by
a collective name, AstomcOa.
The first-named, G-regarinidce, form a group of the very
simplest structural character, and any one of them, setting
minor modifications aside, may be said to consist of a sac,
composed of a more or less structureless membrane, con-
taining a soft semi-fluid substance, in the midst of which
is a circular vacuole or vesicle, having in its centre a more
solid particle or nucleus. Professor Huxley appends to
this description the obvious, but highly important re-
flection, that its statements are all true concerning the ova
of any of the animals much higher in the scale. 1 The
Gregarinidce inhabit the bodies of other animals, and they
multiply by becoming encysted, and dividing into a multi-
tude of minute objects, called pseudo-navicellce, from their
resemblance in shape to the ship-like diatoms (naviculce).
When a young pseudo-nayicella escapes, it behaves some-
what like an amreba, and, if it chance to get swallowed
by an appropriate host, it grows into the parent form.
The whole life-history of these creatures is not known, as
they have not been traced into the exhibition of sexual
properties ; and it is therefore possible that their position
in the scale may not be exactly denned.
In the course of the numerous investigations made of
the flesh of animals dying during the year 1866 from the
3attle-plague, it was noticed that large quantities of pecu-
liar bodies infested the muscular structures, more especially
(1) Huxley's "Lectures on the Elements of Comparative Anatomy."
368 THE MICROSCOPE.
that of the heart, and it was supposed that these had
some share in the production of the disease ; but upon
making further investigations this has been found not to
be so, and since the same bodies are known to be gene-
rally distributed throughout the ultimate fibres of animals
dying from other diseases, the only interest that can
attach to the discovery is, that it promises to add some
valuable facts to our knowledge of the remarkable group
of Protozoa, the Gregarince. The Gregarines observed
in the flesh of oxen, and described by Dr. Beale,
have elongated spindle-shaped sacs, containing granular
reniform bodies arranged horizontally, and apparently
capable of multiplying by division. The investing
sac is covered with minute, motionless, hair-like bodies.
"No nucleus is present in the sac; but the reniform
granular masses are stated by Dr. Cobbold to possess
nucleoli The structure thus presented is not far removed
from that of many Gregarince, particularly of the larger
individuals occurring in the earthworm, though the hair-
like processes sometimes observable on these are con-
sidered as extraneous by Dr. Leiberkiihn. The compacted
leniform- masses may be considered as the results of a pro-
cess of segmentation, similar to that by which the pseudo-
naviculse are formed. The bodies thus described are by
no means peculiar to diseased cattle ; they are met
with in the healthy muscles of the ox, sheep, pig, deer,
rat, mouse, mole, and perhaps other animals. Gregarince,
in various stages, are represented in Plate III. figs. 53,
54, 55, and 56. Miescher, in 1843, described such bodies,
taken from the muscles of a mouse, and a very good
account of them, obtained from the muscles of a pig, is
given by Mr. Eainey, in the " Philosophical Transactions,"
for 1857, though he erroneously regarded them as the
young stage of cestoid entozoa. They have been described
under a variety of titles, such as worm-nodules, egg-sacs,
eggs of the fluke, young measles, " corpuscles produced by
muscular degeneration" &c. When considered in con-
nexion with the minute cysts described by Gabler, Virchow,
and Dressier, from the human liver, they have an especial
interest; and the observations of Lindemann on the psoro-
Bpermiol sacs obtained from the hair of a peasant at
GREGARINA OF EARTHWORM. 369
Nischney-Novgorod, and in the kidneys of a patient who
died from Blight's disease, bear very strongly on the nature
of these bodies. The people of Novgorod are believed to
get these parasites from washing in water in which Grega-
rince abound. 1 The most interesting inquiry which is
placed before us by these various facts is whether, as
Professor Leuckart has observed, " the psorospermiae "
(aid we may add the " spurious entozoa " of cattle, and
even many so-called Gregarince) are to be considered as
the result of a special animal development, or whether
they are the final products of pathological metamor-
phosis.
It appears, from the reseaches of M. Claparede and
others, that some of the unilocular forms do present very
curious, elongated, and active forms, which, from their
movements and general appearance, might be mistaken for
nematodes. Dr. Joseph Leidy has, in the " Transactions
of the Philadelphia Society, 1853," denied the fact that
the Gregarince are unicellular animals, on the following
grounds : In the examinations of some new species of
Gregarince which he has described, and also in the
G. Jllotharum of Siehold, he discovered that the membrane
enclosing the granular mass of the posterior sac was
double. He observes : " Within the parietal tunic of the
posterior sac is a second membrane, which is transparent,
colourless, and marked by a most beautiful set of exceed-
ingly regular parallel longitudinal lines."
M. Leiberkiihn contributed a very elaborate paper
on the Gregarina of the earthworm. He does not express
any very decided opinion upon the two questions which
have been discussed by Leidy and Bruch, but devotes the
principal part of his memoir to the development and re-
production of the Gregariiia3. With regard to the develop-
ment of Gregarinte into a filaria-like worm, which Bruch
thought probable, M. Leiberkiihn says but little, but,
nevertheless, has proved beyond doubt that the nematodes
(1) Many vague and improbable statements appeared at one time on a sup-
posed discovery of Gregarinse in the human hair. Upon a more careful exami-
nation being made by competent persons, the foreign body proved to be a well-
known vegetable fungus, often found associated with a disease, or duty
uoglect'ed stat t of the skin. It is very well known that Gregarines are nevei
found on free >r exposed surfaces.
B B
370
THE MICROSCOPE.
of tlio earthworm are developed from eggs, whence they
emerge, not as Gregarinae, but as true nematodes. The
transformation of two Gregarinae, after a process of encysta
tion, into navicula-like bodies, has been fully described by
Bruch ; but Leiberkiihn has more carefully illustrated the
changes that go on, and has endeavoured to trace the ex-
istence of the pseudo-naviculae after they have Leen
expelled from the cyst. In the perivisceral cavity of the
earthworm he found large numbers of small corpuscles,
exhibiting amoeba-like movements, and likewise pseudo-
navicula?, containing granules, formed from encysted Gre-
garine. He imagines that these latter bodies burst, and
that their contained granules develope into the amoeDiform
bodies which subsequently become Gregarinae. M. Lei-
berkiihn shortly afterwards published another paper, 'in
which he adopts the same view, that the amoebiform
corpuscles of the blood of fish are Gregarines. But few
physiologists will feel disposed to agree with him, in
considering these bodies as parasites.
Mr. E. Eay Lankester has contributed a valuable
and exhaustive paper on this subject ; x he observes : " I
have made careful examination of more than a hundred
worms, for the purpose of studying these questions, but
have succeeded in arriving at no other conclusion than
that certain forms of these may be the products of encysted
Gregarinse. The G. Lumbrid is one of those forms which
are unilocular, and are met with most frequently among
Annelids. It consists of a transparent contractile sac
(which has not hitherto been demonstrated to be formed
by more than a single membrane), enclosing the charac-
teristic granules and vesicle. The vesicle is not always very
distinct, and is sometimes altogether absent ; occasionally
it contains no granules, sometimes several, one of which
is generally nucleated. In some of these cysts a number
of nucleated cells may be seen, developing together from
the enclosed Gregarina, which gradually become fused
together and broken up, until the entire mass is converted
into these nucleated bodies, which are then evident in
different stages of development, assuming the form of a
(1) E. Ray Lankester, " On the Gregarinidae found in the common Earth-
worm," Micros. Trans. voL iii. p. 83.
PROTOZOA. GREGARINJE. 37 1
double cone, like that presented by some species of
Diatomaceae, whence their name pseudo-naviculae. At
length the cyst contains nothing but pseud o-naviculae,
sometimes enclosing granules, which gradually disappear,
and finally the cyst bursts. Encystation seems to take
place much more rarely among the bilocular forms of
Gregarinae than in the unilocular species found in the
earthworm and other Annelids."
In the Gregarince the food is taken in indiscriminately
at every point of the surface of the body by imbibition.
The food most likely is in the fluid state. In Spongilla,
also, this is probably the case. But it is generally agreed
that in Amoeba, Actinophrys, and agastric Infusoria, only
solid alimentary particles are taken as food. The simplest
animal is indeed far more complex than is implied in the
word unicellular, and it can be clearly proved that there
are few points in common between a simple cell and a so-
called unicellular protozoon. The system of contractile
vesicles and dependent sinuses, so general in the least
organized protozoon, is unknown in the history of cells.
Fluid absoption by the surface is the normal method of
feeding in these low types of animal life. This absorptive
faculty is an inherent property of the substance of which
they are composed. It attracts certain aliments, as gela-
tine attracts water. Tissue, distinguished by the same
character, prevails throughout the entire class of the Pro-
tozoa. Although the Gregarince mostly inhabit the intes-
tines of invertebrate animals, they are often found in the
alimentary canal of the Vertebrata. In this class they
appear to be represented, however, by very closely allied
organisms, the Psorospermice. Muller gave this last-
mentioned name to some very singular minute bodies he
discovered within sacs upon the skin and gills, and in the
internal organs, of many fishes. These animals are gene-
rally of a cylindrical or somewhat elliptical form, although
sometimes a sort of head appears to be produced by the
constriction of the anterior extremity of the body, and
this head-like portion is occasionally furnished with a
curious 'soft process and lobes. They are very sluggish in
their movements, although a few possess true cilia. Their
curious mode of development, with other points in the
BBS
372
THE MICROSCOPE.
history of these minute parasites, are well worthy of
investigation.
The Rhizopoda appear as creatures of a low type of
organization, and are considered, with the former, to hold
a medium state between animals and vegetables. Almost
all of them live in water ; it would be a fruitless search
to look for distinct internal organs, as the small bladder-
looking spaces enclosed within their substance, believeo
by Ehrenberg to be stomachs, present only the appear-
ance of transparent gelatinous cells, or rather moving
spaces, within the sarcode envelope, and may be regarded
as the earliest dawn of a circulatory system.
The term Rhizopoda is derived from the Greek, and
Fig. 205. Simple Rhizopods.
A, Difflugia proteiformis. B, Difflugia oUonga. c, D, Arcella acuminata and
dentata.
means "root-footed," the body is composed entirely of
gelatinous matter, sarcode, motion being effected by the
extension of portions of the substance into processes,
which, as in fig. 205, is seen to partake of various forms.
Lobosa. In the deposit formed at the bottom of fresh-
water ponds, we may often meet with a singular minute
gelatinous body, which constantly changes its form even
under our eyes ; and moves about by means of finger-liko
processes, called pseudopodia, which it appears to have tho
power of shooting out from any part of its substance.
PROTOZOA. AMCEB A.
373
This shapeless mass is well known to microscopic observers
under the name of the Proteus (Amoeba diffluens, fig. 206),
which, from the continual changes of shape it presents, is
Pig. 206. Amceba diffluent, or Proteus, in different forms.
honoured with the name of a fabled god, who could be
either animal, vegetable, or mineral in his nature. This
curious animal presents us with the essential characters of
the large class Rhizopoda in their simplest form. It ap-
pears to be of an exceedingly voracious disposition, seizing
upon any minute aquatic animals or plants that may come
in its way, and appropriating them to the nutrition of its
own gelatinous body. The mode in which this tender
and apparently helpless creature effects this object is very
remarkable. The gelatinous matter of which it is com-
posed is capable, as we have seen, of extension in every
direction ; accordingly, when the A moeba meets with any-
thing that it regards as suitable for its support, the sub-
stance of the creature, as it were, grows round the object
until it is completely enclosed within its body. The sub-
stances swallowed (if such a term be admissible) by this
hungry mass of jelly are often so large, that the creature
itself only seems to form a sort of gelatinous coat enclosing
its prey.
Professor Ecker believes in an exact similarity of con-
tractile substance between that of the lower animal forms,
such as the Rhizopoda, and that observed in the Hydra.
He says : " The properties of this substance, in its simplest
form, are seen in the Amoeba, the body of which, as is
known, consists of a perfectly transparent albumen-like
homogeneous substance, in which nothing but a few
gran- lies are imbedded, and which presents no trace of
374 THE MICROSCOPE.
further organization. This substance is in the highest
degree extensible and contractile ; and from the main mass
are given out, now in one part and now in another, per-
fectly transparent rounded processes, which glide over the
glass like oil, and are then again merged in a central mass.
There is no external membrane. In the body of the
Amoeba there occur, besides the granules, clear spaces with
fluid contents, which are sometimes unchangeable in
form, and sometimes exhibit rhythmical contractions."
Belonging to the family is the very curious Acineta of
Ehrenberg, Actinophrys sol, " sun-animalcule." This
creature consists of a jelly-like contractile substance, or
sarcode, with tentacular filaments radiating from the
central mass, in such a manner as to have suggested the
name for the species. It abounds in pools where Desmi-
diacece are found in many parts around London ; they
are ravenous feeders, not only upon the Desmidiacece, but
also upon all kinds of minute spores and animalcules.
(Plate III. fig. 66.) It was on examining some beautiful
Desmidiacece that my attention was arrested by the
curious appearance of two or three very small Actinophrys
floating very lightly upon the surface of the water, in the
form of a ball, with their delicate tentacular filaments
perfectly erect all over their bodies ; in fact, they seemed
to be floating upon these delicate filaments. 1
The most beautiful forms of the Rhizopoda are found
among those possessing a calcareous covering, as the
Polythalamia, Rosalina, Faujasina, &c. ; their systematic
arrangement is founded upon their shells, which exhibit
a very great diversity in form. Out of these forms, it
would appear that the labours of various naturalists in the
last hundred years have made us acquainted with nearly
2,000 recent and fossil Foraminifera ; and although the
observations of Dr. Carpenter 2 tend to show the pro-
bability that very many of these supposed species are
merely varieties, still the number is sufficiently great
fco prove the importance and interesting nature of the
inquiry.
(1) Western, Journ. Micros. Science, vol. iv. New series, p. 110; Clapa-
rede, Ann. Nat. I/is. Second series, vol. xv. p. 211.
(2) Carpenter's "Introduction to the Study of the Foraminifera," published
by theRiySoc. 1862.
FORAMINIFERA
375
Dr. Schultze acknowledges the difficulties attending the
study of the Rhizopoda, and insists, very properly, upon
the necessity of viewing them in all positions, and under
different modes of illumination and of preparation, in
order to arrive at a due conception of their astonishing
conformation. When the shells of Foraminifera are dis-
solved in dilute acid, an organic basis is always left after
the removal of the calcareous matter, accurately retaining
the form of the shell with all its openings and pores.
The earthy constituent is mainly carbonate of lime ; but
Dr. Schultze has satisfied himself of the presence of a
minute amount of phosphate of lime in the shells of
recent Orbiculina adunca from the Antilles and of Poly-
stomella strigilata from the Adriatic.
Fig. 20T.
I, Separated prisms From outer layer of Pinna shell. .?.-Skeletons"of Forami-
nifera from limestone. 3, Recent shell of Polystomella crispa ; viewed wit
dark-ground illuminator.
The solitary Rhizopoda, furnished with a horny shell or
capsule, forming a case for the animal, is nearly the only
representative of the Arcellidce. In the Arcella, from
which the family derives its name, the shell is somewhat
if a bell-shape, with a very large round opening. ID
376 THE MICROSCOPE.
Englypha it is of an oval or flask-like form, with the
opening at the smaller end, and the shell appears asr
though formed of a sort of mosaic of small horny pieces.
In Difflugia^ Fig. 205, A B, the shell is often globular.
Rhizopods which never develop more than one chamber
or loculus are classed as Monothalamia. 1
The Polythalamia, or Multilocular Rhizopods, in their
earliest state, are unilocular ; but, as the animal increases,,
successive chambers are added in a definite pattern for
each family of the order. They all inhabit the sea, and
frequently occur in such great numbers, that the fine
calcareous sand which constitutes the sea-shore in many
places consists almost entirely of their microscopic coats.
At former periods of the earth's history, they existed in
even greater profusion than at present ; and their fragile
shells form the principal constituent of several very
important geological formations. Thus the chalk appears
to consist almost entirely of the shells of these animals,
either in a perfect state, or worn and broken by the action
of the waves ; they occur again in great quantities in the
rnarly and sandy strata of the Tertiary epoch.
In the Stichostegidce the chambers are placed end to-
end in a row, so as form a straight or but slightly curved
shell. In the second family, the Enallostegidce, the
chambers are arranged alternately in two or three parallel
lines ; and as the construction of the shell is always
commenced with a single small chamber, the whole neces-
sarily acquires a more or less pyramidal form. The third
family, the Helicostegidce, presents us with some of the most
beautiful forms that it is possible to meet with in shells.
They, commence by a small central chamber ; and each of
the subsequent chambers, which are arranged in a spiral
form so as to give the entire shell much the aspect of a
minute flattened snail, is larger than the one preceding it.
It is in this family that we find the nearest approach, in
external form, to the large chambered shells of the cepha-
lopodous mollusca, of which the Nautilus pompilius is an
example. The fourth family, the Entomostegidce, stand in the
same relation to the preceding as the Enallostegidoe to the
(1) Diffiugia and Ancella form a connecting link between the naked forms,
Amoeba, Actinophrys, &c. and the shell-bearing Rhizopods, Lagena striata, &c.
GRKGAIUNFDA, POIACVSTINA, FOKAMIMKF.KA, ROTIFKKA, KTC.
PLATE III.
Kduiund Kvans.
FORAMINIFERA.
377
Stichostegidce ; that is to say, the chambers are also arranged
in a spiral form, but in a double series. A fifth family
includes those shells in which the chambers are arranged
round a common perpendicular axis in such a manner that
each chamber occupies the entire length of the shell. The
orifices of the chambers are placed alternately at each end
of the shell, and are furnished with a curious tooth-like
process. The Miliola serve as an example of this family.
Every handful of sea-sand, every shaking of a dried sponge,
and the contents of the stomachs of most Lamellibranch
molluscs, oyster and mussel, are pretty sure to exhibit a
considerable admixture of these minute calcareous, or
occasionally silicious, Foraminifera.
It is considered that the fossil shells, termed Num-
mulites, found in great quantities in the chalk and lowei
tertiary strata, are also to be regarded as members of this
class ; in a fossilized state, whole mountains consist almost
entirely of their shells. The late Professor Quekett had an
opportunity of examining a few living specimens, which, he
says, " are composed of a sarcode element, built up into a
series of chambers with calcareous material."
The great Pyramid of Egypt, covering eleven acres of
ground, is based on blocks of limestone consisting of
Foraminifera, Nummulites, or stone coin, and other fossil
animalcules. Nummulites vary in size from a very minute
object to that of a crown-piece, and many appear like a
snake coiled up in a round form. A chain of moun-
tains in the United States, 300 feet high, seems wholly
formed of one kind of these fossil-shells. The crystalline
marble of the Pyrenees, and the limestone ranges at
the head of the Adriatic gulf, are composed of small
Nummulites. Vast deposits of Foraminifera have been
traced in Egypt and the Holy Land, on the shores of
the Red Sea, Arabia, and Hindostan, and, in fact, may be
said to spread over thousands of square miles from the
-Pyrenees to the Himalayas.
The fossilized Foraminifera in the Poorbaudar lime-
stone, although occasionally reaching the twenty-fifth, do
not average more than the hundredth part of an inch in
diameter ; so that more than a million of them msy be
computed to exist in a cubic inch of the stone. They inay
378 THE MICROSCOPE.
be separated into two divisions those in which the cells
are large, the regularity of their arrangement visible, and
their bond of union consisting of a single constructed por-
tion between each; and those in which the cells are
minute, not averaging more than the 900th part of an
inch in diameter, the regularity of their arrangement not
distinctly seen, and their bond of union consisting of many
thread-like filaments. To ascertain the mineral composi-
tion of the amber-coloured particles or casts, after having
found that it was mostly carbonate of lime with which
they were surrounded, they were placed for a few mo-
ments in the reducing flame of a blow-pipe, and it was
observed that on subsequently exposing them to the influ-
ence of a magnet, they were all attracted by it. Hence, in
a rough way, this rock may be said to be composed of
carbonate of lime and oxide of iron.
By far the greater number of Foraminifera are marine.
They are found in most seas, and in those of the tropics
they increase both in size and variety, forming extensive
deposits.
During the Canadian Geological Survey large masses
of what appeared to be a fossil organism, the Eozoon
Canadense, were discovered in rocks situated near the
base of the Laurentian series of North America. Dr.
Dawson, of Montreal, referred these remains to an animal
of the foraminiferal type ; and specimens were sent by
Sir "W". Logan to Dr. Carpenter, requesting him to subject
them to a careful examination. As far back as 1858 Sir
W. Logan had suspected the existence of organic remains
in specimens from the Grand Calumet limestone, on the
Ottawa river, but a microscopic examination of one of
these specimens was not successful. Similar forms being
seen by Sir William in blocks from the Grenville bed of
the Laurentian limestone were in their turn tried, and
ultimately revealed their true structure to Dr. Dawson.
and Dr. Sterry Hunt.
The masses ot which these fossils consist are composed
of layers of serpentine alternating with calc-spar. It
was found by these observers that the calcareous layers
represented the original shell; and the siliceous layers
the flesh, OT: sarcode y of the once living creature. These
EOZOON CANADENSE. 379
results were arrived at through comparison of the appear-
ance presented by the Eozoon with the microscopic struc-
ture which Dr. Carpenter had previously shown to
characterise certain members of the foraminifera. The
Eozoon not only exceeded other known foraminifera in
size, to an extent that might have easily led observers
astray, but, from its apparently very irregular mode of
growth, its general external form afforded no help in its
identification, and it was only by careful examination of
its minute structure that its true character could be
ascertained. Dr. Carpenter says : " The minute struc-
ture of Eozoon may be determined by the microscopic
examination either of thin transparent sections, or of
portions which have been subjected to the action of
dilute acids, so as to remove the calcareous shell, leaving
only the internal casts, or models, in silex, of the chambers
and other cavities, originally occupied by the substance of
one animal."
Dr. Carpenter found the preservation of minute struc-
ture so complete that he was able to detect " delicate
pseudopodial threads, which were put forth through pores
in the shell wall, of less than 3 ooogth of an inch in
diameter " (see Plate III. figs. 64, 65) ; and in a paper
read at the meeting of the Geological Society he stated
that he had detected Eozoon in a specimen of ophicalcite
from Cesha Lipa in Bohemia, in a specimen of gneiss from
near Moldau, and in a specimen of serpentine limestone
sent to Sir C. Lyell by Dr. Giimbel, of Bavaria, all these
being parts of the great formation of "fundamental"
gneiss, which is considered by Sir Eoderick Murchison
as the equivalent of the Laurentian rocks of Canada.
There can be little doubt that a rich field of research: is
now opened to those who will undertake the examination
of rocks of various ages, which present the appearance
of analogous structure ; as it is, the microscope has been
the means of demonstrating the existence of animal life
at a very ancient geological date ; and, in the words of
Sir W. Logan, " we are carried back to a period so far
remote that the appearance of the so-called Primordial
Fauna may be considered a comparatively modern event."
Recent Foraminifera present symmetrical shells, of
380 THE MICROSCOPE.
minute size for the most part, and consisting, as we
have already seen, either of one, two, or more con-
nected chambers. A jelly-like mass, or " sarcode," occu-
pies the chambers and their connecting passages ; and,
protruding itself both from the external aperture of
Fig. 808.
1, Section of Faujasina . a a, radiating interseptal canals ; *>, their internal
bifurcations ; c, a transverse branch ; d, tubular wall of the chambers. 2,
Rosalina ornata, with its pscudopodia protruded.
the last chamber, and in many cases from the sometimes
numerous perforations in the shell- walls, extends itself not
only over the surface of the shell, but also into radiating
contractile threads or pseudopodia, and into gernniule-like
masses, which latter become coated over with calcareous
matter, and thus form additional segments of the animal. 1
" Foraminifera^ indeed, are to be compared with the
other lowest orders of animals and of plants in the study
of their specific relations. In these several low forms of
creatures we have comparatively few species, but ex-
tremely numerous individuals, with an enormous range of
(1) Among the more important works on Foraminifera, reference may be
made to D'Orbigny's Foraminifkres fossiles du Bassin Tertiaire de Vienna
(Autrihe); Schultze, Ueber den Organismus der Polythalamien, 1854; Car-
penter's and Williamson's Researches on the Foraminifera, Phil. Trans. 1856.
Also an excellent paper by Mr. W. R. Parker, in the Annals of Natural History,
April, 185T. Specimens of Foraminifera may be obtained for examination from
the shaking of dried Sponges; but if required alive they must be dredged for, o
picked off the fronda of living seaweeds, over the surface of which they are
seen to move by the aid of a lens.
FORAMINIFERA.
381
variety. In the higher orders of plants and animals the
specific forms are more definite, there being a more com-
plex organization, harmonizing with the special habits of
each creature ; and the individuals of each species are less
Fig. 209. Foraminifera taken in Deep-sea Sounding*. (Atlantic.)
numerous than is the case in the Protozoans and Proto-
phytes."
These lowly organized Foraminifera, having great
simplicity of structure, more easily adapt themselves to
varying external conditions than the more complex and
specialized higher animals.
382 THE MICROSCOPE.
In the deep-sea soundings, portions of many beau-
tiful Diatoms, figured and described by Professor W.
Smith, in gatherings from the Bay of Biscay, near Biar-
ritz, are Melosira pribrosa, marine, orbicular, cellulate,
Fig. 210. Foraminifera taken in Deep-sea Soundings. (Atlantic.)
cellules, all equal and hexagonal. He writes : " In De-
cember, 1853, I received isolated frustules of this species,
collected on the coast of Normandy, under the above
name, from M. de Brebisson ; and I have since detected
the same in a gathering from the Black Sea. In no case
have I seen the frustules in a recent state, aud do not know
FORAMINIFERA. 383
whether they ever form a lengthened filament. As this is
the only circumstance that would justify their separation
from Coscinodiscus, to which the separated valve would
otherwise seem to belong (Synop. British Diatomacece,
vol. i. p. 22), their position in Melosira must rest upon the
authority of my accurate correspondent."
In figs. 209 and 210 are represented many of the beau-
tiful forms brought up with soundings made in 1856, for
the purpose of ascertaining the depth of the Atlantic,
prior to the laying down of the electric telegraph wire
from England to America; these specimens were taken
from a depth of 2,070 fathoms.
Major S. R J. Owen, while dredging the surface oi
mid-ocean Indian and Atlantic oceans found attached to
his nets a few interesting forms of Ehizopods, belonging to
the two genera Globigerina and Pulvinulina, which always
make their appearance on the surface of the ocean after
sunset. 1
"Many of the forms," writes this observer, "have
hitherto been claimed by the geologist, but I have found'
them enjoying life in this their true home, the siliceous
shells filled with coloured sarcode, and sometimes this
sarcode in a state of distension somewhat similar to that
found projecting from the Foraminifera, but not in such
slender threads. There are no objects in nature more
brilliant in their colouring or more exquisitely delicate in
their forms and structure. Some are of but one colour,
crimson, yellow, or blue ; sometimes two colours are found
on the same individual, but always separate, and rarely if
ever mixed to form green or purple. In a globular
species, whose shell is made up of the most delicate fret-
work, the brilliant colours of the sarcode shine through the
little perforations very prettily. In two specimens of the
triangular and square forms (Plate III. figs. 44, 45, and
46), the respective tints of yellow and crimson are vivid
and delicately shaded. In one the pink lines are concen-
tric ; while another is of a stellate form (fig. 43), the
points and uncoloured parts being bright clear crystal,
while a beautiful crimson ring surrounds the central por-
(1) Journ. Linn. Soc. vol. viii. p. 202 ; vol. ix. p. 147, 1866, and
1867.
384 TIIE MICROSCOPE.
lion. One globular species appears like a specimen of the
Chinese ball-cutting one sphere within another ; but it
is of a marked and distinct kind.
"The shells of some of the globular forms of these
Polycystina, whose conjugation I believe I have witnessed,
are composed of a fine fretwork, with one or more large
circular holes ; and I suspect the junction to take place
by the union of two such apertures. That the figures of
these shells become elongated, lose their globular form
after death, and present a disturbed surface is seen in
some of the figures represented near the bottom part of
Plate III." Major Owen proposes to make Orbulina a
subgenus of Globigerina. The internal chambers of the
former are in form remarkably like those of the latter,
and like them also they present themselves with varying
surfaces, some free from, while others are covered with,
spines. Those without internal chambers have been
known as Orbulina universa, fig. 78, Plate III. while
figs. 75 and 76, although members of the same family,
have been separated ; but he wishes to see all united under
the name of " Globigerina universa"
The minute siliceous shells of Polycystina present won-
derful beauty and variety of form ; all are more or less
perforated, and often prolonged into spines or other pro-
jections, through which the sarcode body extends itself
into pseudopodial prolongations resembling those of Acti-
nophrys. When seen besporting themselves in all their
living splendour, their brilliancy of colouring, says Major
Owen, "renders them objects of unusual attraction." We
have endeavoured to give some idea of the colour of the
living forms in Plate III. Nos. 43 to 52. The same ob-
server believes that they wish to avoid the light, " as they
<ire rarely found on the surface of the sea in the day time ;
it is after sunset, and during the first part of the night
especially, that they make their appearance."
The Polycystina appear to have most affinity with the
Foraminifera. Thirty four genera and about two hundred
nnd ninety species have been described. They are most
abundant in the fossil state ; and are very plentiful in the
rocks of Bermuda, in the tripoli of Richmond, Virginia, in
the marls of Sicily, and other places. Their minute shells
SPONGES. 385
form beautiful microscopic objects for the binocular ; they
must be mounted dry, and viewed either with the dark
ground illuminator, or by condensed light.
SPONGIADyE. SPONGES.
The term Porifera, or Canal-learing Zoophyte, was
applied by Professor Grant to designate the remarkable
class of organized beings known as sponges, which are met
with in every sea, growing in great abundance on the
siirfacc of rocks.
Ellis, in the course of his investigations, was astounded
by discovering that sponges possessed a system of pores
and vessels, through which sea-water passed, with all the
appearance of the regular circulation of fluids in animal
bodies, and for the seeming purpose of conveying ani-
malcules to the animals for food.
The description given of sponges by Dr. Johnston is,
that theyare " organized bodies growing in a variety of
forms, permanently rooted, unmoving and irritable, fleshy,
fibro-reticular, or irregularly cellular ; elastic and bibulous,
composed of a fibre-corneous axis or skeleton, often inter-
woven with siliceous or calcareous spicula, and containing
an organic gelatine in the interstices and interior canals ;
and are reproduced by gelatinous granules called gem-
mules, which are generated in the interior, but in no
special organ. All are aquatic, and with few exceptions
marine." x Our author continues : " Mr. John Hogg, in a
letter to me dated June 25, states that the green colour
of the fresh-water sponge (Spongilla Jluviatilis) depends
upon the action of light, as he has proved by experi-
ments which showed that pale-colonred specimens became
green when they were exposed for a few days to the
light and full rays of the sun ; while, on the contrary,
green specimens were blanched by being made to grow
in darkness or shade."
The living sponge, when highly magnified, exhibits a
reticulated structure, permeated by pores, which united
into cells or tubes, ramify through the mass in every
direction, and terminate in larger openings. In most
(1) See Dr. Johnston's History of British Sponges, ar.d Mr. Bowerbank's revi-
sion of the class, in the publications of the Ray Socic )y.
C C
386
THE MICROSCOPE.
sponges the tissue is strengthened and supported by
spines, spicula, of various forms ; and which, in some
species, are siliceous, and in others calcareous. The
minute pores, through which the water is imbibed, have
a fine transverse gelatinous network and projecting spicula,
for the purpose of excluding large animals cr noxious par-
ticles ; water incessantly enters into these pores, traverses
the cells or tubes, and is finally ejected from the larger
i 2
Fig. 211.
1, A portion of Sponge, Halichondria simulans, showing siliceous spicula
imbedded in the sarcode matrix. 2, Spicula divested of its matrix.
vents. But the pores of the sponge have not the power of
contracting and expanding, as Ellis supposed ; the water
is attracted to these openings by the action of instruments
of a very extraordinary nature (cilia), by which currents
are produced in the fluid, and propelled in the direction
required by the economy of the animal'.
Mr. Bowerbank, in a paper on the " Structure and
Vitality of Spongiadce" states that sponges consist princi-
pally of sarcode, strengthened sometimes by a siliceous or
calcareous skeleton, having remarkable reparative and
digestive powers, and consequently a most tenacious
vitality ; so much so, tfiat having cut a living sponge into
three segments, and reversed the position of the centre
piece, after the lapse of a moderate interval, a complete
junction of the parts became effected, so as to render the
previous separation indistinguishable.
Professor Grant's careful and laborious researches, have
finally classed sponges in the animal series of the creation.
388 THE MICROSCOPE.
He ascertained that the water was perpetually sucked into
the substance of the sponge, through the minute pores that
cover its surface-, and again expelled through the larger
orifices. His own account is so very interesting, that we
cannot resist giving, in his own words, the results arrived
at in these investigations : " Having placed a portion of
live sponge (Sponyia coalita, fig. 1, No. 213) in a watch-
Fig. 213.
1. Spongia coalita. 2, Spongia panicea.
glass with some sea-water. I beheld for the first time the
splendid spectacle of this living fountain, better repre-
sented in No. 2, vomiting forth from a circular cavity an
impetuous torrent of liquid matter, and hurling along in
rapid succession opaque masses, which 'it strewed every-
where around. The beauty and novelty of such a scene
in the animal kingdom long arrested my attention ; but
after twenty-five minutes of constant observation, I was
obliged to withdraw my eye from fatigue, without having
seen the torrent for one instant change its direction, or
diminish the rapidity of its course. In observing another
species (Spongia panicea), I placed two entire portions of
this together in a glass of sea-water, with their orifices
opposite to each other at the distance of two inches ; they
appeared to the naked eye like two living batteries, and
soon covered each other with the materials they ejected.
V placed ccc cf them in a shallow vessel, and just covered
SPONGES. 389
its surface and highest orifice with water. On strewing
some powdered chalk on the surface of the water, tho
currents were visible to a great distance ; and on placing
some pieces of cork or of dry paper over tho apertures, I
could perceive them moving, by the force of the currents,
at the distance of ten feet from the table on which tho
specimen rested."
Dr. N. Lieberkiihn, in his valuable contributions to
the History of the Development of the Spongillce, observes
that with regard to the skeleton of /S y . fluviatttis, the
spicules are not united at the base by a siliceous material,
as stated by Meyen, but by a substance destructible by
heat. The spicules are usually arranged in aggregate
bundles, which meet point to point at an obtuse angle, and
project slightly above the surface of the sponge. Minute
portions of the gelatinous substance exhibit under the
microscope amoeba-like movements, respecting which it is
unknown whether they are vital phenomena, as supposed
by Dujardin, or referable to a process of decomposition. 1
The living spongillae are often seated, not immediately
upon the wood, stone, &c. upon which they may be
growing, but separated from it by a peculiar dark-brown
substance often several inches thick. This mass is com-
posed chiefly of the remains of the dead sponge, empty
gernmulc- cases with their amphidiscs, various forms of
siliceous spicules, &c. ; and occasionally there may be
(1) The motile phenomena hitherto. observed in sponges are connected with
larger or smaller portions of the external integument, and of the exhalent
tubules, or with isolated cells. When the exhalent tubules of Spongilla con-
tract, their walls become shortened and thickened, and the previously smooth
surface uneven, from the presence of the spherical cpntracted cells, whose
outlines at the same time are rendered very distinct, whilst they were before
invisible, or at most here and there perceptible. Other motile phenomena are
witnessed when a Spongilla with external membrane and exhalent canals is
produced from a cut-off portion. The fragment thus cut off may be so thin as
to consist of only a single layer of retictilar parenchymatous fibres. The inter-
stitial rounded, oval, or irregular spaces, under these circumstances, become for
the most part closed, owing to the gradual increase in breadth of the trape-
culye, or cavities may be left when their membranes are stretched over them
only from the upper and under sides of the trabeculse, which enclose a space
between them, and may become portions of the outer membrane with exhalent
canals. It cannot be determined with certainty to what extent this change of
<brm is connected with any multiplication of cells. Lastly, movements in the
individual cells have been noticed, the globular cells becoming stellate, and the
stellate ones globular in turn, but without any locomotion. This phenomenon
occurs, not only in the cells of the uninjured substance, but also in those which
have been detached. N. Leiberkiihn, "On the Motile Phenomena in Sponges,"
Micros. Journ. vol. iv. 1864, p. 189, and Journ. Micros. Science, vol. v. 1857, p>
SU, "On the Development of the Spongilloe."
390
THE MICROSCOPE.
found in it gemmules still retaining their brown colour
and contents capable of development.
Fig. 214. Geodia Barretti (Bowerbank).
A. section at right angles to the surface, exhibiting the radial disposition of the
fasciculi of the skeleton, and a portion of the dermal crust of the sponge,
magnified 50 diameters, a, interrnarginal cavities ; b, the basal diaphragms of
the intermarginal cavities ; c, imbedded ovaria forming the dermal crust of
the sponge ; d, the large p'atentoternate spicula, the heads of which form the
areas, for the valvular bases of the intermarginal cavities ; e, recurvo-ternate
defensive and aggressive spicuia within the summits of the intercellular
spaces of the sponge ; /, portions of the interstitial membranes of the
sponge, crowded with minute stellate spicula ; g, portions of the secondary
system of external defensive spicula. (1)
The usual contents of the gemmules have been described
by Meyen (Muller's Archiv. 1839, p. 83). In many in-
(1) See Bowerbank's Monograph of the British Spougiadcc, Ray Soc. p. 169.
SPONGES.
391
stances Lieberkiihn found that the globular arrangement
no longer existed, the globules being replaced by granules
exhibiting an active molecular motion. That the gem-
niules are formed from agglomerations of sponge-cells may
be readily proved in the branched sponge containing
smooth gemmules. Lieberkiihn notices four kinds of
gernmules characterised respectively by their cases or
8hells.
1. Those with smooth cases.
2. Those with stellate amphidiscs.
3. Those with amphidiscs, in which the discoid ex-
tremities are entire, and not stellate.
4. Gemmules whose case, instead of amphidiscs, is fur-
nished with minute, usually slightly curved siliceous
spicules.
It would appear, therefore, that the " globules " of
Meyen are nothing more than altered sponge-cells. The
autumn is the most favourable season for observing the
process of their formation.
In the journal of the Bombay branch of the Royal
Asiatic Society for 1840, Surgeon H. J. Carter gives a very
accurate account of fresh-water sponges found in the
water tanks of Bombay. Of five species that he disco-
vered, one was the Spongilla friabilis, the others he named
Sp. cinerea, Sp. alba, Sp. Meyeni, Sp. plumosa.
Spongilla cinerea is stated to present on its surface a
dark rusty, copper colour, lighter towards the interior, and
purplish under water. It throws up no processes, but
extends horizontally in circular patches, over surfaces two
or three feet in circumference, or accumulates on small
objects ; and is seldom more than half an inch in thick-
ness. It is found on the sides of fresh-water tanks, on
rocks, stones, or gravel. The ova are spheroidal, about
l-63d of an inch in diameter, presenting rough points ex
ternally. Spicula of two kinds, large and small ; large
epicula, slightly curved, smooth, pointed at both ends,
about l-67th of an inch in length ; small spicula, slightly
curved, thickly spiniferous, about 1-3 80th of an inch in
length.
Spongilla friabilis. Growing in circumscribed masses,
dn fixed bodies, or enveloping floating objects ; seldom
392
THE MICRJSCOPE.
attaining more than two inches in thickness. From tlie
other sponges it is distinguished by the smooth spicula
which surround its seed-like bodies, and the matted
structure.
Spongilla alba. Its texture is coarse and open ; struc-
ture reticulated. The investing membrane abounds in
minute spicula; has seed-like spheroidal bodies about
l-30th of an inch in diameter, with rough points exter-
nally. The large spicula are slightly curved, smooth,
pointed at each end, about l-54th of an inch in length ;
the small spicula are slightly curved, thickly spiniferous,
or pointed at both ends; the former, pertaining to th<g
seed-like bodies, are about l-200th of an inch in length ;
the latter, pertaining to the investing membrane, are more
slender, and a little less in length; these last numerous
small spiniferous spicula when dry present a white- lace
\ppearance, from which Mr. Carter gives them the name
of alba.
Spongilla meyeni is massive, having large lobes, mam-
millary eminences, or pyramidal, compressed, obtuse, or
sharp-pointed projections, of an inch or more in height ;
also low wavy ridges. Its seed-like bodies are spheroidal,
about l-47th of an inch in diameter, studded with little
toothed discs.
Mr. Carter enters very minutely into the structure o-f
" fresh-water sponge, which : ' he believes " is composed
of a fleshy mass, supported on a fibrous, reticulated, horny
Bkeleton. The fleshy mass containing a great number
of seed-like bodies in all stages of development, and
the horny skeleton permeated throughout with siliceous
spicula. When the fleshy mass is examined by the aid of
the microscope, it is found to be composed of a number of
cells, imbedded in and held together by an intercellular
substance.
" In the development of the sponge- cell of Spongilla, a
set of large granules make their appearance at a very early
period, and increase in number and size until they form
a remarkable feature. At this time they are about
1-1 0,000th of an inch in diameter, of an elliptical shape,
und of a light amber colour by transmitted light ; they
are the colour bearing gianules or cells, and give th
SPONGES. 393
colour of chlorophyll to this organism when it becomes
green. The transparent intercellular substance of Spon-
gilla has a polymorphism equally great with the fully
developed cells. This, however, can only be satisfactorily
seen when the new sponge is growing out from the seed-
like body, at which time it spreads itself over the glass in
a transparent film, charged with contracting vesicles of dif-
ferent sizes, and in various degrees of dilatation and con-
traction. How this substance is produced so early, it is
difficult to conceive, since it seems to come into existence
independently of the development of the sponge-ovules,
which are seen imbedded in it, and there undergoing
their transformation into sponge-cells. The spicula, too,
are developed synchronously with the advancing trans-
parent border, from little glairy globules about the size of
the largest ovules, which send out a linear process on
each side, and thus gradually grow into their ultimate
forms. The only way of accounting for the early appear-
ance of this intercellular-substance is to consider that it is
a development from some remnants of the original proto-
plasm ; and perhaps possesses also the power of producing
new sponge-cells, as we see the protoplasm in Vorticella
and the roots of Chara producing new buds, independently
of the cell-nucleus.
" The cells of the investing membrane are characterised
by their uniformly granular composition and colourless
appearance. They are nucleated, possess the contracting
vesicle singly or in plurality, and are spread over the
membrane in such numbers, that it seems to be almost
entirely composed of them ; while they are of such
extreme thinness, and drawn out into such long digitated
forms, that they present a foliated arraugemeut, not unlike
a compressed layer of multifidous leaves, ever moving and
changing their shapes. The apertures are circular or
elliptical holes in the investing membrane in the cells.
Through these apertures the particles of food are admitted
into the cavity of the investing membrane. The Paren-
chyma consists of a mass of gelatinous substance, in which
are embedded the smooth spicules and ovi-bearing cells,
and through which pass the afferent and efferent canals.
The ovi-bearing cells do not curst and allow their con-
394 THE MICROSCOPE.
tents to become indiscriminately scattered through the
gelatinous mass in which they are imbedded, but each
becomes developed separately in the following way : the
ovules and granules of the ovi-bearing cells subside into a
granular mass by the former losing their denned shape
and passing into small mono-ciliated and unciliated sponge
cells this mass then becomes spread over the interior
surface of the ovi-bearing cell, leaving a cavity in the
centre, into which the cilia of the monociliated sponge-
cells dip and keep up an undulating motion ; meanwhile,
an aperture becomes developed in one part of the cell
which communicates with the adjoining afferent canal, and
thus the ovi-bearing cell passes into an ampullaceous
spherical sac. The cilia may now be seen undulating in
the interior ; and if the Spongilla be fed with carmine, this
colouring matter will not only be observed to be entirely
confined to the ampullaceous sacs, but when the Spongilla
is torn to pieces and placed under a microscope, particles
of the carmine will be found in the interior of the mono-
ciliated and unciliated sponge cells, proving that of such
cells the ampullaceous sac is partly composed. This sac
then must be regarded as the animal of Spongilla, as
much as the Polype-cell is regarded as the animal of the
Polype, and the whole mass of Spongilla as analogous to
a Polypidom.
" The united efforts of all the ciliated sponge-cells in
the ampullaceous sac are quite sufficient to produce a con-
siderable current, and thus catch the particles of food as
they pass through the afferent canals. Thus we find
Spongilla composed of a number of stomachal sacs im-
bedded in a gelatinous substance permeated with spicules
for its support, and an apparatus for bringing them food, as
well as one for conveying away the refuse, while the nourish-
ment abstracted by the process of digestion common to
Rhizopodous cells (e.g. Amoeba), no doubt passes through the
intercellular gelatinous substance into the general develop-
ment of the mass ; and if right in comparing the ampul-
laceous sacs to the stomachal cavities of the simplest
polypes, are we not further justified in drawing a resem-
blance between the ciliated sponge-cells and those which
line the stomach of Cordylophora, of Otostoma, and many
*
DEVELOPMENT OP SPONGES. 395
of Ehrenberg's Allotreta, together with those in the stomach
of the Rotifera and Planaria ?
"The 'swarm-spore,' described by M. N. Lieberkiihi^
appears to be a ciliated form of the seed-like body, and
the same as the ' gemmule ' described by Grant ; but this
I have not yet been able to see. The formation of the
seed-like body, however, now that we know the struc-
ture of the ampullaceous sacs, seems very intelligible,
for we have only to conceive an enlargement of the small
sponge-cells lining the interior, with the addition of
ovules to them respectively, and the spicule-bearing
sponge-cells of the cortical substance supplying the
spicular crust to the exterior, to have a globular capsule
thus composed, with a hilum precisely like the seed-like
body a conjecture which seems to derive support from
the fact, that in some instances, when Spongilla is begin-
ning to experience the want of nourishment, these sacs,
small as they are, assume a denned, rigid, spherical form,
from their pellicle becoming hardened and encrusted with
extremely minute spicules." 1
Clionce. Not the least wonderful circumstance con-
nected with the history of sponges, is the power possessed
by certain species of boring into substances, the hardness
of which might be considered as a sufficient protection
against such apparently contemptible foes. Shells (both
living and dead), coral, and even solid rocks, are attacked
by these humble destroyers, gradually broken up, and, no
doubt, finally reduced to such a state as to render sub-
stances which would otherwise remain dead and useless in
the economy of nature available for the supply of the
necessities of other living creatures.
These boring sponges constitute the genus Cliona of
Dr. Grant. They are branched in their form, or consist of
lobes united by delicate stems ; they all bury themselves
in shells or other calcareous objects, preserving their com-
munication with the water by means of perforations in the
outer wall of the shell. The mechanism by which a crea-
ture of so low a type of organisation contrives to produce
such remarkable effects is still doubtful, from the great
difficulties which lie in the way of coming to any satis-
(1) Ann. of Nat. Hist., July, 13. r >7.
38 6 THE MICROSCOPE.
factory conclusions upon the habits of an animal thai
works so completely in the dark as the Cliona celata it
will probably long remain so. Mr. Hancock, to whom we
are indebted for a valuable memoir upon the boring
sponges, published in the Annals and Magazine of Natural
History, attributes their excavating power to the presence
of a multitude of minute siliceous crystalline particles
adhering to the surface of the sponge ; these he supposes
to be set in motion by some means analogous to ciliary
action. In whatever way this action may be produced,
however, there can be no doubt that these sponges are
constantly and silently effecting the disintegration of sub-
marine calcareous bodies the shelly coverings, it may be,
of animals far higher in organisation than they ; nay, in
many instances they prove themselves formidable enemies
even to living rnollusca, by boring completely through the
shell. In this case the animal whose domicile is so unce-
remoniously invaded, has no alternative but to raise a wall
of new shelly matter between himself and his unwelcome
guest ; and in this mariner generally succeeds at last in
barring him out.
Skeletons of Sponges. The skeletons of sponges, which
give shape and substance to the mass of sarcode that con-
stitutes the living animal, is best made out by cutting thin
slices of sponge submitted to firm compression, and view-
ing these slices mounted upon a dark ground, or backed up
with black paper.
The skeletons of sponges are composed principally of
two materials, the one animal, the other mineral ; the first
of a fibrous horny nature, the second either siliceous or
calcareous. The fibrous portion consist of a network of
smooth, and more or less cylindrical, threads of a light-
yellow colour, and, with few exceptions, always solid ;
t f hey frequently aiiastamose, and vary considerably in size ;
when developed to a great extent, needle-shaped siliceous
bodies termed spicula (little spines) are formed in their in-
terior; in a few cases only one of these spicula is met
tvdth, but most commonly they occur in bundles. In some
sponges, as those belonging to the genus Halichondria, the
name horny kind of material is present in greater or less
abundance ; but its fibrous structure has become obscure :
SPONGES.
397
the fibres, however, in these cases are represented ly sili-
ceous needle-shaped spicula, and the horny matter serves
the important office of binding them firmly together, as
Fig. 215.
1. Transverse section of a branch of Myriapore. 2, A section of the stem of
Virgularia miraUlis. 3, A. spiculum from the outer surface of a Sea-pen. 4,
Spicala from crust of Isis hippuris. 5, Spicula from Gorgona elongate,. 6,
Spicula from Alcyonium. 7, Spicula from Gorgonia, umbraculum.
shown in fig. 213, No. 1. There are, however, some re-
markable exceptions to this rule, one, Dictyochalix pumi-
cens, described by Mr. S. Stutchbury, in which the fibrous
skeleton is composed of threads of silex quite as trans-
parent as glass ; another, the Hyalonema, Glass-rope.
The mineral portion, as before stated, consists of spicula
composed either of silica or carbonate of lime ; the first
kind is the most common and likewise most variable in
shape, and presents every gradation in form, from tho
acuate or needle-shaped to that of a star. The calcareous
spicula, on the contrary, are more simple in their form,
39ft
THE MICROSCOPE.
being principally acicular, but not unfrequently branched
or even tri- or quad-radiate ; the two kinds, the sili-
ceous and calcareous, according to Dr. Johnston, not
having hitherto been detected co- existent in any native
sponges.
The spicula exhibit a more or less distinct trace of a
central cavity or canal, the extremities of which are closed,
or hermetically sealed ; in their natural situation they are
invested by an animal membrane, sarcode, which is not
confined to their external surface : but in many of the
large kinds, as pointed out by Mr. Bowerbank. its presence
may be detected in their central cavity, by exposing them
for a short time to a red heat, when the animal matter
will become carbonised, and appear as a black line in their
interior.
Many authors have described the spicula as being crys-
talline, and of an angular figure, and have considered them
analogous to the r aphides in plants ; but it requires no
great magnifying power to prove that they are always
round, and, according to their size, are made up of one or
more concentric layers, as shown in fig. 212, No. 2. The
spicula occupy certain definite situations in sponges ;
some are peculiar to the crust, others to the sarcode,
others to the margins of the large canals, others to the
fibrous network of the skeleton, and others belong exclu-
sively to the gemmules. Thus, for instance, in Pachyma-
tisma Joknstonia, according to Mr. Bowerbank, the spicules
of the crust are simple, minute, and fusiform, having their
surfaces irregularly tuberculated, and their terminations
very obtuse ; whilst those of the sarcode are of a stellate
form, the rays varying in number from three to ten or
twelve.
Silica, however, may be found in one or more species of
sponge of the genus Dysidea, not only in the form of
spicula, but as grains of sand of irregular shape and size,
evidently of extraneous origin, but so firmly surrounded
by horny matter as to form, with a few short and slightly-
curved spicula, the fibrous skeleton of the animal. In these
sponges the spicula are of large size, and are disposed in
lines parallel with the masses of sand.
Most of the sponges of the earlier geological periods had
SPONGES. 399
tubular fibres ; but in all existing species, with one or two
exceptions, they are solid. These tubular fibres are very
commonly filled with portions of iron, which accounts for
the colour of many of the remains in flint.
The Moss-agates, found among the pebbles at Brighton
and elsewhere, are flints containing the fossilised remains of
sponges. The coloured fibres seen in the Green-jaspers of
the East are of the same character. There is reason to
believe that most flints were originally sponges ; those
from chalk even retain their original form. Recent
sponges from the Sussex coast present forms precisely
similar to some chalk flints, but it is from sections made
sufficiently thin to be transparent, for examination under
the microscope, that we learn their true nature and
origin.
Every horny sponge, whilst living, is invested with a
coating of jelly-like substance, which can only be preserved
by placing the sponge in spirit and water immediately
after its removal from its place of growth. Spicula are
not exclusively confined to the body of sponges, but occa-
sionally form the skeleton of the gemmules, and are situated
either on'the external or internal surface of these bodies.
A good example of the former kind occurs in the common
fresh-water sponge (Spongilla fluviatilis), represented in
fig. 216, No. 1, and No. 3. The spicula are very minute
in size, and are disposed in lines radiating from the
centre to the circumference, the markings on the outer
surface of the gemmules being the ends of spicula. In all
the young gemmules the spicula project from i>he outer
margin as so many spines ; but in process of growth the
spines become more and more blunt, until at last they
appear as so many angular tubercles. Turkey sponge
(Spongia officinalis) is brought from the Mediterranean,
has a horny network skeleton rather fine in the fibres,
solid, small in size, and light in colour. In some larger
specimens there is a single large fibre, or a bundle of
smaller ones. In Halichondria simulans the skeleton is a
framework of siliceous needle-shaped spicula, arranged in
bundles kept together by a thick coat of horny matter.
Other species of Halichondria have siliceous spicula
pointed at both extremities aca-rate (fig. 212, No 2) ;
4CO THE MiCROSCOPia.
whib the spicula of some are round at one end, and
pointed at the other acuate ; some have spicula round at
one end, the former being dilated into a knob spinulate.
Fig. 216.
t Gemmule of SpongW * '-/V//(V, enclosed in spicula. 2, Birotulate spicula,
from Fluviatilis. 3, Gem mules of Spongilla fluviatilis, after having been im-
mersed in acid, to show coating of birotulate spicula.
Among the genus Grantia, Geodia, and Levant sponge,
are found spicula of a large size, radiating in three direc-
tions triradiate. In the Levant specimen, a central
communicating cavity can be distinctly seen. Some
Smyrna sponges, and species of Geodia, have four rays
quadriradiate. Some spicula in P. Johnstonia and Geodia
have as many as ten rays multiradiate. In some species
<jf Tethya and Geodia the spicula consist of a central sphe-
rical body, from which short conical spines proceed
stellate spicula. (Fig. 212, Nos. 4 and 5.) Spicula
having both extremities bent alike bicurvate have been
obtained from Trieste sponge. Some South Sea sponges
have spicula twice bent, and have extremities like the
flukes of an anchor bicurvate anchorate ; sometimes the
flukes have three pointed ends. (Fig. 212, No. 6.) The
gemmules in fresh-water sponges are generally found in
the oldest portions near the base, and each one is protected
by a framework of bundles of acerate spicula of the flesh,
us shown in fig. 212, No. 9 ; but m many marine species,
Geodia and Pachymatisma, they are principally confined to
the crust. In the fresh- water sponges, the amount of
animal matter in the gemmules is considerable; but in
SPICULA FROM SPONGES. 401
Pacliymatisma, Geodia, and many other marine species, a
very small quantity only is ever to be found, the substance
of each gemmule being almost entirely composed of
minute siliceous spicula ; if they be viewed when taken
fresh from the sponge, and also after removing the animal
matter by boiling in acid, a slight increase in trans-
parency is the only perceptible difference of appearance
noticed.
HYALONEMA, " GLASS-HOPE" SPONGE. A bundle of from
200 to 300 threads of transparent silica, glistening with a
satiny lustre like the most brilliant spun glass ; each
thread is about eighteen inches long, in the middle the
thickness of a knitting needle, and gradually tapering
towards either end to a fine point ; the whole bundle
coiled like a strand of rope into a lengthened spiral, the
threads of the middle and lower portions remaining com-
pactly coiled by a permanent twist of the individual
threads ; the upper portions of the coil frayed out, so-
that the glassy threads stand separate from each other.
The spicules on the outside of the coil stretch its entire
length, each taking about two and a half turns of the
spiral. One of these long needles is about one-third of a
line in diameter in the centre, gradually tapering towards
either end. The spirally twisted portion of the needle
occupies rather more than the middle half of its entire
length. In the lower portion of the coil, which is em-
bedded in the sponge, the spicule becomes straight, and
tapers down to an extreme tenuity, ultimately becoming
so fine that it is scarcely possible to trace it to its termi-
nation.
"Many spicules of the awl-shaped and simple crosa
types, especially short spicules, are met with within the
siliceous coil to its very centre, and, in cases where the-
coil has been brougi.t home without the sponge, such
needles can be shaken out from the interstices of the
threads. The spicules of Hyalonema are marked in their
character, and all the forms are found in all specimens of
the sponge imbedding the characteristic bundle of enor-
mous spicules ; so that there can be no reasonable doubt
of the specific identity of the sponge in all cases.
" "Within the round apertures on the surface of the
D D
402 THE MICROSCOPE.
sponge there is usually a brownish orange-coloured mem-
brane, which Schultze found presented the marked cha-
racters of a minute parasitic polyp, probably alcyonarian,
which inhabited the oscula and their passages during the
life of the sponge.
" The glassy wisp of Hyalonema is certainly very re-
markable, but it is not entirely without analogy. Hyalo-
nema seems to represent the extreme form of a little group
of sponges, including, with probably a few other forms,
Euplectella (A Icyonellum) speciosa (Quoi and Gaiinard), and
E. cucumer (Owen). The last-named is an oval sponge
with siliceous spicules, in form and character somewhat
like the spicules of Hyalonema. From one end of the
sponge a tuft of long siliceous threads, resembling in
structure those of the Japan sponge, twine round a stone
or other foreign body. Dr. Bowerbank isolated one of
the spines of Euplectella, three inches long." See Intel-
lectual Observer, March, 1867.
INFUSORIA.
The term Infusoria is applied to a certain class of
animals because they were first discovered in water whera
vegetable matter was decomposing, the infusion was con-
sidered necessary for their production. Now, however, it
rs an established fact, that they are in a healthier state of
existence when taken from pure streams and clear ponds
than from putrid and stagnant waters. A little bundle of
hay, or sage leaves, left for about ten days in a mug con-
taining some pure rain-water, caught before entering a
butt, produces the common wheel-animalcules, which are
found adhering to the sides of the mug near to the surface
of the water. The only use of the vegetable matter seems
to be to facilitate in some way the development of the ova
of animalcules which find their way into the water. It
was at one time thought an indispensable condition that
air be admitted to the infusion : but even this element is
not absolutely needed in the case of infusorial life ; and
the appearance of living organisms at all under the circum-
stances, has been regarded as important evidence in favour
of the doctrine of spontaneous generation.
INFUSORIA.
403
The astronomer turns his telescope from the earth, and
ranges over the vast vault of heaven, to detect and delineate
the beautiful objects of his pursuit. The naturalist turns
his microscope to the earth, and in a drop of water finds a
wondrous world of animated beings, more numerous than
the stars of the milky way ; and these he classifies into
genera and families, and catalogues in his history of the
invisible world.
The Infusoria are a mighty family, as they frequently,
in countless myriads, cover leagues of the ocean, and give
to it a beautiful tinge from their vivid hue. They are
discovered in all climes, have been found alive sixty feet
below the surface of the earth, and in the mud brought up
from a depth of sixteen hundred feet of the ocean. They
exist at the poles and the equator, in the fluids of the
animal body, and plants, and in the most powerful acids.
A brotherhood will be found in a little transparent shell,
to which a drop of water is a world ; and within these are
sometimes other communities, performing all the functions
granted them by their Creator, and eagerly pursuing the
chase of others less than themselves.
The forms of the Infusoria are endless ; some changing
their shape at pleasure, others resembling globes, eels,
trumpets, serpents, boats, stars, pitchers, wheels, flasks,
cups, funnels, fans, and fruits.
The multiplication of the species is effected in some by
spontaneous division or fissuration, in others by gemma-
tion or budding, as well as a true sexual process. The
first step in the process by which infusorial animals are
eliminated, is the formation of globular corpuscles or cells,
which, by their aggregation in some cases, and individual
evolutions in others, give birth to organisms which sub-
sequently appear.
The Infusoria have no night in their existence ; they
issue into life in a state of activity, and continue the
duration of their being in one ceaseless state of motion ;
their term is short, they have no time for rest and there-
fore have but one day, which ends only with their death
and decomposition. Nevertheless, they appear to love
that which promotes life, the light of heaven ; while
others, born in the bowels of the earth, never having par-
404 THE MICROSCOPE.
taken of that blessing, like the ignorant among mankind,
find their own contracted round of unenlightened joys,
perform their mechanical duties, and expire hidden and,
but for the microscope, remained unknown.
On examining the structure of infusorial animalcules,
many are seen to have a soft yielding covering, so elastic
as to stretch when food or other circumstances render it
necessary, returning again to its previous condition as the
cause of distension ceases ; these are designated ihoricated,
which signifies shell-less. Others are termed loricate^
from being covered with a shell, which is beautifully
transparent, and flexible like horn. When the delicate
and soft substance in which the functions of life perform,
their allotted duties perishes, the coat that protected it
from injury during its hours of existence remains as a
token of the past labours of nature ; this covering con-
sists mostly of siliceous material or of lime united with
oxide of iron, destructible in some instances either by
chemical agents or by fire.
Some of these minute beings have apportioned to them
seta, or bristles ; these stiff hairs, attached to the surface
of their bodies, do not rotate, but are movable, and appear
to be a means for the support of their bodies, as aids in
climbing over obstacles that present themselves, or as
feelers. Others are possessed of unci, or hooks, projecting
from the under part of the body, which are capable of
motion ; and by their means the little animal can attach
itself to anything that lies in its way. Some, again,
have styles, which are a kind of thick bristle, jointed
at the base, possessing a movement, but not rotary ; they
are in the shape of a cone, large at their base, and delicate at
their summit. Many, also, can extend and withdraw their
bodies at pleasure, in a similar manner to the snail or
leech.
One of the most interesting and important organs pos-
sessed by infusorial animalcules is scientifically known by
the term cilium, which is the Latin word for eyelash, the
plural being cilia. Its appearance is that of a minute
delicate hair.
The cilium is not only useful in the act of progression,
but also as an assistance in Droning food ; the two duties
INFUSORIA CILIA. 405
being performed at the same time, the motion of the
organs that propels it forward causing a current to set
towards the mouth, which carries with it the prey ori
which the animal feeds. From the cilia being found in
the prills of the young tadpole, the oyster, and mussel, it
would appear that they are serviceable as organs of respi-
ration, by imbibing oxygen, and emitting the carbonic acid
generated in the blood during its circulation through the
body; they are also believed to be the medium of taste
and touch. It is not only at the mouth, but over the
whole body that cilia are discovered ; and it is now satis-
factorily shown that cilia exist also in the internal organs
of man and other vertebrated animals; and are agents
by which many of the most important functions of the
animal economy are performed. They vary in size from
the 1000th to the 10,000th of an inch in length. These
minute organs would often be invisible, were it not from
the water being coloured when placed under a microscope ;
then the little currents made by the action of the cilia are
easily perceived; and when the water is evaporated, the
delicate tracing of their formation may be observed on the
glass. They are differently placed, and vary in quantity
in the numerous species of 1-nfusoria. In some they are
in rows the whole length of the body, in others on the
base ; many have them over the whole of the body ; some-
times they fringe the mouth, form bands around projec-
tions on the body ; and many have but two projecting
from the mouth, as long as the body of the creature.
Ehrenberg says they are fixed at their base by the bulb
moving in a socket, in a similar manner to a man's out-
stretched arm; and by their moving round in a circle,
they form a cone, of which the apex is the bulb. Poison,
galvanism applied to the animal, even death, will not im-
mediately stop the motion of the cilia ; they continue
moving some hours afterwards, even longer than nervous
or muscular action can be sustained, until the fluids dry
up, and they stiffen.
Very little is known of the muscular attachment of cilia
In Infusoria ; but the motive power must be derived from
muscular structure in all. Now in the wheel-animalcules
the cilia are in circular rows ; and each revolves around
406 THE MICROSCOPE.
its bulb, giving a singular appearance, seeming to move
together like a wheel upon its axle, whence their name
Rotifer ; in a few of these muscles can be traced. The
cilia must not be mistaken by the young microscopist for
the stiff hairs and bristles found on some, and serving, as
before stated, for the purpose of locomotion in crawling or
climbing.
If the roof of the mouth of a living frog be scraped
with the end of a scalpel, and the detached mucous mem-
brane placed on a glass slide, and examined with a power
of 300 diameters, the ciliated epithelium-cells will be well
seen. When a number of these are collected together, the
movement is effected with apparent regularity; but in
detached scales it is often so violent, that the scale itself is
whirled about in a similar manner to an animalcule pro-
vided with a locomotive apparatus of the same description,
and has frequently been mistaken for such. The animals
commonly employed for the examination of the cilia are
the oyster and the mussel; but the latter are generally
preferred.
To exhibit the movement to the best advantage, the
following method must be adopted : open carefully
the shells of one of those molluscs, spilling as little as
possible of the contained fluid; then with a pair of fine
scissors remove a portion of one of the gills (branchise) ;
lay this on a slide, or the tablet of an animalcule cage, and
add to it a drop or two of the fluid from the shell ; by
means of the needle-points separate the filaments one from
the other, cover it lightly with a thin piece of glass, and
it is ready for examination. The cilia may then be seen
in several rows beating and lashing the water, and pro-
ducing an infinity of currents in it. If fresh water instead
of that from the shell be added, the movement will speedily
stop ; hence the necessity of the caution of preserving the
liquid contained in the shell. To observe the action of any
one of the cilia, and its form and structure, some hours
should be allowed to elapse after the preparation of the
filaments as above given, their movements then will have
become sluggish. If a power of 400 diameters be used,
and that part of the cilia attached to the epithelium scale
carefully watched, each one will be found to revolve a
INFUSORIA. 401
quarter of a circle, whereby a "feathering movement" is
effected, and a current in one direction constantly pro-
duced. In the higher animals, the action of the cilia can
only be observed a very short time after death. In a polypus
of the nose, when situated at the upper and back part of
the Schneiderian membrane, the cilia may be beautifully
seen in rapid action some few hours after its removal ; but
in the respiratory and other tracts, where ciliated epi-
thelium is found, it would be almost impossible ever to
see it in action, unless the body were opened immediately
after death. In some animals it may be seen in the in-
terior of the kidney, as first made known by Professor
Bowman in the expanding extremity of the small tube
surrounding the network of blood-vessels forming the so-
called Malpighian body. In order to exhibit the ciliary
action, the kidney should have a very thin slice cut from
it; and this is to be moistened with the serum of the
blood of the same animal. The vascular and secreting
portions of the organ may then be seen with a power of
250 diameters, and also the cilia in the expanded extremity
of each tube, as it passes over to surround the vessels ; the
epithelium of the tubes themselves is of the spheroidal or
glandular character.
The infusorial and invisible atoms of life have various
periods allotted to them for the enjoyments of existence ;
some accomplish their destiny in a few hours, others in a
few weeks. The watchful devotee in this branch of science
has traced an animalcule through a course of existence
extending to the old age of twenty-three days. The vital
spark flies instantaneously in general ; but in those of a
higher organisation there is a spasmodic convulsion, as if the
delicate and intricate machinery rendered life so exquisite,
that the parting with the " heavenly flame " was reluctant
and painful. The most surprising circumstance attendant
on the nature of some of the Infusoria is that of apparent
death. When the water or mud in which they have sported
in the fulness of buoyant health becomes dried up, they lie
an inanimate speck of matter; but after months, nay, years,
a drop of water being applied, their bodies will be resusci-
tated, and in a short time their frames become active with
life. Leeuwenhoek kept some in a hard and dry condition.
408 THE MICROSCOPE.
and restored them to life after a sleep of more than
twenty-one months. Professor Owen saw an animalcule
that had been entombed in a grave of dry sand four years
reborn to all the activity of life. Spallanzani tried the
experiment of alternate life and death, and accomplished
it in some instances on the same object fifteen times , after
which nature was exhausted, and refused further aid in
this miraculous care of those minute objects of her won-
derful works.
Naturalists consider the phosphoric light of the marine
animalcule to be the effect of vital action. The sparks
are intermittent like the fire-fly, and measure from the
1 2,000th to the 100th of an inch in size. Captain Scoresby
found that the broad expanse of waters at Greenland was
nearly all discoloured by animalcules, and computed that
of some species one hundred and fifty millions would find
ample room in a tumbler of water. The phosphorescence
of the sea is eloquently portrayed bv Darwin, in his
Voyage of the Beagle. Mr. Gosse thus describes the
luminous appearances presented by a closer inspection of
these minute animalcules : " Some weeks afterwards I had
an opportunity of becoming acquainted with the minute
animals, to which a great portion of the luminousness of
the sea is attributed. One of my large glass vases of sea-
water I had observed to become suddenly at night, when
tapped with the finger, studded with minute but brilliant
sparks at various points on the surface of the water. I set
the jar in the window, and was not long in discovering,
without the aid of a lens, a goodly number of the tiny
jelly-like globules of Noctiluca miliaris swimming about
in various directions. They swam with an even gliding
motion, much resembling that of the Volvox globator of
our fresh- water pools. They congregated in little groups,
and a shake of the vessel sent them darting down from
the surface. It was not easy to keep them in view when
seen, owing rather to their extreme delicacy and colourless
transparency than to their minuteness. They were, in
fact, distinctly appreciable by the naked eye, measuring
from l-50th to l-30th of an inch in diameter." Nocti-
luca miliaris belongs to the highest class of the Protozoa,
and with a power of about 200 diameters they are seen
INFUSORIA. 409
of various forms and stages of growth, represented in
fig. 217. 1
Ehrenberg included in his family of Infusoria, Khizop-
oda, Unicellular, and other Algee, embryonic forms, and
Rotifers. Most naturalists, he \vever, now admit that the
Fig. 217. Noctiluca miliaris.
organization of the Rotiferse is of a far higher nature than
had been suspected by Ehrenberg ; and some assert that
their proper place in the classification of animals is the
annulose sub-kingdom ; the true nature of many of the In-
fusoria is still a disputed question. In outward form they
may be said to vary almost indefinitely ; but anatomically
their bodies should be regarded as consisting of three dis-
tinct structures. The cuticle or integument (" pellicula " of
Carter), on which are borne the cilia and other locomotive
apparatus ; the cortical layer or parenchyma of the body
(" diaphane " of Carter) ; and the chyme mass, occupying
the abdominal cavity, or interior of the body (sarcode or
" abdominal mucus " of Carter), within which the par-
ticles of food rotate. The term "ventral" is usually ap-
plied to that side of the body on which the mouth is
placed.
In the well-known Paramaecium we have the true and
most widely distributed type of the Infusoria. The
general structural character of this minute animal is
common to the species ; indeed, its structural features may
be accepted as a fair definition of the whole group. The
Paramcecium is surrounded on its external covering by
cilia, which are constantly in action, and enable it to move
about in its watery element in a most remarkably active
manner. At one point the body appears to be slightly
(1) See Gosse's Naturalist's Rambles : Huxley, Micro. Journal, 1855
410 THE MICROSCOPE.
constricted, and here is a slit seen which opens into a little
funnel-shaped cavity, leading to the gullet and stomach.
The outer or cortical layer is composed of a denser ma-
terial, which indicates a differentiation into cellular layers,
while the internal substance is evidently composed of
sarcode which exhibits, at two points in particular, the
power of contracting and dilating : a process available both
for the expulsion of digested food, and for aeration of the
circulatory system. The whole systemic arrangement
should be regarded as the very simplest form of respiratory
and secretory mechanism. The several circular trans-
parent bodies seen in the interior of these animals led
Ehrenberg to denominate the group " Polygastrica " (many
stomached). The remarkable powers of multiplication by
fission and germination, as well as by a true sexual process,
which these creatures exhibit, have attracted the attention
of all observers; within the last few years, Miiller,
Balbiani, Stein, and others, have shown that the sexual
organs of such animals as Paramcecium are those bodies
which have hitherto been simply regarded as the
" nucleus," and "nucleolus;" and ultimately it was seen
that the Infusoria have a life history as wonderful as that
of the higher classes of animals. Although Ehrenberg
was the first to call attention to the importance of the
" nucleus " in the reproductive process, it is to the observa-
tions of Balbiani that we are indebted for an explanation of
its importance in the generative function : his investiga-
tions also derive additional interest from the very complete
manner in which they have been carried out. As an in-
stance, he states that in his examinations of Paramcecium
aurelice, he could not look upon them as conclusive until
he had succeeded in extracting uninjured some of the eggs
from the parent body, and had subjected them to the
action of the surrounding water, when he saw each egg
resolve itself into two portions, the smaller being enclosed
within the larger ; then by employing re-agents, acetic acid
and iodine, he produced the changes more rapidly ; and in
this way again and again obtained abundant proofs of the
truth of each observation. So much then for Dr. Bal-
biani's researches on the phenomena of reproduction
among the Infusoria, which have added much valuable
INFUSORIA. 411
information to our former meagre knowledge of these in-
teresting forms of organic life.
Some Infusoria undergo a process of encystation before
reproduction by fissure ; that is, they become coated with
a secretion of gelatinous matter, which gradually hardens
so as to enclose the body in a "cyst." According to
Stein, the process of encystation is sometimes followed by
a remarkable succession of phenomena, such as have been
observed to occur in the case of Vorticella microstomcu
An old Vorticella loses or retracts its cilia, becomes en-
cysted, and finally drops off its stalk. The cyst may either
burst and discharge its contents, or become wholly
changed into an Acineta-form body. The latter may sub-
sequently develop a foot-stalk, assume the appearance of
a Podophyra, or even that of the Acineta tuberosa,
Plate III. No. 68. In either case, the band-like nucleus
becomes transformed into a peculiar ovate body, somewhat
like Nos. 71 or 73, the narrow end of which is provided
with a circlet of vibratile cilia, and a mouth leading into
an internal cavity, with a contractile vesicle in its interior,
Relations, somewhat simi-
lar to those which connect
Vorticella and A cineta, have
been stated to exist between
other families, as Aspidisca
or Trichoda,and Oxytricha,
Plate III. No. 71.
BACTERIA. The remark-
able complex bodies bac-
teria or bacilli, are amongst
the most minute forms of Fia 218 ._ Ba cteria of various foam.
organic life with which the
microscope has to deal. It has been conclusively shown
that bacteria are productive of various kinds of ferments
and diseases in the animal body. They require for their
development a free supply of oxygen, and they thrive best
in albuminoid fluids. Whether decomposition of albu-
minoid matters is directly occasioned by their life pro-
cesses, or whether they generate a ferment which induces
fermentation, is not positively known. It is quite clear
however, from the investigations of Pasteur, Cohn,
412 THE MICROSCOPE.
Tyndall, and others, that bacteria are present in certain
ferments, whether of a putrid, lactic, acid, fatty, or
viscous nature. The consequence is that they have a
high amount of interest for the medical profession, the
microscopist, and the sanatarian.
Bacteria can be at any time readily developed by in-
fusing a small piece of fresh beef in water, or by adding
the fibrine of blood of an animal to water, and letting
the solutions stand by in a warm place for about
four- and- twenty hours. Certain forms of bacteria
exhibit greater signs of vitality in dark moist places,
and ihey are almost invariably found in all river- waters
polluted by sewage, and in waters in any way contami-
nated by animal refuse.
Monads vary in colour, some are red, green, or yellow,
others nearly colourless. In shape they are round or
oval (5 and 6, fig. 226), are very active, and are furnished
with one or more flagella.
VIBRIO. Vibriones. In this family Ehrenberg oddly
enough includes eels in paste and vinegar.
Vibrio spirilla, Trembling animalcules, are now classed
among bacteria, and are claimed by the botanist ; when
exerting the powers of locomotion they take a spiral
form, like the threads of a fine screw, and by undula-
tions wind themselves through the water with rapidity.
They are almost invariably found in decaying acetous
and putrefying organic matters. When treated with
iodine and sulphuric acid, their jointed structure
becomes visible to the highest powers of the micro-
scope.
ASTASI.SA. Astasia, signifying without a station, in
contradistinction to those living in groups, is the term
given to a kind of crimson-coloured animalcule, the
350th of an inch in length, that exist in enormous
numbers, and give the waters in which they live the
appearance of their bodies. Ehrenberg described
several varieties of them.
EUGLENA. The Euglence of D ujardin in some respects
Correspond with the Astasice of Ehrenberg ; while other
observers refer Euylence to the vegetable and Astasics
to the animal kingdom. The euglena, like bacteria, are
INFUSORIA.
413
found in sewage water, they are free, and furnished
with flagelloe ; ova are perceptible in Astasia hmmatodes,
and probably exist in other species. From their vary-
ing colour, their apparent changes of form, and the
rapidity of their motions, they are most interesting
objects under the microscope. The immense number in
which these Infusoria are sometimes developed in a few
days, and the blood-red colour they impart, have fre-
quently been the cause of alarm and anxiety to persons
residing in the vicinity of ponds which have become
coloured by their swarming. Ehrenberg describes a
species of Euglena, E. sanguined, and he conjectures
that the miracle in Egypt, recorded by Mose, of
turning the water into blood, might have been eit'ected by
the agency of these creatures. Very lately, Mr. Shep-
pard 1 met with another specimen, probably belonging
to this family, adhering to the submerged stones in a
clear spring, between Ashford and Maids tone. His
specimens were taken home in a piece of glazed paper,
and upon opening them he found the paper " stained
with hues of red, blue, and purple;" and the whole "re-
sembling clots of red jelly, or recently coagulated blood. >r
Upon placing a small quantity on a glass side for viewing
under the Microscope, " the colour appeared to be opaque-
red, looking like a small quantity of vermilion mixed with
the water ; but when held up to the light the red disap-
peared, and a pale transparent blue took its place."
Believing this colour to depend upon the presence of
albumen mixed with the animal organisms, Mr. Sheppard
placed a small quantity of the jelly-like substance in con-
tact with some white of egg diluted with water ; and " soon
the whole became converted into magenta dye," the
solution exhibiting the same colouring properties, namely,
that of reflecting from its surface all the red and yellow
rays, and transmitting the blue and violet/* Mr. Brown-
ing, upon submitting specimens to the micro-spectroscope,
found that it gave a very marked band in the red-ray. The
whole spectrum is, indeed, very remarkable, and, writes.
(1) "An example of the production of a coloured fluid possessing remarkabla
qualities by the action of monads (or some other microscopic organism) upon
organized substances." By J. B. Sheppard. M.R.C.S. Trans. Micros. Soc. July.
'867, p. 64.
414 THE MICROSCOPE.
Mr. Sorby, "it is the only blue solution in class C (of
which, blood is the type) that gives this particular spec-
trum." The fluid emits a most pungent and disagreeable
odour when the bottle in which it is kept is uncorked.
The common form of the Euglence is represented in
Plate III. No. 67, a contracted, 6 elongated. Oxytricha
are larger and the body more elongated ; their movements
are more impulsive, alternately creeping, running, and
climbing. In all the species digestive vacuoles are evi-
dent ; and they multiply by self-division, as well as ova.
Ehrenberg counted ten cilia anteriorly, and four or five
setae posteriorly. The species is found both in fresh and
brackish water. Plate III. No. 70, represents a side view
of 0. gibba, No. 71, 0. Pelliondla. In the genus Glau-
coma, Nos. 73 and 74, Ehrenberg saw ''indications of an
alimentary canal." Dujardin places Glaucoma among
Parama3cia ; the body is oval and covered with cilia ;
inouth large, with vibratory valves ; increase takes place
by self-division. A re-examination of all the enumerated
species of Infusoria is quite necessary before we can come
to any safe conclusion as to their true affinities, especially
as many appear to be only larval forms of life.
" The question of how far individuals belonging to the
same species may vary is one more intimately connected
with that department of Zoology which treats of the dis-
tribution of animals than their development. For it can
be readily shown that animals are capable of becoming
modified to an indefinite extent by the physical conditions
under which they are placed, and, indeed, that one species
may be, so to speak, made to pass into that of another ; so
that many of the apparently dissimilar animal forms found
on the earth may be more correctly viewed as varieties of
the same species, the differences between them being due
to the external agencies to which each has respectively
been subjected."
The remarkable manner in which the Infusoria make
their appearance in fluids, and the seeming inexplicable
phases in their existence, led some early observers to start
a " spontaneous generation " theory of life ; but the re-
searches of M. Pasteur and others have completely exploded
this view of the formation of living organisms. The order
INFUSORIA. 416
In which these minute creatures appear in vegetable in-
fusions has been made the subject of careful inquiry. Mr.
Samuelson, whose researches on this point were carried on
in conjunction with Dr. Balbiani of Paris, and confirmed
by him, he found when a carefully prepared infusion of
vegetable matter in distilled water is exposed to the air,
the Protozoa which first appear in it are Amoebce : these in
a few days disappear, and are succeded by ciliated infusoria,
such as Kolpoda, Cydidium glaucoma, and sometimes Vor-
ticella, and these in their turn by what we have looked
upon as higher forms, Oxytrichum, Euplotes, Kerona, &c.
Mr. Samuelson thinks that Monads are but the larval con-
dition of the ciliated infusoria, and he noticed the constant
occurrence of Monads belonging to the species Circomonas
fusiformis, or acuminata of Dujardin, &c., in pure distilled
water after a certain exposure to the air, and this without
the previous admixture of vegetable matter of any kind in
the water. The same results were obtained upon shaking
rags, from various and distant parts of the world, over the
distilled water; in all cases in about three weeks he
invariably obtained forms of ciliated infusoria. The fusi-
form body of the Circomonas bears a long whip-like cilium
at its anterior end, and a short seta at its caudal extremity :
this finally drops off, and when exposed to excessive heat
and light, it is transformed into an Amoebiform animal.
Mr. Samuelson's results do not very materially differ
from my own, save in one or two particulars. The suc-
cession of generations do not take quite the same course,
and the animal and vegetable bodies generally appear
simultaneously, or so soon after each other that it is at
times difficult to decide the priority of appearance ; but
our experiments have been chiefly confined to collections
of rain and distilled water, without the addition of vege-
table matter of any kind. I am, however, of his opinion
as to the very extensive distribution of these infusorial
germs, and their great tenacity of life. With regard to the
supposed purity of rain-water, at no time can it be taken
without the numerous matters floating in the air being
brought down with it ; and, consequently, within a few hours
after it is caught, Protococcus pluvialis, Amoeba, and Circo-
moms may always be found in vast numbers. It is somewhat
416 THE MICROSCOPE.
remarkable that the purest snow-water, caught in a cleai
glass vessel, and allowed to remain well corked, will, in
the course of two or three weeks, "be found to contain
Amoeba and Circomonas, but it rarely presents other forms
of animal life ; the vegetable matter then completes its
growth very slowly, gradually passes to Conferva, and for a
time no other change is seen to take place ; so that it is
painfully apparent that the atmosphere in which we live and
move and have our being is something more than a mixture
of gases, as apparently determined by chemical analysis.
Fig. 219.
1, Achnanfhidiwn coarotatum. 2, A. lineare. 3, Tryblionella gracillis. 4,
Amphitetras antediluviana. 5, 6, and 7, Orthosira spinosa. Front view, with
globular and oval foims. (Fossil Infusoria from Springfield, Barbadoes.)
Ehrenberg's " Poly gastric Infusoria" have indeed under-
gone a complete revision : some have been degraded to the
vegetable kingdom, as the Desmidiacece, Volvocinece, &c.,
whilst others have been advanced a step higher in the
animal series ; none having received so much attention from
microscopists, or excited so much controversy, as the Desmi-
diacece and Diatomacece. The first of these we have already
disposed of in :-nr remarks on the vegetable kingdom,
where we must be content to leave them for the present;
DIATOMACEuE. 417
cot so the Diatomacece, which offer many interesting struc-
tural characteristics of sufficient importance to warrant our
keeping them in the animal division. They are most
striking objects under the microscope, from the very pecu-
liar beauty and variety of their forms, and from their
bilateral symmetry, external markings, and indestructible
siliceous skeletons ; so that we believe they would be more
correctly placed in a median, or Molluscian sub-kingdom.
Appearing everywhere with the first-born of life, and
wherever matter is found in a condition fit for their deve-
lopment and nourishment, these marvellous indestructible
creatures have been preserved and brought down to us, in
forms unchanged,' from the remotest periods of our globe's
history; and supplying, as they do to the microscopist,
some of the most valuable test-objects, the Gyrosigma,
Grrammatophora, Fragilaria, Ripidophora, Pleurosigma
angulatum, with many others, it cannot be a matter of
surprise that considerable attention should have been di-
rected to them, and an earnest inquiry instituted into their
nature and structure.
"Comparing," says Kiitang, "the arguments which
seem to indicate the vegetable nature of Diatomacece with
those which favour their animal nature, we are of neces-
sity led to the latter opinion. If we suppose them to be
plants, we must admit every frustule, every Navicula to be
a cell. We must suppose this cell with walls penetrated
by silica, developed within another cell of a different
nature, at least in every case where there is a distinct
peduncle, or investing tube. In this siliceous wall we
must recognise a complication certainly unequalled in the
vegetable kingdom. It would still remain to be proved
that the eminently nitrogenous internal substance corre-
sponded with the generic substance, and that the oil
globules could take the place of starch. The multipli-
cation would be a simple cellular reduplication ; but it
would remain to be proved that it takes place, as in other
vegetable cells, either by the formation of two distinct
primitive utricles, or by the intronection or constriction of
the wall itself. Finally, there would still remain un-
explained the external motions and the internal changes ;
and we must prove the accumulated observations on the
B P
418
THE MICROSCOPE.
exterior organs of motion to be false, by a clearer line of
argument than has hitherto been adopted by those who
arc opposed to this view. But again, admitting their
animal nature, much would remain to be investigated,
both in their organic structure and their vital functions ;
excepting this, so far as we know, we have only one diffi-
culty to overcome, that of the probably ternary non-
azotised composition of the external gelatinous substance
of the peduncles and investing tubes. But as the presence
of nitrogen is not a positive character of animal nature,
Fig. 220.
1, Cynibella Ehreribergii. 2, Side view of the same, showing an arrangement of
the sarcode and psevdopodia. 3, Pleurosigmata lanccolatum. 4, Lateral view
of a portion of the same. 5, 6, and 7, Pinnularia. 8, Diatoma vulgare. 9,
NitzscMa varvula.
so the absence of it is not a proof of vegetable. And, in
order that the objection should really have some weight,
it would be well to demonstrate that this substance is
isomeric with starch. For then, supposing all the argu-
ments in favour of the animal nature of Diatomacece were
proved by new and more circumstantial observations, this
peculiarity, if it deserve the name of objection, might still
be regarded as an important discovery. We should then
have in the animal, as well as in the vegetable kingdom, a
ternary substance similar to that forming the bases of the
vegetable tissue."
