04 VEGETABLE ORGANS. 
 
 terminated by a very minute dilatation or knob. The 
 sting contains an acrid liquid,, which escapes when 
 the little knob is broken off in wounding the skin, and 
 produces the well-knoAvn irritation. By the side of 
 the figure of the sting is represented the point of a 
 fine needle (fig. 20), showing that the expression 
 ' ' sharp as a needle " has no force when microscopic 
 bodies are in question. 
 
 Stomata (<jTo/u,a, mouth). On viewing a strip of 
 epidermis, the observer will be sure to notice certain 
 oval or roundish bodies (PL I. fig. 13 a), composed of 
 mostly two kidney-shaped cells in apposition but 
 leaving a chink between them ; these are the stomata. 
 They communicate beneath with the intercellular pas- 
 sages, of which they may be considered the mouths ; 
 and by their agency a direct communication is esta- 
 blished between these passages and the air. The two 
 cells which guard the orifice are termed the " guard 
 cells." 
 
 Stomata are most numerous on the under surface 
 of leaves; they are entirely absent in plants growing 
 under water, and in most of the lower plants. In 
 many of the stomata, viewed in the ordinary way, the 
 air situated between the guard cells is indicated by 
 the black spot or dot present ; but after a time, or by 
 the application of a gentle heat to the slide, the air 
 becomes displaced by the water, and their structure 
 becomes very distinct. 
 
 In certain plants, the epidermis is imbued with 
 flint or sil'ica ; so that even when burnt to an ash the 
 stomata are still quite distinct. Examples of this 
 may be found in the stalk or culm of grasses, as in 
 straw, the shining epidermis of which is siliceous ; or 
 the epidermis of canes. Among the lower plants, 
 this peculiarity is especially curious in the species of 
 Equisetum, or mares'- tails. 
 
 The manner in which the veins of leaves are ar- 
 ranged is worthy of special attention, as it forms one 
 
STEMS. 35 
 
 of the characters by which the two leading divisions 
 of the Vegetable Kingdom are characterized. Thus 
 in one of these divisions the veins are branched, so 
 as to form a network throughout the leaf; the 
 plants with these netted veins, to which belong our 
 trees, shrubs, and most herbs, are the Dicotyledons, 
 or Ex'ogens ; while in the second division, the veins 
 run parallel to each other, being little or not at all 
 branched, and not forming a network. The plants 
 with parallel veins, among which are our grasses, 
 lilies, &c., are the Monocotyledons or En'dogens. 
 
 Stems. In the stems of plants, the tissues are 
 arranged round a centre; otherwise, in the sim- 
 pler and lower plants, they agree in structure with 
 leaves, the centre being occupied by some element 
 of nbro-vascular tissue, as simple wood-cells, a few 
 vessels or ducts. 
 
 In the higher or flowering plants, the stem exists 
 in two distinct forms, corresponding to the differences 
 above noticed in the arrangement of the veins of the 
 leaves ; these must be considered separately. 
 
 In the Dicotyledons or Exogens (PI. I. fig. 36), the 
 centre of the stem, in a transverse section, is seen to 
 be occupied by the pith or medulla, which is repre- 
 sented in the figure by the innermost circle. Imme- 
 diately outside and around this is a narrow ring, in- 
 dicating the section of a sheath to the pith, and called 
 the medullary sheath. Next comes a broad ring of 
 wood of the first year's growth (fig. 36 a), traversed, 
 from the pith to the bark, by wedge-shaped paler 
 rays, termed the medullary rays. Outside the first 
 year's wood is the newer and paler wood of the second 
 year (b] ; and so on, a new ring of wood being added 
 outside the preceding layer for each year of growth 
 of the stem. 
 
 On the outer side of the wood is the inner bark or 
 liber (fig. 36 c) ; and outside this is the spongy outer 
 bark (d), covered by its epidermis. 
 
BIOLOGY 
 LIBRARY 
 

Xon.icn:Jolin. '/an fttrst. 
 
AN 
 
 ELEMENTARY TEXT-BOOK 
 
 OP 
 
 || THE MICROSCOPE; I 
 
 INCLUDING A DESCRIPTION OF THE METHODS OF 
 PREPARING AND MOUNTING OBJECTS, ETC. 
 
 BY 
 J. W. GRIFFITH, M.D., F.L.S., ETC., 
 
 MEMBER OF THE ROYAL COLLEGE OP PHYSICIANS ; CONJOINT AUTHOR OP 
 THE MICROGRAPHIC DICTIONARY, ETC. 
 
 WITH TWELVE COLOURED PLATES, 
 CONTAINING 451 FIGURES. 
 
 LONDON: 
 JOHN VAN VOORST, PATERNOSTER ROW. 
 
 MDOCCLXIV. 
 
 [ The right of translation is reserved.] 
 
PEEFACE. 
 
 THE object of this little work is to furnish an 
 elementary course of instruction in the use of 
 the Microscope, and on its application to the ex- 
 amination of the structure of plants and animals. 
 Assuming that the reader has had no previous 
 acquaintance with the Microscope, or with the 
 study of natural history, I have attempted to render 
 the descriptions of the objects as simple as possible. 
 At the same time, the technical terms have been 
 added and explained, in order gradually to render 
 them familiar to the reader, and thus facilitate 
 the future study of larger and more detailed works. 
 The objects figured and described comprise the prin- 
 cipal structures and more minute forms of both 
 the vegetable and the animal kingdom, those having 
 been selected which are common and readily pro- 
 curable. 
 
 A chapter has been given upon the optical priri- 
 
IV PREFACE. 
 
 ciples on which the action of the instrument depends 
 (which will assist the reader to understand the opera- 
 tion of its constituent parts), including a sketch of 
 the subject of polarized light. The order in which 
 the subjects are treated is scientific, and particular 
 directions have been given for the examination of 
 the objects. 
 
 The small size of the work has necessitated the 
 exclusion of figurative descriptions, so that it is 
 adapted rather for a worker than a reader ; at the same 
 time, the matter forms a course, and must be taken 
 as a whole for the proper comprehension of the sub- 
 jects. The technical terms used are referred to in 
 the Index, so as to furnish to some extent a glossary 
 of terms; and their derivation is given, to facilitate 
 their recollection. The figures, with very few excep- 
 tions, are drawn from nature, and are coloured that 
 the objects may be more easily recognized. The 
 magnifying powers under which they have been drawn 
 are denoted by a small number placed beneath each 
 figure : and the particular attention of the reader is 
 requested to this point ; otherwise the whole subject 
 will be utterly confused ; so much does the appearance 
 of objects vary under different powers. 
 
 Directions are given for preparing and mounting 
 
PREFACE. V 
 
 objects, implying that the reader will collect specimens 
 for himself, which is to be strongly recommended as 
 the best method of acquiring a practical and useful 
 acquaintance with the objects. These will serve to 
 furnish permanent landmarks in the great ocean of 
 structural forms, will probably recall in after-years 
 pleasant recollections of early excursions in search 
 of the beauties of nature, and, surely, deepen the 
 conviction of the existence of their All- wise Creator. 
 
 J. W. G. 
 
CONTENTS. 
 
 I. THE MICROSCOPE 1 
 
 II. THE MOUNTING OF OBJECTS . 10 
 
 III. VEGETABLE ELEMENTS AND TISSUES 19 
 
 IV. VEGETABLE OEGANS 31 
 
 V. FERNS 49 
 
 VI. MOSSES 54 
 
 VII. ALG^E 64 
 
 VIII. LICHENS 91 
 
 IX. FUNGI 96 
 
 X. ANIMAL ELEMENTS AND TISSUES 113 
 
 XI. AKTICULATA 127 
 
 XII. RADIATA 153 
 
 XIII. PROTOZOA , 155 
 
 XIV. OPTICAL PRINCIPLES . 167 
 
PLATE I. [FRONTISPIECE.] 
 VEGETABLE TISSUES, &c. 
 
 Fig. 
 
 1. Leaf of Geranium : cells, chloro- 
 phyll, and intercellular pas- 
 
 2. Cells of Apple. 
 
 3. Starch-granules : a, of Wheat ; 
 
 b, of Arrowroot ; e, of Potato ; 
 d, of Oat; e, of Lentil;/, of Rice. 
 
 4. Cells of Potato, containing Starch. 
 
 5. Garden Rhubarb-stalk : a, ra- 
 
 phides; b, reticulated duct; c, spi- 
 ral vessel ; d, woody fibre ; e, an- 
 nular vessel. 
 
 6. Wood-cells from stem of Chrys- 
 
 anthemum. 
 
 7. Deal, transverse section : a, glan- 
 
 dular tissue ; b, woody fibre. 
 
 8. Deal, longitudinal (radial) sec- 
 
 tion of glandular tissue. 
 
 9. Deal, longitudinal section of woody 
 
 fibre. 
 
 10. Deal, tangential section. 
 
 11. Holly, wood of: a, porous cells; 
 
 b, d,e, wood-cells; c, dotted ducts. 
 
 12. Hairs, vegetable : a, b, of Ground- 
 
 sel ; c, of London Pride ; d, e, of 
 Geranium; /, of Chrysanthe- 
 mum. 
 
 13. Epidermis of Geranium-leaf. 
 
 14. Style of Crocus, with pollen-gra- 
 
 nule and -tube. 
 
 15. Pollen-grain of Crocus, with pol- 
 
 len-tube. 
 
 16. Pollen of Primrose. 
 
 17. Pollen of Sunflower. 
 
 18. Pollen of Convolvulus major. 
 
 19. Caraway-seed. 
 
 20. Needle-point. 
 
 21. Sting of Nettle. 
 
 22. Hair of Spiderwort. 
 
 23. Hair of Spiderwort, single cell. 
 
 Fig. 
 
 24. Epidermis of Geranium-petal. 
 
 25. Petal of Chickweed. 
 
 26. Sepal of Chickweed. 
 
 27. Seed of Poppy. 
 
 28. Epidermis of Deutzia. 
 
 29. Seed of Mignonette. 
 
 30. Pollen of Chickweed, dry. 
 
 31. Pollen of Chickweed, in water. 
 
 32. Flower of Chickweed. 
 
 33. Epidermis of petal of Chickweed. 
 
 34. Hairs of calyx of Chickweed. 
 
 35. Hairs of seed of Collomia. 
 
 36. Stem of Dicotyledon, section of. 
 
 37. Stem of Monocotyledon, section of. 
 
 38. Seed of Shepherd's Purse, trans- 
 
 verse section. 
 
 39. Stamen of Chickweed. 
 
 40. Stigma of Chickweed. 
 
 41. Ovary of Chickweed. 
 
 42. Leaf of Chickweed. 
 
 43. Seed of Wallflower, section of. 
 
 44. Seed of Wallflower, radicle and 
 
 cotyledons. 
 
 45. Embryo-sac of Chickweed. 
 
 46. Embryo-sac of Chickweed. 
 
 47. Embryo-sac of Chickweed. 
 
 48. Wheat, cotyledon and leaves of, 
 
 section. 
 
 49. Mustard-seed, cotyledons and ra- 
 
 dicle. 
 
 50. Mustard-seed, transverse section. 
 
 51. Chickweed, seed of. 
 
 52. Seed of Eccremocarpus scaber. 
 
 53. Grain of Wheat : a, cotyledon ; 
 
 b } embryo ; c, radicle ; d, albu- 
 men. 
 
 54. Ovule of Wallflower. 
 
 55. Cotyledons of Chickweed. 
 
 56. Plum-stone, section of. 
 
A 
 TEXT-BOOK 
 
 OF 
 
 THE MICEOSCOPE. 
 
 CHAPTER I. 
 
 THE MICROSCOPE. 
 
 THE microscope (from pi/epos, little, and cr/conea), to 
 see), so called because it enables us to see objects 
 which are too small to be seen with the naked eye, 
 consists of several parts, each of which has its special 
 use. As the proper management of these is of great 
 importance in the successful application of the in- 
 strument to minute investigations, we shall com- 
 mence with the consideration of their names and 
 uses, including those of the more important pieces of 
 accessory apparatus. 
 
 Microscope. The foot of the microscope is that 
 part which supports the instrument upon the table ; 
 it is connected above with the stand, of which it is 
 often considered a part. The stand sometimes con- 
 sists of a single rod or pillar ; but in the best micro- 
 scopes it is composed of two upright plates, between 
 which, at the upper part, the rest of the microscope 
 swings stiffly upon an axle. Arising from this axle, 
 indirectly through the medium of parts which require 
 no special mention, is an arm, to which the body is 
 
2 THE MICROSCOPE. 
 
 fixed. The body is moveable up and down by one 
 or two large milled heads, connected with a grooved 
 rod or pinion, which works in the teeth of a rack 
 fixed to the back of the body, or of the arm which 
 supports the body. The large milled heads form the 
 " coarse movement/* as it is called. 
 
 On the top of the arm, or on the front and lower 
 part of the body of the microscope, is placed the 
 ' ' fine movement/' consisting of a small milled head, 
 with a fine screw, for moving the body through very 
 small distances. 
 
 Next is the " stage," or flat plate, upon which the 
 objects to be viewed are placed. This is often so 
 arranged that, by turning two milled heads, the ob- 
 ject can be moved backwards and forwards, or from 
 side to side ; it is then a " moveable stage/' 
 
 The eye-piece slides into the upper end of the 
 body ; and the object-glass screws into its lower end. 
 Beneath the stage is the mirror, which reflects 
 the light through the object, the object-glass, and eye- 
 piece to the eye. 
 
 Object-glasses. The object-glasses are the most 
 valuable parts of the instrument. There are gene- 
 rally three or more of them ; and, by means of an 
 " adapter," any object-glass can be made to fit any 
 microscope. Great care is required in their use, 
 especially to avoid scratching the lower surface of 
 the glass, which is sometimes accidentally done by 
 pressing the surface against any hard body, or allow- 
 ing such a body to fall upon it. When not in use, the 
 object-glasses should either be put away in the brass 
 boxes or covered with a small bell-glass, to prevent 
 their receiving any injury. 
 
 The object - glasses possess various magnifying 
 powers, according to the distance at which they re- 
 quire to be placed from the object for distinct vision : 
 this is not, however, absolutely correct, yet may 
 serve as a general expression. Thus we have a 
 
MIRROR. 3 
 
 1-inch, |-inch, |-inch object-glass, &c. The object- 
 glasses, for brevity, are often called powers. 
 
 As a beginner may at first have some difficulty in 
 distinguishing a high from a low power, it may be 
 remarked that the size of the lower glass is larger 
 the lower the power : but, in the case of the better 
 object-glasses, the focal distance is engraved on the 
 box in which the object-glass is packed when put 
 away. 
 
 As the coarse movement raises or depresses the 
 body and object-glass through comparatively large 
 distances, it must be used only with the lower object- 
 glasses, i. e. those of low or little magnifying power, 
 as the 2-inch, 1-inch, or |-inch, or to bring the 
 object-glass near the focal distance with the higher 
 powers ; whereas the fine movement serves to adjust 
 the higher powers, as the J-inch, &c. 
 
 If the object-glasses should become soiled on the 
 lower face, this should be wiped very gently with an 
 old silk handkerchief or piece of very soft wash- 
 leather, previously shaken to displace dust. The 
 same method will answer to cleanse the upper surface 
 of the eye-piece. 
 
 Great care must be taken that a slide which has 
 been warmed in any experiment be not placed near 
 the object-glass until quite cold. 
 
 Mirror. The mirror has sometimes one silvered 
 face only, at others two one flat, the other concave. 
 The flat surface is used to reflect the light upon the 
 object when the light is too great with the concave 
 surface. 
 
 Beneath the stage, in most microscopes, is a cir- 
 cular moveable ' { diaphragm," perforated with holes 
 of various sizes, to allow more or less of the light 
 reflected by the mirror to pass through, as may be 
 required. 
 
 When opake objects are viewed, the mirror should 
 
4 THE MICROSCOPE. 
 
 be turned aside, so as not to reflect any light through 
 the stage. 
 
 Eye-pieces. With all microscopes, two or more 
 eye-pieces are supplied. These possess different mag- 
 nifying powers, and are lettered or numbered accord- 
 ingly; the lowest power with the earliest letters of 
 the alphabet, or with the smallest numbers, thus : 
 A, B, C ; or 1, 2, 3, &c. 
 
 Forceps. These are fine pincers, for holding mi- 
 nute bodies to be viewed as opake objects. In use, 
 they are inserted by a stem connected with a joint, in 
 an aperture, generally in the stage ; and are moveable 
 in all directions. 
 
 Live-box. This is a brass slide, perforated in the 
 middle, to the aperture in which is soldered a short 
 piece of brass tube, closed at the top with a circular 
 plate of thin glass. A rather wider and longer piece 
 of brass tube slides over the former; this is also 
 closed at the top by a thin glass plate, so as to allow 
 of an object being confined or compressed between 
 the two glass plates. It is used for examining living 
 objects in water. 
 
 Knife , fyc. For cutting slices or sections of ob- 
 jects, a very sharp knife with a thin back will be 
 found useful ; or a razor may be used for the same 
 purpose. And for picking minute objects to pieces, 
 or dissection, fine needles, cut off short with pliers, 
 the blunt ends being thrust into hair-pencil sticks, 
 will be requisite. 
 
 A pair of fine surgical forceps will also be required, 
 for taking up minute objects. These should be with- 
 out teeth, and the spring- action so weak that the 
 points can be very easily approximated. 
 
 Dipping -tubes. For removing minute objects from 
 water, two or three narrow glass tubes, of different 
 lengths, are very useful. These are called " dipping 
 tubes/' and are used thus : the tube being held up- 
 right between the second finger and the thumb, the 
 
SIMPLE MICROSCOPE. 5 
 
 fore finger is placed at the top of the tube to close it; 
 the tube is then put into the water until the lower 
 end is close to the object, when, on suddenly re- 
 moving the fore finger, the water will rise in the 
 tube, carrying the object with it. The fore finger is 
 then again applied to the tube, and, as thus held, the 
 water will not run out. The tube is then held over a 
 watch-glass, or a slide, upon which the water and 
 object will fall on removing the fore finger. 
 
 A small glass spirit-lamp will be found very useful. 
 The spirit for burning should be methylated alcohol, 
 or wood-naphtha. As these spirits are inflammable, 
 great care should be taken to keep the stock-bottle 
 away from a candle or other flame, when filling the 
 lamp. 
 
 Achromatic condenser. A very important piece of 
 apparatus, when high powers are used, is the achro- 
 matic condenser ; it is not, however, usually supplied 
 with the cheaper microscopes. It consists of a brass 
 fitting, placed beneath the stage, into which an ob- 
 ject-glass is screwed, in an inverted position, i. e. the 
 small end of the object-glass being placed uppermost. 
 It serves to condense the light to a focus upon the 
 object, so as to illuminate it more brightly ; and as it 
 can be elevated or depressed by a milled head and 
 rack-work, the object can be viewed by either con- 
 verging or diverging rays. 
 
 Simple microscope. For examining the larger 
 kinds of objects, and for dissection, a simple micro- 
 scope is very useful. This consists of a stand, a 
 stage, and an arm supporting a simple lens or com- 
 bination of lenses, but without the body of the com- 
 pound microscope (as the ordinary microscope is 
 distinctively called). For most purposes, common 
 plano-convex or doubly convex lenses are sufficient 
 to form the object-glasses of a simple microscope. 
 With the best microscopes, an " erector," or tube 
 
 3 
 
.-, 
 
 6 THE MICROSCOPE. 
 
 containing a pair of lenses, fitted within the body, 
 renders the compound microscope capable of an- 
 swering most of the purposes of a simple micro- 
 scope. 
 
 Polariscope. An expensive but interesting and 
 useful addition to a microscope is a polarizing appa- 
 ratus, or polariscope. This consists of a Nicol's prism, 
 or a plate of tourmaline, placed beneath the stage, and 
 another in the body of the microscope or above the 
 eye-piece; both in brass fittings. The former is 
 called the polarizer, and the latter the analyzer. 
 
 Rotating disk. Another most useful piece of ap- 
 paratus, for moving opake objects whilst under the 
 microscope, in all directions, is Smith and Beck's 
 " rotating disk." 
 
 Slides. The slides upon which objects, especially 
 those to be viewed as transparent objects, are to be 
 placed, should be made of crown or plate glass. 
 They are usually 3 inches long, and 1 inch wide ; 
 but I prefer them 2J inches long, and 1 inch wide, 
 simply because they take up less room in a cabinet, 
 and because they do not project beyond the stage on 
 either side. They should not be more than ^th of 
 an inch thick, and as colourless and clear as possible. 
 The edges should be ground or filed, to prevent their 
 scratching the stage. 
 
 Covers. The covers are square pieces of very thin 
 glass, less in breadth than the slides, so as not to 
 reach their margins ; and of various thicknesses, the 
 thicker and stronger being used to cover large ob- 
 jects for examination under the lower powers, and 
 the thinner serving to cover very delicate objects 
 requiring the higher powers. 
 
 Side condenser. For illuminating opake objects, 
 a large plano-convex or doubly convex " bull's-eye " 
 lens, or side condenser, is used ; this is fixed to an 
 arm, which slides on a stand, so as to be capable of 
 being raised or lowered to a suitable height. This 
 
GENERAL METHOD OF OBSERVATION. 7 
 
 is placed between the source of light and the stage, 
 and at such a distance from the latter that the light 
 may be brought to a focus upon the object. Some- 
 times a " Lieberkuhn " or concave silver reflector is 
 used for this purpose. 
 
 These are the most important pieces of apparatus 
 required in examining microscopic bodies. But the 
 beginner will do well, if he have the achromatic con- 
 denser and the polarizing apparatus, to lay these 
 aside until he has had considerable practice in ex- 
 amining objects simply with the mirror and the lower 
 powers. 
 
 General method of observation. In the ordinary 
 use of the microscope, the object to be examined is 
 laid upon the middle of a slide, which is placed upon 
 the stage. The object is then brought under the 
 centre of the object-glass, the mirror inclined half 
 towards the light and half towards the object, until 
 the object is seen to be illuminated, when, upon look- 
 ing through the eye-piece and adjusting the coarse 
 and fine movements, the object as it comes into focus 
 will be seen, as it were, drawn upon a white disk, 
 which is called the " field." 
 
 When the object is wet, it cannot be viewed with- 
 out the application of a cover, because the water eva- 
 porates and condenses upon the under surface of the 
 object-glass. 
 
 To avoid the danger of injuring the object-glass, or 
 crushing the object by lowering the body and object- 
 glass too much in adjustment to focus, the best plan 
 is to lower the body by means of the coarse move- 
 ment until the object-glass appears near the object to 
 the eye placed on one side of the stage, and then to 
 apply the eye to the eye-piece, and turn the milled 
 head so as to raise the body and object-glass until 
 the object is brought into focus. 
 
 In the examination of an object, it is best to begin 
 with a low power, so as to obtain a view of the 
 
8 THE MICROSCOPE. 
 
 general arrangement of its parts, and then to apply 
 the higher eye-pieces and powers, so that the more 
 minute structural details may be observed. 
 
 Illumination. The illumination or proper manage- 
 ment of the light in using the microscope is of very 
 great importance. The best light, especially with the 
 low powers, is daylight, particularly that reflected 
 from white clouds ; this is least injurious to the eyes. 
 But as daylight cannot always be used for micro- 
 scopic investigations, and as cloud-light is insufficient 
 with the higher powers, some kind of artificial light 
 must be supplied. That mostly used is the light of 
 a reading oil lamp or of a gas-burner, a candle 
 being quite useless, on account of the flickering of the 
 flame with the slightest draught. A moderator lamp 
 has the defect of too great height; otherwise this 
 would be better than any other oil lamp. A power- 
 ful and excellent light for the highest powers is 
 afforded by a short paraffine-oil lamp. 
 
 As intently looking at strongly illuminated objects 
 is injurious to the sight, the amount of light allowed to 
 pass the diaphragm should be no more than is agree- 
 able, and sufficient to show the object distinctly. 
 
 In using the higher powers, the field is much less 
 bright with the use of the same light than in the case 
 of the lower powers ; and difficulty is often found in 
 obtaining sufficient light for the distinct vision of the 
 object. The achromatic condenser is of most im- 
 portant service here ; but it is sometimes requisite, 
 even when this is used, to condense the light upon 
 the mirror by a shallow bull's-eye ; or a large common 
 metallic reflector may be used for the same purpose. 
 
 The most convenient manner of proceeding in re- 
 gard to the use of the individual eyes is to apply the 
 left eye to the eye-piece, so that the right eye may 
 be used in finding the stage-movements, or in moving 
 the slide, without removing the eye from the eye- 
 piece. If this arrangement be adopted, the light 
 
ILLUMINATION. 9 
 
 should be placed towards the left-hand side of the 
 microscope. But the best way to avoid injuring the 
 sight would be to use both eyes for viewing the 
 objects in turn, although most microscopic observers 
 make use of one eye only for this purpose. 
 
 The structure of many transparent objects can be 
 best seen when the mirror is turned more or less 
 obliquely to one side, so as to view them by oblique 
 light, as it is called : we shall refer to this point here- 
 after. 
 
 As a rule, objects are best seen by transmitted 
 light, or as transparent objects, although it is well to 
 examine objects under both kinds of illumination, 
 i. e. by transmitted and reflected light. 
 
 If during the use of the microscope, after removing 
 the eye from the instrument, the impression of the 
 light remains perceptible to the sight, the light used 
 has been too strong, or its action too long continued ; 
 and the instrument should be at once laid aside for a 
 time. 
 
10 MOUNTING. 
 
 CHAPTER II. 
 
 THE MOUNTING OF OBJECTS. 
 
 THE mounting or " putting up " of microscopic ob- 
 jects signifies their preparation in such way that they 
 may be preserved for future reference and observation. 
 
 As a general rule, objects should be mounted in 
 that manner by which their structure is best and 
 most clearly shown; but in certain instances the 
 objects are mounted so as to make their structure 
 difficult of detection, that they may form test-objects 
 of the power and quality of the microscope. 
 
 Some objects require to be mounted in the dry 
 state, while others are best mounted in liquid ; some 
 again as opake, others as transparent objects : these 
 must be considered separately. 
 
 Dry opake objects were formerly mounted by gum- 
 ming them upon small coin-shaped pieces or disks of 
 cork, blackened upon the surface with a mixture of fine 
 lamp-black and thin warm size, laid on with a hair- 
 pencil. They were kept in a drawer, to the bottom 
 of which a sheet of cork was glued, the disk being 
 transfixed by the pin, so that the free or projecting 
 pointed end of the pin could be thrust into the sheet- 
 cork. This plan may still be adopted in the case of 
 common objects, as seeds, &c. ; but it is objectionable, 
 on account of the facility with which the bare objects 
 are knocked off or injured by dust. 
 
 Hence dry opake objects are usually mounted in 
 such manner as to be enclosed in a cell, the sides 
 being formed by a ring of glass-tube or cork, or a 
 square piece of leather, cardboard, or paper, with a 
 hole cut or punched out of the middle. The glass 
 rings are best ; but as they are expensive, some of the 
 
DRY OPAKE OBJECTS. 11 
 
 other substances are generally used. The size and 
 thickness of the material from which the rings are 
 made must obviously vary according to the size and 
 depth of the object. The rings are cemented to the 
 middle of ordinary slides; and it is best to keep a 
 number of them ready prepared. The cementing 
 material must vary according to the nature of the 
 ring used. If this consists of glass, Canada-balsam 
 or marine glue is best. In using the former, the ring 
 is gently heated over the flame of the spirit-lamp, and 
 a thin layer of the balsam applied to its upper or 
 under surface, by means of an iron wire with a little 
 balsam on its end ; it is next warmed over the spirit- 
 lamp, so that the surface is entirely and evenly coated. 
 A clean slide is then slightly heated, the ring laid 
 upon it, and gentle pressure is used to squeeze out 
 the excess of balsam ; and the slide is kept at a gentle 
 heat, until on cooling the balsam becomes so hard as 
 not to be indented with the finger-nail. Marine glue 
 is applied in the same way as the balsam, except that 
 prolonged heat is not required to harden it, for it be- 
 comes hard on cooling. The balsam may also be 
 replaced by black japan or asphalte. 
 
 The pieces of cork, leather, or paper are best 
 fastened to the slides with solution of shellac or 
 sealing-wax in methylated alcohol, or with white 
 hard varnish. 
 
 When the ring or piece has been firmly fixed to 
 the slide by either of the above cementing materials, 
 so as to form the sides of the cell, the bottom is 
 to be covered with a piece of black paper, cut to fit 
 it exactly, and fastened to the surface of the slide 
 with a little gum, or of either of the above varnishes. 
 As soon as this is thoroughly dry, the upper surface 
 of the cell-wall, whether of glass or cork, &c., is 
 thinly covered with varnish, and a clean thin-glass 
 cover laid upon it, and very lightly pressed; the 
 object is then permanently preserved. 
 
12 MOUNTING. 
 
 The main points to be observed are, that the object 
 and varnish are completely dry, and that the cell is 
 thoroughly closed. If the latter be not the case, 
 more varnish must be applied to any little openings 
 which may have been left ; and it is better to apply 
 the varnish in very small quantities at a time, the 
 application being renewed as soon as the previous 
 layer is quite dry. 
 
 Dry transparent objects are usually small and deli- 
 cate; for, unless they are so, their structure cannot 
 be well seen. In mounting these, a square piece of 
 note-paper or tracing-paper, with the centre cut out, 
 may be fastened to a clean slide with a little paste, 
 gum, or shellac varnish. When this is thoroughly 
 dry, the object is placed in the vacant space, a clean 
 dry cover laid on, and the varnish applied by means of 
 a hair-pencil to the edges in very small quantities. 
 This will run in between the under surface of the 
 edges of the cover and the upper surface of the paper, 
 and when dry will cement the two together. 
 
 Supposing that the object is so delicate that it 
 cannot be removed from the surface of a slide, if it 
 will not be injured by heat, a good plan is to draw a 
 square or circle around the object with a little black 
 japan, then to heat the slide gradually until the japan 
 is not indented with the finger-nail when cold. A 
 clean slide is then laid upon the ring of japan, 
 the whole again gently warmed, until the varnish is 
 softened, and the cover lightly pressed so as to be in 
 contact all round with the varnish. The slide must 
 then be rapidly cooled, by being laid upon a piece of 
 metal, which prevents the varnish from running in so 
 as to spoil the object. 
 
 Many dry transparent objects can be preserved by 
 mounting in Canada balsam. This is the best pro- 
 cess for mounting objects in general; but only those 
 can be so preserved which are not injured by drying, 
 and which are not rendered too transparent by the 
 
DRY TRANSPARENT OBJECTS. 13 
 
 balsam. If the object to be mounted in balsam be 
 small, it is thoroughly dried, and then a drop of oil 
 of turpentine added to it upon a slide ; the slide is 
 then gently warmed, which causes the turpentine to 
 evaporate. When this has nearly all evaporated, a 
 drop of balsam is allowed to fall upon the object from 
 the end of a wire held at a distance above the flame 
 of a spirit-lamp. A warmed cover is next laid upon 
 the balsam, and gentle pressure applied until the 
 cover is sufficiently depressed. The slide is then 
 kept at a gentle heat until the balsam is quite hard 
 when cold. The superfluous portions may be re- 
 moved with the point of a knife, and any residues 
 cleaned off with turpentine or a little benzole on a 
 cloth. 
 
 Another way consists in laying a cover upon the 
 dry object on a slide, adding a drop of turpentine, 
 and warming the whole over a spirit-lamp until all 
 air-bubbles are displaced, then continuing the appli- 
 cation of the heat until most of the turpentine has 
 evaporated. A drop or more of the balsam may next 
 be applied to the edge of the cover, when it will run 
 in and mix with the turpentine. The whole is then 
 gently heated until the balsam is hard when cold, 
 more balsam being added if necessary, to replace the 
 turpentine which has evaporated. 
 
 When the objects are large, they should be pressed 
 as flat as possible without injury between two slides, 
 being retained until dry by enclosure between the 
 prongs of an American clothes-peg; or the slides 
 may be fastened at the ends by sealing-wax. When 
 perfectly dry, the object should be immersed in tur- 
 pentine, kept in a common gallipot, until all the air- 
 bubbles have been entirely displaced, and the object 
 appears very transparent. It is then removed from 
 the turpentine with forceps, drained, laid upon a 
 slide, and melted balsam dropped upon it until it is 
 quite covered. A clean dry slide is then laid upon 
 
 c 
 
14 MOUNTING. 
 
 its surface, and the two slides gently pressed together, 
 the two slides fixed at the ends by sealing-wax, and 
 the whole allowed to cool and dry. If requisite, more 
 balsam is added to fill up any vacuities. When the 
 balsam has become hard, the excess is cleaned away 
 with a knife and turpentine, and the object is per- 
 manently mounted. 
 
 If the object should be spoiled by the presence of air- 
 bubbles, the slides and object should be immersed in 
 turpentine or methylated alcohol, until the whole of 
 the balsam is dissolved ; the remounting may then 
 be proceeded with as at first. If the slides have 
 been immersed in the alcohol (which is the quickest 
 method), the object must be soaked in turpentine 
 before the balsam is reapplied. 
 
 If, after an object has been mounted in balsam, on 
 applying heat, bubbles resembling air-bubbles should 
 be formed, the object must not be considered as 
 spoiled ; for these are merely bubbles of the vapour of 
 turpentine, and will disappear spontaneously after a 
 little time. 
 
 A quick way of mounting in balsam is to drop the 
 melted balsam at once upon the dried object ; but as 
 air-bubbles are very apt to be produced in this way, 
 the beginner had better previously apply the tur- 
 pentine. 
 
 As balsam is very viscid, and adheres firmly to 
 everything with which it comes in contact, some 
 care is required in its use. Young microscopists 
 very generally manage to soil the microscope, tables, 
 chairs, papers, books, and even their clothes with it. 
 It may be easily cleaned off, however, with turpentine 
 or benzole. 
 
 Moist objects are best preserved, whenever prac- 
 ticable, in glycerine. There are, however, two im- 
 portant objections to its use : one is, that it makes 
 objects very transparent; the other is, that it often 
 -wrinkles and distorts them, by withdrawing their 
 
MOIST OBJECTS. 15 
 
 watery contents. Hence only those objects can be 
 preserved in glycerine, which are not too transpa- 
 rent, and which are sufficiently firm to resist the ten- 
 dency to collapse. 
 
 When the objects are tolerably flat, and suffi- 
 ciently firm to bear the pressure of the cover, they 
 may be mounted by adding a small quantity of gly- 
 cerine to them lying on a slide; the cover is then 
 applied, and a little of the cement mentioned below 
 applied warm with a hair-pencil around the edges of the 
 cover to fasten it to the slide. Care is required that 
 the glycerine applied be no more than sufficient ; for 
 wherever it has touched the cover or the slide, the 
 cement will not adhere. Superfluous portions may 
 be sucked up with a piece of clean moist sponge or a 
 corner of blotting-paper. 
 
 When it is required to mount a large number of 
 objects in a short time, the cement need only be 
 applied to two opposite sides of the cover, leaving the 
 other two sides open. 
 
 When the objects require to be protected from the 
 pressure of the cover, the sides of a cell must be 
 made with the cement or black japan upon the slide 
 before the cover is applied, a further quantity being 
 used to close the cell as usual. 
 
 A very strong solution of chloride of calcium may 
 be used for the same purposes and in the same way 
 as the glycerine. It has the advantage of not making 
 the object so transparent; but it has the disadvan- 
 tage of crystallizing slightly in a dry atmosphere. In 
 most cases, I prefer it to glycerine. 
 
 A large number of interesting objects cannot, how- 
 ever, be preserved in either glycerine or chloride of 
 calcium, without their value being impaired by the 
 cause mentioned above. Many kinds of liquid have 
 been recommended for preserving these, all agreeing 
 mainly in being inefficient. The objection to them 
 is, that they are evaporable ; and after the object has 
 
16 MOUNTING. 
 
 been mounted for some time, the liquid creeps be- 
 tween the cement and the slide or cover, at some spot, 
 and evaporates ; and if the cement be not quite hard, 
 the inner and more liquid portion of it runs into the 
 cell, and spoils the object. A solution, containing a 
 grain of salt and a grain of alum to the ounce of dis- 
 tilled water, is as good as any other ; or simply distilled 
 water in which a piece of camphor has been kept. 
 In use, the cell is first formed by making a circle or 
 outline square on the slide with black japan, and 
 heating this carefully until it becomes solid when cold. 
 The object is then laid in the cell, the liquid added, 
 and the cover applied, any excess being removed with 
 blotting-paper. The cell is to be closed with old 
 black japan or gold-size, applied round the margins 
 of the cover with a hair pencil. A second and a third 
 layer of the varnish may be applied upon the first, 
 when it has become hard outside. Although black 
 japan and gold-size are generally used for the cement, 
 I prefer that mentioned below. 
 
 When large preparations are mounted in liquid, 
 the cell-walls are either formed of glass rings, or 
 they are built up with four oblong pieces of glass, 
 cemented to the slide and to each other with marine 
 glue. A very good preservative liquid for large spe- 
 cimens is a solution of chloride of zinc, in the pro- 
 portion of 20 grains to the ounce of distilled water. 
 A mixture of spirit of wine and water, in the propor- 
 tion of 1 part to 2, or 1 to 4, is often used for the 
 same purpose. 
 
 When preparations are mounted, the cement and 
 the adjacent parts of the slide and cover should be 
 coated with a solution of sealing-wax in spirit, which 
 hardens the exterior of the cement. 
 
 The cement above alluded to is made by melting 
 together 5 parts of rosin, 2 parts of balsam, 1 part of 
 bees' -wax, and 1 of red ochre. The cement is best 
 kept in a little metallic cup, and melted over a spirit- 
 
MAGNIFYING POWER. 17 
 
 lamp when used. It should be applied while hot, 
 with a hair pencil ; and cools very quickly. 
 
 The preservative liquids should be kept in corked 
 bottles, a hair pencil being fixed into the under part 
 of the cork ; or, what is better, in stoppered bottles, 
 the stopper being prolonged to a point nearly reach- 
 ing the bottom of the bottle. 
 
 As soon as the preparations are mounted, they 
 should be labelled, the labels being kept ready gum- 
 med. The balsam should be kept in a capped bottle, 
 such as is used for holding solutions of gum, with an 
 iron wire for removing portions as required. By 
 keeping, the balsam becomes thicker; it may be 
 thinned by the addition of oil of turpentine, and the 
 application of a gentle heat. 
 
 The black japan, &c., may be procured at any oil- 
 shop; the glass rings, cell-sides, covers, &c., from 
 Mr. Norman, 178 City Road, or of the microscope- 
 makers. 
 
 Mounted objects should be kept in shallow drawers, 
 and be laid flat not standing on edge. 
 
 Magnifying power. Before entering upon the con- 
 sideration of the objects themselves, a word or two 
 must be said upon the magnifying powers. In the 
 plates of this work, the serial number of each figure 
 is expressed by large numerals placed above the 
 objects, while the number of times the object is mag- 
 nified is indicated by small numerals placed beneath. 
 The latter must be understood to express the number 
 of times the drawing is larger than the object in one 
 dimension. Thus, considering fig. 13, Plate I. to be 
 an inch in width (for it is really somewhat less) , being 
 magnified 150 times in the direction of the width, the 
 object itself is about T joth f an ^ ncn ^ n s ^ ze > an ^ ^ 
 is represented magnified 150 times linear, or 150 dia- 
 meters, as it is called. 
 
 A knowledge of the number of times the object is 
 magnified is of the greatest importance in making 
 
 c 3 
 
18 MAGNIFYING POWER. 
 
 use of the drawings; for, without it, the observer will 
 be unable to apply such a magnifying power of the 
 microscope as will enable him to see the structural 
 appearances figured in the drawings. 
 
 The observer must also be acquainted with the 
 magnifying powers of his microscope with the various 
 object-glasses and eye-pieces. These are usually 
 given when the instrument is purchased. Or they 
 may be determined approximative^ thus : An ivory 
 scale, with y^th of an inch engraved upon it, is 
 placed on the stage, and viewed as an opake object, 
 both eyes being kept open ; and the size of the image 
 of one of the gradations is measured with compasses, 
 upon the stage as seen with that eye which is not 
 applied to the eye-piece. The number of T ^o tns f 
 an inch contained in the measure obtained with the 
 compasses represents the magnifying power. Thus, 
 supposing the image of the T ^o tn f an mcn on the 
 scale appears magnified to the length of 1 inch on 
 the stage ; the magnifying power is 100 diameters, or 
 100 times linear. This proceeding is difficult to any 
 one unaccustomed to the use of the microscope, yet 
 by practice it becomes very easy. Other methods, 
 which require the use of the camera lucida, are given 
 in the Micrographic Dictionary. 
 
VEGETABLE ELEMENTS AND TISSUES. 19 
 
 CHAPTER III. 
 
 VEGETABLE ELEMENTS AND TISSUES. 
 
 WE may now enter upon the consideration of the 
 microscopic structure of objects, beginning with those 
 which are derived from the vegetable kingdom, as 
 they are more easily procured and prepared for exa- 
 mination than those belonging to the animal king- 
 dom j moreover they are not so transparent, and 
 hence are more readily distinguished under the micro- 
 scope, which is of importance in the case of an un- 
 practised observer. 
 
 Cells. The elements of which all plants consist 
 are cells. Cells, in their simplest condition, are 
 microscopic, rounded, colourless, closed sacs or vesi- 
 cles, resembling small bladders (Plate I. fig. 2), and 
 consist of a thin, transparent, colourless, vegetable 
 skin or membrane (a) called the cell-wall. The cells 
 are well seen in a little of the pulp of an apple (fig. 2) , 
 or in a section of almost any soft part of a plant. 
 A high power is usually required to show them dis- 
 tinctly, on account of their minute size. The outline 
 of the cells is seen to be double, one line indicating 
 the inner, the other the outer, surface of the cell-wall, 
 the space between the two lines corresponding to the 
 thickness of the cell-wall. 
 
 In the pulp of the apple, the cells are loosely con- 
 nected, and so retain their rounded form; but in 
 most parts of plants, the cells become crowded and 
 squeezed together, from their ordinary or normal 
 expansion being limited in certain directions, so as 
 mutually to alter each other's shapes. The sides 
 then lose their originally rounded form and outline, 
 becoming more or less straight (PL I. figs. 1 & 4), 
 
20 VEGETABLE ELEMENTS AND TISSUES. 
 
 the cells at the same time mostly adhering to each 
 other, so as to be separated with difficulty. 
 
 The forms thus produced are various and inter- 
 esting, and have all received names by which they 
 are distinguished. They are described in works on 
 botany in two ways according to the outline (which 
 is the most common, as this expresses the appear- 
 ance usually presented in sections and on the surfaces 
 of vegetable structures), or according to the entire 
 or solid form, which it is often a difficult matter to 
 determine. 
 
 Cellular tissue. Cells aggregated thus form a 
 tissue, which is called cellular tissue or parenchyma 
 (Trapa, among, and ey^v/jLa, poured substance), be- 
 cause it fills up the interstices of the other tissues 
 of plants. 
 
 In technical descriptions, the cell- structure is often 
 left out of consideration ; and bodies composed of 
 parenchymatous tissue are described as being reticu- 
 lated or netted, because the united sides of the cell- 
 walls appear as a network covering the surface. 
 
 It must be understood that parenchymatous cells 
 are such only as have the three dimensions of solidity 
 (viz. the length, breadth, and depth) nearly equal. 
 
 Intercellular passages. The observer will not have 
 examined many sections of cellular tissue,, without 
 noticing certain irregular black lines running be- 
 tween the cells, as in a piece of a Geranium- (Pelar- 
 gonium-) leaf (PL I. fig. 1). These lines arise from 
 the existence of passages between the cells, contain- 
 ing air; and they are called intercellular passages. 
 By gently warming a section containing them in 
 water over a spirit-lamp, or by moistening the section 
 with a drop of spirit, the passages will be filled up 
 with the liquid, so as to become transparent. When 
 the intervals between the cells are larger and broader, 
 they are called intercellular spaces. 
 
 So far, cells have been considered simply in regard 
 
CHLOROPHYLL. 21 
 
 to their form, as vesicles, either rounded or altered in 
 shape by mutual pressure. We have now to notice 
 the matters contained within the cells, or the cell- 
 contents. 
 
 Cell-contents. 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 (PI. I. fig. 2 b). And within this nucleus is 
 often to be seen another smaller body, frequently 
 appearing as a mere dot, called the nucle'olus. 
 
 The nucleus is imbedded in a soft substance, which 
 fills up the entire cell (PI. I. fig. 2 c) ; this is the 
 pro'toplasm (TT/JCOTO?, first, TrXaer^a, formative sub- 
 stance) . As it is very transparent, it is readily over- 
 looked ; 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, as in the lower cell of fig. 2. The proto- 
 plasm in some cells is semisolid and of uniform con- 
 sistence, while in others it is liquid in the centre, the 
 outer portion being somewhat firmer and immedi- 
 ately 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 "proto- 
 plasm " and ' ' primordial utricle " are, however, used 
 by some authors synonymously. 
 
 The protoplasm is the essential part 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. 
 
 Chlorophyll (^Xwpo?, green ; (biiXXov, leaf) . On 
 examining a section of any green part of a plant, as 
 the green substance of a Geranium- (Pelargonium-) 
 leaf, it will be seen that the green colour does not 
 arise from the whole substance being coloured, as 
 
22 VEGETABLE ELEMENTS AND TISSUES. 
 
 appears to be the case to the naked eye, but from the 
 presence of little grains or granules of a green colour- 
 ing-matter in the protoplasm of the cells. This green 
 matter is called chlorophyll. If the cells be crushed, 
 the granules will escape, and can be examined in the 
 separate state. Chlorophyll is most abundant in 
 those parts of plants which are exposed to the light. 
 
 Starch. In many cells of plants, particularly those 
 which have attained their full growth, other granules, 
 larger than those of chlorophyll, and colourless, are 
 met with ; these are the starch- granules (PL I. fig. 3). 
 They are usually rounded or oblong, and exhibit on 
 the surface a number of rings, one within the other, 
 or concentric, as it is called. In the centre of the in- 
 nermost ring is a black dot or streak, arising from 
 the presence of a little pit or furrow, and called the 
 hilum. 
 
 The starch- grains may be readily seen within cells 
 in a thin section of a potato (PL I. fig. 4) ; here they 
 are very numerous, and larger than in most other 
 plants. A separate grain is represented in fig. 3. 
 
 The appearance of rings in the separate grains 
 arises from the starch -granules being composed of 
 numerous concentric coats or layers, like those of an 
 onion. 
 
 A very simple and striking method of determining 
 whether any granule is composed of starch or not, 
 consists in adding to it, when placed in water on a 
 slide, a drop of solution of iodine. As soon as this 
 touches the granule, it assumes a beautiful purple 
 . colour, the depth of tint depending upon the quantity 
 of the iodine-solution ; if this be very considerable, 
 the granule appears almost black. The section of 
 potato forms a very interesting object when mois- 
 tened with the iodine- solution, the starch-granules 
 becoming beautifully coloured, whilst the cell-wall re- 
 mains colourless, and the protoplasm becomes yellow. 
 
 The form of the starch-granules differs in differ- 
 
STARCH. 23 
 
 ent plants, so that the kind of plant from which 
 starch has been derived may be distinguished by 
 attention to the size, form, and structure of its starch- 
 granules. Thus, the granules represented in PL I. 
 fig. 3, which it will be noticed are all drawn under 
 the same power, are derived from different plants, 
 a being those of wheat-flour, in which the hilum is 
 obscure, and the rings faint ; b is a granule of West 
 Indian arrowroot, in which the hilum forms a trans- 
 verse crack ; c is a granule of potato-starch, in which 
 the hilum is a dot, and the rings are very distinct; d re- 
 presents the compound granules of the oat, the separate 
 granules being figured below ; e is a granule of lentil- 
 starch, with its long dark hilum and elegant oval 
 concentric rings ; and / represents a compound and 
 separate granule of rice-starch. It will be noticed 
 that the granules of oat- and rice- starch are angular, 
 as it is called. 
 
 The knowledge of the peculiar forms of the starch- 
 granules is important in a practical point of view, for 
 it enables us to recognize them when mixed as an 
 adulteration with other substances, and also to distin- 
 guish the different kinds of starch from each other. 
 Thus table-mustard, as it is called, is principally com- 
 posed of the cheaper wheat- or pea-flour, which is 
 easily recognized by the structure of the starch-grains. 
 Arrowroot is considerably dearer than potato-starch ; 
 hence in trade the latter is fraudulently sold for the 
 former, the adulteration being detected with diffi- 
 culty by the eye, but easily under the microscope. 
 Again, rice is largely mixed with wheat-flour, as it 
 makes inferior flour into very white bread ; and this 
 may also be readily detected under the microscope. 
 The reader can now understand how valuable the 
 microscope is in detecting adulterations, with a know- 
 ledge of the various forms and structures of sub- 
 stances, especially with the aid of a few chemical 
 tests. 
 
24 VEGETABLE ELEMENTS AND TISSUES. 
 
 Starch- grains are altered by boiling in water, be- 
 coming swollen and often changed into curious forms, 
 the rings becoming faint or disappearing. If a piece 
 of boiled potato be examined, the starch- granules 
 will seem to have vanished from the cells, which are 
 swollen and covered with an irregular kind of net- 
 work. The network consists of parts of the proto- 
 plasm situated in the interstices of the starch-granules, 
 and solidified or coagulated by the heat. On crush- 
 ing the cells by pressing upon the cover, the starch- 
 granules will escape, swollen and partly fused toge- 
 ther ; but they may easily be recognized as consist- 
 ing of starch by the iodine test. 
 
