-NRLF 
 

 
 BIOLOGY 
 
 UBRARV 
 

ANIMALS FOUND LIVING TOGETHER IN SHALLOW INLETS FROM 
 THE SEA, LONG ISLAND SOUND 
 
A TEXT-BOOK 
 
 IN 
 
 GENERAL ZOOLOGY 
 
 BY 
 
 HENRY R. LINVILLE, PH.D. 
 
 HEAD OF THE DEPARTMENT OF BIOLOGY, DE WITT CLINTON 
 HIGH SCHOOL, NEW YORK CITY 
 
 HENRY A. KELLY, Pn.D. 
 
 DIRECTOR OF THE DEPARTMENT OF BIOLOGY AND NATURE STUDY 
 ETHICAL CULTURE SCHOOL, NEW YORK CITY 
 
 Two Hundred Thirty-Three Illustrations 
 
 GINN & COMPANY 
 
 BOSTON NEW YORK CHICAGO LONDON 
 
BIOLOGY 
 
 LIBRARY 
 
 G 
 
 ENTERED AT STATIONERS' HA LI. 
 
 COPYRIGHT, 1906 
 BY HENRY K. LINYILLE AND HENRY A. KELLY 
 
 ALL RIGHTS RESERVED 
 06.5 
 
 GINN & COMPANY PRO- 
 PRIETORS BOSTON U.S.A. 
 

 PREFACE 
 
 In offering to the educational public this text-book in general 
 zoology, with its accompanying suggestions for laboratory work, 
 we desire to explain in brief the method of construction we have 
 followed. 
 
 The treatment of the phyla is in a descending order from the 
 Arthropoda to the Protozoa, and in an ascending order from the 
 fishes to man. After many years of experience with classes of 
 young students we believe that an order of treatment resembling 
 this is likely to yield the best results, although we do not deny 
 that good results may be obtained with young students by follow- 
 ing what is sometimes called the " order of evolution," beginning 
 with the Protozoa. Although the chapters are interdependent, 
 we think that there is sufficient unity in each to make it possible 
 for the teacher to diverge from the order we have employed. 
 
 Whatever the order followed, it is evident that recitation on 
 the chapters in the text-book should be held only after the pupil 
 lias made his study in the laboratory, for the text-book in science 
 has its greatest usefulness in connecting, extending, and illumi- 
 nating the work of the laboratory. Laboratory work brings the 
 pupil in touch with actual things, and if the studies are properly 
 conducted, they will aid in developing in the mind the power of 
 independent judgment. But the young and untrained student 
 cannot build up a conception of the science of zoology from the 
 more or less isolated data of the laboratory ; in this fact lies the 
 justification of a text-book in zoology. 
 
 The function of the suggestions for laboratory work is to help 
 the pupil to make the be*st use of his time, and to direct him in 
 such a way that he will become more and more independent, 
 and be able to study intelligently without detailed directions. 
 It seems to us that the kind of directions given to pupils will 
 
 iii 
 
 152365 
 
iv PREFACE 
 
 depend not only on the teacher's training in zoology and his 
 pedagogical skill, but also 011 the age and previous training of 
 the pupils. The problem is a special one for each teacher to 
 solve for himself. The directions given in the accompanying 
 pamphlet, therefore, are to be regarded merely as suggestive. 
 
 The inductive method of presentation, in a necessarily modified 
 form, has been followed in the earlier chapters of the text-book, 
 as being the natural mode of approach to a new subject based 
 upon laboratory work. After the study of the red-legged locust, 
 for example, another animal that has easily recognizable rela- 
 tionship to this form is considered. Not until all the selected 
 representatives of the Orthoptera have been described, are the 
 characters of the order mentioned. By that time the pupil's 
 mind is ready for the definition of Orthoptera. The conceptions 
 of the larger groups of invertebrate classes and phyla are devel- 
 oped in the same manner. 
 
 It has been our earnest endeavor to present all the important 
 aspects of zoology in a well-balanced account. The basis of the 
 subject-matter in a text-book on zoology is necessarily morpho- 
 logical. The pupil must have some understanding of the appear- 
 ance of animals and their organs before he can be supposed to 
 think clearly regarding the uses of the organs or the relation of 
 the animals to their environment. We have described the appear- 
 ance of nearly all the animals mentioned. In certain selected 
 cases we have described the structure and the functions of the 
 systems of internal organs, and the development of the individ- 
 ual ; and in appropriate connections we have spoken of the 
 economic importance of animals, and have given brief sketches 
 of the geographical distribution and the geological history of 
 races. The rapidly developing science of comparative psychology 
 is now sufficiently precise to justify the inclusion in a work of 
 this kind of some of the important studies of the mental behavior 
 of animals. We hope that the facts selected will give a general 
 notion of the increasing complexity of the mental life in the 
 higher animals. We have also presented in as simple a way 
 
PREFACE v 
 
 as possible the doctrine of evolution. Finally, the last chapter 
 deals with the historical development of the science of zoology. 
 It should aid in giving the pupil the necessary perspective for 
 appreciating the processes by which this organized body of 
 knowledge came into existence. 
 