DIATOMACE2E.
419
DiatomacecBj brittleworts, siliceous Bacillaria, are organ-
isms composed of two symmetrical plates or valves, narrow
or wand-like, navicular as a miniature boat or "little
ship ; " hence their name, Navicula. A rectangular or
prismatic figure is, however, the typical form of this
family, and the angles of junction of the valves are" as a
rule, acute. Deeply notched frustules, such as we see in
the Desmids, Micrasterias denticulata, Docidium pristidce,
Plate II. Nos. 30 and 31, do not occur, and tho produc-
tion of spines and tubercles is rare among the Diatoms,
Each individual Diatom is enclosed by a soft organic
matter (sarcode) ; the internal portion is yellowish or
orange-brown in colour. In the discoid forms two por-
tions are commonly distinguishable, viz. the disc and
margin or rim, and these present different markings, with
an occasional central prominence, called an umbo or boss.
Great variety of outline may prevail in a genus, so much
so, that no accurate definition can be safely
laid down : thus in the genera Navicula,
Pinmdaria, the frustules are in one aspect
boat-shaped, and in another oblong with
truncated ends, prismatic. Mr. Brightwell
thus describes and explains the transitions
of form produced by a change in position
of the frustules of the genus Triceratium. 1
" The normal view of the frustule may be
represented by a vertical section of a tri-
angular prism. If the frustule be placed
upon one of its flat sides, we look down
upon its ridge and obtain a front view of
its two other sloping sides. If it be placed
upon one of its ridges, we have a front
view of one of' its flat sides, generally
broader than long, and of its smooth or
,. Fig. 221. Gompho-
transparent suture or connecting mem- nem a eiongatum
brane. If the frustule be progressing ******
towards self- division, it is then often considerably longer
than broad, and when nearly matured for separation, pre-
sents the appearance of a double frustule." So vith re.
1) Journ. Micros. Soc. roL L p. 248.
EE 2
4:20 THE MICROSCOPIC.
gard to the beautiful Surirella constricta, the side view ia
io longer bacillar, but the breadth of the valve is very
considerable, and when about to undergo subdivision it
becomes square-shaped. The distinctive character, how-
ever, of this genus, in addition to the presence of canaliculi,
is derived from the longitudinal line down the centre of
each valve, and the prolongation of the margins into
" alae." The sudden change in appearance presented t<7
the eye as the frustule is seen to roll over, is very remark-
able. As a rule, therefore, we must examine all specimens
in every aspect, to accomplish which very shallow cells
should be selected, say of 1-1 00th of an inch deep, and
covered with glass l-250th of an inch thick. A good
penetrating objective must be used, and careful illumina-
tion obtained. The examination of living specimens
should be conducted during very bright weather, the
mirror directed towards a white cloud, or even sunlight :
with coloured glasses to protect the eyes from injury.
The Diatomaceae are perhaps more widely distributed than
any other class of infusorial life ; they inhabit fresh, salt,
and brackish water ; many grow attached to other bodies
by a stalk (Plate II. No. 33), Licmophora and Achnanthes;
while others, as the Pleurosigma, No. 40, swim about
perfectly free in the water.
There are a considerable number of Diatomacerc which,
while in the young state, are enclosed in a muco-gelatinous
sheath ; while others are attached by a stipes or stalk to
Algae. Ehrenberg recognised a tribe of compound Dia-
toms, with a double lorica, and introduced them into his
great family of acillaria, under the name of Lacernata or
Savicula. Silex enters largely into the composition of
their valves, but, being in combination with organic sub-
stances, it does not depolarize light. In several genera
silex is very deficient, and the wall of the frustule of
great delicacy. Mr. Brightwell, speaking of the lorica or
siliceous covering of the Triceratium, states " that the
valves are resolvable into several distinct layers of silex,
dividing like thin divisions of talc, and frequently of such
exquisite delicacy as to be difficult of detection." Nageli
speaks of a mucilaginous pellicle on the inside of the
organic layer as a sort of third tunic ; and, as Meneghini
DIATOMACE^E.
421
truly observes, " An organic membrane ought to exist, for
the silica could not become solid except by crystallizing or
depositing itself on some pre-existing substance." The
surface of the frustules is generally very beautifully
sculptured, and the markings assume the appearance of
dots (puncta), stripes (striae), ribs (coste), pinnules
(pinnae), of furrows and fine lines ; longitudinal, trans-
verse, and radiating bands ; canals or canaliculi ; and of
cells or areolae ; whilst all present striking varieties and
modifications in their form, character, and degree of deve-
lopment. Again, the fine lines or striae of many frustules
are resolvable into rows of minute dots, such as occur in
Pleurosigma* &c.
The nature of the markings on the Diatom valves is one
of considerable in-
terest, and has ex-
cited much atten-
tion, and attempts
have been made to
produce them arti-
ficially. On the ad-
dition of sulphuric
acid to a mixture of
powdered fluor spar
and sand, an imme-
diate evolution of
fluoride of silicon
takes place, as is
shown by the white
fumes. This white-
ness is due to the
presence of minute
particles of silex
arising out of the
decomposition of the
fluoride by the mois-
ture contained in the
n+TYirxsnTiPrp inrl it *> Plewrosigma attenuatum. 2, Pleurosigma an-
atmOSpnere , ana gulatum, magnified 250 diameters. 3 , Pleura-
a Solid body be ex- sigma Spencerii, imperfectly shown.
posed to these vapours, a portion of the silex will be
deposited on it, in the form of a fine white powder, con-
422 THE MICROSCOPE.
sisting of thin walled vesicles filled with air. If some of
the deposit be crushed between two pieces of glass, and
examined with a power of about 300 diameters, a marking
will be perceived on the outer or convex surface of many of
these vesicles, similar to that of many Diatomaceae, such
as Pleurosigma, Coscinodiscus, &c. Rounded elevations,
more or less hexagonal at the base, and more or less
regularly arranged, cover the surface of the siliceous
pellicle, and not unfrequently this kind of marking is so
regular as to give the fragments exactly the appearance of
portions of diatomaceous valves.
This remarkable circumstance attracted the attention of
Professor Max Schultze, who devoted a great deal of time
to the investigation of the subject, and has recorded in a
voluminous paper 1 the results of his observations. He
says, " The appearances presented under the microscope by
the siliceous pellicles were such as to suggest that they
were due possibly to crystallisation. The minute eleva-
tions on the surface, when viewed on the side, often appear
sharply acuminate, so as readily to convey the impression
that they are formed by minute crystals of silex ; and this
impression is strengthened at first sight by their sharply
denned hexagonal basis, when viewed vertically. The
circumstance, again, that these elevations are sometimes
rounded at the summit and circular at the base, might be
attributed to the accidental interference of free hydrofluo-
silicic acid, &c. But experiments to eleminate the action
of this agent, showed that it had nothing to do with, the
variety of appearance in the elevations.
" Most of the species of the diatornacea3 are characterised
by the presence on their outer surface of certain differences
of relief, referable either to elevations or to depressions
disposed in rows. The opinions of microscopists with re-
spect to the nature of this marking are divided. Whilst
in the larger forms, and those distinguished by their coarser
dots, the appearance is manifestly due to the existence of
thinner spots in the valve, we can not so easily explain the
cause of the striation or punctation in Pleurosigma
angulatum and similar finely-marked forms.
(1) "Verhandl. d. Natur Hist. Vereins der Preussisch. Rheinland, u. West-
phal." Jahr xx,p. 1. Micros. Jour. Science, vol. iii. p. 120.
A.TOMACEJ:. 423
The accompanying illustra.
tion is drawn from, a photo-
graph of Frustulia Saxonica,
one of the most difficult of the
" Probe Platte," Moller's bal-
sam-mounted diatoms, resolved
by a Tolles' ^ duplex front
immersion objective. The lon-
gitudinal lines as well as the
transverse are well seen over
the greater .part of the frustule.
The measurement of the trans-
verse lines given by Mr. Wells,
is 88,'001 inch. Professor Mor-
ley puts them at 81'5 to 82,'001
inch. The midrib and margin
of the diatom are quite thick,
and, consequently, when very
oblique light is used, they pro-
duce diffraction phenomena,
and which, in some instances,
obliterate the whole of the
markings. The f rust ale, how-
ever, in this instance is mount-
ed in balsam, and the lines are
therefore fainter than they
would be if mounted dry. The
kind of illumination employed
by the photographer was Wen-
ham's reflex illuminator. The
beaded appearance of the sur-
face is much better seen in the
photograph than in the wood-
cut. 1
Movements of Diatoms. The
researches of Professor Max
Schultze, of Bonn, published
1865, appear to throw some
light on the vexed question
of the movements of the
Frustulia Saxonica (x 1,800 di- (1) The English Mechanic, July 23, 1880.
ameters) from Moller's balsamed
Probe-Platte. From a photograph by Mr. S. Wells, of Boston, U.S.A.
424 THE MICROSCOPE.
Diatomacece. This author is of opinion that a Barcode
substance envelopes the external surface of the diatom,
and its movement is due to this agent exclusively. He
prefers the P. angulatum, Plate II. IS o. 38, for examination
to the larger P. balticum, because the transverse markings
on its frustule do not impede to so great an extent the
observation of what is going on within. When you have
a living specimen of P. angulatum under the microscope,
it always has its broad side turned to view, with one long
curved "raphe" uppermost, and the other in contact with
the glass on which it is placed; at the central part is seen
the thickened " umbilicus," Plate 2, JSTo. 40. Within the
siliceous frustule is the yellow colouring matter, or "endo-
chrome," which fills the cavity more or less completely,
and is arranged in two longitudinal masses, to the right
and left of the raphe. In the broader part of the frus-
tule these bands of endochrome describe one or two com-
plicated windings. It is only possible in those specimens
in which the bands are narrow properly to trace their
foldings, and ascertain that only two exist, since an
examination of frustules richer in endochrome has led to
the impression that there are three or four of these bands.
"The next objects which strike the eye on examining
a living Pleurosigma are highly refractive oil-globules.
These are four in number ; one pair near either end of the
the Diatom. They are not, however, all in the same place,
one globule of each pair being nearer the observer than
the other ; their relative position is best seen when a view
of the narrow side of the frustule can be obtained, so that
one raphe is to the left and the other to the right. The
blue-black colour, which is assumed by these globules
after the Diatom has been treated with hyperosmic acid,
demonstrates that they consist of oleaginous matter. The
middle of the cavity of the frustule is occupied by a
colourless finely granular mass, whose position in the body
is not so clearly seen in the flat view as in the side view.
Besides the central mass, the conical cavities at either end
of the siliceous shell are seen to be filled with a similar
granular substance, and two linear extensions from each of
the three masses are developed, closely underlying that
port of the shell which is beneath the raphas; so that
DIATOMACE2E. 425
in the side view they appear attached to the right and left
edges of the interior of the frustule. This colourless
granular substance carries in its centre, near the middle
part of the Diatom, an imperfectly developed nucleus
which it is not very easy to see, but may be easily de-
monstrated by the application of acid. The colourless
substance is what, in other Diatoms, Schultze shows to be
Protoplasm, or vegetable sarcode, and which contains
numerous small refractive particles ; on adding a drop
of a one per cent, solution of osmic acid these became
blue-black, and proved to be fat. It is, however,
exceedingly difficult to determine the exact limitations
of the protoplasm, on account of the highly refractive
character of the siliceous skeleton, and the obstruction
presented by the endochrome.
After a short distance, the protoplasm reappears, and
is contracted into a considerable mass within the conical
terminations of the frustule. Schultze observed in this
part of the protoplasm a rapid molecular movement such
as is known to occur in the Closterium, and further, a
current of the granules of the protoplasm along the raphe.
Pleurosigma angulatum " crawls" as do all Diatoms pos-
sessing a raphe, along this line of suture. To crawl along,
it must have a lixed support. He believes free swimming
movements are never to be observed in this or in any
other Diatom. Accordingly, Schultze invariably found
that the raphe is in contact with either the glass slip or
the glass cover, between which the Diatom is placed, or is
in apposition with some foreign body of considerable size.
Schultze repeated the experiments of Siebold, and ob-
served, as he and also Wenham had done long before,
that particles of foreign matter stick to the raphe as
though it were covered with some glutinous material,
and are carried slowly along by the action of a current.
This he observed in many Diatomaceae, and found in-
variably that foreign particles adhered only to the raphe,
or what corresponded to it. "There is obviously," says
Schultze, " but one explanation ; it is clear that there must
be a band of protoplasm lying along the raphe, which
causes the particles of colouring matter to adhere, and
gives rise to a gliding movement For there is but one phe-
426 THE MICROSCOPE.
nomenon which can be compared with the gliding motion
of foreign bodies on the Diatomaceag, and that is, the
taking up and casting off of particles, by the pseudopodia
of the rhizopod, as observed, for instance, on placing a
living Gromia or Miliolina in still water along with
powdered carmine. The nature of the adhesion and of
the motion is in both cases the same in all respects. And
since, with Diatoms as unicellular organisms, protoplasm,
forms the principal part of the cell body (in many cases
two distinctly moving protoplasms), everything suggests
that the external movements are referable to the move-
ments of this protoplasm." It is quite evident to those
who have studied the movements of the Diatoms that
they are surrounded by a sarcode structure far more deli-
cate in its character than that of the Amoeba. Six years
before Schultze's observations were published, the fact
appeared in a third edition of this work, page 307 ; therein
it is stated that "The act of progression rather favours
the notion of contractile tentacular filaments, pseudo-
podia, as the organs of locomotion and prehension. The
hyaline or sarcode covering is of so transparant a nature
that as yet no microscopic power has enabled us to assign
its precise boundary and attachments. 1 Some observers
would deny a membranaceous (hyaline) covering of any
kind to Diatoms, which we have certainly seen." Pro-
fessor Smith, of America, has satisfactorily traced a sar-
code covering in Pinnularia. The defining power, pene-
tration of the objective, and mode of illumination, is
everything in such investigations.
It was in 1841 Messrs. Harrison and Sollitt, of Hull,
discovered the beautiful longitudinal and transverse striae
(groovings) on the Pleurosigma hippocampus. A curved
graceful line runs done the shell, in the centre of which is
an expanded oval opening. Near to the central opening
(1) Referring to the strength and vigour of the movements of the Diato-
fliacese, Dr. Donkin (Quart. Jour. Mic. Sci. vol. VI. new series, p. 26), observed
a species Bacillaria cursoria, discovered by himself, push away "A. arenaria,
& species at least six times their own size ; " and Mr. Barkas states that he has
een them " push away particles of foreign matter, and that with the greatest
apparent ease, at least one hundred times larger than all the frustules com-
bined ; and what is more remarkable still, is that they not only push the accu-
mulated particles away when they are in their direct line of motion, but, i/
they merely touch them in passing, they drag them after them as though they
were literally held by some magnetic attraction, or strong cement."
DIATOMACEjE. 427
the dots elongate crossways, presenting the appearance^of
small short bands. The Pleurosigma angulatum (fig. 223),
was first discovered in the Humber ; the lines upon its
surface resemble the most elegant tracery, \vhich are
resolvable into raised minute dots. The markings are
Been to be longitudinal, transverse, and oblique.
In the vicinity of Hull many very interesting varieties
of Diatomacece have been found, the beauty of the varied
forms of which are such as to delight the microscopist ;
Fig. 223.
, PUwrotigma angulatum. 2, Portion of the same, magnified 1200 diameters.
3, Portion of P. formosum, magnified 5500 diameters.
at the same time some of them are highly useful, as form-
ing that class of test objects which are best calculated above
all others for determining the excellence and powers of
object-glasses. It has been shown by Mr. Sollitt that
the markings on some of the shells are so fine as to range
between tlie 30,000th and 130,000th of an inch; the
Pleurosigma strigilis having the strongest markings, and
the Pleurosiyma acus the finest.
As to the value of the Diatomacece as test-objects, it is
generally admitted, and since Mr. J. D. Sollitt first pro-
posed the use of their shells for this purpose, we append
his measurements of the lines :
Atnphipleura Pellucida, or Acus, 130,000 in the inch, cross line*.
,, Sigmoidea, 70,000 in the inch.
Navicula Rhomboides. 111.000 in the inch, cross lines
428 THE MICROSCOPE.
Plearosigma Fasciola, fine shell, 86,000 in the inch, cross line*.
,, strong shell, 64,000 in the inch, cross lines.
Strigosum, 72,000 in the inch, diagonal lines.
Angulatum, 51,000 in the inch, diagonal lines.
Quaclratum, 50,000 in the inch, diagonal lines.
Spencerii, 50,000 in the inch, cross lines.
Attenuatum, 42,000 in the inch, cross lines.
Balticum, 40,000 in the inch, cross lines.
Formosum, 32,000 in the inch, diagonal lines.
Strigilis, 30,000 in the inch, cross lines.
Mr. Koran an, of Hull, has favoured us with the follow-
ing :
HINTS FOR COLLECTING DIATOMACE^I.
These minute forms are found in all waters, but the
most interesting species are those found in salt water,
especially shallow lagoons, salt water marshes, estuaries of
rivers, pools left by the tide, &c.
Their presence in any quantity is always shown by the
colour they impart to the aquatic plants and sea-weeds
they are found attached to, and if found on the mud,
which is very frequently the case, they impart to it also a
yellowish brown colour approaching to black brown, if in
great numbers. This brownish pellicle, if carefully re-
moved with a spoon (without disturbing the mud) will be
found very pure. Capital gatherings of Diatomaceae
might be obtained by carefully scraping the brown coloured
layer from mooring posts, and piles of wharfs and jetties.
In clear running ditches the plants and stones have
often long streamers of yellowish brown slimy matter
attached to them, which is generally entirely Diato-
maceous.
When found in large quantities on the mud the layer
Is often covered with bead-like bubbles of oxygen. This
often detaches them from the bottom and buoys them to
the surface, where they form a dense brown scum, which
is blown to leeward in large quantities, and presents the
general appearance of dark-coloured yeast. In this form
it may be collected in abundance, often quite free from
particles of sand and other impurities. Good and rare
species have been obtained from the stomachs of oysters,
scallops, and other shell-fish inhabiting deep water. The
sea-cucumbers (Holothuridse) found so frequently in
southern latitudes contain many species. These animals
DIATOMACE.E. 429
might be simply dried and preserved just as found, and
the contents of the stomach afterwards obtained by
dissection.
Noctilucee, which are the cause of phosphorescence in
the sea, are Diatom feeders, and might be caught in large
quantities in a fine gauze towing-net, and preserved. The
Ascidians found attached to oyster shells and stones from
deep water have yielded excellent gatherings. The Salpae
often noticed in warm latitudes floating on the surface of
the sea, and assuming chain and other like forms, should
be bottled up for examination. These Salpae are well
known Diatom feeders. Deep-sea soundings ought to be
preserved, especially from great depths, and are often
exclusively Diatomaceous. Sea- weed from rocks ought to
be preserved, especially the smaller species, and if covered
with a brown furriness, so much the better. Yery rare
species have been found in immense quantities in the
ARCTIC and ANTARCTIC regions, by melting the "pancake
ice," often found discoloured by these minute beings. The
sea is often observed to be covered by brownish patches.
The discoloured water (or " spawn" as it is called) should
be collected, filtered through cotton wool, and the
brown residue preserved. When a fine impalpable dust
is observed to be falling at sea, it ought to be collected
from the folded sails and other places where it lodges.
This may yield Diatomaceoe, which from the method of
collecting would be highly interesting to examine. The
roots of the various species of Mangrove (Ehizaphora),
which form impenetrable barriers along the salt water
rivers and estuaries in the tropical parts of Africa,
Australia, the Eastern Archipelago, &c., are found fre-
quently covered with a brown mucous slime very rich in
Diatomacese. When the Diatomaceae are collected from
any of the above-mentioned sources, they may be at once
transferred to small bottles, or the deposit may be partially
dried and wrapped up in pieces of paper or tinfoil.
When placed in bottles, a few drops of spirits added will
keep them nice and sweet. In all cases it is essential to
keep the gatherings separate and distinct, and that the
locality whence obtained be written on each package.
The collector will probably find that, notwithstanding
430 THE MICROSCOPE.
svery care, his specimens are mixed with much foreign
matter, in the form of minute particles of mud or sand,
which impair their value, and interfere with observation,
especially with the higher powers of his instrument.
These substances the student may remove in various
ways : by repeated washings in pure water, and at the
same time, profiting by the various specific gravities of the
Diatoms and the intermixed substances, to secure their
separation ; but, more particularly, by availing himself of
the tendency which the Diatomacece generally have to
make their way towards the light. This affords an easy
mode of separating and procuring them in a tolerably clean
state ; all that is necessary being to place the gathering
which contains them in a shallow vessel, and leave them
undisturbed for a sufficient length of time in the sunlight,
and then carefully remove them from the surface of the
mud or water. The simplest method of preserving the
specimens, and the one most generally useful to the scien-
tific observer, is simply to dry them upon small portions of
talc, which can at any time be placed under the micro-
scope, and examined without further preparation ; and
this mode possesses one great advantage, that is, that the
specimens can be submitted without further preparation to
a heat sufficient to remove all the cell-contents and softer
parts, leaving the siliceous epiderm in a transparent
state.
ON CLEANING DIATOMACEOUS DEPOSITS. "The first
point to be ascertained is the nature of the material which
binds the mass together. In the generality of deposits,
this seems to be aluminous or earthy matter, often mixed
with some siliceous material which renders the action of
acids of little avail. When the bulk of the deposit is
clayey matter, the best plan is to place the lumps broken
quite small into a vessel and pour on a few ounces of hot
water, rendered thoroughly alkaline with common washing
soda. This plan frequently answers, causing the lumps to
swell, gradually separating into layers, and finally falling
asunder into a pulpy mass. The strong soda ley must
now be removed by repeated washing, and afterwards
boiling in a flask with pure nitric acid ; the whole must
afterwards be transferred to a large stoppered vessel and
FOSSIL INFUSORIA. 431
violently shaken, in order to break up the minute frag-
ments of dirt, and set free the siliceous Diatoms. After
shaking, allow the vessel to stand for half an hour or
more according to the size and density of the valves : the
Diatoms having subdivided, the dirty water is drawn off
by a syphon, and fresh water added, and the shaking re-
peated. The whole secret depends upon getting rid of
the impurities by this violent shaking and washing ; when
quite free from all impurities the material may be trans-
ferred to a test tube, washed in distilled water, and finally
mounted." 1
Fossil Infusoria. Startling and almost incredible as the
assertion may appear to some, it is none the less a fact,
established beyond all question by the aid of the micro-
scope, that some of our most gigantic mountain-ranges,
such as the mighty Andes, towering into space 25,250 feet
above the level of the sea, their base occupying so vast an
area of land ; as also our massive limestone rocks, the sand
that covers our boundless deserts, and the soil of many of
our wide-extended plains; are principally composed of
portions of invisible animalcules. And, as Dr. Buckland
truly observes : " The remains of such minute animals
have added much more to the mass of materials which
compose the exterior crust of the globe than the bones of
elephants, hippopotami, and whales."
The stratum of slate, fourteen feet thick, found at Bilin,
in Austria, was the first that was discovered to consist almost
entirely of minute flinty shells. A cubic inch does not
weigh quite half an ounce ; and in this bulk it is estimated
there are not less than forty thousand millions of indi-
vidual organic remains ! This slate, as well as the Tripoli,
found in Africa, is ground to a powder, and sold for
polishing. The similarity of the formation of each is
proved by the microscope ; and their properties being the
same, in commerce they both pass under the name of
Tripoli : one merchant alone in Berlin disposes annually of
many hundred tons weight. The thickness of a single shell
is about the sixth of a human hair, and its weight the hun-
(1) G. Nomian, Esq. Micros. Journ. vol. iv. p. 238. For other methods of
cleaning and preparing Diatoms, see Smith's Synopsis of the British Diatc-
macece ; also Quar. Journ. Micros. Science, vol. vii. p. 167, and vol. i. N. S. 1891.
p. 143.
432
THE MICROSCOPE.
dred-and-eighty-seven-millionth part of a grain. The
well-known Turkey stone, so much used for the purpose of
sharpening razors and tools ; the Rotten-stone of com-
merce, a polishing material ; and the pavement of the
quadrangle of the Royal Exchange, are all composed of
infusorial remains.
Fig- 224.
1, Shell of Arachnoidiscus. 2, Actinocyclus (Bermuda). 3, Cocconeis (Algtia Bay)
4, Coscinodiscus (Bermuda.) 6, Isthmia enervis. 6. Zygocercs rhombus.
The bergh-mehl, mountain-meal, in Norway and Lapland,
has been found thirty feet in thickness ; in Saxony, twenty-
eight feet thick ; and it has also been discovered in Tus-
cany, Bohemia, Africa, Asia, the South Sea Islands, and
South America ; of this, almost the entire mass is com-
posed of flinty skeletons of Diatomaceoe. That in Tuscany
and Bohemia resembles pure magnesia, and consists
entirely of a shell called campilodiscus, about the 200th
of an inch in size.
FOSSIL INFUSORIA. 133
Darwiu, writing of Patagonia, says : " Here along the
coast, for hundreds of miles, we have our great tertiary for
mation, including many tertiary shells, all apparently
extinct. The most common shell is a massive gigantic
oyster, sometimes a foot or more in diameter. The beds
composing this formation are covered by others of a
peculiar soft white stone, including much gypsum, and
resembling chalk; but really of the nature of pumice-
stone. It is highly remarkable, from its being composed,
to at least one-tenth of its bulk, of Infmoria; and Pro-
fessor Ehrenberg has already recognized in it thirty
marine forms. This bed, which extends for five hundred
miles along the coast, and probably runs to a considerably
greater distance, is more than eight hundred feet in thick-
ness at Port St. Julian." Ehrenberg discovered in the
rock of the volcanic island of Ascension many siliceous
shells of fresh- water Infusoria; and the same indefatigable
investigator found that the immense oceans of sandy
deserts in Africa were in great part composed of the shells
of animalcules. The mighty Deltas, and other deposits of
rivers, are also found to be filled with the remains of this
vast family of minute organization. At Richmond in
Virginia, United States, there is a flinty marl many miles
in extent, and from twelve to twenty-five feet in thickness,
almost wholly composed of the shells of marine animal-
cules ; for in the slightest particles of it they are discover-
able. On these myriads of skeletons are built the towns
of Richmond and Petersburg. The species in these earths
are chiefly Namculce; but the most attractive, from the
beauty of its form, is the Coscinodiscus, or sieve-like disc,
found alike near Cuxhaven, at the mouth of the Elbe, in
the Baltic, near Wismar, in the guano, and the stomachs
of our oysters, scallops and other shell-fish. Another
large deposit is found at Andover, Connecticut ; and
Ehrenberg states "that similar beds occur by the river
Amazon, and in great extent from Virginia to Labrador."
The chalk and flints of our sea- coasts are found to be
principally shells and animal remains. Ehrenberg com-
putes, that in a cubic inch of chalk there are the remains
of a million distinct organic beings. The Paris basin, one
bnndred and eighty miles long, and averaging ninety hi
V B 1
434 THE MICROSCOPE.
breadth, abounds in Infusoria and other siliceous remains.
Ehrenberg, on examining the immense deposit of mud
at the harbour of Wismar, Mecklenburg-Schwerin, found
one-tenth to consist of the shells of Infuswia ; giving a
mass of animal remains amounting to 22,885 cubic feet
in bulk, and weighing forty tons, as the quantity annually
deposited there. How vast, how utterly incomprehen-
sible, then, must be the number of once living beings,
whose remains have in the lapse of time accumulated !
In the frigid regions of the North Pole no less than sixty-
jight species of the fossil Infusoria have been found.
The guano of the island of Ichaboe abounds with fossil
Infusoria, which must have first entered the stomachs of
fish, then those of the sea-fowl, and became ultimately
deposited on the islands, incrustating its surface ; whence
they are transported, after the lapse of centuries, to aid
the fruition of the earth, for the benefit of the present race
of civilized man. The hazy and injurious atmosphere met
with off Cape Verd Islands, and hundreds of miles distant
from the coast of Africa, is caused entirely by a brown
dust, which upon being examined microscopically by
Ehrenberg, was found chiefly to consist of the flinty shells
of Infusoria, and the siliceous tissue of plants : of these
Infusoria, sixty- four proved to belong to fresh- water
species, and two were denizens of the ocean. From the
direction of the periodical winds, this dust is reasonably
supposed to be the finer portions of the sands of the desert
of the interior of Africa.
The deposit of the beneficent Nile, that fertilises so
largo a tract of country, has undergone the keen scientific
scrutiny of Ehrenberg ; and he found the nutritive prin-
ciple to consist of fossil Infusoria. So profusely were they
diffused, that he could not detect the smallest particle of
the deposit that did not contain the remains of one or
more of the extensive but diminutive family that once
revelled in all the enjoyment of animal existence. It is
very remarkable that at Holderness, in digging out a sub-
merged forest on the coast, numbers of fresh -water fossil
D'iat^macece have been discovered, although the sea flows
over the place at every t:de.
Mod 9 , of Preparing Fossil Infusoria. Before entering
PREPARATION OP FOSSIL INFUSOKIA. 435
on further details of the fossil Infusoria, we would first
state how they may be prepared for microscopic examina-
tion. A great many of the infusorial earths may be
mounted as objects without any previous washing or pre-
paration ; some, such as chalk, however, must be repeat-
edly washed, to deprive the Infusoria of all impurities ;
whilst others, by far the most numerous class, require
either to be digested for a long time, or even boiled in
strong nitric or hydro-chloric acid, for the same purpose.
Place a small portion of the earth to be prepared in a test-
tube, or other convenient vessel, capable of bearing the
heat of a lamp ; then pour upon it enough diluted hydro-
chloric acid to about half fill the tube. Brisk effervescence
will now take place, which may be assisted by the applica-
tion of a small amount of heat, either from a sand-bath or
from a lamp : as soon as the action of the acid has ceased,
another supply may be added, and the same continued
until no further effect is produced. Strong nitric acid
should now be substituted for the hydro-chloric, when a
further effervescence will take place, which may be greatly
aided by heat ; after two or three fresh supplies of this
acid, distilled w.ter may be employed to neutralise all the
remains of the acid in the tube ; and this repeated until
the water comes away perfectly clear, and without any
trace of acidity. The residuum of the earth, which con-
sists of silica, will contain all the infusorial forms ; and
some of this may be taken up by a dipping-tube, laid on
a slide, and examined in the usual manner. Should per-
fect specimens of the Coscinodiscus, Gallionella, or Navi-
cula be present, they may be mounted in Canada balsam ;
if not, the slide may be wiped clean, and another portion
of the sediment taken, and dealt with in the same way,
which, if good, after being dried, may be mounted in Canada
balsam.
Dr. Redfern adopts an excellent mode of isolating Navi-
culce and other test-objects. He says : " Having found
the methods ordinarily employed very tedious, and fre-
quently destructive of the specimens, I adopted the follow-
ing plan. Select a fine hair which has been split at its
free extremity into from three to five or six parts, and
having fixed it in a common needle-holder by passing it
436 THE MICROSCOPE.
through a slit in a piece of cork, use it as a forceps under
a two-thirds of an inch objective, with an erecting eye-
piece. When the split extremity of the hair touches the
glass-slide, its parts separate from each other to an amount
proportionate to the pressure, and on beii.g brought up to
the object, are easily made to seize it, when it can be
transferred as a single specimen to another slide without
injury. The object is most easily seized when pushed to
the edge of the fluid on the slide. Hairs split at the ex-
tremity may always be found in a shaving-brush which has
been in use for some time. Those should be selected which
have thin split portions so closely in contact that they
appear single until touched at their ends. I have also
found entire hairs very useful, when set in needle-holders,
in a similar manner ; any amount of flexibility being given
to them by regulating the length of the part of the hair
in use." Professor Smith, of Kenyon, U.S. contrived a
very ingenious "Mechanical finger " for picking up and
arranging diatoms and other minute objects.
Professor J. W. Bailey, of New York, has enriched the
Museum of the College of Surgeons with several valuable
specimens of the skeletons of Infusoria; among them is a
fresh-water Bacillaria, named Meridion circulare, which
Professor Quekett, in the Historical Catalogue, describes
as u consisting of a series of wedge-shaped bivalve siliceous
loricse, arranged in spiral coils j when perfect, and in cer-
tain positions, they resemble circles ; each lorica is articu-
lated by two lateral surfaces." It is asserted that they
creep about when free from the stalk-plate. (Fig. 225, No.
16.) Cocconema lanceolata have two lanceolate flinty cases
that taper towards their ends, one of which is attached to
a little foot. Each lorica has a line marked in its centre,
and transverse rows of dots on both sides : Ehrenberg says
there are twenty-six rows in the one-hundredth of a line.
(Fig, 225, No. 14.) Achnanihes Longipes have at the
margins two coarse convex pieces roughly dotted, and two
inner pieces firmly grooved ; the inside seems filled with
green matter. At one corner they are affixed to a jointed
pedicle, which in many specimens contains green granules.
In a specimen of a fossil Eimotia, found in some Bermuda
earth, the flinty case is \i four parts; it is of a half-
FOSSIL INFUSORIA.
437
lanceolate shape, and a little indented on both margins ;
two of them have curved rows of dots, and the other two
are partly grooved with finer rows. Ehrenberg says they
have four openings, all on one side (fig. 225, No. 13),
Fig. 226.
7, Campilodiscus cli/peus. 8, Biddulpliia. 9, GallioneUa sulcata. 10, Trice-,
ratium, found in Thames mud. 11, Gomphonema geminatum, with their stalk-
like attachments. 12. Dictyocha fibula. 13, Eunolia. 14, Cocconema. 15, Fra-
gilaria pectlnalis. 16, Meridian circniare. 17, Diatomaflncculosum.
presenting a row of dots varying very much in number ;
minute strife in some cases extend from each dot towards
the middle of the lorica ; and on the circumference there
are two of these dots. The spirals and the individual
lorica are very fragile, and therefore easily separated from
each other. Of a glistening whiteness is the ribbou-liko
flinty case of Fragilaria pectinalis, which consists of
many bivalve segments : on the articulating surface there
are smg.ll grooves, represented in fig. 225, No. 15. A gin-
438 THB MICROSCOPE.
gular class of objects are Diatoma ftocculosum, beiig rather
oblong-looking, and joined -to each other at opposite cor-
ners : they are sometimes grooved on each side. (Fig. 225,
No. 17.) The "Swollen Eunotia" is generally about
from the llth to the 200th of an inch in length: a
groove, widest in the centre, and tapering off to the ends,
passes along its centre on both sides ; it has curved lines
proceeding from it. So wonderfully close are these lines
or ribs, that as many as eight of them havt* been
counted in the space of the ] 200th of an inch. They are
usually found when alive adhering to a branch of some
weed that forms the green coating over stagnant waters.
They propagate by self-division ; a slight line running
down the centre marks where the separation will occur,
on each becoming perfectly developed as a distinct crea-
ture ; and thus they grow and separate, filling the earth
with their flinty shells.
Gallionella sulcata is found m many parts of North
America ; it somewhat resembles the cylindrical box for
spices, which was at one time so common among good
housewives; scientifically, it is described as consisting of
chains of cylindrical bivalve loricee, having their outer
surfaces marked or furrowed with longitudinal striae ; short
joints may occasionally be seen, having their ends upper-
most, the depth of the furrows being shown on the margin;
within the margin is a thin transparent rim having ra-
diating striae. Sometimes as many as forty will be found
joined together. (Fig. 225, No. 9.) The Gallionella received
its designation from a celebrated French naturalist named
Gaillon, it is often termed the Box-chain Animalcule, and
when the flinty case is seen lying on its face, it much re-
sembles a coin. These living infusoria are found in almost
all waters, and are stated to be so rapid in their growth,
that one hundred and forty millions will by self-division
be produced in twenty-four hours. A species named the
Striped Gallionella was discovered by Dr. Mantell near
London ; the same species is also found in the ocean.
Sometimes the chains are three inches long; their size is
from the 14th to the 400th part of an inch.
Professor Quekett, in the catalogue already referred tcs
describes an " earth from Bohemia, particularly rich ID
KOSSIL INFUSORIA 433
fossil specimens of Navicula viridis, whiou consists of four
prismatic loricae, two ventral and two lateral ; the former
having round, the latter truncate extremities ; and both
provided with two rows of transverse markings and dots,
longer and more marked on the ventral than on the lateral
surfaces. The specimens having their ventral surfaces
uppermost, exhibit a longitudinal marking in the centre,
with a slight dilatation or knob at each extremity ; this
marking is interrupted in the middle of the lorica, and a
diamond-shaped spot is left ; if one of the lateral loricse be
examined, two of the same spots will be seen, one on each
side ; they are of triangular figure, and appear to be thicker
parts of the shell, described as holes by Ehrenberg." Four
smaller triangular spots may be observed in the same
lorica, one being situated at each corner ; these also have
been considered as openings by Ehrenberg : their length
varies considerably; some exceed the 100th, whilst others
are even smaller than the 1000th of an inch. Isthmia ener-
ms (fig. 224, No. 5) is usually found attached to sea-weed ; it
is in three parts ; and of a trapezoid shape, the centre part
appears like a band passing over, and is bounded by broad
straight lines : its outer surface is covered with a network
of rounded reticulations, arranged in parallel lines. Among
the most remarkable is Amphitetras antediluviana ; thia
is of a cubical or box-like %ure, and consists of three
portions, the one in the centre being in the form of a band,
as shown at fig. 225, No. 8, and the two lateral ones having
four slightly projecting angles, with an opening into each.
When viewed in detached pieces, the central one is like
a box, and the two lateral portions resemble the cover and
bottom. The former may be readily known, as consisting
merely of a square frame-.work with striated sides ; but
both the latter are marked with radiating reticulations.
When recent, they are found in zigzag chains, from their
cohering only by alternate angles. In some instances, as
in Biddidphia, and Isthmia, two young specimens may be
found within an old one. Cocconeis is marked with eight
or ten lines proceeding from the inner margin to the
centre ; between which are dotted furrows, with the earlier
spot in the centre of each. (Fig. 224, No. 3.)
Campilodiscus clypcus is oval, and curved in opposite
440 THE MICROSCOPE,
ways at the long and short diameters. On the margin
there are two series of dots, sometimes joined ; and on the
oval centre there are also dots about the margin, while the
middle is nearly plain. (Fig. 225, No. 7.) Actinocydus has
a round bivalve flinty case, with numerous cells formed by
radiating partitions; very often every alternate cell only
is on the same plane. The specimen in the Museum of
the College of Surgeons is exquisite in its markings ; it
was found in some Bermuda earth, and has a beautifully-
raised margin, and a five-rayed star in the centre ; the
number of cells is ten, five being on one plane and five on
another. One set has the usual hexagonal reticulations
crossed with diagonal lines, the other has the same lines,
with a much smaller series of triangular reticulations, so
disposed that they appear to form with each other parts
of very small circles. One valve from this specimen is
represented in fig. 224, No. 2.
As well as the beautiful shell of the Coscinodiscus, found
both in a fossil and recent state, there is one of exquisite
elegance and richness, of the genus Arachnoidiscus, so
named from the resemblance of the markings of the shell
to the slender fibres of a spider's web. (Fig. 224, No. 1.) This
is found in the guano of Ichaboo, and also in earth from
the United States, as well as among sea- weed from Japan,
and the Cape of Good Hope. Mr. Shadbolt believes :
" These shells are not, strictly speaking, bivalves, although
capable of being separated into two corresponding por-
tions ; but are more properly multivalves, each shell con-
sisting of two discoid portions, and two annular valves
exactly similar respectively to one another." (See Micro-
scopical Society's Transactions, for an excellent paper on
these shells by Mr. Shadbolt.)
Artists who design for art-manufacturers might derive
many useful hints from the revelations of the microscope,
as evidenced in the arrangement of the shell last noticed,
and in that of the genus Coscinodiscus; a very handsome ob-
ject, the shells of which are marked with a network of cells
in a hexagonal form, arranged in radiating lines or circles,
and varying from l-200th to l-800th of an inch in diameter.
A specimen found in Bermuda earth has on one of its valves
two parallel rows of oval cells that form a kind of cross ;
XANTHIDIA.
441
which gradually enlarge from the centre to the margin ;
the angles of the cross are filled up with hexagonal cells
as previously noticed. (Fig. 224, No. 4.)
The unskilled manipulator may for some time endeavour
to adjust a slide, having a piece of glass exposed not larger
in size than a pea, on which he is informed an invisible
object worthy his attention is fixed, before he is rewarded
by a sight of Triceratium favus, extracted from the mud of
the too-muddy Thames. The hexagonal markings, cells,
are beautiful, and at each corner there is a curved pro-
jecting horn or foot. (Fig. 225, No. 10.) In Bermuda earth
there is a small species found, which has its three margins
curved ; and also a curious species, which resembles the
triradiate spiculum of a sponge.
It is remarkable how, in these minute and obscure
organisms, we find ourselves met by the same difficulties
concerning any positive laws governing the formation
of generic types, as in larger and more complex forms of
animal and vegetable life. It appears as if we could
carry our real knowledge little beyond that of species; and
when we attempt to define kinds and groups, we are en-
countered on every side by forms, which set at nought our
definitions.
Man even uses infusorial remains as food ; for the berg-
mehl, or mountain-meal found in Swedish Lapland, and
which, in periods of scarcity, the poor are driven to mix
with their flour, is principally composed of the flinty shells
of the Gallionella sulcata, Navicula viridis, and Gompho-
nema geminatum. Dr. Trail, on analysing it, found it
to consist of 22 per cent of organic matter, 72 of silica,
5 -85 of alumina, and 0'15 of oxide of iron. This would
seem to be the same substance described by M. Laribe the
missionary, and put to a similar use in China : " This
earth," he says, "is only used in seasons of extreme
dearth."
XANTHIDIA. In conjunction with the skeletons of the
former species it will be as well to offer a few remarks upon
animals long classed with Infusoria, and but rarely found
except in the fossil state. There is every reason to believe
that the Xanthidia, double-bar animalcules, are sporangia
of Desmid'aceoe. In proof of this it cau be shown that
442 THE MICROSCOPE.
their skeletons are composed of a horny substance, and not
of silica, as was once supposed.
The name Xanthidia is derived from a Greek word sig-
nifying yellow, that being their prevailing hue. They are
found plenteously in a fossil state, imbedded in flint, as
many as twenty being detected in a piece the twelfth of
an inch in diameter ; in fact, it is rare to find a gun-flint
without them. When living they may be described as
having a round transparent shell, from which proceed
spikes varying in size and shape. One kind, found by Dr.
Bailey in the United States, was of an oval form, the 288th
of an inch in length; and another species circular, found
by the late Dr. Mantell, at Clapham : both were of a
beautiful green colour. Specimens of Branched Xantlii-
dium, found in flint by Dr. Mantell, were from the 300th
to the 500th of an inch in diameter. Mr. Ralfs says:
" That the orbicular spinous bodies so frequent in flint,
are fossil sporangia of Desmidiacece, cannot, I think, be
doubted, when they are compared with figures of the
more recent forms. Indeed, the late Dr. G. Mantel], who,
in his Medals of Creation, without any misgiving, had
adopted Ehrenberg's ideas concerning them, changed his
opinion ; and in his last work regards them as having been
reproductive bodies, although he is still uncertain whether
they are of vegetable origin."
The fossil forms vary as much as recent Sporangia, in
being smooth, bristly, or furnished with spines, some
are simple, and others branched at the extremity. Some-
times, a membrane may be traced, even more distinctly
than in recent specimens, either covering the spines, of
entangled with them. Writers have described the fossil
forms as having been siliceous in the living state ; but
Mr. Williamson informs us that he possesses specimens
which exhibit bent spines and torn margins ; and this
wholly contradicts the idea that they were siliceous be-
fore they were embedded in the fiint. In the present
state of our knowledge, it would be somewhat premature
to identify the fossil with recent species ; it is better,
therefore, at least for the present, to retain the names
bestowed on the former by those observers who have do-
scribed them.
XANTIIIDIA. 443
Near to Sydden Spoint, and the Eouud Down Cliff, on
the Dover beach, Mr. H. Deane cut out a piece of pyrites
with the adherent chalk, which, on examination, " exposed
to view bodies similar to, if not identical with, Xan-
thidia in flints ; he clearly recognised X. spinosum, ramo-
sum, tubiferum, simplex, tubiferum recurvum, malleoferum,
and pyxidiculum, together with casts of Polythalamia, and
other bodies frequently found in flints. In shape they are
somewhat flattened spheres, the greater part of them
having a remarkable resemblance to gemmules of sponge,
with a circular opening in the centre of one of the
flattened sides. The arms or spines of all appear to be
perfectly closed at the ends, even including those which
have been considered in the flint, specimens decidedly
tubiferous ; showing that if the arms are tubes, they could
afford no egress to a ciliated apparatus similar to those
existing among Zoophytes. On submitting them to pres-
sure in water between two pieces of glass, they were torn
asunder laterally, like a horny or tough cartilaginous sub-
stance : and the arms in immediate contact with the glass
were bent. Some specimens, put up after several weeks'
maceration in water, were so flaccid, that, as the water in
which they were suspended evaporated away, the spines or
arms fell inclined to the glass. These circumstances alone
seem clearly to disprove the idea of their being purely
siliceous. The casts of the Polythalamia, portions of
minute crustaceans, &c. appeared also to be, like the Xan-
thidia, some modification of organic matter ; and in the case
of the Polythalamia, the bodies are so perfectly preserved,
that in some the lining membranes of the shells are readily
distinguishable."
Mr. Wilkinson, who examined recent Xanthidia found in
the Thames mud, and slime, on piles and stones at Green-
hithe, said that, in his opinion, they are not siliceous,
but of a horny nature, similar to the wiry sponges, which
Mr. Bowerbank describes as being very difficult to destroy
without the action of fire. He also met with a peculiarity
in a X. spinosum, which he has never seen in any other
species ; it was in a piece of a gun-flint. There appeared,
as it were, a groove or division round the circum-
ference, similar to tiiat formed by two cups when placed
444 THE MICROSCOPE.
5>n each other, so as to make their rims or upper edges
meet.
The other fossil Infusoria, found most abundantly in the
chalk and flint of England, are the Rotalia, or wheel-shaped,
and the Textularia or woven-work animalcules ; the latter
having the appearance of a cluster of eggs in a pyramidical
form, the largest being at the base, and lessening towards
the apex.
We must here bring to a close this short notice of
some of the marvellous creations in the invisible world ;
every glimpse inspiring awe, from the immensity, variety,
beauty, and minuteness of its organised habitants. Immen-
sity, in its common impression on the mind, hardly conveys
the idea of the myriads upon myriads of Infusoria that
have lived and died to produce the tripoli, the opal, the
flints, the bog-iron, the ochres, and limestones of the world.
Professor Owen beautifully explains the uses of this vast
amount of animalcule life: "Consider their incredible
numbers, their universal distribution, their insatiable
voracity ; and that it is the particles of decaying vegetable
and animal bodies which they are appointed to devour
and assimilate. Surely we must, in some degree, be in-
debted to these ever-active, invisible scavengers, for the
salubrity of the atmosphere and the purity of water. Nor
is this all ; they perform a still more important office in
preventing the gradual diminution of the present amount
of organised matter upon the earth. For when this matter
is dissolved or suspended in water, in that state of com-
minution and decay which immediately precedes its final
decomposition into the elementary gases, and its con-
sequent return from the organic to the inorganic world,
these wakeful members of nature's invisible police are
everywhere ready to arrest the fugitive organised particles,
and turn them back into the ascending stream of animal
life. Having converted the dead and decomposing par-
ticles into their own living tissues, they themselves become
the food of larger Infusoria, and of numerous other small
animals, which in their turn are devoured by larger ani-
mals ; and thus a food, fit for the nourishment of the
highest orgar:sed beings, is brought back, by a short route,
from the extremity of the realms of organised matter.
VORTICELLIDJ5. 44 5
These invisible animalcules may be compared, in the great
organic world, to the minute capillaries in the microcosm
of the animal body ; receiving organic matter in its state
of minutest subdivision, and when in full career to escape
from the organic system, turning it back, by a new route,
towards the central and highest point of that system."
Such, then, seem to be some of the purposes for which
are created the wonderful invisible myriads of infusorial
animalcules. In the words of Holy Writ : " All these
things live and remain for ever for all uses ; and they are
all obedient. All things are double one against another ;
and He hath made nothing imperfect. One thing estab-
lisheth the good of another ; and who shall be filled with
beholding His glory ? '
VoRTiCELLiDjE. We now come to a family, which includes
some of the most beautiful of living infusorial animalcules,
and in which we meet with phenomena more curious than
any yet witnessed, and perhaps as wonderful as any that
will be presented to our notice, in the natural history of
the higher classes of animals. The family of VortictUidoe,
bell-animalcules, are characterised by the possession of a
fringe of rather long cilia, surrounding the anterior ex-
tremity, which can be exerted and drawn in at the pleasure
of the creatures. Some are furnished with a horny case
for the protection of their delicate bedies, whilst others
are quite naked.
The genus Vorticella, from which the name given to
the family is derived, consists of little creatures placed at
the top of a loag flexible stalk, the other extremity of
which is attached to some object, such as the stem or leaves
of an aquatic plant. This stem, slender as it is, is never-
theless a hollow tube, through the entire length of which
runs a muscular thread of still more minute diameter.
When in activity, and secure from danger, the little Vor-
ticella stretches its stalk to the utmost, whilst its fringe of
cilia is constantly drawing to its mouth any luckless
animalcule that may come within the influence of the
vortex it creates ; but at the least alarm the cilia vanish,
and the stalk, with the rapidity of lightning, draws itself
up into a little spiral coil. But the Vorticella is not
wholly condemned to pass a sort of vegetable existence,
445
THE MICROSCOPE.
rooted, as it were, to a single spot by its slender stalk ; its
Creator has foreseen the probable arrival of a period in its
existence when the power of locomotion would become
Fig. MS.
1, 3, 3, Hydras in various stages of development. 4, A group of Stentor poly-
morphic, many-shaped Stentor. 5, Englena. 6, Monads.
necessary, and this necessity is provided for in a manner
calculated to excite our highest admiration. At the lower
extremity of the body of the animal, at the point of its
junction with the stalk, a new fringe of cilia is deve-
loped : and when this is fully formed, the Vorticella quits
>ts stalk, and casts itself freely upon its world of waters.
The development of this locomotive fringe of cilia, and
the subsequent acquisition of the power of swimming by
the Vorticella, is generally connected with the propagation
cf the species, which, in this and some of the allied genera,
presents a series of most curious and complicated phe-
nomena
VORTICELLID^:. 447
The Vorticella possess means of propagation which is
denied to other Infusoria, with the exception of a few,
although we meet with the same in other forms of animal
life. The mode of reproduction referred to is called
gemmation; it consists in the production of a sort of
bud, which gradually acquires the form and structure
of the perfect animal. In the Vorticellce, these buds,
when mature, quit the parent stem after developing a
circlet of cilia at the lower extremity, and fix themselves
in a new habitation in exactly the same manner as those
individuals produced by the fissuration of the bell.
At an earlier or later period of their existence, the
Vorticellce withdraw the discs surrounded by cilio. which
forms the anterior portion of their bodies, and co~
tracting themselves into a ball, secrete a gelatinous cover-
ing, which gradually solidifies, and forms a sort of capsule,
within which the animal is completely inclosed. By this
process the little animal is said to become encysted; and
at this point of its history it is seen to be more compli-
cated. Sometimes its further progress commences by the
breaking up of the nucleus into a number of minute ova.1
discs, which swim about in the thin gelatinous mass into
which the substance of a parent has become dissolved.
The body of the parent animal, inclosed within the cyst,
now becomes apparently divided into separate little sacs
or bags, some of which gradually acquire a considerable
increase in size, and at length break through the walls of
the cyst. After a time one of these projections of the
internal substance bursts at the apex ; and through the
opening thus formed the gelatinous contents of the cyst,
enclosed embryos, are suddenly shot out into the water,
there to become diffused, giving rise to new generations.
From the name Acineta given to them by Ehrenberg, who
described them as a new genus, they are denominated
Acineta-forms.
But the final object of this singular metamorphosis
still remains to be described. The nucleus, which at the
change of the encysted animalcule into the Acineta~Jorm
was still distinctly observable, becomes entirely and alto-
gether converted into an active young Vorticella, acquiring
an ovate form, with a circlet of cilia round its narrower
448 THE MICROSCOPE.
extremity, and presenting at the opposite end a distinct
mouth. Within this young animal, whilst still inclosed in
the body of its parent, we see a distinct nucleus, arid the
usual contractile space of the full-grown creature. When
mature, the offspring tears its way through the membranes
inclosing the Acineta, which, however, immediately close
again. The latter continues protruding and retracting it?
filaments, and soon produces in its interior a new nucleus,
which in its turn becomes metamorphosed into a young
Vorticella.
The same faculty of enclosing themselves in a cyst is
said to be made use of by the Vor-
ticella, as a means of self-preservation
if the water in which they have been
living dries up. When the animal is
thus encased, the mud at the bottom
of the pool may be baked quite hard
in the sun without doing it the least
injury ; and in this state the creatures
are often taken up by the wind with
the dust which it raises from the sur-
face of the parched ground, and borne
lg ' ? ' along to great distances, so as to cause
Vorticdla microstoma. . , . 6 . . ,
their appearance in most unexpected
loocalities (they are frequently found in roof gutters), where
the first shower of rain calls them back to active life.
Conochilus vorticella^Qlongmg to the family ^Ecistina,
Plate III. No. 80, is one of the most remarkable and in-
teresting Eotifers met with. It is found in compound
groups of a whitish globular form in shallow ponds about
London. On Hampstead Heath a good supply is often
obtained throughout the summer montns. The group
consists of from twenty to thirty, or more, animals, of about
twice the size of the fall-grown volvox, and, like the
latter, can be readily seen actively rolling abouV when the
collecting-bottle is held up to the light. The colony is
attached to a centre disc, resembling a wheel with its
naves and spokes. The foot-stalk is three or four times
ihe length of the body, and has a somewhat spiral form,
tvhich it contracts at pleasure, drawing the body down in
nil instant close to the axis, although it does not appear to
(1) Commonly called volvox, but this is an error, as it clearly does not belong
tc the Volvocinae.
ROTIFERS. 449
have the power of retracting itself perfectly within tho
hyaline membrane. The hyaline membrane is at certain
periods of the year so very translucent that it cannot be
made out ; later in the season it is found studded with para-
sitic desmids, when its gelatinous form is readily seen. The
body is ovoid or cup-shaped, and the mouth is surrounded
by long cilia, which are always in rapid motion. When
the animal becomes alarmed it instantly retracts, and then
has the appearance of a small round ball. On the frontal
plane four thickish conical erect papillae are placed, each fur-
nished with one or more spines or sefoe ; very near their
base, rather behind, and between the division of the
ciliary band, are the very minute visual organs. The
jaws, it is said, are furnished with teeth, but these we
have not been able to make out, chiefly owing to their
disposition to break up in a short tune after being placed
in confinement. The stomach is oval, and two ovoid
bodies are observed near the termination of the oesophagus ;
below these the ova-sack encloses a single ovum of a dark
colour. The ovum is surrounded by spinous processes, or
cilia, and when first thrown off it lodges for a time in the
hyaline membrane ; but, when set free, moves slowly
about. A few minutes after being placed in the glass-cell
the colony become uneasy, break themselves off one after
the other, and swim away to die. They were formerly
classed among Volvocinece, but bear no resemblance to
them, except in their roll through the water ; and are
more properly placed among the Rotifers.
Acineta tuberosa, Plate 111. No. 68. The researches of
Stein are said to prove that the several members of this
family are simply a developmental phase of Vorticellina;
this view, however, is controverted by Lachmann, Cla-
parede, ~nd others who have witnessed the reproduction of
Acinetce from parent forms. A. tuberosa has a triangular-
shaped body and three obtuso tubercles or horns, each
furnished with tentacula. Many other forms of this
genus are well known ; but, notwithstanding the diversity
in construction, Stein declares their tubular ramified pro-
cesses to be morphologically and physiologically identical
with ordinary tentacula. Vaginicola crystallina he puts
forward as one of the best illustrations to be obtained of
G O
450 THE MICKOSCOPE.
the conversion of an encysted Vorticellina into an Acineta^
He also considers Actinophrys Sol and Podophrya fixa
(Ehr.) to be the acinetiform representatives of Vorticella
microstoma.
Stentors, Trichodina, and a few others are included by
some authors in the Vorticellina. Stentors (fig. 226, No. 4)
are exclusively found in fresh water, between or upon
water plants in still running waters. Some are colourless,
others green, black, or clear blue. " It is," says M. Du-
jardin, " in the Stentors where we can view the several
supposed internal organs isolately, and that new observa-
tions will make known their real nature."
Rotiferce comprise animals which were placed by
Ehrenberg in nine genera ; named Ptygura, jEcistes, Cono-
chilus, Megalotioclia, Lacinularia, Tubicolaria, Limnias,
Melicerta, and Cephalosipkon. As, however, each of these
genera contain but a single species, Mr. Gosse proposes to
reduce the nine to two ; thus, Ptygura, ^Ecistes, Tubico-
laria, Limnias, Melicerta, and Cephalosiphon, as they seem
to be only so many species of one genus, might constitute
one, and Megalotrocha, Lacinularia, and Conochilus, an-
other. Mr. G-osse also wishes to construct a family to be
called Melicertodce; in this he would include two genera,
Melicerta and Megalotrocha, degrading some of the present
genera to form species of Melicerta, and others, to constitute
three species cf Megalotrocha. Each group will be readily
distinguished the former by the circumstance that the
individuals are solitary ; in the latter they are, in adult
life, aggregated in a common envelope spherical masses,
composed of many animals radiating from a central point.
These compound masses are either free or fixed. In the
genus Melicerta, or tube-dwellers proper, the front or
upper part of the body is capable of being turned in
upon itself, concealed with purse-like folds, and of being
expanded, at the will of the animal, into a disc form, which
is usually much wider than the diameter of the body;
this again is either flat or in the form of a shallow funnel.
Its outline will form either a simple circle, as in M. pty-
gura and M. cecistes, two circles united at one point, as in
Limnias (Plate III. No. 72), or four sinuous lobes, more or
less developed, as in M. cephalosiphon, M. tubic)lai*ia, an/1
ROTIFERS, 451
M. rinyens, in each of which there is, according to Pro-
fessor Huxley, a double edge to the disc, of which the
subordinate one is placed on the under-side, and a little
within the line of the principle one. The former is fringed
with minute cilia, whose vibratile waves form well-marked
movements, which run evenly along the margin. The
eggs are usually laid within the case.
To the genus Melicerta Mr. H. Davis a adds one, if not
two, new species, which he has named, provisionally, M.
longicornis and M. intermedias. The two peculiarities of
these new forms are the remarkable length of the antennae,
and the construction of tube-dwellings for the purpose of
concealing themselves and their eggs. (Plate III. No.
69.) jEcistes longicornis : each animal lives in a separate
semi-transparent cylindrical sheath (urceolus), into which
it entirely withdraws on the approach of danger. The foot-
stalk is long, and firmly attached to the bottom of the tube.
Two or three ova are concealed in the lower part of the urce-
olus. The trochal disc is large, and completely surrounded
by a ciliary wreath. The antennae, two, are very long, well
placed below the disc, and terminating in a small brush of
setae. The tube, Mr. Davis believes, is built up in the same
way as that of Melicerta.
In the " Intellectual Observer," a tubicolus Rotifer
was described ; it was discovered on a stem of AnacJiaris,
and exhibits an affinity with JEcistes, Limnias, and
Melicerta, but differs in some particulars, especially in
the antennae. It was named by Mr. Gosse Cephalosi-
phon, and is remarkable for its single siphon of an
extraordinary length. Like Melicerta and Limnias,
it has no visible structure below the disc, whereas in
^Ecistes the contrary holds good.
"The animal inhabits a case slightly trumpet-shaped,
generally of greater length and slenderness compared with
those of its allies, standing erect on the pond-weed. It is
irregular and floccose in outline, very opaque, and of a
deep umber brown by transmitted light, but of a much
lighter hue by reflected light. It is composed, doubtless,
of an excretion from the skin as the foundation layer,
(1) "On two new species of the genus delates," by Henry Davis, P.RM.SL
Mivnos. Soc. Trans. April 1SG7.
452 THE MICEOSCOPE.
thickened and rendered opaque by the addition of the
dark material, which I conjecture to be the faecal pellets
sucessively discharged in process of growth. Contrary to
the rule in the allied genera, the pctaloid disc is made to
open by the bending forward of the head towards the
ventral aspect, and its widest margin is the dorsal one.
Immediately behind the disc are two minute lateral horn-
like points, which project from the head, and curve to-
wards each other. These are sometimes visible both in a
frontal and a lateral view, and with the disc closed or
open ; but at other times the closest scrutiny fails in dis-
cerning them. Behind these, in the median line, there
is an organ which is never concealed : it is the single
siphon, which stands up perpendicularly from the occiput
to a great height (being almost half as long as the body,
exclusive of the foot), and generally arches over the front,
but is capable of vigorous and sudden movements to and
fro, and from side to side. It is evidently tubular through-
out ; either a simple tube with thick walls, or else, if the
walls are thin, furnished with a slender piston which runs
through its length.
" The Cephalosiplion is very lively and active in its
motions. It is very ready to protrude from its case, and
not at all prone to retire upon ordinary alarms, such as a
jar upon the instrument, that would send the Floscularia
or the StcpJianoceros into its retreat in an instant. It is
very curious to see it protruding : the long antenna is first
thrust out, and jerked to and fro as a feeler, exploring the
surrounding water for safety. The entire height of an
average specimen, in its ordinary state of extension, is
l-33d of an inch ; of which the foot is l-50th, the body
l-200th, and the antennae l-400th of an inch.
The rotating or wheel-animalcules occupy the most
conspicuous place among infusorial animals. They re-
quire water for their development, although they are
indwellers occasionally of the cells of mosses and damp
weeds. They do not possess many stomachs, but one,
and generally have teeth and jaws to supply its wants.
They can elongate and contract their bodies, and ecme
species have their extremity prolonged to a tail, or rather
a foot, or a forked process, by means of which they
ROTIFERS
453
fix themselves to extraneous substances ; while the cilia
is in Tapid motion, this prevents the anterior portion of
the body being drawn in by the force of the rotatory
I, The common Wheel-Animalcule, Rotifer vulgaris, with its cilia
6, protruded ; c, its horn ; d, oesophagus ; e, gut ; /, outer case ; g, eggs. 2, Tlu
same in a contracted state, and at rest: at gis seen the development of tlw
young. 3, Pitcher-shaped Brachionus: a, its jaws; 6, shell; c, cilia, or rota-
tors : d. tail. 4. Baker's Brachionus : a, the jaws and teeth ; b, the shell ; i%
the cilia ; c, the stomach.
action. They multiply by eggs ; a few have been seen to
bring forth their young alive. In the atmosphere the eggs
have been discovered whirling along by the force of the
wind to some resting-place, where, when circumstances
admit, they spring into active life, and fulfil their appointed
destiny. The eggs are of an oval form, and some ten,
twenty, or thirty may be seen in an animal, of a brown
colour, others are of a delicate pink and deep golden yel-
Icur. In those ^f a light colour, the young are sometimes
454 THE MICROSCOPE.
3een with their cilia in active vibration. Ehrenberg
accurately described the upper part of a common wheel-ani-
malcule, with the cilia, jaws, teeth, eyes, &c., as seen under
a magnifying power of 200 diameters, and represented in
ng. 228, No. 1. The small arrows indicate the direction of
the currents produced by the cilia b, turning on their base.
At the will of the animal a change is made in the direction
in which the wheels appear to revolve, these it has the
power of withdrawing, with the quickness of thought ; a
cluster of hairs appears at the extremity, that do not
revolve, and certainly differ from the cilia : as they are
usually protruded when the creature is moving from place
to place, their function has been imagined to be that of
feelers.
The red spots, very generally believed to be the eyes of
the Rotiferce, are mostly of a bright red colour ; and the
number and arrangement of these organs vary. In some
species there have been discovered as many as eight, often
placed on either side of the head, in a row, circle,
or cluster, and in some they take a triangular shape.
The Rotiferce delight in the sunshine; and when the
bright luminary is hidden behind clouds, the animals
sink to the bottom of the water, and there remain.
When the water of their haunts is becoming much evapo-
rated, they rise to the top, and give a bright-red tint to
it; but when caught and placed in a jar, their beautiful
colour fades in a few days. Locomotion is performed by
swimming, the rotatory action of the crowns of cilia im-
pelling it forward; in other instances it bends its body,
then moves its tail up towards the head, with the two
processes that serve as feet near the tail ; it then jerks its
head to a further distance, again draws up its tail, and so
proceeds on its journey. Another peculiarity is that
of drawing in the head and tail until nearly globular,
and remaining in this condition fixed by the sucker; at
other times they become a complete ball, and are rolled
about by every agitation of the water.
The body of the wheel-animalcule is of a whitish colour;
its form is indicated in the engraving. The tube for
respiration appears to allow of water passing to the inside.
On the food being drawn by the currents to tbe cup part-
ROTIFERS.
455
of the wheels, it passes through a funnel as it were to the
mouth, which is situated rather lower down, and where
the food is crushed "by teeth placed on the plates of the
jaw, with a hammer-like action ; from this point it passes
through the alimentary canal for the sustenance of the
animal.
BRACHION.EA. Ehrenberg's genus Brachionus, " Spine-
bearing animalcules/' belonging to the Rotifer ce, are truly
interesting, from their very perfect and complex orga-
nisation. Some are entirely enclosed in a horny covering,
others only partially covered. Their structure, so beau-
tiful and symmetrical, has always made them favourites
with those who delight in microscopical studies. Bra-
chionus striatus, " Striped shell animalcule " (No. 3, fig.
228), of an elegant, jug-like form, has the transparent
coat or carapace, striated and scalloped out at the upper
part ; through which the citron-
coloured inhabitant protrudes itself.
Two hornlike processes are appended
to its under-side. As occasions re-
quire, it sinks firmly and securely
within its crystal home, which is suffi-
ciently transparent to permit a view
of its organisation. Its progress is
effected by means of ciliary processes.
Brachionus Pala, or Amerce Cervi-
cornis, "Bent horn animalcule," is
possessed of double rotatory organs,
and four long processes, which project
above the external coat. It measures
theOOthpart of aninch. Brachionus
Ovalis, " Egg-shaped brachionus," is
remarkable for the strength > of its
transparent coat, which is beyond
that of other horny creatures. Its
projecting tail, as well as head, is at
pleasure withdrawn into its very
strong case. Brachionus Dentatus, i, Brachionus Ovalis, closed.
*' Toothed brachionus." This active, 2 > Cilia displayed,
bright pink-eyed little creature, the 90th part of an inch
in size, is apparently enclosed in a two-valved shell, having
Fig. 229.
456 THE MICROSCOPE.
each 2 mi indented so as to form two pair of teeth. Mi.
Pritchard says: "In addition to the rotatory organa
for supplying it with food, 1 have observed it attached
to a stem of confervae, and abrading it with its teeth
fixed in the bulbous esophagus, which, during the opera-
tion, oscillates quickly; the rotatory cilia at the same
time move rapidly, which makes it highly probable that
they perform some office connected with the organs of
respiration, as their motion seems altogether unnecessary
while the creature is feeding in this manner." Brachionus
Bakeri, " Baker s brachionus," (fig. 228, No. 4 ), is a curious
and beautifully-formed animal. At the points of a half-
circle are situated the rotatory organs and cilia, between
which rise some long spines, each side of the shell pro-
ceeding to a point in the lower part, while a square seems
taken out of its body, forming thus two spines ; from the
central part of the body projects a long tail. The eggs are
sometimes attached to these spines, and in other instances
are seen in the ovisac.
Notommata Aurita, the " Eared notommata." The ana-
tomy of this animal, a genus of Rotiferce, family Hyda~
tincea, has been most lucidly explained and illustrated by
Mr. P. H. Gosse, in the Microscopical Society's Transactions.
Mr. Gosse states, that his specimens were found in a jar
of water obtained in the autumn from a pond near \Val-
thamstow, the jar having stood in his study-window
through the winter; and from a swarm in the succeeding
February he selected one the 70th of an inch in length
when extended, but its contractions and elongations
rendered its size variable.
" Its form, viewed dorsally, is somewhat cylindrical, but
it frequently becomes pyriform by the repletion of the
abdominal viscera. Viewed laterally, the back is arched
gibbous posteriorly, with the head somewhat obliquely
truncate, the belly nearly straight. The posterior ex-
tremity is produced into a retractile foot, terminating in
two pointed toes ; this, both in function and structure, is
certainly analogous to a limb, and must not be mistaken
for the tail, which is a minute projection higher up the
body. When not swimming or rotating, the head assume*
a rounded outline, displaying through the transparent
ROTIFERS. 457
integument an oval mark on each side, within winch a
tremulous motion is perceived ; but at the pleasure of the
animal a semi- globular lobe is suddenly projected from
each of these spots by evolution of the integument.
These projections have suggested the trivial name of
aurita. Each lobe is crowned with a wheel of cilia, the
rapid rotation of whose waves forms the principal source
of swift progression in swimming. The protrusions of
these lobes are evidently eversions of the skin, ordinarily
concealed in two lateral cavities. They may be protruded
by pressure, and are then seen to be covered with long
but firm and close-set cilia, which are bent backward, and
move more languidly, as death approaches. The whole
front is also fringed with short vibratile cilia, which extend
all along the face, as far as the constriction of the neck.
The whole body is clear and nearly colourless ; but its
transparency is much hindered by the net-work of dim
lines and corrugations that are everywhere seen, particu-
larly all about the head."
Mr. Gosse, throwing a little carmine into the water, sawthe
jaws working slightly, the points opening a little way, and
then closing; the rods of the hammers were drawn towards
the bottom for opening, and upwards for closing. A little
mass of pigment was soon accumulated beneath the tips
of the jaws, which spread itself over a rounded surface,
but did not pass farther; nor did an atom at this time go
into the stomach.
After entering into further minute details of the little
animal, he observes: "They possess organs that many
others do not, and want some that others possess. They
prove that the minuteness of the animals of this class
does not prevent them from having an organisation most
elaborate and complex, and therefore it justifies the belief
that the Rotiferce should occupy a place in the scale of
animal life much higher than that which has been commonly
assigned to them."
Like most of the class, this Notommata is predatory.
Mr. Gosse once saw one eagerly nibbling at the contracted
body of a sluggish Rotifer vulgaris; the mouth was drawn
obliquely forward, and the jaws were protruded to the food,
so as to touch it. It did not appear, however, to do the
458 THE MICROSCOPE.
rotifer much damage. It appeared chiefly to feed on
monads.
FLOSOULAIII^EA. The Stephanoceros, " Crowned animal-
cule." This beautiful little creature is about the 36th
of an inch in length ; and is enclosed in a transparent
cylindrical flexible case, ovei which it protrudes five long
arms in a graceful manner, which, touching at their points,
give a form from which it derives its name. These
arms are furnished with several rows of short cilia, and
retain the prey brought within their grasp until it can be
Hwallowed. The case is attached to the animal on the
part we may term the shoulders; so that when it shrinks
down in its transparent home, the case is drawn inwards.
To the bottom of its home it is secured by an elongation
of the body; and this part, as well as the body, contracts
instantly on the approach of danger, the arms coming
close together are also withdrawn. Its mouth differs
a little from the common wheel-animalcule ; it has two
distinct sets of teeth, with which it tears and crushes its
food. The eggs of the Stephanoceros, after leaving the ani-
mal's body, remain in their crystal-like shell until hatched ;
and Dr. Mantell from close observation found, that about
eighty hours elapsed before their organs were all developed
and fitted for use.
Limnias Ceratophylli, " Water-nymph," is of this family,
being about the 20th of an inch in size, and is enclosed in
a white transparent cylindrical case, one-half the length of
the animal ; which, being glutinous, becomes of a brownish
colour, from the adhesion of extraneous matter. Its rota-
tory apparatus is divided into two lobes, possessing vibra-
ting cilia, as well as a singular projecting angular chin. Iii
the rows of little eggs in the body of the parent, may
clearly be distinguished most of the young organs in a
state of activity. From its fondness for hormvort, it is
often called by the name of that plant. (Plate III. No. 72.)
Floscularia Ornata, "Elegant floscularia," is a beautiful
type of the family, and has its rotatory organs divided
into several parts ; when it contracts itself into a small
compass, its transparent covering becomes wrinkled. This
creature is an interesting object, as its internal structure
*an be seen through the translucent sheath that constitute*
BOTIFERA 459
its dwelliug. The little beings are very rapacious, although
but the 108th part of an inch in size. Floscularia Pro-
boscidea, " Horned fioscularia," has six lobes, fringed with
cilia shorter than in the preceding species. Its name is de-
rived from a peculiar kind of horn or proboscis, also having
cilia placed in the centre of the lobes. The eggs cast off
by the parent enclosed in a sheath, are very pretty objects
for microscopic observation. In fact, the tinted case, the
light ethereal frame of the tiny animal, the variously
coloured food, &c., in the stomach, combine in rendering it
cingularly interesting.
Melicerta- Ringens, " Beaded melicerta.' 9 Of allthelfe-
licerta the "Horney floscularia " is the most beautiful.
Its crystalline body is first enclosed in a pellucid covering,
wider at the top than the bottom, of a dark yellow or
reddish-brown colour, which gradually becomes encrusted
with zones of a variety of shapes, glued together by some
peculiar exudation that hardens in water : it is these little
pellets, appearing as rows of beads, give the name to
the animal. Mr. Gosse furnishes an excellent account of
the " architectural instincts of Melicerta ringens" which is
not only truly surprising, but fall of interest. He writes :
" This is an animalcule so minute as to be with difficulty
appreciable by the naked eye, inhabiting a tube composed of
pellets, which it forms and lays one by one. It is a mason
who not only builds up his mansion brick by brick, but
makes his bricks as he goes on, from substances which he
collects around him, shaping them in a mould which he
carries upon his body.
" The animal, as it slowly protrudes itself from its inge-
niously-formed mansion, appears a complicated mass of
transparent flesh, involved in many folds, displaying at
one side a pair of hooked spines, and at the other two
slender, short blunt processes projecting horizontally. As
it exposes itself more and more, suddenly two large rounded
discs are expanded, around which, at the same instant,
a wreath of cilia is seen performing its surprising motions.
Often the animal contents itself with this degree of ex-
posure ; but sometimes it protrudes farther, and displays
two other smaller leaflets opposite to the former, but in
the same plane, margined with cilia in like manner. The
460 THE MICBOSOOPE
appearance is not unlike that of a flower of four unequal
petals ; from which circumstance Linnaeus gave it the
name ringens, by which it is still known."
Below the large petals on the ventral aspect, and just
above the level of the projecting respiratory tubes, is a
small circular disc or aperture, within the margin of which
a rapid rotation goes on. This little organ, which seems
to have hitherto escaped observation, Mr. Gosse can com-
pare to nothing so well as to one of those little circular
ventilators which we sometimes see in one of the upper
panes of a kitchen-window, running round and round, for
the cure of smoky chimneys. The gizzard, or muscular
bulb of the gullet, is always very distinct, and its structure
is readily demonstrated. It consists of two sub-hemisphe-
rical portions, or jaws, each of which is crossed by three
developed teeth, which are succeeded by three or four
parallel lines, as if new teeth might grow from thence.
The teeth are straight, slender, swelling towards their
extremity, and pointed. These armed hemispheres work
on each other, and on a V-shaped or tabuliform apparatus
beneath, common to most of the Rotifers, but in this genus
very small.
The pellets composing the case are very regular in form
and position : in a fine specimen, about the l-28th of an
inch in length when fully expanded, of which the tube was
the l-36th of an inch, Mr. Gosse counted about fifteen
longitudinal rows of pellets at one view, which might
give about thirty-two or thirty-four rows in all.
In November, 1850, Mr. Gosse found a fine specimen
attached to a submerged moss from a pond at Hackney;
this he saw engaged in building its case, and at the same
time discovered the use of the curious little rotatory organ
on the neck. When fully expanded, the head is bent back
at nearly a right angle, to the body, so that the disc is
placed nearly perpendicularly, instead of horizontally; the
larger petals, which are the frontal ones, being above the
smaller pair. Now, below the large petals (that is, on the
ventral side) there is a projecting angular chin, which is
ciliated ; and immediately below this is the little organ in
question. It appears to form a small hemispherical cup,
and is capable of some degree of projection, as if on a short
BOTIFER& 461
pedicle. On mixing carmine with the water, the course of
the cilUry current is readily traced, and forms a fine
spectacle. The particles are hurled round the margin of
the disc, until they pass off in front through the great
sinus, between the larger petals. If the pigment be abun-
dant, the cloudy torrent for the most part rushes off, and
prevents our seeing what takes place ; but if the atoms be
few, we see them swiftly glide along the facial surface, fol-
lowing the irregularities of outline with beautiful precision,
dash round the projecting chin like a fleet of boats doubling
a bold headland, and lodge themselves, one after another,
in the little cup-like receptacle beneath. Mr. Gosse, be-
lieving that the pellets of the case might be prepared in
the cup-like receptacle, watched the animal, and presently
had the satisfaction of seeing it bend its head forward, as
anticipated, and after a second or two raise it again ; the
little cup having in the meantime lost its contents. It
immediately began to fill again ; and when it was full, and
the contents were consolidated by rotation, aided probably
by the admixture of a salivary secretion, it was again bent
down to the margin of the case, and emptied of its pellet.
This process he saw repeated many times in succession,
until a goodly array of dark-red pellets were laid upon the
yellowish-brown ones, but very irregularly. After a certain
number were deposited in one part, the animal would
suddenly turn itself round in its case, and deposit some
in another part. It took from two and a half to three and
a half minutes to make and deposit a pellet.
Melicerta may be found in clear ponds, niill-ponds, and
other places through which a current of water gently
flows. It a portion of water-weed be brought home and
placed in a small glass zoophyte-trough, and carefully exa-
mined with a magnifying power of about fifty diameters,
a fe-v delicate looking projections of a reddish brown
colour will probably be seen adhering to the plant ; these
are the tubular cases of melicerta, which, after a short
period of rest, will throw out little animals of one-twelfth
of an inch in length. 1
(1) For further information, see Gosse, Trans. Micros. Soc. voL iii. 1852,
p. 58 ; Slack's Marvels of Pond Life, 1861 ; and Pritchard's EMery of Infusoria.
tth Edition. 1S61.
462
THE MICROSCOPE.
POLYPIFERA. The chief characteristic of this vast race
of animals is, that their mouths are surrounded by
radiating tentacula, arranged some-
what like the ray of a flower; and hence
the term Zoophyte. So plant-like t
indeed, are their forms, that the early
observers regarded tLem as vegetating
stones, and in\ 3nted many theories to
explain their growth.
They belong to a sub-kingdom
termed Coelenterata, now divided and
subdivided by Professor Huxley into
the following :
Septa, &c., x 5 or 6. Septa, &c., x 4.
Simple soft-bodied.
1. ACTIKIDJE. 1. BEROIDJE.
Actinca, Minyat. Cydippe, Cesium.
Compound Skeleton spicular.
2. ZoANrniDffi. 2. ALCYONID.B.
Zoanthus. Alcyonium.
Compound Skeleton sclerobasic.
3. ANTIPATHIDJE. 3. GORGON ID*.
Anlipathes. Gorgonia, Itis,
Corallium.
Compound and Simple Skeleton thecal continuous
4. PERFORATA. 4. TUBIPORID;E.
Porites, Madrepora. Tubipora.
5. TABULATA. 5. RUGOSA.
Millepora, Seriatopora. Stauria, Cyathanonib.
Cyathophyllum.
6. APOROSA. Cystiphijllum.
Cyathina, Oculina.
Astreea, Fungia.
Opposed to all our common ideas
of animal life is this singular portion
of creation. If we cut a limb off a tree,
or sever that of an animal, these parts
Hg.280.-xwro U wither and decom P ose > b J passing
zoophytes. into other forms of matter. Cut a tree
across its middle, and its natural symmetry is irrepa-
rably disfigured; slit it down its centre, and it is de-
stroyed : all animals so treated suffer instant death, with
the exception of the polype tribe ; for they will put forth
new limbs, form a new head or tail, and if slit, become
two separate perfect creatures.
FOLYPIFERA. 463
The seas which wash our shores swarm with beautiful
forms of minute Pclypes, having nearly the same organisa-
tion as the Hydra, but which are protected by an external
horny integument. This peculiar covering sends forth
shoots or buds, which are developed into new polypes, thus
producing a compound animal; but the exercise of this
gemmiparous faculty is prevented by a horny defence
from effecting any other change than that of adding to the
general size, and to the number of tentacles, prehensile
fingers, and digestive sacs ; yet the pattern according to
which new polypes, and branches of polypes, are developed,
is fixed and determinate in each species, and there conse-
quently results a particular form of the whole compound
animal, by which the species can be readily recognized.
Cordylophora, a fresh water group of zoophytes, has
been made the subject of an admirable memoir by Pro-
fessor Allrnan. (See Phil. Trans. 1853, "On the
Anatomy and Physiology of Cordylophora/') In the inte-
resting and pretty group, Corynidce, the tentacles are
not arranged in a single transverse series, as in Hydra,
but are usually scattered more or less irregularly over
the surface of the polype while in Tubularia there are
two transverse rows of tentacles, an upper shorter, and
a lower longer. The reproductive organs, which in Hydra
are extremely simple, attain, in many of the Corynidce, and
Tubular iadce, to the condition of zooids, sometimes be-
coming detached, and swimming about freely before dis-
charging their products. These free zooids have always
the form of a bell or disc, from whose centre a pyriform
or oval body either a closed sac or an open-mouthed
polype is suspended; and they have been regarded as
distinct animals, and grouped together with other forms of
Hydrozoa, under the head of Medusce. The bell possesses
considerable contractility, and at each contraction the
water which fills its cavity is forced out, and the bell itself
is thereby propelled in the opposite direction. In Tubw-
laria a more completely medusiform body is developed,
but is never detached.
In the Sertulariadce, the numerous digestive zooids, or
polypes, developed from the original germ, remain always
attached; but their most remarkable feature is the posses-
464 THE MICROSCOPE.
sion of a " cell," surrounding the base of each polype, and
usually capable of receiving it when retracted. The de-
velopment of this cell at once distinguishes it from the
not altogether dissimilar group, the Diphydce and Physo-
phoridce. In some Sertidariadce (Sertularia dynamena),
the margins of the cells are converted into membranous
valves; and in the genus Plumularia, we find special
organs of offence.
The Diphydce are among the most remarkable and
beautiful inhabitants of the ocean, to whose warmer
regions, they, like the Physophoridce, are principally con-
fined. They are free swimmers in the adult state, and
probably, at all times of their existence ; but while actively
locomotive by means of the contractions of the natatorial
organs with which they are provided, they possess no
special supporting apparatus, or " float," such as that de-
veloped in the Physophoridce. The tentacle of the Diphydce
is a long filiform process of the peduncle, capable of great
elongation and contraction ; the terminal filament of
which is closely beset with minute thread-cells, so that the
whole must constitute a very efficient weapon of offence.
Three genera of the Physophoridce are particularly worthy
of notice : the Physalia, whose air-vesicle may attain the
length of eight or nine inches, while its formidable ten-
tacles hang down for as many feet, inflicting instantaneous
death upon the smaller animals, and giving rise to no small
amount of pain and irritation, even in man ; and the
Velella and Porpita, in which the texture of the air-vesicle
is so exceedingly firm, as to give it the appearance of an
internal shell, while its cavity is subdivided into numerous
chambers. Originally, however, the " shell " of the Velella
is a perfectly simple air-vesicle, like that of any other
Physophorid. In the very peculiar genus Lucernaria,
lovely " Lamp-polype," with little knobbed tentacles we
have a Hydrozoon, in which the polype occupies the centre
of an expanded disc, the two presenting essentially the same
structure and relations as in the Medusiform zooids of
other divisions. In fact, a Lucernaria is in all essential
respects comparable to an Aurelia, or other Medusa fixed
by the middle of the upper surface of its disc.
Mr, Huxley prefers the term Lucernariadw to that o(
POLYPIFERA. 4G5
Medu&ce; and he does so " from the fact that the Medusidcr
of authors consists of two groups, the Naked-eyed (Gym-
nophthalmatd) and the Covered-eyed (Stegnnophthalmata).
Some of which, the Aurelia, is but a derivative zooid form
of an animal, essentially resembling Lucernaria; while so
far as regards the Naked-eyed Medusae, we have no evidence
that any genus except JEginopsis, is other than the repro-
ductive zooid of one of the Hydridce or Sertulariadce. It
seems better, therefore, to avoid the term Medusae, as the
denomination of an ascertained group, reserving it merely
to denote the medusiform creatures of whose origin we
are ignorant, but whose structure entitles them to a pro-
visional place among the Lucernaria dee. As our know-
ledge increases, we shall be able to arrange those Medusas
which are the zooids of Hydridae, Sertulariadce, Diphydce,
or Physophoridce, under their respective groups, while the
rest will form the sub-sections of the Lucernariadae ; the
first consisting of such forms as Aurelia and Rhizostoma^
zooids developed by fission from fixed Lucernariadce ; the
second consisting of such forms as jEginopsis, free Lucer-
nariadce, developed at once from the ovum, without any
fixed state."
The Actinozoa are those Coclenterata in which the
stomach is a sac suspended within and entirely distinct
from the body, from whose parietes it is separated by
a portion of the general cavity of the body, which may
receive the special denomination of " perivisceral cavity. '
The stomach communicates freely by an inferior aperture
with the general cavity. A rough conception of the rela-
tions between % the Actinozoa and the Hydrozoa may b*'
obtained by supposing the walls of the natatorial disc of a
Lucernaria to become united with those of its central
polype ; it would then become, to all intents and purposes,
an Actizozoon. As the Hydra is the type of the Hydro-
toa, so the "Sea-anemone"' (A ztinia) is considered to be the
type of the Actinozoa. As in the Hydrozoa, the body of
the Actinia is essentially composed of two layers, a super-
ficial layer, composed of polygonal cells, frequently de-
tached and renewed again, beneath which lies a granular
layer ; whilst in the deep dermal layer two sets of mus-
cular fibres are found,- -a superficial circular, and a deep
n H
466 THE MICROSCOPE.
longitudinal set : both are flattened, and exhibit no trans-
verse striation. In some Actiniae, such as A. mesembryan-
tkemum, bright blue sacs are placed at the edges of the oral
Fig. 231. Hydra, 'Mth tentacles displayed and magnified, adhering to a tfoft of-
Anacharis alsinaMrutn.
disc, while in A.^gemmacea, A. sessilis, &c. clear spots are
scattered over the integument, which have been regarded
as apertures or tubercles ; M. Ho Hard, however, states, that
these are imperforate Ampullce, possessing a kind of bila-
biate mouth, surrounded by a sphincter- like arrangement of
muscular fibres. Any foreign body introduced into these
ampullae is seized and forcibly held ; or if the finger be
placod within reach, it gives the sensation of a very fine
rasp passing over it. The margins of the radiate tentacles
of the young animal are surrounded by cilia j the gastric
epithelium is likewise ciliated, and doubtless secretes a
powerfully solvent fluid. The majority of the Actinias
are oviparous, the young being developed from ova within,
and evacuated by the mouth : they are also capable of
multiplication by budding, and occasionally by fission,
whiie their power of restoring themselves after muti
POLYPIFEBA. 467
lation appears to be as great as that possessed by the
Hydra. 1
The great majority of the Actinozoa exhibit a structure
closely corresponding with that of the Actimince ; but from
the manner in which they grow up into compound masses
of associated Zooids, produced by gemmation or by fission,
they stand in nearly the same relation to Actinia, as the
compound Hydrozoa to Hydra.