 The granules of " tons les mois " starch are par- 
 ticularly well adapted for showing the concentric 
 rings, the granules being about twice as large as those 
 of the potato. 
 
 Starch-granules are best examined in water; and a 
 small quantity only of the starch must be placed on 
 the slide, if the structure of the granules is to be 
 seen clearly. They may be mounted in glycerine, 
 although this makes them very transparent. 
 
 To those who possess a polariscope, starch-gra- 
 nules are particularly interesting, as they exhibit a 
 black cross, and, with a plate of selenite laid beneath 
 the slide, a beautiful play of colours. 
 
 In addition to the starch and chlorophyll, the 
 cells of plants contain other matters, as gum, sugar, 
 &c. ; but as they are dissolved in the cell-liquid, they 
 are not visible. In the cells of certain plants, how- 
 ever, spherical globules, with light centres and black 
 outlines, will be met with : these consist of oil. 
 
 Raph'ides. Lastly, occurring in the cells of plants, 
 especially such as are soft and juicy (succulent), will 
 be found minute, hard, colourless crystals, called 
 r aphides (pa$>l<$ } a needle) . These are most frequently 
 needle-like or acicular (acus, a needle), but sometimes 
 prismatic or rod-like with flat sides; they are also 
 
WOODY TISSUE. 25 
 
 not unfrequently grouped into little tufts. They 
 may be readily found in a piece of the stem of 
 garden-rhubarb (PL I. fig. 5 a), or of the common 
 balsam. 
 
 Porous and spiral cells. The walls of the cells of 
 cellular tissue are sometimes covered with little 
 dots (PL I. fig. 11 a), or slit-like markings ; the cells 
 are then called porous cells. A specimen of them 
 may be obtained from a section of the pith of the 
 elder (Sambucus nigra). 
 
 Sometimes cells exhibit the appearance of a spiral 
 line marking their walls, as if a little bell-spring were 
 coiled up in them (PL III. fig. 2 a). These are called 
 spiral cells, or spiral fibrous cells, and the tissue 
 formed by them is called fibro-cellular tissue. 
 
 We now leave the cells of ordinary cellular tissue, 
 to examine those in which the dimension of length 
 predominates, so that they form tubular cells ; and 
 first of those required to possess strength and firm- 
 ness, combined with flexibility. These qualities are 
 met with in the cells constituting 
 
 Woody tissue. Of this there are two forms, called 
 respectively wood-cells and woody fibres. 
 
 The wood-cells are moderately long, more or less 
 tapering and overlapping at the ends ; and the cell- 
 walls are thickened, so as to possess considerable 
 firmness. These cells are found in the wood of stems, 
 as in the white woody portion of an ash stick, that of 
 a lime-tree, the stem of a Chrysanthemum, &c. (PL I. 
 fig. 6) . They are closely packed, and the tissue formed 
 by their union is called prosenchyma (TT/OO?, close, 
 ey^y^a, tissue). 
 
 In the other kind of woody tissue the cells are 
 very long and slender, strong, yet flexible, gradually 
 tapering at the ends, where they overlap each other ; 
 and they have thick walls, so that, when divided trans- 
 versely, the cavity appears almost filled up (PL I. 
 figs. 5 d, 9, & 7 b) . This tissue is called woody fibre 
 
26 VEGETABLE ELEMENTS AND TISSUES. 
 
 or pleurenchyma (jr\evpa, rib, e^vfjua), from its 
 strength. 
 
 The walls of the cells of woody tissue are often 
 covered with dots, either simple or with an inner dot 
 (PL I. fig. 6 b, fig. 11 b), or with streaks (PL I. fig. 6 a) 
 or with a spirai fibre (fig. 11 b, c), either alone or 
 with dots also. 
 
 This tissue is of great importance in plants, from 
 its strength and flexibility; it forms a considerable 
 part of the veins of leaves, the inner bark (liber), and 
 of the wood of the stems of trees. It is also very useful 
 to man : for it constitutes hemp, of which rope and 
 string are made ; flax, of which linen is made ; cocoa- 
 nut fibre ; bast, used by gardeners for tying up plants, 
 which is the inner bark of the lime ; and jute, which 
 is the inner bark of an Indian lime-tree. 
 
 In the white woody part of the stems of trees be- 
 longing to the fir-order (Conif erse), as a piece of deal 
 or pine, which is mainly composed of wood- (prosen- 
 chymatous) cells, the cells exhibit rows of minute 
 circular markings (PL I. fig. 10). These were for- 
 merly supposed to be solid bodies or glands ; hence the 
 tissue is still sometimes called glandular. Within the 
 outer ring of each marking is an inner central dot, or 
 sometimes an oblique streak. The side view of the 
 cells (PL I. fig. 8 a), which is seen in a tangential 
 section, shows that the markings are minute pits, 
 each being opposite to one of an adjacent cell, and 
 sunk inwards towards the centre of the cell, the inner 
 dot or streak being a thinner portion of the cell-wall. 
 This glandular tissue of the Coniferse is interesting as 
 forming a test-object for the defining power of the 
 microscope, which should show the two rings sharply 
 and free from colour ; the section of the wood should 
 be examined as a dry transparent object. 
 
 The difference between the woody fibre and the wood- 
 cells of coniferous wood may also be seen well in a piece 
 of deal, as cut up for fire-wood. If the end of a stick of 
 
DUCTS. 27 
 
 this be examined with the naked eye, parts of brown 
 rings will be seen traversing the whiter portion of the 
 wood. These brown rings consist of woody fibre ; the 
 white portion of wood- cells. On making a very thin 
 transverse section, the interior of the woody fibres is 
 seen to be almost entirely filled up (PI. I. fig. 7 b), 
 while the cavity of the wood- cells is much more open 
 (PL I. fig. 7 a) the former also contain globules of 
 turpentine. 
 
 It must be remarked here that some botanical 
 authors include both forms of woody tissue under the 
 term prosenchyma. But, as we shall see hereafter, 
 the form of the prosenchymatous cells being some- 
 times used as a character for distinguishing the cells 
 of leaves, to which the term pleurenchymatous cells 
 would be inapplicable, the above distinction will be 
 found important. 
 
 Vessels } vascular tissue. In the next form of tubu- 
 lar cells, these are broader and softer than the cells of 
 woody tissue, thin-walled, and the ends pointed ; and 
 their walls exhibit spiral or ring-like markings, or 
 rows of dots (PI. I. fig. 5 c, e, b) , indicating the existence 
 of one or more spiral fibres or rings. When the vessels 
 contain spiral fibres, they are called spiral vessels 
 (PL I. fig. 5 c) ; when they contain ring-shaped por- 
 tions of fibre, they are called annular (an'nulus, a 
 ring) vessels (PL I. fig. 5 e) ; and when the spaces 
 between the fibres are partly filled up, leaving only 
 dots, the deposit forming a kind of network, we have 
 a reticulated (rete, a net) vessel (PL I. fig. 5 b). This 
 tissue can easily be obtained from a piece of cooked 
 rhubarb, the stem of a balsam, or from any soft- 
 stemmed plant. Vessels very frequently contain air. 
 
 Ducts. The tubular cells forming ducts (PL I. 
 figs. 5 b, lie) are large, more or less flattened or blunt 
 at the ends (truncated) ; and the cell-membrane at 
 first closing the ends is often removed or absorbed, so 
 that the ducts communicate with each other, to allow 
 
28 VEGETABLE ELEMENTS AND TISSUES. 
 
 of the free passage of the sap through them. Their 
 walls are invariably covered with markings, consisting 
 of either simple or bordered dots, resembling those 
 met with in the preceding forms of tissue. The ducts 
 are often easily recognizable with the naked eye, 
 in transverse sections of stems, by the large pores 
 which they form in the wood. These may be well 
 seen in a section of a piece of cane. The tissue com- 
 posed of dotted ducts is called bothren'chyma (ftoOpos, 
 pit) ; but the term is principally applied to those 
 ducts in which the dots are simple, i. e. have no inner 
 dot. 
 
 The structure of the above forms of tissue may be 
 best understood in relation to their development. It 
 has been stated that the essential part of the cell is 
 the protoplasm. As cells grow older, new matter is 
 deposited by the protoplasm upon the inner surface 
 of the cell-wall, either to a small extent, evenly and 
 uniformly, as in ordinary parenchyma, or unevenly, in 
 the form of spiral layers, forming fibres or bands, 
 leaving bare spaces, where the original cell-wall exists 
 alone. The matter thus deposited is called secondary 
 deposit, the original cell- wall being the primary de- 
 posit. When the secondary deposit covers the in- 
 terior of the cells except at certain slit-like spaces, we 
 have the appearance figured in PL I. fig. 6 a). When 
 the deposit forms a spiral fibre, or a series of rings, 
 we have the spiral or annular vessel or duct. And 
 when the interspaces between the coils of a close 
 spiral fibre are filled up except at certain spots, we 
 have the dotted or reticulated vessel or duct. 
 
 In many instances, these deposits are present to- 
 gether : thus, sometimes the outermost deposit leaves 
 rounded pits or dots, while an inner portion forms a 
 spiral fibre (PL I. fig. 11 b) or one layer leaves simple 
 rounded pits, while the other leaves smaller slits or 
 dots placed opposite the former (PL I. fig. 6 b). 
 
 In some cells the cavity is almost entirely filled up 
 
CELL-FORMATION. 29 
 
 by secondary deposit, which, leaves minute canals 
 radiating from a small cavity in the centre to the cir- 
 cumference, as seen in the transverse section of a 
 plum-stone (PL I. fig. 56) ; here the canals appear as 
 dark lines. In others, again, the secondary deposit 
 forms several distinct layers, leaving channels very 
 similar to those of the last ; an example is met with 
 in the gritty tissue of the pulp of a pear. 
 
 The obvious use of the pits and channels in the 
 above tissues is to preserve the permeability of the 
 walls of the elements, which would be destroyed if 
 the walls were equally thickened all over. 
 
 Cell-formation. New cells are formed by the 
 division of old or parent cells. The actual process 
 of division is difficult to observe, as it requires pro- 
 longed observation ; but cells are often met with in 
 all stages of division, of which some instances will 
 be pointed out hereafter. The cell-division takes 
 place in two ways, either according to the endo- 
 genous (evBov, within, ryevvaw, to produce), or the 
 exogenous (efo>, outside, yevvda)) method. The 
 manner in which the division takes place in the 
 former is this -. At first a slight indentation or con- 
 striction of the protoplasm occurs at the line of 
 division ; this deepens until the protoplasm is com- 
 pletely divided. The freshly divided surfaces then 
 become coated with a new portion of cell-wall, so as 
 to make two or more new cells, which either remain 
 in contact or separate from each other. In some 
 cases, the divided portions of protoplasm become 
 coated all over with new cell- walls. 
 
 In the exogenous process, a portion of the proto- 
 plasm protrudes from the surface of the cell, carry- 
 ing the cell-wall before it, so as to form a little bud- 
 like body ; this is next cut off at its point of junction 
 with the parent-cell, and coated, as in the first case, 
 with a new cell-wall, so as to form a new cell. 
 
 Preparation. In examining the vegetable ele- 
 
 D3 
 
30 VEGETABLE ELEMENTS AND TISSUES. 
 
 ments and tissues, very thin sections must be made 
 with a razor or thin sharp knife ; these are then to 
 be placed in a little water on a slide. As the struc- 
 tures are all minute, the distinctness with which they 
 are seen will mainly depend upon the proper thin- 
 ness of the sections. When sections of dry stems 
 are to be examined, the black margins of the air- 
 bubbles contained in the cells often render the struc- 
 ture indistinct ; these must therefore be displaced by 
 first wetting the tissue with methylated alcohol, and 
 then adding water to it in a watch-glass or on a 
 slide ; or the tissue may be soaked in warm water for 
 some hours : and this is mostly requisite in preparing 
 thin sections of dry tissues. 
 
 Attention must also be paid to the manner in 
 which the section is made, or the direction in which 
 the portion of the plant is cut. There are three im- 
 portant directions which must be distinguished, pro- 
 ducing transverse, longitudinal, and tangential sec- 
 tions. If the cuts be made across the length of a 
 stem, for instance, the section is called transverse. 
 If the cuts be made in the direction of the length, 
 through the centre, the section is longitudinal ; and 
 if the cuts are made in a direction parallel to a line 
 running down the centre of the stem, but nearer its 
 margin, it is a tangential section. It is scarcely 
 necessary to mention that an oblique section is 
 intermediate between a transverse and a longitudinal 
 section. 
 
EPIDERMIS. 31 
 
 CHAPTER IV. 
 
 VEGETABLE ORGANS. 
 
 THE vegetable elements and tissues which have been 
 described form, either separately or by their com- 
 bination in various ways, the organs of plants. To 
 these we shall now pass, and consider the structure 
 of the principal organs of the members of the vege- 
 table kingdom. 
 
 Leaves. Leaves in their simplest form consist of 
 a single sheet or layer of parenchymatous cells or 
 cellular tissue, an example of which may be found 
 in almost any moss (PI. III. fig. 30). The granules 
 of chlorophyll will often be very distinctly seen in 
 these cells. The first addition to this form of leaf is 
 a row or two of prosenchymatous cells running longi- 
 tudinally down the middle of the leaf, so as to form 
 a rudimentary vein or nerve. In other and more 
 highly developed leaves, the layers of cells are nume- 
 rous, and traversed by bundles of wood- cells, vessels, 
 and ducts (fibro-vascular tissue), forming the veins, 
 the entire surface being covered with a skin or mem- 
 brane, called the epidermis. 
 
 Epider'mis (eVl, upon, Se/^a, skin). This mem- 
 brane is composed of one or more layers of colourless, 
 closely packed cells (PI. I. figs. 13&28), the colour 
 it occasionally exhibits usually arising from some of 
 the underlying cells of the leaf being seen through 
 it, or remaining adherent to it when stripped from 
 the leaf. It is easily separated, by making a cut in 
 a soft leaf, and peeling it off with a fine pair of for- 
 ceps, or by soaking a leaf for some time in water 
 and then stripping it off. It must be remarked that 
 
32 VEGETABLE ORGANS. 
 
 the epidermis covers not only the leaves, but every 
 part of the plant. 
 
 Hairs. Arising from the epidermis are the hairs 
 of plants. These are thread-like or filamentous pro- 
 longations of the epidermis beyond the surface of the 
 leaf (PI. I. fig. 12), consisting of cells arranged end 
 to end. They are often branched, sometimes star- 
 shaped (stellate) (fig. 28), and present great varieties 
 in form, as shown in the figures, the plants from 
 which these were drawn being mentioned in the De- 
 scription of the Plates. Sometimes hairs terminate in 
 a little head (PL I. figs. 12 c, d, e\ the cell or cells 
 composing which secrete a colouring or a viscid sub- 
 stance ; they are then termed glandular. The hairs 
 of plants are particularly interesting to the micro- 
 scopic observer, not only on account of their curious 
 forms, but in connexion with the remarkable pheno- 
 menon of the circulation of the cell-contents, or 
 rotation, as it is called, observable in them. This is 
 difficult to be perceived by any one unaccustomed to 
 microscopic observation, because the particles by 
 which the motion of the cell-contents becomes evi- 
 dent are exceedingly minute ; but practice in the use 
 of a high power will overcome this difficulty. The 
 hairs which exhibit the phenomenon best are those of 
 the American Spiderwort (Tradescan'tia Virgin' ica\ 
 which is to be found in every garden. It may, per- 
 haps be recognized thus : The plant is about a foot 
 and a half high; the leaves are sword-shaped and 
 channelled, and the flowers are purple, in heads, and 
 \\ inch in diameter. The hairs are attached to the 
 sides of the stamens, towards the lower part or base. 
 The stamens should be carefully picked off with for- 
 ceps, and placed on a slide in a drop of water ; the 
 hairs should then be separated with the mounted 
 needles, and a cover applied. Under a low power, 
 the hairs are seen to be beaded or momTiform (momle, 
 a necklace), and of a fine purple colour (PL I. fig. 22). 
 
STINGS. 33 
 
 On applying a high power, as the J-inch, the indivi- 
 dual cells will come distinctly into view, and the 
 nucleus will be seen very clearly as a roundish granu- 
 lar mass (PI. I. fig. 23 a). On carefully examining 
 the cell-contents, delicate lines will be observed radi- 
 ating irregularly from the nucleus, some passing to 
 the top of the cells, while others run towards its 
 base, as in the figure ; and on very close inspection, 
 the portions of protoplasm of which these lines con- 
 sist, will be found to move slowly and steadily, the 
 motion becoming perceptible by means of the minute 
 granules of which the protoplasm consists. The 
 currents return at the ends of the cell, there being 
 no passage of the contents of one cell into the cavity 
 of either of those adjacent. During this examina- 
 tion, it will be noticed that the surface of the cell- 
 wall is striated with fine wrinkles. 
 
 It may be remarked that the hairs should be 
 taken from flowers which have only just opened ; for 
 this curious and inexplicable rotation is connected 
 with the growth of the cell ; and when this has at- 
 tained maturity, it no longer occurs. The phenome- 
 non may be observed in many other hairs of plants, 
 as those of common groundsel (Senecio vulgdris) 
 (PL I. fig. 12 a, b), and in the cells of the leaves of 
 some water-plants; but I must refer to the article 
 "Rotation" in the Dictionary for further information. 
 
 The most important variety of hair is that derived 
 from the Cotton-plant (a kind of Mallow), and form- 
 ing the cotton of commerce. These hairs spring 
 from the epidermis of the seeds. The cells com- 
 posing it are very long and soft, becoming flaccid 
 and easily bent when dry (PI. IX. fig. 13). 
 
 Stings. Stinging hairs or stings may be well 
 illustrated by reference to the common large nettle 
 (Urtica dioica). In this plant they consist of a thick- 
 walled cell, bulbous at the base, which is imbedded 
 in the epidermis (PL I. fig. 21), the pointed end being 
 
34 VEGETABLE ORGANS. 
 
 terminated by a very minute dilatation or knob. The 
 sting contains an acrid liquid, which escapes when 
 the little knob is broken off in wounding the skin, and 
 produces the well-known irritation. By the side of 
 the figure of the sting is represented the point of a 
 fine needle (fig. 20), showing that the expression 
 " sharp as a needle " has no force when microscopic 
 bodies are in question. 
 
 Stomata (oTo^a, mouth) . On viewing a strip of 
 epidermis, the observer will be sure to notice certain 
 oval or roundish bodies (PL I. fig. 13 a), composed of 
 mostly two kidney- shaped cells in apposition but 
 leaving a chink between them ; these are the stomata. 
 They communicate beneath with the intercellular pas- 
 sages, of which they may be considered the mouths ; 
 and by their agency a direct communication is esta- 
 blished between these passages and the air. The two 
 cells which guard the orifice are termed the " guard 
 cells." 
 
 Stomata are most numerous on the under surface 
 of leaves; they are entirely absent in plants growing 
 under water, and in most of the lower plants. In 
 many of the stomata, viewed in the ordinary way, the 
 air situated between the guard cells is indicated by 
 the black spot or dot present ; but after a time, or by 
 the application of a gentle heat to the slide, the air 
 becomes displaced by the water, and their structure 
 becomes very distinct. 
 
 In certain plants, the epidermis is imbued with 
 flint or sil'ica ; so that even when burnt to an ash the 
 stomata are still quite distinct. Examples of this 
 may be found in the stalk or culm of grasses, as in 
 straw, the shining epidermis of which is siliceous ; or 
 the epidermis of canes. Among the lower plants, 
 this peculiarity is especially curious in the species of 
 Equisetum, or mares'- tails. 
 
 The manner in which the veins of leaves are ar- 
 ranged is worthy of special attention, as it forms one 
 
STEMS. 35 
 
 of the characters by which the two leading divisions 
 of the Vegetable Kingdom are characterized. Thus 
 in one of these divisions the veins are branched, so 
 as to form a network throughout the leaf; the 
 plants with these netted veins, to which belong our 
 trees, shrubs, and most herbs, are the Dicotyledons, 
 or Ex'ogens ; while in the second division, the veins 
 run parallel to each other, being little or not at all 
 branched, and not forming a network. The plants 
 with parallel veins, among which are our grasses, 
 lilies, &c., are the Monocotyledons or En'dogens. 
 
 Stems. In the stems of plants, the tissues are 
 arranged round a centre; otherwise, in the sim- 
 pler and lower plants, they agree in structure with 
 leaves, the centre being occupied by some element 
 of fib ro- vascular tissue, as simple wood-cells, a few 
 vessels or ducts. 
 
 In the higher or flowering plants, the stem exists 
 in two distinct forms, corresponding to the differences 
 above noticed in the arrangement of the veins of the 
 leaves ; these must be considered separately. 
 
 In the Dicotyledons or Eocogens (PL I. fig. 36), the 
 centre of the stem, in a transverse section, is seen to 
 be occupied by the pith or medulla, which is repre- 
 sented in the figure by the innermost circle. Imme- 
 diately outside and around this is a narrow ring, in- 
 dicating the section of a sheath to the pith, and called 
 the medullary sheath. Next comes a broad ring of 
 wood of the first year's growth (fig. 36 a], traversed, 
 from the pith to the bark, by wedge-shaped paler 
 rays, termed the medullary rays. Outside the first 
 year's wood is the newer and paler wood of the second 
 year (b) ; and so on, a new ring of wood being added 
 outside the preceding layer for each year of growth 
 of the stem. 
 
 On the outer side of the wood is the inner bark or 
 liber (fig. 36 c) ; and outside this is the spongy outer 
 bark (d) , covered by its epidermis. 
 
36 VEGETABLE ORGANS. 
 
 These structures are of different composition, as 
 may be best seen in longitudinal sections. The pith 
 and the medullary rays consist of cellular tissue, the 
 cells being mostly rounded in the former, and more 
 closely pressed together and squarish in the latter. 
 The medullary sheath consists of vascular tissue ; and 
 the wood, of wood- cells traversed longitudinally by 
 bundles of vascular tissue and ducts, the latter being 
 larger and more distinct towards its outer boundary. 
 The liber is composed of woody fibre, and the outer 
 bark of cellular tissue. 
 
 The new woody matter being deposited outside the 
 old, between the bark and the previously formed 
 layer, gives origin to the term exogen (efo), outside, 
 yevvaw, to produce). These structures may be ex- 
 amined in the section of a branch of the lime-tree 
 or lilac. 
 
 In the Monocotyledons or Endogens (PL I. fig. 37), 
 there is no distinct bark, nor pith, nor medullary 
 rays the entire stem consisting of cellular tissue 
 with isolated bundles of fibro-vascular tissue scat- 
 tered through it. Moreover the new substance is 
 added to the centre of the stem, or within the old ; 
 hence the term endogen (eVcW, within, ryevvdw) . A 
 section of a piece of cane will exhibit this structure. 
 
 To examine the structure of stems, sections must 
 be made in various directions. The relative position 
 of the component parts of a stem are best seen in a 
 transverse section ; but the structure of the tissues is 
 most evident in longitudinal sections, and under the 
 higher powers. The annual rings of the Exogens are 
 best observed in transversely sawn-off pieces of per- 
 fectly dry stems, which have been polished with sand- 
 paper, and varnished with spirit varnish. 
 
 Roots. The structure of roots is very similar to 
 that of stems ; there is, however, no distinct pith, nor 
 are there stomata on the epidermis ; and the vessels 
 are replaced by ducts. The very fine rootlets or 
 
FLOWERS. 37 
 
 radicles of water-plants often show the rotation of 
 the protoplasm very distinctly. 
 
 Flowers. The various parts of flowers, being each 
 a modified leaf, present the same general structure 
 as the latter. As the reader may not be acquainted 
 with the names of these parts or organs in the higher 
 plants, and as we shall have to compare them with 
 their representatives in the lower forms of vegetable 
 life, it will be well briefly to indicate them. A com- 
 mon and beautiful yet despised flower (PI. I. fig. 32) 
 may serve for illustration ; this is chickweed (Stella- 
 ria media) } which can be found everywhere. The 
 outermost circle of flower-leaves, which forms a kind 
 of cup to the rest of the flower (a), is the calyx ; the 
 separate leaves being called the sepals. The row 
 within this, in most flowers consisting of brilliantly 
 coloured pieces, forms the corolla (b) ; the individual 
 pieces being the petals. When the two kinds are 
 equally coloured, or not distinguishable, the whole is 
 called the perianth, as in a tulip. When the seg- 
 ments of the perianth are dry and chaffy, as in the 
 flowers of grasses, the outermost are said to con- 
 stitute the glumes, and the innermost the palea. 
 Within the ring of petals are certain thread-like 
 organs called stamens (c) ; and these consist of a 
 filament (fig. 39 ), surmounted at the top or apex by 
 the anther (fig. 39 b), which is usually coloured, and 
 consists of two lobes. The anthers when ripe burst, 
 and discharge a coloured dust; this is the pollen. 
 Lastly, within the stamens is the central organ of the 
 flower, the pistil, and sometimes there are several of 
 them. The pistil consists of three parts, viz. a swollen 
 base, the ovary (fig. 41 b), surmounted by a column 
 or style (fig. 41 a), and which is crowned by a viscid 
 and often hairy summit, the stigma (fig. 40*). In 
 chickweed there are 3 styles. 
 
 It must be remarked that, in the flowers of some 
 plants, stamens alone are present, while others COn- 
 
38 VEGETABLE ORGANS. 
 
 tain pistils only, although most flowers contain both 
 organs. When the stamens and pistils occur in sepa- 
 rate flowers on the same plant, the plant is said to be 
 monoecious (fwvos, single, ottfo?, family) ; when all the 
 flowers of distinct plants contain either stamens only 
 or pistils only, the plant is dioecious (St?, twice, ol/cos) ; 
 and when the stamens and pistils occur together in all 
 the flowers of the same plant, the plant is said to be 
 hermaphrodite. These terms had their origin in the 
 idea that the differences of plants in respect to these 
 organs were analogous to those of the sexes in animals. 
 All the parts of a flower have their special uses : thus 
 the calyx and corolla protect the delicate organs en- 
 closed by them, until they attain maturity. The 
 petals also, by their brilliant colours, attract insects 
 which feed upon or collect the honey of the flowers ; 
 these at the same time conveying the pollen which 
 adheres to their bodies from one flower to the stigma 
 of another. The stamens and pistils are organs of 
 fructification, it being essential for the fertilization of 
 the flowers that the pollen should come into contact 
 with the stigma. We will now consider some inter- 
 esting points of structure in these organs. 
 
 Petals. The petals often form most beautiful mi- 
 croscopic objects, on account of the curious shape 
 and structure of the cells of their epidermis, and the 
 splendid tints of the colouring matters contained in 
 them. As petals are mostly too thick to allow of the 
 cells being distinctly seen in the entire state, a little 
 cut should be made in them while gently stretched 
 on the finger, and the epidermis carefully stripped off 
 with forceps; the strip should then be laid on the 
 slide in water as usual : in this way the curious 
 patterns of the epidermic cells will become very dis- 
 tinct. The petals of a red geranium (Pelargonium) 
 may be used to illustrate them (PL I. fig. 24) . The 
 structure may be best understood by reference to the 
 epidermis of the leaf of a geranium (PL I. fig. 13), 
 
POLLEN. 39 
 
 in which the cells present wavy or undulate walls. 
 In the petal (fig. 24), the walls are inflexed at tole- 
 rably regular distances, so as to give rise to the ap- 
 pearance of a row of teeth lining the cell. If the 
 strip of petal be folded, so as to exhibit the side view, 
 it will also be seen that the cells project outwards 
 from the surface to form a bluntish point or papilla, 
 or the petals are papillose as it is called ; and the 
 surface of the membrane around the papillae is finely 
 wrinkled, so as to present the appearance of very deli- 
 cate radiating lines or striae. Intermediate degrees 
 of this inflexion may be found in various flowers, 
 between the slight condition seen in fig. 13 and the 
 extreme state of fig. 24, as in the snapdragon (An- 
 tirrhinum mdjus). 
 
 Anthers. The cavities of the anthers are lined 
 with fibro- cellular tissue, the fibres of which aid in 
 discharging the pollen ; this may be seen by dissect- 
 ing an anther of London pride (Saxifraga umbrosd], 
 or of a wallflower (Cheiran 'thus cheiri] in water. It 
 also exists in chickweed. 
 
 Pollen. The pollen consists of minute grains called 
 the pollen-granules. They may be viewed either in 
 the dry state as opake objects, or when immersed in 
 water as transparent objects. As it is often difficult 
 to moisten them, they may be touched on the slide 
 with a little spirit, and then a drop of water added. 
 Their forms are very varied and curious, but they are 
 difficult of observation from their minute size. They 
 consist of one or more coloured cells, and these cells 
 are remarkable for their surfaces exhibiting spines, 
 networks, folds, and markings of various kinds. Thus 
 in the primrose the pollen- granules are cylindrical, 
 the surface being furrowed (PI. I. fig. 16) ; in the sun- 
 flower the granules are spherical, and covered with 
 tubercles surmounted by spines (fig. 17) ; in the 
 garden convolvulus the surface of the spherical gra- 
 nules is covered with an elegant network, in the 
 
 E2 
 
40 VEGETABLE ORGANS. 
 
 meshes of which are also situated spines (fig. 18) ; 
 and in the granules of chickweed the surface pre- 
 sents pits, with minute tubercles in the centre 
 (figs. 30 & 31). The pollen-granules are often con- 
 siderably altered by immersion in water; so that, 
 in judging of their structure when examined in 
 water, the resulting alteration must be taken into 
 account. 
 
 When ripe pollen -granules have been immersed in 
 water for a short time, one or more minute tubes 
 will be seen protruding from their surface \ these are 
 the pollen-tubes, and the granular protoplasm con- 
 tained in them is called the fovilla. In the process of 
 fertilization of the flower, the pollen-granules fall 
 upon the viscid stigma ; the pollen-tubes are then 
 protruded, and, passing down the intercellular spaces 
 of the style (PL I. fig. 14), enter an aperture in the 
 ovule or young seed, which is thus endowed with the 
 power of growing into a new plant. The pollen- 
 tubes are often very long, and they do not exist fully 
 developed in the pollen-granules, but grow down the 
 style, just as the little rootlet of a seed grows into the 
 soil. The style of a crocus will serve for dissecting 
 out with mounted needles the long and very slender 
 pollen-tube (PL I. fig. 15). 
 
 O'vary. The ovary by its growth and enlargement 
 becomes the fruit. There are many interesting mi- 
 croscopic structures to be found in fruits and the 
 seeds they contain, a few of which may be noticed 
 here. 
 
 On examining the surface of the rind or pericarp 
 
 epl, around, Kapiros, fruit) of an orange, little dots 
 will be seen, paler than the rest of the surface. These 
 are receptacles of secretion, or glands, containing the 
 evaporable or volatile oil upon which the fragrance of 
 the orange depends. They consist of loose cells, sur- 
 rounding a central cavity, and are imbedded in the 
 rind. 
 
OVARY. 41 
 
 Other receptacles of secretion, called mttcB (vitta, a 
 band), occur in the wall (pericarp) of the fruit of the 
 Umbelliferae, or Parsley Order of plants, and their 
 arrangement forms characters for distinguishing the 
 genera. They may be well seen in caraway- seeds ; 
 for the caraway-plant is one of the Umbelliferse. It 
 must be observed that a caraway " seed " is not really 
 a seed, but consists of half the fruit ; for, on careful 
 examination, one side of it will be found to be flat- 
 tened, the flattening resulting from the mutual pres- 
 sure of the two half-fruits at that part ; moreover the 
 dried style exists at its summit. In the figure (PL I. 
 fig. 19), the flattened part of the seed is next the ob- 
 server. The seed has five evident longitudinal ridges, 
 one at each corner or angle. The vittse are dark- 
 coloured (fig. 19 a), and placed one between each pair 
 of these ridges ; and they consist of long flattened 
 spaces in the substance of the pericarp, with trans- 
 verse markings, indicating internal cross partitions, 
 In botanical works, the presence of five ridges, with 
 single vittse in the intervals, is given as a character 
 by which the half-fruits (carpels) of the caraway are 
 to be distinguished. But on closely inspecting the 
 flattened surface, another ridge is seen running down 
 its middle ; so that the seed really has six ridges, one 
 of which is smaller than the rest from the pressure of 
 the other half. Hence the character of five ridges 
 with single vittse is incorrect. 
 
 The vittse contain the volatile oil to which the 
 fragrance and pungency of the fruit is owing, although 
 some of the oil exists also in the cells of the kernel or 
 albumen, which forms the white and greater part of 
 the seed. 
 
 The skin of a reddish apple, peeled off in the 
 manner described for petals, exhibits beautifully the 
 red colouring matter of different tints in adjacent 
 cells, while the pulp displays the cell-contents, as 
 already mentioned. The latter may also be easily 
 
42 VEGETABLE ORGANS. 
 
 examined, from their large size, in most of the softer 
 fruits, as that of the snowberry or the cucumber. 
 
 As the ovary or fruit approaches maturity, the 
 petals and stamens wither and fall off, the calyx often 
 remaining, and being sometimes adherent to the 
 ovary, at others free or unattached to it. 
 
 Seeds. During the ripening of the fruit, the seeds 
 contained within it are gradually becoming further 
 developed. 
 
 The seeds themselves are covered outside by a skin 
 or coat called the testa (testa, a shell) . This is re- 
 markable for frequently displaying various kinds of 
 figured patterns, consisting of raised networks, ridges, 
 little knobs or tubercles, &c. Examples of these may 
 be found in the seeds of the poppy (PL I. fig. 27), 
 mignonette (fig. 29), and chickweed (fig. 51). 
 
 Some seeds are winged, as it is called, i. e. fur- 
 nished with an extension of the testa beyond the 
 margin of the seed. This not unfrequently consists 
 of aggregated fibre-cells, the spiral fibre being very 
 distinct, as in the seeds of Eccremocar pus scdber 
 (PL I. fig. 52). In the seeds of another curious plant 
 in this respect, viz. Collomia grandiflora, the fibre- 
 cells are separate, so as to resemble hairs, and very 
 mucilaginous, and in the dry seed are closely pressed to 
 its surface. If a portion of the testa of these seeds, 
 which can be procured at the seed-shops, be cut off, 
 laid on a slide, a cover applied, and when the object 
 is in focus, a drop of water be added, in a short time 
 water softens the mucilaginous walls of the cells, the 
 power of the spiral fibres comes into play, and the 
 cells expand so as to form a very interesting object; 
 the cells, in their expansion, apparently writhing like 
 so many minute worms (PL I. fig. 35). 
 
 The seed itself, which is contained within the testa 
 or seed-coat, consists essentially of the young plant or 
 embryo. This is composed of three parts, viz. the 
 plumule (plumuktj a little feather), or the young stem ; 
 
SEEDS. 43 
 
 the racficle (radicula, a little root), or the young root ; 
 and one or two, rarely more, imperfectly developed 
 or rudimentary leaves, the cotyledons (fcoTv\rj&<av, a 
 cup). 
 
 These structures are closely packed in the seed, and 
 are not easily recognized at first. By keeping seeds 
 moist for a day or two until they begin to grow, or 
 germinate as the seed-growth is called, they are readily 
 detected, and may then be more easily found in the 
 dry seed. 
 
 When somewhat advanced in growth, they are 
 familiar to every one, although they may not be re- 
 cognized by their names. In table " mustard and 
 cress," the whole consists of these organs of the two 
 plants ; the white stalk directed downwards being the 
 radicle, the two green leaf-like lobes the cotyledons, 
 and between the latter directed upwards is the very 
 minute plumule, which is more easily seen when the 
 plants have been allowed to grow larger. This struc- 
 ture of the seed is important to be known, because the 
 absence or presence and the number of cotyledons afford 
 characters, corresponding with those already men- 
 tioned in respect to the veins of the leaves and the 
 structure of the stem, for distinguishing the great 
 divisions of the Vegetable Kingdom. Thus, the Ex- 
 ogens are Dicotyledons (819, twice), their seeds having 
 two cotyledons ; while the Endogens are Monocoty- 
 ledons (ftovo9, single), having one only; and the 
 Cryptogam'ic plants are Acotyledons (a, without), 
 their seeds (spores) having none of these organs. 
 
 Some seeds consist entirely of the embryo, sur- 
 rounded by the testa. But in many others there is 
 also present a usually whitish, firm cellular substance., 
 called the albumen (albumen, white of egg) . 
 
 The albumen of seeds often affords good specimens 
 of secondary deposit, the cells being almost entirely 
 filled with it. An example may be found in a section 
 of vegetable ivory, of which ornaments are sometimes 
 
44 VEGETABLE ORGANS. 
 
 made ; its structure resembles essentially that of the 
 plum-stone. In other instances the cells contain 
 secreted matters, as starch, oil, &c. ; and sometimes 
 the cotyledons also contain starch and oil. An ex- 
 ample of the former exists in the albumen of wheat ; 
 and of the latter, in the horse-chestnut, the filbert, 
 and mustard-seed. 
 
 The albumen and cotyledons serve to supply the 
 embryo with nutriment until the roots have grown 
 sufficiently to enable them to absorb it from the soil ; 
 the cotyledons also serve as temporary leaves. 
 
 The form and relative position of the radicle and 
 cotyledons serve to distinguish certain groups of 
 plants. This may be illustrated by the natural order 
 Cruciferse, or that containing the mustard, wall- 
 flower, &c. 
 
 Thus, in one group, which may be represented by 
 the wall -flower, the cotyledons are flat or plane 
 (PL I. figs. 43 & 44), the radicle being applied to their 
 edges. This is best seen in a transverse section 
 (fig. 43). They are then called accum'bent (accumbo, 
 to lie against); and the botanical sign is 0=- In 
 the second group, the cotyledons are plane (PI. I. 
 fig. 38) , with the radicle applied to the back of one 
 of them, as in the seed of the common shepherd's 
 purse (Capsel'la bur'sa pastoris) (PL VII. fig. 19). They 
 are then termed iricumbent (incumbo, to lie upon), 
 and the sign is Oil. While in the third group the 
 cotyledons are folded in the middle, like the leaves 
 of a book (PL I. figs. 49 & 50), and the radicle is 
 enclosed between them, as in the white mustard 
 (Sina'pis alba) . The cotyledons are then called con- 
 duplicate (conduplico, to fold) ; and their sign is 0. 
 
 The plants above-mentioned are evidently all Dico- 
 tyledonous, or their seeds have two cotyledons ; and 
 they contain no albumen. 
 
 In the Monocotyledonous division, which may be 
 represented by a grain of wheat (PL I. fig. 53), the 
 
FERTILIZATION. 45 
 
 single cotyledon forms a minute sheath (a), enclosing 
 the plumule (b), the radicle (c) being here but little 
 developed at first, the greater part of the grain con- 
 sisting of the albumen (d) ; the grain should be soft- 
 ened in water before examination. In the germi- 
 nated grain the cotyledon appears as a pale sheath, 
 surrounding the convolute green leaves of the plu- 
 mule ; which may be best seen in a transverse section 
 (PI. I. fig. 48). 
 
 Fertilization. A few words must now be said 
 regarding the formation of seeds, and the action of 
 the pollen-tubes in the process of fertilization. 
 
 In the earliest stages of growth, the young seeds, 
 or ovules as they are called, appear as little buds, 
 arising from the inner wall of the ovary ; and the 
 part from which they arise is called the placenta 
 (placenta, a cake). In chickweed (PI. I. fig. 41 c), 
 the placenta forms a central column ; and when the 
 ovules are a little older, they are found to have sepa- 
 rated somewhat from the placenta, but retaining a 
 connexion by means of a little cord or stalk, termed 
 the funic'ulus (funis, a cord) . The ovules may be 
 readily found in the ovary or young pod of a wall- 
 flower, the placentas forming four lines, running lon- 
 gitudinally down the interior of the pod. 
 
 In this early condition the ovule consists of a mass 
 of cellular tissue ; and as new formations are soon 
 added to it, it is termed in this state the nucleus. 
 Around the nucleus are then formed two coats, an 
 outer, called the primine, and an inner, termed the se- 
 cun'dine. These coats or membranes are open at one 
 end, so as to leave a passage down to the apex of the 
 nucleus; the opening is called the foramen. These 
 structures are well seen in the ovule of the wallflower 
 (PI. I. fig. 54), the foramen in the figure being indi- 
 cated by a * ; it will be noticed also that the funi- 
 culus runs down one side of the ovule, so as to ter- 
 minate at the bottom or base of the nucleus. In 
 
46 VEGETABLE ORGANS. 
 
 ripe seeds, the spot at which the funiculus has been 
 attached is mostly perceptible in the form of a scar. 
 The slight prominence of the foramen can also often 
 be distiuguished, as in the seed of chickweed (PI. I. 
 fig. 51*) ; in the ripe seed the foramen is termed the 
 micropyle, and towards it the radicle of the embryo 
 is always directed. 
 
 One of the cells of the nucleus near its apex then 
 enlarges, so as to form a sac, called the embryo-sac. 
 This is excessively thin and transparent (PL I. 
 figs. 45 b & 47) ; and in it, also at the end next the 
 foramen, one or more (in the chickweed one) smaller 
 cells are formed from the cell-contents of the em- 
 bryo-sac, which are called the embryonal vesicles 
 (PL I. fig. 45 a). 
 
 Thus far developed, the embryo exists prior to the 
 expansion of the flower and the discharge of the 
 pollen. The embryo -sac is not figured in this early 
 condition, the embryonal vesicle being then smaller 
 than that in fig. 45 b, although occupying the same 
 position. 
 
 When the pollen has escaped from the anthers and 
 fallen upon the stigma, the pollen-tubes growing 
 down the intercellular passages of the style, enter the 
 foramen of the ovule, and so reach the apex of the 
 nucleus, at which the embryonal vesicle contained in 
 the embryo-sac is situated. The end of the pollen- 
 tube then adheres to the embryonal vesicle, and such 
 interchange of cell-contents takes place between them 
 as effects fertilization. 
 
 The process of cell-formation in the fertilized em- 
 bryonal vesicle then takes place rapidly, new cells 
 being formed by the division of its cell- contents 
 (PL I. fig. 45 a) ; and it will be noticed that the new 
 cells are formed at the end of the embryonal vesicle, 
 opposite to that situated at the apex of the embryo- 
 sac. As the cell- division and formation proceed fur- 
 ther, a mass of new cells is produced (PL I. figs. 46 c 
 
FERTILIZATION. 47 
 
 & 47), forming the rudimentary embryo ; and from 
 this, by further growth, the perfected embryo (fig. 55) 
 results ; or, to use a fashionable technical term, the 
 simply cellular embryonic mass becomes differen- 
 tiated into the radicle, cotyledons, and plumule, form- 
 ing the embryo. It will be remarked that the posi- 
 tion of the embryo in fig. 55 is the reverse of that in 
 figs. 46 & 47, the radicle in the former being directed 
 downwards, whilst that of the embryo in the figure of 
 the embryo-sac (fig. 47) is directed upwards. 
 
 The embryonal structures are very difficult of de- 
 tection ; but it happens that in our little chickweed 
 they are more easily dissected out than in most other 
 plants. For this purpose, the ovules, placed on a 
 slide and lying in water, should be picked to pieces 
 with the mounted needles, under the simple micro- 
 scope. They may be preserved in chloride of calcium 
 or glycerine. 
 
 A clear distinction must be drawn between seeds, 
 which result from the process of fertilization, and 
 buds, which are formed independently of this process. 
 Both consist essentially of embryo plants ; but while 
 the former originate from a single cell, the latter are 
 outgrowths of a parent stem, from which their tissues 
 are derived ; and while the former propagate the spe- 
 cies, the latter increase the individual. 
 
 The obvious use of seeds is the distribution of the 
 species by the formation of new individuals. 
 
 In the general outline which has been given of the 
 elements, tissues, and organs of plants, they have 
 been examined principally as existing in the higher 
 groups, or those of more complex structure ; and to 
 enter further upon a description of these plants would 
 involve the consideration of variations in the form 
 and arrangement of the organs of which they are 
 composed. As these can mostly be investigated with- 
 out the use of the microscope, we must pass to those 
 in which the entire plant consists of little more than 
 
48 VEGETABLE ORGANS. 
 
 simple or parenehymatous cells, and in which the 
 representatives of the flower are so inconspicuous, Gl- 
 are reduced to so elementary a condition, that tho 
 plants included in the Division have been termed 
 Cryptogamic (tcpvTrros, concealed, 7^09, union 
 figuratively for reproductive organs) or Flowerless 
 Plants. The reproductive organs of the Cryptogamia 
 are usually termed the fructification, implying that 
 they produce fruit, but not flowers. 
 
PLATE II. [PAGE 49.] 
 FERNS AND LICHENS. 
 
 Fig. 
 
 1. Chlorococcum wig are. 
 
 2. Parmelia parietina. 
 
 3. Parmelia parietina, section of a 
 
 saucer (apothecium). 
 
 4. Parmelia parietina, gonidia and 
 
 asci. 
 
 6. Parmelia parietina, asci and para- 
 physes ; 5 a, spores. 
 
 6. Calicium clavellum. 
 
 7. Calicium clavellum, stalked apo- 
 
 thecia. 
 
 8. Calicium clavellum, apothecium. 
 0. Polypodium vulgare, frond. 
 
 10. Polypodium vulgare, lobe of frond. 
 
 11. Polypodium vulgare, group of cap- 
 
 sules (thecse). 
 
 12. Polypodium vulgare, capsule and 
 
 spores. 
 
 13. Polypodium vulgare, spore germi- 
 
 e. 
 um vulgare, prothallium. 
 um vulgare, portion of 
 prothallium, with archegonia. 
 
 Fig. 
 
 16. Aspidiumjilix mas, frond. 
 
 17. Aspidiumjilix mas, pinnules with 
 
 sori. 
 
 18. Aspidiumjilix mas, single pinnule. 
 
 19. Scolopendrium vulgare, frond. 
 
 20. Scolopendrium vulgare, portion of 
 
 frond. 
 
 21. Cladonia cocci/era. 
 
 22. Cladonia cornuta. 
 
 23. Cladonia pyxidata. 
 
 24. Cladonia rangiferina. 
 
 25. Cladonia rangiferina, ends of po- 
 
 detium. 
 
 26. Graphis scripta. 
 
 27. Graphis scripta, lirellae. 
 
 28. Graphis scripta, asci and spores. 
 
 29. Graphis scripta, spore. 
 
 30. Opegrapha betulina. 
 
 31. Opegrapha betulina, lirellae. 
 S'2. Opegrapha betulina, lirella. 
 
 33. Opegrapha betulina, ascus with 
 
 spores. 
 
 34. Scalarifi 
 
Plate II. 
 
FERNS. 49 
 
 CHAPTER V. 
 
 FERNS, OR FII/ICES. 
 
 THE general appearance of plants belonging to the 
 class of Ferns is so well known that it need scarcely 
 be described, especially since the introduction of the 
 glass plant-cases, by means of which the air can be 
 kept so damp that ferns are now grown in the very 
 heart of our cities. Their bright green and finely 
 cleft leaves (PL II. figs. 9 & 16) or fronds (from, a 
 leaf) as the leaf- like organs of the lower plants are 
 called, arising in tufts from the stems, give them the 
 elegant appearance we are called upon to admire, 
 whenever they are met with. The brownish spots or 
 stripes seen upon the back or under surface of the 
 fronds, and consisting of the fructification, form also 
 a simple character by which they may generally be 
 distinguished ; although in a few of them the fructi- 
 fication is placed upon a distinct stalk. The stem or 
 rhi'zome (pl^aypa, a root) of a fern is mostly situated 
 just beneath or at the surface of the ground, and is 
 commonly mistaken for the real root, which is buried 
 in the earth. It is brownish outside, and covered 
 with scurfy scales or r amenta (ramentum, a shaving). 
 These scales are interesting microscopic objects, from 
 the distinctness with which they exhibit the cellular 
 network. 
 
 A section of the rhizome exhibits the fibro-vascular 
 tissue arranged differently from that in the stems of 
 either Exogens or Endogens. It forms curiously 
 curved longitudinal plates, a very abundant compo- 
 nent of which is the scalar'iform (scala, a ladder) 
 duct (PI. II. fig. 34). The walls of the scalariform 
 ducts are angular, and the secondary deposit is ar- 
 
50 FERN'S. 
 
 ranged in the form of transverse bars, somewhat 
 resembling the steps of a ladder ; which structure is 
 best seen in a transverse or slightly oblique section. 
 The fronds are usually cleft nearly down to the main 
 vein or midrib (fig. 9), or pinnatifid (pinna, a feather, 
 findo, to cleave); sometimes the segments are simi- 
 larly cleft, so that the fronds are bipinnatifid. The 
 manner in which the veins usually branch is also 
 peculiar, each branch separating from the point of 
 division at an acute angle with the original direction 
 of the vein (fig. 20), so as to be forked. It is also 
 worthy of notice, that the young frond is rolled up 
 into a flat spiral, or is cir'cinate (circino, to go round), 
 before it opens. 
 
 We will now examine one or two species more 
 minutely. 
 