 The principles of physiology are reserved for full explanation 
 in the study of the earthworm in Chapter XVI. We desire here 
 to express our deep obligation for the inspiration and example 
 of a similar study presented in General Biology by Professors 
 W. T. Sedgwick and E. B. Wilson. We are indebted to them 
 and their publishers for several figures illustrating the develop- 
 ment of the earthworm. Our purpose in delaying the scientific 
 treatment of the principles of physiology, instead of discuss- 
 ing them in the first chapters, is a double one. In the first 
 place, too much abstraction at the beginning of an exposition 
 is likely to prove discouraging to even a willing student ; in the 
 second place, the conception of physiological processes, it seems 
 reasonable to believe, can be formed best after the learner has 
 some knowledge of systems of organs, including, of course, 
 an elementary knowledge of their uses. It then matters little 
 whether the student learns the more detailed facts of physiology 
 from the earthworm or from some other animal, and it even 
 matters little whether or not he actually sees all the organs in 
 the animal where the processes are described as taking place. 
 
 We believe that the attention given in this book to the subject 
 of animal ecology will prove to be justified. Although the eco- 
 logical sections are set off from the other topics, it should not 
 be forgotten that ecology, or the relation of organisms to their 
 environment, has significance only when the subject is considered 
 from the standpoint of the adjustment or the adaptation in the 
 form of the parts of organisms to the life they carry on. 
 
 We have been to considerable pains to produce original figures 
 that should be comprehensive as well as accurate, and, where the 
 subject permitted, artistic. In this we have been assisted by 
 three gentlemen whose ability is e'vident in their work: Mr. S. F. 
 
vi PREFACE 
 
 Denton, of Wellesley, Mass., Mr. L. H. Joutel, of New York City ; 
 and Mr. E. N. Fischer, of Jamaica Plain, Mass. Mr. Denton 
 made the drawings of the vertebrate dissections and the external 
 view of the lizard and Oniscus. Mr. Joutel made the drawings 
 of the insects and all the invertebrate dissections. Mr. Fischer 
 executed the drawings of all the marine invertebrates shown 
 in their natural environment, and also the ecological studies 
 of the pond-snail, the garden-slug, the garden-spider, the leech, 
 the fresh-water mussel, and the fresh-water sponge, besides 
 copying many figures from publications. Mr. Win. T. Oliver, of 
 Lynn, Mass., made the numerals and the leader-lines for all the 
 drawings. 
 
 We desire to acknowledge the kindness of Professor H. C. 
 Bumpus, Director of the American Museum of Natural History, 
 arid of Professor H. F. Osborn, Curator of Vertebrate Paleontol- 
 ogy, American Museum, in permitting us to make selections from 
 numerous photographs. Mr. C. William Beebe, of the Xew York 
 Zoological Park, supplied us with photographs of many verte- 
 brates and some marine invertebrates. Several photographs in 
 different chapters are from, the authors' own collections. To 
 the following publishers we acknowledge the privilege of using 
 figures: American Book Company; D. Appleton & Co.; G-. W. 
 Crane & Co. ; Doubleday, Page & Co. ; Henry Holt & Co. ; McClure, 
 Phillips & Co. 
 
 It is our hope that the quotations which introduce the chap- 
 ters will serve to suggest to the imagination of young students 
 the poetic side of animal life and of nature generally. For some 
 of the best quotations we are indebted to the search made by 
 personal friends. 
 
 We are especially grateful to several zoologists who have read 
 various portions of the manuscript critically : Professors G. H. 
 Parker and W. E. Castle, of Harvard University ; Professor J. H. 
 Comstock, of Cornell University; Professor H. 8. Jennings, of the 
 University of Pennsylvania ; Professor M. A. Bigelow, of Teachers 
 College, Columbia University ; Dr. J. A. Allen, Mr. Frank M. 
 
PREFACE vii 
 
 Chapman, and Professor R. W. Tower, of the American Museum 
 of Natural History ; and Dr. F. B. Sumner, of the College of the 
 City of New York. For suggestions in regard to some of the 
 more important drawings we extend our thanks to Professors 
 E. L. Mark, G. H. Parker, W. E. Castle, Dr. H. W. Rand, and 
 Dr. W. McM. Woodworth, of Harvard University ; to Professor 
 J. S. Kingsley, of Tufts College ; and to Professor C. W. Hargitt, 
 of Syracuse University. 
 