Sir John Day ell believes that Actiniae conquer their prey
by mere strength ; this is doubtless the case, as from
experience we find nothing like a stinging property be-
longing to the tentacles ; nor are there any poison vesicles
attached thereunto. The tentacles appear to be armed
with rows of spines, which give a clinging and slight
rasping sensation when the finger is thrust against them ;
and by the same means they are able to obtain a firm
hold of any smaller animal that falls within their reach.
Animals with a hard case or shell seem to escape from
their clutches without having sustained the smallest in-
jury. The same remarks apply to the Hydra; they have
neither the power to sting or benumb their prey, as
asserted by many authorities. It has been said that
certain minute organs found in polypes, and variously
styled thread capsules, filiferou* capsules, or urticating
cells, are stinging organs. This thread Agassiz likens t<?
a lasso thrown by the polype to secure its prey. Mr.
Lewes writes : " On a survey of the places where these
' urticating cells' are present, I stumbled upon an unlucky
fact, and one likely to excite our suspicion. They aro
present in a few jelly-fish which urticate, in Actiniae which
urticate, and in all polypes, which, if they do not urticate,
(l)The Author's aquarium affords at this time (1856) a curious illustration of
increase both by budding and fissuration, in a beautiful ^1. dianthus. In the firs,
case an offset was seen to protrude ; it resembled a small bud near the foot; thii
increased until it attained to a perfect animal of a considerable size, when It be-
came detached. In another, the animal, after having remained for several weeks
firmly adherent to the side of the glass, with a part of its disc out of the water, by a
great effort tore itself away, leaving six small pieces behind, attached to the glass.
For some days these pieces served only to mark so many spots, but in about a
week rudimentary tentacles were observed to be sprouting out from each piece,
which went on rapidly increasing, and ultimately six perfect animals resulted
therefrom. The repair of the marginal portion of the disc of the parent animal
was completed in a few days, and it suffered no injury whatever from its self-
mutilation. This furnishes a proof, if one were wanting, of the hydrozoid cha-
racter of this class of animals.
H H 2
^8 THE MICROSCOPE.
are popularly supposed to do so, and at any rate possess
some peculiar power of adhesion. In all these cases, organ
and function may be said to go together ; but the cells are
also present in the majority of jelly- fish which do not
urticate, in JSolids which do not urticate, and in Planance
which do not urticate. Here, then, we have the organ
without any corresponding function; urticating cells,
but no urtication. It thus appears that animals having
the cells, have none of the power attributed to the
cells ; and that even in those animals which have the
power, it is only present in the tentacles, where the cells
are much less abundant than in parts not manifesting the
power ; the conclusion, therefore, presses on us, that the
power does not depend upon these cells. When at rest,
and in an ordinary natural state, the animal is never seen
to dart out these threads, nor upon capturing his prey; it
is only when some force is used to dislodge him from some
spot to which he has securely attached himself, that he
presses or squeezes out these threads ; more for the pur-
pose of compressing himself into a clos.er and smaller
mass, to add to the difficulty of detaching him.
"Actinice do not effect their preparation of nutriment by
chemical means ; that is, they do not, in the strict sense of
the term, digest, but simply derive nourishment by mecha*
nical pressure, exerted upon any particle of food that they
may draw into their stomachs. This has been proved by
experiments made after the manner of Reaumur. A small
piece of meat having been put into a quill, and allowed to
remain in the stomach of the Actinia sufficiently long, and
then withdrawn, no solvent fluid is found to have acted
upon it. When placed under the microscope the muscle
fibres are not at all disintegrated, and the striae are as
perfect as before the experiment, with the exception of a
j ulpiness and loss of colour, as in any ordinary mechanical
maceration.
" Light has been thrown upon the reproductive system
of the Actinice by M. Jules Haime, in the Annales des
Sciences Naturelles, 1854, 4 ieme serie, torn. i. ; which con-
tains accurate and detailed descriptions and plates of the
disposition of ova and spermatozoa in the Actiniae. To
find the ovaries it is only necessary to take a live animal,
POLTPIFERA. 469
anl with a rapid, but not deep incision, lay open the
envelope from the outside; a series of convoluted bands
will bulge through the opening, but if these are quickly
brushed aside, certain lobular or grape-like masses will be
perceived, darker in colour, and almost entirely hidden by
these bands, but growing from the wall of the envelope.
They do not appear to have a fixed locality, as they may
be found near the base, about the centre, or close to tho
disc ; it is, therefore, sometimes necessary to make three
or four incisions before detecting them; once seen, they
will be easily distinguished from the convoluted bands,
although very difficult to remove them without removing
some of the bands."
The manner in which the aggregation of zooids, consti-
tuting a compound coral, is developed from the primarily
solitary Actinozoic embryo, e-xercises an all-important
influence upon the form of the Corallum. Sometimes, as
in most Turbinolidce, neither gemmation nor fission ever
take place. In the Oculinidoe, gemmation alone occurs,
and in these and other Actinozoa, the development of buds
takes place either from the base or from the sides of a
corallite, or from the ccenosarc. Certain of the extinct
fiugosa, however, exhibit calicular gemmation, the buds
being developed from the oral disc or cup, which can
hardly have retained any active vitality. The massive
coralla of some Cyathophyllidce, thus standing like inverted
pyramids, all the buds supported upon the narrow surface
of the primary zooid, have a very singular and striking
aspect. The Beroidce appear at first to differ very widely
from the type of structure which prevails among the
other Actinozoa, but a close examination of any of their
forms suffices to demonstrate the justice of the conclusion
advocated by Frey and Leuckart, as to their essential
identity with Actinia. The Cydippe, which abounds upon
our own coasts, affords, from its small size and extreme
transparency, an excellent subject for the student of Be-
roidce. It is impossible here to enter into the varieties
Df form presented by the Beroidce, and which chiefly arise
from the development of lateral lobes, a process which 13
carried to so great a length in Cesium that the body
becomes ribbon-like. The JJeroidce and the Actinidce
47C TMI MICROSCOPE.
inhabit the shallower and even deeper parts jf all
Alcyonidce and Gorgonidce are found at considerable
depths ; Corallium and Gorgonia abound both in cold
and warm latitudes. The Perforata and Tabulata almost
exclusively haunt the shallower parts of warm seas, but
the Turbinolidce extend into very cold regions. The whole
group of the Rugosa is now extinct, only one genus,
Holocystis, having survived even the palaeozoic period. Not
only heat, but light, and probably rapid and effectual
aeration, are essential conditions for the activity of the
reef-building Actinozoa. Different species of corals exhibit
great differences as to the rapidity of growth, and the
depth at which they nourish best ; and no one must be
taken as evidence for another in these respects. Certain
species of Perforata, Madreporidce, and Poritidce, appear
to be at once the fastest growers, and those which delight
in the shallowest waters. The Astrceidce among the
Aporosa, and Seriatopora among the Tabulata, live at
greater depths, and are probably slower of increase. The
most careful accounts of the structure of corals extant, are
from the pens of M. M. Milne Edwards and Haime, pub-
lished at various times in the Annales des Sciences Natu-
relles, in the Memoires du Museum, and in the publications
of the Palseontographical Society ; and by Mr. Darwin,
whose beautiful work on Coral Reefs will amply repay
perusal.
With these brief introductory observations, the principal
part of which have been derived from Professor Huxley '&
lectures, we proceed to direct the reader's attention to-
some of the more interesting generic forms.
HYDKA, FRESH- WATER POLYPE. In polypes of. this
family the body generally consists of a homogeneous
aggregation of vesicular granules, held together by a sort
of glairy intercellular substance, and capable of great
extension and contraction; so that the creature can at
pleasure assume a great variety of forms, extending its
body and tentacles until the latter become so fine as to be
almost invisible, and again retracting itself until it acquires
the appearance of a small gelatinous mass. The tentacles
which surround the anterior extremity are irregular in
uumber ; they are capable of extension to a very gre*t
HYDRA. 471
length when seeking for prey; and on coining in contact
with any object floating through the water, they imme-
diately twine round it, and convey it to the mouth. In
some genera the tentacles appear to be tubular, the inter-
nal cavity being continuous with that of the stomach.
The mouth is situated in the centre of the circle of ten-
tacles, and leads directly into a simple digestive cavity.
Hydras are found in ponds and rivulets, adhering to the
leaves of aquatic plants, or twigs and sticks that have
fallen into the water. When stretched out, they resemble
pieces of hair, from a quarter to three-quarters of an inch
in length. Some are of a light-green colour, and others
brown or yellow; that is, the five varieties found in
England. It received its name from its several long arms
being supposed to resemble the fifty-headed water-serpent
called Hydra, which was destroyed by Hercules in the
lake of Lerna, as we are informed in fabulous history.
Leeuwenhoek, in 1703, first drew attention to the Hydra;
and in 1739, M. Trembley from the Hague, more accu-
rately described its habits.
Polypes are not vegetarians ; M. Trembley fed Hydrce
on minced fish, beef, mutton, and veal; they are voracious
and active in seizing worms and larvae much larger than
themselves, which they devour with avidity. They care-
fully and adroitly bring their food towards their mouth;
and when near, pounce upon it with eagerness. To make
up for the want of teeth, the mouth enlarges to receive
the food brought to it by the arms that have twined around
the sacrifice. The red worm that tinges the mud of the
Thames appears to be the dainty dish they like best to
have set before them. Dr. Mantell saw the lasso of a
polype thrown over two worms at the same time; yet
they could not escape, and lost all power of motion.
Dr. Johnston states : " Sometimes it happens that two
polypes will seize upon the same worm, when a struggle for
the prey ensues, in which the strongest gains, of course,
the victory; or each polype begins quietly to swallow his
portion, and continues to gulp down his half, until the
mouths of the pair near, and come at length into actual
contact. The rest that now ensues, appears to prove that
they are sensible of their untoward position, from which
472 THE MICROSCOPE.
they are frequently liberated by the opportune break ol
the worm, when each obtains his share ; but should the
prey prove too tough, woe to the unready! the more
resolute dilates the mouth to the requisite extent, ana
deliberately swallows his opponent; sometimes partially,
BO as, however, to compel the discharge of the bait ; while
at other times the entire polype is engulfed ! But a polype
is no fitting food for a polype, and his capacity of endurance
saves him from this living tomb ; for, after a time, when
the worm is sucked out of him, the sufferer is disgorged
with no other loss than his dinner."
The organ of prehension, which is called the hasta, con-
sists of a sac opening at the surface of the tentacle, within
which, at the lower portion, is placed a saucer- shaped
vesicle, supporting a minute ovate body, which again bears
a sharp calcareous piece called the sagitta, arrow. This
can be pushed out at the pleasure of the animal, serving
to roughen the surface of the tentacle, and afford a much
firmer hold of its living prey. The polype increases
rapidly : a portion of the body swells, a young one puts
forth its head from the^ part, its arms begin to grow, it
then is industrious in catching food ; its body, communi-
cating with that of its parent and participating in the
fears and actions of its progenitor, is finally cast off to
wander the world of waters. Sometimes, ere yet free from
parental attachment, it has two generations on its own
body. Four or five offspring are thus produced weekly.
But the most extraordinary circumstance in respect to this
creature is thus described by M. Trembley : " If one of
them be cut in two, the fore part, which contains the head
and mouth and arms, lengthens itself, creeps, and eats on
the same day. The tail part forms a head and mouth at
the wounded end, and shoots forth arms more or less
speedily, as the heat is favourable. If the polype be cut
the long way through the head, stomach, and body, each
part is half a pipe, with half a head, half a mouth, and
some of the arms at one of its ends. The edges of these
half pipes gradually round themselves and unite, beginning
at the tail end ; and the half mouth and half stomach of
each becomes complete. A polype has been cut lengthways
*t seven in the morning, and in eight hours afterwardi
TUBULARIAD.fi. 473
D&ch part has devoured a worm as long as itstlf." Still
more wonderful is the fact, that if turned inside out,
the parts at once accommodate themselves to their new
condition, and carry on all their functions as before
the accident, Indeed, this animal seems so peculiarly
endowed with the germs of vitality in every part of its
body, that it may be cut into ten pieces, and everyone
will become a new, perfect, living animal. This seems
bordering on the vegetable kingdom, in which it is
common to propagate by means of slips from the mature
shrub.
The best known of the British species are Hydra vul-
garis, Common polype, H. viridis, Green polype, H. Fusca,
Brown polype, H. verrucosa, and H. lutea.
Every reflecting person who reads even the slight
sketch we have given of this polype must be struck witl
astonishment at a creature so primitive in structure, pos-
sessing the actions, sensations, and powers of higher
organised beings. The stomach is but one simple struc-
tureless membrane or cell, the external surface-cells form-
ing a kind of double skin, the inside a mere wall of cells
running crosswise, possessed of a velvet-like surface, and
red or brown coloured grains held together by a glutinous
substance. This singular formation, with some of the
functions of animal life, has led to many learned surmises
and discussions tending to the most important results in
the science of physiology.
TUBULARIAD^E. The Tubular or Vaginated Polypes are
of an arborescent appearance ; the animals live near the
ends of branches, and are found attached to stones, sea-
weeds, and shells. 1 The Tubularia indivisa, " Individed
tubes," are found on shells, with a living head resembling
a fine scarlet cluster of blossoms. Ellis says, " they seem
part of an oat-straw with the joints cut off." At the summit
protrudes the scarlet-coloured polypes, well furnished with
tentacula, and connected with a pinkish fluid that fills tha
tubes. It was in these that Dr. Roget discovered the
(singular peculiarity of a circulation, similar to that seen
in many plants. He says, " In a specimen of the Tubu-
(1) These are grouped with Hydroida, and at the head of the family stand
Van Beneden's Hydractinia; and Gaertner's Coryne.
474 THE MICROSCOPE.
laria indivisa, -when magnified one hundred times, a
current of particles was seen within the tubular stem of
the polype, strikingly resembling, in steadiness and
continuity of its stream, the vegetable circulation in
the chara. Its general course was parallel to the slightly
spiral lines of irregular spots on the surface of the tube,
ascending on the one side, and descending on the other ;
each of the opposite currents occupying one-half of the
circumference of the cylindric cavity. At the knots, or
contracted parts of the tube, slight eddies were noticed
in the currents ; and at each end of the tube the par-
ticles were seen to turn round, and pass over to the other
side.
" The particles carried by it present an analogy to those
of the blood in the higher animals of one side, and of the
sap of vegetables on the other. Some of them appear to be
derived from the digested food, and others from the
melting down of parts absorbed ; but it would be highly
interesting to ascertain distinctly how they are produced,
and what is the office they perform, as well as the true
character of their remarkable activity and seemingly
spontaneous motions ; for the hypothesis of their indi-
vidual vitality is too startling to be adopted without good
evidence."
Respecting the singular property of the head dropping
off, Tubularia indivisa, Sir J. G. Dalyell observes, " The
head is deciduous, falling in general soon after recovery
from the sea. It is regenerated at intervals of from ten
days to several weeks, but with the number of external
organs successively diminishing, though the stem is always
elongated. It seems to rise within this tubular stem front
below, and to be dependent on the presence of the internal
tenacious matter with which the tube is occupied. A head
springs from the remaining stem, cut off very near the
root ; and a redundance of heads may be obtained from
artificial sections. Thus, twenty-two heads were produced
through the course of 150 days from three sections of a
single stem."
Included in this family are the T. ramous, T. ramea, the
"branched pipe-coralline, with its dark brown stem termi-
nating in clusters of red and yellow polyps ; and the
TUBCTLARLAJXffi.
475
Hermia Glandulosa of Dr. Johnston, "who says " I found
the name in Shakspeare :
' What wicked and dissembling glass of mine,
Made me compare with Hermia's sphery eyne ?' "
The fancy that the glands which surround the heads
were the guardians of the animal, its " sphery eyne," sug-
gested the name here adopted.
These polypes are adherent by
a tubular fibre, and creep along
the surface of the obj ect on which
they grow ; they are seldom
an inch in height, irregularly
branched; the stem filiform,
tubular, horny, sub-pellucid,
wrinkled, and sometimes ringed
at intervals, especially at the
origin of the branches, each of
which is terminated with an
oval or club-shaped head of a
reddish colour, and armed with
short scattered tentacula,tipped
with a globular apex. The ends
of the branches are not perfo-
rated, but completely covered
with a continuation of the horny
sheath of the stem. The animal
can bend its armed hands at
will, or give to any separate ten-
taculum a distinct motion and
direction ; but all its move-
ments are very slow.
,, , ,. ,,..., ^ 1, Corynt Staundia, Slender
The beautiful little Coryne Coryne. 2, A tubercle detached,
stauridia, "Slender cor yne," and magnilied 20 diameters '
(tig. 232, No. 1), is thus described by Mr. Gosse : " It wa?
found by me adhering to the footstalk of a Eliodymenia,
about which it creeps in the form of a white thread ; by
placing both beneath the microscope, this thread appeared
cylindrical and tubular, perfectly transparent, without
wrinkles, but permeated by a central core, apparently cel-
lular in texture, and hollow; within which a rather slow
Fig. 232.
Corynt Stauridia,
476 THE MICROSCOPE.
circulation of globules, few in number, and remote, is per-
ceived. It sends off numerous branches ; the terminal
head of which is oblong, cylindrical, rounded at the end.
At the extreme point are fixed four teiitacula of the usual
form, long, slender, and furnished with globular heads ;
one of which is shown at No. 2, detached, and more highly
magnified. It is much infested with parasites : a vorticella
grows on it, and a sort of vibrio ; the latter in immense
numbers, forming aggregated clusters here and there ;
the individuals adhering to each other, and projecting in
bristling points in every direction. These animalcules
vary in length ; some being as long as 1-SOth of an inch,
with a diameter of 1 -7000th of an inch. They are straight,
equal in thickness throughout, and marked with distinct
transverse lines ; they bend themselves about with consi-
derable activity, and frequently adhere to the polype by
one- extremity, while the remainder projects freely."
Some of this family attain a considerable size ; the
Corymorpha nutans, one of the most beautiful of the
group, attains a length of four inches and a half. Of
the beauty of its appearance, Forbes, who discovered it in
the British seas, speaks in the following terms : " When
placed in a vessel of sea-water, it presented the appearance
of a beautiful flower. Its head gracefully nodded (whence
the appropriate specific appellation given it by Sars), bend-
ing the upper part of its stem. It waved its long teiitacula
to and fro at pleasure, but seemed to have no power of
contracting them. It could not be regarded as by any
means an apathetic animal, and its beauty excited the
admiration of all who saw it." The general colour of the
creature is a delicate pink, with longitudinal lines of
brownish or red dots. The tentacles are very numerous
and long, and of a white colour ; and the ovaries, which
are situated immediately above the circle of tentacles,
are orange. Most of the Tulndariadce inhabit the sea ;
one species, the Cordylophora lacustris, is found in the
dock of the Grand Canal, Dublin, in water which is per-
fectly fresh.
SERTULARIAD^E. This interesting and beautiful family
of pclypes derive their name from their plant-like appear-
ance, and are readily attainable on our own sea-shores.
SERTULABIADJE.
477
Limiseus made a large genus of them ; but Lamarck con-
siderably reduced his classification. There are seventeen
British species, which Dr. Fleming proposes to divide into
two groups, with stems simple or compound.
The tentacles of Sertularia
are abundantly supplied with
cilia ; the cells are pitcher-
shaped, arranged alternately,
or in pairs obliquely, not
exactly opposite, on the stem
and branches of the poly-
pidom, which is horny. La-
mouroux classed with this
family Thoa; of which there
have been several kinds found
iu Great Britain. The name
is supposed to be derived from
the Greek word for sharp;
but we think, with Dr. John-
ston, that it more probably Fig- 23 3._sickle-Coralline. Sertu-
is a mis-spelling of Thoe, one Zario. Poiypidom of.
of the Nereids, nymphs of the sea. They are generally
of a brown and yellow colour, branched, and from an inch
and a half to six inches in height.
Sertularia pumila. This is parasitic, jind spreads its
brown-coloured shoots over various fuci and sea-shells ;
but rarely attains more than half an inch in height.
Stewart says : " This species, and probably many others,
in some particular states of the atmosphere, emits a phos-
phorescent light in the dark. If a leaf of the fucus
serratus, with Sertularia upon it, receives a smart stroke
in the dark, the whole is most beautifully illuminated,
every denticle seeming to be on fire."
On the south-eastern coast of England the most common
kind found is the Sertularia setacea, or operculata, Seahair-
Coralline : it reaches from six inches and upwards in
height, and grows in tufts, like bunches of hair. The
stem and branches seem composed of separate pieces,
fitting accurately into each other, and terminate in a
star-like head, from which radiate the tentacles. Mr.
Lister was observing a living specimen, when a little
478 THE MICROSCOPE.
globular animalc lie swam rapidly by one of the expanded
polypes; the latter immediately contracted, seized the
globule, and brought it to the inouth or central opening
by its tentacula ; these gradually opened again, with
the exception of one, which
remained folded, with its ex-
tremity on the animalcule.
The mouth instantly seemed
filled with cilia, which, closing
over the prey, was carried
slowly down its stomach ;
here it was imperfectly seen,
and soon disappeared.
Appertaining to this family
are Dr. Fleming's Thuiarea,
so named by him from their
resemblance to a cedar-tree ;
some kinds look more like a
knobbed thorustick with a
bottle-clearer at the top ;
others resemble a fir-tree.
Antennularia are so called
from their resemblance to a
lobster's antenna. They are
plentiful on the north-eastern
coast of England and the
coast of Ireland, brown in
colour, and covered with
i, pivmiizria pinmaia, Feather polype. hair-like little branches; and
j, i>orufii*re*teta, Sea dog. ag the hairy process is con-
tinued up its jointed stem, it is sometimes denominated
Sea-beard. Dr. HassalFs Coppinia is another veiy interest-
ing species.
The Plumularia, so named from their shoots and
oflsets being plumose, are an extensive and beautiful
family. Professor Grant thus describes the Plumularia
falcata : " The Sickle Coralline is common in the deeper
parts of the Frith of Forth ; its vesicles are very numerous,
and its ova are in full maturity at the beginning of May.
The ova are large, of a lighkbrown colour, semi-opaque,
spherical, composed of minute transparent granule?.
Fig. 234.
SERTULARIAD^;. 479
ciliated on the surface, and distinctly irritable. There
are only two ova in each vesicle ; so that they do not
require any external capsules, like those of the Campanu-
laria, to allow them sufficient space to come to maturity.
On placing an entire vesicle, with its two ova, under the
microscope, we perceive through the transparent sides the
cilia vibrating on the surface of the contained ova, and the
currents produced in the fluid within by their motion.
When we open the vesicles with two needles, in a drop of
sea- water, the ova glide to and fro through the water, at
first slowly, but afterwards more quickly, and their cilia
propel them with the same part always forward. They
are highly irritable, and frequently contract their bodies
BO as to exhibit those singular changes of form spoken of
by Cavolini. These contractions are particularly observed
when they come in contact with a hair, a filament of
conferva, a grain of sand, or any minute object ; and they
are likewise frequent and remarkable at the time when
the ovum is busied in attaching its body permanently to
the surface of the glass. After fixing themselves, they
become flat and circular, and the more opaque parts of
the ova assume a radiated appearance ; so that they now
appear, even to the naked eye, like so many minute grey-
coloured stars, having the interstices between the rays
filled with a colourless transparent matter, which seems to
harden into horn. The grey matter swells in the centre,
where the rays meet, and rises perpendicularly upwards
surrounded by the transparent horny matter, so as to form
the trunk of the future zoophyte. The rays first formed
are obviously the fleshy central substance of the roots ;
and the portion of that substance which grows perpen-
dicularly upwards, forms the fleshy central part of the
stem. As early as I could observe the stem, it was open
at the top ; and when it bifurcated to form two branches,
both were open at their extremities ; but the fleshy central
matter had nowhere developed itself as yet into the form
of a polype. Polypes, therefore, are not the first formed of
this zoophyte, but appear long after the formation of the
root and stem, as the leaves and flowers of a plant."
Attached tofucus and shells in abundance on the southern
enist of England, may be found the Plumularia cristata. It
480 THE MICROSCOPE.
is affixed by a horny, branching, interlacing, tubular fibre
to the object on which it grows. At different parts there
fire plumose shoots, usually about an inch in height. The
cells are of a yellow colour, set in the stalk, of a bell-
shape, and are compared to the flower of the lily of the
valley ; the rim is cut into eight equal teeth ; the polype
minute and delicate, tentacles ten and annulate, with a
mouth infundibuliform in shape.
" Each plume, ' says Mr. Lister, in reference to a speci-
men of this species, " might comprise from 400 to 500
polypes ;" " and a specimen," writes Dr. Johnston, " of no
unusual size, before me, has twelve plumes, with certainly
not fewer cells on each than the larger number mentioned :
thus giving 6000 polypes as the tenantry of a single poly-
pidom ! Now, many such specimens, all united too by a
common fibre, and all the offshoots of one common parent,
are often located on one sea- weed, the site then of a popu-
lation which nor London nor Pekin can rival."
Plumularia pinnata, " Feather polyp/' (represented mag-
nified in fig. 234, No. 1,) is as remarkable for the ele-
gance of its form, as its likeness to the feather of a pen.
It serves not among the denizens of the deep the same
purpose as its earthly prototype ; nature writes her
works in hieroglyphics formed by the objects themselves.
It is plumous, and the cells in a close row, cup-like,
and supported on the under side by a lengthened spinoua
process.
An interest pervades the valuable work of Dr. Johnston,
arising from the circumstance that the plates and wood-
cuts which adorn the volume are, with few exceptions,
engraved from drawings made for it by Mrs. Johnston^
who also engraved several of them ; and the Doctor states,
he could not have undertaken the history without such
assistance. From this devotion too, and understanding of
the subject, it was natural, when an opportunity presented
itself, to write in the catalogue of Zoophytes a lasting
memorial of his " colleague :" and thus is written the
graceful compliment of the beautiful Plumularia Catha-
rina: " Catharine's Feather," whose stem is plumous, pinna
opposite, bent inwards; cells distant, campanulate, with
an even margin; vesicles scattered, pear-shaped, smooth.
SERTULARIAD^. 481
Found in old shells, corallines, &c., in deep water; in
Frith of Forth and in Berwick Bay, by Dr. Coldstream.
The sub-families, Campanularia and Laomedea, are also
frequently found on our shores ; they possess a simple
circle of cilia on their feelers or arms, with pitcher-
shaped cells on stalks that branch, twist, or climb on an
axis.
Campanularia volubilis, li Twining polype," is the com-
monest of the family : it is parasitical, and infests the an-
tennae of crabs ; its stem is filiform, and at the end of
its slender branches are situated the cells containing the
polypes. The polype itself is slender when protruded,
somewhat like Plumularia pinnata, and becomes dilated
at the base into a sort of foot which spreads over the dia-
phragm ; widening again at the top, where it fills the
mouth of the cell, and gives origin to about twenty slender
tentacula, set in two or three series. From the central
space, which is surrounded by tentacles, a large fleshy
mouth protrudes, somewhat funnel-shaped, with lips, en-
dowed with the power of protrusion and contraction;
these appear to be very sensitive. Mr. Gosse found the
species in great abundance round Small-mouth Caves.
The Campanularia gelatinosa and its beautiful bell-
shaped cells, out of which the animals protrude, giving the
semblance of a green flower on a delicate pink stalk. It
is indeed an interesting object, and currents may be
seen in its tubes. Dr. Johnston says, " On Saturday, May
29th, 1837, a specimen of Campanularia gelatinosa was
procured from the shore ; and after having ascertained
that the polypes were active and entire, it was placed
in a saucer of sea-water. Here it remained undisturbed
until Monday afternoon, when all the polypes had dis-
appeared. Some cells were empty, or nearly so ; others
were half-filled with the wasted body of "the polype,
which had lost, however, every vestige of their tentacula.
The water had become putrid, and the specimen was
therefore removed to another vessel with pure water, and
again set aside. On examining it on the Thursday, June
1st, the cells were evidently filling again, although no
tentacula were visibly protruded ; but on the afternoon of
Friday, June 2d, every cell had its polype, complete, ami
i i
482 THE MICROSCOPE.
Displayed in the greatest perfection. Had these singular
facts been known to Linnaeus, how eagerly and effectively
would he have impressed them into the support of hia
favourite theory ! Like the flowers of the field, the heads,
or 'flores/ of these polypidoms expand their petaloid
arms, which after a time fall, like blighted blossoms off a
tree ; they do become ' old in their youth/ and, rendered
hebetous and unfit for duty or ornament by age or acci-
dent, the common trunk throws them off, and supplies its
wants by ever-young and vigorous growths. The pheno-
mena are of those which justly challenge admiration, and
excuse a sober .scepticism, so alien are they to all we are
accustomed to observe in more familiar organisms. Faithful
observation renders the fact undeniable ; but besides that,
a reflection on the history of the Hydra might almost
have led us to anticipate such events in the life of these
Zoophytes. * Verily, for mine own part/ observes Baker,
'the more I look into Nature's works, the sooner am
I induced to believe of her even those things that seem
incredible.' "
ACTINIAD^:. All persons accustomed to wander by the
sea-shore must have admired the livid green, dark little
jelly-masses adhering to the rocks, called Actinia., from a
Greek word signifying a ray, and left in some little pool
by the ebbing tide, living as they do principally within
high and low water mark, and expanding their broad sur-
faces and fringing feelers to the finger of inquisitive youth,
so often thrust into the centre, to feel the effect of the
suction and rasping, as the poor animal draws itself up in
the form of a little fleshy hillock.
Some few years ago it might have been necessary to
explain what we meant by an Actinia, or " Sea-anemone '*
thanks to the universal distribution of aquaria, this
beautiful class of animals is no longer unfamiliar to the
world. Nevertheless, much as people read, and hear, and
write, and observe in the matter, we do not hesitate to say
that the natural arrangement of these animals is as little
known in the world of naturalists, as their very existence
was a short time ago to the world at large. A familiar
instance of this position may be given in a few words.
Dr. Johnston (Hist. Brit. Zooph.) describes three distinct
483
Actinia, under the names of A. troglodytes (the Cave-
dweller), A, viduata, and A. Anguicoma (the Snaky-
locked). Mr. Gosse, in his Devonshire Coast, makes A.
viduata synonymous with A. anguicoma ; and gives a
drawing and a description of an anemone which he calls
anguicoma, and which closely resembles undoubted
specimens of Johnston's A. troglodytes. Many objections
might be taken to Mr. Gosse's description of species, which
he makes out from the number of their tentacles, although
found in company with each other, and, as he justly re-
marks, are of " the same size and form."
Of the voracity of the actinia many remarkable state-
ments have been made known; it may nevertheless be
kept in the aqiiarium for many months, if supplied with
Fig. 235.
1, Actinia rubra Sea marigold, near which is one shown retracted. 2, Actinia
bellis, Daisy sea-anemone (side view).
water containing particles of organic matter. Although
the several structures of actinia admit of being resolved
into two foundation membranes, an ectoderm and an en-
doderm, yet each of these, more especially the former,
%nanifests a tendency to differentiate into secondary layers,
so that several apparently distinct tissues are recognisable
in the body of the fully-formed animal. Both membranes
have their free surfaces more or less covered with cilia
Ti2
484 THE MICROSCOPE.
and the margin of the disc is furnished with a series 01
white or "bright blue specks, which some observers believe
to be rudimentary organs of vision ; but they are rather
to be regarded as sac-shaped prolongations of the outer
layer, A transverse section of the
body of the actinia exhibits two
concentric tubes, the outer being
constituted by the body-wall, and
the inner by the digestive sac.
The wide space which intervenes
between these tubes is divided by
a number of radiating partitions, or
"mesenteries," arriving at definite
intervals from the inner surface of
Fig. zw.-Actinia urn, seen the body wall. To the face of the
from above with its crown of mesenteries are attached the repro-
tentacles fully expanded, , . -i i
ductive organs, which occur na
thickened bands of a reddish tint, at certain periods
filled with ova. The animal has the power of effecting
considerable alterations of form, as well as of locomo-
tion ; although if well supplied with food it attaches
itself so firmly as not to be removed without laceration
of its base.
Allied to the family Actinias are those laminated, in-
verted pyramidal looking bodies, Fungia, commonly called
" Sea-mushrooms," often found in great variety. The
colour of the polypidom is white, of a flattened round
shape, made up of thin plates or scales, embedded in a
translucent jelly-like substance, and within which is a
large polype ; the foot-stalk, by means of which the
animal is attached to the rock whereon it lives, is of a
calcareous nature. Ellis says : " The more elevated folds
or plaits have borders like the denticulated edge of
needlework-lace. These are covered with innumerable
oblong vesicles, formed of a gelatinous substance, which
appear alive under water, and may be observed to move
like an insect. I have observed these radiating folds of
the animal, which secrete the lamellae, and which shrink
between them when the animal contracts itself on being
disturbed. They are constantly moving in tremulous un-
dulations ; but the vesicles appeared to me to be air-
ACTIXIJ5.
485
vessels placed along the edges of the folds, and the vesi-
cles disappeared when the animal was touched."
Fig. 237. Actinosoa.
, Fungia agariciformis. 2, Alcyonium, Cydonium Mullen. 3, Cydonivm,
polypes protruding and tentacles expanded, others closed. 4, Zoantharivu.
viewed from above. 5, Madrepore Abrotanoide. 6, Madrepore, cell slightly
magnified, showing internal structure. 7, Corallidce ; CoraL 8, Coral, polypes
protruding from the cells. 9, Gorgonia nobilis, poises expanded. 10, Tubi*
pora vnusica. 11, a tube of same, with polype expanded, and one cut longi-
tudinally to show internal structure. 12, Sertularia, polypes protruded ; ami
others withdrawn into polypidoma.
486 THE MICROSCOPE.
Madrepores, Mother-pores, "tree
corals," differ from other corals in not having a small
skeleton, but one inducted by numbers of small cells for
the residence of the living animal : these are very visible
in the Madrepore muricata, when the polype is dead and
decomposed; but most distinct in the Oculina ramea, as
they are -situated at the apparently broken stumps that
branch from the trunk of the skeleton (fig. 237, No. 5).
Every branch is seen to be covered with multitudes of
small pits or dots, scarcely visible to the unassisted vision ;
but, when viewed under the microscope, are found to be
cells of the most .beautiful construction, remarkable alike
for their mathematical regularity and the exquisite fineness
of the materials employed in their composition. A mag-
nified drawing of a cell is given at No. 6. The living
polypes are exquisite objects for a low power ; their vary-
ing colours adding to the richness of the hues covering the
bed of the ocean.
ASTEROIDE.E. A group of Zoophytes received the name
of Aster oida from the polypes presenting the form of a
star. The fleshy 'mass is supported by hard calcareous
spicula ; some having thick branching processes, perform-
ing the part of the skeleton in the human frame. This
central internal support is usually denominated the axis.
The fleshy mass, or covering, is possessed of sensation, and
is ramified by vascular tubes and canals for the sustenance
of the animal, and carrying on its vital functions. In-
cluded in this genera are Gorgoniadce, Pennatulidce, Alcy-
onidce, Isidce, and Tubiporidce.
The term coral, or corallum, is restricted to the hard
structures deposited in the tissues or by the tissues of the
Actinozoa. The whole of this class, however, which are
thought to possess a framework called a " coral," are not
coralligenous. The CtenopJiora, and several species, as the
soft-bodied non-adherent Zoantharia, deposit no corallum.
There are two kinds of such structure, one called the
" sclerobasic " corallum, a true tegumentary excretion,
ormed by the successive growths from the outer surface of
the ocderon ; and another, the " sclerodermic " corallum,
deposited within the tissues of the animal. Two prin-
cipal modifications of form distinguish the sclerobasis : in
ASTEROIDE.3E, 487
aome it constitutes a free axis, virgate or primately divided
and varying in thickness ; in others it is attached, simple
or branched, and plant-like, as in Gorgonidce, from which
circumstance the name of " Sea-shrubs " has been applied
to them. In the Gorgonia we have, in addition to the
basal corallum / a deposition of tissue secretions, sclero-
dermic spicules appear within the substance of the in-
vesting membrane, and when the animal is dried, and the
soft parts washed away, a thin layer of calcareous spicules
is seen adhering to the horny sclerobasis. M. Valen-
ciennes made out five kinds of spicules, or sclerites, which
he severally designates capitate, fusiform, massive, stellate,
and squamous. These spicules form interesting objects
for the microscope, mounted dry or in balsam. " The
parts of a typical coralite are these : first, an outer wall, or
* theca,' somewhat cylindrical in form, terminating distally
in a cup-like excavation, or ' calice,' and having its central
axis traversed by a columella. The space between this
and the theca is divided into loculi, or chambers, by a
number of radiating vertical partitions, the septa. These
do not, in certain instances, quite reach the columella, but
are broken up into upright pillars or pali, arranged in one,
two, or more circular rows termed * coronets ; ' all of
which are best brought into view by transverse section."
Longitudinal division of a corallite shows certain modifi-
cations and changes in the partitions, or dissepiments ; and
the septa are seen to be covered with " styliform or echi-
nulate processes," which meet to form " synapticulee or
transverse props, extending across the loculi like the bars
of a grate." Nevertheless, there is no difficulty in recog-
nising the close resemblance that sucn an organism pre-
sents to the typical Actinia, and they have accordingly
been classed with the Actinozoa.
The Gorgonidcb are permanently fixed, as are many other
corallitic actinozoa, and multiply by continuous gemma-
tion. As to their muscular system, most of them appear
to be well endowed in this particular. Pennatulidce pos-
Bess so much muscular contractibility, that Mr. Darwin
relates, that on the south coast of America he observed
" a Sea-pen which, on being touched, forcibly drew back
into the sand some inches of its compound, polypi-covered
488 THE MICROSCOPE.
mass." The muscular fibre, however, is wanting in those,
distinct transverse striae, so fully developed in the muscle
of the higher orders of animals.
The ova of the compound Actiniae are of a rounded
form, often brilliantly coloured, and their embryos, by a
series of gradual changes, finally assume the appearance
and condition of the parent. Milne Edwards, to whom
we are indebted for most of our knowledge of the repro-
ductive processes of actinozoa, insists on the necessity of
distinguishing between that of gemmation and fissura-
tion, the polype-bud at first being no more than a pro-
tuberance from the parent " enclosing a csecaj. diverticuluin
of the somatic cavity." Both simple and composite Fun-
yidce occur, and multiply by lateral gemmation.
The Gorgonidce differ from all other Alcyonaria in
having an erect branching caenosarc so firmly rooted that
they are reputed to rival oaks in size ; but it is doubtful
whether they ever attain to a height of more than five or
six feet.
Pennatulidce. This family derives its name from
penna, a quill, and the spicula closely resemble a pen, one
of which is represented in fig. 239, No. 1. The polypes
are fleshy white, provided with eight rather long retractile
tentacula, beautifully ciliated on the inner aspect with two
series of short processes, and strengthened moreover with
crystalline spicula, there being a row of these up the
stalk : the series of smaller processes are ciliated. The
mouth, in the centre of the tentacula, is somewhat
angular, and bounded by a white ligament, a process from
which encircles the base of each tentaculum, and thus
seems to issue from an aperture. The ova lie between the
membraneous part of the pinnae ; they are globular, of a
yellowish colour, and by a little pressure can be made to
pass through the mouth.
Dr. Grant writes : "A more singular and beautiful
spectacle could scarcely be conceived than that of a deep
purple Pennatula phosphorea, with all its delicate trans-
parent polypes expanded and emitting their usual brilliant
phosphorescent light, sailing through the still and dark
abyss, by the regular and synchronous pulsations of the.
minute fringed arms of the polypes." The power of
TUBIPOEID^E. 489
locomotion is doubted by other writers, and the pale blue
light is said only to be emitted when under the influence
of some degree of irritation.
Alcyonaria. Actinozoa, in which each polype is fur-
nished with eight primately fringed tentacles. Corallum
sclerobasic or spicular.
Alcyonium digitatum, " Fingered Alcyonium " (Fig.
237, No. 2). The French call it Main de Her, u sea-
hand," the Germans Diebshand, "thief's hand." Some-
times they are very small ; but when larger are named by
the fishermen Cows-pa}^, and Dead Men's Hands. The
mass, at first repulsive, when placed in sea-water gradually
expands into delicately pellucid polypes, with crowns of
beautiful tentacula. The cells occupied by the polypes are
placed at the terminations of canals which run through
the polypidom, and which, by their union w r ith each
other, serve to maintain a communication between the in-
dividual polypes constituting the mass. The rest of the
polypidom is made up of a transparent gelatinous sub-
stance, containing calcareous spicula, and pervaded by
numerous small fibres, which form a sort of irregular net-
work. Alcyonidce axis always attached to submarine
bodies. The species already mentioned is exceedingly
common round our coasts ; so much so that, as Dr. John-
ston says, " scarce a shell or stone can be dredged from
the deep that does not serve as a support to one or more
specimens."
The ova, as Professor Grant remarks, placed under the
microscope, and viewed by transmitted light, appear as
opaque spheres surrounded by a thin transparent margin,
which increase in thickness as the ova begin to grow,
and such of the ova as lie in contact unite and grow as
one ovum. A rapid current in the water immediately
around each ovum, drawing along with it all the loose
particles and floating animalcules, is distinctly seen moving
with an equal velocity as in other ciliated ova ; and a
zone of very minute vibrating cilia is quite perceptible,
surrounding the transparent margin of all the ova.
TUBIPORHXE. To this family belongs the handsome
Tubiporamusica, "Organ-pipe Coral" (fig. 237, No. 10), the
polypidom of which is composed of parallel tubes, united by
490 THE MICROSCOPE.
lateral plates, or transverse partitions, placed at regular dis-
tances; in this manner large masses, consisting of a congeries
of pipes or tubes, are formed. When^the animals are
alive, each tube contains a polype of a beautiful bright-
green colour, and the upper part of the surface is covered
with a gelatinous mass, formed by a confluence of the
polypes. This species occurs in great abundance on the
coasts of New South Wales, of the Eed Sea, and of the
Molucca Islands, varying in colour from a bright red to a
deep orange. It grows in large hemispherical masses, from
one to two feet in circumstance, which first appear as
small specks adhering to a shell or rock ; as they increase,
the tubes resemble a group of diverging rays, and at length
other tubes are produced on the transverse plates, thus
filling up the intervals, and constituting one uniform
tubular mass ; the surface being covered with a green
fleshy substance beset with stellate polypes.
Dr. Dana, who devoted much time to the examination
of the corals of the Pacific, thus writes of their diversities
of form and character : " Trees of coral are well known ;
and, although not emulating in size the oaks of our forests
for they do not exceed six or eight feet in height they
are gracefully branched, and the whole surface blooms with
coral polypes in place of leaves and flowers. Shrubbery,
turfts of rushes, beds of pinks, and feathery mosses, are
most exactly imitated. Many species spread out in broad
leaves or folia, and resemble some large-leaved plant just
unfolding ; when alive, the surface of each leaf is covered
with polype flowers. The cactus, the lichen, clinging to
the rock, and the fungus in all its varieties, have their
numerous representatives. Besides these forms imitating
vegetation, there are gracefully-modelled vases, some of
which are three or four feet in diameter, made up of a
network of branches and branchlets and sprigs of flowers.
There are also solid coral hemispheres like domes among
the vases and shrubbery, occasionally ten or even twenty
feet in diameter, whose symmetrical surface is gorgeously
decked with polype-stars of purple and emerald green."
Nothing can be more impressive than the manner in
which these diminutive creatures carry out their stupen-
dous undertakings, which we denominate instinct, intelli
ACALEPR& 491
gence, or design. Commencing betimes from a depth of a
thousand or fifteen hundred feet, they work upwards in a
perpendicular direction ; and on arriving at the surface
form a crescent, presenting the back of the arch in that
direction from which the storms and winds generally pro-
ceed : by which means the wall protects the busy millions
at work beneath and within. These breakwaters will re-
sist more powerful seas than if formed of granite ; rising
as they do in a mighty expanse of water, exposed to the
utmost powers of the heavy and tumultuous billows that
eternally lash against them.
As we glance at the map of the world, and think of the
profusion of fragrant vegetation and delicious food almost
spontaneously produced on the lovely sunny islands of the
broad Pacific, how startling does it seem, when we are
told that these islands, bearing on their bosoms gardens of
Eden, are entirely formed by the slow-growing corals,
which, rising up in beautiful and delicate forms, displace
the mighty ocean, defy its gigantic strength, and display a
shelly bosom to the expanse of day ! The vegetation of
the sea, cast on its surface, undergoes a chemical change ;
the deposit from rains aids in filling up the little gaping
catacomb, the fowls of the air and the ocean find a resting
place, and assist in clothing the rocks j mosses carpet the
surface, seed brought by birds, plants carried by the
oceanic currents, animalcules floating in the atmosphere,
live, propagate, and die, and are succeeded, by the assist-
ance their remains bestow, by more advanced vegetable and
animal life ; and thus generation after generation exist and
perish, until at length the coral island becomes a paradise
filled with the choicest exotics, the most beautiful birds
and delicious fruits, among which man may indolently
revel to the utmost desire of his heart.
ACALEPH.&. In great variety of form and colour,
swimming freely about the waters of the ocean, are found
in abundance the beautiful Acalephce. Some of them
have a remarkable stinging property, from which circum-
stance they derive their name of Sea-nettles ; others, from
their gelatinous nature, are known as Sea-jelly, or Jelly-
k.
These interesting animals were first arranged in three
492 THE MICROSCOPE.
orders : A. stabiles (fixed), A. liber ce (free), and A. hydro-
staticce (hydrostatic). Cuvier classed them in two orders :
A. simplices and A. hydrostaticcv. They
are now, however, divided differently,
and arranged in groups according to the
peculiar mode by which they effect their
locomotion. A very interesting point of
connexion between this class and the
preceding is the interchange of form.
Some of the Zoophyta, as the Tubula-
riadce and the Campanulariadce, give
birth to a progeny which are in every
respect Naked-eyed Medusae ; while, on
the other hand, the young of the Medusae
are in their earlier stages stationary
polypes .
The Medusce spread on the surface of the water a beau-
ful jelly-like mass, in form resembling an umbrella ; and.
by a continual contraction and opening out of this, they
swim freely about (Plate IX. c, d, e, h). They are all
more or less- phosphorescent. The Beroe, one of the family
Ctenophora, propel themselves with active ciliated arms.
The Physalidce haye an organ common to fishes, swim-
ming bladders, by filling or emptying which they rise or
sink, and move along in their watery home.
The Medusoid family, Lucernaridce, has, from a mis-
taken view of its organization, been referred to the class
Actinozoa : Milne-Edwards has, however, placed it in a
sub-class, under the name of Podactinaria. In the
Lucemaridoe the body is cup-shaped, about an inch in
height, terminating in a short foot-stalk. Round the
distal margin of the cup arise a number of short tentacles,
which are disposed in eight or nine turfts ; in Carduella
they form one continuous series. Their free extremities
appear sucker-like, and the whole organism is semi-trans-
parent, of a gelatinous consistence, and variously coloured.
The cup, viewed from above, presents in its centre a four-
lobed mouth, which is seen to form the free extremity of
a distinct polypite, occupying the axis of the entire
hydrosoma. Its gastric region exhibits a number of
tubular filaments, arranged in vertical rows dipping ic.to
LUC'ERNARID^B. 493
the digestive cavity. The space between the pclypite-wall
and the inner surface of the cup is equally divided. A
circular sinus has its course beneath the insertion of the
tentacles. By means of a band of muscular fibres which
transverse its margin, and another set which radiate
towards the polypite, the distal extremity of the cup can
be folded or drawn inwards. It has been observed to
detach itself, and swim in an inverted position by the
slowly repeated movements of its cup-like umbrella, thus
resembling Pelagia, a more active and permanently free
member of the same order.
Three families of the beautiful Lucernaridse, all of
which are at once distinguishable by their umbrella, may
be defined as follows :
Family 1, Lucernaridae. Reproductive elements de-
veloped in the primitive hyclrosoma, without the inter-
vention of free zooids. Umbrella with short marginal
tentacles and a proximal hydrorhiza. Polypite single.
Family 2, Pelagidse. Reproductive elements developed in
a free umbrella, which either constitutes the primitative
liydrosoma, or is produced by fission from, an attached
Lucernaroid. Umbrella with marginal tentacles. Poly-
pite single. Family 3, Rhizostomidas. Reproductive ele-
ments developed in free zooids produced by fission from
attached Lucernaroids. Umbrella without marginal ten-
tacles. Polypites numerous, modified, forming with the
genitalia a dendriform mass depending from the umbrella.
For a further description of this intoresting species see
Professor Miiller's paper, Journal of Microscopical Science,
vol. iii. p. 265 j or, Professor Greene's Manual of the
Ccelenterata.
The flat circular horny disc forming the skeleton of
Propita gigantea, to the naked eye exhibits both radiating
and concentric markings ; and, when examined with a
power of 40 diameters, its upper surface is found to be
furrowed, and two rows of small projecting spines occur
upon the ridges between the furrows, the ridges being the
radiating fibres above noticed. The under-surface, or that
to which the greater portion of the soft parts of the
animal are attached, is more deeply furrowed ; and plicse
or folds of the mantle fit accurately into the furrows, from
494 THE MICROSCOPE.
which, they can easily be removed by the application of a
gentle force. The concentric markings have in all cases
small scalloped edges ; they occur at certain regular inter-
vals, and are so many indications of the lines of growth.
In the centre there is a circular depression ; and between
its circumference and that of the first concentric marking
there are eight flattened radii. If the under-surface be
examined with a power of 100 linear, the ridges will all
be found to have small jointed tubular processes like hairs
projecting from them. In no part of this horny tissue is
there a trace of a cellular or a reticular structure.
Wonderfully beautiful as are these creatures in form and
colour, the amount of solid matter contained in their
tissues is incredibly small. The greater part of their sub-
stance appears to consist of a fluid, differing little, if at
all, from the sea-water in which the animal swims ; and
when this is drained away, so extreme is the tenuity of
the membranes which contained it, that the dried residue
of a jelly-fish, weighing two pounds, which was exa-
mined by Professor Owen, weighed only thirty grains.
The transparency of the tissues render the whole of the
Acalephce delightful objects for the microscope. 1
The Echinodermata belong to the division Annuloida, the
most familiar of examples of which are star-fishes and
sea-urchins. The labours of that distinguished comparative
anatomist and physiologist of Berlin, Johannes Miiller,
have made us better acquainted with the structure and
development of these remarkable animals than with those
of most classes of the animal kingdom. The series of feet
which protrude along certain fixed lines from the body of
an Echinoderm have received the name of " ambulacra ; "
and hence, says Mr. Huxley, " we may distinguish their
system of vessels as the ambulacral vascular system. The
existence of an ambulacral vascular system has as yet been
demonstrated only in the following orders : Echinidea,
Ophiuridea, Crinoidea, Asteridea, and ffolothuridea, with
which the fossil Cystidea and Blastoidea are inseparably
connected. I therefore limit the Echinodermata to the
(1) See an excellent paper in the Transactions of the Microscopical Society,
" On tha Anatomy of Two Species of Naked-eyed Medusae," by Q. Busk, Esq. ;
also Professor Forbes' works on this family,
ASTEBIDEA. 495
very natural group formed by these orders. A more or
less complete calcareous skeleton is always developed
within the Echinoderms, resembling that of the Actinozoa,
not only in this respect, but also in consisting of detached
spicula. In this form the skeleton remains in the Holo-
thuridea, but in the other Echinoderms, the spicula coalesce
into networks, which may become consolidated into dense
plates by additional deposits. It is by the different shape
and arrangement of these plates that the diversity ex-
hibited by the skeletons of different Echinodermata is
produced."
Asteridea. Star-fishes have been divided according to
the mode of locomotion into Spinigrades, moving by
means of spines j Cirrhigrades, by suckers ; and Pinni-
grades, by fins or pinnas. Of the last-named division we
have only one British genus, Comatula. At the very
extremity of each ray is an organ like an eye, having
spinous appendages, which are termed the eyelids. It is
doubtful, however, whether these parts have really any
visual endowment ; no proof of their possessing the
faculty of sight has ever been advanced, and, from what
we know of the nature of this sense generally in the
lowest forms of animal life, we should be disposed to con-
sider that the organs in question must serve some other as
yet unknown purpose.
The species OpMura and Ophiocoma, Plate IV. Nos. 88
and 91, may be easily recognised by the great length and
tenuity of their rays, and their excessive fragility. The
whole surface, both of disc and rays, is covered by scales,
which are so closely approximated as to give an almost
perfectly smooth surface. These scales are arranged in
definite and often in very beautiful patterns, and in some
species the primary scales are edged or encircled by series
of circular bosses or tubercles, giving a reticulated appear-
ance to the disc and rays. Ophicoma rosula has its spines
tipped with curious anchor-shaped processes, which are
supposed to facilitate the motion of the creature. In
OpMura they are very short, and not apparent without
careful inspection ; while in Ophiocoma they are so long
as to give quite a bristly, sinous appearance to the animal,
being sometimes, in fact, very much longer than the
496 THE MICROSCOPE.
breadth of the rays. A striking species is the Palmipe*
membranaceus, the " Bird's-foot Sea-star," which is almost
as thin as parchment, and might, as Professor Forbes says,
be readily mistaken for the torn-off skin of some bulkier
species. Its surface is covered with a number of raised
tubercles, and very closely-set fasciculi of short and sharp
spines. Aster ias aurantiaca and Luidia fragilissima
present a surface- structure very different from any of the
species previously noticed, their tuberculated epidermis
being so closely set with upright spines as to be almost
wholly invisible. These spines are arranged in a radiated
or rosette-shaped manner, and have a roughened surface.
A portion of the ray of Luidia forms a microscopic object
of exquisite beauty. A single spine is given in Plate IV.
No. 89.
The cirrhigrade star-fishes are furnished with certain
curious appendages, the use of which is at present very
imperfectly understood. These are the " pedicellarice " and
" madreporiform tubercle." The latter is a rounded,
cushion-like eminence of considerable size, situated on the
disc, tnoatly very much out of the centre. It is irregularly
fissured in a radiate manner, and is not at all unlike the
animal from which it derives its name. Various conjec-
tures have been made as to the use of this tubercle.
Forbes looks upon it as being merely the analogue of the
stalk which exists in the young condition of the crinoid
star-fishes. The pedicellarice (Plate IV. Nos. 93 and 94)
are pincer-like organs irregularly scattered over the surface
of the animal, and which have distinct characters in the
different species. They were supposed to be parasitic
creatures, but are now generally admitted to be true epider-
mic appendages. They are in a constantly active motion
during the life of the star-fish, and grasp firmly anything
which is brought between their blades. Their nearest
analogues are the birds' -head processes which occur in
certain zoophytes. The Pedicellarice of Echinus are par-
tially covered with ciliated epithelium : they are also
placed upon a stalk, the lower portion of which encloses
a calcareous nucleus, whilst the other portions are soft, and
spirally retractile.
The Feather-star (Comatula rosacea) is perhaps t l ie most
ASTERIDEA. 497
interesting of the British star-fishes, and quite unique in
the gracefulness of its form and the exquisite beauty of its
colouring ; its life- history is not only remarkable, but it
possesses the additional interest of being the only living
representative in our seas of the group of organisms so
familiar to us in the fossil state as JEncriniles. The deli-
cate structure of this species renders it impossible to ex-
hibit it satisfactorily in a dry or mounted state. The cen-
tral cup-shaped body gives off five rays, which divide so-
near the base as to appear like ten. These are furnished
throughout their length with membranaceous pinnae.
Tubularia Dumortierii, Plate IV. No. 92, appears rather
to belong to Comatula than Tubularia. A description of
this interesting polype will be found in Johnston's EriL
Zoophytes, p. 53.
The late Sir Wyville Thompson, in a paper on " Sea-
Lilies " (Intellectual Observer, August, 1864, says:
" Comatula rosacea, the most common British species, is
found abundantly in Lamlash Bay, in Arran and Strang-
ford Loughs, in Dulkey Sound, in Kirkwall Bay, and
generally distributed in deep water all round the British
and Irish coasts. In general structure it resembles very
closely the head of Neocrinus decorus ; it has, however, no
stem, but in the position of the stem, and forming the
base of the cup, there is a hemispherical plate covered
with rows of cirrhi, exactly like the stem-cirrhi on the
stalked forms. When at rest it holds on to a stone or
weed, and spreads out its beautiful feathery crimson
arms, like the petals of a flower. At other times it swims
rapidly through the water by graceful impulses of its arms..
In spring, the hundreds of ovaries dotted over its pinnules
are turgid with eggs, and if at this time it is captured, and
placed with some sea-weed in a tank, bunches of bright
orange-coloured eggs hang in clusters around, giving the-
delicate pinnatic arms the appearance of the fronds of
some wonderfully graceful fern in rich fructification.
"The phases passed through by the young before they
come to resemble their parents in form and mode of life
are of extraordinary beauty, and most instructive in deter-
mining the true zoological relation which the free crinoids
bear to their fixed ancestors. At first a minute, almost
K K
498
THE MICROSCOPE.
invisible, pale yellow germ escapes from tlie egg ; this, if
placed under the microscope the first day after its birth,
has a very definite form, but not the least like a star-fish.
Pour bands of long vibratile cilia guard the body at dif-
ferent points, and by their motion the little animal whirls
about in the water. About the end of the second day two
rows of five each of delicate calcareous trellised plates may
be seen, making a kind of five^ided basket. A dark niaso
now collects within the trellised basket, and the rings are
united together by little bundles of rods, till they form
what looks like a joined pillar supporting the basket.
Gradually the plates enlarge and distort the outer wall ;
and the stem-like series of joints lengthen, stretching out
the narrow end with it. The old mouth disappears, the
gelatinous wall settles round the little living skeleton, a
round sucker appears, and the animal fixes itself upright
to a sea-weed or a stone at the bottom of the tank. Five
leaf-like valves, each supported by one of the upper tier of
plates, now open on the top of the wider extremity, and
the little creature looks when these valves are open much
like a microscopic wine-glass, and when closed like a
tulip bud."
Echinidce.' 1 Sea-urchins are found in abundance upon
our sea-shores, lurking among the rocks, where they entrap
their prey. Their spines and suckers are used as feet, or
as a mode of progression, even to the climbing of rocks, in
order to feed upon corallines and zoophytes : they march
along with ease where apparently no footing could be found,
or dig holes with their spines to bury themselves in the
sand, to escape pursuers, or hide from observation. The
(1) Description of Plate 9 :
ASTEROIDS.
a, Astrophyton scutatum.
n, Ophiocomarosula.
NUDIBRANCHIATA GASTROPODA.
&, Doris pinnatifida back and
side view.
ACALEPUiB.
c, JEquorea Forbesina.
d, Medusa Bud.
e, TTmumantias corynetes.
\, Cydippe pyleus.
ECHINOIDE.E.
/, Echinus (A Young Se-urchin)t
g, Echinus sphcera.
TUNICATA.
i, Ascidiaz.
Tc t Botryllus violaceus, on a FUCKS.
CRUSTACEA.
I, Corystes cossivelaunus.
m, Eurynome aspera.
o, Pagurus Prideauxii.
p t Ebalia Permantii.
PLATE IX. Asteroidea, Echinidea, Crustacea, dec,
K K 2
ECHINIDEA. 501
Eckinodermata, 1 sea-urchins, or sea-eggs, derive their name
from these curious spinous processes.
lu most Echinidea all the feet are expanded into sucker
discs, at their extremities, and are here strengthened by a
calcareous plate or plates ; but in the Echino-cidaris and
some others, the feet of the oral portion of the ambulacra
only have this structure, while those of the apical portion
are pectinated, flattened, and gill-like. Miiller distinguishes
four kinds of feet in the Spatangoidea, simple locomotive
feet, without any sucking disc ; locomotive feet, provided
with terminal suckers, and containing a skeleton ; tactile
feet, whose expanded extremity is papillose ; and gill-like
feet, triangular, flattened, with more or less pectinated
lamellae
In the Clypeastrodea the pctaloid portions of the am-
Lulacra possess branchial feet, interspersed with delicate
locomotive sucker feet, provided with a calcareous
skeleton. In the Ophiuridea and Crinoidea the feet are
tentaculiform ; and there are no vesicles at the bases of
the feet, while in the Asteridea they are well developed, but
.simpler than those of the Echinidea. The madreporic cana!
is, in the Asteridea, strengthened by a remarkable cal-
careous framework, which has given rise to the notion
that it is filled with sand, and to the name " sand-canal,"
which has been applied to it. The canal terminates in
the madreporic tubercle, which is always placed inter-
radially on the antambulacral surface of the star-fish.
In some, ffolothuridea, the feet are scattered over the
whole ambulacral region, as well in the inter-ambulacra
as in the ambulacra. In others, Psolus, the feet are de-
veloped only from three of the five ambulacra ; while in
the Synaptce and Chirodatce there is only a circlet around
the mouth.
Many star-fishes, and Synapta among the Holotlmridea,
have the curious habit of breaking themselves up into
fragments when taken ; Miiller has pointed out the very
curious fact, that in Synapta, at any rate, this act may be
prevented by cutting through the oral nervous circle. The
nervous circle in the Echinus surrounds the oesophagus near
the mouth, and is enclosed by the alveoli, between which the
(1) Derived from ccliinos, a syine, and derma, skin.
502 THE MICROSCOPE.
ambulacral nerves pass to reach it. In the Asteridea, the
circle lies at the extreme limit of the soft membrane, which
surrounds the mouth, and may be readily exposed by cut-
ting away the hard inter-ambulacral oral lips. In the
Holothuridea it lies immediately beneath the perisoma of
the oral disc. The only known organs of sense in the
JEchinodermata are the pigmented " eye-spots," developed
in connexion with the ends of the ambulacral nerves, and
on the oral nervous circle in many Holothuridea.
The great majority of the JSchinodermata commence
their existence as free-swimming larvae covered with cilia,
but a great difference exists in their further course, accord-
ing as they belong to the Asteridea, the Holothuridea, and
the Crinoidea on the one hand, or to the Ecliinidea and
Ophiuridea on the other. Of the development of the
Crinoidea we know very little, beyond the observations of
Mr. Thompson, that the larva of the Comatula is provided
with several transverse bands of cilia, almost like that of
a Holothuria, and that the development of the Echinoderm
commences while the larva is still free. At a later period,
the young Comatula is seated upon a long, jointed stem, so
as to resemble a Pentacrinus; and it becomes detached
from this stem, in assuming its adult condition.
Mr. Huxley, after mature examination of this class of
animals, says, "he can see no reason for retaining them
amongst the Eadiata of Cuvier, but, on the other hand,
thinks them properly placed among the Annuloida"
The skeleton of the JEchinoderuis generally consists of an
assemblage of plates, or joints, of calcareous matter. The
minute structure of which presents a reticulated character,
and the solid parts are usually composed of a series of
super-imposed laminae or scales. The openings, or areolse,
in one layer being always placed over the solid cell-walls
of the layer beneath it, the spines are situated on the ex-
ternal surface of the shell ; they are generally of a conical
figure, and are articulated with the tubercles by a ball-
and-socket joint. When a thin transverse section of one of
these spines is examined with the naked eye, it appears to
be made up of a series of concentric layers, varying
considerably in number; not, however, with the size of
the spine, but. with the distance from the base at which
ECHINIDEA.
503
the section was made : when a section taken from the
middle of the spine is examined with a power of fifty
diameters, it will be seen that the centre is occupied by a
reticulated structure ; around the margin of this may" be
observed a series of small
structureless spots, ar-
ranged at equal distances
apart (Fig. 240, No. 1) ;
these are the ribs or pil-
lars, and indicate the
external surface of the
first layer deposited ; pass-
ing towards the margin,
other rows of larger pil-
lars may be seen, giving
it a beautiful indented
appearance ; all the other
parts of the section are
occupied by the usual
reticulated tissue. In the
greater number of spines
the sections of the pillars
present no structure, in
others they exhibit a
series of concentric rings
of successive growth,
which strongly remind
us of the medullary rays
of plants ; occasionally
they are traversed by
reticulated structures, as
represented in Fig. 246,
No. 1. When a vertical
section of a spine is ex-
amined, it is found to Fig. 239.
be Composed of COnea l > Polypklom of Pennatula phosphorea. 2,
i i , ,1 Synapta Chirodota. 3, AncHor-shaped
placed one over the other, spicuium and plate from skin of V
the outer margin of each na P ta -
cone being formed by the series of pillars. In the genus
Echinus the number of cones is considerable, while in that
of Cidaris there are seldom more than one or two ; so that
504
THE MICROSCOPE.
from these species transverse sections may fee made, having
no concentric rings, and in which only the external row of
pillars can be seen.
" The skeleton of the Echinodenrata contains very little
organic matter. When it is submitted to the action of
very dilute acid, to dissolve out the calcareous matter, the
residuum is very small in amount. When obtained, it is
found to possess the reticular structure of the calcareous
shell (Fig. 240, No. 1) j the meshes or areoles being bounded
Fig. 240.
1, Section of spine of Echinut, exhibiting reticulated structure, fiie calcareous
portion haying been dissolved out by acid. 2, Transverse section of shell
of the Pinna ingens. 3, Horizontal section of shell of Terebratulata rubicunda,
showing its radiating perforations.
by a substance in which a fibrous appearance, intermingled
with granules, may be discerned under a sufficiently high
magnifying power, as originally pointed out by Professor
Valentine. This tissue bears a close resemblance to the
areolar tissue of higher animals ; and the shell may pro-
bably be considered as formed, not by the consolidation of
the cells of the epidermis, as in the Mollusca, but by the
calci6cation of the fibro-areolar tissue of the true skin.
BOHINIDEA. 505
This calcification of areolar or simply fibrous tissue, >>y the
deposit of mineral substance, not in the meshes of areolse.
but in intimate union with the organic basis, is a condition
of much interest to the physiologist; for it presents us
with an example, even in this low grade of the animal
kingdom, of a process which seems to have an important
share in the formation and growth of bone, namely, in
the progressive calcification of the fibrous tissue of the
periosteum membrane covering the bone." x
From their peculiarity of structure they may be said to
be almost imperishable. Their shells exist abundantly in
all our chalky cliffs, innumerable specimens of which may
be obtained, exhibiting the same wondrous forms and
characters as those which now frequent our shores.
The Crinoidea, " Sea-lilies," so called from the resem-
blance which many of them present to the lily, were ex-
ceedingly abundant in former ages of the world ; and their
remains often form the great bulk of large masses of rock,
fig. 241. These animals were all supported upon a long
stalk, at the extremity of which they floated in the waters
of those ancient seas, spreading their long arms in every
direction in search of the small animals which constituted
their food. Each of the arms, again, was feathered with
a double series of similarly jointed appendages ; so that
the number of separate calcareous pieces forming the
skeleton of one of these animals was most enormous. It
has been calculated that one species, the Pentacrinus
briareus, must have been composed of at least 150,000
joints; and "as each joint," according to Dr. Carpenter,
"was furnished with at least two bundles of muscular
fibre, one for its contraction, the other for its extension,
we have 300,000 such in the body of a single Penta-
crinus an amount of muscular apparatus far exceeding
any that has been elsewhere observed in the animal
creation." A furrow runs along the inside of the arms,
which is covered with a continuation of the skin of the
disc; and from this the ambulacra are protruded, as in
other Echinodermata.
In the family of Ophiuridea, so called from the resem-
blance of their arms to a serpent's tail, (Gr. ophis, a anake^
(1) Dr. Carpenter, Cyclopaedia of Anatomy and Phyticlegy*
506 THE MICROSCOPE.
aura, a tail) ; the body forms a roundish or somewhat
pentagonal disc, furnished with five long simple arms,
which have no furrow for the protrusion of the ambulacra.
Ophiuridea are exceedingly plentiful in all
our seas, and their remains occur in all
the more recent marine strata of the
earth's crust. They are more commonly
called Sand Stars, or Brittle Stars.
"However much the faunas of the
various geologic periods may have differed
from each other, or from the fauna which
now exists, in their aspect and character,
they were all, if I may so speak, equally
underlaid by the great leading ideas which
still constitute the master types of animal
life. And these leading ideas are four in
number. First, there is the star-like type!
of life, life embodied in a form that, as
in the corals, the sea anemones, the sea
urchins, and the star fishes, radiates out-
wards from a centre ; second, there is
the articulated type of life, life embodied
in a form composed, as in the worms,
crustaceans, and insects, of a series of
rings united by their edges, but more or
less moveable on each other ; third, there
is the bilateral or molhcscan type of life,
Fig. 24i. Encrinus, life embodied in a form in which
there is a duality of corresponding parts,
ranged, as in the cuttle fishes, the claws, and the snails,
on the sides of a central axis or plane ; and fourth there is
the vertebrate type of life life embodied in a form in
which an internal skeleton is built up into two cavities
placed the one over the other, the upper for the reception
of the nervous centres, central and spinal, the lower for
the lodgment of the respiratory, circulatory, and digestive
organs. Such have been the four central ideas of the
faunas of every succeeding generation, except perhaps the
earliest of all, that of the Lower Silurian System, in which,
so far as is yet known, only three of the number existed,
the radiated, articulated, and molluscan ideas or types.
ECHINIDEA. 507
That Omnipotent Creator, infinite in His resources who,
in at least the details of His workings, seems never yet to
have repeated Himself, but, as Lyell well expresses it,
breaks, when the parents of a species have been moulded,
the dye in which they were cast, manifests Himself, in
these four great ideas, as the unchanging and unchangeable
Fig. 242. HolotTiuridea, Sea-cucumbers.
One. They serve to bind together the present with the
past, and determine the unity of the authorship of a wonder-
608 THE MICROSCOPE.
fully complicated design, executed on a groundwork broad
as time, and whose scope and bearing are deep as
eternity." l
The Synaptidce are characterised by a total absence of
ambulacra, the motions of the animals being assisted by
peculiar anchor-like processes which project from the skin,
and roughen the surface of the animal. The spiculuni re-
presented in fig. 239 is serrated on the convex edge, and,
Dr. Herepath says, apparently belongs to S. Galliermii t
but that the drawing of the animal near it is singularly
inaccurate, although taken from Professor Forbes' work ;
and that the oral tentacles are imaginary developments of
S. digitata. See Herepath, " On the Genus Synapta,"
Quar. Journ. Micros. Science, 1865, p. 1. The spicules
are beautiful objects for polarised light. (Plate IV. No.
87, shows a side view of one set in the skin.)
ffolothuridea, " Sea-cucumbers." In this family the
body acquires a slug-like form. The radiate structure is
in fact scarcely recognisable in these animals, except in
the arrangement of the tentacles which surround the
mouth. The body is always more or less elongated, with
the mouth at one end and the anal opening at the other ;
the calcareous deposit in the skin is reduced to scattered
granules; and in one family the ambulacra are entirely
wanting.
The integument consists of a number of minute reticu-
lated plates, set closely on the substance of the skin. The
forms of the plates are various, as well as the spicula set
in them. The Australian seas furnish many varieties :
Plate VIII. K"os. 171 and 172, are representations of
plates and spicula under polarised light. Objects of this
class are also well suited for black-ground illumination.
The structure of the spines and other solid parts of the
skeleton of Echinodermata can only be displayed by
making thin sections, in the way described for cutting
bone, at page 209. Their peculiar texture requires that
certain precautions should be taken to prevent the section
from breaking whilst being reduced to a desirable thin-
ness, and to prevent the interspaces of the network from
being clogged by the particles abraded in the reducing
O) Miller's Testimony of tile Rocks.
PRESERVATION OP THE POLYPIDOMS OP ZOOPHYTES. 509
process. In mounting the specimens, liquid balsam must
be employed, and only a very gentle heat should be ap-
plied ; and if, after it has been mounted, the section
should be found too thick, it will be easy to remove the
glass cover and reduce it further, care being taken to
harden the balsam, as directed in preparing bone sections.
PRESERVATION OP THE POLYPIDOMS OF ZOOPHYTES.
The following excellent and simple plan for preserving
zoophytes as fluid preparations, so as to retain the polypes
and their tentacular arms in situ, was adopted by the late
Dr. Golding Bird. For this purpose a lively specimen
should be chosen, and then plunged into cold pure water ; l
the polypes are killed almost immediately, and their ten-
tacles often do not retract : proper-sized specimens should
then be selected, and preserved in weak alcohol. Little
phials about two inches long should be procured, made
from thin flat glass tubes, so as to be half an inch wide,
and about a quarter of an inch, or even less, from back to
front. The specimens should be fixed to a thin platinum
wire, and then placed in one of these phials (previously
filled with weak spirits), so as to reach half-way down.
When several are thus arranged, they should be put on a
glass cylinder, and removed to the air-pump. On pump-
ing out the air, a copious ebullition of bubbles will take
place ; and many of the tentacles previously concealed
will emerge from their cells. After being left in vacuo
for a few hours, the bottles should be filled up, closely
corked, and tied over, like anatomical preparations in
general. For all examinations with a one or two-inch
object-glass, these bottles are most excellent, and afford
cheap and useful substitutes for the more expensive and
difficultly-managed cells. In this manner, specimens of
the genera Membraniporce, Alcyonidce, and Crisiadce, &c.,
exhibit their structure most beautifully.
A few dozen of these little bottles hardly occupy any
room, and would form a useful accompaniment to the
microscopist by the sea-side. Any one visiting the caverns
(1) A small quantity of gin thrown into distilled water answers the purpose
better than pure water, and specimens maybe put up in the same. The animals
we nearly always preserved in their po'ypidoms by using this fluid to kill thort.
510 THE MICROSCOPE.
in St. Catherine's Island at Tenby, might reap a harvest
which would afford amusement and instruction for many
weeks. These caverns are so rich in zoophytes and
sponges, that they are literally roofed with the Lqomedecc,
Grantice, and their allies ; whilst the elegant Tubularice
afford an ornament to the shallow pools on the floor ; and
the walls are wreathed with the ,pink, yellow, green, and
purple Actinice.
When these objects are examined by polarised light,
most interesting results are produced. For this purpose,
let a piece of selenite be placed on the stage of the micro-
scope, and the polarising prisms arranged so that the ray
transmitted is absorbed by the analyser. If a specimen of
Sertularia operculata be placed on the selenite stage, and
examined with a two-inch object-glass, the central stem is
shown to be a continuous tube, assuming a pink tint
throughout its whole extent. The cells appear violet in
colour -, their pointed orifices are seen much more distinctly
than when viewed with common light The vesicles are
paler than the rest of the object ; and their lids, which* so
remarkably resemble the operculum of the theca of a
moss, are beautifully distinct, being of an orange-yellowish
colour. This zoophyte is often covered with minute
bivalve shells, distinguished by the naked eye from the
vesicles only by their circular form ; and these, when pre-
sent, add much to the beauty of the specimen, presenting
a striated structure, and becoming illuminated with most
beautiful colours.
ECHINO1>EBMATA, TlYlHio/OA, PoiA/.OA. ]J Kl.MTNTHOlDA
Tufffcn Wt. del.
PT.ATK TV.
(!iim;i<1 Kvan.
CHAPTER JI.L
POLYZOA MOLLUSCA GASTEROPODA BRACHIOPODA COTfCHIFKBA -
CEPHALOPODA PTEROPODATUJTICATA CRUSTACEA ENTOMOSTBACA-
ANNULOSA CIBRIPEDA ENTOZOA AXNELIDA.
HE term Mollusc, derived from mollis,
soft, is one which at once indicates a
chief structural characteristic of the
class of animals about to occupy our atten-
tion. The body of most of the molluscous
sub-kingdom is soft and fleshy ; and all except
the Tunicata and a few Pteropoda are covered
or protected by a hard calcareous shell. The
shell is of two kinds; first of an epidermal
character, being formed upon the surface of a
filmy cloak-like organ called a mantle, an-
swering to the true skin of otber animals;
and next of a dermal character, being con-
cealed within the substance of the mantle,
and frequently moulded into a great diversity
of forms, and coloured with various tints.
The molluscs belonging to the class Gaste-
ropoda have become a large and important
section of the animal series, presenting very
many objects of great interest for the micro-
scop^st. Of the large family of molluscs, the
only species which have any resemblance in structure to
the Polyzoa, the Brachiopoda, now form a portion of
the molluscous division. The resemblance is chiefly
confined to their internal conformation.
512
THE MICROSCOPE.
The Polyzoa were placed by Dr. Johnston under
the head Ascidioida; in the generality of works they are
named Bryozoa, and the individual, Bryozoon ; derived
from the Greek \vords flpvov, sea-
moss ; {.our, animal. (Pig. 243.)
The Polyzoa are all compound as-
sociated animals, whence their
name ; but when a polyzoon egg is
hatched, as in the case of Pluma-
tella, it commences life as an iso-
lated being, and by subsequent
growth, resembling budding, mul-
tiplies into a colony. All are most
bountifully supplied with cilia, and
the play of these is most energetic,
for the purpose of securing an
abundant supply of food, and ap-
parently without exertion on the
part of the creature itself. From
this most marked characteristic,
Dr. Farre was induced to give them
the name of Ciliobrachiata. But
it has at length been determined to
transfer the Polyzoa, Flustra, Le-
structure ; another to the sub-molluscan kingdom ]
*iA*w into it* p i yioa are generally found living
together in great manners, resem-
bling in this respect some of the Actinozoa, and &rr>
protected by membranaceous coverings or polypidoma?
Protrusion and retraction are performed by two seta of
muscles, one acting on the body of the animal, the other
(1) Mr.-Gosse, in his Manual of Marine Zoology, adopts the idea, now pretty
general, that the Polyzoa belong to the Molluscous division, in spite of their
external resemblances to Polypes, and he places them among Molluscs. In this,
perhaps, he has thought more of systematic views on classification than of the
student's convenience. It seems to us quite clear that, without adopting De
Blainville's principle of classifying animals according to their envelope as the
best principle of scientific classification, we should adopt it in works of refer-
ence like the present, since the external characters are necessarily those most
Immediately recognised by the student ; and in the case of the Polyzoa, they are
BO remarkably similar in external characteristics to the hydroid polypes, that
they were always classed with them, until the profounder investigations of Van
Beneden, Allman, and others, revealed the resemblances betv.en the internal
rharactoriatics of the Polysoz and thoce of Molluscs.
POLTZOA. 513
upon its cell. The oral extremity is surrounded by a circle
of long tubular tentacles covered with cilia ; at each of these
feelers or arms there is an aperture, the one at the base
communicating with a canal that passes round the edge of
the oral aperture or mouth. The food passes down a long
gullet, that contracts during the process of swallowing. At
the end of this is an orifice that opens into what appears
to be a gizzard, having two bodies opposite to each other,
with a rough surface, as if for the comminution of food,
moved by muscular fibres. Those of the species without
this gizzard have a digestive stomach that secretes a
coloured fluid. From the upper part of the stomach near
the entrance from the gizzard arises an intestine, having
a narrow opening surrounded by cilia that proceeds
upwards, ending in an orifice near to the tentacles, from
which the refuse food is ejected.
Their cells are of various shapes, and from one, a family
of millions come, budding forth from its sides; and
though the living matter disappears, the catacombs exist
for the foundation of their families, branching out and
enduring for ages.
Bryozoon Bowerbankia received its name from Dr. Arthur
Farre, in honour of the well-known microscopis-t, Mr.
Bowerbank. A magnified representation of the animal is
seen in fig. 243. " When fully expanded, it is about one-
twelfth of an inch in length. In its retracted state, it is
completely enclosed in a delicate horny cell, sufficiently
transparent to admit of the whole structure of the con-
tained animal being seen through its walls. The cells are
connected together by a cylindrical creeping stem, upon
which they are thickly set, sessile, ascending from its
sides and upper surface. The animal, when completely
expanded, is seen to possess ten arms of about one-third
the length of the whole body; each arm being thickly
ciliated on either side, and armed at the back by about
a dozen fine hair-like processes, which project at nearly
right angles from the tentacles, remaining motionless,
while the cilia are in constant and active vibration."
Notamia, Back-cell, so named from the cells being exactly
opposite, and united back to back with a thick partition
&nd having a joint above and below each \air. In some
L L
514
THE MICROSCOPE.
species of the Flmtrce the interior of the cell is protected
by a lid which bears some appearance to the head and
beak of a bird, and hence it is termed the birds-head
process. This has been made the subject of investigation
by many naturalists. George Busk, Esq., F.R.S., 1 con-
tributed to the Transactions of the Microscopical Society,
1849, an admirable paper on the Notamia bursaria,
"Shepherd's-purse Coralline," (represented in fig. 244,
Nos. 1 and 3), which adds to our knowledge of thia
curious process. He says : " This most beautiful pearl-
Fig. 244.
1, Notamia lunaria, Shepherd' s-purte Coralline. 2, Anguinaria spatutota,
Snake Coralline, growing with the Campanularia Integra. 3, The Shepherd'*
purse Animalcule withdrawn iuto its cup, and the internal organism
shown greatly magnified.
coloured coralline adheres by small tubes to fuci, from
whence it changes into flat cells; each single cell, like
(1) Mr. Busk has added to the description here given of this b!rd'*-he4
process in the Quarterly Journal of Microicopical Science, for January 135*.
POLYZOA. 515
the bracket of a shelf, broad at top and narrow at the
bottom : these are placed back to back in pairs, one above
another, on an extremely slender tube that seems to
run through the middle of the branches of the whole
coralline. The cells are open at top. Some of them have
black spots in them ; and from the top of many of them
a figure seems to issue out like a short tobacco-pipe, the
small end of which seems to be inserted in the tube that
passes through the middle of the whole. The cells in pairs
are thought by some to have the appearance of the small
pods of tfce plant " Shepherd's Purse," by others the shape
of the seed-vessel of the Veronica, Speedwell.
" The polypidom of this bryozoon, like those of most of
its congeners, may be said to consist of a radical portion,
by which it is affixed to the objects upon which it grows,
and of a celliferous portion or branches, upon which the
polypes themselves are lodged. The radical portion in the
present species consists of a central discoid body of a
nearly circular form, and of branches radiating from the
periphery of the disc, which thence exhibits something of
the aspect of the body of an ophiura. The radical tubes
or branches springing from the margin of the disc are
usually five or six in number, and they are given off at
pretty regular distances apart ; but besides these radical
tubes, one or more celliferous branches are not unfrequently
seen to arise immediately from the upper surface of the
discoid portion.
" The central disc, and the radical tubes arising from it,
exhibit a similar structure, and are formed of a thick, firm,
apparently horny envelope, containing a coarse granular
matter, of a yellowish-white colour, and which in some
portions of the tubes assumes the form of distinct irregu-
larly-globular masses, of nearly uniform size. The central
disc is subdivided into distinct compartments by septa of
considerable thickness, and each radiating branch arises
from one of these distinct compartments; so that there
appears to be no communication between one radical
branch and another. The radical branches give off at
irregular distances secondary branches, which ultimately
become celliferous. Each of these secondary branches,
however, arises from a distinct compartment, as it were, of
LL 2
516 THE MICROSCOPE.
the tube from which it springs. This compartment is
formed, like those of the central disc, by a thick septum,
which shuts off the origin of the secondary branch from
the main cavity of the primary one."
The larger, or polypiferous cells, Mr. Busk proposes to
term cells, and the smaller tobacco-pipe-shaped organs
cups; the latter being usually above the former through-
out the polypidom, "excepting immediuiely below each
fork, where the cup is invariably absent above one of the
cells of the pair from between which the fork springs.
The polype-cells are several times larger than the cups,
and their walls are much thinner ; in fact, sufficiently
transparent to allow of the contents of the cell being
pretty well seen, without any preparation, even during the
life of the animal. In shape they are inversely conical,
and the outer and upper angle is usually produced into a
prominent, sharp point. From the internal and upper
angle arises the tubular prolongation going to form the
next cell or cup, as the case may be, in succession. They
are entirely closed at the top, contrary to what is stated
by previous observers ; and, as has been shown, there is no
connexion whatever between the cell and the cup placed
immediately above and behind it. The aperture of the cell
is on the anterior face, and towards the upper margin ; it
is of a crescentic form, and placed obliquely, as it were,
across the upper and internal angle of the cell, with the
convexity of the curve directed upwards and inwards. The
lips of the aperture are strengthened by thin bands of
horny material ; and, under favourable circumstances,
indications of short muscular fibres, for the purpose or
opening or closing the aperture, may be seen."
The shell, which Mr. Busk believes to be entire at the
bottom, though closed only by a very delicate membrane,
contains an ascidoid polype of the usual typical form of
that class. " It has ten tentacles, and no gizzard. Two
sets of muscular fibres at least may be distinguished as
appertaining to the polype. The most important of these
are the retractor muscles, which, arising from the bottom
of the cell, in the form of long, somewhat flattened,
transversely striped, isolated fibres, about the one ten
thousandth of an inch in width, are inserted, some of them
CELLEPORnXE. 5j'7
at the base of the tentacles, and others lower down the
body of the polype."
When we consider the minuteness of the delicate little
sprig which is the natural size of this polype, we cannot
but wonder at the triumphs of the microscope in giving
such precise details as Mr. Busk relates of the Notamia
bursaria. Its beautiful and perfect organisation, the care-
ful provision for the safety and engagements of this
minute being, make us awe-stricken at the power of Divine
intelligence.
The Halodactylus, better known as Alcyonidium, is re-
markable among the marine forms of Polyzoa, for the largo
size of its tentacular crowns; these when expanded are
distinctly visible to the unassisted eye, and present a spec-
tacle of great beauty when viewed with the binocular
microscope. Its polyzoary has a spongy aspect very much
resembling that of the Alcyonian zoophyte : when how-
eve* the animals are expanded, they are at once seen to be
widely dilferent, as the plumose turfts which then issue
from the surface of Halodactylus give it the appearance of
a beautiful downy film. The opacity of its polyzoary
renders it unsuited for the examination of anything more
than the tentacular crown.