 POLYPODIACE./E. Polypodium vulgdre (PL II. fig. 9, 
 one-third of the natural size), a member of this 
 family, is very common on old trunks of trees, on 
 banks, &c. The frond is deeply pinnatifid, the seg- 
 ments being oblong, blunt (obtuse), scalloped (cre- 
 nate) at the edges (PL II. fig. 10), and becoming 
 gradually shorter towards the apex of the frond. 
 
 On the back of the fronds are the little orange- 
 coloured groups of capsules (PL II. figs. 9 & 10); 
 these are called sor'i (atopos, a heap) . The capsules 
 or thecce (Otf/cr), a case), a magnified group of which is 
 represented in fig. 11, consist each of an aggregation 
 of cells, fixed to a stalk (fig. 12) ; and along the back 
 of the capsule is a close row of thicker cells, forming 
 an elastic ring, the annulus. When the seed-like 
 bodies or spores (o-Tropa, a seed) are ripe, the annulus 
 becomes straightened from its elastic power, and tears 
 the capsule open, so that the spores are set free and 
 scattered. 
 
 Aspid'ium filix mas (PL II. fig. 16, reduced to one 
 third.or fourth of the natural size), is the most common 
 British fern. In this the fronds are pinnate, i. e. the 
 
REPRODUCTION. 51 
 
 segments (pinnae) corresponding to those of Polypo- 
 dium are cleft entirely to the main stalk,, the pinnae 
 (fig. 1 7) being pinnatifid ; and the segments of the 
 pinnae or the pinnules (fig. 18) are oblong, obtuse, and 
 saw-edged (serrate) . In all botanical works the fronds 
 are incorrectly said to be bipinnate. 
 
 The sori are brown, kidney-shaped (fig. 18), and 
 differ from those of Polypodium in being covered by a 
 thin membrane (indusium), which is fixed to the frond 
 at the notch. 
 
 Scoloperi drium vulgdre (PL II. fig. 19), the Hart's- 
 tongue Fern, is common in hedges and on moist banks. 
 Its fronds are simple or undivided, strap-shaped, 
 heart-shaped at the base, and narrowed to a point at 
 the apex. The sori (fig. 20) are brown, narrow, 
 longish (linear), and transverse or slightly oblique. 
 The indusium is cleft down the middle, so as to form 
 a longitudinal fissure or suture. 
 
 Reproduction. The spores of the ferns (PL II. fig. 
 12 a] resemble in appearance the seeds of flowering plants 
 on a small scale. They are usually brown, covered on 
 the surface with little tubercles or other markings, 
 and when kept on a slide in a moist atmosphere, as 
 over a saucer of water covered with a bell-glass, they 
 germinate. When this takes place, one or more 
 short, brownish, hair-like radicles emerge from one 
 part of the surface (PL II. fig. 13), and a process con- 
 taining chlorophyll issues from an adjacent spot. As 
 growth proceeds, the latter by cell-division gives rise 
 to a flattened two-lobed leafy cotyledon-like body or 
 prothaHium (irpb, before, 0aXXo9, leaf), with nume- 
 rous rootlets springing from the base of the lobes. 
 The prothallium is of a peculiar dull-green colour, 
 different from that of the young frond which is subse- 
 quently formed. This arises from the absence of 
 stomata and intercellular passages containing air ; for 
 the air in these passages of leaves and petals contri- 
 butes greatly to the production of the brightness of 
 
52 FERNS. 
 
 their colours. Moreover, the cells of the prothallium 
 resemble those of the parenchyma of a leaf, the epi- 
 dermis with its wavy-margined cells being absent. 
 
 When the prothallium has attained its full develop- 
 ment, minute scattered protrusions from its cells occur 
 on the margin or under surface, resembling short and 
 blunt hairs ; and each of these becomes partitioned 
 off to form a new cell, within which a number of 
 crowded smaller cells are produced. These organs are 
 called antherid'ia (anther, and etSo?, resemblance) ; and 
 within each of the crowded smaller cells is contained 
 a very minute, colourless, coiled fibre, furnished with 
 still finer filaments, called cilia (cilium, an eyelash) ; 
 the ciliated fibres being termed spermatozo' a (crTrepfjia, 
 seed, foSov, animal). At a later period, other organs 
 are found also on the back of the prothallium. These 
 are larger than the antheridia, and are composed of 
 several cells, arranged around a central canal which 
 leads to an embryo- cell situated at its base (PI. II. 
 fig. 2). These organs are the archegonia (apxrj, be- 
 ginning, 7ovo9, offspring). When the antheridia are 
 ripe, they discharge the spermatozoa, which are 
 enabled to swim about by means of their cilia in 
 water (rain), and entering the canal, reach the embryo- 
 cell, which thus becomes fertilized. When fertilized, 
 the embryo-cells produce the little fronds which after- 
 wards grow into the mature plants. 
 
 Hence the spores of ferns differ strikingly from the 
 seeds of the higher plants in not containing the em- 
 bryo radicle and cotyledons already formed, these 
 being produced during or after germination ; also in 
 the fertilizing organs, viz. the antheridia or represen- 
 tatives of the anthers, and the archegonia or the re- 
 presentatives of the pistils, being produced from the 
 cells of the prothallium. 
 
 The more minute of these structures are too diffi- 
 cult of observation and preparation for any one un- 
 accustomed to microscopic manipulation, so that they 
 
PRESERVATION. 53 
 
 have not been figured in detail; the figures given 
 will, however, serve to guide the observer in tneir 
 recognition. 
 
 Preservation. The ferns may be easily preserved 
 in the entire state, by laying them flat between sheets 
 of coarse unsized paper, and subjecting them to mode- 
 rate pressure in a screw-press; the paper should be 
 changed, or dried before a fire every two or three days, 
 and the pressure repeated until the specimens become 
 dry and rigid. They may then be mounted on sheets 
 of paper, being fastened eitherwith thread passed round 
 the stalk or portions of the frond with a needle, and 
 tied in a knot behind, or with strips of paper gummed 
 at the ends. 
 
 The minute structures may be preserved either in 
 the dry state or in glycerine. 
 
 r3 
 
54 MOSSES. 
 
 CHAPTER VI. 
 
 MOSSES, OR MTJS'CI (MUSCUS, MOSS) . 
 
 I NEED scarcely refer to the figures in PL III. to 
 enable the reader to recognize the Mosses ; every one 
 knows them at once by their remarkably uniform 
 general appearance, their miniature-plantlike form, 
 their crowded little leaves, concealing the slender 
 wiry stems, their growth in patches, and their curious 
 urn-shaped fruits raised up on slender bristle-like 
 stalks. 
 
 The leaves of the mosses are simple, i. e. not cut 
 into segments, and consist of one or two layers of 
 cells. The thinness of the leaves enables these cells to 
 be seen very distinctly, the closely united cell-walls 
 giving the leaves a netted or reticulated appearance 
 (fig. 48), and the grains of chlorophyll being gene- 
 rally few and readily distinguished. The veins of the 
 leaves, or the nerves as they are usually called, scarcely 
 deserve the name ; for neither they nor even the stems 
 contain fibro-vascular tissue, but consist simply of 
 elongate closely packed cells, and often the leaves 
 have no nerves. 
 
 The fruit of the mosses consists of a capsule, some- 
 times called a sporangium (aTropd, seed, ^7709, vessel), 
 usually placed at the end of a slender stalk, called 
 the seta (seta, a bristle) ; but sometimes the stalk is 
 absent or extremely short, when the capsule is said 
 to be ses'sile (sessilis, sitting). The young capsule is 
 covered with a thin extinguisher-like cap or calyptra 
 (/ca\i>7rTpa, a cover), which is carried up as the cap- 
 sule and its stalk grow, so as to be either entirely 
 thrown off, or to remain covering a greater or less 
 portion of the capsule, when this attains maturity. 
 
PLATE III. [PAGE 54.] 
 MOSSES. 
 
 Fig. 
 
 1. Sphagnum acutifolium, expanded 
 
 leaf. 
 
 2. Sphagnum acutifolium, cells of leaf. 
 
 3. Spermatozoa of Polytrichum pili- 
 
 ferum. 
 
 4. Sphagnum acutifolium. 
 
 5. Sphagnum acutifolium, capsule. 
 
 6. Gymnostomum truncatulum. 
 
 7. Gymnostomum truncatulum, leaf. 
 
 8. Gymnostomum truncatulum, cap- 
 
 sule and operculum. 
 
 9. Gymnostomum truncatulum, spore. 
 
 10. Dicranum heteromallum. 
 
 11. Dicranum heteromallum. 
 
 12. Dicranum heteromallum, leaf. 
 
 13. Dicranum heteromallum, opercu- 
 
 lum. 
 
 14. Dicranum heteromallum, calyptra. 
 
 15. Dicranum heteromallum, capsule; 
 
 15 a, peristome. 
 
 16. Torttda muralis. 
 
 17. Tortula muralis, leaf. 
 
 18. Tortula muralis, capsule : a, tooth 
 
 of peristome. 
 
 19. Tortula muralis, operculum. 
 
 20. Tortula muralis, calyptra. 
 
 21. Tortula muralis, archegonia. 
 
 22. Polytrichum piliferum. 
 
 23. Polytrichum piliferum, leaf. 
 
 24. Polytrichum piliferum, calyptra. 
 26. Polytrichum piliferum, antheridial 
 
 stems. 
 
 Fig. 
 
 26. Polytrichum piliferum, single head. 
 
 27. Polytrichum piliferum, antheridia 
 
 and paraphyses. 
 
 28. Funana hygrometrica. 
 
 29. Funaria hygrometrica. 
 
 30. Funaria hygrometrica, leaf. 
 
 31. Funaria hygrometrica, capsule ; 
 
 a, operculum. 
 
 32. Funaria hygrometrica, atalk-like 
 
 body. 
 
 33. Funaria hygrometrica, young ar- 
 
 chegone. 
 
 34. Funaria hygrometrica, more ad- 
 
 vanced archegone. 
 
 35. Funaria hygrometrica, section of 
 
 young capsule. 
 
 36. Funaria hygrometrica, calyptra. 
 
 37. Funaria hygrometrica, antheridia. 
 
 38. Funaria hygrometrica, spores. 
 
 39. Funaria hygrometrica, annulus. 
 
 40. Funaria hygrometrica, archego- 
 
 nia. 
 
 41. Funaria hygrometrica, antheridial 
 
 head. 
 
 42. Funaria hygrometrica, peristome. 
 
 43. Hypnum rutabulum. 
 
 44. Hypnum rutabulum, leaf. 
 
 45. Hypnum rutabulum, capsule. 
 
 46. Hypnum rutabulum, spores. 
 
 47. Hypnum rutabulum, peristome. 
 
 48. Hypnum rutabulum, cells of leaf. 
 
 49. Bryum capillare. 
 
MOSSES. 55 
 
 The calyptra is either simply mitre-shaped, or mitri- 
 form (PI. III. fig. 24), or it is half-cleft, or dimid'iate 
 (figs. 14, 36) . When the capsule is ripe, the upper 
 part usually separates at a circular horizontal line 
 (fig. 8) as a kind of lid, which is called the oper- 
 culum (operculum, a lid), and thus the spores are 
 enabled to escape. The rim of the capsule, from 
 which the operculum has separated, forms its mouth, 
 and this often exhibits a fringe of teeth (figs. 15, 18, 
 31), arranged in one or more rows; sometimes the 
 teeth are replaced by a membrane, or, again, both 
 teeth and a membrane may be present. This mouth- 
 fringe is iheperistome (-Trepl, around, oro/i-a, mouth). 
 In many mosses, an elastic row or ring of cells is 
 situated between the mouth of the capsule and its 
 operculum, called the annulus (figs. 18 & 39) ; this, 
 when the capsule is ripe, aids in throwing off the 
 operculum. 
 
 It is important to become acquainted with the 
 structure and arrangement of these parts, as they 
 form characters by which the families and genera of 
 mosses are distinguished. 
 
 The capsules of the mosses form very beautiful 
 microscopic objects, especially those furnished with a 
 toothed peristome. 
 
 Most of the mosses produce their fructification in 
 the winter and spring. 
 
 The class of mosses is divided into two Orders, 
 according to whether the fruit-stalk is terminal, i. e. 
 arises from the end of the stem or its branches, or 
 whether it is lateral, arising from the side of the 
 stem. Those with the fruit-stalk terminal, or the 
 end fruited (PL III. fig. 22), form the Ac'rocarpi 
 (a/cpa, summit, /capTros, fruit) ; while those with the 
 fruit-stalks lateral, or the side-fruited mosses (fig. 43), 
 constitute the Pleurocarpi (irXevpa, side). The new 
 shoots or young branches of the stems of mosses are 
 termed innovations. 
 
56 MOSSES. 
 
 We will now examine a few common mosses more 
 in detail, beginning with the ACROCARPI. 
 
 Sphagnum acutifolium (PI. III. fig. 4) is found in 
 pools or bogs, growing at the margins so as "to be 
 partially immersed. In this moss, the upper branches 
 are grouped into a head. The leaves are crowded, 
 and overlapping or im'bricate (imbrex, a tile) on the 
 elongate stems; they are egg-shaped (ovate) on the 
 main stems (fig. 1), and narrower or ovate-lanceolate 
 on the branches; they are nerveless, and finely 
 toothed at the apex. The capsule (fig. 5) is roundish- 
 ovate, without a peristome, and the operculum is 
 flattened. The grouped arrangement of the upper 
 branches renders the species of Sphagnum easily re- 
 cognized. The structure of the leaves is also very 
 peculiar and characteristic (fig. 2) . The cells of which 
 they consist are of two kinds, one (fig. 2 a) being 
 colourless, elongate, pointed, and containing a spiral 
 fibre ; the other consisting of shorter and narrower 
 obtuse cells, containing chlorophyll, and situated be- 
 tween the former. In many of the former kind of 
 cells, little round apertures exist on the under surface, 
 and minute animals may sometimes be found im- 
 prisoned in them. 
 
 Another species of Sphagnum, S. obtusifolium, is 
 common, and greatly resembles the above, but has 
 shorter and thicker stems, and rounded-ovate, very 
 concave, and obtuse leaves. 
 
 Gymnos'tomum truncat'ulum (PL III. fig. 6) is a 
 common little moss, found on banks and in fields 
 and gardens. 
 
 In this there is no peristome, although, in the 
 young condition, a membrane extends more or less 
 over the interior of the mouth of the capsule. The 
 stem is slender, rigid, and simple, or but little 
 branched. The calyptra is dimidiate ; the operculum 
 is present (fig. 8), and terminates above in an oblique 
 beak, or it is obliquely rostrate (ros'trum, a beak) as 
 
DICRANUM. 57 
 
 it is called. The leaves are obovate (fig. 7) or ovate 
 with the broader part remote from the stem, and 
 narrowed at the apex, where the nerve protrudes or 
 is ex'current (excurro, to run out). The spores 
 (fig. 9) are reddish brown and smooth. 
 
 Dicrdnum heteromal' lum (PI. III. figs. 10 & 11) is 
 probably the first moss the reader will meet with on 
 banks and heaths in the early spring ; and it will be 
 sure to be noticed on account of the bright green 
 colour of the patches and the beautiful orange- 
 brown capsules. 
 
 In this moss the capsule is nodding (cer'nuous) 
 (PI. III. fig. 15), and has a single peristome, con- 
 sisting of sixteen equidistant teeth, each being deeply 
 cut or cleft longitudinally (fig. 15 ), so that there are 
 thirty- two teeth altogether; and these are marked with 
 internal cross-bars, or transverse ridges. The calyptra 
 is dimidiate (fig. 14) ; and the lid is furnished with 
 a long oblique beak (fig. 15 b). The leaves are 
 crowded, strongly nerved (fig. 12), lanceolate at the 
 base, and very narrow towards the apex, which is 
 toothed ; they are, moreover, curved^ and bent towards 
 one side, or secund. 
 
 Tor' tula murdlis (PI. III. fig. 16) may be found on 
 the top of almost every wall and on waste ground. 
 
 In this moss the peristome is single (fig. 18), con- 
 sisting of thirty-two spirally twisted teeth, arranged 
 in pairs. They are narrow and slender, and each is 
 composed of two longitudinal portions (fig. 18 #), one 
 of which is pale yellow, the other reddish brown, like 
 the capsule, and both are fringed and covered with 
 very minute papillae. The capsule (fig. 18) is oblong, 
 the ring or annulus remaining for some time. The 
 lid is conical (fig. 19), with a longish somewhat ob- 
 lique beak, and the calyptra is dimidiate (fig. 20). 
 The stems are very short; the leaves (fig. 17) are 
 oblong, obtuse; the nerve strong, and projecting as a 
 colourless spirally striated bristle. The bristles often 
 
58 MOSSES. 
 
 give the patches of the moss a hoary appearance on 
 wall-tops. The margins of the leaves are folded back 
 or recurved, giving them a peculiar thickened ap- 
 pearance. 
 
 The largest of our mosses are contained in the 
 next genus, viz. Polyt'richum, some of them having 
 the stems from 2 to 4 inches, or even more, in height ; 
 they are common on heaths and in woods. 
 
 Polyfrichum piliferum (PL III. fig. 22) is very 
 common on open dry heaths. This moss has simple 
 stems, with the leaves crowded on the lower part of 
 those which are fertile or fruit-bearing. The fruit- 
 stalk is terminal (acrocarpous) ; the capsule ovate, 
 4-sided or quadrangular, with a knob or struma 
 (struma, a swelling) at the base, the lid having a 
 short beak. The calyptra (fig. 24) is half-cleft (di- 
 midiate) and very hairy. The peristome is single, 
 and consists of sixty-four teeth. The leaves (fig. 23) 
 are lanceolate, nearly upright, the margins folded 
 inwards or inflexed ; and they end abruptly in a saw- 
 edged or serrated hair-like point. 
 
 Poly'trichum commune, which is also very common, 
 is larger than the last species, and may easily be dis- 
 tinguished by the curved and serrate leaves, which 
 have no bristle-point. 
 
 In the early spring, patches of both these mosses 
 may be found, in which the stems are terminated by 
 little rosettes (figs. 25 & 26) ; these will be referred 
 to presently. 
 
 Keeping still to the end-fruited or Acrocarpous 
 mosses, we have next to mention Funaria hygro- 
 met'rica (PL III. figs. 28, 29), which is readily dis- 
 tinguished from most other mosses by the pale apple- 
 green colour which it possesses before the capsule 
 ripens. It is extremely common on walls and waste 
 ground. 
 
 The capsule of this moss (fig. 31) differs from 
 those of the preceding mosses in the peristome being 
 
BRYUM. 59 
 
 double (fig. 42), or composed of an outer and an inner 
 row of teeth. The outer row consists of sixteen ob- 
 lique reddish teeth, which are marked with trans- 
 verse bars or trabe'culae (trabecula, a little beam), and 
 their points are connected by a net-like thin plate. 
 The inner row contains also sixteen teeth, arising 
 from the division of the membrane lining the cap- 
 sule ; these are yellowish, thin, and placed opposite 
 the outer teeth. The capsule itself is pear-shaped or 
 pyriform, orange-red when ripe, curved, and with the 
 mouth oblique. The calyptra (fig. 36) is half-cleft, and 
 expanded as if blown out below. The lid (fig. 31 a) 
 is convex and obtuse ; and the annulus (fig. 39) is 
 large and easily separable. The fruit-stalks are 
 curved near the top. The leaves (fig. 30) are ovate, 
 concave, entire, with a nerve reaching the apex, 
 which is acute and prolonged into a little point, or 
 apic'ulate. The spores (fig. 38) are small and reddish 
 brown. The specific name (hygromet'ricd) of this 
 moss expresses its hygrometric property ; for if either 
 the recent and moist moss be dried or the dry moss 
 wetted, the fruit-stalk gradually twists in opposite 
 directions in the two cases. 
 
 The last of the Acrocarpous mosses which we shall 
 notice, Bry'um capiHare (PI. III. fig. 49), is tolerably 
 common on trunks of trees, on the ground, and 
 sometimes on walls. 
 
 The capsule of this moss has a double peristome 
 or mouth-fringe ; the outer consisting of sixteen red- 
 dish-brown, equidistant, transversely striped teeth; 
 the inner composed of sixteen thin keeled teeth, more 
 or less split down the middle, and with two or three 
 intermediate cilia. The capsule is nodding, smooth, 
 oblong, pear-shaped, slightly narrowed below the 
 mouth ; the lid being somewhat convex, and furnished 
 with a short slender beak. The calyptra is dimidiate. 
 The leaves (fig. 50) are obovate, the nerve extending 
 
60 MOSSES. 
 
 beyond the point, rendering them bristle-pointed. 
 The seeds (fig. 49 a) are small and green. 
 
 This moss serves to illustrate a great difficulty, 
 which will often occur to the student, in determining 
 whether a moss is end-fruited or side-fruited. For in 
 this, as in many other end-fruited mosses, a little 
 side-shoot or young branch (innovation) grows from 
 the main stem immediately below the leaves sur- 
 rounding the base of the fruit-stalk, so that the fruit- 
 stalk appears to arise from the side of the stem. The 
 only method of overcoming the difficulty is to ex- 
 amine carefully the comparative size and thickness of 
 the stem and the shoot, and to determine which is 
 the weaker and so the newer. The leaves surround- 
 ing the base of the fruit-stalk, which are mostly 
 somewhat different in structure from the stem- 
 leaves, are called the perichce tial (Tre/ot, around, %a/r?7, 
 bristle) leaves. 
 
 From among the side-fruited or Pleurocarpous 
 mosses we shall select one only, Hypnum rutab'ulum 
 (PL III. fig. 43), which is common on the trunks of 
 trees and on banks. 
 
 In this moss, the nodding unequal curved capsule 
 (fig. 45) has a double peristome, resembling that of 
 Bryum (fig. 47). The calyptra is half-cleft, and the 
 lid conical and shortly beaked. The stem is reclining 
 or procumbent, and the pale green imbricated leaves 
 (fig. 41) are ovate and pointed, faintly saw-edged, the 
 nerve becoming indistinct at about the middle. It 
 will be noticed that the cells of the leaf (fig. 48) 
 have the prosenchymatous form, or are elongate with 
 pointed ends ; and that the fruit-stalk (fig. 45) is 
 rough with little grains. 
 
 Fructification. The fruit-producing organs of the 
 mosses are of two kinds, comparable to those of the 
 flowering plants, but with their names changed, as in 
 the case of the ferns; the representatives of the 
 anther being called antheridia, and those of the pistil 
 
FRUCTIFICATION, 61 
 
 archegonia. The antheridia may be best examined 
 in Polytrichum piliferum or commune, the patches 
 of stems with red rosette-like heads (figs. 25, 26) be- 
 ing readily found in the spring on open heaths. The 
 coloured leaves forming these heads differ in form 
 from those of the stem, being broader and very sharp- 
 pointed, and have received the distinctive name of 
 perigonial (irepl, around, 701/09, offspring) leaves. In 
 the centre of these leaves, which must be separated 
 with mounted needles in a drop of water, the anthe- 
 ridia (fig. 27), forming oblong cellular green sacs, will 
 be seen ; and intermingled with them will be found 
 some slender pale filaments, composed of mostly two 
 rows of cells, which are the paraptiyses (TrapdQvais, 
 a side growth). If the antheridia are quite ripe, they 
 swell somewhat in the water, and from the free or 
 unattached end a very delicate, colourless, cellular 
 mass gradually escapes. If the antheridia are not 
 quite ripe, the mass must be liberated by dissection. 
 
 On carefully examining this mass under a high 
 power, it will be seen to consist of very delicate 
 rounded cells (fig. 3 a), each containing a coiled fila- 
 ment, revolving more or less rapidly. After a time, 
 these filaments (fig. 3 b) escape, so that they may be 
 examined more minutely. They are excessively de- 
 licate, and are best seen when dried on the slide. 
 Each consists of a very slender curved filament, with 
 a still finer filament, or cilium, arising from it on 
 each side. These are the spermatozoa or spermatd- 
 zoids (a-Trippa, seed, fcoov, animal, eZSo?, resemblance). 
 
 In Fundria the antheridia (fig. 37) may also be 
 found, by careful examination, in the little green 
 heads terminating some of the stems (fig. 41, of 
 the natural size). In this moss, the paraphyses are 
 inflated at the summit into little knobs, or they are 
 capitate (fig. 37). The pistil-like organs of mosses, 
 or the archegonia, from which the capsule is formed, 
 must be looked for in the winter or early spring. 
 
62 MOSSES. 
 
 They occur in the parts of the stems from which the 
 fruit-stalk subsequently arises, and are surrounded 
 by perichsetial leaves, so as to resemble in general 
 aspect the antheridial heads. They are readily found 
 in Tor tula and Funaria, which are always at hand. 
 
 The archegonia (PL III. fig. 21) differ in form from 
 the antheridia, being flask-shaped, with a neck and 
 a dilated base. The neck contains a slender canal, 
 and within the base is a special embryonal cell, from 
 which the capsule is subsequently formed. The 
 spermatozoa of the antheridia pass down the canals 
 of the archegonia, and fertilize the embryonal cells ; 
 but one archegonium only comes to maturity in each 
 head, the others ceasing to grow, and withering, in 
 which condition they are found at the base of the 
 fruit-stalk when the capsule is fully formed. The 
 embryonal cell grows by subdivision, so as to form a 
 stalk-like body, which as it rises extends the arche- 
 gonium upwards until it splits across near the base. 
 Thus the archegonium becomes split horizontally 
 into two parts, the upper and longer of which forms 
 the calyptra, whilst the lower remains as a very short 
 tube or sheath (vagi'nula) surrounding the base of the 
 fruit-stalk. The cellular stalk-like body then swells 
 at the summit, the swollen portion gradually be- 
 coming developed into the capsule, by resolving 
 itself into an outer wall lined inside with a coat 
 forming the outer row of teeth at the top, and within 
 this a thinner membrane or spore-sac, the cleft upper 
 margin of which forms the inner teeth ; and within 
 this are contained the spores. The mass of cells 
 within the spore-sac remains, forming a central 
 column, called the columella. 
 
 These stages of growth may be readily traced in 
 Funaria. In Plate III., fig. 40 represents two ferti- 
 lized archegonia of the natural size, surrounded by the 
 perichsetial leaves ; fig. 33 is a still more advanced 
 archegone. In fig. 34 the calyptra has separated from 
 
MOSSES. 63 
 
 the vaginule, and contains the stalk-like body, which 
 is represented alone in fig. 32, the dark summit indi- 
 cating the commencing formation of the capsule. 
 Fig. 35 represents the young capsule, in which all the 
 parts are more advanced in growth. 
 
 When the seeds of mosses germinate, they produce 
 at first a green Conferva-like filament, which branches 
 at one end, the cells containing green endochrome, 
 while brownish little roots are given off from the 
 other end. The young leafy buds or young stems 
 arise from these confervoid filaments. 
 
 Examination. In the examination of the mosses, 
 the capsules should be viewed as opake objects while 
 fixed in the forceps; and to discover the minute 
 structure of the teeth of the peristome, a capsule 
 should be wetted with spirit, then immersed in water, 
 slit up with fine scissors, and spread out with the 
 mounted needles, so as to form a transparent object. 
 In this way, the curious structure of the teeth be- 
 comes very distinct. 
 
 It must be noticed that, in the mosses, the anthe- 
 ridia and the archegonia usually occur in separate 
 flower-like heads ; or the mosses are either monoecious 
 or dioscious (p. 38). 
 
 Preservation. The mosses may be dried under 
 pressure, and preserved entire in the same manner as 
 the ferns or the flowering plants. If simply dried 
 without pressure, their structure can be readily made 
 out at any future time, by immersing them in water, 
 or by keeping them for a few hours in a moist atmo- 
 sphere. The minute structures of mosses may be 
 mounted in solution of chloride of calcium, or in 
 glycerine ; they keep extremely well without closing 
 the cells. 
 
64 
 
 CHAPTER VII. 
 
 (ALGA, SEA- WEED). 
 
 THE plants belonging to the Class Algae grow in 
 water, either in that of the sea or in fresh water ; a 
 few of them, however, being found on damp earth, 
 damp walls, &c. The marine Algae are commonly 
 known as sea-weeds ; but the fresh- water Algae gene- 
 rally receive but little popular notice, forming, as they 
 do, slimy masses or strata, of a green or brownish, 
 sometimes red, colour. 
 
 Algae are of simple structure, consisting entirely of 
 cells ; in some these are single, in others, united end 
 to end, to form threads or filaments, or grouped into 
 a leaf-like expansion, or collected few together into a 
 little spherical group or a flat plate. They possess 
 none of the fibres, vessels, or ducts of the higher 
 plants, although some long and slender cells, existing 
 in the stalks of the fronds of the larger kinds, bear 
 considerable resemblance to woody fibre. They ex- 
 hibit no distinction of stem and leaf, but consist of 
 fronds representing the stem and leaf combined and 
 undistinguishable. And the term frond must be un- 
 derstood to signify the separate parts arising from 
 the point of attachment when they are fixed ; and in 
 the case of those which are unattached or free, the 
 entire plant is called a frond. 
 
 The Algae are divided into three Orders, viz. the 
 Fucoid'eae or olive-coloured Algae, the Florid' eae or 
 red, and the Confervoid'eae or green Algae. 
 
 FUCOID'EAE, Fucoid Algae, or Melanospor'eae (yu-eXa?, 
 black or dark). The plants composing this order 
 form our largest sea- weeds, and are found everywhere 
 
PLATE IV. [PAGE 64.] 
 MABINE 
 
 Fig 
 2. 
 3. 
 
 4. 
 5. 
 6. 
 
 7. 
 
 8. 
 
 9. 
 10. 
 11. 
 12. 
 13. 
 14. 
 
 15. 
 
 16. 
 
 17. 
 
 18. 
 19. 
 
 Dasya coccinea, piece of. 
 Dasya coccinea, portion with cap- 
 sule (ceramidium). 
 Dasya coccinea, portion of main 
 
 filament. 
 
 Dasya coccinea, section of filament. 
 Meldbesia polymorpha. 
 Melobesia polymorpha, portion 
 
 with capsules (ceramidia). 
 Jania rubens. 
 Jania rubens. 
 Lithocystis AUmanni. 
 Ceramium nodosum. 
 Ceramium nodosum, filament. 
 Ceramium rubrum, filament. 
 Ceramium rubrum, tetraspore. 
 Ceramium rubrum, end of fila- 
 ment. 
 Ceramium rubrum, capsule (fa- 
 
 veUa). < 
 
 Fucus vesiculosus, receptacles of. 
 Fucus vesiculosus, capsules (con- 
 
 ceptacles). 
 Fucus serratus, antheridial con- 
 
 ceptacles. 
 Spore of Fucus vesiculosus. 
 
 Fig. 
 
 20. Antheridia of Fucus serratus. 
 
 21. Plocamium eomWMW,sporophyll. 
 
 22. Plocamium coccineum, with cap- 
 
 sule (coccidium). 
 
 23. Plocamium coccineum, portion of 
 
 frond. 
 
 24. Plocamium coccineum, tetraspore 
 
 from sporophyll. 
 
 25. Polysiphonia fastigiata, portion of. 
 
 26. Polysiphonia fastigiata, filament 
 
 with capsules (ceramidia). 
 
 27. Polysiphonia fastigiata, portion of 
 
 filament. 
 
 28. Corallina officinalis. 
 
 29. Corallina officinalis, portion of fil- 
 
 ament. 
 
 30. Corallina ojfficinalis, capsule (cera- 
 
 midium). 
 
 31. Enter omorpha compressa. 
 
 32. Enteromorpha compressa, cells of 
 
 frond. 
 
 33. Hypnea purpurascens, capsule 
 
 (coccidium). 
 
 34. Hypnea purpurascens, spores. 
 
 35. Hypnea purpurascens, filament. 
 

FTTCOIDE^E. 65 
 
 in the sea and on the sea-shore. They are of an olive- 
 green or olive-brown colour, and usually become 
 darker on drying. 
 
 Fucus vesiculosus, with its parallel-sided or linear 
 olive-brown fronds, is known to every one as the sea- 
 weed which is hung up to act as a weather-glass. The 
 fronds have a central stout vein, or midrib, and scat- 
 tered air-bladders, mostly in pairs. 
 
 The fructification consists of yellowish oval enlarge- 
 ments of the ends of the fronds, called the receptacles 
 (fig. 16) ; but these are somewhat variable in form, 
 being often angular or truncate. On holding one of 
 the receptacles to the light, it will appear to contain 
 a number of little grains imbedded in its substance, 
 slightly projecting above the surface, and in the centre 
 of each is a minute dot or pore. These grains are 
 the capsules, or conceptacles, and contain the spores. 
 The substance of the receptacles is composed of a 
 beautiful network of colourless, jointed, cellular fibres 
 (figs. 17 a and 18 a), the meshes of which are filled with 
 a transparent gelatinous substance ; but immediately 
 around the conceptacles the cells are shorter and 
 more closely packed. The spores (fig. 19) are arranged 
 in the conceptacles in a radiate manner; they are 
 brown, and surrounded by a colourless sac, called the 
 perispore (Kepi, around, (nropa, seed) ; and between 
 them are numerous slender, colourless, jointed fila- 
 ments, the paraph'yses. The spores are not, how- 
 ever, truly single spores, for they ultimately divide 
 into eight segments or sporules, each of which is 
 capable of producing a new plant. 
 
 In the conceptacles of some fronds of Fucus no 
 spores will be found, the conceptacles (fig. 18) being 
 filled with elegantly branched colourless filaments 
 (fig. 20), the ends of many of them being distended 
 into little yellowish sacs ; these are the antherid'ia. 
 The antheridia contain large numbers of exceedingly 
 minute spermatozoa, furnished with two cilia, and 
 
66 ALQM. 
 
 very similar to those existing in the antheridia of the 
 mosses ; these, escaping through the pore of the con- 
 ceptacle, fertilize the spores. 
 
 The figure (20) in the plate was drawn from a con- 
 ceptacle of Fucus serrdtus, another common species, 
 differing from F. vesiculosus in having the margins of 
 the frond serrate ; the antheridia of the two species 
 do not, however, differ in any important respect. 
 To examine the conceptacles of Fucus and their con- 
 tents, the receptacles should be soaked in water, if 
 not fresh, and thin sections made with a sharp knife. 
 They form very beautiful objects, and may be pre- 
 served in chloride of calcium or glycerine. 
 
 FLORID'E^E, or Rhodosper'mese (poSov, rose, crTrep- 
 fj,a, seed). The second Order of Algse, forming the 
 Floridese (flos, a flower), comprises the red sea-weeds; 
 a few of them are purple, or greenish-red ; so that by 
 the colour alone they may be readily distinguished 
 from the Fucoids, and from nearly all those of the 
 next Order, the Confer' voids. A few of them are leaf- 
 like, or possess flat fronds ; but most of them consist 
 of finely divided or feathery fronds. They are often 
 found upon the sea-shore of a dirty white colour, the 
 colouring matter having been decomposed or washed 
 out by rain. 
 
 We shall consider a few of the genera and species 
 under the heads of the families to which they belong. 
 
 CORALLINA'CE^E, the Corallines, or calcareous Algae. 
 In this family we have the beautiful Corallina offi- 
 cindlis (PI. IV. fig. 28), the common Coralline, which 
 is very abundant on the sea-shore, attached to larger 
 sea- weeds, shells, and rocks. It is hard and chalky, 
 from the presence of a large proportion of carbonate 
 of lime in its minute cells. The fronds are composed 
 of jointed and branched filaments. The fructification 
 (figs. 29 and 30) consists of ovate cellular capsules, or 
 ceramid'ia (/eepa/uov, earthen vessel), placed mostly 
 at the ends of pinnate stalks, and containing a tuft 
 
RHODOMELACE.E. 67 
 
 of somewhat club-shaped jointed spores, springing 
 from the base of the capsules (fig. 30) . When ripe, 
 the spores escape from a pore or hole in the end of 
 the capsules. The spores are 4-jointed, and hence 
 are called tet'raspores (rerpa, four) . 
 
 To observe these spores, the capsules must be soaked 
 in strong vinegar for some hours, and then washed 
 with water, to dissolve the calcareous matter. 
 
 Jdnia rubens (PL IV. figs. 7 and 8) is another 
 common and very elegant little coralline, and is of a 
 pale red colour. It differs from the last in the branches 
 being dichot'omous (S/%a, in two, ro/zo?, cutting) or 
 forked, instead of pinnate. The capsules, or ceramidia, 
 have also two short horn-like branchlets, placed one 
 on each side, near the end. 
 
 The genus Melobesia has the frond crustaceous, i. e. 
 forming a hard crust or layer. M. polymor'pha (PL 
 IV. figs. 5 and 6) is common on shells, stones, &c. 
 The capsules (ceramidia) here form little blunt cones, 
 scattered over the crusts, and containing the tufted 
 tetraspores, as in Corallina. 
 
 Lit ho cydtis Allman'ni (fig. 9) is very minute, and 
 not uncommon upon sea- weeds, stones, &c. It con- 
 sists of a single fan-shaped crustaceous layer of cells, 
 closely investing the body to which it is attached ; its 
 fructification is unknown. 
 
 Leaving the family of crustaceous Floridese, we 
 shall now pass to those of softer consistence, although 
 all the marine Algae contain a considerable quantity 
 of calcareous matter. 
 
 RHODOMELA'CE^:. In this family we have the large 
 genus Polysiphonia, in which the frond (PL IV. figs. 25 
 and 26) is filamentous, the filaments being apparently 
 jointed and longitudinally striated. The filaments 
 are composed of rings of cells (fig. 27), arranged end 
 to end, and containing dark endochrome. The ends 
 of the colourless cell- walls separating the endochromes 
 of the cells of adjacent rings produce the jointed ap- 
 
68 ALG^E. 
 
 pearance ; while the striated appearance is caused by 
 the dark cells being elongate and the cell-walls thick, 
 so as to form white interspaces. 
 
 The fructification consists of capsules (ceramidia), 
 attached to the sides of the branches, containing pear- 
 shaped spores, with tetraspores imbedded in swollen 
 branches of separate plants. 
 
 Polysiphonia fastigidta (fig. 25, a small piece) is 
 common, attached to the fronds of Fucus. Its fila- 
 ments are rigid, bristle-like, of the same breadth 
 throughout, forked, and forming globular brown or yel- 
 lowish tufts, from 2 to 4 inches long. The joints are 
 broader than long, each with 16-18 of the dark cells. 
 In the centre of the branches of this sea- weed is a 
 row of curious objects (fig. 26 ), consisting of a dark- 
 coloured body surrounded with irregular spiny mar- 
 ginal processes, and with a colourless short process 
 above and below. These require further investiga- 
 tion. 
 
 P. nigredcens is also common among masses of sea- 
 weeds. Its filaments are brown, pinnate, the branches 
 awl-shaped, and the joints about as long as broad. 
 
 Ddsya coccin'ea (PL IV. figs. 1 and 2, representing 
 small portions of a filament) is a very common fila- 
 mentous red sea-weed of the same family. The fila- 
 ments are 6-8 inches long, and bipinnate, the larger 
 ones somewhat resembling those of Polysiphonia, in 
 being composed of parallel longitudinal cells, arranged 
 round the centre, but containing also smaller inter- 
 mediate cells ; while the smallest branches (fig. 2), 
 which arise in tufts, consist of a single row of cells, 
 little longer than broad. The fruit consists of ovate 
 capsules (ceramidia), placed at the base of the branches, 
 and containing a round mass of spores. There is also 
 another kind of fructification, occurring on distinct 
 plants ; this is formed of one or two rows of tetra- 
 spores, immersed in pod-like capsules, called stichid'ia 
 (cr/%09, row). 
 
CERAMIACE.E. 69 
 
 DELESSERIA'CE^E. In this family, the typical or 
 most highly developed genus of which, Delesseria, has 
 beautiful leaf-like rose-red fronds, we shall examine 
 the common Plocdmium coccin'eum (PL IV. figs. 23 
 and 22) . This is of a fine red colour ; the fronds are 
 from 2 to 12 inches long, and consist of numerous 
 branched and bushy filaments. These are compressed, 
 with the branchlets arranged in alternate rows on the 
 two margins of the stem. The end branchlets are 
 acute and pectinate (pecten, a comb), or arranged 
 like the teeth of a comb. The cells of which the fila- 
 ments consist are small and angular, giving the surface 
 the appearance of being elegantly netted under a high 
 power. The fruit (fig. 22) consists of globular cap- 
 sules, called coccid*ia (KOKKOS, a berry), placed in the 
 axils or forks at which two branches separate, and 
 containing a mass of angular spores. There are also 
 tetraspore-pods (stichidia), as in Dasya ; and tetra- 
 spores (fig. 24) in little leaf-like altered branches 
 (fig. 21), called spor'ophylles (o-Tropa, seed, $>v\\ov, 
 leaf), and antheridia are present. 
 
 RHODYMENIA'CE^E. In this family we have Hyp'nea 
 purpuras 1 cens (PL IV. fig. 35). The filamentous pale 
 purple frond of this sea-weed is from 6 inches to a 
 foot or more in length, the branches being alternate 
 and spreading. The fructification consists of capsules 
 or coccidia (fig. 32), immersed in the branches, and 
 containing the spores (fig. 34). Tetraspores also 
 occur in the cells of the surface of the filaments. 
 
 CERAMIA'CE^;. This is the last family to be noticed. 
 Cerdmium nodosum (PL IV. figs. 10 and 11), which 
 belongs to it, is a most delicate and elegant filament- 
 ous sea-weed, commonly found attached to other sea- 
 weeds. The filaments are hair-like or capillary, irre- 
 gularly dichot'omous ; they consist of colourless cells, 
 3 or 4 times as long as broad, and with thick walls. 
 The junctions of the cells are swollen (fig. 11), and 
 covered with very minute dark red cells, giving them 
 
70 ALGJS. 
 
 a knotty and jointed appearance to the naked eye or 
 under a low power. The globular capsules, orfavel'ke 
 (favus, a honeycomb) , containing the numerous spores, 
 are situated at the ends of the branchlets, and the 
 tetraspores (fig. 11) in twos or threes on the outer 
 margins of them. 
 
 In Cerdmium rubrum, which is also very common, 
 being found attached to stones, rocks, and the larger 
 Algae, the filaments (PL IV. fig. 12) are stouter than 
 in C. nodosumiy branched so as to form tufts from 2 
 to 10 inches long, and their ends forked, with the 
 tips hooked inwards (fig. 14). The central cells of 
 the filaments are large and rounded, and their walls 
 are entirely covered with a layer of very small angular 
 red cells. The globular capsules (fig. 15), orfavella, are 
 situated on the suter surface of the branches, stalked, 
 and supported by 3 or 4 short branchlets. The tetra- 
 spores (fig. 13) are imbedded in the branches, towards 
 the ends. The capsules called favellse differ from 
 the coccidia in the walls being simply membranous, 
 while the walls of the coccidia, like those of the cera- 
 midia, are composed of cells. 
 
 The tetraspores are usually imbedded, among the 
 cells of the superficial layer of the filaments, and are 
 not very easily recognized by an unpractised eye ; it 
 will be observed in the figures that they are some- 
 times cleft horizontally, at others obliquely. 
 
 CONFERVOID'E^E. This Order consists principally of 
 the green freshwater Algae, although some of them 
 are yellowish brown, purple, or red, and some are 
 marine. Their general structure may be best illus- 
 trated by selecting certain common examples from 
 the families composing the order. The families are 
 13 in number. The species which are figured in the 
 plates are found in fresh water, except when other- 
 wise stated. 
 
 CONFERVA'CE^E. On removing some of the soft 
 green matter found adhering to the stems of water- 
 
PLATE V. [PAGE 70.] 
 FRESHWATER ALGJB. 
 
 Fig. 
 
 1. Conferva floccosa, single filament. 
 
 2. Lyngbya muralis, single filament. 
 
 3. Ulothrix mucosa (?), filament. 
 
 4. Synedra radians, prepared frus- 
 
 tules. 
 
 5. Synedra radians, tuft of natural 
 
 frustules. 
 
 6. Cladophora crispata, with zoo- 
 
 spores (a). 
 
 7. Batrachospermum moniliforme, 
 
 portion of filament. 
 
 8. Batrachospermum moniliforme, 
 
 filament. 
 
 9. Closterium acerosum. 
 
 10. Draparnaldia glomerata. 
 
 11. Spirogyra quinina. 
 
 12. Spirogyra nitida, filaments con- 
 
 jugating. 
 
 13. Zygnema cruciata. 
 
 14. Coleochfete scutata. 
 
 15. Xanthidia in flint. 
 
 16. Micrasterias rotata. 
 
 17. Gomphonema acuminatum. 
 
 I Fig. 
 
 18. Gomphonema acuminatum, pre- 
 
 pared frustules. 
 
 19. Ankistrodesmus falcatus. 
 
 20. Pediastrum Boryanum. 
 
 21. Hyalotheca dissiliens. 
 
 22. Pinnularia viridis. 
 
 23. Fragilaria capudna. 
 
 24. Fragilaria capudna, prepared 
 
 frustules ; s* side view of F. 
 virescens. 
 
 25. Scenedesmus quadricauda. 
 
 26. Schizoffonium, probably a form of 
 
 Lyngbya. 
 
 27. Campylodiscus costatus. 
 
 28. Nitzschia minutissima, front view. 
 
 29. Nitzschia minutissima, valves. 
 
 30. Epithemia turgida. 
 
 31. Diatoma elongatum, natural frus- 
 
 tules. 
 
 32. Diatoma elongatum, prepared frus- 
 
 tules. 
 
 33. Cocconeis placentula. 
 
Plate V. 
 
 i I & 
 
CH^ETOPHORACE^E. 71 
 
 plants in any pool or pond, one of the species of Con- 
 ferva, C. flocculosa, is almost sure to be met with. 
 On close inspection with the naked eye, the green 
 filaments of which it consists are just visible, as ex- 
 tremely fine, soft, silky threads ; and, under a high 
 power of the microscope, the filaments are seen to be 
 uiibranched, and composed of a single row of cells 
 (PL V. fig. 1), or joints, as they are called in technical 
 works ; these are 2 or 3 times as long as broad. In 
 some specimens the joints are swollen, so as to present 
 a rounded outline. In another common species, C. 
 bombydina, the filaments are somewhat more slender, 
 and the joints are from 3 to 5 times as long as broad. 
 
 Cladoph'ora crispdta. This Confervoid forms large, 
 entangled, dull-green masses, composed of branched, 
 tufted, somewhat rigid and coarse filaments. It is 
 often a troublesome overrunner of the fresh-water 
 vivarium. The filaments are composed of thick- walled 
 cells (PL V. fig. 6), from 4 to 6 times as long as 
 broad, and often containing minute starch-granules. 
 
 The Confervacese have two modes of reproduction. 
 The first of these consists in the division of the endo- 
 chrome of the joints into a number of distinct seg- 
 ments, each of which becomes furnished at one end 
 with two very slender cilia (PL Y. fig. 6 a). After a 
 time, these ciliated bodies, which are called zo'ospores 
 (wov, animal, airopd, seed) or gonid'ia (701/77, seed, 
 eZSo?, resemblance), escape from the cells either by 
 their rupture or through a papillary orifice, and swim 
 about in the water, ultimately losing their cilia and 
 growing into cells resembling those of the parent 
 plant. In the second method, which occurs, for in- 
 stance, in Conferva bombycina, certain of the joints 
 enlarge so as to become rounded or inflated ; their 
 endochrome then becomes coated with a new cell- wall, 
 and so forms a spore, which subsequently escapes 
 from the cell and germinates. 
 
 :. Draparnal 'dia glomerdta forms 
 
72 ALG^E. 
 
 small green jelly-like masses, adhering to sticks and 
 stones in water. These consist of branched filaments 
 (PL V. fig. 10), prolonged at the ends into colourless 
 hair-like points, and composed of single rows of cells, 
 the green endochrome forming a band across the 
 middle of each cell, the ends being colourless. 
 
 In Coleochdte scutdta (PL V. fig. 14) the cells are 
 closely united, so as to form a minute flat green disk. 
 In the natural state, this beautiful little object adheres 
 to the submerged leaves and stems of water-plants, 
 and is therefore difficult to be found. But if a few 
 healthy water-plants be kept for some time in a glass 
 jar, the little Coleochcete, which is about as large as 
 a pin's head, will often be found adhering to the side 
 of the glass. 
 
 BAT'RACHOSPEB/MEJE. The members of this family 
 resemble to the naked eye the little masses of Drapar- 
 naldia, and they are found in the same localities. 
 They are of various colours, being green, brown, 
 purple, or red. They consist, as in Bat'rachosper'mum 
 monilifor'me (PL V. fig. 8), of branched filaments, 
 which have a knotty appearance under a low power. 
 The larger filaments are composed of cells arranged 
 end to end, the knots consisting of numerous smaller 
 whorled filaments, i. e. filaments arising from around 
 them at the same level (fig. 7). The cells composing 
 the whorled filaments are beaded or moniliform, and 
 are prolonged into colourless hair-like points. The 
 globules seen among the branches (fig. 7) consist of 
 groups of spores. 
 
