TWENTIETH CENTURY TEXT-BOOKS 
 
 A. F. NIGHTINGALE, PH.D., LL.D. 
 
 FORMERLY SUPERINTENDENT OF HIGH SCHOOLS, CHICAGC
 
 TWENTIETH CENTURY TEXT-BOOKS 
 
 ANIMAL FORMS 
 
 A TEXT-BOOK OF ZOOLOGY 
 
 BY 
 
 DAVID S. JORDAN, M. S., M. D., PH. D., LL. D 
 
 PRESIDENT OF LELAND STANFORD JUNIOR UNIVERSITY 
 AND 
 
 HAROLD HEATH, PH. D. 
 
 PROFESSOR IN LELAND STANFORD JUNIOR UNIVERSITY 
 
 NEW YORK 
 
 D. APPLETON AND COMPANY 
 1902
 
 COPYRIGHT, 1902 
 BY D. APPLETON AND COMPANY 
 
 Published Mny, 1902
 
 PKEFACE 
 
 THE present volume is designed to meet the needs of 
 the beginning student of zoology. Accordingly, technical 
 and scientific names have been avoided as far as possible, 
 and those used are fully explained in the text or elsewhere. 
 The opening chapters deal with the characteristics of living 
 things, and, in contrasting animals and plants, attempt to 
 bring into relief the distinguishing marks of all animals. 
 Then follows a discussion of the cell and protoplasm, pre- 
 paring the way for the examination of a series of animals 
 representative of each of the great groups, from the sim- 
 plest to the most complex. These are considered from the 
 view-point of structure ; but considerable attention is also 
 paid to the functions of their parts, to their habits and life- 
 history, so that while the representatives examined are, for 
 the sake of simplicity, relatively few in number, they are, it 
 is believed, thoroughly typical. Hence, with a knowledge 
 of the facts presented, the student should have a broad 
 view of the animal kingdom, and a foundation on which to 
 base future study and observation. It is perhaps unneces- 
 sary to add that from the study of books alone no one can 
 really make such knowledge his own. A personal acquaint- 
 ance with even a few animals in their native haunts, and 
 an understanding of the structure and the function of their
 
 vi ANIMAL FORMS 
 
 parts gained from dissection and experiment, is essential to 
 a full comprehension of what the student learns from text- 
 book and teacher. 
 
 The greater number of illustrations are new, and have 
 been drawn or photographed from living or preserved ma- 
 terial. When not otherwise accredited, the drawings have 
 been made by Miss Mary H. AVellman and J. Carter Beard, 
 to whom the authors extend their sincere thanks. Our 
 obligations are also due to Mr. Walter K. Fisher, who has 
 made the drawings of the vertebrate dissections ; to Messrs. 
 A. L. Melander and C. T. Brues, of Chicago, 111. ; Mr. Wm. 
 H. Fisher, of Baltimore, Md. ; Kev. H. K. Job, of Kent, 
 Conn. ; Mr. Wm. Graham, of Pasadena, Cal. ; and Dr. K. W. 
 Shufeldt, of New York city, for numerous photographs. 
 
 DAVID STABB JOBDAN, 
 HABOLD HEATH.
 
 CONTENTS 
 
 CHAPTER 
 
 PAGE 
 1 
 
 II THE CELL AND PROTOPLASM . . 
 
 7 
 
 III. THE PROTOZOA . .... 
 IV. THE SPONGES . . . . . . 
 
 V. THE Co3LENTERATES . -. ' . 
 
 . 11 
 . 19 
 29 
 
 V>VI. THE WORMS . . " 
 VII. ANIMALS OF UNCERTAIN RELATIONSHIPS^". 
 
 \yni. MOLLUSKS 
 
 IX. ARTHROPODS. CLASS CRUSTACEA .... 
 X. ARTHROPODS. CLASS INSECTS . ' , . 
 XL ARTHROPODS. CLASS ARACHNID A .... 
 
 XII ECHINODERMS 
 
 . 44 y 
 
 . 66 
 
 . 93 
 . 114 
 . 133 
 140 
 
 XIII. THE CHORDATES 
 XIV. THE FISHES^. 
 
 'N^xXV. THE AMPHIBIANS "^ . . .... 
 
 . 151 
 
 . 154 
 
 \_XVI. THE REPTILES s. .' . 
 .:VIL THE BIRDSX" 
 -XVIIL THE MAMMALS / 
 
 vii 
 
 1 
 
 . 184v/ 
 . 201 
 . 2Q5^
 
 ANIMAL FORMS 
 
 CHAPTEE I 
 
 INTRODUCTION 
 
 tlBfeT) 
 
 1. Divisions of the subject. Biology is the science which 
 
 treats of living things in all their relations. It is sub- 
 divided into Zoology, the science which deals with animals, 
 and Botany, which is concerned with plants. The field 
 covered by each of these branches is very extensive. 
 Within the scope of zoology are included all subjects bear- 
 ing on the form and structure of animals, on their devel- 
 opment, and on their activities, including the consideration 
 of their habits and the wider problems of their distribution 
 and their relations to one another. 
 
 These various subjects are often conveniently grouped 
 under three heads : Morphology, which treats of the form 
 and structure or the anatomy of organisms ; Physiology, 
 which considers their activities ; and Ecology, which in- 
 cludes their relations one to another and to their surround- 
 ings. All the phases of plant or animal existence may be 
 considered under one or another of these three divisions. 
 
 2. The difference between animals and plants. Generally 
 speaking, we have little difficulty in seeing that the objects 
 about us are either living or lifeless ; but the boundary line 
 between the two great divisions of living things, the animals 
 and plants, can not always be so clearly drawn. This is es- 
 pecially true of the simpler forms of life which frequently 
 combine both animal and plant characteristics ; but in the 
 
 1
 
 2 ANIMAL FORMS 
 
 greater number of more highly developed species the line 
 of separation is clearly marked. It is very easy, for example, 
 to distinguish the oak-tree or the rose from a horse or a 
 butterfly, and, as we shall see, the differences are not based 
 merely on outward appearance. 
 
 In the oak-tree, for example, the roots reaching down 
 into the earth, with the branches and leaves spreading out 
 into the air and sunlight, are admirably fitted for taking up 
 the food, which consists of very simple materials, less com- 
 plex than those forming the diet of an animal. This 
 permits a continuous existence in one place, and accord- 
 ingly we note the entire absence of locomotion and the or- 
 gans controlling it, which form so conspicuous a part of the 
 body of an animal. Also in the production of flowers and 
 seeds, and in the growth of the seed into the tree, we detect 
 many characteristics peculiar to plants. 
 
 3. Characteristics of an animal On the other hand, the 
 squirrel, for example, or any other animal, is unable to sub- 
 sist on water, air, and elements from the soil. These crea- 
 tures demand the highly diversified materials found in the 
 bodies of plants and of animals. Such being the case, they 
 do not remain anchored to one spot (except in a relatively 
 few cases), but are compelled to lead an active existence. 
 The power of voluntary movement, or movement in response 
 to internal impulse, is thus the first and one of the most 
 striking peculiarities of animals. 
 
 In the second place, the food of plants enters the body 
 in a soluble condition and is readily transferred to the or- 
 gans requiring it. While in the animals, the nutritive ma- 
 terials pass into the body in an insoluble state and de- 
 mand a varied preliminary treatment, usually within a 
 special digestive tube, before they are fit to be absorbed. 
 In the squirrel, by way of illustration, the food is first 
 ground to a pulp by the action of the teeth, and, moistened 
 with saliva, is swallowed and passed into the stomach, 
 where it is subjected to the solvent action of the gastric
 
 ANIMAL FORMS 
 
 juice. From the stomach it is made to enter the intestine, 
 and is further acted upon by fluids from the liver, the 
 pancreas, and the glands of the 
 intestines themselves. Thus 
 treated it becomes changed from 
 an insoluble state into a fluid 
 which readily penetrates the 
 coats of the digestive tract. 
 
 Many of the organs of the 
 body are placed at a considera- 
 ble distance from the food as 
 it comes through the coats of 
 the stomach and intestine. In 
 order to supply them with the 
 necessary nourishment a distrib- 
 uting apparatus is required. 
 This is the office performed by 
 the circulatory system, for as 
 rapidly as the food penetrates 
 the walls of the digestive tract 
 it enters the blood, and by the 
 beating of the heart is driven 
 to all parts of the body, which 
 are thus continually kept in a 
 state of repair. The blood serves 
 also to remove waste substances 
 from the various structures or 
 organs of the animal body and 
 to transfer them to the kidneys, 
 skin, or lungs, which effect their 
 removal from the body. 
 
 4. Muscular and nervous sys- 
 tems. Owing to the fact that 
 animals, as a rule, are compelled 
 to move about in search of food, we find two highly devel- 
 oped systems, the muscular and nervous, which are absent 
 
 FIG. 2. Diagram of heart and blood- 
 vessels of the squirrel or other 
 mammal, a.o., aorta ; h, vessels 
 of head ; l.a., left auricle ; Lex., 
 vessels of lower extremities ; lg., 
 lung ; l.v., left ventricle ; p.a., 
 pulmonary artery ; p.v., pulmo- 
 nary vein ; r.a., right auricle ; 
 r.v., right ventricle ; v., vessels of 
 viscera. Arteries are represented 
 by heavy walls.
 
 INTRODUCTION 5 
 
 in the plants. The first of these, constituting what is usu- 
 ally known as the lean meat, is a relatively complex system 
 of organs, differing widely according to the work performed. 
 In the higher animals the squirrel, for example there are 
 not less than five hundred muscles, which are under the 
 control of the nervous system. 
 
 The nervous system consists of the brain and spinal 
 cord, which in the squirrel are concealed and protected 
 
 FIG. 3. Skeleton of squirrel, showing its relation to the body. 
 
 within the skull and back-bone. From them many nerves 
 pass outward to the muscles, and as many pass inward from 
 the eye, ear, nose, tongue, or skin. By the action of these 
 sense-organs the animal determines the nature of its sur- 
 roundings, detects its food, recognizes the presence of its 
 enemies, and is thus able to direct its movements to the 
 greatest advantage. 
 
 5. Multiplication of animals. The organs thus far con- 
 sidered serve to perpetuate the animal as an individual ; 
 but some provision must also be made for the continuance 
 of the race. In the economy of nature each animal before
 
 6 ANIMAL FORMS 
 
 its death should leave offspring to take the place of the 
 parent when it falls from the ranks. This is effected in 
 various ways. In some of the simpler animals the body 
 may divide into two equal parts, each of which becomes a 
 complete individual. In other cases the animal detaches 
 a relatively small portion of its body, much as a gardener 
 cuts a slip from a plant, and this likewise develops into a 
 new organism. In the greater number of animals, very 
 clearly illustrated by the birds, eggs are produced which 
 under favorable conditions develop into an organism resem- 
 bling the parents. 
 
 6. Summary. Animals are thus seen to lead active, busy 
 lives, collecting food, avoiding enemies, and producing and 
 and caring for their young. While the activities of all 
 animals are directed to their own preservation and to the 
 multiplication of their kind, these processes are carried on 
 in the most diverse ways. The manner in which an organ 
 or an organism is made, and the method by which it does 
 its work, are mutually dependent one on the other. As 
 there is an enormous number of species of animals, each 
 differently constructed, there is, accordingly, a very great 
 variety of habits. As we shall see, the lower forms are 
 remarkably simple in their construction, and their mode of 
 existence is correspondingly simple. In the higher types 
 a much greater complexity exists, and their activities are 
 more varied and are characterized by a high degree of elabo- 
 ration. In every case, the animal, whether high or low, is 
 fitted for some particular haunt, where it may perform its 
 work in its own special way and may lead a successful life 
 of its own characteristic type.
 
 CHAPTER II 
 
 THE CELL AND PROTOPLASM 
 
 7. Cells. If we examine very carefully the different parts 
 of a squirrel under the high powers of the microscope 
 we find that they are composed of a multitude of small 
 structures which bear the same relations to the various 
 organs that bricks or stones do to a wall ; and if the inves- 
 tigation were continued it would be found that every or- 
 ganism is composed of one or more of these lesser elements 
 which bear the name of cells. In size they vary exceedingly, 
 and their shapes are most diverse, but, despite these differ- 
 ences, it will be seen that all exhibit a certain general re- 
 semblance one to the other. 
 
 8. Shape of cells. In many of the simpler organisms 
 the component cells are jelly-like masses of a more or less 
 spherical form, but as we ascend the scale of life the condi- 
 tion of affairs becomes much more complex. In the squir- 
 rel, for example, we have already noted the presence of 
 various organs for carrying on different functions, such as 
 those of digestion, circulation, and respiration ; and, further, 
 the cells composing these various parts have been modified 
 in accordance with the duties they have to perform. In 
 the muscles the cells are long and slender (Fig. 4, D) ; 
 those forming the nerves and conveying sensations to and 
 from all parts of the body, like an extensive telegraph sys- 
 tem, are excessively delicate and thread-like ; in the skin, 
 and lining many cavities of the body, where the cells are 
 united into extensive sheets, they range in shape from high 
 and columnar to flat and scale-like forms (Fig. 4, E, F, G). 
 
 2 7
 
 8 ANIMAL FORMS 
 
 The cells of the blood present another type (Fig. 4, B) ; and 
 so we might pass in review other parts of the body, and con- 
 tinue our studies with other groups of animals, always find- 
 ing new forms dependent upon the part they play in the 
 organism. 
 
 9. Size of cells. Also in the matter of size the greatest 
 variations exist. Some of the smallest cells measure less 
 than one micromillimeter (j^f^o f an i ncn ) in diameter. 
 Over five hundred million such bodies could be readily 
 stowed away into a hollow sphere the size of the letter be- 
 ginning this sentence. In a drop of human blood of the 
 same size, between four and five million blood-cells or cor- 
 puscles float. And from this extreme all sizes exist up to 
 those with a diameter of 2.5 or 5 c.m. (one or two inches), 
 as in the case of the hen's or ostrich's egg. On the average 
 a cell will measure between .025 to .031 m.m. ( TT5 Vfr and 
 -g-J-o of an inch) in diameter, a speck probably invisible to 
 the unaided eye. While the size and external appearance 
 of a cell are seen to be most variable, the internal structures 
 are found to show a striking resemblance throughout. All 
 are constructed upon essentially the same plan. Differ- 
 ences in form and size are superficial, and in passing to a 
 more careful study of one cell we gain a knowledge of the 
 important features of ali. 
 
 10. A typical cell. Some cell, for example that of the 
 liver (Fig. 4, A), may be chosen as a good representative of 
 a typical cell. To the naked eye it is barely visible as a 
 minute speck ; but under the microscope the appearance is 
 that of so much white of egg, an almost transparent jelly- 
 like mass bearing upon its outer surface a thin structure- 
 less membrane that serves to preserve its general shape and 
 also to protect the delicate cell material within. The com- 
 parison of the latter substance to egg albumen can be car- 
 ried no further than the simple physical appearance, for 
 albumen belongs to that great class of substances which 
 are said to be non-living or dead, while the cell material
 
 THE CELL AND PROTOPLASM 9 
 
 or protoplasm, as it is termed, is a living substance. We 
 know of no case where life exists apart from protoplasm, 
 and for this reason the latter is frequently termed the 
 physical basis of life. 
 
 In addition to the features already described, the proto- 
 plasm of every perfect cell is modified upon the interior to 
 
 FIG. 4. Different types of cells composing the body of the squirrel or other highly 
 developed animal. A, liver-cell ; /, food materials ; n, nucleus. B, blood-cell. 
 C, nerve-cell with small part of its fiber. D, muscle fiber. E, cells lining the 
 body cavity. F, lining of the windpipe. G, section through the skin. Highly 
 
 form a well-defined spherical mass known as the 
 Other structures are known to occur in the typical cell. 
 Experiment shows that the nucleus and cell protoplasm are 
 absolutely indispensable, whatever their size and shape, and
 
 10 ANIMAL FORMS 
 
 therefore we are at present justified in defining the cell as 
 a small mass of protoplasm enclosing a nucleus. 
 
 11. Structure of protoplasm. When seen under a glass 
 of moderate power protoplasm gives no indication of any 
 definite structure, and even with the highest magnifica- 
 tion it presents appearances which are not clearly under- 
 stood. According to the commonly accepted view, it con- 
 sists of two portions, one, the firmer, forming an excessively 
 delicate mesh work (Fig. 4, A) enclosing in its cavities 
 the second more fluid part. Therefore, when highly mag- 
 nified, the appearance would be essentially like a sponge 
 fully saturated with water ; but it should be remembered 
 that in the protoplasm the sponge work, and possibly the 
 fluid part, is living, and that both are transparent. 
 
 There are reasons for thinking that the structure and 
 the composition of protoplasm may change somewhat under 
 certain circumstances. It certainly is not everywhere alike, 
 for that of one animal must differ from that of another, and 
 different parts, such as the liver and brain, of the same form 
 must be unlike. These differences, however, are minor 
 when compared to the resemblances, for, as we shall see, 
 this living substance, wherever it exists, carries on the pro- 
 cesses of waste, repair, growth, sensation, contraction, and 
 the reproduction of its kind.
 
 CHAPTER III 
 
 THE PROTOZOA 
 
 12. Single-celled and many-celled animals. In almost 
 every portion of the globe there are multitudes of animals 
 whose body consists of but a single cell ; while those forms 
 more familiar to us, and usually of comparatively large 
 size and higher development, such as sponges, insects, 
 fishes, birds, and man himself, are composed of a multitude 
 of cells. For this reason the animal kingdom has been 
 divided into two great subdivisions, the Protozoa including 
 all unicellular forms and the Metazoa embracing those of 
 many cells. 
 
 13. Single-celled animals. The division of the Protozoa 
 comprises a host of animals, usually of microscopic size, 
 inhabiting fresh or salt water or damp localities on land in 
 nearly every portion of the globe. The greater number 
 wage their little, though fierce, wars on one another with- 
 out attracting much attention ; others, in the sharp struggle, 
 have been compelled to live upon or within the bodies of 
 other animals, and many have become notorious because of 
 the diseases they produce under such circumstances. A 
 few are in large measure responsible for the phosphores- 
 cence of the sea ; and still others have long been favorite 
 objects of study because of their marvelous beauty. Adapted 
 for living under diverse conditions, the bodily form differs 
 greatly, and yet all conform to three or four principal types, 
 of which we may gain a good idea from the study of a few 
 representative forms. 
 
 11
 
 12 
 
 ANIMAL FORMS 
 
 14. The Amoeba. Among the simplest one-celled ani- 
 mals living in the ooze at the bottom of nearly every fresh- 
 water stream or pond is the Amoeba (Fig. 5, A), whose body 
 is barely visible to the unaided eye. Under the microscope 
 
 FIG. 5. A, the Amoeba, highly magnified, showing c. r., pulsating vacnole ; /, food 
 particle ; n, nucleus. The arrows show the direction of movement. B, shape of 
 same individual 30 seconds later. C, an amoeba-like animal (Difflugia) partially 
 enclosed in a shell. D, an Amoeba in the process of division. E, Gromia, another 
 shelled protozoan (after SCHULZE). 
 
 it is seen to consist of an irregular, jelly-like mass of proto- 
 plasm totally destitute of a cell wall. Unlike those animals 
 with which we are familiar, the body constantly changes its 
 shape. A rounded bud-like projection will be seen to appear 
 on one side of the body and the protoplasm of adjacent 
 regions flows into it, thereby increasing its extent. Similar 
 projections at the opposite end of the cell are withdrawn, 
 and their substance may flow into the newly formed lobe, 
 which gradually swells in size and pushes forward. Thus, 
 by constantly advancing the front part of the body and
 
 THE PROTOZOA 13 
 
 , retracting the hinder portion, the cell glides or flows along 
 from place to place. 
 
 Upon meeting with any of the smaller organisms upon 
 which it lives, projections from the body are put out which 
 gradually flow around the prey and it becomes pressed into 
 the interior of the cell. The process is not unlike pushing 
 a grain of sand into a bit of jelly. There is no mouth. 
 Any point on the surface serves for the reception of food. 
 Oxygen gas also is taken into the body all over the surface, 
 and wastes and indigestible material are cast out at any 
 point. Nothing exists in these simple forms comparable to 
 the complex systems of organs that carry on these processes 
 in the squirrel. 
 
 The bodily size of animals is limited, and to this general 
 rule the Amceba is no exception, for upon gaining a certain 
 size, the nucleus divides into two exactly similar portions, 
 and very soon afterward the rest of the body separates into 
 two independent masses of equal size (Fig. 5, D), each of 
 which, when entirely free, contains a nucleus. In this way 
 two daughter amrabae are formed possessing exactly the 
 characters of the parent save that they are of smaller size ; 
 but it is usually not long before they reach their limit of 
 growth, when division occurs again, and so on, generation 
 after generation. 
 
 It not infrequently happens, however, that the pond or 
 stream, in which the Amoeba and other Protozoa live, dries 
 up for a portion of the year. In such an event the body 
 assumes a spherical shape, develops a firm, horn-like mem- 
 brane about itself, and thus encysted it withstands the sum- 
 mer's heat and dryness and may be transported by the wind, 
 or otherwise, over great distances. When the conditions 
 again become favorable the wall ruptures and the Amoeba 
 emerges to repeat its life processes. 
 
 15. Some relatives of the Amoeba. All amoeba-like forms, 
 to the number of perhaps a thousand species, possess this 
 same method of locomotion, but many present some inter-
 
 14 ANIMAL FORMS 
 
 esting additional characters. For example, the form repre- 
 sented in Fig. 5, C, constructs a sac-like skeleton of tiny 
 pebbles cemented together, into which it may withdraw for 
 protection. Others construct similar envelopes of lime or 
 flint, and still others, as they continue to grow, build on 
 additional chambers, giving rise to a great variety of forms 
 often of wonderful beauty. In the tropics, particularly, 
 some of the shelled Protozoa are so abundant that they may 
 impart a whitish tinge to the water, and in some places 
 their empty shells on falling to the bottom form immense 
 deposits. The chalk cliffs of England are in large measure 
 made up of such shells. 
 
 16. The Infusoria. A little over two hundred years ago 
 it was discovered that wherever water remained stagnant it 
 became favorable for the rapid multiplication of a large 
 number of species of Protozoa which live in such situations. 
 These are known as Infusoria, and, like the preceding spe- 
 cies, are usually of microscopic size and of the most varied 
 shapes. The first striking feature of their organization is 
 the presence of a delicate though relatively firm external 
 cell membrane known as the cuticle, which preserves a defi- 
 nite shape to the body. Such a method of locomotion as 
 exists in the preceding group is consequently an impossi- 
 bility, but other and more highly developed structures per- 
 form the office. These latter organs are of two types, and 
 their general characteristics may be readily understood 
 from an examination of a few species living in the same 
 localities as the Ammla. 
 
 17. The Euglena. The first type exists in the common 
 fresh-water organism known as Euglena, represented in 
 Fig. 6, A. Here the spindle-shaped body is surrounded by 
 a delicate cuticle perforated at one point, where a funnel- 
 shaped depression, the gullet, leads into the soft proto- 
 plasmic interior. From the base of this depression the 
 protoplasm is drawn out in the form of a delicate whip-like 
 process known as the flagellum. This structure, always
 
 THE PROTOZOA 
 
 permanent in form, constantly beats backward and forward 
 with great rapidity in a general direction represented in 
 the diagram (Fig. 6, c). The movement from a to b is 
 much more rapid than the reverse, from b to a, which 
 results, like the action of the human arm in swimming, in 
 driving the organism forward. Not only does the flagel- 
 lum serve the purpose of locomotion, but it also produces 
 currents in the water which 
 may serve to bear minute 
 organisms down into the 
 gullet, whence they read- 
 ily pass into the soft pro- 
 
 3. 6. Flagellate Infusoria. A, 
 Euglena xlridis ; c, pulsating 
 vacuole ; e, eye-"spot ; g, gullet ; 
 w, nucleus ; t, flagellum. B, Co- 
 dosiga, with collar surrounding 
 the flagellum. C, diagram illus- 
 trating the action of the flagel- 
 lum. All figures greatly enlarged. 
 
 c.v. 
 
 FIG. 7. Paramcecium aurelia, a 
 ciliate infusorian. c, cilia; c.v., 
 pulsating vacuotes ; /, food 
 particles ; g, gulfet ; m, buccal 
 groove ; . nucleus. 
 
 toplasm of the body, there to undergo the processes of di- 
 gestion and assimilation. In some forms the protoplasm in 
 the region of the flagellum is drawn out in the form of a 
 collar (Fig. 6, B), whose vibratory motion also aids in con- 
 veying and guiding food into the body. 
 
 18. The Slipper Animalcule. The second type of loco- 
 motor organ may be understood from a study of the
 
 16 
 
 ANIMAL FORMS 
 
 Slipper Animalcule (Paramcecium, Fig. 7), abundant in 
 stagnant water. In this form the cuticle surrounding the 
 somewhat cylindrical body is perforated by a great number 
 of minute openings through which the 
 internal protoplasm projects in the form 
 of delicate threads. Each process, 
 termed a cilium, works on the same 
 principle as the flagellum, but it beats 
 with an almost perfect rhythm and in 
 unison with its fellows, drives the an- 
 imal hither and thither with considera- 
 ble rapidity. 
 
 On one side of the body is a furrow 
 which deepens as it runs backward and 
 finally passes into the gullet (#), which 
 leads into the interior of the body. 
 Throughout the entire extent it is lined 
 with cilia which create strong currents 
 in the surrounding water and in this 
 way conduct food down the gullet into 
 the body. Embedded in the outer sur- 
 face of the body, in among the cilia, 
 are also a number of very minute sacks, 
 each containing a coiled thread which 
 may be discharged against the body of 
 any intruder, so that this form is sup- 
 plied with actual organs of defense. 
 Two pulsating vacuoles (c.v.) or simple 
 kidneys are also present, consisting of a 
 central reservoir into which a number 
 of radiating canals extend. 
 
 19. The Bell Animalcule and other 
 species. The Bell Animalcule (Vorti- 
 cella, Fig. 8) is often found in the same situations as the 
 Slipper Animalcule, which in certain respects it resembles. 
 It is generally attached by a slender stalk, and where many 
 
 FIG. S.Vorticella, an at 
 tached ciliate infusori 
 an, highly magnified, a 
 fully extended Individ 
 ual ; c.v., pulsating va 
 cuole ; ff, gullet ; n, mi 
 cleus. b, contractec 
 specimen, c, small free 
 swimming individual, 
 which unites with a sta- 
 tionary individual (one 
 partly united is shown 
 m specimen b).
 
 THE PROTOZOA 17 
 
 are growing together they appear like a delicate growth 
 of mold upon the water weed. The stalk is peculiar in 
 being traversed by a muscle fiber arranged in a loose spiral, 
 which upon any unusual disturbance contracts together 
 with the body into the form shown in Fig. 8, b. 
 
 These few examples serve to show the general plan of 
 organization and the method of locomotion of the Infuso- 
 ria ; but, as upward of a thousand species exist, with widely 
 differing habits, many interesting modifications are present. 
 Some have been driven in past time to adopt a parasitic 
 mode of life within the bodies of other animals. At pres- 
 ent they are devoid of locomotor organs, and as they absorb- 
 nutritive fluids through the surface of the body all traces 
 of a mouth are also absent. The reproductive processes 
 also are peculiar, but they do not concern us now. 
 
 20. Characteristics common to the Protozoa. We have 
 now studied the principal structures which serve in loco- 
 motion among these simple one-celled forms, also the means 
 by which they catch their food, and we shall now glance at 
 the internal processes, Avhich are much the same in all. 
 
 After the food has been taken into the cell, it is prob- 
 ably acted upon by some digestive fluid, for it soon assumes 
 a granular appearance and finally undergoes complete solu- 
 tion. In every case the oxygen is absorbed through the 
 general surface of the body, and uniting with the living 
 substance, as in the squirrel, liberates the energy necessary 
 for the performance of the animal's life work. The wastes 
 thus produced in a large number of forms simply filter out 
 from the body without the agency of anything comparable 
 to a kidney, but in several species they are borne to a 
 definite spot, the pulsating vacuole (Figs. 5, 7, 8, c.v.), where 
 they gradually accumulate into a drop about the size of the 
 nucleus. The wall between it and the exterior now gives 
 way and the excretions are passed out. In active indi- 
 viduals this process may be repeated two or three times a 
 minute, but it is usually of less frequent occurrence.
 
 18 ANIMAL FORMS 
 
 The loss in bodily waste is continually made good by 
 the manufacture of the food into protoplasm, and if the in- 
 come be greater than the outgo growth ensues. But, as in 
 all other forms, growth is limited, and ultimately the cell is 
 destined to divide, resulting in two new individuals. This 
 process may be repeated many times, but not indefinitely, 
 for sooner or later various members of the same species 
 unite in pairs temporarily or permanently, exchange nu- 
 clear material, and separate again with apparently renewed 
 energy and the ability to divide for many generations. 
 
 21. Simple and complex animals. It is important to note 
 that these same processes of waste, repair, growth, feeling, 
 motion, and multiplication are the same as those of the 
 squirrel, and, furthermore, are common to all living crea- 
 tures, so that the difference between animals is not in their 
 activities, but in their bodily mechanisms ; and according to 
 the perfection of this, the animal is high or low in the 
 scale. Comparing, for example, the Amoeba and Slipper 
 Animalcule, which are relatively low and high Protozoa, we 
 find in the former that any part of the body serves in loco- 
 motion and in the capture of food, while in the latter these 
 same functions are performed by definite structures, the 
 cilia and gullet. Now it is well known that a workman is 
 able to make better watch-springs, when this is his sole 
 duty, than another who must make all parts of the watch ; 
 and likewise where a definite task is performed by a defi- 
 nite structure, it is more efficiently done than where any 
 and every part of the body must carry it on. So the 
 Amoeba, in which definite tasks are performed by any part 
 of the body indifferently, is less perfect and thus lower than 
 the Paramcecium, where these functions are performed by 
 special organs. As we ascend the scale of life we find this 
 division of labor among special parts of the body more 
 complete, the organs and therefore the animal more com- 
 plex, and better fitted to carry on the work of its life.
 
 CHAPTER IV 
 
 THE SPONGES 
 
 22. Their relation to the Protozoa. While the greater 
 number of one-celled forms are not united with their fel- 
 lows, there are several species where the reverse is true. In 
 Fig. 9, for example, a fresh-water form known as Pandorina 
 is represented, consisting of sixteen cells embedded in a 
 spherical, jelly-like substance, 
 each one of which is precisely 
 like its companions in form 
 and activity. The aggregation 
 may be looked upon as a colo- 
 ny of sixteen Protozoa united 
 together to derive the benefit 
 of increased locomotion and 
 a larger amount of food in 
 consequence. As a result of 
 such a union they have not 
 lost their independence, for if 
 one be separated from the main 
 company it continues to exist. 
 
 From such a simple colonial 
 
 type we may pass through a series of several more complex 
 forms which reach their highest development in the beau- 
 tiful organism, Volvox (Fig. 10). In this form the indi- 
 vidual members, to the number of many thousand, are ar- 
 ranged in the shape of a hollow sphere. The united efforts 
 of the greater number, which bear on their outer surfaces 
 two flagella, drive the colony with the rolling movement 
 
 19 
 
 FIG. 9.Pandwina (from Nature). 
 Highly magnified.
 
 20 
 
 ANIMAL FORMS 
 
 from place to place. As just indicated, some individuals 
 lack the flagella, and their subsequent careers show them 
 to be of a peculiar type. Sooner or later each undergoes 
 
 a series of divisions form- 
 ing a little globe of cells, 
 which migrates into the in- 
 terior of the parent sphere 
 and develops into a new 
 colony. Within a short time 
 the walls of the parent 
 break, liberating the im- 
 prisoned young, which con- 
 tinue the existence of the 
 species while the parent or- 
 ganism soon decays. 
 
 Under certain circum- 
 stances, instead of develop- 
 * n & c l n i es by such a meth- 
 
 od ' some of the cells ma y 
 
 store up food matters and 
 become eggs, while others, 
 known as sperm-cells, de- 
 velop a flagellum, and sep- 
 arating from the colony 
 swim actively in the sur- 
 rounding water, where each 
 finally unites with an egg. 
 This union, like that of the 
 two individuals in Vorticel- 
 la (Fig. 8, J, c), results in 
 
 tne POWCr of division, and 
 
 FIG. 10.-A, Volvox minor, entire colony 
 
 (from Nature). B, C, and D, reproduc- the egg enters Upon its de- 
 tive cells of Volvox globator All highly i j . \ 
 
 magnified. velopment, dividing again 
 
 and again. The cells so pro- 
 
 duced remain together, form a sphere, and finally develop 
 a Volvox colony.
 
 THE SPONGES 21 
 
 In such associations as Volvox an important step has 
 been taken beyond that of Pandorina, for there is a division 
 of the labors of the colony among its various members, 
 some acting as locomotor cells while others are germ-cells. 
 These are now so dependent one upon the other that they 
 are unable to exist after separation from the main com- 
 pany, just as a part of the squirrel is incapable of leading 
 an independent existence. A higher type of organism has 
 thus arisen intermediate between the simple one-celled 
 animals and those of many cells, especially the sponges a 
 relation which is more readily recognized after an examina- 
 tion of the latter. 
 
 23. Development of the sponge. As with all many- 
 celled animals, the sponge begins its existence as an egg, 
 in this case barely visible to the sharp unaided eye. Fer- 
 tilized by its union with a sperm cell, development com- 
 mences, and the first apparent indication of the process 
 will be the division of the cell into two halves (Fig. 11, A, B). 
 Each half redivides into four, these again into eight cells, 
 and this process is repeated, giving the young sponge the 
 general form of Pandorina. The divisions of the cells 
 still continue and result in the formation of a hollow 
 globe of cells (called the Uastula, Fig. 11, E, F) similar 
 to Volvox, and at this point the young larva leaves the 
 parent. 
 
 The next transformation consists in a pushing in of one 
 side of the sphere, just as one might press in the side of a 
 hollow rubber ball. The depression gradually deepens, and 
 finally results in the formation of a two-layered sac known 
 as the gastrula (Fig. 11, G). At this stage of its existence 
 the sponge settles down for life in some suitable spot, by 
 applying the opening of its sac-like body to some foreign 
 object. In assuming the final form a new mouth breaks 
 through what was once the bottom of the sac, canals per- 
 forate the body wall, a skeleton is developed, and the char- 
 acteristic features of the adult are thus attained.
 
 ANIMAL FORMS 
 
 24. Distribution. The sponges are aquatic animals, and, 
 with the exception of one family consisting of relatively 
 few species, all are inhabitants of the sea in every part of 
 
 FIG. 11. Diagrams illustrating the development of a sponge. A, egg-cell ; n, nu- 
 cleus. B, C, D, 2-, 4-, and 16-cell stages. E, blastula. F, section through some- 
 what older larvre. G, gastrula. H, young sponge. I, section through somewhat 
 younger larvse than H. 
 
 the globe. The larger number occupy positions along the 
 shore, becoming especially abundant in the tropics ; but 
 other species occur at greater depths, several species living
 
 THE SPONGES 23 
 
 between three and four miles from the surface. Unlike 
 the majority of animals, all members of this group are 
 securely fastened to some foreign object, such as rocks, the 
 supports of wharves, or with one extremity embedded in 
 the sand. As we have seen, the young enjoy a free-swim- 
 ming existence and are swept far and wide by means of 
 tidal currents, but sooner or later these migrations are 
 terminated ?n some suitable locality, where the sponge 
 passes the remainder of its existence. During this time 
 some species may never exceed the size of a mustard-seed, 
 while others attain a diameter of three feet, or even more. 
 Sponges also vary exceedingly in shape, some having the 
 form of thin encrusting sheets, others being globular, tubu- 
 lar, cuplike, or highly branched (Fig. 12). 
 
 25. The influence of their surroundings. In by far the 
 larger number of cases an animal possesses the bodily form 
 of the parent. External agencies may modify this to some 
 extent, but usually only to a limited degree. A squirrel, 
 for example, resembling its parent, may grow to a relatively 
 large or stunted size according to the food supply, and it 
 may become strong or weak according to the amount of 
 exercise, and various other changes may result owing to 
 outside causes ; but as a result of these influences the 
 animal is rarely so modified that one is unable to distinguish 
 the species. Many of the sponges, however, are exceptions 
 to this general rule. If, for example, some of the young 
 of a certain parent develop in quiet water or in an un- 
 favorable locality, they will usually be low, flat, and un- 
 branched ; while the others, growing in swiftly running 
 waterways, develop into tall, comparatively delicate and 
 highly branched individuals. Under such circumstances 
 not only does the external form become modified, but 
 the internal organization may undergo profound change. 
 The entire organism is plastic and readily molded by 
 the influence of its surroundings, and the consequent 
 lack of definite characters often renders it impossible
 
 ANIMAL FORMS 
 
 to assign such forms to a definite position among the 
 
 sponges. 
 
 26. Structure of a simple sponge. In the simpler sponges 
 
 the body is usually vase-shaped (Fig. 13), with the base 
 
 fastened to some foreign 
 object, while at an oppo- 
 site end an opening leads 
 into a comparatively large 
 internal cavity. This lat- 
 ter space is also put in 
 communication with the 
 exterior by a multitude of 
 minute pores which pene- 
 trate the body wall. In 
 
 FIG. 12. Various forms of sponges, natural size. (From Nature.) 
 
 the living condition currents of water continually pass 
 through these smaller canals, and out of the large termi- 
 nal opening, thus bringing within reach of the body minute
 
 THE SPONGES 
 
 floating organisms or organic remains which serve as food. 
 The mechanism by which this process is effected, and the 
 various other structures of the body, are in large part invis- 
 ible from the exterior, requiring the 
 study of thin sections of the sponge 
 to make them clearly understood. 
 
 Under the microscope such a sec- 
 tion shows the body of a sponge to 
 consist of an immense number of va- 
 riously formed cells constituting three 
 distinct layers (Fig. 14). Xot only 
 do these layers consist of different 
 kinds of cells, but the duties per- 
 formed by each are different. For ex- 
 ample, a glance at Fig. 14 will show 
 that in the inner layer certain colum- 
 nar cells exist, provided with a fla- 
 gellum and encircling collar, the ap- 
 pearance being strikingly like certain 
 of the Protozoa (Fig. 6, B). During 
 life their whip-like processes, lashing 
 backward and forward in perfect uni- 
 son, produce currents of water which 
 continually pass through the body. 
 The food thus entering the animal is 
 taken up by the cells of the inner 
 layer as it passes by. The supply, 
 however, is usually more than suffi- 
 cient to meet the demands of this 
 layer, and the excess is passed on to 
 the middle and outer layers. The 
 exact method by which this occurs is still a matter of 
 doubt, but there seems to be little question but that 
 each cell of the body receives its food in a practically un- 
 modified condition, requiring that it digest as well as 
 assimilate. The oxygen necessary to this latter process 
 
 FIG. 13. One of the sim- 
 plest sponges (Calcolyn- 
 tlnm primigenius (after 
 HAECKEL). A portion 
 of the wall has been re- 
 moved to show the in- 
 side.
 
 ANIMAL FORMS 
 
 is absorbed by all parts of the body in contact with the 
 
 water. 
 
 27. Skeleton of sponges. When it is remembered that 
 
 the protoplasm composing the cells of the sponge has about 
 
 the same consistence 
 as the white of egg, 
 it will be readily un- 
 derstood why the 
 greater number of 
 sponges possess a skel- 
 eton. Without such 
 
 FIG. 14.-Portion of wall of sponge, showing three & support the larger 
 layers, e, outer layer ; i, inner layer, consisting rr 
 
 of collared cells ; TO, middle layer, consisting of globular Or branched 
 
 irregular cells, among which are the radiate epic- f ormg cou ld not CX- 
 ules and egg-celte. . , 
 
 ist, and even in the 
 
 smaller members there would be danger of a collapse of the 
 body walls and consequent stoppage of the food supply, 
 owing to the closure of the pores. So in all but a very few 
 thin or flat forms a skeleton appears in the young sponge 
 almost before growth ..... 
 has fairly begun, and 
 this increases with the 
 body in size and com- 
 plexity. It is formed 
 by the activity of the 
 cells of the middle layer, 
 and may be composed 
 either of a lime com- 
 pound resembling mar- 
 ble, or of flint, or of a 
 horn-like substance resembling silk, or these may exist in 
 combination in certain species. When consisting of either 
 of the first-named substances it is never formed in one 
 continuous piece, but of a vast multitude of variously shaped 
 crystal-like bodies termed spicules (Fig. 15). These occur 
 everywhere throughout the body, firmly bound together 
 
 
 \ 
 
 FIG. 15. Different types of sponge spicules.
 
 THE SPONGES 27 
 
 by means of cells, or so interlocked that they form a rigid 
 support to which the fleshy substance is bound and through 
 which the numerous canals penetrate. 
 
 In a relatively few species only does the skeleton con- 
 sist of horn, though there are many in which horn and flint 
 exist together. In the former event, if the skeleton be 
 elastic and of sufficient size, it becomes valuable to others 
 than the naturalist, for the familiar sponges of commerce 
 are the horny skeletons of forms usually taken in the West 
 Indies or in the Mediterranean Sea. In these localities the 
 animals are pulled off by divers, or with hooks, and are then 
 spread out in shallow water where the protoplasmic sub- 
 stance rapidly decays. The remaining skeleton, thoroughly 
 washed and dried, is ready for the markets of the civilized 
 world. 
 
 Examining a bit of such a " sponge " under a magnify- 
 ing glass, it will be seen that the skeleton is not composed 
 of various pieces, but of one continuous mass of branching 
 fibers, which interlace and unite in apparently the greatest 
 confusion ; yet in the living animal these were perfectly 
 adapted to the position of the canals and the general needs 
 of the animal. 
 
 Besides being a scaffold-work to which the fleshy portions 
 of the body are fastened, the skeleton serves also for pro- 
 tection. In some species, needle-like spicules as fast as 
 they are formed are partly pushed out over the entire sur- 
 face of the body, giving the appearance of a spiny cactus ; 
 or in other cases they are arranged in tufts about the canals, 
 effectually preventing the entrance of any marauder. 
 Thus perfectly protected, the sponges have but few natural 
 enemies, and hence it is that in favorable localities they 
 grow in great profusion. 
 
 28. Race histories and life histories. We have now traced 
 living things from their simplest beginnings, where they 
 exist as single cells, and have seen that in bygone times 
 similar forms have united into simple colonies, and these
 
 28 ANIMAL FORMS 
 
 through a division of labor among the constituent cells 
 have resulted in Volvox-\ike colonies. There are the strong- 
 est reasons for the belief that as these simple forms scat- 
 tered into various surroundings and underwent changes to 
 meet the shifting conditions, they assumed different de- 
 grees of complexity that have resulted in the animal forms 
 of the present day. 
 
 It may have been noticed also that the sponge in its 
 development passes through these stages : a single-celled 
 egg ; later, a young form similar to Pandorina, then growing 
 to look like Volvox, and finally assuming its permanent form. 
 The history of the race of sponges and their development 
 through a long line of ancestry of increasing complexity is 
 thus told by the sponge as it develops from the egg into 
 the adult ; and, so far as we know, all the many-celled ani- 
 mals in their growth from the egg repeat more or less 
 clearly the stages passed through by their forefathers.
 
 CHAPTEE V 
 
 THE CCELENTEBATES 
 
 29. General remarks. This division of the roany-eelled 
 animals includes the jelly-fishes, sea-anemones, and corals. 
 A few species live in fresh water, but the majority are con- 
 fined to the sea, being found everywhere from the shore- 
 line and ocean surface to the most profound depths. 
 Adapted to different surroundings and modes of life, they 
 constitute a vast assemblage of the most bewildering di- 
 versity. In some cases their resemblance to plants is re- 
 markable, and the term zoophyte or " plant animal," occa- 
 sionally applied to them, is the relic of former times when 
 naturalists confounded them with plants. Even to-day 
 certain species are sometimes collected and preserved as 
 seaweeds by the uninformed. 
 
 The general plan on which all co3lenterates are con- 
 structed is a simple sac, in some respects resembling that 
 of the lower sponges, yet, since the modes of life of the 
 members of the two groups are usually quite unlike, we 
 shall find many profound differences between them. 
 
 30. The fresh-water Hydra. The bodily plan comes out 
 most clearly in the Hydra (Fig. 16, A, D), which occurs 
 upon the stems and leaves of submerged fresh-water plants 
 in this and other countries. Its body, of a green or grayish 
 color, according to the species, scarcely ever attains a diam- 
 eter greater than that of an ordinary pin nor a length ex- 
 ceeding half an inch. One end of the cylindrical organism 
 is attached to some foreign object by means of a sticky 
 secretion, but as occasion requires it may free itself, and by 
 
 29
 
 30 
 
 ANIMAL FORMS 
 
 means of a " measuring-worm " movement travel to another 
 
 place. 
 
 Examined under a hand lens, the free end of the body 
 
 will be found to support six to eight prolongations known 
 
 as tentacles, which 
 serve to convey 
 food to the mouth, 
 centrally located 
 in their midst. 
 This opening, un- 
 like that of the 
 sponges, is the 
 only one leading 
 directly into the 
 large central gas- 
 tric cavity which 
 occupies nearly 
 the entire animal 
 (Fig. 16, D). As 
 in the sponge, the 
 cells of the body 
 
 v the form of defi- 
 nite layers, but the 
 middle one is rep- 
 resented only by 
 a thin gelatinous 
 sheet. 
 
 31. Organs of 
 defense. These 
 
 FIG. 16. The fresh-water Hydra. A. entire animal, de- 
 
 veloping a new individual (enlarged 25 times). B ; C, are the SO-Called 
 nettle-cells (after SCHNEIDER) ; D, section through l asso or nettle-cells 
 
 (Fig. 16, C). Some 
 
 of the cells of the outer layer possess, in addition to the 
 elements of the typical cell, a relatively large spherical sac 
 filled with a fluid, and also a spirally wound hollow thread
 
 THE CCELENTE RATES 31 
 
 provided with barbs near its base. On the outer extremity 
 of the nettle-cell projects a delicate bristle-like process, the 
 trigger hair. These cells are especially abundant on the 
 tentacles (Fig. 16, A, D), forming close, knob-like eleva- 
 tions or " batteries," thus rendering it practically impossi- 
 ble for any free-swimming organism to avoid touching them 
 in brushing against the body. In such an event the dis- 
 turbances conveyed through the trigger hair set up in some 
 unknown way very rapid changes in the cell. This causes 
 the sac to discharge the coiled thread and barbs into the 
 body of the intruder, which is rendered helpless by the par- 
 alyzing action of the fluid conveyed through the thread. 
 Thus benumbed it is rapidly borne to the mouth and swal- 
 lowed. In time new nettle-cells develop to take the place 
 of those discharged and consequently worthless. 
 
 32. Digestion of food. Upon the interior of the body of 
 Hydra and all of the coalenterates the food, by reason of its 
 large size, is incapable of being taken into the various cells. 
 It is necessary, therefore, to break it up into smaller masses, 
 and this is accomplished through the solvent action of the 
 digestive fluid poured over it from some of the cells of the 
 adjacent inner layer. When subdivided, the granules swept 
 about the gastric cavity by the beating of the flagella (Fig. 
 16, D) are seized by the processes on the free surfaces of the 
 remaining inner layer cells, where they undergo the final 
 stages of digestion ; then in a dissolved state they become 
 absorbed and assimilated by all the cells of the body. 
 