Lepralia, "Sea-scurf," from the Greek for marine
leprosy, is the name given to this family of the Celle-
poridce by Dr. Johnston.
Lepralia nitida, found attached to shells, is thus
described : " Crust spreading circularly, closely adherent,
rather thin, greyish white, calcareous j cells contiguous,
in radiating rows, large, subalternate, ovate, ventricose,
silvery, the walls fissured with six or seven cross slits
which are on the mesial line ; aperture subquadrangular,
depressed, terminal ; anterior to it there is often fou:id a
globular, pearly, smooth, oviferous operculum, with a round
even aperture. The remarkable structure of the cells
renders this one of the most interesting species under the
microscope. There is sometimes an appearance of a spine
on each side of the lower angle of the mouth, which ia
merely the commencement of the walls of the next cell."
L. coccinea, L. variolosa, L. ciliata, L. trispinosa, and
L. immersa, are the other British species.
518 THE MICROSCOPE.
The family Cellularia, little-cells, have a curious and
wonderful provision of nature for their piotection, an
operculum, a lid or cover over the apertures of each cell.
Cellularia ciliata is parasitical, branching, calcareous,
white and tufted ; grows about half an inch in height, and
the oblique aperture is armed on the outer edge with four
or five long hollow spines. The operculum is pearly, and
near the base there is that singular appendage, described
as the birds-head process. Its beauty and transparency
render it a favourite object with microscopists.
The Cellularia (nowHugula) avicularia are very accurately
described by Mr. Gosse, from his own observations upon
specimens secured on the Devonshire coast, during a resi-
dence there. He says : " Well does it deserve the name of
Bird's-head Coralline, given to it by the illustrious Ellis ;
for it presents those curious appendages that resemble vul-
tures' heads in great perfection. All my specimens were
most thickly studded with them ; not a cell without, its
bird's head, an'd all see-sawing, and snapping, and opening
their jaws with the most amusing activity ; and what was
marvellous, equally so in one specimen from whose cells
all the polypes had died away, as in those in which they
were still protruding their lovely bells of tentacles. The
stem ascends perpendicularly from a slender base, which is
attached to the rock, or to the cells of a Lepralia growing
from the rock. The central part of the spine is most ex-
panded, the diminution above and below being pretty
regular ; during life, the usual colour is a pale buff, but
the cells become nearly white in death. When examined
microscopically it is, however, that the curious organisa-
tion of this zoophyte is discovered, especially when in full
health and vigour, with all the beautiful polypes protruded
and expanded to the utmost, on the watch for prey. It
seems to me as poor a thing to strain one's eyes at a
microscope over a dead and dry polypidom, as it does to
examine a shrivelled and blackened flower out of a her-
barium ; though I know well that both are often indispen-
sable for the making out of technical characters. But if
you want to get an insight into the structure and functions
of these minute animals, or if you would be charmed
with the perception of beauty, or delighted with new
CRISIAD^. 519
and singular adaptations of mewis to an end, or if you
desire to see vitality under its most unusual, and yet most
interesting phases, or if you would have emotions of
adoring wonder excited, and the tribute of praise elicited
to that mighty Creator who made all things for His own
glory, then take such a zoophyte as this, fresh from the
clear tide-pool, take him without inflicting injury ; there
fore detach with care a minute portion of the surface-rock,
and drop your prisoner, with every organ in full activity,
into a narrow glass cell with parallel sides, filled with clear
sea-water, and put the whole on the stage of the micro-
scope, with a power of not more than 100 linear, at least,
for the first examination. I greatly mistake if you will
not confess that the intellectual treat obtained is well
worth ay, ton times more than worth all your trouble."
CRISIAD.E, signifying a separation; applied to a parasi-
tical family. Crisia cornuta, " Goat's-horn Coralline " of Ellis,
having cells linked in a single series ; the same remark ap-
plies to G. chelata, " Bull's-horn Coralline ;" the latter look
like a number of shoes fitting close to the ancle, joined by
the toe-part to the heel of others. Ellis says : " This beau-
tiful coralline is one of the smallest we meet with. It rises
from tubuli growing upon fuci, and passes from thence into
sickle-shaped branches, consisting of single rows of cells,
looking when magnified like bull's horns inverted, each one
arising out of the top of the other. The upper branches take
their rise from the fore-part of the entrance of a cell, where
we may observe a stiff, short hair, which seems to be the
beginning of a branch. The opening of each cell, which
is in the front of its upper part, is surrounded by a thin
circular rim ; and the substance of the cells appears to
consist of a fine transparent shell or coral-like substance."
Crisia eburnea, "Tufted-ivory Coralline," attains the
height of an inch, and displays its beautiful white, bushy
tufts, with often a dash of light-red intermingled. Its cells
are loosely aggregated and cylindrical, with bent tubular
orifices free ; while the Crisia aculeata have cells closely
aggregated, cylindrical, nearly straight, with long slender
spines springing from the margin of every cell, giving it a
delicate and pretty appearance.
EUCRATIAD^E. We select from this family a specimen of
520 THE MICROSCOPE.
great interest, the Anguinaria, from the Latin anguis, a
snake. This, and also Notamia, belong to the class Polyzoa.
An account of the Anguinaria spatulata, "Snake-head
Coralline," appeared in the Transactions of the Microscopical
Society, by Mr. Busk, who corrects the errors of other ob-
servers. The polype is parasitical upon fuci, and is not uri-
frequently associated with other kinds on the same plants,
as in fig. 244, No. 2, on Campanularia. The A. spatulata
"as a whole, consists, like all its congeners, of two distinct
portions, one usually termed the radical, and another which
constitutes the proper polype cells. In the present instance,
the arrangement of these parts is in some respects
very peculiar and curious ; but it will be found upon
strict examination to accord accurately with the uni-
versal type."
<: In the radical tubes, and on the dorsal or upper surface
of the dilated extremity of the polype-cell, represented
at No. 2, this earthy matter is deposited in the form of
minute angular or rounded particles, presenting faint
traces of a linear arrangement ; but in the main body
of the polype-cell, or the upright portion, the calcareous
material is arranged in beautifully regular rings, giving
that part of the zoophyte a peculiarly elegant appear-
ance under the microscope. This calcareous ingredient
is sufficiently abundant to render the contents of the
radical tubes and polype-cells indistinct ; and to obtain
a satisfactory view of these parts it is necessary to remove
the earthy matter by some weak acid. When this is
done, it will be found that the contents of the radical
portion are coarsely granular, and the wall rather thicker
than those of the proper polype-cell. The latter contains
an ascidian polype, which has about twelve tentacles, and
no gizzard." The polype, as far as Mr. Busk has observed,
is always lodged in the upright portion of the cell ; but
the long retractor muscular fibres arise near the com-
mencement of the horizontal portion of the cell, from its
upper wall, and nearly at one point.
The expanded portion of the cell, besides the special
muscles of the aperture, contains other muscular fibres, in
all respects resembling those described by Dr. Farre, aa
conducing to the extrusion of the polype in owerbankia f
BSCHABIDJB.
521
and which are also very distinct in the Notamia ; but
which, in the present instance, would seem to have for
their chief function the drawing-up or corrugation of the
membraneous portion of the polype- cell. These muscular
fibres have a distinct central nucleus or thicker'portion, as
is the case in the analogous muscles in some other polypes.
ESCHARIDJS. This interesting family justly deserves
the great attention many naturalists have bestowed upon
it. Linnasus named itFlustra, from the
Saxon wordflustran, to weave ; it is
commonly called a Seamat, and re-
sembles fine network spread over
stones, rocks, shells, and marine plants.
This network, when submitted to the
powers of the microscope, is found to
be a cluster of cells, in each of which
dwells an animal, that protrudes its
feelers when searching for food, and
sinks into its little home when tired,
or alarmed by approaching danger.
Dr. Grant estimates that a single
Flustra has as many as four hundred
millions of cilia on these restless ten-
tacles. The tentacula vary from ten to
twelve ; the general organization con-
sists of a gullet, a gizzard, a stomach,
and intestines, the body itself being quite transparent.
When collected together in clusters they take the form of
a delicate minute tree, having cells in all parts, and of
vario as colours. Lamouroux says : " When the animal
has acquired its full growth, it protrudes from the opening
of its cell a small globular body, which it fixes near the
aperture, and as it increases in size, soon assumes the form
of a new cell ; it is yet closed, but through the trans-
parent membrane that covers its surface the motions of
a polype may be detected ; the habitation at length
bursts, and the tentacles protrude ; eddies are pro-
duced in the water, and conduct to the polype the
atoms necessary for its subsistence. The aperture of
the cells is formed by a semicircular ]id, convex ex-
ternally and concave internally, which folds down when
FIG. 245. Eschara cer-
vicoTiiis, Sea-moss po-
lype ; the animal i&
represented out of its
polypidom.
522 THE MICROSCOPE
the polype is about to advance firm the cell. The opening
of this lid in the F. truncata, where it is very long, appears
through the microscope like the opening of a snake's jaws ;
and the organs by which this motion is effected are not
perceptible. The lids of the cells open and shut in the
Flustrce without the slightest perceptible synchronous
motion of the polypes."
In the formation of their stony skeletons, the animals
appear to take a most insignificant part ; they are princi-
pally secreted by the integuments or membranes with which
they are invested, in like manner as the bones and nails in
man are secreted by tissues designed for that purpose, and
acting slowly and imperceptibly. From an analysis of the
stony corals, it appears that their composition is very
analogous to that of shells. The porcellaneous shells, as
.he cowry, are composed of animal gluten and carbonate
of lime, and resemble, in their mode of formation, the
enamel of the teeth; whereas the pearly shells, as the
oyster, are formed of carbonate of lime and a gelatinous or
cartilaginous substance, the earthy matter being secreted
and deposited in the interstices of a cellular tissue, as in
bones. In like manner, some corals yield gelatine upon
the removal of the lime, while others afford a substance in
every respect resembling the membranous structure ob-
tained by an analysis of the nacreous (pearly) shells.
A recent elaborate analysis of between thirty and forty
species of corals, by an eminent American chemist (Mr. B.
Silliman), has shown, contrary to expectation, that they
contain a much larger proportion of fluorine than of
phosphoric acid.
Flustra foliacea, the broad-leaved Horn-wrack of Ellis,
is about four inches high, and of a brown colour. The cells
are small, in alternating rows ; and sometimes covered by
a lid opening downwards. Hook says : " For curiosity and
beauty, I have not, among all the plants or vegetables
I have yet observed, seen any one comparable to this
sea-weed." Flustra truncata is abundant in deep water,
and grows to a height of about four inches ; it is of a
delicate yellow colour, and bushy. This is the narrow-
leaved Horn-wrack of Ellis ; for it must not be forgotten
that the older writers regarded the whole genera as plants.
ESCHARID^J 523
Flustra chartacea. Ellis states : " The cells of this sea
mat are of an oblong square figure, swelling out a little in
the middle of each side. The openings of the cells are
defended by a helmet-like figure ; from hence the polype-
shaped suckers extend themselves. This sea-mat is of a
slender and delicate texture, like a semi-transparent paper,
of a very light straw-colour. It was first found on the
coast of Sussex, adhering to a shell. I have since met, on
the same coast, about Hastings, in the year 1765, with
several specimens whose tops are digitated, and others that
were very irregularly divided."
The Flustra carbasea grow out in a leaf-like manner,
gradually widening to the end : they are found on shells of
a yellowish-brown colour ; on one of the sides the cells are
both large and smooth. The animals have about twenty-
two arms or feelers, which, says Dr. Grant, after a most
careful examination of these polypes, " are nearly a third
of the length of the body; and there appear to be about
fifty cilia on each side of a tentacle, making 2200 cilia
on each polype. In this species there are more than
eighteen cells in a square line, or 1800 in a square inch of
surface ; and the branches of an ordinary specimen pre-
sent about ten square inches of surface j so that a common
specimen of the F. carbasea presents more than 18,000
polypes, 396,000 tentacles, and 39,600,000 cilia.
" They are very irritable, and frequently observed to
contract the circular margin of their broad extremity,
and to stop suddenly in their course when swimming ;
they swim with a gentle gliding motion, often appear
stationary, revolving rapidly round their long axis, with
their broad end uppermost, and they bound straight for-
ward, or in circles, without any other apparent object than
to keep themselves afloat till they find themselves in a
favourable situation for fixing and assuming the perfect
state. The transformation of the ova, from that moving,
irritable, free condition of animalcules, to that of the fixed
and almost inert zoophytes, exhibits a new metamorphosis
in the animal kingdom not less remarkable than that of
many reptiles from their first aquatic condition, or that of
insects from their larva state."
Flustra avicularis. This is another of the little beauties
524 THE MICROSCOPE
of the deep, found usually on old shells, an inch in height,
spreading itself fan-like, and of an ashy colour, deeply
divided in a dichotomous manner into narrow, thin, plane
segments, truncate at the end, formed of four or five series
of oblong cells, capped with a hollow, globose, pearly, oper-
culum seated between the spines, of which there is one on
either side of the circular aperture. The opercula are so
numerous, that they give to the upper surface the appear-
ance of being thickly strewn with orient pearls ; the under-
surface is even and longitudinally striated, the number of
stria) corresponding to the number of rows in which the
cells are disposed. Dr. Johnston describes, amongst many
other British species, F. membranacea, " a gauze-like incrus-
tation on the frond of the sea-weed, spreading irregularly
to the extent of several square inches."
Dr. Perceval Wright discovered on the western coast of
Ireland a new genus of Alcyonidce, which he named after
the well-known naturalist Mr. Harte, Hartea elegans, Plate
IV. No. 86. This polype is solitary, the body cylindrical,
and fixed by its base to the rock; it has eight ciliated
tentacles, which are knobbed at their base and most freely
displayed. It is a very beautiful polyzoon of a clear white
colour, and when fully expanded stands three-quarters of
an inch high. 1
The fresh-water Polyzoa are peculiarly interesting ob-
jects for microscopic observation, from the very beautiful
manner in which they display their ciliated tentacula, set
upon a crescentic, horseshoe-shaped "lophopore." The
arrangement of the latter appendage has been the cause of
separating the fresh-water Polyzoa, from their marine
allies, into a sub-class ; the former being named Hippocrepa
(horseshoe-like ), and the latter Infundibulata (funnel-
like). 2 The most striking form among the Hippocrepa is
the Cristatella Mucedo a wandering Polyzoon, capable of
moving freely through the water. It may be met with
during a great part of the summer in our ponds and streams,
amidst the stems and leaves of aquatic plants (Plate IV.
(1) On a new genus of Alcyonidce. By Dr. E. Perceval "Wright. Micros.
Journ. Science, vol. v. p. 213. 1865.
(2; The reader is referred to a valuable treatise on the structure and classift-
oation of this group by Professor Allman, Monograph of the Britiih
ttater Polyzoa, published by the Ray Society, 1857.
POLTZOA. 525
.No. 97). It is always regarded as one of the most exqui-
site specimens of the class Polyzoa ; should there be
any difficulty in finding the animal itself, the eggs, met
with late in the summer or autumn, should be care-
fully stored in an aquarium without fish. The eggs or
" statoblasts," No. 95, are small, dark, circular bodies,
about the size of a pin's head, surrounded by a series of
minute hooked spines ; the animal conceals them among
tangled masses of decayed grasses and conferae. Polyzoa
are known to live upon Desmids and Algae ; and to keep
them alive the tank must be freely supplied with such
kinds of food. Cristatella Mucedo is rarely found in the
same spot a second day, it wanders about apparently in
search of food ; it is, therefore, provided with a contractile
disc or foot, and by means of this it creeps about not far
from the surface of the water, for it delights to display its
beautiful crests of tantacula (about eight in number), in the
broad light of day or sunlight ; in this respect Cristatella also
differs from most Polyzoa. Below the external margin is
a series of tubular chambers visible through the translucent
membrane ; and the csensecium or common dermal system
is of a light yellow colour, often concealing several dark,
brownish-looking eggs.
LopJiopus crystallinus is a finer Polyzoon than the former,
and displays beautiful plumes of transparent tentacles
arranged in a double horseshoe-shaped series. They at
times abound in slow running streams, adhering to the
stems of water-plants. "When first removed from the water
they resemble masses of the ova of one of the water snails,
and have often been mistaken for them. On putting one
of those jelly-like masses into a glass trough with some of
the clear water from the stream, delicate tubes will be
cautiously protruded, and then the beautiful fringes of cilia
are soon brought into play. The organization of L. Crys-
tallinus is simple, although it is provided with organs
of digestion, circulation, respiration, and generation. A
nervous 1 and muscular system are also tolerably well
(1) It has been demonstrated by Fritz Muller that the Polyzoa possess a ner-
vous system : "The nervous system of each branch consisting of 1st, a consi-
derable sized ganglion situated at its origin ; 2d, of a nervous trunk running tha
entire length of the branch, at the upper part of which it subdivides into
branches, going to the ganglia of the iuternodes arising at this part ; and 3d, of
626 THE MICROSCOPE.
developed. It increases both by budding and by ova,
both of which conditions are shown in Plate IV. !No. 98.
The ova are generally seen enclosed in the transparent
case of the parent In Lophopus and most other fresh-
water genera, such as Cristatella, Flumatdla, and A Icyo-
nclla, the neural margin of the lophopore is extended into
two triangular arms, giving it the appearance of a deep
crescent
Alcyonella is a genus of fresh-water polyzoa, found
usually about the autumnal period of the year in the
several Docks at the East end of London, adhering to
floating pieces of timber. It assumes the form of an
irregular sponge-like mass, with an aggregation of niem-
branaceous tube-like openings covering the surface.
From these openings, the polypes are seen to project, the
mouths of which are encircled with a single series of
filiform ciliated tentacles, which keep the surrounding
water in active motion. The polypidom seen in water
has the appearance of a blackish-green sponge.
Trembley gave an interesting account of the family of
Alcyonella; and Mr. J. Kewton Tomkins favours us with
the following tbservations on the development of the
Alcyonella stagnorum (fiuviatdla) :
"The ova now under examination (J-inch obj. A. eye-
piece 100 lin. diam., Wollaston's condenser), are the
products of some healthy specimens of Alcyvnella stag-
norum given me by Mr. Lloyd, and sketched in full
activity in September 1856 Soon after this period
their movements decreased in energy, numerous ova were
detached, which floated to the surface of the water of
the jar in which they were confined, and in the course
of a very few weeks no trace remained of the parent
animals, except a spongy mass of an almost gelatinous
character, which still exists, though devoid of definite
form, and appears composed of a mass of broken and
disorganized cells.
" In November, with a view of preserving the water in
a normal condition, I introduced a sprig of Anacharis
a rich nervous plexus resting on the trunk, and connecting the ganglia just
mentioned, as well as the basal ganglia of the individual polypides." For
farther account, see paper in the Jtficiv*. Joum. voL i. New Series p. 330.
POLYZOA. 527
Akinastrum, and finding it grew freely, but soon covered
with a filamentous confervoid growth, threw in two small
water-snails, which are there still About January last,
the ova, which till then had floated on the surface of the
water, began to sink and attach themselves to the leaves of
the Anacharis and elsewhere. Latterly, they have all
subsided to the bottom of the jar, where they fie in com-
pany with a quantity of decayed vegetable matter, spawn
of the Limnaeus, &c. They are of a light-brown colour,
ovoid in shape, longest diameter *0089, shortest diameter
0172. The outer rim seems built up of cells of oblong
shape, but necessarily ill-defined, owing to their being ob-
served by light transmitted through two surfaces; the
inner or central portion also cellular, but from the con-
vexity of the object, more easy to determine as to its true
nature, formed of larger hexagonal-shaped cells. Seen by
higher power (J-in. obj. A. eye-piece 220 bin. diam.),
these central cells, besides being unmistakably hexagonal
in form, have each a distinct dark nucleus in the centre :
this, however, may be an optical fallacy, due to their
peculiar position on a curved surface. No movement yet
visible, April 25, 1857."
Plumatdla Repent, Plate IV. No. 99, so named from its
feather-like crown of tentacles, is a well-known fresh-water
Polyzoon, found in ponds and rivulets attached to aquatic
plants, generally choosing the under-surface for the pur-
pose of avoiding the strong light. It is a very elegant
variety, rather timid, withdrawing on the least disturbance
of the water, and not again venturing to display its beau-
tiful plume until all is once more perfectly quiet Pro-
fessor Allman says of it IT-" Except in the condition of
the dermal system the structure of Plumatdla differs in
no essential point from that of Alcyonella. This system,
however, in the coalescence of the tubes into a common
mass in A Icycmetta, while they remain totally distinct in
Plumatella, presents us with a difference of sufficient im-
portance to justify the placing the two forms in separate
generic groups. The number of known species are twelve,
of which nine are Britiph. The camaeciuni consists of a
linear-branched series of tubula. cells of membrano-
corneous consistence, which is terminated by the orifice
528
THE MICROSCOPE
destined for the egress of the polypides. The tentacula
are about sixty in number, long, and ciliated on either
side. The statoblasts are ovoid, of a dark-brown colour
without marginal spines, and contained within the poly-
1, Portion of a transverse section of the spine of an Bchiwu. 2, Crystal? ol
carbonate of Lime, from the surface of shell of Oyster. 3, Horizontal section
of shell of Haliotis splendens, with stellate pigment in the interior.
Portion of shell of a Crab, showing granules beneath the articular layor. b,
Another portion of the same shell, showing its hexagonal structure.
pidom, through the transparent walls of which they can be
readily seen. It occurs in greatest perfection during the
SHELL OP MOLLUSC A 529
summer and towards autumn, often obtaining to a consi-
derable size." Most of the species may be found in the
ponds around London, and fe\v objects are capable of
affording greater pleasure than these Polyzoa when examined
in a living state under a moderate power, and with a dark-
ground illuminator. The withdrawal of the Polyzoa
from the Eadiate sub-kingdom, and their location among
Mollusca, was a step in the right direction ; while the
important division of the molluscan sub-kingdom by
Milne-Edwards into primary sections of the Mollusca and
Molluscoida, the latter including the Tunicata and the
Polyzoa, is all that can be desired in the systematic
location of the Polyzoa.
Shell of Mollusca. The simplest form of shell occurs in
the rudimentary oval plate of the common Slug, Limax
rufm ; it is imbedded in the shield situated at the back
and near the head of the animaL
When a molluscous or conchiferous shell is composed of
a single piece, it is then termed univalve ; when of two
pieces, bivalve. The bivalve Mollusca exhibit no trace of
any distinct head ; whilst in the univalve this part of the
body is well-marked, and usually furnished with special
organs of sense (tentacles, eyes, nerves, &c.).
The older naturalists recognised a group of multi-
valve shells, or shells composed of several valves, the
majority of which belonged to the Cirrhopod order of
Crustacea, and were regarded as Mollusca by earlier ob-
servers. The Pftolades, however, which in other respects
are trae bivalve Mollusca, are furnished with a pair of
accessory plates in the neighbourhood of the hinge ;
whilst the Chitons, a small but sin-
gular group of Molluscs nearly
allied to the univalve limpets, have
an oval shell composed of eight
movable plates, which gives them a
great resemblance to enormous
woodlice ; and they have been re-
garded as forming a sort of transi-
tion towards the articulated divi-
sion. Those Mollusca not furnished
with a shell, or having only a small calcareous plate en-
M M
530 THE MICROSCOPE.
closed within the mantle, are called Nudibranchiata : an
example of this family is seen in fig. 248, Aplysia ; but it is
remarkable that most of them are provided with a small
shell when they lirst quit the egg. In the shell-bearing
or Testaceous Mollusca, this embryonic shell, which often
differs greatly in shape and texture from the shell of the
mature animal, is, however, a commencement of the latter ;
additions being constantly made to the free edge by the
secretion of calcareous matter at the margin of the mantle.
The delicate membranaceous part of the mantle, which
lines the internal portion of the shell inhabited by the
animal, has also the power of secreting a thin layer of
shelly matter upon its inner surface. This is frequently of
a pearly lustre ; and in many bivalves a new layer q.f this
substance is deposited at the time when the size of the
shell is increased by additions to its margins, for it must
be observed that the formation of new shell is not con-
stantly going on, but appears to be subject to periodical
interruptions, as indicated by lines on the surface of the
shell ; which are called lines of growth. In many cases,
the margin of the mantle, instead of being even, presents
lobes of tubercles ; these produce corresponding irregula-
rities, ribs, tubercles, or spines, on the surface of the
shell.
Dr. Bowerbank says, " Shell is developed from cells
that in process of growth have become hardened by the
deposition of calcareous matter in the interior." This
earthy matter consists principally of carbonate of lime,
deposited in a crystalline state ; and in certain shell, as in
that of the common Oyster (fig. 247, No. 2), from the
animal-cell not having sufficiently controlled the mode of
deposition of the earth particles, they have assumed the
form of perfect rhomboidal crystals.
The shell of the genus Pinna, " Wing-shells," is com-
posed of a series of hexagonal cells filled with transparent
calcareous matter, seen in fig. 240, No. 2, the outer layer
of which can be split up into prisms, like so many basaltic
columns ; as at No. 1.
Organs of sense are possessed by some of this class in an
advanced state of development. Ir\ the Scallop (Pecten),
for example, eyes occur in great numbers, placed among
MOLLLSCA. 533
the tentacles on the borders of the mantle. In othei
genera, the eyes are differently placed, in Pinna on the
lore part of the mantle, and around the siphon-orifices in
Pholas and Solen. In the Cockle (Cardium) the short
siphons are surrounded with an extraordinary number of
tentacles, capable of protrusion, each of which bears a
pretty little eye; these are beautiful objects under the
microscope. Cockles are able to perform vigorous leaps by
means of a well developed foot, which they possess ; in
other species the foot is grooved j and being associated
with a gland which has the power of secreting a gluti-
nous substance, the latter is drawn out into slender
threads, with a sucker-like or flattened extremity, by
which they attach themselves to rocks. The grooved foot
is then withdrawn, and the thread hardens into an elastic
sort of cord, called a byssus. It is by an aggregation of
these threads that the common Mussel moors itself
securely. The hinge of the shell is formed of variously
shaped dentations ; those under the beak are called car -
dinal teeth ; those on either side are lateral teeth.
The PholadidcB are a series of animals remarkable for
their destructive boring propensities. The Teredo, ship-
worm, is well known for the damage it does to the
bottoms of ships, especially in the tropical seas. Others
of this family give a preference to sandstone, and even the
most compact marble has been found bored through by
them.
Mr. J. Robertson says : : " Having, while residing here
(Brighton), opportunities of studying the Pholas dactylus,
I have endeavoured during the last six months to discover
how this mollusc makes its hole or crypt in the chalk, by
a chemical solvent 1 by absorption ? by ciliary currents ?
or by rotatory motions ? My observations, dissections, and
experiments set at rest controversy in my mind. Between
twenty and thirty of these creatures have been at work in
lumps of chalk in sea water in a finger glass and a pan, at
my window, for the last three months. The Pholas dac-
tylus makes its hole by grating the chalk with its rasp-like
valves, licking it up when pulverized with its foot, forcing
it up through its principal or branchial siphon, and
squirting it out in oblong nodules, The crypt protects the
M M 2
632 THE MICROSCOPE.
Pholas from Conferva?, which, when they get at it, grow
not merely outside, but even within the lips of the
valves, preventing the action of the siphons. In the foot
there is a gelatinous spring, or style, which when taken
out has great elasticity, and which seems the mainspring
of the motion of the Pholas dactylus"
Tunicata, The most remarkable group of animals be-
longing to this order are the Asddians. The cell of the
Polyzoon is represented in the Ascidian by a test or tunic
from which they derive their name of a membraneous or
cartilaginous consistence, and often including calcareous
spicules, having two orifices, within which is another
envelope, distinguished as the mantle. Few microscopic
spectacles are more interesting than the sight of the circu-
lation along this network of muslin- like fabric, and that
of the ciliary movement by which the circulating fluid is
kept moving. In the transparent species, such as Clave-
Una and Perophora, this movement is seen to great advan-
tage. The animals are found very commonly adhering to
the broad fronds of fuci, or on pieces of shell, near low
water-mark. They thrive in tanks, and multiply both b>
fissuration and budding. Two species are figured in Plate
IX. i and k, Botryllm violaceus belonging to the family
Didemnians, the zooids of which are often arranged in the
beautiful stellate clusters seen in the plate. 1
Pteropoda. The most prominent character of this class
is the possession of two broad muscular fins, one on either
side of the neck, somewhat resembling the expanded
wings of a butterfly, whence Cuvier gave them the name
of Pteropoda, "wing-footed." In Clio, the anatomy of
which has been carefully investigated, there is a very
curious apparatus developed for seizing its prey. On each
side of the mouth are three fleshy warts, covered with
minute red specks. Under the microscope, these specks,
numbering about three thousand on each tentacle, are seen
to be transparent cylinders, each containing in its cavity
twenty stalked discs, and forming so many adhesive
suckers.
(1) For information respecting the Compound Ascidians, Bee the admirable
monograph of Milne- Edwards, Art. Tunicata in the Cyclop. Anatomy and Phy-
eiology, Huxley in Phil. Trans, for 1851, or Journ. Micros. Soc. voL ir. 1856 ;
alao Prof. Allraan, same journal, voL vii. 1859.
MOLLUSCA. 533
The Oyster is the type of the tribe Ostracea, all of
nrhich are Acephalus, that is, animals without a distinct
head. The gills, or breathing apparatus, form what is
commonly called the beard of the oyster. The creature
is attached by strong muscles to its shell. The mouth of
the oyster is a mere opening in the body, without jaws or
teeth ; its food consists of nourishing substances suspended
in the water, and which are drawn into the shell when it
is open by means of cilia. Oysters attach one of their
valves to rocky ground, or some fixed substance, by a mu-
cilaginous liquid, which soon becomes as hard as the shell
itself. They spawn some time in May ; and their growth
is so rapid, that in three days after the deposition of the
spawn, the shell of the young oyster is nearly a quarter of
an inch broad ; in three months it is larger than a shil-
ling. The spawn is a very interesting object for micro-
scopic examination, especially with polarised light. The
young fry is represented in fig. 254 ; some with cilia pro-
truded.
In the stomach of the Oyster, and in the alimentary
canal, myriads of living Paramaecium and other Infusoria
are found swimming in great activity ; swarms of a con-
glomerate and ciliated living organism, somewhat resem-
bling the Volvox globator, and so extremely delicate in
their structure that they require a good objective to define
them.
Pearls are usually met with in the Meleagrina Marga-
ritifera, " Pearl Oyster," which, however, does not belong
to the family Ostracea. They are likewise found in the
Mussel known as Mya Margaritifera, and an inferior kind
in many Mussels of the rivers of Great Britain ; and, at
one time, the pearl-fishery of Ireland was justly cele-
brated. Naturalists somewhat differ in their opinions as
to the mode in which pearls are formed. Some think that
they are produced by particles of sand getting into the
stomach ; the animal, to prevent the roughness of these
particles from injuring its delicate structure, covers them
over with a secretion from a gland, and, by continual ad-
ditions, they gradually increase in size. Mussels, in which
artificial pearls were said to have been formed by tho
Chinese, have frequently found their way to this country.
534
THE MICROSCOPE.
It is now, however, very generally admitted to be a dis-
eased condition. Pearls are matured on a nucleus, con-
sisting of the same matter as that from which the new
layers of shell proceed at the edge of the Mussel or
Oyster. The finest kinds are formed in the body of the
animal, or originate in the pearly-looking part of the shell.
It is from the size, roundness, and brilliancy of pearls
that their value is estimated.
The microscope discloses a difference in the structure of
pearls : those having a prismatic cellular structure have a
brown horny nucleus, surrounded by small imperfectly-
Fig. 249.
I, A transverse section of a Pearl from Oyster, showing its" prismatic structure.
2, A transverse section of another Pearl, showing its central cellular struc-
ture, with outside rings of true pearly matter. (Magnified 50 diameters.)
formed prismatic cells ; there is also a ring of horny
matter, followed by other prisms, and so on, as represented
MOLLUSCA.
535
in fig. 249 ; and all transverse sections of pearls from
Oysters show the same successive rings of growth or
deposit.
In a segment of a transverse section of a small purple
pearl from a species of Mytilus (fig. 250), all trace of
prismatic structure has disappeared, and only a series of
fine curved or radiating lines is seen. This pearl consists
of a beautiful purple-coloured series of concentric laminae ;
many of which have a series of concentric zones, and are
of a yellow tint. The most beautiful sections for micro-
scopic examination are obtained from Scotch pearls.
Brachiopoda, " Lamp-shells/ ' or, as the name literally
250.
1, A transverse section of a small Pearl- from a species of Mytilus. 2, Hori-
zontal section of same Pearl magnified 250 diameters, to show prismatic
structure and transverse striae.
signifies, arm-footed, is intended to express a most re-
markable characteristic of these animals, the presence of a
pair of arms, often of great length, rolled up in a spiral
form, and believed by Cuvier to replace the foot in othec
bivalves. Professor Owen has shown that these organs
are tubes closed at each end, and contain a fluid, wtiich by
536 THE MICROSCOPE.
the contraction of the circular muscular fibres of which
the walls of the tube are composed, is propelled from the
base to the extremity, thereby unrolling, as he believes,
the spiral coils. One side of each arm is fringed with a
vast number of long filaments : these are ciliated. The
shell is opened by a peculiar process, which has given to
the Terebratula the name of Coach-spring Shell. In. the
shell there are minute openings surrounded by a series of
radiating lines : these at first appear like dark oval spots ;
but in a vertical section they are seen to be perforations or
tubes running obliquely from the inner to the outer surface
of the shell, and having a series of radiating lines on the
edge, as in fig. 240, No. 3. The outer layer has been re-
moved, to show a radiating structure around the perfora-
tions. Dr. Carpenter fully describes Terebratula in the
Philosophical Magazine, 1854.
Not less curious than beautiful is the internal layer of
many kinds of bivalves, which present an iridescent
lustre, the whole surface being varied with a series of
grooved lines running nearly parallel to each other. The
well-known gorgeously coloured univalve, the Ear-shell,
Haliotus splendens, has been ascertained to consist of
numerous plates, resembling tortoise-shell, forming a series
of hexagonal cells, in the centre of which the stellate
pigment is deposited (fig. 246, No. 3), alternating with
thin layers of pearl, or nacre; and this exhibits, when
highly magnified, a series of irregular undulating folds, re-
presented in the upper portion of the section. The iride-
scent lines are often extremely pleasing ; and if a piece be
submitted to the action of diluted hydrochloric acid, until
the calcareous portion of the nacreous layers are dissolved
out, the plates of animal matter fall apart, each one carry-
ing with it the membraneous residuum of 'the layer of
nacre that belonged to its inner surface. But the nacre
and membrane covering some of these horny plates remain
undisturbed ; and their folded or plaited surfaces, although
divested of calcareous matter, exhibit iridescent hues of
the most gorgeous description. If the membrane be
spread out with a needle, and the plates unfolded to a
considerable extent, the iridescence is no longer seen; a
Tact which clearly demonstrates that the beautiful colours
GASTEROPODA. 537
presented by the nacreous portions of shells, commonly
called mother-of-pearl, are produced solely by the disposi-
tion of single membraneous layers in folds or plaits, lying
more or less obliquely to the general surface.
In the Chitonidce, Coat of mail Shells, the shell consists
of eight transverse plates, imbedded in the mantle ; in the
Limpets, the ordinary form is that of a cone. The
arrangement of the teeth is somewhat remarkable.
The majority of Gasteropoda are furnished with a
shell, denominated spirivahe. The cause of this spiral
arrangement is said to be owing to the shape of the body
of the animal inhabiting the shell, which, as it grows,
enlarges its shell principally in one direction ; thus, of
course, making it form a spire, modified in shape according
to the degree in which each successive turn surpasses in
bulk that which preceded it. It would rather appear that
this is principally owing to the ciliary motion imparted to
the early stage of the embryo ; the first deposit of calca-
reous matter forming the axis, the tube continues to rotate
upon its axial pillar or columella, as it is called ; and by
reason of some other peculiar vital tendency, the shell is
gradually deposited in a series of cells ; thus enlarging its
conical form, and winding obliquely from right to left.
Every turn around the axis is termed a wliorl ; and when
the columella is hollow, it is said to be umbilicated. In
the spirivalve-shelled Gasteropoda, we find a difference in
structure between that part of the mantle which enve-
lopes the viscera, and which is always concealed within
the cavity of the shell, and the portion placed around its
aperture.
The mouths of most Gasteropoda consist of a strong
muscular cavity, and a crescentic-shaped tooth-bearing
membrane, armed with sharp points, and separated by
semi-circular cutting spaces, admirably adapted for the
division of the food upon which they feed. Most of them
are beautiful objects for the microscope.
Professor Huxley very properly objects to the use of the
commonly accepted term tongue for the tooth-bearing
membrane of the mollusca, and more appropriately desig-
nates it " the odontophore."
" The odontophore consists essentially of a cartilaginous
538 THE MICROSCOPE.
strap, which bears a long series of transversely-disposed
teeth. The ends of the strap are connected with muscles
attached to the upper and lower surface of the hinder ex-
tremities of the cartilaginous cushions ; and these muscles,
by their alternate contractions, cause the toothed strap to
work backwards and forwards over the end of the pulley
formed by its anterior end. The strap consequently acts
2
Fig. 251.
1, Palate of Buccinum undatum, common Whelk, seen under polarised light
2, Palate of Doris tubercufata, Sea-slug.
after the fashion of a chain-saw (rather of a rasp,) upon
any substance to which it is applied, and the resulting
wear and tear of its anterior teeth are made good by the
incessant development of new teeth in the secreting sac in
which the hinder end of the strap is lodged. Besides the
chain-saw-like motion of the strap, the odontophore may
be capable of a licking or scraping action as a whole." 1
In the constant growth of the band we observe the
development of new teeth. In some the teeth on the
extreme part of the band differ much, both in size and
form, from those in the median line : so much, that if at
any time one portion be separated from the other and
then examined, it might be supposed to belong to another
species.
Since the investigations of Professor Loven, of Stock-
holm, into the lingual dentition of the glossophorous Mol-
lusca, various observers have studied the subject with
great advantage to our knowledge of the affinities of those
animals. Although the patterns or types of the lingual
membranes are, on the whole, remarkably constant, yet
il) Elements of Comparative Anatomy, p. 36.
ifVcn West, del.
W. F. Maples, ad. nut. del.
PLATE V.
3ASTEROPODA. 539
'heir systematic value is not uniform ; and therefore ilia
jfctempts to remodel the arrangement of the Gasteropoda
"by their peculiarities of dentition have not become so com-
plete a success as was at first expected. Some, how
ever, hold a different opinion ; and Dr. J. E. Gray writes :
" One result of the study of these papers (Loven's, On
the Tongues of Mollusca) and the examination of the
tongues of several molluscs has been to establish more
firmly the theory which I have long entertained, that no
species of gasteropodus molluscous animal can be properly
placed in the system unless we are enabled to examine the
animal, the shell, the operculum, and the structure of its
tongue ; and as none of these parts but the shell can be
examined in the fossil species, their position in the various
genera must be always attended with more or less uncer-
tainty." 1
Dr. Troschel has laboured much in this field of investi-
gation, and in his valuable work on the subject attempts a
classification of the principal types by their lingual den-
tition. The union under one formula of so many creatures
widely differing in anatomy, habits, and shell structure,
clearly indicates that, if the lingual ribbon contains
generic characters, they have not yet been ascertained. At
the same time, it does present differences which may offer
collateral evidence in cases otherwise difficult of discrimi-
nation. It does not help us to separate carnivorous from
phytophagus animals ; but it seems possible to make use
of it as a mark between species ; for, in all, there is a dis-
tinct difference between the tongues even of the most
closely allied/ Thus, amongst other changes, it has been
found necessary to remove the Proserpinadas from the
neighbourhood of the Cydophoridce, to which they were
formerly supposed to be nearly related, and to place them
in a more natural position near the Neritidce. That these
investigations are of value is also shown by the light
which has been shed on the true position of Aporrhais,
supposed by so great a naturalist as Forbes to be akin to
the Cerithiidce, but which is shown by its dentition to
lelong to the Strombidce?
(1) Annah of Nat. Hist. Ser. ii. vol. x. p. 413.
(2) See a paper on the subject in the Trans. Linn. Soc. 1S67.
510 THE 3IICROSCOPE.
The relations of the freshwater operculata are as varied
as those of the land. Ampullaria seems to find its nearest
marine relative in Natica, an opinion which seems con-
firmed by the form of the shell. A West Indian species
found on the trees of the forests of those islands, and placed
by Lamarch in the Helicina, would rather appear to belong
to Neritina. The several peculiarities of their teeth, espe-
cially that of H. nemoralis, with its numerous uncini, its
sub-opaque trapezoid laterals, which seem heretofore to
have been overlooked, confirm the belief in its close rela-
tionship to Neritina. The horny mandibles of the Mol-
lusca may be deserving of some attention with a view to
the elucidation of their affinities. In Cyclotus translucidus
the mandible is divided into two portions by a median
articulation, and it is covered with fine denticulations
in regular rows, somewhat like that of Velutina, Plate Y.
No. 109. In most of the inoperculata, the mandible is
horse-shoe-shaped, and striate or corrugate. In Ampul-
laria, the same organ is beak-shaped, like the upper man-
dible of Octopus or Loligo.
" The lingual band, we should premise, has been, for con-
venience of description, divided into longitudinal areas,
which are crossed by many rows of teeth. There are
five, distinguishable by the different characters of the teeth
they bear ; but the characteristics are not always present.
The teeth are consequently named median, lateral, and
uncini, although the latter are not necessarily more hooked
than the others. The areas bearing the uncini have been
called pleurae. Since each row is a repetition of all the
rest, the system of teeth admits of easy representation by
a numerical formula, in which, when the uncini are very
numerous, they are indicated by the sign oo (infinity), and
the others by the proper figure. Thus, oo * 5 1 5 oo ,
which represents the system in the genus Trochus, signifies
that each row consists of one median, flanked on both
sides by five lateral teeth, and these again by a large
number of uncini. When only three areas are found, the
outer ones are to be considered as the pleurae, inasmuch as
there is frequently a manifest division in the membrane
between them and the lateral areas."
Most of tho Cephalopod molluscs are provided with
TEETH OF GASTEROPODA. 541
strong, well developed teeth ; they are all animal feeders,
Loven describes those of the cuttle-fish (Sepia officinalis,
Plate V. No. Ill), as like Pteropoda, formula of teeth,
3*1 '3. The Sepia is also furnished with a retractile
proboscis, and a prehensile spiny collar, apparently for the
purpose of holding its prey while the teeth are employed
in drilling or abrading it. In the Squid (Loligo, No. 113),
the medians, broad at the base, approach the tricuspid form
with a prolonged acute central cusp ; while the uncini are
much prolonged and slightly curved. The lingual band
increases in breadth towards the hinder part, in some in-
stances to twice the diameter of the anterior. The band,
when mounted dry, forms a fine object for the black-
ground illuminator, or side reflector. The lingual band of
Octopus tuberculatus differs slightly with Sepia.
The Nudibranchiata have become more attractive since
the publication of the valuable and beautifully-illustrated
monograph of Messrs. Alder and Hancock. The nudi-
branchs are without a shelly covering, slug-like in their
appearance, and most voracious feeders, greedily devouring
zoophytes, sponges, &c. (Plate IX. b.) They possess the
remarkable property of restoring lost parts ; their powers
of endurance are great, so that they may be kept alive for
some time in a small glass jar of sea-water. While keep-
ing a specimen of the Piplida in confinement, the Rev.
Mr. Lowe noticed on several occasions a display of a bril-
liant phosphorescence. Many of the genus Dorididce and
Eolidida are infested with parasitic Entromostraca, which
either live freely on the surface, under the skin, or adhere
to the branchiae of the animals. Oncidoris bilamellata (the
Sea-lemon) belongs to the Dorididse ; its mouth is provided
with a narrow band of strong hooked teeth (Plate Y. No.
120), which in some species are serrated ; all are provided
with mandibles, consisting of two horny plates uniting
near the fore part. The median row of teeth are small and
inconspicuous; the band is represented by the formula
2 1 2. A portion of the mandible of Aplysia hybrida
(the Sea-hare) is shown in Plate V. No. 112.
Patella radiata (the Rock-limpet). The band of this
mollusc, No. 116, may be readily distinguished from the
common limpet of our coasts ; the remarkably long ribbon-
542 THE MICROSCOPE.
like membrane, which lies folded up in the abdominal
cavity, is furnished with numerous rows of strong, nearly
opaque, dark brown tricuspid teeth. The teeth of Acmcea.
(No. 117) are; differently arranged ; their formula is 3 1 3.
Chitonidce are said to be near relatives of the Patellidce ; the
mouths of all are furnished with mandibles.
Testacella maugei, belonging to the Pulmonifera, is slug-
like in its appearance, and, curiously enough, is subter-
ranean in its habits, chiefly feeding on earth- worms. During
winter and in dry weather it forms a kind of cocoon,
and thus completely encloses itself in an opaque white
mantle, which effectually protects it from atmospheric
influences. Its lingual membrane is large, and covered
with about fifty rows of divergent teeth, which gradually
diminish in size towards the median row ; each tooth is
barbed and pointed, broader towards the base, and fur-
nished with an articulating nipple set in the basement
membrane. A few rows are represented slightly mag-
nified, Plate V. No. 121. Their formula is 1 0.
Cymba olla (the Boat-shell) belongs to the species
Velutinidae, formula, 1 * 0, or 1 * 1 1. The lingual band,
No. 118, is narrow and ribbon-like in its appearance, with
numerous trident-shaped teeth set on a strong muscular
membrane. The end of the strap and its connexion with
the muscles at the hinder extremity of the cartilaginous
cushion is shown in the drawing. The blueish appearance
seen in the Plate is due to a selenite film and polarised
light. Scapander ligniarius (the Boatman shell). The
band (Plate V. No. 119), is narrow, but the teeth are bold
and of extraordinary size ; their formula is 1 1. This
mollusc is said to be without eyes. Pleurobranchus plu-
mula belongs to the same family ; its teeth are simple, re-
curved, and convex, and arranged in numerous divergent
rows ; the medians of which are largest. The mandible
(Plate V. No. 122), presents an exceedingly pretty tesse-
lated appearance, and the numerous divergent rows have
tricuspided denticulations. Velutina Icevigata (the Velvety
shell), formula 3 1 3. The teeth (Plate V. No. 108) are
small and fine ; medians recurved, with a series of deli-
cate denticulations on either side of the central cusp,
Mfhich is much prolonged : 1st laterals, denticulate, with
GASTEROPODA. 543
outer cusp prolonged ; 2d and 3d laterals, simple curved
or hooked-shaped. The mandible, .No. 109, divided
in the centre, forms two plates of divergent denticu-
lations.
Haliotit tuberculatus (the Ear-shell), is a well-known
beautiful shell much used for ornamental purposes. The
lingual band, Plate V. No. 114, is well developed. The
medians are flattened out, recurved obtuse teeth ; 1st
laterals, trapezoidal or beam-like ; uncini numerous, about
sixty, denticulate, the few first pairs are prolonged into
strong pointed cusps. Turbo marmoratus (the Top-shell).
After the outer layer of shell is removed, it presents a
delicate pearly appearance. The lingual band, No. 123,
closely resembles Trochus ; it is long and narrow, the
median teeth are broadest, with five recurved laterals, and
numerous rows of uncini, slender and hooked. A single
row only is represented in the plate. Cydotus transit
<*idus, a family of operculate land-shells, belongs to the
Cydostomalidce. The teeth shown at No. 110, formula
3 1 3, are arranged in slightly divergent rows on a narrow
band ; they are more or less subquadrate, recurved, with
their central cusps prolonged. Cistula catenata, one of
the family CydopJwrid& ; its band, No. 115, formula
2 1 2, shows teeth resembling those of Littorina, and
should certainly be separated from Cydop/ioridce. It
would also seem that the teeth of Cydostomatidce point to
a near alliance with the Trochidce; but this question can
only be determined by an examination of several species,
when it may, perhaps, be decided to give them rank as a
sub-order. They are numerous enough ; the West Indian
islands alone furnish us with 200 species.
Professor William Thompson, in his paper " On the
Dentition of British Pulmonifera," Ann. Nat. His. vol.
vii. 1851, pointed out that the length of the lingual band,
and number of rows of teeth borne on it, vary greatly in
different species. The rows, however, being closely set
are usually very numerous ; but it is among the Pul-
monifera we meet with the most astonishing instances
of large numbers of teeth. Limax maximus possesses
26,800, distributed through 180 rows of 160 each; the
individual teeth measuring only one 10,000th of an inch,
544 THE MICROSCOPE.
Helix pomatia has 21,000, and its comparatively dwarfed
congener, H. obvoluta, no less than 15,000. When it is
remembered that these estimates refer to series of forms,
curiously carved and sculptured, the total area sustaining
them not measuring in most of the molluscs half an inch in
length, we must be filled with admiration at the marvellous
creative power bestowed upon the organization of these
lowly-creeping creatures.
The Preparation of Teeth of Mollusca. The method
of preparing the lingual membranes of Mollusca is as
follows : Under a dissecting microscope and a large
"bull's-eye condenser cut open and expose to view the
floor of the mouth ; pin back the cut edges throughout
its length, and work out the dental band with knife and
forceps. The band being detached place it in a watch-
glass, and boil over a spirit lamp in caustic potash solu-
tion. Having by this process freed the tongue from
its integuments, remove it, wash it well, and place it for
a short time in a dilute acid solution, acetic or hydro-
chloric. Wash it well in water, float it upon a slide ;
and with a fine sable brush lay it open flat, and remove
whatever dirt or fibre may adhere to it. Lastly, place
it in weak spirit and water, and there let it remain for
a few days before mounting. It is better to mount
specimens in glycerine, Kimmington's glycerine-jelly,
or Groadby's solution. Canada balsam renders them so
very pellucid that the finer teeth are completely lost.
Thread-cells. These curious appendages, so commonly
met with in the Actinozoa, and in the tentacles surround-
ing the mouth of the Medusae, are also seen in some
species of Mollusca.
These prehensile threads, now generally termed " urti-
cating organs," were discovered in 1835, in the Hydra, by
Corda and by Ehrenberg. About the same time they were
found by R. Wagner in the Actinia, who at first regarded
them as zoosperms. Subsequently, however, he recog-
nised their identity with similar organs in the Medusa?,
and gave them the name of urticating organs. Since then
numerous observations have shown that these organs exist
in the entire class of polypes ; in that of the Hydra,
Medusae, as well as in the Synaptce, many Turbellariae,
OVA OF MOLLUSCA, 545
some -Annelids, and lastly among the Mollusca, the
Eolidse in particular.
Max Schultze has divided these organs into two cate-
gories ; one including those of a rod-like form, or the
bacillar, which are found pretty generally in the Turbel-
larise ; and the other containing the urticating capsules
armed with a long filament. But the researches of other
observers, including Dr. Bergh, have shown that this dis-
tinction is unimportant.
Dr. Bergh has devoted mi^h attention to the urticating
filaments or cnida of the Moliusca, which are far less well
known than those of the Cselenterata. The existence of
sacs with cnida that is to say, the existence of true
urticating batteries is then at the present day a well-
established fact as regards the typical forms of the Eolida3,
i.e. in the genera JSolidida, Montagna, Facelina.
In every case the urticating batteries are planted au the
extremities of the papillae above the hepatic lobe. The
sac opens to the exterior by a minute pore situated at the
summit. Its walls are muscular, a circular layer of fibres
being the most considerable element The interior is filled
with urticating cells, together with cysts full of closely-
packed filaments and free filaments. The genus Pleuro-
phyllidium, according to Dr. Bergh, is the only mollusc
besides the Eolidse in which cnida are met with, and it is
to be remarked that in their anatomical conformation these
animals appear to approach very closely to the Eolidse.
The use of these cnida is still involved in doubt. Mr.
Lewes, however, has shown that they do not serve to
paralyse the animals upon which Actiniae feed.
Ova of Mollusca. It is interesting to watch the develop-
ment of the spawn of the Mollusca under a low magnifying
power. The ova of the Limnceus is usually found adhering
to the surfaces of stones, pieces of weed, or other matters in
the water ; they are always contained in a long ribbon-
like delicate ova-sac of a curious and beautiful form.
The mass of eggs deposited by the Doris resembles a frill
of lace of great beauty. In Aplysia the spawn resem-
bles long strings of vermicelli, of varying tints through-
(1) On Urticating Filaments in the Mollusca, by Dr. Bergh. Journ. Micro*. ScL
vol ii. p. 274. 1862.
N N
546
THE MICROSCOPE.
out the different parts of the thread. The Limnceus stag-
nalis deposits small sacs, containing from fifty to sixty
Fig. ?52. LimncBd stagnalis.
ova ; one of which is represented at a, fig. 252. When
examined soon after they are deposited, the vesicles appear
to be filled with a perfectly clear fluid; at the end of
twenty-four hours a very minute yellow spot, the nucleus,
or germ, may be seen near the side of the cell-wall. In
about forty- eight hours afterwards, this small germ has a
smaller central spot rather deeper in colour, which is the
nucleolus. On the fourth day the nucleus has changed its
position, and is enlarged to double the size : a magnified
view is given at b ; upon viewing it more closely, a trans-
verse fissure or depression is seen ; this on the eighth day
most distinctly divides the small mass into the shell and
soft part of the future animal, c. It is then detached from
the side of the cell, and moves with a rotatory motion
around the cell-interior; the direction of this motion is
from the right to the left, and is always increased when
the sunlight falls upon it. The increase is gradual up to
the sixteenth day, when the spiral axis can now be made
out as at d; it presents a striking difference in appearance
to the soft parts. On the eighteenth day, these changes
are more distinctly visible, and the ova crowd down to the
mouth of the ova-sac ; by using a higher magnifying power,
a minute black speck, the future eye, is seen protruded
GASTEROPODA.
547
with the tentacles, at e. Upon closely observing it, a
fringe of cilia is noticed in motion near the edge of the
shell. It is now apparent that the rotatory motif u first
observed must have been in a great measure due to this ;
and the current kept up in the fluid contents of the cell
by the ciliary fringes. For days after the young animal
has escaped from the egg, this ciliary motion is carried
on. not alone by the fringe surrounding the mouth, but
by cilia entirely surrounding the tentacles themselves,
which whips up the supply of nourish-
ment, and at the same time the proper
aeration of the blood is effected. Whilst
in the ova, it probably is by this motion
that the cell-contents are converted into
tissues and shell. From the twenty-sixth
to the twenty-eighth day, it appears
actively engaged near the side of the
egg, using all its force to break through
the cell- wall, which at length it succeeds
in doing; leaving the shell in the ova-
sac, and immediately attaching itself to
the side of the glass-vase, to recommence
its ciliary play, and appears in the ad-
vanced stage represented at /. It is still
some months before it grows to the
perfect form represented at fig. 253,
where the animal is drawn with its sucker-like foot adhering
closely to the side of the glass-vase. One of these snails
may deposit from two to three of these ova-sacs a week ;
producing, in the course of six weeks or two months, from
900 to 1,000 young, thus supplying food for fish.
The shell itself is deposited in minute cells, which take
up a circular position around the axis; on its under-surface
a hyaline membrane is secreted. The integument expands,
and at various points an internal colouring-matter or pig-
ment is deposited. The increase of the membrane goes
on until the expanded foot is formed, the outer edge of
which is rounded off and turned over by condensed tissue
in the form of a twisted wire ; this encloses a net- work of
small vessels filled with a fluid in constant and rapid
motion. The course of the blood or fluid, as it
N N 2
Fig.
"548 THE MlCROSCOfJE.
from the heart, may be traced through the larger branches
to the respiratory organs, consisting of branchial-fringes
placed above the mouth; the blood may also be seen
returning through other vessels. The heart, a strong mus-
cular apparatus, is pear-shaped, and enclosed within a
pericardium or enveloping membrane, which is extremely
thin and pellucid. Affixed to the sides of the heart are mus-
cular bands of considerable strength, the action of which
appears very like the alternate to-and-fro motion occasioned
by drawing out bands of India-rubber, and which, although
so minute, must be analogous to the muscular cords of the
mammal heart ; it beats or contracts at the rate of about
sixty times a minute ; and is placed rather far back in the
body, towards the axis of the shell. The nervous system
is made up of ganglia, or nervous centres, and distributed
throughout the various portions of the body.
The singular arrangement of the eye cannot be omitted ;
it appears at an early stage of life to be within the tentacle,
and consequently capable of being retracted into it. In the
adult animal, the eye is situated at the base of the tentacle ;
and although it can be protruded at pleasure for a short
distance, it seems to depend much upon the tentacle for
protection as a coverlid it invariably draws down the ten-
tacle over the eye when that organ needs protection. The
eye itself is pyriform, somewhat resembling the round
figure of the human eye-ball, with its optic-nerve attached.
In colour it is very dark, having a central pupillary-open-
ing for the admission of light. The tentacle, which is cylin-
drical in the young animal, becomes flat and triangular in
shape in the adult. The young animal is for some time
without teeth; consequently, it does not very early betake
itself to a vegetable sustenance : in place of teeth it has
two rows of cilia, as before stated, which drop oft* when the
teeth are fully formed. The lingual band bearing the
teeth, or the " tongue," as it is termed, consists of several
rows of cutting spines, pointed with silica.
It is a fact of some interest, physiologically, to know
that if the young animal is kept in fresh water alone,
without vegetable matter of any kind, it retains its cilia,
but arrest of development follows, and it acquires no
gastric teeth, and never attains perfection in form or size.
GASTEROPODA.
If, at the same time, it is confined within a narrow cell, or
space, it grows only to such a size as will enable it to move
about freely; thus it is made to adapt itself to the neces-
sities of a restricted state of existence. Some young
animals in a narrow glass-cell, at the end of six months,
were alive and well, and the* cilia retained around the
tentacles in constant activity; whilst other animals of the
same brood and age, placed in a situation favourable to
growth, attained their full size, and produced young, which
grew in three weeks to the size of their elder relations.
Should any injury occur to the shell, or a portion of it
become broken off, the calcareous deposit is quickly resumed,
in order to replace the lost part; the cells being apparently
only half the size of those originally deposited. This
may be thought to afford some proof of the statement
made by Sir. Jas. Paget, " that, as a rule, the reparative
power in each perfect species, whether it be higher or
lower in the scale, is in an inverse proportion to the
amount of change through which it has passed in its
development from the embryonic to the perfect state.
And the deduction to be made from them is, that the
powers for development from the embryo are identical
with those exercised for the restoration from injuries ; in
other words, that the powers are the same by which per-
fection is first achieved, and by which, when lost, it is
recovered. Indeed, it would almost seem as if the species
that have the least means of escape or defence from
mutilation were those on which the most ample power of
repair has been bestowed, an admirable instance, if it be
only generally true, of the beneficence that has prepared
for the welfare of even the least of the living world, with
as much care as if they were the sole objects of the Divine
regard."
The primordial cell-wall of the cell does not appear to
enter into the formative process of the embryo the cell-
contents alone nourishing the vital blastema of the nucleus.
A gradual cycle of progressive development once set up,
goes on, until the animal is sufficiently matured to break
through the cell- wall and escape from the ova-sac. At
the same time, it may be inferred, that all this is in some
measure aided by the process of endosmose ; and that cer-
550 THE MICROSCOPE.
tain gases or fluids are drawn into the interior, and thus aid
in the supply of nourishment for the growth of the animal.
The cell- wall appears to bear the same relation to the
future perfect animal that the egg-shell of the chick does
to it ; it is, in fact, hut an external covering to a certain
amount of gaseous and fluid matter, used for placing the
germ of life in a more favourable state for development,
assisted, as it is, by an increase of temperature, usually
the resultant of a chemical action, set up or once begun
in an organism and a medium. " The ovum destined to
become a new creature originates from a cell, enclosing
gemmules, from which its tissues are formed, and nutriment
is assimilated, and which eventually enables the animal to
successively renew its organs, through a series of meta-
morphoses that give it permanent conditions, not only
different, but even directly contrary to those which it had
primitively."
Cephalopoda. Molluscous animals without a foot, or
a distinct head, and covered with fleshy arms, bearing
sucker-like discs. The Cuttles and Squids form the prin-
cipal groups of this class, only a few species of which are
found on our shores. These molluscs are the nearest
approach of all invertebrate animals to the vertebrate
forms ; and their organs of sense appear to be highly de-
veloped. 1 Cuttle-fish bone, cut in thin sections, or broken
into small fragments, are interesting microscopic objects :
the peculiarities of structure are best seen when small
pieces are detached with a sharp knife. In the living
state these creatures have the power of suddenly changing
the colour of their skins.
Structure of Shell. We may exhibit the structure of
shell by using an acid solvent in the following manner.
If a sufficient quantity of hydrochloric acid, considerably
diluted with water (say one part acid to twenty-four of
water), be poured upon a shell contained in a glass vessel,
it will soon exhibit a soft floating substance, consisting of
innumerable membranes, which retain the figure of the
shell, and afford a beautiful and popular object for th3
(1) In the Cephalopoda \?e have the first indication of a true internal
skeleton, in the form of a broad flattened cartilage which protects the central
Coptic) ganglia of the nervous system.
STRUCTURE OP SHELL. 551
microscope. In analysing shells of a finer texture than
such as are generally submitted to the test of experiment,
the greatest circumspection is necessary. So much so,
that M. Herissant, whose attention was particularly devoted
to the subject, after placing a porcelain shell in spirits of
wine, added, from day to day, for the space of two months,
a single drop of spirits of nitre, lest the air, generated or
let loose by the action of the hydrochloric acid on the
earthy substance, should tear the net-work of the fine
membranaceous structure. This gradual operation was
attended with complete success, and a delicate and beauti-
fully reticulated film, resembling a spider's web in texture,
rewarded the patience of the operator ; the organization of
which film, from its extreme fineness, he was not, however,
able to delineate. In shells of peculiar delicacy, even five
or six months are sometimes necessary for their complete
development ; but in others of a coarser texture the process
is soon completed. Sections of shells are usually mounted
in Canada balsam, or in shallow cells with glycerine.
Mr. George Eainey pointed out the remarkable fact
that many of the appearances presented by the shell or
hard structures of animals, and which had been usually
referred to cell-development, are really produced by the
physical laws which govern the aggregation of certain crys-
tallizable salts when exposed to the action of vegetable and
animal substances in a state of solution. Mr. Eainey gives
a process for obtaining artificially a crystalline substance
which closely resembles shell in its chemical structure.
" The chemical substances to be employed in the pro-
duction of the artificial calculi are, a soluble compound of
lime, and carbonate of potash or soda, dissolved in separate
portions of water; and some viscid vegetable or animal
substance, such as gum or albumen, mixed with each of
these solutions. The mechanical conditions required to
act in conjunction with the chemical means are, the pre-
sence of such a quantity of the viscid material in each
solution as will be sufficient to make the two solutions,
when mixed together, of about the same density as that of
the nascent carbonate of lime, and a state of perfect rest
of the fiuid in which the decomposition is going on, so
that the newly-formed compound may be interfered with
552 THE MICROSCOPE.
as little as possible in its subsidence to the sides and
bottom of the vessel. This will require two or three
weeks, or longer, according to the size and completeness*
of the calculi. But I have not found that they increase-
at all after six weeks."
Mr. Eainey shows 1 the analogy or identity of his arti-
ficially formed crystals with those found in natural pro-
ducts both in animals and vegetables, chiefly confining
himself to the structure and formation of shells and bone r
pigmental and other cells, and the structure and develop-
ment of the crystalline lenses, which he contends are all
formed upon precisely the same physical principles as the
artificial crystals. Take, for instance, the calculi found in
the body : these cannot be distinguished from the crystals
of artifically formed carbonate of lime. Again, the shell
of the crustaceans ; the resemblance between these and the
artificial products is, in some respects, more complete than
in that of calculi. All the appearances in shells can,
be best observed by merely cleaning them in water, and
examining them in glycerine, grinding being unnecessary
and injurious. Polarised light is indispensable ; as in the
young hermit-crab, at the part where the calcareous and
membranous portions of the shell are continuous, the cir-
cular forms of globular carbonate are so delicate that no-
evidence whatever of its presence can be detected under
powerful lenses, and with the best illumination, until
polarised light is brought to bear upon the specimen. To
obtain the most satisfactory results in the investigation of
the process of calcification of animal tissues, it is indis-
pensably necessary that the parts examined should be in
the earliest stages of the process, and before the calcifying
membrane is entirely covered with the globular coalescing
deposit. The usual plan of examining shells in thin
vertical sections is entirely useless, unless it be simply to
see the number and arrangement of their layers ; the part
of the section in such specimens, in which the calcifying
process ought to be best seen, being entirely ground off.
This part, being the softest, can only be preserved in
the process of grinding by extreme care, and by keep-
(1) G. Rainey, "On the Mode of Formation of Shells, Bone, &c. by aprooae oj,
Molecular Coalescence." 1858.
STRUCTURE OP SHELL. 553
ing the lower edge of the section always thicker than the
upper.
Dr. Carpenter describes the shell of the Crab and Lobster
as being composed of three layers, viz. the epidermis 01
cuticle, the rete-mucosum or pigment, and the coriuin.
The epidermis is of a horny nature, being generally more
or less brown in colour, and under the highest magnifying
powers presenting no trace of structure (fig. 247, No. 2) ;
it invests all the outer parts of the shell, and has in many
instances large cylindrical or feather-like hairs developed
from certain portions of its surface. The rete-mucosum,
or pigment cells, consist of either a series of hexagonal
cells, forming a distinct stratum, or of pigmental matter
diffused throughout a certain thickness of the calcareous
layer. (Fig. 247, No. 5.) In the Crab and Lobster it is
very thin, but in the Crayfish it occupies in some parts
more than one-third of the entire thickness of the shell ;
when examined by the microscope, this portion appears to
be composed of a large number of very thin laminae, which
are indicated by fine lines taking the same direction on
the surface of the shell, the number of lines being the
greatest in the oldest specimens ; these layers, even in the
Crayfish, are covered 'by a thin stratum of very minute
hexagonal cells, without any trace of cell matter in their
interior. The corium is the thickest layer of the three,
being the one on which the strength of the shell depends,
in consequence of the calcareous material deposited in it.
(Fig. 247, No. 4.) When a vertical section of the shell of
the Crab is examined, it is found to be traversed by parallel
tubes, resembling those in the dentine of the human tooth ;
these tubes extend from the inner to the outer surface of the
shell, and are occasionally covered by wavy lines, probably
those of growth, shown in a portion of No. 3, fig. 247. If
a horizontal section of the same shell be made, so that the
tubes be divided at right angles to their length, the sur-
face will clearly exhibit their open ends, surrounded by
calcareous matter. In Shrimps and very small Crabs, the
deposition of the calcareous matter takes place in concen-
tric rings like those of agate ; and occasionally small cen-
tres of ossification, somewhat like Pinna, with radiating
striae, are met with in the Shrimp. If the calcareous
554
THE MICROSCOPE,
portion of the shell be steeped in hydrochloric acid, a
distinct animal structure or basis is left behind, and the
characters of the part will be very accurately preserved.
The calcareous matter, like that of bone, generally pre-
sents a more or less granular appearance, as at "No. 4, and
so angular in figure as to resemble certain forms of rhom-
boidal crystals : JS"o. 2 is a section from the outer brown
shell of the Oyster. The beauty of all such structures is
much increased if viewed with polarised light on the
selenite stage. 1
Crustacea. The skeletons of Crustacea are external to
the soft parts ; in a great number of species the shell is
thin and membranous, in others it is of a horny material,
thickened with calcareous matter, having a distinct serios
of pigment cells of a stellate
figure, all supplying beautiful
objects for microscopic examina-
tion and polarised light. The
Astacus, Crayfish, may be taken
as the type of that large and
important group of Crustacea to
which the term Podophthalma,
Stalk-eyed, is applied. 2
Cirrkopoda or Cirripedia,
when mature, attach themselves
to rocks and other objects. The
Barnacle (fig. 254) and Acorn-
shell are the best known exam-
ples of this order; they gene-
rally select floating objects to
L, Young fry of the Oyster, a dwell upon ; and bottoms of
portion of them with cilia <VhirQ "hovp "hppn rnvprpH Twtlipni
protruded. 2, Body and cirri bill P s nave ' L Dy tl
of Barnacles. to such an extent as even to
impede their progress through the water. The soft bodies
of these animals are enclosed in a case composed of five
calcareous plates ; from this circumstance they were
grouped with the multivalve shells of the older ccncholo-
(1) See Prof. Huxley's article on the "Tegumentary Organs," Cyclop. Anut.
and Physio, vol. v. p. 487.
(2) Some valuable information will be found on the minute structure of shells
In Prof. Williamson's paper, " On some Histotogical Features in the Shells ol
Ihe Crustacea," Journ. Micros. Scien. vol. viii. p. 35, 1860.
Fig. 254.
ENTOMOSTRACA. 555
gists. Their limbs are converted into tufts of jointed
cirri, and protrude through an opening in the mantle
which lines the interior of the shell. The cirri, twelve
in number, are covered with cilia, which, when the animal
is alive, are in continual motion. The intestinal canal is
complete, and the nervous system exhibits the usual
series of ganglia, characteristic of the articulate type.
The head is marked only by the position of the mouth,
and is armed with a pair of jaws, if we may so term
the shells.
Salanidce, " Sea-acorns," a sessile species, whose curious
little habitations may constantly be met with upon the
rocks of the sea-shore, and not unfrequently upon many
species of marine shells. The shell forms a short tube,
and is usually composed of six segments securely united
together. The lower part of the tube is firmly fixed to the
object 011 which the Ealanus has taken up its abode ; whilst
the superior orifice is closed by a movable roof, composed
of from two to four valves, between which the little tenant
of this curious domicile protrudes his delicate cirri in search
of nourishment. In the young state the Balanidce freely
swirn about, and somewhat resemble the following group,
Entomostraca.
Entomostraca, or Water-fleas, undergo a series of remark-
able changes from the moment of their escape from the
egg to the attainment of their fully matured form. And
it is of the highest interest to remark that, in obedience
to a law which, if not universal, is at any rate widely pre-
valent in the animal kingdom, these temporary or larval
forms are themselves closely analogous to the prefect forms
of groups still lower in the scale of existence, so that many
of them in their early forms were formerly, before their
life-history was known, either classed as distinct species, or
placed in a position very far from that which they are now
seen to occupy. The embryo of the Shore-crab (Carcinus
moenas) before, and for a short time after, its liberation
from the ovum, presents both in size and general outline
a strong resemblance to Entomostraca. In this transi-
tion stage it was assigned to a distinct genus under the
aaine of Zoea ; and having undergone a still further trans-
formation \vas called Megalopa. In this latter stage it
656
THE MICROSCOPE.
puts on somewhat the appearance of the Lobster crab
(Galathea), and after another step attains its true crab
form, being the highest development of which it is capable.
These changes are not produced gradually, but by a suc-
cession of " moults," the animal becoming at times sluggish,
casting its hard covering, and reappearing in a new guise.
The after growth of a crustacean is carried on by the system
of moulting ; the hard calcareous case of the animal pre-
venting its growth in any other mode. And as in the
higher orders of Crustacea, so also amongsb the Entomos-
traca, transformations of this kind constantly take place.
Cyclops quadricornis, when first born, is totally unlike its
parents, being of an ovoid shape, having only two shoit
antennae and two pairs of feet ; in three moults the
animal reaches its perfect form, with its two pairs of an-
tennae, five pairs of feet, and body divided into several
distinct rings or segments.
The animals comprising the order Ostracoda are generally
of very minute size ; the body,
which strongly resembles that
of the Copepoda, is always
enclosed in a little bivalve
shell, the feet and antenna}
being protruded between the
lower edges of the valves.
These little shells so closely
resemble those of minute
bivalve Mollusca, that those
of some of the larger species
have actually been described
by conchologists as the cover-
ing of animals belonging to
that class. The antennae are
often curiously branched ; and
the hinder extremity is usu-
ally prolonged into a sort of
tail, which is seen in constant
action when the animal is in
motion ' In Oypridina, the
body is entirely enclosed by
a shell, of which the genus Cypris (fig. 25f>) is an example ;
Fig. 255.
ENTOMOSTRACA, 557
and in Daphnia, " Water-fleas," the head is protruded be-
yond the shell. In Polyphemidce the head is large, and
almost entirely occupied by an enormous eye, giving the
creatures a most singular appearance ; the Monoculus is
a well-known example of this group. Another family,
not provided with a shell or carapace, called Branchio-
poda, from the name of the typical genus, Branchiopus
stagnalis (fig. 255), is often found after heavy rains in
cart-ruts and other small pools.
Daphnia pulex is found commonly in fresh water, and
is scarcely inferior to its marine relative, Talitrus locusta,
in agility. The Corophium longicorne, remarkable for its
long antennae, is not less so for its singular habits. It
is found at Eochelle, where it burrows in the sand, and
wages constant war with all other marine creatures of
moderate size that come in its way.
Dr. Baird has followed up the successive generations in
Daphnia pulex ; so far as the fourth change in the Daphnia
born from the ordinary ova, and so far as the third in those
born from the ephippial eggs. These ephippia, or " winter
eggs," require a few words of explanation. They are, in fact,
eggs covered with envelopes of more than usual hardness
and thickness, being enabled to withst-and an excess of
cold, which would surely prove fatal to the parent. This
observer found, upon examining ponds which had been
filled up again by the rain after remaining two months
dry, numerous specimens of the Cyclops quadricornis in
all stages of growth. Dr. Baird, in his " Natural History
of British Entomostraca," 1850, tells us that they have
many enemies.
" The larva of the Corethra plumicornis, known to micro-
scopical observers as the skeleton larva, is exceedingly rapa-
cious of the Daphnia. Pritchard tells us they are the choice
food of a species of Nais ; and Dr. Parnell states that the
Lochlevin trout owes its superior sweetness and richness of
flavour to its food, which consists of small shell-fish and En-
tomostraca." These animals abound both in fresh and salt
water. A rtemice are formed exclusively in salt water, in salt
marshes, and in water highly charged with salt. " Myriads
of these Entomostraca are to be found in the salterns at
Lymington, in the open tanks or reservoirs where the brine
658 THE MICROSCOPE.
is deposited previous to boiling. A pint of the fluid
contains about a quarter of a pound of salt, and this con-
centrated solution, destroys most other marine animals."
During the fine days in summer Artemice may be observed
in immense numbers near the surface of the water, and, as
they are frequently of a lively red colour, the water appears
tinged with the same hue. 1 There is nothing more elegant
than the form of this little animal. Its movements are
peculiar. It swims almost always on its back, and by means
of its tail it runs in all directions, its feet being in constant
motion. They are both oviparous and ovoviviparous, accord-
ing to the season of the year. At certain periods they only
lay eggs, while during the hot summer months they pro-
duce their young alive. In about fifteen days the eggs are
expelled in numbers varying from 50 to 150. As is the
case with many of the Entomostraca, the young present a
very different appearance from the adult animals ; and
they are so exactly like the young of CMrocephalus, that with
difficulty they can be distinguished the one from the other.
The ova of other species are furnished with thick cap-
sules, and imbedded in a dark opaque substance, presenting
a minutely cellular appearance, and occupying the inter-
space between the body of the animal and the back of the
shell. This is called the ephippium. 2 The shell is often
beautifully transparent, sometimes spotted with pigment :
it consists of a substance known as chitine, impregnated
with a variable amount of carbonate of lime, which pro-
duces a copious effervescence on the addition of a small
quantity of acid, and when boiled it turns red, like the
lobster. Their shells vary in structure. Sometimes they
consist of two valves united at the back, and resembling
(1) It is a curious fact that salt-water when highly concentrated frequently
assumes a red colour, and that this should have been attributed to the presence
of the Artemia salina, as in the case of fresh-water noticed elsewhere found
coloured red by a species of Paramcecmm.. The cause of this red colour, which
was well known to take place in the salt marshes and reservoirs of salt-water
at Montpellier, was made the subject of a very grave discussic a in France.
Some maintained that the colour was caused by the presence of A rtemice, while
others declared that it arose from vegetable matter, either HcKmatococcus or
Protococcus. M. Joly, came to the conclusion, after many careful examinations,
that the red colour depends upon the presence of myriads of monads, and that
the Artemice living upon these partook of the same red hue, and thus the water
appeared to be of the same colour.
(2) See paper on " Reproduction in DapJinia," by Sir John Lubbock, PAiZoj,
Trans 1857, p. 79.
ANNUL0SA. 559
the bivalve shell of a mussel ; others are simply folded at
the back, so as to appear like a bivalve, but are really
not so ; or they consist of a number of rings or seg-
ments. The body of the Cypris presents a reticulated
appearance, resembling that of cell structure. All the
Entomostraca are best preserved in a solution of chloride
of calcium.
ANNULOSA. Articulata. The animals composing the
sub-kingdom Articulata are characterised by having the
body enclosed in a tunic, or integument, consisting of a
series of rings, segments, or joints, " articulated ;> together
by a flexible membrane.
The Annulosa are divided, by Professor Huxley, into
two principal groups, the Arthropoda and the Annuloida.
The Arthropoda, comprising Inseckt, Myriapoda, Crustacea,
and Arachnida, possess a definitely segmented body ; the
segments being provided with appendages, the anterior of
which are so modified as to subserve the functions of sen-
sation and manducation. They have almost always a heart,
communicating with the general cavity of the body, for
propelling the true corpusculated blood which that cavity
contains. The nervous system consists of a longer or a
shorter chain of ganglia,
Nothing can be more variable than the characters of the
body, the appendages, and the nervous system, among the
rest of the Annulosa, which are included under the Annu-
loida; nevertheless, there are two features in which they
all agree ; firstly, they possess a remarkable system of
vessels, either ciliated, or deprived of cilia, and containing
a fluid very different from the true blood which fills the
general cavity of the body or perivisceral space ; secondly,
in no annuloid animal has any true heart been hitherto
discovered. Contractile vessels belonging to the system
just referred to abound, but no organ comparable in struc-
ture to the heart of other animals has yet been found in
any of the Annuloida.
The Annuloida, as thus defined and limited, fall into
two parallel series ; in one of which, for the most part,
dioecious forms predominate, as the Annelida, while of
the latter, the Trematoda may be regarded as the typical
example ; on the other hand, the Echinodermata and
560 THE MICROSCOPE.
Rotifera, the Tceniadce and the Nematoidea, may be con-
sidered as the most aberrant groups of their respective
series.
Under the head Annelida, Mr. Huxley includes the
errant and tubicular Annelids of Cuvier, and the Gephyrea
of De Quatrefages; he thinks that the Terricola the
Earthworms and Naides should be separated from the
Scoledce of Milne Edwards, and brought into the same
group. So far as external structure is concerned, the
genus Polynoe is, perhaps, the best fitted to serve as the
type to which other Annelida may be referred: the com-
monest form of the genus being the P. squamata. 1 The
best developed branchiae among the Annelids are possessed
by the Amphinomidce, the Ennicidce, the Terebellidce, and
the Serpulidoe. The branchias in the three former families
are ciliated, branched plumes or tufts attached to the
dorsal surface of more or fewer of the segments. In the
last they are exclusively attached to the anterior segments
of the body, and present the form of two large plumes,
each consisting of a principal stem, with many lateral
branches; this stem is itself supported on a kind of
cartilaginous skeleton.
The teeth in a great number of the Annelida are very
curious and distinctive. In the Polynoe there are four,
planted in the muscular wall of the proboscis. In the
Nereis there are two powerful teeth working horizontally,
besides minute accessory denticles. In Syllis there is a
circle of sharp teeth, surrounding a triangular median
tooth. In Glycera there are a pair of teeth ; but the most
complex arrangement of teeth is that presented by the
Ennicidce. The tubicular Annelids possess neither pro-
boscis nor teeth.
Many Annelids pass through a larval condition, in
which the body exhibits mere indications of segments,
and the appendages are entirely absent; locomotive
function being performed by a circlet of cilia, disposed
around the anterior part of the body. There is a large
group of very remarkable organisms, observes Mr. Huxley,
the minute " wheel animalcules," JRotifera, whose whole
(1) Consult a valuable paper on this genus in Miiller's Archiv. 1857. Alo
Huxley's "Elements of Comparative Anatomy."
ANNULOBA. 561
organization demonstrates, not merely their annulose
nature, but their position among the Annuloida, and
which exhibit precisely the same indistinct segmentation,
the same general absence of appendages, and whose means
of locomotion are in like manner confined to one or two
ciliated circlets at the anterior part of the body. The
connexion between the Annelida and the Rotifera is
further illustrated by such remarkable forms as the
Polyophthalmus of De Quatrefages, a true Annelid, which,
nevertheless, possesses on each side of the head a ciliated
lobe, capable of being voluntarily protruded and retracted,
and presenting a close resemblance to the trochal disc of a
Rotifer. Hydatina senta has been so well and accurately
described by Dr. Cohn, 1 and others, that it may be taken
as the typical form of the Rotifera. The trochal disc in
the species, undergoes great changes of form. In Hydatina,
it is circular, and its margin is skirted by two distinct con-
tinuous bands of cilia, the one immediately in front of, the
other behind the mouth. In Brachionus the ciliated circlet
fringing the edges of the trochal disc is horseshoe-shaped,
but the circlet is produced into three lobes or processes,
which stand out perpendicularly to the surface of the.
trochal disc. In Stephanoceros it fringes the edges of a
number of tentaculiform processes, into which the trochal
disc is produced, so as to give the whole animal somewhat
the appearance of a Polyzoon.
The Turbellaria, a group of serpent-like worms, for
the most part the inhabitants of fresh and salt waters, a
few only being found in damp siuations on land, are
characterised by the ciliation of the entire surface of the
body. In their internal organisation they approximate in
many respects to the Trematoda, while in others they
exhibit a certain affinity with the other great group of
parasitic Annuloida, the Nematoidea. Polycelis Icevigatus,
one of the Dendrocoela so well described by De Quatrefages
in his Monograph on the Marine Planarice, may be most
advantageously selected as a type of the group. The
Nernertida* have engaged the attention of the same learned
authority, the ova of which undergo a remarkable kind of
(1) Ueiter die Fortflawzung der Raderihiere, Von Dr. F. Cohn, in Breslau
O
562 THE MICROSCOPE.
metamorphosis. The embryo has at first a ciliated non-
contractile, oval body, exhibiting no structure but a semi-
lunar superficial cleft, provided with raised edges. After
a time, a small actively-contractile, vermiform creature,
resembling the parent, escapes from the interior of the
larval form, which it leaves behind like a cast skin. The
semiluuar cleft becomes the mouth of the imago, and is
only part of the larva carried away. The Gordiacei l best
enable us to connect the Turbellaria with the very puzzling
group Nematoidea, and the structure of several species
belonging to the two genera which compose the group
Mermis and Gordius, have recently been made the subject
of two elaborate monographs by Meissner. 2
The Gordiacei are excessively elongated, thread-like
worms, plentiful enough in Thames rnud, and, as Von
Siebold discovered, partake both of the free habit of the
Nemertidw, and of the parasitic nature of the Nematoidea.
The young Mermis, for instance, is parasitic upon insects,
inhabiting the perivisceral cavity of the larva or of the
imago.
The Nemertidcc seem to differ from their close allies the
Turlellaria, in possessing a va??ular system distinct from
and added to the water-vessels. In the Hirudinidce, Leeches
and Earthworms, a system of vessels homologonous with
the pseud-hsernal system exists, and, in addition a series
of more or less coiled tubules lie in the perivisceral cavity,
and open, by pores, on the ventral surface of the body.
These organs have been regarded sometimes as secretory,
sometimes as respiratory apparatus; but all that we
know about them in reality is that they are tubular, and
are more or less richly ciliated within, and that, in some
cases (Nais, Lumbricus), they present at their internal ex-
tremities a ciliated aperture, whereby they freely com-
municate with the perivisceral cavity.
There remains, however, yet another system of vessels
in the Annuloida the ambulacral vessels of the Echino-
dermata. These are frequently termed " water- vessels,"
and, indeed, if we regard the structure with reference to
(1) Huxley, General Natural History.
(2) Beitrdge zurAnatomie und Physiologic von Mermis Albicaus, v. Zeitschrift
fiir Wiss,Zoologie, Bd. v 1854 ; and Beitrdge zurAnat. $ Physiol. des Gordiacen,
Ibid Bd. vii 1855.
ANNULOSA 563
aeir peculiar functions, they singularly resemble true
water-vessels; they open by an external pore, and are
ciliated internally ; they unite around the gullet, as do the
water- vessels in some Trematoda, and are eventually shut
off from such communication ; the ambulacral vessels of
the Holothuridoe undergo precisely this change, and thus
they facilitate our comprehension of a transition from the
water-vessels of the Trematoda to the pseud-hsemal vessels
of the Annelida. We may take it as an established fact
that, whatever the functions of this varied vascular system
and its contents in different classes of the Annuloida,
they have nothing to do with the blood or true blood
vessels. The latter are entirely absent in all the Annu-
loida at present known, the blood (improperly called
" chyle-aqueous fluid ") being simply contained in the peri-
visceral cavity and its processes. The development of
the Nematoidea appears to take place without metamor-
phosis ; the embryo assuming within the egg a form nearly
resembling that of the adult. Encysted asexual nematoid
worms are frequently found in various parts of the body
of fishes; and the remarkable Trichina spiralis is the
asexual state of a nematoid worm, encysted within the
substance of the muscles of man. Zooid development is
only known to occur in one nematoid, the Filaria Medi-
nensis, Guinea-worm. Mr. Busk's careful observations
have long since placed this fact beyond a doubt.
The Tceniadce and the Acanthocephala, like the Trema-
toda, entirely parasitic in their habits, differ from them in
the total absence of mouth or digestive cavity. The
Taniadce, Tapeworms, are ribbon-like creatures, usually
divided throughout the greater part of their length into
segments, whose usual habitation is the intestinal cavity
of vertebrate animals ; and appai'ently of a carnivorous
vertebrate, in fact, though capable of existence elsewhere,
it is there alone that they are able to attain their complete
development. The anterior extremity of a tsenoid worm
is usually called the head, and bears the organ by which
the animal attaches itself to the mucous membrane of the
creature which it infests. These organs are either suckers
or hooks, or both conjoined. In Tcenia, four suckers are
combined with a circlet of hooks, disposed around a median
oo 2
564 THE MICROSCOPE.
terminal prominence. The embryo passes through a
similar course of development to the Trematoda; viz.
four forms or changes : but the embryo itself is very
peculiar, consisting of an oval non-ciliated mass, provided
upon one face with six hooks, three upon each side of the
middle line. The Tceniadce are found in many other
situations besides the alimentary canal : the eye, the brain,
the muscular tissues, the liver, &c. ; the following cystic
worms are included in this genera, Cysticercus Anthoce-
p/talus, Ccenurus, and T. E chine-coccus. Plate IV. No. 100,
this figure shows an entire and full-grown Tcenia with
rostellum and suckers, and then three succeeding segments,
the last of which contains the ova, &c. The water-vascular
system is represented coloured with carmine. This para-
site infests the human body more frequently than other
varieties. This accuratelv-drawn figure is copied from
Cobbold.