 ZYGNEMA'CEVE. The members of this family re- 
 semble the Confervacese in consisting of simple cel- 
 lular filaments (Pl.V.figs.ll, 13), but differ from them 
 in the elegant arrangement of the endochrome : this 
 forms beautiful spiral bands, as in Spirog'yra quini'na 
 (fig. 11), or star-shaped masses, as in Zy grid ma cru- 
 cia'ta (fig. 13). A remarkably curious phenomenon 
 met with in them is the manner in which the spores are 
 
DESMIDIACE.E. 73 
 
 formed, and which is known as conjugation. In this 
 process the opposite cells of two distinctfilaments, lying 
 near together, push out protrusions of the cell-walls, 
 which meet and open into each other, forming cross 
 tubes, as in Spirog'yra nit'ida (PL V. fig. 12). The 
 contents of the opposite cells of the filaments then 
 unite, forming large spores, which remain either in 
 the cells of one of the filaments or in the cross 
 tubes. 
 
 The three species figured are common in clear 
 pools. 
 
 DESMIDLA/CE^E. The Desmidiacese are truly micro- 
 scopic, few of them being even perceptible to the naked 
 eye without the very closest examination. They are 
 very beautiful, on account of their bright green co- 
 lour and often elegant forms. Many of them are 
 very common, existing in every pond or ditch; but 
 they abound most in clear open boggy pools on heaths. 
 On placing some water containing them in a glass 
 jar and exposing it to the light, they will often be 
 found adhering to the glass, or forming a layer on 
 the surface of the muddy sediment. 
 
 The Desmidiacese consist mostly of single cells 
 (PL V. figs. 9, 16) ; and these consist of two equal halves 
 or segments, as indicated either by a paleness of the 
 endochrome or a deep constriction at the line of 
 junction, which is called the suture. The cells are 
 often elegantly lobed and cut, or spiny; and in 
 many the surface exhibits minute markings, consist- 
 ing of little protrusions of the cell-wall outwards, or 
 inflations, as they are called. 
 
 Their reproduction is effected by division and con- 
 jugation. In the process of division the cells gradually 
 separate at the suture, and a new half-cell is formed 
 upon each old half, which grows until it attains the 
 size and form of the original half of the parent-cell. 
 The conjugation is effected by two cells approximating 
 so that their sutures are near together, the cells then 
 
74 ALG.E. 
 
 open at the sutures, and the effused contents become 
 united to form a spore or sporange, from which one 
 or more individuals are formed. These spores are 
 often elegantly spinous on the surface. 
 
 Among the species selected for illustration is Clos- 
 terium acerosum (PI. V. fig. 9), in which the cells are 
 single, elongate, very slightly curved or lunate ; the 
 endochrome forms long bands, often containing nu- 
 merous globules or transparent vesicles. At each 
 end of the cells is a round transparent vesicle, con- 
 taining exceedingly minute granules, which exhibit a 
 trembling kind of motion. Between the cell- wall 
 and the cell-contents very fine currents may also be 
 detected, forming a circulation resembling that in the 
 hairs of Tradescantia. 
 
 In Micrasterias rotdta (PL V. fig. 16) the cells, 
 which are single, are deeply cleft into two segments 
 at the suture, the segments being again regularly cut 
 into five lobes, which are toothed or dentate. 
 
 In Hyalotheca dissil'iens (PL V. fig. 21) the cells 
 are united into a cylindrical filament, and are sur- 
 rounded by a very delicate gelatinous sheath. In 
 Ankistrodes'mus falcdtus (PL V. fig. 19) the cells re- 
 semble those of Closterium in shape, but are aggre- 
 gated into faggot-like bundles, and are very much 
 smaller. In the beautiful little Pediadtrum borydnum 
 (PL V. fig. 20) the cells are aggregated into a disk, 
 the marginal cells being bidentate or having each two 
 points, so that the whole resembles a star. The species 
 of Pediastrum are reproduced by the contents of each 
 cell subdividing into numerous ciliated segments or 
 zoospores, which subsequently escape in a mass from 
 the cell, ultimately losing their cilia, and reuniting 
 to form a new individual. 
 
 In Scenedes'mus quadricauda (PL V. fig. 25) the 
 oblong cells are united, side by side, the outermost 
 cells being furnished with a bristle at each end. The 
 division of these cells takes place obliquely, so that 
 
DIATOMACE.E. 75 
 
 in the divided groups the cells are situated in two 
 alternate rows. 
 
 The spores of many of the Desmidiacese are spi- 
 nous, and they are often found fossil in flint (PL V. 
 fig. 15). To detect them in this substance, thin slips 
 of flint may be examined under a half-inch power ; 
 or the chips of flint may be cemented to a slide with 
 balsam, and ground down on a hone. 
 
 The Desmidiacese must be mounted in the moist 
 state : the smaller ones will keep well in chloride of 
 calcium \ but the larger ones are injured both by 
 that liquid and by glycerine. The remarks made upon 
 mounting, at page 15, are especially applicable to these 
 delicate organisms. 
 
 DIATOMA'CE^E, or Siliceous Algae. The members 
 of this family are singly very minute ; but when ex- 
 isting in large numbers, as they are often found at 
 the bottom of ditches and ponds, on the submerged 
 stems of water-plants, or upon damp ground, they 
 form yellowish-brown evident masses or strata. They 
 occur both in sea- and in fresh water. They usually 
 consist, like the Desmidiacese, of single cells, which 
 are called frustules. But they are especially charac- 
 terized by the cell-walls being imbued with silica or 
 flint, so that if the frustules be heated to redness upon 
 the point of a knife or a slip of platinum-foil, which 
 destroys the organic part of the cells, the coat of 
 silica remains, exhibiting the perfect form of the 
 original cells or frustules. The form of the frustules 
 is very different in the various genera and species, as 
 represented in PL V. tigs. 22, 23, 27, 30, 31, and 
 PL VI. figs. 16, 17, 23; and it will be noticed that, 
 in the figures, two views are given of each frustule, 
 / indicating the front view, and s the side view. In 
 all the front views, as in PL V. fig. 22, one or more 
 lines will be observed running longitudinally down 
 the middle of the frustules, and corresponding to the 
 indications of division existing in the cells of the 
 
 H2 
 
76 . ALG.E. 
 
 Desmidiaceee. Each half of a frustule is called a 
 valve, and the line at which these valves meet is 
 called the suture. That side or aspect of the frustule 
 in which the suture lies (fig. 22/) is the front view, 
 and the other aspect of the frustule (fig. 22 s) is the side 
 view. The frustules are mostly four-sided the main 
 breadths of the two opposite valves forming two sides, 
 and the bent margins of the valves, with the back and 
 front of the hoop, forming the two other sides - y so 
 that the view presented by the side of a frustule is the 
 same as that of a single valve. The suture is the line at 
 which the division of the frustules takes place in the 
 formation of new individuals. In this process the 
 cell-contents divide into two parts, as in ordinary endo- 
 genous cell-formation, the two new surfaces thus 
 produced becoming coated with a new portion of cell- 
 wall or valve, so that two frustules now occupy the 
 place of the original one. At the same time a silice- 
 ous band, encircling the frustules at the line of suture, 
 is formed to fill up the interval between the edges of 
 the parent valves; this is the hoop (PI. V. fig. 22 /;. 
 PL VI. fig. 10/), and beneath it lie the two newly 
 formed valves. In many cases I believe that each 
 half-frustule becomes coated with a new entire cell- 
 wall, with its siliceous valves. 
 
 The frustules of the Diatomaceae are constantly 
 undergoing division when in vigorous growth. After 
 the frustules have divided, the new ones either sepa- 
 rate entirely, as is perhaps most commonly the case ; 
 or they remain united, sometimes completely, so as 
 to constitute a filament (PI. V. fig. 23), while at others 
 the frustules cohere only at the angles (PL VI. fig. 
 23), so as to form a zigzag chain. 
 
 In some species, the frustules are attached to foreign 
 bodies by means of a gelatinous cushion (PL V. fig. 5 ; 
 PL VI. fig. 7) j while in others they are situated upon 
 a simple or branched gelatinous stalk (PL V. fig. 17) 
 or stipes (stipes, a stem) . 
 
DIATOM ACE ;E. 77 
 
 When the frustules are examined in the living 
 state, the cell- contents resemble those of ordinary 
 vegetable cells, excepting in regard to the colour, and 
 exhibit granules and globules, and sometimes a nucleus 
 is visible. It will also be noticed that many of the 
 free frustules move slowly across the field of the 
 microscope ; but the cause of the motion is unknown. 
 
 When the frustules have been properly prepared, 
 the surface of the valves exhibits a number of coarser 
 or finer markings, consisting of dots, lines (striae), 
 flutings, or networks, &c., arranged with great re- 
 gularity and symmetry, often of extreme minuteness, 
 and rendering them exquisite objects under the mi- 
 croscope. The exhibition of these markings requires 
 not only that the valves shall be properly prepared 
 and mounted, but that the object-glasses be of good 
 quality, and that the management of the light be 
 thoroughly understood ; so that to a beginner, their 
 examination is often a matter of great difficulty ; for 
 only the very coarsest or largest of these markings 
 can be perceived in the natural frustules. 
 
 The appearance of these markings, and even their 
 apparent absence or presence, frequently depends 
 upon the kind of illumination used : thus, under one 
 kind of illumination the valves may appear simply 
 white or coloured, while under another they appear 
 covered with lines, and under a third with dots. It 
 will often be observed, also, that the colour of the 
 valves varies according to the illumination and the 
 power used the same valve appearing white, yellow, 
 brown, blue, &c; and the wet or dry state of the 
 frustules often cause a decided difference in their ap- 
 pearance as regards colour. 
 
 To illustrate the forms and markings of the frus- 
 tules and valves, we may select the following species 
 taking first those which occur in fresh water. 
 
 In Epithemia tur'gida (PI. V. fig. 30), the side- 
 view or valve (s) exhibits transverse or slightly radia- 
 
 H 3 
 
78 ALG.E. 
 
 ting lines, with intermediate rows of dots these 
 markings being continued over the margins of the 
 valves so as to appear also in the front view (fig. 30/), 
 ceasing at the hoop. The frustules are curved or 
 arcuate (ar'cus, a bow) in the side view, oblong and 
 narrowed at the ends in the front view. 
 
 In Fragildria capucina (PL V. fig. 23), which is ex- 
 tremely common in fresh- water pools, &c., the frus- 
 tules are united side by side into long filaments, 
 which are often twisted. In the separate and pre- 
 pared frustule, the front view (PL V. fig. 24/) is rect- 
 angular, the valves (s) being narrowly lance-shaped 
 or lanceolate. The valves under ordinary illumina- 
 tion appear colourless and without markings, but, by 
 proper management of the light, very fine transverse 
 striae are seen upon them, consisting of rows of very 
 minute dots. Fig. 24 s* represents the valve of Fra- 
 gilaria vires' cens, a nearly allied species. 
 
 Diat'oma elongdtum (PL V. fig. 31) is often found 
 with the above. Its frustules are coherent at the 
 angles. The front view (fig. 32 /) is rectangular, 
 often slightly narrowed in the middle ; and the valves 
 are narrowly linear, and capitate at the ends ; they 
 are also transversely striated. 
 
 In Synedra splen'dens {PL V. fig. 5) the frustules 
 radiate from a soft gelatinous cushion. They are 
 linear in the front view (fig. 4 f) , the valves (fig. 4 s) 
 being gradually narrowed or attenuated from the 
 middle to the ends, and exhibit transverse striae 
 interrupted opposite a middle longitudinal line. 
 
 In Campy lodis 'cus costdtus (PL V. fig. 27) the frus- 
 tules are disk-shaped and curved, so as somewhat to 
 resemble a saddle. The markings consist of central 
 dots, with radiating coarse flutings. 
 
 Nitzsch'ia minutis' sima (PL V. fig. 28) has oblique 
 valves, i. e. the front half of the suture is not opposite 
 the back portion ; the valves (fig. 29) are constricted 
 in the middle, and the ends narrowed and prolonged. 
 
DIATOMACE.E. 79 
 
 The markings consist of a row of oblong dots or 
 puncta (punctum, a point) . This species often forms 
 yellowish layers upon damp paths, &c. 
 
 In the next group, the valves have a longitudinal 
 line running down the middle of the valves, with a 
 little knob or nodule in its centre (PL V. fig. 22 s), 
 both consisting of internal thickened portions of the 
 valves. 
 
 In Cocconeis placen'tula (Pl.V. fig. 33) the valves are 
 oval, and the markings consist of longitudinal rows 
 of minute dots, with a marginal row of puncta ; these 
 markings are invisible under ordinary illumination. 
 
 InGomphonema acumindtum (Pl.V. fig. 17) thefrus- 
 tules are attached to a branched stalk (stipes) ; they are 
 wedge-shaped or ciineate (cuneus, a wedge) and trans- 
 versely striate (fig. 18), the striae consisting of dots. 
 
 In Pinnuldria vir'idis (PL V. fig. 22), which is very 
 often seen slowly traversing the field of the micro- 
 scope when a drop of pond-water is examined, the 
 frustules in the front view are linear, the valves being 
 elliptic oblong, and transversely striated, the striae 
 consisting of furrows. 
 
 In Gyrosig'ma (Pleurosig'ma) attenudtum (PL VI. 
 fig. 16) the valves are sigmoid, or somewhat resemble 
 a Greek 9 (sigma) in outline, and the markings con- 
 sist of rectangularly crossed rows of very fine dots ; 
 in the front view, the frustules are linear-oblong with 
 truncate ends. 
 
 Tabelldria flocculosa (PL VI. fig. 23) has the frus- 
 tules adherent only at the angles, as in Didtoma. They 
 are rectangular, and in the front view exhibit a row 
 of longitudinal dark lines interrupted in the middle ; 
 these have been compared to the vittse of the fruit of 
 the Umbelliferae, and have received the same name. 
 
 Among the marine species may be mentioned 
 Melosira nummuloides (PL VI. fig. 9), in which the 
 frustules are united into a chain or cylindrical fila- 
 ment. This is very common among sea- weeds, &c, ; 
 
80 ALG.E. 
 
 and it illustrates well the process of division of the 
 frustules (fig. 10 /) . The valves are covered with 
 fine dots, and near each end of the frustules is 
 a projecting rim encircling it, and appearing as a 
 curved line extending beyond the margin of the 
 frustule in the front view. In Actinocy 1 clus un- 
 duldtus (PI. VI. fig. 5) the frustules are separate, 
 disk-shaped, and the valves are divided into six equal 
 parts by six rays, each alternate portion of the surface 
 of the valves being situated on a lower level than 
 those adjacent, so that an alteration in the focus is 
 required to bring into view the dots on any two ad- 
 jacent divisions of the valve. The surface of the 
 valves is covered with easily recognized dots. The 
 form of the surface is best seen in the front view 
 (fig. 5 /) when the frustule is placed on its edge. 
 
 Rhabdonema arcudtum (PI. VI. fig. 7), which is 
 very commonly found attached to sea- weeds, resem- 
 bles Tabelldria in the frustules having the vittae 
 (PI. VI. fig. 8/). The frustules form short filaments, 
 attached by a little gelatinous cushion. The valves 
 have transverse striae, interrupted in the middle 
 (fig. 8 *). 
 
 Gyrosig'ma (Pleurosig ma) anguldtum (PL VI. fig. 17) 
 resembles G. attenudtum in the sigmoid form ; but the 
 markings consist of lines crossing each other obliquely; 
 and these are resolvable into rows of dots (fig. 17 a) 
 under suitable illumination. 
 
 In Coscinodis'cus radidtus (PI. VI. fig. 3) the frus- 
 tules are disk-shaped, the valves being elegantly 
 sculptured with easily recognized cell-like markings 
 or dots, so as to resemble a piece of vegetable cellular 
 tissue. But in some other species the dots are very 
 minute, and difficult to be shown satisfactorily. 
 These markings consist of depressions or pits in the 
 surface of the valves. That this is the case may 
 easily be seen by examining a fragment of the valve, 
 when the shadings of the broken ends of the netted 
 
DIATOMACE.E. 81 
 
 thicker portions, which project like teeth, strongly 
 contrast with the difficultly distinguishable portions 
 of the thin interspaces. The fossil forms from the 
 Bermuda deposit are best for the investigation of 
 this structure ; many of these are extremely beautiful 
 microscopic objects, their markings resembling those 
 on the engine-turned back of a watch. 
 
 The detection of the finer markings of the Diato- 
 macese, which, according to my view, consist of de- 
 pressions like those upon the valves of Coscinodiscus t 
 is a matter of great difficulty to those who are un- 
 accustomed to the use of the microscope, and who 
 have not a complete set of apparatus. The main 
 point to be attended to in bringing them into view, 
 is to use one-sided oblique light, i.e. to turn the 
 mirror by its stem as much as possible to one side, 
 and then to incline it so as to throw the light upon 
 the object. In this way the valves of the species of 
 Gyrosigma, for instance, appear covered with lines 
 (PL VI. figs. 16 and 17) ; but the lines are spurious, 
 i. e. they are the optical expression of rows of minute 
 dots (figs. 16 0, 17 a) ; and when oblique light is 
 thrown upon the valves from all sides, by means of a 
 special achromatic condenser, in which the central rays 
 are excluded, the dots become distinct, and the mark- 
 ings resemble those on the valves of Coscinodiscus. To 
 show the finer dots clearly, a valve should be crushed, 
 so as to obtain a fragment as flat as possible ; for the 
 surface of the valves is curved more or less in all the 
 species. The valves of G. angulatum are generally 
 used to test the quality of the object-glasses of the 
 microscope, and also for practice in " making out " 
 the lines and dots ; there are, however, many Diato- 
 macese more difficult. 
 
 As the nature of these markings is a disputed 
 point, the discussion of which is not adapted for an 
 elementary work, I must refer for further details to 
 the ' Micrographic Dictionary ; 3 it may be remarked, 
 
82 ALG^E. 
 
 however, that some observers have regarded them as 
 cells, and others as elevations or tubercles on the 
 surface of the valves. 
 
 The preparation of the valves for showing the 
 markings should be effected by burning the frustules, 
 or the mass containing them, on a strip of platinum- 
 foil over a spirit-lamp. The incinerated mass should 
 then be transferred to a slide, and the valves separated 
 with the greatest care by a bristle mounted in a hair- 
 pencil stick under a low power of the microscope. 
 
 This is, however, a substitute for the proper method, 
 which is dangerous in the hands of one unpractised 
 in chemical manipulation. It is this : The mass of 
 Diatomacese (the water containing it having been 
 carefully poured off as far as possible) is put into a 
 Florence oil-flask, and strong nitric acid (aquafortis) 
 gently added, more than sufficient to cover it. The 
 mixture is then carefully boiled over a spirit-lamp 
 for some time. When it is cold, distilled water is 
 added, the whole shaken, and allowed to settle. The 
 watery part is then gently poured off, more water 
 added, and this poured off after settling, and the pro- 
 cess repeated until a drop of the water evaporated to 
 dryness on a slide leaves no residue. The Diato- 
 maeese then form a white sediment at the bottom of 
 the water, and can be transferred to a slide with a 
 dipping-tube. The drop is then dried with a gentle 
 heat, and the valves mounted as dry transparent 
 objects (p. 12). 
 
 If the valves have coarse markings, they may be 
 mounted in balsam; but if the markings are fine, 
 balsam makes them much more difficult of detection. 
 
 Many of the most beautiful Diatomacese are found 
 in the fossil state ; and specimens of these are sold 
 already mounted. I would advise those unacquainted 
 with them to purchase a slide of the ' ' Bermuda " or 
 " Richmond " earth, which abounds in the species 
 of Coscinodiscus ; and of the " San Fiore deposit," 
 
VOLVOCINE.E. 83 
 
 which contains many species of Epithemia, Navicula, 
 Pinnularia, &c. These may be procured from Mr. 
 Norman, 178 City Road, or from the microscope- 
 makers. 
 
 VOLVOCIN'EJE. The Volvocinese are inhabitants of 
 clear fresh-water pools, on heaths and bogs. They 
 are very minute, of a rounded or plate-like (tabular) 
 form, of a green colour, and are pretty readily distin- 
 guished from most of the other Algse by their free 
 motion ; for they swim about in the water like animals, 
 as which they were formerly considered. They consist 
 usually of groups of thick- walled soft cells, each being 
 furnished with one or two cilia, by means of which 
 the movement of the compound bodies is produced. 
 
 In the beautiful Volvox globdtqr (which is not 
 uncommon) the cells form a hollow sphere (PL VI. 
 fig. 18), studded with exceedingly minute green spots 
 or zoospore-like bodies, representing the green endo- 
 chrome of the component cells, and from each of 
 which very fine radiating lines extend, so as to give 
 the surface a netted appearance ; the lines consisting 
 of delicate processes of the endochrome, which may 
 be compared with those existing in the cells of the 
 hairs of Tradescantia. In the interior of the parent 
 globes are often seen several young organisms, usually 
 eight, of a deep green colour ; these escape by the 
 rupture of the parent, so as to form independent 
 beings. Sometimes they are found of a yellow 
 colour, and furnished with a thick transparent coat ; 
 these are called ' ' resting spores," as they remain for 
 some time before undergoing their full development. 
 
 The cilia of Volvox, of which there are two to each 
 of the component cells, are difficult to detect ; they 
 are best seen when the organism is dried without a 
 cover, or after moistening them with a little solution 
 of iodine, which dyes them brown. 
 
 Synura volvox (PL VI. fig. 13) is a still more 
 minute member of this family, and is often found 
 
ALG.E. 
 
 rolling along among Conferva. The greenish zoospore- 
 like bodies of this Alga have one cilium only, and 
 arise from a common centre by a narrowing of the base 
 (%. 14). 
 
 In Gonium pectordle (fig. 11 a) the green bodies, 
 which are sixteen in number, and furnished each with 
 two cilia, are grouped into a flat square plate ; and in 
 the very minute Gonium tranquil' lum (fig. 11 c) these 
 bodies are also sixteen in number, and arranged in a 
 tabular form, but are without cilia. 
 
 SIPHONA'CE^E. The structure of this family may be 
 illustrated by the genus Vaucheria, of which two or 
 three species are common on damp ground or in 
 freshwater pools, forming a green layer. At first 
 sight, the filaments of which the little plants consist 
 appear like those of a stout Conferva ; but on close 
 examination they are found to be branched, and not 
 jointed, consisting of a single cell from end to end 
 (PL VI. fig. 26). The reproduction is effected by 
 the agency of two kinds of organs, antheridia 
 and capsules (sporangia), situated near each other 
 (fig. 26 a) on the walls of the filaments, of which they 
 are protrusions or outgrowths their cavities being 
 separated from that of the filament by a partition 
 or septum. The antheridia produce spermatozoa, 
 and the sporangia each a spore, the one fertilizing the 
 other in the ordinary manner. In addition to this 
 method of fructification, zoospores are also produced 
 the ends of the filaments becoming swollen, the con- 
 tents cut off by a septum, and forming single large 
 zoospores covered with cilia, the farther development 
 of which resembles that occurring in the Confervacese. 
 
 OSCILLATORIA'CE/E. The members of this family 
 are commonly found in stagnant water or on shaded 
 damp ground, . especially in the cold seasons of the 
 year, forming green strata or masses. 
 
 Oscillatoria autumndlis (PL VI. fig. 1) occurs every- 
 where upon damp shaded banks of ditches, espe- 
 
PLATE VI. [PAGE 84.] 
 FRESHWATER 
 
 Fig. 
 
 1. Oscillatoria aittumnalis. 
 
 2. Oscillatoria nigra. 
 
 3. Coscinodiscus radiatus. 
 
 4. Nostoc minutissimum. 
 
 5. Actinocyclus undulatus. 
 
 6. Bacterium. 
 
 7. Rhabdonema arcuatum. 
 
 8. Rhabdonema arcuatum, prepared 
 
 frustules. 
 
 9. Melosira nummuloides. 
 
 10. Melosira nummuloides, prepared 
 
 frustules. 
 
 11. a, b, Oonium pectorale : 11 c. Go- 
 
 nimn tranquittum. 
 
 12. Spirulina oscillarioides. 
 
 13. Synura volvox. 
 
 14. Synura volvox. 
 
 16. Gyrosigma attenuatum, front view. 
 
 Fig. 
 
 16. Gyrosigma attenuatum, side view ; 
 
 16 a, portion of a valve. 
 
 17. Gyrosigma angulatum ; 17 a, por- 
 
 tion of a valve. 
 
 18. Volvox globator. 
 
 19. Glozocapsa. 
 
 20. Chara vulgaris, globule. 
 
 21. Chara vulgaris, portion of fila- 
 
 ment. 
 
 22. Chara vulgaris, branch with nu- 
 
 cule and globule. 
 
 23. Tabellariajlocculosa. 
 
 24. Tdbellaria flocculosa, prepared 
 
 frustules. 
 
 25. Palmella cruenta. 
 
 26. Vaucheria Ungeri (sessilis). 
 
 27. Vaucheria Ungeri, capsule. 
 
Plate VI 
 
OSCILLATORIACEjE. 85 
 
 cially when newly made, forming a greenish-black 
 closely adherent stratum. Under the microscope it is 
 seen to consist of innumerable palish-green filaments ; 
 these are jointed or transversely striated, some being 
 straight, others curved, the ends often exhibiting a 
 writhing or worm-like movement. The appearance 
 of these fibres is peculiar, seeming as if they were 
 solid throughout, and so differing from that of the 
 Confervacese, in which the cell-walls are readily dis- 
 tinguishable from the cell- contents. The fibres easily 
 break across at the joints ; and the last few segments 
 are often narrowed and rounded, so as to form a blunt 
 point. When they have been left in water, they ex- 
 hibit colourless tubular sheaths surrounding and 
 extending beyond them. These sheaths consist of 
 the consolidated outer portions of the cell- walls ; for 
 when the cells undergo transverse division, and ex- 
 pand by growth in the direction of the length of the 
 filament, the original septa or inner walls are broken 
 through, and their remains may often be seen on the 
 inner surface of the sheath, appearing as little teeth. 
 
 Oscillatoria nigra (PL VI. fig. 2) is another very 
 similar species, forming blackish-green masses, and 
 is common in ditches. It has longer filaments than 
 the last, with narrowed and slightly curved ends ; and 
 the endochrome is distinctly granular. 
 
 In two other genera of this family, Vib'rio and 
 Spirulma, the filaments are spiral. Vib'rio spiril'lum 
 is excessively minute, colourless, and found in decom- 
 posing vegetable mixtures. The short filaments move 
 rapidly through the water, with a corkscrew-like 
 motion. In Spirulina oscillarioides (PL VI. fig. 12), 
 which is more rarely found in clear pond- waters among 
 Conferva, the filaments are greenish, and form a 
 beautiful simple spiral, resembling that of a very 
 slender spiral vessel. 
 
 Lyngbya murdlis (PL V. fig. 2) is very common on 
 damp walls, gravel walks, &c. It forms a bright 
 
86 ALGM. 
 
 grass-green layer, consisting of somewhat rigid curled 
 filaments. The endochrome is usually broader than 
 long ; and the cells of the filaments are often found 
 empty, the endochrome having escaped in the form 
 of gonidia. 
 
 PL VI. fig. 6 represents a species of Bacterium 
 which is not uncommon in decomposing vegetable 
 liquids ; the filaments are short, curved, pointed at the 
 ends, and have four joints. 
 
 Fig. 26 represents a Schizogonium, found upon 
 damp paths. The filaments resemble those of Lyngbya, 
 but are united in pairs. 
 
 Fig. 3 represents a filament of a Vlothrix, which 
 is common in freshwater pools, showing the curious 
 manner in which the endochrome is arranged in the 
 cells, forming bands partially lining the cell-walls. 
 
 NOSTOCHA CEM. Two species of the typical genus 
 Nos'toc will serve to represent this family. Nos'toc 
 commune is found on damp ground or in ponds, and 
 forms to the naked eye firmish, olive-green, skin-like 7 
 plaited masses, an inch or more in diameter. Under 
 the microscope it is seen to consist of numerous 
 beaded fibres, imbedded in worm-like gelatinous 
 sheaths ; these are curved and interwoven to form the 
 compound mass. In the middle of many of the fila- 
 ments is an enlarged colourless cell, called the vesi- 
 cular cell, which is related to the reproduction, but 
 in a manner not yet determined. 
 
 Nostoc minutissimum (PL VI. fig. 4) forms solid 
 gelatinous bluish-green masses, varying in size from 
 a pin's head to a pea; it is found upon unhealthy 
 water-plants kept in glass vessels. The component 
 filaments are very slender, wavy, and the sheaths 
 often have a brownish tinge. 
 
 ULVACE.E. These Algae are mostly marine some, 
 however, being found in brackish or fresh water, or 
 on damp ground, thatch, moss, &c. They are gene- 
 rally of considerable size, forming flat or tubular 
 
PALMELLACE.E, 87 
 
 fronds, often several inches long, a few being fila- 
 mentous. They consist of one or more sheets or 
 layers of cells, containing mostly green endochrome. 
 This at first fills the cells, but subsequently becomes 
 converted into single spores, or subdivided into nume- 
 rous ciliated zoospores. 
 
 Ul'va latissima is very common on the sea-coast, 
 being found attached to stones, shells, &c. It forms 
 a broad, flat, green, rounded or^oblong, thin frond, 
 wavy and crumpled at the margins, and from 6 to 
 18 inches in length. The minute cells form two 
 layers, adherent to each other. The zoospores formed 
 are numerous in each cell. 
 
 Enteromorpha compres sa (PL IV. fig. 31) is also 
 common in the sea and in brackish ditches ; it is 
 often found floating. The frond is green, tubular, 
 flattened or compressed, and branched, the branches 
 being usually simple and narrowed at the base. The 
 frond consists of two layers of minute cells, separated 
 .by a space rendering it hollow. The zoospores are 
 numerous in the cells (fig. 32) . 
 
 PALMELLA'CE^. These Algae are found in fresh or 
 salt water, or on damp earth, wood, &c. They are 
 green or red, forming round or irregular masses or 
 strata. They consist of loosely connected cells, im- 
 bedded in a gelatinous mass or matrix, thus forming 
 a frond. 
 
 Chlorococcum vulgdre (PL II. fig.l) is very common 
 upon the bark of elm-trees, palings, &c., forming a 
 green granular crust. It consists of minute rounded 
 or oval cells, mostly undergoing division into twos, 
 fours, or eights. These cells are attached to the 
 sides or ends of very fine colourless filaments. It is 
 most probable that this organism, which is usually 
 placed among the Algae, consists of the gonidia of a 
 Lichen. 
 
 Chlorococcum muror'um forms a somewhat similar 
 .but soft and thin green layer, upon damp walls or 
 
88 ALGJE, 
 
 other porous bodies. It consists of very minute oval 
 green cells,, with thick walls, and imbedded in the 
 ends of prolongations of a gelatinous matrix. 
 
 Palmel'la cruerita (PI. VI. fig. 25) forms a portwine- 
 red layer at the bottom of damp walls or on the 
 ground. It is composed of pale red cells, imbedded 
 in no definite order in a colourless gelatinous matrix. 
 The cells are filled with red granules, and are often 
 found undergoing division. 
 
 PI. VI. fig. 19 represents a species of Glceocap'sa, 
 in which the cell- envelopes do not soften and unite to 
 form a gelatinous matrix, as in Palmetto, and other 
 members of the family, but are persistent. This 
 species occurs in fresh water containing Confervae. 
 
 CHARA'CE^E. This family consists of the single 
 genus Chdra, the systematic position of which is not 
 agreed upon by authors ; as however its structure will 
 be better understood after what has been gone over, 
 it may be conveniently considered here. 
 
 There are several species of Chara, the one illus- 
 trated, Char a vulgdris (PI. VI. fig. 21), being com- 
 monly found in ditches and pools. It consists of long 
 main stems, often a foot in length, which are branched, 
 and surrounded at tolerably regular intervals by whorls 
 of branchlets. In some species, the stems and branches 
 consist simply of elongated cells, arranged end to end ; 
 while in others, of which Chara vulgaris is one, the 
 central cells are surrounded by a number of narrower 
 spirally arranged cells, forming an outer coating. 
 
 The Charse have long formed interesting micro- 
 scopic objects, on account of the circulation of the 
 protoplasm being visible in the cells, as in the hairs 
 of Tradescantia. This is best seen in those species 
 in which the outer layer of cells is absent from the 
 stems, and which were formerly arranged in a sepa- 
 rate genus (Nitella) . But it may also be seen in the 
 stems and especially the young branchlets of any of 
 the other species ; and as the granules of the proto- 
 
CHAEACE^E. 89 
 
 plasm are large, the phenomenon is more easily wit- 
 nessed than in Tradescantia. 
 
 The fructification consists of two kinds of organs, 
 viz. red globules (PL VI. fig. 22) representing the 
 anther-organ, and green capsules (fig. 22), or nucules, 
 corresponding to the ovaries. The structure of the 
 globules is very curious. Their transparent walls 
 (fig. 20) consist of eight somewhat triangular plates, 
 each of which is composed of cells radiating from a 
 centre ; and from the inside of each of these centres 
 arises a tubular cell extending to the middle of the 
 globule, the unattached ends giving origin to nume- 
 rous colourless coiled filaments, consisting of minute 
 cells arranged end to end, each containing a very 
 minute coiled spiral fibre, to which are attached two 
 exceedingly slender cilia. These ciliated fibres are 
 the spermatozoa. The capsules or nucules (fig. 22), 
 which are situated near the globules, are urn-shaped, 
 coated with spiral cells, and crowned with five shorter 
 cells. When the globules are ripe, they become rup- 
 tured by the separation of the valves ; and the sperma- 
 tozoa, escaping from the cells of the coiled filaments, 
 swim about and enter a canal in the capsules to 
 fertilize the ovule contained within. 
 
 The Charge grow readily in a glass jar of fresh water, 
 with a few pebbles at the bottom ; and if the plants 
 be not overgrown with Confervoids, the fructification 
 will continue to be produced almost throughout the 
 year. 
 
 The circulation is best seen in the whorled branch- 
 lets, a portion of the growing ends being placed in a 
 live-box, or simply laid upon a slide in water and 
 covered with thin glass. 
 
 Preservation. The Algae are best preserved in two 
 ways, the entire fronds being dried upon paper under 
 pressure, as directed for the Ferns ; and small portions, 
 showing the minuter structures and fructification, 
 being mounted in chloride of calcium or glycerine. If 
 
 i3 
 
ALGM. 
 
 it is required to preserve the marine Algae according to 
 the first method, they should first be immersed for a 
 time in fresh water, to dissolve out the saline matters 
 derived from the sea-water, which would keep them 
 damp and ultimately spoil them. After these matters 
 have been removed, the fresh water should be changed, 
 and pieces of paper placed beneath them while sus- 
 pended in the water ; on withdrawing the paper care- 
 fully, keeping the Algse at the same time spread out, 
 they may be made to retain the required position; 
 and when the water has drained away, and the re- 
 maining moisture has mostly evaporated, they may 
 be submitted to pressure in a press. 
 
 The Confervoid Algse may be conveniently spread 
 out upon paper and preserved in the same manner, 
 as some of the distinguishing characters are founded 
 upon their appearance in the dry state, their adhesion 
 to the paper, &c. Moreover they can then at any 
 time be minutely examined, by the immersion of a 
 small portion in water. 
 
LICHENS. 91 
 
 CHAPTER VIII. 
 
 LICHENS. 
 
 THE Lichens are found growing upon the bark of 
 trees, old palings, &c. Those most easily seen 
 with the naked eye form grey or coloured dryish 
 patches or pendulous tufts; while the smaller ones 
 are singly easily overlooked, from their minute size 
 and close adhesion to the matrix or hody upon which 
 they grow, forming, by their aggregation, the grey or 
 otherwise-coloured dry and brittle coatings of almost 
 every tree or decaying branch. 
 
 The Lichens derive their nourishment from the air, 
 and not from the matrix in this respect differing 
 from the Fungi, with some of which, as we shall pre- 
 sently see, they agree in the structure of the fruit. 
 
 The structure of the Lichens is simple, no distinc- 
 tion of root, stem, and leaves existing in them, although 
 certain dry root-like fibres exist in many of them, by 
 which the plant is fixed to the matrix. The whole 
 consists mainly of a frond or thal'lus (0a\\o$, a leaf) . 
 This is either raised above the surface of the matrix 
 in a shrubby form, or spread upon the surface as a 
 flexible lobed layer (PL II. fig. 2), or it is dry and 
 brittle (crustaceous) and closely adherent (PI. II. 
 fig. 26), 
 
 The fructification consists of little saucers, disks, or 
 streak-like furrows, often of a different colour from 
 the thallus, the structure of which will be best illus- 
 trated by reference to a few common species. 
 
 PARMELIA'CE^E. Parmelia parietina (PL II. fig. 2) 
 is a very common Lichen, found on the bark of trees, 
 on old palings, &c. It is of an orange-yellow colour, 
 
92 LICHENS. 
 
 the thallus being flat, lobed, and scalloped (crenate) 
 at the margins. The structure of the thallus may 
 serve to represent that of most of the Lichens. It 
 consists of three layers, an upper cortical or epider- 
 mic layer, which is continued over the margins to the 
 under surface of the thallus, to form the under layer ; 
 and between these is the middle or medullary layer. 
 The medullary layer consists of interwoven fibres, 
 which are more closely packed towards the upper and 
 under surfaces, so as to give them a cellular appear- 
 ance. Near the upper part of the medullary layer, 
 a number of minute rounded green cells exist, lying 
 loosely in its meshes (PI. II. fig. 4 a). These green 
 cells (gonidia) appear to correspond to the buds of 
 the higher plants, and, when detached from the plants, 
 they are capable of growing into new individuals. 
 
 On the upper surface of the thallus of Parmelia 
 (fig. 2) the fructification may be observed. This 
 consists of saucers or shields (apothecia, airoBriK^ a 
 repository), formed of a raised and expanded portion 
 of the thallus (fig. 3), and containing the spores. 
 The spores are enclosed in closely set upright cells, 
 or spore-sacs (figs. 4 b and 5 b), called as'd (acro9, a 
 bottle) or thecse ; and intermingled with the asci are 
 filaments, enlarged and coloured at the ends (para- 
 physes), which are probably abortive asci. 
 
 In systematic works upon the Lichens, the saucers 
 and their contents are included in the term apothecia, 
 the saucer alone being called theexcip'ulum (excipulum, 
 a receiver) ; the mass of asci and paraphyses forming 
 the nucleus or thaldmium (OdXafios, a bed) . 
 
 The yellow spores are very minute, each ascus con- 
 taining eight of them, and they are divided by a trans- 
 verse partition or septum. 
 
 Near the margins of the lobes of the thallus are 
 small dark points. These are the pouting mouths of 
 little capsules (spermogonia) sunk in the substance 
 of the thallus, and containing numerous filaments, 
 
GRAPHIDE^E. 93 
 
 terminated by very minute stick-shaped bodies (sper- 
 matia), which break off and escape through the orifices 
 of the capsules. These are probably the representa- 
 tives of the anthers of flowering plants and of the 
 antheridia of the ferns. They are, however, so dif- 
 ficult to find and examine, that I must refer to the 
 Dictionary for a further description and figures of 
 them. 
 
 LECIDIN'E^;. This family contains the genus 
 Cladonia, three or four species of which are common 
 on boggy heaths, banks, &c., viz. Cladonia coccifera, 
 the Scarlet Cup-moss (PL II. fig. 21); C. pyxiddta, 
 the Common Cup-moss (PL II. fig. 23) ; C. vermicu- 
 Idris (PL II. fig. 22) ; and C. rangiferma, the Rein- 
 deer Moss (PL II. fig. 24) . The thallus of these Lichens 
 forms little rounded irregularly overlapping scales, 
 with scalloped edges, overgrowing the surface upon 
 -which the Lichens are found. The fruit-stalks, or 
 podetia (irovs, a foot), are hollow (fistulose), and 
 either simple and dilated into cups (PL II. fig. 23), 
 or branched with the corners or angles between the 
 adjacent branches perforated. The apothecia in the 
 young state resemble those of Parmelia on a small 
 scale; but as they approach maturity, the centre 
 becomes pushed up, so that the spore-layer is extended 
 over the ends of the stalks. In C. coccifera and 
 pyxidata the cups are proliferous at the margin ; i. e., 
 branches upon which the apothecia are placed arise 
 from it. The asci and paraphyses are very minute, 
 but do not differ essentially in structure from those 
 of Parmelia. In C. vermicularis the podetia are 
 pointed and more solid than in the other species, the 
 apothecia forming very minute spots at their apices. 
 
 GRAPHID'E^E. To this family belong Gr aphis 
 scripta (PL II. fig. 26) and Opeg'rapha betulina (PL II. 
 fig. 30). These little Lichens are easily overlooked, 
 from the thin and but slightly raised thallus being only 
 visible to the naked eye as a discoloration of the bark 
 
94 LICHENS. 
 
 of the trees upon which they grow ; while the fructi- 
 fication is very minute, forming little black streaks 
 or lireVla (lira, a furrow), irregularly arranged, and 
 resembling somewhat the letters of some of the Ori- 
 ental alphabets. 
 
 In Gr aphis script a (fig. 26) the thallus is thin, 
 somewhat membranous, smoothish, shining, greyish 
 white, and faintly bordered with black. The lirellse 
 (fig. 27) are partly sunk in the bark, winding and 
 narrow, some being simple, others branched; and 
 they are surrounded by a raised border, formed by 
 the thallus. The lirellse are lined at the sides with 
 a black (carbonaceous) layer or excip'ulum, within 
 which are situated the asci and paraphyses. The 
 spores (PL II. fig. 29) are 8-cleft, the segments being 
 again divided longitudinally into little spores or 
 sporidia. 
 
 In Opegrapha betulina (PL II. fig. 30), which is 
 found on the bark of the birch-tree, the thallus is 
 thin, dirty yellowish white, bordered with black. The 
 lirellse (figs. 31, 32) are mostly simple, without a 
 raised border of the thallus, and the excipulum forms 
 a complete lining to them. The spores (fig. 33 a] are 
 3-cleft, and taper at the ends. 
 
 CALICI'EJE. Calidium claveVlum (PL II. fig. 6) is 
 a pretty little Lichen, growing upon old boards and 
 farm-buildings. The thallus is granular and greyish 
 white. The apothecia (fig. 7) are stalked and black, 
 but of a lighter colour than the mass of spores form- 
 ing the nucleus. The spores are very minute, black, 
 oblong, and divided by a transverse septum. 
 
 The Lichens are divided into two Orders, according 
 to whether the apothecia are open before the spores 
 are ripe, as in the species noticed above, or whether 
 the apothecia only open to discharge the ripe spores. 
 The first Order forms the Gymnocar'pi (yt>/-tvo?, naked, 
 /capTrbs, fruit) ; the second forms the Angiocar'pi (dy- 
 yeiov, vessel, capsule). 
 
LICHENS. 95 
 
 Preservation. The Lichens are readily preserved, 
 on account of their dry nature ; they need simply be 
 kept in a dry place, and glued to pieces of card. If 
 room is an object, they may be dried under pressure, 
 as in the case of the flowering plants. When re- 
 moistened, the minute structures may be easily made 
 out by sections. The smaller ones may be mounted 
 dry, in cells made of the wax cement (p. 16). The 
 minute structures keep well in chloride of calcium or 
 glycerine. 
 
96 FUNGI. 
 
 CHAPTER IX. 
 
 FUNGI. 
 
 THE Fungi form the lowest class of plants : as ex- 
 amples of them, may be mentioned mushrooms, toad- 
 stools, puff-balls, the mould of paste, the blue mould 
 of cheese, &c. The more minute Fungi are very 
 common, forming beautiful microscopic objects, al- 
 though they are rarely studied by the microscopic 
 observer. 
 
 Fungi live usually upon rotting or decaying vege- 
 table substances, as rotten wood, the dead leaves and 
 stems of plants, &c. ; but sometimes they are found 
 upon living plants, and some of them exist upon de- 
 caying animal matters, and even in living animals. 
 
 Fungi exhibit no separation of root, stem, or leaves, 
 as exists in the higher plants ; nor do they contain 
 chlorophyll, the presence of which is so generally 
 associated with the idea of a plant. But they consist 
 of aggregations of mostly elongate cells, forming 
 branched and interlacing colourless fibres, buried like 
 roots in the substance (matrix) upon which they grow, 
 and from which they derive their nourishment ; this 
 portion of the Fungus is called the mycelium (JJLVKTIS, 
 a fungus). The portion of the Fungus projecting 
 beyond the surface of the matrix is the fructification ; 
 and this is the part usually called the fungus, the 
 mycelium being overlooked by a casual observer. So 
 that here we have a character distinguishing the 
 Fungi from the Lichens, which derive their nourish- 
 ment from the air, and not from the matrix. The 
 absence of the green cells, or gonidia, forms another 
 
PLATE VII. [PAGE 96.] 
 FUNGI. 
 
 Fig. 
 
 1. Agaricus micaceus : a, gills. 
 
 2. Agaricus campestris : a, spores ; 
 
 b, basidia. 
 
 3. Physarum album, on a piece of 
 
 stick. 
 
 4. Physarum album, spores. 
 
 5. Uredo segetum, spores. 
 
 6. Uredo caries, spores. 
 
 7. Uredo Candida, on leaf of Shep- 
 
 herd's ~Pu.T8,e(Capsella) : s, spores. 
 
 8. JEcidium grossularice, sorus. 
 
 9. jEcidium grossularice : p, spore- 
 
 capsules (peridia): s, anther- 
 capsules (spermogonia). 
 
 10. Nemaspora crocea : a, spores. 
 
 11. Tonda casei. 
 
 12. Torula herbarum, on a piece of 
 
 stick. 
 
 13. Torula herbarum, spores. 
 
 14. Phragmidium bulbosum, on bram- 
 
 ble-leaf. 
 
 15. Phragmidium bulbosum, stylo- 
 
 spores and paraphyses. 
 
 16. Puccinia graminis, on a piece of 
 
 straw. 
 
 Fig. 
 
 17. Puccinia graminis, spores. 
 
 18. Sporocybe alternata, filament and 
 
 19. Botrytis parasitica, on Shepherd's 
 
 Purse. 
 
 20. Botrytis parasitica, spores and fil- 
 
 aments. 
 
 21. Rhinotrichum, species of. 
 
 22. Rhinotrichum, heads of spores. 
 
 23. Rhinotrichum, spores detached. 
 
 24. Rhinotrichum, spores. 
 
 25. Penicillium glaucum, 
 
 26. Penicillium glaucum, ,head of spores. 
 
 27. Coremium leucopus. 
 
 28. Tuber cularia vulgaris. 
 
 29. Tubercularia vulgaris, divided re- 
 
 ceptacle. 
 
 30. Tubercularia vulgaris, filaments. 
 
 31. Tubercularia vulgaris, spores. 
 
 32. Spharia fragiformis. 
 
 33. Trichothecium roseum, on a piece 
 
 of stick. 
 
 34. Trichothecium roseum. 
 
 35. Trichothecium roseum, filaments 
 
 and spores. 
 
Plate VII 
 
 I.onSon,-John Mm Fee 
 
HYMENOMYCETES. ' 97 
 
 character by which the nearly allied members of this 
 class of plants can be distinguished. 
 
 The fructification of the Fungi occurs in two dis- 
 tinct forms, in one of which the seeds or spores are 
 naked, and situated at the ends of slender cells or 
 filaments, whilst in the other the spores are contained 
 in usually flask-like cells, called asci, similar to those 
 occurring in the Lichens. In a few Fungi, antheridial 
 organs, called spermogonia, as in the case of the 
 Lichens, have also been detected. The Fungi are 
 divided into six Orders, from each of which a few 
 species may be selected to illustrate their structure 
 more in detail. 
 
 HYMENOMYCE'TES (v^v, membrane, ILVKVIS, fungus). 
 This is the highest Order of Fungi, containing a large 
 number of genera and species ; as examples of which 
 may be mentioned the common Mushroom, Toad- 
 stools, &c. 
 
 Their general structure may be illustrated by the 
 examination of the common Mushroom (Agai^icus 
 campes'tris) ; the species figured (PL VII. fig. 1), how- 
 ever, being Agaricus micdceus, which is common at 
 the root of trees, the bottom of decaying posts, &c. 
 
 The vegetative part of the fungus consists of a 
 cotton-like mycelium, which is composed of slender, 
 colourless, interwoven filaments, popularly known as 
 the spawn. The portion commonly called the mush- 
 room corresponds to the fructification, and consists 
 of certain parts visible to the naked eye. These are 
 an expanded portion at the top, forming a hemi- 
 spherical cap, receptacle, or pileus (pileus, a cap), and 
 a stalk, or stipes, upon which the cap is supported. 
 On the under surface of the cap are a number of 
 nearly parallel, radiating, dark-coloured plates or gills, 
 somewhat resembling the gill-plates of a fish. The 
 dark colour of the gills arises from the presence of 
 the spores, which are coloured, although in some 
 species they are white. The surface of the gills, upon 
 
 K 
 
100 FUNGI. 
 
 caying stems, sticks, &c. The mycelium consists of 
 inconspicuous, fine filaments, which run beneath the 
 epidermis and bark of leaves and stems, or exist in 
 the intercellular passages, the fruit bursting through 
 the surface. The spores are short-stalked, forming 
 stylospores (o-ruXo?, stalk, O-TTO/OO?, seed) or conid'ia 
 (tcov&iov, little dust). But there is great confusion 
 in the descriptions of the spores of the same Fungus 
 by different botanical authors, some describing the 
 fruit (in PI. VII. fig. 15, for instance) as composed of 
 rows of spores, while others regard it as forming a 
 single septate (septum, a partition) or partitioned spore. 
 