 Certain little-known species have been identified for us in the 
 tunicates, leeches, holothurians, crustaceans, gasteropods, and 
 sponges, respectively, by the following : Professor W. E. Ritter, 
 of the University of California ; Professor J. Percy Moore, of 
 the University of Pennsylvania ; Professor H. L. Clark, of Olivet 
 College ; Dr. Walter Faxon, of the Museum of Comparative 
 Zoology, Cambridge, Mass. ; Dr. L. P. Gratacap, of the American 
 Museum of Natural History ; Professor H.V.Wilson, of the Uni- 
 versity of North Carolina ; and Mr. Edward Potts, of Philadelphia. 
 
 To Mr. D. C. MacLaren, of the DeWitt Clinton High School, 
 we are very much indebted for transposing into equivalent Eng- 
 lish letters the roots of the Greek derivatives. 
 
 THE AUTHORS 
 
CONTENTS 
 
 CHAPTER PAGE 
 
 I. THE COMMON RED-LEGGED LOCUST 1 
 
 II. THE ALLIES OK THE RED-LEGGED LOCUST: ORTHOPTERA 15 
 
 III. THE MAY-FLIES (PLECTOPTERA) AND THE DRAGON- 
 
 FLIES (Ol)ONATA) 25 
 
 IV. THE BUGS: HEMIPTERA 30 
 
 V. THE BEETLES: COLEOPTEKA 37 
 
 VI. THE BUTTERFLIES AND MOTHS: LEPIDOPTERA ... 4(5 
 
 VII. THE FLIES: DIPTEHA 58 
 
 VIII. THE ANTS, BEES, AND WASPS : HYMENOPTERA . . . 05 
 
 IX. THE INSECTS: HEXAPODA 81 
 
 X. THE DOCTRINE OK EVOLUTION 101 
 
 XL THE SPIDERS AND ALLIES (ARACIINIDA) AND THE CEN- 
 
 TIPEDS AND MlLLEPEDS (MYRIAPODA) . . . .110 
 
 XII. THE CRAYFISH 125 
 
 XIII. THE JOINTED-FOOT ANIMALS: ARTHROPODA . .v . . 138 
 
 XIV. THE CLAM AND OTHER BIVALVES: PELECYPODA . . 157 
 XV. ALLIES OF THE PELECYPODA: MOLLUSCA . . . ". . 177 
 
 XVI. THE EARTHWORM 195 
 
 XVII. ALLIES OF THE EARTHWORM: VERMES 222 
 
 XVIII. THE STARFISH AND SOME ALLIES : ECHINODERMA .x f 230 
 XIX. THE SEA-ANEMONE AND SOME ALLIES: CCELENTERA . 252- 
 XX. THE FRESH-WATER SPONGE AND SOME ALLIES: 
 
 PORIKERA .* .... 273 
 
 XXI. AMCEBA AND SOME ALLIES: PROTOZOA 280 
 
 XXII. THE EVOLUTION OF INVERTEBRATES AND THE ANCESTRY 
 
 OF THE VERTEBRATES ....." 292 
 
 XXIII. THE YELLOW PERCH 305 
 
 ix 
 
x CONTENTS 
 
 CHAPTER PAGE 
 
 XXIV. THE ALLIES OE THE PERCH: PISCES 310 
 
 XXV. THE GREEN FROG 327 
 
 XXVI. THE ALLIES OE THE FROG : AMPHIIJIA 339 
 
 XXVII. THE PINE-LIZARD AND ITS ALLIES: REPTILIA . . 348 
 
 XXVIII. THE DOMESTIC PIGEON 304 
 
 XXIX. THE ALLIES OF THE PIGEON: AYES 374 
 
 XXX. THE GRAY SQUIRHEI 398 
 
 XXXI. THE ALLIES OF THE SQUIRREL: MAMMALIA . . . 408 
 
 XXXII. THE HISTORICAL DEVELOPMENT OF ZOOLOGY . . . 430 
 
 INDEX . 4f)3 
 
GENERAL ZOOLOGY 
 
 CHAPTER I 
 THE COMMON RED-LEGGED LOCUST 
 
 Though I watch their rustling flight, 
 
 I can never guess aright 
 
 Where their lodging-places are ; 
 
 'Mid some daisy's golden star, 
 
 Or beneath a roofing leaf, 
 
 Or in fringes of a sheaf, 
 
 Tenanted as soon as bound. EDITH M. THOMAS. 
 