Von Siebold, Leuckart, and others, have shown, by many
interesting experiments, such as feeding puppies with Cys-
iicercus pisiformis, that in the course of a few weeks these
tntozoa are transformed into fully formed Tcenia serrata ,
again, rabbits fed with the embryo of the Tcenia, the
embryo bore their way, by means of hooks, through the
walls of the intestine, until they reach some blood-vessel :
by the current of blood they are carried into the liver,
and here Leuckart has traced their further development.
The embryos grow to the 1-1 6th of an inch in length, and
become elongated, so as almost to resemble an Ascarid in
form ; they then make their way to the surface of the liver,
and pass out into the peritoneal cavity.
In like manner, Cysticercusfasciolaris is rapidly developed
within the liver of white mice ; Cysticercus cellulosce seen
in the muscles of the pig fed with the Tcenia solium, pro-
duces the diseased state of pork familiarly known as
" measly pork" If a larnb is the subject of the feeding
experiment with Tcenia serrata, the final transformation
will be very different ; within a fortnight, symptoms of 'a
disease known as "staggers" are manifested, and in the
tourse of a few weeks, the Ccenurus cerelralis will be found
transformed and developed within the brain. Von Siebold
pointed out the bearing of this fact upon the important
TREMATODA. 565
practical problem of the prevention of " staggers." Others
of the same family of parasites are quite as remarkable, in
giving a preference to the alimentary canal of fishes. The
JEchinorhynchus is developed in the canal of the Flounder,
Tricenophorus nodulus in the liver of the Salmon, attain-
ing a more perfect development in the alimentary canal of
the Perch and Pike. Another, found in the Stickleback,
becomes changed in the intestines of water birds, which
devour these fish ; and thus, by careful and repeated
observations with the microscope, the connexion existing
between the Cystic and Cestoid Entozoa have been most
satisfactorily established.
The Fluke belongs to the order Trematoda, which
signifies that they are internal parasites, suctorial worms,
or helminths ; they are all usually visible to the naked
eye, although a few of the smallest scarcely exceed l-100th
of an inch in length ; many are larger, and the species best
known, Fasciola Jiepatica, attains to an inch or more in
length. The Fluke shown in Plate IV. No. 103, is cone-
shaped : it is the Amphistome conicum of Kudolphi. This
parasite is common in oxen, sheep, and deer, and it has also
been found in the Dorcas antelope. It almost invariably
takes up its abode in the first stomach, or rumen, attaching
itself to the walls of the interior. 1 In the full-grown state
it never exceeds half an inch in length ; in our plate it is
represented magnified. On closer inspection it will be seen
that the animal is furnished with two pores or suckers, one
at either extremity of the body, the lower being by far the
larger of the two. By means of the latter the Amphistome
anchors itself to the papillated folds of the paunch, or first
stomach, as this organ is improperly called.
In the figure the oral sucker at the anterior end, or head,
leads into a narrow tube, forming the throat or oesophagus,
and this speedily divides, or rather widens out, into a pair
of capacious canals. These cavities are correctly regarded
(1) The larval condition of AmphiiAoma in all probability lives in or upon the
body of snails. This we infer from the circumstance that the larvae, cercarice,
of a closely allied species, the Amphistoma subclavatum, which is kuown to infest
ihe alimentary canal of frogs and newts, have been also found on the surface of
the body of the Planorbis by ourselves, whilst Van Beneden discovered the
larvse in a species of Cyclas. The cercarice, larvae, are taken, it is supposed, by
the cattle while drinking. They then a1 ^ch themselves to the walla of the
itomach, where they soon complete their further stigea of development
566 THE MICROSCOPE.
as together constituting the stomach ; but they are caeca],
that is, closed below, having no other outlet than the
entrance above mentioned. The water-vascular system,
artificially coloured in the plate, or rather the vessels thus
named, bear a very striking resemblance to that of arteries
or veins ; and the centrally-placed pouch, shown in the
figure, might very easily be taken to represent the heart.
This large cavity gives origin to two primary trunks, which
pass forward along the inner sides of the digestive caeca ; in
their passage they send off secondary branches, which divide
and sub-divide until we arrive at a series of minute capil-
lary ramifications ; the latter, according to Blanchard,
terminating in small oval-shaped sacs or lacunre.
" It should be further observed, that the surface of the
Amphistome, though quite smooth to the naked eye, is
clothed with a series of minute tubercles, which may be
readily brought into view under a half- inch object glass.
Beneath the cuticle we find a layer of cellules forming the
true skin ; and beneath this, again, there are two, if not
three, layers of muscular fibre ; an anterior longitudinal
series and an inner circular set being readily distinguish-
able. The substance of the body is traversed by bands of
cellular parenchyma or connective tissue, which here and
there form thickened sheaths for the support of the various
delicate organs above described." The reproductive organs
of flukes possess the greatest amount of interest both from
an anatomical and physiological point of view. They are
produced from eggs, which are found in large numbers in
the ova-sac ; varying in size from l-150th to l-250th of
an inch,
"'The large fluke (Fasciola hepatica) is not only of
frequent occurrence in all varieties of grazing cattle, but
has likewise been found in the horse, the ass, and also in
the hare and rabbit, and in some other animals. Its occur-
rence in man has been recorded by more than than one
observer ; the oral sucker forming the mouth leads to the
short oasophagus, which very soon divides into two primary
stomachal or intestinal trunks, which latter in their turn
give off branches and branchlets ; the whole together form-
ing that beautiful dendritic system of vessels which has
often been compared to plant-venation. This remarkably-
TREMATODA. 567
formed digestive apparatus is accurately represented in
Plate IV. Nos. 106 and 107, Fasciola gigantea of Cobbold,
which should be contrasted with the somewhat similarly
racemose character of the water- vascular system. Let it be
expresely noted, however, that in the digestive system the
majority of the tubes branch out in a direction obliquely
downwards, whereas those of the vascular system slope
obliquely upwards. A further comparison of the dis-
position of these two systems of structure, with the
same systems figured and described as characteristic of
the Amphistome, will at once serve to demonstrate the
important differences which subsist between the several
members of the two genera, if we turn to the con-
sideration of the habits of Fasciola hepatica, which,
in so far as they relate to the excitation of the liver
disease in sheep, acquire the highest practical import-
ance. Intelligent cattle-breeders, agriculturists, and veteri-
narians have all along observed that the rot, as this
disease is commonly called, is particularly prevalent after
long-continued wet weather, and more especially so if
there have been a succession of wet seasons ; and from this
circumstance they have very naturally inferred that the
humidity of the atmosphere, coupled with a moist condi-
tion of the soil, forms the. sole cause of the malady. Co-
ordinating with these facts, it has likewise been noticed that
the flocks grazing in low pastures and marshy districts are
much more liable to the invasion of this endemic disease
than are those pasturing on higher and drier grounds ; a
noteworthy exception occurring in the case of those flocks
feeding in the salt-water marshes of our eastern shores." 1
Plate IY. IsTo. 106, Fasciola gigantea: the anterior surface
is exposed to display oral and ventral suckers, and the
dendriform digestive apparatus injected with ultramarine ;
Ifo. 107, shows the dorsal aspect of the specimen and
the multiramose character of the water- vascular system,
tie vessels injected with vermilion.
One of the most remarkable of the Trematode helminths
is Bilharzia hcematobra of Cobbold ; Distomia hcematobium
of some other authors. Plate IV. No. 102. This genus
(1") Sntozoa: An Introduction to the Study of Helminthology. By T. Spencer
CobWd. M.D. F.R.S. 1866. P. 148.
668 THE MICROSCOPE.
of fluke, discovered by Dr. Bilharz in the human portal
system of blood vessels, gives rise to a very serious state of
disease among the people of Egypt. So common is the
occurrence of this worm, that this physician expressed his
belief that half the grown-up people are infested with it.
Griesinger conjectures that the young of the parasite exists
in the waters of the Nile, and in the fishes which abound
therein. Dr. Cobbold thinks "it more probable that the
larvae, in the form of cercarise, redise, and sporocysts, will
be found in certain gasteropod mollusca proper to the
locality." The anatomy of this fluke is fully described in
Kuchenmeister's able work on Parasites, by Leuckart, and
by Cobbold. The eggtt and embryos of BilJiarzia are
peculiar in possessing the power of altering their forms in
both stages of life ; and it is more than probable that the
embryo form has been mistaken for some extraordinary
form of ciliated infusorial animalcule, their movements
being most quick and lively. AVe cannot fail to notice
the curious leech-like form of the male animal, and, re-
markable enough, he is generally found carrying the female
about. The whip-like appendage seen in the figure is a
portion of the body of the female. The disease produced
by them is said to be. more virulent in the summer months,
which is probably owing to the prevalence of the cercarian
larvas at the spring time of the year.
Trichina spiralis. This, the smallest of the helminth.*,
measures only the l-20th of an inch. The female is a little
larger j it was discovered by Professor Owen in a portion
of the human muscle sent to him from St. Bartholomew's
Hospital, 1834. The young animal presents the form of
a spirally- coiled worm in the interior of a minute oval-
shaped cyst (Plate IV. No. 104), a very small speck
scarcely visible to the naked eye. In the muscle it resem-
bles a little particle of millet seed, more or less calcareous
in its composition. The history of the development of
Trichinae in the human muscle is briefly that in a fev
hours after the ingestion of diseased flesh, Trichinae, dis-
engaged from the muscle, are found free in the stomaci :
they pass thence into the duodenum, and afterwaids
advance still further into the small intestine, where tley
become developed. From the third or fourth day, ov* or
TRICHINA. SPIRALIS. 569
spermatic cells are found, the sexes in the mean while be-
coming distinctly marked. Shortly afterwards the ova are
impregnated, and young living entozoa are developed within
the bodies of the female. The young have been noticed
(by Virchow) under the form of minute Filarice, more
especially in the serous cavities, in the mesenteric glands,
&c. Continuing their migrations, they penetrate as
far as the interior of the primitive muscular fasciculi,
where they may be found as early even as three days
after ingestion, in considerable numbers, and so far deve-
loped that the young entozoa have almost attained a size
equal to that of the full-grown Trichinae. They pro-
gressively advance into the interior of the muscular fasci-
culi, where they are often seen several in a file one after
the other. Behind them the muscular tissue becomes
atrophied, and around them an irritation is set up, and
from the commencement of the third week they are found
3ncysted. The sarcolemma is now thickened, and the
contents of the muscular fibres exhibit indications of a
more active cell-growth ; the cyst is the product of a sort
of inflammatory irritation.
Professor Virchow draws the following conclusions :
" 1. The ingestion of pig's-flesh, fresh or badly dressed,
containing Trichinae, is attended with the greatest danger,
and may prove the proximate cause of death. 2. The
Trichinae maintain their living properties in decomposed
flesh ; they resist immersion in water for weeks together,
and when encysted may, without injury to their vitality,
be plunged in a sufficiently dilute solution of chromic acid
for at least ten days. 3. On the contrary, they perish and
are deprived of all noxious influence in ham which has
been well smoked, kept a sufficient length of time, and
then well boiled before it is consumed."
The Ecliinococcus found in cysts, chiefly in the human
liver, is represented in Plate IV. No. 101. A large col-
lection was taken from the liver of a boy who died in
Charing-cross Hospital from accidental rupture of the
liver. The cysts containing these parasites are always
situated in cavities in the interior of the body. These
cavities may be situated in any part of the tissues or organs
of the body, but are more frequently found in the solid
570 THE MICROSCOPE.
visceia, and especially in diseased livers. Fig. 256 repre-
sents the microscopical appearance of the contents of a cyst.
Fig. 256.Ctysc Disease c/ Ziwr. (Human).
n, Cyst with an ecliinococcus enclosed. 6, Detached booklets from the head of
Echinococcus, magnified 250 diameters, c, Crystals found in the cyst, choles-
terine. d, Cylindrical epithelium, some enclosed in structureless globules.
e. Puro-mucus, and fat corpuscles.
Mr. Busk, who has examined several of these cysts,
says : ""When a large hydatid cyst, for instance, in the
liver of the sheep, very shortly after the death of the
animal, is carefully opened by a very small puncture, so. as
to prevent at first the too rapid exit of the fluid, and con-
sequent collapse of the sac, its internal surface will be
found covered with minute granulations resembling grains
of sand. These bodies are not equally distributed over
the cyst, but are more thickly situated in some parts than
in others. They are detached with the greatest facility,
and on the slightest motion of the cyst, and are rarely
found adherent after a few days' delay. When detached,
they subside rapidly in the fluid, and consequently will
then be usually found collected in the lowest part of the
cyst, and frequently entangled in fragments of the inner
thin membrane. When some of these granulations are
placed between glass under the microscope, and viewed
with a power of 250 diameters, upon pressure being em-
ployed it will be seen, after rupture of the delicate enve-
loping membrane, that the Echinococci composing the gra-
nulations are all attached to a common central mass by
^hort pedicles ; which, as well as the central mass, appear
bo be composed of a substance more coarsely granular by
ANGUILLULA, 571
far than that of which the laminae of the cyst are formed.
This granular matter is prolonged "beyond the mass of
Ecliinococci into a short pedicle, common to the whole, ana
by which the granulation is attached to the interior of the
hydatid cyst, as represented in No. 101. In specimens
preserved in spirits, Echinococci of all imaginable forms and
appearances are to be met with, differences owing to de-
composition or to mechanical injury ; and in many cases
no traces of them can be found except the booklets or
spines, -which, like the fossil remains of animals in
geology, remain as certain indications of their source, and
not unfrequently afford the only proof we can obtain of
the true nature of the hydatid." 1
The Echinorhynchi, or Acantho cephali, constitute a
group of entozoa, with respect to whose development and
life-history we are indebted to Prof. Leuckart of Giessen.
Most observers, and in particular Von Beneden and G.
Wagner, have been disposed to assign to the Echinorhynci
a simple metamorphosis, hardly perhaps more remarkable
than that which has been shown to take place in some
other of the Nematode worms. The latter observer goes
so far even as to believe that the organization of the per-
fect animal may be discerned in the embryo. Leuckart
instituted, in 1861, a series of experiments with the ova
of Echinorhynchus Proteus, which is found parasitic upon
the Gammarus Pulex. The ova " of E. Proteus resemble
in form and structure those of the allied species. They
are of a fusiform shape, surrounded with two mem-
branes, an external, of a more albuminous nature, and an
internal, chitinous one. When the eggs have reached the
intestine, the outer of these membranes is lost, being in
fact digested ; whilst the inner envelope remains until
ruptured by the embryo." 2
Anguillulce are very small eel-like worms, of which one
species, 3 Anguillula fluviatilis, is found in rain-water
amongst Confervas and Desmidiacece, in wet moss and
moist earth, and sometimes in the alimentary canal of the
(1) Microscopical Society's Transactions. 1st Series.
(2) Prof. Leuckart "On Echinorhynchus." Journ. Micro. Soc. vol. iii. p. 57. 1863.
(3) For the fullest information of marine, land, and fresh-water species, con-
suit Dr. Bastian's "Monograph on the Anguillulidse." Lin. Soc. Trans, vol.
jrcv. p. 75. The "Anguillula Aceti." Popular Science Review, Januaiy, 1863.
572 THE MICRO VXDFE.
Limneus, the frog, fish, <fec. ; another speoies is met with
in the ears of wheat affected with a blight termed the
" cockle ;" another, the A. glutinis, is found in sour paste;
and another, A. aceti, in stale, bad vinegar. If grains
of the affected wheat are soaked in water for an hour
or two before they are cut open, the eels will be seen in
a state of activity when placed under the microscope.
The paste-eel makes its appearance spontaneously in the
midst of paste that is turning sour ; but tho best means of
securing a supply for any occasion, consists in allowing
any portion of a mass of paste in which they show them-
selves, to dry up, and then lay it by for stock; if at any
time a portion of this is introduced into a little fresh
made paste, and the whole kept warm and moist for a few
days, it will be found to swarm with these curious little
worms. A small portion of paste spread over one face of
a Coddington lens is a ready way of showing them.
Planarioe: a genus of the order Turbellaria. Some of the
species are very common in pools, and resemble minute
leeches ; their motion is continuous and gliding, and they
are always found crawling over the surfaces of aquatic
plants and animals, both in fresh and salt water. The
body has the flattened sole-like shape of the Trematode
Entozoa; the mouth is surrounded by a circular sucker,
this is applied to the surface of the plant from which the
animal draws its nourishment. The mouth is also fur-
nished with a long funnel-shaped proboscis, and this, even
when detached from the body, continues to swallow any-
thing presented to it.
" In imitation of the name bestowed on the trunk of
the elephant, the extensile organ serving to imbibe the
nutriment of many of the smaller animals is called a pro-
boscis, whether it simply unfolds from the root, protrudes
from a sheath, or unwinds from a regular series of volu-
tions. But in none is the designation equally strict and
appropriate as in the Planarice. There it is absohitely the
organ of the elephant in miniature, with this exception,
that it is neither annulated nor composed of segments.
It is of surprising length, being little, if any, shorter when
fully extended than the whole animal. It seems of greater
consistency, harder, and tougher than the rest of the body
HIRUDINUXE. 573
BO as to admit insertion into decaying vegetaoles, and
w jen stretched to the utmost the root becomes an apex of
the slenderest cone." 1
Planarice multiply by eggs, and by spontaneous fissura-
tion, in a transverse direction, each segment becoming a
perfect animal. Professor Agassiz believes that the infu-
sorial animals. Paramcecium and Kolpoda, are nothing else
than Planarian larvae.
Hirudinidce, the Leech tribe, are usually believed to
form a link between the Annelida on the one hand, and
the Trematoda on the other; but their affinities are closer
connected with the latter than the former. Totally deprived
of the characteristic setae of the Annelida, and exhibiting
no sectional divisions, they are provided with suckers so
constantly possessed by the Trematoda, and present no
small resemblance to them in their reproductive organs.
On the other hand, in the arrangement of their nervous
system and in their vascular system, the Hirudinidce
resemble the Annelida. The head in most of these animals
is distinctly marked, and furnished with eyes, tentacles,
mouth, and teeth, and in some instances with auditory
vesicles, containing otolithes. The nervous system con-
sists of a series of ganglia running along the ventral
portion of the animal, and communicating with a central
mass of brain.
The medicinal leech puts forth strong claims to our
attention, on the ground of the services which it renders
to mankind. The whole of the family live by sucking the
blood of other animals ; and, for this purpose, the mouth
of the leech is furnished with an apparatus of horny teeth,
by which they bite through the skin. In the common
leech, three of these teeth exist, arranged in a triangular,
or rather triradiate form, a structure which accounts for
the peculiar appearance of leech-bites in the human skin
The most interesting part of the anatomy of the leech ta
microscopists is the structure of the mouth (fig. 257).
"This piece of mechanism," says Professor Rymer Jones,
" is a dilatable orifice, which would seem at first sight to
be but a simple hole. It is not so ; for we find that just
(1) Sir John Dalyell's Observations on seme interesting Phenomena exhibited
by icveral Specie* of Planar ice. 1814.
574 THB MICROSCOPE.
the margin of this hole three beautiful little semi.
eircular sawa arc situated, arranged so that their edges
meet in the centre. It is by means
of these saws that the leech makes
the incisions whence blood is to be
procured, an operation which is per-
formed in the following manner :
No sooner is the sucker firmly fixed
to the skin, than the mouth becomes
slightly everted, and the edges of
the saws are thus made to press
upon the tense skin ; a sawing
movement being at the same time
civen to each, whereby it is made
* fLcech - gradually to pierce the surface, and
cut its way to the small blood-vessels beneath. Nothing
could be more admirably adapted to secure the end in view
than the shape of the wound thus inflicted, the lips of which
must necessarily be drawn asunder by the very contrac-
tility of the skin itself; and that the enormous sacculated
stomach, which fills nearly the whole body of the leech,
was designed to contain its greedily devoured meal, there
can be no reasonable question. The leech, in its native
element, could hardly hope for a supply of hot blood
as food ; and, on the other hand, its habits are most
abstemious, and it may be kept alive and healthy for
years, with no other apparent nourishment than what is
derived from pure water frequently changed ; even when
at large, minute aquatic insects and their larvse form its
usual diet."
In Clepsinidce, the body is of a leech -like form, but very
much narrowed in front, and the mouth is furnished with
a protrusile proboscis. These animals live in fresh watei,
where they may often be seen creeping upon aquatic
plants. They prey upon water-snails.
Tubicola. The worms belonging to this series of
branchiferous Annelida are all marine, and distinguished
by their invariable habit of forming a tube or case,
within which the soft parts of the animal can be en-
tirely retracted. This tube is usually attached to stones
or other submarine bodies. It is often composed of various
ANNELIDA. $75
foreign materials, such as sand, small stones, and the
debris of shells, lined internally with a smooth coating of
hardened mucus ; in others it is of a leathery or horny
consistency ; and in some it is composed, like the shells of
Mollusca, of calcareous matter secreted by the animal.
The Tubicolce generally live in societies, winding their
tubes into a mass which often attains a considerable size :
a few are solitary in their habits. They retain their posi-
tion in their habitations by means of appendages very
similar to those of free worms, with tufts of bristles and
spines ; the latter, in the tubicular Annelids, are usually
hooked ; so that, by applying them to the walls of its
domicile, the animal is enabled to oppose a considerable
resistance to any effort to draw it out of its case. In the
best known family of the order (Sabellidce), the branchiae
are placed on the head, where they form a circle of
plumes or a tuft of branched organs. The Serpulce form
irregularly twisted calcareous tubes, and often grow
together in large masses, when they secure themselves to
shells and similar objects j ether species, Terebella, which
build their cases of sand and
stones, appear to prefer a
life of solitude. The curious
little spiral shells seen upon
*he fronds of sea-weeds, are
formed by an animal be-
longing to the family Spi-
rorbis.
If the animals be placed
in a vessel of sea-water, a
very pleasing spectacle will
soon be witnessed. The mouth
of the tube is first seen to
open, by the raising of an
exquisitely-constructed door,
and then the creature cauti-
ously protrudes the anterior KO
*; f * u J T Fig 2&8 - A Serpula protruded from iit
part 01 its body, spreading calcareous tube.
out at the same time two beautiful fan-like expansions, of a
rich purple, or scarlet colour, which float elegantly in the sur-
rounding water, and serve as branchial or breathing organs.
576 THE MICROSCOPE.
The Serpula, if withdrawn from its calcareous tube (fig.
260), is found to have the lower part of the body com-
posed of a series of flattened rings, and entirely destitute
of limbs or other appendages. Its food is brought to its
mouth by currents created by the cilia on the branchial
tufts.
Some of the Annelids are without tubes or cells of any
sort, and simply bury their bodies in the sand about the
tidal mark. The Arenicola, lob-worm, is a well-known
specimen of the class ; its body is so transparent that the
circulating fluids can be distinctly seen under a moderate
magnifying power. Two kinds of fluids flow through the
vessels, one nearly colourless, the other red ; the vessels
through which the latter circulate are looked upon as
blood-vessels. A few also have not only no tubes but are
free and active swimmers. Drs. Carpenter and Claparede,
during a sojourn at Lamlash Bay, Arran, met with an
interesting member of this class of Annelids, the Tomopteris
onisciformis. It possesses a remarkable pair of "frontal
horns," projecting laterally from the most anterior part of
head, as well as pair of greatly elongated appendages,
designated by those observers as " the second antennae" in
contradistinction to another and a shorter pair of appen-
dages situated just in advance of them, the first pair
being characteristic of the larval, and the second of the
adult state of the annelid.
" The head also bears on its dorsal surface a pair of
ciliated epaulettes, which extend over the edges of the
bilobed nervous ganglion. These, at a certain stage of
development, are fringed with long cilia both at their
margins and their base ; but as the cilia are only occa-
sionally to be seen in activity, they may escape the atten-
tion of the observer. Cilia are likewise distinguishable on
certain parts of that innermost layer of the general integu-
ment which forms the external boundary of the peri-
visceral space, and by their agency a special movement is
imparted to the corpuscles of the fluid contained in the
cavity."
The development of the caudal prolongation is peculiar,
and this as well as other points of interest are given
in the Lin. 'Soc. Trans, vols. xxii. and xxiii. pp. 335
I.NSKCTS' Kens. KTC,
147
lilfll \\>-t. lipl.
PLATE VT.
Edmund Kvans.
ANGUILLULE 677
and 59. Dr. Carpenter believes that this creature ''is
a degraded form of the annelidan type its nearest affi-
nities being (as already pointed out by Drs. Leuckart
and Pagenstecher) the chsetopod or setigerous Annelids.
Every part of the characteristic organization of the type
is here reduced to the extreme of simplicity. The alimen-
tary canal passes in a straight line from one extremity of
the body to the other, without either sacculations or glan-
dular appendages. The nutritive fluid which transudes
through its walls, and which finds its way into the peri-
visceral cavity, is distributed throughout the body solely
by means of extensions of that cavity, through which it is
propelled in part by the agency of cilia that clothe its walls.
This fluid is obviously the homologue of the blood of higher
animals, that we cannot but regard the existence of the type
of structure before us (the wonderful transparency of the
body not permitting the slightest doubt as to the absence
of anything resembling a dorsal vessel) as affording a
further confirmation of the view of the so-called circulat-
ing apparatus of the higher Annelida, which regards their
perivisceral cavity and its extensions as representing the
proper sanguiferous system, and which looks upon the
system of vessels containing coloured fluid as a special
arrangement having reference rather to the respiratory
functions. 1 The extreme tenuity of the walls of the body
and its appendages renders it unnecessary that any special
provision should be made for the aeration of the nutritive
fluid ; and we accordingly find neither branchiae nor any
trace of what is commonly described as the sanguiferous
system in Annelida. The centres of the nervous system
would seem to consist solely of the cephalic ganglia the
absence of the ordinary longitudinal series being apparently
related to the very incomplete segmentation of the body,
and constituting a link of affinity to the Turbellarian
Worms. The ocelli present a condition of extreme sim-
plicity, yet the duplication of the corneale in each of them
marks that tendency to repetition which so peculiarly
distinguishes the Articulate type. It is, however, the
extreme simplicity of its generative apparatus that con-
(1) See Prof. Huxley's Lectures in Medical Times and Gazette, July 12 and 26^
1856.
p P
578 THE MICROSCOPE.
Btitutes one of the chief points of interest in the organiza*
tion of Tomopteris."
Not solely in this class, but in that of the Annelida
generally, does much interest attach to the developmental
period. Most of them come forth from the egg in a con-
dition so closely resembling the cililated gemmules of
polypes, that competent observers have been known to
mistake them for animals of a lower class ; fortunately a
few hours' careful watching is sufficient to dispel the
illusory belief, and the embryonic globular shapeless
mass is seen soon to change its form ; segmentation takes
place, and the various internal organs become more and
more developed ; eye spots appear, and the young animal
assumes the likeness of its parent.
The Actinotrocha, even in the adult state, in many parti-
culars resembles the "bipinnarian larva of the star-fish."
Its long body is surmounted by a head, or mouth, around
which is placed a number of ciliated ventacula : they are
not only employed for feeding purposes, but also for
enabling it to swim about ; and in this particular, accord-
ing to Dr. A. Schneider and other competent authorities,
it is quite remarkable. 1 Dr. Carpenter tells us that he
has captured these free-swimming Annelids among other
marine animals by the careful use of the " stick-net."
ill Se Ann. Nat. Hiat. vol. ix 1862. p. i8&
CHAPTER IV,
BUB-KINGDOM AETICULATA. IKSECTA. AKACH1ODA.
MONG the numerous objects
which engage the attention
of the microscopist, the in-
sect tribes in general are far
(from being the least
interesting ; their
curious and won-
derful economy is a subject
well deserving especial in-
vestigation. Earth, air, and
water, teem with the
various tribes of insects,
many of which are invisible to the unassisted eye, but
presenting, when viewed with the microscope, the most
beautiful mechanism in their frame-work, the most perfect
regularity in their laws of being, and exhibiting the same
wondrous adaptation of parts to the creature's wants,
which, throughout creation, furnishes traces of the love
and wisdom that so strongly mark the works of God. 1
" I cannot," says the learned Swammerdam, " after an
attentive examination of the nature and structure of both
the least and largest of the great family of nature, but
allow the less an equal, perhaps a superior degree of
dignity. "Whoever duly considers the conduct and instinct
of the one with the manners and actions of the other,
must acknowledge all are under the direction and control
of a superior and supreme Intelligence ; which, as in the
(1) We commend to the reader the excellent Introduction to Entomology, by
Kir by and Spence. Longmans. Art. "Insecta," Oclop. Ant. and Physio.
pp 2
580 THE MICROSCOPE.
largest it extends beyond the limits of our comprehension,
escapes our researches in the smallest. If, while we dis-
sect with care the larger animals, we are filled with wonder
at the elegant disposition of their limbs, the inimitable
order of their muscles, and the regular direction of their
veins, arteries, and nerves, to what a height is our astonish-
ment raised when we discover all these parts arranged in
the least of them in the same regular manner ! How is
it possible but that we must stand amazed, when we reflect
that those little animals, whose bodies are smaller than the
point of the dissecting knife, have muscles, veins, arteries,
and every other part common to large animals ! Crea-
tures so very diminutive that our hands are not delicate
enough to manage, nor our eyes sufficiently acute to see
them."
The Articulate sub-kingdom, Insecta, is divided and
sub-divided into orders, families, genera, species, as for
example :
Lepidoptera; typical fora, Butterfly, Moth.
Dipteria; 1 typical form, Fly, Gnat, &c.
Aptera ; typical form, Flea, Louse, Springtail.
Goleoptera ; typical form, Beetle, Water Beetle, &c.
Orihopttra ; typical form, Locust, Grasshopper.
Neuroptera ; typical form, Dragon-fly, May-fly.
llymenoptera ; typical form, Bee, Wasp, Ant.
Homoptera; typical form, Plant-louse (Aphis), Lan-
tern-fly.
Ilemiptera ; typical form, Water-scorpion, Water-boat-
man.
Arachnida; typical form, Spider, Scorpion, &c. The
Acarina belong to this genus, family Acarea, well known
as " Mites " and " Ticks."
Insects are characterised by a simple breathing ap-
paratus ; by the division of the body into distinct regions
or segments ; when three, the middle one, the thorax,
bears three pairs of jointed legs, and usually two pairs
of wings ; and by the possession of a single pair of jointed
(1) Comprised within the order Diptera, or two-winged flies, are several
genera having no wings, the apterous and suctorial Pulex, and the apterous and
pupiparous Episboscidcs: among the latter, we have the winged Hippobotoa, o>
Lorse-fly, and some others.
IN8BCTA. 581
The metamorphoses which all undergo, before
they arrive at the perfect state and are able to fulfil all
the ends of their existence, are more curious and striking
than in any other department of nature ; and in the
greater number of species the same individual differs so
materially at the several periods of life, both in its in-
ternal and external conformation, in its habits, locality,
and kind of food, that it becomes one of the most inter-
esting investigations of the physiologist to ascertain the
manner in which these changes are effected, to trace the
successive steps by which that despised and almost un-
noticed larva that but a few days before lay grovelling in
the earth, with an internal organization fitted only for
the reception and assimilation of the crudest vegetable
matter, has had the whole of its external form so com-
pletely changed, as now to have become an object of
admiration and delight, and able to " spurn the dull
earth," and wing its way into the wide expanse of air,
with internal parts adapted only for the reception of the
purest and most concentrated aliment, which is now ren-
dered absolutely necessary for its support, and the reno-
vation increased energies demand.
The greater number of insects undergo a complete series
of changes. They are for the most part oviparous, and
their eggs assume a variety of forms, colour, &c. as
will be seen in Plate VI. On first leaving the egg, they
assume a more or less worm-like appearance, known as
larva, maggot, or caterpillar. The next stage is that of
the nympha, pupa, or chrysalis ; this is succeeded by that
of the perfect insect or imago. In some insects the
changes are incomplete ; the body, legs, and antennae
are nearly similar, but wings are wanting. In others the
pupa continues active, is of a large size, and acquires
rudimentary wings ; and some are without material altera-
tion of structure, the change consisting in what is termed
" scdysis," a casting off, or moulting only.
The heads of insects present many points of interest;
Plate VI. No. 134, shows the head of the Tortoise butter-
fly in profile, with large compound eye, palpi, and spiral
tongue. No. 131 is a portion of the head with lancets,
&c. of the Glossina morsitans, Tsetse-fly of Africa. In
582
THE MICROSCOPE,
the mouths and tongues of insects, the most admirable art
and wisdom are displayed ; and their diversity of form is
almost as great as the variety of species. The mouth is
usually placed in the fore part of the head, extending
somewhat downwards. Many have the mouth armed with
strong jaws, or mandibles, provided with muscles of great
9ig. 259,Under-surface of a Wasp's tongue, Feelers, &c. (Within the circle tlia
same is seen life-size.)
power, with which they bruise and tear their food, answer-
ing to the teeth of the higher animals ; and in their
various shapes and modifications serving as knives, scissors,
augers, files, saws, trowels, pincers, or other tools, accord-
ing to the requirements of each insect.
The tongue is generally a compact instrument, used
principally to extract the juices on which the insect feeds,
varying greatly in its length in the different species. It ia
capable of being extended or contracted at the insect's
INSECTA. 583
pleasure ; sometimes it is dexterously rolled up in a taper and
spiral form, as in the Butterfly ; tubular and fleshy, as in the
Wasp. In fig. 259, the under lip of the Wasp is represented
with its brush on either side ; above which are two jointed
feelers (palpi labiales), the use of which is probably for the
purpose of making an examination of the food before it is
Fig. 260. Eye of Fly (magnified 150 diameters.)
taken into the mouth, or that of cleaning the tongue. Near
these feelers the antennae or horns are placed, as curious in
form as they are delicate in structure. The antennae of the
male generally differ from those of the female : some writers
believe these are organs of smell or hearing ; others that
they are solely intended to add to the perfection of touch
or feeling, increasing their sensibility to the least motion,
or disturbance. Apart from their use, they are the most
interesting and distinguishing characteristics of insects,
and appear to be often employed for the purpose of ex-
amining every object they alight upon.
584
THE MICROSCOPE.
Tlic structure of the eye is in all creatures a most
admirable piece of mechanism, in none more so than in
those of the insect tribe. The eyes differ in each species ;
varying in number, situation,
figure, simplicity of con-
struction, and in colour. Fig.
260 represents a portion of
the eye of the common Fly,
drawn by the light of the sun
upon a prepared photographic
surface of wood ready for the
engraver. Fig. 261 repre-
sents a side view of the eye
when thrown down, showing
the compound nature of the
Fig. aOl.
organ, with its series of
cylindrical tubes j better seen in fig. 262.
" On examining the head of an insect, we find a couple
of protuberances, more or less prominent, and situated
symmetrically one on each side. Their outline at the base
is for the most part oval, elliptical, circular, or truncated ;
while their curved surfaces are spherical, spheroidal, or
pyriform. These horny, round, and naked parts seem to
be the cornese of the eyes of insects ; at least, they a_e
with propriety so termed, from the analogy they bear to
those transparent tunics in the higher classes of animals.
They differ, however, from these ; for, when viewed by the
microscope, they display a large number of hexagonal
facets, which constitute the medium for the admission of
light to as many simple eyes. Under an ordinary lens,
and by reflected light, the entire surface of one cornea
presents a beautiful reticulation, like very fine wire gauze,,
with a minute papilla, or at least a slight elevation, in the
centre of each mesh. These are resolved, however, by the
aid of a compound microscope, and with a power of from
80 to 100 diameters, into an almost incredible number
(when compared with the space they occupy) of minute,
regular, geometrical hexagons, well denned, and capable of
being computed with tolerable ease, their exceeding minute-
ness being taken into consideration. When viewed in this
way, the entire surface bears a resemblance to that which
might easily and artificially be produced by straining a
INSECTS' EYES.
585
portion of Brussels lace with hexagonal meshes over a
email hemisphere of ground glass. That this gives a toler-
ably fair idea of the intricate carving on the exterior may
be further shown from the fact, that delicate and beautiful
casts in collodion can be procured from the surface, by
giving it three or four coats with a camel-hair pencil.
When dry it peels off in thin flakes, upon which the-
impressions are left so distinct, that their hexagonal form
can be discovered with a Coddington lens. This experi-
ment will be found useful in examining the configuration
of the facets of the hard and unyielding eyes of many o*
the Coleoptera, in which the reticulations become either
distorted by corrugation, or broken by the pressure re-
quired to flatten them. It will be observed also, that by
this method perfect casts can be obtained without any dis-
section whatever ; and
that these artificial
exuviae for such they
really are become
available for micro-
scopic investigations,
obviating the necessity
for a more lengthened
or laborious prepara-
tion. The dissection
of the cornea of an
insect's eye is by no
means easy. I have
used generally a small
pair of scissors, with
well - adjusted and
pointed extremities, and a camel-hair pencil, having a por-
tion of the hairs cut off at the end, which is thereby flat-
tened. The extremity of the cedar handle should be cut
to a fine point, so that the brush may be the more easily
revolved between the finger and thumb ; and the coloured
pigment on the interior may be scrubbed off by this
simple process. A brush thus prepared, and slightly
moistened, forms by far the best forceps for manipulating
these objects preparatory to mounting ; as, if only touched
with any hard-pointed substance, they will often spring
from the table and be lost.
A, is a section of the eye of Melolontha vulgans,
Cockchafer. B, a portion more highly mag-
nified, showing the facets of the cornea, and
its transparent pyramids, surrounded with
pigment. At A they meet, and form the optic
nerve.
586
THE MICROSCOPE.
"Each hexagon forms the slightly horny case of an
eye. 1 Their' margins of separation are often thickly set
with hair, as in the Bee ; in other instances naked, as in
the Dragon-fly, House-fly, &c. The number of these lenses
has been calculated by various authors, and their multi-
tude* cannot fail to excite astonish-
ment. Hooke counted 7,000 in the
eye of a House-fly ; Leeuwenhoek
more than 12,000 in that of a
Dragon-fly ; and Geoffry cites a
calculation, according to which
there are 34,650 of such facets in
the eye of a Butterfly." 2
The trunk is situated between
the head and the abdomen j the legs
and wings are inserted into it. The
thorax is the upper part of the
trunk ; the sides and back of which
are usually armed with points or
hairs. The abdomen forms the
posterior part of the body, and is
Fig. 263. Breathing - amr- generally made up of rings or seg-
fi^SS^jSKl ments, by means of which the
ject about the natural size.) insect lengthens or shortens itself.
Running along the sides of the abdomen are the spiracles,
or breathing apertures, fig. 263, communicating directly
with the internal respiratory organs. Pure air being thus
freely admitted to every part, and the circulating fluids
(1) "Each of the eyelets, or 'ocelli,' which aggregated constitute the com-
pound eye of a Bee, is itself a perfect instrument of vision, consisting of two
remarkably formed lenses, namely, an outer 'corneal' lens and an inner or
' conical' lens. The 'cornea!' lens is a hexahedral or six-sided prism, and it is
the assemblage of these prisms that forms what is called the ' cornea ' of the
compound eye. This ' cornea ' may easily be peeled off, and if the whole or a
portion be placed under the microscope, it will be seen that each cornea! lens is
not a simple lens but a double convex compound one, composed of two plano-
convex lenses of different densities or refracting powers, joined together by their
plane surfaces. The effect of this arrangement is, that if there should be any
aberration of the rays of light during their passage through one portion of the
lens, it is rectified in its transit through the other. It appears questionable
whether the normal shape of these lenses is hexagonal, or whether this form is
not rather a necessity of growth, &c., that is, that they are normally round, but
assume the hexagonal shape during the process of development in consequence
of their agglomeration." J. Samuelson and B. Hicks, ' On the Eye of the
Bee," Journ. Micros. Soc. vol. i. p. 51.
(2) "Remarks on the Cornea of the Eye in Insects," by John Gorham,
M.R.C.S. Journ. Micros Science, p. 76, 1853.
INSECTS FEET.
587
kept exposed to the vivifying influence of the atmosphere,
the necessity for more complicated and cumbersome
breathing organs is at once obviated ; and the whole body
is at the same time rendered lighter. The spiracles are
usually nine or ten in num-
ber, and consist of a horny
ring, of an oval form. The
air-tubes are exquisitely
composed of two thin
membranes, between which
a delicate elastic thread or
spiral fibre, is interposed,
forming a cylindrical pipe,
and keeping the tube always
in a distended condition ;
thus wonderfully preserving
the sides from collapse or
pressure in their passage
through the air, which
Otherwise might Occasion
/v> !_ TM at* A
Suffbcation. Fig. 264 re-
presents the beautiful me-
chanism of a portion of the tracheae of Hydropilus,
showing the peculiar arrangement of the spiral tubes,
which give it elasticity and strength.
The legs of insects are extremely curious and interest-
ing ; each leg consists of -several horny cylinders, connected
by joints and ligaments, inclosing within them sets of
powerful muscles, whereby their movements are effected.
Feet of Flies, &c. " The tarsus, or foot of the Fly, con-
sists of a deeply bifid, membranous structure, pulvillus ;
anterior to the attachment of this part to the fifth tarsal
joint, or the upper surface, are seated two claws, or ' tarsal
ungues,' which are freely movable in every direction.
These ungues differ greatly in their outline, size, and rela-
tive development to the tarsi, and to the bodies of the
insects possessing them, and in their covering ; most are
naked over their entire surface, having however a hex-
agonal network at their bases, which indicates a rudimen
tary condition of minute scale-like hairs, such as are common
on some part of the integument of all insects. Flexor and
& 264 - Magnified portions of tfa
trachea of the HydropMlus, show-
ing spiral tubes and their arrange-
ment -
5S8
THE MICROSCOPE.
extensor muscles are attached to both ungues and the
flaps ; the flaps, corrugated or arranged on the ridge and
furrow plan, are in some cases perfectly smooth on
their superior surface, in others this surface is covered
with minute scale-like hairs. The thickness of the flaps
on the Blow-fly does not exceed the 1 -2000th of an inch
at the margin ; thence they increase in thickness towards
the point of attachment. Projecting from their inferior
surface are the organs which have been termed ' hairs,'
* hair-like appendages/ * trumpet-shaped hairs,' &c. That
these are the immediate
agents in holding is now
admitted by most obser-
vers, and it will be con-
venient to term them
'"tenent" hairs,' in allu-
sion to their office. Plate
VI. No. 140, the under
surface of left forefoot of
Musca Vomitoria, is shown
with tenent'hairs a and b
are more magnified hairs,
a from below, b from the
Oside. No. 142 is the left
forefoot of Amara commu-
nis, showing under surface
Fig. 265. Sucker on the leg of a Water- J f nTrn n f fpripnt irmpn
beetle. (The dot in circle shows the ancl Iorm Ol tenent appen-
object natural size.) dages, one of which is seen
more magnified at a. Nc. 143, under surface of left forefoot,
Epliydra riparia. This fly is met with sometimes in im-
mense numbers on the water in salt marshes ; it has no
power of climbing on glass, which is explained by the
structure of the tenent-hairs : the central tactile organ is
also very peculiar, the whole acting as a float, one to each
foot, to enable the fly to rest on the surface of the water ; a
is one of the external hairs. No. 135, under surface of left
forefoot of Gassida viridis (Tortoise-beetle), showing the
bifurcate tenent appendages, one of which is given at a
more magnified. These, in the ground-beetles, are met
with only in the males, and are used for sexual purposes.
The delicacy of the^structure of these hairs in the fly, the
INSECTS' HAIRB. 589
bend near their extremity, in each of which supervenes an
elastic membranous expansion, and from which a very
minute quantity of a clear, transparent fluid is -emitted
when the fly is actively moving, explains its capacity for
clinging to polished surfaces. It simply remains to add
that the tubular nature of the shaft of the tenent-hairs on
the foot cf this insect has been surmised, although its
minute size and homogeneity hardly admits of actual con-
firmation. At the root of the pulvillus, or its under sur-
face, is a process, which in some instances is short and
thick, in others long and curved, and tapering to its ex-
tremity (Scatophaga), setose (Empis), plumose (Hippobos-
cidce), or, in '?ne remarkable example (Ephydra), so closely
resembling in its appearance the very rudimentary pul-
villus with which it is associated. Just at the base of the
fifth tarsal joint, on its under surface, there is present, in
Eristalis, a pair of short, very slightly curved hairs, which
point almost directly downwards. It became desirable to
endeavour to ascertain how far the structure of these
tenent-hairs agrees with that of true hairs, on which some
valuable critical observations were made last year by Dr.
Hicks. 1
" Tenent-hairs are usually present in some modification
or other, that it is really difficult to name a beetle which
has not some form of them ; the only one I yet know that
seems to me really to possess nothing of the kind is a
species of Helops, which lives on sandy heaths ; I suppose
the dense cushion of hairs on the tarsi here to be for the
protection, simply, of the joints to which they are attached.
I have detected them on the tarsal joints of species of
Ephydra, and on the first basal tarsal joint of the Drono
of the Hive-bee. A very rudimentary form of tenent-hairs
is present on the under surface of some of the Tree-bugs
(Pzntatomidce), which have in addition a large, deeply-cleft
organ at the extremity of the tarsus, which appears to be
a true sucker.
" When walking on a rough surface, the foot represents
ihat of a Coleopterous insect without any tenent appen-
dages. The ungues are always attached to the last joint of
(1) See Trans. Linn. Soc. vol. xxiii. p. 143.
590 THE MICROSCOPE.
an insect's tarsus. They are not attached to the fifth tarsal
joint of a Dipterous insect ; neither are they attached to
the fifth tarsal joint of a Hymenopterous insect, but to the
terminal sucker, which again, in this great order, is a
sixth tarsal joint, membranous, flexible, elastic in the
highest degree, retractile to almost its fullest extent within
the fifth tarsal joint a joint modified to an extraordinary
degree for special purposes.
" The plantula of Lucanus, with its pair of minute claws,
at once occurred as a case strictly in point. The ungues
are hairs modified for special purposes ; and they have the
structure of true hairs. The sustentacula of Eptira, the
analogous structures on the entire under surface of the
last tarsal joints in Pholcus, the condition of the parts in
the hind limbs of Notonecta, in both its mature and earlier
conditions, as well as in Sarcoptes, Psoroptes, and some
other Acari, all contribute to the proof of this fact. The
various orders of insects have, for the most part, each their
own type of foot. Thus there is the Coleopterous type, the
Hymenopterous type, the Dipterous type, the Homop-
terous type, &c. ; and so very distinctive, that in critical
instances they will sometimes serve at once to show
to which order an insect should be referred. Thus,
amongst all the Diptera, I have as yet met with but one
subdivision which presents an exception to the structure
described. This exception is furnished by the Tipulidce,
which have the Hymenopterous foot. With hardly an
exception, then, I believe the form of foot described will
be found universal amongst the Diptera, and will be found
amongst the members of this order alone. It may be
desirable to add a few words on the best plan of conduct-
ing observations on these parts. Their action should be
studied in Kving insects under the influence of chloroform,
careful notes taken of appearances, and accurate drawings
made. It is of the greatest advantage to preserve carefully
all the parts examined : for this purpose Deane's medium
or glycerine jelly suits very well; some of the delicate
preparations, however, can only be kept satisfactorily in a
solution of chloride of zinc. The old plan of soaking in
caustic potash, crushing, washing, putting into spirits of
wine (or pressing and drying first), and then into turpen-
INSECTS TONGUES.
591
tine, and lastly into Canada balsam, is perfectly useless,
except in rare instances where points connected with the
structure of the integument have to be made out. Oi
course, the parts should be viewed from above, from below,
and in profile, in order to gain exact ideas of their rela-
tions. The binocular microscope, however, promises to
diminish vastly the difficulties which had until recently
to be encountered, as by its use the parts may be clearly
viewed just as they are, without preparation of any kind." 1
Fig. 266.
1, Foet and leg of Qphion. 2, Foot and leg of Flesh-fly. 3, Foot and leg ol
Drone-fly. (The small circles inclose objects about natural size.)
Fig. 267 represents the tongue and piercing apparatus
of the Drone-fly. This remarkable compound structure,
together with the admirable form and exquisite beauty of
the apparatus, must strike the mind with wonder and
delight, and lead the observer to reflect on the weakness
and impotence of all human mechanism, when compared
with the skill and inimitable finish displayed in the object
before us. The harder structures which surround it have
(1) Tuffen West, Trains. Linn. Soc. vol. xxiii. p. 393.
592
THE MICROSCOPE.
Fig 267. Tung ue and Piercing Apparatus of Drone-fly.
593
been removed for the purpose of bringing the several parts
into view, and which consist of two palpi, or feelers,
covered with short hairs, and united to the head by a se 4
of muscles ; these feelers appear to be in frequent requisi-
tion for guarding the other organs from external injury.
The two lancets seen above them are formed somewhat like
a cutlass, or the dissecting knife of the anatomist, and are
purposely intended for making a deep and sharp cut, also
for cutting vertically with a sweeping stroke. The other
and larger cutting instrument appears to be intended to
enlarge the wound, if necessary; or it may be for the
purpose of irritating and exciting the part around, thereby
increasing the flow of blood to the part, being jagged or
toothed at the extremity. The larger apparatus, with its
three peculiar prongs, or teeth, is tubular, to permit of the
'olood passing through it and thence to the stomach; this
is inclosed in a case which entirely covers it. The spongy
tongue itself projects some distance beyond this apparatus,
and is composed of a beautiful network of soft muscular
spiral fibres, forming a series of absorbent tubes; and these
are moved by powerful muscles and ligaments, the retrac-
-ile character of which may be seen in the drawing of the
proboscis*of the Fly, fig. 268 : by the aid of two booklets
placed in each side, he is enabled to draw in and dart
out the tongue with wonderful rapidity. Another set of
muscles is seen at the root of the whole apparatus.
'* In the organization of the mouth of various insects we
have a modification of form, to adapt them to a different
mode of use ; as in the Muscidce, or common House-flies.
When the food is easily accessible, and almost entirely
liquid, the parts of the mouth are soft and fleshy, and
simply adapted to form a sucking tube, which in a state of
rest is closely folded up in a deep fissure, on the under
surface of the head. The proboscis at its base appears to
be formed by the union of the lacinia above and the labium
below, the latter forming the chief portion of the organ,
which-is tenanted by dilated muscular lips. In the TabaniLS
these are exceedingly large and broad, and are widely ex-
panded, to encompass the wound made by the insect with
its lancet-shaped mandibles in the skin of the animal it
aY,acks. On their outer surface they arc fleshy and
QQ
594 THE MICROSCOPE.
muscular, to fit them to be employed as prehensile organs ;
while on their inner they are more soft and delicate, but
thickly covered with rows of very minute stiff hairs,
directed a little backwards, and arranged closely together.
There are very many rows of these hairs on each of the
lips ; and from their being arranged in a similar direction,
they are easily employed by the insect in scraping or tear-
ing delicate surfaces. It is by means of this curioui
structure that the busy House-fly often occasions much
mischief to the covers of our books, by scraping oif the
white of egg and sugar varnish used to give them the
polish, leaving traces of its depredations in the soiled and
spotted appearance which it occasions 011 them. It is by
means of these also that it teases us in the heat of summer,
when it alights on the hand or face, to sip the perspiration
as it exudes from and is condensed upon the skin. The
fluid ascends the proboscis, partly by a sucking action,
assisted by the muscles of the lips themselves, which are
of a spiral form, arranged around a highly elastic, ten-
dinous, and ligamentous structure, with other retractile
additions for rapidity and facility of motion." l
The beautiful form of the spiral structure of the tongue
should be viewed under a magnifying power of '250 dia-
meters, or a quarter-inch object-glass.
These insects are of great service in the economy of
nature, their province being the consumption of decaying
animal matter, which is found about in quantities so small
as to be imperceptible to most people, and is not removable
by ordinary means, even in the best-kept apartments, during
hot weather. It was asserted by Linnaeus, that three flies
would consume a dead horse as quickly as a lion. This
was, of course, said with reference to the offspring of
such three flies ; and it is possible the assertion may be
correct, since the young begin to eat as soon as they are
born. A single Blow-fly has been known to produce twenty
thousand living larvae (one of which is represented in Plate
VI. No. 141), and in twenty -four hours each has. increased
its own weight above two hundred times ; in five days it
attains to its full size. When the larvae are of full size,
(1) Mr. G. Newport, Cyclopcedia of Anatomy and Physiology.
INSECTA.
595
they change into the pupa state, and remain in that state
a few days; they then become flies, soon produce thou-
Fig. 268. Proboscis of House-fli/. Drawn, from a preparation by Topping. (The
small circle incloses the same about natural size.)
Q Q 2
596 THE MICROSCOPE.
sands of eggs, larvae, and flies, and this is repeated again
and again until the whole brood is destroyed by winter's
cold. 1
The " Tsetse" fly of tropical Africa (Glossing morsitans}:
the mouth, proboscis, and piercing apparatus of one, viewed
from the under-side, is represented in Plate VI. No. 131.
The biting apparatus consists of four parts, of which two
are lateral setose palpi ; if a horny case for the protection
of the proboscis and its contained style can be so called.
The palpi, although arising from two roots, when joined
together, and accurately embracing the proboscis, as they
will do when the fly is at rest, appear as one only ; but
when the insect is in the act of piercing or sucking, they
divide, and are thrown directly upwards. The palpi are
furnished on the outer, or convex sides, with long and
sharply pointed, dark-brown setae or hairs ; while the
inner or concave sides which are brought in contact with
the proboscis are perfectly smooth and fleshy. Three cir-
cular openings seem to indicate the tubular character of
what in the common fly is a fleshy, expanded, and highly-
developed muscular proboscis : in the Glossina it is a
straight, horny-looking, red-coloured bristle, the apex of
which is slightly dilated and rounded, and apparently
barbed, while it expands a little towards the base, and
there dilates into a large-sized fleshy bag, or muscular sac,
filled with a red-coloured fluid. The proboscis is grooved
on the under-side for the purpose of receiving a slender
glassy style, acutely pointed, and equal to it in length.
The style, nicely adapted to the groove, and taking its
rise from the poison gland, is the penetrating instrument,
A series of long and thin muscular bands embrace this
gland, and their tendinous insertions are so arranged as to
bring considerable force to bear upon its contents. Phy-
siological science has made us familiar with the fact, that
(1) Dead flies may be constantly observed, about autumn, surrounded by n
ort of halo, which, upon examination, is found to consist of the spores of a
oingus. The abdomen is much distended, and the rings composing it are
separated from each other, the intervals being occupied by white prominent
jsones, constituted of a fungoid growth proceeding from the interior of the
body. Further examination will show that the whole of the contents or the
body of the fly have been consumed by the parasitic growth, and that nothing
remains but an empty shell, lined with a thin felt-like layer composed of the
interlaced mycelia of the innumerable fungi. See Dr. F. Colm's observations
upon the parasite in vol. v. p. 154, Journ. Micros. Sci. 1857.
HXG8 OP INSECTS. 597
all fluid poisons are enormously increased in their power
for good or for evil, when injected beneath the skin ; this
knowledge prepares us to understand how it is that a drop
from the poison gland of that wonderful little fly is suffi-
ciently potent and virulent to destroy a large animal in
a few minutes. Dr. Livingstone tells us that on one
occasion he lost forty-three oxen in as many minutes,
" when not more than a score of the ' Tsetse' flies could
be seen." The tongue is neither large nor well developed,
but this is in a measure balanced by the mouth and lips ;
the latter are muscular, and capable of affording great
assistance while the fly is in the act of sucking the blood
of its victim. The w T ings are long and powerful ; the legs
strong and muscular ; the feet provided with the usual
appendages, terminating in a pair of strong claws of a
rather large size.
The wings of insects exhibit variety in form and struc-
ture, as well as beauty of colouring ; the art with which
they are connected to the body, the curious manner in
which some are folded up, the fine articulations provided
for this purpose, with the various ramifications by which
the nourishing fluids are circulated and the wings strength-
ened, all afford a fund of rational investigation highly
entertaining, and exhibiting, when examined under the
microscope, beautiful and wonderful design in their forma-
tion. Take the Libellulidce (Dragon-flies) as an example,
whose wings, with their horny framework, are as elegant,
delicate, and as transparent as gauze; often ornamented
with coloured spots, which, at different inclinations of the
sun's rays, show all the tints of the rainbow. One species
(Calepteryx virgo) will be seen sailing for hours over a piece
of water, all the while chasing, capturing, and devouring
the numerous insects that cross its course ; at another time
driving away competitors, or making its escape from an
enemy, without ever seeming tired or inclined to alight.
In fine weather, female Dragon-flies are seen to deposit
their eggs upon the water, making a strange noise, as
though they were beating the water; the cluster of eggs
looks like a floating bunch of small grapes. The larvaB,
when hatched, live in the water ; and it is scarcely pos-
sible to fancy more strange-looking creatures. They are
598 THE MICROSCOPE.
ehort and comparatively thick, with movements heavy and
clumsy, and after shedding their skins become pupae : still
continuing to live in the water. The pupae differ from
the larvae principally in having four small scales on their
sides ; these conceal their future wings. While the Dragon-
fly continues in its aquatic state, both as larva and pupa,
it devours all the insects it can entrap ; and as it only
moves slowly, it is furnished with a very curious apparatus
near its head, which it projects at pleasure, and uses as
a trap. This apparatus consists of a pair of very large,
jointed, movable jaws, which the insect keeps closely
folded over its head, like a large mask, till it sees its
prey; when it does, it creeps softly along till it is suffi-
ciently near ; it then darts out those long, arm-like jaws,
and suddenly seizing its prey, conveys it to its mouth.
When the Dragon-fly is about to emerge from its pupa-
case, it places itself .on the brink of the pond, or on the
leaf of some water-plant sufficiently strong to bear its
weight, and there, divests itself of its pupa-case. When the
perfect insect first appears, it has two very small wings ;
these gradually increase, and in a short time two other
wings appear. As soon as the wings are fully expanded,
and have attained their beautiful gauze-like texi/ure, the
Dragon-fly begins to dart about, and then commences its
work of destruction.
Equally rapid, exactly steered, and unwearied in its
flight is the Gnat. The wings of a Gnat have been calcu-
lated, during its flight, to vibrate 3,000 times in a minute ;
these wonderful wings are covered on surface and edge
with a fine down or hair. The alternations of bright sun-
shine and rain, so commonly seen in March, are extremely
favourable to the appearance of Gnats. The first that
appear are called Winter Midges (Tricliocera hyemalis). As
the spring advances, these Midges are succeeded by others
somewhat different ; and as the weather becomes warmer,
the true Gnats appear. The sting of the Gnat (Culex
pipiens) is well known ; although the insects themselves,
so very rapid in their movements, are so much dreaded
that very few people care to examine the delicacy and
elegance of their forms. The sting is very curiously con-
trived (see fi^. 269), and inclosed in. a sheath, folds up
STINGS OP INSECTS.
599
after one or more of the six lancets have pierced the flesh ;
it will inflict a severe though minute wound, the pain of
which is increased by an acrid liquid injected into it
through a curiously-formed proboscis ; this latter is covered
over with feathers or scales. A magnified view of one of
these feathers is seen at No. 3. Another scale from a
Fig. 269.
L Head of Culex pipiens, Fo.male Gnat, detached from the body. 2, Wing.
3 A Scale from the Proboscis. 4, Proboscis and Lancets. The reticulation
on each side of the head shows the space occupied by the eyes. The feather
or scale from proboscis is magnified 250 diameters
600 THE MICROSCOPE,
Gnat's wing is magnified! 350 diameters, fig. 273, No 7.
The proboscis is protected on either side by antennae, 01
feelers.
The metamorphosis of the larva of Corethra plumi-
comis, one of the Gnat tribe, has been carefully in-
vestigated by Professor Rymer Jones, F.RS. 1 This
competent observer brings out many points of interest ;
one in particular deserves notice, namely, the use of
the four remarkable-looking jet-black bodies situated
in the body of the larva, two of which are placed in the
thoracic region, and two near the centre of the posterior
half of the body. These, which had hitherto puzzled
all observers, were satisfactorily explained by the late
Professor Jones, who had the good fortune to witness a
metamorphosis. In form these bodies are more or less
kidney-shaped, and to all appearance completely isolated
in the body. Upon crushing the insect in the compresso-
rum, they are seen to be filled with air, and it is by their
aid the creature is enabled to rise and sink at pleasure.
They are composed of a series of small vesicles, each of
which has several coats : of these the outermost, when feebly
magnified, seems of a uniform hue of black, but under a
higher power is seen to be made up of many pigment cells,
so as to give the organ a reticulated appearance ; and it is
only when this black pigment has been removed, together
with a dull opaque membrane whereon the black patches
rest, that the real air-sac is displayed. When thus denuded,
the true walls of the air-sac appear to be composed of
a dense membrane, possessing great refractive power, the
effect of which upon transmitted light is extraordinary.
When highly magnified, it is found to be entirely com-
posed of numerous coils of a delicate fibre,, similar to that
which maintains the permeability of the tracheae of ordi-
nary insects, arranged in several superimposed layers, and
having the appearance of being closed in on all sides. It is
not until the larva thus constituted has arrived at its full
size that the appearances described become complicated by
intermixture with organs belonging to the pupa condition
of the insect. At this period, however, the rudiments of
(1) See Trans. Micros. Soc. Oct. 1867, " On the Structure and Metamoiphosi*
of the larva of Corethra plumieornis."
INSECTA. 601
future limbs begin to show themselves under the form of
transparent vesicles, which, as they enlarge, crowd the
thoracic region of the body. The change from the larva
to the pupa condition involves phenomena of the most
startling character. The air-sacs, situated both in the
thoracic region and in the hinder portion, burst and
unfold themselves into an elaborate tracheal system, and
a pair of ear-shaped tubes, of which not the slightest trace
could hitherto be discerned, make their appearance upon
the dorsal aspect of the thorax ; two long tracheae seem to
be thus simultaneously produced, occupying the two sides
of the body, and constituting the main trunks, from which
large branches are given off to supply, in front, the head,
the eyes, and the nascent limbs; while posteriorly they
spread over the now conspicuous ovaries, and terminate by
ramifying largely through the thin lamella that constitute
the caudal appendages. In individuals subjected to micro-
scopic examination within a very brief period after their
assumption of the pupa state, the places originally filled
by the air-sacs of the larva are found to be occupied by
the lateral remnants of their external coats, clearly indi-
cated by ragged membranes, covered with patches of black
pigment, in the immediate vicinity of which numerous
air-bubbles are met with, extravasating, as it were, into
the cellular tissue.
The family Phryganeidce, the larvae of which are aquatic,
present almost as little resemblance to the imago as those
of some metabolous insects. They are long, softish grubs,
furnished with six feet, and with a horny head armed with
jaws, generally fitted for biting vegetable matters, although
some appear to be carnivorous. To protect their soft
bodies, which constitute a very favourite food with fishes,
the larvae are always inclosed in cases formed of bits of
straw and sticks, pebbles, and even small shells. The
materials of these curious cases are united by means of
fine silken threads, spun like those of the caterpillars of
the Lepidoptera, from a spinnaret situated on the labium.
In increasing the size of its case to suit its growth, the
larva is said to add to the anterior part only, cutting off a
portion of the opposite extremity. When in motion, tho
larva pushes its head and the three thoracic segments,
602 THE MICROSCOPE.
which are of a harder consistence than the rest of the
body, out of its case ; and as the latter is but little, if at
all, heavier than the water, the creature easily drags it
along behind, thus keeping its abdomen always sheltered.
It adheres stoutly to the inside of its dwelling by means of
a pair of articulated caudal appendages, generally assisted
by three tubercles on the first abdominal segment. Before
changing to the pupa state, the larva fixes his case to some
object in the water, and then closes up the two extremities
with a silken grating, through which the water necessary
for the respiration of the pupa readily passes. The pupa
is furnished with a large pair of hooked jaws, by means of
which, when about to assume the perfect state, it bites
through the grating of its prison, and thus sets itself free
in the water. In this form the pupae of some species
swim freely through the water by means of their long hind
legs, or creep about plants with the other four ; frequently
rising to the surface of the water, they there undergo their
final change, using their deserted skin as a sort of raft,
from which to rise into the air ; others climb to the surface
of aquatic plants for the same purpose.
The perfect insect (Phryganea grandis) has four wings,
with branched nervures, the anterior pair of which, clothed
with hairs, are more frequently used than the posterior.
The organs of the mouth, except the palpi, are rudimen-
tary, and apparently quite unfit for use. The head is fur-
nished with a pair of large eyes, and with three ocelli ;
the antennae are generally very long. Some species are so
exactly like Moths, that they have often been supposed to
belong to the Lepidopterous order ; in point of fact, these
insects may be considered to form a connecting link
between the Neuroptera and the Lepidoptera. The females
have been seen to descend to the depth of a foot or more
in the water, to deposit their eggs.
Eggs of Insects, Plate VI. No. 124, &c. In form,
colour, and variety of design, the eggs of insects are more
surprisingly varied than those of the feathered tribes ;
but as from their smallness they escape observation, our
acquaintance with their structure and peculiarities is neces-
sarily limited and imperfect. Although the eggs of the
animal series differ much in their external characteristics,
EGGS OF INSECTS. 603
they closely resemble each other while yet a part of the
ovarian ova, and prior to their detachment from the ovary.
At one period of their formation all eggs consist of three
similar parts : 1st. The internal nucleated cell, or ger-
minal vesicle, with its macula ; 2d. The vitellus, or yolk-
substance ; and 3d. The vesicular envelope, or vitelline
membrane. The germinal vesicle being the first produced
may be regarded as the ovigerm ; then comes the yolk-
substance, which gradually envelopes it, or is deposited
around it ; and the vitelline membrane, the latest formed,
incloses the whole. The chemical constituents of the egg
contents are albumen, fatty matters, and a proportion of a
substance precipitable by water. The production of the
chorion, or shell membrane, does not take place till the
ovum has attained nearly the full size, and it then appears
to proceed, in part at least, from the consolidation over the
whole surface of one or more layers of an albuminous fluid
secreted from the wall of the oviduct. The observations
of H. Meyer have shown that a part of the outer mem-
brane is derived from a conversion into it of the inner
cellular or epithelial lining membrane of the oviduct, at
the place where it is in closest contact with the surface of
the ovum. Dr. Allen Thompson therefore thinks that
"many of the varieties in. the appearance and structure of
the external covering of eggs may probably depend on the
different modes of development of these ceils."
The embryo cell is so directly connected with the
germinal vesicle that at a certain period it disappears alto-
gether, and is absorbed into the germinal yolk, or rather
becomes the nucleus of the embryo, when a greater degree
of compactness is observed in the yolk, and all that remains
of the germinal vesicle is one or more highly refracting
fat globules and albuminoid bodies. Towards the end of
the period of incubation, the head of the young cater-
pillar, according to Meissner, lies towards the dot or
opening in the lid, which he terms the micropyle* from its
resemblance to a small gate, or opening through which the
worm emerges forth. From a number of careful observa-
(1) The term micropyle (a little gate) has heretofore only been used in its re-
lation with the vegetable kingdom : it is used to denote the ODening or foramen
towards which the radicle is always pointed.
604 THE MICROSCOPE.
tions made on the silkworm, we have not been able to
satisfy ourselves of the correctness of these particulars :
in every case, indeed, the young worm makes its way out
from a point generally below this spot. Leuckart, how-
ever, expresses his belief in this micropyle, and says, " It
becomes at a later period converted into a funnel, which is
connected directly with the mouth of the embryo, and
serves to convey nourishment from without to it." "We,
on the contrary, look upon it as an involuted portion of
membrane, indicating the spot where the formative pro-
cess of the outer membrane terminated, or where at a still
earlier stage, and while the ova was yet in the ova-sac, the
spermatozoa passed in to fecundate the yolk mass.
The germinal vesicle is very large and well marked,
while the egg is yet in the ova-sac of the insect. By. pre-
paring sections, after Dr. Hallifax's method, 1 we find that
the germinal vesicle in the bee's egg is not situated imme-
diately near or even below the so-called micropyle, but
rather more to the side of the egg ; just in the position
which the head of the embryo is subsequently found to
occupy when it arrives at maturity.
The egg membrane, or envelope, of all the Lepidop-
tera, is composed of three separate and distinct layers :
an external slightly raised coat, tough and hard in its
character, a middle one of united cells, and a line trans-
parent vitellina lining membrane, perfectly smooth and
homogenous in structure, imparting solidity, and giving a
tine iridescent hue to the surface, such as most of us admire
in old glass exhumed from the ruins of Pompeii. The
germinal vesicle is of a proportionately large size for the
egg, and its macula is at first single, then multiple. In
the silk-worm's egg the outer membrane is comprised of
an inner reticulated membrane of non- nucleated cells, and
in the outer layer the cells are arranged in an irregular
circular form, also non-nucleated, with minute interstitial
Betas or hairs projecting outward.
The outer surface of the egg-shell of Coccus Persicce is
(1) Dr. Hallifax adopts the method of killing the insect with chloroform : he
then immerses it in a bath of hot wax, in which it is allowed to remain until the
wax becomes cold and hard ; now with a sharp knife a section is easily made in
the required direction without in the least disturbing any of the fragile parts,
>r internal organs.
EGGS OP IXSECTS. 605
covered by minute rings, of which the ends somewhat over-
lap. These rings are thought to be identical in their
character with the whitish substance which exudes through
pores on the under-side of the body ; and it is more than
probable that these layers of rings and their arrangement
account for the beautiful prismatic hues which they pre-
sent when viewed as opaque objects under the microscope,
and by the aid of the side-condenser. This white sub-
stance, it should be observed, becomes a part of the intimate
structure of the egg-shell, and is in nowise affected by
either strong spirit or dilute acids. Sir John Lubbock 1
states that in the greenish eggs of Phryganea, " the colour
is due to the yolk-globules themselves. In Coccus, how-
ever, this is not so ; the yolk-globules are slightly yellow,
and the green hue of the egg is owing to the green granules,
which are only minute oil globules. When, however, the
egg arrives at maturity, and the upper chamber has been
removed by absorption, these green granules will be found
to be replaced by dark-green globules, regular in size, and
about 1 -8000th of an inch in diameter, and which appear
to be in no way the same in the yolk of Phryganea eggs."
Another curious fact has been noticed, which partially
bears on the question of colour : the production of parasite
bodies within the eggs of some insects. In the Coccus, for
instance, parasitic cells of a green colour occur, " shaped
like a string of sausages, in length about the 1 -2000th of
an inch by about the I -7000th in breadth."
The eggs of Moths and Butterflies present many varying
tints of colour ; in speaking of this quality we do not re-
strict the term solely to those prismatic changes to which
allusion is so often made, and which are liable to constant
mutations according to the accident of the rays of light
thrown upon them ; but we more particularly refer to the
several natural transitions of colour, the prevailing tints
of which are yellow, white, grey, and a light-brown. In
some eggs the yellow, white, and grey are delicately blended,
and when viewed with a magnifying power of about fifty
diameters, and by the aid of a side-reflector (parabolic-
Deflector), present many beautiful combinations. The
aiost delicate opalescent or rather iridescent tints appear
a) Phil. Trans. 1S0, p. 341.
606 THE MICROSCOPE.
on others, of wlich the eggs of the feathered tribes
furnish no example. The egg of the Mottled Umber
Moth (Eranni* defolarid), Plate VI. No. 137, is in every
particular very beautiful. It is ovoid, with regular
hexagonal reticulations, and at each corner studded with
a raised knob or button ; the space within the hexagon is
finely punctated, and the play of colours is exquisitely
delicate. In this egg no micropyle can be seen. The
egg of the Thorn Moth (Ennomos ' erosaria), Plate VL
No. 138, is of an elongated brick-looking form, one end of
which is slightly tapered off, while the other in which
the lid is placed is flattened and surrounded by a beauti-
fully white-beaded border, having for its centre a slightly
raised reticulated micropyle. The empty egg-shell gives
a fine opalescent play of colours, while that containing the
young worm appears of a brownish-yellow.
The egg of the Straw-belle Moth (Aspilates g&varia),
Plate VI. No. 139, is delicately tinted, somewhat long
and narrow, with sides slightly flattened or rounded off,
and irregularly serrated. The top is con-vex, and the base
a little indented, in which are seen the lid and micropyle.
The young worm, however, usually makes its way through
the upper convex side : the indentation represented in the
drawing shows the place of exit.
An example of those eggs possessing a good deal of
natural colour is presented in that of the Common Puss
Moth (C. Vinula), a large spheroidal-shaped egg, having,
under the microscope, the appearance of a fine ripe
orange ; the micropyle exactly corresponds to the depres-
sion left in this fruit by the removal of the stalk ; the sur-
face is finely reticulated, and the natural colour a deep
orange.
The egg of the Mottled Eustic Moth (Caradina
Morpheus), No. 124, is subconical, and equally divided
throughout by a series of ribs, which terminate in a well-
marked geometrically-formed lid. The Tortoise-shell
Butterfly (Vanessa urtica), No. 125, presents us with a
delicate ovoid egg, divided into segments, the ribs of
which turn in towards the micropyle. The Common
Footman (Lithosia campanula), No. 126, produces a per-
fectly globular egg covered with fine reticulations, and of
TONGUES OF INSECTS. 607
a delicate buff colour. The egg of the Shark Moth (Cu-
cullia umbrattca), No. 127, is subconical in form, with
ribs and cross-bars passing up from a flattened base to the
summit, and turning over to form the lid. No. 136, the
Egg of Blue Argus Butterfly (Poiyommatus Argus). That
of the Small Emerald Moth (JodisVernaria),No. 134, is
an egg of singular form and beauty, an oval, flattened on
both sides, of silvery iridescence, and covered throughout
with minute reticulations and dots. It is particularly
translucent, so much so that the yellow-brown worm is
readily seen curled up within. The lid or micropyle is
not detected until the caterpillar eats its way out of the
shell. It should be stated that the whole series of eggs
in the plate are considerably over-coloured, and conse-
quently lose much of their beautiful transparency. The
eggs of Elies and Parasites also present much variety in
form, colour, and construction. Many of their eggs are
provided with a veritable lid, which opens up with a hinge-
like articulation. The cover is shown in Plate VI. No.
144, Egg of Bot-fly, from which the larva is seen just
escaping ; No. 146, Egg of Scatophaga ; No. 147, Egg of
Parasite of Magpie. 1
Moths and Butterflies supply the microscopist with
some of the most beautiful objects for examination. What
can be more wonderful in its adaptation than the antenna
of the Moth, represented in fig. 271, No. 1, with a thin,
finger-like extremity almost supplying the insect with a
perfect and useful hand, moved throughout its extent by
a muscular apparatus of the most exquisite construction !
The tongue of Butterfly, No. 2, is evidently made for the
purpose of dipping into the interior of flowers and extracting
the juices ; this is furnished with a spiral band of muscle :
an enlarged view of a portion is given at No. 3. See also
Plate VI. Nos. 132 and 133, Antennae of Vapour Moth.
The inconceivably delicate structure of the maxillse or
tongues (for there are two) of the Butterfly, rolled up like
the trunk of an elephant, and capable, like it, of every
variety of movement, has been carefully examined and
described by Mr. Newport. " Each maxilla is convex on
(1) A paper on the Eggs of Insects, giving many other forms wiH be found in
the Intellectual Observer, Oct. 1867.
608
THE MICROSCOPE.
Fig. 271.
I, The AnUwa of the Silkworm-moth. 2. Tongue of a Butterfly. 3, A portion
of the Tongue highly magnified, showing its muscular fibre. 4, The Trachea
of Silkworm. 5, The Foot of Silkworm. (The small circles enclose each some-
what near tho natural size).
IN8ECTA. G09
its outer surface, but concave on its inner ; so that when
the two are approximated, they form a tube by their union,
through which fluids may be drawn into the mouth. The
inner or concave surface, which forms the tube, is lined
with a very smooth membrane, and extends throughout
the whole length of the organ; but that each maxilla is
hollow in its interior, forming a tube ' in itself,' as is
generally described, is a mistake; which has doubtless
arisen from the existence of large trachese, or breathing-
tubes, in the interior of each portion of the proboscis. In
some species, the extremity of each maxilla is studded
externally with a great number of minute papilla?, or
fringes as in the Vanessa atalarita in which they are
little elongated barrel-shaped bodies, terminated by smaller
papillae at their extremities." Mr. Newport supposes that
the way in which the insect is enabled to pump up the
fluid nourishment into its mouth is this : " On alighting on
a flower, the insect makes a powerful expiratory effort, by
which the air is expelled from the interior air-tubes, and
from those with which they are connected in the head and
body ; and at the moment of applying its proboscis to the
food, it makes an inspiratory effort, by which the central
canal in the proboscis is dilated, and the food ascends it at
the same instant to supply the vacuum produced; and
thus it passes into the mouth and stomach : the constant
ascent of the fluid being assisted by the action of the
muscles of the proboscis, which continues during the whole
time that the insect is feeding. By this combined agency
of the acts of respiration and the muscles of the proboscis,
we are also enabled to understand the manner in which
the Humming-bird sphynx extracts in an instant the honey
from a flower while hovering over it, without alighting;
and which it certainly would be unable to do, were the
ascent of the fluid entirely dependent upon the action of
the muscles of the organ." 1
The wings of Moths and Butterflies are covered with
scales or feathers, carefully overlapping each other, as tiles
are made to cover the tops of houses. The iridescent variety
of colouring on their wings arises from a peculiar wavy
arrangement of the scales. Figs. 272 and 273 are tnagni-
(1) Cyclop, Anat. PhysioL, article "Insecta."
R R
S10
THE MICROSCOPE.
fied representations of a few of them. No. 1 is a scale of
the AfSrpho menelaus, taken from the side of the wing, of a
272. Scaletfrom Butterflies' and Moths' wings. (Magnified 200 diarceters.)
J, Scale of Morpho Menelaus. 2, Large Scale of Polyommatus Argiolus, azure
blue. 3, Hlpparchia Janira Argiolus. 4, Pontia Brassica. 5, Podura
Plum&ea. 6, Small Scale of Azure Blue.
pale-blue colour : it measures about 1-1 20th of an inch in
length, and exhibits a series of longitudinal stripes or lines,
between which are disposed cross-lines or striae, giving it
the appearance of brick-work. The microscope should be
enabled to make out these markings with the spaces
between them clear and distinct, as shown in fig. 273,
No. la.
Polyommatus argiolus, Azure-blue, Nos. 2 and 6, are
large and small scales taken from the under-side of the
wing of this beautiful blue butterfly; the small scale is
covered with a series of. spots, and exhibits both longitu-
INSECTA.
611
dinal and transverse strise, which should be clearly denned,
and the spots separated : this is a good test of the denning
power of a quarter-inch object-glass.
No. 3, Ripparcliia janira, Common Meadow Brown
Butterfly scale : on this we see a number of brown spots
of irregular shape and longitudinal striae.
No. 4, Pontia brassica, Cabbage-butterfly, affords an
excellent criterion of the penetration and definition of a
microscope: it is provided at its free extremity with a
brush-like appendage. With a high power, the longitu-
dinal markings appear like rows of little beads. Cheva-
lier's test-object is the scale of the Pontia brassica, the
granules of which must be rendered distinct. Mohl and
Schacht use Hipparchia janira as a test for penetration,
with a moderate angular aperture and oblique illumina-
tion. Amici's test-object is Navicula Rhomboides, the dis-
play of the lines forming the test ; this is a very good test
for angular aperture.
Fig.273. Portions of Scales, magnified 500 diameters.
la, Portion of Scale of Morpho Menelaus. 5a, Portion of Large Scale of Podura
Plumbea. 7, Scale from the Wing of Gnat; its two layers are here represented.
8, Portion of a Large Scale of Lepisma Saccharina.
The Tinea vestianella, Clothes-moth, possesses very deli-
cate and unique scales; two of these are imperfectly
represented near the Acarus taken from one of these moths,
at page C41. The feathers from the under-side of the
R R 2
612 THE MICROSCOPE.
wing are the best, requiring some management of illumi-
nation to bring out the lines sharp and clear.
The common Clothes-moth generally lays its eggs on
the woollen or fur articles it is bent upon destroying; the
larva begins to eat immediately it is hatched ; then with
the hairs or wool it first gnaws off, it forms a case or
tube, under the protection of which it devours the sub-
stance of the article on which it fixes its abode. This
tube is of parchment4ike consistence, and quite white;
is cylindrical in its shape, and furnished at both ends with
a kind of flap, which the insect raises at pleasure, and
crawls out; or it projects the front part of its body with
its fore-feet through the opening, just enough to enable
it to creep about without removing the rest of its body from
the tube, which it draws after it. There are several kinds
of Clothes-moths, the caterpillars of many bury them-
selves in the article on wnich they feed,
instead of making the tube before-men-
tioned. The moths also differ very much
in appearance ; the commonest is of a light
r;cr 074 -The BiucJ- ^ u ^ co ^ our > one s P ecies > Tinea tapetzella,
'aothes-motk. ac " fig. 274, is nearly black, with the larger
wings white tipped, or pale grey.
The wavy appearance seen in the Gnat's scale (fig.
273) is most certainly an error of interpretation. For
this reason I have had prepared a more highly magni-
fied drawing of the body-scale of the Gnat. The scales
of Culex pip ens may very properly be divided into three
if not four varieties. Those found on the proboscis, palpi,
and legs, and which form a complete covering to these
parts, are of a battledore shape ; those on the nervures
and marginal portions of the wings differ in form, whilst
the intermediary portions of the wings and the under
surface of the body have feathery tufts of a trumpet-
shape. A slight variation is seen in some other scales,
but each scale is inserted into the membrane by a pedi-
cle or foot-stalk, terminating in short rootlets, shown
in the wood-cut. These transverse markings of the
scale, when seen slightly out of focus, give an ideal wavy
appearance. It is not improbable that, on a more care-
ful comparison of the scales of Culicidw, it will be found
GNATS' SCALES.
613
that I have overlooked other characteristic variations :
for, on cursorily going over the collection of Gnats in
the British Museum, I came across a variety quite new
to me. Culex annulatus offers a body colour variety.
Alternate rings of dark and white coloured battledore
scales cover the greater part of the body ; and the
thin fringe of hairs projecting out on either side are
longer and more numerous than in
C. musquito. The feathered antlers,
pectinate-antennae, of the male insect
are very attractive objects under a
moderate magnification, and these
surmount a brilliant sparkling set of
compound ocelli.
In the genus Coccina (Dortkesia),
several species are found; the fe-
male although apterous and active
in all stages is completely covered
with a snowwhite secretion.
In another genus.the Phytophthiria,
both sexes are indifferently wingless
or furnished with four distinctly
veined wings. The rostrum spring-
ing apparently from the breast ;
whilst the tarsi, two-jointed, are
furnished with two claws. The
most familiar species of this tribe
are the Aphides, Plant-lice.
The Gnat-like midges, so very
common in England, are also fur-
nished with plumed antennae, and
are not unfrequently in consequence
mistaken for Culex pipens. They
belong, however, to Tipulidce, and
are quite destitute of scales, and
their larvae differ very materially.
The Maple-aphis, better known as the Leaf Insect
(Plate VI. No. J.28), averages about the one-fiftieth of an
inch in length, and, although long sold and exhibited
under the name of the "Leaf Insect," nothing was
known of its origin and history, with the exception of
Body-scale of Gnat
magnified 850 di-
ameters.
614 THE MICROSCOPE.
what the Eev. J. Thornton stated in 1852, to whom
we owe its discovery on the leaves of the maple ; he,
believing it to be a species of Aphides, called it Phyl-
loplwrus testudinatus. Subsequently it attracted the
attention of the Dutch naturalist Van der Hoeven,
who regarded it as the larval form of an undetermined
species of Aphis, and named it Periphyllus. It has more
recently engaged the attention of Dr. Balbiani and M.
Siguoret, whose united investigations are given in the
" Comptes Eendus " of June 17, 1867. They have posi-
tively ascertained that it is the larva of Aphis aceris ; a
brown species is also met with during a great part of the
year upon the young shoots of the maple. At the sanio
time a curious fact was made out, constituting a new and
remarkable peculiarity in the development of this group
of insects, already presenting so many curious phenomena
in connexion with their reproduction. It really appears
that the female produces two kinds of young one normal,
the other abnormal ; the first are alone capable of con-
tinuing the course of their development, and capable of
reproducing the species ; whilst the latter retain their
original form, which is never changed throughout their
existence. They increase so little in size, that it appears
almost doubtful whether they eat ; the mouth is so very
rudimentary that this surmise in some measure gains sup-
port from the circumstance ; they undergo no change of
skin, never acquire wings like the reproductive insect,
and their antennae always retain the five joints which
are peculiar to all young Aphides before the first moult.
Neither are they all of the same colour, some being of a
bright green, as represented in our Plate, while others are
of a darker, or brownish-green, colour. The brown-green
embryos differ from the adult female only in those cha-
racters analogous to all other species ; and that chiefly
with regard to the hairs, which are long and simple. In
the green embryos, in the place "of hairs, the body is sur-
rounded with scaly, transparent lamella, more or less
oblong in shape, each of which is traversed by divergent
ramifying nervures. These lamellae not only occupy the
body, but also the anterior part of the head, the first joint
of the antennae, and the outer edge of the tibia3 of the
APHIDES. 615
two anterior pair of legs. The dorsal surface in these
insects is covered with a mosaic of hexagonal plates, very
closely resembling the plates of the carapace of the tor-
toise. In this particular our artist has certainly fallen
into an error. Another peculiarity is that the body is
much flattened out, and looks so much like a scale on the
surface of the leaf, that it requires considerable practice,
as well as quickness of sight, to detect the young Maple-
aphis. One of the lamellae is seen highly magnified at c,
and a tenent-hair at b. The antennae taper off towards the
apex, are serrate on both edges, and terminate in fine
setse, one of which is shown at a. Below the insertions
of the antennas, brilliant scarlet-coloured compound eyes
are placed, which receive their nervous supply from the
central ganglion.
Aphides live upon plants, the juices of which they
suck, and, when they occur in great numbers, cause con-
siderable damage to vegetation ; a fact well known to
the gardener and farmer. Many plants are liable to be
attacked by swarms of these insects, which cause the
leaves to curl up : they grow sickly, and their produce is
greatly reduced. One striking instance is presented in the
devastation caused by the Hop-fly (Aphis humuli).