 Torula herbdrum (PI. VII. fig. 12) is very common 
 on the decaying stems of plants, especially those be- 
 longing to the Parsley order (Umbelliferse), forming 
 greenish-black streaks or patches. The spores (fig. 13) 
 are grouped into chains or beaded (moniliform) rows, 
 with very short stalks, and these are crowded to form 
 the black patches visible to the naked eye. Under 
 the microscope the spores appear of a brown colour. 
 
 Torula cdsei (PL VII. fig. 11) forms reddish or 
 white patches upon decaying cheese. It consists of 
 branched, interwoven, tufted filaments (flocci), with 
 comparatively large spherical spores arranged in rows 
 at their ends. 
 
 Nemas'pora crocea (PL VII. fig. 10) is a very curious 
 member of this Order, and is found upon decaying 
 beech-sticks. It appears as an orange-coloured tendril- 
 like gelatinous mass of spores, bursting through a 
 little pore on the surface of the bark. The spores 
 (fig. 10 a) are very minute, slender, and curved, and 
 under a high power appear jointed. 
 
 dEcid'ium grossuldriae (PL VII. fig. 8) is found very 
 commonly on the leaves of the gooseberry-bush. It 
 forms to the naked eye oval or rounded spots (sori), 
 of a red colour ; and on close examination, the spots 
 appear dotted with yellow points. Each point is the 
 rifice of an open capsule ( peridium), which has burst 
 
CONIOMYCETES. 101 
 
 through the epidermis of the leaf (PI. VII. fig. 
 The capsules are split or lacerated at the margins, and 
 form little cups containing the spores. The spores 
 are very minute, yellow, and are arranged in closely 
 packed moniliform rows. The red colour depends 
 upon the altered chlorophyll of the leaf. On the 
 leaves containing the spore-capsules or peridia will 
 be found smaller, brownish-yellow capsules (spermo- 
 gonia) partly imbedded in their substance (PL VII. 
 fig. 9 s). These contain minute filaments (sterigmatd], 
 terminated by short rows of rounded cells (spermatia], 
 which are supposed to exert an antheridial function. 
 The species ofJEcidium are very numerous, and many 
 of them are extremely common as those upon the 
 nettle, the barberry, the dandelion, the wood-ane- 
 mone, the violet, and buttercups. The groups of 
 capsules form exquisite opake objects under a low 
 power of the microscope. 
 
 PhragmicFium bulbosum (PL VII. fig. 14) is another 
 very beautiful coniomycetous Fungus. It forms little 
 reddish, afterwards sooty dots upon the under surface 
 of the leaves of various species of Bramble (Rubus) . 
 The oblong spores (fig. 15) are from 2- to 4-septate, 
 and stalked, the stalks being swollen or bulbous at 
 the base. The spores, which appear brown when 
 magnified, are covered with little knobs (tuberculate) 
 on the surface; and the uppermost little spore or 
 sporidium is terminated by a minute point (apiculate) . 
 Among the spores are numerous barren filaments or 
 paraphyses. 
 
 Pucciriia gram'inis (PL VII. fig. 16) is to be found 
 everywhere upon damp rotting straw, and upon grasses. 
 It forms sooty irregular streaks, consisting of densely 
 crowded, one-partitioned (uniseptate) spores (fig. 17), 
 which appear brown under the microscope. This 
 Fungus is sometimes called "mildew." There are 
 numerous other species of Puccinia which occur upon 
 common plants. 
 
 K3 
 
102 FUNGI. 
 
 Uredo seg'etum is the " smut" of wheat, barley, and 
 oats a fungus too well known to the farmer. It 
 forms sooty masses, bursting through the epidermis 
 of the stalk and ears of the corn, and soiling the 
 fingers when handled. The spores (PL VII. fig. 5) 
 ar^ exceedingly minute, and the stalks are so slender 
 and loosely connected with them that they are not 
 readily detected. Under the microscope the spores 
 appear brown and faintly dotted, this appearance 
 arising from a reticulated structure of the surface, 
 similar to that of the poppy-seed on a very small 
 scale. 
 
 Uredo caries is the " bunt " of corn. It grows 
 within the grain, filling it with a sooty, foetid mass. 
 The spores (PL VII. fig. 6) are considerably larger 
 than those of the last species, and their surface is 
 distinctly reticulated. They are attached to the fila- 
 ments of the mycelium, as in Uredo segetum. 
 
 The spores of both these species of Uredo may be 
 found in most kinds of flour and bread, especially in 
 those of inferior quality. 
 
 Uredo can'dida (PL VII. fig. 7) is another species, 
 forming white dots upon the leaves of the common 
 Shepherd's Purse (Capsel'la bursa pastor' is] which 
 is easily recognized by the form and arrangement of 
 the pods (fig. 19). The spores (s) are rather large 
 and white. 
 
 Other species of Uredo are very common upon 
 numerous species of weeds or wild flowering plants ; 
 and they so closely resemble each other that, when 
 one is known, the others are easily recognized. Usually 
 each species occurs upon a distinct species of plant, 
 as is the case with parasites generally. In many of 
 them the spots (sori) exhibit a thin membrane cover- 
 ing the spores, which bursts down the middle, so as to 
 bear some resemblance to a capsule. But there is no 
 true capsule, the membrane consisting of the epider- 
 mis of the leaf or stalk of the plant, which is raised and 
 
HYPHOMYCETES. 103 
 
 torn by the expansion of the growing fungus ; so that 
 the peridium is spurious, as belonging to the matrix, 
 and not to the fungus. It may be mentioned here that 
 the so-called species of Uredo are not truly distinct 
 species, but are the forms of species of Puccinia } 
 Phragmidium, &c. ; so that the latter genera have two 
 kinds of fruit, one of which is a Uredo, the other a 
 Puccinia. But I must refer to the Dictionary for 
 further details upon this point. 
 
 HYPHOMYCE'TES (vcfxia), to weave, fjLV/crjs, fungus). 
 In this, the 4th Order of Fungi, are contained many 
 of the commonest moulds which are found growing 
 upon decaying substances, and sometimes upon living 
 plants. The mycelium creeps among the particles of 
 the substance, or the elements of the tissues, upon 
 which the Fungus lives, in the form of slender threads 
 or filaments. The spores, which are either simple or 
 partitioned (septate), and naked, occur either singly or 
 in rows at the ends of fine interwoven cottony threads 
 or floc'ci (floc'cus, a flock of wool), which are generally 
 very evident to the naked eye. The threads support- 
 ing the spores form the ped'icels (pedicel'lus, a little 
 foot). In technical descriptions, these filaments, 
 which are usually composed of cells arranged end to 
 end, are said to be septate (PI. VII. fig. 26), and not 
 jointed, as in the case of the filaments of the Conferva, 
 which are constructed in a similar manner. When 
 not septate, the filaments are said to be continuous. 
 
 STILBA'CEI. To this family belongs Tuberculdria 
 vulgaris (PI. VII. fig. 28), which is found upon decay- 
 ing sticks and branches of trees, especially the lime- 
 tree. It forms little firm red knobs or tubercles, 
 each of which is a receptacle. On making a section 
 of a receptacle (PI. VII. fig. 29), the interior is seen 
 to be paler than the bright red surface, and a short 
 broad stalk comes into view. The receptacle is com- 
 posed of crowded cell-filaments, so short near the base 
 as rather to resemble cellular tissue (fig. 30) ; but 
 
104 FUNGI. 
 
 towards the surface the filaments become extremely 
 slender and branched ; and each branch is terminated 
 by a minute oblong spore, or a short row of them 
 (fig. 31). 
 
 If a stick with this Fungus upon it be kept for some 
 time in a damp place, short whitish fibres, branched 
 at the ends, and visible to the naked eye, will be seen 
 sprouting from around the base of the receptacle 
 (PL VIII. fig. 1). These, when examined under the 
 microscope, appear composed of fine filaments (PL 
 VIII. fig. 2), resembling those of Tuber cularia, and 
 having the minute spores at the ends. After a con- 
 siderable time, the entire receptacle of the Tubercu- 
 laria becomes resolved into these fibres. In this 
 state the Fungus assumes the characters of an Isdria, 
 a genus of a different family of Fungi (Isariacei), so 
 that we have here an /s0H#-form of Tubercularia. 
 
 Sometimes the tubercles of the Tubercularia be- 
 come darker, almost black, harder, and granular on the 
 surface. On making a section of them in this state, 
 the whole of the under portion of the surface is found 
 to contain little roundish capsules, containing asci 
 and spores, and it constitutes Sphdriafragifor'mis (PL 
 VII. fig. 32). As the Spharia is the more complex 
 and highly organized condition of this Fungus, the 
 other two conditions must be regarded as forms, and 
 not as species of separate genera. 
 
 DEMATIE'I. In this family the filaments upon 
 which the spores are placed are not compacted as in 
 Tubercularia, but separate ; and they are of a dark 
 brown or black colour. 
 
 Sporoc'ybe alterndta (PL VII. fig. 18) is occasion- 
 ally found upon decaying vegetable substances, form- 
 ing little black velvety spots or patches. The my- 
 ceHal filaments are exceedingly minute, septate, ta- 
 pering at the ends, and terminated by a little tuft of 
 pear-shaped cells, from which the black simple spores 
 arise singly. 
 
PLATE VIII. [PAGE 104.] 
 
 FUNGI. 
 
 Fig. 
 
 1. /sana-form of Tubercularia. 
 
 2. /sana-form of Tubercularia, fila- 
 
 ments. 
 
 3. Aspergillus glaucus. 
 
 4. Aspergillus glaucus, filaments and 
 
 heads of spores; a, separate 
 spores. 
 
 5. Aspergillus glaucus, head of spores. 
 
 6. Peziza omphalodes. 
 
 7. Peziza stercorea. 
 
 8. Peziza stercorea, cup (receptacle). 
 
 9. Peziza stercorea, asci and para- 
 
 10. Peziza stercorea, divided recepta- 
 
 cle. 
 
 11. Peziza stercorea, bristles. 
 
 12. Dothidea typhina, on leaf-stalk of 
 
 grass. 
 
 13. Dothidea typhina, surface of patch 
 
 (stroma). 
 
 14. Dothidea typhina, capsules (peri- 
 
 thecia). 
 
 15. Dothidea typhina, ascus contain- 
 
 ing spores. 
 
 16. Sphceria rubella, on nettle-stem. 
 
 17. Sphceria rubella, asci. 
 
 18. Sphceria rubella, capsules (peri- 
 
 thecia). 
 
 19. Sphceria rubella, ascus and spores. 
 
 20. Sphceria buttata, on piece of stick ; 
 
 Fig. 
 
 20 a, section of tubercle (recep- 
 tacle). 
 
 21. Sphceria buttata, asci and spores. 
 
 22. Sphceria complanata, on piece of 
 
 stick. 
 
 23. Sphceria complanata, tubercles (re- 
 
 ceptacles). 
 
 24. Dothidea ulmi, on elm-leaf. 
 
 25. Dothidea ulmi, asci. 
 
 26. Dothidea ulmi, section of recep- 
 
 tacle. 
 
 27. Dothidea ulmi, spores. 
 
 28. Chcetomium elatum ', 28 a, spores ; 
 
 28 b, filaments. 
 
 29. Chcetomium elatum, on piece of 
 
 stick. 
 
 30. Hysterium fraxini, on piece of 
 
 stick. 
 
 31. Hysterium fraxini, receptacle. 
 
 32. Hysterium fraxini, ascus with 
 
 spores. 
 
 33. Erysiphe guttata, on hazel-leaf. 
 
 34. Erysiphe guttata, capsule. 
 
 35. Erysiphe guttata, capsule (concep- 
 
 tacle) with fulcra. 
 
 36. Mucor mucedo : a, columella ; 
 
 s, spores. 
 
 37. Acrostalagmus : a, spores. 
 
 38. Gall on oak-leaf. 
 
 39. Gall on oak-leaf. 
 
Plate VIII. 
 
 r 
 
HYPHOMYCETES. 105 
 
 MUCED'INES. Many of the Fungi belonging to 
 this family are extremely common on decaying vege- 
 table substances, and some are found upon living 
 plants, to which they are very injurious. To the 
 naked eye they usually appear as mouldy or cottony 
 masses, either white, black, or coloured blue, yellow, 
 &c. The spores are attached singly or in rows to 
 branchlets arising from the ends of the filaments, so 
 as to form little heads. 
 
 Bot'rytis parasit'ica (PI. VII. fig. 19) is common 
 upon the flower-stalks of the Shepherd's Purse, form- 
 ing white mealy patches. The fruit-stalks are com- 
 paratively large and thin-walled, the branchlets 
 being slender, mostly curved, and terminated each 
 by a large, spherical, smooth, simple, white spore. 
 
 Botrytis vulgdris is also common on various decay- 
 ing plants. Its filaments are grey, and the branchlets 
 lobe-like ; the spores being minute, spherical, either 
 white or greenish, and placed simply at the tips. 
 
 Botrytis infes'tans is the potato- Fungus. It forms 
 white spots upon the under side of the leaves of the 
 potato-plant, and by some authors is considered to 
 be the cause of the potato-disease. The filaments are 
 branched at the ends, and terminated by single oval 
 spores, which are apiculate at the free end, and con- 
 tain minute little spores or sporidia. 
 
 Oid'ium Tuck'eri is the well-known destructive grape- 
 Fungus. It forms white cottony masses upon the 
 vine and its grapes, the fruit-stalks being short and 
 terminated by one or two end- to- end oblong spores. 
 It appears to be the Coniomycetous form of another 
 Fungus (Erysiphe). 
 
 Trichothecium roseum (PL VII. fig. 33) is found 
 upon rotting sticks; very frequently upon willow- 
 baskets kept in a damp place. It forms little rounded, 
 slightly raised, pinkish spots, less than the size of a 
 pin's head. The branched and septate foot-stalks 
 (figs. 34, 35) are terminated each by a little group of 
 
106 FUNGI, 
 
 obovate spores, divided by a transverse partition (uni- 
 septate). Sometimes this little Fungus is quite white, 
 at others greenish; when perfectly ripe, the spores 
 become oblong. 
 
 PeniciVlium glaucum (PL VII. fig. 25) is the com- 
 mon Blue Mould found upon decaying substances, as 
 cheese, &c., the interwoven mycelial filaments often 
 forming large cakes or crusts upon the surface. The 
 septate fruit-stalks (fig. 26) are fork-branched at the 
 ends, the branchlets being terminated each by a row 
 of very minute spherical smooth spores. On some 
 decaying substances, as apples, gum, &c., the fruit- 
 stalks are found aggregated into a thick stalk, the 
 branchlets and spores forming a rounded head, so 
 that the whole resembles a little blue mushroom 
 (fig. 27) . In this form the Fungus has been placed 
 in a distinct genus, and called Coremium leucopus. 
 In other species the spores are pink and white. 
 
 This little Fungus is of special interest, on account 
 of one form of it constituting the yeast-plant, or yeast 
 as it is commonly called. This consists of rounded 
 or oblong cells, which grow very rapidly in ferment- 
 ing liquids by budding the large quantity of sugar 
 and gluten present favouring the vegetative or simple 
 growing process, at the expense of the fructifying 
 process. But this is only an instance of what we 
 constantly find in flowering plants, the use of very 
 rich soil rendering flowers double, which is really re- 
 ducing their organs to the state of leaves. When the 
 sugar has become exhausted, the cells of the yeast 
 become longer and thinner, as if starved ; they then 
 form a more recognizable mycelium, which extends 
 to the surface of the liquid, and produces finally the 
 fruit-stalks and the Penicillium fruit. 
 
 Aspergil'lus glaucus (PL VIII. fig. 3) is an ex- 
 tremely common mould upon cheese, jams, &c. It 
 resembles the last in appearance to the naked eye, 
 except that it has rather a green tinge, the heads of 
 
ASCOMYCETES. 107 
 
 fruit being much more compact and rounded. The 
 fruit-stalks (fig. 4) are large, bulbous or inflated at 
 the ends (fig. 5), and from the inflations arise the 
 crowded rows of spores. The spores are rounded, 
 and rough (scabrous) on the surface. On removing 
 most of the spores from the head of fruit, each row 
 of spores is found to arise from a very short stalk. 
 
 Plate VII. fig. 21 represents a beautiful species of 
 Rhinot'richum, which is found upon decaying and sickly 
 plants, and upon rotting sticks, forming a minute 
 grey mould. The fruit-stalks (fig. 22) are large, 
 sparingly branched, septate or jointed, appearing 
 brownish under the microscope. Their ends are 
 branched, mostly biternate (fig. 23), i. e. each branch 
 dividing into three branchlets, and these again into 
 three still finer ones. The ends of the branchlets are 
 inflated, and coated with little points, upon each of 
 which a smooth white spore (fig. 24) is placed. 
 
 ASCOMYCETES (aoveo?, a bottle, fjLv/cijs, fungus). The 
 Fungi belonging to this Order are found upon the 
 stems and leaves of plants, and upon decaying sub- 
 stances, as dung, &c. They are usually evident to 
 the naked eye, some even equalling the Hymenomy- 
 cetous Fungi in size ; and many of them are brilliantly 
 coloured. They are in general distinguishable with 
 facility from the Fungi of other Orders, by the arrange- 
 ment of the spores in colourless sacs or asci (PL VIII. 
 fig. 9), resembling those noticed in the case of the 
 Lichens. These asci are usually enclosed in a cap- 
 sule or perithecium. The mycelium is usually buried 
 in the matrix, so as not to be conspicuous. 
 
 Helvelldcei. To this family belongs the large genus 
 Peziza, some of the species of which are beautifully 
 coloured, yet scarcely microscopic. Among these 
 may be mentioned Peziza omphalodes (PL VIII. fig. 6), 
 which forms little red masses upon damp ceilings. It 
 does not possess the ordinary form of a Peziza, which 
 is that of a cup fixed at the end of a stalk, like a 
 
108 FUNGI. 
 
 mushroom with the cup turned inside out, the asci 
 lining its interior. 
 
 Peziza cocciriea is not uncommon in woods. It is 
 whitish outside, the interior of the cup being of a 
 brilliant scarlet colour. It is from half an inch to an 
 inch in height. 
 
 Peziza stercor'ea (PI. VIII. fig. 7) is often found 
 upon dung. The surface of the cup of this Fungus is 
 granular and covered with bristles (figs. 8 & 11). The 
 cup is concave (fig. 10), and lined with the asci (fig. 9), 
 among which are simple paraphyses. 
 
 The Pezizce are excellent Ascomycetous Fungi for 
 exhibiting the asci, as they are more or less soft, and 
 thus sections of them may be easily prepared, or they 
 may readily be picked to pieces with the mounted 
 needles. 
 
 TTTBERACEI. In this family is contained the Truffle 
 (Tuber cibdrium). The asci are situated upon the 
 inner surfaces of the winding canals traversing the 
 substance of the fleshy fruit (peridium) of which the 
 truffle consists. 
 
 PHACIDIA'CET. To this family belongs Hysterium 
 frax'ini (PL VIII. fig. 30), which is found upon ash- 
 twigs. The drawn-out capsules or perithecia (fig. 31) 
 are black and elliptical, with a longitudinal fissure or 
 orifice, and contain the asci (fig. 32) with the spores. 
 
 SpH^RilcEi. Dothid'ea typhina (PL VIII. fig. 12) 
 is a common Fungus upon the stems of living grasses. 
 It forms an orange-coloured patch or layer encircling 
 the stem, and covered with little dots. On making 
 a section (fig. 14), it appears composed of a row of 
 oblong or obovate closely placed capsules (perithecia) 
 immersed in and continuous with a finely fibrous re- 
 ceptacular mass (stroma). The asci (fig. 15) are very 
 slender, arising in a tuft from the bottom of the cap- 
 sules, and containing eight still more slender spores. 
 Except under a very high power, the spores appear 
 as interrupted lines running down the interior of the 
 
SPH./ERIACEI. 109 
 
 asci. The little dots visible to the naked eye are the 
 slightly projecting mouths of the capsules, which are 
 more distinctly seen in the magnified portion of the 
 Fungus (fig. 13). In the young state, this Fungus is 
 whitish. 
 
 This Fungus cannot be mistaken for a UredOj two 
 species of which occur upon grasses Uredo linedris 
 forming yellowish-brown spots, and Uredo rubigo 
 yellow spots. 
 
 Dothidea utmi (PL VIII. fig. 24) forms black, 
 slightly raised, and somewhat star- shaped spots upon 
 the upper surface of the leaves of the elm. In a sec- 
 tion (fig. 26) the cavities are seen, containing the 
 very delicate asci (fig. 25). The spores (fig. 27) are 
 oval, with a minute septum at one end. 
 
 Sphdria rubel'la (PL VIII. fig. 16) is extremely 
 common on the dead stems of the nettle, &c. In this 
 Fungus the black bottle-like perithecia (fig. 18), con- 
 taining the asci and paraphyses (fig. 17), are at first 
 situated beneath the epidermis, through which they 
 at length burst. The spores (fig. 19 a) are spindle- 
 shaped, and from four- to seven- sept ate. When ripe, 
 they escape by a hole or pore in the neck. 
 
 Sphce'ria complandta (PL VIII. fig. 22) is another 
 common species, found in hedges, on dead sticks of 
 the softer (herbaceous) plants, as the parsley-order 
 (Umbelliferae) . Here the minute capsules, which are 
 scattered over the stems, are at first rounded, then 
 flattened on the top (depressed), the neck being very 
 minute (fig. 23). The spores in this species are 
 exceedingly minute, oblong, and not contained in 
 asci. 
 
 Sphdria bulldta also belongs to this family. It 
 occurs upon decaying birch-sticks, presenting to the 
 naked eye the appearance represented in PL VIII, 
 fig. 20. The black, raised tubercles (receptacles) in 
 their growth burst through the bark, splitting the 
 epidermis. They consist of a white stroma (fig. 20 a), 
 
110 FUNGI. 
 
 in which, the bottle-shaped capsules (perithecia) are 
 immersed, the necks projecting slightly above the 
 surface as little points (papillae). The tufted spore- 
 sacs or asci (fig. 21), with the thread-like paraphyses, 
 are contained within the capsules; and within the 
 asci are the densely packed, very numerous and minute 
 curved spores. 
 
 Another species, Sphceria discifor'mis, is also com- 
 mon on birch-sticks. It differs from the last in the 
 tubercles being perfectly flat; the spores are also 
 longer, straight, and spindle-shaped (fusiform). 
 
 PERISPORACEI. Erys'iphe guttdta (Pl.YIII. fig. 33) 
 is a member of this family. It appears on the under 
 side of the leaves of the common hazel as a pale spot ; 
 and on closely examining it with the naked eye, little 
 black dots are seen scattered on the surface. These 
 are the capsules (conceptacles), which are seated upon 
 straight white filaments. The filaments (fulcra) are 
 six or seven in number, and are placed under the 
 capsule, like the legs of a stool (fig. 34) ; they are 
 rigid, and swollen or inflated at the base (fig. 35). 
 The asci are broad and short, and contain only two 
 spores. 
 
 Erysiphe maculdris is the very destructive hop-mil- 
 dew ; and other species are common on various plants. 
 
 Ch&tomium eldtum (PI. VIII. fig. 29) resembles 
 little tufts of brown hairs, occurring upon decaying 
 herbaceous stems. The capsule (fig. 28) is crusta- 
 ceous, and covered with interlaced, rough, branched 
 hairs (fig. 28 b). The spores (fig. 28 a) are oval, with 
 a little point at one end (apiculate). 
 
 PHYSOMYCETES ($i)<ra, bladder, (JLVKTJS, fungus). 
 The Fungi belonging to this order include some of the 
 commonest moulds growing upon decaying vegetable 
 substances ; while others are found upon leaves, &c. 
 The flocci are generally very evident ; and the spores 
 are contained in little naked, bladder-like capsules 
 (peridiola) at the ends of free filaments. 
 
MTTCORINI. Ill 
 
 MUCORINI. In this family we have the common 
 mould of paste, Mucor mucedo (PL VIII. fig. 36). 
 It is easily recognized by the little spherical capsules 
 terminating the long and tufted fruit -stalks (pedicels), 
 which are perceptible to the naked eye. Each cap- 
 sule consists of a simple enlarged cell, the cavity of 
 which is separated from that of the stalk by a septum. 
 They are white at first, subsequently becoming brown 
 and black. The minute crowded spores (fig. 36 s) 
 are at first oblong, afterwards spherical. In the centre 
 of the capsule is a club-shaped body, or columefla 
 (fig. 36 a), formed by the elevation and inflation of the 
 septum. 
 
 A beautiful little Fungus of this family, apparently 
 referable to the genus Acrostalag'mus (PL VIII. fig. 
 37), is sometimes found upon soft decaying stems. 
 The main filaments are soft, smooth, and not septate. 
 The pedicels are very brittle, whorled, dichotomously 
 branched, scabrous, and terminated each by a little 
 scabrous spherical vesicle (fig. 37 a), containing two 
 or three oblong spores. 
 
 ANTENNARIEI. In this family is Racodium (or An- 
 tenndria) celldre, the Wine-cellar Fungus, forming the 
 well-known cobweb-like masses hanging from the 
 walls, &c. The little black capsules are seated upon 
 slender septate filaments, and contain numerous round 
 spores. 
 
 In examining leaves with the view of procuring 
 Fungi, the reader will most likely meet with the two 
 kinds of bodies represented in Plate VIII. figs. 38 
 & 39. These are not Fungi, but galls. They arise 
 from an abnormal growth of the leaf-structures, pro- 
 duced by the deposition of the eggs of insects (Cyni- 
 piddt). The well-known oak-apple, and the red hairy- 
 looking body found upon hedge-roses, are both galls 
 produced in the same way. 
 
 Examination and Preservation. The examination 
 of the Fungi scarcely requires any special remarks. 
 
 L2 
 
112 FUNGI. 
 
 They should be viewed first as opake objects under a 
 low power ; and then sections should be made, or the 
 textures separated with the mounted needles. 
 
 There is some difficulty in moistening the smaller 
 filamentous Fungi with water, which is requisite in 
 the determination of the arrangement of the spores 
 upon the branches. Hence the best plan is to lay 
 the Fungus upon a slide, apply a cover, then to add a 
 drop of spirit of wine and afterwards a little water to 
 the edge of the cover. When thus wetted, the spores 
 may be more or less removed with a wet hair-pencil, 
 when the ends of the branches will become perfectly 
 distinct. In examination of the dried smaller Fungi 
 as the Sphteria, the capsules should be macerated for 
 a time in water. 
 
 The softer Fungi are very difficult of preservation 
 in the entire state ; but the sections or minute struc- 
 tures may be mounted in chloride of calcium or 
 glycerine. 
 
 The harder and drier Fungi may be preserved by 
 drying and gentle pressure between coarse absorbent 
 paper. They may then be glued to pieces of paper 
 and labelled, in the same manner as the flowering 
 plants. Specimens of the capsules, as of the Sph<eri<e, 
 &c., may also be mounted in the dry state, the asci 
 being preserved in the chloride of calcium or gly- 
 cerine, in which liquids most of the smaller Fungi 
 will keep extremely well. 
 
PLATE IX. [PAGE 113.] 
 
 ANIMAL TISSUES, &c. 
 
 Fig. 
 
 1. Blood-corpuscles, Human. 
 
 2. Blood-corpuscles of Bird (Fowl). 
 
 3. Blood-corpuscles of Reptile (Frog). 
 
 4. Blood-corpuscles of Fish (Stickle- 
 
 back). 
 
 5. Hair of Bat. 
 
 6. Hair of Mouse. 
 
 7. Hair of Mouse. 
 
 8. Hair, human. 
 
 9. Hair, human. 
 
 10. Wool, fibre of. 
 
 11. Flax, fibres of. 
 
 12. Cotton, fibres of. 
 
 13. Silk, fibres of. 
 
 14. Feather, portion of: a, barbs; 
 
 b, c, pinnae. 
 
 15. Bone, section of: a, lacunas. 
 
 16. Cartilage, section of. 
 
 17. Feather, downy. 
 
 18. Feather, downy : pinna. 
 
 19. Shell, pearly or nacreous portion of. 
 
 20. Muscle : a, cellular tissue ; 6, fi- 
 
 brillae j c, bundle of fibrillae. 
 
 21. Tongue of Whelk : a, natural size. 
 
 22. Scale of Dace. 
 
 Fig. 
 
 23. Scale of Perch. 
 
 24. Scale of Cod. 
 
 25. Spermatozoa of Chub. 
 
 26. Flustra foliacea'. , cells of: b, ani- 
 
 mal, with the tentacles expanded. 
 
 27. Flustra foliacea. 
 
 28. Shell of Oyster, brown portion of. 
 
 29. Shell of Oyster, prisms of. 
 
 30. Cyclops quadricornis. 
 
 31. Daphnia pulcx, female. 
 
 32. Daphnia pulex, head of male. 
 
 33. Canthocamptus minutus, an Ento- 
 
 mostracan. 
 
 34. Cypris tristriata. 
 
 35. Cypris tristriata, eggs of; 35 #, b, <*, 
 
 the same hatching. 
 
 36. Acarus domesticus (Cheese-mite), 
 
 female. 
 36*. Cilia of gills of Oyster. 
 
 37. Trombidium fuliginosum : a, pulp: 
 
 b, mandible ; c, foot ; d, natural 
 size ; e, hair ; /, hair of T. holo- 
 sericeum. 
 
 38. Acarus domesticus, male. 
 
 39. Membranipora pilosa. 
 
Plate IX. 
 
 Jfc Pi 
 
 , 
 
 // 
 
ANIMAL TISSUES. 113 
 
 CHAPTER X. 
 
 ANIMAL ELEMENTS AND TISSUES. 
 
 THE tissues of which animals consist, like those of 
 plants, are primarily derived from cells ; in fact the 
 essential part of the egg or ovum, from which all per- 
 fect animals originate consists at first only of a simple 
 cell, with its nucleus and nucleolus. 
 
 The animal cell- wall differs from that of the vege- 
 table cell in its softness and delicacy also in its che- 
 mical composition, the former consisting of albu- 
 minous (albumen, white of egg) matter, while the 
 latter is composed of cellular or vegetable-cell sub- 
 stance. 
 
 There is also a striking difference between vegetable 
 and animal tissues, in the circumstance that, while 
 the former retain their cellular condition to a very 
 great extent, the cells of the latter are frequently so 
 altered by compression and fusion together, or are 
 obscured by the great development of the cell-con- 
 tents, that the cell-form is obliterated, or can only be 
 discovered by the application of chemical reagents ; 
 and in many instances, the relation of the tissues to 
 the cell can only be discovered by tracing the growth 
 or development of the latter from its earliest stages. 
 Hence the examination of the elements and tissues 
 of animals is not well adapted for those who are un- 
 practised in the use of the microscope ; and in treat- 
 ing of them, we shall simply notice a few which are 
 most easily examined, beginning with those found 
 in animals belonging to the subkingdom Vertebrata 
 (ver'tebra, a spine-bone) . 
 
 MAMMALIA. The animals belonging to this class 
 
 L3 
 
114 MAMMALIA. 
 
 suckle their young; and their blood-vessels contain 
 red blood. 
 
 Blood. This blood consists of a yellowish liquid, in 
 which very numerous red blood-corpuscles or globules 
 (PL IX. fig. 1) are suspended, and to which the red 
 colour is owing. The blood-corpuscles are not glo- 
 bular, but discoidal, i. e. they are circular and flat- 
 tened, the sides being slightly sunk in. Their form 
 is best seen as they roll over on a slide, after the 
 application of a glass cover. The coloured corpuscles 
 are cells ; they appear yellowish red under the micro- 
 scope, the deep red colour of the blood depending 
 upon the large number of them seen at once and 
 crowded together. It need scarcely be stated that a 
 drop of blood may easily be obtained, by puncturing 
 the wrist with a clean needle. The blood is con- 
 tained in the blood-vessels. These consist of the 
 ar'teries, which convey the blood from the heart ; the 
 veins, which return it to the heart ; and a very fine 
 set of intermediate vessels, called the cap'illaries. If 
 a little water be added to a drop of blood on a slide, 
 colourless corpuscles, rather larger than the coloured 
 disks, will be seen scattered among the latter. These 
 are the colourless or lymph-corpuscles of the blood. 
 They are truly spherical, and granular on the surface. 
 
 Bone. In examining a transverse section of a bone, 
 one or several very large cavities will be seen with 
 the naked eye in the centre of the section ; these 
 contain the marrow, or medulla. In tne long bones, 
 the medullary cavity is single, and runs longitudinally 
 down the bone ; whilst in the flat bones the cavities 
 are numerous, forming cancelli. Under the micro- 
 scope, thin transverse sections of bone exhibit oval or 
 rounded holes, or foramina (PL IX. fig. 15), which are 
 sections of canals conveying blood-vessels through the 
 bone; these are the Haver sian canals. Around the 
 sections of these canals are seen numerous concentric 
 rings, indicating layers or lamellae of bony matter. 
 
BONE. 115 
 
 The substance of bone presents numerous black, some- 
 what elongated bodies (fig. 15 a), called the lacuna 
 (lacuna, a little hollow) or bone-corpuscles, which are 
 however hollow, therefore not truly corpuscles, as 
 they were formerly considered. Between the adjacent 
 lacunae run numerous fine, dark, branched lines, con- 
 sisting of very minute canals, or canalic'uli. If the 
 section of bone be viewed by reflected light, the 
 lacunae and canaliculi will appear white. In the dried 
 bone they contain air. 
 
 The structure of bone is best seen when viewed as 
 a transparent object in the dry state; for when the 
 section is immersed in liquid, the lacunae and canali- 
 culi become filled up. 
 
 The size and form of the bone-corpuscles and canali- 
 culi vary in different animals, so much so that the 
 Class or Order to which an animal belongs may be 
 determined by reference to these particulars. 
 
 Bone consists of earthy salts deposited in a finely 
 granular form throughout the substance of cartilage. 
 By soaking a piece of bone in vinegar or other dilute 
 acid, the earthy salts will be dissolved, the soft carti- 
 lage being left. But the structure of cartilage may be 
 best observed by making thin sections of the gristle 
 covering the ends of bones. It exhibits a bluish- 
 white basis (PL IX. fig. 16), in which are imbedded 
 numerous cells or cartilage-corpuscles, often under- 
 going cell-division. In some kinds of cartilage, the 
 basis is composed of fibres. 
 
 Muscle. On examining a piece of the red flesh of 
 an animal under a low power, the mass will exhibit 
 a number of coarse, parallel, longitudinal, dark lines 
 (PL IX. fig. 20), the substance between these lines 
 being marked with cross or transverse striae, or lines, 
 and with fine longitudinal lines. The coarse longitu- 
 dinal lines indicate the intervals between bundles of 
 slender fibres, or fibril'lce, of which muscle consists. 
 The fibrillae (fig. 20 b, c) are very difficult to separate ; 
 
116 MAMMALIA. 
 
 but when perfectly separated, they are seen to be 
 exceedingly slender, and to consist of alternately light 
 and dark portions in regular series. When the fibrillae 
 of the bundles are in close apposition, as in the natu- 
 ral muscle, the dark portions, being in the same lines, 
 by their coincidence form the transverse striae. The 
 bundles into which they are combined are surrounded 
 by a delicate skin or membrane, with a little cellular 
 tissue. 
 
 The structure of muscle may be observed in a piece 
 of ham which has been soaked for a day or two in 
 spirit of wine, the mounted needles being used to pick 
 it to pieces. 
 
 The above-mentioned transversely striated muscu- 
 lar fibre is that found in the voluntary muscles, or 
 those under the influence of the will. But there are 
 other muscles in animals which are involuntary, or 
 not subject to the will; in these the fibrillar structure 
 is absent, the muscular tissue consisting of simple 
 elongated and nucleated cells. 
 
 Cel'lular tissue This fills the interstices between 
 the other tissues and organs of animals, in the 
 same manner that the vegetable parenchyma does 
 those of plants. It is not, however, composed of cells, 
 but of very fine, soft, colourless, and wavy fibres 
 (PL VIII. fig. 20 ), aggregated into bundles, which 
 interlace so as to leave spaces or areolse between 
 them. 
 
 The cellular or areolar tissue may be found in a 
 piece of beef or mutton, in the intervals of the 
 muscular fibres. 
 
 Skin, The skin is composed of cellular tissue, its 
 outer surface presenting a number of projecting blunt 
 points, called papil'lae. It contains a large number 
 of blood-vessels; and when the capillaries are well 
 filled by injection with a coloured composition, it 
 forms a beautiful microscopic object. 
 
 The skin is covered by the epider'mis or cuticle, 
 
HAIR. 117 
 
 which consists of several layers of cells. It is the 
 epidermis which is raised and covers the bladders 
 formed by the action of a blister applied to the skin. 
 
 Hair. The hair consists of long solid filaments 
 (PL IX. fig. 9), and not of hollow tubes, as was 
 formerly supposed. It presents varieties of structure 
 in different animals, which agree generally in animals 
 belonging to the same Orders. 
 
 Hairs are implanted in pits in the skin; each is 
 swollen at the base to form the bulb, which is seated 
 upon a papilla of the skin, by which it is formed or 
 secreted. The hair is an epidermic formation, con- 
 sisting of epidermic cells more or less flattened and 
 altered in shape by mutual pressure. 
 
 The colour of the hair is usually seated in the outer 
 or cortical portion of the stem or shaft, and arises 
 from the presence of aggregations of minute granules 
 of colouring-matter or pigment, as the colouring-mat- 
 ter of animals is called : in the human hair it forms 
 short longitudinal stripes (fig. 9). In the central 
 pith or medullary portion of the hair the cellular 
 structure is more open and distinct than in the cortical 
 portion, in which the cells are so compressed and 
 consolidated as only to exhibit the cell-structure after 
 treatment with reagents; and the medullary cells 
 often contain air. 
 
 In grey or white hairs, the whiteness depends 
 mainly upon the presence of air in the cells of the 
 pith. In the gnawing or rodent animals, as the 
 mouse or the rabbit, the pigment is partially at least 
 situated in the cells of the medulla. 
 
 In the hairs of many animals, the cuticular or sur- 
 face-cells of the shaft are distinctly imbricated (fig. 5), 
 and form beautiful microscopic objects. 
 
 The principal interest in the structure of the hair 
 relates to the three points above mentioned, viz. the 
 position of the pigment, the arrangement of the cuti- 
 cular cells or scales, and that of the cells of the pith. 
 
118 MAMMALIA. 
 
 The pigment is best examined in hairs moistened 
 with a little spirit of wine, which displaces the air 
 from the cells of the pith, and renders the hair trans- 
 parent ; a little water should be subsequently added. 
 The cuticular scales are also well shown by this pro- 
 ceeding. Towards the root of the hairs in the mouse, 
 they project beyond the margin, giving it a toothed 
 or dentate appearance; in the hair of the mole, 
 the bat (fig. 5), or the wolf, this dentation may 
 also be seen. In the hairs of some of the foreign 
 bats, the scales are whorled, forming very beautiful 
 objects. 
 
 The cells of the pith (PI. IX. fig. 7) also present 
 interesting varieties, being sometimes arranged in a 
 single row, at others in two or more rows (fig. 6). 
 These are best seen in hairs recently immersed in 
 spirit or in oil of turpentine ; for if the hair be too 
 long soaked in these liquids, the air will be entirely 
 displaced by them. The cells of the pith appear black 
 by transmitted and white by reflected light, in the 
 dry hairs, from the presence of air. They may be 
 well examined in the hair of the mouse (figs. 6 & 7), 
 or in that of the mole. Wool, which is the hair of the 
 sheep, consists of curled fibres (PL IX. fig. 10), in 
 which the imbricated arrangement of the surface- 
 scales is very distinctly seen. 
 
 In PL IX. figs. 10-13 the fibres of wool, flax or 
 woody fibre, cotton, and silk are represented together, 
 to allow of comparison ; for the microscope is of great 
 assistance in discriminating these substances when 
 existing in textile fabrics. The fibres of wool (fig. 10) 
 are distinguished by their solidity, wavyness, and 
 the imbricated scales ; those of flax (fig. 11) by their 
 thick walls, great length, acute ends, and their knotty 
 appearance at intervals. The fibres of cotton (fig. 12) 
 are soft, flaccid, flattened, and often twisted; and 
 those of silk (fig. 13) are solid and very slender. By 
 a little chemical testing, the discrimination is made 
 
- BIRDS. 119 
 
 still more easy ; but for an account of this I must 
 refer to the Dictionary. 
 
 BIRDS. In the Class of Birds, the structure of the 
 feathers deserves special notice. Feathers are epi- 
 dermic formations, or consist of aggregations of epi- 
 dermic cells, yet so altered by compression and fusion 
 together that the cell-structure is in most parts dif- 
 ficult to detect. In a feather three parts are dis- 
 tinguishable, the transparent cylindrical quill; its 
 opake continuation, which is more or less flattened 
 at the sides, forming the shaft; and the vanes or 
 beards, which arise from the sides of the shaft, con- 
 sisting of numerous closely set, parallel, flattened 
 fibres, called the barbs. The structure of the barbs 
 forms the interesting object to the microscopist. On 
 examining a piece of the coloured vane of a somewhat 
 large feather (PL IX. fig. 14), a row of fine parallel 
 colourless filaments (pinnae) will be observed, arising 
 from the opposite sides, the filaments of one side 
 lying obliquely across those arising from the other ; 
 and while the filaments or pinnae of one side present 
 a row of little teeth (fig. 14 c) near their base, those 
 of the opposite side (fig. 14 b) are provided with as 
 many hooks near their apex, which curve over the 
 teeth to connect the barbs together. This curious 
 arrangement is adapted to keep the parts of the 
 feather firmly united, and yet to allow of their play 
 and flexibility. To observe this structure, a portion 
 of a vane should be soaked in oil of turpentine, and 
 mounted in balsam. 
 
 In the downy feathers (PL IX. fig. 17) the barbs 
 are not furnished with the pinnae, but present simply 
 whorls of minute spines (fig. 18). 
 
 The bones of birds present the same general struc- 
 ture as that of mammals, the lacunae being, however, 
 more numerous and smaller. 
 
 The blood of birds (PL IX. fig. 2) differs entirely 
 from that of mammals, in the red corpuscles being 
 
120 REPTILES. 
 
 oval instead of circular, and convex instead of con- 
 cave ; and each contains a distinct oval and granular 
 nucleus. 
 
 REPTILES. In reptiles, as the frog, toad, or water- 
 lizard (Triton) , the bone-corpuscles or lacunae are 
 larger and more numerous than in either of the former 
 classes ; and the blood- corpuscles (PL IX. fig. 3) are 
 comparatively very large, oval, rather concave, and 
 contain a large granular nucleus. 
 
 The smooth water-newt or triton, properly called 
 Lissotriton punctdtus, is a very interesting animal in 
 a microscopic point of view. It may be found in most 
 ponds ; and if several are removed in a net, and kept 
 in a large glass jar, with water-plants, they will live 
 for a long period. In the spring or early summer 
 they will deposit their eggs upon the aquatic plants, 
 generally on the under surface of a leaf, which they 
 bend downwards, so as to protect them. The eggs or 
 ova, are about half the size of a pea, and consist of a 
 sac containing a transparent liquid, with a yellowish 
 globule within. After a time these eggs will hatch, 
 and the larvae or young newts must be removed from 
 the water, otherwise the parents will devour them. 
 
 If one of these larvae, which resemble little fish in 
 appearance, be placed with a little water in the ' ' live- 
 box/ 7 and the cap be very gently pressed down, so as 
 to fix the body of the animal, the circulation of the 
 blood may be very beautifully seen in either the 
 fringe-like gills, which are placed on each side of 
 the neck, or in the tail, a low power being used; 
 at the same time the beautiful stellate pigment- 
 cells of the skin will be observed. The struc- 
 ture of the rudimentary spinal column, which runs 
 down the middle of the back, and consists of simple 
 large cartilage-cells, may also be made out, when the 
 animal is dead, by a little dissection with the aid of 
 needles. 
 
 FISHES. In the fourth class of vertebrate animals, 
 
FISHES. 121 
 
 which consists of the fishes, we find interesting struc- 
 tures in the blood, the scales, and the roe. The corpus- 
 cles of the blood (PL IX. fig. 4) differ from those of the 
 Mammalia, but agree with those of birds and reptiles, 
 in being oval instead of round. The scales of fishes 
 (PL IX. figs. 22, 23) are usually rounded or oval, 
 as in most of our freshwater fishes, when they are 
 called cycloid (KVK\OS, circle) ; but sometimes they 
 are toothed at one end (fig. 23 a), forming ctenoid 
 (/tret?, a comb) scales, as in the perch. Most scales 
 exhibit a number of concentric rings, which are the 
 indications of lamince ; and many of them are lobed 
 at the margin, sometimes also having radiate furrows. 
 In the centre are often seen little rounded solid 
 bodies, having somewhat the appearance of cells, 
 which are very well seen in the scales of the perch ; 
 and in some scales these bodies are arranged in 
 concentric rows throughout the substance, as in 
 those of the eel or the cod (fig. 24). The substance 
 of which scales consist is generally cartilaginous ; in 
 some of them, however, true bony matter is present. 
 Fish-scales are contained within the substance of the 
 skin, and not merely attached to it by one end, as 
 appears to be the case in many fishes. In most of 
 our common fishes, as the roach or perch, the scales 
 project beyond the level of the skin ; but the projecting 
 portion is covered by a thin layer of the skin ; and 
 when the scales are scraped off, this layer, with its 
 elegant stellate pigment- cells, is usually found ad- 
 herent to it. In some other fishes, as the cod and 
 eel, the scales are entirely sunk below the surface ; 
 and these are commonly supposed to have no scales. 
 They may, however, be easily found by dissection, 
 or by drying a piece of the skin under pressure be- 
 tween two plates of glass, and mounting a portion 
 in balsam. 
 
 The beautiful silvery lustre of the skin of fishes 
 depends upon the presence of innumerable very minute 
 
 M 
 
122 MOLLUSCA. 
 
 and thin crystals ; these may be well examined in the 
 skin of a sprat. 
 
 The roe of fishes consists of the ova or eggs,, and 
 the spermatozoa, the ova being contained in the 
 hard, the spermatozoa in the soft roe. The eggs 
 consist of a cell surrounded by one or two membranes; 
 and the latter are often traversed by numerous fine 
 radial canals, or present a funnel-shaped tube leading 
 to the ovum. The spermatozoa of the soft roe consist 
 of exceedingly slender filaments (fig. 25), terminated 
 at one end by a kind of head. The reader will not 
 fail to detect the analogy between the ovum of the 
 animal and that of the ovule of the plant ; and it need 
 scarcely be stated that the spermatozoa of the animal 
 fertilize the ova, in the same manner that the pollen- 
 tubes and spermatozoa of plants fertilize the ovules ex- 
 isting in them. In the case of fishes, the spermatozoa 
 of the soft roe escaping into the water, and moved by 
 the ciliary action of the filament, enter the micropyle- 
 like canals of the ova, which are deposited by the 
 fish upon the bottom of rivers. 
 
 The scales of fishes may be prepared for examina- 
 tion by scraping them off and macerating them in water 
 until the adherent portion of the skin is softened and 
 decomposed, so that it may be washed away. They 
 should be dried between glass plates, and viewed 
 under a low power, as dry transparent objects. 
 
 The structure of muscle can be more easily made 
 out in fishes than in other animals. A portion of 
 the flesh should be macerated in spirit as directed 
 above. 
 
 MOLLUS'CA. We shall now leave the vertebrate 
 animals, and pass to the subkingdom Mollusca, the 
 marine kinds of which are popularly called shell- 
 fish : three of their structures form interesting ob- 
 jects for examination the shell, the tongue, and the 
 gills. 
 
 Shell. The general structure of the shell of the 
 
TONGUE. 123 
 
 Mollusca may be illustrated by reference to that of 
 the oyster. Two kinds of shell-substance are at once 
 distinguishable in an oyster-shell, an outer brown, and 
 an inner pearly or nacreous. The brown portion ex- 
 hibits under the microscope the appearance of a cell- 
 structure (PL IX. fig. 28), the angular forms from 
 mutual pressure being very distinct. The component 
 bodies of this portion are seen to be more or less 
 elongated and flattened in the side view, forming 
 prisms (fig. 29). The structure of the pearly part of 
 the shell is more difficult of examination, and can only 
 be seen distinctly in ground and polished sections. 
 In these, under a high power, it exhibits numerous 
 fine, somewhat parallel wavy lines (fig. 19), which are 
 the indications of thin layers, or laminae, of which it 
 is composed. 
 
 Shell consists of a basis of animal matter in which 
 carbonate of lime (chalk) is deposited, the whole 
 being poured out or secreted by the skin or mantle 
 of the mollusk. 
 
 Pearls, which possess the same structure as the 
 nacreous part of shell, consist of the nacre formed 
 around some foreign body, as a grain of sand, &c., 
 by which the mantle has been wounded. 
 