 33. Methods of multiplication. Very frequently, espe- 
 cially if the Hydra has been well fed, two or three pro- 
 cesses arising as outpushings of the body wall may be 
 noted upon the sides of the animal (Fig. 16, A, D). If 
 these be watched from time to time they are found to in- 
 crease in size, and finally, upon their free extremities, to 
 develop a mouth and surrounding tentacles. Up to this 
 point growth has taken place as a result of the assimilation 
 of nutritive substances supplied from the parent ; but a con-
 
 32 
 
 ANIMAL FORMS 
 
 striction soon occurs which 
 separates the young from the 
 parent, and from that time 
 on the two lead independent 
 existences. At other times 
 this asexual method of mul- 
 tiplication is replaced by sex- 
 ual reproduction, where new 
 individuals arise from fertil- 
 ized eggs. Both eggs and 
 sperm arise in Hydra and in 
 some other animals in the 
 same individual, but in all 
 such cases the eggs are fertil- 
 ized by sperm which escape 
 from some other individual. 
 The fertilized egg, surround- 
 ed by a firm coat, separates 
 from the parent, drops to the 
 bottom, and after a period of 
 rest develops into a little Hy- 
 dra which hatches and enters 
 upon a free existence. 
 
 FIG. 17. Different types of Hydrozoan 
 colonies. From Nature, the lower 
 species magnified about 50 diameters.
 
 THE CtELENTERATES 33 
 
 34. Hydrozoa, or Hydra-like animals. Attention has al- 
 ready been directed to the fact that the structure of Hydra 
 is the simplest of the coelenterates ; nevertheless, the thou- 
 sand or more species belonging to this class which present 
 a much more complicated appearance (Fig. 17) possess 
 many fundamental Hydra-like characters. It is owing to 
 this fact that this assemblage of forms has been placed in 
 the class of the Hydrozoa, or Hydra-like animals. 
 
 With but very few exceptions the members of this class 
 are marine, usually living near the shore-line, where at 
 times their plant-like bodies occur in the greatest profusion 
 attached to rocks, seaweeds, or the bodies of other animals, 
 particularly snails and crabs. Fig. 17 (upper colony) gives 
 a good idea of one of the more complex forms, whose tree- 
 like body attains in some cases the relatively giant height of 
 from 15 to 25 c.m. (six to ten inches). In early life it bears 
 a close resemblance to a Hydra. Buds form in much the 
 same way, but they retain permanently their connection with 
 the parent, and in turn bear other buds, until finally the form 
 shown in the figure is attained. In the meantime root-like 
 processes have been forming which afford firm attachment 
 to the object upon which the body rests. Also during this 
 process the cells of the outer layer form a horny external 
 skeleton ensheathing the entire organism except the ter- 
 minal portions (the hydranths, Fig. 18, B) bearing the ten- 
 tacles. The gastric cavities of all communicate, and the 
 food captured by one ministers in part to its own needs 
 and, swept through the tubular stalks and roots, is also 
 shared by all other members. 
 
 35. Jelly-fishes and the part they play. During the pro- 
 cess of growth a number of stubby branches arise which 
 differ from the ordinary type in shape, and also in many 
 cases as regards color/ . These club-like, fleshy portions de- 
 velop close-set buds (Fig. 18, c) which early assume a bell- 
 like shape, the point of attachment corresponding to the 
 handle, while the clapper is represented by a short, slender
 
 34 ANIMAL FORMS 
 
 process bearing on its end an opening which becomes the 
 mouth (Fig. 18, A). Around the margin of the bell nu- 
 merous tentacles develop, and at the same time the gelati- 
 nous substance situated between the outer and inner layers 
 of the bell expands to a relatively enormous degree, giving 
 it an increasing globular form and glassy appearance. 
 
 FIG. 18. A jelly-fish (Gonionemus), slightly enlarged. The stalked mouth is shown 
 in dotted outline. B. C, enlarged portions of a hydroid colony bearing the 
 mouth and tentacles ; j, a capsule within which the jelly-fish develop ; D, dia- 
 gram of jelly-fish, illustrating its method of locomotion. 
 
 Finally, vigorous movements rupture the connection with 
 the parent, and this newly developed outgrowth, usually 
 small, becomes an independent organism popularly termed 
 a jelly-fish. While the external form of the jelly-fish appears 
 to be widely different from the hydranths, a more careful 
 study shows the difference to be superficial. Some zoolo- 
 gists believe that jelly-fishes are simply buds which have 
 become fitted to separate and swim away from the colony 
 in order to distribute the young, as described hereafter. 
 When the stalked colonies are very abundant the jelly-
 
 THE CCELENTERATES 35 
 
 fishes may be liberated in such multitudes that the upper 
 surface of the- ocean for many miles may be closely packed 
 with them in numbers reaching far into the millions. In 
 these positions they are carried both by oceanic currents 
 and through the alternate expansion and contraction of the 
 bell, a movement resembling the partial closing and open- 
 ing of an umbrella. In the jelly-fish the contraction is the 
 more vigorous and rapid, and as it takes place the opening 
 in the velum or veil (Fig. 18, 5) is so narrowed that the water 
 in the subumbrella space (a) is driven through it with con- 
 siderable force, which results in driving the body in the 
 opposite direction. 
 
 The life of a jelly-fish is perhaps of short duration, last- 
 ing not more than a few hours in some species, up to two 
 or three weeks in others, but during that period they pro- 
 duce multitudes of eggs which develop into minute free- 
 swimming young. These settle down on some rock or sea- 
 weed, and soon develop a Hydra-like body which, after the 
 fashion described above, grows into another tree-like colony. 
 
 36. Alternation of generations. It will be noticed that 
 the offspring of the jelly-fishes are not jelly-fishes, but stalked 
 colonies, and these latter forms give rise to jelly-fishes. 
 This is known as the alternation of generations, the jelly- 
 fish generation alternating with the colonial form. This 
 characteristic is of the greatest service in preventing the 
 extermination of the race. Were the stalked forms to 
 give rise directly to other stationary colonies, it is obvious 
 that before long all the available space in the immediate 
 locality would be filled. The food supply, always lim- 
 ited, would not suffice, and starvation of some or imper- 
 fect development of all would result ; but by means of the 
 free-swimming jelly-fish new colonies are established over 
 very extensive areas, and favorable situations are held 
 by all. 
 
 37. More complex types. As mentioned above, there are 
 perhaps upward of a thousand species of Hydrozoa, all with
 
 36 
 
 ANIMAL FORMS 
 
 essentially the same structure but with various modes of 
 branching (for some of the commoner modes, see Fig. 17)- 
 In some of the higher forms a division of labor has arisen 
 among various members of the association which has led to 
 most interesting results. For example, Fig. 19 represents 
 a species of hydroid found investing the shells of sea-snails 
 occupied by hermit crabs (Fig. 60). To the unaided eye 
 its appearance is that of a delicate vegetable growth, but 
 when placed under the microscope it is found to consist of 
 
 a multitude of Hydra-like 
 animals united by a hollow 
 branching root system con- 
 necting the gastric cavities 
 of all of them (Fig. 19). 
 Certain individuals (a) 
 with tentacles and a mouth 
 resemble a Hydra ; others, 
 without a mouth and ten- 
 tacles, are reduced to a 
 
 FIG. 19.-An enlarged portion of a hydroid club-like form (b) liberally 
 
 colony (Ilydracliniq), showing (a) the 
 nutritive polyp, (b) the defensive polyp, 
 and (c) the reproductive polyp. 
 
 supplied with nettle-cells 
 upon their free extremi- 
 ties; while the third type 
 (c), likewise devoid of a mouth, possesses rudiments of ten- 
 tacles below which are borne numerous clumps of repro- 
 ductive cells. The first type, the only one possessing a 
 mouth, captures the food, and after digesting it distributes 
 the greater portion to the remaining members by means of 
 the connecting root system ; those of the second form, de- 
 fending the others by means of their nettle-cells against 
 the inroads of a foreign enemy, are the soldiers of the colo- 
 ny; while the third type produces the eggs from which 
 new individuals develop. 
 
 In some of the higher Hydrozoa, the Portuguese man- 
 of-war (Fig. 20), this division of labor has reached a more 
 advanced stage of development, and in addition the entire
 
 THE CCELENTERATES 
 
 37 
 
 colony is fitted for a free-swimming existence. "What cor- 
 responds ordinarily to the attached stalk in other forms 
 terminates in a bladder-like expansion, distended with 
 gas, that serves as a float. From it are suspended individ- 
 uals resembling great stream- 
 ers sometimes many feet in 
 length, without mouths, but 
 loaded with nettle-cells that 
 enable them to capture the 
 food, which is conveyed to the 
 second type, the nutritive 
 polyps. Each of these is a 
 simple tube bearing a mouth, 
 and within them the food is 
 digested and distributed by 
 means of a branching gastric 
 cavity extending throughout 
 the entire colony. Then there 
 are individuals like mouthless 
 jelly-fishes which bear 'the 
 eggs and care for the perpet- 
 uation of the colony ; and be- 
 sides these there may be some 
 whose duty it is to defend the 
 rest, and others whose active 
 swimming movements, to- 
 gether with the wind, drive 
 the colony about. Thus uni- 
 ted, sharing the food supply 
 and working for the general welfare of all, the members of 
 this colony live in greater security and with less effort than 
 if, as separate individuals, each was fighting the battles of 
 life alone. 
 
 38. Scyphozoa. The greater number of the larger and 
 more conspicuous jelly-fishes are included under this term. 
 In general shape and locomotion they resemble those of the 
 
 PIG. 30. -A colonial jelly-fish (Physaiia). 
 From Nature.
 
 ANIMAL FORMS 
 
 preceding group (Fig. 21), but, while the latter are generally 
 very small, these forms are commonly from four to twelve 
 inches in diameter, and some measure one to two meters 
 (three to six feet) across the bell. They are also distin- 
 guished by means of tentacles which extend from the cor- 
 ners of the mouth sometimes to a distance of several feet, 
 
 and together with the 
 marginal tentacles are 
 formidable weapons for 
 capturing small crabs, 
 fishes, and other ani- 
 mals which serve as 
 food. In turn these 
 forms serve as the food 
 of many whales, por- 
 poises, and numerous 
 fishes which hunt them 
 down, though the 
 amount of nourishment 
 they contain is prob- 
 ably relatively small 
 owing to the fact that 
 in their composition 
 there is a large percent- 
 age of water (99 per 
 cent in some species). The lobed margin of the bell, the 
 absence of a definite swimming organ or velum, and the 
 character of several of the internal organs, distinguish the 
 larger from the smaller jelly-fish ; but the greatest differ- 
 ence, however, is in the method of development. 
 
 39. Development. The eggs arise from the inner layer 
 of the jelly-fish and drop into the gastric cavity, where each 
 develops into a ciliated two-layered sac in some respects 
 like that of a young sponge. Swimming away from the 
 parent, they finally settle down, and attaching themselves 
 (Fig. 22, a) assume the external form and habits of the sea- 
 
 ?IG. 21. A jelly-flsh (Rkizostmna), about one- 
 fourth natural size.
 
 THE CCELENTERATES 
 
 39 
 
 anemones, described in the next section. In the course of 
 time remarkable changes ensue, which first manifest them- 
 
 FIG. 22. Stages in the development of a scyphozoan jelly-fish, a, the attached 
 young, which in b has separated into a number of disks, each of which becomes a 
 jelly-fish, c. After KOBSCHBLT and HEIDEB. 
 
 selves in a series of grooves encircling the body. These 
 grow deeper, and the body of the animal finally comes to 
 resemble a pile of sau- 
 cers with the edge of 
 each developed into a 
 number of lobes (Fig. 
 22, #). One after an- 
 other each saucer, to 
 preserve the simile, 
 raises itself from the 
 top of the pile and 
 swims away, and is 
 clearly seen to be a 
 jelly-fish, though con- 
 siderably unlike the 
 
 adult. As growth pro- FlG - 23 - An att * ched ^yphozoan Jelly-fish 
 
 1 (Halidystus). Natural size, from Nature. 
 
 ceeds, however, it un- 
 dergoes a series of transformations which result in the 
 adult form. 
 
 4
 
 40 ANIMAL FORMS 
 
 40. Sea-anemones. In its external appearance the sea- 
 anemone (Fig. 24) bears some resemblance to the Hydra, but 
 is of a much larger size (1 to 45 c.m., or | inch to 1 feet 
 in diameter), and is frequently brilliantly colored. The 
 number of tentacles is also more numerous, and the mouth 
 leads into the body by means of a slender esophagus (Fig. 
 25). Numerous partitions from the body wall extend in- 
 ward, and many unite to the esophagus, keeping the latter 
 
 FIG. 24. Sea anemones (.the two upper 
 
 ;ary coral polyps. 
 
 in position. Below the esophagus each partition projects 
 into the great cavity of the body and bears upon its inner 
 free edge several important structures. The first of these, 
 known as the mesenteric filaments (Fig. 25), appearing like 
 delicate frills, plays an active part in the digestion of the 
 food. Associated with these are long, slender threads,
 
 THE CCELENTERATES 
 
 closely packed with innumerable lasso-cells, which may be 
 thrown out through openings in the body wall when the 
 animal is attacked. Lasso-cells are also very numerous on 
 the tentacles, which are thus to some extent defensive, but 
 are chiefly active in capturing the crabs and small fish 
 which serve as food. 
 
 The partitions also carry eggs which may undergo the 
 first stages of their growth within the body, and when 
 finally able to swim 
 are sent out through 
 the mouth opening 
 by hundreds to seek 
 out favorable situa- 
 tions, there to set- 
 tle down and re- 
 main. In some spe- 
 cies the young may 
 sometimes arise as 
 buds, as in Hydra 
 (Fig. 24), and in 
 others the animals 
 have been described 
 as splitting longi- 
 tudinally into two 
 equal-sized young. 
 
 41. Corals. The 
 coral polyps also 
 
 belong to this group, showing a very close resemblance to 
 the sea-anemones. In most cases they develop a firm skel- 
 eton of lime, commonly known as " coral," which serves to 
 protect and support the body. In a few species the polyps 
 throughout life are solitary, and with skeleton comparative- 
 ly simple (Fig. 24) ; but the larger number of species be- 
 come more complex by developing buds, which retain their 
 connection with the parent, and in turn produce other out- 
 growths with the ultimate result that highly branched 
 
 FIG. 25. Longitudinal section through the body of a 
 sea-anemone, oe, esophagus; m. /., mesenterial 
 filaments ; r., reproductive organs.
 
 42 ANIMAL FORMS 
 
 colonies are produced (Fig. 26). At the same time the 
 outer layer of the body is continually forming a skeleton 
 which encloses the colony as a sheath, except at the ter- 
 mination of each branch, where the mouth and tentacles 
 are located. In certain species for example, the sea pens 
 (Pennatula) and sea fans (Gorgonid) a skeleton may be 
 
 FIG. 26. Small portions of 
 
 with some of the polyps expanded. 
 
 formed of myriads of lime spicules, somewhat like those 
 of the sponge, which are bound together by the fleshy 
 substance of the body; but the skeleton of most of the 
 common forms in the ocean, and the coral found in 
 general collections, is stony. According to their method 
 of branching, such specimens have received various popu- 
 lar names, such as brain, stag-horn, organ-pipe, and fun- 
 gous corals.
 
 THE CCELENTEEATES 43 
 
 Nearly all species, like the sea-anemones, are brilliantly 
 colored during life, and several are highly phosphorescent. 
 All are marine, and while they are found everywhere, from 
 the shore-line to great depths, the more abundant and 
 larger species inhabit the clear, warm waters of the tropics 
 down to a depth of one hundred and sixty feet. In such 
 regions the stag-horn corals especially grow in the wildest 
 profusion, and become tall and greatly branched. Except 
 in quiet water they are continually being broken by the 
 waves, beaten into fragments, and the resulting sand is 
 deposited about their bases. As a result of this continu- 
 ous growth and erosion, there have been formed from coral 
 sand mixed with the shells of mollusks and the skeletons 
 of various Protozoa several of the islands along the Florida 
 coast and many of those of the Pacific, some of them 
 hundreds of miles in extent.
 
 CHAPTER VI 
 
 THE WORMS 
 
 42. General Characteristics. The bodies of the animals 
 comprising the two preceding groups are exposed on all 
 sides equally to the water in which they live and are radi- 
 ally symmetrical ; but in the worms, one side of the body 
 is fitted for creeping, and for the first time we note a well- 
 marked dorsal (back) and ventral (under) surface. In the 
 former, the body, like a cylinder, may be divided into simi- 
 lar halves by any number of planes passing lengthwise 
 through the middle ; but in the worms, the right and left 
 halves only are exposed equally to their surroundings, and 
 there is, accordingly, only one plane which divides the body 
 into corresponding halves, so that these animals, like all 
 higher forms, are bilaterally symmetrical. In creeping, also, 
 one end of the body is directed forward and it thus be- 
 comes correspondingly modified. It usually bears the 
 mouth, and may be provided with eyes, feelers, or organs 
 of touch, and various other structures which enable the 
 worm to recognize the nature of its surroundings. The 
 nervous and muscular systems are better developed than in 
 the foregoing groups, and we note a greater vigor and defi- 
 niteness in the animal's movements, and in various ways the 
 worms appear better able to avoid or ward off their enemies, 
 recognize and select their food, and in general adapt them- 
 selves to the conditions of life. 
 
 The division of the worms is a very large one, and in 
 some respects difficult to define, owing to the close resem- 
 44
 
 THE WORMS 
 
 45 
 
 blance which many of them show to animals in other 
 groups. All the invertebrates, therefore, except the crabs 
 and insects, were placed in one group until subsequent 
 study made it possible to classify them more exactly. Ac- 
 cording to the general shape of the body, and the arrange- 
 ment of internal organs, worms are divided into a number 
 of groups, chief among which are the flatworms, the thread 
 or roundworms, and the ringed worms or annelids. 
 
 THE FLATWORMS 
 
 43. Form and habitat. The flatworms, as their name 
 indicates, are much flattened, leaf-like forms, some species 
 living in damp places on land, 
 in fresh - water streams or 
 ponds, or along the seacoast, 
 while a variety of other spe- 
 cies are parasitic. The free 
 forms (Fig. 27) are usually 
 small, barely reaching a length 
 greater than five or seven cen- 
 timeters (2 to 3 inches), but 
 some of the parasitic species 
 (Fig. 31) attain the great 
 length of six to thirteen me- 
 ters (20 to 40 feet). 
 
 The free-living forms usu- 
 ally occur on the under side 
 of stones, and frequently are 
 so delicate that a touch is 
 sufficient to destroy them. A 
 
 few Species are almost trans- FIG. 27.-A, fresh-water flatworm (Pla- 
 . naria) ; B, marine flatworm (Lepto- 
 
 parent, while many are col- ^ ana) Enlarged, from Nature. 
 ored to harmonize completely 
 
 with their surroundings, so that, even though fragile and 
 defenseless, they escape the attacks of enemies by being 
 overlooked. The night-time or dark days are their hunting
 
 46 
 
 ANIMAL FORMS 
 
 season, and at such periods they may be found moving about 
 with a steady gliding motion (due to cilia covering the en- 
 tire body), varied occasionally by a looping, caterpillar move- 
 ment, or by swimming with a napping of the sides of the 
 body. When watched at such times they may sometimes 
 be seen to snatch up small worms, snails, small crabs and 
 insects, which serve as food. 
 
 More closely examining one of these forms, for example, 
 the species usually found on the under side of sticks and 
 stones in our shallow fresh-water streams (Fig. 27, A), we note 
 that the forward end is not developed into a well-defined 
 head as in the higher worms, 
 but is readily determined by 
 the presence of very simple 
 eyes and tentacles, while the 
 lower creeping surface is dis- 
 tinguished by a lighter color 
 and the presence of the 
 mouth. Through this small 
 opening a slender proboscis 
 (in reality the pharynx) may 
 be extended some distance, 
 and may be seen to hold the 
 small organisms upon which 
 it lives until they are suffi- 
 ciently digested to be taken 
 into the body. 
 
 44, Digestive system. In 
 the smaller flatworms, some 
 of which are scarcely larger 
 than many of the Protozoa, 
 the alimentary canal is a sim- 
 ple unbranched tube ; but in 
 the larger forms such an ap- 
 paratus is replaced by a greatly branched digestive tract 
 which furnishes an extensive surface for the rapid absorp- 
 
 FIG. 28. Anatomy of fresh-water flat- 
 worm (Planaria). exs, excretory sys- 
 tem, with flame-cell (/). The ali- 
 mentary canal is stippled. B, nerv- 
 ous system.
 
 THE WORMS 
 
 47 
 
 tion of food, and extending deep into the tissues of the 
 body, carries nutriment to otherwise isolated regions. In 
 the fresh-water forms and their allies there are three main 
 branches of the intestine (Fig. 28), while in many of those 
 from the sea there are several, and their arrangement 
 affords a basis for their general classification. 
 45. Excretory system. In the sponges and ccelenterates 
 the wastes are cast out by the various cells into the gastric 
 cavity or at once to the exterior with- 
 out the aid of any pronounced system 
 of vessels; but in the flatworms sev- 
 eral of the organs are deeply buried 
 within the tissues of the body and a 
 drainage system becomes a necessity. 
 This consists of a paired system of ves- 
 sels extending the length of the ani- 
 mal (Fig. 28) and provided with numer- 
 ous branches, some of which open at 
 various points on the surface of the 
 body, while the others terminate in 
 spaces (Fig. 29, s) among the organs in 
 what are known as flame-cells. The 
 substances which accumulate in these 
 spaces are gathered up by the flame- 
 cell, poured into the space it contains, and by means of the 
 vibratory motion of its flagellum (/), a movement bearing 
 a fancied resemblance to the flickering of a flame in the 
 wind, are borne through the tubes to the exterior. 
 
 46. Nervous system and sense-organs. In the sponges no 
 definite nervous system is known to exist, the slight move- 
 ments which the cells are able to undergo being regulated 
 somewhat as they are in the Protozoa. Among the ccelen- 
 terates certain of the cells scattered over the surface of the 
 body are set aside as nerve-cells, and, more or less united by 
 means of fibers extending from them, convey impulses over 
 the body. In the flatworms the larger number of nerve-cells 
 
 FIG. 29. Flame-cell of flat- 
 worm (after LANG). /, 
 flagellum ; n, nucleus; 
 s, spaces among the or- 
 gans of the body ; v, 
 waste materials.
 
 48 ANIMAL FORMS 
 
 are collected into two definite masses (Fig. 28, B), which 
 constitute a simple brain on which the eyes are situated 
 and from which bundles of nerve fibers pass to all parts of 
 the body, the two extending backward being especially 
 noticeable. As in the squirrel, these are distributed to the 
 muscles and other organs to regulate their activity, while 
 those distributed to the skin, especially in the forward 
 part of the body, convey stimuli produced by touch. The 
 branches connecting with the eyes enable the animal to 
 distinguish light from darkness, but are probably too sim- 
 ple to allow it to clearly distinguish objects of the outside 
 world. The sense of smell and possibly that of taste are 
 also present, but are relatively feeble. 
 
 Some other characters of this class will be noted in the 
 consideration of the two following classes. 
 
 47. Parasitic flatworms (trematodes) parasitism. Men- 
 tion has already been made of the associations of two ani- 
 mals as " messmates " for mutual benefit, such as the Hy- 
 dractinia growing on the surface of the shell inhabited by 
 the hermit crab, to which it gives protection by means of 
 its nettle-cells, while in turn being borne continually into 
 regions abounding with food. More frequently, however, 
 one animal derives benefit from another without making 
 any compensation. For example, many species of flatworms 
 live within the shells of certain snails and upon the bodies 
 of sea-urchins and starfishes, where they gather in their 
 food supply safe from the attacks of enemies. Such asso- 
 ciations are probably without much if any inconvenience to 
 the animal thus inhabited, and it also appears probable 
 that the tenants are transients, using the mollusk or star- 
 fish only as a temporary home. But from this condition of 
 affairs it is only a short step to the parasitic habit, where 
 the association becomes permanent and the occupant is 
 provided with various structures which prevent its sepa- 
 ration from its host. This latter kind of union occurs 
 throughout the group of trematodes ; all are parasitic, and
 
 THE WORMS 
 
 their internal organization, so closely resembling that of 
 the free-living forms as to need no further description, in- 
 dicates that they are 
 descendants of the lat- 
 ter. In the greater 
 number the body is 
 flat, and a few species 
 still retain their outer 
 coat of cilia ; but since 
 these are no longer of 
 service as locomotor 
 organs they have gen- 
 erally disappeared, and 
 in their place numer- 
 ous adhesive organs, 
 such as spines, hooks, 
 and suckers (Fig. 30), 
 have arisen, which en- 
 able the animals to 
 hold on with great te- 
 nacity. Thus attached 
 to its host, and using 
 it as a convenient and 
 comparatively safe 
 means of locomotion, 
 the parasite may still 
 
 continue to capture small animals for food or may derive 
 its nourishment from the tissues of the host. In addition 
 there are numbers of internal parasites, living almost ex- 
 clusively in the bodies of vertebrate animals, scarcely a sin- 
 gle one escaping their ravages. 
 
 48. Life history. In the external parasites the young 
 hatch out and with comparative ease make their way to 
 another host ; but the young of an internal parasite, inhab- 
 iting the alimentary canal, have a very slight chance in- 
 deed of ever reaching a similar location in another host. 
 
 FIG. 30. A parasitic flatworm (Epidetta). m 
 mouth ; o, opening of reproductive system ; 
 , sucker and spines for attachment. The di- 
 gestive system is stippled ; nervous system 
 black. Enlarged 8 times, from Nature.
 
 50 ANIMAL FORMS 
 
 For this reason an almost incredible number of eggs is laid, 
 and some extraordinary measures are employed in effecting 
 the desired result. Probably the best-known example is that 
 of the liver fluke inhabiting the bile-ducts in the sheep. 
 Each worm lays several hundred thousand eggs, which make 
 their way from the host, and if they chance to fall in pools 
 of water or damp situations may proceed to develop, other- 
 wise not. If the surroundings be favorable, the young, like 
 little ciliated Infusoria, escape from their shells and rest- 
 lessly swim or move about for a short time, and if during 
 this time they come in contact with certain species of 
 snails living in these situations they at once bore into their 
 bodies. Here they produce other young somewhat resem- 
 bling a tadpole, that now make their escape from the snail. 
 In a short time each one crawls upon a blade of grass, and 
 surrounds itself with a tough shell, where it may remain for 
 several weeks. If the grass on which they rest be eaten by 
 a sheep, they finally make their way to the bile-ducts and 
 there become adult. The life cycle is now complete ; the 
 young form has found a new host ; and the process shows 
 how wonderfully animals are adapted to the conditions which 
 surround them, and how closely they must conform to these 
 conditions in order to exist. 
 
 49. The tapeworms (cestodes). The cestodes, or tape- 
 worms, are also parasitic flatworms in which the effects of 
 such a mode of life are strongly marked. They occur 
 almost exclusively in the bodies of vertebrate hosts and 
 exhibit a great variety of bodily forms, in some cases resem- 
 bling rather closely the trematodes, but in others strikingly 
 different. In the latter type the body is usually of great 
 length (from a few centimeters to upwards of sixteen meters 
 (50 feet) ), and terminates in a "head" (Fig. 31) provided, 
 in the different species, with a great variety of hooks and 
 spines and numbers of suckers for its attachment to the 
 body of the host. From the head the body extends back- 
 ward in the gradually enlarging ribbon-like body, slender at
 
 THE WORMS 
 
 51 
 
 first and scarcely showing the segments which finally be- 
 come so prominent a feature. 
 
 When carefully examined, a two-lobed brain is found 
 in the " head," and from it nerves extend the entire length 
 of the body, followed throughout their 
 course by the tubes of the excretory 
 system ; also each segment contains a 
 perfect reproductive system, so that 
 even if it be separated from the others 
 it may continue to exist for a consid- 
 erable length of time. Furthermore, 
 the tapeworms are surrounded by the 
 predigested fluids of their host ; a 
 special alimentary canal is therefore 
 superfluous, and all traces of it have 
 disappeared. 
 
 50. Development. As the animal 
 clings in this passive way to the body 
 of its host the segments, loaded with 
 eggs ready for development, separate 
 one after another from the free end 
 of the body, pass to the exterior, and 
 
 slowly crawling about like independent organisms, lay great 
 numbers of eggs, which may find an intermediate host as in 
 the life cycle of the liver fluke, and so in time find their 
 permanent resting-place. Fortunately in all these parasitic 
 forms, though an inconceivably great number of eggs are 
 laid, only a comparatively few reach maturity. Even these, 
 however, may cause at times great destruction among the 
 higher, and especially our domestic, animals, often doing 
 damage amounting to many millions of dollars per year. 
 
 51. The tapeworm in relation to regeneration. It has 
 been known for more than one hundred and fifty years that 
 some of the lower animals possess to a surprising degree 
 the ability to regenerate parts of the body lost through 
 injury. The Hydra, hydroids, and some of the jelly-fishes 
 
 PIG. 31. Tapeworm (Tcenia 
 solium). In upper left- 
 hand corner of figure is 
 the much enlarged head. 
 After LEUCKART.
 
 52 ANIMAL FORMS 
 
 may be cut into a number of pieces, each of which will 
 develop into a complete individual ; and this power of recov- 
 ery from the injuries produced by enemies is of the great- 
 est service in the perpetuation of the species. This ability 
 is also present in certain flatworms, and some species are 
 known which voluntarily separate the body into two por- 
 tions, each of which becomes an adult. In other species a 
 similar process results in the formation of a chain of six 
 individuals, placed end to end, the chain finally breaking 
 up into as many complete worms. It is possible that the 
 tapeworm may also be looked upon as a great chain of 
 united individuals produced by the division of a single 
 original parent, which becomes adapted for attaching the 
 others until they separate. These latter are capable only of 
 a very sluggish movement, and, devoid of mouth and ali- 
 mentary canal, are not able to digest their food, but their 
 life work is to so lay their eggs that they may develop into 
 other individuals, and for this they are well adapted. 
 
 NEMATODES (THREADWORMS) 
 
 52. General characters. This class of worms is com- 
 posed of an enormous number of different species, some para- 
 sitic, others free all or a portion of their lives, and in view of 
 the fact that they inhabit the most diverse situations it is 
 remarkable that they are so uniform in their structure. In 
 all the body is slender, and the general features of its organ- 
 ization may be readily understood from an examination of 
 the "vinegar eel" (Fig. 32, A). This small worm (not an 
 eel), a millimeter or two in length, lives on the various forms 
 of mold that grow in fermenting fruit juices, especially 
 after a little sugar or paste has been added. A tough cuti- 
 cle surrounds the body, preserving its shape and at the 
 same time protecting the delicate organs against the action 
 of the acids in which it lives. Through this may be seen 
 great bands of muscles extending the entire length of the 
 body and producing the wriggling movements of swimming
 
 THE WORMS 
 
 53 
 
 or crawling. They also give support to a brain, which is in 
 the form of a collar encircling the pharynx near the head, 
 and to the great nerves which extend from it. Still fur- 
 ther within the transparent body the alimentary canal may 
 be distinguished as a straight tube 
 passing directly through the ani- 
 mal. This latter system lies freely 
 in a great space, the body cavity, 
 traces of which may exist in the 
 flatworms in the form of small hol- 
 lows among the organs into which 
 the kidneys open. It is possible 
 that in this form also the kidneys 
 open into this space, and it is 
 roomy enough besides to afford 
 lodgment for the reproductive or- 
 gans in addition to a large amount 
 of fluid which is probably somewhat 
 of the nature of blood. A space in 
 some respects similar to this occurs 
 in all the animals above this group, 
 and as we shall see, it is often cu- 
 riously modified and serves for a 
 number of different and highly im- 
 portant purposes. In the round- 
 worms the fluid it contains proba- 
 bly acts in the nature of a blood 
 system, distributing the food and 
 oxygen to various parts of the body and carrying the wastes 
 to the kidneys for removal. 
 
 53. Multiplication. In the matter of the production of 
 new individuals the greatest differences exist. In some 
 threadworms, for example the " vinegar eel," eggs develop 
 within the body and the young are born with the form of the 
 parent. In other cases the eggs are laid in the water, where 
 they, too, may directly grow to the adult condition ; but in 
 
 FIG. 32. Thread- or round- 
 worms. A, vinegar eel (An- 
 guittula) ; m, mouth ; ph., 
 pharynx ; i, intestine ; ov., 
 developing young. B, TH- 
 china. From Nature, greatly 
 enlarged.
 
 54 ANIMAL FORMS 
 
 the greater number of species the development is round- 
 about, and one or more hosts are inhabited before the young 
 assume the adult condition. Such is the case with the 
 dreaded Trichina (Fig. 32, B), which infests the bodies of 
 several animals, particularly the rat. When these forms 
 are introduced into the alimentary canal of the rat, for 
 example, they soon lay a vast quantity of eggs, sometimes 
 many millions, which develop into young that bore their 
 way into the muscles of the body, where they may remain 
 coiled up for years. If the body of the rat be eaten by some 
 carnivorous animal, these excessively small young are lib- 
 erated during the process of digestion and rapidly assume 
 the adult condition in the alimentary canal, likewise giving 
 rise to young which pursue again this same course of 
 development. 
 
 Another example of a complicated life history is in 
 the Gordius or " horsehair snake " (a true worm and not a 
 snake) frequently seen in the spring in pools where it lays 
 its eggs. These eggs develop into young which bore their 
 way into different insect larva?, which are in turn eaten by 
 some spider or beetle, and the worm thus transferred to a 
 new host. In this they grow to a considerable size, and 
 then make their exit from the body of the host and finally 
 become adult. 
 
 54. Spontaneous generation. It is only within compara- 
 tively recent years that such life histories have been under- 
 stood. Formerly the sudden appearance of these and other 
 forms in various situations were accounted for on the ground 
 that they arose spontaneously without the intervention of 
 any living creature. Even yet we hear of the transforma- 
 tion of horsehairs into hairworms, and of frogs, earthworms, 
 and several other animals from inorganic matter, but such 
 assertions are based on superficial observations, and at the 
 present time no exception is known to the law that living 
 creatures arise from preexisting living parents. " All life 
 from life " (omnium vivum ex vivo) is a universal law.
 
 THE WORMS 55 
 
 ANNELIDS OK SEGMENTED WORMS 
 
 55. The earthworms and their relatives. Leaving the 
 groups of the parasitic animals, which have been driven from 
 the field of active existence and in many ways are degraded 
 by such a mode of life, we pass on to the higher free-living 
 worms, where brilliant colors, peculiar habits, or remarkable 
 adaptations render them peculiarly interesting. In consid- 
 ering first their general organization, we may use the earth- 
 
 FIG. 33. Earthworm (Lumbrlcus terrestris). m, mouth ; c, girdle or clitellum. 
 
 worm (Fig. 33) (sometimes called angle-worm or fish-worm) 
 as a type because of its almost universal distribution. 
 
 The body is cylindrical, shows well-marked dorsal and 
 ventral surfaces, and, as in all of the annelids, is jointed, 
 each joint being known as a segment. Anteriorly it tapers 
 to a point, and the head region bearing the mouth is ill- 
 defined, unlike many sea forms, yet serves admirably for 
 tunneling the soil in which all earthworms live. In this 
 process the animal is also aided by bristles or setce which 
 project from the body wall of almo'st every segment and 
 may be stuck into the earth to afford a foothold. 
 
 56. Foodjmd digestive system. The earthworms are 
 nocturnal animals, seldom coming to the surface during the 
 day except when forced to do so by the filling of their tun- 
 nels with water or when pursued by enemies. At night 
 they usually emerge partially, keeping the posterior end of 
 the body within the burrow, and thus they scour the sur- 
 rounding areas for food, which they appear, in some cases 
 at least, to locate by a feeble sense of smell. They also 
 frequently extend their habitations, and in so doing swallow 
 enormous quantities of earth from which they digest out 
 any nutritive substances, leaving the indigestible matter in 
 5
 
 5G ANIMAL FORMS 
 
 coiled " castings " at the entrance of the burrows. In thus 
 mixing the soil and rendering it porous they are of great 
 service to the agriculturist. 
 
 Although earthworms are omnivorous they also manifest 
 a preference for certain kinds of food, notably cabbage, 
 celery, and meat, which leads us to think that they have a 
 sense of taste. All these substances are carried within their 
 retreats and devoured, or are used to block the entrance 
 during the day. The food thus carried within the body is 
 digested by a system (Fig. 34) composed of several portions, 
 
 FIG. 34. Earthworm ( Lwtnbricus) dissected from left side, b, brain; c, crop; rf, 
 outer opening of male reproductive system ; dr, dorsal blood-s-essel : g. gizzard : 
 h, pulsating vessels or ' hearts " ; i, intestine ; k, kidney ; , month ; n. c.. nerve- 
 cord ; oe, esophagus ; o, ovary ; od, oviduct : ph. pharynx ; r, testes : g.r.. sem- 
 inal receptacles ; v.v., ventral vessel. 
 
 each of which is modified for a particular part in the pro- 
 cess. The mouth (m) leads into a muscular pharynx (ph) 
 whose action enables the worm to retain its hold on various 
 objects until swallowed, and this in turn is continuous with 
 the esophagus. From here the food is passed into the thin- 
 walled crop (c),and from this storehouse is gradually borne 
 into the gizzard (#), whose muscular walls reduce it to a fine 
 pulp now readily acted upon by the digestive fluids. These, 
 resembling in their action the pancreatic juice of higher 
 animals, are poured out from the walls of the intestine into 
 which the food now makes its way ; and as it courses down 
 this relatively simple tube the nutritive substances are ab- 
 sorbed while the indigestible matters are cast away. 
 
 57. Circulatory system. In all the groups of animals up 
 to this point the digested food is carried over the body by 
 a simple process of absorption, or in the threadworms by
 
 THE WORMS 
 
 57 
 
 means of the fluid in the body cavity ; but in the earthworm 
 the division of labor between different parts of the body is 
 more perfect, and a definite blood system now acts as a 
 distributing apparatus. This consists primarily of a dorsal 
 vessel lying along the dorsal surface of the alimentary canal 
 (Fig. 34), from which numerous branches are given off to 
 the body wall, and to the digestive system through which 
 they ramify in every direction before again being collected 
 into a ventral vessel lying below the digestive tract. In 
 some of the anterior segments a few of the connecting 
 vessels are muscular and unbranched, and during life pul- 
 sate like so many hearts to force the blood over the body, 
 forward in the dorsal vessel, through the " hearts " into the 
 ventral vessel, thence into the dorsal by i 
 
 means of the small connecting branches. 
 
 Some of the duties of this vascular 
 system are also shared by the fluid of 
 the body cavity, which is made to cir- 
 culate through openings in the parti- 
 tions by the contractions of the body 
 wall of the animal in the act of crawl- 
 ing. In this rough fashion a consider- 
 able amount of nutritive material and 
 oxygen are distributed to various or- 
 gans, and wastes are carried to the kid- FlG 35 
 neys to be removed. 
 
 58. Excretion. In nearly all of the 
 segmented worms there is a pair of 
 kidneys to every segment (Figs. 34, 35). 
 Each consists of a coiled tube wrapped in a mass of small 
 blood-vessels, and at its inner end communicating with the 
 body cavity by means of a funnel-shaped opening. In 
 some unknown way the walls of the kidney extract the 
 waste materials from the blood-vessels coursing over it and 
 pass them into its tubular cavity. At the same time the 
 cilia about the mouth of the funnel-shaped extremity are 
 
 Diagram of earth- 
 worm kidney. 6, blood- 
 vessel ; /, funnel open- 
 ing into body cavity ; 
 o, outer opening ; , 
 septum ; w, body wall.
 
 58 ANIMAL FORMS 
 
 driving a current from the body-cavity fluids, which wash 
 the wastes to the exterior. 
 
 59. Nervous system. The nervous system of the earth- 
 worm consists first of a brain composed of two pear-shaped 
 masses united together above the pharynx (one shown in 
 Fig. 34), from which nerves pass out to the upper lip and 
 the head, which are thus rendered highly sensitive. Two 
 other nerves also pass out from the brain, and, coursing 
 down on each side of the pharynx like a collar, unite below 
 it and extend side by side along the under surface of the 
 digestive system throughout its entire extent. In each 
 segment the two halves of this ventral nerve-cord are united 
 by a nerve, and others are distributed to various organs, 
 whichare thus made to act and in proper amount for the 
 good of the body as a whole. 
 
 In its relation to the outside world the chief source of 
 information comes to the earthworm through the sense of 
 touch, for definite organs of sight, taste, and smell are but 
 feebly developed, while ears appear to be entirely absent. 
 Nevertheless these are sufficient to enable it to lead a suc- 
 cessful life, as is evidenced by the great number of such 
 forms found on every hand. 
 
 60. Egg-laying. In digging up the soil where earth- 
 worms abound one frequently finds small yellowish or 
 brownish bodies looking something like a grain of wheat. 
 These are the cocoons in which the earthworms lay their 
 eggs, and the method by which this is performed is unique. 
 We have already noted the presence of a swollen girdle 
 (the clitellum] about the body of the worm. At the breed- 
 ing season this throws out a fluid which soon hardens into 
 an encircling band. By vigorous contractions of the body 
 this horn-like collar is now slipped forward, and as it passes 
 the openings of the reproductive organs the eggs and 
 sperms are pushed within it. They thus occupy the space 
 between the worm and the collar, and when the latter is 
 shoved off over the head its ends close as though drawn to-
 
 THE WORMS 
 
 50 
 
 gether by elastic bands. A sac, the cocoon, is thus pro- 
 duced, containing the eggs and a milky, nutritive substance. 
 In a few weeks the worm 
 develops and, bursting the 
 wall of its prison, makes its 
 escape. 
 
 61. Distribution. The 
 earthworms and their allies 
 are found widely distributed 
 throughout the world, and 
 all exhibit many of the 
 characters just described. 
 The greatest differences 
 arise in their mode of life : 
 some are truly earthworms, 
 but others are fitted for a 
 purely aquatic existence in 
 fresh water or along the 
 seacoast ; a few have taken 
 up abodes in various ani- 
 mals and plants, and in 
 some of these situations they 
 extend far up the sides of 
 the higher mountains. In 
 all, the head is relatively 
 indistinct, the number of 
 
 bristles OU each segment Fl - 36. A marine worm (Nereis). A, ap- 
 
 few, and for this and other j;~ mes^" 8 """*' "* * 
 
 reasons all are included in 
 
 the subclass Oligochaste, or " few-bristle " worms. 
 
 62. Nereis and its allies. In many of the above-men- 
 tioned situations members of a more extensive group of 
 worms are found, with highly developed heads and many 
 bristles arranged along the sides of the body. These are 
 the Polychaetes or " many-bristle " worms, and as a repre- 
 sentative we may take Nereis (Fig. 36), a very common
 
 60 
 
 ANIMAL FORMS 
 
 form along almost any seashore. The body presents the 
 same segmented appearance as the earthworm, but the 
 head (Fig. 37, A) is provided with numerous sense organs, 
 chief among which are four eyes and 
 several tentacles or " feelers." 
 
 The segments behind the head 
 
 
 FIG. 37. A. head and one of the lateral appendages (B) of a marine worm (Nereis 
 brandtii) ; al. intestine ; /, " gill " ; k, kidney ; n, nerve cord ; s, bristles for loco- 
 motion. 
 
 differ very little from one another, and, unlike those of 
 the earthworm, each bears a pair of lateral plates (Figs. 
 36, 37, B) or paddles with many lobes, some of which bear 
 numerous bristles. By a to-and-f ro movement these organs 
 aid in pushing the animal about, or may enable certain spe- 
 cies to swim with considerable rapidity. 
 
 As in all other worms, respiration takes place through 
 the surface of the body, the area of which is increased by 
 the development, on certain portions of the paddles (para- 
 podia), of plates penetrated with numerous blood-vessels, 
 which thus become special respiratory organs or gills 
 (Fig. 37, B). 
 
 In their internal organization the Polychaetes are con- 
 structed practically on the same plan as the earthworms, 
 the principal difference being in the reproductive system. 
 In the earthworm this is restricted to some of the forward 
 segments, while in the present group the eggs and sperms
 
 THE WORMS 
 
 fit 
 
 are developed in almost every segment, whence they are 
 finally swept to the exterior through the tubes of the kid- 
 neys (Fig. 37, B). 
 
 The Nereis and its immediate relatives are all active 
 forms, and by means of powerful jaws, which may be quickly 
 extended from the lower part of the mouth cavity, they 
 capture large numbers of small crustaceans, mollusks, and 
 worms which happen in their path. Others more distantly 
 related make their diet of seaweed, and 
 many living on the sea bottom swallow 
 great quantities of sand, from which they 
 absorb the nutritious substances. 
 
 63. Sedentary forms. Preyed upon by 
 many enemies, a large number of species 
 have been forced to abandon an active ex- 
 istence save in their early youth, and to 
 construct many interesting devices for their 
 protection. Numerous species, shortly after 
 they commence to shift for themselves? 
 build about their bodies tubes of lime (Fig. 
 39), from which they may emerge to gather 
 food and into which they may dash in times 
 of danger. As the worm grows the tube is 
 correspondingly enlarged, and these tubes, 
 in all stages of construction and variously 
 coiled, may be found on almost every avail- 
 able spot at the seashore, and may often 
 be seen on the shells of oysters in the 
 markets. 
 
 In other species the tube is like thin 
 horn, and may be further strengthened or 
 concealed by numerous pebbles, bits of carefully selected 
 seaweeds, or highly tinted shells, which give them a very 
 attractive appearance. Such species usually develop out 
 of immediate contact with other forms, but a few live 
 so closely associated together that their twisted tubes 
 
 FIG. 38. A common 
 marine worm (Po- 
 lynas brevisetosa), 
 with extended pro- 
 boscis and over- 
 lapping plates cov- 
 ering the back.
 
 62 
 
 ANIMAL FORMS 
 
 form great stony masses, sometimes several feet in dia- 
 meter. 
 
 64. Effects of an inactive life. In many species such a 
 sedentary life has resulted in the almost complete disap- 
 pearance of the lateral appendages, which therefore no 
 longer serve as organs of respiration, and this function has 
 been shifted accordingly on to other structures. These 
 new organs are situated principally on the exposed head, 
 
 FIG. 39. Sedentary tube-dwelling marine worms, upper left ha 
 
 natural size), the remainder Serpula (enlarged twice). From life. 
 
 (.one-half 
 
 and Fig. 39 shows the general appearance of some com- 
 mon species. The corners of the mouth have expanded 
 into great plumes, sometimes wondrously colored like a 
 full-blown flower, and these, bounteously supplied with 
 blood-vessels, act as gills. "When disturbed, the plumes are 
 hastily withdrawn into the tube, and some of the so-called 
 serpulids (Fig. 39, bottom of figure) close the entrance with 
 a funnel-shaped stopper. While the plumes are primarily 
 respiratory organs, they also act as delicate feelers, and may 
 even bear a score or more of eyes ; and in addition, being
 
 THE WORMS 
 
 63 
 
 P h 
 
 covered with cilia, create the currents of water which 
 bring minute organisms serving as food within reach of 
 the mouth. 
 
 65. Development. Unlike the earthworms, the Poly- 
 chastes lay their eggs in the sea water, where they are left 
 alone to develop as best they may. Both the male and 
 female Nereis, as the egg-laying time approaches, undergo 
 remarkable changes in their external appearance, resulting 
 in the form shown in Fig. 36, A. 
 
 They are now active swimmers, and 
 thus are able to scatter the fertilized 
 eggs over wide and more or less favor- 
 able areas. The young also for a 
 time are free-swimming, but finally 
 end their migrations by settling to 
 the sea bottom, where they gradually 
 attain the adult condition. 
 
 As in some of the flatworms, re- 
 production may also arise asexually 
 by the division of the animal into two 
 or more parts, each of which subse- 
 quently becomes a complete indi- 
 vidual. In other species growth of 
 various parts may result in two com- 
 plete worms at the time of separation ; 
 and from such forms we may trace a 
 fairly complete series up to those in 
 which the original parent breaks up FIG. 40.-A leeci; 
 
 . . la). Right-hand figure il- 
 
 into twenty to thirty young. lustrau alimentar y canal . 
 