The Aphrophora lifasciata, common Frog-hopper, has
the antennas placed between the eyes, and the scutellum
visible that is to say, not covered by a process of the
prothorax. The eyes, never more than two in number,
are sometimes wanting. These little creatures are always
furnished with long hind legs, which enable them to per-
form most extraordinary
leaping feats. The best-
known British species, be-
cause so very abundant in
gardens, is the Cuckoo-spit,
Froth-fly, fig. 275. The
names Cuckoo- spit and
Froth-fly both allude to the Fig ^ 5 .- A pTirophora spumaria,
peculiar habit of the insect, cuckoo-spit.
while in the larva state, of The froth y substance, i, The pupa. 1
enveloping itself in a kind of frothy secretion, somewhat
resembling saliva ; and this, indeed, was at one time sup-
C16 THE MICROSCOPE.
posed to be the saliva of the cuckoo, heing found on the
young shoots of plants just about the time the cuckoo is
heard in the woods.
The Hymenoptera are distinguished from other insects
with membranous wings by the presence of an ovipositor
of peculiar construction at the extremity of the abdomen
of the females, which serves for placing the eggs in the
required position ; and in the males of some (Bees, Wasps,
fee.) constitutes a most formidable offensive weapon. As
ehe structure of this organ, which is rarely absent, is
essentially the same throughout the order, the form of its
component parts being merely modified to suit the exigencies
of the different insects, a short description of its structure
will not be considered out of place. The ovipositor,
borer, or sting, generally consists of five pieces : a pair of
horny supports (fig. 279) forming a sheath for the borer
or ovipositor, being jointed at the point where they issue
from the cavity of the last abdominal segment, and the
last joint is usually as long as the borer itself. The latter
consists of three bristles, of which the superior is grooved
along its lower surface, for the reception of a pair of fine*
styles, and these are barbed at the point. The threa
pieces, when fitted together, form a narrow tube, through
which the eggs pass to their destination, the poisonous
fluid also, which renders the sting of the Bee so painful,
is forced down the same into the wound. In the Saw-fly,
a part of this organ remains rudimentary, in other respects
it does not very much differ.
The larvaB of most Hymenoptera are footless grubs
furnished with a soft head, and exhibiting but little, ii
any. advance upon those of Diptera (Plate VI. No. 141).
In the Saw-fly, however, the larva, instead of being, as
above described, a mere footless maggot, presents the
closest resemblance to the caterpillar of the Lepidoptera ;
it is provided with a distinct head, with six thoracic legs,
and in most cases, from twelve to sixteen pro-legs are
appended to the abdominal segments.
The Saw-fly, fig. 276, most destructive to the goose-
berry-bush, is remarkable for the way in which the female
provides for the safety of her eggs. This fly has a flafc
yellow body, and four transparent wings, the outer two oi
OVIPOSITORS OF INSECTS.
61'
which have brown edges. The female lays her eggs on
the under-side of the leaf, along the projecting veins;
these are firmly attached, and cannot be removed without
Fig. 27& T7w? Caterpillar and Saw-fly of Gooseberry- tree.
crushing. The instrument which the little insect uses for
the purpose of cutting the leaf is the most remarkable
piece of perfect mechanism imaginable ; securely lodged,
Fig. 277. Saws of Saw-fly. (The small circle incloses the same nearly tit*
natural size.)
when not in use, in a long narrow slit beneath the abdomen,
and protected by two horny plates, which at first appear
to consist of a single piece ; but upon closer inspection
618 THE MICROSCOPE.
four plates are seen to enter into their construction:
namely, two saws, placed side by side, as in fig. 277 ;
and two supports, somewhat like the saws in shape. A
deep groove runs along the thicker edge of the latter,
which is so arranged that the saws glide backwards and
forwards, without a possibility of running out of the
groove. When the cut is made, the four are drawn
together; and through a central canal, which is now
formed by combining the whole, an egg is protruded
into the fissure made by the saws in the leaf. The cutting
edges of the saws are provided with about eighteen or
twenty teeth : those have sharp points of extreme delicacy,
and together make a serrated edge of the exact form
given to the finest and best-made surgical saws. In the
summer-time the proceedings of this little insect can bo
watched, and the method of using this curious instrument
seen, by the aid of a hand magnifier ; they are not easily
alarmed when busy at their work.
Many other insects are provided with instruments for
boring into the bark or solid wood itself. The Cynip bores
a hole into the side of the oak-apple,
for the purpose of depositing her egg.
The larva when hatched finds a com-
fortable lodging, and a good supply of
food ; when full grown, it eats its way
out of the nut, and, dropping to the
ground, it assumes the form of the per
feet fly. The most important of this
family is the Cynip gallce tinctorive,
. 278, which is the cause of the gall-
Gall-fly and larva. nu ^ a nut most extensively employed
in the manufacture of ink and for dyeing purposes.
Some of the Wasp tribe, so very peculiar in their habits,
are active agents in the economy of nature. The solitary
Mason-wasps curiously construct nests in the form- of
cells, for the purpose of carefully rearing their young.
The social-wasps, like bees, live in communities, and
have nearly the same divisions of labour and regulations
for the good government of the colony. The struc-
ture and mechanical contrivance of the wasp's sting can
only be seen under the microscope. The sting consists of
STINGS OP INSECTS.
619
barbed darts, which will penetrate the flesh deeply,
and, from a peculiar arrangement of their serrated edges,
their immediate withdrawal is prevented ; by the great
muscular effort required for this purpose, a small sac or
i Bting of Wasp. 2j Sting of Bee. (The small circles show ;act nenrlf tbt
620 THE MICROSCOPE.
bag near the root is pressed upon, and its irritating con
tents squeezed out into the wound. After the fluid is
injected, the wasp has the power of contracting the
barbed points, and then it withdraws the sting from its
victim. In fig. 279 the sting of the wasp is shown, with
its attachments and muscular arrangement ; and it will be
seen that the sting is most wonderfully adapted to become
an instrument of a very effective and dangerous character.
The palpi near it are placed there for the purpose of
cleaning or wiping it ; at all events, this appears to be one
of the uses they are put to.
The proboscis or trunk of the Honey-bee next demands
attention; this is used, with its curious accessories, to
collect the honey while roving about from flower to
flower. The proboscis itself (fig. 280) is very curiously
divided ; the divisions are elegant and regular, beset with
triangular hairs, which, being numerous, appear at first
sight as a number of different articulations. The two
outside lancets are spear-shaped, of a membranaceous or
horny substance, set on one side with short hairs, and
having their interior hollow; at the base of each is a
hinge-articulation, which permits of considerable motion
in several directions, and is evidently used by the busy
insect for the purpose of opening the internal parts of
flowers, and thus facilitating the introduction of its pro-
boscis. The two shorter feelers are closely connected to
the proboscis, and terminate in three-jointed articulations.
Swammerdani thought these were used as fingers in
assisting the removal of obstructions ; but it is more pro-
bable that they are made use of by the insect for storing,
and removing the bee-bread to and from the pocket-
receptacles in the legs. The lower part of the proboscis
is so formed that it can be considerably enlarged at its
base, and thus made to contain a larger quantity of the
collected juice of flowers ; at the same time, it is in this
cavity that the nectar is transformed into pure honey by
some peculiar chemical process. The proboscis tapers on*
to a little nipple-like extremity, and at its base will be
seen two shorter and stronger mandibles, which serve the
nttle insects in the construction of their cells, and from
between which is protruded a long and narrow tongue
TONGUE OF BEE.
621
OT lance ; the whole is most ingeniously connected to the
head by a horny sheath, and a series of muscles and
ligaments. The proboscis, being cylindrical, extracts the
juice of the flower in a somewhat similar way to that of
the butterfly ; when loaded with honey, the insect's next
I, Honey-bee's
Fig. 2SO.
-bee's tongue. 2, Leg, showing pocket for carryin^ the
(The small circles show the objects about the naSraf size.)
Bee-bread.
622 THE MICROSCOPE.
care is to fill the very ingenious pockets situated in its
hind legs (one of which is shown at No. 2) with bee-bread ;
when these little pockets are filled with as much pollen
as the bee can conveniently carry, it flies back to the hive
with its valuable load, where it is speedily assisted to
unload by its fellow- workers ; the pollen is at once
kneaded and packed closely in the cells provided for its
preservation. The quantity of this collected in one day
by a single hive during favourable weather is said to be
at least a pound ; this chiefly constitutes the food of the
working-bees in the hive. The wax is another secretion
exuding through the skin of the insect ; it is found in
little pouches in the under-part of the body, but is not
collected and brought home ready for use, as lias been
generally supposed. The waxen walls of the cells are,
when completed, strengthened by a varnish, called pro-
polis, collected from the buds of the poplar and other
trees, and besmeared over by the aid of the wonderful
apparatus represented in the engraving. If a bee is
attentively observed as it settles down upon a flower,
the activity and promptitude with which it uses the
apparatus is truly surprising; it lengthens the tongue,
applies it to the bottom of the petals, then shortens it,
bending and turning it in all possible directions, for the
purpose of exploring the interior, and removing the pollen.
In the words of Brook :
" The dainty suckle and the fragrant thyme,
By chemical reduction they sublime ;
Their sweets with bland attempering suction strain,
And curious through their neat alembics drain ;
Imbib'd recluse, the pure secretions glide,
And vital warmth concocts th' ambrosial tide."
The leading characteristic of the vast order Coleoptera,
Beetles, consists in the leathery or horny texture of the
anterior wings (elytra), which serve as sheaths for the
posterior wings in repose, and generally meet in a straight
line down the back.
The elytra present us with wing-cases of many CutculioSj
Diamond beetles, the most brilliant of opaque objects.
Some are improved by being mounted in Canada balsam,
whilst others are more or less injured by it : a trial of -a
imall portion, by first touching it with turpentine, decides
IXSECTA
623
this point. Oblique or side illumination shows the play
of colours on the scale to the greatest advantage.
To the genus Ptinus belongs a small beetle known as
the Death-watch, fig. 281. This and the species Anobium
are found in our houses, doing much in-
jury whilst in the larval state. The eggs
are often deposited near some crack in a
piece of furniture, or on the binding of an
old book. As the larvse are hatched, they
begin to eat their way into any furniture
on which they may have been deposited ;
and, having attained a sufficient depth, Fig 281
they undergo transformation, and return, The De ath-watch,
by other passages, as perfect beetles. In Atropus, magnified,
furniture attacked by them, small round holes, about
the size of the head of a pin, may be seen, and to these
holes the term worm-eaten has been applied ; and the
noise, made by the insect striking its head against the
wood, has given rise to the name of Death-watch. The
larva is called a Book-worm when it attacks books ; old
books and those seldom used, are often found bored
through by it. Kirby and Spence mention, that in one
case twenty-seven folio volumes were eaten through, in a
straight line, by this insect. The beetle is very small, and
almost black. The head is particularly small ; and from
the prominence of the thorax, looks as
if it were covered with a hood. The
Anobium puniceum, fig. 282", attacks
dried objects of natural history, and all
kinds of bread and biscuits, particularly
sailors' biscuits, in which maggots fre-
quently abound. In collections of in-
sects, it first consumes the interior;
when the larva assails birds, it is gene-
rally the feet that it devours first ; and
in plants, the stem or woody part. The
larva is a small white maggot, the body
of which is wrinkled, and consists of several segments
covered with fine hairs ; its jaws are strong and horny,
and of a dark brown. The body is white, and so trans-
parent, that the internal organs of the insect can te seen
Fig. 282. AnoUum pu-
niceum, magnified.
624 THE MICROSCOPE.
through it. The beetle itself is of a reddish-brown
colour, covered with fine hairs.
The Bacon -beetle (Dermestes lardarius) is another of
the destructive beetle family. The larva of this beetle is
particularly partial to the skin
of any animal that may fall in
its way; consequently it de-
stroys stuffed animals and birds
in collections of natural his-
tory, whenever it can gain ac-
cess to them. It attacks hams
and bacon for the skin's sake ;
Fig. 283.- Dermestes lardarius. and, being a Very glutton, 6X-
Larva, pupa, and imago.
This larva is long and slender, its body nearly round, and
is divided into thirteen segments, of a blackish-brown in
the middle, and white at the edge ; the whole being fur-
nished with bristle-shaped reddish-brown hairs.
The Dermestidce belong to the family of Necrophagous
beetles, six genera of which have been found in Great
Britain. The D. lardarius is black about the head and
tail, with an ash-grey band across the back, having three
black spots on each wing-case. Sometimes this band takes
a yellowish tinge, and then the hairs, which are here dis-
posed in tufts, are likewise of a yellowish-grey colour.
The beetle is most destructive in spring. The larvse, like
those of the clothes moths, are but seldom seen, being
careful to conceal themselves in the bodies they attack,
and their presence can only be guessed at by finding
occasionally their cast-off skins, which they change several
times during their larvae state. Specimens of hair put
up by the mounters and labelled "Hair of Dermestes,"
do not belong to the species at all. These hairs, long
favourite objects with microscopists, and placed by them
among test-objects, may, it is believed, be those found in
tufts at the extremity of the body of Anthrenus muse-
orum. Westwood says that the larvse of these beetle*
are furnished with tufts of hairs, which are " individually
formed of a series of minute conical pieces placed in suc-
cession, the base being very slender, and the extremity
a large obiong knot, placed on a slender footstalk." This
FOOT OF WATER-BEETLE.
625
description comes very near to that of the hair in question.
It is also suggested that the larvae of another genus, that
of Tiresius serra, furnish these hairs ; but, however that
may be, it is quite clear that the hairs called " Dermestes "
(fig. 307) are not obtained from the Bacon-beetle.
In the Gyrinus, Whirligig, we have a combination of
contrivances to facilitate the creature's movements in the
element in which it lives. The hind legs are converted
into a pair of oars of remarkable efficiency, the point of
Fig. 284.
1, Leg of Gyrinus, Whirligig, with paddle expanded. 2, With paddle closed up.
their connexion with the body being adapted with great
precision to ensure the most effectual application of the
propelling power ; as it strikes out behind in the act of
swimming, a membranous expansion of a portion of the
legs enables the insect to move about with great rapidity ;
upon the legs being drawn back again towards the body,
the membrane closes up, and thus offers but a small
resistance to the water (fig. 284). The eyes are not the
least curious part of the merry little creature ; while one
s s
626 THE MICROSCOPE.
portion of them, that fitted for seeing in the air, is fixed
on the upper part of the head, the lower portion, for
seeing under the water, is placed at the lowest part, a
thin division separating the two.
Sir John Lubhock, writing of aquatic insects, says : *
"Though most of the great orders are represented, no
aquatic Hymenoptera or Orthoptera had till now (1864)
been discovered. Great, therefore, was my astonishment,
when I saw a small Hymen opterous insect, evidently quite
at its ease, and actually swimming by means of its wings,
At first I could hardly believe my sight ; but having found
several specimens, and shown them to some of my friends,
there can be no doubt about the fact. Moreover, the same
insect was again observed, within a 'week, by another ento-
mologist, Mr. Duchess, of Stepney. It is a curious coinci-
dence that, after remaining so long unnoticed, this little
insect should thus be found almost simultaneously by two
independent observers. Mr. "Walker at first considered
the insect to be Polynema fuscipes, but though allied to
that species, it is not identical with it. So completely
aquatic is it in its habits that it can remain immersed for
at least twelve hours ; but it nevertheless requires to come
to the surface at certain intervals to renew the air in its
tracheae. It is uncertain whether P. natans can also use
its wings in flight. They are at any rate not easily incited
to do so. It is a very minute species, and well fitted for
microscopical observation, the female measuring 0'3S of an
inch, and the male 0'42."
Dytiscus marginalis, derived from dutes, a diver. Larva
narrow, body composed of twelve segments, including
head, which is large and strong, bearing antenna, and
armed with two powerful jaws. Several varieties of this
beetle are met with in fresh and still waters. The Iarva3
feed upon other aquatic larvse, such as the Gnat, Dragon-
fly, &c. The suckers on the legs, the feet, &c. are very
interesting objects, and should be mounted for viewing
both as transparent and opaque objects.
To the Orthoptera belong Locustina, Gryllina, and Ache-
iina, all herbivorous insects. The first is represented by our
well-known Grasshopper (Gryllus viridissimus), the secor d,
(1) Joury,. Micros. Soc. vol. iv. p 139. 1864.
SPRING-TAILS, 627
the Gryltina, appear to frequent trees and shrubs more
than the other tribes, the members of which generally
keep among herbage ; and, in accordance with this habit,
many of the exotic species have wing-cases which present
the most perfect resemblance to leaves both in colour and
venation. Of the AcJietina, the common Cricket (Acheta
domestica), fig. 285, the noisy little denizen of the kitchen-
nearth, is the best example. Thesp, insects have the
antennas slender and tapering, and often considerably
.onger than the body. They agree with the Gryllina in
the structure of their singing apparatus ; but the wings,
instead of being arranged in the form of a high-pitched
?oof, are laid flat upon the back. Some of them possess
ocelli, whilst others are destitute of those organs. The
wings are very long, and folded up in such a manner as
to project beyond the wing-cases in the form of a pair of
tapering tails ; the abdomen is also furnished, in both
sexes, with a pair of pilose, bristle-shaped, caudal appen-
dages : in the female these form a long slender ovipositor,
the two filaments being placed side by side, and somewhat
thickened at the tip. The tarsi are three- jointed. The
horny covering and muscular apparatus under the wing-
cases of the Cricket
are very curious, and
will repay microscopi-
cal examination. The
Cricket has tWO wingS, Fig- 285. The Cridreu
covered by elytra or wing-cases of a dry membranous consis-
tency, near the base of which is a horny ridge having trans-
verse furrows, exactly resembling a rasp or file ; this it rubs
against its body with a very brisk motion, and produces
the well-known merry chirp ; the intensity of which is
increased by a hollow space, called the tympanum, acting
as a sounding-board. The gastric teeth are numerous.
In Thysanura there is a remarkable diversity of struc-
ture ; they undergo no metamorphosis, and have no wings.
This order contains two families, Spring-tails, Poduridce,
and Lepismence. In the former, the caudal appendage
has the form of a forked tail (Podura, fig. 286), which is
bent under the body when not in use ; by its sudden ex-
tension the insect causes itself to spring to a very great
88 2
628 THE MICROSCOPE.
distance, in comparison -with its size. The body ie
covered with numerous minute scales, mostly of a beau-
tiful silvery or pearly lustre, and curiously striated.
Podura plumbea, Lead-colour Springtails, are generally-
found in damp places, leaping about like fleas. They
prefer a moist atmosphere,
some take to the surface
of the water in secluded
places ; their food seems
to be vegetable matter of
any kind in a stage of
Fig. 286. Podura plumbea. (In the small decay; the little active
circle the insect appears life-size.) creatures are seen to leap
about if a stone in a damp situation in the garden is
turned up, or if a dark, damp corner of the cellar, about
the beer-barrel, is searched; or if we peep among the
roots of the ferns in the fern-case. Poduridaj, varying in
form, colour, &c. are produced from, eggs, undergo no
metamorphosis, are not parasitic, have from twelve to-
sixteen simple eyes ; are furnished with strong mandibles,
and a broad, curious- looking snout, and a rather long
body, terminating in a bifid tail, which by alternately ex-
panding and contracting, enables them to leap great dis-
tances. The antennae are very long, and covered with
scales and fine hairs. To obtain the scales from the body
without damage which is certain to occur if the Podura
is touched by the fingers take a small test-tube and
quickly place it over the insect, when it instantly springs
up and clings to the side of the tube; insert a thin glass-
cover beneath, and close up the open end. One drop of
chloroform carefully administered instantly kills the in-
sect ; in a very short time this evaporates and leaves the.
tube quite dry. By gently shaking the tube a number of
scales will drop off and adhere to the thin glass cover ;
remove this, and make it secure to the ordinary glass-slip.
Mr. B. Beck says, "that the best scales are obtained
from insects found in comparatively dry places." Mr.
S. J. Mclntire, in an interesting paper on the Podura, 1
confirms this statement, but believes that the "test-scale"
figured by Mr. Beck belongs to a distinct species. The
(1) Science Gossip, March, 1867.
SCALES OF LEPISMA. 629
markings on the scale are better seen when an achromatic
condenser is employed with a good objective. Under a
power of 500 diameters, the surface appears to be covered
with extremely delicate longitudinal and wavy lines. The
smaller scales are much more difficult to resolve than the
larger, and these form a good test of the denning power
of a l-8th or 1-1 2th object-glass. No. 5 a, fig. 274, is a
portion of a large scale. Fig. 273, No. 5, the longitudinal
markings are shown under a lower power. " But the
transverse striaB on the scale of the speckled Podura are
rendered more distinct when the central rays are stopped
out. Any error in the correction of the lenses, whether
in the manufacture or in the adjustment of the thin
covering glass, is immediately detected by the peculiar
appearance which these markings present."
Lepisma saccharina has a spindle-shaped body covered
with silvery scales, the sides of the abdomen being fur-
nished with a series of appendages or false feet, with
long-jointed bristle-like organs at their extremities. The
head is concealed under a pro-thorax ; the eyes are usually
compound, and generally occupy the greater part of the
head. The antennae are very long, and composed of
numerous joints ; the maxillary palpi, which are from five
to seven jointed, are very conspicuous. These insects are
also inhabitants of moist places. The Lepisma saccharina
is commonly found about houses, in sash-frames, old sugar-
casks, &c. ; from the latter circumstance it derives its
name. The scales (fig. 273, No. 8) have long been
favourite objects, and much used for testing the power of
penetration and definition of object-glasses. The scales
should be mounted under thin glass covers ; oblique light
shows some portions of the scale to advantage ; other
parts are rendered more distinct when the central rays of
the achromatic condenser are stopped out.
The metamorphosis is complete in the Suctoria, or
Siphonaptera, a wingless family the larva, pupa, and
imago of which are very distinct in their appearances
the well-known Flea is the best example of this small
group. By many authors these insects have been arranged
with the Diptera : this is most decidedly incorrect, since
they differ ia many particulars. The external covering of
630
THE MICROSCOPE.
the Flea (fig. 287) is a horny case, divided into distinct
segments ; those upon the thorax being always disunited.
Although apterous, the Flea has the rudiments of four
Fig. 287
Female Flea. 2 Male Flea. (The small circles enclose flens the actual or
life size.)
THE FLEA. 631
wings, in the form of horny plates on both sides of the
thoracic segments. Its mouth consists of a pair of sword-
shaped mandibles, finely -serrated ; these, with a sharp,
penetrating needle-like organ, constitute the formidable
weapons with which it pierces through the skin.
The neck is long, the body covered over with scales, the
edges of which are set with short spikes or hairs ; from its
"head project a pair of antennae, feelers or horns, a pro-
boscis, which forms a sheath to the pair of lance-shaped
weapons. On each side of the head a large compound eye
is placed. It has six many-jointed powerful legs, termi-
nating in two-hooked claws ; a pair of long hind legs are
kept folded up when the insect is at rest, which in the
act of jumping it suddenly straightens out, at the same
time exhausting all its muscular force in the effort. The
female Plea, fig. 287, lays a great number of eggs, sticking
them together with a glutinous secretion j the Plea infest-
ing the dog or cat glues its eggs fast to the roots of the'
hairs ; in four days' time the eggs are hatched, and a small
white larva or grub is seen crawling about, and feeding
most actively. No. 4 (fig. 289) is a magnified view of one,
covered with short hairs, doubtless for the purpose of
preventing its dislodgment. After remaining in this
state about nine or ten days,, it assumes the pupa form ;
this it retains four days ; and in nine days more it be
comes a perfect Flea. The head of the Flea found in the
oat (No. 3, fig. 289) somewhat differs in form from that
of the species infesting the human being. Its jaws are
furnished with more formidable-looking mandibles, and
from between the first and second joints behind the head
short strong spines project.
Arachnida. The animals forming the class Araclmida
include spiders and their allies, most of which are looked
upon with disgust and aversion by the generality of man-
kind. Arachnida are divided into two orders, Trachearia
and Pulmonaria. The first includes the Acaridce or
Mites, in which we find tracheae, as in insects, but no
distinct vascular apparatus : in the second, spiders and
ccorpions are included, and these have a pulmonary cavity,
and a well-developed circulatory system. The above are
distinguished from Podopthalmia or Arthropoda by their
G32 THE MICROSCOPE.
aerial respiration, their possession of four pairs of legs
attached to an anterior division of the body, and the total
absence of antennae. The body is also covered with a
softish skin, which sometimes attains a horny consistency,
but nothing more. In the higher forms, the body is
divided into two parts, the anterior of which, as in Crus-
tacea, consists of a thoracic segment, amalgamated with
the head, and forming together a whole called the cephalo-
thorax. In the highest classes the division of the thorax
into separate segments becomes apparent; the anterior
segment is, however, amalgamated with the head. The
structure of the abdomen varies greatly. In some cases
it forms a soft round mass, without any traces of seg-
mentation ; whilst in others, as scorpions, it is continued
into a long flexible jointed tail.
Acarea, an order of animals not strictly belonging to
insects, but rather to Arachnida, Spiders, Scorpions, &c.
'The general description of the class is that the head
is united with the thorax, forming a cephalo-thorax ; no
antennae, simple eyes, body presenting transverse striae or
furrows between the second and third pair of legs, whicli
are eight in number, terminated by an acetabulum and
claws. These animals are commonly called mites, and
the best known species is that found in cheese, iheAcarus
domesticus. Most of the species are oviparous and vivi-
parous, their eggs are very numerous. The spider enve-
lopes its eggs in a beautiful silken cocoon. Scorpions
produce their young alive, and it is deserving of notice
that in this family the embryo is developed in the ovum
while it still remains in the ovary. The existence of a
"nicropyle has not yet been made out in the ova of Arach-
nida. For the sake of convenience we have included
Parasites in this part of our work, and in Plate VI. Nos.
144 to 147 are representations of their eggs, from some of
which the Iarva3 are just emerging.
The Malophagus, or Sheep-tick, fig. 288, is apterous,
and seems to be a connecting link between acarina and
insects proper. The Sarcoptes scabiei produces the itch in
the human being : it is also found to be the cause of mange
in the dog. In one pustule on a dog suffering from this
iisoase, as many as thirty parasites have been found.
THE SHEEP-TICK. 633
The Louse (fig. 290, No. 1). Whenever wretchedness,
disease, and hunger seize upon mankind, this horrid
parasite seldom fails to appear in the train of such
calamities, and to increase in proportion as neglect of
Fig. ilSS. Malophagus ovinus, Sheep-tick. (The small circl') encloses one
of life size.)
personal cleanliness engenders loathsome disease. When
examined under the microscope, our disgust of it is in no
way diminished. In the head may he distinguished two
large eyes, and near to them are the two antenna ; the
front of the head is long, and somewhat tapering off to
form a snout, which serves as a sheath to the proboscis
and the instrument of torture with which it pierces the
flesh and draws the blood. To the fore part of its body
six legs arc affixed, having each five joints, terminated
by two unequal hooks ; these, with other portions, are
covered with short hairs. Around the outer margin of
C34
THE MICROSCOPE.
the body may be seen small circular dots, the breathing
apertures, with which all the class are freely provided,
rendering them very tenacious of life, and difficult to kill.
There is another louse, rather differing in its characteristics
I, Dog's parasite. 2, Rat Arams. 3, Head of Cat-Flea. 4, Larva, or.grnb oi
Flea. (The life size of each is given in the small circles )
ACARINA.
Fig. 290. Parasites. Acarina.
i, Louse, Human; magnified 50 diameters. 2, Acarus domesticus, Cheese-
Mite ; under surface. 3, Sarcoptes Scabiei, Itch-Insect ; magnified 350 dia-
meters. 4, Entozoon folliculorum, Grub from the human skin in various
stages of existence, from the egg upwards : magnified 350 diameter?
(The small circles near represent the objects about the natural size )
636 THE MICROSCOPE.
from this, found upon the body of the very poor and dirtft
known as the body or crab-louse. Leeuwenhoek carried his
researches on the habits of these insects further than most
investigators, even allowing his zeal to overcome his disgust
for such creatures as the louse. In describing its mode of
taking food, &c., he observes : " In my experiments,
although I had at one time several on my hand drawing
blood, yet I very rarely felt any pain from their punctures ;
which is not to be wondered at, when we consider the
excessive slenderness of the piercer ; for, upon comparing
this with a hair taken from the back of my hand, I judged,
from the most accurate computation I could form by the
microscope, that the hair was 700 times larger than this
incredibly slender piercer, which consequently by its
punctures must excite little or no pain, unless it happens
to touch a nerve. Hence I have been induced to think
that the pain or uneasiness those persons suffer who are
infested by these creatures, is not so much produced from
the piercer as from a real sting, which the male louse
carries in the hinder part of his body, and uses as a
weapon of defence." He found, from experiments made
to ascertain the possible increase of these pests, that from
two females he obtained in eight weeks the almost in-
credible number of 10,000 eggs.
The Itch-insect, Sarcoptes scaliei (fig. 290, No. 3,
magnified 350 diameters). Dr. Bononio was among the
first to detect the parasitic character of the disease
known as the itch. On turning out one of the pustules,
or little bladders, from between the fingers, with the
points of very fine needles, tinder the microscope, a
minute animal was discovered, very nimble in its motion,
covered with short hairs, having a short head, a pair of
strong mandibles or cutting jaws, and eight legs, ter-
minating in remarkable sucker-like appendages.
It has no eyes ; and when disturbed it quickly draws
in its head and feet, and then somewhat resembles the
tortoise in appearance ; its march is precisely that of the
tortoise. It usually lays sixteen eggs, which are care-
fully deposited in the furrows of the skin in pairs, and
hatched in about ten days. It is an air-breathing
insect, and to find it carefully search around the skin
ACAP^JS DOMESTICUS. 637
about the pustule, -and -a red line or spot communicat-
ing -with it will be seen ; this part, and not the pus-
tule, must be probed with a fine-pointed instrument ;
the operator must not be disappointed by repeated
failures. Dr. Bourguignon bestowed much time in
studying the habits of this troublesome parasite. To
arrive at a knowledge of its haunts he arranged his mi-
croscope so as to enable him to observe it under the skin
of the diseased person. The rays of light from a lamp or
candle must be carefully brought to a brilliant focus by
means of the condensing or bull's-eye lens upon the
chosen point of observation ; a Leiberkiihn should also be
attached to the object-glass.
No. 4, fig. 290, Demodex folliculorum, is another re-
markable parasite found beneath the skin of man : it is
sometimes obtained from a spot where the sebaceous folli-
cles, or fat glands, are abundant ; such as the forehead, the
side of the nose, and the angles between the nose and
lip ; if the part where a little black spot or a pustule is
seen be squeezed rather hard, the oily matter there accu-
mulated will be forced out in a globular form ; if this be
laid on a glass slide, and a small quantity of oil added to
it, to cause the separation of the harder portions, the
parasite in all probability will float out ; after the addition
of more oil, it can then be taken away from the oily
matter by means of a fine-pointed sable pencil-brush, and
transferred to a clean slide ; when dry it should be im-
mersed in Canada balsam, covered over with thin glass,
and mounted in the usual way.
The Cheese-mite, A cants domesticus (fig. 290, No. 2),
has a peculiar elongation, of its snout, forming strong,
cutting, dart-shaped mandibles, "which it has the power of
advancing separately or together. The powder of old and
dry cheese almost entirely consists of mites and their eggs,
which are hatched in about eight days ; if deprived of
food, they have been seen to kill and eat each other.
Acari infest almost the whole of our dried articles of
food. Ac. passularum has two very longbuccalbristl.es; it
lives upon dried figs, and other saccharine fruits. Ac. de-
structor has long black hairs ; it feeds upon the contents
of entomological cabinets, especially butterflies ; Ac. pru-
538 THE MICROSCOPE.
norum is found on dried plums, &c. ; Ac. favorum finds
its food in old honeycombs ; A earns saccJtari (fig. 291) is
commonly present in the more impure kinds of sugar.
The discovery of the general prevalence of this acarus
rests, we believe, with Dr. Hassall.
The Sugar acarus resembles somewhat, in its organisa-
tion and habits, Acarus domesticus ; it attains to a size so
considerable, that it is plainly visible to the unaided eye.
Fig. 291.
Ova and young of the Acarus sacchari, Sugar-Insect, after HassalL
When present in sugar, it may always be detected by the
following proceeding : two or three drachms or teaspoonfuls
of sugar should be dissolved in a large wine-glass of tepid
water, and the solution allowed to remain at rest for an
hour or so ; at the end of that time the acari will be
found, some on the surface of the liquid, some adhering to
the sides of the glass, and others at the bottom, mixed up
with the copious and dark sediment, formed of fragments
of cane, woody fibre, grit, dirt, and starch-granules, which
usually subside on the solution of even a small quantity of
sugar in hot water. The Acarus sacchari, when first
hatched, is scarcely visible ; as it grows it becomes elon-
gated and cylindrical, until it is about twice as long as
ACARINA PARASITES.
639
broad; after a time the legs and proboscis begin to protrude
The body is partially
covered by setae, and the
feet terminate in hooks.
These stages of the de-
velopment of the acarns
are exhibited in-fig. 291.
The Acarus farinae,
Flour-mite. This is of
occasional occurrence in
flour, but is never pre-
sent unless it has be-
come damaged. Any
flour, therefore, contain-
ing the animal in ques-
tion is in a state unfit
for consumption. We
believe that it is found
more frequently in the
flour of the Legumlnosce
than that of the G-ra-
minece.
This acarus differs con-
siderably in structure
from the Sugar-mite,
particularly so in its
pennate setse.
Dr. Burnett esta-
Wished to his satisfac-
tion the following facts :
"1. That though there
are single species of pa-
rasites peculiar to parti-
cular animals, there are
others which are found
on different species of
the same genus; as is
the case in the para-
sites living on birds of
the genus Lams (gulls), Fig. 2931
mid thp ^nrnol Vn'wla r>f } ' H tppobosca Hintnd inis. 2, Nirmi, man
ana tne aiumai DiraS OI an a female, parasites infecting Swal.ows.
292. Acarus farince, Meal-Mite, magni-
lied 250 diameters.
640
THE MICROSCOPE.
prey. 2. The parasites of the human body confine them-
selves strictly to particular regions; when they are found
Fig. 294.
1, Parasite of Turkey. 2, Acarus of common Fowl, under surface. 3, Parasite
of Pheasant. (The small circle encloses each about life size.)
elsewhere, it is the result of accident. Thus, the Pediculi
capitis live in the head; P. vestimenti, upon the surface of
the body; the P. tabescentium, on the bodies of those dying
of marasmus; and the P. inguinalit, about the groins, arm-
ACARINA PARASITES.
641
pits, mouth, and eyes." From an examination of the
structure of these parasites, Dr. Burnett is of opinion that
Fig. 295.
1, Icarus of Beetle. 2, Acarus of Fly. 3, Icarus of Clothes-Moth. (The
circles enclose each about life size.)
they should be placed in an order by themselves, closely
allied to Insecta ; the mandibulate parasites occupying the
highest, and the haustellate the lowest, position in the
order : thus confirming to some extent the observations
made by Mr. Denny.
There is a remarkable species of acarus described by
T T
642 THE MICROSCOPE.
Dr. Robins, found spinning a white silken web on the bas
of the sparrow's thigh, or on the fore-part of its body; on
raising this delicate web, you perceive that it is filled with
minute eggs, from which the young issue, being in due
time hatched by the warmth of the body it is destined to
annoy. In fig. 296 aro
seen some eggs of a
parasite infesting the
hornbill ; they are
glued to the feathers
near the head of the
bird ; the larvae are
ready to leave the egg
in two days. Another,
curiously enough, se-
lects the pulmonic ori-
fice of the snail : when
Fig. 29A-Ion of iU Parasite of Hornlill ^ animal dilates ^
orifice, for the purpose of allowing the air to penetrate its
respiratory cavity, the female acarus slips through the open-
ing, and lays her eggs in the folds of the mucous membrane,
where they are gradually developed. The young, upon
issuing forth from the eggs, select some portion of the
snail's body upon which to feed and perfect their growth.
Ixodidce are furnished with a powerful rostrum, armed
with recurvate spines, with which they pierce the skin of
the unfortunate animal upon whose blood they live. So
firmly do these anchor-like organs retain their hold, that if
the parasite is pulled away it usually carries a portion of
the skin of its victim with it. These creatures live upon
a great variety of animals. The dog is very liable to their
attacks, and many species fix themselves exclusively upon
serpents and other reptiles. Glyciphagus cursor is found
in the feathers of the owl, and in the cavities of the bones
of skeletons. Gamasidce are furnished with a sucking
apparatus very similar to that of Ixodidce, usually attaching
themselves to the bodies of beetles ; the common Dung-
beetle (Geotroupes) is often found with its lower surface
nearly covered with them.
There are other families leading a more active life,
being furnished with eyes. One family, ffydrachnid<je,
ACARINA PARASITES.
643
Water-mites, inhabit the water, where they swim about
with considerable rapidity by means of their fringed legs,
Fig. 297.
I, Parasite of Eagle. 2, Parasite of Vftlture. 3, Parasite of Pig 3 on.
circles 3iiclose each about life size).
(Tii
In their young state, they attach themselves parasitically
to aquatic animals ; they then possess only six legs, and
pass through a quiescent or pupa state before acquiring
the fourth pair. Orbitadce, unlike other Acarea, live
upon vegetable matter, principally damp leaves and moss ;
T T 2
844 THE MICROSCOPE.
they have a mouth adapted for biting such food, and are
covered with a hard and very brittle skin. The Bddlidce
live among damp rnoss, have the body divided appaiently
into two parts by a constriction, and the rostrum and
palpi very long ; whilst Trombidiidce, of which the little
scarlet mite so often seen in gardens is an example, have
their palpi converted into little raptorial organs.
Another family of parasites are commonly met with in
the bodies of fishes, attaching themselves to the branchiae,
to the soft skin under the fins, or to the eyes, much to
the annoyance, of the unfortunate victim. Some of these
found on fresh-water fish are sufficiently transparent to
show the circulation of their fluids most interesting
objects for the microscope.
The Water-snail, Limnceus, is tormented by a larva of
the family Amphistoma, which attaches itself by a series
of booklets and bristles to various parts of the body and
mantle ; under a low magnifying power, when congre-
gated together, they appear somewhat like tufts of threads. 1
ARACHNIDA, Spiders. Epeira diadema is the best
known of the British species of Garden Spiders: it
is readily recognised by the beautiful little gem-like
marks -on its body and legs. Spiders abound on every
shrub ; and if we consider that the Spider is destitute of
a distinct head, without antennae, one-half of its body
.attached to the other by a very slender connexion, and so
soft as not to bear the least pressure, its limbs so slightly
attached to its body that they fall off at a very slight
touch, it appears ill-adapted either to escape the many
dangers which threaten it on all sides or to supply itself
with food ; and the economy of such an animal is deserving
of the microsccpist's attention.
The several important organs peculiar to the Spider
tribe are represented in fig. 299. Of these, No. 1 show
the spinning apparatus; four only are the spinnarets, or
organs by which their silky threads are emitted. Their
structure is very remarkable ; the surface of each spinnaret
is pierced by an infinite number of minute holes, shown
(1) The earliest known account of the parasite tribes is given in Redi's
Treatise de Generatioiie Insectorum ; see also H. Denny's Monograph ia A noplv
rorum Britannia:. 1842.
AIIACHNIDA.
645
in No. 2, from each of which there escapes as many little
drops of a liquid as there are holes, which, drying the
moment they come in contact with the air, immediately
form so many delicate threads. Immediately after the
filaments have passed through the pores, they unite first
together, and then with those of the next, to form one
common thread ; so that the thread of the spider is coin-
\
\
Fig. 298. Epeira diadema, Diadem Spider.
posed of a large number of minute filaments, perhaps
many thousands, of such extreme tenuity that the eye can-
not detect them until they are twisted together into the
working thread. In the two pairs of spinnarets a different
anatomical structure can be detected ; the pair above,
which are a little the longest, show a multitude of small
perforations, the edges of which do not project, and which
therefore resemble a sieve. The shorter pair have pro-
jecting tubes independent of the perforations which exist
C4G
THE MICROSCOPE.
in those above. The tubes are hollow, and perforated at
their extremities ; and it is supposed that the agglutinating
threads issue from these tubes, while those emitted from
the perforations do not possess that property. It will be
seen, by throwing a little dust on a circular Spider's web,
that it adheres to the threads which are spirally disposed,
but not to those that radiate from the centre to the cir
cumference ; the latter are also the stronger of the set.
Fig. 299.
1, Spinnarcts of Spider. 2, Extreme end of one of the upper pair of spinna-
rets. 3, End of under pair of spiunarcts. 4, Foot of Spidei. 5, Side view
of eye. 0, The arrangement of the four pairs of eyes.
The rapidity with which these webs are constructed is
as astonishing as is the accuracy with which the webs
are formed. There are many different kinds of Spiders ;
but nearly all of them envelop their eggs in a covering of
silk, forming a round ball, which the Spider takes care to
hang up in some sheltered place till the spring. The
mode in which the ball is formed is very curious : the
mother Spider uses her own body as a guage to measure
her work, in the same way as a bird uses its body to
guage the size and form' of its nest. The Spider first
spreads a thin coating of silk as a foundation, taking care
to have this circular by turning its body round during the
process. In ths same manner it spins a raised border
ABACHNIDA. 647
round this till it takes the form of a cup ; it is at this
stage of the work that it begins to lay its eggs in the cup,
and not content to fill it up to the brim, it also piles up
a large round heap, as high as the cup is deep. Here,
then, is a cup full of eggs, the under half covered and pro-
tected by the silken sides of the cup, but the upper still
bare and exposed to the air and the cold. She now sets
to work to cover these also : the process is similar to the pre-
ceding, that is, she weaves a thick web of silk all round
them, and, instead of a cup-shaped nest, like some birds,
the whole partakes of the form of a ball much larger than
the body of the Spider.
The feet of the Spider, one of which is represented at
"So. 4, are curiously constructed. Each foot, when mag-
nified, is seen to be armed with strong horny claws, with
serrations on the under-surface. By this arrangement the
Spider is enabled to regulate the issue of its rope from the
spinnarets. Some have, in addition, a remarkable comb-
like claw, for the purpose of separating certain threads
which enter into the composition of their delicate webs.
One of the most remarkable members of the family, the
Argyroneta aquatica, Diving Spider, weaves itself a curious
little bell-shaped globule, which it takes with it to the
bottom of the water, whither it retires to devour its prey.
Notwithstanding its aquatic habits, this, like the rest of
its order, is fitted only for aerial respiration ; it therefore
fills its miniature balloon with air, which it carries down
with it entangled amongst the hairs of its body. This
closely resembles the earliest diving-bells.
Mr. Quekett recommended the following as a simple
method of obtaining a perfect system of tracheal tubes
from the larvae of insects : A small opening having been
made in the body, it is to be placed in strong acetic acid,
which softens or decomposes all the viscera : the trachea
must then be well washed with a syringe, and removed
from the body, by cutting away the connexions of the
main trunks with the spiracles, by means of fine-pointed
scissors. For mounting, they should be floated on to the
glass-slide, and laid out in the position best adapted for
displaying them. If we wish to mount them in Canada
balsam, they should be allowed to dry upon the slide,
648 fHE MICROSCOPE.
but their natural appearance is best preserved by mount-
ing in weak spirit and water, or Goadby's solution, using a
very shallow cell, to avoid pressure. The spiracles should
be dissected out with a fine knife and scissors.
Mr. Hepwortk's Mode of Preparing and Mounting In-
sects. He destroys life with sulphuric ether, then washes
the insects thoroughly in two or three waters in a wide-
necked bottle ; he afterwards immerses them in caustie
potash or Brandish's solution, and allows them to remain
in it from one day to several weeks or months, according
to the opacity of the insect ; with a camel-hair pencil he
then presses the contents of the abdomen and other soft
parts dissolved by the potash out in a saucer of clean
water, holding the head and thorax with one brush, and
gently pressing the other with a rolling motion against the
body from the head to the extremities. The potash must
afterwards be completely washed out, or crystals may
form. The insects must then be dried, the more delicate
specimens being spread out or floated on to glass-slides,
covered with thin glass and tied down with thread.
'When dry, they must be immersed in rectified spirits of tur-
pentine, and placed under an air-pump. When sufficiently
saturated they are ready for mounting in Canada balsam ;
but they may be retained for months in the turpentine
without injury. Before mounting, as much turpentine as
possible must be drained and cleaned off the slide ; but
the thin glass must not be removed, or air would be re-
admitted. Balsam thinned with chloroform is then to be
dropped on the slide so as to touch the cover, and it will
be drawn under by capillary attraction. After pressing
down the cover, the slide may be left to dry and to be
finished off. If quicker drying be required, the slide
must be warmed over a spirit-lamp, but not made too hot,
?,s boiling disarranges the object. Vapours of turpentine
or chloroform may cause a few bubbles, but these dis^
appear when condensed by cooling. 1
\ TRANSFORMATION OP INSECTS.
The metamorphoses of the insect race offer some of
the most curious and wonderful of nature's phenomena for
(1) Journ. Micros. Soc. vol. i. p. 73.
TRANSFORMATION OF INSECTS. 619
contemplation. " We see," says an old author, " some of
these creatures crawl for a time as helpless \vorms upon
the earth, like ourselves ; they then retire into a covering,
which answers the end of a coffin or a sepulchre, wherein
they are invisibly transformed, and come forth in glorious
array, with wings and painted plumes, more like the inha-
bitants of the heavens than such worms as they were in
their former state. The transformation is so striking and
pleasant an emblem of the present, intermediate, and
glorified state of man, that people of the most remote
antiquity, when they buried their dead, embalmed and
enclosed them in an artificial covering, so figured and
painted as to resemble the caterpillar in the intermediate
state ; and as Joseph was the first we read of that was
embalmed in Egypt, where this custom prevailed, it was
probably of Hebrew origin."
Faint and imperfect symbol though it be, yet it may,
perchance, offer a glimpse of the metamorphosis awaiting
nur own frail bodies. Between the highest and lowest
degree of corporeal and spiritual perfection, there are
many intermediate degrees, the result of which is one
universal chain of being, no one can for a moment gain-
say. Thus the angel Kaphael soliloquizes in Milton's
Paradise Lost,
"What surmounts the reach
Of human sense, I shall delineate so,
By likening spiritual to corporeal forms,
As may express them best : though wiiat if earth
lie but the shadow of heaven, and things therein
Each to other like, more than on earth is thought ! "
The great class of insects, which furnishes four-fifths of
the existing species of the animal kingdom, has two chief
divisions. In the one, the Ametabola, we have an imper-
fect, in the other, the Metabola, a perfect metamorphosis ;
that is, in the former there is no quiescent pupa state, and
the metamorphosis is accompanied by no striking change
of form ; in the latter, there is an inactive pupa that takes
no nourishment, and so great a change of form, that only
by watching the progress of the metamorphosis can we
recognise the pupa and the imago as belonging to the
same animal.
The degree of metamorphosis is, however, very different
650 THE MICROSCOPE.
in different groups of insects. In its most complete form,
as exemplified in the Butterflies, Moths, Beetles, and many
other insects, the metamorphosis takes place in three very
distinct stages. In the first, which is called the larva state,
the insect has the form of a grub, sometimes furnished
with feet, sometimes destitute of those organs. Different
forms of insects in this state are popularly known as Cater-
pillars, Grubs, and Maggots. During this period of its
existence, the whole business of the insect is eating, which
it usually does most voraciously, changing its skin repeat-
edly, to allow for the rapid increase in its bulk ; and after
remaining in this form for a certain time, which varies
greatly in different species, it passes to the second period
of its existence, in which it is denominated a pupa. In
this condition the insect is perfectly quiescent, neither
eating nor moving. It is sometimes completely enclosed
in a horny case, in which the position of the limbs of the
future insect is indicated by ridges and prominences j
sometimes covered with a case of a softer consistence,
which fits closely round the limbs, as well as the body,
thus leaving the former a certain amount of freedom.
Pupce of this description are sometimes enclosed within
the dried larva skin, which thus forms a horny case for the
protection of its tender and helpless inmate. After lying
in this manner, with scarcely a sign of life, for a longer or
shorter period, the insect, arrived at maturity, bursts from
its prison in the full enjoyment of all its faculties. It is
then said to be in the imago or perfect state. This meta-
morphosis is one of the most remarkable phenomena in
the history of insects, and was long regarded as perhaps
the most marvellous thing in nature ; although recent
researches have shown that the history of many of the
lower animals presents us with circumstances equally if
not more wonderful, nevertheless the metamorphosis of the
higher insects is a phenomenon which cannot fail to arrest
our attention. To see the same animal appearing first as
a soft worm-like creature, crawling slowly along, and de-
vouring everything that comes in its way, and then, after
an intermediate period of death-like repose, emerging from
its quiescent state, furnished with wings, adorned with
brilliant colours, and confined in its choice cf food to the
TRANSFORMATION OF INSECTS. 651
most delicate fluids of the vegetable kingdom, is a spec-
tacle that must be regarded with the highest interest;
especially when we remember that these dissimilar crea-
tures are all composed of the same elements, and that the
principal organs of the adult animal were in a manner
shadowed out in all its previous stages.
Nor is the singularity of their natural history the 'only
claim that these insects have upon our attention. Lowly
as they seem in point of organization, there are few
animals that exceed them in commercial importance. To
give an instance or two ; the finest red dyes known to our
manufacturers are derived from insects. The Lecanium
ilicis, an inhabitant of the Ilex, Evergreen-oak, growing in
countries near the Mediterranean, was employed for this
purpose by the ancient Greeks and Romans, as it is still
by the Arabs ; and, until the introduction of the Mexican
cochineal, another species, the Coccus polonicus, living
on the roots of the Scleranthus perennis in Central Europe,
was much used for the same purpose. The Mexican cochi-
neal, which has driven all other kinds out of the market, is
one of the species Coccinia ; this pretty insect was long
regarded as a parasite upon the Cactus opuntia, Prickly-
pear a plant common in Central America. The com-
mercial importance of this insect is shown by a single fact :
in 1850, no less than 2,514,512 Ibs. of cochineal were im-
ported into Great Britain alone (value about 7s. per Ib.) ;
and as about 70,000 insects are required to weigh a
pound, we may form some idea of the almost countless
numbers annually destroyed. Eor -many years the culti-
vation, or rather feeding, of. cochineal was entirely confined
to Mexico ; but the insect has lately been introduced into
Spain, and the French possessions in Africa, with every
prospect of success. A fourth species, of great import-
ance, is the Lac insect, Coccus lacca, an inhabitant of the
East Indies, where it feeds upon the Banian-tree, Ficus
religiosa, and other trees. It is to this insect we are
indebted, not only for the dye-stuffs known as lac-dye
and lac-lake, of which upwards of 18,000 cwts. were
imported in 1850, but also for the well-known sub-
substance called shell-lac, so much used in the preparation
of sealing-wax and varnishes. It is somewhat remark-
652 THE MICROSCOPE.
able that only the female insects yield a good colouring
matter.
Of all the secretions peculiar to insects, silk may well
be regarded as the most valuable, since it has become as
much an essential to the purposes of mankind as to the
economy of its producers. The fluid, before it comes in
contact with the air, is viscous and transparent in the young
larva, but thick and opaque in the more mature. It is found,
by chemical analysis, to be chiefly composed of Bombic
acid, a gummy matter, a portion of a substance resembling
wax, and a little colouring matter. Silk may be placed in
boiling water without undergoing any change ; the strongest
acids are required to dissolve it; and it has never yet been
imitated artificially. More than 500,000 human beings
derive their sole support from the culture and manufacture
of silk ; and the importance of the Silkworm to Great
Britain alone is represented by the large sum of 16,500,000/.
annually. Then we have large sums of money changing
hands from the labours of the useful little Bee ; tons'
weight of honey and wax are yearly consumed ; England
pays more than 50,000^. for foreign honey and wax, in
addition to her own valuable produce. A great variety of
scents, which from their agreeable odours are much used in
perfumery, are manufactured from insects. The Spanish
Ply is an indispensable article in the treatment of certain
forms of disease ; and that invaluable agent, Chloroform,
was first made from formic acid ; an acid discovered in the
Formic ant, and from which it has derived its name.
Then there are Gall-nuts, produced by a small fly, for which
a substitute could not be found in dyeing and ink-making.
" Much more extensive and important than any of the
foregoing, but, as less palpable, even more disregarded, are
the general uses of insect existence. Disease, engendered
of corruption in substances animal and vegetable, would
defy all the precautions of man, unless these were aided
by scavenger- insects, those myriads of flies and carrion
beetles, whose perpetual labours, even in our tempered
climate but infinitely more so in warmer regions are
sssentially important to cleanliness and health.
" A use of this nature, and one performed perhaps to an
extent we little think of is the purification of standing
TRANSFORMATION OF INSECTS. 653
waters by the innumerable insects -which usually inhabit
them. We have witnessed ample proof of the efficacy in
this respect of Gnat larvae, when keeping them to observe
their transformations. Water swarming with these ' lives
of buoyancy ' has been perfectly sweet at the end of ten
days ; while that from the same pond, containing only
vegetable matter, has become speedily offensive.
"We have already pointed out the utility of insects in
affording ever-new subjects of interesting inquiry. And
fet those who will look scorn upon our pursuit ; but few
are more adapted to improve the mind. In its minute
details, it is well calculated to give habits of observation
and of accurate perception ; while, as a whole, tiie study
of this department of nature, so intimately linked with
others above and below it has no common tendency to lift
our thoughts to the great Creative Source of Being, to
Him who has not designed the minutest part of the
minutest object without reference to some use connected
with the whole."
" The shapely limb anJl nbricated joint
Within the small dimensions of a point,
Muscle and nerve miraculously spun,
His mighty work, who speaks, and it is done ;
The invisible in things scarce seen revealed,
To whom an atom is an ample field."
\
CHAPTER V.
VERTEBRATA.
VMYSIOLOGY HISTOLOGY BOUNDARY BETWEEN THE TWO KINGDOMS C5.LL
DEVELOPMENT GROWTH OF TISSUES SKIN, CARTILAGE, TEETH,
BONE, ETC.
HE most complicated state in which
matter exists, is where, under
the influence of life, it forms
bodies with a curious internal
structure of tubes and cavities,
in which fluids are moving and
producing incessant internal
changes. These are called orga-
nised bodies, because of the
various organs which they contain, and
they form two remarkable classes ; those
of the lowest class are for the most part
fixed to the soil, and are recognised as
vegetables, the structure of these we have
already considered ; those of the higher
order are endowed with power of locomo-
tion, andTare called animals. Some of the peculiarities
and minute structure of the invertebrate animals have
already been made the subject of investigation, and we
now propose to extend our observations to the vertebrate.
The study of the Science of Life, or the building up of
the living structure, is termed Physiology, or Biology ; *
and that part of it more particularly relating to the minute
structure of the organs of animals has been termed
Histology?
(1) From /Jtos-, life, and \oyot, discourse a. discourse on life ; a nore expre*
live term than physiology.
(2) From loror, a lisswe, or web, and Xo-vor, a discourse.
INJECTIONS, ETC.
Tuften West. del.
PT.ATK VII.
Kfiraund Evans
ANIMALS AND "VEGETABLES. 655
Physiology has for its object the scientific co-ordination
of the phenomena and laws of life ; yet, writes Mr. Lewes,
" the attempts to define what we are to understand by Life,
have hitherto proved almost if not quite valueless." In
our previous investigations, we must have seen the value
and advantage of " studying Life in its simpler forms,
if Life is to be understood in its more complex ; and
no sooner do we comprehend the fact that the lower
animals present to us the more important phenomena of
Life under simpler forms and conditions, than we at once
recognise the study as indispensable."
It was Ehrenberg who first asserted that there was an
absolute boundary between animals and plants ; finding
even, as he fancied he did, in the smallest of the former,
the Infusoria, which had previously been regarded as
mere unorganised masses of mucus, the same systems of
organs as those by which the most highly-developed animal
is characterised, that is to say, distinct nutritive, motile,
vascular, sexual, and sensitive systems. Siebold called
the existence of these organs in question, regarding the
organisation of the Infusoria as a homogeneous paren-
chyma, in which he recognised only a nucleus, and in one
division a mouth and oesophagus. Nevertheless he asserted
that plants and animals were essentially distinct, and that
there was no transition from one to the other, the nature
of the plant being always im motile and rigid, whilst the
animal possessed the faculty of contracting and expanding
its body. This contractility is, in his opinion, alone to be
taken as the characteristic feature. It is not, however, the
animal organisation itself which is contractile, but only a
single tissue in it ; all the rest, skin, bones, and connective
tissue, are as rigid or passive as the vegetable membrane,
or, at most, only elastic ; in the higher animals the muscles
only are contractile, and in those of the lowest classes, viz.
the Infusoria, the entire body.
Whence Ecker assumed the existence of a special con.
tractile substance, which sometimes occurs in a formed
state, as a contractile cell or as muscular substance, some-
times amorphous, as in the bodies of the Infusoria, Rhizo-
pod a, and Hydrozoa. Kb'Uiker confirmed this view, and
carried it out, particularly in the case of the Infusoria,
656 THE MICROSCOPE.
which, he at one time declared to be unicellular animals
with a contractile cell-menibrane and contents. The con-
tractile substan.ce is characterised by the following attri-
butes : it is homogeneous, or finely granular, transparent,
of the consistence of albumen, gelatiniform, soft, more
refracti re than water, but less so than oil ; insoluble in.
water, but gradually decomposed; destroyed by caustic
potash ; coagulated and contracted by carbonate of potash,
as well as by alcohol and nitric acid ; having the power of
forming aqueous cavities, which originate either by the
separation of the water contained in it, or by its reception
from without ; owing to which the remainder becomes
denser and more granular, and lastly, it represents the
appearance, in water, of contractile drops, which move like
an Amoeba. All these properties had already been observed
by Dujardin, in a substance of which the Infusoria and
Rhizopoda are principally composed, and which he termed
" sarcode ; " the aqueous spaces or hollows he named
"vacuoles," regarding them as the most characteristic
features of the substance ; these spaces had been errone-
ously regarded by Ehrenberg as stomachs. All these
properties, however, are possessed by a substance in the
plant-cell, which must be regarded as the prime seat of
almost all vital activity, but especially of all the motile
phenomena in its interior the protoplasm. Not only do
its optical, chemical, and physical relations coincide with
those of the "sarcode," or contractile substance, but it
also possesses the faculty of forming " vacuoles " at all
times, and even externally to the cell ; a property, it is
true, which has for the most part been hitherto overlooked
or misinterpreted. These clear, aqueous spaces, the so-
termed vesicular contents, are present in all young
cells, and play a considerable part in cell-division, and the
sap-currents ; they are in all respects analogous to the
vacuoles of the sarcode. 1
(1) Mr. Huxley has satisfied himself that in all the animal tissues the so-
called nucleus (endoplast) is the homologue of the primordial utricle, with
nucleus and contents (endoplast) of the plant, the othsr histological elements
being invariably modifications of the periplastic substance. Upon this view we
find that all the discrepancies which had appeared to exist between the animal
and vegetable structure disappear : and it becomes easy to trace the absolute
identity of plan in the two, the differences between them being produced merely
to) the nature and form of the deposits in, or modifications of, the periplastio
HISTOLOGY. 657
In organised beings, the way in winch nature works out
her most secret processes is by far too minute for observa-
tion by unassisted vision ; even with the aid of the improved
microscope, comparatively a very small portion has, up to
this time, been revealed to us. To point out in detail the
discoveries made through the employment of this instru-
ment, as regards physiology, would be to give a history of
modern biological science ; for there is no department in
this study which is not more or less grounded upon the
revelations and teachings of the microscope.
To the casual observer, the brain and nerves appear to
be composed of fibres. The microscope, however, reveals
to us, as was first pointed out by Ehrenberg, that these
supposed fibres do not exist, or rather, that they all consist
of numerous tubes, the walls of which are distinct, and
contain a fluid which may be seen to flow from their broken
extremities on pressure. In looking at a muscle, it appears
to be made up of fine longitudinal fibres only. The micro-
scope tells us that each of these supposed fine fibres is com-
posed of numerous smaller ones, and that these are crossed
by lines which have received the name of transverse striae ;
that muscular contraction, the cause of motion in animals,
is produced by the relaxation or approximation of these
transverse striae.
The microscope has shown us that a distinct network of
vessels lies between the arteries and veins, partaking of
the properties of neither, and possessed of others peculiar
to themselves. These have been denominated intermediary
vessels by Berres, and, serving to connect the arterial with
the venous system, are commonly known as capillaries.
On regarding with the naked eye the different glands
in which the secretions are formed, how complex they
appear, how various in conformation ! Tbe microscope
teaches us that they are all formed on one type ; that the
substance. In both plants and animals there is but one histological element
the endoplast which does nothing but grow and vegetatively repeat itself;
the other element the periplastic substance being the subject of all the che-
mical and morphological metamorphoses in consequence of which specific
tissues arise. The differences between the two kingdoms are mainly, first,
That in the plant the endoplast grows, and the primordial utricle attains a
large comparative size, while in the animal the endoplast remains small, the
principal bulk of its tissues being formed by the periplastic substance; and
secondly, In the nature of the chemical changes which take place in the peri-
plastic subbtance in each case.
U U
658 THE MICROSCOPE.
ultimate element of every gland is a simple sacculated
membrane, to which the blood-vessels have access; and
that all glands are formed from a greater or less number,
or different arrangement only of the primary structure.
Our notions respecting the skin were vague until the
microscope discovered its real anatomy, and showed us
the existence and relations of the papillse, of the sudorific
organs and their ducts, the inhalent muscular apparatus,
and so on. All our knowledge of epidermic structures,
such as hair, horn, feather, &c., the real structure of
cartilage, bone, tooth, tendon, cellular tissue, and, in a
word, of all the solid textures, has been revealed to us by
the same agency ; so that it may be truly said, that all our
real knowledge of structural anatomy, and all our acquaint-
ance with the true composition of every organ in the body,
have been arrived at by means of the microscope, and
could never have been known without it.
In addition to this, and what is of greater importance,
after having studied the healthy structure of the body,
most beneficial aid is afforded in the investigation of
changes produced by disease. We may cite one notable
example. Dr. Andrew Clarke, after having carefully
studied the appearances of sputa from patients under his
care, says, " that the microscopical inspection of expecto-
ration affords, at a very early period of consumption, defi-
nite information, not otherwise attainable, regarding the
nature of the malady; and at all times must furnish
valuable aid in forming a prognosis regarding the cause of
the complaint." The expectoration generally shows pus,
cells, lung tissue, blood corpuscles, and granular material,
mixed -with, at times, a small amount of fat corpuscles.
The space allotted to this division of our subject enables
us to give only a short and imperfect sketch of a few of
the fundamental tissues of the animal body. First, enu-
merating merely the elementary substances recognised by
chemistry as entering into the formative processes, we shall
proceed to inquire into that most interesting and wonderful
starting-point of life, the cell ; admitted to be, and indeed
demonstrable as, the common centre alike of animal and
vegetable organisms.
HISTOLOGY.
659
tHE HUMAN Bi)DY, ITS PHYSIOLOGICAL COMPOSITION
CHARACTER.
The elementary substances found in the human hody are
oxygen, hydrogen, carbon, nitrogen, phosphorus, sulphur,
chlorine, fluorine, iron, manganese, titanium, and calcium.
Silenium is found in the hair, and fluorine in combination
13 1*
Fig. 300. Diagram showing various forms of development in Animal Cells.
1, Shows a newly formed cell. 2, Subdivision of the nucleus. 3, The nucleus
changes its situation, and at 4, subdivides and disappears. 5, The walls of
the cell increase in thickness. 6, the cell becomes branched, or stellate. 7,
Two cells are seen to coalesce. 8, They have coalesced and run into each
other. 9, Again they take another form and become multilocular. 10,11,12,
Cells sprouting out to form membrane and vessels. 14, Development of
complicated cells, which, at 13, have coalesced to form tissue.
with lime forms the enamel of the teeth. Iron is the
chief colouring-matter of the blood, the black pigm-ent of
the choroid of the eye, and the skin of the negro,
u u 2
660 THE MICROSCOPE.
Cells. All animal and vegetable structures, the micro-
scope has revealed to us, are developed from cells or their
nuclei ; and the materials for building up animal structures
are furnished from the yolk and the blood.
The animal nucleated cell, fig. 300, is more or less of a
globular form ; within the delicate cell-wall a granular
matter is inclosed suspended in a fluid ; the wall being
somewhat darker than the rest. There are usually one or
two spherical masses termed nuclei ; these enclose central
dots, termed the nucleoli. The size of a cell may be
1 -300th part of an inch in diameter, some are larger, some
smaller ; the nucleus may be 1,3000th of an inch in dia-
meter ; the nucleolus l-10,000th of an inch in diameter,
more or less.
Of the Cell. Dr. Beale's views of the cell are so ori-
ginal, and his theory of its development so carefully
studied and worked out, that we shall attempt, in as few
words as possible, to place them before our readers. The
cell has always been considered, and is still so, by many
good authorities, to consist, as just stated, of certain defi-
nite parts, viz. cell- wall, cell-contents, and nucleus ; to each
of which various different functions have been assigned.
Many affirm that the vital force is resident in the nucleus
alone, while others attribute to the cell- wall, or even to the
inter-cellular substance, the power of producing chemical
and other changes. Dr. Beale considers this view to be
entirely erroneous, and states that every cell or "anatomi-
cal elementary part" consists of matter in two different
states or stages of existence matter which lives (germinal
matter), and matter which is formed (formed material),
and which has ceased to manifest purely vital phenomena ;
all living entities, from the smallest living particle to the
most complex cell, consist of matter in these two states,
the relative proportions of which differ at different periods
of the life of the cell, and vary with the different con-
ditions under which it may be placed. If a tissue be
examined before development has proceeded to any great
extent, masses of germinal matter will be found almost
continuous with each other, without any appearance of the
cells from which all tissues are said to be originally formed.
CEIL FORMATION. 661
As growth proceeds, these masses become separated, and
the small processes or tubes which connected them are
drawn out, as it were, and become thinner and thinner ;
so that, for instance, in the formation of stellate tissue, so
far from the rays having been shot out by unequal growth
from special points of the original cell- wall, they have
been continuous from the very first.
Of the Structure and Formation of the simple Cell Muce-
dines. The mucedines, commonly called mildews, are
among the simplest living things known, and are therefore
well adapted for observation. If the membranous invest-
ment of a fully developed spore taken from one of these
fungi be ruptured, innumerable minute particles, some not
more than l-100,000th of an inch in diameter, are set free :
these constitute the living growing matter, in contradis-
tinction to the envelope or outer part of the cells. " Ger-
minal matter " may always be readily distinguished from
formed material by its capability of becoming dyed by an
alkaline solution of carmine, while the latter remains
perfectly colourless. Directly such a minute living par-
ticle comes into contact with air or water, a thin layer
upon its outer part becomes changed into a soft, passive,
transparent homogeneous substance (cell- wall), exhibiting
a membranous character, which protects the matter within.
Kutrient matter passes through this into the interior, and
there becomes changed into living matter ; so that growth
takes place, not by additions to the outside, but by the
introduction of new matter into the interior. If pabulum
be abundant, and the external conditions (temperature,
moisture, &c.) favourable, it readily passes through the
thin external membrane, and the living matter rapidly
increases. But if the external conditions be unfavourable,
less pabulum transudes, and the living matter within dies,
layer after layer, until the envelope becomes very much
thickened, with a proportionate decrease in the size of the
living matter. If all this living matter die, and only
formed material remain, no increase can take place ; but if
the smallest particle remain alive, any amount of living
matter, and afterwards of tissue or formed material, may
be produced. The position of the germinal matter in the
cell varies with the direction in which the pabulum reaches
662 THE MICROSCOPE.
it ; thus in the columnar epithelial cells covering the villi
of the intestines, in which the pabulum flows from the
free surface towards the attached extremity, the germinal
mass is found near the centre or near the free edge of the
cells ; but in the mucus-forming cells from the mouth and
fauces, in which the pabulum flows in the opposite direc-
tion, the germinal mass is found to be placed quite at the
attached end of the cells, where it has consequently easier
access to the pabulum, upon which its growth and secretive
power depends.
Cell-wall and Cell-contents. In the mucus cells above
mentioned, and in many other cells, two kinds of formed
material are produced from the original germinal matter ;
these are spoken of as the cell-wall, and the peculiar
matter found inclosed in it, the cell-contents. For instance,
in the starch-containing cell of the potato, the cell-wall is
formed around and invests the germinal matter, while the
starch is deposited as small insoluble particles in the very
substance of the germinal matter. So that by the death
of particles on the surface of the cell-wall the cellulose
cell-wall is produced, while by the death of some of the
particles further inwards, and therefore under different
conditions, starch is formed. This outer part of the ger-
minal matter, which eventually lies between the starch
grains on the inside and the cell wall on the outside, is
known as the "primordial utricle" of the vegetable cell.
Fat-cells or adipose vesicles are formed in precisely the
same way ; fat may, moreover, be deposited amongst the
germinal matter of other cells, such as the cartilage or
nerve cell.
Of tlie so-called Intercellular Substance. In cartilage,
tendon, and some other tissues there is no line of sepa-
ration between the portions of formed material which
belong to each respective mass of germinal matter ; and
hence it has been supposed that these tissues were deve-
loped in a different way to the epithelial structures. A
"cell," or elementary part of adult cartilage or tendon,
merely differs from the epithelial cells, spoken of above,
in not having a distinct margin around its own particular
formed material, and if a line were drawn midway between
the various germinal masses, it would roughly mark out
CELL FORMATION. 663
the point to which the formed material corresponding to
each extended; and each cell would then be exactly
analogous to the mucous-forming cells. In all of these cells,
of mucous membrane, tendon, cartilage, muscle, &c., there
is no abrupt demarcation between the germinal matter and
the formed material, but the one passes gradually into the
other. All living cells consist of matter in these two
different states ; the one being an active condition, -vital ;
the other merely passive, in which no vital actions are
exhibited : upon matter in this first state, all growth,
multiplication, conversion, all life depends ; while in the
second condition, matter may exhibit many very peculiar
properties, but it does not grow or multiply, or convert or
form ; in short, it does not live, though it ma} r increase by
new matter being superadded to it.
Of the Nucleus and Nucleolus. A mass of germinal
matter, besides increasing in quantity, may divide into
several, and thus cell-multiplication may occur ; and in all
cases it is to be observed that this multiplication is not
due to a "growing-in," or constriction of the cell-wall or
formed material, but entirely to changes occurring in the
germinal matter. In many cases a smaller spherical mass
may be observed in the centre of the germinal mass,
which often divides before the parent mass itself does;
but it is by no means a necessary part of the process, for
division as often takes place where no such bodies are to
be seen ; and it frequently happens that these small
bodies may make their appearance only after the division
of the original mass. And again, within these, other still
smaller ones are sometimes produced. The former are
termed nuclei, the latter nucleoli. These are to be regarded
as but new living centres appearing in centres already pre-
existing, and may perhaps mark the commencement of a
set of changes differing in some minor particulars from
the first that have occurred. But although both nuclei
and nucleoli are germinal or living matter, they are not
undergoing conversion into formed material. Nuclei do
not always exhibit their vital powers, but under certain
circumstances they may do so, and then they exhibit the
characters of ordinary germinal matter ; they absorb pabu-
lum and increase in size, and the original germinal mattei
664 THE MICROSCOPE.
becomes changed into formed material, while fresh nuclei
and nucleoli are developed. And so far from nuclei being
formed first, and the other elements of the cell deposited
around them, they always make their appearance in the
substance of pre-existing matter, and have neither a
different constitution to ordinary germinal matter, nor
perform any special function.
Of the Increase of Cells. Several distinct modes of cell-
multiplication have been described, but in all cases the
germinal matter divides, and is the only material actively
concerned in the process ; which may, however, take place
in different ways.
1. The parent mass may simply divide into two equal
parts, apparently in obedience to a tendency of the por-
tions to niovo away from each other as soon as the original
mass has reached a certain size.
2. The parent mass may divide in three, four, or more
equal portions.
3. From every part of the parent mass protrusions may
occur, each of which, when detached, absorbs nutrient
matter, and soon attains the same size as its parent.
During these processes of increase and multiplication, the
formed material is perfectly passive, and when a septum
or partition exists, it does not result from a " gro wing-in"
of this dead structure, but is produced by the conversion
of part of the germinal matter into a thin layer of formed
material.
Of the Changes of tlw Cell in Disease. If the conditions
under which cells ordinarily live be modified beyond a
certain extent, a morbid change may result. For instance,
if cells, which normally grow slowly, be supplied with an
excess of nutrient pabulum, they grow that is, convert
certain of the constituents of the pabulum that come into
contact with them into matter like themselves at an
increased rate. In this way the inflammatory product
pus results. " The abnormal pus-corpuscle may be pro-
duced from the germinal or living matter of a normal
epithelial cell, the germinal matter of which has been supplied
with pabulum much more freely than in the normal state"
In cells in which the access of nutrient pabulum is more
restricted than in the abnormal state t as in normal cells
CELL FORMATION. 665
passing from the embryonic to the adult state, the outer
part of the germinal matter undergoes conversion into
formed material, which increases as the supply of pabulum
becomes reduced.
Dr. Beale, in short, considers that " all formed matter
results from changes in the germinal matter, and that tho
action of the cell really consists in a change from the living
to the lifeless state of the matter of which it is composed ;
and that the products formed by the cell do not depend
upon any metabolic action exerted by the cell-wall or
nucleus upon the pabulum, nor are they simply separated
from, or deposited by, the blood." And he looks upon
the "living cell" as a minute body, consisting partly of
living matter influenced by vital force, and partly of life-
less matter resulting from the death of the first, in which
chemical and physical changes occur, which may be
modified by the influence of surrounding substances arid
external forces.
In pursuing the subject of cell development, we shall
proceed by the aid of our old lights in this intricate path
of physiological science. And it is only right that we
should add, that the views we have endeavoured to place
fairly before our readers have not been unhesitatingly
accepted, but, on the contrary, those of the German school
are greatly preferred by many physiologists.
Change of Cells into Tissues. This may take place by
a joining together or coalescence of cells in a rudimentary
state. Cells may meet, and at the point of contact coalesce
and run into each other, thus forming a tube ; indeed,
in this manner minute tubular structures are formed.
Another mode is : cells aggregate into a mass, and at the
point of contact run into each other, thus producing a
multilocular cavity ; No. 9, fig. 300. Glandular struc-
tures are formed in this way. Membrane is formed of a
deposit from the cytoblastema ; before the cell-membrane
is formed, the substance from the cytoblastema coalesces
with those particles close at hand, thus forming a delicate
film- like membrane. This membrane Professor T. Wharton
Jones calls endosmotic, retentive membrane. "We have
the cells coalescing to form a filament or fibre. The nucleus,
may disappear, or form another structure j and where
C66 THE MICROSCOPr.
regeneration of tissue is proceeding, there is found a
larger number of granules.
According to some histologists, cells may be formed in
eytoblastema independent of any pre-existing cells ; this
is cited as an instance of that mysterious agency desig-
nated spontaneous generation. There are cells which, so
far as we know, after full development, undergo no further
metamorphosis ; such as those of the epithelium, the blood
corpuscles, &c.
As an instance where previously- existing cells exert an
influence on those about to be formed, we may adduce a
fractured bone, between the ends of which osseous matter
is deposited. We infer from this, that the substance of the
bone determines, as it were, the formation of other cells,
first into cartilage, and then into bone. Generally, how-
ever, where a part has to be repaired, it does not seem to
determine the generation of a texture similar to itself
for example, muscle and skin. We have an exception to the
last observation in the case of nerves, which if cut across,
a substance is formed between the ends which transmits
the nervous influence, but the ends must not be separated
to any great distance, or this will not occur. The
same remark applies to bone. There may be a single
layer of cells so arranged side by side, and presenting
a columnar or basaltic form ; this arrangement is seen
in the cells of the intestinal tract, fig. 303 a. Another
change of cell is this : they shoot out processes from
certain parts of them, as seen in fig. 300, Nos. 10, 11;
this kind of formation occurs on the inner surface of
the sclerotic coat of the eye. The cylindrical form of cell
is found with delicate processes shooting out from the
broad end ; these are called ciliated, fig. 303 d, and the
cilia having a vibratile motion urge on the secretions of
the part in a particular direction.
In some cases the walls of the cell increase in thickness
(fig. 300, No. 5). Under the microscope, some cells
appear to be composed of concentric laminie. In plants
this is the common mode of increase in the thickness of
the cell, but the deposit does not take place entirely
around, but only here and there, so that vacant spaces
are left which form canals, and may become branched :
CELL-GROWTH. 667
these canals are named pore-canals (fig. 300, No. 6).
They do not perforate the outer layers ; consequently the
"blind ends seen through the outer membrane, and which
were supposed to "be apertures, are nothing of the kind.
Henle believes he has found canals in cells in animals
similar to those in vegetables in the cartilage of the
epiglottis, for instance. In other instances, cells may
"be aggregated, like a bunch of raisins, and the parts
in contact with each other disappear, so constituting
a multilocular cavity : examples of this are seen in
the racemose glands . (fig. 300, No. 9). Schwann
conjectures another mode of coalescence. From cells
formed as usual, processes sprout out ; but this change
takes place at the expense of the cell-membrane itself,
and when it has gone on to some extent, we have
the appearance of a net-work formed (fig. 300, No.
11, and 12). Capillary vessels are formed in this way.
Cells, we thus perceive, coalesce to form tissues, when
they have not attained their full growth as such ; or when
they have been fully formed they become flattened, and
assume the solid form. Deposits of matter may take
place from the cytoblastema with similar adjoining sub-
stance, constituting a delicate membrane, with here and
there nuclei, as in the capsule of the lens, the membrane
of the aqueous humour of the eye, or sheath of the primi-
tive fasciculus of muscle ; or the cells may coalesce in the
linear series, to form fibre.
Development of Complicated Cells. Here the nucleated
cell is surrounded by a deposit, and that again surrounded
so as to constitute a membrane ; so that the nucleated eel]
may be looked upon as the nucleus to the cell so formed
(fig. 300, Nos. 13 and 14). Sometimes the nucleus under-
goes important changes in the development of tissues, as
well as the cell itself. In some cases, where the cells have
joined in the linear series, the nucleus becomes oval, elon-
gated, so that the nucleus of one cell tends to meet the
nucleus of another cell ; they subsequently coalesce, and
thus fibre is said to be formed.
Action of Cells. The subsequent changes of the cell
depend in a great degree on endosmosis, or diffusion. Tho
nature of the membrane is a necessary condition, for it
668 THE MICROSCOPE.
determines the way in which the stream should pass ; and
we find in general that the current is from the rarer to the
denser fluid. If we immerse a porous tube half filled with
a strong solution of common salt in a jar of water, we notice
that the level of the fluid inside the tube rapidly rises
above the outside, while the water becomes slightly salt
to the taste. It is not a constant circumstance that the
stream is from the rarer to the denser fluid ; with alcohol
and water, for instance, the stream is from the latter to
the former. Mineral substances, even pipeclay and chalk,
permit of endosmosis in a low degree. In glands, the cells,
being filled with their peculiar fluid, are conveyed to the
wall of the intercellular passage, and through this the
secretion arrives at the surface of the body.
The Epithelium. If we cut very thin slices from the
superficial portions of the skin, we can raise from it a
delicate membrane ; or, what is better, by using chemical
or mechanical irritation, we obtain what is ordinarily
called a blister ; to it we give the name of epidermis. The
microscope has shown this to be a tissue of high and
remarkable organisation ; being, in point of fact, an aggre-
gation of cells, differing, in different
situations, in regard to form, colour,
and composition. These laminated ele-
mentary cells, found on the surfaces,
have generally nuclei. The form of
the nucleus is rounded or oval, and is
the 1 -3000th to l-5000th of an inch
in diameter. Each nucleus has two or
three nucleoli, with outlines more or
less irregular. The epithelium cells
may be divided into three kinds : the
1st is termed the tess^lated or pave-
ment ; 2d, the columnar or basaltic ;
3d, the ciliated or vibratile epithelium.
Fig. wi.Asectwn of the Some make a 4th, combining the tesse-
lated and the columnar : this may be
considered as transition epithelium, and is found only in
certain mucous passages. These various cells are repre-
sented in fig. 303, a, 6, c, and d.
EPITHELIAL CELLS.
669
Tesselated epithe-
lium is the simplest
form, and, as its name
implies, resembles flags
of pavement, over-
lapping each, other
at their edges. They
assume, more or less,
the polygonal form,
and their size varies in
the different mem-
branes. The cells of the
pericardium, or cover-
ing membrane of the
Fig. 302.
heart are much smaller I, Simple isolated cells containing reproductive
T ' , ,, , , granules. 2, Mucous membrane of stomach,
tnan those OI tne COVer- showing nucleated cells. 3, One of the
ITICT rnpmhrqTiP of flip tubular follicles from a pig's stomach. 4, Sev
' ine tion of a lymphatic, magnified 50 diameters.
lungs, &c. On some
surfaces we have many
layers in the skin, for
instance ; if a verti-
cal section of such
be made, and viewed
under the microscope,
it will be seen to be
composed of number-
_ess layers, shown in
fig. 304. The skin
taken from the sole
of the foot, in con-
sequence of the con-
tinued pressure there Fi<T S03 ^
(1) a is a diagram of a portion of the involuted mucous membrane, showing
the continuation of its elements in the follicles and villi, with a nerve entering
its submucous tissue. The upper surface of one villus is seen covered with
cylindrical epithelium ; the other is denuded, and with the dark line of base-
ment membrane only running round it ; b, pavement epithelium scales, sepa-
rated and magnified 200 diameters ; in the centre of each is a nucleus, with a
smaller spot in its interior, called the nucleoli. c, pavement epithelium scales,
from the mucous membrane of the bronchial or air tubes of the lung ; d
-epresents another form of epithelium, termed the vibratile or ciliated : tho
nuclei are visible, with cilia at their upper or free surfaces, magnified 250
diameters.
67C THE MICROSCOPE.
experienced, presents a distinctly stratified appearance.
These layers of cells are held together by intercellular
substance, which exists in quantities ; if the epithelium
be taken from these membranes it is more easily seen, be-
cause the cells are not so closely aggregated together as in
the skin ; therefore a piece of epithelium from the mouth
is recommended for display under the microscope, and by
the addition of a drop of the solution of iodine the cells are
much better seen. The cells from serous and mucous mem-
branes are acted upon by acetic acid, and dissolved if the
acid be of considerable strength : but if the acid be weaker,
the cells swell up. Cells are not affected by alcohol, ether,
ammonia, or its salts; but they are dissolved by caustic
potash, which also dissolves the intercellular substance.
Columnar or Cylindrical Epithelium, Fig. 303, a. The
nucleus is generally better seen than in the former kind of
cells, although formed from them. If we examine a portion
sideways, it resembles those at d, the upper part being
broader, and the nucleus being midway between the two
extremities. When the cells of the cylindrical epithelium
are closely aggregated together, they become compressed
into the prismatic form ; when they are less so, the rounded
shape prevails. Consequently, when we take a bird's-eye
view of them, from above or below, they appear like the
pavement epithelium, at c, and thus error might creep in ;
but we must become fully satisfied by examining them
sideways, and with various reagents. Their chemical com-
position is the same, and the cells dissolve in strong acetic
acid. As examples of the situations in which this form of
epithelium is found, we may instance the intestinal tract
along the ducts of the glands, as the liver, &c.
In no situations do we find these two kinds of epithe-
lium terminating abruptly the one in the other ; but there
is a gradual change of the one kind into that of the
adjoining; foi example, where the tesselated epithelium
is gradually supplanted by the cylindrical, as it passes from
jhe oesophagus to line the interior of the stomach ; it is
then termed transition epithelium.
Ciliated Epithelium^i^. 303, d. The cells do not differ
materially from those of the cylindrical ; the great distinc-
tion between he two is, that in the former there are no
CILIATED EPITHELIUM. 671
cilia attached to the broad end. Examples of the situations
in which these are found are, investing membrane of the
respiratory passages, u-pper part of the pharynx, larynx,
bronchi, and the lateral ventricles of the brain, &c.
Epithelium is found to grow from the surface of the
cutis outwards in most places it is constantly growing
outwards, and as continually being thrown off from the
surface : it must at the same time be remembered, that
though the epithelium is in close contact with the cutis,
or true skin, it is not a deposit from it, but derives only
its materials of formation and nourishment from it.
The epidermis is destitute of sensibility, yet it invests
very sensitive parts : it is not vascular, but invests very
vascular parts. Its exfoliation takes place regularly, as
may be exampled in reptiles and the Batrachia, who throw
off their skin : the moulting of birds is analogous. In the
early periods of life in the human subject, exfoliation takes
place from the surface of the skin ; from the mouth the
morsel of food is always mixed with detached cells. In
the process of digestion the same thing occurs in fact, it
is only when the epithelium cells are thrown off that the
gastric juice is secreted by the tubes of the stomach.
Cilia. The most remarkable circumstance in connexion
with cells is the movement of their cilia. There are three
ways in which the cilia ordinarily move the rotatory, the
undulatory, and the wavy, like a field of wheat set in
motion by a steady breeze. No satisfactory explanation
has been given of the cause of this vibratile motion. The
current produced by them is from within outwards, in most
places ; in the respiratory passages, on the contrary, it is
from without inwards. In the Frog's mouth, it takes the
same course. The ciliary motion may be seen in the kidney
of the Erog or Newt ; the cilia in the latter continue in
active motion for some minutes after the animal is dead.
Make a very thin section of the kidney with a sharp knife,
and take care to disturb the structure as little as possible ;
then moisten it with a little of the serum of the animal,
place it in a glass cell, and cover with thin glass and a
magnifying power of 250 diameters.
Pigment. Pigment granules are found in greater 01
^ss quantities in the skin and bodies of white and dark
672
THE MICROSCOPE.
Fig. 304 Pigment cells
from the eye.
races. In the eye there is pigment, and it affords a good
example of nucleated cells, in which are contained the
pigment particles, fig. 304. These are placed there for an
optical purpose, that of absorbing
the rays of light. In the peculiar
> colouration found in the eyes of some
I animals, called Tapetum lucidum, the
colour is not owing to the pigment
particles, but to the interference of
the light : it is reflected from it, as
in mother-of-pearl, coloured feathers,
scales of fishes, &c. The colour of
the skin is owing to the granular
contents of the pigment cells ; these-
are like ordinary elementary gra-
nules, with the addition of colour ;
and this latter may be removed by
the action of chlorine.
The Nails are appendages to the
epidermis, and present a mould of
the cutis beneath; from the cutis
the materials are furnished for the
formation and growth of the nail.
Like the epidermis, the nail is
stratified, the markings are parallel
to the surface, and the appearance
is produced by the coalescence of the
cells and their lying over each other.
See Plate VII., No. 149, toe of mouse.
The stratified arrangement when a
section is examined by polarised
light, presents the appearance seen
in the processes of the cat's tongue,
Plate V III. No. 174.
Hairs, however much they may
differ in form, are more or less flat-
tened out scales. A hair is divided
into a body or shaft, and a root
which is in the skin (fig. 305).