 Tongue. The structure of the tongue of the Mol- 
 lusca is very interesting, on account of the curious 
 teeth which are found upon it. It may be illustrated 
 by the common Whelk (Budcinum unddtum), which 
 is sold at the street- stalls. As, to one unacquainted 
 with the anatomy of the Mollusca, there is some diffi- 
 culty in finding the tongue, it may be well to point out 
 how it is to be found. If the shell containing the 
 animal be placed so that its orifice is directed up- 
 wards, the point or apex of the spire being towards 
 the reader, the lid (oper'culum) which closes the shell 
 will be at once evident. On drawing the animal from 
 the shell by means of the lid, the foot or portion 
 which is applied by the animal to the surface upon 
 
 M2 
 
124 MOLLUSCA. 
 
 which it creeps will be seen. At the upper part of 
 this is the head, with its two horns (ten'tacles) . 
 Below the roots or bases of the tentacles, and be- 
 tween them and the upper part of the foot, is 
 the little round mouth. On slitting this up with 
 scissors, a cavity will be opened, and in it will be 
 seen a reddish tube (the proboscis), about as large as 
 a goose- quill, with an aperture at the end. This 
 must be carefully slit up, when the tongue, which is 
 of about the size of a crow-quill, will come into view. 
 The tongue is moveable in the proboscis, and can be 
 protruded or withdrawn by the animal at will. If 
 the surface of the tongue be viewed under a hand- 
 lens, the rows of teeth will be seen at once. It is 
 better not to pull the tongue out with forceps, as 
 the teeth are easily displaced and injured. The best 
 plan is to dissect away the muscular structures with 
 forceps and a pair of fine-pointed scissors, then to 
 cut off the tongue at its root, and to soak it in water 
 for some hours, when the skin or epidermis containing 
 the teeth can be separated with the mounted needles 
 under a simple lens or microscope. After any loose 
 particles have been washed away with a hair pencil, 
 the object may be spread flat on a slide, and dried 
 between two slides. The upper slide should then be 
 removed, the tongue soaked in oil of turpentine, and 
 mounted in balsam with the least possible heat. 
 
 As thus prepared, the horny teeth (PL IX. fig. 21) 
 are seen to be arranged in rows, united by a colourless 
 membrane, so as to form a long ribbon. The teeth 
 form three longitudinal parallel rows, a central and 
 two lateral. Each tooth, considering the separate 
 pieces as constituting distinct teeth, has little teeth 
 or denticles at its lower edge. These are curved 
 inwards, four in number, and connected by a basal 
 plate in the side teeth ; while the middle teeth have 
 six or seven straight denticles. These teeth serve 
 to enable the animal to scrape or rasp the algae, 
 
GILLS. 125 
 
 and other matters forming their food, from the sur- 
 faces upon which they grow. And if some water- 
 snails are placed in a glass jar the inside of which is 
 covered with confervoid growths, the curious patterns 
 left after the action of the snails' tongues will be 
 found to present a very curious appearance. 
 
 Gills. The gills or "beards" of the oyster or mussel 
 exhibit very strikingly the phenomenon of ciliary mo- 
 tion. The gills (branchiae) are respiratory organs, 
 consisting of folds of the skin, covered with cilia, by 
 means of which the water in which the animal lives 
 is set in motion, and constantly changed to aerate 
 the blood within them. The currents thus induced 
 serve also to bring the food which floats in the water 
 towards the mouth of the animal. By snipping off 
 a thin portion of one of the brown beards of a fresh 
 oyster, laying it upon a slide, adding a drop of the 
 ( ' liquor " contained within the shell, and lightly pressing 
 a cover upon the whole, the remarkable phenomenon 
 to one who has not before viewed it will be seen 
 under a somewhat high power about J-inch. The 
 whole field will appear in motion, and the lashing or 
 whip-like action of the cilia will be seen, especially 
 towards the edges of the bars (PI. IX. fig. 36) of the 
 gills. The rapid motion of any floating particles 
 present will also be noticed, showing the direction of 
 the currents of liquid, which, as the liquid is trans- 
 parent, would not otherwise be recognizable. 
 
 BRYOZOA (ffpvov, moss, pwov, animal). The animals 
 included in this Class, which belongs to the Mollusca, 
 are mostly marine. They are microscopic, and con- 
 tained in horny or calcareous sacs or cells, aggregated 
 together to form polyp'idoms (polype, and Sw/,ta, a 
 house) . They are sometimes plant-like or leafy (PL IX. 
 fig. 27), at others filamentous and branched, or they 
 form a layer or crust upon the objects to which they 
 are attached. The polypidoms, which are often some 
 inches in length, are frequently met with on the sea- 
 
 M 3 
 
126 BEYOZOA. 
 
 shore, the cells (fig. 26 a) having slit-like valvular 
 orifices. The bodies of the animals are soft and 
 polype-like, and are furnished at one end with a circle 
 of tentacles, covered with rows of cilia, by which the 
 water is changed for respiration, and particles of food 
 are brought to the mouth. The tentacles can be 
 protruded or withdrawn at the will of the animal. 
 The Bryozoa are what are called compound animals, 
 each individual body having its own set of organs ; 
 yet the whole are connected together. 
 
 The two species figured are very common. Fludtra 
 folidcea (PL IX. fig. 27) is found everywhere upon 
 the sea-shore. The polypidom has cells upon both 
 sides ; and they are narrowed at one end, and rounded 
 at the other. Membranip'ora pilosa (PL IX. fig. 39) 
 occurs upon sea- weeds and other marine bodies, form- 
 ing a closely adherent layer. The orifices of the cells 
 are surrounded with teeth, and are usually furnished 
 below with a very long bristle the polypidom appear- 
 ing to the naked eye as a white hairy crust. In the 
 variety figured, the long bristles are replaced by a 
 spine ; and this is not uncommon. 
 
 The polypidoms of the Bryozoa form interesting 
 microscopic objects, the cells being furnished with 
 variously arranged spines and punctures or dots. In 
 some the cells are erect and arranged in rows upon the 
 branches of a plant-like stem, while in others they are 
 scattered irregularly over a creeping filament. 
 
 For examination they should be prepared by macer- 
 ation in fresh water, and drying between glass plates 
 or sheets of paper, and either viewed as opake objects 
 or, after soaking in 'turpentine and mounting in bal- 
 sam, as transparent objects. 
 
 It may be remarked that the name Bryozoa for 
 this class of Mollusca, which was thoroughly estab- 
 lished, has recently been changed in this country to 
 Polyzoa (TToXu?, many, o>ov, animal), and that the 
 name of polypidom has been altered to polyzoary. 
 
ENTOMOSTRACA. 127 
 
 CHAPTER XL 
 
 ARTICULATA (ARTIc'lJLUS, A JOINT). 
 
 THE animals belonging to this subkingdom are spe- 
 cially distinguished by the body and limbs being 
 jointed : as familiar instances, may be mentioned the 
 lobster, the wood-louse, spiders, insects, and worms. 
 
 Taking the class Crustacea, to which the two first 
 animals belong, we find interesting microscopic forms 
 in the subclass Entomos'traca (evrofiov, insect ; ocrT/ao- 
 KOV, shell). 
 
 ENTOMOSTRACA. The animals contained in this 
 Order are met with in every pool or pond, some of 
 them inhabiting the sea. They are mostly minute, 
 yet visible to the naked eye, forming specks swimming 
 actively or leaping through the water ; hence some 
 of them have been called water-fleas. The body of 
 the animal is protected by a shell or car'apace, which 
 in some consists of a single piece (PL IX. fig. 30), 
 while in others it consists of two similar parts or 
 valves (fig. 31), in the latter case the joints of the 
 body being indistinctly visible. The head is furnished 
 with usually two projecting feelers or antennae (an- 
 ten'na, a sail-yard), one of which is uppermost or su- 
 perior (PL IX. figs. 30, 31, 34 a], the other lowermost 
 or inferior (figs. 30 and 34 b) ; and these are often 
 used for swimming. The antennae are jointed, and 
 sometimes beautifully plumose (pluma, a feather) or 
 feathery, i. e. furnished with rows of long and very 
 slender filaments. There are several pairs of jointed 
 legs, some of which serve as jaws (foot-jaws), while 
 others are finely filamentous to serve for swimming 
 
128 ENTOMOSTKACA. 
 
 and as respiratory organs (branchial feet). The four 
 species figured are very common. 
 
 Cypris tristridta (PL IX. fig. 34) is found in ponds 
 and ditches. The carapace is bivalve, or has two valves, 
 which are convex and oval ; and it is of a greenish 
 colour, with three irregular dark stripes behind. 
 The superior antennae (a) are jointed and finely fea- 
 thery, the inferior antennae (b) having a tuft or pencil 
 of fine filaments arising from their anterior margin. 
 The eye is single. The animal swims steadily and 
 freely through the water. 
 
 The eggs of Cypris (PL IX. fig. 35) are often found 
 in glasses of water containing the animals. They are 
 rounded or oblong, of a red colour, glued together by 
 an amorphous jelly, and adherent to pieces of stick 
 or the sides of the glass. They are enclosed in a 
 thick shell, which exhibits a cellular appearance in 
 the surface view, and is striated in the side view ; so 
 that the structure of the shell is prismatic, as in that 
 of the oyster. When the eggs escape from the shell, 
 they present the appearance represented in fig. 35 #, 
 the body of the young animal being enclosed in a 
 transparent envelope, one end of which forms a blunt 
 protrusion; there is also a separate slender process 
 enclosing the superior antennae. After a time, the 
 envelope is cast off (fig. 35 b) } when the animal begins 
 its active stage of life. Theeast-ofF envelopes (fig. 35 c), 
 with the protruded portions wrinkled, are often found 
 in the sediment of water containing the animals. 
 The structure of these ova is that of what are called 
 winter ova, which agree with the resting-spores of the 
 lower plants or the Algae. 
 
 Cy clops quadricor'nis (PL IX. fig. 30) is another 
 common species. In this the body is closely sur- 
 rounded by the jointed shell, as in a lobster. The 
 superior antennae (a) are very long and many-jointed, 
 each joint having short bristles arising from it, while 
 the inferior antennae are short and four-jointed. There 
 
DAPHN1A. 129 
 
 is no separate head, this being united to or conso- 
 lidated with the first joint of the thor'ax or chest, the 
 head and thorax together comprising fonr joints. The 
 remaining joints enclose the belly, or abdomen, which 
 has the appearance of a tail ; but the tail is constituted 
 by the two last parallel pieces, which are furnished 
 with fine feathery filaments. 
 
 The female is most commonly met with, and is 
 easily known by having the egg-pouch, or ovary (o) 
 external on each side, and filled with eggs or ova. 
 The little Cyclops is readily recognized by its form and 
 jerking motion through the water. 
 
 Daph'nia pulex (PI. IX. fig. 31) is a very common 
 Entomostracan, and is very well adapted to illustrate 
 the structure, on account of its size and transparence. 
 In this animal the body is loosely connected with a 
 bivalve shell, which, on careful examination, is seen to 
 be reticulated or marked with net-like lines. The 
 superior antennae (a) are very small, placed under a 
 small beak, and have at the end a minute tuft of hairs. 
 The inferior antennae (b) resemble arms, being large 
 and branched ; and by means of them the animal rows 
 itself through the water. The structure of the eye is 
 curious, consisting of a number of round lenses aggre- 
 gated together, the fine muscular threads by which it 
 is moved being easily distinguished with a high power. 
 The legs are flattened, and furnished with elegant 
 feathery setae (seta, a bristle), serving as gills or 
 branchiae. They are constantly in motion, fanning 
 the water so as to change incessantly the portion with 
 which they are in contact. About the middle of the 
 back is placed the little transparent heart, with its 
 colourless blood, which may be distinctly seen beating, 
 or contracting and dilating, in the living animal ; and 
 between the back of the animal and the shell are seen 
 the ova, which remain there until they are hatched. 
 
 The genera and species of the Entomostraca are 
 very numerous. Those mentioned above will serve 
 
130 ARACHNIDA. 
 
 to illustrate the general structure of the order. To 
 distinguish the man'dibles (mandib'ula, a jaw) or 
 proper jaws, the foot-jaws, and the branchial legs, 
 the animals must be dissected in water with the 
 mounted needles. The very delicate feathery fila- 
 ments of the branchiae may be best observed when 
 these organs are dried on a slide. 
 
 The Entromostaca may be kept alive in a jar 
 of water with water-plants for a long period. They 
 may be removed from the water for examination 
 by the dipping-tube, and are best observed in a live- 
 box. 
 
 ARACH'NIDA (apa^vrj, spider) is the Class of spiders, 
 scorpions, and mites. 
 
 Araneida. This Order contains the more highly 
 developed forms of the Class, among which are the 
 common spiders of houses and gardens ; and some of 
 their structures are very curious and interesting. 
 
 The head of spiders is united or fused with the 
 thorax, forming one piece, which is called the ceph'alo- 
 ihorax (tce<f>a\rj, head, copal;, chest). 
 
 The claw-jaws, or mandibles, are terminated by a 
 curved and pointed claw, with which the spiders hold 
 their prey. It is traversed by a slender canal, con- 
 taining a slender tube or duct leading from a poison- 
 gland, and opening near its point; and when the 
 insect prey is transfixed by the mandible, the poison 
 is pressed out and enters the wound. 
 
 Near the root or base of the mandibles on each 
 side is a jointed feeler, or pal'pus ; but spiders have 
 no anten'nse. The eyes are simple, forming separate 
 round shining dots, and are called ocel'li (ocel'lus, 
 a little eye) ; they are usually placed on the top of 
 the head, and are often arranged in a geometrical 
 form, as a triangle, &c. 
 
 The legs are four pairs ; they are hairy, and ter- 
 minated by two or three claws, which are fringed 
 with minute teeth, or pec'tinate. These claws serve 
 
ACARINA. 131 
 
 to comb the fibres of the web, just as we comb our 
 hair with a common comb. 
 
 The spinnerets, with which spiders form their web, 
 are very curious organs. They are situated at the 
 under and hind part of the body, and consist of two 
 or three cones, or papillae, on each side. On the 
 summits of these papillae are very numerous bristle- 
 like tubes, through which the secretion of certain 
 glands passes ; this secretion, when hardened by ex- 
 posure to the air, forms the fibres of the web. 
 
 On carefully examining a spider's web, the radial 
 fibres, or those which pass from the centre to the cir- 
 cumference, will be found to be smooth, these fibres 
 serve to fix the web ; while the cross fibres are covered 
 with numerous viscid globules, which serve to attach 
 flies or other prey to them. This difference of the 
 fibres is best observed with a hand-lens. 
 
 ACARINA, or the Order of Mites. Here belongs 
 cheese-mite, Ac? arm domes' ticus (PL IX. fig. 36) . Its 
 body is somewhat milky white, oval, and furnished 
 with feathery hairs. When viewed from beneath, 
 there is seen a transverse line, indicating the separa- 
 tion of the thorax from the abdomen ; and another 
 line in front of this, with four minute tubercles, from 
 each of which arises a hair. The head is pointed and 
 beak-like, forming a ros'trum (rostrum, a beak), con- 
 sisting of two mandibles pressed together ; these can 
 only be seen to be separate when dissected apart with 
 the mounted needles. Each mandible is chelate 
 (jCflW) forceps), or has the form of a lobster's claw ; 
 and beneath the two mandibles is a flat membranous 
 under lip or labium, consolidated on each side with a 
 palp. The legs are four pairs, as in all the Arachnida ; 
 they are pinkish, 6-jointed, and terminated by a leaf- 
 like sucker and a minute claw. 
 
 The males (fig. 38) are smaller than the females, 
 the fore legs being much stouter, and furnished with 
 a blunt tooth (fig. 38 a). The eggs can often be dis- 
 
132 ACARINA. 
 
 tinguished within the body of the female (fig. 36) ; 
 they are oval and granular. 
 
 Another species of Acarus, A. sac'chari, is found 
 abundantly in ordinary moist sugar. If a little of 
 the sugar be placed in a wine-glass, some water added, 
 and the mixture be stirred until the sugar is dissolved, 
 the Acari will be found both in the sediment and 
 floating on the surface. 
 
 A somewhat larger member of the order occurs as 
 a parasite upon a species of Dung-beetle (Geotrupes 
 ster cor arms] which is vulgarly known as the Lousy 
 Watchman. The beetle is black, shaded with 
 purple, about three-quarters of an inch long, and is 
 found under cow-dung. The mites cling pertinaci- 
 ously to the under parts of the beetle, and can easily 
 be seen with the naked eye. They are whitish, with 
 the mandibles, the sucker, and two claws very dis- 
 tinct ; and the palpi are unattached to the labium, 
 or free. These mites form the species Gam'asus 
 coleoptrator'um. Another species, Gamasus teldrim, 
 is the red spider of the greenhouse. 
 
 Trombirfwm fuliginosum (PL IX. fig. 37 d) is a 
 common red spider of gardens. It is of a scarlet 
 colour, appearing velvety from the presence of a dense 
 coat of feathery hairs (fig. 37/) . The palpi of this 
 mite are large, free, the last joint but one (PL IX. 
 fig. 37 a) being furnished with a claw, while the last 
 joint is obtuse, and resembles a lateral appendage. 
 The mandibles (fig. 37 b) are furnished with a sharp 
 curved claw. The legs are long, especially the an- 
 terior pair, and terminated by two claws, with a de- 
 licate sucker-like appendage (fig. 37 c). 
 
 Another species of Trombidium, T. holoseric'eum, 
 greatly resembling the last, is also found in gardens. 
 It may be easily distinguished from the last by the 
 club-shaped hairs (fig. 37 e) existing upon the body. 
 The harvest-bug, which causes such irritation of the 
 legs of persons who frequent corn-fields in the 
 
PLATE X. [PAGE 133.] 
 
 INSECTS. 
 
 Fig. 
 
 1. Atropospukatorius : * natural size. 
 
 2. Aphis of Geranium: a, foot; &, anal 
 
 tube j c, antenna. 
 
 3. Scales on wing of Apollo-butter- 
 
 fly. . 
 
 4. Lithobius forcipatus. 
 
 5. Litho1riwforcipatw,]iea&of: #, an- 
 
 tennae ; b, mandibles ; c, labial 
 palpi ; d, labium. 
 
 6. Dytiscus marginolis, head of larva. 
 
 7. Young larva of Dytiscus margi- 
 
 nalis. 
 
 8. Pupa of Gnat ( Cidex pipiens). 
 
 9. Larva of Gnat. 
 
 10. Head of Gnat, male. 
 
 11. Head of Gnat, female. 
 
 12. Coccinella 7-punctata (large Lady- 
 
 bird), labium of. 
 
 13. Coccinella 7-punctata, mandible of. 
 
 14. Coccinella 7-punctata, labrum of. 
 
 15. Coccinella 7-punctata, antenna of. 
 
 16. Coccinella 7-punctata, maxilla of: 
 
 a, palp ; b, c, lobes of maxilla. 
 
 17. Head of Musca domestica (House- 
 
 fly) : a, antenna ; b, labial palpi ; 
 c, proboscis. 
 
 18. Head ofStomoxys calcitrans : 18 a. 
 
 antenna. 
 
 19. Scales of insects : a, scale of Po- 
 
 dura] b, of House-moth {Tinea 
 
 Fig. 
 
 vestianelld) j c, of Podura ; d, of 
 Lepisma', e, hair of Podura', 
 f, scale of Cabbage-Butterfly 
 (Pontia brassicce). 
 
 20. Head of Cabbage-Butterfly: ^an- 
 
 tennae broken off"; b, palp ; 
 c f tongue (antlia)j d, club of 
 antenna. 
 
 21. Head of human Flea (Pulex irri- 
 
 tans), female ( ) : a, palpi ; 
 b, niaxillsB. 
 
 22. Flea of the Rat (Pulex muris), 
 
 male (cJ). 
 
 23. Pterostichus (Steropus) madidus; 
 
 23 a, antenna. 
 
 24. Part of leg of Pterostichus madi- 
 
 dus : a, tibia j b, tarsus. 
 
 25. Labrum of Pterostichus madidus. 
 
 26. Mandible of Pterostichus madidus. 
 
 27. Labium of Pterostichus madidus : 
 
 a, mentum ; b, labial palp. 
 
 28. Maxilla of Pterostichus madidus : 
 
 a, claw j b, c, maxillary palps. 
 
 29. Proboscis of House-fly. 
 
 30. Larva of Flea. 
 
 31. Larva of Chironomus plumosus. 
 
 32. Foot of House-fly. 
 
 33. Eye of House-fly. 
 
 34. Leg of Ant (Formica fused) ; 
 
 34*, pectinate process. 
 
Plate X. 
 
INSECTS. 133 
 
 autumn, is also a species of Trombidium T. autum* 
 ndle. 
 
 Preparation. The organs of the mouth, &c., of the 
 Spiders are easily prepared for examination, by care- 
 fully pulling them off with forceps or the mounted 
 needles, then drying them under pressure between 
 two glass slips, macerating in turpentine, and mount- 
 ing in balsam. Those of the Acarina should be dis- 
 sected out with the needles, after the body has been 
 crushed in a drop of water on a slide, and the internal 
 substance has been gently washed away with a hair 
 pencil. They may then be dried on a slide, with a 
 cover laid on, and turpentine applied to the edge of 
 the cover, balsam being added when most of this has 
 evaporated. The various parts may also be mounted 
 in chloride of calcium or glycerine. 
 
 INSECTS. The members of the class of Insects are 
 extremely interesting to the microscopic observer, 
 not only on account of the beautiful structures which 
 they present, but also from these being comparatively 
 large, usually coloured, and easily distinguished under 
 the lower powers. Hence they form admirable ob- 
 jects for study to those who are but little accustomed 
 to the use of the microscope. 
 
 MYBJAP'ODA (yitu/oto?, myriad, TTOI)?, foot. This 
 Order contains those insects which are popularly 
 known as the hundred-legs and millepedes ; by many 
 zoologists they have been arranged in a distinct 
 class. 
 
 The most common member of this Order is Litho- 
 bius forcipdtus (PL X. fig. 4), which is found under 
 stones, in cellars, and among garden-rubbish. It is 
 of a yellowish-brown colour, with long, many-jointed, 
 gradually tapering or setaceous (seta, a bristle) anten- 
 nae (figs. 4 0, 5 fl), and two large and powerful mandi- 
 bles (fig. 5 b) resembling those of the spiders. It 
 has also a broad, notched, and toothed lower lip, or 
 labium (fig. 5 d), above which are two toothed jaws, 
 
134 INSECTS. 
 
 or maxillae, and two lip-feelers, or labial palpi (c). 
 The eyes consist of a group of ocelli on each side (e) . 
 The body is protected by alternately larger and smaller 
 dorsal plates, which are fifteen in number; and there are 
 fifteen pairs of legs, which are terminated by a single 
 claw. On the sides of the body will be found some 
 oval dark-looking bodies, fringed with hairs; these 
 are the spir'acles (spirac'ulum, a breathing-hole) or 
 breathing-pores. They form the orifices of certain 
 branched and transversely striated tubes, which are 
 distributed throughout the body ; the tubes are called 
 tracheae (trachea, the windpipe), and their walls con- 
 tain an elastic spiral fibre which keeps them open. 
 These parts of the insect can only be distinctly seen 
 when the body has been slit up on the under side ; 
 and, after washing away the animal matter with water 
 by the aid of a hair pencil, pressed between two slides 
 with a clip, dried, soaked in turpentine, and mounted 
 in balsam. 
 
 THYSAN^JRA (Ovaavoi,, fringe, ovpa, tail). The in- 
 sects belonging to the genus Podura, of this Order, are 
 very minute and difficult to examine ; but they are 
 specially interesting, on account of the structure of 
 their scales. They are common in gardens and 
 cellars, under flower-pots, &c., and are about one-tenth 
 of an inch long. They are of a brownish or silvery- 
 leaden colour, wingless, with six legs, and when 
 touched they leap like a flea. The leaping motion is 
 produced by the action of the tail, which is forked 
 and bent under the body. 
 
 The body is usually covered with minute scales 
 (PI. X. fig. 19, #, c), and these are used as test-objects. 
 The structure of the scales varies in the different 
 genera and species; those usually used (fig. 19 #) are 
 stated to belong to Podura plum'bea- it appears, 
 however, that this is not correct. The scales sold as 
 test-objects under this name are covered with minute 
 and short raised lines (fig. 190), arranged in irregular 
 
ANOPLURA. 135 
 
 but somewhat parallel wavy rows. It requires a 
 good microscope and a high power to show them dis- 
 tinctly, and they should appear perfectly black and 
 separate. The little lines are much coarser in some 
 scales than in others; so that there are easy and difficult 
 scales, as they are called. 
 
 The Podura may be caught by holding a sheet of 
 paper near their haunts and disturbing them; and 
 when they have jumped upon the paper, a slide laid 
 upon them and gently pressed will remove some of 
 the scales for examination. 
 
 The scales should be mounted as dry transparent 
 objects ; for if wetted, they become very transparent, 
 and the markings appear removed, which however is 
 not really the case. 
 
 The scales of Lepisma saccharma (PI. X. fig. 19 d), 
 a member of this Order, were formerly used as test- 
 objects ; but they are too easily made out to serve 
 for this purpose with modern microscopes. The in- 
 sect is not common. The scales (fig. 19 d] exhibit 
 continuous nearly parallel longitudinal lines or ribs. 
 
 ANOPL<JRA (avoTrXo?, unarmed, oupa, tail). This 
 third Order of insects consists of the Lice of the Mam- 
 malia and birds. They are minute, resembling mites 
 to the naked eye, but may be at once distinguished 
 from them by the distinct head and thorax and the 
 presence of six instead of eight legs. 
 
 Some of them are suctorial, i. e. have a short and 
 slender tube, with which they suck the blood of the 
 animals of which they are parasites ; while others are 
 mandibulate, or have mandibles, and also maxillae, 
 their food consisting of portions of feathers, hairs, 
 and scurf. The legs are usually short and stout, and 
 the claws large and powerful, to enable them to hold 
 firmly to the hairs, &c. The Anoplura are most 
 abundant on dirty and diseased animals. 
 
 SUCTOR'IA. The fourth Order of insects consists of 
 the genus Pulex, Pulex irritans being the human 
 
1S6 INSECTS. 
 
 flea. Other species are found upon different animals, 
 as upon the dog, the rat (PL X. fig. 22) , the fowl, the 
 pigeon, &c. 
 
 The head and the dark eye (fig. 21, head of the 
 human flea) are very evident. The antennae or head- 
 feelers are very minute and difficult to find, being 
 sunk in a little pit or fossa behind the eye ; they may, 
 however, generally be recognized by the detection of 
 the last joint, which is pectinate or cut like a comb. 
 The body, including the head, consists of thirteen 
 joints, one for the head, three for the chest or thorax, 
 and nine for the belly or abdomen, it being under- 
 stood that by "joint" is meant a segment, and not the 
 line of junction of two segments. The indication of 
 these joints is afforded by the horny integument, 
 which consists of a corresponding number of rings, 
 forming in fact the skeleton of the animal. This in 
 the flea, as in all insects and other Articulata, is ex- 
 ternal or cutaneous (cutis, skin), and consists of the 
 hardened skin, the peculiar animal substance of which 
 it is composed being called chitine (^trcov, tunic). 
 These chitinous rings overlap, and are composed of a 
 dorsal or upper, and a ventral or lower half; and 
 near the middle of each is a row of hairs directed 
 backwards. Along the sides of the body of the in- 
 sect may be seen a row of dots ; these are the spiracles 
 or orifices of the breathing-tubes (tracheae) . 
 
 The legs are many -jointed, long, furnished with 
 numerous spines, and terminated by two slightly 
 curved claws, each with a little blunt tooth at its 
 base. The claws are not perfectly smooth on the 
 inside, but are covered with slightly raised lines, like 
 a file, so that a better hold can be taken of bodies. 
 
 But the most interesting parts of the flea are those 
 of the mouth, with which it punctures the skin and 
 sucks the blood. There are nine of these; and they are 
 best seen when the head of the flea is pulled off with 
 the mounted needles, and the parts spread out and 
 
DIPTERA. 137 
 
 mounted in balsam, a high power being used to ex- 
 amine them. One of them forms a long and slender 
 bristle (seta) or tongue, furnished with distant mi- 
 nute teeth. On each side of this is a flattened seta, 
 with two rows of teeth on the edges ; these are the 
 lancets, and when not in use these organs are inclosed 
 in two jointed sheaths. Outside these are two re- 
 presentatives of jaws, or maxillae (b), each having a 
 jointed feeler or palp (a) arising from it ; the probable 
 use of the palps being to feel the position of the 
 skin, so that the animal may be able to adjust the 
 lancets at a proper distance for puncture. 
 
 The eggs of the flea are often visible within the 
 body of the parent ; and when this is crushed, they 
 are more distinctly seen, of various sizes, and con- 
 tained within a long tube, which is the ovary or egg- 
 bag. The eggs are laid by the animals upon carpets, 
 woollen garments, or in the cracks of dirty floor- 
 boards ; they are just perceptible to the eye as white 
 oblong specks, and they may always be found on the 
 rug when a cat is kept in the house. When hatched, 
 they give rise to a minute white worm-like maggot, 
 or larva (fig. 30), having a 12-jointed body, with two 
 rudimentary antennae and two slightly curved hooks 
 appended to the last joint. The mouth-organs of the 
 larva are adapted for biting, and not for sucking, as 
 in the perfect animal, the jaws or maxillae being dis- 
 tinctly toothed. When they have acquired full 
 growth, which takes place in about twelve days in 
 warm weather, they spin around themselves a little 
 silky cocoon, and become transformed into a chrysalis 
 or pupa ; and from this, in about a fortnight, the per- 
 fect insect escapes. 
 
 DIP'TERA (819, twice, irrepov, wing). This, which 
 forms the fifth Order of Insects, consists of the two- 
 winged insects, or flies, as the house-fly, the blue- 
 bottle, the gnats, &c. 
 
 MUS'CID^E. The house-fly, and the blue-bottle or 
 
 N3 
 
138 INSECTS. 
 
 meat-fly, are both species of the genus Musca, be- 
 longing to this family, the former being Musca do- 
 mes tica, the latter Musca vomit or' ia. Both these 
 insects are seen to be wonderfully constructed when 
 minutely examined, and they possess considerable re- 
 semblance in general structure. 
 
 On examining the head of the house-fly (PI. X. 
 fig. 17) under a low power, and as an opake object, 
 the observer will be struck with the remarkable ap- 
 pearance presented by the two eyes, which are large, 
 placed one on each side of the fore part of the head, 
 and composed of very numerous little eyes closely 
 packed together, or they are compound, as it is called. 
 The use of this compound structure is evidently to 
 enable the little animal to see in all directions with- 
 out moving the head and eyes. Each little eye has 
 a lens to bring the rays of light emanating from 
 objects to a focus upon a nerve. The packing of the 
 eyes together gives rise to their angular form or 
 their straight sides, each of the little surfaces or facets 
 being hexagonal, or bounded by six sides (fig. 33). 
 In front of and between the eyes are seen the two 
 small antennae ; these have three joints, the third of 
 which is larger than the rest (fig. 170), and arising 
 from near its base is a feathery bristle or seta ; these 
 structures are best seen when the antennae are pulled 
 off with a pair of forceps and mounted separately. 
 Below the antennae, and extending downwards and 
 forwards is the proboscis, or tongue, as it is called, 
 which can be entirely retracted within a pit in the 
 fore part of the head, or protruded at the will of the 
 animal. This is a very beautiful and complicated in- 
 strument, and is best examined when spread out and se- 
 parately mdunted (PL X. fig. 29). It consists of a fleshy 
 tube, dilated at the end into two lobes, which are 
 flattened beneath to form a sucking-disk. The end 
 is furnished with two solid horny lateral branches to 
 keep it expanded, and with two longitudinal tubes 
 
DIPTERA, 139 
 
 beneath, running parallel, from the outer sides of 
 which arise numerous nearly parallel branches. These 
 tubes and their branches are incomplete beneath, and 
 consist of imperfect rings, otherwise greatly resembling 
 tracheae. On each side of the proboscis is a lip-feeler 
 or labial palpus , for the organ represents the labium 
 of other insects. All these parts are better seen in 
 the proboscis of the blow-fly than in that of the house- 
 fly, on account of their larger size. The head, the 
 thorax, and the abdomen are very distinct in the fly, 
 being separated from each other by well-marked con- 
 strictions. 
 
 The legs are composed of five parts, each having a 
 separate name. The first piece or joint, which is 
 that attached to the body, is called the hip, or coxa ; 
 the next is a very small, somewhat triangular piece, 
 and is the trochan' ter ; next comes the long and stout 
 thigh, or femur ; this being succeeded by the tib'ia, 
 which, as in most insects, is furnished with strong 
 spines at the end ; and lastly is the foot, or tar'sus, 
 consisting of five joints, the three last of which are 
 represented in the figure (PL X. fig. 32) . At the 
 end of the fifth or last joint of the tarsus (fig. 32) 
 (for it must be noted that the joints of the limbs of 
 insects are always numbered in order of distance from 
 the body) are two soft little cushions, or pulvil'li, 
 which are covered on the under surface with numer- 
 ous hair-like bodies dilated at the end, acting as 
 suckers in enabling the fly to adhere to smooth sur- 
 faces. In addition to these organs are two curved 
 claws, and between them a sharp straight spine. 
 
 The eggs of the fly are deposited upon heaps of de- 
 caying animal and vegetable matters, as dungheaps, 
 &c. The blow-fly deposits its eggs in the same situ- 
 ations, but especially those where the animal matters 
 are most abundant : every one knows the eggs as de- 
 posited upon tainted meats, when they are called fly- 
 blows. When the eggs are hatched, the larva or 
 
140 INSECTS. 
 
 maggots make their appearance. The larvae of the 
 blow-fly are well known to the angler, who uses them 
 for bait, and calls them gentles. 
 
 These larvae exhibit some interesting points of 
 structure. The jointed or ringed condition of the 
 body is distinct to the naked eye. The head is pro- 
 vided with two rudimentary palpi, placed each upon 
 a rounded papilla ; also with two brown curved and 
 horny hooks or jaws. On the posterior end of the 
 body are two brown spots, which consist of spiracles, 
 and have three sieve-like oblong orifices ; and at the 
 anterior margin of each segment of the body are very 
 numerous little short spines, with the points directed 
 backwards. These answer the purpose, to some extent, 
 of legs ; for when the larva is moving, and has forced 
 itself through the matter in which it burrows, the little 
 spines prevent the body being forced backwards as 
 the head is pushed forwards and meets any resist- 
 ance. 
 
 To examine the structure of these larvse, the 
 gentles should be killed by immersion for a time in 
 warm water, and then dried by touching them with 
 blotting-paper. The hooks and palpi can be seen by 
 holding the body in the forceps as an opake object. 
 To observe the spiracles, the end of the body should be 
 cut off, and the animal matter washed away in a watch- 
 glass with water and a hair pencil, then spread out, 
 dried between two slides, and mounted in balsam. 
 
 The larvae of the house-fly and of the blow- fly very 
 closely resemble each other, so much so that the 
 former are generally overlooked; hence it is often 
 wondered where flies come from, although they are 
 so numerous in every house. When the larvae of 
 these flies are fully developed, they gradually assume 
 a brown colour, the organs of the head are retracted, 
 and the skin becomes dry and hard. This is the 
 state of pupa, or chrysalis ; and while remaining in 
 this state of rest, the development of the wings, legs. 
 
DIPTERA. 141 
 
 &c., takes place ; so that when the insect emerges 
 from the shell of the chrysalis, it has attained its 
 highest state of development, and forms the imago or 
 perfect insect. It may be remarked here, that when 
 insects pass through the three states of larva, pnpa, 
 and imago, they are said to undergo complete me- 
 tamorphosis. There is not a more curious object 
 than that presented by the young fly contained in its 
 case, as seen on carefully cutting away portions from 
 one end of the case of the chrysalis. The body and 
 head are quite white, with beautiful blood -red eyes. 
 
 Most persons must have noticed another kind of 
 house-fly, having the wings more widely separated 
 than in the common fly, and moving more slowly 
 through the air. This is Stomoxys catcitrans. The 
 proboscis of this fly (PL X. fig. 18) differs from that 
 of the house-fly in being longer, more bent, and but 
 little expanded at the end ; also in being provided 
 with two long setae, one forming a slender sharp 
 lancet, the other being somewhat stouter, and form- 
 ing its sheath. The fly is thus enabled to pierce the 
 flesh and suck the blood. 
 
 CULIC'ID^E. We will now say a few words about 
 the gnats, which are old favourites for microscopic 
 examination. The three states of larva, pupa, and 
 imago must be considered separately. 
 
 The imago or perfect form is well known. The 
 males are easily distinguished from the females by 
 the difference in structure of the antennae, which 
 in the males (PL X. fig. 10, head) are very beauti- 
 fully plumose or feathery, whilst in the females 
 (fig. 11) the hairs are very short the long proboscis, 
 or rostrum, or bundle of biting-organs forming the 
 striking feature ; this difference is immediately evident 
 to the naked eye. 
 
 The antennae of the males (fig. 10 a) consist of 
 numerous small joints, from each of which arises 
 a ring of long hairs, giving the appearance of a tuft 
 
142 INSECTS. 
 
 on each side when flattened for view as a transparent 
 object under the microscope; at the end are two 
 longer joints, the first having a small ring of shorter 
 hairs. 
 
 The proboscis of the female is a very complicated 
 organ, consisting of six separate bristle-like pieces or 
 setae, all nearly of the same length. Two of these 
 are somewhat curved near the end, and provided on 
 the inside with fine teeth ; another pair consists of 
 very thin lancet-pointed instruments; then comes 
 another lancet-pointed seta, very sharp at the end, 
 and traversed by a canal ; next, a stouter and darker- 
 looking tube, slit up underneath, which serves to 
 contain the two toothed setae; and lastly, a stout 
 and broader sheath, also slit up throughout its length 
 beneath, in which all are packed. This sheath has 
 two lobes at the end, and has some resemblance to 
 the proboscis of the fly, of which organ it is the re- 
 presentative. 
 
 The gnat lays its eggs in water. The eggs are 
 longish oval, with a kind of neck at the upper end ; 
 they are glued together side by side in large numbers, 
 and form a boat-like mass, floating on the surface 
 of the water. The larvae (PI. X. fig. 9) are very com- 
 monly found skipping through the water, or hanging, 
 as it were, by the tail from the surface. The head 
 is very broad ; and arising from each joint of the body 
 are tufts of hairs. Near the end of the body is a 
 tube which communicates with the tracheae; and 
 when the animal is quiet, this tube is brought to the 
 surface ; so that when the animal appears hanging to 
 the surface, it is breathing. In addition to this me- 
 thod of respiration, there are other respiratory or- 
 gans attached to the last joint of the body, consisting 
 of leaf-like plates ; hence these larvae have an aquatic 
 as well as an aerial respiration : the respiratory or 
 branchial plates also serve as a tail to aid in swimming. 
 Running down the back of the larva will be seen a 
 
HYMENOPTERA. 143 
 
 thin delicate vessel, dilated opposite the thorax, and 
 beating or contracting at regular intervals. This is 
 the dorsal vessel, the dilatation representing the heart 
 of the higher animals ; and it serves to propel the 
 colourless blood throughout the body. 
 
 After several moultings or castings of the skin, to 
 allow of the growth of the insect (for insects grow 
 only in the larval state), the larva becomes trans- 
 formed into the pupa (PL X. fig. 8). In this state 
 the animals still move about in the water, and are 
 often found suspended from its surface by two respi- 
 ratory tubes, which, however, are not connected with 
 the tail, but arise from the thorax; and the various 
 parts of the perfect insect may be seen through the 
 case or skin, within which they are closely packed. 
 
 When the pupa has attained its full development, 
 the perfect insect emerges from it, leaving the water 
 to fly about and seek food. 
 
 TIPU'LIDJE. In the water of ponds and pools a young 
 larva (PL X. fig. 31) will often be met with, which 
 is that of Chiron omus plumostts, a largish gnat- like 
 insect, belonging to the daddy-long-legs family (Tipu- 
 lidse). This larva exhibits the usual thirteen seg- 
 ments, including the head. In the young state the 
 body is nearly colourless ; but in the mature larva it 
 is of a blood-colour, and about an inch in length. 
 Beneath the first joint of the body are two foot-like 
 processes covered with hair; and at the end of the 
 body are also two processes, surmounted with hooks. 
 The three last joints of the body are also furnished 
 each with a pair of fleshy processes, those of the first 
 pair being very short. 
 
 HYMENOP'TERA (v/j,r)v, membrane, irrepov, wing) . 
 This, which forms the sixth Order of insects, contains 
 the bee, the wasp, the ant, &c. 
 
 In the Hymenoptera there is a curious contrivance 
 for linking the two wings on each side, so that they 
 may form a single piece in the flight of the insect. 
 
144 INSECTS. 
 
 It consists of a row of hooks, placed upon the anterior 
 nerve of the hind wing, which play upon the folded- 
 in corresponding edge of the fore wing ; the hooks, 
 sliding along this edge, allow of freedom of motion, 
 although still holding the two wings together. This 
 structure may be well seen in the wings of the Humble 
 Bee when mounted in balsam. 
 
 The sting of the wasp and bee is also a singular 
 organ. In both insects it is much alike, consisting 
 of a sheath, slit up beneath, in which are contained 
 two long setae, or lancets, with bent-back (recurved) 
 teeth near the end. These setae are inserted into 
 the flesh during the act of stinging, and at the same 
 time the poisonous secretion from two glands is 
 forced into the wound, which causes the severe pain 
 resulting from the sting. 
 
 In the wingless neuters of the common ant, attached 
 to the end of the tibia (PI. X. fig. 34 c) is a beautiful 
 pectinate process, somewhat resembling a comb (fig. 
 34 a). 
 
 LEPIDOP'TERA (\67rl$, scale, Tnepov, wing). This 
 Order contains the butterflies and the moths, the 
 entire bodies of which are covered with minute scales. 
 When the insects are handled, these scales adhere to 
 the fingers as a fine dust ; and on pressing a slide 
 against the insects, they may be removed for examina- 
 tion. They consist of a very slender and short quill, 
 by which they are attached, and a flattened plate of 
 various forms (Pl.X. fig. 19, b,f) ; it is, however, ge- 
 nerally narrower near the quill, and expanded towards 
 the free end, where it is often cut into lobes or tooth- 
 like segments. The scales are usually covered with 
 continuous longitudinal lines or ridges, with granules 
 of colouring-matter (pigment) situated between the 
 two thin layers of which the scales consist. In some 
 of them the form is that of a filament, either simple 
 or branched at the end (fig. 19 e), when they resemble 
 minute hairs. In the males of the large white Cab- 
 
LEPIDOPTERA. 145 
 
 bage Butterfly (Pi'eris brass'icce), certain of the scales 
 of the wings are covered with longitudinal rows of 
 very minute dots (fig. 19/), and have little tassel-like 
 bodies at the end. The males may be distinguished 
 from the females by the front wings having no black 
 spots, while those of the females have two upon each 
 wing. When the scales are examined as they exist 
 upon the wings of the Lepidoptera, they are found to 
 be imbricated (PL X. fig. 3) or overlapping each other 
 like the tiles on the roof of a house. 
 
 The Lepidoptera suck the honey of flowers by 
 means of a spiral tongue (PL X. fig. 20 c) or ant'lia 
 (antlia, a sucking-tube) ; this consists of two halves, 
 which represent the maxillae of other insects; and 
 their margins are fringed with little tassel-like bodies, 
 probably organs of taste. The antennae (fig. 20 a) 
 are many-jointed, clubbed at the ends (d) in the 
 butterflies, and simple in the moths. The palpi 
 (fig. 20 b) are short and densely covered with scales. 
 In the large eyes the facets are very distinct and 
 suitable for examination. 
 
 The larvae are well known as caterpillars. They 
 have six legs, as in the perfect insects, but rudimentary 
 and with single claws ; also some additional pairs of 
 pro-legs, as they are called, with a crown of hooks, 
 towards the hind part of the body. The spiracles of 
 caterpillars are very favourable for observation. 
 
 NEUROP'TERA (vevpov, nerve, Trrepbv, wing). This 
 Order contains the Dragon-flies (Libellulidae), the 
 Day-fly (Ephem 1 era] , &c., in which the wings are 
 usually so large and so beautifully netted. The 
 species figured (PL X. fig. 1), which is wingless, is 
 very common in old books and in collections of dried 
 plants. It is whitish, mite-like, with setaceous many- 
 jointed antennae, 3-jointed tarsi, and very broad thighs 
 (femora) . Its name is Apropos pulsator'ius. 
 
 HEMIP'TERA (rj/ucri;?, half, Trrepbv, wing). This 
 Order contains the bugs and other noxious insects. 
 
 o 
 
146 INSECTS. 
 
 Those which we shall notice are the species of A'phis, 
 commonly known as Plant-lice and Green-fly, which 
 are found too frequently upon unhealthy plants. The 
 species figured (PL X. fig. 2) is that of the geranium 
 (Pelargonium). The head is small and notched or 
 emarginate. The body is oval and furnished behind 
 with two prolonged tubercles, these being covered 
 with scales, giving them a somewhat striated appear- 
 ance (fig. 2b). The antennae are 6-jointed (c), the 
 second joint being very small, the last joint long, ex- 
 cavated on one side, and ringed : these organs are 
 reflexed over the body in the natural state. There 
 are two compound eyes, and three simple eyes or 
 ocelli, forming a triangle on the top of the head. 
 The proboscis or rostrum is bent under the body, 
 4-jointed, and contains three setse, two of them form- 
 ing very slender lancets. The legs are long; the 
 tarsi (fig. 2 a) 2-jointed, the first or basal joint being 
 very minute, and the last furnished with two claws. 
 
 In a colony of these insects, some are winged and 
 some wingless; those without wings being usually 
 in the larva state, the pupse having rudimentary 
 wings, and the males and females usually perfect 
 wings. Aphis brass'icae is the destructive turnip-fly. 
 
 COLEOP'TERA (/coXep?, sheath) . This, which is the 
 last Order to be noticed, contains the Beetles, so 
 easily recognized by their hard and horny fore wings 
 or wing-cases. The parts of the mouth in these 
 insects are exceedingly well adapted for examination ; 
 and as they are not fused or consolidated with each 
 other, they serve to illustrate the typical constitution 
 of the organs as existing in these animals. 
 
 Pteros'tichus (Ster'opus) mad'idus (PL X. fig. 23) is 
 common in cellars and garde as among vegetable rub- 
 bish. The body of this beetle is shining black, the 
 head projecting; the antennae (fig. 23 a) are filiform, 
 and compressed towards the end. The thorax is some- 
 what rounded, with a deep rough pit and a longi- 
 
COLEOPTERA. 147 
 
 tudinal stria at each posterior angle. The wing- 
 cases, or elytra, are longitudinally striated ; the wings, 
 which in most beetles are concealed beneath the elytra 
 when the insects are at rest, being absent. The tibiae 
 of the fore legs are notched on the inside (fig. .24 a), 
 a fringe of hairs being situated in the notch ; the 
 tarsi are 5 -jointed (fig. 245), the first four joints 
 being triangular, the last elongate and terminated 
 by two curved claws. In the male the three first 
 joints of the tarsi of the anterior legs (fig. 24 b) are 
 dilated and heart-shaped. 
 
 The parts of the mouth (which are named after an 
 analogy with those of the higher animals) consist of 
 the following pieces : An upper lip, or Idbrum (fig. 
 25 0), which is squarish (quad'rate) and slightly 
 notched ; a quadrate lower lip, or Idbium (fig. 27), with 
 a process on each side, and two 4-jointed lip-feelers 
 or labial palpi (b) ; and below the labium is a chin, or 
 mentum (fig. 270), with a projecting bifid tooth: 
 these parts form the roof and the floor of the mouth. 
 Next come the man'dibles (fig. 26), one on each side, 
 which are stout, curved, and pointed ; beneath which 
 are the maxil'lce (fig. 28), also one on each side, and 
 provided with a fixed claw (a), ciliated on the in- 
 side, and furnished with two pairs of jaw- feelers, or 
 maxillary palpi, the inner (b) being 2-jointed, while 
 the outer (c) are 4-jointed. It will be noticed that 
 the jaws work laterally, or from side to side, and not 
 perpendicularly as in the higher animals. 
 
 These parts may be found in most beetles which 
 the observer may submit to examination, being how- 
 ever somewhat modified in different genera. We 
 may consider those existing in the Lady-birds, or 
 species of Coccinetla, by way of comparison. The 
 body in these insects is very convex, and the head 
 sunk deeply in the thorax. The antennae (fig. 15) 
 are short, clubbed (clavate), and compressed. The 
 thorax is short and lunate, or half-moon shaped. 
 
 o2 
 
148 INSECTS. 
 
 The mandibles (fig. 13) are curved, bifid at the apex, 
 and with a tooth on the inside near the base. The 
 labrum (fig. 14) is transverse, or broader than long. 
 The labium (fig. 12) is furnished with two palpi, which 
 are 3-jointed. The maxillae (fig. 16) are two-lobed, 
 the lobes (b, c) being ciliated, and the 4-jointed palpi 
 (a) have the last joint large and hatchet-shaped. 
 
 Coleopterous insects undergo complete metamor- 
 phosis, the larvae being commonly known as grubs. 
 The larvae of the aquatic beetles will often be met 
 with in the water of ponds or ditches, especially that 
 of the common large water-beetle (Dytis'cm margi- 
 ndlis), or water-boatman as it is called (PI. X. fig. 7), 
 and in various stages of growth. The structure of 
 the mouth-organs (fig. 6), which are, however, im- 
 perfect or rudimentary in some parts, can be readily 
 made out ; and their names may easily be found by 
 comparison with what has been stated in regard to 
 the organs of the perfect beetle. 
 