 66. The leeches. At first Sight Ph, pharynx ; c, crop ; p, 
 
 the leeches (Fig. 40), or at least the latcral pouche9; '*" in " 
 
 smaller, more leaf-like forms, might 
 be mistaken for flatworms, especially for some of the para- 
 sitic species. As in the latter, the mouth is surrounded by 
 a sucker, and another is located at the hinder end of the 
 body, but beyond this point the resemblance ceases. The
 
 64 ANIMAL FORMS 
 
 outer surface is delicately marked off into eighty or a hun- 
 dred rings, of which from three to five are included in one 
 of the deeper true segments corresponding to those of 
 other annelids. From two to ten pairs of simple eyes are 
 borne on the head, and owing to the fact that they are 
 active swimmers, or move by caterpillar-like looping, loco- 
 motor spines are unnecessary and absent. In their internal 
 organization, however, there are many features which in- 
 dicate a close relationship with the Oligochsetes or few- 
 bristle worms. The nervous, circulatory, and certain char- 
 acteristics of the excretory systems are decidedly similar, 
 but, on the other hand, some facts are difficult to explain 
 on such a theory, and have led some zoologists to the belief 
 that the relationship of these animals can not at present 
 be determined. 
 
 67. Haunts and habits. The leeches usually dwell in 
 among the plants in slowly running streams, but some 
 occur in moist haunts on land, and a considerable number 
 live in the sea. All are " bloodsuckers " fierce carnivo- 
 rous worms, whose bite is so insidiously made that the vic- 
 tim frequently is ignorant of their presence. Fishes, frogs, 
 and turtles are the most frequently attacked, but cattle and 
 other animals which come down to drink also become their 
 prey. In some of the tropical countries the land-leeches 
 are present in large numbers secreted among the leaves, and 
 so severe are their attacks that various animals, even man, 
 succumb to their united efforts. Adhering by their suck- 
 ers, they puncture the skin, some using triple jaws, and 
 fill themselves until they become greatly distended, when 
 they usually drop off and digest the meal at leisure. In 
 certain species the intestine is provided with lateral 
 pouches (Fig. 40), which serve to store up the food until 
 the time for digestion arrives. A full meal is sufficient 
 with some species to last for two or three months, and the 
 medicinal or horse-leech when gorged with food may con- 
 sume a year in digesting it.
 
 THE WORMS 65 
 
 68. Egg-laying. The eggs of some leeches are stored 
 up in a cocoon like that of the earthworm, which is attached 
 to submerged plants or placed under stones. When the 
 young are able to lead independent lives they emerge with 
 the form of the parent. A leaf-like form, Clepsine, some- 
 times found adhering to turtles, fastens the eggs to the 
 under side of its body, and the young when hatched 
 remain there for several days, adhering by their posterior 
 suckers.
 
 CHAPTER VII 
 
 ANIMALS OF UNCERTAIN RELATIONSHIPS 
 
 IN this chapter we shall consider in a brief way a number 
 of different groups of animals whose relationships are un- 
 certain. Up to the present time the study of their habits, 
 structure, and development has been of too fragmentary 
 or unrelated a character to enable the majority of zoologists 
 to agree upon their classification. Nevertheless, many of 
 them are highly interesting and attractive, 
 often very common, and in some respects 
 they hold important positions in the animal 
 kingdom. 
 
 69. The rotifers or wheel-animalcules. 
 The rotifers or wheel-animalcules are rela- 
 tively small and beautiful organisms, rarely 
 ever longer than a third of an inch, but at 
 times so abundant that they may impart a 
 reddish tinge to the water of the streams 
 and ponds in which they live. At first 
 sight they might be mistaken for one-celled 
 animals, but the presence of a digestive 
 tract and of reproductive elements soon dis- 
 pels such a belief. .Examined under the 
 animaicuie"cffo/7r). microscope, the more common forms are 
 seen to possess an elongated body terminat- 
 ing at the forward end in two disk-like expansions beset 
 along the edges with powerful cilia. These serve to drive 
 the animal about, or, when it remains temporarily attached 
 
 FIG. 41 A whee
 
 ANIMALS OF UNCERTAIN RELATIONSHIPS 6T 
 
 by the sticky secretion of the foot, to sweep the food-par- 
 ticles down into the mouth. Through the walls of the 
 transparent body such substances are seen to pass into the 
 stomach, where they are rapidly hammered or rasped into 
 a pulp by the action of several teeth located there. In 
 the absence of a circulatory system the absorbed food is 
 conveyed by the fluid of the body-cavity, which also con- 
 veys the wastes to the delicate kidneys. Several other 
 features of their organization are of much interest, espe- 
 cially to the zoologist, who believes that he gains from 
 their simple structure some ideas of the ancestors of the 
 modern worms, mollusks, and their allies. During the 
 summer the rotifers lay two sizes of " summer eggs," 
 which are remarkable for developing without fertilization. 
 The large size give rise to females, the smaller to males, the 
 latter appearing when the conditions commence to be un- 
 favorable. The " winter eggs," fertilized by the males and 
 covered with a firm shell, are able for prolonged periods to 
 Avithstand freezing, drought, or transportation by the wind. 
 The adults also are able under the same adverse conditions 
 to surround themselves with a firm protective membrane 
 and to exist for at least a year. Once again in the presence 
 of moisture the shell dissolves, and in a surprisingly short 
 space of time they emerge, apparently none the worse for 
 the prolonged period of quiescence. 
 
 70. Gephyrea. There is a comparatively large group of 
 worm-like organisms, over one hundred species in all, which 
 at present hold a rather unsettled position in the animal 
 kingdom. Some of the more common forms (Fig. 42) 
 living in the cracks of rocks or buried in the sand, usually 
 in shallow tide pools along the seashore, have a spindle- 
 shaped body terminated at one end by a circlet of tentacles 
 which surround the mouth. On account of their external 
 resemblance to many of the sea-cucumbers (Fig. 92), they 
 were earlier associated in the same group ; but an examina- 
 tion of their internal organization inclines many zoologists
 
 68 
 
 ANIMAL FORMS 
 
 to the belief that the ancestors of some of these animals 
 were segmented worms whose present condition has arisen 
 possibly in accordance with their sluggish habits. This 
 view is strengthened by the fact that in a very few species 
 
 the- larvae are dis- 
 tinctly segmented, 
 but lose this char- 
 acter in becoming 
 adult. As before 
 mentioned, the 
 greater number of 
 species live in bur- 
 rows in the sand 
 or crevices in the 
 rocks, from which 
 they reach out and 
 gather in large 
 ^quantities of sand. 
 As these substances 
 
 FIG. 42. Agephyrean worm (Dendrostoma). Specimen pass down the in- 
 on left opened to show k, kidney, m, muscle bands, , , . ,, 
 
 and .., nerve-cord. testme the niltri- 
 
 tive matters are di- 
 gested and absorbed, while the indigestible matters are 
 voided to the exterior. When large numbers are associated 
 together they are doubtless important agents in modifying 
 the character of the sea bottom, thus acting like the earth- 
 worms and their relatives. 
 
 71. The sea-mats (Polyzoa). The sea-mats or Polyzoa 
 constitute a very extensive group of animals common on 
 the rocks and plants along the seashore, and frequently 
 seen in similar situations in fresh-water streams. A few 
 lead lives as solitary individuals, but in the greater number 
 of species the original single animal branches many times, 
 giving rise to extensive colonies. In some species these 
 extend as low encrusting sheets over the objects on which 
 they rest; while in others the branches extend into the
 
 AXIMALS OF UXCERTAIX RELATIOXSHIPS 60 
 
 surrounding medium and assume feathery shapes (Fig. 43), 
 which often bear so close a resemblance to certain plants 
 
 FIG. 43.-Lamp-shells 
 
 eft of figure), fossil and living, and (.on 
 
 right) plant-like colonies of sea-mats. 
 
 that they are frequently preserved as such. What their 
 exact position is in the animal scale it is somewhat difficult 
 to say ; but judging especially from their development, it 
 appears probable that they are distant relatives of the seg- 
 mented worms.
 
 70 ANIMAL FORMS 
 
 72. Lamp-shells or Brachiopods. Occasionally one may 
 find cast on the beach or entangled in the fishermen's 
 lines or nets a curious bivalve animal similar to the form 
 shown in Fig. 43. These are the Brachiopods, or lamp- 
 shells. The remains of closely related forms are often 
 abundant as fossils in the rocks (Fig. 43). Over a thousand 
 species have been preserved in this way, and we know that 
 in ages past they nourished in almost incredible numbers 
 and were scattered widely over the earth. Unable to adapt 
 themselves to changing conditions or unable to cope with 
 their enemies, they have gradually become extinct, until 
 to-day scarcely more than one hundred species are known. 
 These are often of local distribution, and many are com- 
 paratively rare. 
 
 For a long period the Brachiopods, owing to their pecul- 
 iar shells, were classed together with the clams and other 
 bivalve mollusks. The presence of a mantle also strength- 
 ened the belief ; but closer examination during more recent 
 years has shown that the shells are dorsal and ventral, and 
 not arranged against the sides of the animal as in the 
 clams. Another peculiar structure consists of two great 
 spirally coiled " arms," which are comparable in a general 
 way to greatly expanded lips. The cilia on these create, in 
 the water currents which sweep into the mouth, the small 
 animals and plants that serve as food. The internal organ- 
 ization resembles in a broad way that of the animals con- 
 sidered in the previous section, and it now appears that 
 both trace their ancestry back to the early segmented 
 worms. 
 
 73. Band or nemertean worms. In a few cases band or 
 nemertean worms have been discovered in damp soil or in 
 fresh-water streams. These are commonly small and incon- 
 spicuous, and are pigmies when compared with their marine 
 relatives, which sometimes reach a length of from fifty to 
 eighty feet. Many of the marine species (Fig. 44) are often 
 found on the seashore under rocks that have been exposed
 
 ANIMALS OF UNCERTAIN RELATIONSHIPS 
 
 71 
 
 B 
 
 by the retreating tide. They are usually highly colored 
 with yellow, green, violet, or various shades of red, and are 
 so twisted into tangled 
 masses that the differ- 
 ent parts of the body 
 are indistinguishable. 
 As the animal crawls 
 about, a long thread- 
 like appendage, the pro- 
 boscis, is frequently shot 
 out from its sheath at 
 the forward end of the 
 body and appears to be 
 used as a blind man 
 
 USeS his Stick. At Other FIG. 44.-A band or nemertean worm. A, entire 
 worm ; B, head, bearing numerous eyes and 
 times, when Small WOrmS spine-tipped proboscis. 
 
 and other animals are 
 
 encountered, the proboscis is shot out farther and with 
 greater force, impaling the victim on a sharp terminal spine 
 (Fig. 44). The food is now borne to the mouth, located 
 near the base of the proboscis, is passed into the digestive 
 tract, traversing the entire length of the body, and is far- 
 ther operated on by systems of organs too complex to be 
 considered here.
 
 CHAPTEK VIII 
 
 MOLLUSKS 
 
 74. General characters. For very many years the mol- 
 lusks that is, the clams, snails, cuttlefishes, and their allies 
 have been favorite objects of study largely because of the 
 durability, grace, and coloration of the shell. The latter 
 may be univalve, consisting of one piece, as in the snails, or 
 bivalve, as in the clams and mussels, and may possess almost 
 every conceivable shape, and vary in size from a grain of 
 rice to those of the giant clam (Tridacna) of the East Indian 
 seas, which sometimes weighs five hundred pounds. These 
 external differences are but the expression of many internal 
 modifications, which, while adapting these animals for dif- 
 ferent modes of life, are yet not sufficient to disguise a 
 more fundamental resemblance which exists throughout 
 the group. In some respects the mollusks show a close 
 resemblance to the annelid worms, but, on the other hand, 
 the body is usually more thick-set and totally devoid of any 
 signs of segmentation. In every case the skin is soft and 
 slimy, demanding moist haunts and usually the protection 
 of a shell, and the body is modified along one surface to 
 form a foot or creeping disk which serves in locomotion. 
 The internal organization is somewhat uniform, and will 
 admit of a general description later on. Mollusks are 
 divided into three classes, viz. : The Lamellibranchs, em- 
 bracing the clams ; the Gasteropods, or snails ; and the 
 Cephalopods, or cuttlefishes, squids, and related forms. 
 
 75. Lamellibranchs (clams and mussels). Numerous rep- 
 resentatives of this class, such as the clams and mussels, 
 
 72
 
 MOLLUSKS T3 
 
 occur along our seacoasts or are plentifully distributed in 
 the fresh-water streams and lakes. They are distinguished 
 from other mollusks by a greatly compressed body, which 
 is enclosed in a shell consisting of two pieces or valves 
 locked together by a hinge along the dorsal surface. Rais- 
 ing one of these valves, the main part of the body may be 
 seen to occupy almost completely the upper (dorsal) part 
 of the shell (Fig. 45), and to be continued below into the 
 muscular hatchet-shaped foot (ft.}, which aids the clam in 
 plowing its way through the sand or mud in which it lives. 
 Arising on each side of the back of the animal and extend- 
 ing its entire length is a great fold of skin, which com- 
 pletely lines the inner surface of the corresponding valve 
 of the shell. These are the two mantle lobes (m) instru- 
 mental in the formation of the shell, and enclosing between 
 them a space containing the foot and a number of other 
 important structures, the most conspicuous of which are 
 the gills (g), consisting of two broad, thin plates attached 
 along the sides of the animal and hanging freely into the 
 space (mantle cavity) between the mantle and the foot. 
 Owing to this lamella-like character of the branchia or gills 
 the class derives its name, lamellibranch. To illustrate the 
 relations of these various organs to one another the clam has 
 been compared to a book, in which the shells are repre- 
 sented by the cover, the fly-leaves by the mantle lobes, the 
 first two and last two pages by the gills, and the remaining 
 leaves by the foot. In the clams, however, the halves of 
 the mantle, like the halves of the shell, are curved, and 
 thus enclose a space, the mantle cavity, which is partly 
 filled by the gills and foot. 
 
 Unlike the other mollusks which usually lead active 
 and more aggressive lives, the clams show scarcely a sign of 
 a head and tentacles, and other sense organs are likewise 
 absent from this region. The mouth also lacks definite 
 organs of mastication, and as devices for catching and 
 holding food are not developed, the food is brought to the
 
 T4 ANIMAL FORMS 
 
 mouth by means of the cilia on the great triangular lipa or 
 palps which bound it on each side (Fig. 45, A,j9). 
 
 FIG. 45. Anatomy of fresh-water clam. A, right valve of shell removed ; B, dissec 
 tion to show internal organs, a, external opening of kidney ; a.a., the anteYior 
 muscle for closing the shell ; b, opening of reproductive kidney ; c. brain ; //., 
 foot ; g, gill ; h, heart ; i, intestine ; k, kidney ; I, liver ; m, mantle (upper fig.), 
 mouth (lower fig.) ; p, palp (upper fig.), foot nerves (lower fig.) ; p.a., hinder 
 muscle for closing the shell ; #. space through which the water passes on 
 leaving the body ; si, stomach ; v, nerves snpplying'viscera. 
 
 Between the halves of the shell in the hinge region is a 
 horny pad that acts like a spring, and without any muscu- 
 lar effort on the part of the clam keeps the shells open.
 
 MOLLUSKS 75 
 
 These are also united by two great adductor muscles, located 
 at opposite ends of the animal (Fig. 45, A, a.a., J9.a.), which 
 in times of disturbance contract and firmly close the shell. 
 Upon their relaxation the shell opens, the clam extends its 
 foot, and plows its way leisurely through the mud, or re- 
 mains buried, leaving only the hinder portion of its gaping 
 shell exposed. Through this opening a current of water 
 is continually passing in and out, owing to the action of 
 the cilia covering the gills, and by placing a little car- 
 mine or coloring matter in the ingoing stream we may 
 trace its course through the body. Passing in between the 
 mantle and the foot it travels on toward the head, giving 
 off small side streams which are continually made to enter 
 minute openings in the gills, whence they are conducted 
 through tubes in each gill up to a large canal at its base, 
 where it is carried backward to the exterior. In this pro- 
 cess oxygen gas is supplied to the number of blood-ves- 
 sels traversing the gills, and at the same time considerable 
 quantities of minute organisms and organic debris are 
 hurried forward toward the head, where they encounter the 
 whirlpools made by the cilia on the lips and are rapidly 
 whisked down into the mouth and swallowed. 
 
 75. Rock- and wood-boring clams. Other similar forms 
 are rendered even more secure through their ability to 
 bore in solid rock. In the common Piddock, for example 
 (Fig. 46), the shell is beset with teeth like a rasp, which 
 gradually enlarge the cavity as the animal grows, until it 
 becomes a prisoner with no means of communication with 
 the exterior save the small opening through which the 
 siphons project. This is also the case with the Teredo, 
 improperly called the shipworm, which swims about for 
 some time during early life and then, about the size of a 
 small pinhead, settles down upon the timbers of wharves 
 or unsheathed ships, into which it rapidly tunnels. 
 Throughout life its excavation is extended sometimes to a 
 distance of two to three feet, and imprisoned yet safe at
 
 76 
 
 ANIMAL FORMS 
 
 the bottom of its burrow, it extends its slender siphons up 
 the tube and out of the entrance for its food supply. 
 Often hundreds of individuals enter the same piece of 
 wood, which becomes thoroughly riddled within a short 
 
 FIG. 46. The piddock (Zirph&a 
 
 time, and though giving no outward sign of weakness may 
 collapse with its own weight. Incalculable damage is thus 
 rendered to the shipping interests, and in consequence 
 much has been done to check their ravages, but they are 
 far from being completely overcome. 
 
 76. Other stationary species. A large number of other 
 species, while small and inconspicuous, are also free to
 
 MOLLUSKS 
 
 77 
 
 move about, but as they become larger they lose this ability 
 either wholly or periodically. In the edible mussels (Myti- 
 lus, Fig. 47), for example, which are associated in great 
 numbers on the rocks along our coasts, the foot early be- 
 comes long and slender and capable of reaching out a con- 
 siderable distance from the shell to attach threads (byssus), 
 which it spins, to foreign objects. These are remarkably 
 strong, and when several have been spun it becomes a mat- 
 ter of much difficulty to dislodge them. After remaining 
 anchored in one situation for a while the mussel may vol- 
 
 FIG. 47. The edible mussel (Mytilus edulin), showing the threads by which it is 
 attached. Natural size, from life. 
 
 untarily free itself, and in a labored fashion move to some 
 other more favorable spot where it again becomes attached, 
 but there are numerous species, such as "fan shells" 
 (Pinna), scallops, Anomia, and a few fresh-water forms, 
 where the union is permanent. 
 
 Finally, in the oysters, some of the scallops, and a num- 
 ber of less familiar forms, the young in very early life drop 
 down upon some foreign object to which the shell soon 
 becomes firmly attached, and in this same spot they pass 
 the remainder of their lives. The oyster usually falls upon 
 the left half of its shell, which becomes deep and capacious 
 enough to contain the body, while the smaller right valve
 
 78 ANIMAL FORMS 
 
 acts as a lid. As locomotion is out of the question, the foot 
 never develops, and the shell is held by only one adductor 
 muscle, whose point of attachment in the oyster is indicated 
 by a brown scar in the interior of the shell. 
 
 77. Internal organization. It is thus seen that the ex- 
 ternal features of the clam are variously modified, according 
 to the life of the animal, but the internal organization is 
 much more uniform. In nearly every species the food con- 
 sists of floating organisms, which are driven by the palps 
 into the mouth and on to the simple stomach, where it is 
 subjected to the solvent action of the fluids from the liver 
 (Fig. 45, B, /) before entering the intestine. This latter 
 structure is usually of considerable length, and in the active 
 species extends down into the foot, and it is also peculiar in 
 penetrating the ventricle of the heart. Traversing the in- 
 testine the nutritive portion of the food is absorbed, and is 
 conveyed over the body by a circulatory system more highly 
 developed than in the higher worms. On the dorsal side 
 of the clam, in a spacious pericardial chamber, the large 
 heart is situated (Fig. 45, h), consisting of a median highly 
 muscular ventricle surrounding the intestine and of two 
 thin auricles, one on either side. From the former, two 
 arteries with their numerous branches convey the blood to 
 all parts of the body, where it accumulates, not in capilla- 
 ries and veins, but in spaces or sinuses among the muscles 
 and various organs, constituting a somewhat indefinite sys- 
 tem of channels which lead to the gills and kidneys. In 
 these latter organs the blood delivers up the waste which it 
 has accumulated on its journey, and absorbing a supply of 
 oxygen, it flows into the great auricles, which in turn pass 
 it into the ventricle to circulate once more throughout 
 the body. 
 
 The excretory apparatus, consisting usually of two kid- 
 neys, of which one may degenerate in many snails, bears a 
 close resemblance to that of the annelids. In the clam, for 
 instance, each consists of a bent tube symmetrically ar-
 
 MOLLUSKS 79 
 
 ranged on each side of the body (Fig. 45, B, &), and the inner 
 ends (), corresponding to the ciliated funnel of the anne- 
 lid kidney, open into the pericardial cavity. Their walls 
 are continually active in extracting wastes from the blood 
 supplied to them, and these, together with the substances 
 swept out from the pericardial cavity, traverse the tube and 
 are carried to the exterior. In other mollusks the kidney 
 may be more compact, or greatly elongated, or otherwise 
 peculiar, but in reality they bear a close resemblance to 
 those of the clam. 
 
 78. Nervous system. The nervous system, like the ex- 
 cretory, differs considerably in different mollusks, yet the 
 resemblances are fairly close throughout. In the clam the 
 cerebral ganglia corresponding to the " brain " in annelids 
 is located at either side, or above the mouth, and from it 
 several nerves arise, the larger passing downward to two 
 pedal ganglia ( p) embedded in the foot and to the visceral 
 ganglia (v) far back in the body (Fig. 45, B). These nerve 
 centers continually send out impulses which regulate the 
 various activities of the body and also receive impressions 
 from without. These come chiefly through the sense of 
 touch, for in the clams the other senses are usually either 
 feebly developed or altogether absent. 
 
 79. Development. In the mollusca new individuals al- 
 ways arise from eggs, which are commonly deposited in the 
 water and there undergo development. In the fresh-water 
 clams the reproductive organ is usually situated in the foot 
 (Fig. 45), while in the oyster and similar inactive species it is 
 attached to, the large adductor muscle. In these latter, and 
 in many other marine forms, the eggs are shed directly into 
 the sea, where they are left to undergo their development 
 buffeted by winds and waves and subject to the attack of 
 numerous enemies. Under such circumstances the chances 
 of survival are slight, and for this reason eggs are laid in 
 vast numbers, which have been variously estimated for the 
 oyster, for example, from two to forty million. Develop-
 
 80 ANIMAL FORMS 
 
 ment proceeds at first much as in the sponge, but soon the 
 shell, foot, gills, and various other molluscan structures 
 put in an appearance, and the few surviving young Avhich 
 have been free-swimming now settle down in some favor- 
 able spot, and attach themselves or burrow according to 
 their habit. 
 
 80. Life history of fresh-water clams. The life history of 
 our common fresh-water clams is perhaps one of the most 
 remarkable known among mollusks. The parent stores the 
 eggs, as soon as they are laid, in the outer gill plate, and 
 there, well protected, they undergo the first stages of their 
 development, which results in the formation of minute 
 young enclosed in a bivalve shell beset with teeth. These 
 are often readily obtained, sometimes as they are escaping 
 from the parent, and when examined under the microscope 
 are seen to rapidly open and close their shells in a snapping 
 fashion when in the least disturbed. In a state of nature 
 this latter movement may result in attaching the young to 
 the fins or gills of some passing fish, which is necessary to 
 its further development. Within a short time it becomes 
 completely embedded in the flesh of its host, from which, 
 as a parasite, it draws its nourishment, and during the 
 next few weeks undergoes a wonderful series of transforma- 
 tions resulting in a small mussel, which breaks its way 
 through the thin skin of the fish and drops to the bottom. 
 
 81. The gasteropods. The gasteropods, including snails, 
 slugs, limpets, and a host of related forms, fully twenty 
 thousand different species in all, are found in most of our 
 fresh-water streams and lakes and in moist situations on 
 land, while great numbers live along the seashore and at 
 various depths in the ocean, even down as far as three 
 miles. Examining any of them carefully we find many of 
 the same organs as in the clams, but curiously changed and 
 adapted for a very different and usually active life. In our 
 common land snails (Fig. 48), which we may well examine 
 before passing on to a general survey of the group, the first
 
 MOLLUSKS 81 
 
 striking peculiarity is in the univalve shell, with numerous 
 whorls, into which the animal may at any time withdraw 
 completely. Ordinarily this is carried on the back of the 
 spindle-shaped body, which is fashioned beneath into a great 
 
 Fio. 48. The slug (Ariolimax) and commoi 
 
 flat sole or creeping surface that bears on its forward bor- 
 der a wide opening through which mucus is continually 
 issuing to enable the snail to slip along more readily. Slime 
 also exudes on other points on the surface of the body and 
 affords a valuable protection against excessive heat and 
 drought. 
 
 Unlike the clams, the forward end of the body is devel- 
 oped into a well-marked head bearing the mouth and a 
 complicated mechanism for gathering and masticating food, 
 together with two pairs of tentacles, one of which carries the 
 eyes. On the right side of the animal, some distance behind 
 the head, is the opening of the little sac-like mantle cavity 
 (Fig. 48) which contains the respiratory organs, and into 
 which the alimentary canal and the kidneys pour their 
 wastes. The relation of these organs to the mantle cavity 
 is the same as in the clams, though the cavities differ much 
 in size and position. 
 
 82. Other snails. The shell. Extending our acquaint- 
 ance to other species of snails, we find the same general 
 plan of body, although somewhat obscured at times by
 
 82 ANIMAL FORMS 
 
 many modifications. A foot is generally present, also a 
 more or less well-developed head, and the body is usually 
 surrounded by a shell which varies widely in shape and 
 size in different species. In the common limpets the early 
 coiled shell is transformed into an uncoiled cap-like one, 
 and in the keyhole limpets is perforated at its summit. The 
 
 chitons or armadillo- 
 snails (Fig. 49), often 
 found associated with 
 the limpets, carry a 
 most peculiar shell con- 
 sisting of eight plates, 
 which enables the ani- 
 mal to roll up like an 
 armadillo when dis- 
 
 FIG. 49. -The chiton, armadillo-snail or sea-era- tlirbed. A shell is by 
 die. The left-hand figure shows mouth in ., 
 
 center of proboscis, the broad foot on each no means a necessity, 
 
 side of which are numerous small gills. The however, f Or in many 
 right-hand figure shows the mantle and shell, , 
 
 composed of eighties. From life, one- Species, Such as the 
 
 half natural size. beautiful naked snails 
 
 or Xudibranchs (Fig. 
 
 50) common along our coasts, it may be entirely absent, 
 or, as in the ordinary slugs, reduced to a small scale em- 
 bedded in the skin. 
 
 83. Respiration. A considerable quantity of oxygen is 
 absorbed through the skin, as in all mollusks, but the chief 
 part of the process is usually taken by the plume-like gills, 
 one or two in number, which are located in the mantle 
 cavity. In the chitons (Fig. 49) the number of gills is 
 greater, amounting in some species to over a hundred, 
 while in the Xudibranchs (Fig. 50) gills are absent, their 
 places being taken by more or less feathery expansions of 
 the skin on the dorsal surface. 
 
 Many of the gasteropods left exposed on the rocks by a 
 retreating tide retain water in the mantle cavity, from 
 which they extract the oxygen until submerged again.
 
 MOLLUSKS 83 
 
 Others breathe by means of gills while under water, and by 
 the surface of the body and the moist walls of the mantle 
 
 FIG. 50. Three different species of naked marine snails or Nudibranchs. Natural 
 size, from life. 
 
 cavity when exposed. In some of the small Littorinas 
 attached so far from the sea as to be only occasionally 
 washed by the surf this latter method may prevail for days 
 together in fact they live better out of water than in it. 
 It is not difficult to imagine that such forms, keeping in 
 moist places, might wander far from the sea, and, losing 
 their gills, become adapted to a terrestrial life. It is 
 believed that in past times this has actually occurred, and 
 that our land forms trace their descent from aquatic ances- 
 tors. To-day they breathe by a lung that is, they take 
 oxygen through the walls of the mantle cavity, as the slug 
 may be seen to do, though in some species traces of the old 
 gill yet remain. 
 
 84. Food and digestive system. Many mollusks live upon 
 seaweeds, and the greater number of terrestrial forms are 
 fond of garden vegetables or certain kinds of lichens, but, 
 on the other hand, the latter, together with a large number 
 of marine snails, are carnivorous. In all cases the food 
 requires to be masticated, and, unlike the clams, the mouth 
 is usually provided with horny jaws, and an additional
 
 ANIMAL FORMS 
 
 FIG. 51. A small portion of the radnla or 
 tongue-rasp of a snail (Sycolypus). 
 
 masticatory apparatus which consists of a kind of tongue 
 with eight to forty thousand minute teeth in our land 
 forms (Fig. 51), while in certain marine snails they are 
 beyond computation. With the licking motion of the 
 tongue this rasp tears the food into shreds before it is 
 swallowed, and in the whelks or borers it serves to wear a 
 circular hole through the shells of other mollusks, which 
 are thus killed and devoured. 
 This latter process, is facili- 
 tated by the secretion of the 
 salivary glands, which has a 
 softening effect upon the 
 shell. Ordinarily the saliva 
 of snails exercises some di- 
 gestive action. 
 
 In the stomach of some 
 snails are teeth or horny 
 ridges which also are instrumental in crushing the food, 
 and in numerous minor respects peculiarities exist in differ- 
 ent species according to the nature of the food; but in its 
 general features the digestive tract is similar to that of 
 the clams. 
 
 The processes of circulation and excretion are also car- 
 ried on by means of systems which show a certain resem- 
 blance to those of the clams. As might be expected, certain 
 differences exist, sometimes very great, but they are of too 
 technical a nature to concern us further. 
 
 85. Sense-organs of lamellibranchs and gasterqpods. 
 The eyes of mollusks differ widely in their structure and 
 the position they occupy in the body. In our common 
 land snails two pairs of tentacles are borne on the head, 
 the lower acting as feelers, while each of the upper ones 
 bears on its extremity the eye, appearing as a minute black 
 dot (Fig. 48). In this same position the eyes of many 
 marine snails occur, but there are numerous species in 
 which there are other accessory eyes. In many of the
 
 MOLLUSKS 85 
 
 limpets, for instance, there are numbers of additional eyes 
 carried on the mantle edge just under the eaves of the 
 shell, and forming a row completely encircling the body. 
 (In the scallops there are two rows of brilliantly colored 
 eyes, set like jewels on the edges of the mantle just within 
 the halves of the shell.) In the chitons the eyes of the 
 head disappear by the time the animal attains maturity, 
 and in some species at least their place appears to be taken 
 by great numbers of eyes, sometimes thousands, which are 
 embedded' in the shells. On the other hand, eyes are com- 
 pletely absent in certain species of burrowing snails and in 
 several living in the gloomy depths of the sea far from the 
 surface ; they appear to be absent also from fresh-water 
 clams ; but the fact that certain species close their shell 
 when a shadow falls upon them, leads to the belief that 
 while actual eyes are not present the skin is extremely 
 sensitive to light. This is also the case with many snails. 
 ' 86. Smell. Since the sense of sight is generally unde- 
 veloped in the mollusks, they rely chiefly upon touch and 
 smell for recognizing the presence of enemies and food. 
 Tentacles upon the head and other parts of the body, and 
 a skin abundantly supplied with nerves, show them to pos- 
 sess a high degree of sensibility ; but in the greater num- 
 ber of species the sense of smell is of chief importance. 
 Many experiments show that tainted meat and strongly 
 scented vegetables concealed from sight and several feet 
 distant from many of our land and sea mollusks will attract 
 them at once. In these forms the sense of smell appears to 
 be located on the tentacles, but additional organs, possibly 
 of smell, are located on various portions of the body, usu- 
 ally in the neighborhood of the gills. 
 
 87. Taste and hearing. Several mollusks appear to be 
 almost omnivorous, but others are decidedly particular in 
 their choice of food, which leads us to suspect that they 
 possess to some extent the sense of taste. Nerves supply- 
 ing the base of the mouth have also been detected, which
 
 86 ANIMAL FORMS 
 
 may be those of taste ; but experiments along the line are 
 difficult to perform, and our knowledge of this subject is 
 far from complete. The same is true of hearing. Certain 
 organs, interpreted as ears and located in the foot, have 
 the form of two hollow sacs, containing one or more solid 
 particles of sand or lime, whose jarrings, when effected by 
 sonorous bodies, may result in hearing. On the other hand, 
 it is held by some that they, like the semicircular canals of 
 higher animals, may regulate the muscular movements 
 which enable the animal to keep its balance. 
 
 88. Egg-laying habits and development. The egg-laying 
 habits of the gasteropods differ almost as widely as their 
 haunts. The terrestrial forms lay comparatively fevr eggs, 
 ranging in size from small shot to a pigeon's egg in some 
 of the tropical species. These are buried in hollows in the 
 ground or under sticks and stones, and after a few weeks 
 hatch out young snails having the form of the adult. The 
 same is also true of most of the fresh-water snails, which 
 lay relatively smaller eggs embedded in a gelatinous mass 
 frequently found attached to sticks and leaves, or on the 
 walls of aquaria in which they are confined. Many marine 
 species construct capsules of the most varied patterns 
 which they attach to different objects, and in these the 
 young are protected until they hatch. In the limpets and 
 many of the chitons the eggs are laid by thousands directly 
 in the water, and after a short time develop into free-swim- 
 ming young, differing considerably from the parent in ap- 
 pearance. Those escaping the ravages of numerous enemies 
 finally settle down in a favorable situation and gradually 
 assume the form of the adult. 
 
 89. Age, enemies, and means of defense of lamellibranchs 
 and gasteropods. How much time is consumed by the young 
 in growing up, and the length of time they live, are ques- 
 tions generally unsettled. It is said that the oyster requires 
 five years to attain maturity, and lives ten years ; the fresh- 
 water clam develops in five years, and some species live from
 
 MOLLtTSKS 87 
 
 twelve to thirty years ; and the average length of life of 
 the snail appears to be from two to five years. Certain it 
 is that mollusks have numerous enemies besides man which 
 prevent multitudes from living lives of normal length. 
 Birds, fishes, frogs, and starfishes beset them continually, 
 and many fall a prey to the ravages of internal parasites or 
 to other mollusks. Under ordinary circumstances the shell 
 is sufficient protection, and the spines disposed on the sur- 
 face in many species render the occupant still less liable to 
 attack. Many snails carry on the foot a horny or calcare- 
 ous plate known as the operculum, which closes the en- 
 trance of the shell like a door against intruders. Certain 
 noxious secretions poured out from the skin also serve as a 
 means of defense, and many Xudibranchs (Fig. 50) bear 
 nettle-cells on the processes of the body, which probably 
 render them distasteful to many animals. Finally, there 
 are numerous clams, mussels, snails, and slugs whose colors 
 harmonize so closely with their surroundings that they al- 
 most completely baffle detection, and enable them to lead 
 as successful a life as those provided with special organs of 
 defense. 
 
 90. Cephalopods. The animals belonging to this class, 
 such as the -squids and cuttlefishes (Fig. 52), are by far 
 the most highly developed mollusks. They are of great 
 strength, capable of very rapid movements, and several spe- 
 cies are many times the largest invertebrates. In almost 
 every case there is a well-defined head bearing remarkably 
 perfect eyes, and also a circle of powerful arms provided 
 with numerous suckers which aid in the capture of food 
 (Fig. 52). Posteriorly the body is developed into a pointed 
 or rounded visceral mass which to a certain extent is free 
 from the head, giving rise to a well-marked neck. Some 
 forms, such as the squids (Fig. 52, upper figure), are pro- 
 vided with fins which drive the animal forward, but in com- 
 mon with other cephalopods they are capable of a very rapid 
 backward motion. By muscular movements water is taken
 
 88 
 
 ANIMAL FORMS 
 
 into the large mantle cavity within the body, a set of valves 
 prevents its exit through the same channels, and upon a 
 vigorous contraction of the body walls the water is forced 
 out rapidly through the small opening of the funnel, which 
 
 FIQ. 52. Cephalopods. Lower figure, the devil-fish or octopus (Octopus jninctatm). 
 The upper figure represents the squid (Loligo pealii) swimming backward by 
 driving a stream of water through the small tube slightly beneath the eyes. From 
 life, one-third natural size. 
 
 drives the animal backward after the fashion of an explod- 
 ing sky-rocket. In this way they usually escape the fishes 
 and whales that prey upon them, but an additional device 
 has been provided in the form of a sac within the body, 
 whose inky contents may be liberated in such quantity as 
 to cloud the water for a considerable distance, and thus 
 enable them to slip away unseen into some place of safety. 
 Most of the cephalopods are further protected by their 
 ability to assume, like the chameleon, the color of the object
 
 MOLLUSKS 89 
 
 upon which they rest. In the skin are embedded multi- 
 tudes of small spherical sacs filled with pigments of various 
 colors, chiefly shades of red, brown, and blue, each sac be- 
 ing connected with a nerve and a series of delicate muscles. 
 If the animal settles upon a red surface, for example, a 
 nerve impulse is sent to each of the hundreds of color sacs 
 of corresponding shade, causing the muscles to contract 
 and flatten the bag like a coin, and thus exposing a far 
 greater surface than before, they^give the animal a reddish 
 hue. In the twinkling of an eye they may completely 
 change to another tint, or present a mottled look, and some 
 may even throw the surface of the skin into numerous 
 small projections that make the animal appear part of the 
 rock upon which it rests. These devices not only serve for 
 protection, but they also aid in enabling these mollusks to 
 steal upon their prey, chiefly fishes, which they destroy in 
 great numbers with lionlike ferocity. 
 
 The devil-fishes and a number of other species are usu- 
 ally found creeping along the sea bottom, generally near 
 shore, and are solitary in their habits, while the squids re- 
 main near the surface and frequently travel in great com- 
 panies, sometimes numbering hundreds of thousands. In 
 size they usually range from a few inches to a foot or two 
 in length, but a few devil-fishes and squids attain a greater 
 size, some of the latter reaching the enormous length of 
 from forty to sixty feet. There are many stories of their 
 great strength and of their voluntarily attacking people 
 and even overturning boats, but the latter are in almost 
 every case sailors' yarns. 
 
 In their external organization the cephalopods have 
 little to remind one of any of the preceding mollusks, and 
 their internal structure shows only a distant resemblance. 
 In the Octopi (Fig. 52) the shell is lacking ; in the squid it 
 is called the pen, and consists of a horn-like substance with- 
 out any lime deposit ; in the cuttlefishes it is spongy and 
 plate-like, and is a familiar object in the shops ; and, finally,
 
 90 ANIMAL FORMS 
 
 in the nautilus it is coiled and of considerable size, and, un- 
 like that of any other cephalopod, it is carried on the out- 
 side of the animal. Interiorly it is divided by a number of 
 partitions into chambers, the last one of which is occupied 
 by the animal. 
 
 The alimentary canal shows some resemblance to that 
 of other mollusks, but, as in the case of the other systems 
 of the body, it possesses a far higher state of development. 
 The mouth is situated in the center of a circle of arms, 
 which in reality are modified portions of the foot, and is 
 furnished with two parrot-like jaws. From this point the 
 esophagus leads back into the body mass to the stomach, 
 which with the liver and intestine are sufficiently like 
 those of the clam and snail to require no further comment. 
 
 Eespiration is effected by the skin to a certain extent, 
 but chiefly by two gills (four in the nautilus), and the cir- 
 culatory system, which conveys the blood to and from these 
 organs and over the body with its complex heart, arteries, 
 capillaries, and veins, is more highly developed than in 
 any other invertebrate. 
 
 As might be expected in animals with so great sagacity 
 and cunning, the nervous system of the sense-organs reach 
 a degree of development but little short of what we find in 
 some of the vertebrates. The chief part of the nervous 
 system is located in the head, protected by a cartilaginous 
 skull, a very rare structure among invertebrates ; and while 
 the different ganglia may be recognized in a general way 
 and be found to correspond to a certain extent to those 
 of foregoing mollusks, they are so largely developed and 
 massed together that it is impossible at present to under- 
 stand them fully. From this point nerves pass to all 
 regions of the body, to the powerful muscles, the viscera, 
 and the organs of special sense, controlling the complex 
 mechanism in all its workings. 
 
 There is no doubt that the cephalopods see distinctly 
 for considerable distances, and a careful examination of
 
 MOLLUSKS 91 
 
 the eye of the squids and cuttlefishes has shown them 
 to be remarkably complex and in many respects to be 
 constructed upon much the same plan as those of the 
 vertebrates. As to the other senses not so much is known, 
 but undoubtedly many species of cephalopods are possessed 
 of a shrewdness and cunning not shared by any other 
 invertebrates, save some of the insects and spiders, and are 
 vastly more highly organized than their molluscan rela- 
 tives. 
 
 91. How species originate. We have now examined a 
 considerable portion of the animal kingdom, tracing its 
 members from their simplest beginnings as single cells, 
 through the formation of colonial types, and up through 
 the sponges, ccelenterates, worms, and mollusks. It is im- 
 portant once more to note that they all perform the func- 
 tions concerned in nutrition and reproduction, and only 
 these. The differences which exist are those of structure. 
 The Hydra and the clam, for example, perform the same 
 duties, but their bodily apparatus differs widely, and the 
 completeness and perfection of the work varies accord- 
 ingly. The more the work to be performed by an organ- 
 ism is divided up among especially adapted organs, so that 
 each of the latter has, as far as possible, only one thing to 
 do, the higher is the organism. 
 
 As stated earlier in the account, it is believed that the 
 more complex animals arose from the simpler ; that if we 
 could trace the history of any of the great groups back 
 toward their first beginnings, we would find them all to 
 have originated from one ancestral form, that in turn owes 
 its descent from yet simpler forms. 
 
 Let us see something of how this has come about. We 
 all know that vast numbers of young are born into this 
 world which never come to maturity. It is said that if all 
 the young of the codfish were to live their allotted time, 
 it would be less than fifteen years before the sea would 
 become literally packed with them. Numerous enemies,
 
 92 ANIMAL FORMS 
 
 the lack of food, and other agencies annihilate the larger 
 part. We also know that no two offspring are exactly 
 alike. They exhibit individual differences. One bird may 
 have a larger bill than another of the same brood which 
 excels in length of wing. As noted above, all the offspring 
 will not attain maturity. Those best adapted to their sur- 
 roundings will have the best chances of survival. The 
 increased length of bill or wing may be. slight, but it may 
 be just this amount which enables the bird to probe deeper 
 or fly farther and thus secure the requisite amount of food. 
 A premium is placed on length of wing or bill generation 
 after generation, with the result that a long-billed species 
 arises distinct from the long-winged which trace their 
 ancestry back to the same parents. It is the same prin- 
 ciple which enables the breeder to increase the swiftness 
 of the race-horse and the strength of the draft-horse, or 
 the gardener to develop from the wild rose the great num- 
 ber of widely different varieties. In the same way other 
 slight peculiarities over very many generations may en- 
 .able other forms to gradually adapt themselves to still dif- 
 ferent modes of life. Thus vast numbers of organisms 
 gradually become modified in form and complexity, and 
 are adapted to lives which insure them a comparative 
 degree of safety and less competition with other species.
 
 CHAPTER IX 
 
 ARTHROPODS. CLASS CRUSTACEA 
 
 92. General characters. In the Arthropods, that is, the 
 crabs, lobsters, shrimps, insects, spiders, and a vast host 
 of related forms, the body is bilaterally symmetrical, and 
 is composed of a number of segments arranged in a series, 
 as in the earthworm and other annelids. A hornlike cu- 
 ticle, sometimes called the shell, bounds the external sur- 
 face in early life thin and delicate, but later relatively 
 thick, and often further strengthened by lime salts. Along 
 the line between the segments this coat of mail remains 
 thin and forms a flexible joint. Appendages also are borne 
 on each segment, not comparatively short and fleshy out- 
 growths like the lateral appendages of many of the worms, 
 but usually long and jointed (hence the name Arthropod, 
 meaning jointed foot), and variously modified for many 
 different uses. 
 
 93. Classification. The species belonging to this group 
 outnumber the remainder of the animal kingdom. Their 
 haunts also are most diverse. Some are adapted for lives 
 in the sea and fresh water, others for widely different sit- 
 uations on land, and a great number are constructed for a 
 life on the wing. A certain resemblance exists among them 
 all, but the modifications which fit them for their different 
 habitats are also profound, and have resulted in the division 
 of the Arthropods into five classes. The first class ( Crus- 
 tacea) contains the crayfish, crabs, etc. ; the second (Ony- 
 chophora) includes the curious worm-like peripatus (Fig. 
 
 93
 
 94 ANIMAL FORMS 
 
 66); the third (Myriapoda, meaning myriad-footed) em- 
 braces the centipeds and "thousand-legs"; the fourth (In- 
 secta] contains the insects; and the fifth (Arachnida) in- 
 cludes the scorpions, spiders, and mites. 
 
 94. The Crustacea. The number of species of crusta- 
 ceans is estimated to be about ten thousand, and while the 
 greater number of these are marine, many are found in 
 fresh water and a few occur on land. In size they range 
 from almost microscopic forms to the giant crabs and 
 lobsters. They differ also in shape to a remarkable degree, 
 but at the same time there is a decided resemblance through- 
 out the group, except in those species which have become 
 modified by a parasitic habit. The characteristic external 
 skeleton is invariably present, and gives evidence of the 
 deep internal segmentation of the body. In the simple 
 Crustacea this is very apparent, but in the higher forms it 
 is usually more or less obscured, owing to the fusion of some 
 of the different segments, especially those of the head, as in 
 the crayfish (Fig. 59). 
 
 The class of the Crustacea is subdivided into two sub- 
 classes (Entomostraca and Malacostraca), the first containing 
 the fairy-shrimps (Branchipus, Fig. 53) and their allies, the 
 copepods (such as Fig. 54), the barnacles (Fig. 55), and a 
 number of other species. In their organization all are com- 
 paratively simple, usually small, and the appendages show 
 relatively little specialization. The other subclass contains 
 the more highly developed and usually large-sized Crustacea, 
 among which are the shrimps, crayfishes, lobsters, crabs, 
 and a number of other forms. 
 
 95. Some simple Crustacea. While the members of the 
 first subclass are minute and inconspicuous, several species 
 are often remarkably abundant in our small fresh-water 
 pools. Among these is the beautifully colored fairy-shrimp 
 (Branchipus, Fig. 53), with greatly elongated body and 
 leaf-like appendages, whose relatively simple character leads 
 the zoologist to think that they are among the simplest
 
 ARTHROPODS. CLASS CRUSTACEA 95 
 
 Crustacea, and in several points resemble the ancestral form 
 from which all the modern species have descended. Some 
 nearly related forms are provided with a great fold of the 
 body-wall, which may almost completely conceal the animal 
 from above, or it may be formed like a bivalve clam-shell, 
 within which the entire body may be withdrawn. This 
 
 FIG. 53. Fairy-shrimp (Branchipvs). b, brood-pouch ; <?, e', 
 compound and simple eyes ; /, paddle-shaped feet ; h, tu- 
 bular heart ; i, intestine. 
 
 latter character is also found in the water-fleas (Daphnia), 
 very much smaller forms, and sometimes occurring in mil- 
 lions on the bottoms of our ponds and marshes. They are 
 readily distinguished from the fairy-shrimp by the short- 
 ness of the body, the small number of appendages, and by 
 their habit of using their antennae as swimming organs, 
 which gives to their locomotion a jerky, awkward character. 
 96. Cyclops and relatives. Cyclops (Fig. 54), the repre- 
 sentative of a number of lowly forms belonging to the order 
 of Copepods, is one of the commonest fresh-water Crustacea. 
 The forward segments of the spindle-shaped body are cov- 
 ered by a large shield or carapace, the feet are few in num- 
 ber, and, like its fabled namesake, it bears an eye in the 
 center of the forehead. Nearly related species are also re- 
 markably abundant at the surface of the sea, at times occur-
 
 ANIMAL FORMS 
 
 ring in such vast numbers that they impart a reddish tinge 
 to the water over wide areas, and at night are largely re- 
 sponsible for its phos- 
 phorescence. Many oth- 
 ers are parasitic in their 
 habits, and scarcely a 
 salt-water fish exists but 
 that at one time or an- 
 other suffers from their 
 attacks. On the other 
 hand, many fresh- and 
 salt-water fishes depend 
 upon the free-swimming 
 forms for food, and 
 hence, from an economic 
 point of view, they are 
 highly important organ- 
 isms. 
 