The shaft is again divided into
two parts : the external is termed
the cortical portion, and the internal the medullary
Fig. 305. A single Hair,
seen near its bulb.
HAIRS, SECTIONS OF.
673
portion ; the latter does not usually exist in the whole
length of the shaft. The cortical part consists of fibres,
Fig. 306.
1, Transverse section of human hair, showing the internal of medullary sub-
stance. 2 Longitudinal section, snowing the fibrous character of the same
pigment or colouring matter, and serrated edges.
arranged parallel to each other: besides these there are,
on the exterior, minute epithelial scales, which are ar-
ranged like the tiles on a house, producing the appearance
of transverse markings. The fibres gradually expand out,
Fig. 307.
Hair from the Indian Bat, magnified 500 diameters. 2, Hair supposed to
belong to (Dei mestes?) Anihrenus, magnified 250 diameters. 3, Hair from the
Mouse, magnified 250 diameters.
X X
674 THE MICROSCOPE.
forming a wall to the bulb enclosed in its capsule. The
development of a hair commences at the bottom of the
follicle, and by the aggregation of successive cytoblasts,
or new cells, are gradually protruded from the follicle, both
by the elongation of its constituent cells, and by the addition
of new layers of these to its base ; the apex and shaft of
hair being formed before the bulb, just as the crown of a
tooth is before its fang. The cytoblasts are round and
loose at the base of the hair, but are more compressed and
elongated in the shaft ; and by this rectilinear arrange-
ment the hair assumes a fibrous appearance. Of sixteen
species of the Bat tribe, the hairs of which were examined
by the late Professor Quekett, all were analogous in struc-
ture ; and the diversity of surfaces which these hairs pre-
sent are in reality owing to the development of scales
on their exterior. By submitting hairs to a scraping pro-
cess, these minute scale-like bodies, tolerably constant as
regards their size and figure, can be procured; so that
Bats' hair may be said to consist of a shaft invested with
scales, which are developed to a greater or less degree, and
varying in their mode of arrangement in the different
species of the animal ; that part of the hair nearest the
bulb is nearly free from scales, but as we proceed toward
the apex the scaly character becomes evident. Many of
the scales are not unlike those procured from the wings
of butterflies, but, being very much smaller, exhibit no
trace of striae on their surfaces ; those taken from dark-
coloured hairs have colouring-matter deposited on them in
small patches. In some cases they appear to terminate in
a pointed process ; in others the free margin is serrated. By
scraping, many of them will
be detached separately ; but in
some few cases, as many as
four or five will be found joined
together : in the larger hairs,
the cellular structure of the
interior, as well as the fibrous
Fig. 308. Transversesectionof Hair character of the shaft, are
of Pecari, showing its fibrous better seen after the scales
and cellular structure.
The hair owes the greater part of its colour to pigment"
SKIN, GLANDS OF.
675
cells: as these decay, and "become gradually divested of
their colouring-matter, they appear whitened, or "turn
grey." These hexagonal cells also give colour to the skin
of the negro, and are situated immediately beneath the
transparent coat. A small por-
tion is shown in fig. 309, the
vacant space denoting the situa-
tion of a lost hair.
Certain parts of the skin and
mucous membranes are espe-
cially supplied with papillae,
which serve as organs of touch ;
throughout the greater part of
the skin there are papillae more
or less sensitive, but only at
the extremities of the fingers,
lips, and in a few other situa-
tions, are these highly dev
loped, as in fig. 310. Papillae
are either filiform or tubiform,
and have entering into them nerves and blood-vessels;
the former supplying the sensibility of the skin, and termi-
nating in loops, as shown in fig. 310. Papillae injected are
shown in Plate VII. No. 150, tongue of mouse j villi from
small intestine of rat, No. 154.
The skin is the seat of two
processes in particular ; one of
which is destined to free the
blood from a large quantity
of fluid, and the other to
draw off a considerable
amount of solid matter.
To effect these processes we
meet with two distinct classes
of glandulae in its substance : _
., G , . f , Fig. 310. A section of skin from, the
the sudoriferous, or sweat finger, showing the vascular net-
glands; and the sebaceous, workofpapiZto, at the surface of
Fig. 309. Pigment Cells from
the skin.
or oil glands. They are both
formed, however, upon the same simple plan, and can
frequently be distinguished only by the nature of their
secreted product. The oil-glands of the skin ar<
x x 2
376
THE MICROSCOPE.
similar in structure to the perspiratory ducts, being com-
posed of three layers derived respectively from the scarf-
skin, which lines their interior ;
the sei sitive skin, which is the
medium of distribution for the
vessels and nerves ; and the
corium, with its fibres, giving
them strength and support.
Like the sudoriferous ducts, they
are in some situations spiral ;
Fig.311. Capillary network and dis- but this is not a Constant lea-
directly to their destination ; they are also larger, as
shown in fig. 312, proceeding from th3 oil or fat vesicle
situated at its
lower extremity.
Oil - glands are
freely distributed
to some parts,
whilst in others
they are entirely
absent : in a few
situations they are
Fig. ^.-Distribution of tlie tactile n&rves at the Worthy of parti-
extremity of the fingers, as seen in a thin perpen- cillar notice, as in
the eyelids, where
they possess great elegance of distribution and form, and
open by minute pores along the edges of the lids ; in the
ear- passages, where they produce that amber-coloured
substance known as the wax of the ears ; and in the scalp,
where they resemble small clusters of grapes, and open in
pairs into the sheath of the hair, supplying it with a
pomade of Nature's own preparing.
Internal parts of the body. We shall now have under
consideration cells of a much higher order than any before
referred to ; the cell found floating in the animal fluids is
known as the blood-cell, and requires a vascular system of
its own for distribution over the whole animal body.
The red blood cells, or corpuscles, have a circular form,
somewhat flattened ; their size is about l-3,200th of an
inch in diameter. It is well known that the blood-cor-
SECTION OP SKIN.
677
puscles, when floating in their own serum, or after having
been treated with acetic acid or water, appear to he fur-
nished with perfectly plain coverings, composed of a simple
homogeneous memhrane, without distinction of parts. But,
when the hlood is treated with a solution of magenta (nitrate
of rosanilin) or with a dilute solution of tannin, the cor-
puscles present changes which seem irreconcileable with
such a proposition. Dr. W. Eoberts, of Manchester, com-
municated an account of his observations on this subject to
Fig. 313. A vertical section of the Human Skin, showing the sweat-glanda, sur-
rounded by fat-globules, the ducts passing upwards through the epithelial
layer to the epidermis or external cuticle, magnified 250 diameters.
thd Koyal Society (Proc. Roy. Soc. vol. xii. p. 481), in
which he shows that nearly every disc possessed a parietal
macula, capable of being st lined by a dye. It was com-
monly of a lenticular shape, but sometimes square, and as
a rule very minute, not cover ng more than l-20th or l-30th
of the circumference. Mor< 'over, in the blood of many of
678 THE MICROSCOPE.
the lower animals a similar tinted particle appeared when
the corpuscles were treated with magenta. The conclusion
to be drawn from this and other observations noted by
Dr. Roberts, is that a duplication at one, or at most at
two points only, is indicated by direct proof; but certain
appearances occasionally observed jivour the notion of a
complete duplication.
The wall of the cell is a transparent structureless mem-
brane, and is of greater thickness than we find the analogous
membrane of cells to be generally. The red corpuscles of
birds, reptiles, &c. possess a distinct nucleus ; but, on
examining those of the human subject and other Mam-
malia, no distinct nucleus can be made out. By applying
dilute acetic acid, the red corpuscle becomes bleached, and
its walls distended, but no nucleus appears. If a red cor-
puscle from the Frog be treated in the same manner, we
see a nucleus, and the red colouring matter is drawn out
by exosmosis. Water causes the corpuscle to swell up,
and the colouring-matter disappears, but its real nature is
masked ; upon employing a drop of solution of iodine, the
wall is coloured or tinged, and made distinct. The cells
themselves have a tendency to undergo spontaneously
certain changes, one of the most common is a wrinkling up
of the walls, with a surface somewhat like that of a mul-
berry ; this may also be produced by mechanical pressure,
the addition of oil, &c.
There is another set of corpuscles, slightly larger than
the red set ; these are termed colourless corpuscles, which,
when distended by the action of water, are seen as nucleated
cells, whose diameter is about the 1-2, 500th of an inch,
and a double contour of the walls is observed ; sometimes
there is a slight tinge of colour to be seen in the nucleus.
There is a third kind of corpuscles in the blood, more
numerous than those above referred to, but of about the
same diameter ; when distended, they are seen to be cells
filled with granular matter ; sometimes a clear spot is
noticed on one side ; very dilute acetic acid being applied,
the granules are dissolved out, and a clear central nucleus
remains, if the acid be used stronger, an appearance is
seen as if there were several nuclei aggregated together.
This latter appearance was considered to be the natural
BLOOD CELLS.
679
state of the nucleus, the particles of which were either
tending to unite with one another, or there was a sepa-
ration of the nucleus into several smaller portions.
Wharton Jones, however, says there is no subdivision of
the nucleus.
If we examine a drop of blood under the microscope
Fig. 314.
I, A portion of the web of a Frog's foot, spread out and slightly magnified to
show the distribution of the blood-vessels. 2, A portion magnified 250 dia-
meters, showing the ovoid form of the blood-discs in the vessel, beneath
which a layer of hexagonal nucleated epithelium-cells appear. 3, Human
blood discs, as they appear when fresh drawn (magnified 250 diameters).
the corpuscles aggregate themselves together like rolls of
coins, fig. 314, No. 3, presenting a kind of network so
long as they remain suspended in their liquor sanguinis.
After the lapse of a few minutes, the fibrin, from its elasti-
city, contracts more and more, and a yellow fluid, called
serum, is pressed out, or, in other words, the components
of the liquor sanguinis, with exception of the fibrin, and
only a shrunken, jelly-like mass remains.
The blood-corpuscles of the lower animals Mr. Gulliver
hae especially studied. In the blood-corpuscles of birds,
680 THE MICROSCOPE.
and animals below them, there are nuclei ; but the cells,
instead of being circular, as in the human subject, are
elliptical, and larger. The corpuscles in Mammalia in
general are like those of man in form and size, being a
little larger or smaller. The most marked exception is in
the blood of the Musk-deer, in which the corpuscles are
of extreme smallness, about the l-12,000th of an inch in
diameter. The Elephant has the largest, which are about
1- 2,000th of an inch in diameter. The Goat, of all common
animals, has very small corpuscles ; but they are, withal,
twice as large as those of the Musk-deer. Another excep-
tion in regard to form is in the Camel-tribe, where they
are oval, and resemble those of the oviparous Vertebrata,
as the Frog, shown in fig. 314, No. 2. In the Meno-
branchus lateralis, they are of a much larger size than in
any animal, being the l-350th of an inch ; in the Proteus,
the l-400th of an inch in the longest diameter ; in the
Salamander, or Water-newt, l-600th; in the Frog, l-900th;
Lizards, l-l,400th ; in Birds, l-l,700tli ; and in Man, the
1-3, 200th of an inch. Of Fishes, the cartilaginous have
the largest corpuscles ; in the Gold-fish, they are about the
1-1, 700th of an inch in their longest diameter.
The large size of the blood-discs in reptiles, especially^in
the JBatrachia, has been of great service to the physiologist,
by enabling him to ascertain many particulars regarding
their structure which could not have been otherwise deter-
mined with certainty. The value of the spectroscope in
the chemical examination of the blood has been already
pointed out in our remarks on the application of this
instrument to the microscope. See page 119.
An interesting subject to Physiologists has been noticed
the production from the blood, under certain conditions,
of red albuminous crystals, which, although formed from
animal matter, and sometimes, in all probability, during
life, have the same regular forms as inorganic crystals.
Virchow was the first who paid particular attention to
their actual nature, and proved them to differ from saline
or earthy crystals. If we add water to a drop of blood
spread out under the object-glass of the microscope, as the
drop is beginning to dry up, the edges of the heaps of blood-
corpuscles are seen to undergo a sudden change : a few
BLOOD-CKYSTALS. 681
corpuscles disappear, others have dark thick edges, become
angular and elongated, and are extended into small well-
defined rodlets. In this manner an enormous quantity of
crystals are formed, which are too small to enable us to
determine their shape j they rapidly move lengthways, the
entire field of vision being gradually covered by a dense
network of acicular crystals, crossing one another in every
direction, with other crystals presenting a rhomboid form.
Dr. Garrod discovered, that by a slow evaporation of
portions of the serum of blood taken from patients labour-
ing under gout, he could obtain strings of crystals of uric
acid. His mode of procedure is to pour a little serum
into a watch-glass, and add a few drops of acetic acid ;
in this mixture place a few very fine filaments of silk or
tow, and stand it by for twenty-four hours under a glass-
shade. Upon removing the glass and submitting the
filaments to microscopical examination, they are found
studded with minute crystals.
A peculiar fatty matter was discovered by Yirchow in the
tissues of the human body and in certain nerves which he
termed Myelin. In the liver it exists in large quantities,
and much is found in the yolk of the egg. It is colour-
less, glistening, semi-fluid, prone to form drops, and capable
of being drawn out into long threads, which curve and
twist into very peculiar forms. The masses often exhibit
double contours, or many lines are observed equi-distant
from one another and vary-
ing in thickness. Choles-
terin is a component of all
forms of nyelin ; Beneke
has, in fact, shown that it
is a mechanical mixture of
cholesterin and cholate of
lipyl. No. 1, fig. 314,
the foot of the Frog, when ^ 5l5 ._ H ~ ad of Long . eared Bot
stretched out, shows the (Piecotus Auritus.)
distribution of the blood-vessels in the web : the two
sets of vessels the arteries and veins are very readily
made out when kept steadily on the stage of the micro-
scope ; the rhythm and valvular action of the latter may
be observed, although they are much better seen in the ear
682
THE MICROSCOPE.
or wing of the Long-eared Bat, as Professor Wharton Jones
pointed out.
To view the circulation of blood in the Frog's foot, the
older microscopists, Baker, Adams, and others, were in the
habit of tying the frog to a frame of brass ; at the present
time the entire body of the animal, with the exception
of the foot about to be examined, is secured in a black
eilk bag, and this is fastened to a plate, termed the frog-
plate, shown at a a a in fig. 31 6. The bag provided should
Fig. 316.
be from three to four inches in length, and two and a half
inches broad, shown at b b, having a piece of tape, c c,
sewn to each side, about midway between the mouth and
the bottom ; and the mouth itself capable of being closed
by a drawing-in string, d d. Into this bag the frog is
placed, and only the leg which is about to be examined
kept outside ; the string d d must then be drawn suf-
ficiently tight around the small part of the leg to prevent
the foot from being pulled into the bag, but not to stop
the circulation ; three short pieces of thread, ///, are now
passed around the three principal toes; and the bag with
the frog must be fastened to the plate a a by means of the
tapes c c. When this is accomplished, the threads ///
are passed either through some of the holes in the edge
of the plate, three of which are shown at g g g, in order
to keep the web open ; or, what answers better, in a series
TADPOLE, CIRCULATION IN. 683
of pegs of the shape represented by h, each having a slit i
extending more than half-way down it ; the threads are
wound round these two or three times, and then the end
is secured by putting it into the slit i. The plate is now
ready to be adapted to the stage of the microscope : the
square hole upon which the foot must be placed is brought
over the aperture in the stage through which the light
passes to the object-glass, so that the web may be strongly
illuminated by the mirror.
The circulation of the Tadpole is best seen by placing
the creature on its back, when we immediately observe
the beating heart, a bulbous-looking cavity, formed of the
most delicate, transparent tissues, through which are seen
the globules of the blood, perpetually, but alternately, en-
tering by one orifice and leaving it by another. The heart
is enclosed within an envelope or pericardium ; and this
is, perhaps, the most delicate and certainly the most
elegant thing in the creature's organism. Its extreme
fineness makes it often elude the eye under the single
microscope, but under the binocular its form is distinctly
revealed. Passing along the course of the great blood-
vessels to the right and left of the heart, the eye is
arrested by a large oval body, of a more complicated
structure. This is the inner gill, which, in the tadpole, is
formed of delicate, transparent tissue, traversed by arteries,
and presenting a crimson network of blood-vessels.
The Tadpole is hatched with respiratory and circulatory
organs resembling those of the fish. It lives in, and
breathes oxygen from the air contained in, the water,
and during the early period of its existence respires ex
clusively by gills.
It will be remembered that in nearly all fish the heart
has but two cavities, an auricle and ventricle ; that tlie
blood of the latter is returned by the veins to the auricle,
passes into the ventricle, is then transmitted to the gills,
where, being exposed to the air contained in the water, it
becomes deprived of carbonic acid, aerated, and rendered
fit for ret irculation through the system. In the reptile we
find a modification of plan. The heart has three cavities,
two auricles and one ventricle ; by this contrivance there
is a perpetual mixture in the heart of the impure car-
684 THE MICROSCOPE.
bonized blood which, has already circulated through the
body, and flows into the ventricle from the right auricle,
with the pure aerated blood returned from the lungs, and
which also flows at the same instant into the ventricle
from the left auricle. Thus the habitual circulation of
this " cold-blooded" mixture is the cause of the low tone
of vitality that distinguishes reptiles.
For the purpose of observation the tadpole must, of
course, be selected during the period in which the skin
is perfectly transparent. The first examinations reveal
plainly enough the appearances already described of the
fcrm and situation of the heart, and the three great arte-
rial trunks proceeding (right and left) from it. Many ob-
servations are required to arrive at the true anatomical
arrangement of these vessels. First, they are closely
connected with the corresponding gill. The upper one
(the cephalic} runs along the upper edge of the gill, and
gives off, in its course, a branch which ascends to the
mouth, which, with its accompanying vein, is termed the
labial artery and vein. The oephalic artery continues its
course around the gill, until it suddenly curves upwards
and backwards, and reaches the upper surface of the head,
where it dips between the eye and the brain, towards
which it is evidently travelling.
It would be a mistake to suppose that you can make
this out distinctly, in the average of tadpoles taken,
without some preparation. The great obstacle is the large
coil of intestines, usually distended with dark-coloured
food. This must be got rid of by making your tadpoles
live on plain water for some days. Plate VII. JSTo. 158,
exhibits the view of the vessels obtained under the in-
fluence of low diet, and we are now enabled to trace the
course of the three large arteries. The third trunk,
traversing the lung, is seen to emerge from the lower
edge and descend into the abdomen to form the great
abdominal aorta. A small black-looking starved little
tadpole shows the heart beating and the blood circulating,
but the latter is quite colourless, not a single red globule
visible anywhere. The globules chase one another away
like globules of water, the heart is a colourless globe, the
gills two transparent ovals, and the bowels a colourless,
TADPOLE, CIRCULATION IN, 685
transparent coil. Through the empty coil the artery is seen
on each side descending from the gills, converging to the
spine, meeting its fellow, and with it uniting to form the
abdominal aorta, the large central vessel coloured red in
the figure. After the aorta has supplied the abdominal
viscera, a prolongation, or caudal artery is seen descend-
ing to the tail, the all-important organ of locomotion in
the tadpole. This artery, entering the root of the tail, is
imbedded deeply in the flesh, whence it emerges, and then
continues its course, closely accompanied by the vein, to
within a short distance of the tail's extremity, where,
being reduced to a state of extreme fineness, it terminates
in a capillary loop, which is composed of the end of the
artery and the beginning of the vein. The artery, in its
course, gives off branches continually to supply the neigh-
bouring tissue. We may often observe that the blood
current in the tail, even in the main artery or vein, is
sluggish or even still. This occurs independently of
the heart, which may continue to beat as usual ; it
happens, because the circulation in the tail depends very
much on the motion of the organ. When this is sus-
pended (as in confining the tadpole under the microscope),
the blood moves sluggishly, or stops, till the tail regains
its freedom and motion, when the activity of the current
is restored. This fact is thus alluded to by Dr.
Grant : " It is the restless activity of the worm and of
the insect that makes every fibre of their body, as it were,
a heart to propel their blood and circulate their fluids,
while the slow-creeping snail that feeds upon the turf has
a heart as complicated as that of the red-blooded, verte-
brated fish, that bounds with such velocity through the
deep. It is because the fish is muscular and active in
every point that it requires no more heart than a snail to
keep up the necessary movements of its blood."
Having traced the arterial system, which conveys the
blood from the heart to the extremities, we will now note
its return by the veins back again to the heart.
The caudal vein runs near to the artery during the greater
part of its course, with its stream, of course, towards the
heart. This stream is swollen by perpetual tributaries from
vessels so numerous that their loops form a network which
686 THE MICROSCOPE.
covers the entire surface of the tail. As the vein approaches
the root of the tail it lies superficially to the artery, and
diverges from it at the point of entering the abdomen,
Here it approaches the kidneys, sends off branches to
them, while the main trunk continues its course on-
ward ; and, passing upwards behind a coil of intestine, it
approaches the liver, and runs in a curved course along the
margin of that organ. This blood is seen to enter the
vena cava by numerous fine channels, which converge
towards the great vein as it passes in close proximity to
the organ. Beyond the liver the vena cava continues its
course upwards and inwards to its termination in the sinus
venosus or rudimentary auricle of the heart. This ter-
mination is the junction of not less than six distinct venous
trunks, incessantly pouring their blood into the heart.
The circulation in the fringed lips forms a most compli-
cated network of vessels, out of which proceeds a vein
corresponding to the artery already traced. This descends
in a direct course till it joins the principal vein of the
head, which corresponds to our own Jugular.
Thus we have traced the blood through its main chan-
nels, and completed the circle of its course.
The blood is driven by the heart into each inner gill
through three large blood-vessels, which arise directly from
the truncus arteriosus, and may be called the afferent vessels
of the gill. (See enlarged view of gill, Plate VII. No. 156).
It will be seen that " each internal gill or entire
branchial organ consists of cartilaginous arches (No. 156),
with a piece of additional framework of a solidly tri-
angular form, stretching beyond the arches, and composed
of semi-transparent, gelatinous-looking material. These
parts, forming the framework of the organ, support upon
their upper surface the three rows of crests with their
vascular network, and the main arterial and venous trunks
which lie parallel with and between them. The three
systemic arteries arising, right and left, from the truncus
arteriosus, enter each gill on its cardiac side, and then
follow the course of the crests, lying in close proximity to
them. The upper of these branchial arteries runs alone
on the outside of the upper crest, and another branch
leaving the trunk and passing into the network of the
TADPOLE, CIRCULATION IN. 687
crest, whence a returning vessel may be traced carrying,
back the blood across the branchial artery, and to a vessel
lying close to and taking the same course as the artery
itself. Carrying the eye along the latter vessel we find,
at a short distance from the first of these crest branches, a
second, which leaves the main trunk and enters the crest,
when a corresponding returning vessel conveys the blood
across the arterial trunk into the vessel lying beside it, as
in the former instance. A succession of these branches
(each taking a similar course) may be traced from one end
of the crest to the other. But it is now to be observed
that the trunk from which these arterial branches spring
diminishes in size as it proceeds in its course (like the gill
artery in fishes), while the vessel running parallel to it and
receiving the stream as it returns from the crest enlarges in
the same degree. Thus, the artery or afferent vessel which
brings the blood to the gill is large at its entrance, but
gradually diminishes and dwindles to a point at the op-
posite end of the crest ; while the venous or efferent vessel,
beginning as a mere radical, gradually enlarges, and thus
becomes the trunk that conveys the blood out of the gill
to its ultimate destination. Calling this vessel the upper
branchial vein as long as it remains in contact with the
gill, we subsequently change its name when it leaves the
gill and winds upwards for distribution to the head, and
then designate it the cephalic artery. The middle branchial
artery and vein proceed in like manner in connexion with
the middle crest, and the lower artery and vein in connexion
with the lower crest. The middle and lower venous trunks,
having reached the extremity of the crests, curve down-
wards and inwards, and then leave the gill. The former
trunk, converging towards the spine, meets its fellow, and
with it forms the ventral aorta. The latter gives origin to
the pulmonary artery, and supplies also the integuments
of "the neck. Curious and beautiful is the final stage of
the metamorphosis, when the waning tadpole and incipient
frog coexist, and are actually seen together in the same
subject. The dwindling gills and the shrinking tail the
last remnants of the tadpole form are yet seen, in com-
pany with the coloured, spotted skin, the newly-formed
and slender legs, the flat head, the wide and toothless
88 THE MICROSCOPE.
mouth, and the crouching attitude of the all but perfect
reptile.
" By the process now described, the three systemic
arteries become continuous with the corresponding efferent
trunks that convey the blood for distribution through the
body, while, simultaneously, the vital fluid is being
abstracted from the special trunks belonging to the gill
and its vascular crests. These, with the gill structure
connected with and dependent upon them, being thus
deprived of their blood, shrink, become absorbed, and
disappear. Such appears to be the beautifully simple
mechanism by which the transition in the type of the
respiratory function from fish to reptile is accomplished.
If we take a tadpole a few days old, when the outer gills
are fully developed, and immerse it for another few days
in a weak solution of chromic acid (Mr. Archer's method),
we may, by placing the tadpole under a dissecting micro-
scope, and with the aid of a needle and camel-hair brush,
then remove the integuments, disclose the tufts of the
inner gills, and by carefully getting rid of a prominent roll
of intestine that occupies the upper part of the abdomen,
succeed in revealing the incipient lungs. These are situated
behind the gut and close to the spine, and appear as a pair
of minute tubular sacs, united at their upper and open
extremities. The chromic acid renders the tissues friable,
so that they can be readily peeled away."
That we may see how the circulation is carried on during
life in the gills, the outer covering must be carefully raised,
or even stripped off. This can be accomplished by put-
ting the Tadpole under the influence of chloroform a
drop of the fluid is sufficient for the purpose. 1
The blood-vessels of mammals are divided with refer-
ence to their structure into arteries, capillaries, and veins ;
yet these three divisions are by no means broadly separated
from each other, inasmuch as the capillaries are continued
into the veins just as imperceptibly as they arise from the
arteries. But with reference to their structure, while the
capillaries possess only a single coat without any special
structure, the larger vessels present, with but few excep-
'!) We refer the reader to Mr. W. U. Whitney's highly interesting and valuable
paper in the Trans. Micros. So for 1861 and 1867.
CAPILLARY CIRCULATION. 689
kions, three layers, which are designated as the inner coat,
or tunica intima ; the middle coat or circular fibrous coat,
tunica media; and an outer coat, tunica externa or ad-
ventitia. The first is the thinnest coat, and consists of a
cellular layer, the epithelium. ; generally, also of an elastic
coat, with the fibres disposed in a longitudinal direction.
The second, middle coat, is a thicker layer, and the principal
seat of the muscular fibres of the vessels ; in the veins,
however, it contains numerous longitudinal fibres, and in
the largest vessels more or less elastic elements and con-
nective tissue. The third coat has its fibres again arranged
for the most part longitudinally, and it is as thick as, or even
thicker than, the middle coat, and consists of connective
and elastic tissues. This coat, the tunica adventitia of
large arteries, contains muscular fibres in animals, but none
in man. According to J. Lister (Quart. Journ. Micros.
Scien. 1857, p. 8), the smallest arteries of the frog's web
show contractile fibre-cells, which measure from the 1-1 00th
to l-200th of an inch, and run in a spiral direction, making
one and a half up to two and a half turns round the inner
coat of the vessel, and such fibre-cells in a single layer
constitute the only muscular elements of the vessel.
The blood-vessels of the eye are extremely numerous,
and present different conditions in the several parts. In
the choroid coat, they are arranged in a most beautiful
stellate manner, and the capillary network of the inner-
most layer of the choroid coat, when injected, forms an
attractive object. A vertical section of the eye of a cat,
showing its several vascular and nervous coats, is given in
Plate VII. No. 157.
The circulation in the foot of the Frog and the tail
of the Newt is, for the most part, the capillary circula-
tion. The ramifications of the minute arteries form a
continuous network, from which the small branches of
the veins take their rise The point at which the arteries
terminate and the minute veins commence, cannot be
exactly defined ; the transition is gradual ; but the inter-
mediate network is so far peculiar, that the small vessels
which compose it maintain nearly the same size through-
out y they do not diminish in diameter in one direction,
like arteries and veins ; hence the term capillary, from
Y Y
690
THE MICROSCOPE.
capillus, a hair. (Fig. 317.) The size of the capillaries
is proportioned in all animals to that of the blood-cor-
puscles ; thus, amongst the fieptilia, where the blood-cor-
puscles. are the largest, the capillaries are also the largest :
but it does not follow that they
should be always of the same
size in all the tissues of one
and the same animal ; for if
we examine and carefully mea-
sure in the human subject
their sizes in different tissues,
we shall find that they vary
greatly even in individual tis-
sues, and, at a rough estimate,
examples may occur as large as
a thousandth, whilst others are
as small as the four or five-
thousandth of an inch. They
should be measured, if possible,
in their natural state j when in-
.-A network of capilktrits J ected their size
conveying Hood to the lungs. increased ; but, when dried, they
diminish so considerably that in some specimens vessels
imperfectly filled with injection have been known to shrink
from the three to the twenty -thousandth of an inch.
Kg. 318.
1, Blood-vessels of the Eye ; back view of the Iris and ciliary processes. 2, Vessel
of the meiribrana pupillaris, from the eye of a Kitten. 3, Fibres or tubes from
the lens of the Ox. (A sectional view of a Cat's eye is given in Plate VII.
Vo.157.)
CAPILLARIES.
691
Capillaries are, with very few exceptions, always sup--
ported by an areolar network, which serves not only as an
investment to them, but connects them intimately with
the tissues they are destined to supply. A possibility
arises, in first examinations, of mi staking or confounding
capillaries with nerves,
especially if the part
under observation should
have been left for some
time in strong preserving
or alkaline solutions.
A weak solution of
caustic soda, and also
another of acetic acid, are
both of use ; the first is
available for the purpose
of tracing nerves ; the
latter in making out
vessels, structure of pa-
pillae, unstriped muscle,
&c. , inasmuch as it renders
their nucleimore obvious Fif 319 _ m ^^ a ^
Willie SOda thickens and air-tubes for supplying the lungs with ai
makes them less so. It is very useful sometimes to use
these re-agents alternately ; the rule is, to apply them to the
object while under
the microscope, so as
to watch their gra-
dual operation.
It is not in the
blood alone that cells
float in a fluid ; the
chyle and lymph are
colourless corpuscles
flowing along their
especially - adapted
tubes and ducts, and
carrying the nutritive
particles gathered
from the food to the ^g- 320 - A capillary of blood-vessels distributed
Klnr^ -,r ,1 f 4--U to the fat tissue. Better seen in some of the j>
blOOd-vessels, for the jected specimens, Plate VII.
692
THE MICROSCOPE.
reparation of the framework, or growth that incessantly
goes on in the animal body.
Classification of the Animal Tissues. Professor Schwann
classifies the fundamental tissues of the human body as
follows : and it will be seen that more than half are
made up of cellular tissue or simple membrane.
1. Simple membrane : employed alone '
in the formation of compound
membranes . . .
2. Fibrous tissues.
3. Cellular tissues.
4. Sclerous, calcareous, or hard tissues |
5. Compound membranes : composed -N
of simple membrane and a layer of I
cells of various forms (ephithelium >
or epidermis), or of areola or con- \
nective tissue and epithelium . . J
6. Compound tissues ; a, those com- \
posed of tubes of homogenous ^
membrane, containing a peculiars
substance /
b, those composed of white fibrous )
tissues and cartilage }
Examples : Walls of cells, capsule of
lens of the eye, sarcolemma of
muscle, fec.
Examples : White and yellow fibrous
tissue, areola tissue, elastic tissue,
&c.
Examples : Cartilage, fat, pigment,
grey nervous matter, &c.
Examples : Rudimentary skeleton of
invertebrata, bone, teeth, &c.
Examples : Mucous membrane, skin,
true or secreting glands, serous and
synovial membranes.
Examples : Muscle, nerve.
Example : Fibro-cartilage.
Cellular or Formative Tissue. Areolar or connective
tissue is generally distributed throughout the body, and
various forms of this tissue an
found ; it is seen uniting to-
gether component parts, filling
up interstices between them,
and affording a support to the
blood-vessels and nerves, be-
fore they are distributed to the
various organs. This tissue is
soft, clear, smooth, and ex-
tremely minute, being the
1-1 2,000th of an inch in dia-
meter, sometimes less. The
fibre is usually found united
together in bundles; if
Fig. 32i. Fibrous tissue, lining the in- these be acted upon by dilute
S&EUijS[ acetic acid, they swell up,
in dilute hydrochloric acid. become transparent, and the
appearance of fibrous structure is no longer seen, although
FIBROUS TISSUE.
603
Borne fibres that were not previously observed may become
more distinct. The first kind does not refract the light
strongly; the second kind does, showing some chemical
difference in their composition.
Cellular tissue, if dried, becomes a yellowish, brittle,
transparent mass ; but regains its former state if placed in
water. The fibres have a remarkable arrangement and
disposition. They are often deposited in a spiral manner;
at other times they are regularly undulating. In fibres
taken from some parts of the body, we find a fasciculus
wound round in a spiral form. As a consequence, when
acetic acid is applied, we perceive projections of swollen
cellular tissue, and the depressions, from not having been
acted on, have a constricted appearance. The fibrous tissue
lining the eggshell, fig. 321, is the simplest form in which
it is found.
Fat is generally found in the cellular tissue ; it is not
secreted from it, but is contained in its proper cells, and
termed adipose tissue ; the elementary cells of which are
from the l-300th to the l-600th of an inch in diameter
(fig. 322). The cell-wall is very delicate and transparent;
sometimes there are one or two nuclei enclosed.
dissolves out the fat-cells from
the tissues. Acetic acid acts
upon the cell-wall, and causes
the contents to pass from within
outwards.
Fibrous tissue, elastic an&
non-elastic, is usually divided
into white and yellow fibrous
tissue. The yellow is elastic,
and of great strength, consisting
of bundles of fibres which are
highly elastic. (Fig. 3 2 4, No. 2.)
The white (fig. 324, No. 1),
though non-elastic, is of great
strength, and of a shining,
silvery appearance.
These two kinds of fibrous tissue differ from each other
in many respects, but chiefly in their ultimate structure,
their physical properties, and their colour : both are largely
604
THE MICROSCOPE.
employed in those parts subservient to the organs of loco-
motion.
The white fibrous tissue is (when perfectly cleared of
the areolar) of a silvery lustre, and composed of bundles
of fibres running, for the most part, in a parallel direc-
tion ; but if there be more than one
plane of fibres they cross or inter-
lace with each other. In some
specimens it is very difficult to
make out the fibres distinctly,
except with oblique light; from
this circumstance it would appear
that this tissue is composed of
rig. m.- content, of a longitudinally striated membrane,
single fat-cell, separated and which IS often found Split UD into
fibres. The white fibrous tissue is
principally employed in the formation of ligaments and
tendons a purpose for which it is admirably fitted on
account of its inelasticity : it also enters into the formation
Fig. 324.
I, White fibrous or non-elastic tissue. 2, Yellow fibrous or elastic tissue
taken near a ligament.
of fibrous membranes, viz. the pericardium, dura mater,
periosteum, perichondrium, sclerotic coat of the eye. and
MUSCULAR FIBRE.
695
Fig. 325. White fibrous tissue from the
sclerotic coat of the eye.
all the fasciae. It is sparingly supplied with capillaries
and nerves : the former always run in the areolar tissue,
connecting the bundles ot' fibres together ; in the gene-
rality of the fibrous tissues, the capillaries are not well
seen, except in that of the dura mater and periosteum ;
in other parts it must be injected to show them.
The yellow fibrous tissue
is highly elastic ; it consists
of bundles of fibres covered
with, and connected together
by, areolar tissue : the fibres
are of a yellow colour, some
round, others flattened ;
they are not always paral-
lel, but frequently bifurcate
and anastomose with neigh-
bouring fibres. It is always
difficult to separate the fibres
from each other ; and when
separated, the elasticity of
each individual fibre is shown
by its tendency to curl up at the end. The fibres in the
human subject vary in diameter from the l-5,000th to
l-10,000th of an inch. Acetic acid of ordinary strength
does not act on yellow fibrous tissue; nor for a veiy
long time after maceration in water or spirit does its
elasticity diminish. Very long boiling extracts from it a
minute quantity of a substance nearly allied to gelatine ;
neither nuclei nor a trace of a cell can be seen in it after
the addition of acetic acid : both are readily seen when
white fibrous element is treated with this acid.
Muscular Fibre. There are three different kinds of
muscular fibre found in the animal body : 1st, in the
muscle of the skeleton ;. 2d, in the muscle of the heart ;
and 3d, in the stomach, intestine, &c. The functions of
muscular fibre may be referred to two kinds voluntary
and involuntary. The muscles endowed with voluntary
power are those of the skeleton; the involuntary are those
of the heart, stomach, intestine, &c.
Muscular fibre is held together by a very delicate tubular
sheath, nearly resembling simple structureless membrane.
696
THE MICROSCOPE.
structureless membrane, myolemma.
(Magnified 100 diameters.)
This cannot always be discerned : but when the two ends
are drawn asunder it will be perceived to rise up in
wrinkles, or the fragments of Uie torn muscle will be
seen to be connected by the nntorn membrane, as at
fig. 326. This membrane is termed Myolemma. It is best
seen when a piece of muscle is - ubjected to the action of
fluii.s, as diluted acetic or
citric acid, or the fluid alka-
lies which occasion it to swell
and become easy of separa-
tion It has no share in the
co i raction of the muscle itself,
win 'h is made up of a series
of 1 1 undies of highly elastic
fibres : portions of a separated
buij<lle are shown at fig. 327,
and the ultimate structure of
a fibre, under a magnifying po ver of 600 diameters, at
fig. 328, No. 1.
Dr. Hyde Salter pointed out. that in the tongue the
muscles pass directly into the b indies of the submucous
connective tissue, which
8ei ve as their tendons. Such
a t ransition is shown in fig.
32 3, No. 2 ; the tendon, the
lo> er part of which may be
se n passing insensibly into
t.L striped muscle, the glan-
dular sarcous elements of
th latter appearing, as it
w- e, to be deposited in the
sii ^stance of the tendon (just
Calcareous particles are
ng the tissue about the
lasts, and that in some
portions, which would
Fig. 327. Muscular fibre, IroTcenup
into irregular and distinct bands;
a few blood globules are distributed
about. (Magnified 200 diameters).
deposited in bone), at first le*.
walls of the cavities of the eix
other directions, unaltered. r J
have represented the elastic elei
tissue, disappear in the centre <
the endoplasts are immediate
ut in ordinary connective
ue muscular bundle, and
surrounded by muscle ;
just as, in many specimens of 1 ue (see figs, of bone), the
lacunae have no distinguishable alls. On the other hand
MUSCULAR FIBRE. 697
at the surface of the bundle the representative of the
elastic element remains, and often becomes as much de-
veloped as its sarcolemrna. There is no question here of
muscle resulting from the contents of fused cells. It
is obviously and readily seen to be but a metamorphosis
of the periplastic substance, in all respects comparable
to that which occurs in ossification, or in the develop-
ment of tendon. In this case, we might expect that, as
there is an areolar form of connective tissue, so ehould
Fig. 328.
, Muscular fibre, and a fasciculus of a muscle taken from a young Pig. (Mag-
nified 600 diameters.) 2, Muscular fibre from the tongue of Lamb, showing
continuity of the upper portion, with connective tissue of the lower portion.
3, Branched muscle, ending in stellate connective cells, from the upper lip ol
the Rat.
we find some similar arrangement of muscle ; such may,
indeed, be seen very beautifully in the termination of the
branched muscles, as they are called. In fig. 328, No. 3,
the termination of a muscular fibre from the lip of a Eat,
is shown : and the stellate " cells" of areolated connective
tissue are seen passing into the divided extremities of
the muscular bundle, becoming gradually striated as they
do so. In the muscle it is obvious enough, that what-
ever homology there may be between the stellate "cells"
and the muscular bundles with which they are con-
tinuous, there is no functional analogy, the stellate bodies
having no contractile faculty. The nervous tubule is
developed in essentially the same manner as a muscular
fasciculus, the only difference being, that fatty matters
take the place of syntonin. Now it commonly happens
that the nerve-tubule terminates in stellate bodies (fig.
330) of a precisely similar nature ; these are supposed to
698
THE MICROSCOPE.
possess important nervous functions ; and are now known
as " ganglionic cells."
The muscular fibre, known as the non-striated, or invo-
luntary, consists of a series of tubes presenting a flattened
appearance, without the transverse striae so characteristic
of the former : elongated nuclei immediately appear upon
the application of a little dilute acetic acid. Professor
Wharton Jones first demonstrated this structure in his
lectures at Charing Cross Hospital, about 1843 : he was
led to infer, from appearances in very young fibre, that
the striped muscular fibre is originally composed of
similar elements to the unstriped, or plain muscular tissue,
which, in the process of deve-
lopment, becomes enclosed in a
sarcolemma (simple membrane)
common to many of them ; the
fibres then split into smaller
fibres (fibrillce). Thus account-
ing for the nuclei of striped
muscular fibre; which, accord-
ing to his views, are " the per-
sistent nuclei of the primitive
muscular-fibre cells."
The non-striated fibre is beau-
tifully seen in connexion with
the skin surrounding the hairs
of the head, a few fibres of
which are separately shown in
fig. 329. Professor Kolliker ori-
ginally described these muscles
of the skin, of which there appear
Fiij. 329. A portion of (he invoiun- to be one or two in connexion
tary muscular fibre surrounding ,-, i_ i. j? iv i
the Mir with each hair-follicle, arising
from the more superficial parts
of the outer skin, then passing down to the root of the hair,
close behind the fat-gland, and there embracing it. It is
indeed most remarkable that skin, when covered with
hair, should alone be provided with these muscular
fibres ; the effect of the contraction of which must be
to thrust up the hair-follicles and depress the inter-
mediate portions of skin, and thus produce that peculiar
NERVOUS STRUCTURE.
699:
and before unaccountable state of the surface known as
n.
Nerves. The nervous system consists of
brain, spinal marrow, and nerves. There
are two sets of nerves in the body ; in the
one set the nerves are white, firm, shining,
more or less rounded, with trans verse mark-
ings ; in the other, they are softer, not so
consistent, of a reddish grey colour, and
generally flat.
Under the microscope, nerves are seen to
be composed of minute fibres or tubules, full
of nervous matter, arranged in bundles,
and connected by an intervening fibro-cel-
lular tissue, through which capillaries ramify.
A layer of the same, or of a more delicate,
transparent, structureless tissue surrounds
the whole nerve, forming a sheath. The
slight pressure of the thin glass, when
placed on the nerve-fibre, causes nearly the
whole of the contents to flow out in the
form of a granular material j it therefore
becomes necessary to exercise considerable
care in breaking up structures to view these
tubules, which should be immersed in a
very weak solution of spirit and water.
On Microscopical Examination of Nerves It would
scarcely be necessary to insist on the great importance of
removing and examining the
nervous centres as soon as
possible after death, were it
not that the practice is too
often neglected. Great cau-
tion also should be exercised
to avoid injuring the parts, so
that when hardened, perfect
or entire sections of them may
be obtained for examination
under the microscope. After they have been carefully
examined externally, by the assistance of a lens, if neces-
sary, incisions should be made, not at random, but in a
330. A Stel-
late nerve corpus-
cle, with tubular
processes issuing
out, which at a
is filled with a
corpuscle con-
taining black
pigment, above
this are corpus-
cles with nuclei
and their nu-
cleoli ; at 6 is a
corpuscle en-
closing within
its sheath gra-
nular matter :
this is taken,
from the root of
a spinal nerve.
3Bl ,_ Termination of nerve . loop ,
in muscles.
700 THE MICROSCOPE.
regular manner through them ; and wherever there is
reason to suspect the existence of disease, small portions
should be removed, and examined while perfectly fresh
under high magnifying powers. The nature of the lesion
having been thus ascertained, the morbid parts, with
some of the surrounding healthy tissue, should be re-
moved, and after being divided, if necessary, into smaller
portions, should be macerated in a weak solution of chromic
ucil. It is very important to cut and subdivide the
parts, when necessary, in such a manner, that their rela-
tion to the rest may be recognised after they have become
hardened for the purpose of making sections. Thus,
unless the locality of the lesion require a different course,
one incision may be made through the crura cerebri,
immediately in front of the small or motor root of the
trifacial nerves, and a third through the base of the
anterior pyramids, immediately below the attachment of
the sixth pair of cerebral nerves. "With regard to the
spinal cord, if it be cut up into small portions and
hardened in chromic acid, it will be found better to divide
it in three places : 1st, through the middle of the cervical
enlargement; 2nd, through the middle of the dorsal
region ; and 3rd, through the middle of the lumbar
enlargement.
I however, the lesion be suspected to exist at another
point, the cord must be divided there; as it is highly
important that the nature of any morbid portion that
may be found should be examined under the microscope
in a perfectly fresh state ; for the nerve-fibres undergo a
considerable and very deceptive alteration by the action
of chromic acid. But it is no less important, and indeed is
absolutely necessary for an exact and complete investiga-
tion, that entire portions of the cord, in the locality of the
lesion, be hardened in chromic acid, so that thin, but
perfect sections may be made for examination under the
microscope.
" The strength of the chromic acid solution should differ
for different parts of the cerebro-spinal centres. For the
convolutions of the cerebral hemispheres and cerebellum,
the proportions should be one of the crystallised acid to
about four hundred of water, while for the pons varolii,
SECTIONS OF SPINAL CORD 701
medulla oblongata, and spinal cord, the strength of the
solution may be in the proportion of one of the acid to
about three or even two hundred of water. It is best,
however, to begin with the weaker solution and increase
its strength at the end of some hours. If the cerebral
and cerebellar hemispheres be hardened in a solution of
greater strength, they become friable and unfit for making
perfect sections." 1
Method of Preparing Sections of the Spinal Cord. By
a peculiar method, the late Dr. Lockhart Clarke obtained
beautiful sections showing the arrangement of the
nerve-fibres and vesicles of the spinal cord and other
parts of the nervous system. The results are recorded in
the Philosophical Transactions for 1851, Part 2. Thecord,
it appears, must be hardened in acetic acid and alcohol,
when excessively thin sections may be readily obtained
with a sharp knife. These are then soaked in pure spirit,
which permeates the texture in every part, and drives out
the acetic acid, and afterwards transferred to turpentine
which expels the spirit, and lastly the sections are
mounted in Canada balsam. By this plan the tissues of
the embryos of mammalian animals can also be rendered so
transparent that the smallest ossific points can be seen in
the temporary cartilages. To render the specimen more
transparent immerse it in alcohol to which a few drops
of a solution of soda have been added, and allow it to
remain quietly for a few days. When sufficiently acted
on, remove it, and preserve permanently in weak spirit. The
principle of the action of the fluid may be explained
thus : alcohol alone tends to coagulate albuminous textures
and render them opaque, at the same time that it hardens
them. The alkali, on the other hand, renders the tissues
soft and transparent, and if time were allowed, would
cause their complete solution. These two fluids in con-
junction harden the texture and at the same time make it
clear and transparent. Many soft tissues may thus be har-
dened sufficiently to enable us to cut very thin sections.
Nerves may be examined in thin sections of the skin
after the addition of acetic acid and a solution of soda.
Gerber boils the skin until it becomes quite transparent
(1) Lockhart Clarke on the Microscopical Examination of Nerves.
702 THE MICROSCOPE.
then allows it to remain a few hours in turpentine, or
until the nerves are seen to be white and shining, when
they are ready for cutting into perpendicular sections with
the double (Valentine's) knife.
It is proposed to employ chloride of gold to stain the
tissues of the body. Tissues soaked in a weak solution
of from one to two per cent, of this salt in distilled water,
and afterwards exposed to light, are found to exhibit
certain parts, as nerve-fibres, connective tissue, corpuscles,
and cells generally, stained of violet-red colour, while
other parts, as intercellular substance, &c. are left un-
touched. The soaking must be continued until the tissue
assumes a straw-yellow colour, then taken out of the solu-
tion and placed in dilute acetic acid of one to two per
cent. The colour will be seen to gradually develop itself,
and Kolliker and Cohnheim, who have tried it, say that
nerve-fibre, &c. are exceedingly well shown in this way.
Consolidated Tissues. Such tissues are formed by a
chemical combination with the albumen and gelatine of
the fibre ; this in cartilaginous
formations is termed chondrine,
the cells of 'which become con-
solidated by calcareous deposits,
and a gradual transition results
therefrom. Cartilage is the
firmest structure next to bone
met with ; it is very elastic,
and, as an intercellular sub-
stance, is generally divided into
two kinds. Between the ribs
we find this substance presenting
a uniform bluish appearance,
Fig. 332. Cartilage from, ear of and slightly granular I this 18
Mouse, resembling a section of , v-i. J.-T TII
vegetable tissue, with superim- true, or white cartilage. Ihe
posed layers. other form of intercellular sub-
stance is developed in fibrous substances ; and it is in
this peculiarly-formed felt- work that cells with nuclei are
found. This is known as yellow, fibrous, or spongy car-
tilage, the yellow colour depending on the mode of fibrous
arrangement of the intercellular substance : it is found in
the ears, and other parts.
CARTILAGE. 703
Cartilage forms the entire skeleton in some kinds of
fishes, the Skate, Lamprey, &c. In man it is placed
1 FIG. 333. 2
1, Cartilage from Rabbit's ear, showing large cells embedded in a fibrous
matrix. 2, Cartilage from Human ribs, with cells in groups, each having
a granular nucleus. (Magnified 200 diameters.)
between all the long bones, and also the bones of the
vertebral column, there acting as an elastic cushion.
Cartilage receives its nourishment
by minute blood-vessels. When ex-
amined microscopically, the simplest
form of cartilage is seen to resemble
in a striking manner the cellular
tissue of vegetables ; it consists of
an aggregation of cells of a spherical
or oval form, capable in some cases
of being separated from each other,
and every cell having a nucleus,
with a nucleolus in its interior. In
figs. 332, 333, and 334, we have vari-
eties of this structure. In the more
highly organized scale of animals,
a strong fibrous capsule, or sheath,
surrounds the cartilage-cells ; some FlG - 3M-Qa>rWage from
J.T- i T L j_i the Cuttle-fish, showing
ot the fibres dip in amongst the stellate form of cells.
cells, and bind them firmly to-
gether. In those inhabitants of the water, the Ray
and Shark, the entire skeleton being cartilaginous,
the cell is embedded in a matrix, which may
704
THE MICROSCOPE.
be strictly termed intercellular. Cells are frequently 01
entirely isolated, as in the section from the ear of a Mouse
(fig. 332), they then rarely become converted into bone.
In the highest animals it is generally invested by a fine
1 Pig. 886.
.1, Cartilage from the head of Skate, with clusters of nucleated cells and
nuclepli inclosed. 2, Cartilage from the Prog, with cells having nucleoli,
magnified 200 diameters.
and delicate membrane, termed perichondrium, which brings
the blood-vessels in close contact with the cartilage ; and,
when in actual contact with the extremities of bones, is
covered by a vascular membrane having a large number of
vessels terminating in it, for the purpose of supplying a
lubricating fluid to the end of the bones : this, the synovial
membrane, is a very beautiful structure when injected and
viewed under a 1-inch power.
In the earliest stages of existence, the entire framework
or a very large proportion is composed of cartilage, which,
by a gradual addition of earthy matter, becomes consoli-
dated into bone. The mode of development, and the
change from one to the other, is represented in the section
(fig. 336) ; it will there be seen that the calcareous matter
is deposited in nearly straight lines, which stretch from
the ossified surface into the substance of the matrix of
the cartilage, the amount of calcareous matter in which
gradually diminishes as we recede from the ossified part.
If the deposit has taken place to any great extent, the
TEETH.
705
calcareous matter becomes crowded and consolidated ; as
the process advances, the bone thickens, and a series .of
grooves, of a stellate form as in the annexed cut (fig. 337,
No. 2), are found upon its sur-
face, which become gradually
converted into canals for the
passage of blood-vessels.
In certain forms of disease,
many of the soft parts of the
human body are converted into
cartilaginous and bony masses,
which have received the name
of Enchondroma (figs. 338 and
339). The microscopical cha-
racteristics of this change have
been described by the author
k n the Transactions of the PatJw-
logical Society of London, vol. iv.
Teeth. It is desirable to be-
come acquainted with the struc-
ture of teeth under the micro-
scope ; they are highly interest-
ing to the physiologist, and im-
portant guides to the naturalist
in the classification of animals.
Professor Owen has said, "If
the microscope is essential to
the full and true interpretation
of the vegetable remains of a
former world, it is not less in-
dispensable to the investigator
of the fossilised parts of animals.
It has sometimes happened that
a few scattered teeth have been
the only indications of animal
life throughout an extensive stratum; and when these
teeth happened not to be characterised by any well-marked
peculiarity of external form, there remained no other
test by which their nature could be ascertained than that
of the microscopic examination of their intimate tissue,
By the microscope alone could the existence of Keuper-
z z
Fig. 336. A vertical section oj
cartilage, with clusters of cells
arranged in columns -previous tv
conversion into lone, which is
seen consolidated at the upper
surface. The greater opacity of
this portion is owing to the in-
crease of osseous fibres, the
opacity of the cell contents,
and the multiplication of oil-
globules; the dark intercel-
lular spaces become occupied
by vessels.
706 THE MICROSCOPE.
reptiles in the Lower sandstones of the New red system,
Fig. 337.
1, Section of the tendo-Achillis as it joins the oscalcis ; showing the stellate
cells of tendon gradually coalescing to form the round or oval cells of the
cartilage. 2, A small transverse section of enchondroma, showing the gradual
change of the cartilage-cells at a into the true bone-cells, termed lacunce,
at 6, with their characteristic eanalwuli.
in Warwickshire, have been placed beyond a doubt. By
the microscope, the
supposed monarch
of theSaurian tribes
the so-called BGL-
silosaurus has
been deposed, and
removed from the
head of the Kepti-
lian to the bottom
of the Mammalian
division. The mi-
croscope has de-
graded the Sauro-
cephalus from the
class of reptiles to
that of fishes. It
has settled the
doubts entertained
by some of the
highest authorities
in palaeontology as
to the true affinities
of the L'kjantic Me-
Fig. 338. Microscopical character of Enchondroma,
/nm a finger. The cartilage undergoes a gra-
dual change, and is seen converted into bone
t the upper portion.
gatherium ; arid by
TEETH.
707
demonstrating the identity of its dental structure with
that of the Sloth, has yielded us an unerring indication of
the true nature of its food."
i The teeth of Man and of most of the higher animals
are composed of three different
substances, Dentine (known as
ivory in the tusk of the elephant),
.Enamel, and Cementum, or crusta
petrosa. These are variously dis-
posed, according to the purposes
which the tooth is to serve : in
Man the whole crown of the
tooth is covered with enamel,
shown in the darker marginal Fig . ^I Portion of an enchon _
part of fig. 340 ; its root or fang dromatous mass, nucleated cells,
is covered with cementum, <^ 6 * to -
whilst the substance or body of the tooth is composed of
dentine.
In the human subject, two sets of teeth are developed,
the milk and permanent : the first are formed from one
1 Fig. 340. Sections of Human Molar Tooth (magniried 50 diameters)
1, Vertical Section. 2, Horizontal Section.
set of bulbs, which in time shrink, and let the teeth fall
out ; the permanent set is then produced from new bulbs,
z z 2
708
THE MICROSCOPE.
situated by the side of the old ones. Blandin was the first
to point out that the teeth are developed in the mucous
membrane, in a similar way to hair and nails. Other ob-
servers have been led to the same conclusion ; and, more
lately, Professor Goodsir demonstrated that the teeth are
first formed in grooves of the mucous membrane, and sub-
sequently converted into closed sacs by a process of involu-
tion, and that their final adhesion to the jaw is a com-
paratively late part of the process. It is now generally
conceded that teeth belong to the muco-dermoid, and not
?ig. 341.
I, "A section of a cusp of the posterior molar, upper jaw of a Child. The inner
outline represents it before the addition of acetic acid the outer after-
wards, when Nasmyth's membrane g is seen raised up in folds ; /, the enamel
organ ; e, the dentine. The central portion is tilled up with pulp. 2. Edge
of the pulp of a molar cusp, showing the first rudiment of the. dentine, com-
mencing in a perfeetly transparent layer between the nuclei of the pulp and
the membrana preformativa. 3, Nasmyth's membrane detached from the
subjacent enamel by acetic acid. 3, The stellate-cells of the enamel-organ.
5, Tooth of the Frog, acted on by dilute hydrochloric acid, so as to dissolve
out the enamel and free Nasmyth's membrane. The structure of the dentine
e is rendered indistinct. At the base, Nasmyth's membrane is continued over
the bony substance at z, in which the nuclei of the lacunce are visible. (After
Huxley.) 6. Decalcified tooth-structure; a, the dentine; 6, enamel organ;
c, enamel ; d, Nasmyth s membrane.
to the periosteal, series of tissues; that, instead of standing
in close relation to the endo-skeleton, they are part of the
dermal or exo- skeleton ; their true anologues being the
hair, and some other epidermic appendages. Professor
Huxley has proved that, although teeth are developed in
TEETH.
709
two ways, these are mere varieties of the same mode in
the animal kingdom. In the first, which may be typified
by the Mackerel and the Frog, the pulp is never free, but
from the first is inclosed within the capsule, seeming to
sink down as fast as it grows. In the other, the pulp pro-
jects freely at one period above the surface of the mucous
membrane, becoming subsequently included within a cap-
sule formed by the involution of the latter ; this occurs
in the human subject. The Skate offers a sort of inter-
mediate stage.
The enamel forms a continuous layer, and invests the
crown of the tooth; it is thickest upon the masticating
surface, and decreases towards the neck, where it usually
terminates. The external surface of the enamel
Fig. 342. Tooth Structure.
1, Longitudinal section of superior canine tooth, exhibiting general nrran Ce-
ment, and contour markings, slightly magnified. 2 and 3, Portions from same,
highly magnified, showing the relative position of bone-cells, cementum at
2, dentine libres, and commencement of enamel at 3. 4, Dentine fibres
decalcified. 5, Nasmyth's membrane separated and the calcareous matter
dissolved out with dilute acid. 6, Cells of the pulp lying between it and the
ivory. 7, A transverse section of enamel, showing the sheaths of fibres
contents removed, and magnified 300 diameters.
smooth, but is always marked by delicate elevations and
transverse ridges, and covered by a fine membrane (Na-
smyth's membrane), containing calcareous matter : this
membrane is separable after the action of hydrochloric acid;
it then appears like a network of areolar tissue, shown in
fig. 342, No. 6; which is Huxley's "calcified membrana
710 THE MICROSCOPE
preformativa" of the ivliole pulp. Nasmyth says : "In all
cases where this covering has been removed by means of
acid, it has, of course, the appearance of a simple mem-
brane, in consequence of the earthly deposit having been
dissolved out, and the animal tissue only remaining. The
structure and appearance of the covering detached in this
manner from, the enamel is the same in every respect as
that observed in the capsule of the unextruded tooth, and
consisting, like it, of two layers, fibrous externally, and
having on its external surface the peculiar reticulated
appearance common to both."
" On examining carefully fine sections of several teeth
under the microscope, I perceived here also," observes
iNasmyth, " that the structure in question was continuous
with the crusta petrosa of the fang of the tooth."
The enamel has a fibrous bluish aspect, is very brittle,
and much harder than the other dentinal structures ; it
is, indeed, so hard, that it strikes fire with steel ; if an
attempt be made to cut it without the application of water
to keep it cooled down, it burns with an ammoniacal
odour, such as we perceive when horse-hoof is burnt. It is
composed of prisms, about l-5,000th of an inch in breadth,
more or less wavy, and transversely striped. Two kinds of
bands or stripes are seen traversing enamel, the direction
of one of which nearly coincides with that of the dentine
fibres ; the other set of stripes indicate the laminated struc-
ture of enamel. Under polarised light, a third set become
visible, arising from the variable inclination of the axes
of the fibres to the plane of polarisation. The enamel
is often traversed by cracks or fissures, mostly running
parallel with one set of the fibres : these are sometimes
described as canals ; but as they resemble splits, and are
seldom seen in young teeth, it is more likely that they
are caused by the nature of the food and drink, which is
taken into the mouth at temperatures varying many de-
grees ; we also trace the commencement of disease from
a fissure in the enamel. When a section of the enamel
is cut obliquely, it has somewhat of a hexagonal or six-
sided appearance. The dentine consists of a transparent
basement membrane, with alternating layers of cal-
careous matter, traversed by very fine branching tubuli,
TEETH. 7 1 1
which, commence at the pulp cavity, and pass up to the
enamel.
Czermak discovered that the curious appearances of
globular conglomerate formations in the substance of
dentine depend on its mode of calcification and the
presence of earthy material ; and he attributes the contour
lines to the same cause. Contour markings vary in in-
tensity and number; they are most abundant in the rool
and most marked in the crown. Vertical sections exhibit
them the best; as fig. 342, JSTo. 1. In preparing a specimen,
first make the section accurately,
then decalcify it by submersion in
dilute muriatic acid ; then dry it
and mount in Canada balsam with
continued heat, so as to allow the
specimen to soak in the fluid resin
for some time before it cools. It is
the white opacity at the extremity
Of the COntOUr markings Which Fig. 343. Transverse section o/
gives the appearance of rings on &&$SSttiSS!f&
the tooth-fang. gg. rf-jH-^ffl.
" The tOOtll-SUbstance appears, Haversian canals in true
says Czerniark, " on its inner sur- bttne *
face, not as a symmetrical whole, but consisting of balls
of various diameter, which are fused together into a
mass with one another in different degrees, and on which
the dentinal tubes in contact with the germ cavity are
terminated. By reflected light, back-ground illumination,
one perceives this stalactite-like condition of the inner
surface of the tooth-substance very distinctly, by means of
the varied illumination of the globular elevations, and by
the shadows which they cast. Here one has evidently to
do with a stage of development of the tooth-substance;
for the older the tooth is, the less striking in general are
these conditions, and the more even is the surface of the
wall of the germ-cavity. In very old teeth considerable
unevenness again makes its appearance; these, however,
are not globular, but have a cicatrised, distorted appear-
ance. It is best to make the preparation from a tooth of
which the root is not perfectly completed. "With such
preparations, one is readily convinced that the ground-
i 12 THE MICROSCOPE.
substanco of the last-formed layer of the tooth-substance
appears, at least partly, in the form of balls, which are
fused one among another, and with the balls of the penul-
timate layers ; and one also perceives that in general theif
diameter becomes less and less, somewhat in the form of a
point, towards the periphery of the tooth-substance. To
obtain specimens, procure a tooth of which the fang is
half-grown; then introduce the point of a penknife into its
open extremity, and scraping the inner surface, detach
small portions, which exhibit the globules admirably." l
The cementum is the
cortical layer of osseous tis-
sue, forming an outer coat-
ing to the fangs, which it
sometimes cements toge-
ther. It commences as a
very thin layer at the part
Fi S . ^.-Transverse section of Too* of wh f re the enamel ceases,
Myliobates, Eagle-ray, viewed as an and increases in thickness
opaque object to show its radiating +-__,}<, A-L _ n J Q n f j.u
flbrous structure. towards tne ends ol tne
fangs. Its internal surface
is intimately united with the dentine, and in many teeth
it would appear as if the earliest determined arrangement
of the fibres of the dentine started from the canaliculi, as
they radiate from the lacunae in the cement. The inter-
lacunar layer is often striated, and exhibits a laminated
structure : sometimes it appears as if Haversian canals
were running in a perpendicular direction to the pulp
cavity. The canaliculi frequently run out into numerous
branches, connecting one with another, and anastomising
with the ends of the dentine fibres. The thick layers of
cement which occur in old teeth show immense quantities
of aggregated lacuna of an irregular and elongated form.
Professor Owen believes that by age the pulp ceases to pro-
duce or nourish the dentine, which then becomes converted
into osteo-dentine, and thereby the layer of crusta is so
much increased as often to fill up the pulp cavity of the
ooth. Professor Simonds assures us that this is not the case
In the Herbivora. For instance, in the horse, the oblitera-
(1) C'zermak: translated by James A. Salter, M.B., Qwrterly Journal qj
Microscopical Science, July, 1823.
BONE.
713
tion of the cavity is gradually effected by an increased
formation of dentine ; and this is not supplanted by ar
abnormal or diseased growth, as would be the case were
the pulp to become ossified, but as the pulp diminishes,
so is the supply of nutriment to the tooth lessened, and at
length entirely cut off from the interior. " To provide foi
the vitality of the tooth under
these circumstances, the crusta
increases in quantity on the
fang, at the expense of the per-
fectly-formed dentine, which is
lying in immediate contact with
its inner surface. Through the
medium of the canals in the
crusta, which open on its
borders, the tooth now draws
its nourishment from the blood-
vessels of the socket ; and thus
it continues, long after the obli-
teration of its pulp cavity, to
serve all the purposes as a part
of the living organism." *
Bone. The elements Of bone Fig- 345. A transverse section of the
i -11 I -i -i human clavicle, or collar-bone, mag-
are Iamelia3 and Small COr- nified 95 diameters ; which ex-
puscles j the latter are possibly hibits * h . e Haversian canals, the
* - ' ... J-IP concentric lammse, and the con-
merely spaces between the for-
mer, in which is deposited the
earthy substance. The lamellae
have for their basis a cartila-
ginous substance combined
with earthy matter, or salts.
These salts are chemically com-
bined with the organic basis.
earthy salts, and leave the organic basis of the same
form as the bone itself. The lamellae are homoge-
neous throughout, like the intercellular substance of car-
tilage, but chemically different, being resolved by boiling
in water into colla, whereas cartilage is resolved into
chondrine.
centric arrangement of bone-cella
around them. Some of the Ha-
versian canals are white, others
black ; the latter are filled with
a deposit of opaque matter, used
in the grinding and polishing tha
section. When viewed under a
lower power, they appear to be
only a series of small black dots,
as shown in fig. 346.
Acids dissolve only the
(1) Professor Simonds, on the ''Structure and Development of Teeth of
Animals."
714
THE MICROSCOPE.
of small Hack dots.
Professor Quckett's paper, Micros. Soc. Transactions,
furnishes the earliest reliable
information on the " In-
timate structure of Bone." To
this paper we are indebted
for the following microscopica'
investigation of bone :
Bone consists of a hard and
soft part ; the hard is com-
posed of carbonate, phosphate,
and fluate of lime, and of car-
bonate and phosphate of mag-
nesia, deposited in a cartila-
ginous or other matrix ; whilst
the soft consists of that matrix,
and of the periosteum which
invests the outer surface of
the bone, and of the medullary
membrane which lines its in-
terior or medullary cavity, and
is continued into the minutest
pores. If we take for exami-
nation a long bone of one of
the extremities of the human
subject, or of any mammalian
animal, we shall find that the
bony substance, or shaft, is
slightly porous, or rather oc-
cupied, both on its external
and internal surfaces, by a
series of very minute canals,
which, from their having been
first described by our coun-
tryman Clopton Havers, are
. termed to this day the Haver-
Fig. 347. A transverse section oj tM . -. , ^ /. , ,
Kumerus, or fore-arm bone, of a sian canals, and serve lor tne
Turtle (Chelonia mydas). It ex- trfT>jrm<?<?ioTi of blood -VPSSels
hibits traces of Haversian canals, transmission (
with a slight tendency to a con- into the interior of the bone.
If now a thin transverse sec-
,
and be examined by the micro-
BONE STRUCTU11E.
715
scope with a power of 200 linear, we shall see the Haversian
canals very plainly, and around them a series of concentric
bony laminae, from three to ten or twelve in number. If
the section should consist of the entire circle of the shaft,
we shall notice, besides the concentric lamince round the
Haversian canals, two other series of laminae, the ono
around the outer margin of the section, the other round
the inner or medullary cavity.
Between the laminae is situ-
ated a concentric arrangement
of spider-like looking bodies,
which have, by different au-
thors, received the name of
osseous corpuscles, lacunae, or
bone -cells, according as to
whether they were ascertained
to be solid or hollow : these
bone- cells have little tubes or
canals radiating from them,
which are termed canaliculi.
The average length of the
lacunas, or bone-cells, in the
human subject is the l-2,000th
J ,, Fig. 348. A transverse section lo f tJig
ot an men ; they are of an
oval figure, and somewhat flat-
tened on their opposite sur-
faces, and are usually about
one-third greater in thickness
than they are in breadth ; hence, as will be presently
shown, it becomes necessary to know in what direction
a specimen is cut, in order to judge of their comparative
size. The older anatomists supposed them, from their
opacity, to be little solid masses of bone ; but if the sec-
tion be treated with spirits of turpentine coloured with
alkanet-rcofc, or if it has been soaked in very liquid
Canada balsam for any great length of time, it can
then be unequivocally demonstrated that both these sub-
stances will gain entrance into the bone-cells through the
canaliculi. The bone cells, when viewed by transmitted
light, for the most part appear perfectly opaque ; and they
will appear the more opaque the nearer the section of
Femur, or leg-bone of an Ostrich
(magnified 95 diameters). When
contrasted with the preceding
figure, it will be noticed that the
Haversian canals are much smaller
and more numerous, and many o
them run in a transverse direction.
716
THE MICROSCOPE.
them approaches to a transverse one : for when the cells
are cut through their shorter diameter, they are often of
such a depth that the rays of light interfere with each
other in their passage through them, and darkness results ;
whereas if the section be made in the long diameter of the
cells, they will appear transparent. When viewed as an
opaque object, with a dark ground at the back and con'
densed light, the bone-cells and canaliculi will appear quite
white, and the intercellular substance, which was trans-
parent when viewed by transmitted light, is now perfectly
dark. The soft part consists
of the periosteum, which in-
vest the outer, and of the
medullary membrane, which
invests the inner surface, lines
the Haversian canals, and is
continued from them, through
the canaliculi, into the interior
of the bone-cells ; and of the
cartilaginous or other matrix,
which forms the investment
of the minute ossific granules.
The earthy matter of the bone
may be readily shown by
macerating the section for a
. 349. A horizontal section of the short time in a dilute solution
which exhibits a single plane of of caustic potash. The animal
bone-cells arranged in parallel lines, matter mav be procured bv
There are no Haversian canals pre- . ,., J , , r , , . , J ,
sent ; and when this specimen is USing dilute hydrochloric acid
contrasted with that of fig. 347, i^qfpp^ n f ponejfiV -nntfusVi
it will be noticed that the canali- m Stead 01 Caustic potasft ,
cuii given off from each of the when all the earthy matter
bone-cells of this fish are very few j ,*i -11
hi number in comparison with ls removed the Section Will
that of the reptile. exhibit nearly the same form
as when the earthy constituent was present ; and if then
viewed microscopically, it will be noticed that all the
parts characterising the section previous to its maceration
in the acid will be still visible, but not so distinct as
when both constitutents were in combination. When,
however, the animal matter is removed, the bone will not
exhibit the cells and the canaliculi, but is opaque and
very brittle, and nothing but the Haversian canals and a
BONE STRUCTURE.
717
granular structure can be seen.
The parts which a transverse
or a longitudinal section of a
long bone of a mammalian
animal exhibits, will be the
Haversian canals, the con-
centric bony laminae, the bone-
cells and their canaliculi ;
even these, except the bony
laminre, may be seen in all
mammalian bones (fig. 345).
Whether long or otherwise,
they are, nevertheless, so dif-
ferently arranged in the flat
bones, such as those of the
skull, and in the irregular
bones, as the vertebra, as to
require notice. Ihose 01 the which are larger in this animal than
head are composed of two thin
layers of compact texture; sian canals are present.
enclosed between which is
another layer of variable thick-
ness, of a cellular or cancel-
lated structure. The two outer
layers are called tables the
one being the outer, the other
the inner table ; and the middle
or cancellated layer is termed
the diploe : in this last the
principal blood-vessels ramify.
The outer table of the skull
is less dense than the inner ;
the latter, from its brittle-
ness, is termed by anatomists
the vitreous table. When
a vertical section of a bone .
/, ,-, -, -,-, , rig. Vol. A small portion of bone
01 tne SKUll IS made SO as taken from the exterior of the shaft
to include the three layers &f^SS^SSSf&.
above mentioned, bone-Cells cells characteristic of the order
may be seen in all ; but each Reptilia \
of tbe three layers differ in structure : the middle or car
ris
THE MICROSCOPE.
collated structure will 'be found to resemble the cancellated
structure in the long bones viz. thin plates of bone, with
one layer of bone-cells without Haversian canals ; the outer
layer will exhibit Haversian canals of large size, with bone-
cells of large size, and a slightly laminated arrangement ,
but the inner or vitreous layer resembles the densest bone,
as the outer part of the shaft of a long bone, for instance,
and will exhibit both smaller Haversian canals and more
numerous bone-cells of ordinary shape around them.
A transverse section of the long bone of a bird, when
contrasted with that of a mammal, exhibits the following
peculiarities : the Haversian
canals are more abundant,
much smaller, and often run
in a direction at right angles
to that of the shaft, by which
means the concentric laminated
arrangement is in some cases
lost ; the direction of the canals
follows the curve of the bone ;
the bone-cells also are much
smaller and more numerous ;
but the number of canaliculi
given off from each of the cells
is less than from those of mam-
mals, fig. 348 : the average
length of a bone-cell of the
Fig. 352.-^ Horizontal section o/a^trich is l-2,000thof an inch,
scale, or flattened spine, from the the breadth l-6,000tll.
fxSbS S^lSn^S I* *"> ZepM, the bones
with numerous wavy parallel tubes, ma y b e either hollow. Cancel-
like those of dentine, communicat- , . 7 1 ,., . ,,-,'
ing with them. This specimen iated, Or solid ; but the specific
shows, besides these wavy tubes, o-ravitv is nor <?n rrrpif aa fhaf
numerous bone-cells, whose cana- S ravi [y 1S nol} so S reat as tnat
liculi communicate with the tubes, of birds or mammals. TllO
deutine.
Chelonian reptiles are solid, but the long bones of the
extremities are either hollow or cancellated; the ribs of
the Serpent tribe are hollow, the medullary cavity per-
forming the office of an Haversian canal ; the bone-cells
are accordingly arranged in concentric circles around the
canal The vertebrae of these animals are solid ; and the
BONE STRUCTURE. 719
bone, like that of some of the birds, is remarkable for it*
density and its whiteness. When a transverse section is
Jaken from one of the long bones, and contrasted with
that of a mammal or bird, we shall notice at once the
difference which the reptile presents : there are very few,
if any, Haversian canals, and these of large size ; and at
one view, in the section, fig. 347, we shall find the canals
and the bone-cells arranged both vertically and longi-
tudinally : the bone-cells are most remarkable for the
great size to which they attain ; in the Turtle they are
1-3 7 5th of an inch in length, the canaliculi are extremely
numerous, and are of a size proportionate to that of the
bone-cell.
In fishes we have a greater variation in '.the minute
structure of the skeleton than in either of the three classes
already noticed. Of all the varieties of structure in the
bones of fishes, by far the greater number exhibit nothing
more than a series of ramifying tubes, like those of teeth ;
others exhibit Haversian canals, with numerous fine tubes
or canaliculi, like ivory tubes, connected with them ; a few
consist of Haversian canals, with fine tubes and boner
cells, fig. 349; and a rare form, found only as yet in tho
sword of the Swordfish (Istiophorus), exhibits Haversian
canals and a concentric laminated arrangement of the
bone, but no bone-cells. The Haversian canals, when
they are present, are of large size, and very numerous, and
then the bone-cells are, generally speaking, either absent
or but few in number; their place being occupied by
tubes or canaliculi, which are often of a very large size.
The bone-cells are remarkable for their graduate figure,
and the canaliculi which are derived from them are few in
number; they are seen to anastomose freely with the
canaliculi given off from neighbouring cells; and if the
specimen under examination is a thin layer of bone, such
as the scale of an osseous fish, from the cells lying nearly
all in one plane, the anastomoses of the canaliculi are
seen beautifully distinct. In the hard scales of many of
the csseous fishes, such as the Lepidosteus and Calicthys,
and in the spines of the Siluridce, the bone-cells are
beautifully seen ; in the true bony scales comprising the
txc skeleton of the cartilaginous fishes, the bone-cells are
720 TKS MICROSCOPE
to be seen in great numbers. In the spines of some of the
Eay family may be noticed a peculiar structure : the Haver-
sian canals are large and very numerous, and communi-
cating with each canal are an infinite number of wavy
tubes, which are connected with the canals in the same
manner as the dentinal tubes of the teeth are connected
with the pulp-cavity ; and if such a specimen were placed
by the side of a section of the tooth of some of the Shark
tribe, the discrimination of one from the other would bo
no easy matter. In the spine of a Eay, fig. 352, the
analogy between bone and the ivory of the teeth is made
more evident ; for in this fish we have tubes, like those of
ivory, anastomosing with the canaliculi of bone-cells.
Now, if we proceed at once to the application of the
facts which have been laid down, and make a fragment of
bone of an extinct animal the subject of investigation ;
we first find that the bone-cells in Mammalia are tolerably
uniform in size ; and if we take 1 -2,000th of an inch as a
standard, the bone-cells of birds will fall below that
standard; but the bone-cells of reptiles are very much
larger than either of the two preceding; and those of
fishes are so entirely different from all three, both in size
and shape, that they are not for a moment to be mistaken
for one or the other ; so that the determination of a minute
yet characteristic fragment of fishes' bone is a task easily
performed. If the portion of bone should not exhibit
bone-cells, but present either one or other of the characters
mentioned in a preceding paragraph, the task of discrimi-
nation will be as easy as when the bone- cells exist. We
have now the mammal, the bird, and the reptile to deal
with ; in consequence of the very great size of the cells
and their canaliculi in the reptile, a portion of bone of one
of these animals can readily be distinguished from that of
a bird or a mammal ; the only difficulty lies between these
two last : but, notwithstanding that on a cursory glance
the bone of a bird appears very like that of a mammal,
there are certain points in their minute structure in which
they differ ; and one of these points is in the difference ir
size of their bone-cells. To determine accurately, there-
fore, between the two, we must, if the section be a trans-
Verse one, also note the comparative sizes of the Haver?iap
FISH SCALES.
721
canals, and the tortuosity of their course ; for the diameter
of the canal bears a certain proportion to the size of the
bone-cells, and after some little practice the eye will
readily detect the difference.
A curious modification of horn is presented in the ap-
pendage borne by the Ehinoceros upon its snout, which
in many points resembles a bundle of hairs. When a
transverse section is made and viewed by polarised light,
ach cylinder is seen to have
a cross diverging from a cen-
tral spot ; the lights and
shadows of this cross are
replaced by bands of con-
trasted complementary co-
lours, if the selenite plate is
interposed (fig. 353). See'
Platp VTTT "N"o 178 Whnlp *"ig-353. Transverse section of Hern
FL . VHL.1MO. KB. vvnaie- of BhinoceroSt secn by f lark . ,,
bone is almost identical in light
structure, and is similarly affected by polarised light.
A knowledge of the form and structure of scales ol
fishes (fig. 354), like that of
teeth, has been "shown by
M. Agassiz to afford an uner-
ring indication of the particu-
lar class to which the fish may
belong: in the examination
of fossil remains, the appli-
cation of this knowledge has
been attended with extraor-
dinary results. As a class of
objects for the microscope, the
scales of fishes are exceedingly-
curious and beautiful, especially
when mounted in fluid or
Canada balsam, and viewed by
polarised light. Many are seen
best as opaque objects, and are'
then mounted dry between Fig. 354. ScaZe o/ Sok. *j
glasses. M. Agassiz divides the scales into four orders,
which he names Placoid, Ganoid, Ctenoid, and Cycloid;
in the first two the scales are more or less coated with
3 A
722 THE MICROSCOPE.
enamel, in the others they are of a horny nature. To the
Placoid order belong the Skates, Dog-fish, Kay, and Sharks ;
cartilaginous fishes, having skins covered with small prickly
or flattened spines. To the Ganoid belong the Sturgeon,
Lepidosteus, Hassar-fish, and Polypterus ; fishes of this
order are more generally found in a fossil state, and tho
scales are of a bony character. To the Ctenoid belong the
Pike, Perch, Pope, Basse, Weaver-fish, &c. ; their scales
are notched like the teeth of a comb. To the Cycloid
belong the Salmon, Herring, Eel, Carp, Blenny, and the
majority of our edible fishes ; their scales are circular and
laminated. The scales of the Eel tribe are of an oval
figure, and are among the most remarkable that can be
selected for microscopic examination. To procure them, a
sharp knife must be passed beneath the epidermal layer y
and a portion of it raised, in a similar manner as directed
for tearing off the cuticle from plants : after a few trials
some will be detached. They are of an oval figure, rather
softer than the scales of other fishes, and in some parts of
the skin do not form a continuous layer. When the skin
has been stripped off, previous to the fish being cooked,
the scales can be obtained from the under surface, with a
knife or pair of forceps. The scales of the viviparous
Blenny are of a circular figure, situated under the epider-
mal layer ; they were described by Mr. Yarrell as mucous
glands, from their figure and small number. The surface
of the skin of this fish, when fresh, appears to bo covered
with follicles ; if, however, a portion be scraped off, it will
be found to be a mass of delicate circular scales. A piece
of the skin, when dried, exhibits the scales to great
advantage, and, like those of the Eel, are beautiful objects
for polarised light. The prismatic colours exhibited by
fish are said to be due to the presence of fatty matter in
the skin ; but the beautiful metallic tints displayed by
so many of them are rather due to the numerous micro-
scopic plates, or scales, distributed over its surface.
Having thus brought our brief examination of a few of
the more important structures of the animal economy to
a close, it only remains for us to express a hope that it
will be found to smooth the way, or in some degree assist
the investigations of the student to a better and more
EKEORS OF INTERPRETATION. 723
general survey of the whole fabric. Such a survey will
not be unattended with its difficulties and disappoint-
ments, but it will bring its own reward for any amount
of labour bestowed. To the medical student, desirous
of obtaining further information, I would recommend
Klein and Sanderson's " Handbook for the Physiological
Laboratory," and Dr. Stirling's " Text- Book of Prac-
tical Histology."
The importance of becoming thoroughly familiar with
the structural and microscopical characters of any par-
ticular organ in a healthy condition, cannot be too strongly
urged upon the attention of the student ; as to a want of
this knowledge must be attributed many erroneous de-
scriptions of morbid appearances. All who wish to use
the microscope successfully, with reference to the exami-
nation of organs in a diseased state, will do well to
acquaint themselves with minute anatomy generally, not
only of the human subject, but of the lower animals ;
without such knowledge it will be found impossible to
study pathology, or prosecute pathological inquiries with
any degree of success.
A large amount of wrong observation has been recorded
on cells and cellular structures : since Schwann announced
his "cell theory," almost everything round has been
regarded as a cell ; any single body within this, or where
there are several, the largest, has been regarded as a
nucleus, and any spot within the nucleus has been viewed
as a nucleolus. Whereas many of the so-called cells are
homogeneous spheres; many of the nuclei are vacuoles,
and so forth.
Such errors are natural, at first inevitable ; they can be
corrected only by practice, by testing observations in other
ways, especially by chemical re-agents, and by comparison
with the observations of others. " The marvel is not that
the microscope should suggest false views do not our
eyes play us that trick? but that it should reveal so
many astounding facts as it really does ; and the one con-
(1) The Cyclopedia of Anatomy and Physiology will be found a most valuable
book of reference for the student in all matters relating to physiology and
minute anatomy. Numerous valuable papers are distributed throughout the
Trans, cf the Royal Micros. Soc. : Huxley's Lectures on Comparative Anatomy
Owen's lectures on Comparative Anatomy ; Carpenter's Physiology, edited by H.
Power, and Kolliker's Manual of Human Microscopic Anatomy.
3 A2
124 THE MICROSCOPE.
solatory reflection which accompanies the difficult task ol
microscopic investigation is the unanimity which now
reigns among observers on so vast a body of observations.
If wo read in physiological works of the yolk cells and
coloured oil globules of the yolk, and the beautiful
function of assimilation which has been attributed to
them, they exist but in the imagination of the authors
who have regarded the one as cells simply because they
are round, and the other as consisting of fat because they
are highly refractive, such errors of interpretation do
not discredit it any more than the mis-interpretations,
which have helped to make Ehrenberg's name at once
famous and suspicious, alter the facts which he saw, and
could not rightly interpret. In truth, the eye is only
a preliminary instrument in science. What we see has to
be interpreted ; and, as it is very difficult to confine our-
selves to pure observation unmixed by hypothetical inter-
pretation, we need many collateral confirmations."
The principal physical characters to be regarded in micro-
scopic examinations may be summed up as follows :
1. Shape. Accurate observation of the shape of bodies
is very necessary, as many are distinguished by this phy-
sical property. Thus the human blood-globules present
a round biconcave disc, and are in this respect different
from the oval corpuscles of birds, reptiles, and fishes.
The distinction between round and globular is very requi-
site. Human blood corpuscles are round and flat; but
they become globular on the addition of water. Minute
structures seen under the microscope may also be likened
to the shape of well-known objects, such as that of a pear,
balloon, kidney, heart, &c.
2. Colour. The colour of structures varies greatly, and
often differs under the microscope from what was pre-
viously conceived regarding them. Thus the coloured
corpuscles of the blood, though commonly called red, are,
in fact, yellow. Many objects present different colours,
according to the mode of illumination ; that is, as the light
is reflected from or transmitted through their substance, as
in the case of certain scales of insects, feathers of birds, &c.
Colour is often produced, modified, or lost, by re-agents ;
<M when iodine comes in contact with starch-granules, when
ANIMAL STRUCTURES MODE OF INVESTIGATING. 725
nitric acid is added to chlorophyle, or chlorine-water to the
pigment-cells of the choroid, and so on.
3. Edge or Border. This may present peculiarities
worthy of notice. Thus, it may be dark and abrupt on the
field of the microscope ; so fine as to be scarcely visible ;
or it may be smooth, irregular, serrated, beaded, &c.
4. Size. The size of the minute bodies, fibres, or tubes,
which are found in the various textures of animals, can
only be determined with exactitude by actual measure-
ment. It will be observed, for the most part, that these
minute structures vary in diameter ; so that when their
medium size cannot be determined, the variations in size
from the smaller to the larger should be stated. Human
blood-globules in a state of health have a pretty general
medium size, and these may consequently be taken as a
standard with advantage, and bodies described as being two,
three, or more times larger than this structure ; or all may
be measured with a micrometer, as explained at page 51.
5. Transparency. This physical property varies greatly
in the ultimate elements of numerous textures. Some
corpuscles are quite diaphanous ; others are more or less
opaque. The opacity may depend upon corrugation or
irregularities on the external surface, or upon contents of
different kinds. Some bodies are so opaque as to prevent
the transmission of the rays of light ; in this case they
look black when seen by transmitted light, though white
if viewed by reflected light : others, such as fatty particle:,
and oil-globules, refract the rays of light strongly, and
present a peculiarly luminous appearance.