 Examination, fyc. The means of catching insects 
 will readily occur to the reader. A bag-net made of 
 a curved piece of cane, to which is fitted a bag made 
 of net, will serve to catch those which trust to flight 
 for escape from their enemies, such as the Lepidoptera; 
 and these may be killed by firm pressure of the thorax 
 between the finger and the thumb. The running 
 insects, as the beetles, may be caught in a spoon or 
 with forceps ; and they may be killed by immersion 
 in boiling water or in camphorated spirit. In an 
 excursion, most insects may be carried in a well- 
 corked bottle containing a little wool and a lump of 
 camphor, which stupifies them. When the insects 
 are dead, the limbs should be extended into the na- 
 tural position by means of pins, the insect being 
 transfixed by a pin run through the thorax or one of 
 the elytra and extending into a sheet of cork. To 
 preserve them, they may be kept in a box, the bottom 
 
ROTATORIA. 149 
 
 of which is covered with sheet cork, into which the 
 pins are stuck. 
 
 The smaller beetles, &c., which cannot be trans- 
 fixed with a pin, may be mounted as opake objects 
 upon slips of card, the legs &c., being carefully 
 spread out, and gummed in position with a strong 
 solution of gum-tragacanth in boiling water. Many 
 of the smaller Curculion'idse or diamond-beetles, in 
 which the labium forms a rostrum or beak, with 
 elbowed or half-bent antennae, form beautiful opake 
 objects when thus mounted, on account of the brilliant 
 scales with which they are covered. 
 
 There are two ways of examining insects either in 
 the entire state as opake objects or the separate parts 
 mounted as transparent objects. In the former case 
 the pin with which the insect is transfixed should be 
 stuck into a slide made of cork, and this laid upon 
 the stage, or the pin may be held by the forceps. In 
 this way, with the use of the side condenser and a 
 low power, the general form and arrangement of the 
 parts of the insect can be made out. The more 
 minute details must be searched for in the individual 
 organs which have been picked off with forceps, and 
 mounted in balsam. 
 
 If it be required to submit the parts of a dried 
 insect to examination, this must be previously soaked 
 in warm water for a time, as the legs, &c., become 
 very brittle when dry, and are thus easily injured. 
 
 ROTATOR IA (rota, a wheel) or ROTIF'ERA (rota and 
 fero, to bear). The animals contained in this class 
 are minute, being just distinguishable to the naked 
 eye as white specks. They are common in long-kept 
 infusions and among Conferva in the water of pools 
 and ditches. Their body is usually longer than broad, 
 often presenting indications of rings ; and at or near 
 the posterior end is frequently found a prolongation 
 resembling a tail, but terminated by two short move- 
 able thumb-like processes, rarely a sucker, which 
 
 o3 
 
150 ROTATORIA. 
 
 enable the animals to cling to objects. The most 
 characteristic organ, however, is a kind of rounded or 
 oval disk, placed at the anterior end of the body, and 
 furnished with cilia. When these are in active mo- 
 tion, the organ appears as a revolving wheel, whence 
 the name of Wheel-animalcules, by which they are 
 sometimes designated. The wheel-organ enables the 
 animals to swim through the water, and also brings 
 their food to the mouth by the currents which it 
 produces. It is usually cleft into two or more lobes, 
 and can be retracted, as is commonly the case when 
 the animals are disturbed. 
 
 In many of these animals the body is more or less 
 covered by a horny shell or carapace ; and in some it 
 is fixed at the bottom of a tube, within which it can 
 be withdrawn. On the anterior part of the body are 
 frequently seen two or more red spots, which re- 
 present eyes. The alimentary canal is mostly dis- 
 tinct, being indicated by the colour of its contents, 
 and it is lined with cilia. Towards its front portion is 
 a gizzard (PL XI. fig. 2 a) containing teeth, which 
 are sometimes attached to a jointed jaw-like frame- 
 work ; these are usually in active motion. No heart 
 or blood-vessels have been observed in the Rotatoria ; 
 but on each side of the body in many of them is a 
 long wavy tube, containing at intervals minute cili- 
 ated bodies, the cilia propelling the water through 
 the tubes, and so exerting an aerating or respiratory 
 function. The reproduction of the Rotatoria takes 
 place by the formation of ova, which may often be 
 distinguished within the body of the parent. 
 
 Rot'ifer vulgdris (PL XI. fig. 2) is a common species. 
 It has a spindle-shaped body, which is capable of con- 
 traction almost into a ball. The front or head end 
 is sometimes protruded (fig. 2), at others retracted 
 and obscured by the exserted disk (fig. 2*) ; and be- 
 neath it is a tentacle-like organ, supposed to repre- 
 sent an antenna (fig. 2 b] . The position of the jaws 
 
PLATE XI. [PAGE 150.] 
 
 ROTATORIA, INFUSORIA, &c. 
 
 Fig. 
 
 1. Anguillula (Dorylaimus), species 
 
 of. 
 
 2. Rotifer vulgaris'. a, jaws and 
 
 teeth; b, antenna; 2*, wheel- 
 organ expanded. 
 
 3. Pterodina patina. 
 
 4. Floscularia ornata. 
 
 5. Hydra viridis. 
 
 6. Arcella vulgaris. 
 
 7. Arcella aculeata. 
 
 8. Arcella aculeata, shell with ani- 
 
 mal. 
 
 9. Arcella dentata. 
 10. Amoeba diffiuens. 
 
 12. Actinophrys sol. 
 
 13. Sponge, fibres of; 13 a, 5, c, spi- 
 
 cules of Sponge. 
 
 14. Sertularia pumila, polypidom. 
 
 15. Sertulana pumila, polypidom with 
 
 16. Manas lens. 
 
 17. Cercomonas globulus. 
 
 18. Cercomonas crassicauda. 
 
 19. Heteromita ovata. 
 
 20. Anthophysa Mulleri. 
 
 21. Dinobryon sertularia. 
 
 22. Trachelomonas volvocina. 
 
 23. Chcetoglena volvocina. 
 
 24. Euglena viridis. 
 
 Fig. 
 
 25. Astasia hcematodes. 
 
 26. Enchelys nodulosa ; a, undergoing 
 
 transverse division. 
 
 27. Oxytricha gibba] 27 , side view. 
 
 28. Paramecium aurelia : a, contrac- 
 
 tile vesicle ; b, a gastric sacculus. 
 
 29. Amphileptus fasciola. 
 
 30. Colpoda cucullus: a, contractile 
 
 vesicle. 
 
 31. Nassula elegans : a, vesicle ; 31 b, 
 
 encysted form. 
 
 32. Coleps hirtus. 
 
 33. Vaginicola crystallina. 
 
 34. Vorticella convallaria : a, stalk spi- 
 
 rally contracted ; b, body^ under- 
 going longitudinal division. 
 
 35. Vorticella convallaria encysted and 
 
 discharging the young brood. 
 
 36. Vorticella convallaria, body with 
 
 nucleus (a). 
 
 37. Chilodon cucullulus. 
 
 38. Stentor polymorphus : a, body ex- 
 
 tended; b, body contracted; 
 C) bodies aggregated around a 
 globule of jelly; d, bodies ad- 
 herent to the side of a glass. 
 
 39. Alyscum saltans. 
 
 40. Podophryafixa, or the Podophrya- 
 
 form of Vorticella. 
 
Plate XI. 
 
ENTOZOA. 151 
 
 is indicated at a. The alimentary canal is seen run- 
 ing down the body ; and two ova exist, one on each 
 side of it, these being often recognizable by the ex- 
 istence of the eyes and jaws. At the end of the body 
 are two lateral processes, and a tail-like piece, which 
 can be withdrawn or protruded and is furnished with 
 two moveable portions or toes. 
 
 Pterodina pat'ina (PL XI. fig. 3). This species has 
 a shell or carapace on the back, a two-lobed rotatory 
 organ, two eyes, and a slender wrinkled tail ciliated 
 at the extremity. The curved alimentary canal, and 
 the two strong muscles inclined at an angle, are easily 
 distinguishable. 
 
 Flosculdria orndta (PI. XI. fig. 4) is a very beauti- 
 ful member of the Rotatoria, and is found adhering 
 to Conferva and other water-plants. The body is 
 club-shaped, and contained in a transparent tube, 
 the ringed narrower portion being fixed to its base. 
 The rotatory organ is divided into five or six lobes, 
 furnished with long, slender, radiating tentacular 
 filaments ; these are not vibratile like ordinary cilia, 
 but can be slowly moved. In the contracted state, 
 the filaments form a pencil-like bundle. 
 
 Examination, fyc. The Rotatoria are best examined 
 in the living state, the drop of water in which they 
 are viewed being very small, so that their movements 
 may be impeded ; and while they are struggling to 
 escape, the various parts of the body will come into 
 view. Their preservation has been attempted by 
 drying on a slide ; but when dead they become so 
 contracted and altered, that it is difficult to make out 
 their structure. Should the observer wish to record 
 any observations on their reproduction or habits, it 
 will be well to preserve a specimen of the jaws and 
 teeth, as the species might be with certainty identi- 
 fied by careful examination of their minute struc- 
 ture. 
 
 ENTOZOA (eVros, within, Jwov, animal). This class 
 
152 ENTOZOA. 
 
 consists of the parasitic worms, as the Tape-worm 
 (Ttenia), the Thread-worm and Kound-worm (As'- 
 cam), which live within the bodies of man and ani- 
 mals. It also inclndes the microscopic eel-like ani- 
 malcules (species of AnguiVlula) which are found in 
 sour paste (A. glutinis), in vinegar (A. aceti), and in 
 blighted wheat (A. trit'ici). Some of the species of 
 allied genera are met with in damp moss and in the 
 debris or fragments of vegetable substances decaying 
 in water. The general appearance of the microscopic 
 species is that of a minute colourless eel, writhing in 
 the water (PI. XI. fig. 1). Their internal organs are 
 difficult to distinguish. The alimentary canal is 
 usually evident, and dilated into a kind of stomach, 
 containing near its commencement some rod-like or 
 otherwise-formed teeth. In the species figured there 
 are two apparently tubular lancets, which are capable 
 of protrusion, and evidently serve to wound the prey. 
 
RADIATA. 153 
 
 CHAPTER XII. 
 
 RADIATA. 
 
 DESCENDING in the scale of animal organization, we 
 come next to the subkingdom RADIATA, or that in 
 which the parts are arranged in a radiate manner 
 around a centre. Of this there are three classes, the 
 ECHINODER'MATA (e^tvo?, hedgehog, Sepfia, skin), con- 
 taining the Sea-urchins (Echinus), Starfishes, &c., in 
 which the skin is furnished with hard calcareous 
 projecting spines or curiously formed imbedded cal- 
 careous corpuscles, forming a rudimentary skeleton ; 
 the ACALEPH.E (a/caXr}^, a nettle), or Sea-nettles; 
 and the POL'YPI (77-0X1)5, many, TTOU?, foot), to which 
 we shall confine our notice. It may be remarked 
 that the last two classes have recently been united to 
 form the single class CCELENTERATA (icolKov, hollow, 
 evrepovj intestine). 
 
 POLYPI. These animals are mostly marine. They 
 are either single (PL XI. fig. 5), or compound (PL XI. 
 fig. 15), i.e. the bodies are united ; in the latter 
 case the bodies being usually situated in horny cells 
 upon a branched polypidom. But in many of them, 
 which do not occur in this country, there is an in- 
 ternal solid calcareous skeleton, of which coral is an 
 example. The animal bodies are soft, and furnished 
 at the front end with a crown of tentacles (fig. 15 a) 
 these are contractile, and serve to enable the animals 
 to catch their prey. The horny, branched, and plant- 
 like polypidoms are often found on the seashore, and 
 are popularly confounded with sea-weeds. 
 
 Hydra vulgdris (PL XI. fig. 5) is a fresh-water 
 species, which is commonly met with among collec- 
 
154 RADIATA. 
 
 tions of water-plants, and may generally be obtained 
 by collecting some of these and placing them in a 
 glass jar of fresh water. When the water has stood 
 for some hours, the Polypes will be seen, on careful 
 examination, adhering to the sides of the glass. The 
 body of the animals is cylindrical, hollow, and fur- 
 nished with from six to ten tentacles, arranged in a 
 circle, in the centre of which is the mouth. The 
 tentacles are hollow, and communicate with the 
 cavity of the body. On examination with a high 
 power, the tentacles will be found to exhibit minute 
 oval sacs, containing a long fibre coiled up within 
 them ; and when the tentacles are touched by any 
 foreign body, the fibres are suddenly discharged. 
 These are the stinging or urticating organs. The 
 Hydra move very slowly ; but the body is very con- 
 tractile, and is often seen of various forms. When 
 a minute animal, as an Entomostracan, happens to 
 come into contact with the tentacles, these curve 
 around it, holding it firmly, and finally bringing it 
 to the mouth. It is then forced into the cavity of 
 the body of the animal, where it is digested, the re- 
 mains being discharged at the mouth. The move- 
 ments of the Hydra, when devouring its prey, form 
 a very curious and interesting spectacle. The Hydras 
 are propagated by budding or gemmation, also by 
 the formation of capsules in the walls of the body, 
 containing ova and spermatozoa. The young Polypes 
 formed by budding are represented in the figure, ad- 
 hering to the base of the parent. 
 
 Sertuldria pumila (PL XI. fig. 15) is a marine 
 species, the polypidom being frequently found ad- 
 hering to Fuel and other sea-weeds ; it is about half 
 an inch long. The cells are opposite, pointed at the 
 ends, and with an oblique orifice. The tentacles are 
 fourteen in this species. In the summer large ovate 
 cells are found, arising from the polypidom; these 
 contain the eggs, and are called ovisacs or ovig'erous 
 vesicles. 
 
PROTOZOA. 155 
 
 CHAPTER XIII. 
 
 PROTOZOA (7TpWT09, FIRST, OV, ANIMAL) . 
 
 THE members of this subkingdom are the lowest in the 
 scale of animal organization, their bodies consisting of 
 a soft gelatinous and structureless mass, which has a 
 remarkable tendency to form little cavities or vacuoles 
 in its substance, and is called saf 'code (crapi;, flesh). 
 They exhibit no organs, unless the cilia and certain 
 variable processes formed of the common substance 
 of the body, and which form their agents of locomo- 
 tion, be considered as such, this substance exercising 
 the combined functions of motion, sensation, and se- 
 cretion, for which separate organs exist in the higher 
 animals. 
 
 EHIZOP'ODA (pi&, root, 7701)9, foot). The animals 
 belonging to this class consist of the structureless 
 colourless substance to which reference has been 
 made as sarcode, and they exhibit no organs. The 
 sarcodic body is slowly contractile, and portions of 
 it can be protruded at will in the form of irregular 
 root-like processes, acting both as legs for locomotion 
 and as tentacles by which the animal grasps its prey, 
 which is then forced into the substance of the body, 
 where it becomes surrounded by the surface, and a 
 cavity is formed, within which it is digested. 
 
 Amcsba difflluens (PI. XI. fig. 10) is common in 
 water in which portions of plants have been kept for 
 some time. When first placed on the slide, the body' 
 appears as a minute, transparent, rounded mass of 
 jelly -, but if observed for some time, it will be seen 
 
156 PROTOZOA. 
 
 slowly to protrude its root-like processes ; and foreign 
 bodies, as Diatomaceae or other minute Algae, will 
 often be found imbedded in its substance. 
 
 Arcella vulgdris (PL XI. fig. 6) is found among 
 Confervas in ponds and ditch-water. It is contained 
 in a hemispherical shell or carapace, from the round 
 orifice of which the lobed processes are protruded. 
 The shell is covered with minute pits. 
 
 Arcetla aculedta (PL XI. fig. 7) has the convex 
 shell furnished with spines; fig. 8 represents the 
 animal with its processes extended ; while Arcella 
 dentdta (PL XI. fig. 9) exhibits an angular or some- 
 what toothed membranous shell. Both the latter 
 species are met with in the same localities as the 
 first. 
 
 Actinophrys sol (PL XI. fig. 12) is a very beautiful 
 and excessively delicate Rhizopod. The body is 
 spherical, and covered with very delicate and slender 
 cilia-like processes. Its movements are exceedingly 
 slow, and can only be observed by prolonged watch- 
 ing. The body appears to be reticulated, from the 
 presence of numerous vacuoles. 
 
 Two large groups of genera and species of Rhizo- 
 poda, the animal bodies possessing the above general 
 characters, mostly with very slender processes, exist, 
 in one of which (the FORAMINIFERA) they are con- 
 tained in calcareous shells, often of elegant forms; 
 while in the other (the POLYCYSTINA) the shells are 
 siliceous or composed of flint, both kinds of shells 
 being perforated with holes. These shells, which occur 
 in the fossil state in enormous numbers, sometimes 
 forming mountain-masses, are extremely beautiful 
 objects for the microscope. 
 
 SPON'GI^E. This class contains the Sponges, almost 
 all of which are marine and foreign, and therefore 
 not likely to come under observation in the per- 
 fect state. The substance commonly called sponge 
 is the horny skeleton of the animal, consisting usually 
 
INFUSORIA. 157 
 
 of rounded fibres (PL XI. fig. 13), irregularly netted 
 and interlacing. The surface of a sponge exhibits 
 minute pores and larger pouting orifices ; the former 
 of which admit currents of water, to be discharged at 
 the latter, both being the mouths of continuous chan- 
 nels. The surfaces of the channels are lined with 
 sarcodic matter, which takes the form of ciliated 
 amoebiform bodies, by which the currents of liquid 
 are produced. 
 
 The horny fibres of sponges are strengthened by 
 little siliceous or flinty bodies of various forms (PL XI. 
 fig. 13 a, bj c), which are imbedded in the substance of 
 the fibres or attached to their surface, and form very 
 curious microscopic objects. They are called spicula 
 (spiculum, a dart), being often of a pointed form. In 
 some sponges they are calcareous. 
 
 INFUSOR'IA. The animals contained in this class 
 are usually very minute, being rarely even perceptible 
 to the naked eye, except when existing in very large 
 numbers, so as to render the water milky, green, or 
 red. They are found in all kinds of water, but espe- 
 cially in stagnant pools and in decomposing solutions 
 or infusions of vegetable matters. The true structure 
 of their bodies is a matter of doubt, some authors 
 having considered them as being highly organized, 
 while others have regarded them as consisting of 
 simple cells ; and whether they are correctly referred 
 to the Protozoa must remain at present a matter of 
 doubt. The body is of various forms, as represented 
 in Plate XI. figs, 16-40. In some of them it con- 
 sists of a simple sarcodic mass, evidently without 
 any outer skin, as shown by its ready adhesion and 
 laceration on accidental contact with foreign bodies ; 
 while in others the surface is regularly dotted with 
 little depressions, or with nodules, so as to resemble 
 a definitely organized structure. 
 
 The most striking character of the Infusoria is the 
 presence of vibratile cilia, which are variously ar- 
 
 p 
 
158 .PROTOZOA. 
 
 ranged; in some entirely covering the body, irregularly 
 or in regular rows, in others being situated at definite 
 parts only. By the action of the cilia they are en- 
 abled to swim freely in the water, also to obtain their 
 food, which consists of minute Algse or fragments of 
 animal matter. In many of them there is a special 
 row or set of cilia, which, by the currents it produces, 
 urges the particles of food suspended in the water 
 towards the mouth. The cilia also act as respiratory 
 organs, by changing the water with which their bodies 
 are in contact. In some of the species there are 
 stout bristles or setae, by which they are enabled to 
 crawl upon water-plants. 
 
 On carefully examining the bodies of the Infusoria, 
 rounded granular spots will be seen, frequently con- 
 taining minute Algae, &c. (fig. 28 b). These spots are 
 the digestive cavities, and have been called gastric 
 sac culi ; but whether they are definite sacs or mere 
 excavations, formed by the particles of food having 
 been forced into the softer internal substance of the 
 body, has not been positively determined. The sac- 
 culi may be filled artificially by mixing very fine 
 indigo, or carmine, on a slide with the water in which 
 the Infusoria are contained. A definite food-tube or 
 alimentary canal has been detected in a few of the In- 
 fusoria ; but it cannot be shown to exist in the ma- 
 jority of them. 
 
 A mouth exists in most of them, and is sometimes 
 indicated by a row or set of cilia somewhat larger 
 than those existing upon other parts of the body, 
 and leading to or placed near it. The particles of 
 food which have entered the body are often seen to 
 pass round it, as if circulating, descending on one 
 side and ascending on the other. 
 
 In addition to the gastric sacculi, certain clear 
 transparent spots may also be seen within the body, 
 appearing light or dark according to the adjustment 
 of the focus. If these are attentively watched, they 
 
INFUSORIA. 159 
 
 will be seen to contract and finally disappear, be- 
 coming again distended and vanishing at tolerably 
 regular intervals. These are the contractile vesicles 
 (figs. 27 a, 28 a, 37 a), and they contain a clear 
 liquid, the nature of which is uncertain. 
 
 In many of the Infusoria is a round or elongate 
 granular body (figs. 31 a, 36 a), which is called the 
 nucleus, the term having been applied to it from a 
 notion that the Infusoria consisted of simple cells. 
 A minute red spot is also often seen at the anterior 
 end of the body, which is supposed to represent an 
 eye, and is called an eye-spot. The Infusoria are 
 propagated in several ways : by budding or gem- 
 mation, new beings sprouting out in a bud-like form, 
 usually from the base of the parent; by division, 
 either transverse (fig. 26 a) or longitudinal (fig. 34 b), 
 of the body gradually into two parts, each of which 
 subsequently becomes a perfect animal ; by encyst- 
 ing, the body contracting into a globular form, and 
 forming a firm coat around it, the contents becoming 
 resolved into a numerous progeny of young ; and by 
 conjugation and the agency of spermatozoa and ova. 
 We will now proceed to the examination of a few 
 species, arranging them in the order of the families 
 to which they belong. 
 
 MONAD'INA. In this family the bodies of the In- 
 fusoria are very soft, and without a skin or integu- 
 ment ; they are also exceedingly minute, and will not 
 admit the particles of indigo. 
 
 Mori as lens (PI. XI. fig. 16) is very minute, and 
 commonly found in old infusions. Its body is rounded 
 and flattened, and granular on the surface. At the 
 front end of the body is a whip-like or flagel'liform 
 (flagel'lum, a whip) filament, differing from a cilium 
 in being rigid at the base and moveable at the end 
 only, by which it is enabled to row itself through the 
 water with a wriggling motion. 
 
 Cercom'onas glotiulus (fig. 17) has a spherical body, 
 
160 PROTOZOA. 
 
 with two flagelliform filaments, one arising from the 
 front, the other from the end of the body. In Cer- 
 comonas crassicau'da (fig. 18) the posterior filament 
 is replaced by a tail-like narrowing of the body. 
 
 Heteromita ovdta (fig. 19) has the body ovate, 
 with two long anterior flagelliform filaments, one of 
 which is directed forwards, while the other trails 
 behind. 
 
 Anthophysa mul'leri (fig. 20) has the monad bodies 
 arranged in little heads at the ends of an irregularly 
 branched brown stalk. After a time they become 
 detached and revolve freely in the water. 
 
 DINOBRY'INA. Dinobry'on sertuldria (PL XI. fig. 
 21) forms a minute Sertularia-like polypi dom, con- 
 sisting of rows of cells, each containing an oval 
 monad with a single anterior filament. The two last 
 species are common in bog-water. 
 
 THECAMONAD'INA. In these Infusoria the body is 
 inclosed in a firm and sometimes brittle shell or cara- 
 pace. 
 
 Trachelomonas volvoc'ina (PL XI. fig. 22) has a 
 spherical red shell, the body being furnished with a 
 single filament and a minute red eye-spot ; while 
 Chatoglena volvoc'ina (fig. 23) has an oblong shell, 
 covered with little spines. 
 
 EUGLENIA. In this family the form of the body 
 is constantly changing, being at one time spherical, 
 at another fusiform or ovate. It is covered with a 
 contractile skin or firmer external portion, and has 
 one or more flagelliform filaments for locomotion. 
 The species are common in stagnant pools, often 
 colouring the water green or red. 
 
 Euglena viridis (PL XI. fig. 24) has a spindle- 
 shaped body when fully expanded, the ends being 
 pale ; and at the front end is a red eye-spot. 
 
 Astdsia haematodes (fig. 25), which is probably a 
 form of the Euglena, is found in stagnant pools, which 
 it renders red. It has no eye-spot. 
 
INFUSORIA. 161 
 
 ENCHELIA. These Infusoria are found in stagnant 
 water and in decomposing infusions. The body is 
 covered with cilia variously arranged, but there is no 
 integument nor mouth. 
 
 En'chelys nodulosa (PL XI. fig. 26) has a colourless, 
 oblong, irregularly nodular body, coated with very 
 slender radiating cilia, and often exhibits numerous 
 vacuoles. It is frequently found undergoing trans- 
 verse division (fig. 26 a), the body becoming gradually 
 constricted until it separates into two parts, which 
 become perfect animals. 
 
 Alys'cum sal'tans (fig. 39) has an ovoid-oblong, 
 slightly furrowed body, surrounded with radiating 
 cilia, and has a side bundle of long retractile cilia, by 
 means of which it leaps from place to place in the 
 water. 
 
 KERONIA. In this family the body is soft, irregu- 
 larly ciliated, without a special integument, but has 
 an oblique row of vibratile cilia leading to the mouth, 
 and stouter cilia or bristles (setae) on certain parts of 
 the body. The sacculi often contain Diatomacese, &c. 
 
 Oxyt'richa gib'ba (PL XI. fig. 27) has a colourless, 
 oblong body, somewhat expanded in the middle, with 
 setae at the two ends. In the side view (fig. 27 a), 
 the body is seen to be convex above and flattened 
 beneath. 
 
 PARAMEC'INA. The species belonging to this family 
 have a soft, flexible body, which is usually oblong and 
 flattened beneath, with an integument covered regu- 
 larly with pits and rows of cilia. 
 
 Col'poda cucul'lus (PL XI. fig. 30) has a slightly 
 compressed body, ciliated all over, and kidney- shaped 
 or rounded on one side and notched on the other, the 
 surface exhibiting rows of nodules. The mouth is 
 situated at the bottom of the notch. 
 
 Paramecium aurelia (fig. 28) has the body oblong 
 or oblong-ovate, the mouth being placed near the 
 anterior third of its under part. This infusorium is 
 
 p3 
 
162 PROTOZOA. 
 
 of comparatively large size, and is often found in 
 immense numbers in infusions, which it renders milky. 
 It is admirably adapted for showing the sacculi, which 
 are easily tilled with indigo. The body exhibits two 
 remarkable stellate organs, consisting of a central 
 contractile vesicle, surrounded by several radiately 
 placed oval vesicles, which may be seen to contract 
 and dilate with great regularity. The body is coated 
 with very fine cilia. 
 
 Amphilep'tusfasciola (fig. 29) is furnished with an 
 elongate fusiform or lanceolate flattened body, with a 
 lateral oblique mouth. 
 
 Chitodon cucul'lulus (fig. 37) has an oblong thin 
 body, irregularly wavy on the sides ; the mouth being 
 situated obliquely in front of the middle, and fur- 
 nished with a cylinder of parallel rod-like teeth. 
 
 Nas'sula eVegans (fig. 31) has the body ovoid or 
 oblong, becoming globular when contracted, the 
 mouth being furnished with teeth as in Chilodon. It 
 is often found among Oscillatorise. 
 
 URCEOLARNA. Vorticel'la convalldria (PI. XI. fig. 
 34) is very commonly met with in decomposing infu- 
 sions. The bell-shaped body is fixed at the end of a 
 slender stalk, which is often seen to be extended and 
 then suddenly contracted into a spiral (fig. 34 a). 
 The cilia are arranged around a raised rim at the 
 front of the body, and extend down a fissure leading 
 to the mouth. The sacculi of this infusorium may 
 be readily filled with indigo. The process of longi- 
 tudinal division may also often be observed, taking 
 about an hour for its completion ; and when the new 
 individual is about to separate from the parent, a ring 
 of cilia may be noticed to have sprung up around the 
 base (fig. 36). The encysting process is also often 
 visible, the cilia disappearing, and the body becoming 
 globular and secreting a cyst around it ; after a time 
 the contents become resolved into a number of em- 
 bryos, which escape by the bursting of the cyst 
 
INFUSORIA. 163 
 
 (fig. 35). In some cases the Vorticella assumes the 
 form of a Podoph'rya (fig. 40), the surface becoming 
 covered with tentacle-like processes. This Podophrya 
 was formerly considered a distinct species. 
 
 Vaginic'ola crystal'lina (fig. 33) is contained in a 
 crystalline tube, from which the body can be pro- 
 truded. The body is of variable form, presenting 
 when fully extended a trumpet shape. The cilia exist 
 at the anterior end, and extend down a lateral fissure 
 as in Vorticella. It is found attached to Confervas in 
 the water of ponds and bog-pools. 
 
 Stentor polymor'phus (fig. 38) is a very beautiful 
 trumpet-shaped infusorium, the body being covered 
 with spiral rows of cilia. The rim is furnished with 
 stouter cilia, its margins at the notch being spirally 
 turned inwards. This infusorium is often found in 
 little groups attached to a gelatinous mass (fig. 38 c) ; 
 and it is met with also in a free or unattached state. 
 
 COLEP'INA. Coleps hiatus (fig. 32) has a barrel- 
 shaped carapace, transversely and longitudinally fur- 
 rowed, the furrows being occupied by cilia. It has 
 two or three spines behind, and ten or twelve at the 
 front end of the carapace. It is common among 
 Confervse, and is very voracious, feeding upon dead 
 Entomostraca, &c. ; and if disturbed, at its meal by 
 moving the cover, it will soon return and resume 
 feeding as before. 
 
 Examination. The Infusoria must be examined 
 during life ; for they are so altered by preservative 
 liquids that they cannot be well preserved. The 
 shells of those that are provided with them may be 
 kept simply dried upon a slide, and in this way a few 
 will retain their form, and the cilia of all may be more 
 easily distinguished ; the vacuoles may also then be 
 seen very distinctly. When they are confined in a 
 small quantity of water and are about to die, a curious 
 phenomenon may be observed in them, a number of 
 oil-like sarcodic globules exuding from the body, and 
 
164 CLASSIFICATION. 
 
 within these, vacuoles may often be seen to form 
 spontaneously. 
 
 The Infusoria may be collected in small phials ; but 
 it is difficult to keep them, as they form the food of 
 the Entomostraca, the Rotatoria, and the larvae of 
 insects ; so that their enemies are very numerous, and 
 they soon disappear. 
 
 CLASSIFICATION. Before leaving the subject of 
 living bodies, it may be well to make a few remarks 
 upon their systematic relation as denned by classi- 
 fication. 
 
 All natural bodies are referable to one of three 
 great kingdoms, viz. the Animal, the Vegetable, or 
 the Mineral Kingdom. The bodies belonging to the 
 latter seldom come under the notice of the micro- 
 scopic observer, as they are mostly visible to the 
 naked eye, and their minute structure is the same as 
 that of the larger masses. The general structure of 
 the members of the vegetable and animal kingdoms 
 has been illustrated in the preceding pages. These 
 bodies are distinguished from those of the mineral 
 kingdom by their vital power of appropriating sur- 
 rounding matters to their own nutrition and growth 
 this power being exercised by their organs, or, in the 
 lowest forms, by any portion of their substance. 
 Hence animals and vegetables or plants are termed 
 organic bodies, while minerals are termed inorganic 
 bodies, as having no organs; and the material of 
 which organic bodies consist is termed organic mat- 
 ter, that of minerals being inorganic matter. But in 
 both animals and plants inorganic matter is mixed 
 with the organic matter, having been taken up or 
 absorbed from the inorganic kingdom, although it 
 does not usually exist in its characteristic condition, 
 which is that of crystals, i. e. angular solids, as crystals 
 of Epsom salts, &c. The individual members of the 
 
CLASSIFICATION. 165 
 
 animal and vegetable kingdoms are systematically 
 divided into certain groups, and these into successively 
 smaller groups until we arrive at the species. These 
 groups are founded upon the possession of certain 
 points of resemblance by their members, forming the 
 distinguishing characters, and their names are signi- 
 ficant and definite. They usually run as follows, the 
 larger and higher groups standing first in order : 
 Kingdoms, Subkingdoms, Classes, Orders, Families, 
 Tribes, Genera, and Species. But it must be observed 
 that the term species has a different value from that 
 of the other terms ; for the individuals of which the 
 species consist are not only related by resemblance 
 of structure, but also by their origin being supposed 
 to have derived their origin from a parent of original 
 creation ; while the other groups have, as far as we 
 know, no other relation than that of similarity of 
 structure. 
 
 It is obvious that the characters of the various 
 groups might be founded upon peculiarities of any 
 kind. But on this point two methods must be speci- 
 ally distinguished, in one of which the groups are 
 founded upon the sum of all the peculiarities, while 
 in the other they are based upon the structure of 
 single parts or organs. In the former case the system 
 is called natural, in the latter artificial. And while the 
 latter often brings together beings which have per- 
 haps but one or two points of resemblance, and sepa- 
 rates others which are closely related, the former 
 associates those which are really and naturally similar. 
 
 All the groups have special names, so that they 
 may be referred to and spoken of as in the case of 
 common things ; the names being composed of Greek 
 or Latin words, so that they may be intelligible to all 
 nations ; and as these are dead languages, they will 
 remain good for all time. 
 
 In mentioning the name of an animal or plant, the 
 name of the genus is always used with that of the 
 
166 CLASSIFICATION. 
 
 species ; thus, the name of Chickweed is Stellaria 
 media. Because there are mostly several species in 
 a genus ; so that if the name of the genus only were 
 used, the species meant would be uncertain ; and as 
 there are often species of the same name in different 
 genera, if the name of the species only were used, the 
 genus meant would be doubtful. 
 
 The classification of animals and plants serves two 
 important purposes : one is that the structural pecu- 
 liarities and affinities of the groups may be contrasted 
 and a knowledge of their absolute and their differ- 
 ential characters acquired, and for this a natural 
 system is eminently serviceable ; the second is that of 
 enabling any animal or plant to be simply distin- 
 guished from any other, for which an artificial or 
 analytical system is extremely useful. 
 
OPTICAL PRINCIPLES. 167 
 
 CHAPTER XIV. 
 
 OPTICAL PRINCIPLES. 
 
 WE shall now devote a few pages to the consideration 
 of the nature of light, and the optical principles in- 
 volved in the construction and use of the microscope. 
 Two theories of light have been propounded. Accord- 
 ing to one, light consists of minute particles emana- 
 ting from self-luminous bodies, as the sun, a candle, 
 or a red-hot piece of iron ; this is called the corpuscular 
 theory. According to the other, light consists of 
 waves or undulations like those of water or the 
 ears of corn set in motion by the wind, of the mole- 
 cules of an extremely subtle and rarified elastic mat- 
 ter, called ether, existing everywhere, and set in mo- 
 tion by the causes which produce light ; this is called 
 the undulatory theory. The consideration of the 
 merits of these two theories would be foreign to our 
 purpose : suffice it to say that the evidence in favour 
 of the undulatory theory preponderates, so that the 
 corpuscular theory is now laid aside. 
 
 It will often be requisite to make use of the term 
 ray of light, by which must be understood the small- 
 est bundle of luminous undulations which can be 
 separated from a mass of light as by passing light 
 through a small hole in an opake body, or by any 
 equivalent method. 
 
 The most casual observer must have noticed that 
 the rays of light move in straight lines; as when the 
 sun's rays are seen entering a dark room through a 
 small window or other aperture, their direction being 
 then distinctly visible ; the manner in which ordinary 
 shadows are formed also illustrates the same fact. 
 
168 OPTICAL PRINCIPLES. 
 
 Refraction. But when the rays in their passage 
 impinge or are incident upon and enter a transpa- 
 rent medium or material, of a different density from 
 that which they were at first traversing, their course 
 becomes altered, and the line of their direction broken, 
 whence they are said to be refracted. If the medium 
 upon which the rays impinge be denser than that 
 through which they were at first passing, they will 
 be refracted towards a line perpendicular to the sur- 
 face, or they will be refracted towards the perpen- 
 dicular, as it is expressed. 
 
 Thus, as shown in PL XII. fig. 1, the incident ray 
 i, entering the plate of glass, will be refracted at its 
 surface in the direction a r, towards the line JP, which 
 is perpendicular to the surface. 
 
 The extent to which the rays undergo refraction 
 depends upon the degree of density of the medium, 
 and varies in the case of each individual substance ; 
 but it follows a definite law. If, as in PL XII. fig. 2, 
 a circle be drawn around the point b, at which the ray 
 a is incident, b r representing the refracted ray, the 
 lines s i and t r, drawn at right angles to the perpen- 
 dicular p, will form respectively the sines, as they are 
 called, of the angles s b i and t b r ; si being the sine of 
 the angle of incidence s b i } or the angle formed by the 
 incident ray with the perpendicular, and / r the sine 
 of the angle of refraction t b r, or of that formed by 
 the refracted ray with the perpendicular. These sines, 
 for brevity, are called the sines of incidence and of 
 refraction ; and they bear a constant ratio or propor- 
 tion to each other. Taking the sine of refraction as 
 the unit, or as =1, the value of the sine of incidence 
 represents the refractive index or the refractive power 
 of the medium for a ray entering the medium from a 
 vacuum; or, the refractive power of air being ex- 
 tremely small, the value of the sine of incidence may 
 be considered as representing the refractive power 
 from air into the medium. 
 
PLATE XII. [PAGE 168.] 
 OPTICAL PRINCIPLES. 
 
 Fig. 
 
 1. Refraction through a glass plate. 
 
 2. Law of refraction. 
 
 3. Reflexion from a plane surface. 
 
 4. Reflexion from a concave mirror. 
 
 5. Refraction at a curved surface. 
 
 6. A doubly convex lens. 
 
 7. A plano-convex lens. 
 
 8. A doubly concave lens. 
 
 9. A plano-concave lens. 
 
 10. A concavo-convex lens, or me- 
 
 niscus. 
 
 11. Refraction through a convex lens. 
 
 12. Relation of a convex lens to 
 
 prisms. 
 
 13. Relation of a concave lens to 
 
 prisms. 
 
 14. Refraction of parallel rays through 
 
 a convex lens. 
 
 15. Refraction of converging rays 
 
 through a convex lens. 
 
 Fig. 
 
 16. Refraction of diverging rays 
 
 through a convex lens. 
 
 17. Refraction of parallel rays through 
 
 a concave lens. 
 
 18. Spherical aberration. 
 
 19. Dispersion and formation of a 
 
 spectrum. 
 
 20. Chromatic aberration. 
 
 21. Formation of images in the eye. 
 
 22. Angle of vision. 
 
 23. Objects too near the eye. 
 
 24. Action of convex lens in vision. 
 
 25. Aplanatism. 
 
 26. Aberration produced by cover. 
 
 27. Course of rays through the mi- 
 
 croscope. 
 
 28. Achromatism. 
 
 29. Waves of light conspiring (a, b), 
 
 and interfering (b, c). 
 
 30. Polarization: ^tourmaline; d, cry- 
 
 stal j s, crystal of calcareous spar. 
 
REFRACTION. 160 
 
 Although the ratio of the sines is constant, the re- 
 fractive index varies in different media. Thus that 
 of air is 1-0003; of water, 1 '336,- of Canada balsam, 
 1*549; of crown glass, from which window-panes are 
 made, 1*535; of flint glass, from which bottles are 
 made, 1*6 ; of Faraday's heavy glass, composed of sili- 
 cated borate of lead, 1*8; and of that consisting of 
 borate of lead, 2*0, 
 
 A knowledge of this " law of the sines " is of prac- 
 tical importance in determining the direction which 
 the rays will pursue when transmitted through glass 
 lenses, &c. the refractive index of which is known; 
 or in ascertaining the curve which should be given to 
 their surfaces for producing a particular refraction 
 and focal length. Thus, supposing the plate of glass 
 in PL I. fig. 2 to consist of crown glass, the refractive 
 index of which is 1*5, the length of the sine of re- 
 fraction, t r, will be equal to one part or dimension, 
 while the sine of incidence, s i } is equal to one part 
 and a half. 
 
 It must be remarked that when light is incident at 
 a right angle to the surface of the medium, no re- 
 fraction takes place, the transmitted ray pursuing its 
 original course. 
 
 When a ray of light leaves a denser medium, such 
 as glass, to enter a rarer medium, such as air, it be- 
 comes refracted from the perpendicular. In such case, 
 the angle of refraction being greater than the angle 
 of incidence, its sine will also be greater than that of 
 the latter ; but the ratio is still preserved. 
 
 Reflexion. When rays of light fall upon a plane 
 surface, as the flat surface of the mirror, a greater or 
 less number of them are reflected, and this accord- 
 ing to a definite law, by which the angle of incidence, 
 or that formed by the incident ray with the perpen- 
 dicular, is equal to the angle of reflexion, or that 
 formed by the reflected ray with the same. Thus, as 
 shown in PL XII. fig. 3, the angle i bp, formed by 
 
 Q 
 
170 OPTICAL PRINCIPLES. 
 
 the incident ray ib with the perpendicular^, is equal 
 to the angle p b r, formed by the reflected ray b r 
 with the perpendicular p b. 
 
 If the body upon the surface of which the rays are 
 incident be transparent, some of the rays will be re- 
 fracted and will pass through it, whilst others will be 
 reflected. The proportion of those reflected is small- 
 est when the rays are incident perpendicularly to the 
 surface; but this increases as the incident rays be- 
 come more oblique, i. e. as the angle of incidence be- 
 comes greater, although at no degree of obliquity are 
 the whole of the rays reflected. The case is different, 
 however, with those rays which enter the substance 
 and impinge upon its inner or second surface; for 
 these at a particular angle of incidence undergo total 
 reflexion, so that none of the rays are transmitted at 
 the second surface. The angle of total reflexion is 
 constant for the same medium, but different for dif- 
 ferent media : thus in crown glass it is equal to about 
 40, in flint-glass 38, &c. ; and this internal reflexion 
 from the second surface of transparent media is more 
 perfect than that occurring at the surface of opake 
 reflecting surfaces or mirrors. 
 
 If the reflecting surface be concave, as in PL XII. 
 fig. 4, parallel rays will be reflected to a focus , nearer 
 the mirror than the centre of its curvature b, and this 
 focus is called the principal focus; while diverging 
 rays are brought to a focus nearer the centre of cur- 
 vature; and converging rays form a focus further 
 from the centre of curvature. 
 
 Lenses. In most instances, as far as the microscope 
 is concerned, the surfaces of the glass through which 
 the rays of light are transmitted are not plane or flat, 
 but curved being either convex or concave, and be- 
 longing to convex or concave lenses. In considering 
 the course of rays through curved surfaces, the re- 
 fraction may be viewed as taking place at a plane 
 surface forming a tangent at the point of incidence of 
 
LENSES. 171 
 
 each ray ; or each curved surface may be regarded as 
 consisting of a number of minute plane surfaces 
 placed at right angles to the perpendicular. Thus, in 
 PI. XII. fig. 5, the ray a, incident at the point b of 
 the curved surface, is refracted towards the perpen- 
 dicular p, as if it had fallen upon the plane surface 
 represented by the tangent t. The forms of the most 
 common lenses are represented in PL XII. figs. 6-10; 
 fig. 6 being doubly convex, or both surfaces being 
 convex; fig. 7, plano-convex, or one surface plane, 
 the other convex; fig. 8, doubly concave, or both 
 surfaces being concave ; fig. 9, plano-concave, one sur- 
 face being plane, the other concave ; and fig. 10 is a 
 meniscus, in which one surface is convex and the other 
 concave. The curved surfaces of lenses are usually 
 portions of spheres. 
 
 The manner in which the course of a ray may be 
 traced through a lens is illustrated by PL I. fig. 11, 
 which requires no explanation after what has been 
 already stated. 
 
 To facilitate the comprehension of the general ac- 
 tion of lenses, they may be regarded as composed of 
 two triangular prisms, with their bases in contact in 
 a convex lens, as in fig. 12 ; their apices being op- 
 posed in a concave lens, as in fig. 13. 
 
 The point to which the rays converge after passing 
 through a convex lens is called the focus (PL XII. 
 fig. 14/), the distance of which from the centre of the 
 lens, called the focal length, obviously depends upon 
 the direction of the incident rays. When these are 
 parallel, which those coming from distant objects 
 may be considered to be, the focus at which they 
 meet is called the principal focus, or the focus for 
 parallel rays : thus, in PL XII. fig. 14, the parallel 
 rays meet at/, which is the principal focus. 
 
 If the incident rays are convergent, as in PL XII. 
 fig. 15, the focus o will be situated nearer the lens 
 than the principal focus,/. If, on the other hand, 
 
172 OPTICAL PRINCIPLES. 
 
 they are divergent, as in PL XII. fig. 16, the focus/will 
 be situated further from the lens than the principal 
 focus o. By concave lenses the incident rays are ren- 
 dered divergent, as in PL XII. fig. 17, as if they ema- 
 nated from a point /, situated on the same side of the 
 lens as that upon which the rays are incident, and 
 called the virtual focus. 
 
 Spherical aberration. Although, as a general ex- 
 pression, we have stated that the rays of light meet 
 at a focus on passing through a convex lens, this is 
 not strictly correct. For, in ordinary convex lenses, 
 the marginal rays are more refracted than the central 
 ones, and meet at focal points nearer the lens than the 
 latter, as shown in PL "XII. fig. 18. This important 
 defect is called spherical aberration, and arises from 
 the lateral rays being incident upon more oblique 
 portions of the curved surface of the lens than the 
 central rays. Hence objects seen through such lenses 
 appear misty and confused, the central and lateral 
 parts of a flat object not being visible at the same 
 time ; and even when the marginal parts are visible, 
 they appear distorted or deformed. 
 
 Spherical aberration is greatest in the most convex 
 lenses ; and, in a plano-convex lens, it is least when 
 parallel rays enter at or emerge from its convex sur- 
 face. 
 
 In certain lenses, the convex surface of which has 
 the form of a parabola, a hyperbola, or an ellipse, 
 the spherical aberration is absent; but it is impos- 
 sible to grind microscopic lenses of these forms with 
 absolute accuracy, so that the fact is of no practical 
 value. 
 
 The form of simple convex lens most free from 
 aberration is that in which the curves of the two sur- 
 faces form parts of a sphere, the radii of the curves 
 being as 1 to 6; the focal length being rather less 
 than twice the length of the radius of the most con- 
 vex surface. This form of lens comes very near to 
 
DISPERSION. 173 
 
 a plano-convex lens, which is consequently the best 
 form for a simple lens. 
 
 Dispersion, or Chromatic Aberration. The rays of 
 light have so far been considered as simple. They 
 are, however, in reality compound, consisting of a 
 number of primary- coloured rays, of which seven kinds 
 are easily distinguishable, viz. red, orange, yellow, 
 green, blue, indigo, and violet. The coloured rays of 
 the sun are, as is well known, often seen separated 
 by the action of the triangular glass bars or prisms 
 forming the lustres of a chandelier ; the separation 
 arising from the different refrangibility of the coloured 
 rays, by which each is refracted to a different degree 
 from that of the others. This is shown in PL XII. 
 fig. 19, representing a ray of white light entering a 
 triangular prism, at the surface of which the paths of 
 the rays become different according to the degree of 
 their refrangibility, whence they emerge separately, 
 forming a spectrum at v r ; the most refrangible violet 
 rays (v) being most refracted, the less refrangible red 
 (r) least so, the intermediate rays being refracted to 
 intermediate degrees according to their respective re- 
 frangibilities. This separation of the coloured rays 
 is called dispersion; and as different substances or 
 media disperse the coloured rays over a larger or 
 smaller space, so as to produce spectra of different 
 lengths, they are said to possess different dispersive 
 powers. Thus the dispersive power of flint glass and 
 balsam are about equal, while that of crown glass is 
 considerably less. 
 
 The extent to which dispersion is produced by the 
 same medium also depends upon the angle of the 
 prism, being greater as the angle is larger ; increased 
 obliquity of the incident light also increases the dis- 
 persion, so that the spectrum produced by a small 
 prism may be equal to that produced by a larger one 
 upon which the light is less obliquely incident. 
 
 In consequence of the dispersion of light, rays pass*. 
 
174 OPTICAL PRINCIPLES. 
 
 ing through a convex lens do not meet at a single 
 point or focus (PL XII. fig. 20), but form as many 
 foci as there are coloured rays. 
 
 When the spectrum is received upon a convex lens, 
 the coloured rays are brought to a focus, and the light 
 appears again white ; for it is only when the primary- 
 coloured rays are parallel, and seen close together, 
 that they produce the impression of white or colour- 
 less light. The spectra produced by different disper- 
 sive media not only differ in length, but also in the 
 breadth of the coloured spaces not being in the same 
 ratio to each other ; hence the spectra are said to be 
 irrational, or the dispersion is said to be irrational. 
 
 Vision. The visibility of an object depends upon 
 the rays of light which emanate from each point of 
 its surface presented to the eye being brought to a 
 focus upon the ret'ina or expansion of the nerve of 
 sight lining the inside of the back of the eye ; so that, 
 an image of each point being impressed upon the re- 
 tina, the sum of the images forms the compound 
 image of the entire object. 
 