 97. Barnacles. The 
 parasitic habit and the 
 lack of locomotion has 
 also produced marvelous 
 changes among the bar- 
 nacles, so great that 
 originally they were 
 placed among the mol- 
 lusks ; and as with the parasitic copepods, their true posi- 
 tion was only known after their life-history had been de- 
 termined. In the goose-barnacles * the body, attached by 
 a fleshy stalk to foreign objects, is enclosed by a tough 
 membrane, corresponding to the carapace of other Crus- 
 tacea, in which are embedded five calcareous plates. This 
 
 FIG. 54. Cyclops, e. s., eggs ; i, intestine 
 reproductive organ. 
 
 * So called because of the belief, which existed for three hundred 
 years prior to the present century, that when mature these animals 
 give birth to geese.
 
 ARTHROPODS. CLASS CRUSTACEA 
 
 97 
 
 is open along one side, and allows the feather-like feet to 
 project and produce currents in the surrounding water 
 which brings food within reach. In the acorn-barnacles 
 (Fig. 55) the stalk is absent, and the body, though possess- 
 
 FIG. 55. Barnacles. Acorn-barnacles chiefly in lower part of figure ; goose-barnacles 
 above. Natural size. 
 
 ing the same general character as the goose-barnacles, is 
 shorter, and enclosed in a strong palisade consisting of six 
 calcareous plates. 
 
 The larger number of barnacles attach themselves to 
 the supports of wharves, the hulls of ships, floating tim- 
 bers, the rocks from the shore-line down to considerable 
 depth, and a few species occur on the skin of sharks and 
 whales. On the other hand, there are severaLspecies which 
 are parasitic, and in accordance with this mode of life ex- 
 hibit various degrees of degeneration. In the most extreme
 
 98 ANIMAL FORMS 
 
 cases (Sacculina) the sac-like body, attached to the abdo- 
 men of crabs, is entirely devoid of appendages and any 
 signs of segmentation. A root-like system of delicate fila- 
 ments extends from the exposed part of the animal into 
 the host and absorbs the necessary nutriment. The mouth 
 and alimentary canal are accordingly absent in fact, the 
 body contains little but the reproductive organs and a very 
 simple nervous system. 
 
 98. Structure. In the internal organization of these 
 smaller crustaceans many differences may be noted, though 
 they are usually less profound than the external. Ordi- 
 narily the- alimentary canal is a straight tube passing 
 through the body, and is provided with a pouch-like 
 stomach, and a more or less clearly defined liver. In 
 all, except the parasitic species, the external mouth-ap- 
 pendages masticate the food, and in a very few of the 
 above-described groups it may be further ground between 
 the horny ridges on the stomach-walls. After this pre- 
 liminary treatment it is subjected to the action of the 
 digestive juices, and when liquefied is absorbed into the 
 body. Here it is circulated by a blood-system of widely 
 different character. In many cases definite arteries and 
 veins are absent. The blood courses through the body in 
 the spaces between the different organs propelled by the 
 beating of the heart, which it is made to traverse. In 
 Cyclops (Fig. 54) even the heart is absent, and the blood 
 is made to circulate by contractions of the intestine. In 
 most of these smaller Crustacea considerable oxygen is ab- 
 sorbed through the body-wall ; but in several species, for 
 example, the fairy-shrimp (Fig. 53), special gills are devel- 
 oped on the appendages of the body. 
 
 99. Multiplication. Among the Crustacea thus far con- 
 sidered the males are usually readily recognized owing to 
 their small size. The females also are usually provided 
 with brood-pouches in which the developing eggs are pro- 
 tected. In almost every case the young are born in the
 
 ARTHROPODS. CLASS CRUSTACEA 
 
 99 
 
 form of minute larvae, provided with three pairs of append- 
 ages, a median eye (Fig. 56), and a firm external skeleton 
 or cuticle. This latter prevents the continuous growth of 
 the larvae or nauplius, and every few days it is thrown off, 
 and while the new one is forming the body enlarges. Dur- 
 ing this time new appendages are developed, so that after 
 each moult the young crusta- 
 cean emerges less like its 
 former self and more and more 
 like its parents. In the bar- 
 nacles, after several moults 
 have taken place, the young 
 become permanently attached 
 by means of their first anten- 
 nae, their thoracic feet change 
 into feathery appendages, and 
 several other changes occur. 
 In some of the parasitic bar- 
 nacles (Sacculina) the larva 
 attaches itself to a crab, throws 
 off its various appendages, and, 
 after other great degenerative 
 changes, enters its host. For 
 a time, therefore, their development is toward greater com- 
 plexity, but the later stages constitute a retrograde meta- 
 morphosis. 
 
 100. More complex types. The larger, more useful, and 
 usually more familiar Crustacea belong to the second divi- 
 sion (subclass Malacostraca). It comprises such animals as 
 the shrimps, crayfish, lobsters, crabs, and a number of other 
 forms which are at once distinguished from the preceding 
 by the constant number of segments composing the body. 
 Of these, five constitute the head, eight the thorax, and 
 seven the abdomen. The head segments are always fused 
 together, and with them one or more thoracic segments 
 unite to form a more or less complete cephalothorax. Also, 
 
 FIG. 56. Development of a barnacle 
 (Lepas). a, larva ; b, adult.
 
 100 ANIMAL FORMS 
 
 some of the head segments give rise to a great fold of the 
 body-wall, the carapace, which extends backward and covers 
 all or a part of the thorax, with which it may firmly unite, 
 as in the crayfish. The appendages are usually highly spe- 
 cialized, and are made to perform a variety of functions. 
 
 101. The shrimps. Among the simplest of these are the 
 opossum-shrimps (Fig. 57) and their relatives, small trans- 
 
 FIG. 57. The opossum-shrimp (Mysis americana). 
 
 parent creatures often seen swimming in great numbers at 
 the surface of the sea or hiding among the seaweeds along 
 the shore. In general appearance they resemble crayfishes 
 or prawns, but are readily distinguished by the two-branched 
 thoracic feet. This " split-foot " character also occurs 
 among many of the preceding Crustacea, and is generally 
 a badge of low organization, tending to disappear in the 
 more highly organized forms. In this and other respects 
 the shrimps are especially interesting in their relation to 
 the preceding Crustacea, and in the fact that they may 
 closely resemble the ancestors of the modern prawns (Fig. 
 58), lobsters, crayfishes, and crabs. 
 
 102. Crayfishes and lobsters. The last-mentioned spe- 
 cies and their allies, usually large and familiar forms, con- 
 stitute a group known as the decapods (meaning ten feet), 
 referring to the number of thoracic feet. Among the mem- 
 bers of this division probably none are more familiar than 
 the crayfishes, which occur in most of the larger rivers and 
 their'tributaries throughout the United States and Europe. \ 
 It is their habit to remain concealed in crevices of rocks
 
 ARTHROPODS. CLASS CRUSTACEA 
 
 101 
 
 or in the mouths of the burrows which they excavate, and 
 from which they rush upon the small fish, the larvae of 
 
 FIG. 58. Prawn (Heplacarpus brevirostris). 
 
 many animals, and other equally defenseless creatures 
 which constitute their bill of fare. In turn they are 
 eagerly sought by certain birds and four-footed animals, and, 
 especially in France, 
 are extensively used for 
 food by man. 
 
 Closely related to 
 .the crayfishes and dif- 
 fering but little from 
 them structurally are 
 the lobsters. In this 
 country they are con- 
 fined to the rocky coasts 
 from Xew Jersey to 
 Labrador, living upon 
 fish, fresh or otherwise, 
 various invertebrates, 
 and occasionally sea- 
 weeds. Far more than 
 the crayfish, the lobster 
 is in demand as an arti- 
 cle of food. By the aid 
 
 Of nets or Various traps FIG. 59. The crayfish (Astacus).
 
 102 ANIMAL FORMS 
 
 millions are caught each, year, and to such an extent has 
 their destruction proceeded that in many places they are 
 well-nigh exterminated. At the present time, however, leg- 
 islation, numerous hatcheries, and a careful study of their 
 life habits is doing much to better matters and inciden- 
 tally to put us in possession of many interesting zoological 
 facts along this line, some of which will be mentioned later. 
 Frequently the prawns, especially the larger ones, and a 
 spiny lobster (Palinurus), are mistaken for crayfishes or 
 lobsters, but they differ from them in the absence of the 
 large grasping claws. 
 
 Along almost any coast some of these animals are to be 
 found, often beautifully colored and harmonizing with the 
 seaweeds among which they live, or so transparent that 
 their internal organization may be distinctly seen. Farther 
 out at sea other species swim in incredible numbers, feed- 
 ing upon minute organisms, and in turn fed upon by numer- 
 ous fishes and whales ; and, especially on the Pacific coast, 
 shrimp-fishing is an important industry. 
 
 103. The hermit-crabs. The last of these long-tailed 
 decapods is the interesting group of the hermit-crabs, 
 which occur in various situations in the sea. In early life 
 they take possession of the empty shell of some snail, and 
 the protected abdomen becomes soft and flabby, while the 
 appendages in this region almost completely disappear. 
 The front part of the body, on the other hand, continually 
 grows in firmness and strength, and is admirably adapted 
 for the continual warfare which these forms wage among 
 themselves. As growth proceeds the necessity arises for a 
 larger shell, and the crab goes "house-hunting" among the 
 empty shells along the shore, or it may forcibly extract the 
 snail or other hermit from the home which strikes its- fancy. 
 
 Many of the hermit-crabs enjoy immunity from the 
 attacks of their belligerent relatives by allowing various 
 hydroids to grow upon their homes. Others attach sea- 
 anemones to their shells or to one of their large claws,
 
 ARTHROPODS. CLASS CRUSTACEA 
 
 103 
 
 which they poke into the face of any intruder. While 
 the anemones or hydroids are made to do valiant service 
 
 FIG. 60. Hermit-crab (Pagurus bernhardus) in snail shell covered with Hydractima. 
 
 with their nettle-cells, they also enjoy the advantages of 
 a large food-supply which is attendant upon the free ride. 
 
 104. The crabs. The most highly developed Crustacea 
 are the crabs or short-tailed decapods which abound between 
 tide-marks alongshore, and in diminishing numbers extend 
 to great depths. The cephalothorax is usually relatively 
 wide, often wider than long, and the greatly reduced abdo- 
 men is folded against the under side of the thorax. Corre- 
 lated with the small size of the abdomen, the appendages 
 of that region disappear more or less, but the remaining 
 appendages are similar to those of the crayfish or lobsters. 
 All these different parts, however, are variously modified in 
 each species to fit it for its own peculiar mode of life. In 
 some forms, such as the common cancer-crab (Fig. 61), the 
 legs are comparatively thick-set and possessed of great 
 strength, enabling them to defend themselves against most 
 enemies. On the other hand, there are the spider-crabs 
 with small bodies and relatively long legs, withal weak, and
 
 104: 
 
 ANIMAL FORMS 
 
 yet so harmonizing with their surroundings that they are 
 as likely to survive as their stronger relatives. In this 
 
 Fio. 61. Kelp-crab (Epialtus productus) in upper part of figure ; to the right the 
 edible crab (Cancer productus), and the shore-crab (Pugettia richii). 
 
 connection it is interesting to note that the giant crab of 
 Japan, the largest crustacean, being upward of twenty feet 
 from tip to tip of the legs, is a spider-crab, constructed on 
 
 FIG. 62. The fiddler-crab (Gelasimtu). Photograph by Miss MABV RATHBUS. 
 
 the same general pattern as our common coast forms. 
 Between these two extremes numberless variations exist,
 
 ARTHROPODS. CLASS CRUSTACEA 
 
 105 
 
 some for known reasons, biit more often not readily under- 
 stood. And not only does the form vary, but the external 
 surface may be sculptured or beset with spines or tubercles 
 which frequently render the animal inconspicuous amid its 
 natural surroundings. Such an effect is heightened by the 
 presence of sponges, hydroids, and various seaweeds which 
 the crab often permits to gather upon its body. 
 
 105. Pill-bugs and sandhoppers. Finally there remain the 
 groups of the pill- or sow-bugs (Isopods) and the sand-fleas 
 or sandhoppers (Amphipods). In the first of these the 
 body is usually small and compressed, the thorax more or 
 less plainly segmented, and the seven walking (thoracic) 
 legs are similar. In the female each leg bears at its base a 
 thin membranous plate which extends inward and hori- 
 
 FIG. 63. Isopod or pill-bug (Porcellio laevis). 
 
 zontally, thus forming on the under side of the body a 
 brood-pouch (Fig. 63) in which the young develop. As 
 one may readily discover in any of the common species, 
 the abdominal segments are more or less fused, and bear 
 appendages adapted for respiration and, in the aquatic 
 forms, for swimming.
 
 106 
 
 ANIMAL FORMS 
 
 The marine isopods occur in the sand, under rocks, and 
 in the seaweeds ; many are parasitic upon fishes ; and the ter- 
 restrial forms (Fig. 63) are very common objects under old 
 
 FIG. 64. Amphipods or sand-fleas (Gammarm, upper species, and Caprella). 
 
 logs and in cellars, where they live chiefly on vegetable mat- 
 ter. In the sand-fleas the body is compressed from side to 
 side, and while the thorax shows distinct segments, the legs 
 are frequently dissimilar, and some may bear pincers. One 
 of their most distinctive marks concerns the last three ab- 
 dominal appendages, which are usually modified for leaping. 
 The sand-fleas (Fig. 64) are familiar objects to any one 
 who has collected along the beach and has turned over the 
 cast-up seaweeds, while numbers of small species often oc- 
 cur among the plants in our fresh-water ponds. Some most 
 curious and highly modified forms, whose general appear- 
 ance is shown in the lower part of Fig. 64, occur among
 
 ARTHROPODS. CLASS CRUSTACEA 107 
 
 hydroid colonies, with which their bodies harmonize in 
 form and color. And, lastly, most bizarre creatures, known 
 as " whale-lice," attach themselves to the skin of whales, of 
 which each species acts as host for one or more kinds. 
 
 106. Internal organization. Most Crustacea are carnivo- 
 rous, preying upon almost any of the smaller animals within 
 convenient reach ; a much smaller number live on vege- 
 table food ; and there are many, such as the crayfishes, lob- 
 sters, and numerous crabs, which are also notorious scaven- 
 gers. In these latter forms the food is held in one of the 
 large pincers, torn into shreds by the other, and transferred 
 to the mouth-parts, where, as in all Crustacea, it is soon 
 reduced to a pulp by their rapid movements. In many 
 species the food is now ready for the digestive process, 
 but not so in the higher forms. If the stomach of any of 
 these, for example, the crabs or crayfishes, be opened, three 
 (Fig. 65, *) large teeth operated by powerful muscles will 
 be noted, and beyond these a strainer consisting of many 
 closely set hairs. In operation this " gastric mill " takes 
 the food passed on from the mouth-parts, and crushes and 
 tears it until fine enough to pass through the strainer, 
 whereupon it is dissolved by the juices from the liver and 
 is absorbed as it passes down the intestine. 
 
 The circulatory system is usually highly developed, and 
 consists of a heart, in some species almost as long as the 
 body, though usually shorter (Fig. 65), from which two or 
 more arteries branch to all parts of the body. Here the 
 blood, instead of emptying into definite veins, pours into a 
 series of spaces or sinuses in among the muscles and other 
 organs of the body, through which it makes its way back to 
 the heart. During this return journey it is usually made 
 to traverse definite respiratory organs, either situated upon 
 the legs or, as feathery outgrowths, upon the sides of the 
 body, and generally concealed under the carapace. A por- 
 tion of the blood is also continually sent to the kidneys, 
 which are located either at the base of the second antenna?
 
 108 ANIMAL FORMS 
 
 (and known as green glands), as in the crayfishes or crabs, 
 or on the second maxillae (shell-glands) in many of the 
 
 FIG. 65. Dissection of crayfish, b, brain ; h, heart ; i, intestine ; k, kidney ; /, liver ; 
 n, nerve-cord ; r, reproductive organ ; s, stomach, showing two teeth in position. 
 
 simpler crustaceans. Their method of operation is much 
 like that of the kidneys in the earthworm. 
 
 107. Nervous system and special senses. The nervous sys- 
 tem also shows a decided resemblance to that of the anne- 
 lids. The cerebral ganglia or brain is situated above the 
 alimentary canal in the head, and connects with the ven- 
 trally lying cord by a collar. As in the earthworm, this 
 ventral cord is double, and bears a pair of swellings or gan- 
 glia in each segment. In the crayfish, crabs, and other 
 highly modified forms, where the segments tend to fuse, 
 several of these ganglia may also unite, and except in early 
 life their number cannot be determined. 
 
 Among the less specialized Crustacea the order of intel- 
 ligence is low, though perhaps it may prove to be higher 
 than is usually supposed when such forms have been more 
 thoroughly studied. The following quotation relating to 
 the lobster applies even more to the higher forms, the 
 crabs : " Sluggish as it often appears when out of water and 
 when partially exhausted, it is quite a different animal when 
 free to move at will in its natural environment on the sea-
 
 ARTHROPODS. CLASS CRUSTACEA 109 
 
 bottom. It is very cautious and cunning, capturing its 
 prey by stealth, and with weapons which it knows how to 
 conceal. Lying hidden in a bunch of seaweed, in a crevice 
 among the rocks, or in its burrow in the mud, it waits until 
 its victim is within reach of its claws, before striking the 
 fatal blow. The senses of sight and hearing are probably 
 far from acute, but it possesses a keen sense of touch and 
 of smell, and probably also a sense of taste." 
 
 Although enclosed in a horny and often very thick and 
 strong armor, the sense of touch is very keen in the 
 Crustacea and in arthropods generally. On many of the 
 more exposed portions delicate hairs or pits connected 
 with the nervous system occur in great abundance. Some 
 of these, usually on the antennae, undoubtedly serve in 
 detecting odors, but the remainder are considered to be 
 tactile. In the higher Crustacea, such as the crayfish, 
 lobsters, and crabs, ears are usually found, consisting of 
 sacs lined with similar delicate hairs, and containing sev- 
 eral minute grains of sand, which in many cases make their 
 way through the small external opening. Vibrations com- 
 ing through the water gently shake the grains of sand, 
 causing them to strike against the hairs which communi- 
 cate with the nervous system a very simple ear, yet suffi- 
 cient for the needs of the animals. 
 
 The eyes of the Crustacea and arthropods in general are 
 either simple or compound. The simple and frequently 
 single eyes usually consist of a relatively few cells embedded 
 in a quantity of pigment and connected with the nervous 
 system. It is doubtful whether they perceive objects as 
 anything more than highly blurred images, and perhaps 
 they merely recognize the difference between light and 
 darkness. The compound eyes, on the other hand, are 
 remarkably complex structures, often borne on the tops of 
 movable stalks, as in the common crabs and crayfishes. 
 Each consists of an external transparent cornea, divided 
 into numerous minute hexagonal areas corresponding to as
 
 110 ANIMAL FORMS 
 
 many internal rods of cells, provided with an abundant 
 nerve-supply. These latter elements may perhaps repre- 
 sent simple eyes grouped together to form the compound 
 one ; and it appears possible that each element may form 
 a complete image of an object, as each of our eyes is known 
 to do. On the other hand, many hold that the complete 
 eye forms only one image, a mosaic, each element con- 
 tributing its share. 
 
 108. Growth and development. As we have seen, the 
 simpler Crustacea hatch as minute larvae (Fig. 56), and dur- 
 ing their growth to the adult condition are especially sub- 
 ject to the attacks of multitudes of hungry enemies. In 
 the higher forms, such as the crabs, some of these early 
 transformations take place while the young are still within 
 the egg and attached to the parent. Accordingly, the little 
 ones are fairly similar to their parents, and their later his- 
 tory is very well exemplified by the lobster. 
 
 The eggs of the lobster are most frequently hatched in 
 the summer months, usually July, after they have been 
 carried by the parent for upward of a year. The young, 
 about a third of an inch in length, at once disperse, undergo 
 four or five moults during the next month, then, ceasing 
 their swimming habits, settle to the bottom among the 
 rocks. At this time, twice their original size, they closely 
 resemble their parents, and their further development is 
 largely an increase in size. " The growth of the lobster, 
 and of every arthropod, apparently takes place, from in- 
 fancy to old age, by a series of stages characterized by the 
 growth of a new shell under the old, by the shedding of 
 the outgrown old shell, a sudden increase in size, and the 
 gradual hardening of the shell newly formed, ^ot only is 
 the external skeleton cast off in the moult and the linings 
 of the masticatory stomach, the esophagus, and intestine, 
 but also the internal skeleton, which consists for the most 
 part of a complicated linkwork of hard tendons to which 
 muscles are attached.'?
 
 ARTHROPODS. CLASS CRUSTACEA 
 
 111 
 
 109. Peripatus (class Onychophora). It is generally be- 
 lieved that the Crustacea, insects, and spiders, together 
 with their numerous relatives, trace their ancestry back to 
 animals that bore a certain resemblance to the segmented 
 worms. Most of these ancient types have 
 
 long been extinct, but here and there 
 throughout the earth we occasionally meet 
 with them. 
 
 Among the most interesting of these 
 are a few widely distributed species belong- 
 ing to the genus Peripatus (Fig. 66), but as 
 they are comparatively rare we shall dis- 
 miss them with a very brief description. 
 They usually dwell in warm countries, un- 
 der rocks and decaying wood, emerging at 
 night to feed on insects, which they ensnare 
 in the slime thrown out from the under 
 surface of the head. Their external form, 
 their excretory system, and various other 
 organs are worm-like. On the other hand, 
 the appendages are jointed, and one pair 
 has been modified into jaws. The peculiar 
 breathing organs characteristic of the in- 
 sects are also present. Peripatus therefore 
 gives us an interesting link between the 
 worms and insects, and also affords an idea 
 of the primitive insects from which the 
 modern forms have descended. 
 
 110. The centipeds and millipeds (class 
 Myriapoda). Many of the myriapods that 
 is, the centipeds and thousand-legged worms 
 are familiar objects under logs and stones 
 throughout the United States. The first of these (Fig. 67) 
 are active, savage creatures, devouring numbers of small 
 animals, which they sting by means of poison-spines on the 
 tips of the first pair of legs. The bite of the larger tropical 
 
 FIG. 66. Peripatns 
 (Peripatus eiseni). 
 Twice the natural
 
 112 ANIMAL FORMS 
 
 species especially causes painful but not fatal wounds in 
 man. 
 
 On the other hand, the millipeds (Fig. 68) or thousand- 
 legs are cylindrical, slow-going animals, feeding on vegetable 
 
 PIG. 67. Centiped. 
 One-half natural size. 
 
 FIG. 68. Thousand-legs or milliped (Julus). 
 Natural size. 
 
 substances without causing any particular damage, except in 
 the case of the " cutworms," which often work great injury 
 to crops. When disturbed they make little effort to escape, 
 but roll into a coil and emit an offensive-smelling fluid, 
 which renders them unpalatable to their enemies. 
 
 All present a great resemblance to the segmented worms, 
 as their popular names often testify ; but, on the other 
 hand, many points in their organization indicate a closer 
 relationship to the insects. As in the latter, the head is 
 distinct, and bears a pair of antennae, the eyes, and two or 
 three pairs of mouth-parts. The trunk is more worm-like, 
 and consists of a number of similar segments, each bearing
 
 ARTHROPODS. CLASS CRUSTACEA 113 
 
 one or two pairs of jointed legs. In their internal organ- 
 ization the character of the various systems closely resem- 
 bles that of the insects, and will be more conveniently 
 described in that connection. 
 
 Among the myriapods the females are usually larger 
 than the males. Some of the centipeds deposit a little 
 mass of eggs in cavities in the earth and then abandon 
 them, while others wrap their bodies about them and pro- 
 tect them until the young are hatched. The millipeds lay 
 in the same situations, but usually plaster each egg over 
 with a protective layer of mud. After several weeks the 
 young appear, often like their parents in miniature, but in 
 other species quite unlike, and requiring several molts to 
 complete the resemblance.
 
 CHAPTER X 
 
 ARTHROPODS (Continued}. CLASS INSECTS 
 
 111. Their numbers. It has been estimated that upward 
 of three hundred thousand named species of insects are 
 known to the zoologist, and that these represent a fifth, or 
 possibly a tenth, of those living throughout the world. Many 
 of these species, as the may-flies and locusts, are represented 
 by millions of individuals, which sometimes travel in such 
 great swarms that they darken the sky. With nearly all 
 of these the struggle for existence is fierce and unrelenting, 
 and it is little wonder that such plastic animals have 
 changed in past times and are now becoming modified in 
 order to adapt themselves to new situations where food is 
 more abundant and the conditions less severe. Owing to 
 such modifications we find some species fitted for flyiug, 
 others for running and leaping, or for a life underground, 
 and many for a part or all of their lives are aquatic in their 
 habits. 
 
 112. External features. The body of an insect the 
 grasshopper, for example consists of a number of rings 
 arranged end to end, as we have seen them in the Crustacea 
 and the segmented worms. In the abdomen these are 
 clearly distinct, but in the thorax, and especially the head, 
 they have become so intimately united that their number 
 is a matter of uncertainty. These three regions head, 
 thorax, and abdomen are usually clearly defined in most 
 insects, but they are modified in innumerable ways in ac- 
 cordance with the animal's mode of life. 
 
 114
 
 ARTHROPODS. CLASS INSECTS 115 
 
 The head usually carries the eyes, a pair of feelers (an- 
 tennae), and three pairs of mouth-parts which may be fash- 
 ioned into a long, slender tube to be used in sucking, and 
 frequently as a piercing organ ; or they may be constructed 
 for cutting and biting. The thorax bears three pairs of 
 legs and often one or two pairs of wings. The appendages 
 of the abdomen are usually small and few in number, or 
 even absent. 
 
 113. Internal anatomy. The restless activity of insects 
 is proverbial. Some appear to be incessantly moving about, 
 either on the wing or afoot, and are endowed with com- 
 paratively great strength. Ants and beetles lift many times 
 their own weight. Numerous insects are able to leap many 
 times their own length, and others perform different kinds 
 of work with a vigor and rapidity unsurpassed by any other 
 class of animals. As is to be expected, the muscular sys- 
 tem is well developed, and exhibits a surprising degree of 
 complexity. Over five hundred muscles are required for 
 the various movements of our own bodies, but in some of 
 the insects more than seven times this number exist. The 
 amount of food necessary to supply this relatively immense 
 system with the required nourishment is correspondingly 
 large. Many insects, especially in an immature or larval 
 condition, devour several times their own weight each day. 
 Their food may consist of the juices of animals or plants, 
 which they suck out, or of the firmer tissues, which are 
 bitten or gnawed off. 
 
 Xot only do the mouth-parts stand in direct relation to 
 the habits of the animal and to its food, but, as we have 
 often noticed before, the internal organization is also 
 adapted for the digestion and distribution of the nutritive 
 substances in the most economical way. For this reason 
 we find the alimentary canal differing widely in the various 
 forms of insects. In each case it extends from the mouth 
 to the opposite end of the animal, and ordinarily consists 
 of a number of different parts. In the insect shown in
 
 116 
 
 ANIMAL FORMS 
 
 Fig. 69 the mouth soon leads into the esophagus, which 
 in turn leads into the crop that serves to store up the food 
 until ready for its entry into the stomach ; or in some of 
 the ants, bees, and wasps it may contain material which 
 
 may be disgorged and fed 
 to the young. In many 
 cases the stomach is small 
 and ill-defined as in Fig. 69, 
 and again it may reach 
 enormous dimensions, near- 
 ly filling the body. It may 
 also bear numerous lobes or 
 delicate hair-like processes, 
 which afford a greater sur- 
 face for the absorption of 
 food. Behind the stomach 
 are a number of slender 
 outgrowths that are believed 
 to act as kidneys. Beyond 
 their insertion lies the in- 
 testine, which, like the 
 stomach, is the subject of 
 many modifications in the 
 different kinds of insects. 
 
 The digested food is rap- 
 idly absorbed through the coats of the stomach and intes- 
 tine and enters a circulatory system which reminds us of 
 what exists in many of the Crustacea. The heart is situ- 
 ated above the digestive tract, and from it arteries pass out 
 to different parts of the body. Here the blood leaves the 
 vessels and is poured directly into the spaces among the 
 viscera, whence it is finally conducted through irregular 
 channels to the heart by its pulsations. 
 
 In the Crustacea the blood is made to pass through a 
 respiratory system usually in the form of definite gills, and 
 the oxygen with which it is charged is distributed to all 
 
 FIG. 69. Cockroach, dissected to show ali- 
 mentary canal, al. c. After HATSELEK 
 and CORI.
 
 ARTHROPODS. CLASS INSECTS 117 
 
 parts of the body. In the insects the blood serves almost 
 entirely to carry the food, and the oxygen is conveyed 
 through the animal by a remarkable contrivance found 
 only in the insects, the spiders, and a few related forms. 
 
 114. Respiratory system. If we examine an insect, the 
 grasshopper for example, we find a number of small brown 
 spots on each side of the abdomen, each of which under a 
 magnifying-glass is seen to be perforated by a narrow slit. 
 Carefully opening the body, we find that each slit is in 
 communication with a white, glistening tube that rapidly 
 branches and penetrates to all parts of the animal. When 
 the body is expanded the air rushes into the outer openings, 
 on through the open tubes, and is distributed with great 
 rapidity to all the tissues of the body. In many insects 
 some of these tubes connect with air-sacs which probably 
 serve to buoy up the insect during its flights through 
 the air. 
 
 115. Wingless insects (Thysanura). The simplest of all 
 insects are the fishmoths and springtails, relatively small 
 organisms covered with shining scales or hairs. The first 
 of these is occasionally seen running about in houses feed- 
 ing upon cloth and other substances, while the latter live 
 in damp places under stones and logs. They are without 
 wings, but are able to run rapidly and to leap considerable 
 distances. In addition to the ordinary appendages, the 
 abdomen bears what are perhaps rudimentary legs, a fact 
 which, together with their relatively simple structure, 
 strengthens the belief that the insects have descended 
 from centiped-like ancestors. 
 
 116. Grasshoppers, crickets, katydids, etc. (Orthoptera). 
 Rising higher in the scale of insect life, we arrive at the group 
 of the cockroaches, crickets, grasshoppers, locusts, and 
 other related insects. Four wings are present, the first pair 
 thickened and overlapping the^ second thinner pair. The 
 latter are folded lengthwise like a fan, which is said to have 
 given the name Orthoptera (meaning straight-winged) to
 
 118 ANIMAL FORMS 
 
 this group of insects. These extend all over the world, 
 being particularly abundant in the warmer countries, and 
 their strong biting mouth-parts and voracious appetites 
 render many of them dreaded pests to the farmer. The 
 cockroaches are nocturnal in their habits, racing about at 
 night, devouring victuals in the pantry and gnawing the 
 bindings of books. During the day their flat bodies enable 
 them to secrete themselves in crevices wherever there is 
 sufficient moisture. 
 
 In the grasshoppers, locusts, katydids, and crickets the 
 body is more cylindrical, and the hind pair of legs are often 
 greatly lengthened for leaping. The crickets and katydids 
 are nocturnal, the former re- 
 maining by day in burrows 
 which they construct in the 
 earth, the latter resting qui- 
 etly in the trees. At night 
 
 FIG. 70. The Rocky Mountain locust. . * , 
 
 After RILEY, from The insect World. they f east upon vegetable 
 matter principally, though 
 
 some species are known to prey on small animals. Those 
 insects we usually term grasshoppers (properly called lo- 
 custs) are specially destructive to vegetation. Some spe- 
 cies are strong fliers, and this, connected with their abil- 
 ity to multiply rapidly, renders them greatly dreaded pests. 
 They have been described as flying in great swarms/form- 
 ing black clouds, even hiding the sun as far as the eye 
 could reach. The noise made by their wings resembled 
 the roar of a torrent, and when they settled upon the earth 
 every vestige of leaf and delicate twig soon disappeared. 
 
 The eggs of the majority of Orthoptera are laid in the 
 ground, where they frequently remain through the winter. 
 When hatched the young quite closely resemble the parents, 
 and, after a relatively slight metamorphosis, assume the 
 adult form. 
 
 117. Dragon-flies, may-flies, white ants, etc. (Neuroptera). 
 The dragon-, caddis-, may-flies, ant lions, and the white ants
 
 ARTHROPODS. CLASS INSECTS 
 
 119 
 
 possess four thin and membranous wings incapable of being 
 folded. These possess a network of delicate nervures, giv- 
 ing the name Neuroptera (meaning nerve-winged) to the 
 class. Of the forms mentioned above, all but the white 
 ants lay their eggs in the water, and the developing larvae 
 
 FIG. 71. Dragou-fly (LibeUula pulchella). 
 
 spend their lives in this medium until the time comes for their 
 complete metamorphosis into the adult. The larvae of the 
 caddis-flies protect themselves within a tube of stones or sticks 
 bound together with silken threads, which they usually 
 attach to the under side of stones in running water. On 
 the other hand, the young of the dragon- and may-flies, pro- 
 vided with strong jaws, are active in the search of food and 
 very voracious. In time they emerge from their larval skin 
 and the water in which they live, and after a life spent on 
 the wing they deposit their eggs and perish. The adult 
 ant-lion, which has somewhat the appearance of a small 
 dragon-fly, lays its eggs in light sandy soil. In this the 
 resulting larvae excavate funnel-shaped pits, at the bottom 
 of which they lie concealed. Insects stumbling into their 
 9
 
 120 
 
 ANIMAL FORMS 
 
 pitfalls are pelted with sand, which the ant-lion throws at 
 them with a jerky motion of the head, and are speedily 
 tumbled down the shifting sides of the funnel to be seized 
 and devoured. 
 
 While the white ants are not in any way related to the 
 true ants, they possess many similar habits. Associated in 
 great companies, they excavate winding galleries in old logs 
 and stumps, and, further, are most interesting because of 
 the division of labor among the various members. The 
 wingless forms are divided into the workers, which exca- 
 vate, care for the young, and otherwise labor for the good 
 of the others ; and into the soldiers, huge-headed forms. 
 
 
 Fiu. 72. Ant-lion larva plowing its way through the sand (upper figure) while an- 
 other is commencing the excavation of a funnel-shaped pit similar to one on right. 
 
 Photograph by A. L. MEL&NDER and C. T. BRCES. 
 
 whose strong jaws serve to protect the colony. The re- 
 maining winged forms are the kings and queens. In the 
 spring many of the royalty fly away from home, shed their 
 wings, unite in pairs, and set about to organize a colony. 
 The queen rapidly commences to develop eggs, and in some
 
 ARTHROPODS. CLASS INSECTS 
 
 121 
 
 species her body becomes so enormously distended with 
 these that she loses the power of locomotion and requires 
 to be fed. A single queen has been known to lay eggs at 
 the rate of sixty per minute (eighty thousand a day), and 
 
 FIG. 73. Termites or white ants, a, queen ; b, winged male ; c, worker; d, soldier. 
 
 those destined to royal rank are so nursed that they advance 
 farther in their development than the remaining sterile 
 and wingless forms. 
 
 118. The bugs (Hemiptera). .The large and varied group 
 of the bugs (Hemiptera) includes a number of semi-aquatic 
 species, such as the water-boatmen, often seen rowing 
 themselves along in the ponds by means of a pair of oar- 
 shaped legs, in search of other insects. Somewhat similar 
 at first sight are the back-swimmers, with like rowing 
 habits, but unique in swimming back downward. Both of 
 these bugs frequently float at the surface, and when about 
 to undertake a subaquatic journey they may be seen to 
 imprison a bubble of air to take along. Closely related are 
 the giant water-bugs (Fig. 74), which often fly from pond 
 to pond at night. In such flights they are frequently
 
 122 
 
 ANIMAL FORMS 
 
 attracted by lights, and have come to be called " electric- 
 
 light bugs." 
 
 Among our most dreaded insect pests are the chinch- 
 
 bugs small black-and-white insects, but traveling in com- 
 panies aggregating many millions. 
 As they go they feed upon the 
 stems and leaves of grain, which 
 they devour with extraordinary ra- 
 pidity. The squash-bug family is 
 also extensive, and destructive to 
 the young squash and pumpkin 
 plants in the early spring. 
 
 The lice are small, curiously 
 shaped bugs, which suck the blood 
 of other animals. The plant-lice, 
 also small, suck the juices of 
 plants, and are often exceedingly 
 destructive. This is especially true 
 of the phylloxera, a plant-louse 
 
 h j h caugeg ammally the l oss Q f 
 .1 
 
 millions of dollars among the vine- 
 yards of this and other countries. 
 
 Even more destructive are tha scale-insects, curiously mod- 
 ified forms, of which the wingless females may be found on 
 almost any fruit-tree and on the plants in conservatories, 
 their bodies covered with a downy, waxy, or other kind of 
 covering, beneath which they remain and lay their eggs. 
 
 119. The flies (Diptera). The group of the Diptera 
 (meaning two-winged) includes the gnats, mosquitoes, fleas, 
 house-flies, horse-flies (Fig. 75), and a vast company of 
 related forms. Only a single pair of wings is present, the 
 second pair being rudimentary or fashioned into short, 
 thread-like appendages known as balancers, though they 
 probably act as sensory organs and are not directly con- 
 cerned with flight. The mouth-parts are adapted for pier- 
 cing and sucking. The eyes, constructed on the same plan 
 
 FIG. '-l.-Giant water-bug 
 
 phus dtlalatus), with eggs at- 
 
 tached.
 
 ARTHROPODS. CLASS INSECTS 
 
 123 
 
 FIG. 75. Horse-fly ( Therio- 
 plectes). 
 
 as those of the Crustacea, are comparatively large, and are 
 frequently composed of a great number of simple eyes 
 united together, upward of four 
 thousand forming the eye of the 
 common house-fly. 
 
 These insects are widely distrib- 
 uted throughout the world, where 
 they inhabit woods, fields, or houses 
 as best suits their needs. Their 
 food is varied. Some suck the 
 juices of plants, others attack ani- 
 mals, and, while many are trouble- 
 some pests, others, especially in the 
 early stages of their existence, are 
 of great benefit. 
 
 120. Familiar examples. Owing 
 to the widely different habits and 
 structure of the members of this group, we shall briefly 
 consider two examples, the mosquito and the house-fly, 
 which will give us a fairly good idea of the characteristics 
 of all. The eggs of the mosquito are laid in sooty-look- 
 ing masses on the surface of stagnant pools. Within a 
 very short time the young hatch, and, owing to their pecul- 
 iar swimming movements, are known as "wrigglers." They 
 are then active scavengers, devouring vast quantities of 
 noxious substances and performing a valued service. They 
 frequently rise to the surface, take air into the tracheal 
 system, which opens at the posterior end of the body, and 
 descend again. After an increase in growth and many in- 
 ternal changes resulting in a chrysalis-like stage, they rise 
 to the surface, split the shell, and, using the latter as a float, 
 carefully balance themselves and soon fly away. 
 
 The house-fly usually lays its eggs in decaying vegetable 
 matter, and the young, maggot-like in form, are active 
 scavengers. They too undergo deep-seated changes during 
 the next few days, finally transforming into the adult.
 
 124 
 
 ANIMAL FORMS 
 
 Many of this great group of the flies spend their early life 
 in the water or other medium acting as scavengers ; but, on 
 the other hand, numbers attack domestic and other animals, 
 and throughout their entire lives are an intolerable plague. 
 121. The beetles (Coleoptera). Owing to the ease of pres- 
 ervation and their bright colors, the beetles have probably 
 been more widely collected than other insects. Fully ten 
 
 **^T 
 
 FIG. 76. Long-honied borer (Ergates). Larva (left-hand figure), pupa, and adult 
 
 thousand distinct species are known in Xorth America 
 alone. They are all readily recognized by the two firm, 
 horny sheaths enclosing the two membranous wings, which 
 alone are organs of flight. The mouth is provided with 
 jaws, which are used in gnawing. Some prey on noxious 
 insects or upon decaying vegetable or animal matter, and 
 are often highly beneficial ; but others attack our trees and 
 domestic animals, and work incalculable damage.
 
 ARTHROPODS. CLASS INSECTS 125 
 
 In some of the stag- or wood-beetles (Fig. 76), which 
 we may select as types, the adults are often found crawling 
 about on or beneath the bark of trees, living on sap or 
 small animals. The eggs laid in these situations develop 
 into grub-like larvae, which bore their way through living 
 or dead wood, and in this condition sometimes live four or 
 five years. They then transform into quiescent pupae (Fig. 
 76), which finally burst their shells and emerge in the 
 adult form. Others, like water-beetles and the whirligig- 
 beetles, whose mazy motions are often seen on the surface 
 of quiet streams, pass the larval period in the water. 
 Under somewhat different conditions we find the potato- 
 bugs, lady-bugs, fire-flies, and their innumerable relatives, 
 but the changes they undergo in becoming adult are essen- 
 tially the same as those described for the other members of 
 the order. 
 
 122. The moths and butterflies (Lepidoptera). The moths 
 and butterflies occur all over the world. In their mature 
 
 FIG. 77. Monarch-butterfly (Anoaia i>lezipi)i/ti>. From photograph by A. L. MELAN- 
 DER and C. T. BRUES. 
 
 state they are possessed of a grace of form and movement 
 and a brilliancy of coloration that elicit our highest admi- 
 ration. The mouth-parts are developed into a long pro- 
 boscis, which may be unrolled and used to suck the nectar 
 out of flowers, though in many of the adult moths, which 
 never feed, it may remain unused. The wings, four in 
 number, are covered with beautiful overlapping scales that
 
 126 
 
 AN 7 IMAL FORMS 
 
 adhere to our fingers when handled. This feature, and 
 the general plan of the body, which is much the 
 
 FIG. 78. The silver-spot (Argyituis cybele). Photograph by A. L. MELANDEK and 
 C. T. BRI-ES. 
 
 throughout the group, enables us to recognize most of 
 them at once. 
 
 123. Development and metamorphosis. In some of the 
 simplest insects, as in the bugs, the young at birth resemble 
 their parents. In other insects the resemblance is not so 
 close. The young grasshopper, for example, hatches, from 
 an egg laid in the ground, with a ridiculously large head 
 and staring eyes ; still there is no difficulty in recognizing 
 its relationships. During the next week internal changes 
 take place. The shell is burst, and the grasshopper emerges, 
 looking more like its parents than before. This process is 
 repeated four or five times during the next few weeks, and 
 the gradual changes thus produced finally bring the young 
 insect to the adult form. This latter state has been attained 
 by an incomplete metamorphosis.
 
 ARTHROPODS. CLASS INSECTS 
 
 127 
 
 In the flies, beetles, butterflies, and numerous insects 
 the differences between the newly hatched young and the 
 adult are vastly greater. No one looking on a caterpillar 
 or a grub for the first time would suspect its origin, and 
 the changes they undergo have attracted attention for cen- 
 turies. Placing any of the ordinary caterpillars with their 
 favorite food in a glass-covered box, we may readily watch 
 their transformations. Provided with biting mouth-parts 
 and a voracious appetite, they devour vast quantities of 
 vegetation for several days. Finally they cease eating, and 
 
 FIG. 79. Life : history of silk-moth (Bombyx mori). A, adult ; B, C. D, caterpillars of 
 different ages ; E, F, G, silken cocoon and pupa ; H, eggs. 
 
 suspend themselves head downward by means of a kind of 
 cobweb. After remaining quiet a few hours, they burst 
 their skin, and within appears a chrysalis or pupa. In the 
 moths, for example, the silk-moth (Fig. 79), the caterpillar 
 or silk-worm, after eating the favorite mulberry leaves, 
 spins a silken cocoon, in which the pupa is produced. The 
 larvae of beetles and many other insects excavate tunnels in 
 wood or in the earth, and there undergo their transforma- 
 tions. Invariably the pupa remains quiet for days, months,
 
 128 ANIMAL FORMS 
 
 or even years, but when the proper time arrives the fully 
 formed insect emerges, and takes to the wing. 
 
 Wonderful internal changes have been taking place 
 during this time. The organs fitted for the proper treat- 
 ment of the vegetable food of the caterpillar or grub are 
 destroyed, at least in part, and new systems are produced 
 ready for the nectar and vegetable juices which are to be 
 the food of the adult insect. All insects that pass through 
 a pupal quiescent stage are said to undergo a complete 
 metamorphosis. 
 
 124. The ants, bees, wasps, etc. (Hymenoptera). The ants, 
 bees, and wasps are the best-known insects belonging to 
 this order. They are characterized by four membranous 
 wings, by biting and sucking mouth-parts, and the female 
 is often provided with a sting. All undergo a complete 
 metamorphosis. The eggs may be laid in the bodies of 
 other insects, many of which are pests, and are thus de- 
 stroyed ; or they may be deposited in the nests of other 
 insects, the foster-parents being compelled to feed them ; 
 or they may be placed in marvelously constructed homes, 
 and be the objects of the greatest attention, the parents or 
 attendants often risking or losing their lives in their 
 defense. The members of this order have long attracted 
 attention, largely on account of their remarkable instinc- 
 tive powers. They live in highly organized communities 
 and certain of their characteristics may be illustrated by 
 a study of some of the more familiar forms. 
 
 125. The ants. The ants live in communities consisting 
 of anywhere from a dozen to many thousands of individuals, 
 according to the species. Each of these colonies contains 
 the queen, several young winged males and females, des- 
 tined as kings and queens to found new colonies, and of a 
 far greater number of wingless sterile females, the workers. 
 The workers construct the greater part of the nest, which 
 often consists of extensive galleries, nurseries, and grana- 
 ries, excavated in wood or in the earth. They also attend
 
 ARTHROPODS. CLASS INSECTS 129 
 
 to the acquisition of food, which consists of the sweet 
 juices of plants, of other insects, or of leaves and seeds. 
 These may be fed at once, or placed in storehouses until 
 times of need. 
 
 Certain species of ants make carefully planned attacks 
 upon other weaker forms. The young are carried off, at 
 times only after a prolonged and fierce struggle, and all 
 are soon eaten, or a few may be allowed to develop and act 
 as slaves. Some species are unable to exist without serv- 
 ants, which feed them, wash them, and otherwise minister 
 to their comfort. 
 
 In some of their raids numerous plant-lice (delicate, 
 usually green, insects, such as occur on our household 
 plants) are often captured and carried into the nest. These 
 so-called " ant-cows " are carefully tended, and in return 
 yield up a tiny drop of a sugary fluid to the hungry ant 
 that solicits it. 
 
 The eggs laid by the queen develop into white worm- 
 like creatures, which ordinarily spin cocoons when about to 
 become pupae. These are incorrectly called "ant-eggs." 
 Many, probably on account of insufficient nourishment, 
 never develop reproductive organs. They become the neu- 
 ters or workers. The winged royalty fly away from the 
 colony, pair and found homes of their own, and become 
 surrounded by a numerous progeny. 
 
 126. The bees. Among the bees we find a considerable 
 number which lead solitary lives, excavating tunnels in 
 earth or wood, as in the case of many of the wasps, but, 
 unlike them, supplying the young with honey or pollen. 
 Others may constitute a band of worthless insects which 
 steal their food from their more industrious relations, in 
 whose nests they also secretly deposit their eggs, leaving the 
 young to be nourished with food rightly belonging to others. 
 