6. Surface. Many textures, especially laminated ones,
present a different structure on the surface from that
which exists below. If, then, in the demonstration, these
have not been separated, the focal point must be changed
by means of the fine adjustment. In this way the capil-
laries in the web of the Frog's foot may be seen to be
covered with an epidermic layer, and the cuticle of certain
minute Fungi or Infusoria to possess peculiar markings.
Not unfrequentiy, the fracture of such structures enables
us, on examining the broken edge, to distinguish the dif-
ference in structure between the surface and the deeper
! ayers of the tissue under examination.
726 THE MICROSCOPE.
7. Contents. The contents of those structures which
consist of envelopes, as cells, or of various kinds of tubes,
are very important. These may consist of included cells or
nuclei, granules of different kinds, pigment matter, or
crystals : a fair illustration of the changes effected by dis-
ease is given in fig. 256, from a cyst in a diseased liver :
occasionally their contents present definite moving cur-
rents, as in the cells of some vegetables; or trembling
rotatory molecular movements, as in the ordinary globules
of saliva in the mouth.
8. Effects of Re-agents. These are most important in
determining the structure and chemical composition of
numerous tissues. Thus water generally causes cell- for-
mations to swell out from endosmosis ; while syrup, gum-
water, and concentrated saline solutions, cause them to
collapse from exosmosis. Acetic acid possesses the valu-
able property of dissolving coagulated albumen, and in
consequence renders the whole class of albuminous tissues
more transparent. Thus it operates on cell-walls, causing
them either to dissolve, or become so thin as to display
their contents more clearly. Ether, on the other hand,
and the alkalies, operate on fatty compounds, causing theii
solution and disappearance. The mineral acids dissolve
most of the mineral constituents that are met with ; .so
that in this way we are enabled to tell with tolerable cer-
tainty, at all events, the group of chemical compounds to
which any particular structure may be referred.
All animal tissues should be stained, as previously
directed, and cut into sections, otherwise an accurate
idea of their general structure cannot be obtained. It
is also of importance to examine specimens by reflected
light, transmitted light, and by polarised light ; when
immersed in water, or in a highly refracting fluid, such
as glycerine, oil, turpentine, and Canada balsam ; with
a cover and without a cover. The most scrupulous
cleanliness should always be observed in microscopical
examinations ; many errors of interpretation have
arisen in consequence of a want of sufficient care
in preventing the admixture of various accidental
substances. The better way of avoiding errors from
this cause is to become familiar with the characters
ANIMAL STRUCTURES MODE OF INVESTIGATING. 727
of common substances which are likely to be mixed up
with preparations, as the following: oil globules, air
bubbles, portions of worsted, cotton, and linen, silk and
wool fibres, hairs from plants, vegetable tissues, human
hair, portions of feathers, and the starches wheat and
potato starch from bread crumbs. In taking fluids from
bottles and vessels, the possibility of mixing small portions
of their contents must be avoided ; the pipette should be
washed immediately after it has been used. Another
fallacy arises from the great transparency of some struc-
tures ; a membrane may appear perfectly clear and trans-
parent when in reality it is covered with a delicate layer
of epithelium, which only becomes visible after the appli-
cation of some chemical re-agent j on the other hand, by
the action of re-agents, a fibrous appearance is produced.
Acetic acid, when added to many preparations, frequently
produces a swelling of the tissue, which looks like base-
ment membrane, but which in reality has been formed by
the action of the acid. The mechanical pressure of the
thin glass, if pressed down tightly, alters structures very
much; the appearance of the blood discs are, at times,
much distorted in this way, and lead to false conclusions
and erroneous descriptions,
To examine Hood, prick the finger with a fine needle,
and let it drop on a strip of glass. To differentiate
the corpuscles, add a drop of the following solution :
Sulphate of Soda 104 grains ;
Acetic Acid 1 drachm ;
Distilled Water 4 ounces.
The contour of each disc will then be seen much
clearer.
To the advanced observer, tne examination of the mucous
membrane will afford some instruction. Should the speci-
men be small, it will be better to pin it to a piece of cork;
then well wash it by means of a small syringe. If the
investing epithelium is required for examination, a por-
tion can be detached from the surface by a knife ; when
placed on a glass slide, add a drop of iodine solution, then
view it with a J-inch power. Villi and papillse are best
made out in injected specimens, as will be seen on reference
to Plate VII.
CHAPIEE VI.
THE MINERAL KINGDOM.
MATTER FORMATION OF CRYSTALS POLARISATICW, ISO,
our mea o re search through organic nature
we met with an endless variety of beautiful
and instructive materials for the employment
of the microscope. If we now turn our atten-
tion to the inorganic or mineral kingdom we
shall find a vast storehouse filled with objects
of unsurpassed interest to the microscopist.
In the examination of the many beautiful
forms presented to us in the phenomena of crystallisation,
and the study of the varied chemical combinations, the
student will discover a never-ending source of useful occu-
pation.
We are as yet in great ignorance of the manner ilk
which the majority of crystals belonging to the mineral
kingdom are formed : we know, however, that very few can
be reproduced by the chemist. But, although ignorant of
the means whereby the great majority of crystals have
been formed in the vast laboratory of nature, we can
crystallise an immense number of substances, watch their
numerous intricate modes of formation, and that in the.
smallest appreciable quantities, when aided by the micro-
scope. Among natural crystals those employed in the
formation of rocks open up a wide field to our view. The
varieties of granites present us with the earliest crystal-
lised condition of the earth's crust as it cooled down, the
structure of which is beautifully exhibited under polarised
light. Plate VIII. No. 160, is a section of a granlm
FORMATION OF CRYSTALS.
shown on a red selenite ground. Crystallisation under a
somewhat different condition and combination is seen in
the New Eed Sandstone, No. 158.
The prismatic rings of another crystalline substance,
Quartz, represented in No. 159, possess great interest
Again, that 'of Arragonite, Tremolite, and Carbonate of
Lime. The latter is frequently seen in combination with
animal structure, and is then productive of many re-
markable changes and modifications, such as we have
represented in Plate VIII. Nos. 171, 172, 175, and 180,
all of which should be prepared for examination with as
well as without the polariscope.
The formation of artificial crystal may be readily
effected, and the process watched, under the microscope, by
simply placing a drop of a saturated solution of any salt
upon a previously warmed slip of glass. The following
list of salts and other substances form a beautiful series
of objects for polarised light :
Alum.
Asparagine.
AsparticAcid. Plate VIII. No. li
Bitartrate of Ammonia.
Boracic Acid.
Borax. Plate VIII. No. 164.
Carbonate of Lime.
Soda.
Chlorate of Potash.
Chloride of Barium.
Cobalt.
Copper and Ammonia.
Sodium.
Cholesterine.
Chromate of Potash.
Cinchonine.
Cinchonidine.
Citric Acid.
Ilippuric Acid.
Iodide of Mercury.
Potassium.
,, Quinine,
lodo-disulphate of Quinine.
Murexide.
Nitrate of Bismuth.
,, Barytes.
Brucine.
Copper.
Potash.
Strontian.
Uranium.
Oxal
te of Ammonia.
Chromium.
Chromium and Potash.
Lime.
Soda.
Oxalic Acid.
Oxalurate of Ammonia.
Permanganate of Potash.
Phosphate of Lead and Soda.
Platino-cyanide of Magnesia.
Plumose Quinidine.
Prussiate of Potash, red and yellow,
Quinidine.
Santonine.
Salicine.
Salignine. Plate VIII. No. 162.
Sulphate of Cadmium.
,, Copper.
Copper and Potash.
Sulphate of Iron.
Iron, Cobalt, and Nickel
,, Magnesia.
Nickel and Potash,
Soda.
Zinc.
Sugar.
Tartar ic Acid.
Thionurate of Ammonia.
Triple Phosphate.
Urate of Ammonia.
Soda.
Urea, and all the urinary deposits..
Uric Acid.
MINERALS.
Agates, various.
Asbestiform Serpentinn.
Avanturine.
Carbonate of Lime.
Carrara Ma-hle
730
THE MICROSCOPE.
Indurated Sandstone, Howth.
Indurated Sandstone, Bromsgrove.
Gibraltar rock.
Granite, various localities. No. 160.
Hornblend Schist.
Labrador Spar.
Norway Eock.
Quartz Rock, various. No. 159.
,, in Bog Iron Oro.
Quartzite, Mont Blanc.
Sandstone, Plate VIII. No. 158.
Satin Spar.
Selenites, various colours.
Tin Ore, with Tourmalin.
VEGETABLE SUBSTANCES.
CUTICLE of Leaf of Correa Cardinal!*.
,, Dentzia scabra.
PI. VIII. No. 173.
Elaiagnus.
,, ,, Onosma taurica.
Equisetum. No. 174.
Fibro cells from orchM. No. 1C9.
,, Oucidium bicallosum.
Scalariform vessels from Fern.
Scyllium. No. 177.
SILICIOUS CUTICLES. Various.
Starch. Various. No. 167.
Very interesting results will be obtained by combining
two or more chemical salts. Mr. Davies 1 succeeded ia
forming numerous beautiful double salts in the following
manner. To a nearly saturated solution of the sul-
phate of copper, add a drop of a solution of the sulphate
of magnesia, on the glass-slide, and dry quickly. To effect
this, heat the slide so as to fuse the salts in its water of
crystallisation, and there remains an amorphous film on
the hot glass. Put the slide aside and allow it to cool
slowly ; it will gradually absorb a certain amount of
moisture from the air, and begin to throw out crystals.
If now placed under the microscope, numerous points
will be seen to start out here and there. The starting
points may be produced at pleasure by touching the
film with a fine needle point, so as to admit of a slight
amount of moisture being absorbed by the mass of
salt. Development is at once suspended by applying
gentle heat ; cover the specimen with balsam and thin
glass. The balsam should completely cover the edges
of the thin glass circle, otherwise moisture will probably
insinuate itself, and destroy the form of the crystals.
Mr. Thomas succeeded in crystallising " the salts of
the magnetic metals " at very high temperatures, which
gave interesting results, and produced curious forms of
crystals. Plate VIII. JSTo. 163 are representations of
crystals of sulphate of iron and cobalt, No. 165, of nickej
and potash, obtained in the following manner : To form
the sulphate of iron crystal, add to a concentrated solution
of iron a small quantity of sugar, to prevent oxidation.
Put a drop of the solution on a glass slide, and drive out the
(I) Quart. Journ. Micros. Scien., rol. ii. p. 128. 1862.
SUBLIMATION OP ALKALOIDS. 73 i
water of crystallisation as quickly as possible, by the
aid of a spirit lamp ; then with a Bunsen's burner bring
the plate to a high temperature. Immediately a remark-
able change is seen to take place in the form of the crystal,
and if properly managed the " foliation " represented in
the plate will be fairly exhibited. The slide must not be
allowed to cool down too rapidly or the crystals will
probably absorb moisture from the atmosphere, and in so
doing the crystals alter their forms. Immerse them in
balsam, and cover in the usual way before quite cold.
Sublimation of Alkaloids. Dr. Guy a few years ago
directed the attention of microscopists to the fact that the
crystalline shape of bodies belonging to the inorganic
world might lead to their detection. Subsequently, Dr.
A. Helwig, of Mayence, took the matter up, and showed
that the plan was applicable not only to inorganic but also
to organic substances, and especially to the poisonous alka-
loids. By improving on Dr. A. Hel wig's process, and
substituting a bit of porcelain, Dr. Guy has been able to
watch the process more minutely, and to regulate it more
-exactly. He has by this means been able to obtain
characteristic crusts composed of crystals of strychnine
weighing not more than l-3,000th or 1 -5,000th of a grain.
Morphia gives equally characteristic results. For the
examination of these, Dr. Guy recommends the use of a
binocular microscope with an inch object-glass. But it is
not to crystalline forms alone that one need trust; the
whole behaviour of a substance as it melts and is converted
into vapour is eminently characteristic, and when once
deposited on the microscopical slide, under the object-
glass, the application of re-agents may give still more satis-
factory results. The re-agents, however, which are here to
be applied are not of the kind ordinarily employed. Colour-
tests under the microscope are, comparatively speaking,
useless : those that give rise to peculiar crystalline forms
are rather to be sought after. For instance, the crystals
produced by the action of carbazotic acid on morphia are
by themselves almost perfectly characteristic. These ex-
periments should not, however, be undertaken for medico-
legal purposes by one unskilled in their conduct, for the
effects of the re-agents themselves might be mistaken by
732 THE MICROSCOPE.
the uninitiated for the result of their action on the sub-
stances under examination.
Dr. Guy's 1 method of procedure is as follows : " Pro-
vide small crucibles, covers, slabs, or fragments of white
Porcelain ; a few microscopic cell-glasses, with a thickness
of about one-eighth of an inch and a diameter of circle of
about two-thirds of an inch : and discs of window-glass
about the size of a shilling. Place the porcelain slab on
the ring of a retort-holder or other convenient support ;
then the glass cell ; and upon the porcelain in the centre
of the cell a minute portion of the alkaloid or other white
powder, or crystal reduced to powder ; then pass the clean
glass dish through the flame of the spirit-lamp till the
moisture is driven off, and adjust it with the forceps over
the glass ring ; now apply the flame of the spirit-lamp to
the porcelain, underneath the powder or crystal, and con-
tinue the heat till the powder undergoes its characteristic
change and gives off vapour. Watch the deposit of this
vapour on the glass dish, and remove the spirit-lamp,
either directly or after a short interval, as experience may
determine.
" The white surface of porcelain being visible through
the glass disc, as through a window, the behaviour of
the substance under examination is easy to observe. It
may be driven off without undergoing change or leaving
residue, and the disc may be covered with crystals, as
happens with arsenious acid, or with an amorphous
sublimate, as happens with calomel ; it may coalesce,
throw out long silky crystals, to be gradually transferred
as crystals to the glass disc, as is the case with corrosive
sublimate; and it may melt, with or without previous
change of colour, retain or shift its place, deposit carbon
more- or less abundantly, and yield a sublimate of detached
crystals (veratrine), twigs (solanine), tufts (meconine),
branching patterns (strychnine, morphine, cryptopia, &c.),
watered patterns with or without crystalloids (several alka-
loids and glucosides), the melting and deposition of carbon
being a common property of the alkaloids and of some
analogous active principles.
(1) Dr. W. A. Guy, F.R.S. &c. on the "Sublimation of the Alkaloids."
ha~maceutical Journal, June and August, 1867. Micros. Jour. Dec. 1867
SUBLIMATION OP ALKALOIDS. 733
"The principal precaution to be observed in tlio
application of heat is, that it should be moderate and
gradual. It is best to act on the assumption that the
substance under examination may be one of a considerable
group of bodies, some of which sublime at very moderate
temperatures. The spirit-lamp should, therefore, be placed
at first three or four inches below the slab of porcelain, so
that the point of its flame may not touch it ; and if, under
this low temperature, the disc of glass is not dimmed, the
lamp should be raised by degrees till the mist makes its
appearance. Then, as a general rule, the lamp should be
withdrawn, the disc removed, and a new one put in its
place. It may be well to state that, as the disc has been
passed through the flame to drive off moisture, and has in
this way been heated, the flame of the spirit lamp should
not be allowed to play on the porcelain slab after the mist
has appeared on the disc, at least not for any length of
time ; for, if this precaution be neglected, it may happen
with the alkaloids as with arsenious acid or corrosive sub-
limate, that the mist does not form at all, or that it is
driven off as soon as it is deposited. Perhaps, too, it may
not be quite unnecessary to recommend that each disc of
glass, as it is removed, should be placed with the subli-
mate upwards against a glass slide or fragment of porcelain ;
and that in this position (sublimate upwards) it should be
retained. If this very simple precaution be overlooked, it
is quite possible that we may mistake one surface for the
other, and find ourselves applying our re-agents to the
wrong one. The chief precaution relating to the ex-
amination and disposal of the sublimates consists in
aieasures for preserving their identity during the examina-
tion to which we may have to subject them. This is best
done by writing the names and that of the reagents on
discs of paper, and placing paper and disk together in
sunken grooves or circular spaces.
" As a precaution omitted by an experimenter so prac-
tised as Dr. Helwig is very likely to be overlooked by
others, it is well to insist upon and to prescribe as the
first step to be taken with a crystalline solution which wo
are about to use as a test, the determination of its proper
crystalline form or forms as evaporated on a flat surl'ace of
734 THE MICROSCOPE.
glass. Another mistake, arising out of a similar want of
caution, may consist in confounding the effect of some
saline re-agent with that of the water which holds it in
solution.
" ftow these remarks have a direct practical "bearing on
the selection of tests. A preference ought to be given to
re-agents which leave no residue of their own : to distilled
water, to alcohol, ether, chloroform, benzole, and fusel oil ;
and to acetic acid and the dilute mineral acids. Then
those salts should be preferred of which the solutions
yield dry residues of one or two definite forms, not such as
put on many different shapes, are deliquescent themselves,
and are likely to leave moist and unstable compounds.
]S T or is the strength of the solution a matter of little or no
importance ; for it should be borne in mind that the sub-
limates to which we apply them contain very minute frac-
tions of a grain; and that a very strong solution, after
acting on this minute quantity, would leave a coarse
deposit of its own, both over the general surface and at
the margin of the spot, which, blending with the reaction,
would obscure and confuse it. As a general rule, there-
fore, solutions of a moderate strength are to be preferred,
*uch as 1 grain of carbazotic acid to 250 of water, and 1
grain of bichromate of potash to 100, the same of the red
prussiate of potash, and of the nitro-prusside of sodium."
Other than the alkaloids and volatile metallic poisons
were found to yield sublimates when heated, as urea,
uric acid, hippuric acid, alloxan, uramile, <fcc.; but these
results scarcely prepared one to expect a sublimate from a
blood-stain. Yet, on separating the fibres of a small spot
of a cotton texture stained with blood about twenty-five
years since, and submitting a section of the fibre an eighth
of an inch long to heat, a figured pattern of the colour of
blood was obtained, such as might be caused by a solution
of blood in some thin oily liquid : this figured pattern was
surrounded by a colourless border, having bright figured
patterns such as those which mark the less characteristic
portions of crystalline sublimates. Dr. Guy, on repeating
his experiments, found the results constant ; and on con-
ducting them with care, and under the guidance of micro-
scopic examinations, two sublimates were uniformly ob-
SPECTRUM ANALYSTS. 735
tained, the first colourless and apparently crystalline, the
second, under a high temperature, of the colour of the
blood-stain from which it was procured, and of the figured
pattern mentioned.
Mr. Sorby's attention has been directed to obtain a defi-
nite method of qualitative analysis of "animal and vegetable
colouring matters," and of animal substances generally, by
means of the spectrum microscope. He has also so com-
bined the spectroscope with the binocular microscope as
to make it available for the purpose of distinguishing
minute portions of coloured minerals in thin sections of
rocks and meteorites. He employs an ordinary large
binocular microscope, with an object-glass of about three-
inches focal length, corrected for looking through glass an
inch thick ; the lenses being at the top, and as far as pos-
sible from the slit. This objective is placed at the focus,
and between it and the lenses, at a distance of about half
an inch from them, is a compound prism, composed of a
rectangular prism of flint-glass and two of crown-glass, of
about 61, one at each end. This arrangement gives direct
vision and a spectrum of a suitable size for these inquiries,
since a wide dispersion often produces indistinctness of
the absorption bands. That we may have the opportunity
of comparing two spectra side by side, a small rectangular
prism is fixed over half the slit, and with the acute angle
parallel to it and passing beyond it. 1
" This gives an admirable result, the only defect being
that, when the spectra are in focus, their line of junction
is some distance within it ; and therefore to correct this
employ a cylindrical lens of about two feet focal length,
with its axis in the line of the slit, which can easily be
fixed at such a distance between the slit and the prisms
as to bring the spectra and their line of contact to the
same focus. In front of the slit, close to the small rectan-
gular prism., is a stop with a circular opening, to shut out
lateral light, and a small achromatic lens of about half
an inch focal length, which gives a better field, and
counteracts the effect of the concave surface of the liquid
in the tubes used in the experiments, if they are not
(1) Mr. Sorby's prisms and thei-r arrangement have been entrusted to Mr
Browning's skilful hands, who is prepared to adapt them to any microscope.
736 THE MICROSCOPE.
quite full. These are cut from barometer-tubes, having
an internal diameter of about one-seventh of an inch, and
an external diameter of about three-sevenths of an inch.
They are made half an inch long, ground flat at each end,
and fixed with Canada balsam on slips of glass two inches
long and about six- tenths of an inch wide, so that the
centre of the tube is about one-fourth of an inch from
one edge. By this arrangement the liquid may be
examined through the length of the tube by laying the
slip of glass flat on the stage of the microscope, or through
the side of the tube, by placing the slip vertical and the
tube horizontal. Cells of this size can be turned upside
down and deposits removed without any liquid being
lost ; and the upper surface of the liquid is sufficiently
flat, even when inclined at a considerable angle. If
requisite, small bits of thin glass can be laid on the top,
which are held on by capillary attraction, or fastened
on with gold-size, if it be desirable to keep the solution
for a longer time. When the depth of colour is too great
in tne line of the length of the cell, we can at once see
what would be the effect of about one-fourth of the colour
by turning it sideways ; and thus we can save much time,
and quickly ascertain what strength of solution would
give the best result. Very frequently an excellent
spectrum is obtained in one direction with one reagent,
and in the other with another, without further trouble.
" The scale of measurement consists of two small NicoFs
prisans, and an intermediate plate of quartz. If white
light, passing through two such prisms, without the plate
of quartz, be examined with the spectrum-microscope, it
of course gives an ordinary continuous spectrum ; but if
we place between the prisms a thick plate of quartz or
seknite, with its axis at 45 to the plane of polarisation,
thf jigh no difference can be seen in the light with the
nak^d eye, the spectrum is entirely changed. The light is
still white, but it is made up of alternate black and
coloured bands, evenly distributed over the whole spec-
trum. The number of these depends on the thickness of
the depolarising plate, so that we may have, if we please,
almost innumerable fine black lines, or fewer broader
bands, black in the centre and shaded oft' at each side.
SPECTRUM ANALYSIS. 737
These facts are of course easily explained by the inter-
ference of waves. It would be impossible to have a mope
convenient or suitable scale for measuring the spectra of
coloured solids and liquids. If we use a micrometer in
the eyepiece, an alteration in the width of the slit modifies
the readings, and the least movement of the apparatus
may lead to error, whereas this scale is not open to either
objection. Besides this, the unequal dispersion of the
spectrum makes the blue end too broad, so that a given
width, as measured with a micrometer in the eyepiece,
is not of the same optical value as the same width in
the red. The divisions in the interference-spectrum
bear, on the contrary, the same relation to the length
of the waves of light in all parts of the spectrum, and
no want of adjustment in the instrument alters their
position. As will be seen from the diagram (tig. 355),
the unequal dispersion makes the distance between the
bands in the blue about twice as great as in the
red. The perfection of a spectrum would be one in
which they were all at equal intervals ; but possibly
no such uniform dispersion could be produced. By
having a direct-vision prism, composed of one of flint-
glass of 60, and two of crown-glass of suitable angle, we
can place it over the eyepiece, and can diminish the
dispersion at the blue end, or increase that at the red end,
by turning it in one position or the other, and thus see
either end to the greatest advantage.
" Since the number of divisions depends on the thick-
ness of the interference-plate, it became necessary to decide
what number should be adopted. Ten it was thought
would be most suitable ; but, on trying, it appeared to be
too few for practical work. Twenty is too many, since it
then becomes extremely difficult to count them. Twelve
is as many as can be easily counted ; it is a number easily
remembered, gives sufficient accuracy, and has a variety of
other advantages. With twelve divisions the sodium-line
D comes very accurately at 3^ ; and thus, by adjusting the
plate so that a bright sodium-light is hid in the centre of
the band, when the Nicol's prisms are crossed, it is accu-
rately at 3J, when they are arranged parallel, so as to give
a wider field. The general character of the scale will
3 B
738 THE MICROSCOPE,
be best understood from the following figure, in which
the bands are numbered, and given below the principal
Fraunhofer lines. The centre of the bands is black, and
01234
(Red end.) II f | ft || || || (Blue Mid.)
Fig. 355. A B ci >
they are shaded off gradually at each side, so that the
shaded part is about equal to the intermediate bright
spaces. Taking, then, the centres of the black bands as
1, 2, 3, &c., the centres of the spaces are 1J, 2^, 3^, &c.,
the lower edges of each J, If, &c., and the upper 1J, 2J,
&c., we can easily divide these quarters into eighths by
the eye ; and this is as near as is required in the sub-
ject before us, and corresponds as nearly as possible to
1-1 00th part of the whole spectrum, visible under ordinary
circumstances by gaslight and daylight. Absorption-bandj
at the red end are best seen by lamplight, and those at the
blue end by daylight.
On this scale the position of some of the principal lines
of the solar spectrum is about as follows :
A f B 1J C 2| D 33-
E 5ft 6 6t! F 7* G 10f
At first plates of selenite, which are easily prepared,
were used, because they can be split to nearly the re-
quisite thickness with parallel faces ; but its depolarising
power varies so much with the temperature, that even
the ordinary atmospheric changes alter the position of the
bands. However, quartz cut parallel to the principal
axis of the crystal is so slightly affected in this manner
as not to be open to this objection, but is prepared with
far .greater difficulty. The sides should bo perfectly
parallel, the thickness about -043 inch, and gradually
polished down with rouge until the sodium-line is seen in
its proper place. This must be done carefully, since a
difference of l-10,000th inch in thickness would make it
decidedly incorrect.
The two Nicol's prisms and the intervening plate are
mounted in a tube, and attached to a piece of brass in suck
SPECTRUM ANALYSIS. 739
k manner that the centre of the aperture exactly corre-
sponds to the centre of any of the cells used in the experi-
ments, which are all made to correspond in such a manner
that any of them, or this apparatus, may be placed on the
stage and be in the proper place without further adjust-
ment, which, of course, saves much time and trouble. 1
In the preparation of vegetable colouring matters foi
the spectroscope, care must be taken to employ a small
quantity of spirits of wine ; filter the solution, and
evaporate it at once to dryness at a very gentle heat,
otherwise if we attempt to keep the colouring matters in
a fluid state they quickly decompose. It is necessary to
employ various reagents in developing characteristic spectra.
The most valuable reagent is sulphite of soda, which
admits of the division of colours into groups. Of the
mode of applying reagents, ample directions are given.
Mr. Sorby's qualitative analysis is just the kind of thing
to employ in detecting adulterations in many substances met
with in commerce, as well as in inquiries where very small
quantities of material are at command. By this method
we might be able in a few minutes to form a very satisfac-
tory opinion, or at least one that might meet all practical
requirements, and narrow the inquiry to a surprising
extent ; if this can be said even now, surely further re-
search cannot fail to make it most useful in cases where
ordinary chemical analysis would be of little or no use - y
for in this way we may be able to detect the presence
of chlorophyll in some of the lower animal forms as
the amoeba, hydra, &c., or, on the other hand, the red
colouring matter of the blood, cruorine, in worms, molluscs^
and insects. A number of colouring matters can be
obtained, by using ether, from sponges, polyzoa, and the
crustaceans; these, if examined in this way, may give
unexpected results.
For further information on this interesting subject we
must refer the reader to Mr. Sorfcy's paper " On a Definite
Method of Qualitative Analysis of Vegetable and Animal
Colouring Matter by means of the Spectrum Microscope,"
published in the Proc. Roy. Soc. No. 92, 1867.
(1) See a paper by Dr. Gladstone, on the Spectra of Solutions of Salt*
Quart. Journ. Cliem. Soc. vol. xi. p. 86.
740 THE MICROSCOPE.
It would be a vain attempt were we to try to convey
to our readers any idea of the great discoveries which have
been made by the microscope, or of the important pur-
poses to which it has been applied. Second only to the
telescope, though in many respects superior to it, the
microscope transcends all other instruments in the scientific
value as well as in the social interest of its results. While
the human eye, the telescope and microscope combined,
enables us to enjoy and examine the scenery around us, to
study the forms of life with which we are more imme-
diately connected, it fails to transport us into the depth of
space, to throw into relief the planets and the stars, and
to indicate the forms and arrangements in the worlds of
life and motion, which distance diminishes and conceals.
To these mysterious abodes, so long unrevealed, the tele-
scope has at last conveyed us. It has shown us those
worlds and svstems, of which our own earth and our ^own
system are the types ; but it fails to satisfy us entirely
as we would wish respecting the nature and constitu-
tion of the celestial bodies, and the forms of life for
which they are created.
In its downward scrutiny, as well as in its upward
aspirations, the human eye has equally failed. In the
general view which it commands of animal, vegetable, and
mineral structures, it cannot reach those delicate organiza-
tions on which life depends, or those structures of inor-
ganic matter from which its origin and composition can be
derived. Into these mysterious regions, where the philo-
sopher has been groping his way, the microscope now
conducts him. The dark abodes of unseen life are lighted
up for his contemplation, organizations of transcendent
i^eauty appeal to his wonder new aspects of life, new
forms of being, new laws of reproduction, new functions
in exercise, reward the genius of the theoretical and
practical optician, and the skill and toil of the naturalist.
With wonders like these all nature is pregnant : the earth,
the ocean, and the air times past and times present, now
surrender their secrets to the microscope.
What we know at present, even of things the most near
.and familiar to us, is so little in comparison of what we
know not, that there remains an illimitable scope for OUT
inquiries and discoveries j and every step we take serves to
CONCLUSION.
741
enlarge our capacities, and give us still more noble and
just ideas of the power, wisdom, and goodness of God.
This marvellous universe is so full of wonders, so teems
with objects of latent beauty, that perhaps eternity alone
will open up and develop sufficient opportunities to enable*
us to survey and admire and appreciate them all.
" And lives the man, whose universal eye
Has swept at once th' unbounded scheme of things,
Mark'd their dependence so, and firm accord,
As with unfaltering accent to conclude
That this availeth nought ? Has any seen
The mighty chain of beings, lessening down
From infinite perfection to the brink
Of dreary nothing, desolate abyss !
From which astonish'd thought, recoiling, turns t
Till then, alone let zealous praise ascend.
And hymns of holy wonder, to that Power,
Whose" wisdom shines as lovely on our minds
As on our smiling eyes his servant sun." THOIVIOH
743
APPENDIX.
THE MICROSCOPICAL EXAMINATION OF WATER.
IT must have struck most persons, as it lias myself, as
a remarkable circumstance that water analysts should
lay so much stress on the presence in water of chlorides,
nitrates, and ammonia, when these compounds are
inorganic and harmless. Why is it that, whereas a
few years ago chemists said plainly, " This or that
water contains so much organic matter," that now
" organic matter " should be estimated from " organic
elements," " oxygen consumed," or " albuminoid am-
monia ? " The reason of this change is, that the
several processes which promised to verify the weight
of organic matter in a water have proved very un-
reliable, and at the present time no process is known
by which the actual weight of organic matter can be
determined. So far as the public is concerned this is
perhaps a misfortune, but to the chemist it is of less
moment, for although the actual weight of organic
matter cannot be determined, yet it is possible, by
estimating the amount of organic carbon in water, or
in some other way, to obtain a comparative measure of
the quantity, while the presence of chlorine (sodium
in the water) and of nitric acid and ammonia, act as
tell-tales of the presence of sewage and animal matter
respectively. No doubt, every step in a water analysis
is undertaken with an object and reveals a fact. Al-
though this may be very interesting when it is known, it
is evidently a language that must be thoroughly under-
stood and read before it can become of the slightest
value to any one. It is almost impossible for any ques-
tion about water to be broached without the analysis
or report of some chemist or another being brought
forward to refute and confound you j it is therefore
744 THE MICROSCOPE.
desirable that those who are called upon to advise on
snch matters should be able to appreciate the chemist's
arguments, and criticize his data. To do so properly
we must know something of the theory of water
analysis, and must bear in mind, or have at hand, the
arbitrary standards which experience suggests as valu-
able in classifying waters.
It is perfectly clear, however, that the organic
matter found in water that known to be most detri-
mental to health is completely destroyed by chemical
analysis, and, therefore, the conclusion arrived at by
the chemist as to the wholesomeness of water is either
misleading or entirely fallacious.
The organic matter in water may be either animal or
vegetable, or the two may be combined ; the first being
the more dangerous contamination, and to distinguish
between the two kinds is, after all, important. Both
animals and plants yield albumen ; and, chemically
speaking, albuminoid matters, whether of animal or
vegetable origin, are practically identical in composi-
tion. It is an admitted fact that " chemical analysis
is one of the poorest things possible to rely upon as
giving a true indication of the actual nature of organic
matter, much less to reach the delicate quantities which
show that a particular specimen of water is free from
sewage or infective organisms." No analysis of water
can be pronounced complete without having been first
submitted to microscopical examination. For the detec-
tion of living organisms, and of germs believed to set
up disease in the animal body, we must at all times
have recourse to the microscope. The determination
of the organic impurity of water by the microscope
is of immense value, as by its aid we are in a position
to say what has had access to it, and thus approximately
measure its unwholesomeness.
The mode of examining specimens of water is as
follows : A Winchester quart bottle at least should be
taken and stood by, in a warm, quiet place, for twenty-
four hours. If, after standing twenty or thirty hours,
no great amount of deposit is thrown down, recourse
should be had to other means of collecting the suspended
EXAMINATION OF WATER. 745
matter. A tall white glass vessel, holding a gallon at
least, must be filled and allowed to stand by forty-eight
hours. When all the sediment is settled down, the
water must be siphoned off, with the exception of just
a sufficient quantity to permit of the residual sediment
being shaken up and poured out into a conical glass.
After standing a short time, small portions of the sedi-
ment may be dipped out with a pipette, dropped on to
a glass-slide, and covered over with a thin glass cover.
The thin glass cover tends to equalize refraction and
spread the drop evenly out before it is placed under
the microscope.
M. Certes, when dealing with small quantities of
organic matter taken from water, and having only a
very minute amount of sediment, employs osmic acid.
This re-agent kills all animal life and blackens it ; it
is then more readily seen. A single drop of a half per
cent, solution of osmic acid is quite sufficient. If used
stronger it produces, by reason of its too rapid action, a
(shrivelling or charring of the organisms. For the better
detection of bacteria and other minute bodies, dissolve
ten grains of pure white sugar in ten ounces of the sus-
pected water in a tall white glass measure, cover it over
with muslin and let it stand exposed to light for forty,
eight hours. If sewage be present the water will become
turbid and a thin scum of bacteria form on the top.
Banvier recommends the use of picro-carmine solu-
tions, with glycerine for staining and colouring the
living organisms in the water, and by means of which
they are more easily detected. In this way the very
minutest forms of life bacteria, amoebiform particles
of protoplasm, the delicate flagellae, and the locomotive
organs of Monads, will become visible under a high-
angled one-eighth objective.
The sanitary import of such organisms as bacteria,
their probable danger to health and life, their per-
sistency and great power of multiplication, all tend to.
render them objects of deep interest to the physiologist
and the medical practitioner. Bacteria have been long
known to microscopists ; their active vibratory motion
have attracted the attention of every observer. From
746 THE MICROSCOPE.
their peculiar wriggling motion they were formerly-
called Vibrios ; Nageli named them " Schizomycetes."
Whether they are fungi, algae, belong to the genus Os-
cillatorise, or to the animal kingdom, is yet undecided.
Bacteria are sure to be found wherever albuminoid
matter affords the material for sustaining life : in water,
in blood, in animal juices and secretions of all kinds :
in plants, in the sediment of waters, and upon glaciers
or the highest mountains. They appear in abundance
when organic matter is putrefying slowly and exposed
to the air. Their spores float in the air in every region,
and accumulate if the atmosphere is moist and bat little
jdisturbecl. Thus bacteria are easily obtainable for in-
vestigation, but it is only by the highest powers of the
microscope that it has been found possible to study
their development and variations.
Most forms of bacteria once recognized that is, after
carefully conducted observations can scarcely again
be confounded with other bodies. Only the smallest
forms of micrococci or spheroidal bacteria present much
difficulty ; these may be mistaken for inorganic matter.
The chemical reaction of colonies of micrococci was
pointed out by Weigert. The granular mass is insoluble
in acetic acid, hydrochloric acid, caustic potash, gly-
cerine, alcohol, chloroform, and oil of cloves, and is not
killed by immersion in either of these agents. Hsema-
toxylin alum solution colours the mass dark blue, as
also does methyl violet solution if it is subsequently
washed in dilute acetic acid.
So far, it appears that all bacteria consist of single
cells, and consequently their forms are not very mani-
fold. Four fundamental forms at least are recognized :
the spheroidal, rod-shaped, thread-like and spiral.
The question naturally arises, are the different species
true, and confined to one definite form, or can one
species pass into that of another ? Hallier saw the
growth of bacteria into threads. Klebs saw the con-
version of micrococci into bacteria, and these into con-
tractile pigment granules. Billroth takes the funda-
mental form to be the spheroid bacteria Coccobacteria
septica ; these are said to multiply by elongation and
EXAMINATION OF WATER. 747
division. Nageli takes the same standpoint, and as-
sumes the spheroid cell to be the fundamental form, like-
wise ascribing to it tb 3 power of elongation and trans-
verse division. On the whole, the morphological dis-
tinctions of the different forms appear to Nageli to be
" too small ; " whilst other investigators maintain the
truly specific character of the different bacteria, Fitz
distinguishes them as ethyl and butyl.
It is very generally believed that the forms are
quite definite which produce the known fermentations
of infective diseases ; that these forms are not changed
by grafting upon other substances. That they are con-
fined within quite narrow conditions of life has been
shown by experiments ; for instance, Koch upon
Bacillus antliracis, carbuncle bacillus; Klein, upon
Bacillus minimus , in the typhoid of swine ; Klebs
and Tommase, upon Bacillus malarice, the excitant of
malarial fever; Obermeyer, Heidenrich and others,
upon forms of Spirochsetes in relapsing fever, &c. A
similar perplexity existed for years in distinguishing
Diatomaceee. Many species based upon differences in
size had to be abandoned when investigators became
acquainted with their developmental history.
Hallier, a German botanist, having made a careful
examination of bacteria, concluded that they were the
cleavage of the nuclei of fungoid cells, and he claimed
to place them amongst unicellular plants. Consum-
ing oxygen and giving off carbonic acid, their mode
of respiration certainly implies that they are more
closely allied to animals than to plants. The disputed
question of the animal or vegetable nature of bacteria
was only a very small one amongst the many bones of
contention that botanists and zoologists waxed warm
over in the early days of the microscope. Some years
before bacteria received any special attention, Dr. A.
Farre (1842) observed a new and strange form of fever,
and this he found was associated with and due to
a tangled mass of green- coloured filaments. On closer
examination these were seen to belong to the genus
Oscillatoriae, the fine threads of which measured about
the 1- 5000th of an inch in diameter. Subsequently
748 THE MICROSCOPE.
it was discovered that the spores of the confervse had
been swallowed in drinking-water. Soon after this a
distressing stomach malady was discovered to be due to
the growth of another unicellular plant, Sarcina. This.
however, should rather be described as a compound
cellular plant, the first simple cubical cell splitting up
and dividing into many other cells, all being closely
united together by a cellulose membrane, and increasing
from one to two, four, eight, and sixteen, in regularly-
arranged series. Sarcinae are not easily killed that is,
they resist the action of strong acids, in this respect
resembling the silicious frustules of diatoms. Sarcina
veniricnli is believed to be nearly allied to, if noi
identical with, ferment fungus; it is doubtless the
product of a contaminated water supply.
Another internal entophyta, which I am inclined to
believe belongs rather to the genus Oscillatorise than
to bacteria, is termed corkscrew-thread or spirilla. It
is an extremely fine, cylindrical, filamentous organism,
of rather sluggish habits, and of a very destructive
nature. The supposed relation of spirilla to epidemic
visitations of famine fever have been confirmed. The
disease was first observed in the eastern parts of Europe
and in India, where a certain recurrent form of fever is
indigenous amongst a badly-fed people, and in the
blood of those who have died corkscrew-like threads are
invariably found. Spirillum, or famine fever, appeared
at Berlin in 1872, and then it was that the attention of
the medical profession became more particularly directed
to it, and the exact relation between certain specific
organisms present in the blood, and the contagium of
this peculiar form of fever became fairly established.
During the same year famine fever appeared in Bres-
lau, and in more than a hundred cases spirilla were
seen to almost completely block up the blood-vessels.
In. some instances a single drop of blood, placed under
the microscope, was observed to literally swarm with
minute undulating spiral rods. In India, the specific
nature of the disease has been proved by the inocula-
tion of quadrumans with infected human blood.
Splenic fever, cha-.-bon, or anthracoid fever, is another
SPIRILLUM AND SPLENIC FEVEE. 749
remarkable fever ; the chief interest in which centres
in the fact that the specific organisms which induce
it are bacteria. Splenic fever attacks horses, cattle,
sheep, rodents, and even man ; it covers a wide range
of country, extending over Europe, Asia, and Africa.
In Russia, it is known as Siberian plague ; in India,
as the Pali plague ; in Germany and Austria, where
it is endemic as well as epidemic, as Milzbrand. In
Zululand it was the cause of an enormous loss of
horses, as many as fifty per cent, a week dying from
the fever. The algoid, rod-like bodies discovered in the
blood are from the 1 -20,000th to the 1 -40,000th of an
inch in diameter. When acted upon by a fluid of less
density than blood, and near to the commencement of
the putrefactive process, they break up into spheroids,
each with a slightly darker spot or nucleus in the centre.
A striking feature of the disease is its very rapid pro-
gress. An animal is observed to refuse its food, this
is followed by a shudder, a convulsive or apoplectic fit,
and in the course of a few hours it will be dead. The
symptoms are accounted for by the rapidity of multi-
plication of bacteria in the blood.
For the preservation of bacteria Koch's method is
the best. It consists in drying the liquid containing
the bacteria in a very thin layer upon slips of glass,
so as to fix the bacteria in a plane, treating this layer
with the colouring material, and then again moistening
it to restore the bacteria to their natural form and make
them distinctly perceptible, so that the preparation may
be enclosed in a preservative liquid and finally mounted
in glycerine. Glass slips with dried bacteria last for a
long time, and can be transmitted by post. For the
moistening of the layer Koch uses a solution of one
part of acetate of potash in two of water. In this
solution the bacteria assume their original form without
becoming loosened from the glass. For colouring he
uses a mixture of a few drops of a concentrated spirit-
ous solution of fuschin or methyl violet with 15 to 30
grams of water. Preparations so coloured may be
mounted in concentrated solution of acetate of potash
or in Canada balsam.
750 THE MICROSCOPE.
THE EXAMINATION OF RIVER-WATER.
At the present time, the Thames basin drains more
than two and a half million acres of land, the greater
portion of which is highly cultivated and heavily
manured. It might be safely predicted, on taking
specimens of water from any part of the river, that it
will contain organic impurities, in suspension and solu-
tion. A bottle of Thames water, taken near Windsor
in the spring of 1881, abounded in various species of
animal life. On standing the bottle in the light, in a
very short time a considerable sediment was deposited,
consisting of vegetable, animal, and mineral matters.
On removing a drop with a pipette, and placing it
under the microscope, numerous portions of conf'ervae,
diatoms, decaying vegetable matter, the outer cases
of entomostraca, &c., were visible, and apparently only
very few of the minuter kinds of animal life. Allow-
ing the water to stand by some forty-eight hours, ex-
posed to light and warmth, another dip was taken, and
a higher magnifying power used, when a number of
embryos were seen moving about the field, the more
noxious of which were minute filiform nematode w r orms,
Chcetogaster lymnceus, Anguillula fluviatilis, Hydra
ftisca, Thames mud-worm, Cyclops quadricornis, Daplinia
pulexj Paramoecium, pupa of culex, bacteria, &c.
Now, considering how little the Thames had been dis-
turbed by floods or rains during the previous three or
four weeks of April and May, it must be admitted that
this small quantity of water, containing, as it did, the ova
and embryos of animals, constituted a serious amount of
contamination. The habits, or rather the natural his-
tory, of some of these creatures are well worth a careful
examination. First, nematode worms ; these have
obtained an unenviable notoriety amongst the greater
pests of animal life. The typical form of filarian
worms is the thread-worm : this affects human beings,
sheep, and other ruminants, as well as several kinds of
birds. There are eight or ten different kinds belonging
to the genus, and some of which, like Fasciola hepatica.
fluke, change their hosts once or more before attaining
THAMES WATER. 751
to sexual maturity. One species of filaria penetrates
1. Klarian worm ; 2. Chcetogastcr lijmnceus : 2a. Enlarged head of same :
3. Anguillula fluviatilis ; 4. Thames mud-worm ; 5. Hydra fusca; 6.
Paramoacium (e'ngraver has made it too irregular in outline : it is nearly
ovoid) ; 7. Egg of culex ; 8. Pupa of Chironomus viridulus : 0. Bacteria ;
10. Spirilla ; 11. Starch and epithelium scales. The various objects magni-
fied from 5 to 350 diameters.
the bronchial tubes of sheep, producing a debilitating
752 THE MICROSCOPE.
kind of cough ; in lambs filarian worms accumulate
rapidly in the air-passages and lungs, and a number of
animals perish annually from what is called " the lamb
disease." The worm represented in fig. 1 is the much-
dreaded Trichina spiralis. This nematode worm derives
its name from the circumstance that it was found spir-
ally encysted in the flesh of pigs. It is usually found
curled up in a spiral form in the middle of the large
muscles. Before attaining to the encysted stage, it has
a free existence, lives an aquatic or wandering life, and
hides in moist situations or in bogs. It very closely
resembles the filarian worm Anguillula fluviatilis (fig.
3) . Very many of the Anguillulidae are parasitic upon
water- snails, slugs, earthworms, and the larvae of in-
sects. They are remarkable for their tenacity of life,
resisting the extremes of heat and cold.
Trichina spiralis infests man and numerous warm-
blooded animals the pig, dog, rabbit, rat, &c. In
forty-eight hours after the embryos are taken into the
stomach they attain to maturity. They are most active
little worms, in four days are full-grown, and are then
rapidly carried by the blood-current and deposited in
the muscles in almost every part of the animal body.
The nature of the fever produced by these terrible
parasites is as remarkable as it is fatal.
Another species of filarian worm, found in Thames
water, is named by Von Baer Chcetogaster lymncetis
(fig. 2), from its having been first observed crawling
over water-snails, Lymnaeus, and Planorbis. These
worms are often found in specimens of Thames water,
and they attract attention from their rapid, cater-
pillar-like motion over the body of their host. Chce-
togaster lymnceus is a very translucent, thread-like,
whitish worm. The oral aperture is capable of a con-
siderable amount of distension, like that of the eel.
Its action is very rapid, and its body so transparent,
that it is a difficult matter to trace the nervous system.
It is affirmed by some observers that it feeds upon
cercariae. I cannot, however, confirm this observation,
but I have seen its stomach filled with diatoms.
Chsetogaster are found in the body of the common
EXAMINATION OF THAMES WATEE. 753
earthworm. Amongst other larvae which abound in
Thames water are the well-known blood-red Thames
mud-worm. This worm is familiar to Londoners, as it
not only finds its way into cisterns, but is frequently
observed during the summer months covering the mud-
banks at low water, and imparting to the mud a deep
blood-red colour. The presence of mud-worms cer-
tainly indicates a dangerous contamination; their
favourite breeding-haunts being the sewage-polluted
mud-banks of rivers. The larvae of the genus Culi-
cidae, especially that of Chironomus viridulus (fig. 8)
a very minute species of the gnat tribe, are at cer-
tain periods numerous. This larva, unlike most other
species, builds up a brown tubular case, which it
anchors to the bottom or side of the bottle. Therein
it very quietly secretes itself. In a few days' time its
larval stage is completed, and it becomes transformed
into the imago, and towards evening, just as the sun is
declining, it quits its dwelling and floats up to the sur-
face of the water, and, having fairly balanced itself, it-
spreads its gossamer wings and flies away. The head of
the male is surmounted by a pair of plumose antennae,
which are long and delicate. The body is of a pale
green colour, apparently destitute of scales or feathers,
a well-known characteristic of Culicidse. All the gnat
tribe, inclusive of the dreaded mosquito of the tropics,,
lurk and thrive in malarious and fever- stricken locali-
ties. The eggs of Chironomus viridulus are extremely
minute, about the l-100th of an inch in size (fig. 7).
It may be remarked of gnats, that, like vultures, they
are bred amongst carrion.
As usual, the smaller crustaceans, entomostraca, &c.,
are found in large numbers in Thames water. 1 In
warm weather, and as soon as the temperature of all
river- water reaches 60 Fahr., Daphnia pulex increase
with amazing rapidity, and if swallowed may produce
diarrhoea and dysentery. In Boston, America, the water
at one time was much infested by water-fleas, and the-
consumers of the water suffered from fatal attacks of
Bummer cholera. At Dorpat, Sweden, an epidemic
(1) See a paper by the author in the English Mechanic, April 30, 1880.
3 c
754 THE MICROSCOPE.
visitation of a peculiar fever was clearly traceable to
the presence of Paramcecium (fig. 6) ; and numerous
deaths were attributable to them. Frogs, newts, and
other aquatic animals have been killed by these noxious
creatures. The water of the Firth of Forth is
frequently seen, in summer time, deeply coloured by
moving masses of minute crustaceans. To some rivers
and seas they impart a deep red colour. The rate of
increase of daphnia and cyclops is truly surprising.
Such is their amazing fecundity, as estimated by the
late Dr. Baird, that a single pair of Cyclops <juadri-
cornis will, in the course of six months, produce a
progeny numbering four billions five hundred millions
(4,500,000,000). A large number of species of ento-
mostraca are parasitic on marine and freshwater fish.
It is contended, however, that they attack the sickly,
and so make way for the " survival of the fittest."
Probably this is so, unless it will be conceded that
the sickness of the fish is a consequence of the presence
of the parasite. Fish thus afflicted are said, by fisher-
men, to be "lousy." A vegetable parasite, the Sapro-
legnia, is the cause of the Salmon disease, producing
a sort of leprosy over the body of the fish.
Thames water favours the presence of hydroid
polyps ; consequently, various species of hydra may be
found adhering to pieces of weed and decaying vege-
table substances. Fig. 5 is a full-grown Hydra fusca.
Starch granules and epithelium (fig. 11) are held in sus-
pension, and nearly always form a small portion of the
sediment of sewage-polluted river- water. Such bodies
can in no way be estimated by chemical analysis, as they
only form a minute part of any residual ash. Starch
enters largely into the food of animals, and it may be
assumed that this albuminoid product must have been
conveyed into river- water in the excreta of animals.
The microscopical analysis of water is a large and
very important one, and those of my readers who wish
for further information on the subject will do well to
consult Dr. J. D. Macdonald's " Guide to the Micro-
scopical Examination of Drinking Water," published
by Churchill.
INDEX.
ABERBATION, chromatic, 32.
of lenses, 63.
how corrected, 63.
spherical, 31.
Abbe, Professor, on aperture, 75.
binocular eye-piece, 11 i>.
Absorption bands of blood, 131.
AcalephsB, 491.
Acarina, 632.
Acarus beetle, 455.
cloth moth, 641.
. domesticus, 637.
of dog, 634.
farinse, 639.
of fly, 641.
of fowl, 640.
of rat, 634.
sacchari, 638.
scabiei, 635.
of swallow, 639.
Achetina, 627.
Achnanthes Longipes, 420.
Achorion, 296.
Achromatic condenser, the, 176.
Gillett's, 177.
Ross's improved, 178.
Beck's, 179.
Swift's, 181.
Hyde's, 184.
object-glasses, SO.
Acineta-f orm infusoria, 401.
vorticella, 447.
Acineta tuberusa, 41T, 449.
Actinia actinozoa, 465.
bellis, 484.
rubra, 483.
Actiniforum zoophytes, 485.
Actinophrys sol, 374.
Actiiiotrocha, 578.
Actinozoa, 485.
Adams' microscope, 10.
Adipose tissue, 693.
Adulteration of food, 345.
/Ecidium, 293.
Pastes, 451.
Agates, 399.
Alcyonella stignorum, 526.
Alcyonidse, 489, 524.
Alcyonium digitatum, 489.
polypidoms, preparation of, 509.
Alder, section of, 334.
Algse, development of, 269.
Alkaloids, sublimation of, 731.
Amici's microscopes, 12.
.- prisms, 187.
Aniphistome conicum, 565.
Amphitetras, 416.
Amoeba, 373.
Amreboid stat I of volvox, 277.
Anacharis alsinastrum, 321.
Analysis, spectrum, 735.
Angle of aperture, 69.
measurement of, 75.
Anguillulae, 571.
Anguinaria spatulata, 520.
Animalcule, Sun, 374.
Animalcules, 402.
collecting bottle, 193.
history of, 403.
infusorial, 414.
troughs and cells, 195.
Animal cell, 659.
action of cilia in, 671.
colls, change into tissues, 665.
cellular membrane, 692.
connective tissue, 662.
elementary substance, 659.
epithelium, 668.
fibrous tissue, 694.
kingdom, division of, 366.
life, 655.
structure, 661.
structure, mode of invest*
gating, 724.
tissues, classified, 692.
tissue consolidated, 702.
tissues, staining, 225.
Annelida, 575.
Annulosa, 559.
Anobium, 633.
Antennae of insects, 607.
Anthony's, Dr., diaphragm, 169.
Aperture of the object-glass, 69.
numerical, 73.
Aphides, 613.
Aphrophora bifasciata, 615.
Aplanatic doublet lens,
Aplysia, 529.
Apparatus for mounting, 210.
Aquatic box, 194.
Arachnida, 631, 644.
Arachnoidiscus, 432.
Arcella acuminata, 372.
Archer on amoeboid bodies, 277.
Arenicola, 576. [?.
Aristophanes, microscope known to*
Artemiae, 557.
Articulata, 579.
Asci of lichens, 305.
Aspergillus, 301.
Astasia, 412.
Asteroidea, 495.
Atlantic soundings, 382.
Atropus, 623.
BACC-ILLARIA paradoxa, 269.
C 2
756
INDEX.
Bacteria, 411. 746.
Baird, Dr., on entomostraca, 557.
Baker on the microscope, 10.
Baker's microscope, 98.
dissecting microscope, 200.
Balanidse, 555.
Balbiani, Dr., on paramsecium, 410.
Barnacle, 554.
Bartley s warm stage, 146.
Bat, head of, 681.
Beale, Dr., on cell development, 659.
Beck's microscope, 94.
achromatic condenser, 179.
cell-making instrument. 209.
double nose-piece. 96.
lamp, 190.
opaque disc-revolver, 188.
side-reflector, 189.
Bee's eye, 586.
tongue, leg, <tc., 612.
Beetles, 623.
bacon, 624.
diamond, 622.
tortoise, 5S8.
water, 625.
Bell-animalcule, 445.
Berg-mehl, 432.
Bergh, Dr., on urticating organs, 545.
on podura scales, 628.
Berkeley on two new British fungi,
304.
on fungi, 290.
Beroe', 492.
Biddulphia, 437.
Bilharzia haematobra, 567.
Binocular microscope, 116.
Bird's-head coralline, 518.
Bleaching sections, 246.
Blood-corpuscles, 678.
crystallization of, 680.
disc, size of, 680.
spectrum, 131
vessels, structure of, 688.
Blow-fly, 590.
Bockett's lamp, 164.
Bone, 714.
cutting sections of, 205.
eel, 716.
. fishes, 719.
human, 713.
ostrich, 715. '
reptiles, 714.
sting ray, 718.
Bot-fly, egg of, 607.
Botrytis, 301.
Bourgingnon, Dr., on acarus scabiei,
635.
Bowerbank on sponges, 386.
Bowerbankia, 512.
Braohionus, 455.
Brachiopoda, 535.
Brewster, Sir David, diamond lens,
11.
Brightwell on navicula, 419.
Brooke's double nose-piece, 96.
Browning's microscope, 90.
Browning's spcctro-microscope, 123.
Bryozoa Bowerbankia, 512.
Buccinum undatum, palate, 538.
Bull's-eye condenser, ISO.
Burnett, Dr., on parasites, 639.
Busk, Mr., on anguinaria spatulata,
520.
on cchinococci, 570.
on starch granules, 342.
or volvox, 276.
Butte fli.-s, eggs of. 605.
t^n^ues of, 607.
CALCIFICATION of animal tissues,552.
Calepteryx virgo, 597.
Callithamnion, 273.
Camera-lucida, 132.
Campanularia volubilis, 481.
gelatinosa, 481.
Campilodiscus clyneus, 439
Cancer-cell, 296.
Cane, section of, 341.
Capillaries, 689.
in fat, 691.
Carbolic acid fluid, 220.
Carbonate of lime in shell, 528.
Carpenter, Dr., on volvocinese, 27&.
on diatomacese shell, 553,
on eozoon, 379.
on tomopteris, 576.
Carter, Mr. , on chara development
318.
on spongilla, 391.
Cartilage, 702.
from ear of mouse, 702.
rabbit's ear, 703.
Cassida viridis. 588.
Cedar, stem of, 357.
Cell formation, 659.
action of, 667.
animal, 660.
changes, 258, 661.
changes in disease, 664,
contents, 662.
development, 239, 659.
making, 209.
mounting, 216.
nucleus, 663.
pigment, 671.
Cells, complicated, 6C7.
for desmids, 230.
growing, 195,
motile, 261.
vegetable, 257.
Cellularia, 518.
avicularia, 518.
Cellular tissue of plants, 323.
in animals, 662.
Cements, 246.
Cementing, method of, 221.
Cephalopod, tongue of, 540.
Cephalopoda, 550.
Cephalosiphon, 451.
Characeae, 315.
anthcridia of, 317.
development, 318.
757
Cheese-mite, 637,
Chemical re-agents, 225.
China-grass, 353.
Chitonidfe, 537.
Chloride of gold, 701.
Chloroform and balsam mixture for
mounting, 223.
Cilia, 404, 671.
movement of, mode of exhibit-
ing, 406.
Ciliated epithelium, 670.
Cimex lecticularis, egg of, 117.
Circular disc, f!09.
Circulation of blood in frog, to view,
682.
Cirrhopoda, 554.
Clarke, Lockhart, on the preparation
of spinal cord, 7G1.
Clematis, wectioii of, 333, 357.
Clepsmidae, 574.
Clionse, 395.
Clip for mounting, 211.
Closterium lunula, 285.
Clothes moth, u!2.
Clypeastrodea, 501.
Coal, structure of, 363.
Cobbold, Dr., on helminths, 567.
Cocconema, 437.
Coccus persicae, 604.
. egg of, 605.
Cochineal insect, its value, 651.
Cocoa, adulteration of, 346.
Coddington's lens, 38.
Coelenterata, 462.
Coffee, structure of, 347.
Cohn on stephanosphseni, 265.
Cole's stained specimens, 242.
Coleoptera, 622.
bottle, 193.
net, 193.
Collins's microscope, 105.
mounting cabinet, 254.
Collodion casts, 585.
Comatula, 490.
Compressorium, 1^4.
Condensers, Beck's achromatic, 179.
Collins's, 183.
Gillett's, 177.
- oil immersion, 185.
Powell and Lealand's, 180.
Boss's, 178.
Swift's, 181.
Confervoidese, 267.
Conjugation in desmids, 279.
Conr.chilus, 448.
Consolidated tissues, 702.
Cook, Dr., on staining, 236.
Coral reefs, 491.
Corals, 490.
Cordylophora, 463.
Corethra plumicorr.is larva, 600.
Corn-blights, 293.
Corymorpha nutans, 476.
Coryne-stauridia, 475.
CoBcinodiscus, 440.
Cosmarium, 282.
Crabshell, 528.
Crayfish, 553.
shell of, 553.
Cricket, 627.
Crinoidea, 505.
Crisiadae, 519.
Cristatella mucedo, 524.
Crustacea, 554.
Crystals, formation of, 729.
mode of showing optical Axis,
146.
of snow, 153.
Cuckoo-spit, 615.
(Julex pipiens, 598, 612.
Cutleria dichotoma, 273.
Cutting sections, 203.
Cuttlefish-bone, 546.
Cyclops, 556.
Cymba olla, tongue of, 542.
Cyrnbella Ehrenbergii, 418.
Cynips gallse, 618.
Cypridae, 556.
Cystic disease of liver, 570.
Cysticercus fasciolaris, 5b4.
pisiformis, 564.
Czermak on tooth substance, 711.
DALLMEYER'S objective, 81.
Dalyell, Sir J. G., on tubularidae,
474.
on actiniae, 467.
D.uirv, Prof., on corals, 490.
Daphnia pulex, 557.
Darker 's selenitc stage, 148.
Dark field illuminators, IV 2.
Darwin on infusoria, 433.
Dasya Kiitzingiana, 272.
Davis on a new rotifer, 451.
Death-wntch beetle, 623.
De Bary on fungi, 291.
Deep-sea soundings, 381.
Defining power of objectives, 58.
Delabarre's microscope, 10.
Delessaria, 274.
Demodex folliculorum, 637.
Dentine, 707.
Deparia prolifera, 313.
Dermestes lardarius, 624.
Dermestidae, 624.
Designing from microscopic
440.
Desmidiaceae, 278.
finding and preserving, 288.
Deutzia scabia, 339.
Diamond beetle, scales o', 622.
Diaphragm, description of, 169.
Dr. Anthony's stage, 169.
the Iris, 170.
Diatomaceae, 416.
Kiitzing on, 417.
on collecting, 428.
their value as testa, 68.
Diatoms, movements of, 423.
Difflugia, 372.
Diphydfe, 464.
Dipping tubes, 102,
758
INDEX.
Directions for mounting and pre-
paring objects, 211.
Dissecting knives and needles, 202.
microscopes, 199.
scissors, '201.
Distoma, 567.
Divini's microscope, 7.
Doris tuberculata, palate of, 538.
Dragon-fly, 597.
Draper's microphotographie appa-
ratus, 161.
Drone-fly, 591.
Dytiscus marginalis, 626.
sucker from leg of, 588.
ECHINID^E, 498.
Echinococci, 569.
Echinodermata, 494.
Echinorhynchus, 571.
Ecker, on protozoa, 373.
Eel, scales of, 722.
Eggs of insects, 602.
of gasteropoda, 545.
Egyptian cloth, 354.
Ehrenberg's brachionus, 455.
on boundary between plants
and animals, 655.
Elder-root, section of, 363.
Elm, section of, 3u6.
Enamel, 709.
Enchondroma, 704.
Encrinus, 506.
Entomostraca, 555.
Entozoa, 565.
Eozoon canadense, 378.
Epeira diadem, (J45.
Epithelium, tesselated, 668.
columnar, 670.
Equisetacese, 311.
Equisetum, section of, 332.
Errors of interpretation, 165, 723.
Escharidw, 521.
foliacea, 522.
Euastrum, 2SO.
Eucratiadte, 519.
Euglena, 412.
Eunotia, 437.
Euphorbia neriifolia, 329.
Euplectella, 402.
Eye-glasses, their value 50.
Eye, human, vessels in, 6S9.
. pigment, 672.
section of cat's, 689.
Eye-pieces, 47.
Huyghenian, 48.
micrometer, Jackson's, 52.
Ramsden, 51.
stereoscopic, 71.
Eyes of insects, 584.
FASCIOLA HEPATICA, 566.
Fat cells, 094.
Pavus fungus, 296.
Feather-star, 496.
Feet of insects, 587-
Ferns, 311.
Ferns, section of root, 335.
Fibre, muscular, 695.
in the tongue, 697.
involuntary, G9S.
Fibrous tissue, 693.
white and yellow, 694.
Finders, Amyot's, 191.
Maltwood's, 192.
Finger, mechanical, 218.
Fishes' scales, 721.
Flax, 353.
Flea, 630.
cat's, 634.
larva of, 634.
Flora of coal measure, 364.
Floridese, 271.
Flower buds, 351.
Flowers, colouring matter of, 354
Flukes, 565.
Floscularia ornata, 458.
Floscularise, 453.
Flustne, 521.
avicularis, 523.
chartacea, 523.
foliacea, 522.
Fly, foot and leg of, 587, 591.
tongue, 595.
fungoid dir--ertse of, 590.
Tsetse, of Africa, 59(5.
Follicles of pig's stomach, 669.
Foraminifera, 375.
fangasina, section of, 380.
fossil, 377.
skeletons of, 381.
Forceps for dissecting, 201.
Fossil infusoria, 431.
mode of preparing, 434.
plants, 362.
Fragillaria pectinalis, 437.
Frauenhofer's glasses, 10.
lines, 738.
Frog-plate, 632.
bit, 321.
circulation, 679.
hopper, 015.
Frustulia Saxonica, 423.
Funaria, capsule of, 309.
Fungi, 290.
Berkeley on, 290.
De Bary on, 291.
floating, 295.
Fungige, 484.
Fungoid growths, 296.
GALL-FLY, 618.
Gallionella sulcata, 438.
Garrod's, Dr., crystals in blood, 681.
Gasteropoda, 537.
lingual bands of, 538.
Gemmules of sponges, 400.
Geodia Barretti, 390.
Gilburt's staining process 242.
Gillett's condenser, 177.
Gill of tadpole, circulation in, 686.
Glass-cells for mounting, 216
Glass-rope sponge, 401.
INDEX.
Glaucoma, 414.
Globigerina, 384.
Glossina morsitans, 596.
Glycerine for mounting, 247.
Rimmington's, 219.
Gnat, description of, 598.
Gnat's scale, 612.
Goadby's fluid, 223.
Gomphonema, 419.
Goniometer, Schmidt's, 56.
Gordiacea, 562.
Gorgonidse, 487.
spiculse from, 487.
Gorham, T., on eyes of insects, 584.
Gosse on notommata, 456.
on cellularia, 518.
on coryne stauridia, 475.
on melicerta ilngens, 459.
Gourd seed, section of, 335.
Graminacete, 340.
Grant, Dr., on fiustra, 521.
on alcyonidse, 489.
- on plumularia, 4~S.
- on sponges, 386
Grass, cuticle of, 339.
Gray, Dr., on mollusca, 539.
Gregarina of earthworm, 270.
Gregarinida, 367.
Groves oil staining, 230.
Growing cell, 196.
Guinea-worm, 563.
Gulliver on raphides, 337.
on blood discs, 679.
Guy, Dr., on sublimation, 731.
Gyrinus, paddle of, 625.
HAILES' section-cutting machine,203.
Hair, human, 672.
bat, Indian, 673.
gregarines in, 369.
moss, 311.
mouse, 673.
pecari, 674.
Haliotus splendens, 536.
tuberculatus, tongue of, 543.
Hallifax,Dr.,onpreparinginsects,604.
Hard tissues, preparation of, 205.
Hardening, preserving, and section-
cutting, 237.
Hartea elegans, 524.
Hassall, Dr., 011 the adulteration of
food, 349.
Henfrey, Prof., on ferns, 313.
Hemp, 353.
Hepatic:*}, 308.
Hepworth, Mr., on mounting insects,
648.
Herapath's, Dr., polarising crystal,
143.
on polarisation as a test, 149.
Hermia glandulosal, 475.
Herschel's aplanatic doublet lens, 38.
Hicks, Dr.B.,onamo3boid bodies, 227.
on lichens, goiiida of, 306.
Highley's photographic camera, 159.
Hill's micr3sco|e, 10.
Hipparchia janira, 611.
Hirudinidae, 573.
Holman's life-cell, 196.
syphon slide, 197.
Holothuridse, 508.
drawing of, life-size, 507.
Honey-bee, 620.
Hooke's microscope, 7.
Horn, rhinoceros, 721.
Human body, composition of, 659.
Huxley, T. H., on animal tissues, 656.
on actinozoa, 468
on echiiiidse, 494.
on tongue of mollusca, 538.
on rotifera, 560.
on tooth development, 708.
Huygheiiian eye-piece, 48.
Hyalonema, 401.
Hydatids, 570.
Hyde's condenser, 183.
Hydra, 446, 466, 470.
Hydrachnidfe, 642.
Hydractinia, 473.
Hydrophilus, trachea of. 587.
Hymenoptera, 616.
aquatic, 626.
ICELAND SPAE, 137.
Illumination, test of, 164.
Immersion system, 81.
Condenser, 185.
Homogeneous, Powell's, 86
Stephenson on the, 83.
India-rubber tree, 329.
section of leaf, 334.
Indicators, 191.
Infusoria, 402.
cilia, 405.
fossil, 431.
history of, 403.
Infusorial animalcules, 402.
Pasteur's researches on, 414.
Injecting, 248.
different systems of vessels, 250.
lower animals, 251.
Injections, transparent, 251.
Insects, 579.
commercial importance of, 651.
dissection of, by Swammerdana,
579.
transformations of, 648.
wings of, 597.
Insects' eggs, 602.
eyes, 584.
feet, 587.
hairs, tenent, 589.
heads, 582.
injecting, 240.
itch, 635.
ovipositors, 616.
preparing and mounting #30
648.
proboscis, 599
spiracles, 586.
stings, 61.9.
tongues, 582, 607.
760
INDEX.
Interpretation, errors of, 165.
Intercellular substance, 662.
Iris-leaf, 336.
Isthmia enervis, 432.
Ivory nut, section of, 350.
Ixodidse, 642.
JACKSON'S micrometer, 58.
Jelly-fish, 491.
Johnstone, Dr., on sponzes, 385.
on campanularia, 481.
on hydra, 471.
Jones, Wharton, on non-striated
muscular fibre, 698.
Rymer, on the corethra plumi-
cornis, 600.
Jungermannia bidentata, 310.
KAISER'S glycerine gelatine, 220.
Knives for dissecting, 202.
Kolliker on the muscles of the skin,
698.
Klitzing on vegetables and animals,
2?6.
- on diatornaeese, 417.
LADD'S microscope, 115.
Lamps, Microscope, 190.
Lamp-shells, 535.
Lankester, E. R., on Gregarina Lum-
brici, 870.
Lathe for polishing, 206.
Leaf-insect, 613.
Leech, medicinal, 573.
Leeuwenhoek's microscope, 6.
Lenses, amplification of, 57.
angular aperture of, 69.
chromatic aberration of, 32.
concavo-convex, 31.
condensing, 1 98.
correction of, 63.
curvature of, 29.
double convex, 26.
forms of, 26.
. magnifying power of, 34.
meniscus, 29.
periscopic, 38.
plano-convex, 28.
platyscopic, Browning's, 39.
refraction of light through, 37.
Lepidoptera, eggs of, 605.
tongue of, 608.
witg-scales of, 609.
Lepisma, 529.
scale of, as a test, 166.
Lepralia nitida, 517.
Leuchart on echinorhynchus, 571.
Lewes on actinise, 4t ; 7.
on life, 655.
thread cells, 467.
Libellulidse, wings of, 597.
Lichens, 304.
Lieberkiihn, Dr. N., on gregarina,
369.
on spongiila, 389.
the speculum of, 187.
Life, animal, 655.
Light, polarisation of, 138.
Limax rufus. 529.
Limnsea stagnalis, 545.
Limnias ceratophylli, 458.
Lister's lenses, 13.
achromatic correction of, 63,
Liver, diseased, 567.
Liverworts, 308.
Lobb on micrasterias, 279.
Lob-worm, 576.
Loligo, palate of, 548.
Lophopus crystallum, 525.
Loven on mollusca, 538.
Louse, 633.
Lubbock, Sir J., on the eggs of i
sects, 605.
on aquatic insects, 626.
Lucernaridye, 493.
Luidia fragilissima, 496.
Lung, capillaries of, 690.
Lymphatic, vessels of, 669.
MADREPORID^E, 486.
Magnifiers, hand, 38.
Magnifying power of single lenses,
39.
of object-glasses and eye-
pieces, 57.
Maple-aphis, 613.
Marehantia polymorphia, 308.
MayaH's, Mr. J., semi-cylinder illu
minator, 176.
diaphragms, 186.
Mechanical arrangements, 70.
Medusae, 492.
Meissner on the micropyle, 603.
Melicerta ringens, 459.
Melolantha, eye of, 585.
Mesoglia vermicularis, 268.
Micrasterias, 280.
Micrometers, 53.
Microscope, the, 1.
Abbe's binocular, 119.
Baker's compound, 98
binocular dissecting, 98.
student's, 96.
Beck's popular, 93.
ideal, 95.
Brewster's diamond, 11.
Browning's improved, 99.
platyscopie, 39.
Collins's binocular, 107.
dissecting, 108.
student's, 106.
Crouch's, 110.
Frauenhofer's lenses for, 10,
G. Adams's, 10.
Hooke's compound, 7.
water, 5.
How's student's, 112.
Ladd's, 115.
Lieberkiihn's, 5.
. Murray and Heath's, 113.
class, 114.
Xachet's portable, 115.
INDEX.
7*51
Microscope, Newton's speculum, 9.
. Pillischer's binocular, 104.
Powell and Lealand's, 90.
* arranged for test-objects,
92.
. Ross-Wenham, 15.
Ross-Zentmayer, 87.
compound student's, 89.
student's, 90.
S. Gray's globule, 4.
- simple, 5, 40.
the stage of, 43.
hot stage of, 46.
Stephenson's safety stage of, 46.
the mirror of, 47.
the stand of, 86.
- management of, 162.
Swift's, 109.
Watson's new stand, 101.
binocular, 116.
medical or college, 103.
Wollaston's, 36.
Microspectroscopy, 122.
Microtome, Swift's, 239.'
Miller, Hugh, on fossil plants, 364.
Mineral kingdom, 728.
Mite, cheese, 637.
flour, 639.
Molecular movements, 168.
rotation, 156.
Mollusca, 511.
injecting, 240.
tongues of, 539.
Monads, 411.
Morpho Menelaus, scale of, 611.
Moss-agates, 399.
Mosses, 309.
Moths and butterflies, 607.
Motile organs in cells, 262.
Mottled umber moth, 606.
Mounting and preparing, general
directions for, 211.
apparatus, 210.
medium, 219.
spring-clip for, 211.
Movements of diatoms, 423.
Mucidines, development of, 661.
Mucor mucedo, 292.
Mucous membrane, 669.
Muscular fibre, 695.
Mushroom spawn, 343.
Mussel, 531.
Myelin, 681.
Myolemma, 696.
Mytilus, 535.
NAILS, the, 672.
Naviculae, 419.
Neckera antipyretica, 310.
Needles for dissecting, 202.
Nelson's sub-stage condenser, 171.
Nematoidea, 563.
Nemertidae, 562.
Nerves, 699.
perfection of sections, 701.
stellate corpuscles. 699.
Xewport on moths' tongues, 607.
Nicol's prism, 137.
Nitella, 320.
Nobert's ruled micrometer lines, 5&
Noctiluca miliaris, 409.
Notommata aurita, 456.
Nudibranchiata, 530.
tongues of, 541.
Nummulites, 377.
OBJECT-GLASS, the, 58, 80.
aperture of, 69.
numerical aperture, 78.
their selection, 80.
the immersion, 81.
Object-glasses, forms of, 62.
the correction of, 63.
Powell and Lealand's homogeneous
immersion, 85.
Swift's taper, 60.
Wenham's binocular, 59.
Objectives and eye-pieces, magnify.
ing power of, 57.
Objects, directions for viewing, 162
O'idmm, 293,
Onion, section of, 338.
Ophiocoma, 495.
Ophiura, 495.
Opuntia, 356.
Orchideaj, 350.
Organ of vision, 17.
Orthoptera, 626.
Osborne, Lord S. G., on fungi, 295,
on closterium lunula, 284.
Oscillatorise, 266.
Ostracoda, 556.
Ova mollusca, 545.
Owen, Major, on foraminifera, 383.
Professor, on animalcule life,
444.
on microscopic investigation
705.
Oxytricha, 414.
Oyster, 533.
fry, 554.
pearl, 533.
PALATES OP MOLLUSCA, 539
Panax Lessonii, 329.
Papillae of skin, 675.
Parabolic reflector, Wenham's, 17&.
Pciramseciura, 409.
Parasites, 612.
of dog, 634.
of eagle, 643.
eggs of, 607.
of fowl, 640.
of hornbill, 642.
human, 633.
of pheasant, 640.
of pigeon, 643.
of sheep, 633.
of swallow, 639.
of turkey, 640.
of vulture, 643.
Parasitic fungi, 293.
762
INDEX.
Parmelia, 305.
stellate, 306.
Patella, tongue of, 541.
Pear cells, 338.
Pearl oyster, 533.
Pearls, artificial, 533.
Pedicellarife of starfish, 496.
Pediculi, 636.
Penetrating power of object-glasses,
75.
Penium, 283.
Pennatulidfe, 488.
phosphorea, 488.
Peronosporse, 290.
Peziza, 304.
Pholas dactylus, 531.
Photography applied to microscope,
1ST.
Phryganea, eggs of, 605.
Phrygaiieidae, 601.
Phyllactinia, 294.
Pigment ceUs from skin, 6_75.
Pillischer's binocular microscope,
104.
Pinna, 530.
Planarise, 562.
Plants and animals, 257.
amuilar vessels, 358.
. cellular tissue of, 323.
. circulation in, 320.
crystals in, 337.
fossil, 362.
hairs of, 824.
lactiferous tissue of, 334.
lice, 613.
pollen and seeds from, 361.
pollen grains, 361.
preparation of tissues, 359.
raphides in, 337.
silicia in, 340.
silicious cuticle of, 339.
starch in, 341.
starch of potato, 345.
starch, wheat flour, 344.
stellate tissue, 333.
structure of, 323.
unicellular, 260.
- vascular system of, 327.
vascular tissue of, 324.
vital characteristics, 257.
woody tissue, 353.
Phosphorescence, marine, 408.
Pleurobranchus, mandible of, 542.
Pleurosigma, 421.
as a test-object, 5&.
Plurnatella repens, 527.
Plumularia, 478.
pinnata, 480.
Podura plumbia, 628.
scale, as a test, 67, 610.
Polarisation of light, 133.
Polarised light, objects for, 729.
Polariser, 138.
Polyzoa, 512.
mounting, 222.
^ fresh-water, 524.
Polycystina, 384.
Polygastrica of Ehreuberg, 416.
Polyommatus argiolus, 610.
Polypifera, 462.
Polythalamia, 376.
Pontia brassica, 611.
Potato mould, 290.
starches, 155, 343.
Powell and Lealand's microscopes.
90.
Powell's immersion condenser, 180.
Preparation of insects, 648.
Preparing and mounting objects,
211.
sections of hard tissues, 205.
tongues of mollusca. 544.
vegetable tissues, ,359.
Prism for binocular ilS, 121.
for microspectroscope, 125.
polarising, method of using,
139.
Propita gigantea, 493.
Proteus, the, 373.
Protoooccus pluvialis, 259.
Protozoa, 363.
Pteropoda, 532.
Puccinia, 292.
buxi, 294.
Pumpkin fungi, 301.
QUEKETT on the vascular tissue of
plants, 358.
on fossil infusoria, 438.
on polarised light, 155.
on the structure of boi>3, 714.
Quinidine, test for, 152.
Quinine, its detection, 150.
RAINEY on artificial shell, 551.
Ealfs, Mr., on desmidiaceaj, 288.
carbolic acid fluid, 220.
K aphides in plants, 337.
Re-agents, effects of, 726.
Redfern on separating iiaviculfe, 435,
Ked seaweeds, 271.
Reflector, parabolic, Wenham's, 173.
Rezner's mechanical finger, 218.
Rhinoceros horn, 721.
Rhizopoda, 372.
Rhubarb cells, with raphides and
starch, 388.
spiral vessels, 355.
Ringworm, 296.
Roberts, Dr., on blood cell, 677.
Robertson, J., on pholas, 531.
Ross's microscopes, 87.
object-glasses, 89.
Rotifera3, 452.
Rush, stem of, 333.
SALTEB, DR. HYDE, on muscle, 496.
Salts, urinary, 150.
Samuelson, J., on infusoria, 4rl5.
Sandstone, 729.
Sarciua ventriculi, 295.
Sarcode, 656.
INDEX.
763
Saw-fly, 016.
Scales of fish, 721.
of lepidoptera, 609.
of podura, (528.
Scapander, tongue of, 542.
Suhultze, Dr., on rhizopoda, 375.
on the diatom valve, 422.
Schwann's classification of tissues,
692.
Scissors, dissecting, 201.
Sea-cucumbers, 508.
jelly fish, 491.
lilies, 497, 505.
slug, 529.
soundings, 3S3.
urchins, 498.
Section-cutting machine, 204, 239.
Sections, method of making, 2u3.
Seller's test-slide, 165.
Selenite, 142.
stage, 148.
Sepia, palate of, 541.
Serpula, 575.
Sertulariadse, 476.
pumila, 477.
setacea, 477.
Sheep tick, 633.
Shell, structure of, 546.
artificial formation of, 551.
Sheppard,J.B., on coloured monads,
413.
Silk, 354.
Silkworm moth, antenna of, 608.
Silkworm's breathing aperture, 586.
Single microscope, 4.
Skin, capillaries of, 675.
fungoid diseases of, 296.
nerves of, 676.
section of, 677.
Slack, H. J.. on a rotifer, 451.
Smith and Beck's microscope, 95.
Smith's, Prof., condenser, ISO.
mechanical finger, 436.
Snow, crystals of, 153.
Sollitt on diatoms as test-objects, 426.
measurement of markings on
diatoms, 428.
Sorby's standard interference spec-
trum, 738.
spectroscope, 126.
Sori of ferns, 315.
Sphacelaria cirrhosa, 2G9.
Spectro-microscopy, 122.
Spectrum analysis, 735.
Spencer, Herbert, 011 the formation
of fibre in plants, 325.
Sphferiacei, 294.
Bphaerosira volvox, 276.
Sphagnum, 309.
Spiders, 644,
diving, 647.
Spiderwort, 350.
Sponges, 385.
skeletons of, 396.
spicula from, 387, 390.
Bpongia coalita, 388.
Spongia ^eodia, 390.
Spongilla cinera, 391.
alba, 392.
development of, 389.
gemmules of, 400.
Spring-clip, 211.
Staining animal and vegetable
tissues, $24.
Groves on, 230.
Schafer'd method, 234.
Stirling's method, 227.
Starches, 343.
in plants, 342.
potato, polarised, 155.
tests for, 283.
Star-fishes, 495.
Staurastrum, 282.
Stellate tissue from a rush, 333.
Stentors, 450.
Stephanoceros, 458.
Stephanosphoera pluvialis, 265.
Stepheiison's safety-stage, 46.
catoptric illuminator, 185.
on homogeneous immersion, 83.
Stichostegidfe, 276.
Stinging-nettle hairs, 324.
Stokes's, Prof., absorption bands,
131.
Stomach, mucous membrane of, 669.
Structure of shell, 529.
Suctoria, 629.
Sugar insect, 638.
cane, section of, 336.
detection of, 156.
Surirella constricta, 420.
Swammerdam's dissection of insects,
579.
Swift's condenser, 181.
microscope, 109.
microtome or section-cutter,
239.
taper object-glasses, 60.
Syiiapta chirodota, 503.
Synaptidse, 508.
TADPOLE, circulation of, 683.
gill of, 686.
Taeniada?, 563.
Tapeworms, 563.
Tea, adulterated, 349.
Teeth, preparing sections of, 206.
of mollusca, how to prepare,
544.
sections, mounting of, 208.
Terebratula, 536.
Teredo, 531.
Test-objects, 423, 610.
Testaoella, tongue of, 542.
Theory of microscopical vision, 19.
Thomas on crystallization, 730.
Thompson on mollusca tongue?, 543,
Prof. W., on sea-Lilies, 49?.
Thread cells, 544.
- in actiniae, 467.
in mollusca, 544.
Thuiarea, 478.
764
INDEX.
Thysanura, 627.
Tinea vestianella, 611.
Tissue, woody, 353.
Tissues, consolidated animal, 702.
' elastic and non-elastic, G94.
hard, 205.
Tomato, diseased, 300.
Tomkins, Mr. J. N., on alcyonella,
526.
Tomopteris onisciformis, 576.
Tooth, section of, 707.
structure, 709.
i of eagle-ray, 712.
of prestis, 711.
Torula cevevisia, 300.
diabetica, 295.
Tourmaline, 139.
artificial, 144.
Tradescantia, circulation in, 350.
Transformation, insect, 648.
Transparent injections, 251.
Trernatoda, 563.
Trembley on hydra, 471.
Triceratium, 419.
Trichohasis, 294.
Trichocera hyemali?, 598.
Trichoda, 411.
'i richina spiralis, 568.
Trochell, Dr., 011 mollusca, 539.
Trough for exhibiting circulation,
193.
Beck's, 195.
Botterill's live, 194.
Truffles, 302.
Tsetse-fly of Africa, 596.
Tubercibarium, 302.
Tubicola, 574.
Tubiporidae, 489.
Tubularia Dumortierii, 497.
Tubularidae, 473.
Tunicnta, 532.
Turbellaria, 561.
Turbo marmoratus, tongue of, 543.
ULV;E, development, 271.
Uredo, 291.
Urinary salts, 150.
Uromyces, 291.
Urticating organs in actiniae, 467.
in mollusca, 544.
VALLISNERIA, 321.
Varley, on chara, 315.
Vaucheria, 274.
Vegetable structure, 323.
cell, 255.
cellular tissue, 360.
Vegetable kingdom, 255.
division between
and, 256.
preparation of, 359'.
preparation of tissues, 359.
starch, 341.
tissues, method of staining, 240.
vascular tissue, 324.
Velutina, palate of, 540.
Vertebrata, 654.
Vertical illuminator, 186.
Vibrio spirilla, 412.
Virchow on trichina, 569.
Volvox globator, 275.
Vorticellidse, 445.
WALE'S Iris diaphragm, 170.
Wasp, 618.
tongue of, 582.
Water, microscopical examination
of, 743.
organic matter in, 751.
Water-beetle, 625.
Water-microscope, 5.
Water-mites, 643.
Wenham's binocular object-glass, 59
immersion illuminator, 174.
binocular microscope, 121.
method of using object-glasses,
66.
parabolic reflector, 173.
West, Tuffen, on feet of flies, 588.
Wheat, portion of husk of, 340.
flour, adulterations of, 314.
Whelk, palate of, 537.
Whirligig, 625.
Whitney, W. U., on the tadpole, 683.
Wing-shell, 530.
Wood, cutting sections of, 204.
Woodward, Mr., on polarised light,
140.
Wool, 354.
Wright, Dr., on alcyonida, 524.
XANTHIDLE, 282, 441.
YE AST- PLANT, 299.
Yew, section of, 356.
ZEIS'S objectives, 80.
Zoophytes, canal-bearing, 385.
a fresh-water group, 463.
preservation of polypidoms o
509.
skeletons of, 490.
Zygoceros rhombus, 432.
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