 The manner in which the image is formed is 
 shown in PL XII. fig. 21, in which, to prevent con- 
 fusion, the rays coming from three points of the arrow 
 only have been represented. The rays diverging from 
 these three points, a b c, form cones in contact by 
 their bases ; the apex of each cone outside the eye 
 being situated at the points a b c, the common base 
 of each being situated at the crystalline lens x, im- 
 mediately behind the pupil or rounded aperture in 
 the coloured curtain of the eye, called the iris, i i, and 
 which limits the base of the cones. The apices of the 
 cones within the eye, a'b'c', are formed by the rays 
 brought to foci upon the retina by the crystalline lens. 
 The marginal cones of rays coming from the object 
 cross within the eye, so that the uppermost rays from 
 the object become lowermost upon the retina, and thus 
 an inverted image of the object is formed. This ap- 
 
MAGNIFICATION. 175 
 
 pears to the eye to "be erect, because the eye or rather 
 the mind judges the parts of an object to be situated 
 in that direction in which the rays coming from them 
 are impressed upon it. Hence, as in fig. 21, the rays 
 impressed upon the retina at the lower part a, appear 
 to come from the upper part of the cross, although 
 they are lowermost in the image, and so on for the 
 other rays. For distinct vision the rays of each cone 
 must be parallel, or nearly so. 
 
 Angle of Vision. The marginal rays coming from 
 the object cross at a point corresponding to the centre 
 of the pupil, and thus form an angle, as seen in fig. 22, 
 where the cones are omitted, to avoid confusion ; this 
 angle is the angle of vision. Now the size which ob- 
 jects appear to possess is measured by this angle, or 
 by the linear magnitude of their images (i. e. their 
 size estimated in one direction, as of length or breadth) 
 upon the retina. When the object is distant, the an- 
 gle and its linear magnitude are small, and it appears 
 small and distant ; whilst if it be large, or if small 
 and brought near the eye, the reverse will be the case. 
 
 Magnification. Hence an object may be made to 
 appear larger, or may be magnified, by increasing the 
 linear magnitude of its image upon the retina, which 
 can be done by bringing it nearer the eye, as shown 
 in fig. 22, where the image of b formed at b r is larger 
 than the image of a formed at a 1 . But when an object 
 is brought nearer the eye than about 8 or 10 inches 
 (for the distance varies with different persons), its 
 image becomes indistinct and misty ; and this because 
 the rays composing the cones are too divergent to 
 meet at a focus upon the retina, as shown in fig. 23. 
 By interposing a convex lens, however, between the 
 eye and the object, the too divergent rays may be 
 made to meet at a focus upon the retina, as in fig. 24, 
 the object at the same time being rendered apparently 
 larger or magnified, from the refracting action of the 
 lens upon the cones. 
 
176 OPTICAL PRINCIPLES. 
 
 Apian 1 atism (a, not, TrXavdw, to wander) . The ef- 
 fect of spherical aberration in rendering the image of 
 an object seen through a lens indistinct and misty may 
 now be intelligible. In order that such image may 
 be distinct, the rays emanating from each point of 
 the object must converge at one spot upon the retina. 
 But since, when spherical aberration exists, the mar- 
 ginal rays are more refracted than the central ones, 
 they will meet at foci before those formed by the lat- 
 ter ; and when the foci of one set are coincident with 
 the retina, so that the image would otherwise be di- 
 stinct, the latter is rendered confused and indistinct 
 by the rays of the other set. 
 
 In this consideration, we imply that there are only 
 two sets of rays, the central and the marginal ; but 
 the central and marginal rays are not separate, for 
 the rays possess every intermediate degree of obliquity, 
 hence the foci and images are really innumerable. 
 
 Now there are evidently two methods of destroying 
 or correcting spherical aberration, viz. by excluding 
 the marginal rays, or by altering their direction. 
 
 The exclusion of the marginal rays is often adopted ; 
 and is effected by means of a diaphragm, or stop as 
 it is called. This consists of a plate of metal, with a 
 round aperture in the middle, and it is placed behind 
 the lens ; but it has the serious defect of diminishing 
 considerably the amount of light transmitted. 
 
 The alteration of the direction of the marginal rays 
 is produced by refraction, a thin plano-concave lens 
 being placed in front of the convex one (PL XII. 
 fig. 25) . The doubly convex lens is composed of crown 
 glass, and the concave lens of flint glass, which has a 
 higher refractive and dispersive power than crown 
 glass. In this way we get a compound lens, which, 
 if the two lenses had the same refractive power, would 
 simply amount to a plano-concave lens with the mar* 
 ginal portions removed. But as the concave lens 
 consists of more highly refracting material than the 
 
ACHROMATISM. 177 
 
 convex, if the curve and thickness of the two lenses 
 be properly adapted, the marginal portions of the con- 
 cave correct the too great convergence of the mar- 
 ginal rays produced by the convex lens, and so the 
 rays are brought to nearly the same focus. An idea 
 of this action may be obtained from fig. 25, the dotted 
 lines indicating the direction which the rays would 
 take, if passing through the convex lens only. 
 
 A lens in which the spherical aberration is cor- 
 rected is said to be aplanatic. 
 
 Achromatism. Supposing the spherical aberration 
 of a lens to be corrected, there still remains the 
 chromatic aberration (p. 173) ; for although the cen- 
 tral or mean coloured rays may meet at a focus, the 
 other coloured rays belonging to the same compound 
 or ordinary ray will meet at different foci, so that a 
 series of coloured images of the object will be formed 
 at different distances from the lens ; hence, at which- 
 ever focus the object is viewed, it will appear coloured. 
 
 Now the coloured primary rays can only be made 
 to coincide in direction, so that the light parts of an 
 object may appear white, by refraction. And the 
 correction is produced by the same plano-concave 
 lens as that which corrects the spherical aberration. 
 But in this case the relative dispersive powers of the 
 media composing the convex and the concave lenses 
 form the point to be considered. If the dispersive 
 power of the media of which the convex and concave 
 lenses are composed were the same, the dispersive 
 power of the convex lens would be in excess, and the 
 coloured rays in each compound ray could not become 
 parallel. But by forming the concave lens of a more 
 highly dispersive medium, with a less proportional 
 mean refraction than the convex, when the curves of 
 the surfaces and the relative thickness of the lenses 
 are properly adjusted, the dispersive action of the 
 concave lens may be made equal to that of the con- 
 vex ; and being exerted in the opposite direction, the 
 
178 OPTICAL PRINCIPLES. 
 
 coloured rays will become parallel and meet at a 
 single focus. 
 
 This may be elucidated by considering the lenses 
 as composed of prisms. Thus, let fig. 28 represent 
 the compound lens, the two halves of the doubly 
 convex lens acting as two triangular prisms (fig. 19) 
 with their bases opposed, converging the compound 
 white rays w w, and dispersing the coloured elemen- 
 tary rays, which would form spectra at ss. In the 
 plano-concave lens the triangular prisms may be 
 considered as placed with their apices towards each 
 other, and so would tend to disperse the coloured 
 rays in the opposite direction, to form spectra at 1 1. 
 Then, supposing the dispersions to be equal and in 
 opposite directions, the coloured rays would become 
 parallel and meet at a definite focus, the colour being 
 destroyed. At the same time, the spherical action 
 of the concave lens being opposite to that of the 
 convex, the converging action of the latter will be 
 diminished, so that the focus of the compound lens 
 will be longer than that of the convex alone ; but as 
 the dispersive power of the concave is greater rela- 
 tively than that of the convex, the mean refraction is 
 less altered than the refraction or dispersion of the 
 separate coloured rays ; so that the concave wholly 
 opposes or corrects the dispersion produced by the 
 convex, while it only partially corrects its mean 
 refraction. 
 
 A lens in which the chromatic and spherical aber- 
 rations are corrected or destroyed is commonly called 
 achromatic; although the term properly applies to 
 the correction of the colour only. 
 
 If in a compound lens the chromatic aberration is 
 only partially corrected, so that the red rays still 
 meet at a focus beyond the violet, as in a simple 
 uncorrected lens (fig. 20), the lens is said to be under- 
 corrected, or the aberration to be positive ; while if 
 the correcting action of the plano-concave lens be too 
 
ACHROMATISM. 179 
 
 great, so that the violet rays meet before the red, as 
 in a simple concave lens, the lens is said to be over- 
 corrected, and the aberration is called negative. Al- 
 though the positive chromatic aberration of the ex- 
 treme rays passing through a convex lens may be 
 corrected by the negative aberration of a concave 
 lens, there still remains a certain amount of uncor- 
 rected colour, arising from the irrationality of the 
 spectra of the two refracting media. This evil cannot 
 be overcome, and the remaining colour is said to 
 arise from the secondary spectrum. 
 
 The object-glasses of the microscope, consisting of 
 the compound lenses, have their aberrations balanced 
 to a considerable extent on the above principles the 
 lowest combination being under-corrected, while the 
 upper combinations are over-corrected ; and, by suit- 
 able adaptation of their distance from each other, 
 further correction may be obtained, the aberration 
 of the object-glass altogether being, however, over- 
 corrected or negative. 
 
 The eye-piece consists of two simple plano-convex 
 lenses, the upper or eye-glass (fig. 27 e) having a 
 shorter focus than the lower (/) or field-glass, and 
 the two placed at the distance of half the sum of 
 their focal lengths. The object-glass alone would 
 form an enlarged and reversed image of the object 
 within the body of the microscope, the cones of rays 
 from each point of the object terminating at the 
 larger arrows in the figure (fig. 27). But the rays 
 meeting the field-glass are brought by it to a focus 
 at the position of the smaller arrows, where they 
 form a reduced image ; and, subsequently passing 
 through the eye-glass, they are so altered in direc- 
 tion as to enter the eye at a greater angle, and to 
 present a magnified image of the object. 
 
 The eye-piece produces several important effects. 
 The refraction being produced by two less convex 
 lenses instead of one of greater convexity, the 
 
180 OPTICAL PRINCIPLES. 
 
 rical aberration is considerably reduced ; and the con- 
 vexities of the lenses in the eye-piece being situated 
 in an opposite direction to that of those in the object- 
 glass, the spherical aberration of the former reverses 
 and so neutralizes that of the latter. Also the under- 
 correction of the field-glass compensates the over- 
 correction of the object-glass the blue rays which 
 are refracted more than the red by the field-glass, 
 being thrown upon the eye-glass nearer its centre, 
 where the refraction is less, and thus the coloured 
 rays become parallel or nearly so on reaching the 
 eye. Moreover the field- glass collects a larger num- 
 ber of rays than the eye-glass could do alone, so that 
 it enlarges the field and increases its brightness. 
 
 In the best object-glasses the aberrations are so 
 well balanced that the mere covering an object with 
 thin glass is sufficient to disturb the balance and 
 render very delicate markings either misty and co- 
 loured or wholly invisible. The effect produced by 
 a plate of glass may be understood by reference to 
 fig. 26, the rays being supposed to emanate from the 
 object at a ; and it is evident that the refraction of 
 the glass so alters the direction of the rays that they 
 will fall upon the lower combination nearer the centre 
 than if the cover were absent, and thus negative 
 aberration is produced. In the best object-glasses, 
 however, this aberration may almost entirely be re- 
 moved, the lower combination being susceptible of 
 approximation by a screw movement to the second or 
 next above it, so that the ascending rays, being able 
 to continue their oblique course through the increased 
 distance between the object and the lower combina- 
 tion, may fall upon the same portions of the latter 
 that they did before the cover was applied. 
 
 POLARIZATION OF LIGHT. In attempting to give a 
 sketch of this curious and difficult subject, we must 
 suppose the reader to be in possession of a natural cry- 
 stal of calcareous spar, and either two NicoPs prisms 
 
POLARIZATION. 181 
 
 (forming the ordinary polariscope) or two plates of the 
 mineral called tourmaline cut in the direction of the 
 length or axis of the crystal. 
 
 Hitherto we have considered rays of light falling 
 upon transparent substances as simply refracted or 
 reflected according to the ordinary laws of refraction 
 or reflexion. We have now to notice some curious 
 exceptions, forming the basis of many interesting 
 phenomena, especially in connexion with the micro- 
 scope, in which these laws are more or less deviated 
 from. If we place a plate of tourmaline, cut as above 
 directed, upon or beneath the stage of the microscope, 
 the light will pass through it, appearing tinged with 
 the green or brown colour natural to the tourmaline ; 
 but on laying another slice upon the eye-piece, and 
 turning the latter round or rotating it, the light will 
 be transmitted in certain positions only, being par- 
 tially or entirely arrested in others, so that the field 
 appears black. And, on careful examination, it will 
 be noticed that the change from black to white 
 occurs at each quarter of a rotation, being twice black 
 and twice white in an entire rotation, the changes 
 occurring alternately. The same phenomena may 
 also be exhibited by substituting two Nicol's prisms 
 for the tourmalines. 
 
 Again, if we take a natural crystal of calcareous 
 spar, and paste upon one side of it a piece of black 
 paper with a small hole in the middle, on holding the 
 crystal to the light or over a piece of white paper, 
 with the covered side next the light, two holes or two 
 images of the hole will be seen ; and if the crystal 
 without the paper be placed over some print, the print 
 will appear double. Hence the light passing through 
 the hole is twice or doubly refracted, one ray following 
 the ordinary law of refraction, while the other follows 
 a different law, being retarded and pursuing a longer 
 course ; and so the two rays are called respectively 
 the ordinary and extraordinary ray. And on viewing 
 
OPTICAL PRINCIPLES. 
 
 these through a tourmaline or a NicoPs prism, as in 
 the experiment with the two tourmalines, the images 
 will become alternately visible and invisible, just as 
 was then the case with the entire mass of light. 
 
 The light which has undergone this singular change 
 is said to be polarized, because the rays appear to 
 have acquired poles or sides. In the above experi- 
 ments the lower prism or tourmaline is called the 
 polarizer, because it polarizes the light, and the upper 
 is called the analyzer, because it analyzes or tests the 
 light altered by the former. 
 
 An idea of the cause of this change may be ob- 
 tained by reference to the undulatory theory of light. 
 Ordinary light consists of waves or undulations taking 
 place in planes at right angles to each other, or in all 
 planes; while in polarized light the undulations are 
 all in one plane or in parallel planes. This may per- 
 haps be understood by considering that books in a 
 book-case are situated in parallel planes, the shelves 
 being in planes at right angles to the former. And 
 by imagining in polarizing substances the existence of 
 some structure acting like a grating, a notion can be 
 obtained how the rays in the different planes may be 
 transmitted or intercepted. If the grating be so 
 placed that the bars (representing the planes of polari- 
 zation) are perpendicular, the books can pass between 
 them ; while if the grating be turned round a quarter 
 of a circle, they will become transverse, and the books 
 cannot pass, while the shelves could do so. Carrying 
 on this analogy, the tourmaline or NicoPs prism po- 
 larizes the light by transmitting only those rays whose 
 undulations are in planes parallel to the bars ; while 
 the analyzer allows these undulations to pass through 
 it when the direction of the planes coincides with that 
 of the bars, but interrupts them when their direction 
 is at right angles to the bars. And it is evident that 
 the planes of polarization of the ordinary and extra- 
 ordinary rays are opposite, from the opposite action 
 of the analyzer upon them. 
 
POLARIZATION. 183 
 
 The power of doubly refracting and polarizing is 
 not possessed by all crystalline bodies, but only those 
 belonging to other than the cubic system; crystals 
 belonging to this system neither doubly refract nor 
 polarize light. In all doubly refracting crystals there 
 are one or more lines or directions in which the light 
 is not doubly refracted. These are called the optic 
 axes, and sometimes they coincide with the geometric 
 axis of the crystals, at others they do not ; and they 
 may be regarded as positions or directions of equili- 
 brium of certain molecular forces existing within the 
 crystal, which, acting in opposition, neutralize each 
 other. 
 
 If light, polarized by the polarizer, be transmitted 
 through thin doubly refracting crystals, and analyzed 
 by the analyzer, splendid colours will become visible ; 
 and on rotating separately either the polarizer or the 
 analyzer, at each quarter rotation the colours will 
 change, being complementary to those at first visible, 
 or such as are requisite with the first to make white 
 light. We have seen (fig. 19) that white light con- 
 sists of seven coloured rays, or of three primary 
 colours red, yellow, and blue, which, by superposi- 
 tion, form the others ; and thus red is complementary 
 to green, which consists of blue and yellow, the two 
 sets of complementary colours appearing and vanish- 
 ing as the light and darkness did when the crystals 
 were not used. 
 
 These colours are produced by interference. The 
 compound rays of white light (fig. 30 /) passing through 
 the polarizer (t) are all polarized in one plane; the 
 crystal (d) depolarizes this light, i. e. doubly refracts 
 and resolves it into two sets of rays polarized in planes 
 at right angles to each other, forming the ordinary, o, 
 and the extraordinary ray, E. Each of these two sets 
 of rays is resolved by the analyzer (s) into two other 
 sets, polarized in planes at right angles to each other ; 
 so that in all there are four sets, two in one plane 
 
184 OPTICAL PRINCIPLES. 
 
 and two in the other ; and, the primary rays of the 
 two sets in each plane being in different stages or 
 phases of undulation, in consequence of the retarda- 
 tion of the extraordinary rays, the undulations of cer- 
 tain coloured rays check and annihilate each other, 
 while the remainder or complementary conspire and 
 pursue their course, producing the appearance of 
 colour, this effect being reversed at each quarter- 
 revolution of the analyzer. 
 
 An idea of what is meant by phases of undulation 
 may be obtained by reference to fig. 29, in which the 
 undulations, , b, are in similar states or phases, and 
 so conspire in action, while the wave c is in a different 
 phase and half an undulation behind the others; 
 hence it would check or interfere with either of the 
 other waves (a, b), the etherial molecules of the two, 
 which vibrate perpendicularly or at right angles to 
 the direction of the wave, acting to the same extent 
 and in opposite directions. 
 
 In fig. 30 the analyzer is represented as composed 
 of a natural crystal (rhomb) of calcareous spar, which 
 transmits both sets of rays; but in the ordinary 
 analyzer or NicoPs prism which is made by dividing 
 a rhomb through the obtuse angles into two wedge- 
 shaped pieces and cementing them together again 
 with balsam, only one set of rays is transmitted at 
 each quarter-revolution, the other being refracted out 
 of the field. In the case of the tourmaline, one of the 
 sets of rays is absorbed ; so that the tourmaline, like 
 the NicoFs prism, is single-imaged. 
 
 Thus the colours produced by polarization are the 
 same as those of the spectrum, but separated in a 
 different way, both arising from the elementary co- 
 loured rays of the compound white light. For while 
 the spectral rays are separated by dispersive refrac- 
 tion, the polarized coloured rays are separated by the 
 interference and annihilation of some rays, the re- 
 mainder passing on to produce the colours. 
 
POLARIZATION. 185 
 
 When the position of the depolarizing crystal is 
 such that the plane of the polarized light coincides 
 with the direction of the optic axis or axes, the light 
 is not doubly refracted nor polarized in certain parts ; 
 hence these parts appear white if the plane of the 
 polarizer and analyzer coincide, and black if they be 
 crossed. A crystal cut at right angles to its optic 
 axis, with its length directed towards the polarizer 
 and analyzer, is in this position, and it exhibits alter- 
 nately a black and white cross, with one or two sets 
 of concentric rings of complementary colours at each 
 quarter of a rotation. 
 
 To prepare crystals for examination by polarized 
 light, a little Epsom salt, nitre, or borax should be 
 dissolved in water, a drop placed upon a slide, and 
 dried at a gentle heat. The crystals should then be 
 mounted in balsam, and viewed as transparent objects. 
 
 To see the cross and rings, the crystals should 
 be sawn or cut across transversely, the ends being 
 polished on a strained piece of silk moistened with 
 water, and the sections mounted in balsam. 
 
 The property of doubly refracting and polarizing 
 light is not confined to crystalline substances, being 
 also possessed by many organic bodies, for the de- 
 tails of which I must refer to the article Polariza- 
 tion in the ' Micrographic Dictionary/ 
 
INDEX. 
 
 Abdomen, 129. 
 Aberration, chromatic, 
 
 173. 
 Aberration, spherical, 
 
 172. 
 
 Acalephae, 153. 
 Acarus, 131. 
 Accumbent, 44. 
 Achromatic, 178. 
 Achromatic condenser, 
 
 5. 
 
 Achromatism, 177. 
 Acicular, 24. 
 Acotyledons, 43. 
 Acrocarpi, 55. 
 Acrostalagmus, 111. 
 Actinocyclus, 80. 
 Actinophrys, 156. 
 Adapter, 2. 
 Adulteration, 23. 
 ^cidium, 100. 
 Agaricus, 97. 
 Albumen, of seeds, 43. 
 
 , of eggs, 113. 
 
 Algaa, 64. 
 Alyscum, 161. 
 Amoeba, 155. 
 Amphileptus, 162. 
 Angiocarpi, 94. 
 Angle of vision, 175. 
 Anguillula, 152. 
 Angular, 23. 
 Animal tissues, 113. 
 Ankistrodesmus, 74. 
 Annular vessels, 27. - 
 Annulus, of Ferns, 50. 
 
 , of Fungi, 98. 
 
 , of Mosses, 55. 
 
 Anoplura, 135. 
 
 Ant, 143. 
 
 Antennae, of Entomos- 
 
 traca, 127. 
 Antennaria, 111. 
 Anthers, 37, 39. 
 Antheridia, of Algse, 65. 
 , of Ferns, 52. 
 
 Antheridia, of Mosses, 
 
 Blood, of Fishes, 121. 
 
 61. 
 
 rvf "Rorvf il/io 1 On 
 
 
 Anthophysa, 160. 
 
 Blood-corpuscles, 111. 
 
 Antlia, 145. 
 
 Blood-worm (Chirono 
 
 Apex, 37. 
 
 mus), 143. 
 
 Aphis, 146. 
 
 Blue-bottle, 137. 
 
 Apiculate, 101. 
 
 Blue mould, 106. 
 
 Aplanatic, 177. 
 
 Bone, of Birds, 119. 
 
 Aplanatism, 176. 
 
 , of Eeptiles, 120. 
 
 Apothecia, 92. 
 
 , of Mammals, 114. 
 
 Apple-pulp, 19. 
 
 Bordered dots, 28. 
 
 Apple, skin of, 41. 
 
 Bothrenchyma, 28. 
 
 Arachnida, 130. 
 
 Botrytis, 105. 
 
 Arcella, 156. 
 
 Branchiae, 125. 
 
 Archegonia, of Ferns,52. 
 
 Bread, 23. 
 
 , of Mosses, 62. 
 
 Bryozoa, 125. 
 
 Arcuate, 78. 
 
 Bryum, 59. 
 
 Areolse, 116. 
 
 Buds, 47. 
 
 Areolar tissue, 116. 
 
 Bug, 145. 
 
 Arrow-root, 23. 
 
 Bull's-eye, 6. 
 
 Arteries, 114. 
 
 Bunt, 102. 
 
 Articulata, 127. 
 
 Butterflies, 144. 
 
 Asci, of Fungi, 97. 
 
 Cabbage-butterfly, 145. 
 
 , of Lichens, 92. 
 
 Calicium, 94. 
 
 Ascomycetes, 107. 
 Ash, 25. 
 
 Calyptra, 55. 
 Calyx, 37. 
 
 Aspergillus, 106. 
 
 Calcareous, 66. 
 
 Aspidium, 50. 
 
 Camera lucida, 18. 
 
 Astasia, 160. 
 Atropos, 145. 
 
 Campylodiscus, 78. 
 Canaliculi, 115. 
 
 Bacterium, 86. 
 
 Cancelli, 114. 
 
 Balsam, garden-, 25. 
 , Canada, 12. 
 
 Capillaries, 114. 
 Capillary, 69. 
 
 Bark, 36. 
 
 Carapace, 127. 
 
 Basidia, 98. 
 
 Caraway, 41. 
 
 Bast, 26. 
 
 Carpels, 41. 
 
 Batrachospermese, 72. 
 
 Cartilage, 115. 
 
 Batrachospermum, 72. 
 Beards of Oyster, 125. 
 
 Caterpillars, 145. 
 Cell-contents, 21. 
 
 Bee, 143. 
 
 Cell-formation, 29. 
 
 Beetles, 146. 
 
 Cells, 19. 
 
 Bermuda deposit, 81. 
 Bipinnatifid, 50. 
 
 Cell-wall, 19. 
 Cellular tissue, animal, 
 
 Bivalve, 128. 
 
 116. 
 
 Blood, 114. 
 
 tissue of plants, 20. 
 
 , of Birds, 119. 
 
 Cement, 16. 
 
188 
 
 INDEX. 
 
 Cephalothorai, 130. 
 Ceramiaceae, 69. 
 
 Conferva bombycina,71. 
 floccosa, 71. 
 
 Ceramidia, 66. 
 
 Confervaceae, 70. 
 
 Ceramium nodosum, 69 
 
 Confervoideae, 70. 
 
 rubrum, 70. 
 
 Conidia, 100. 
 
 Cercomonas, 159. 
 
 Coniferae, 26. 
 
 Chsetomium, 110. 
 
 Coniomycetes, 99. 
 
 Chsetophoraceas, 71. 
 
 Conjugation, 73. 
 
 Chara, 88. 
 
 Continuous, 103. 
 
 Cheese-mite, 131. 
 
 Convolvulus, pollen of, 
 
 Chelate, 131. 
 
 39. 
 
 Chickweed, 37. 
 
 Coral, 153. 
 
 , seeds of, 42. 
 
 Corallina, 66. 
 
 Chilodon, 162. 
 
 Corallinaceas, 66. 
 
 Chin of Insects, 147. 
 
 Corallines, 66. 
 
 Chironomus, 143. 
 
 Coremium, 106. 
 
 Chitine, 136. 
 
 Corolla, 37. 
 
 Chloride of calcium, 15. 
 
 Coscinodiscus, 81. 
 
 Chlorococcum, 87. 
 
 Cotton, 118. 
 
 Chlorophyll, 21. 
 Chrysalis, 141. 
 
 Cotton-plant, 33. 
 Cotyledons, 43, 44. 
 
 Chrysanthemum, 25. 
 
 Covers, 6. 
 
 Cilia, 52, 157. 
 
 Coxa, 139. 
 
 Circulation in Plants, 
 
 Crenate, 50. 
 
 31. 
 
 Crocus, pollen-tubes of, 
 
 Cladonia, 93. 
 
 40. 
 
 Cladophora, 71. 
 
 Cruciferae, 44. 
 
 Classification, 164. 
 
 Crustacea, 127. 
 
 Clavarini, 99. 
 
 Crustaceous, 91. 
 
 Clavate, 147. 
 
 Cryptogamic plants, 48. 
 
 Closterium, 74. 
 
 , seeds of, 43. 
 
 Coarse movement, 2. 
 
 Ctenoid, 121. 
 
 Coccidia, 69. 
 
 Cucumber, 42. 
 
 Coccinella, 147. 
 
 Culex, 141. 
 
 Cocconeis, 79. 
 
 Culm, 34. 
 
 Cocoa-nut fibre, 26. 
 
 Cuneate, 79. 
 
 Ccelenterata, 153. 
 
 Cup-moss, 93. 
 
 Coleochaste, 72. 
 
 Curculionidse, 149. 
 
 Coleoptera, 146. 
 
 Cycloid, 121. 
 
 Coleps, 163. 
 
 Cyclops, 128. 
 
 Collomia, seeds of, 42. 
 
 Cypris, 128. 
 
 Colpoda, 161. 
 
 Dacrymyces, 99. 
 
 Columella, of Mosses, 
 
 Daphnia, 129. 
 
 62. 
 
 Dasya, 68. 
 
 , of Mucor, 111. 
 
 Day-flies, 145. 
 
 Complementary co- 
 
 Deal, 26. 
 
 lours, 183. 
 
 Delesseria, 69. 
 
 Compound animals, 126. 
 
 Dematiei, 104. 
 
 Concentric, 114. 
 
 Desmidiaceae, 73. 
 
 Conceptacles, of Algae, 
 
 Diamond-beetles, 149. 
 
 65. 
 
 Diaphragm, 3. 
 
 Conduplicate, 44. 
 
 Diatoma, 78. 
 
 Diatomaceae, 75. 
 
 , fossil, 82. 
 
 , markings on, 81. 
 
 , preparation of, 82. 
 
 Dichotomous, 67. 
 Dicotyledons, leaves of, 
 
 35. 
 
 , seeds of, 43. 
 
 , stems of, 35. 
 Dicranum, 57. 
 Differentiation, 47. 
 Dimidiate, 55. 
 Dinobryina, 160. 
 Dinobryon, 160. 
 Dioecious, 38. 
 Dipping-tubes, 4. 
 Diptera, 137. 
 Dispersion, 178. 
 Division, spontaneous, 
 
 159. 
 
 Dothidea, 108. 
 Dragon-flies, 145. 
 Draparnaldia, 71. 
 Dry rot, 98. 
 Ducts, 27. 
 Dung-beetle, 132. 
 Dytiscus, 148. 
 Eccremocarpus, seeds of, 
 
 42. 
 
 Echinodermata, 153. 
 Echinus, 153. 
 Elbowed, 149. 
 Elder, 25. 
 
 Elements, vegetable, 19. 
 Elytra, 147. 
 Emarginate, 146. 
 Embryo, 42. 
 Embryo-sac, 46. 
 Embryonal vesicles, 46. 
 Enchelys, 161. 
 Encysting, 159. 
 Endogenous, 29. 
 Endogens, leaves of, 35. 
 seeds of, 44. 
 stems of, 44. 
 Enteromorpha, 87. 
 Entomostraca, 127. 
 Entozoa, 151. 
 Ephemera, 145. 
 Epidermis, animal, 117. 
 
 , vegetable, 31. 
 
 Epithemia, 77. 
 
INDEX. 
 
 189 
 
 Equisetum, 34. 
 
 Fucus, 65. 
 
 Erector, 5. 
 
 Fulcra, 110. 
 
 Erysiphe, 110. 
 
 Funaria, 58. 
 
 Euglena, 160. 
 
 Fungi, 96. 
 
 Excipulum, 92. 
 
 Funiculus, 45. 
 
 Excurrent, 57. 
 
 Fusiform, 110. 
 
 Exogenous, 29. 
 
 Galls, 111. 
 
 Exogens, leaves of, 35. 
 
 Gamasus, 132. 
 
 , seeds of, 43. 
 
 Gasteromycetes, 99. 
 
 , stems of, 35. 
 
 Gemmation, 159. 
 
 Eye-pieces, 4, 179. 
 
 Gentles, 140. 
 
 Eyes, compound, 138. 
 Facets, 138. 
 
 Geranium, leaf of, 21. 
 , petals of, 20, 38. 
 
 Favellce, 70. 
 
 Germinate, 43. 
 
 Feathers, 119. 
 
 Gills, of Fungi, 97. 
 
 Feathery, 127. 
 
 , of Mollusca, 125. 
 
 Femur, 139. 
 
 Glands, 40. 
 
 Ferns, 49. 
 
 Glandular, 31. 
 
 , reproduction of, 
 
 tismip 2fi 
 
 llSMlLj '). 
 
 51. 
 
 Gloeocapsa, 88. 
 
 Fertilization, 45. 
 
 Glumes, 37. 
 
 Fibro-cellular tissue, 25. 
 
 Glycerine, 14. 
 
 Fibro-vascular tissue, 
 
 Gnats, 141. 
 
 31. 
 
 Gomphonema, 79. 
 
 Field, 7. 
 
 Gonidia, of Algse, 71. 
 
 Filament, 37. 
 
 , of Lichens, 92. 
 
 , flagelliform, 159. 
 
 Gonium pectorale, 83. 
 
 Fine movement, 2. 
 
 tranquillum, 84. 
 
 Fish-crystals, 122. 
 
 Grape-Fungus, 105. 
 
 Flagelliform, 159. 
 
 Graphis, 94. 
 
 Flax, 26, 118. 
 
 Green fly, 146. 
 
 Flea, 136. 
 
 Gristle, 115. 
 
 Flocci, 103. 
 
 Groundsel, 33. 
 
 Florideae, 66. 
 
 Guard -cells, 34. 
 
 Floscularia, 151. 
 
 Gymnocarpi, 94. 
 
 Flowers, 37. 
 
 Gymnostomum, 56. 
 
 Flustra, 126. 
 
 Gyrosigma angulatum, 
 
 Fly, 138. 
 
 80. 
 
 Fly-blows, 139. 
 
 of-f/vn ofnw 'TO 
 
 dl U , 1 1 lidl UI 1 1 ; | / 
 
 Focus, 171. 
 
 Hairs, 31. 
 
 Foot-jaws, 127. 
 
 o-nirrml 117 
 
 , ciiu nidi, xx I* 
 
 Foramen, 45. 
 
 Hart's-tongue Fern, 51. 
 
 Foramina, 114. 
 
 Harvest-bug, 132. 
 
 Foraminifera, 156. 
 
 Haversian canals, 114. 
 
 Forceps, 4. 
 
 Helvellacei, 107. 
 
 Forked veins, 50. 
 
 Hemiptera, 145. 
 
 Fovilla, 160. 
 
 Hemp, 26. 
 
 Fragilaria, 78. 
 Fronds, 49. 
 
 Hermaphrodite, 38. 
 Heteromita, 160. 
 
 Fruit, 40. 
 
 Hilum, 22. 
 
 Frustules, 75. 
 
 Hoop, 76, 
 
 Fucoideae, 64. 
 
 Humble Bee, 144. 
 
 Hundred-legs, 133. 
 Hyalotheca, 74. 
 Hydnei, 99. 
 Hydra, 153. 
 Hymenium, 98. 
 Hymenomycetes, 97. 
 Hymenoptera, 143. 
 Hyphomycetes, 103. 
 Hypnea, 69. 
 Hypnum, 60. 
 Hysterium, 108. 
 'Illumination, 8. 
 Imago, 141. 
 Imbricate, 56. 
 Incumbent, 44. 
 Indusium, 51. 
 Inflated, 110. 
 Infusoria, 157. 
 Injection, 116. 
 Innovations, 55. 
 Insects, 133. 
 Intercellular passages, 
 
 20. 
 
 Intercellular spaces, 20. 
 Iodine, 22. 
 !haria, 104. 
 Jania, 67. 
 
 Jaws, of Insects, 147. 
 Joints, of Insects, 136. 
 Jute, 26. 
 Knife, 4. 
 Labels, 17. 
 Labial palpi, 134. 
 Labium, 147. 
 Labrum, 147. 
 Lacunas, 115. 
 Lady-bird, 147. 
 Lanceolate, 78. 
 Leaves, 31. 
 Legs, of insects, 139. 
 Lenses, 170. 
 Lentil, 23. 
 Lepidoptera, 144. 
 Lepisma, 134. 
 Liber, 26, 35. 
 Lice, 135. 
 Lichens, 91. 
 Lieberkuhn, 7. 
 Light, 167. 
 Lime, 25. 
 
 Lips, of insects, 147. 
 Lirellse, 94. 
 
190 
 
 INDEX. 
 
 Lithobius, 133. 
 Lithocystis, 67. 
 Live-box, 4. 
 London pride, anthers 
 
 of, 39. 
 
 Longitudinal, 30. 
 Lunate, 147. 
 Lyngbya, 85. 
 Magnification, 175. 
 Magnifying power, 17. 
 Mammalia, 113. 
 Mandibles, of insects, 
 
 147. 
 
 , of Spiders, 130. 
 
 Mantle, 123. 
 Marrow, 114. 
 Matrix, 91, 96. 
 Maxillae, 147. 
 Medium. 168. 
 Medulla,' 35. 
 Medullary sheath, 35. 
 Melanosporeae, 64. 
 Melobesia, 67. 
 Melosira, 79. 
 Membrane, 31. 
 Membranipora, 126. 
 Mentum, 147. 
 Merulius, 98. 
 Micrasterias, 74. 
 Micropyle, of seeds, 46. 
 Microscope, 1. 
 
 , simple, 5. 
 
 Midrib, 50, 
 
 Mignonette, seeds of, 42. 
 Mildew, 101. 
 Mirror, 2, 3. 
 Mitriform, 55. 
 Mollusca, 122. 
 Monadina, 159. 
 Monas, 159. 
 Moniliform, 31. 
 Monocotyledons, leaves 
 
 of, 35. 
 
 , seeds of, 43. 
 
 , stems of, 36. 
 
 Monoecious, 38. 
 Mosses, 54. 
 Moths, 144. 
 Mould of paste, 111. 
 Moulds, 96. 
 Mounting, 10. 
 Mouth of insects, 147. 
 
 Mucedines, 105. 
 Mucor, 111. 
 Muscles, 115. 
 Mushroom, 97. 
 Mustard and cress, 43. 
 , cotyledons of, 44. 
 
 Mycelium, 96. 
 Myriapoda, 133. 
 Nacre, 123. 
 Nassula, 162. 
 Needles, mounted, 4. 
 Nemaspora, 100. 
 Nerves, of leaves, 31. 
 Neuroptera, 145. 
 Newt, 120. 
 
 Nicol's prism, 6, 184. 
 Nitella, 88. 
 Nitzschia, 78. 
 Nodding, 59. 
 Nodule, 79. 
 Nostoc, 86. 
 Nucleolus, 21. 
 Nucleus, 21. 
 
 , of Infusoria, 159. 
 
 , of ovule, 45. 
 
 Oak-apple, 111. 
 Oat, 23. 
 Object-glasses, 2. 
 Oblique, 30. 
 
 light, 9. 
 
 Obovate, 57. 
 Obtuse, 50. 
 
 Ocelli, of Spiders, 130. 
 Oidium, 105. 
 Opegrapha, 94. 
 Operculum, 55. 
 Optic axes, 183. 
 Orange, rind of, 40. 
 Organs, vegetable, 31. 
 Oscillatoria autumnalis, 
 84. 
 
 nigra, 85. 
 
 Oscillatoriaceae. 84. 
 Ovary, of animals, 137. 
 , of plants, 37, 40. 
 
 Ovate, 56. 
 
 O vigorous vesicles, 154. 
 
 Ovisacs, 154. 
 
 Ovules, 45. 
 
 Ovum, 113. 
 
 Oxytricha, 161. 
 
 Oyster-shell, 123. 
 
 Paleze, 37. 
 Palmella, 88. 
 Palmellaceae, 87. 
 Palpi, of insects, 147. 
 Papilla, 39. 
 Papilke, of skin, 116. 
 Papillose, 39. 
 Paramecium, 161. 
 Paraphyses, 61. 
 Parenchyma, 20. 
 Parmelia, 91. 
 Pear, 29. 
 Pearls, 123. 
 Pectinate, 69. 
 Pediastrum, 74. 
 Pedicels, 103. 
 Pencil, 128. 
 Penicillium, 106. 
 Perianth, 37. 
 Pericarp, 40. 
 Perichaetial, 60. 
 Peridiola, 110. 
 Peridium, 99, 100. 
 Perigonial, 61. 
 Perispore, 65. 
 Peristome, 55. 
 Perithecium, 107. 
 Petals, 37, 38. 
 Peziza, 107. 
 Phases, 184. 
 Phragmidium, 101. 
 Physarum, 99. 
 Physomycetes, 110. 
 Pigment, 117. 
 Pileus, 97. 
 Pinnae, 51. 
 Pinnate, 51. 
 Pinnatifid, 50. 
 Pinnularia, 79. 
 Pinnules, 51. 
 Pistil, 37. 
 Placenta, 45. 
 Pleurenchyma, 26. 
 Pleurocarpi, 55. 
 Pleurosigma, 79. 
 Plocamium, 69. 
 Plumose, 127. 
 Plum-stone, 29. 
 Plumule, 43. 
 Podetia, 93. 
 Podophrya, 162. 
 Podura, 134. 
 
INDEX. 
 
 191 
 
 Polariscope, 6. 
 Polarization of light, 
 
 Reproductive organs,48. 
 Reptiles, 120. 
 
 Side condenser, 6. 
 Silk, 118. 
 
 180. 
 
 Resting spores, 83. 
 
 Simple microscope, 5. 
 
 Pollen, 37. 
 
 Reticulated, 54, 129. 
 
 Sines, 168. 
 
 Pollen -granules, 39. 
 
 vessel, 27. 
 
 Siphonaceae, 84. 
 
 Pollen-tubes, 40. 
 
 Rhabdonema, 80. 
 
 Skin, 116. 
 
 Polycystina, 156. 
 
 Rhinotrichum, 107. 
 
 Slides, 6. 
 
 Polypi, 153. 
 
 Rhizome, 49. 
 
 Smut, 102. 
 
 Polypidom, 125. 
 Polypodiaceae, 50. 
 
 Rhizopoda, 155. 
 Rhodomelacese, 67. 
 
 Snapdragon, petals of, 
 39. 
 
 Polypodium, 50. 
 
 Rhodospermeae, 66. 
 
 Snowberry, 42. 
 
 Polyporei, 99. 
 
 Rhodymeniaceae, 69. 
 
 Sori, of Ferns, 50. 
 
 Polysiphonia, 68. 
 
 Rhubarb, 25. 
 
 Spawn, of Fungi, 97. 
 
 Polytrichum, 58. 
 
 Rice, 23. 
 
 Spectrum, 173. 
 
 Polyzoa, 126. 
 
 Richmond earth, 82. 
 
 Spermatia, 93. 
 
 Polyzoary, 126. 
 
 Rings, annual, 36. 
 
 Spermatozoa, of Algae,6 5. 
 
 Poppy, seeds of, 42. 
 
 Roe of fishes, 122. 
 
 , of Ferns, 52. 
 
 Pore, 109. 
 
 Rootlets, 36. 
 
 nf TTisVipq 1 99 
 
 j CM JjlMlL^, J _j-j. 
 
 Pores, in wood, 28. 
 
 Roots, 36. 
 
 , of Mosses, 61. 
 
 Porous cells, 25. 
 
 Rostrate, 56. 
 
 Spermogonia, of Fungi, 
 
 Potato, 22, 
 
 Rostrum, 131. 
 
 101. 
 
 Potato-fungus, 105. 
 
 Rotating disk, 6. 
 
 , of Lichens, 92. 
 
 Primine, 45. 
 
 Rotation, 31. 
 
 Spharia, 109. 
 
 Primordial utricle, 21. 
 
 Rotatoria, 149. 
 
 fragiformis, 104. 
 
 Primrose, pollen of, 39. 
 
 Rotifer, 150. 
 
 Sphagnum, 56. 
 
 Prismatic, 24. 
 
 Rotifera, 149. 
 
 Spicula, 157. 
 
 Proboscis, 146. 
 
 Sacculi, gastric, 158. 
 
 Spiders, 130. 
 
 Prolegs, 145. 
 
 San Fiori deposit, 82. 
 
 Spiderwort, 31. 
 
 Prosenchyma, 25. 
 
 Sarcode, 155. 
 
 Spinnerets, 131. 
 
 Prothallium, 51. 
 
 Scalariform ducts, 49. 
 
 Spiracles, 134. 
 
 Protoplasm, 21. 
 
 Scales, of fishes, 121. 
 
 Spiral cells, 25. 
 
 Protozoa, 155. 
 
 , of Podura, 134. 
 
 Spiral vessels, 27. 
 
 Pterodina, 151. 
 
 , of insects, 144. 
 
 Spirit-lamp, 5. 
 
 Puccinia, 101. 
 
 Scar of seeds, 46. 
 
 Spirogyra, 72. 
 
 Puff-balls, 99. 
 
 Scenedesmus, 74. 
 
 Spirulina, 85. 
 
 Pulex, 135, 
 
 Schizogonium, 86. 
 
 Sponges, 156. 
 
 Pulvilli, 139. 
 
 Scolopendrium, 51. 
 
 Spongidae, 156. 
 
 Puncta, 79. 
 
 Sea-weeds, 64. 
 
 Sporangium, of Ferns, 
 
 Pupa, 141. 
 
 Sections, 30. 
 
 54. 
 
 Quadrate, 147. 
 
 Secundine, 45. 
 
 Spores, 50. 
 
 Racodium, 111. 
 
 Seeds, 42. 
 
 Sporocybe, 104. 
 
 Eadiata, 153. 
 
 Selenite, 24. 
 
 Sporophylles, 69. 
 
 Radicle, 43. 
 
 Sepals, 37. 
 
 Stage, 2. 
 
 Ramenta, 49. 
 
 Septa, 99. 
 
 Stamens, 37. 
 
 Eaphides, 24. 
 
 Septate, 100. 
 
 Starch, 22. 
 
 Receptacles, of Algse, 
 
 Serrate, 51. 
 
 Starfishes, 153. 
 
 657 
 
 Sertularia, 154. 
 
 Stellate, 31. 
 
 , of secretion, 40. 
 
 Sessile, 54. 
 
 Stems, 35. 
 
 Red Spider, 132. 
 
 Setaceous, 133. 
 
 Stentor, 163. 
 
 Reflexion, 169. 
 
 Seta, 129. 
 
 Sterigmata, 98. 
 
 Refraction, 168. 
 
 of Infusoria, 158. 
 
 Steropus, 146. 
 
 Reindeer moss, 93. 
 
 Shell, 123. 
 
 Stichidia, 68. y/i 
 
192 
 
 INDEX, 
 
 Stigma, 37. 
 Stilbacei, 103. 
 Sting, of Wasp, 144. 
 Stinging-organs, 154. 
 Stings, 33. 
 Stipes, 76, 97. 
 Stomata, 34. 
 Stomoxys, 141. 
 Striated, 33. 
 Stroma, 108. 
 Strurna, 58. 
 Style of plants, 37. 
 Stylospores, 100. 
 Suctorial, 135. 
 Suture, 73, 76. 
 Synedra, 78. 
 Synura, 83. 
 Tabellaria, 79. 
 Tabular, 83. 
 Tangential, 30. 
 Tape- worm, 152. 
 Tarsus, 139. 
 Tentacles, 124, 153. 
 Testa, 42. 
 Tetraspores, 167. 
 Thalamium, 92. 
 Thallus, 91. 
 Thecce, 50. 
 Thorax, 129. 
 Thread- worm, 152. 
 Tibia, 139. 
 
 Tissues, vegetable, 19. 
 Toad-stools, 96. 
 Tongue, of Mollusca, 
 
 123. 
 
 Tortula, 57. 
 Torula, 100. 
 Tourmaline, 181. 
 Tous les mois, 24. 
 
 Trabeculas, 59. 
 Trachea, 134. 
 Trachelomonas, 160. 
 Tradescantia, 31. 
 Transverse, 148. 
 
 section, 30. 
 
 Tremellini, 99. 
 Trichothecium, 105. 
 Triton, 120. 
 Trochanter, 139. 
 Trombidiurn, 132. 
 Truffle, 108. 
 Truncated, 27. 
 Tuberacei, 108. 
 Tubercularia, 103. 
 Tuberculate, 101. 
 Tubular cells, 25. 
 Tufts, 25. 
 Turnip-fly, 146. 
 Turpentine, 27. 
 Ulothrix, 86. 
 Ulva, 87. 
 Ulvaceoe, 86. 
 UmbellifenB, 41. 
 Uncorrected lens, 178. 
 Uniseptate, 101. 
 Uredo, 102. 
 
 Candida, 102. 
 
 caries, 102. 
 
 linearis, 109. 
 
 rubigo, 109. 
 
 segetum, 102. 
 
 Vaginicola, 163. 
 Vaginule, 62. 
 Valve, 76. 
 Vascular tissue, 27. 
 Vaucheria, 84. 
 Vegetable elements, 19. 
 organs, 31. 
 
 Veil, 98. 
 
 Veins, of animals, 114. 
 
 , of leaves, 31, 35. 
 
 Velum, 98. 
 Vertebra, 113. 
 Vertebrata, 113. 
 Vesicles, con tractile, 159. 
 , embryonal, 46*. 
 
 Vessels, 27. 
 Vibrio spirillum, 85. 
 Vision, 174. 
 Vitta3, of seeds, 40. 
 Volva, 98. 
 Volvocineae, 83. 
 Volvox, 83. 
 Vorticella, 162. 
 Wallflower, anthers of, 
 
 39. 
 
 Wasp, 143. 
 Water-beetle, 148. 
 Web, spider's, 131. 
 Wheat, cotyledon of, 45. 
 Wheat-flour, 23. 
 Wheel-animalcules, 150. 
 Whelk, 123. 
 Wine-cellarFungus, 111. 
 Winged seeds, 42. 
 Winter ova, 128. 
 Wood-cells, 25. 
 Wood-louse, 127. 
 Woody fibre, 25. 
 
 tissue, 25. 
 
 Wool, 118. 
 Xanthidia, 75. 
 Yeast, 106. 
 Zygnema, 72. 
 Zygnemaceae, 2. 
 Zoospores, 71 
 
 TAYLOR AND FRANCIS, PBINTBB8, RED HON COURT, FLEET STRBKT. 
 
UNIVERSITY OF CALIFORNIA LIBRARY 
 
 THIS BOOK IS DUE ON THE LAST DATE 
 STAMPED BELOW 
 
 
 SEP 3 
 
 19 '823 
 
 JUN 2 6 1950 
 DEC 28195Q 
 
 JUN i 8 ^ 
 
 6 1921 
 
 30 
 
 MAR 2 2 1946 
 
 MAY 3 1946 
 
 NOV 2 2 1948 
 
 NOV 2 1963 
 
 , 2 1 
 
 50m-! 
 
y.W