 But it is with the social bees we are most familiar the 
 bumble- and honey-bees. The former usually build in the 
 ground, and form colonies consisting of the queen and from
 
 130 ANIMAL FORMS 
 
 twenty to two hundred workers. Regular combs are not 
 constructed, the young at first feeding on pollen masses or 
 " bee-bread," and finally spinning cocoons. In the late 
 summer males and females appear, but as winter conies on 
 all perish except the queens, which seek a sheltered place, 
 and in the spring revive to establish new colonies. 
 
 In a wild state the honey-bees dwell in cavities of trees 
 and other protected places, where they form colonies, 
 consisting of the queen, of per- 
 haps two hundred males or 
 drones if the nest be examined 
 in the spring and summer, and 
 of a hundred times as many 
 sterile females, the workers. 
 These form among the most 
 highly organized insect soci- 
 eties known. All work for the 
 
 FIG. 80.-Bumblebee (Bombus). 
 
 good of the colony. To each 
 
 worker is assigned a definite task, which is never shirked. 
 It must collect the honey, supply the wax for making the 
 comb, take care of the brood, or in other ways minister to 
 the welfare of the community. On the queen devolves 
 the entire task of egg-laying. She may lay three thousand 
 eggs a day and be fully occupied during the three or four 
 years that she lives. The drones, or males, fertilize most 
 of the eggs, and are then driven out from the hive, after 
 a stay of a month or two. The eggs unfertilized by the 
 drones are placed in large cells, and the young fed on 
 pollen develop into males. The fertilized eggs may pro- 
 duce queens or workers at the discretion of the queen. If 
 the latter be desired, the eggs are placed in small cells with 
 a scant amount of food, which apparently causes the repro- 
 ductive system to remain undeveloped. The same eggs, if 
 placed in the large queen cells and supplied with highly 
 nutritious food, would have developed into queens. When 
 these latter appear they are vigorously attacked and killed
 
 ARTHROPODS. CLASS INSECTS 
 
 131 
 
 by the parent if not protected by the workers. If the 
 young queen survive, the old queen departs with many of 
 her subjects, and collects them into a dense swarm attached 
 to a limb of a tree, where they remain until scouts return to 
 conduct them to their new home. 
 
 127. The wasps. The digger-wasps are frequently to be 
 seen gnawing tunnels in the wood or earth, at the inner end 
 
 
 FIG. 81. Nest of Vespa, a social wasp. Photograph by A. L. MELANDEK and 
 C. T. BRUES. 
 
 of which an egg is laid. In some species the developing 
 young is nourished by food carried in to it day by day. In 
 other cases the parent may never see her child, dying or 
 abandoning it before its birth ; but before departing she is 
 careful to place within reach a sufficient supply of spiders, 
 caterpillars, beetles, or locusts that shall nourish the little 
 one until it becomes a motionless pupa. This stage is soon 
 over, and the adult wasp now digs its way to the surface. 
 
 Passing by the familiar mud-wasps or mud-daubers, 
 whose nests are common objects under stone's or against
 
 132 ANIMAL FORMS 
 
 the rafters of barns and houses, we arrive at the social 
 wasps. As the name indicates, these insects, such as the 
 yellow-jackets and hornets, live together in companies 
 which consist, as in the ants and bees, of males, females, 
 and workers. They also are fond of the juices of fruits, 
 and many of them destroy insects which may be fed to the 
 young. Their nests are variously situated and constructed, 
 but all of them agree in being composed, at least in part, of 
 a grayish substance which is in reality a kind of paper. 
 With their jaws they scrape off from old logs and fences 
 small particles of wood, which they probably mix with saliva, 
 and rolling the mass into a ball set out for home. These 
 pellets are then flattened out into thin sheets, and worked 
 up into hexagonal cells, in which the eggs are laid. 
 
 Along with the nests of the mud-daubers one frequently 
 notices the nests of some of the familiar wasps (Polistes), 
 which build cake-like nests composed of thirty or forty, 
 hexagonal cells attached by a stalk. Somewhat similar 
 nests, though usually more extensive, are constructed by 
 the yellow-jackets in cavities in the ground. The numer- 
 ous combs of the hornet are surrounded by several sheets of 
 wood-pulp, and the whole structure is attached generally 
 to the limb of a tree. 
 
 In the spring the nests of all these species of wasps are 
 commenced by a single female, who has lived in a dormant 
 condition through the winter. She builds a small nest and 
 in time is surrounded by numerous workers, which live in 
 perfect harmony, enlarging the nest and rearing the young. 
 As autumn approaches the young males and females leave 
 the nest ; but the males, together with the workers, all suc- 
 cumb to the cold, and none but the females persist to found 
 a new colony the following spring.
 
 CHAPTER XI 
 
 ARTHROPODS (Continued). CLASS ARACHNIDA 
 
 128. General characters. In this group, comprising the 
 spiders, mites, and a large assemblage of related species, we 
 again meet with great differences in form and structure 
 which fit them for lives under widely different conditions. 
 The three regions of the body, head, thorax, and abdomen, 
 so clearly marked in the insects, are here less plainly de- 
 fined. The head and thorax are usually closely united, and 
 in the mites the boundaries of the abdomen are also indis- 
 tinct. The appendages of the head are two in number, and 
 probably correspond to the antenna? and mandibles of other 
 Arthropods. In the scorpions and some species of mites 
 these are furnishw with pincers for holding the prey, and 
 in other forms they act as piercing organs. Usually the 
 thorax bears four pairs of legs, a characteristic which readily 
 separates such animals from the insects. 
 
 The internal organization differs almost as much as does 
 the external. In many species it shows a considerable re- 
 semblance to that of some insects, but in others, especially 
 those of parasitic habits, it departs widely from such a type. 
 Eespiration is affected by means of tracheae, or lung-books, 
 which consist of sacs containing many blood-filled, leaf -like 
 plates placed together like the leaves of a book. 
 
 Usually, as in the insects, the young hatch from eggs 
 which are laid, but in the scorpions and some of the mites 
 the young develop within the body and at birth resemble 
 the parent. Almost all of these organisms live either as 
 
 133
 
 134 
 
 ANIMAL FORMS 
 
 parasites or as active predaceous animals upon other animals. 
 For this purpose many are provided with keen senses for 
 detecting their prey and poisonous spines for despatching it. 
 129. The scorpions. Owing to the stout investing armor, 
 the strong pincers, and the general form of the body, the 
 scorpions might at first sight be mistaken for near relatives 
 
 of the crayfish or lobster. 
 A more careful examina- 
 tion will show that the 
 two pairs of pincers prob- 
 ably correspond to the 
 antennae and mandibles of 
 the Crustacea that have 
 become modified for seiz- 
 ing the food. The swol- 
 len part of the animal 
 lying behind the four 
 pairs of legs is a part of 
 the abdomen, of which 
 the slender " tail " consti- 
 tutes the remainder. On 
 the tip of the tail is a 
 curved spine supplied 
 with poison glands. Sev- 
 eral pairs of eyes are borne 
 on the dorsal surface of 
 the head and thorax, while 
 on the under side of the animal several slit-like openings 
 lead into as many small cavities containing the lung-books. 
 The scorpions are the inhabitants of warm countries, 
 where they may be found under sticks and stones through- 
 out the day. At night they leave their homes in search of 
 food, which consists chiefly of insects and spiders. These 
 are seized by means of the pincers, and the sting is driven 
 into them with speedily fatal results. It is doubtful if the 
 poison causes death in man, but the sting of some of the 
 
 '.Scorpion, showing pincer-like mouth- 
 parts and spine-tipped tail.
 
 ARTHROPODS. CLASS ARACHN1DA 135 
 
 larger species, which measure five or six inches in length, 
 may produce certain disorders chiefly affecting the circula- 
 tion. In this country there are upward of thirty species, 
 most of which are comparatively small. 
 
 130. The harvestmen. The harvestmen or daddy-long- 
 legs are small-bodied, long-legged creatures which resemble 
 in general appearance several of the spiders. They differ 
 from them, however, in the possession of claws correspond- 
 ing to the smaller ones of the scorpion, and in their method 
 of respiration, which is similar to that of insects. During 
 the day they conceal themselves in dark crevices or stride 
 slowly about in shaded places ; but at night they emerge 
 into more open districts and capture small insects, from 
 which they suck the juices. 
 
 131. The spiders. The spiders are world-wide in their 
 distribution, and are a highly interesting group, owing 
 chiefly to their peculiar habits. Examining any of our 
 familiar species, it will be seen that the united head and 
 thorax are separated by a narrow stalk from the usually 
 distended abdomen. To the under side of the former are 
 attached four pairs of long legs, a pair of feelers, and the 
 powerful jaws supplied with poison-sacs, while eight shin- 
 ing eyes are borne on the top of the head. On the abdo- 
 men, behind the last pair of legs, are small openings into 
 the lung cavities which contain a number of vascular, leaf- 
 like projections known as lung-books. In some species 
 a well-marked system of tracheae are also present. At the 
 hinder end of the body are four or six little projections, 
 the spinnerets, each of which is perforated with many 
 holes. Through these the secretion from the glands be- 
 neath is squeezed out in the form of excessively delicate 
 threads, often several hundred in number, which harden on 
 exposure to the air. According to the use for which these 
 are intended, they may remain a tangled mass or become 
 united into one firm thread ; and according to the habits 
 of the animal, they may be used for enclosing their eggs, 
 
 10
 
 136 ANIMAL FORMS 
 
 for lining their burrows, or for the construction of webs of 
 the most diverse patterns. 
 
 132. The habits of spiders. Many species of spiders, some 
 of which are familiar objects in fields and houses, construct 
 sheets of cobweb with a tube at one side in which they may 
 
 Pie. 83. A tarantula-spider (Eurypelma lentzii). Natural size. Photograph by 
 A. L. MELANDER and C. T. BRUES. 
 
 lie in wait for their prey or through which they may escape 
 in times of danger. In the webs of the common orb- or 
 wheel-weavers several radial lines are first constructed, and 
 upon these the female spider spins a spiral web. Resting 
 in the center of this or at the margin, with her foot on 
 some of the radial threads, she is able to detect the slight- 
 est tremor and at once to rush upon the entangled captive. 
 Some of the bird-spiders and their allies, living in trop- 
 ical America, and attaining a length of two inches, con- 
 struct web-lined burrows in the ground. From these they 
 stalk their prey, which consists of various insects and even
 
 ARTHROPODS. CLASS ARACHNIDA 
 
 137 
 
 small birds. These are almost instantly killed by the poison- 
 fangs, and are then carried to the burrow, where the juices 
 of the body are extracted. 
 
 The trap-door spiders of the southwestern section of the 
 United States also dig tunnels, which they cover with a 
 closely fitting lid com- 
 posed of earth. Raising v ,t 
 this they come out in w$ MjS8aSSf$^*~ 
 search of insects, but if 
 sought in turn, they dash 
 into the burrow, closing 
 the door after them, and 
 holding it with such firm- 
 ness that it is rarely forced 
 open. If this should hap- 
 pen, there are sometimes 
 blind passage-ways, also 
 closed with trap-doors, 
 which usually baffle the 
 pursuer. 
 
 Finally, there are 
 among the thousand spe- 
 cies of spiders in the United States a considerable propor- 
 tion which construct no definite web. Many of these may 
 be seen darting about in the sunshine on old logs and 
 fences, often trailing after them a thread which may sup- 
 port them if they fall in their active leaping after in- 
 sects. 
 
 133. Breeding habits. The male spiders are usually much 
 smaller than the females, and some species are only one- 
 fifteenth as long as the female and one one-hundredth of 
 its weight. They are" usually more brilliantly colored, more 
 active in their movements, yet rarely spinning their own 
 webs and capturing their own food, preferring to live at 
 the expense of the female. At the breeding season the 
 males of several species make a most interesting display 
 
 FIG. 84. Trap-door spider and burrow 
 ( C(eniza).
 
 138 ANIMAL FORMS 
 
 of their colors, activity, and gracefulness before the females ; 
 and the latter, after watching these exhibitions, are said to 
 select the one who has " shown off " in the most pleasing 
 fashion. The life after this may be stormy, resulting in 
 the death of the male ; but ordinarily the results are not 
 so disastrous, and in a little while the female deposits her 
 eggs in cases which she spins. In these the young develop, 
 sometimes wintering here, and emerging in the spring to 
 scamper about in, search of food, or to drift through the 
 air to more favorable spots on fluffy masses of cobweb. 
 
 Few groups of animals are more interesting objects of 
 study and more accessible. Their bites are rarely more 
 serious than those of the mosquito never fatal ; and a 
 careful study of any species, however 
 common, will undoubtedly bring to 
 light many interesting and unknown 
 facts. 
 
 134. The mites and ticks. The 
 mites and ticks are the simplest and 
 among the smallest of the animals 
 belonging to this group. To the at- 
 tentive observer they are rather com- 
 mon objects, with homes in very dif- 
 ferent situations. Some occur on liv- 
 FIG. 85.-The itch-mite (Sar- j ng and decaying vegetation, in old 
 
 coptes scabei). -, , ,1 
 
 flour and unrefined sugar, while oth- 
 ers live in fresh water and a few in the sea. Almost all 
 tend toward parasitism. Some of the insects which they 
 pierce and destroy are a pest to man, but on the other hand 
 some are intolerable owing to the diseases they produce. 
 
 As to other parasitic organisms, degradation of structure 
 is manifest. The respiratory system, so important to the 
 active life of the insects, may be absent, the animal breath- 
 ing through its skin. The circulatory system may be want- 
 ing, the blood occupying spaces among the various organs 
 being swept about by the animal's movements. And many
 
 ARTHROPODS. CLASS ARACHNIDA 
 
 139 
 
 other peculiarities have arisen which fit them for their 
 different modes of life. 
 
 135. The king crab (Limulus). The king crab may be 
 found crawling over the bottom or plowing its way through 
 the sand and mud in many of the quiet bays from Maine 
 to Florida. The large head and thorax of these animals 
 are united into a horse- 
 shoe-shaped piece, be- 
 hind which lies the 
 triangular abdomen. 
 On the curved front 
 surface of the former 
 are a pair of small me- 
 dian eyes, and farther 
 outward are two larger 
 compound ones. On 
 the ventral side are 
 six pairs of append- 
 ages, instrumental in 
 capturing and tearing 
 the small animals that 
 serve as food, and 
 functioning in con- 
 nection with the ter- 
 minal spine as locomo- 
 tor organs. On the 
 ventral surface of the abdomen are numerous plate-like flaps 
 which serve in respiration, and in the imperfect swimming 
 movements in which these animals occasionally indulge. 
 
 These relatively large and clumsy creatures are the rem- 
 nant of a great number of strange, uncouth animals that in- 
 habited the earth in past ages. Many of them show a close 
 resemblance to the scorpions. The anatomy and develop- 
 ment also show certain points of resemblance, and by some 
 are thought to give us an idea of the ancient type of spider- 
 like animal from which the modern forms have descended. 
 
 FIG. 86. The king or horseshoe crab (Limulus 
 polyphemus).
 
 CHAPTER XII 
 
 ECHINODERMS 
 
 136. General characters. The division of the echino- 
 derms includes the starfishes, sea-urchins, serpent- or brittle- 
 stars, sea-cucumbers, and crinoids or sea-lilies. All are ma- 
 rine forms, and constitute a conspicuous portion of the 
 animals along almost any coast the world over. From 
 these shallow-water situations they extend to the greatest 
 depths of the ocean, and the bodily form possesses a great 
 number of variations, adapting them to lives under such 
 diverse conditions; and yet there is perhaps no group of 
 organisms so clearly defined or exhibiting so close a resem- 
 blance throughout. At one time it was thought that their 
 radial symmetry was an indication of a close relationship 
 to the ccelenterates, but more careful study has shown them 
 to be much more highly developed than this latter group, 
 and widely separated from it. A skeleton is almost always 
 present, consisting of a number of calcareous plates embed- 
 ded in the body-wall, and often supporting numbers of pro- 
 tective spines, which fact has given to the group the name 
 Echinoderm, meaning hedgehog skin. 
 
 137. External features. The body of a starfish (Fig. 87) 
 consists of a more or less clearly defined disk, from which 
 the arms, usually five in number, radiate like the spokes 
 of a wheel. At the center of the under side the mouth is 
 located, and from it a deep groove, filled with a mass of 
 tubular feet, extends to the tip of each arm. Innumerable 
 calcareous plates firmly embedded in the body-wall serve 
 
 140
 
 ECHINODERMS 141 
 
 for the protection of the internal organs, and at the same 
 time admit of considerable movement. 
 1 In the brittle-stars (Fig. 88) the central disk is much 
 more sharply defined than in the preceding forms, and the 
 long snake-like arms are capable of a very great freedom of 
 movement, enabling the animal to glide over the sea-bottom, 
 or through the crevices of the rocks, at a surprising rate. 
 In several species, otherwise closely resembling those 
 
 FIG. 87. Starfish (Asterias ocracea), ventral view. One-half natural size. 
 
 in Fig. 88, the arms divide repeatedly. These are the so- 
 called basket-stars, living in the deeper waters of the sea, 
 where they, like other brittle-stars, act as scavengers and 
 devour large quantities of decomposing plant or animal 
 remains. 
 
 At first sight the globular spiny sea-urchins (Fig. 90) 
 would scarcely be recognized as close relatives of the star- 
 fishes. A closer examination, however, shows the mouth to 
 be located on the under side of the body ; from it five rows 
 of feet radiate and terminate close to the center of the 
 dorsal side, and the arrangement of the plates forming the
 
 142 
 
 ANIMAL FORMS 
 
 skeleton indicate that the sea-urchin is comparable to a 
 starfish, with its dorsal surface reduced to insignificant 
 proportions. 
 
 In the sea-urchins the calcareous plates possess a great 
 regularity, and are so closely interlocked that they prevent 
 
 FIG. 88. Brittle- or serpent-stars (species undetermined). Natural size. 
 
 any motion of the body-wall. Also, each plate is usually 
 provided with highly developed spines, movable upon a ball- 
 and-socket joint. These spines serve for locomotion, and, 
 in some instances, for conveying food to the mouth. A 
 considerable number of sea-urchins show an irregularity in 
 form which destroys to a corresponding degree the radial 
 symmetry. This is due to various causes, but especially to 
 a compression of the body, which, in the "sand-dollars,"
 
 ECHIXODERMS 143 
 
 has resulted in the production of a thin, cake-like form 
 (Fig. 91). 
 
 If the spherical body of a sea-urchin were to be stretched 
 in the direction of a line joining the mouth and the center 
 
 FIG. 89. Basket-star (Astrophyton). One-half natural size. 
 
 of the dorsal surface, a form resembling a sea-cucumber 
 (Fig. 92) would be the result. These latter organisms live 
 among crevices of the rocks, embedded in the mud or bur- 
 rowing in the sand at the bottom of the sea. In such situa- 
 tions they are well protected, and a highly developed skele- 
 ton, such as that of the sea-urchin, would not only be of 
 little value, but a positive hindrance to locomotion. The 
 skeleton, therefore, is much reduced, consisting of a few 
 scattered calcareous plates embedded in the fleshy body- 
 wall. Another peculiar feature is almost universally pres- 
 ent, in the form of a circlet of tentacles surrounding the 
 mouth, which serve either for the purpose of respiration, 
 for locomotion, or to convey food to the mouth. 
 
 A very good imitation of the general plan of a sea-lily 
 or crinoid (Fig. 93) could be made by attaching a serpent-
 
 144 
 
 ANIMAL FORMS 
 
 star, especially one of the basket-stars, by its dorsal side 
 to a stalk. In the crinoids the numerous branches of the 
 
 arms are compara- 
 tively short, and in 
 the arrangement of 
 the internal organs 
 there are numer- 
 ous differences, but 
 for all that the re- 
 semblance of these 
 organisms to the 
 other echinoderms 
 is undoubted. 
 
 138. Haunts. 
 The greater num- 
 ber of starfishes 
 occur alongshore, 
 slowly crawling 
 about in search of 
 food, or concealed 
 in dark crevices of 
 
 the rocks, where they may often be found as the tide goes 
 out, and we know that in gradually lessening numbers other 
 species lead similar lives at different levels far down in the 
 dark and gloomy depths. In these same locations the sea- 
 urchins occur, sometimes singly, but more usually associa- 
 ted in great numbers, several species excavating hollows in 
 the rocks, within which they obtain protection. The brit- 
 tle-stars and sea-cucumbers may also be found occasionally 
 in open view, but more often they make their way about in 
 search of food buried in the sand. The crinoids are usual- 
 ly inhabitants of deeper water, where they are found asso- 
 ciated often in great numbers. A few species upon attain- 
 ing the adult condition separate from the stalk, and are 
 able to move about (Fig. 95), but the remaining species 
 never shift their position. 
 
 FIG. 90. Sea-urchin (Strongylocentrotus pitrpuratus). 
 Natural size.
 
 ECHIXODERMS 145 
 
 139. The organs of defense and repair of injury. As we 
 have seen, the body-wall of the echinoderms is provided 
 with a series of plates, often bearing spines which serve as 
 organs of defense, and to protect the internal organs. The 
 starfishes and sea-urchins also possess numerous modified 
 spines (pedicellarid) scattered over the surface of the body, 
 which have the form of miniature birds' beaks, fastened to 
 slender muscular threads. During life these jaws continu- 
 ally open and close, and it is said they clean the body of 
 debris that settles on it ; but on the other hand there are 
 several reasons for the belief that they also act as organs 
 of defense. Thus protected, the natural enemies of echino- 
 derms appear to be relatively few, and are confined chiefly 
 to some of the fishes whose teeth are especially modified 
 for crushing them. In this 
 way, and owing to the action 
 of the breakers, they suffer 
 frequent injury, but many 
 species exhibit to a remark- 
 able degree the ability to re- 
 generate lost parts. Experi- 
 ments show that if all the 
 arms of a starfish be separa- 
 ted from the disk the latter 
 will within two or three 
 months renew the arms ; and FlG - i.-sand-doiiar. a flat sea-urchin. 
 
 . Natural size. 
 
 a single arm with a part of 
 
 the disk is able to renew the missing portions in about the 
 
 same length of time. 
 
 The brittle-stars, as their name indicates, are usually ex- 
 cessively delicate, often dropping all of their arms upon the 
 slightest provocation ; but here again the ability is present 
 to develop the lost portions. 
 
 Sea-cucumbers resent rough treatment by vigorously 
 contracting their muscular walls and removing from the 
 body almost the entire digestive tract, the respiratory tree,
 
 146 
 
 ANIMAL FORMS 
 
 and a portion of the locomotor system ; but some species, at 
 least, renew them again. In some of the starfishes and 
 brittle-stars portions of the body 
 appear to be voluntarily de- 
 tached and to develop into new 
 individuals, and it is thought 
 that such self-mutilation is a 
 normal method of reproduction. 
 140. Locomotor system. One 
 of the most characteristic and 
 remarkable features of the echi- 
 noderms is the water- vascular 
 system, a series of vessels con- 
 taining water which serve in the 
 process of locomotion. Their 
 arrangement and mode of opera- 
 tion are, with slight modifica- 
 tions, the same throughout the 
 group, and may be readily un- 
 derstood from their study in 
 the starfish. 
 
 On the dorsal surface of a 
 starfish, in the angle between 
 
 two of the arms, is a round, slightly elevated, calcareous 
 plate, the madreporic body (Fig. 95, m.p.), which under 
 the microscope appears full of holes, like the " rose " of a 
 watering-pot. This connects with a tube that passes to 
 the opposite side of the body, where it enters a canal 
 completely encircling the mouth. On this ring-canal a 
 number of sac-like reservoirs with muscular walls are at- 
 tached, and from it a vessel extends along the under sur- 
 face of each arm from base to tip. Each of these radial 
 water-mains gives off numerous lateral branches that open 
 out into small reservoirs similar to those located on the 
 ring-canal, and a short distance beyond communicate 
 through the wall of the body with one of the numerous 
 
 PIG. 92. Sea-cucumber {Cucu- 
 maria sp.). Natural size.
 
 ECHINODERMS 
 
 147 
 
 tube-feet, which, as we have seen, are slender tubular or- 
 gans, many in number, filling the grooves on the ventral 
 surface of each arm. This entire system of tubes and 
 reservoirs is full of water, taken in, it is said, through the 
 perforated plate, and, when the starfish wishes to advance, 
 many of the little reservoirs con- 
 tract, forcing water into the cav- 
 ity of the feet, with which they 
 are in communication, thus ex- 
 tending the extremity of the tubes 
 a considerable distance. The 
 terminal sucker of each foot, act- 
 ing upon the same principle as 
 those on the cuttlefish, attaches 
 firmly to some foreign object, 
 whereupon the muscles of the 
 foot contract, drawing the body 
 toward the point of attachment. 
 This latter movement is similar 
 to that of a boatman pulling him- 
 self to land by means of a rope 
 fastened to the shore. When the 
 shortening of the tube-feet has 
 ceased, the sucking disks release 
 their attachment, project them- 
 selves again, and this process is 
 repeated over and over. At all 
 times some of the feet are con- 
 tracting, and a steady advance of 
 the body is the result. 
 
 This method of locomotion 
 
 also obtains in the sea-urchins and cucumbers, but in the 
 serpent-stars the tube-feet have become modified into feel- 
 ers, and the animal moves, often rapidly, by means of twist- 
 ing movements of the arms. The feet have this character 
 also in the crinoids, where the animal is generally without 
 
 PIG. 93. Sea-lily or crinoid.
 
 148 ANIMAL FORMS 
 
 the power of locomotion. In some of the sea-cucumbers 
 five equidistant rows of tube-feet extend from one end of 
 the body to the other, and the animal crawls worm-like 
 upon any side that happens to be down ; but certain spe- 
 cies living in the sand, 
 
 &&* where tube - feet will 
 
 not work satisfactorily, 
 have lost all traces of 
 them, and creep like an 
 earthworm from place 
 to place. In all the 
 sea-cucumbers the feet, 
 situated nearthe mouth, 
 "^'4^^''^^^'' have been curiously 
 
 F,,.,, -An unattached crinoid(^ rf0 ,0. One- modified to form a cir- 
 
 half natural size. clet of tentacles, which 
 
 range in form from 
 
 highly branched to short and thick structures, and in func- 
 tion from respiratory organs and those of touch to con- 
 trivances for scooping up sand and conveying it to the 
 mouth. 
 
 141. Food and digestive system. In the echinoderms the 
 body-wall is comparatively thin (Fig. 95), and encloses a 
 great space, the body-cavity, in which the digestive and re- 
 productive organs are contained. As the former in various 
 species is adapted for acting upon very different kinds of 
 food, it shows many modifications ; but there are a few prin- 
 cipal types which may be briefly considered. 
 
 In the starfishes the mouth enters almost directly into 
 the cardiac division of the stomach, a capacious, thin-walled 
 sac, much folded and packed away in the disk and bases of 
 the arms (Fig. 95, b). This in turn leads into the second 
 pyloric portion (), with thicker walls and dorsal, to the 
 first, from which a short intestine leads to the exterior, 
 near the center of the disk. Another conspicuous and im- 
 portant feature is the so-called liver, consisting of a pair
 
 ECHINODERMS 149 
 
 of closely branched, fluffy glands (I), extending the entire 
 length of each arm and opening into the pyloric stomach. 
 
 The starfishes are carnivorous and highly voracious, de- 
 vouring large numbers of barnacles and mollusks which hap- 
 pen in their path. If these are small and free they are 
 taken directly into the stomach, but when one of relatively 
 large size is encountered the starfish settles down upon it, 
 and, slowly pushing the cardiac stomach through the mouth, 
 envelops it in the folds. Digestive fluids are now poured 
 over it, and the victim is speedily despatched and in a partly 
 digested condition is gradually absorbed into the body, leav- 
 
 FIG. 95. Dissection of starfish to show : a, pyloric stomach ; b, bile-ducts (above), 
 cardiac stomach (below) ; b.c., body-cavity ; /, feet ; g, spines ; i, intestine ; 
 /, liver ; m, mouth ; m.p., madreporic plate ; /', reservoir ; r.c., ring canal ; 
 r.m., stomach retractor muscle ; r.v., radial vessel ; s, stone canal ; t, respira- 
 tory tree. 
 
 ing the shell and other indigestible matters upon the exte- 
 rior. Oysters and clams close their shells when thus attacked, 
 but a steady, continuous pull on the part of the starfish 
 finally opens them, and the stomach is spread over the fleshy 
 portions with speedily fatal results. In the interior of the 
 body the food is transferred to the pyloric stomach, sub- 
 jected to the action of the liver, and when completely dis- 
 solved is borne to all parts of the body.
 
 150 ANIMAL FORMS 
 
 The digestive system of the starfishes, with its various 
 subdivisions and appendages, is in some respects more com- 
 plicated than in the other classes. This is most strikingly 
 the case with the serpent-stars, where the entire system for 
 disposing of the minute animals and plants on which it 
 feeds consists of a simple sac communicating with the 
 exterior by a single opening the mouth. 
 
 In the sea-cucumbers large quantities of sand are taken 
 into the body, and the minute organisms and organic mat- 
 ter are digested from it. In the sea-urchins the mouth is 
 provided with five teeth, and the food consists of minute 
 bits of seaweeds, which these snip off. Such diets evidently 
 require a comparatively simple digestive apparatus, for in 
 both it consists throughout its whole extent of a tube of 
 equal caliber, in which the various divisions of esophagus, 
 stomach, and intestine are little, if at all, defined. This 
 is usually somewhat longer than the body, and therefore 
 thrown into several loops ; and in the sea-cucumbers its last 
 division is expanded and furnished with more highly mus- 
 cular walls, which aid in respiration. 
 
 142. Development. With but a few exceptions, the eggs 
 of the echinoderms are laid directly in the surrounding 
 water, and for many days the exceedingly minute young 
 are borne great distances in the tidal currents. During 
 this period they show no resemblance to their parents, and 
 only after undergoing remarkable transformations do they 
 assume their permanent features. In every case they have 
 a five-rayed form in early youth, but in several species of 
 starfishes additional arms develop until there may be as 
 many as twenty or thirty.
 
 CHAPTER XIII 
 
 THE CHOBDATES 
 
 143. General characters. Up to the present time we have 
 been studying the representatives of a vast assemblage of 
 animals whose skeletons, if they have any at all, are located 
 on the outside of the body. In the corals, the mighty com- 
 pany of arthropods, and the echinoderms, it is external. On 
 the other hand, we shall find that the animals we are now 
 about to consider, the fishes, frogs, lizards, birds, and mam- 
 mals, are in possession of an internal skeleton. In some of 
 the simpler fishes and in a number of more lowly forms (Fig. 
 96) it is exceedingly simple, and consists merely of a gristle- 
 like rod, the notochord (Fig. 98, nc), extending the length 
 of the body and serving to support the nervous system, which 
 is always dorsal. This is also the type of skeleton found in 
 the young of the remaining higher animals, but as they grow 
 older the notochord gives way to a more highly developed 
 cartilaginous or bony, jointed skeleton, the vertebral column. 
 
 In the young of all these back-boned or chordate ani- 
 mals, the sides of the throat are invariably perforated to 
 form a number of gill-slits. In the lower forms these per- 
 sist and serve as respiratory organs, but in the higher ani- 
 mals they disappear in the adult. The chordates are thus 
 seen to be distinguished by the possession of a dorsal nerv- 
 ous cord supported by an internal skeleton and by the 
 presence of gill-slits, characters which separate them widely 
 from all invertebrates. 
 
 The chordates may be divided into ten classes, seven of 
 11 151
 
 152 
 
 ANIMAL FORMS 
 
 which (the lancelets, lampreys, fishes, amphibians, reptiles, 
 birds, and mammals) are true vertebrates, while the others 
 embrace several peculiar animals of much simpler organiza- 
 tion. 
 
 144. The ascidians. Among the latter are a number of 
 remarkable species belonging to the class of ascidians or 
 
 sea-squirts (Fig. 96). 
 These are abundantly 
 represented along our 
 coasts, and are readily 
 distinguished by their 
 sac -like bodies, which 
 are often attached at 
 one end to shells or 
 rocks. On the opposite 
 extremity two openings 
 exist, through which a 
 constant stream of water 
 passes, bearing minute 
 organisms serving as 
 food. When disturbed 
 they frequently expel 
 the water from these 
 pores with considerable 
 force, whence the name 
 " sea-squirt." While 
 many lead solitary lives, 
 
 numerous individuals of other species are often closely 
 packed together in a jelly-like pad attached to the rocks, 
 and others not distantly related are fitted to float on the 
 surface of the sea. 
 
 The young when hatched resemble small tadpoles both in 
 their shape and in the arrangement of some of the more 
 important systems of organs. For a few hours each swims 
 about, then selecting a suitable spot settles down and ad- 
 heres for life. From this point on degeneration ensues. 
 
 FIG. 96. Ascidian or sea-squirt.
 
 THE CHORDATES 153 
 
 The tail disappears, and with it the notochord and the 
 greater part of the nervous system. The sense-organs van- 
 ish, the pharynx becomes remodeled, and numerous other 
 changes occur, leaving the animal in its adult condition, 
 with little in its motionless, sac-like body to remind one of 
 a vertebrate. 
 
 145. The vertebrates. Since the remainder of this vol- 
 ume is concerned with the vertebrates it will be well at the 
 outset to gain some knowledge of their more important 
 characteristics. One of the most apparent is the presence 
 of a jointed vertebral column, composed of cartilage or 
 bone, which supports the nervous system. To it are also 
 usually attached several pairs of ribs, two pairs of limbs, 
 either fins, legs, or wings, and in front it terminates in a 
 more or less highly developed skull. In the space par- 
 tially enclosed by the ribs, the body-cavity, a digestive sys- 
 tem is located, which consists of the stomach and intestine, 
 together with the attached liver and pancreas. The cir- 
 culatory system is also highly organized, and consists of a 
 muscular heart, arteries, and veins which ramify through- 
 out the body. Breathing, in the aquatic animals, is car- 
 ried on by means of gills, and in the air-breathing forms 
 by means of lungs, which, like the gills, effect the removal 
 of carbonic-acid gas and the absorption of oxygen. The 
 nervous system, consisting of the brain situated in the 
 head and the spinal cord extending through the body 
 above the back-bone, even in the lower vertebrates, is far 
 more complex than in the invertebrates. The sense-organs 
 also attain to a high degree of acuteness, and in connec- 
 tion with the highly organized nervous system enable these 
 forms to lead far more varied and complex lives than in 
 any of the animals heretofore considered.
 
 CHAPTER XIV 
 
 THE FISHES 
 
 146. General characters. In a general way the name fish- 
 is applied to all vertebrates which spend the whole of their 
 life in the water, which undergo no retrograde metamor- 
 phosis, and which do not develop fingers or toes. Of other 
 aquatic chordates or vertebrates the ascidians undergo a 
 retrograde metamorphosis, losing the vertebral column, and 
 with it all semblance of fish-like form. The amphibians, 
 on the other hand, develop jointed limbs with fingers and 
 toes, instead of paired fins with fin rays. A further com- 
 parison of the animals called fishes reveals very great dif- 
 ferences among them differences of such extent that they 
 cannot be placed in a single class. At least three great 
 groups or classes must be recognized : the Lancelets, the 
 Lampreys, and the True Fishes. The general characters of 
 all these groups will be better understood after the study 
 of some typical fish, that is one possessing as many fish-like 
 features as possible, unmodified by peculiar habits. Such an 
 example is found in the bass, trout, or perch. In either fish 
 the pointed head is united, without any external sign of a 
 neck, to the smooth, spindle-shaped body, which is thus fitted 
 for easy and rapid cleaving of the water when propelled by 
 the waving of the powerful tail (Fig. 97). A keel also has 
 been provided, enabling the fish to steer true to its course. 
 This consists of .folds of skin arising along the middle line of 
 the body, supported by numerous bony spines or cartilaginous 
 154
 
 THE FISHES 155 
 
 rays. These are the unpaired fins, as distinguished from 
 the paired ones, which correspond to the limbs of the higher 
 vertebrates. In the bass or perch the latter are of much 
 service in swimming, and are also most important organs in 
 directing the course of the fish upward or downward, or for 
 
 FIG. 97. Yellow perch (Perca Jlavescem). df, dorsal fins ; pc. pectoral fin ; pf, pelvic 
 fin ; v, ventral fin. 
 
 aiding the tail in changing the course from side to side ; 
 or they may be used to support the animal as it rests upon 
 the bottom in wait for food ; and, finally, they may serve to 
 keep the body suspended at a definite point. 
 
 In addition to an internal skeleton the bass or perch, 
 like the greater number of fishes, is more or less enclosed 
 and protected by an external one, consisting of a beautifully 
 arranged series of overlapping scales, which afford protec- 
 tion to the underlying organs, and at the same time admit 
 of great freedom of movement. These usually consist of a 
 horny substance, to which lime is sometimes added, and 
 are peculiar modifications of the skin, something like the 
 feathers, nails, and hoofs of higher forms. 
 
 147. The air-bladder. Xaturally a fish's body is heavier 
 than the water in which it lives, and there are reasons for 
 thinking that the air-bladder (Fig. 106, a.bl.) acts in the
 
 156 ANIMAL FORMS 
 
 bass and perch and many other fishes as a float to enable 
 them, without much effort, to remain suspended at a defi- 
 nite level. By compressing this sac, partly by its own mus- 
 cles and partly by those of the body-wall, the bulk of the 
 fish is made less, and it sinks ; upon the relaxation of these 
 same muscles the body expands and rises again. Deep-sea 
 fishes, when brought to the surface, where the pressure is 
 relatively slight, are found with their air-bladders so dis- 
 tended that they can not sink again, and the float of surface 
 fishes would be as useless if they were to be carried into the 
 depths below, so that such fishes are compelled to keep 
 within tolerably definite limits of depth. Morphologically 
 considered, the air-bladder is a modified or degenerate lung, 
 and in many fishes it is lost altogether. 
 
 148. Respiration. Looking down the throat of the perch, 
 or any other fish, a series of slits (the gill-openings), usually 
 four or five in number, may be seen on each side communi- 
 cating with the exterior. In the sharks these outer open- 
 ings are readily seen, but in the bony fishes they open into 
 a chamber on each side of the head, covered by a bony plate 
 or gill-cover that is open behind. On raising these flaps 
 the gills may be seen composed of great numbers of bright- 
 red filaments attached to the bars between each slit. Dur- 
 ing life the fish may be seen to open its mouth at regular 
 intervals, and, after gulping in a quantity of water, to close 
 it again, contracting the sides of the throat to force it out 
 of the gill-openings and over the gill-filaments to the exte- 
 rior. During this process the blood traversing the excess- 
 ively thin filaments extracts the oxygen from the water and 
 carries it to other parts of the body. 
 
 With this information, let us return to the study of the 
 three classes of fishes. 
 
 149. The lancelet (Branchiostoma). The lancelet, some- 
 times called amphioxus (Fig. 98), the type of the class Lepto- 
 cardii, is a little creature, half an inch to four inches long, in 
 the different species, transparent and colorless, living in the
 
 THE FISHES 
 
 157 
 
 sand in warm seas, the nine species known being found in 
 as many different regions. A lancelet may be regarded as 
 a vertebrate reduced to its lowest terms. Instead of a 
 jointed back-bone, it has a cartilaginous notochord, running 
 from the head to the tail. A nervous cord lies above it, 
 enclosed in a membranous sheath. Xo skull is present, and 
 the nerve-cord does not swell into a brain. There are no 
 eyes and no scales. The mouth is a vertical slit, without 
 jaws. There is no trace of the shoulder-girdle (shoulder- 
 blade and collar-bone) or pelvis (hip-bone) from which 
 
 
 FIG. 98. The California lancelet ( Branchiostoma californiense). Twice the natural 
 size, g, gills ; I, liver ; m, mouth ; n, nerve-cord ; nc, notochord. 
 
 spring the paired fins, which, in true fishes, correspond to 
 arms and legs. The circulatory system is fish-like, but there 
 is no heart, the blood being driven about by the contraction 
 of the walls of the vessels. Along the edge of the back and 
 tail is a rudimentary fin, made of fin-rays connected by mem- 
 brane. In the character and arrangement of its organs the 
 lancelet is certainly like a fish, but in degree of develop- 
 ment it differs more from the lowest fish than the fish does 
 from a mammal. 
 
 150. Lampreys (or Cyclostomes). The class of lampreys 
 stands next in development (Fig. 99). The notochord gives 
 way anteriorly to a cartilaginous skull, in which is con- 
 tained the brain, of the ordinary fish type. There are eyes, 
 and the heart is developed, and consists of an auricle and 
 a ventricle. As distinguished from the true fish, the lam- 
 preys show no trace whatever of limbs or of the bones 
 which would support them. The lov -r u, v is wholly want- 
 ing, the mouth being a roundish sucking lisk. The fins
 
 158 
 
 AX DIAL FORMS 
 
 are better developed, but of the same structure as in the 
 lancelet. There is no bony matter in the skeleton, and 
 there are no scales. The nasal opening is single on the top 
 of the front of the head. 
 
 There are about twenty-five species in this class. Some 
 of them, called lampreys, ascend the streams from the sea 
 
 
 FIG. 99. Lampreys. 
 
 in the spring for the purpose of spawning. The young 
 undergo a metamorphosis, at first being blind and tooth- 
 less. The adults feed mostly on the blood of fishes, which 
 they suck after scraping a hole in the flesh with their rasp- 
 like teeth. The others, called hag-fishes, live in the sea 
 and bore into the bodies of other fishes, whose muscles they 
 devour. All are slender, smooth, and eel-shaped. 
 
 From their structure and a few fossil remains we sup- 
 pose that these eel-like forms existed long ago, probably be- 
 fore the more highly developed sharks and bony fishes made 
 their appearance, but it is difficult to determine whether 
 their simple organization is of such long standing or is not 
 in part the result of semiparasitic habits, or a life spent
 
 THE FISHES 159 
 
 largely in burrowing. Like the lancelet and other simple 
 chordates, they are of the greatest interest to the zoologist 
 who gains from them some idea of the lowly vertebrate 
 forms that peopled the earth long ago. 
 
 151. True fishes. The third class, Pisces or true fishes, 
 to which the shark as well as the bass and perch belong has 
 a well-developed skeleton, skull, and brain. The lower jaw 
 is developed, forming a distinct mouth, and there is at least 
 a shoulder-girdle and pelvis ; although the fins these should 
 bear are not always developed, the general traits are those 
 we associate with the fish. Of the true fishes, there are 
 again several strongly marked groups, usually called sub- 
 classes. Of these, three chiefly interest us. 
 
 152. The sharks and skates. Very early in the life of 
 the sharks (Fig. 100) and skates (SelacTiii or Elasmobranchii) 
 
 FIG. 100. Dogfish (Squalus acanthias). One-seventh natura 
 
 a notochord appears, similar to that in the lancelet and the 
 lampreys. As growth proceeds its sheath becomes broken 
 up into a series of cartilaginous rings, which thus appear 
 like spools strung on a cord. As the fish grows older these 
 " spools " or vertebrae grow solid, cutting the notochord into 
 little disks, and great flexibility is thus secured. Cartilagi- 
 nous appendages also grow up and cover the spinal nerve- 
 cord lying above, and give strength to the unpaired fins ; 
 the paired fins also have their supports. The shoulder-
 
 160 ANIMAL FORMS 
 
 girdle is placed behind the skull, leaving room for a distinct 
 neck ; strong bars of cartilage bear the gills ; others form jaws 
 to carry the teeth ; and a complex skull protects the brain 
 and sense-organs, which are of a relatively high state of devel- 
 opment. Throughout life the skeleton is of cartilage, with 
 perhaps here and there a little bone where greater strength 
 is required. Besides these, there are numerous minor 
 characters which the student will readily find for himself. 
 
 The sharks and skates or rays live chiefly in the sea, 
 and some reach an enormous size, the largest of all fishes. 
 Some are very ferocious and voracious ; others are very mild 
 and weak, and the development of teeth is in direct pro- 
 portion to their voracity of habit. In earlier geologic times 
 there were many more species of them than now exist. 
 
 153. The lung-fishes. The lung-fishes (Dipnoi) are pe- 
 culiar forms living in some of the rivers of Australia and 
 the tropical regions of Africa and South America. In these 
 the air-bladder is developed as a perfect lung. During the 
 wet season they breathe like other fishes by means of gills, 
 but as the rivers dry up they burrow into the wet mud and 
 breathe by means of lungs which are spongy sacs of which 
 the air-bladder of other fishes is a degenerate representative. 
 As we shall see, they resemble in this respect the tadpoles 
 and some adult Amphibia (frogs and salamanders). The 
 paired fins are also peculiar in structure, having an elongate 
 jointed axis, with a fringe of rays along its length, a struc- 
 ture almost as much like that of the limbs of a frog as that 
 of a fish's fin. In fact the Dipnoi must be regarded as an 
 ancestral type, an ally of the generalized form from which 
 Amphibia and bony fishes have descended. Only four liv- 
 ing species of dipnoans are known, but great numbers of 
 fossil species are found in the rocks. 
 
 154. The bony fishes (Teleostei). The bony fishes, or 
 Teleosts, are distinguished by the bony skeleton, the sym- 
 metrical tail, and by the development of the air-bladder as 
 a more or less completely closed sac, useless in respiration.
 
 THE FISHES 161 
 
 Often this organ is altogether wanting, as in the common 
 mackerel. About ten thousand kinds of bony fishes are 
 known. The species swarm in every sea, lake, or river 
 throughout the earth, and some form or another among 
 them is familiar to every boy in the land. These fishes are 
 divided into about two hundred families, and these may be 
 arranged in fifteen to twenty orders. As these are mostly 
 distinguished by features of the skeleton, we need not name 
 them here. In Jordan and Evermann's Fishes of North and 
 Middle America, as well as in various other books, the stu- 
 dent of fishes can find the characters by which orders may 
 be distinguished. 
 
 155. Sturgeons and garpikes (Ganoidea). While the great 
 majority of the typical fishes possess a bony skeleton, there 
 are a few quaint types the ganoid fishes, such as the stur- 
 geons (Fig. 101) and garpikes in which it is cartilaginous or 
 partly bony. In past ages these were probably the highest 
 type of fishes, and from their fossil remains we may con- 
 clude that they flourished in vast numbers ; but at present 
 they are almost extinct. In this country the ganoids are 
 represented by several species, the best known being the 
 sturgeons which inhabit the Great Lakes, the Mississippi, 
 and its tributaries ; while on the East coast the common 
 sturgeon (Acipenser sturio) often leaves the sea and ascends 
 rivers. They are the largest fishes found in fresh water, 
 attaining a length of ten or twelve feet, and a weight of 
 five hundred pounds. Their food consists of small plants 
 and animals, which they suck in through their tube-like 
 mouth. The garpikes live in the larger lakes and rivers 
 throughout the East and Mississippi Valley. Their bodies, 
 from three to ten feet in length, according to the species, 
 are covered with comparatively large regularly arranged 
 square scales, and the upper jaw is elongated to form a 
 kind of beak, abundantly supplied with teeth. They are 
 carnivorous, voracious fishes, working great havoc among 
 the more defenseless food-fishes.
 
 THE FISHES 163 
 
 156. The catfishes. Lowest of all the bony fishes we may 
 place the great group to which almost all fresh-water fishes 
 belong. In this group the four vertebrae situated next the 
 head are firmly united, and by means of certain small lever- 
 like bones a connection is formed between the air-bladder 
 and the ear of the fish, which is sunk deep in the skull. 
 The air-bladder thus becomes a sounding organ in the 
 function of hearing. The family of catfishes possesses this 
 structure, and the student should look for it in the first one 
 he catches. The catfishes are remarkable for the long feel- 
 ers about the mouth, with which they pick their way on the 
 bottom of a pond. There are many kinds the world over. 
 The small ones are known as horned pout or bullhead. In 
 these the dorsal and pectoral fins are armed each with a 
 strong, sharp spine, which is set stiff when the fish is dis- 
 turbed, and makes them very troublesome to handle. The 
 catfishes have no scales. 
 
 157. The carp-like fishes. The still greater carp family 
 includes all the carp, dace, minnows, and chubs. They 
 have the air-bladder joined to the ear, just like the catfish, 
 but they lack the long feelers and the fin spines, while the 
 soft body is covered with scales, and there are no teeth in 
 the mouth. In the throat are a few very large teeth, which 
 the ingenious boy should find. In the sucker family these 
 throat teeth are like the teeth of a comb, and the mouth is 
 fitted for sucking small objects on the river bottom. 
 
 158. The eels. In the great order of eels the body is 
 long and slim, scaleless, or nearly so, with no ventral fins. 
 The shoulder-girdle has slipped back from the head, so as 
 to leave a distinct neck, while ordinary fishes have none. 
 Of eels there are very many kinds some large and fierce, 
 some small as an earthworm ; and one kind comes into fresh 
 water. 
 
 159. Herring and salmon. In the great order which in- 
 cludes the herring and salmon the vertebras are all alike, 
 the ventral fins far from the head, and the scales smooth to
 
 164 ANIMAL FORMS 
 
 the touch. The herring and shad are examples, as also the 
 salmon and trout. Some live in the great depths of the 
 sea, even five miles below the surface. These are very soft 
 in body, being under tremendous pressure. They are inky 
 black for the sea at that depth seems black as ink and 
 most of them have luminous spots which give them light 
 in the darkness. Some species have the forehead luminous, 
 like the headlight of an engine. Most of these deep-sea 
 fishes are very voracious, for there is nothing for them to 
 feed on save their neighbors. 
 
 160. The pike, sticklebacks, etc. Several small orders 
 stand between these soft-rayed, smooth-scaled fishes and 
 
 Jfte. 108. The blindfish and. its parentage. A, Dismal Swamp fish (Chologaster 
 atelvj), the ancestor of (B) Agassiz's cave fish (Chologaster agassizi) and (C) 
 cave bJindfish (Typhlichlhys subterraneus). 
 
 the form, like the perch and bass, which has many spines in 
 the dorsal fin. Among these transitional forms is the pike 
 (Fig. 103) long, slender, circumspect, and voracious, lying 
 in wait under a lily-pad ; the blindfish, which lost its eyes 
 through long living in the streams of the great caves ; the 
 stickleback, small, wiry, malicious, and destructive, steal- 
 ing the eggs and nibbling the fins of any larger fish ; the 
 sea-horse, clinging with its tail head downward to floating
 
 ' 

 
 166 ANIMAL FORMS 
 
 seaweed, the male carrying the eggs about in his pocket 
 until they hatch ; the mullet, stupid, blundering, feeding 
 on minute plants, crushing them in a gizzard like that of 
 a hen, but withal having soft flesh, good for the table ; the 
 flying-fishes, which sail through the air with great swiftness 
 to escape their enemies. 
 
 161. The spiny-rayed fishes. In the group of spiny- 
 rayed fishes the ventral fins are brought forward and joined 
 to the shoulder-girdle. The scales are generally rough to 
 the touch, and the head is usually roughened also. There 
 are many in every sea, ranging in size from the Everglade 
 perch of Florida, an inch long, to the swordfish, which is 
 thirty. These are the most specialized, the most fish-like 
 of all the fishes. Leading families are the perch, in the 
 fresh waters, the common yellow perch, familiar to all boys 
 in the Northeastern States ; the darters, which are dwarf 
 perches, beautifully colored and gracefully formed, living 
 on the bottoms of swift rivers ; the sunfishes, with broad 
 bodies and shining scales, thriving and nest-building in 
 the quiet eddies ; the sea-bass of many kinds, all valued for 
 the table ; the mackerel tribe, mostly swimming in great 
 schools from shore to shore. After these come the multi- 
 tude of snappers, grunts, weakfishes, bluefishes, rose-fishes, 
 valued as food. Then follow the gurnards, with bony 
 heads; the sculpins, with heads armed with thorns, the 
 small ones in the rivers most destructive to the eggs of 
 trout ; and at the end of the long series a few families in 
 which the spines once developed are lost again, and the 
 fins have only soft and jointed rays. It is a curious law of 
 development that when a structure is once highly special- 
 ized it may lose its usefulness, at which point degeneration 
 at once sets in. Among fishes of this type are the cod- 
 fishes, with spindle-shaped bodies, and the flounders, with 
 flat bodies. The flounders lie on the sand with one side 
 down, and the head is so twisted that the eyes come out to- 
 gether on the side that lies uppermost. This side is col-
 
 168 ANIMAL FORMS 
 
 ored like the bottom sand colored or brown or black and 
 the under side is white. When the flounder is first hatched, 
 the eyes are on each side of the head, and the animal 
 swims upright in the water like other fishes. But it soon 
 rests 011 the bottom ; it turns to one side, and as the body 
 is turned over the lower eye begins to move over to the 
 other side. Finally, we may close the series with the an- 
 glers (Fig. 105), in which the first dorsal spine is trans- 
 formed into a sort of fishing-pole with a bait at the end, 
 which may sometimes serve to lure the little fishes, which are 
 soon swallowed when once in reach of the capacious mouth. 
 
 162. Internal anatomy. A few fishes are vegetarians, but 
 the greater number are carnivorous. Some swallow large 
 quantities of sand of the sea-bottom and absorb from it the 
 small organisms living there. Others are provided with 
 beaks for nipping off corals and tube-dwelling worms. Huge 
 plate-like teeth enable others to crush mollusks, sea-urchins, 
 and crabff, and many are adapted for preying upon other 
 fishes. /The latter are often able to escape, owing to the 
 presence of numerous spines, sometimes supplied with 
 poison-glands ; or their colors are protective, and a vast 
 number of devices are present which enable them with 
 some degree of surety to escape their enemies and capture 
 food. 
 
 Usually, without mastication, the food passes into the 
 digestive tract (Fig. 106), which in the main resembles that 
 of the squirrel, but varies considerably according to the 
 nature of the food it is required to absorb. As in other 
 animals, it is usually longer in the vegetable feeders. In 
 most fishes the walls of the canal are pushed out at the 
 junction of the stomach and intestine, to form numerous 
 processes like so many glove-fingers (the pyloric cceca, Fig. 
 106, py.c.), which probably serve to increase the absorptive 
 surface. The same result is obtained in other ways, chiefly 
 by numerous folds of the lining of the canal. 
 
 The blood-system is much more complex in the fishes
 
 THE FISHES 
 
 1P>9 
 
 than in any of the invertebrates. It also differs in its gen- 
 eral plan from that of most adult vertebrates, owing to the 
 peculiar method of respiration. In almost every case the 
 
 FIG. 105. Angler or frogfish (Lojrfiin* piscatorius}. One-tenth natural size. After 
 BASKETT. 
 
 vessels returning from all parts of the body unite into one 
 vein leading into the heart, which consists of only one 
 auricle and ventricle (Fig. 106). From the heart the blood
 
 170 ANIMAL FORMS 
 
 is forced through the gills, with all their delicate filaments, 
 and now, laden with oxygen and nutritious substances al- 
 ready absorbed from the coats of the digestive tract, it 
 
 Fie. 106. Dissection of a bony fish, the tront (Salmo). a.U., air-bladder : an. 
 
 opening; aw., auricle; gl.st., gills; ffttl., esophagus; int., intestine; id., kidney ; 
 lr., liver ; Lor., ovary; optJ., brain ; py.c., pyloric 'coeca ; gp.c.. spinal cord ; ?])!., 
 spleen ; */., stomach ; v., ventricle. 
 
 travels on to all parts of the body, continually unloading 
 its cargo in needy districts and waste matters in the kid- 
 neys before returning once more to the heart. 
 
 163. The senses of fishes. The habits of fishes indicate 
 that they know considerable of what is going on in the 
 outside world, and their well-developed sense-organs show 
 the degree of their sensitiveness. A share of this informa- 
 tion comes through the sense of touch, which is distributed 
 all over the surface of the body, chiefly in the more ex- 
 posed regions sometimes especially provided with fleshy 
 feelers, like those on the chin of the catfish. 
 
 The sense of smell appears to be fairly developed, as is 
 that of hearing ; but there is no evidence of a sense of taste. 
 A few fishes chew their food, and may possibly taste it, but 
 there are others that swallow it whole, and in all there are 
 relatively a few nerves going to the tongue or floor of the 
 mouth.
 
 THE FISHES 171 
 
 The eyes of most fishes are highly developed, and are of 
 the greatest use at all times. Exceptions to the rule are 
 found in certain species which live in caves or in the dark 
 abysses of the ocean. In some of these the eyes have dis- 
 appeared almost completely, and the sense of touch be- 
 comes correspondingly more acute ; in other deep-sea forms 
 they have grown to a large size, enabling them to distin- 
 guish objects in the gloom, like the owls and other noc- 
 turnal animals. Embedded in the skin of some of these 
 deep-sea fishes, and certain nocturnal ones, are peculiar 
 spots, composed of a glandular substance, which produces 
 a bright glow like that of the fireflies. These may be located 
 on the head or arranged in patterns over various parts of 
 the body, and may serve to light the fish on its way and 
 enable it to see its food to better advantage, or it may act 
 as a lure to many fishes that become victims to their own 
 curiosity. In those fishes which are active most of the 
 time the eyes are located on the sides of the head, and in 
 those which remain at or near the bottom they are turned 
 toward the top ; in every case where they can be used to 
 the best advantage. 
 
 164. Breeding habits. Among fishes the egg-laying time 
 usually comes with the spring, when the males of several 
 species become more resplendent, and sometimes engage 
 in struggles for their respective mates. In others this 
 ceremony is performed without show of hostility. Some 
 make nests, while others lay their eggs loosely in the water. 
 
 In all the salmon family the young fishes are born in 
 the colder fresh-water rivers, and later make their way into 
 the sea, where they spend the greater part of their lives. 
 When the time comes for them to lay their eggs they 
 migrate in great companies, and make their way hundreds, 
 perhaps thousands, of miles to .the rivers in which they 
 spent their youth. Up these streams they rush in crowds, 
 leaping waterfalls and rapids, and, dashed and battered on 
 the rocks, many, and in some species all, die from injuries
 
 172 ANIMAL FORMS 
 
 or exhaustion after the breeding season is passed. The 
 eggs, like those of the chubs, suckers, sunfishes, and cat- 
 fishes, are usually buried in shallow holes in the sand, and 
 the males of most fishes keep a faithful watch over the 
 young until they are able to live in safety. In some of 
 the sticklebacks and several marine species elaborate nests 
 are composed of grass or seaweeds ; some of the catfishes 
 carry the eggs until they hatch in their mouths or else in 
 folds of spongy skin on the under side of the body ; in the 
 pipefishes and sea-horses a slender sac along the lower sur- 
 face of the male acts as a brood-pouch, in which the female 
 places the eggs to remain until developed ; and some fishes, 
 such as the surf-fishes and a number of the sharks, bring 
 forth their young alive. On the other hand, the young of 
 many of the herrings, salmon, cod, perch, and numerous 
 other fishes are abandoned at their birth, and fall a prey to 
 many animals, even their parents often included. 
 
 In the former cases, where the young are protected, only 
 a relatively few eggs are produced : where they are aban- 
 doned the female often lays many millions. In every case 
 the number of eggs is in direct relation to the chances the 
 young have of reaching maturity, a few out of each brood 
 surviving to perpetuate the race. 
 
 165. Development and past history. The eggs of the 
 higher bony fishes are usually small (one-tenth to one-third 
 of an inch in diameter), and the young when they hatch 
 are accordingly little ; in the sharks the eggs are larger, 
 the size of a hen's egg or even larger, and the young when 
 born are relatively large and powerful. Thes% differences, 
 however, do not greatly affect the early development, for 
 in every case the head and then the trunk soon become 
 formed, gills arise, the nervous system appears, which is 
 invariably supported by a skeleton in the form of a gristly 
 rod the notochord. In the lower forms of fishes this per- 
 sists throughout life ; but in the sharks and skates it be- 
 comes replaced in the adult by another and higher type of
 
 THE FISHES 173 
 
 skeleton, which is much more specialized with the bony 
 fishes. 
 
 Those who study the fossils on the rocks tell us that 
 the first fishes were very simple, and many believe that 
 their skeleton, like that of the little growing fish, consisted 
 only of a notochord. Many of these old forms died out 
 long ago, while others gradually changed in one way and 
 another to adapt themselves to their surroundings, the con- 
 stant need of adaptation having resulted in the multitude 
 of present-day types. Some, such as the lamprey, have 
 probably changed relatively only to a slight extent ; others, 
 like the sharks and skates, are much more altered; and 
 the bony fishes are far from their original low estate, 
 though their development has been rather toward a greater 
 specialization for aquatic life than an advance upward. 
 The little fish in its growth from the egg thus repeats the 
 history of its ancestral development ; but as though in 
 haste to reach the adult condition, it omits many impor- 
 tant details. Moreover, the record in the rocks is not 
 complete, and we have many things yet to learn of the 
 ancient fishes and their development from age to age to 
 the present day.
 
 CHAPTEK XV 
 
 THE AMPHIBIANS 
 
 IN many respects the amphibians toads, frogs, and sala- 
 manders resemble the fishes, especially the lung-fishes 
 (Dipnoi). The modern amphibians are essentially fishes 
 in their early life, but in developing legs and otherwise 
 changing their bodily form they become adapted for a life 
 on land under conditions differing from those of the fishes. 
 Judging from this class of facts, we may assume that fish- 
 like ancestors, by the development of the lungs, became 
 fitted for a life on land, and that from these the amphib- 
 ians of our times have been derived. 
 
 166. Development. The eggs of the Amphibia are laid 
 during the spring months in fresh-water streams and ponds. 
 They are globular, about as large as shot, and are embedded 
 in a gelatinous envelope (Fig. 107). They are either de- 
 posited singly or in clumps, or festooned in long strings over 
 the water-weeds. During the next few days development 
 proceeds rapidly under favorable conditions, resulting in an 
 elongated body with simple head and tail. In this condition 
 they are hatched as tadpoles. As yet they are blind and 
 mouthless, but lips and horny jaws soon appear, along with 
 highly developed eyes, ears, and nose. External fluffy gills 
 arise on the sides of the head, and slits form in the walls of 
 the throat, between which gills are attached, and over which 
 folds of skin develop, as in the fishes. A fin-fold like that 
 of the lancelet or lamprey appears on the tail. The brain 
 and spinal cord, extending along the line of the back, are 
 supported by a gristly notochord, and complete and com- 
 174
 
 THE AMPHIBIANS 175 
 
 plex internal organs adapt the animal to a free-swimming 
 existence for days to come. 
 
 The t&dpole is now, to all intents and purposes, a fish 
 a fact most clearly recognized in its form, method of loco- 
 
 FIG. 107. Metamorphosis "of the toad. Partly after GAGE, from Animal Life. 
 
 motion, the arrangement of the gills, and the general plan 
 of the circulatory system. 
 
 167. Further growth. In the course of the next few 
 weeks hind limbs develop beneath the skin, through which 
 they finally protrude. In the same manner, fore limbs arise 
 at a later date. In position these organs are like the paired 
 fins of fishes, but they are intended for crawling or leaping 
 on land, and are modified in accordance with this need. As 
 in the higher vertebrates, the limbs develop as arms and 
 legs, with long fingers and toes, between which are stretched 
 webs of skin, which serve in swimming.
 
 176 ANIMAL FORMS 
 
 In the meantime large internal changes are also taking 
 place. The wall of the esophagus has gradually pouched 
 out to form the lungs. They are richly supplied with blood- 
 vessels, closely resembling in their general features the 
 lungs of the lung-fishes. The animal now rises to the sur- 
 face occasionally to gulp in air, and it also continues to 
 breathe by means of gills. At this stage of its existence, 
 therefore, the larva is amphibious (two-living), and we have 
 the interesting example of an animal extracting oxygen 
 from both the water and the air. The diet of the tadpole 
 at this time changes from vegetable to animal substances, 
 and horny teeth give way to the small teeth of the frog, 
 and the digestive system undergoes an entire remodeling 
 to adapt it to its new duties. The young amphibian 
 whether frog, toad, or salamander is now a four-legged 
 creature, with well-developed head and tail, with lungs and 
 gills, though the latter are usually fast disappearing, and is 
 rapidly assuming those characters which will fit it for a 
 terrestrial or semiaquatic existence. 
 
 108. The salamanders. The changes which now ensue in 
 such a larva in reaching the adult condition are relatively 
 slight in the lower salamanders. The external gills often 
 persist (Eig. 110), the lungs are also functional, and the 
 changes are largely those of increase of size. In the larger 
 number of species the gills disappear more or less com- 
 pletely (Fig. 108), such species often abandoning the water 
 for homes in damp soil or under stones and logs, returning 
 to it only when the time comes for their eggs to be laid. 
 The limbs are always relatively weak, never supporting the 
 body from the ground, but serving in a clumsy way to push 
 it from place to place. In the aquatic forms the tail con- 
 tinues to serve as a swimming organ. In some species the 
 hind legs become rudimentary, or even entirely lacking. 
 A still further modification occurs in a few burrowing spe- 
 cies, which move by wrigglings of the body, and are with- 
 out either pairs of legs.
 
 THE AMPHIBIANS 
 
 m 
 
 In geological times many of the salamanders were of 
 great size, several feet in length, and some were enclosed 
 in an armor consisting of bony plates. All now living have 
 the skin naked, and with the exception of the giant species 
 of Japan, three feet in length, and a few similar forms in 
 America, the modern representatives are comparatively 
 
 FIG. 108. Blunt-nosed, salamander (Amblysloma opacum). Photograph by W. H. 
 
 FlSHBB. 
 
 feeble and measure their length by inches. Only a few, on 
 account of their bright colors, are particularly attractive, 
 while the others are usually shunned and considered re- 
 pulsive, chiefly because of their supposed poisonous char- 
 acter, though in reality few animals are more harmless. 
 
 169. Tailless forms. In the frogs and toads the meta- 
 morphosis which the young undergo is almost as profound 
 as that which takes place with the insects. The gills, to- 
 gether with their blood-vessels, disappear completely. The 
 tail, with its muscles, nerve-supply, and skeleton, is ab- 
 sorbed. The cartilaginous notochord gives way to a jointed 
 back-bone. A skull is developed ; numerous bones form in 
 the limbs, affording an attachment for the powerful muscles 
 which make the toad, and especially the frog, expert swim-
 
 ITS ANIMAL FORMS 
 
 mers and leapers, and thus equipped they hereafter lead a 
 wholly terrestrial or seiniaquatic life. 
 
 170. Distribution and common forms. All the Amphibia 
 are dependent upon moisture. Almost all are hatched and 
 developed in fresh water, and those which leave the water 
 return to it during the breeding season. So we find repre- 
 sentatives of the group all over the world having much the 
 same range as the fresh- water fishes. The great majority 
 of the salamanders are confined to the northern hemisphere, 
 but the toads and frogs are almost universally distributed. 
 
 Among the salamanders in this country only a relatively 
 few species completely retain their external gills. This is 
 the case with sirens and mud-puppies or water-dogs (Fig. 
 110), which may occasionally be seen in the clear waters 
 of our lakes and rivers crawling slowly about in search of 
 food, and every now and then rising to the surface to gulp 
 in air. The remainder lose their gills more or less com- 
 pletely, and usually leave the water for damp haunts on 
 land. One of the blunt-nosed salamanders, known as the 
 tiger salamander (Amblystoma tigrinuni), is found in moist 
 localities in most parts of the United States. Besides these 
 are numerous small species, among them the newts (Die- 
 myctylus], ranging widely over the United States, living 
 under logs and stones and feeding upon the small insects 
 and worms inhabiting such situations. In several species 
 of salamanders the lungs disappear with age, and respira- 
 tion is performed solely through the surface of the skin. 
 
 The tailless amphibians are much more abundant and 
 familiar objects than the salamanders, and from the open- 
 ing of spring until late in the fall they are met with on 
 every hand. With few exceptions the frogs live in or about 
 ponds and marshes, in which they obtain protection in 
 troublous times and from which they derive the store of 
 worms and insects that serve as food. On the other hand, 
 the tree-frogs, as their name indicates, usually abandon the 
 water and repair to moist situations in trees and other vege-
 
 THE AMPHIBIANS 1YO 
 
 tatiou. Their shrill, cricket-like calls are often heard in 
 the summer. The fingers and toes are more or less dilated 
 into disks at their tips, enabling them to climb with con- 
 siderable facility; and they are further adapted to their 
 surroundings on account of their protective colors. The 
 toads undergo their metamorphosis while very small, and 
 approach only the water at the breeding season. During 
 the day they remain concealed in holes and crevices, but at 
 the approach of evening come out in search of food. 
 
 171. Means of defense. The food of the members of this 
 group consists chiefly of small fishes, insect larvae, snails, 
 and little crustaceans, which are swallowed whole. On the 
 other hand, many Amphibia prey on each other, while most 
 of them are eagerly sought by birds and fishes. Some, as 
 the toads, stalk their food only during the night-time or 
 depend upon their agility to escape their enemies. Others 
 are colored protectively, the markings of the skin resem- 
 bling the foliage of the earth upon which they rest, and in 
 some species, as the tree-toads, this color-pattern changes 
 as the animal shifts its position. A few species are most 
 brilliantly colored with red, green, yellow, or combinations 
 of these, in striking contrast to their surroundings. They 
 have apparently few enemies, possibly because of an un- 
 pleasant odor or taste, and it has been suggested that their 
 gorgeous tints are danger-signals, warning their would-be 
 captors from attempting a second time to devour them. At 
 the same time it is well known that the somber-hued toads 
 emit a milky secretion from the warty protuberance of 
 their skin which is intensely bitter, irritating to delicate 
 skin, and poisonous to several animals. 
 
 172. Skeleton. As in all vertebrates, the skeleton of the 
 amphibian first arises as a cartilaginous rod, the notochord, 
 which is afterward replaced by a jointed back-bone, to 
 which the limbs are attached. The back-bone is anteriorly 
 modified into a flat, usually complex, skull. In the sala- 
 manders the number of vertebrae is sometimes very large,
 
 180 
 
 ANIMAL FORMS 
 
 and the body correspondingly long and snake-like ; but in 
 other cases parts of the vertebrae are reduced in number, 
 and the body is rather short and thick. In the frogs and 
 toads this reduction reaches its culmination, for only nine 
 distinct vertebrae are present, the tail vertebrae, correspond- 
 ing to those of the salamanders, being represented by a 
 rod-like bone, the urostyle, made of segments grown to- 
 gether. 
 
 173. Digestive and other systems. In its main characters 
 the digestive tract of the amphibian (Fig. 109) resembles 
 
 bl. 
 
 Ir. 
 
 FIG. 109. Dissection of toad (Bnfo). an., anal opening; a., auricle; U., bladder; 
 duo., duodenum ; Ing., lung ; Ir., liver; pn., pancreas ; ret., rectum ; spl., spleen; 
 St., stomach ; v., ventricle. 
 
 that of the fishes and the squirrel. The mouth is usually 
 large, and the teeth are very small, as in the frog or sala- 
 mander, or are lacking completely, as in the common toad. 
 In many salamanders the tongue, like that of a fish, is fixed 
 and incapable of movement. In most of the frogs and 
 toads it is attached to the front of the mouth, leaving its 
 hinder portion free, and capable of being thrown over and 
 outward for a considerable distance. In the throat region 
 gill-clefts may persist, but they usually close as the lungs 
 reach their development. The succeeding portions of the 
 canal are comparatively straight in the elongated forms, or
 
 THE AMPHIBIANS 181 
 
 % 
 
 more or less coiled in the shorter species. In some cases 
 no well-marked stomach exists, but ordinarily the different 
 portions, as they are shown in Fig. 109, are well denned. 
 
 As noted above, the circulation in the tadpole is the 
 same as in fishes, then lungs arise, and for a time respi- 
 ration is effected both by gills and lungs, and the cir- 
 culation resembles in its essential points that of the 
 lung-fishes. This may continue throughout life, but more 
 frequently the gills and their vessels disappear, and the 
 circulation approaches that of the reptiles. In such forms 
 the heart consists of two auricles and one ventricle. Into 
 the left auricle pours the pure blood from the lungs ; into 
 the right the impure blood from the body. To some 
 extent these mix as they are forced into the general cir- 
 culation by the single ventricle. The amount of oxygen 
 carried is therefore smaller than in the higher air-breathers, 
 the amount of energy is proportionately less, and hence it 
 is that all are cold-blooded and of comparatively sluggish 
 habits. 
 
 In some sp'ecies of salamanders the lungs may also dis- 
 appear, and breathing is carried on by the skin, as it is to 
 a certain extent in all amphibians. In the frogs and toads 
 lungs are invariably present, and vocal organs are situated 
 at the opening of" the windpipe in the throat. These pro- 
 duce the characteristic croaking or shrilling, which in many 
 species are intensified through the agency of one or two 
 large sacs communicating with the mouth-cavity. 
 
 Although the brain is small in the amphibians, it is 
 more complex in several respects than it is in fishes. 
 The eyes are also usually well developed, but in some of 
 the cave and burrowing salamanders they are concealed 
 beneath the skin, and are rudimentary. The ear varies 
 considerably in complexity in the different species, but in 
 the possession of semicircular canals and labyrinth resem- 
 bles that of the fishes. In the frogs and toads, as one may 
 readily discover, the drum or tympanum is external, ap-
 
 182 
 
 ANIMAL FOKMS 
 
 pearing as a smooth circular area behind the eye. Organs 
 of touch, smell, and taste are likewise developed in varying 
 degree of perfection. 
 
 174. Breeding-habits. While the great majority of am- 
 phibians mate in the spring and deposit their eggs in the 
 water, often to the accompaniments of croakings and pip- 
 ings almost deafening in intensity, several species, for 
 various reasons, have adopted different methods. Some of 
 the salamanders bring forth young alive, and several species 
 of toads and frogs are known in which the young are cared 
 for by the parent until their metamorphosis is complete. 
 In one of the European toads (Alytes) the male winds 
 the strings of eggs about his body until the tadpoles are 
 
 FIG. 110. Salamanders. The 
 axolotl (the larva of Am- 
 blystoma tigrimtm} and 
 the newt (Diemyctyhts to- 
 rosits). 
 
 ready to hatch ; and in a few species of tree-toads the eggs 
 are stored in a great pouch on the back of the parent until 
 the early stages of growth are over. In the Surinam toad 
 of South America the eggs are placed by the male on the 
 back of the female, and each sinks into a cavity in the 
 spongy skin. Here they pass through the tadpole stage 
 without the usual attendant dangers, and emerge with the 
 form of the adult.
 
 THE AMPHIBIANS 183 
 
 Sunlight and warmth are apparent necessities for speedy 
 development. Tadpoles kept in captivity where the con- 
 ditions are generally unfavorable may require years to as- 
 sume the adult form. As mentioned above, the tiger sala- 
 mander (AmUystoma tigrinum) occurs in most parts of the 
 United States and Mexico. In the East this species drops its 
 gills in early life as other salamanders do, and assumes the 
 adult form, but in the cold water of high mountain lakes, 
 in Colorado and neighboring States, it may never become 
 adult, always remaining as in Fig. 110. This peculiar form 
 is locally known as axolotl. In this condition it breeds. It 
 is thus one of the very few examples of animals whose un- 
 developed larvaB are able to produce their kind. Owing to 
 this trait it was at first considered a distinct species, and 
 many years elapsed before its relationship to the true adult 
 form was discovered.
 
 CHAPTER XVI 
 
 THE REPTILES 
 
 175. General characteristics. In all the reptiles the gen- 
 eral shape of the body, and to some extent the internal 
 plan, is not materially different from that seen among the 
 amphibians. In spite of external resemblance the actual 
 relationship is not very close. It appears to be true that 
 ages ago the ancestors of the modern reptiles were aquatic 
 animals, possibly somewhat similar to some of the sala- 
 manders; but they have become greatly changed, and 
 are now, strictly speaking, land animals. At no time in 
 their development after leaving the egg do we find them 
 living in the water and breathing by gills. Some species, 
 such as the turtles, lead aquatic or semiaquatic lives, but 
 the modifications which fit them for such an existence 
 render them only slightly different from their land-inhabit- 
 ing relatives. The skin bears overlapping scales or horny 
 plates, united edge to edge, as in the turtles, enabling them 
 to withstand the attacks of enemies and the effects of heat 
 and dryness. Indeed, it is when heat is greatest that rep- 
 tiles are most active. In no other class of vertebrates, and 
 very few invertebrates, do normal activities of the body 
 appear to be so directly dependent upon external warmth. 
 In the presence of cold they rapidly grow sluggish, and 
 sink into a dormant state. 
 
 As in the case of all animals, habits depend upon 
 structure, and accordingly among the reptiles we find 
 many remarkable modifications, enabling them to lead 
 184
 
 THE REPTILES 
 
 185 
 
 widely different lives. Nevertheless all are constructed 
 upon much the same plan. 
 
 176. The lizards (Sauria). As in the amphibians, es- 
 pecially the salamanders, the body (Fig. Ill) consists of 
 a relatively small head united by a neck to the trunks, 
 
 FIG. 111. Common lizard or swift (ScelojxMits tindulatus). Photograph by \V. II. 
 FISHER. 
 
 which, in turn, passes insensibly into a tail, usually of con- 
 siderable length. Two pairs of limbs are almost always 
 present, and these exhibit the same skeletal structure as 
 in the amphibians ; but in their construction, as in the 
 other divisions of the body, we note a grace of propor- 
 tion and muscular development which enable the lizards 
 to execute their movements with an almost lightning-like 
 rapidity. The mouth is large and slit-like, well armed with 
 teeth, and the eyes and ears are keen. Scales of various
 
 186 ANIMAL FORMS 
 
 forms and sizes, always of definite arrangement, cover the 
 body. The scales are always colored, in some species as 
 brilliantly as the feathers of birds, and usually harmonize 
 with the surroundings of the animal, enabling it to escape 
 the attacks of its many enemies. Altogether the lizards 
 are a very attractive group of animals. As in the salaman- 
 ders, the vertebral column is usually of considerable length, 
 but it too presents a lighter appearance and a greater flexi- 
 bility. Slender ribs are present, and a breast-bone and the 
 girdles which support the limbs. Although more ossified 
 than in the amphibians, the skull still continues to be com- 
 posed here and there of cartilage. The roof also is yet 
 incomplete, but with the firm plates on the surface of the 
 head ample protection is afforded the small brain under- 
 neath. As above mentioned, the limbs are slender and 
 insufficient to support the body, which accordingly rests 
 upon the ground, and by its wrigglings and the pushing of 
 the limbs is borne from place to place. It will be recalled 
 that some of the salamanders living in subterranean haunts 
 and burrowing in the soil have no need of limbs, and the 
 latter have accordingly disappeared. This condition is 
 paralleled by certain species of lizards. The blindworms 
 (which are neither blind nor worms, but true lizards, though 
 snake-like in appearance) are devoid of limbs, as are also 
 the " glass-snakes." In some species the hinder pair arise 
 in early life, but they remain small, and ultimately disap- 
 pear. In almost all lizards the tail is very brittle, breaking 
 at a slight touch. In such case the lost member will grow 
 again after a time. 
 
 177. The snakes (Serpentes). The snakes are character- 
 ized by a cylindrical, generally greatly elongated body, in 
 which the divisions into head, neck, trunk, and tail are not 
 sharply defined. As we have seen, this is also true of cer- 
 tain lizards, but the naturalist finds no difficulty in detecting 
 the differences between them. Another peculiarity of the 
 snakes is in the great freedom of movement of the bones
 
 THE REPTILES 
 
 187 
 
 not concerned with the protection of the brain. In the 
 reptiles the lower jaw does not unite directly with the 
 skull, as in the higher animals, but to an intermediate 
 bone, the quadrate, which is attached to the skull. In the 
 snakes these unions are made by means of elastic liga- 
 ments. The two halves of the lower jaw are also held 
 
 FIG. 112. Blacksnake (B 
 
 iistrictor). Photograph by W. H. FISHER. 
 
 together by a similar band, so that the entire palate and 
 lower jaw are loosely hung together. This enables the 
 snake to distend its mouth and throat to an extraordinary 
 degree, and to swallow frogs and toads but slightly smaller 
 than itself. Where the prey is of relatively small size, the 
 halves of the lower jaw alternate with each other in pulling 
 backward, thus drawing the food down the throat. The 
 food is never masticated. The teeth are usually small and 
 recurved, and serve only to hold the food until it may be 
 swallowed. The latter process is facilitated by the copious 
 secretion of the salivary glands, which become very active 
 at this time. 
 
 A further character of the snakes is the absence exter-
 
 188 ANIMAL FORMS 
 
 nally of any trace of limbs. However, in some of the 
 pythons and boas hind limbs are present in the form of 
 small groups of bones embedded beneath the skin and ter- 
 minating in a claw. There thus appears to be no doubt 
 that the ancestors of the modern snakes were four-footed, 
 lizard-like creatures, which have assumed the present form 
 in response to the necessity of adaptation to new conditions. 
 
 More than any other order of vertebrates do the snakes 
 deserve the name of creeping things, and yet their method 
 of locomotion enables them to crawl and swim with a ra- 
 pidity equal to that of many of the more highly developed 
 animals. This depends chiefly upon certain peculiarities 
 of the skeleton, which consists merely of a skull, vertebral 
 column, and ribs. The vertebrae, usually two or three hun- 
 dred in number, are united together by ball-and-socket 
 joints, and each attaches by similar joints a pair of slender 
 ribs. These in turn are attached to the broad outer plates 
 upon which the body rests, and the whole system is operated 
 by a powerful set of muscles. Upon the contraction of the 
 muscles the ventral plates are made to strike backward 
 upon the ground or other rough surface, which drives the 
 body forward. Also, the ribs may be made to move back- 
 ward and forward, and the snake thus progresses like a 
 centiped or "thousand-legs." 
 
 178. The turtles (Chelonia). In many respects the tur- 
 tles are the most highly modified of all the reptiles. The 
 body (Fig. 113) is short and wide and enclosed in a shell or 
 heavy armor, consisting of an upper portion, the carapace, 
 and a flat ventral plate, the plastron. The shape of the 
 carapace varies greatly from a low, flat shield to a highly 
 vaulted dome, remaining cartilaginous throughout life, as 
 in the soft-shelled turtles, or becoming bony and of great 
 strength. These two portions of the shell form a box-like 
 armor, through whose openings the head, tail, and limbs 
 may be extended. The latter organs are superficially unlike 
 those of any other order of animals. The head is generally
 
 THE REPTILES 189 
 
 thick-set and muscular, and provided with horny jaws 
 entirely destitute of teeth, like those of the birds. The 
 limbs also are usually short and thick and variously shaped, 
 and adapted for aquatic or terrestrial locomotion. The 
 number of vertebrae in the body and tail are relatively few, 
 and the thick and heavy body is devoid of the elements of 
 grace and agility of movement characteristic of the other 
 reptiles. On the other hand, the former enjoy a freedom 
 from the attacks of enemies not accorded to animals in 
 general. 
 
 At first sight the appearance of a turtle does not indi- 
 cate a close relationship to the other reptiles, but a more 
 
 FIG. 113. Box-turtle (Terrapene Carolina). 
 
 careful examination, and especially of their development, 
 discloses a remarkable resemblance. The head, tail, and 
 limbs are essentially similar to those of the lizards, but in 
 the trunk region peculiar modifications have taken place. 
 The ribs at first separate, as in other animals, flatten 
 greatly, and unite with a number of bones embedded in 
 the skin, thus forming one great plate overlying the back 
 of the animal. About the circumference of the shield 
 other dermal or skin-bones are added, which increase the 
 area of the carapace, and at the same time still others have
 
 190 AXIMAL FORMS 
 
 arisen and united on the ventral surface to form the plas- 
 tron. In this process the shoulder- and hip-girdles which 
 attach the limbs come to be withdrawn into the body, and 
 we have the curious example of an animal enclosed within 
 its back-bone and ribs. This is even more the case with 
 the box-turtles (Fig. 113), common in the eastern United 
 States, whose ventral plate is hinged so that after the 
 limbs, head, and tail have been withdrawn it may be made 
 to act like a lid to completely enclose the fleshy parts of 
 the body. 
 
 Scales and horny plates are present, as in other reptiles, 
 the former covering all parts of the body except the cara- 
 pace and plastron, which support the plates. In nearly all 
 species the latter are of considerable size, and in the tor- 
 toise-shell turtles are valuable articles of commerce. They 
 also are sculptured in a fashion characteristic of each spe- 
 cies, and may, like the colors of other animals, render them 
 more like their surroundings, and consequently incon- 
 spicuous. 
 
 179. Crocodiles and alligators (Crocodilia). The alligators 
 (Fig. 114) and crocodiles are much more complex in struc- 
 ture than the lizards, though their general form is much the 
 same. The body is covered with an armor of thick bony 
 shields and horny scales. These, along the median line, are 
 keeled, and extending along the length of the laterally com- 
 pressed tail form an efficient swimming organ and rudder. 
 The mouth is of large size, and is bounteously supplied with 
 large conical teeth, which are set in sockets in the jaw, and 
 not fused with it, as in many of the lizards. The nose and 
 ears may be closed by valves to prevent the entrance of 
 water, and a similar structure blocks its passage beyond 
 the throat while the mouth is open. When large animals, 
 such as hogs or calves, are captured as they come to drink, 
 these devices enable the alligator or crocodile to sink with 
 them to the bottom and hold them until drowned. The 
 limbs, short and powerful, are efficient organs of locomo-
 
 THE REPTILES 191 
 
 tion on land, and together with the general shape of the 
 body, are also well adapted for swimming. 
 
 FIG. 114. Alligator (Alligator mississippiensis). 
 
 180. Distribution of the lizards. In a general way the 
 number of reptiles is greatest where the temperature is 
 highest. The tropics therefore abound in species, often 
 of large size, and usually of bright coloration. As one 
 travels northward the numbers rapidly diminish, their size 
 is smaller, and the tints less pronounced. In all probability 
 not less than four thousand known reptiles exist, whose 
 haunts are of the most varied description. 
 
 In ^North America the lizards are almost exclusively 
 confined to the southern portions, only a very few species 
 extending up to the fortieth parallel. Among these the 
 skinks (Eumeces] are most widely distributed. The blue- 
 tailed skink is probably the most familiar, a small lizard 
 eight or ten inches in length, dark green with yellowish 
 streaks and a bright-blue tail. On sunny days it may 
 sometimes be seen darting about on the bark of trees in 
 search of insects, upon which it feeds. 
 
 One of the most familiar lizards in this country is the 
 "glass-snake," found burrowing in the drier soil of the 
 southern half of the United States east of the Mississippi.
 
 192 
 
 ANIMAL FORMS 
 
 Both pairs of limbs are absent, but by wriggling movements 
 of the body this lizard is able to force its way through light 
 soil with considerable rapidity. It is a matter of some 
 difficulty to secure entire specimens, for with other than 
 the gentlest handling the tail severs its connection with 
 the body, as the vertebra in this portion are extremely 
 brittle. This peculiarity, together with its shape, has given 
 it the popular name of glass-snake. Many species of liz- 
 ards will thus detach the tail, a habit which is a means of 
 protection, enabling the animal to scamper away into a 
 place of safety while its enemy is concerning itself with 
 the detached member. Later on a new tail develops, 
 though usually of a less symmetrical form. 
 
 181. Horned toads. The horned toads (Phrynosoma) are 
 lizards peculiar to the hot, sandy deserts and plains of 
 
 
 FIG. 115. Gila monster (Heloderma susjxctum). One-third natural size. 
 
 Mexico and the western United States. The body is com- 
 paratively broad and flat, almost toad-like, and is covered 
 with scales and spines of brownish and dusky tint, so like 
 dried sticks and cactus spines in form and color as to ren- 
 der them difficult of detection. In captivity they readily
 
 THE REPTILES 193 
 
 adapt themselves to their new surroundings, become tame, 
 and feast on flies, ants, and other insects, which they cap- 
 ture by the aid of their long tongue. The horned toads 
 are perfectly harmless creatures, but when irritated some- 
 times perform the remarkable feat of spurting a stream of 
 blood from the eye toward the intruding object for a dis- 
 tance of several inches. This has been regarded by some 
 as a zoological fable ; but there are many who have watched 
 the horned toad in its natural state and in captivity, and 
 they assure us that it is a fact. 
 
 In the hot deserts of Arizona and Sonora is another 
 peculiar species of lizard known as the Gila monster (Hclo- 
 derma) (Fig. 115), having the distinction of being the only 
 poisonous lizard known. Further protection is afforded 
 by bony tubercles on the head and by scales over the 
 remainder of the body, all of which are colored brown or 
 various shades of yellow, giving the animal a peculiar 
 streaked and blotched appearance. 
 
 182. Distribution of the snakes. The snakes are much 
 more common than the lizards. All over the United States 
 one meets with them, especially the garter- or water-snakes. 
 Of less wide distribution are the black-, grass-, and milk- 
 snakes, and a number of less known species, all of which 
 are perfectly harmless and often make interesting pets. 
 Some of them when cornered show considerable temper, 
 flatten the head and hiss violently, and imitate poisonous 
 forms, but venomous snakes are comparatively few in num- 
 ber in northern and eastern United States. In the south- 
 ern portions of the country they become more abundant. 
 Along the streams and in the swamps the copperheads, and 
 especially the water-moccasins, often lie in wait for frogs 
 and fish. Both these species are especially dreaded, as they 
 strike without giving any warning sound, but the name 
 and bad reputation of the moccasin is often, especially in 
 the 'South, transferred to perfectly harmless water-snakes. 
 On higher ground are the rattlesnakes (Crotalus), once
 
 194 
 
 ANIMAL FORMS 
 
 abundant but now in many regions well-nigh exterminated. 
 In these species the tail terminates in a series of horny 
 
 rings that produce a buzzing sound like that of the locust 
 when the tail is rapidly vibrated. 
 
 183. Distribution of the turtles. The turtles are perhaps 
 somewhat less dependent upon warmth than other reptiles, 
 yet they too delight to bask in the sunshine, and soon grow 
 sluggish in its absence. In all our fresh-water streams and 
 ponds they are familiar objects, and several species extend 
 up into Canada. Among the turtles the soft shell, the 
 painted and the snapping turtles have the widest distri- 
 bution, scarcely a good-sized stream or pond from the Gulf 
 of Mexico to Canada, and even farther north, being without 
 one or more representatives. All are carnivorous and vora- 
 cious, and the snapping turtles are especially ferocious, and 
 "for their size are the strongest of reptiles." In the woods 
 and meadows the wood-tortoise and box-turtles are occa-
 
 THE REPTILES 
 
 195 
 
 sionally met with, and at sea several turtles exist, some of 
 them of great size. Among these is the leather-turtle, 
 found in the warmer waters of the Atlantic, lazily floating 
 at the surface or actively engaged in capturing food. They 
 attain a length of from six to eight feet, and a weight of 
 over a thousand pounds, and are sometimes captured for 
 food when they come ashore to bury their eggs in the sand. 
 By this same method the loggerheads, the hawkbills, and 
 the common green turtles are also captured in consider- 
 able numbers. These are of smaller size, and the second 
 named is of considerable value, as the horny plates cover- 
 
 FIG. 117. Hawkbill turtle (Eretmochelys imbricata). 
 
 ing the shell furnish the tortoise-shell of commerce. These 
 plates are removed after the animal is killed, by soaking 
 in warm water or by the application of heat. 
 
 184. Food and digestive system. Some reptiles, among 
 which are a number of species of lizards and the box- and 
 green turtles, are vegetarians, but the great majority are
 
 196 ANIMAL FORMS 
 
 carnivorous, and usually very voracious. The lizards espe- 
 cially devour large quantities of insects and snails, together 
 with small fishes and frogs. The latter figure largely in 
 the turtle's bill of fare, and in that of the snakes, which 
 also capture birds and mammals. On the other hand, many 
 of the reptiles prey upon one another ; and they are the 
 favorite food of hawks and owls and numerous water-birds, 
 of skunks and weasels and many other animals, which look 
 for them continually. Many of the turtles, owing to their 
 protective armor, and the snakes because of their poison- 
 ous bite or great size and strength, are more or less ex- 
 empt, but this is not true of their eggs and young. The 
 smaller species depend upon keenness of sense, agility, and 
 inconspicuous tints. These latter may undergo changes 
 according to the character of the surroundings, but usually 
 only to a slight extent. The chameleons of the tropics 
 and a similarly colored green lizard on the pine-trees in 
 the Southern States are able to change with great rapidity 
 from green, through various shades, to brown. 
 
 185. Respiration and circulation. While still in the egg 
 the young lizard develops rudimentary gills, and thus bears 
 
 nntl I II 
 
 '(rbh ned Inc ' ^ duff-MMM. M. 
 
 'Wj 
 
 extna.-. 
 
 ndcw sts&^j^jjgjm 
 7 , OJL^-- : 
 
 FIG. 118. Dissection of lizard (Sceloporus). an., anal opening ; au., auricle ; crb.h., 
 brain ; coec., intestine ; kd., kidney ; Ling., left lung ; lr., liver ; pn., pancreas ; 
 sp.c., spinal cord ; spl., spleen ; st.. stomach ; v., ventricle of heart. 
 
 evidence to the fact that its distant ancestors were aquatic ; 
 but before hatching they disappear, and lungs arise, which
 
 THE REPTILES 197 
 
 remain functional throughout life. Corresponding to the 
 shape of the body, these are usually much elongated and 
 ordinarily paired (Fig. 118, Ling.}. The snakes are peculiar 
 in having the left lung rudimentary or even lacking com- 
 pletely, while the right one becomes greatly elongated and 
 extends far back into the body. In nearly all the reptiles 
 the amount of oxygen brought into the lungs is relatively 
 large and the activity of the animal is proportionately 
 great. The circulation of reptiles shows an advance be- 
 yond that of the Amphibia. As in the latter, there are 
 two distinct auricles ; but the chief difference arises from 
 the fact that the ventricle is more or less divided by a par- 
 tition which to a considerable degree prevents the blood 
 returning from the lungs from mixing with the impure 
 blood as it returns from its journey over the body. In the 
 crocodiles and alligators the partition is complete, and the 
 circulation thus approaches close to that of the higher 
 animals. 
 
 186. Hibernation. Attention has already been called to 
 the fact that reptiles are very susceptible to cold, rapidly 
 growing less active as the temperature lowers. When win- 
 ter comes on they seek protected spots, and either alone 
 or grouped together hibernate. The various activities of 
 the body during this period are at very low ebb. The blood 
 barely circulates, breathing is imperceptible, and stiff 
 and insensible to the world about them they remain until 
 the warmth again stirs them to their former activity. 
 Some of our common turtles must also pass a somewhat 
 similar sleep while embedded far down in the mud during 
 the disappearance of the ponds in summer. At such times 
 no food is taken, but owing to their loss in weight it is 
 probable that a slow consumption of the. body supplies the 
 small amount of necessary energy. 
 
 187. Nervous system and sense-organs. At first sight one 
 is struck with the small size of the brain of fishes, Am- 
 phibia, and reptiles. Their intelligence likewise is at low
 
 198 ANIMAL FORMS 
 
 ebb. Almost all the movements and operations of the body 
 appear to be carried on by the animal with little apparent 
 thought. Their acts, like most of the animals below them, 
 are said to be instinctive ; yet they are sufficiently well done 
 to enable the animal to procure its food, avoid its enemies, 
 and lead a successful life. As is true of other animals, the 
 ability of the reptile to cope with its surroundings depends 
 to a great extent upon the keenness of one or all of its or- 
 gans of special sense. In the reptiles the sense of sight is 
 perhaps sharpest, but there is considerable variation in this 
 respect. Eyelids are present in all except the snakes, to- 
 gether with a third, known as the nictitating membrane, a 
 thin, transparent fold located at the inner angle of the eye, 
 over which it is drawn with great rapidity. In the snakes 
 eyelids are absent, giving the eye its characteristic stare. 
 Furthermore, their sense of sight, except in a few tree-dwell- 
 ing species, appears to be defective, the majority depending 
 largely upon the sense of touch. 
 
 In all the vertebrates a very peculiar organ known 
 as the pineal gland or eye is situated on the roof of the 
 brain. In several lizards its position is indicated by a trans- 
 parent area in one of the plates of the head, and by an 
 opening in the bones of the roof of the skull. In young 
 reptiles, and especially in one of the New Zealand lizards 
 (Hatteria, Fig. 119), its resemblance to an eye is decidedly 
 striking. Lens, retina, pigment, cornea, are all present 
 much as they are in some of the snails, but they finally 
 degenerate more or less as the animal reaches maturity. 
 It is a general belief that it represents the remnant of an 
 organ of sight, a third eye, which looked out through the 
 roof of the skull in some of the ancient vertebrates. 
 
 With the possible exception of the few species of reptiles 
 which produce sounds, probably to attract their mate, the 
 sense of hearing is not particularly well developed. The 
 senses of smell and taste are also comparatively feeble. The 
 latter sense is located in the tongue, which is also popularly
 
 THE REPTILES 199 
 
 supposed to serve for the purpose of defense, and that it is 
 in someway related to the poison-glands. This, however, 
 is an error. The tongue is used primarily as an organ of 
 
 FJG. 110. Tnatera (Sphenodon punctatus). 
 
 touch, and in snakes especially it is almost continually 
 darted in and out to determine the character of the animal's 
 surroundings. 
 
 188. Egg-laying. The eggs of the reptiles are relatively 
 large and enclosed in a shell like a bird's egg, the shell, 
 however, being leathery rather than made of lime. These 
 are deposited in some warm situation, and generally left to 
 themselves to hatch. Under stones, logs, and leaves, or 
 buried lightly in the soil, are the positions most frequently 
 chosen by the lizards and snakes. The turtles almost inva- 
 riably select the warm sand at the edge of the water, and 
 after scooping a hole lay several perfectly spherical eggs, 
 usually at night. The alligators lay upward of a hundred 
 eggs about the size of those of a goose, and guard them 
 jealously until and even after they hatch. On the other 
 hand, the young of many lizards and snakes are born alive, 
 the eggs being hatched within the body. 
 
 Many reptiles are surprisingly slow in attaining maturity, 
 and live to an age attained by few other animals. It is a 
 well-known fact that turtles live fully a hundred years, and 
 14
 
 200 ANIMAL FORMS 
 
 probably the same is true of the crocodiles and alligators 
 and some of the larger snakes. Their enemies are few, and 
 death usually results when the natural course is run. 
 
 Throughout life all reptiles periodically shed their skin, 
 as birds do their feathers and mammals their fur. In the 
 snakes and some of the lizards the skin at the lips loosens, 
 and the animal gradually slips out of its old slough, bright 
 and glossy in the new one which previously developed. In 
 the others the old skin hangs on in tatters, gradually com- 
 ing away as they scamper through the grass.
 
 CHAPTEE XVII 
 
 THE BIRDS 
 
 189. Characteristics. Birds form one of the most sharp- 
 ly defined classes in the animal kingdom, and the variations 
 among the different species are relatively small. "The 
 ostrich or emu and the raven, for example, which may be 
 said to stand at opposite ends of the series, present no such 
 anatomical differences as may be found between a common 
 lizard and a chameleon, or between a turtle and a tortoise," 
 and these we know to be relatively slight. 
 
 In many respects the birds resemble the reptiles, and 
 long ago in the world's history the relationship was much 
 closer than now, as we know from certain fossil remains in 
 this country and in Europe. One of the earliest of these 
 fossil birds, that of the Archaeopteryx, is a most remarkable 
 combination of bird and lizard. Unlike any modern bird, 
 the jaws were provided with many conical reptile-like teeth. 
 The wings were rather small, and the fingers, tipped with 
 claws, were distinct, not grown together, as in modern birds. 
 The tail was as long as the body, and many-jointed, like a 
 lizard's, each vertebra carrying two long feathers. The 
 bird was about the size of a crow, and it probably could 
 not fly far. Other ancient types have been discovered 
 principally sea-birds many of which existed when the 
 Pacific extended over the region now occupied by the 
 Eocky Mountains. These were all of the same generalized 
 type, intermediate between reptile and bird. This fact 
 leads us to the belief that birds descended from reptilian 
 
 201
 
 202 ANIMAL FORMS 
 
 ancestors, and in becoming more perfectly adapted for an 
 aerial life have developed into our modern forms. 
 
 In the modern birds the most important peculiarities, 
 those which separate them from all other animals, are 
 correlated with the power of flight. The body is spindle- 
 shaped, for readily cleaving the air. The fore limbs serve 
 as wings. The hind limbs, supporting the weight of the 
 body from the ground, are usually well developed. A series 
 of air-chambers usually exists in powerful fliers. This 
 serves a purpose analogous to that of the air-bladder of a 
 fish, giving buoyancy. But the most characteristic mark 
 of a bird, as above stated, is its feathers, universally present 
 and never found outside the class. Like the scales of 
 lizards, and probably derived from similar structures, thej 
 are of different forms, and serve a variety of purposes. 
 The larger ones, with powerful shafts, and forming the tail, 
 act as a rudder. Those of the wings give great expanse 
 with but little increase in weight, and are so constructed 
 that upon the down-stroke they offer great resistance to 
 the air, and push the bird forward, while in the reverse 
 direction the air slips through them readily. In flight 
 these movements of the wing may be too rapid for us to 
 follow, as in the humming-birds, though they are usually 
 much slower, two to five hundred a minute in many power- 
 ful fliers, such as the ducks, and frequently long-continued 
 enough to carry them many hundreds of miles at a single 
 flight. The remaining feathers are soft and downy, giving 
 roundness to the body and enabling it to cleave the air with 
 greater ease, and, being poor conductors of heat, they aid in 
 keeping the body at the high temperature characteristic of 
 birds. In most birds the body is not uniformly clothed in 
 feathers. Xaked spaces, usually hidden, intervene between 
 the feather tracts, and on the feet and toes scales exist. 
 
 190. Molting. As we all know, the growth of feathers, 
 unlike that of hair and nails, is limited, and after they have 
 become faded and worn out they are shed, and new ones
 
 THE BIRDS 203 
 
 arise to take their place. This process of molting is 
 usually accomplished gradually, without diminishing the 
 powers of flight ; but in the ducks and some other birds all 
 the wing- and tail-feathers drop out simultaneously, leaving 
 the bird to escape its enemies by swimming and diving. 
 The mol ting-process usually takes place in the fall, after 
 the nesting and care for the young is over, and often when 
 the need for a heavy winter coat commences to be felt. 
 Many birds also don what are called courting colors, ruffs, 
 crests, and highly colored patches, in the spring, previous 
 to the mating season, doubtless for the purpose of attract- 
 ing or impressing their mates. In other cases the change 
 appears to be related to the bird's surroundings. A most 
 beautiful example of this is the ptarmigans grouse-like 
 birds living far to the north. During winter they are per- 
 fectly white and are almost invisible against the snow ; but 
 in the spring, as the snow disappears, the white feathers 
 gradually fall out and new ones arise. The latter so har- 
 monize "with the lichen-colored stones among which it 
 delights to sit, that a person may walk through a flock of 
 them without seeing a single bird." 
 
 There are also numerous birds, chiefly those that go in 
 flocks, which possess what are known as color-calls or recog- 
 nition-marks. These may consist of various conspicuous 
 spots or blotches on different parts of the head or trunk, 
 such as we see in the yellowhammer or meadow-lark ; or 
 one or more feathers of the wings or tail may be strikingly 
 colored, as in many sparrows and warblers. During the 
 time the bird remains at rest these usually are concealed 
 under neighboring feathers, but during flight they are 
 strikingly displayed. It may possibly be true, as many 
 have urged, that these color-signals are for the purpose 
 of enabling various members of the flock to readily follow 
 their leader ; but this and many other interesting questions 
 regarding the color of birds and other animals have not yet 
 received final answers.
 
 204: ANIMAL FORMS 
 
 In very many animals, fishes as well as birds, the tints 
 on the under side of the body are usually relatively light 
 colored, shading gradually into a darker tint above. This 
 is in all probability a protective device, as was recently 
 shown by Mr. A. H. Thayer, an American artist. His ex- 
 periments show that the light from above renders the back 
 less dark, and that the shadow beneath is neutralized by 
 the light color. The bird thus appears uniformly lighted, 
 and this effect, together with streaks and blotches, renders 
 them invisible at surprisingly short distances. 
 
 191. Skeleton. Turning now to the internal organization 
 of birds, we find many points in common with other verte- 
 brates, especially the reptiles, but many interesting modifi- 
 cations are also present that adapt them for flying and for 
 collecting their food. According to the nature of the food, 
 the beak may have a great variety of forms. The skull may 
 be thick and heavy, or thin and fragile, but these are mat- 
 ters of proportion of the various parts possessed by all 
 birds. The neck also is of differing length ; but it is in the 
 trunk region that the greatest changes have arisen, as we 
 may see in any of our ordinary birds. For example, the 
 vertebrae of this part of the body are more or less fused 
 together into rigid framework, to which are attached the 
 ribs that in turn unite with the breast-bone. In the fliers 
 the latter bears a vertical plate or keel, to which the great 
 muscles that move the wings are attached. The tail con- 
 sists, like that of the old-fashioned birds, of several verte- 
 brae, but these are of small size and fused together into a 
 little knob that supports the tail-feathers. The fore limbs 
 are used for flight, but there are the same bones that exist 
 in the fore limbs of other vertebrates one for the upper 
 arm, two for the lower, a thumb carrying a few feathers, 
 and known as the bastard wing, and indications of several 
 bones that form the hand. In the hind limb the resem- 
 blance is equally apparent, though its different parts are 
 of relatively large size to support the body. It is interest-
 
 THE BIRDS 205 
 
 ing to note that the knee has been drawn far up into the 
 body, and that the joint above the foot is in reality the 
 ankle. 
 
 We thus see that the bird's skeleton presents the same 
 general plan as that of the lizard, for example ; but in order 
 to combine the elements of strength, lightness, and com- 
 pactness essential to successful flight, it has been necessary 
 to remodel it to a considerable degree. 
 
 192. Other internal structures. The lungs of birds con- 
 sist of two dark-red organs buried in the spaces between the 
 ribs along the back. Each communicates with extensive 
 thin- walled air-sacs extending into the space between the 
 
 intnal. 
 
 FIG. 120. Anatomy of a bird, au., auricle ; cbl. and crb.h., cerebellum and cerebral 
 hemispheres (divisions of the brain) ; duo., intestine (with portion removed) ; 
 giz., gizzard; kd., kidney; r.lng., lung; tr., trachea or windpipe; vent., ven- 
 tricle. 
 
 various organs, and in many birds of flight they even extend 
 into the bones of the body, and thus decrease their weight. 
 " The enormous importance of this feature to creatures 
 destined to inhabit the air will be readily understood when 
 we learn that a bird with a specific gravity of 1.30 may 
 have this reduced to only 1.05 by pumping itself full of air." 
 As we know, air is taken into the body in order that the 
 oxygen it contains may combine with the tissues of the 
 body to liberate the energy necessary for the work of its
 
 206 ANIMAL FORMS 
 
 life. The deeper and more frequent the breathing the 
 greater the amount of energy produced. Birds habitually 
 breathe deeper breaths than other animals. The air pass- 
 ing into the body traverses the entire extent of the lung 
 on its way back to the air-sacs, with the result that large 
 quantities of oxygen are taken into the body. This is dis- 
 tributed by a circulatory system of a more highly developed 
 type than in any of the preceding groups of animals. The 
 ventricles of the heart no longer communicate with each 
 other, and the pure and impure blood never mingle. Fur- 
 thermore, the beating of the heart is comparatively rapid, 
 rushing the oxygen as fast as it enters the blood to all por- 
 tions of the body. The result is that everywhere heat is 
 being generated, so necessary to life and activity. 
 
 In the lower animals no special means are employed to 
 husband the energy thus produced, but in the birds the 
 body is jacketed in a non-conducting coat of feathers which 
 prevents its dissipation. For this and other reasons the 
 birds, summer and winter, maintain an even and relatively 
 high temperature (102-110). Like the mammals, birds 
 are warm-blooded animals, full of energy, restlessly active 
 to an extent realized in few of the cold-blooded animals. 
 
 193. Digestive system. This life, at high pressure, de- 
 mands a relatively large amount of food to make good the 
 losses due to oxidation. The appetites of some growing 
 birds is only satiated after a daily meal equal to from one 
 to three times their own weight, and after reaching adult 
 size the amount of daily food required is probably not less 
 than one-sixth their weight. The nature of the food is 
 exceedingly varied, and the digestive tract and certain ac- 
 cessory structures are obviously modified in accordance 
 with it. The beak, always devoid of teeth in the living 
 form, varies extremely according to the work it must per- 
 form. The same is true of the tongue, and many correlated 
 modifications exist in the digestive apparatus. In the 
 birds of prey and the larger seed-eating species, such as the
 
 THE BIRDS 207 
 
 pigeons and the domestic fowls, the esophagus dilates into 
 a crop, in which the food is stored and softened before being 
 acted upon by the gizzard. The latter is the stomach, pro- 
 vided with muscular walls, especially powerful in the seed- 
 eaters, and with an internal corrugated and horny lining 
 which, in the absence of teeth, serves to crush the food. In 
 some species, such as the domestic fowls and the pigeons, 
 this process is aided by the grinding action of pebbles 
 swallowed along with the food. The remaining portions, 
 with pancreas and liver, vary chiefly in length, and are 
 sufficiently shown in Fig. 120 to require no further descrip- 
 tion. 
 
 194. Nesting-habits. A few birds, such as the ostriches 
 and terns, merely scoop a hollow in the earth, and make no 
 further pretense of constructing a nest. On the other 
 hand, some birds, such as the humming-birds and pewees, 
 build wonderful creations of moss, lichens, and spider-webs, 
 lining it with down, and concealing it so skilfully that 
 they are not often found. Every bird has its own particular 
 ideas as to the fitness of its own nest, and the results are 
 remarkably different, and form an interesting feature in 
 studying the habits of birds. Usually the female takes 
 upon herself the choice of the nest and its construction ; 
 but these duties are in some species shared by the male. 
 After the eggs are laid, the male may also aid in their 
 incubation, or may carry food to the female. In other 
 species for example, the pigeons and many sea-birds the 
 parents take turns in sitting upon the eggs and in the sub- 
 sequent care of the young. Finally, there are certain birds, 
 such as the cuckoo and cowbirds, which take advantage of 
 the industry of other species and deposit an egg or two in 
 the nests of the latter. All the work of incubation and 
 care of the young is assumed by the foster-parents, which 
 sometimes neglect their own offspring in their desperate 
 attempts to satisfy the appetites of the rapidly growing and 
 unwelcome guests.
 
 208 ANIMAL FORMS 
 
 The eggs of birds are relatively large, and are often 
 delicately colored. In some species the blotches and streaks 
 of different shades are probably protective, as in the plovers 
 and sandpipers, whose eggs blend perfectly with their sur- 
 roundings, but many other cases exist not subject to such 
 an explanation. 
 
 The young require a high degree of heat for their devel- 
 opment, and this is usually supplied by the parent. In a 
 very general way the length of sitting, or incubation, is 
 proportional to the size of the egg, being from eleven to 
 fourteen days in the smaller species, to seven or eight weeks 
 in the ostriches. Before hatching, a sharp spine develops 
 on the beak, and with this the young bird breaks its way 
 through the shell. Among the quails, pheasants, plovers, 
 and many other species, the young are born with a covering 
 of feathers, wide-open eyes, and the ability to follow their 
 parents or to make their own way in the world. Such 
 nestlings are said to be precocial, in distinction to the dltrical 
 young of the more highly specialized species, such as the 
 sparrows, woodpeckers, doves, birds of prey, and their allies, 
 which are born helpless and depend for a considerable time 
 on the parents for support. 
 
 Some of the owls, crows, woodpeckers, sparrows, quails, 
 etc., remain in the same localities where they are bred. 
 They are resident birds. The greater number, at the ap- 
 proach of winter, migrate toward the southern warmer 
 climes, some species traveling in great flocks, by day or 
 night, and often at immense heights. In some cases this 
 movement appears to be directly related to the food-supply ; 
 but there are many apparent exceptions to such a theory, 
 and it is possible that many birds migrate for other reasons. 
 Certain species migrate thousands of miles, along fairly 
 definite routes, the young, sometimes at least, guided by 
 the parents, which in turn appear to remember certain 
 landmarks observed the year before. Sea-birds, in their 
 journeys northward or southward, keep alongshore, occa-
 
 THE BIRDS . 209 
 
 sionally veering in to get their bearings or to rest, espe- 
 cially in the presence of fogs. 
 
 195. Classification. Most zoologists make two primary 
 divisions of the living types of birds those like the ostrich 
 with flat breast-bones, and the other the ordinary birds, in 
 which the breast-bone has a strong keel for the attachment 
 of the powerful muscles used in flight. This distinction is 
 not of high importance, but we may use it as a convenience 
 in the description of a few typical forms belonging to sev- 
 eral orders into which these two divisions are subdivided. 
 
 196. The ostriches, etc. (Ratitae). From specimens in- 
 troduced or from pictures we are doubtless familiar with 
 the ostriches and with some of their relatives. The African 
 ostrich (Struthio camelus, Fig. 121) is the largest of living 
 birds, attaining a height of over seven feet, and is further 
 characterized by a naked head and neck, two toes, and 
 fluffy, plume-like feathers over parts of the body. They 
 are natives of the plains and deserts of Africa, where they 
 travel in companies, several hens accompanying the male. 
 When alarmed, they usually escape by running with a swift- 
 ness greater than that of the horse, but if cornered they 
 defend themselves with great vigor by means of their 
 powerful legs and beaks. Their food consists of insects, 
 leaves, and grass, to which is added sand and stones for 
 grinding the food, as in the domestic fowl. The American 
 ostriches or rheas, are smaller ostrich-like birds, living on 
 the plains of South America. Their habits are essentially 
 the same as those of the African species. 
 
 197. The loons, grebes, and auks (Pygopodes). The birds 
 in this and some of the following orders are aquatic in 
 their habits. All have broad, boat-like bodies, which, with 
 the thick covering of oily feathers, enables them to float 
 without effort. The legs are usually placed far back on 
 the body a most favorable place for swimming, but it ren- 
 ders such birds extremely awkward on land. The grebes 
 are preeminently water-birds. The pied-billed grebe or dab-
 
 Hindus). Photograph by WIL- 
 
 IAM GKAUAM.
 
 THE BIRDS 211 
 
 chick (Podilymbuspodiceps), for example, found abundantly 
 on the larger lakes and streams throughout the United 
 States, captures its food, sleeps, and breeds without leaving 
 the water. The loons living in the same situations as the 
 dabchick are also remarkable swimmers and divers. Of 
 the three species found in this country, the common loon 
 or diver ( Garia imber) attains a length of three feet, and is 
 otherwise distinguished by its black plumage, mottled and 
 barred with white, which is also the color of the under 
 parts. The auks, murres (see frontispiece), and puffins are 
 marine, and, like their inland relatives, are expert swim- 
 mers and divers, strong fliers, and spend much of their 
 time on the open sea. During the breeding-season they 
 assemble in vast numbers on rugged cliffs along the shore, 
 and lay their eggs on the bare rock or in rudely constructed 
 nests. 
 
 198. The gulls, terns, petrels, and albatrosses (Longi- 
 pennes). The birds belonging to this group are among the 
 most abundant along the seacoast, and several species make 
 their way inland, where they often breed. All are char- 
 acterized by long, pointed wings and pigeon or swallow-like 
 bodies, which are carried horizontally as the bird waddles 
 along when ashore. Many are excellent swimmers and 
 powerful fliers, especially the petrels and albatrosses, which 
 sometimes travel hundreds of miles at a single flight. 
 
 The gulls are abundantly represented along our coasts, 
 where they frequently associate in companies, usually rest- 
 ing lightly on the surface of the water, or wheeling lazily 
 through the air on the lookout for food. The terns are 
 of lighter build than the gulls and are more coastwise in 
 their habits, and are further distinguished by plunging like 
 a kingfisher for the fishes on which they live. Both the 
 gulls and terns breed in colonies, every available spot over 
 acres of territory being occupied by their nests, which are 
 usually built of grass and weeds placed on the ground. 
 
 The petrels and albatrosses are at home on the high
 
 212 
 
 ANIMAL FORMS 
 
 seas, rarely coining ashore except at the breeding-season. 
 Some species of the former are abundant oif our shores? 
 especially the stormy petrel (Procellaria pelagica) or Mother 
 Carey's chickens ( Oceanites oceanicus), which are often seen 
 winging their tireless flight in the wake of ocean vessels. 
 Among the dozen or so albatrosses few reach our shores. 
 The wandering albatross (Diomedea exulans), celebrated in 
 story and as the largest sea-bird (fourteen feet between the 
 tips of its outstretched wings), is an inhabitant of the 
 southern hemisphere, and only rarely extends its journeys 
 to more northern regions. 
 
 199. Cormorants and pelicans (Steganopodes). The cor- 
 morants and pelicans are comparatively large water-birds 
 
 FIG. 122. White pelicans (P. erythrorhynchus) and whoopiug-crane (Grus ameri- 
 cana). Photograph by W. K. FISHER. 
 
 usually abundant along the seashore and in many sections 
 of the United States. The cormorants or shags are glossy
 
 THE BIRDS 213 
 
 black in color, with hooked bills, long necks, and short 
 wings, which give them a duck-like flight. The much 
 larger pelicans (Fig. 122) are at once distinguished by long 
 bills, from which is suspended a capacious membranous sac. 
 All these birds are sociable in their habits, breeding, roost- 
 ing, and fishing in great flocks. Their food consists of 
 fishes, which the shags pursue under water and capture in 
 their hooked beaks ; while the pelicans, diving from a con- 
 siderable height or swimming rapidly on the surface, use 
 their pouches as dip-nets. The nests, usually built of sea- 
 weed or of sticks, are placed on rocky cliffs or on the 
 ground in less elevated places. 
 
 200. Ducks, geese, and swans (Lamellirostres). The birds 
 of this order, with their broad, flat, serrated beaks, short 
 legs, and webbed feet, are well known, for in a wild or 
 domesticated state they extend all over the earth. All are 
 excellent swimmers, many dive remarkably well, and are 
 strong on the wing. While a considerable number breed 
 within the United States, their nesting-grounds are gener- 
 ally farther north, and in the early spring it is not unusual 
 to see them migrating in flocks from their warmer winter 
 homes. Among the ducks, the mergansers, mallards (from 
 which our domestic species have been derived), the teals, 
 and the beautiful wood-duck remain with us the year 
 round, dwelling on quiet streams and shallow ponds, living 
 on fish, Crustacea, and seeds. In the more open waters of the 
 larger lakes and along the seacoast we find the canvasback, 
 the scaup-ducks, and the eiders (Fig. 123) which supply the 
 famous down of commerce. Of the few species of geese 
 which inhabit the United States, the Canada goose (Brant a 
 canadensis) is perhaps the most familiar. During their 
 migrations to the nesting sites they fly in V-shaped flocks, 
 their " honks " announcing the opening of spring. The 
 brant (B. bernicla) is also common in the eastern part of 
 the country, where it, like its relations, lives on vegetable 
 substances entirely. The swans are familiar in their semi-
 
 FIG. 133. American eider-duck (Somateria dnxsti-i}.
 
 THE BIRDS 215 
 
 domesticated state, but the two beautiful wild swans found 
 in this country are rarely seen. 
 
 201. The herons and bitterns (Herodines). The herons 
 and bitterns are also aquatic in their habits, but, unlike the 
 swimming-birds, they seek their food by wading. Adapting 
 them for such an existence, the legs and neck are usually 
 very long, and the bill, longer than the head, is sharp and 
 slender. Among the relatively few species in the United 
 States, the great blue heron (Ardea herodias) is widely dis- 
 tributed, and may often be seen standing motionless in 
 some shallow stream on the lookout for fish, or it may 
 wander away into the meadows and uplands to vary its diet 
 with frogs and small mammals. Even more familiar is the 
 little green heron or poke (Ardea virescens), which also is 
 seen widely over the country. The night-herons, as their 
 name indicates, stalk their prey by night, and during the 
 day roost in companies a characteristic common to most 
 herons. The bitterns or stake-drivers are at home in reedy 
 swamps, where they live singly or in pairs, and throughout 
 the night, during times of migration, utter a booming noise 
 resembling the driving of a stake into boggy ground. As 
 a rule, the herons breed as they roost in companies build- 
 ing bulky platforms, usually in trees. The bitterns, on the 
 other hand, secrete their nests on the ground in the rushes 
 of their marshy home. 
 
 202. Cranes, rails, and coots (Paludicolae). In their ex- 
 ternal form the cranes and rails resemble the herons, but 
 in their internal organization they differ considerably. 
 They likewise inhabit marshy lands, but usually avoid 
 wading, picking up the frogs, fish, and insects or plants 
 along the shore or from the surface of the water. The cranes 
 are comparatively rare in this country, yet one may occasion- 
 ally meet with the whooping-cranes (Grus americana) and 
 sand-hill cranes (Grus mexicand), especially in the South 
 and West. They are said to mate for life, and annually 
 repair to the same breeding-grounds, where they build their 
 
 15
 
 216 ANIMAL FORMS 
 
 nests of grass and weeds on the ground in marshy places. 
 The rails are more abundant, though rarely seen on ac- 
 count of their habit of skulking through the swamp 
 grasses. Only rarely do they take to the wing, and then 
 fly but a short distance, with their legs dangling awk- 
 wardly. Closely related to them are the coots or mud-hens 
 (Fulica americana), which may be distinguished, however, 
 by their slaty color, white bills, and lobed webs on the toes, 
 and consequent ability to swim. All over the United 
 States they may be seen resting on the shores of lakes or 
 quiet streams, or swimming on the surface gathering food. 
 The nest consists of a mass of floating reeds, which the 
 young abandon almost as soon as hatched. 
 
 203. The snipes, sandpipers, and plovers (Limicolse). The 
 snipes, sandpipers, and plovers are usually small birds, 
 widely scattered throughout the country wherever there 
 are sandy shores and marshes. In most species the legs 
 are long, and in connection with the slender, sensitive bill 
 fit the bird for picking up small animals in shallow water 
 or probing for them deep in the mud. During the greater 
 part of the year they travel in flocks, but at the nesting- 
 season disperse in pairs and build their nests in shal- 
 low depressions in the earth. The eggs are usually 
 streaked and spotted, in harmony with their surroundings, 
 as are the young, which leave the nest almost as soon as 
 hatched. 
 
 Fully fifty species of these shore-birds live within the 
 confines of the United States. Among these the woodcock 
 (Philohela minor} and snipe (Gallinago delicald) are abun- 
 dant in many places inland, where they probe the moist soil 
 for food, and in turn are eagerly sought by the sportsman. 
 Even more familiar are the sandpipers and plovers, which 
 are especially common along the seacoast, and are also 
 abundantly represented by several species far inshore. 
 Among the latter are the well-known spotted sandpiper or 
 "tip-up" (Actitis macularid) and the killdeer plover
 
 THE BIRDS 
 
 21V 
 
 alitis vocifera), which inhabit the shores of lakes and 
 streams throughout the country. 
 
 204. Quail, pheasants, grouse, and turkeys ( Gallinae). The 
 quail, grouse, and our domestic fowls are all essentially 
 
 FIG. 124. California quail (Lophortyr californicus). Two-thirds natural 
 
 ground-birds, and their structure well adapts them to such 
 a life. The body is thick-set, the head small, and the beak 
 heavy for picking ope'n and crushing the seeds and berries
 
 218 ANIMAL FORMS 
 
 upon which they live. The legs and feet are stout, and 
 fitted for scratching or for running through grass and 
 underbrush. Protective colors also prevent detection, but 
 if close pressed they rise into the air with a rapid whirring 
 of their stubby wings, and after a short flight settle to the 
 ground again. During the breeding-season the male usu- 
 ally mates with a number of hens, which build rough nests 
 in hollows in the ground, where they lay several eggs. The 
 young are precocial. 
 
 The quail or bob-white (Colinus virginianus) and the 
 ruffed grouse (Bonasa umbellns) occur throughout the 
 Eastern States. Over the same area the wild turkey 
 (Meleagris gallopavo) once extended, but is now almost 
 extinct. The prairies of the middle West support the 
 prairie-hen (Tympanuchus americanus), and the valleys 
 and mountains of the far West are the home of several 
 species of quails, some of which are beautifully crested. 
 
 205. Pigeons and doves (Columbae). The pigeons and 
 doves belong to a small yet well-defined order, with upward 
 of a dozen representatives in the United States. They are 
 of medium size, with small head, short neck and legs, and 
 among other distinguishing characters frequently possess a 
 swollen, fleshy pad in which the nostrils are placed. In 
 former years the passenger-pigeon (Ectopistes migrator i us), 
 inhabiting eastern Xorth America, was probably the most 
 common species in this country. Their flocks contained 
 thousands, at times millions, of individuals, which often 
 traveled hundreds of miles a day in search of food, to return 
 at night to definite roosts a trait which enabled the hunter 
 to practically exterminate them. At present the mourning- 
 or turtle-dove (Zenaidura macroura) is the most familiar 
 and wide-spread of the wild forms. The domestic pigeons 
 are all descendants of the common rock-dove (ColumM 
 Uvid) of Europe, the numerous varieties such as the tum- 
 blers, fantails, pouters, etc., being the product of man's 
 careful selection. In the construction of the nest, usually
 
 THE BIRDS 219 
 
 a rude platform of twigs, and in the care of the young 
 both parents have a share. The young at hatching are 
 blind, naked, and perfectly helpless, and are fed masticated 
 food from the crops of the parents until able to subsist on 
 fruits and seeds. 
 
 206. Eagles, hawks, owls, etc. (Raptores). The birds of 
 prey, all of which belong to this order, are carnivorous, 
 often of large size and great strength, and are widely dis- 
 tributed throughout this country. The vultures live on 
 carrion, some of the small hawks and owls on insects, while 
 the majority capture small birds and mammals by the aid of 
 powerful talons. In every case the beak is hooked, and the 
 perfection of the organs of sight and hearing is unequaled 
 by any other animal, man included. They live in pairs, 
 and in many species mate for life. As a rule, the female 
 incubates the eggs, and the male assists in collecting 
 food. 
 
 Among the vultures, the turkey-buzzard (Cathartes aura) 
 is most abundant throughout the United States, especially 
 in the warmer portions, where it plays an important part 
 as a scavenger. Of the several species of hawks, the white- 
 rumped marsh-hawk (Circus hudsonius), the red-tailed 
 hawk (Buteo borealis), the red-shouldered hawk (Buteo 
 lineatus), and above all the bold though diminutive spar- 
 row-hawk (Falco sparverius) are the most abundant and 
 familiar. In the more unsettled regions live the golden 
 eagle (Aquila chrysaetus) and bald eagle (Haliaetus leuco- 
 ceplialus). The owls are nocturnal, and not so often seen 
 as the other birds of prey, yet the handsome and fierce 
 barn or monkey-faced owl (Strix pratincola}, and the larger 
 species, such as the great gray owl (Scotiaptex cinereua), 
 and the beautiful snowy owl (Nyctea nyctea], are more or 
 less common, and occasionally seen. Much more abundant 
 is the little screech-owl (Megascops asio), and in the West- 
 ern States the burrowing-owl (Speotyto cunicularia), which 
 lives in the burrows of the ground-squirrels and prairie-
 
 ANIMAL FORMS 
 
 dogs. Fiercest and strongest of the tribe is the great 
 horned owl (Bubo virginianus). 
 
 FIG. 125. -Bald eagle (Haliaetus Ifucocephulugj. 
 
 207. Cuckoos and kingfishers (Coccyges). Omitting the 
 order of parrots (Psittaci)', whose sole representative in this 
 country is the almost exterminated Carolina parrakeet
 
 THE BIRDS 221 
 
 (Conurus carolinensis)^ we next arrive at the cuckoos and 
 kingfishers, which differ widely in their habits. The black- 
 or yellow-billed cuckoos or rain-crows are shy, retiring 
 birds, with drab plumage, and though seldom seen are often 
 fairly abundant, and are of much service in destroying 
 insects. Unlike their shiftless European relatives, which 
 lay their eggs in the nests of others birds, they build their 
 own airy homes in some bush or hedgerow, and raise their 
 brood with tender care. The belted kingfisher (Ceryle 
 alcyon) is also of a retiring disposition, and spends much 
 of its time on some branch overlooking the water, occa- 
 sionally varying the monotony by dashing after a fish, or 
 flying with rattling cry to another locality. Their nests 
 are built in holes in banks, and six or eight young are 
 annually reared. 
 
 208. The woodpeckers (Pici). The woodpeckers are 
 widely distributed throughout the world, and are preemi- 
 nently fitted for an arboreal life. The beak is stout for 
 chiseling open the burrows of wood-boring insects, which are 
 extracted by the long and greatly protrusible tongue. The 
 feet, with two toes directed forward and two backward, are 
 adapted for clinging, and the stiff feathers of the tail serve 
 to support the bird when resting. Almost all are bright- 
 colored, with red spots on the head, at least in the males, 
 which may further attract their mates by beating a lively 
 tattoo with their beaks on some dry limb. The glossy 
 white eggs are laid in holes in trees, and both parents are 
 said to share the duties of incubation and feeding the 
 young. Among the more abundant and well-known species 
 is the yellowhammer or flicker (Colaptes auratus), which 
 extends throughout the United States. Somewhat less 
 widely distributed is the red-headed woodpecker (Melaner- 
 pes erythroceplialus), and the small black-and-white downy 
 woodpecker (Dryobates pulescens}. This is often called 
 sapsucker, but incorrectly so, as, like all but one of our other 
 woodpeckers it feeds on insects. The yellow-bellied wood-
 
 222 
 
 ANIMAL FORMS 
 
 pecker (Sphyrapicus varius) is a real sapsucker, living on 
 the juices of trees. A close relative of the red-headed 
 woodpecker, the California woodpecker (Melanerpes formi- 
 civorus), is renowned for its habit of boring holes in bark 
 and inserting the acorns of the live oak. Subsequently the 
 bird returns, and breaking open the acorns, devours the 
 grubs which have infested them, and apparently eats the 
 acorns also. 
 
 209. Swifts, humming-birds, etc. (Macrochires). The birds 
 of this order are rapid, skilful fliers, and their wings are 
 very long and pointed. The feet, on the other hand, are 
 
 FIG. 126. Night-hawk ( Chordeiles mrgimamts) on nest. Photograph by H. K. JOB. 
 
 small, relatively feeble, and adapted for perching or cling- 
 ing. Accordingly, the insects upon which they feed are 
 taken during flight by means of their open beaks. The 
 night-hawk (Chordeiles virginianus), roosting lengthwise on 
 a branch by day, at nightfall takes to the wing, and high 
 in the air pursues its food after the fashion of a swallow. 
 In the same haunts throughout the United States the whip-
 
 THE BIRDS 223 
 
 poorwill (Antrostomus vociferus) occurs, sleeping by day, 
 but active at night. Neither of these birds constructs nests, 
 but lays its streaked and mottled eggs directly on the 
 ground. The chimney- swifts (Chcetura pelayica], swallow- 
 like in general form and habits, but very unlike the swallows 
 
 FIG. 127. Anna hummers (one day old), showing short bill and small size of body. 
 Compare with last joint of little finger. 
 
 in structure, frequent hollow trees or unused chimneys, to 
 which they attach their shallow nests. The nearly related 
 humming-birds are chiefly natives of tropical America, only 
 a few species extending into the United States. Of these 
 the little, brilliantly colored, and pugnacious ruby throat 
 (Trocliilus colubris] is the most widely distributed. Its 
 nest, like that of other hummers, is composed of moss and 
 lichens bound together with cobweb and lined with down. 
 
 210. Perching birds (Passeres). The remaining birds, 
 over six thousand in all, belong to one order, the Passeres 
 or perchers. They are characterized by great activity, 
 interesting habits, frequently by exquisite powers of song, 
 and in addition to several other structural arrangements 
 have the feet adapted for perching. Their nesting habits
 
 224 
 
 ANIMAL FORMS 
 
 differ widely, but in every case the young are helpless at 
 the time of hatching, and. require the care of the parents. 
 
 The perchers constitute the greater number of the birds 
 living in the meadows and woods, and are more or less 
 
 Fia. 128. Anna hummer (Calypte anna) on nest. 
 
 common, and consequently familiar everywhere. Among 
 the families into which the order is divided that of the fly- 
 catchers (TyrannidcB), the crows and jays (CorvidcB), the 
 orioles and blackbirds (Icteridce), the finches and sparrows 
 (Fringillid<B)i the swallows (Hinindinidce), the warblers 
 (Mniotiltidce), the thrushes, robins, and bluebirds (Turd idee), 
 are the more familiar, though the others are equally inter- 
 esting.
 
 CHAPTEE XVIII 
 
 THE MAMMALS 
 
 211. General characteristics. The mammals, constituting 
 the last and highest class of the vertebrates, comprise such 
 forms as the opossum and kangaroo, the whales and por- 
 poises, hoofed and clawed animals, the monkeys and man. 
 All are warm-blooded, air-breathing animals, having the 
 skin more or less hairy. The young are born alive, except 
 in the very lowest forms, which lay eggs like reptiles, and 
 for some time after birth are nourished by milk supplied 
 from the mammary glands (hence the word mammals) of 
 the mother. The skeleton is firm, the skull and brain 
 within are relatively large, and, with few exceptions, four 
 limbs are present. 
 
 Most of the mammals inhabit dry land. A number, 
 however, such as the whales and seals, are aquatic ; while 
 others, such as the beavers, muskrats, etc., though not 
 especially adapted for an aquatic life, are, nevertheless, 
 active swimmers, and spend much of their time in the 
 water. 
 
 Mammals tend to associate in companies, as we may 
 witness among the ground-squirrels, prairie-dogs, rats, 
 mice, and the seals and whales. In many cases they band 
 for mutual protection, and often fight desperately for one 
 another. Claws, hoofs, and nails are efficient weapons, and 
 spiny hairs, as on the porcupines, bony plates, such as 
 encircle the bodies of the armadillos, and thick skin and 
 hair, serve as a protection. The hair is also frequently 
 colored to harmonize the animal with its surroundings. 
 
 225
 
 226 ANIMAL FORMS 
 
 Some rabbits and hares in the far north don a white coat 
 in the winter season. 
 
 212. Skeleton. As in other vertebrates, the external 
 form of mammals is dependent in large measure upon the 
 internal skeleton. This consists of relatively compact 
 bones, the cavities of which are filled with marrow. Those 
 forming the skull are firmly united, and, as in other verte- 
 brates, afford lodgment for several organs of special sense 
 and for the brain, which, like that of the birds, completely 
 fills the cavity in which it rests. The vertebral column to 
 which the skull is attached differs considerably in length, 
 but it invariably gives attachment to the ribs, and to the 
 basal girdles supporting one or two pairs of limbs. Gener- 
 ally speaking, the number of bones in the head and trunk 
 of all mammals is the same, so the variations we note in 
 the species about us, for example, are simply due to differ- 
 ences of shape and proportion. As we are aware, there is a 
 great dissimilarity between the length of the neck of man 
 and that of the giraffe, yet the number of bones in each 
 is precisely the same. On the other hand, the variations 
 occurring in the limbs are often due to the actual disap- 
 pearance of parts of the skeleton. Five digits in hand 
 and foot is the rule, and yet, as we well know, the horse 
 walks on the tip of its middle finger and toe, the others 
 being represented by small, very rudimentary, splint bones 
 attached far up the leg. The even-hoofed animals walk on 
 two digits, two smaller hoofed toes being often plainly 
 visible a short distance up the leg, as in the pig. In the 
 whales the hind limbs have completely disappeared, and in 
 the seals, where the fore limbs are modified, as in the 
 whales, into flippers, the hind limbs show many signs of 
 degeneration. 
 
 213. Digestive system. Some mammals, such as man, 
 monkeys, and pigs, are omnivorous ; others, like the cud- 
 chewers and gnawers, are vegetarians ; and still others, 
 like the foxes, weasels, and bears, are carnivorous. In
 
 THE MAMMALS 227 
 
 every case the food substances are acted on by a digestive 
 system constructed on the same general plan as that in man, 
 yet modified according to the specific work it is required to 
 perform. The teeth especially afford a valuable indication 
 of the animal's feeding habits, and, as we may notice later, 
 are also of much value in classification. They consist of 
 incisors used in biting, canines for tearing, and premolars 
 and molars for crushing and grinding. 
 
 The remaining portions of the digestive tract, esopha- 
 gus, stomach, and intestine, with their appended glands, are 
 usually not unlike these possessed by the squirrel (Fig. 1). 
 The chief differences are in the size of the various regions. 
 The stomach, for example, may be long and slender or of 
 great dimensions, and its surface may further be increased 
 by several lobes, which are especially well developed in the 
 ruminants or cud-chewers. The intestine, relatively longer 
 in the mammals than in any other class of vertebrates, also 
 exhibits great differences in length and size. In the flesh- 
 eating species its length is about three or four times the 
 length of the body, while in the ruminants it is ten or 
 twelve times the length of the animal. 
 
 214. Nervous system and sense-organs. As before noted, 
 the nervous system of mammals is characterized by the 
 large size and great complexity of the brain. Even in the 
 simpler species the cerebral hemispheres (large front lobes 
 of the brain, Fig. 1) are well developed, and in the higher 
 forms of the ascending series they form by far the larger 
 part of the brain. The sense-organs also are highly de- 
 veloped, and are constructed and located much as they are 
 in man. The greatest variations occur in the eyes. In 
 some of the burrowing animals they are usually small, and 
 in some of the moles and mice may even be buried beneath 
 the skin and very rudimentary. On the other hand, they 
 are large and highly organized in nocturnal animals ; more 
 so, usually, than in those which hunt their prey by day. 
 The ears also have different grades of perfection, which
 
 228 AXIMAL FORMS 
 
 appear to be correlated with the habits of the animal. 
 Among the species of subterranean habits the sense of hear- 
 ing is largely deficient ; but, on the other hand, it is ex- 
 ceedingly keen in the ruminants, and enables them to detect 
 their enemies at surprisingly great distances. In these 
 creatures the outer ears are of large size and great mobility, 
 and, placed as they are on the top of the head, serve to con- 
 centrate the sound-waves on the delicate apparatus within. 
 In the mammals the sense of smell reaches its highest de- 
 velopment, especially among the carnivores which scent their 
 prey. On the other hand, it is said to be absent in the 
 whales and very deficient in the seals. The sense of taste, 
 closely related to that of smell, is located in taste-buds on 
 the tongue, and is also more acute than in any other class of 
 animals. The sense of touch, located over the surface of 
 the body, is especially delicate on the tips of the fingers, 
 the tongue, and lips, which often bear long tactile hairs, 
 called whiskers or vibrissee. 
 
 215. Mental qualities. Correlated with the high degree 
 of perfection of the brain and sense-organs the mammals 
 show a higher degree of development of the intellectual 
 faculties than any other class of animals. In many cases 
 their acts are instinctive, and not the result of previous 
 training and experience. Just as the duck hatched in an 
 incubator instinctively takes to the water and pecks at its 
 food, or as the bee builds its symmetrical comb, many of 
 the mammals perform their duties day by day. On the 
 other hand many other mammals are also undoubtedly in- 
 telligent. They possess the faculty of memory ; they form 
 ideas and draw conclusions ; they exhibit anger, hatred, and 
 self-sacrificing devotion for their companions and offspring 
 that is different from that in man only in degree and not 
 in kind. In fact, intelligence differs from instinct primar- 
 ily in its power of choice among lines of action. 
 
 216. Classification. Of the eleven orders into which the 
 mammals have been divided eight are represented in this
 
 FIG. 129. Three-toed sloth (Bradypus). About one-tenth natural size.
 
 230 ANIMAL FORMS 
 
 country. Of the other three the first (Monotremes) and 
 simplest of the eleven is represented by the duck-mole 
 
 > 
 
 FIG. 180. Australian duck-mole (Ornithorhynchus paradoxus). One-fifth natural 
 
 6ize. 
 
 (Ornithorliynclms) living in the Australian rivers. Its 
 general appearance and mode of life are represented in
 
 THE MAMMALS 
 
 231 
 
 Fig. 130. The duck-moles are the only mammals which 
 lay eggs. One egg a year is deposited in a carefully con- 
 structed nest where the young are hatched. Another order 
 (Edentata) includes a number of South and Central Ameri- 
 can forms, among which are the ant-eaters, armadillos, 
 and tree-inhabiting sloths (Fig. 129). Still another order 
 (Sirenia) includes the fish-shaped marine dugong and sea- 
 cows or manatees, of which one species is found occasion- 
 ally on the Florida coast. The remaining orders are de- 
 scribed in the succeeding sections. 
 
 217. The opossums and kangaroos (Marsupialia). The 
 lowest order of mammals represented in the United States 
 
 FIG. 131. Opossum (Didelphys virginiana). One-tenth natural size. Photograph 
 by W. H. FISHER. 
 
 is that of the marsupials. It includes the opossums and 
 kangaroos, together with a number of comparatively small 
 and unfamiliar animals living chiefly in and about Australia. 
 16
 
 232 ANIMAL FORMS 
 
 The opossums, fairly abundant throughout the warmer 
 portions of this country, are rat-like creatures, with scaly 
 tails, yellowish-white fur, large head, and pointed snout. 
 Except at the breeding season they lead solitary lives, 
 sleeping in the holes of trees by day and at night feeding 
 on roots, birds, and fruits. 
 
 The kangaroos, familiar from specimens in menageries 
 or museums, chiefly inhabit the plains of Australia. The 
 giant gray kangaroos (Macropus giyanteus], attaining a 
 height of over six feet, go in herds, and owing to the great 
 development of their hind limbs and tails are able, when 
 alarmed, to travel with the swiftness of a horse. Several 
 smaller species, some no larger than rabbits, live among 
 the brush, and like their larger relatives crop the grass and 
 tender herbage with sharp incisor teeth. 
 
 While the marsupials do not lay eggs as does the duck- 
 mole, they allow them to develop within the body for a 
 very short time only. Hence the young, when born, are 
 scarcely more than an inch in length, and are blind, naked, 
 and perfectly helpless. At once they are placed by the 
 mother in the pouch of skin, or marsupium, on the under 
 side of her body. In this the young are suckled and pro- 
 tected until able to gather their own food and fight their 
 own way. 
 
 218. Rodents or gnawers (Glires). The rodents are a 
 large group of mammals, including such forms as the rats, 
 mice, squirrels, gophers, and rabbits. They are readily dis- 
 tinguished by their clawed feet adapted for climbing or 
 burrowing, and by large curved incisor teeth. Unlike 
 ordinary teeth, they grow continually, and, owing to the 
 restriction of the hard enamel to their front surfaces, wear 
 away behind faster than in front, thus producing a chisel- 
 like cutting edge. 
 
 The largest of our native rodents is the porcupine 
 (Eretliizon dorsatus), which ranges from Maine to Mexico, 
 and attains a length of nearly three feet. Many of the hairs
 
 THE MAMMALS 
 
 233 
 
 of the body have the form of stiff, barbed spines (Fig. 132), 
 readily dislodged so that the animal requires no other wea. 
 pon of defense. The rabbits and hares are of smaller size, 
 and the cottontails especially are widely distributed. West 
 of the Mississippi the jack-rabbits are familiar, and are 
 
 FIG. 132. Porcupine (Hystrix cristata). One-tenth natural size. After BREHM. 
 
 famous for their great speed. Like the porcupines, they 
 feed on leaves and grass, and are often very destructive. 
 The mice, especially the field and white-footed mice, are 
 abundant in woodland and meadow throughout the United 
 States. The house-mouse (Mus musculus) is a native of 
 Europe, as is the common rat (M. decumanus), which was 
 imported over a century ago. The wood-rat (Neotoma), 
 however, is native, and may be found in many localities 
 from east to west. The muskrat (Fiber zibethicus), beaver 
 (Castor canadensis), and woodchuck (Arctomys monax) were 
 also more or less plentiful formerly, but in'irtany localities 
 are well-nigh exterminated. The squirrels, on the other 
 hand, continue to exist in large numbers. The prairie-
 
 234 ANIMAL FORMS 
 
 dogs, ground-squirrels, and chipmunks of the terrestrial 
 species are of frequent occurrence, and of the tree-dwellers 
 the fox, gray and red squirrels are well known in many 
 sections of the United States. 
 
 219. Insect-eating mammals (Insectivora). The shrews 
 and moles belonging to this order are representatives of a 
 large group of small animals, which, unlike the major 
 number of rodents, live on insects. The shrews, of which 
 there are several species in this country, are small, mouse- 
 like creatures, nocturnal in their habits, and hence rarely 
 seen. The moles are of much larger size, and owing to 
 their burrowing proclivities scarcely ever appear above 
 ground, but excavate elaborate burrows with their shovel- 
 like feet, devouring the insects which fall in their way. The 
 common mole (Scalops aquaticus) extends from the eastern 
 seaboard to the Mississippi River, where it is replaced by 
 the prairie-mole (S. argenteus), which extends far to the 
 west, into a country inhabited by other species. 
 
 220. The bats (Cheiroptera). The bats are also insectiv- 
 . orous, but their habits are widely different from those of 
 
 the shrews and moles. The forearm and the fingers of the 
 fore limbs are greatly elongated, and are connected by a 
 thin papery membrane, which also includes the hind limbs 
 and tail, and serves as an efficient organ of flight. During 
 the day they remain suspended head downward in some 
 dark cranny, awakening at nightfall to capture flying 
 insects. Several species are found in this country, the 
 most common being the little brown bat ( Vespertilio fus-, 
 cus), with small, fox-like face, large erect ears, and short 
 olive-brown hair. The red bat (Lasiurus borealis) is also 
 plentiful everywhere throughout the United States, and is 
 distinguished from the preceding by its somewhat larger 
 size and long reddish-brown fur. 
 
 221. The whales and porpoises (Cete). The animals 
 belonging to this order, the whales (Fig. 133), porpoises, and 
 dolphins, are aquatic animals bearing a resemblance to fishes
 
 THE MAMMALS 
 
 235 
 
 only in external form. The cylindrical body has no distinct 
 neck, the comparatively large head uniting directly with 
 
 the cylindrical body, which terminates in the tail with hori- 
 zontally placed fins. Xo external signs of hind limbs exist,
 
 236 ANIMAL FORMS 
 
 while the fore limbs are short and capable of being moved 
 only as a whole. External ears are also absent. The eyes 
 are exceedingly small, those of individuals attaining a length 
 of from fifty to eighty feet, being in some species, at least, 
 but little larger than those of an ox. These are often placed 
 at the corners of the mouth. The nasal openings, often 
 known as blow-holes, are situated on the forehead, and as 
 the whale comes to the surface for air afford an outlet for 
 the stream of breath and vapor often blown high in the 
 air a process known as spouting. In some of the whales, 
 such as the dolphin, porpqise, and sperm-whales, the teeth 
 persist throughout life, but in most of the larger species 
 they never " cut " the gum, but early disappear, and their 
 place is taken by large numbers of whalebone plates with 
 frayed edges which act as strainers. The smaller-toothed 
 forms (porpoises, dolphins, and several species of grampus) 
 are frequently seen close to the shore, where they are usu- 
 ally actively engaged in capturing fish. On the other hand, 
 the larger species, such as the humpback, right whale, and 
 sulfurbottom, not uncommon along our coasts, especially 
 to the northward, live on much smaller organisms. With 
 open mouth these whales swim through the water until 
 they collect a sufficient quantity of jelly-fishes, snails, and 
 Crustacea, then closing the mouth strain out the water 
 through the whalebone fringes and swallow the residue. 
 
 As noted above, the animals of this order are almost 
 wholly devoid of hair, but the heat of the body is retained 
 by a thick layer of fat beneath the skin. This " blubber " 
 also gives lightness to the body (as do the voluminous lungs), 
 and, furthermore, yields large quantities of oil, which in 
 former times made " whale-fishing " a profitable industry. 
 The whales bear one, rarely two offspring, which are solicit- 
 ously attended by the mother for a long time. The smaller 
 species grow to a length of from five or eight feet (por- 
 poises, dolphins) to twice this size (grampuses) ; while the 
 larger whales, by far the largest of animals, range from
 
 THE MAMMALS 237 
 
 thirty to over a hundred feet in length with a weight of 
 many tons. 
 
 222. Hoofed mammals (Ungulata). The order of hoofed 
 animals or ungulates includes a large number of forms like 
 the zebra, elephant, hippopotamus, giraffe, deer, and several 
 other wild species, some of which are domesticated, such 
 as horses, sheep, goats, and cattle. All of these animals 
 walk on the tips of their toes, and the claws have become 
 developed into hoofs. The order is divided into the odd- 
 toed forms (perissodactyls), such as the rhinoceros with 
 three toes and the horse with one, and the even-toed (artio- 
 dactyls), as the pigs with four, and the ox, deer, etc., with 
 two toes. The even-toed forms are again divided into 
 those which chew the cud (ruminants) and those which do 
 not (non-ruminants). Xo living native odd-toed mammal 
 exists in this country, and of the wild even-toed species all 
 are ruminants. In the members of this latter group the 
 swallowed food passes into a capacious sac (the paunch), is 
 thoroughly moistened, and passed into the second division 
 (the honeycomb), later to be regurgitated and ground by 
 the powerful molars. It is then reswallowed, and under- 
 goes successive treatment in the other two divisions of 
 the stomach (the manyplies and reed) before entering the 
 intestine. 
 
 Among the Xorth American ruminants, the deer fam- 
 ily (Cervidce) is the best represented. In the more unsettled 
 regions of the East the red deer is still common, and the 
 same may be said of the white-tailed, black-tailed, and 
 mule-deer of the West. Among the woods and lakes to 
 the northward live the reindeer and caribou, and the largest 
 of the deer family, the moose, which attains the size of the 
 horse. Of nearly the same size is the wapiti or elk, whose 
 general characters are shown in Fig. 134. In all of the 
 above-mentioned species the horns, if present, are confined 
 to the male (except in the reindeer), and are annually shed 
 after the breeding season.
 
 THE MAMMALS 239 
 
 The native hollow-horned ruminants (Bovidce) are at 
 present confined to the Western plains, and comprise the 
 pronghorn antelope (Antilocapra americana), the wary big- 
 horn or Kocky Mountain sheep (Ovis canadensis), living 
 in mountain fastnesses, and the buffalo or bison (Bison 
 bison). All of these species were formerly abundant, 
 especially the pronghorn and buffalo, which roamed the 
 plains by thousands, but their extermination has been 
 nearly complete, small herds only persisting in a few wild, 
 inaccessible regions, or protected in parks. 
 
 Our domestic sheep and cattle are probably the descend- 
 ants of several wild species living in Europe and other 
 portions of the world. Of the domesticated even-toed 
 ungulates the horse is the direct descendant of Asiatic 
 wild breeds ; while the pig traces its ancestry back to the 
 wild boar (Sus scrofa) of Europe, and probably a native 
 species (S. indicus) of eastern Asia. 
 
 223. Flesh-eating mammals (Ferae). The order of Ferae 
 or Carnivora is typically exemplified by such animals as the 
 lions, tigers, bears, dogs, cats, and seals, forms which differ 
 from all other mammals by the large size of the canine teeth 
 (often called dog-teeth) and the molars, which are adapted 
 for cutting, not crushing. The limbs, terminated by four 
 or five flexible digits, bear well-developed claws, which, to- 
 gether with the teeth, serve for tearing the prey. While 
 the bears shuffle along on the soles of their feet, the greater 
 number of species, as illustrated by the dog and cat, tread 
 noiselessly on tiptoe. Almost all are fierce and bold, with 
 remarkably keen senses and quick intelligence, and are the 
 dreaded enemies of all other orders of mammals. 
 
 The largest land-inhabiting carnivora are the bears, of 
 which the brown or cinnamon bear ( Ursus americanus], 
 inhabiting Xorth America generally where not extermi. 
 nated, and the huge grizzly ( Ursus horribilis) of the West- 
 ern mountains, are the best-known species. The former 
 lives on berries and juicy herbs, while the grizzly prefers
 
 240 
 
 ANIMAL FORMS 
 
 the flesh of animals which it kills. The raccoon (Fig. 135) 
 (Procyon lotor] is found in wooded districts all over the 
 United States, and its general appearance and thieving 
 propensities are well known. Almost everything is accept- 
 
 able as an article of food, and its fondness for poultry and 
 vegetables makes it an unmitigated nuisance. The otters, 
 skunks, badgers, wolverenes, sables, minks, and weasels, while 
 differing considerably in general appearance and habits, nev-
 
 THE MAMMALS 
 
 241 
 
 ertheless belong to one family (the weasel family, Mustelidce), 
 and are more or less valued for their fur. Almost all are 
 characterized by a .fetid odor, especially the skunk, which 
 is notoriously offensive, and in consequence is avoided by 
 all other animals. 
 
 The dog family is represented by several widely distrib- 
 uted varieties of the red fox ( Vulpes pennsylvanicus] and 
 gray fox ( Urocyon cinereo-argentatus), and by the coyotes 
 
 FIG. 136. Silver fox (Vulpes pennsylvanicus, var. argentatus). Photograph 
 by \V. K. FISHER. 
 
 (Canis latrans] and wolves (Ganis nubilus}. The domestic 
 dog (C'anis familiar is) is probably the descendant of the 
 wolf, and owing to man's careful breeding during thou- 
 sands of years has formed several widely differing varieties. 
 The cat family, comprising the most powerful, savage, 
 and keenest-scented carnivora, is represented by the lion, 
 tiger, jaguar, and hyena. In this country the group is 
 represented by the lynx (Lynx canadensis), the wildcat 
 (Lynx ntfus), and the panther or puma (Felis concolor), 
 which attains the length of nearly five feet. The domestic 
 cat has, like the dog, been domesticated for centuries, and 
 has possibly descended from an African species (Felis
 
 FIG. 137. Panthers (Felis concdor) and peccaries (Dicotylts torquatw).
 
 THE MAMMALS 
 
 243 
 
 caff r a), which was held sacred by the Egyptians, who em- 
 balmed them by thousands. 
 
 224. Man-like mammals (Primates). The last and high- 
 est order of mammals, the Primates, includes the lemurs, 
 monkeys, and man. The first of these are strange squir- 
 rel-like forms living chiefly in trees in Madagascar and 
 neighboring regions where they feed on insects. The apes 
 and monkeys are divided into Old and Xew World forms, 
 which differ widely from each other. The American species 
 are marked by flat noses, with the nostrils far apart. All are 
 arboreal, many have long prehensile tails, and the digits bear 
 nails, not claws. Among them are several species of marmo- 
 sets, the howling monkeys (Myocetes), the spider-monkeys 
 (Ateles), and the capuchins (Cebus), all of which are more or 
 less common in captivity. In the Old World apes, on the 
 other hand, the nostrils are close together and are directed 
 downward, the tail is never 
 prehensile, and in some cases 
 is rudimentary, and may even 
 disappear. The lowest spe- 
 cies (the dog-like apes) in- 
 clude the large, clumsy ba- 
 boons, among them the fa- 
 miliar blue-nosed mandrill 
 (Cynocephalus maimon) and 
 several other species of light- 
 er frame, such as the long- 
 tailed monkey (Cercopithe- 
 cus) (Fig. 139), the tailless 
 Macacus, common in menag- 
 eries, and the Barbary ape, in- 
 habiting northern Africa and 
 
 extending Over into Spain. FIG- 1S8. Baby orang-utan. From life. 
 
 The remaining anthro- 
 poid or man-like apes include the gibbons (Hylobates), orang- 
 utan (Simia), gorilla (Gorilla], and chimpanzee (Anthropo-
 
 FIG. 139. A monkey (Cercopithecus) in a characteristic attitude of watchfulness.
 
 THE MAMMALS 
 
 245 
 
 pithecus). The gibbons, inhabiting southeastern Asia, pos- 
 sess arms of such length that they are able to touch their 
 hands to the ground a's they stand erect. They are thus 
 adapted for a life in the trees, where they spend most of their 
 time feeding on fruit, leaves, and insects. In the same dis- 
 trict the orang occurs, walking when on the ground on its 
 knuckles and the sides of its feet. It prefers the life in 
 the trees, however, in 
 which it builds nests 
 serving for rest and 
 concealment, The go- 
 rilla (Fig. 140), the 
 largest of apes, attain- 
 ing a height of over 
 five feet and a weight 
 of two hundred 
 pounds, is a native of 
 Africa, where it lives 
 in families and sub- 
 sists on fruits. The 
 same region is the 
 home of the chimpan- 
 zee, which in its vari- 
 ous characteristics ap- 
 'proaches most nearly 
 to man. 
 
 Man (Homo sapi- 
 ens) is distinguished 
 
 by the inability to oppose the big toe as he does his thumb 
 a feature associated with his erect position and by the rela- 
 tively enormous size of the brain. Even in an average four- 
 year-old child or an Australian bushman the brain is twice as 
 large as in the gorilla. With this relatively great develop- 
 ment of the nervous system is correlated superior mental 
 faculties, which together with social habits and powers of 
 speech exalt man to a position far above the highest ape. 
 
 FIG. 140.-Gorilla (Gorilla).
 
 246 ANIMAL FORMS 
 
 As usually understood, the family of man (Hominidce) 
 contains but a single species, cosmopolitan and highly vari- 
 able. This species is "now split up into many subspe- 
 cies or races, the native man of this continent, or ' Ameri- 
 can Indian,' being var. americanus. Other races now 
 naturalized in America are : the Caucasian race, var. euro- 
 pceus ; the Mongolian race, var. asiaticus ; and the negro 
 race, afer. The first of these is an immigrant' from Europe, 
 the second from Asia, and the third was brought hither 
 from Africa by representatives of var. europaus to be used 
 as slaves."
 
 CLASSIFICATION OF AKIMALS 
 
 The following table of classification is designed to show the systematic position 
 of the more important animals mentioned in the text. 
 
 ANIMAL KINGDOM 
 
 ONE-CELLED ANIMALS: 
 
 BRANCH- L PROTOZO'A (protos, first ; zoon, animal) 
 Class I. Rhizop'oda (rhiza, root ; pous, foot). 
 
 Amw'ba, Difflii'gia. 
 
 Class II. Infuso'ria (organisms found in infusions). 
 Order 1. Flagella'ta (flagellum, a whip). 
 
 Euglen'a, Codosig'a, Panddrl'na, Vol'vSx. 
 Order 2. Cilia'ta (cilium, an eyelash). 
 Paramoz'cium, Vorticel'la. 
 
 MANY-CELLED ANIMALS (Metazoa) : 
 
 BRANCH II. PORIF ERA (porus, pore ; fero, to carry.) 
 Class I. Porifera (or sponges). 
 
 BRANCH III. CQELENTERA TA (animals with combined body and 
 
 stomach cavity) 
 Class I. Hydrozo'a (hydra, water-serpent ; zoon, animal). 
 
 Hydra, Gonionemus, Hydractiriia, Portuguese man-of-war. 
 Class II. Scyphozo a (scyphos, cup; zoon, animal). 
 
 RJuizijs'toma, Haliclys' tus. 
 Class III. Actinozo'a (actis, a ray ; zoon, animal). 
 
 BRANCH IV. PLATYHELMIN THES * (platus, flat ; helminthos, 
 
 a worm) 
 
 Class I. Plata' da (platus, flat; eidos, likeness). 
 Plana'ria, Leptopla'na. 
 
 * For purposes of convenience, the flatworms (Platyhelminthes), 
 roundworms (Xematelminthes), and segmented worms (Annelids) are 
 combined in one branch (The Worms) in the text. 
 
 17 247
 
 248 ANIMAL FORMS 
 
 Class II. TrematS da (trematodes, pierced with holes, from the 
 erroneous belief that the suckers are holes into the body). 
 
 Liver fluke, Epidel'la. 
 Class III. Cesto'da (cestos, a girdle; eidos, likeness). 
 
 Tapeworm. 
 
 BRANCH V. NEMATELMINTHES (nema, thread; helminUios. a 
 
 worm) 
 Class I. Nemato da. 
 
 Vinegar eel (Anguillula), Trtchl'na, horsehair snake (Gordius). 
 
 BRANCH VI. NEMERTIN EA (nemertes, a sea-nymph) 
 BRANCH VII. ROTIF ERA (rota, a wheel ; fero, to carry) 
 
 BRANCH VIII. ANNE L IDA (annelus, a ring) 
 Class I. Chaetop oda (cltaiie. bristle; pous, foot). 
 Order 1. Polychae te (polus. many ; chaite, bristle). 
 
 Ner'eis, Polyno'e, Ser'pula, Sabella. 
 Order 2. Oligochae te (oligos,few; cJi a ite, bristle). 
 
 Earthworm (Lum'bricus). 
 Class II. Hirudin ea (hirudo, a leech). 
 
 Leeches. 
 
 Class III. Gephyrea (gephura, a bridge, because these animals were 
 once supposed to bridge the gap between the worms and sea- 
 cucumbers). 
 
 BRANCH IX. MOLLUSCOIDA 
 Class I. PSlyzo'a (polus, many ; zoon, animal colonial animals). 
 
 Polyzoa, sea-mats. 
 Class II. BrachiSp oda (brachion, arm ; pous, foot). 
 
 Lamp-shells (brachiopods). 
 
 BRANCH X. MOLLUS CA (mollin, soft) 
 Class I. Lamellibranchia ta (lamella, a plate; bronchia, gill). 
 
 Clams, mussels, oysters, ship-worm (Tere'do). 
 Class II. GastrSp oda (gaster, stomach ; pous, foot). 
 
 Snails, slugs, armadillo snails, naked snails, nudibranchs. 
 Class III. OephalSp'oda (cephale, head ; pous, foot). 
 
 Squids, cuttlefishes, devil-fishes (Oc'topus), nautilus. 
 
 BRANCH XI. EOHINODER MAT A (echinos, a hedgehog; derma, 
 
 skin) 
 
 Class I. Asteroidea (aster, star; eidos, likeness). 
 'Starfishes.
 
 CLASSIFICATION OF ANIMALS 249 
 
 Class II. Ophiuroi'dea (ophis, serpent ; oura, tail ; eidos, likeness). 
 
 Serpent- or brittle-stars, basket-stars. 
 
 Class III. Holothuroi dea (holotlmrion, a kind of water polyp; 
 eidos, likeness). 
 
 Sea-cucumbers. 
 Class IV. Orinoi'dea (crinon, lily ; eidos, likeness). 
 
 Sea-lilies or crinoids. 
 Class V. Echinoi dea (echinos, hedgehog; eidos, likeness). 
 
 Sea-urchins. 
 
 BRANCH XII. ARTHROF ODA (arthron, joint ; pous, foot) 
 Class I. Orusta cea (crusta, a crust or shell). 
 
 Fairy-shrimp (Brdnchip'us), water-fleas (Daph'nia), cop'epod, 
 Cy'clops, goose barnacle, acorn barnacle, Saccull'na, opossum- 
 shrimp, prawn, lobster, crayfish, cancer-crab, rock-crab, pill- 
 bug or i'sopod, sand-hopper or amphi'pod. 
 Class II. OnycSph'ora (onyx, claw ; phero, to carry). , 
 
 Pertp'atus). 
 Class III. Myribp oda (myrios, numberless; pous. foot). 
 
 Cent'iped, thousand-legs. 
 
 Class IV. Insec'ta (insectum, cut in, owing to the grooves surround- 
 ing the body). 
 
 Fishmoth, springtail, cockroach, grasshopper, cricket, katydid, 
 locust, dragon-fly, caddis-fly, may-fly, white ants or termites, 
 ant-lion, water-boatman, water-bug, back-swimmer, chinch- 
 bug, squash-bug, lice, plant-lice, Phijttox' era, scale-insect, 
 gnat, mosquito, flea, house-fly, stag-beetle, wood-beetle, water- 
 beetle, potato-beetle, ladybug, firefly, moth, butterfly, ants, 
 honey-bees and bumblebees, wasps, hornets, yellow-jackets. 
 Class V. Arach nida (arachne, spider). 
 
 Garden-spider, taran'tula, bird-spider, trap-door spider, mite, 
 tick, king-crab or horseshoe crab. 
 
 BRANCH XIII. CHORDATA (chorda, a cord, referring to the 
 
 notochord) 
 
 SUBBRANCH I. Adelochor da. Class Adelochorda. 
 SUBBRANCH II. Urochor da. Class Urochorda. 
 
 Sea-squirts, Tunica'ta, Ascid'ians. 
 SUBBRANCH III. Vertebra'ta (vertebratus, jointed). 
 
 Division A. Acra'nia (a, without ; cranion, skull). Class Lepto- 
 
 cardii. 
 
 Lancelot (Branchic'is'toma = Amphiox'us). 
 Division B. Crania'ta.
 
 250 ANIMAL FORMS 
 
 Class I. Cyclostbm ata (cydos, circle ; stoma, mouth). 
 Hagfishes, lamprey. 
 
 Class II. Pis'ces (piscis, fish). 
 
 Shark, skate or ray, lung-fish, sturgeon, garpike, catfish, horned 
 pout, bullhead, carp, dace, chub, minnow, eel, herring, shad, 
 salmon, trout, pike, stickleback, blindfish, sea-horse, mullet, 
 flying-fish, perch, darter, sunfish, sea-bass, mackerel, snapper, 
 grunt, weakfish, bluefish, rose-fish, gurnard, sculpin, codfish, 
 flounder, angler. 
 
 Class III. Amphibia (a mphi, double ; bios, life). 
 
 Siren, mud-puppy, water-dog, tiger salamander, axolotl, toad, 
 frog, tree-frog. 
 
 Class IV. ReptiTia (reptans, creeping). 
 
 Skink, " glass-snake/' swift, chameleon, horned toad, Gila mon- 
 ster, blacksnake, grass-snake, milk-snake, rattlesnake, copper- 
 head, water-moccasin, soft-shell turtle, snapper, painted turtle, 
 box-turtle, leather-turtle, loggerhead, hawkbill, crocodile, alli- 
 gator. 
 
 Class V. A'ves (avis, bird). 
 
 Ostrich, loon, grebe, auk, murre, puffin, gull, tern, petrel, alba- 
 tross, cormorant, pelican, duck, goose, swan, heron, bittern, 
 crane, rail, mud-hen or coot, snipe, woodcock, sandpiper, kill- 
 dee plover, quail, grouse, wild turkey, prairie-chicken, pigeon, 
 dove, eagle, hawk, owl, turkey-buzzard, cuckoo, kingfisher, 
 woodpecker, sapsucker, swift, humming-bird, night-hawk, 
 whippoorwill, crow, jay, swallow, warbler, thrush, robin, 
 bluebird. 
 
 Class VI. Mammalia (mamma, breast). 
 
 Duck-mole, ant-eater, sloth, armadillo, sea-cow, opossum, kanga- 
 roo, porcupine, mouse, rat, muskrat, woodchuck, beaver, rabbit, 
 squirrel, chipmunk, prairie-dog, shrew, mole, bat, whale, gram- 
 pus, dolphin, porpoise, zebra, elephant, giraffe, deer, antelope, 
 goat, sheep, horse, cow, pig, buffalo, bear, raccoon, otter, skunk, 
 badger, wolverene, sable, mink, weasel, dog, fox, wolf, cat, 
 lynx, panther, monkey, ape, baboon, gibbon, orang-utan, 
 gorilla, chimpanzee, man.
 
 INDEX 
 
 Acipenser sturio (illus.), 162. 
 
 Acorn-barnacle (illus.), 97. 
 
 Air-bladder, 155. 
 
 Albatross, 212. 
 
 Alligator mississippiensis (illus.), 
 
 191. 
 
 Alternation of generations, 35. 
 Altricial, 208. 
 Amoeba (illus.), 12; structure and 
 
 habits, 12. 
 
 Amoeba-like protozoa, 12. 
 Amphibian, development of, 174 ; 
 
 distribution, 178 ; anatomy and 
 
 habits, 179. 
 Amphibious (amphi, double; bios, 
 
 life), 176. 
 
 Amphioxus (illus.), 157. 
 Amphipod (illus.), 106. 
 Anatomy (anatemno, to cut up), 
 
 defined, 1. 
 Angler (illus.), 169. 
 Angle-worm (illus.), 55. 
 Anguillula aceti (illus.), 53. 
 Animals, characteristics of, 2 ; sim- 
 ple and complex, 18. 
 Animals and plants compared, 2. 
 Annelids, 55. 
 
 Anosia plexippus (illus.), 125. 
 Ant, 128 ; white (illus.), 120. 
 Anteater, 231. 
 Antedon (illus.), 148. 
 Antelope, 239. 
 
 Ant-lion (illus.), 120. 
 
 Apes, 243. 
 
 Arachnida, characteristics of, 133. 
 
 Arcliceopteryx, 201. 
 
 Argynnis cybele (illus.), 126. 
 
 Ariolimax columbianus (illus.), 81. 
 
 Armadillo, 231. 
 
 Arthropods, general features of, 
 
 93. 
 
 Ascidian (illus.), 152. 
 Asexual reproduction, 31. 
 Aste'rias ocracea (illus.), 141. 
 Astrophyton (illus.), 143. 
 Auk, 209. 
 Axolotl, 183. 
 
 Back-swimmer, 121. 
 Balancers, 122. 
 Band-worm (illus.), 70. 
 Barnacles (illus.), 96. 
 Bascanion constrictor (illus.), 187. 
 Basket-star (illus.), 141. 
 Bass, 166. 
 
 Bat, brown, 234; red, 234. 
 Bear, 239. 
 Beaver, 232. 
 Bees, 238. 
 Beetles, 124. 
 
 Bell animalcule (illus.), 16. 
 Bilateral symmetry, 44. 
 Biology (bios, life ; logos, a dis- 
 course) defined, 1. 
 
 251
 
 252 
 
 ANIMAL FORMS 
 
 Birds, characteristics of, 201 ; anat- 
 omy of, 204 ; habits of, 207. 
 
 Bird spider, 136. 
 
 Bittern, 215. 
 
 Black-snake (illus.), 193. 
 
 Blastula (illus.), 21. 
 
 Bombus (illus.), 130. 
 
 Bony fish (illus.), 160. 
 
 Botany, defined, 1. 
 
 Brachiopod (illus.), 70. 
 
 Bradypus tridactylus (illus.), 229. 
 
 Branchiostoma californiense (il- 
 lustration), 157. 
 
 Branchipus (illus.), 94. 
 
 Brittle-star (illus.), 141 ; regenera- 
 tion of, 145. 
 
 Bugs, 121. 
 
 Bumblebee (illus.), 130. 
 
 Butterflies, 125. 
 
 Buzzard, 219. 
 
 Byssus, 77. 
 
 Caddis-fly, 119. 
 
 Calcolynthus primigenius (illus.), 
 
 25. 
 
 Calypte anna (illus.), 224. 
 Cancer productus (illus.), 104. 
 Caprella (illus.), 106. 
 Carapace, of Crustacea, 95, 99 ; of 
 
 turtle, 188. 
 Carp, 163. 
 
 Cat, domestic, 239 ; wild, 239. 
 Catfish, 163. 
 Cell (cella, a little room), 7 ; shape 
 
 and size, 7; typical (illus.), 8. 
 Centipeds (illus.), 111. 
 Cephalopod (illus.), 87. 
 Cephalothorax, 99. 
 Cercopithecus (illus.), 244. 
 Cervus canadensis (illus.), 238. 
 Cestode (illus.), 50. 
 Cete, 234. 
 
 Cheiroptera, 234. 
 
 Chelonia, 188. 
 
 Chinch-bug, 122. 
 
 Chiton (illus.), 82. 
 
 Chologaster avetus (illus.), 164 ; C. 
 agassizi (illus.), 164. 
 
 Chordate, characteristics of, 151. 
 
 Chordeiles virginianus (illus.), 
 222. 
 
 Chub, 163. 
 
 Cilium (ciHum, an eyelash), 16. 
 
 Circulatory system, use of, 4. 
 
 Clam (illus.), 72 ; anatomy, 72, 78 ; 
 rock- and wood-boring, 75. 
 
 Clitellum, 58. 
 
 Coccyges, 220. 
 
 Cockroach, 118. 
 
 Ccelenterates, general character- 
 istics of, 18. 
 
 Coleoptera (illus.), 124. 
 
 Columbae, 210. . 
 
 Complex animals, characteristics 
 of, 18. 
 
 Compound eyes, 109. 
 
 Coot, 215. 
 
 Copperhead, 193. 
 
 Corals (illus.), 41. 
 
 Cormorant, 212. 
 
 Correlation of function and struc- 
 ture, 6. 
 
 Cottontail, 233. 
 
 Courting colors, 203. 
 
 Crab, hermit (illus.), 102 ; cancer 
 (illus.), 103; rock (illus.), 104; 
 fiddler, 104. 
 
 Crane (illus.), 215. 
 
 Crayfish (illus.), 101. 
 
 Cricket, 118. 
 
 Crinoid (illus.). 143. 
 
 Crocodile, 190. 
 
 Crocodilia (illus.), 190. 
 
 Crolalus adamanteus (illus.), 222.
 
 INDEX 
 
 253 
 
 Crustacea, 93 ; anatomy of, 98, 107 ; 
 
 multiplication of, 98, 110. 
 Cteniza (illus.), 137. 
 Cuckoo, 220. 
 Cucumaria (illus.), 146. 
 Cuticle, 14. 
 Cuttlefish, 87. 
 Cutworm, 112. 
 Cyclops (illus.), 95 ; anatomy of. 
 
 '98. 
 Cyclostomes, 157. 
 
 Daddy-long-legs, 130. 
 
 Decapods, 102. 
 
 Deer, 222. 
 
 Dendrostoma (illus.), 68. 
 
 Devil-fish (illus.), 87. 
 
 Diddphys virginiana (illus.), 231. 
 
 Diemyctylus torosus (illus.), 182. 
 
 Digestive tract, use of, 3. 
 
 Diptera (illus.), 119. 
 
 Division of labor, 21. 
 
 Dog, 223. 
 
 Dolphin, 221. 
 
 Dove, 205. 
 
 Dragon-fly (illus.), 118. 
 
 Duck-mole (illus.), 216. 
 
 Ducks (illus.), 200. 
 
 Eagle, golden, 205; bald (illus.), 
 205. 
 
 Earthworm (illus.), 55: anatomy, 
 55 ; distribution, 59. 
 
 Echinoderms, 141 ; locomotor sys- 
 tem, 146 ; development of, 150. 
 
 Ecology, 1. 
 
 Eel, 163. 
 
 Egg, fertilization of, 20, 21. 
 
 Elk (illus.), 222. 
 
 Encystment of protozoa, 13. 
 
 Epialtus produdus (illus.), 104. 
 
 Epidella squamula (illus.), 49. 
 
 Eretmochelys imbricata (illus.), 
 
 195. 
 
 Esox (illus.), 165. 
 Euglena (illus.), 17. 
 Eurypelma lentzii (illus.), 136. 
 
 Fairy shrimp (illus.), 94. 
 
 Felis concolor (illus.), 242. 
 
 Ferse, 239. 
 
 Firefly, 124. 
 
 Fish, general characters of, 154; 
 
 respiration, 155 ; anatomy, 168 ; 
 
 breeding habits, 171. 
 Fishmoth, 117. 
 Fish- worm (illus.), 55. 
 Flagellum (flagellum, a whip), 14. 
 Flea, 122. 
 Flicker, 221. 
 
 Flies, 122 ; development of, 123. 
 Flounders, 168. 
 Fox (illus.), 241. 
 Frog, 178. 
 
 Gammarus (illus.), 106. 
 
 Gallinje, 217. 
 
 Ganglion (ganglion, a swelling), a 
 swelling of the nerve-cord due 
 to the accumulation of nerve- 
 cells, 79. 
 
 Ganoidea, 161. 
 
 Garpike, 161. 
 
 Garter-snake, 193. 
 
 Gasteropod (illus.), 80; anatomy and 
 physiology, 81. 
 
 Gastric mill (illus.), 107. 
 
 Gastrula (diminutive of gaster, 
 stomach), 21. 
 
 Geese, 213. 
 
 Gelasimus (illus.), 104. 
 
 Gephyrean worms (illus.), 67. 
 
 Gila monster (illus.), 193. 
 
 Glass-snake, 191.
 
 254 
 
 ANIMAL FORMS 
 
 Glires, 232. 
 
 Gnat, 122. 
 
 Gonionemua vertens (illus.), 34. 
 
 Goose barnacle (illus.), 96. 
 
 Gordius, 54. 
 
 Gorilla (illus.), 245. 
 
 Grasshopper (illus.), 117. 
 
 Grebe, 209. 
 
 Green gland, 108. 
 
 Grouse, 218. 
 
 Grus americana (illus.), 212. 
 
 Gull, 211. 
 
 Habitat (habitare, to dwell), 45. 
 
 Hagfish, 157. 
 
 Halicetus leucocephalus (illus.), 
 220. 
 
 Halidystus (illus.), 39. 
 
 Harvestman, 135. 
 
 Hawks, 219. 
 
 Helix (illus.), 81. 
 
 Heloderma suspeclum (illus.), 192. 
 
 Hemiptera, 121. 
 
 Heptacarpus brevirosfris (illus.), 
 101. 
 
 Hermit-crab (illus.), 102. 
 
 Herodines, 215. 
 
 Herons, 215. 
 
 Herring, 163. 
 
 Homo sapiens, 245. 
 
 Honey-bee, 130. 
 
 Hoofed animals, 237. 
 
 Horned toads, 192. 
 
 Hornet, 132. 
 
 Horse-fly (illus.), 119. 
 
 Horsehair-snake, 54. 
 
 Horseshoe-crab (illus.), 139. 
 
 Humming-bird (ilhis.), 222. 
 
 Hydra, structure of, 29 ; multipli- 
 cation of, 31 ; regeneration of, 
 51. 
 
 Hydractinia (illns.), 36, 103. 
 
 Hydranth, 33. 
 
 Hydrozoa, 34 ; regeneration of, 51. 
 Hymenoptera (illus.), 128. 
 Hystrix cristata (illus.), 233. 
 
 Incubation (incumbo, to rest upon), 
 
 207. 
 
 Infusoria, 17. 
 Insectivora, 234. 
 Insects, numbers, 114; anatomy, 
 
 115 ; respiration, 117. 
 Isopod (illus.), 101. 
 
 Jelly-fish, of Hydrozoa, 33 ; of Scy. 
 
 phozoa, 37. 
 Julus (illus.), 112. 
 
 Kangaroo, 232. 
 Katydid, 117. 
 Keyhole-limpet, 82. 
 King-crab (illus.), 139. 
 Kingfisher, 221. 
 
 Lacertilia, 185, 
 Lamellibranch (illus.), 72. 
 Lamellirostres, 213. 
 Lamprey (illus.), 157. 
 Lamp-shell (illus.), 70. 
 Lancelot (illus.), 157. 
 Lasso-cell, 30. 
 Leeches (illus.), 63; haunts and 
 
 habits, 64. 
 Lemur, 243. 
 Lepas (illus.), 99. 
 Lepidoptera (illus.), 125. 
 Lepomis megalotis (illus.). 167. 
 Leptoplana (illus.), 45. 
 Lice, 122. 
 Life histories and race histories, 
 
 27. 
 
 Limicolae, 216. 
 Limuhis polyphemus (illus.), 139.
 
 INDEX 
 
 255 
 
 Littorina, habits of, 83. 
 
 Liver-fluke, 49. 
 
 Lizard (illus.), 185. 
 
 Lobster, 102. 
 
 Locust (illus.), 117. 
 
 Long-horned borer beetle (illus.), 
 
 124. 
 
 Longipennes, 211. 
 Loon, 209. 
 
 Lopliius piscatorius (illus.), 169. 
 Lophortyx californicus (illus.), 217. 
 Lumbricus terrestris (illus.), 55. 
 Lung-fish, 160. 
 Lynx (illus.), 241. 
 
 Macroldella (illus.), 63. 
 
 Macrocheira, 222. 
 
 Mammals, characteristics of, 225 ; 
 anatomy, 226 ; classification, 228. 
 
 Man, 245. 
 
 Many-celled animals, 11. 
 
 Marsupialia, 231. 
 
 Marsupium (marsupium, a purse 
 or bag), 232. 
 
 May-fly, 118. 
 
 Megapfera versdbilis (illus.), 235. 
 
 Mesenteric filaments, 40. 
 
 Messmates, defined, 48. 
 
 Metamorphosis, retrograde, 99 ; in- 
 complete, 126 ; complete, 128. 
 
 Metazoa, defined, 11. 
 
 Mice, 233. 
 
 Millipeds (illus.), 111. 
 
 Minnow, 163. 
 
 Mite (illus.), 138. 
 
 Mole, 234. 
 
 Mollusks, general characters of, 72. 
 
 Molt, of Crustacea, 99, 110; of 
 birds, 202. 
 
 Monarch butterfly (illus.), 125. 
 
 Monkeys, 243. 
 
 Morphology, defined, 1. 
 
 Mosquito, 122; development of, 
 123. 
 
 Moths (illus.), 125. 
 Mud-hen, 215. 
 Mud-puppy (illus.), 178. 
 Multiplication of animals, 5. 
 Muscle-cell (illus.), 7. 
 Muscular system, use of, 4. 
 Mussel, 77. 
 
 Mysis americana (illus.), 100. 
 Myhlus edulis (illus.), 77. 
 
 Nauplius (illus.), 99. 
 Nematoda (illus.), 52. 
 Nemertean worm (illus.), 70. 
 Nereis (illus.), 59. 
 Nerve-cell (illus.), 7. 
 Nettle-cell (illus.), 30. 
 Neuroptera, 118. 
 Newt (illus.), 178. 
 Night-hawk (illus.), 222. 
 Notochord, 151. 
 Nucleus (illus.), 9. . 
 
 Octopus punctatus (illus.), 87. 
 Oligocha?tes, 59. 
 
 Operculum (operculum, a lid), 87. 
 Opossum (illus.), 231. 
 Opossum-shrimp (illus.), 100. 
 Orang-utan (illus.), 243. 
 Orb-weaving spider, 136. 
 OrnitliorhyncJius paradoxus (illus- 
 tration), 230. 
 Orthoptera, 117. 
 Ostrich (illus.), 209. 
 Oyster, 77. 
 Owls, 219. 
 
 Pagurus bernhardus (illus.), 103. 
 Paludicola?, 215. 
 Pandorina (illus.), 19. 
 Panther (illus.), 241.
 
 256 
 
 ANIMAL FORMS 
 
 Paramcecium (illus.), 15. 
 
 Parapodium (para, alongside of; 
 pom, foot), 60. 
 
 Parasitism, 48. 
 
 Passeres, 223. 
 
 Pelican (illus.), 212. 
 
 Pelicanus erythrorhynchus (illus.), 
 212. 
 
 Perca flavescens (illus.), 155. 
 
 Perch, 166. 
 
 Perching birds, 223. 
 
 Peripatus eiseni (illus.), 111. 
 
 Pheasant, 217. 
 
 Physalia (illus.), 37. 
 
 Physiology (physis, the nature of 
 a thing ; logos, a discussion), 1. 
 
 Pici, 221. 
 
 Piddock (illus.), 75. 
 
 Pigeons, 218. 
 
 Pike (illus.), 164. 
 
 Pill-bug (illus.), 105. 
 
 Pineal gland, 198. 
 
 Planaria (illus.), 45. 
 
 Plants and animals, differences be- 
 tween, 1. 
 
 Plants, characteristics of higher, 2. 
 
 Plant-lice, 122 ; in ant-nests, 129. 
 
 Plastron, 188. 
 
 Plover, killdee, 216. 
 
 Polychaetes, 59; sedentary (illus.), 
 61 ; development of, 63. 
 
 Polynoe, brevisetosa (illus.), 61. 
 
 Polyzoa (illus.), 68. 
 
 Porcellio scaber (illus.), 105. 
 
 Porcupine (illus.), 232. 
 
 Porpoise, 234. 
 
 Portuguese man-of-war (illus.), 36. 
 
 Prairie-dog, 233. 
 
 Prawn (illus.), 100. 
 
 Precocial birds, 208. 
 
 Primates, 243. 
 
 Proboscis, of flatworms, 46. 
 
 Procyon lotor (illus.), 240. 
 Protoplasm (protos, first; plasma, 
 
 anything molded), 9 ; structure 
 
 of, 10. 
 Protozoa, 11 ; characteristics of, 
 
 17; colonial, 19. 
 Pugettia richii (illus.), 104. 
 Pulsating vacuoles, 16, 17. 
 Pygopodes, 209. 
 
 Quail (illus.), 217. 
 
 Rabbit, 233. 
 
 Raccoon (illus.), 240. 
 
 Race histories and life histories, 27. 
 
 Radial symmetry, 44. 
 
 Rail, 215. 
 
 Rain-crow, 220. 
 
 Raptores, 219. 
 
 Rat, house-, 233 ; wood-, 233 ; 
 musk-, 233. 
 
 Ratita?, 209. 
 
 Rattlesnake (illus.), 191. 
 
 Recognition-marks, 203. 
 
 Regeneration, 51. 
 
 Reproduction, sexual and asexual, 
 5,32. 
 
 Reptiles, general characteristics, 
 185; distribution, 191; anat- 
 omy, 195. 
 
 Retrograde metamorphosis, 99. 
 
 Rotifer (illus.), 66. 
 
 Ruminant, 237. 
 
 Sabella, 62. 
 
 Salamander (illus.), 176; distribu- 
 tion, 178 ; structure of, 179. 
 Salmon, 163. 
 Sand-dollar (illus.), 142. 
 Sandhopper (illus.), 105. 
 Sandpiper, 216. 
 Sapsucker, 221.
 
 INDEX 
 
 257 
 
 Sarcoptes scabei (illus.), 138. 
 
 Scelophorus undulatus (illus.), 185. 
 
 Scorpion (illus.), 134. 
 
 Scyphozoa, 37 ; development of, 38. 
 
 Sea-anemone, 40. 
 
 Sea-cucumber (illus.), 143 ; regen- 
 eration of, 145. 
 
 Sea-lily (illus.), 143. 
 
 Sea-mat (illus.), '68. 
 
 Sea-urchin (illus.), 141. 
 
 Sea-squirt (illus.), 152. 
 
 Sedentary life, effect of, 62. 
 
 Segments, of worms, 55 ; of arthro- 
 pods, 94. 
 
 Segmented worms, 55. 
 
 Serpentes, 186. 
 
 Serpent-star (illus.), 141. 
 
 Serphus dilatatus (illus.), 122. 
 
 Serpula (illus.), 62. 
 
 Serpulids, 62. 
 
 Seta, 55. 
 
 Sexual reproduction, 32. 
 
 Shark (illus.), 159. 
 
 Shell-gland, 108. 
 
 Shipworm, 75. 
 
 Shrew, 234. 
 
 Shrimp, fairy, 94 ; opossum (illus.), 
 100. 
 
 Silk-moth (illus.), 127. 
 
 Silver-spot butterfly (illus.), 126. 
 
 Simple animals, characteristics of, 
 18. 
 
 Single-celled animals, 11. 
 
 Sinus, blood, 78. 
 
 Siren (illus.), 178. 
 
 Slug (illus.), 80. 
 
 Snail, common (illus.), 80; arma- 
 dillo (illus.), 82 ; naked (illus.), 82. 
 
 Snakes, 186 ; distribution of, 193. 
 
 Snipes, 216. 
 
 Somateria dresseri (illus.), 214. 
 
 Species, origin of, 91. 
 
 Sperm-cell, 20. 
 
 Sphenodon punctatus (illus.), 199. 
 
 Spicule, of sponge (illus.), 26; of 
 coral, 42. 
 
 Spiders, organization of, 135 ; hab- 
 its, 136. 
 
 Spinnerets, 135. 
 
 Spiny-rayed fishes, 166. i 
 
 Sponge, development of (illus.), 
 21; distribution, 22; shape and 
 structure, 23. 
 
 Spontaneous generation, 54. 
 
 Springtail, 117. 
 
 Squalus acanthias (illus.), 159. 
 
 Squash-bug, 122. 
 
 Squid (illus.), 87. 
 
 Squirrels, 233. 
 
 Starfish (illus.), 140 ; regeneration, 
 145 ; structure, 146. 
 
 Steganopodes, 212. 
 
 Stickleback, 164. 
 
 Structure and function, correla- 
 tion of, 6. 
 
 Strongylocentrotus purpuratus (il- 
 lustration), 144. 
 
 StrutMo camelus (illus.), 210. 
 
 Sturgeon (illus.), 161. 
 
 Sunfish (illus.), 166. 
 
 Symmetry, radial and bilateral, 44. 
 
 Swan (illus.), 213. 
 
 Swift, 222. 
 
 Tcenia solium (illus.), 51. 
 
 Tapeworm (illus.), 50; develop- 
 ment, 51 ; in relation to regen- 
 eration, 51. 
 
 Tarantula (illus.), 137. 
 
 Teeth, use of, 2. 
 
 Teleostei, 160. 
 
 Termites (illus.), 120. 
 
 Tern, 211. 
 
 Terrapene Carolina (illus.), 189,
 
 258 
 
 ANIMAL FORMS 
 
 Thousand-legged worms (illus.), 
 111. 
 
 Threadworms (illus.), 52. 
 
 Thysanura, 117. 
 
 Tick, 138. 
 
 Tiger salamander, 178. 
 
 Toad (illus.), 178. 
 
 Trap-door spider (illus.), 137. 
 
 Trematode (illus.), 48 ; develop- 
 ment, 51. 
 
 Trichina spiralis (illus.), 53. 
 
 Trigger hair, 31. 
 
 Turkey, 218. 
 
 Turtles, 188; structure, 189; dis- 
 tribution. 194. 
 
 Typhlichthys subterraneus (illus.), 
 163. 
 
 Ungulata, 237. 
 
 Vacuole, pulsating, 16 ; use of, 17. 
 Velum (illus.), 35. 
 Vespa, nest of (illus.), 131. 
 Vinegar eel (illus.), 53. 
 Volvox (illus.), 19 ; multiplication 
 
 of, 20. 
 Vertebrates, characteristics of, 145 . 
 
 classification, 143. 
 
 Vorticella (illus.), 16. 
 
 Vulpes pennsylvanicus (illus.), 241. 
 
 Wasps, 128 ; habits of, 131. 
 Water-boatman, 121. 
 Water-bug (illus.), 121. 
 Water-dog (illus.), 178. 
 Water-flea, 95. 
 Whale, humpback (illus.), 235; 
 
 sperm, 236. 
 Whale lice, 107. 
 Wheel-animalcule (illus.), 66. 
 Wheel-weaving spiders, 136. 
 Whippoorwill, 222. 
 White ant (illus.), 120. 
 Wood-beetle (illus.), 124. 
 Woodchuck, 233. 
 Woodcock, 216. 
 Woodpeckers, 221. 
 Worms, general characters of, 44 ; 
 
 classification, 45. 
 
 Yellowhammer, 221. 
 Yellow-jacket, 132. 
 
 Zirphcea crispata (illus.), 76. 
 Zoology, 1. 
 Zoophyte, 29. 
 
 (1) 
 
 THE END
 
 IS'B 
 
 Form L-9-10w-5,'28
 
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