 Habitat and Distribution. Locusts are found almost every- 
 where in the United States, usually in fields, meadows, and 
 along roadsides. They are often spoken of as grasshoppers, 
 but, as we shall see later, they differ from the true grass- 
 hoppers in several important particulars. The species (see 
 p. 95) which heads this chapter is one of the most widely 
 distributed of the insects to which the name locust is cor- 
 rectly applied. It is known to naturalists as Melan'oplus l 
 fe'mur-ru'brum. Its habitat (the locality where it is naturally 
 found) comprises grassy areas in almost every state except 
 on the high western plains, where its place is taken by a 
 species much resembling it, the Rocky Mountain locust 
 (Melanoplus spre'tus). Another species, the lesser locust 
 (Melanoplus atlan'is), somewhat smaller and darker in color, 
 is also found in nearly every part of the country. These, 
 and several other locusts, are about three centimeters (a little 
 
 1 The first time a scientific name is used, a mark is placed after the 
 accented syllable as an aid in pronunciation. 
 
 1 
 
...........GENERAL ZOOLOGY 
 
 over an inch) in length, and resemble each other so closely 
 that the following description will apply nearly as well to 
 one as to another. 
 
 External Plan of Structure. The body is made up of a 
 series of rings, called somites (Fig. 2), externally hardened by 
 a horny substance, chitin, for protection of the interior organs. 
 The somites are grouped in three clearly marked regions, 
 the head, thorax, and abdomen (Fig. 2, 1, 2-4, 5). While the 
 characteristic appearance of a ring is clearer in the abdo- 
 men than elsewhere, it is nevertheless true that the head and 
 thorax are made up of several somites, much altered and 
 pressed together. The head probably consists of at least five 
 somites, of which four bear appendages, the feelers, or anten- 
 na? (Fig. 2, 0); the jaws, or mandibles (Fig. 1, 2; Fig. 2, 8); 
 the first maxilla? (Fig. 1, 4) ; and the second maxilla* (Fig. 1, 5). 
 The thorax plainly consists of three somites, on each of which 
 is borne a pair of legs (Fig. 2, 14, 15, 10). Ten somites can with- 
 out much difficulty be distinguished in the abdomen (Fig. 2, 5). 
 The external plan upon which the locust is built is thus seen 
 to be a series of somites, of which the anterior (front) somites 
 bear jointed appendages modified for various uses. 
 
 The Head. The short, several-jointed antennas are organs 
 of touch and of smell, and, in most insects, of hearing as well. 
 The maxillas are constructed on the plan of jaws, though 
 fitted for guiding and holding food rather than for crush- 
 ing it. Each maxilla bears a short, several-jointed " feeler," 
 or palpus (Fig. 1, 4, 5 ; Fig. 2, 9, 11). The anterior boundary of 
 the mouth is a flap-like piece, the upper lip, or labrum (Fig. 1, 1; 
 Fig. 2, 7) ; and the posterior (hind) boundary is made by the 
 union of the bases of the second maxilla (Fig. 1, 5), forming 
 a flap called the lower lip, or labium (Fig. 2, 10). 
 
 On the sides of the head are large, oval, compound eyes 
 (Fig. 2, 12), composed externally of a number of transparent 
 divisions, facets, each of which has beneath it the necessary 
 
THE COMMON RED-LEGGED LOCUST 
 
 structures for sight, so that the whole may be regarded as 
 a mosaic of single eyes. In addition, there are simple eyes, or 
 ocelli (Fig. 2, 13), placed 
 in the form of a triangle 
 on the front of the head. 
 Notwithstanding these 
 two kinds of eyes, it is 
 doubtful whether the 
 locust is able to per- 
 ceive well the outlines 
 of objects, or to dis- 
 tinguish much except 
 light and movement. 
 The ocelli probably do 
 not perceive objects at 
 a greater distance than 
 a few inches, nor the 
 compound eyes at a 
 greater distance than a 
 few feet. It has been 
 surmised from the 
 structure of the com- 
 pound eyes that each facet perceives only a 
 field of vision. 
 
 The Thorax. The first somite of the thorax, called the pro- 
 thorax (Fig. 2, 2), bears the first pair of legs. It is free from 
 the rest of the thorax. The dorsal surface (Latin, dorsum, 
 back) is thickened and raised into a ridge ; the sides (lateral 
 surfaces) are also thickened, and the whole forms a protective 
 shield or collar. The second somite, the mesothorax (Fig. 2, 3), 
 bears the second pair of legs ; to the third, or metathorax 
 (Fig. 2, 4), the last pair of legs is attached. Each leg is com- 
 posed of a number of divisions, or segments, of which the 
 principal are the thick femur (Fig. 2, 14, 15, 16 ; Fig. 3, 5) 
 
 FIG. 1. Mouth-Parts of Red-Legged Locust, 
 x 4 
 
 1, labrum; 2, mandible; 3, hypopharynx ; 4, first 
 maxilla with its palpus; 5, second maxillre 
 with palpi 
 
 jmall part of the 
 
4 GENERAL ZOOLOGY 
 
 and the spiny tibia (Fig. 3, o). Each leg ends in a series of 
 three segments, forming the tarsus (Fig. 3, 7), the last segment 
 of which bears two claws (Fig. 3, 8), with a pad, the pulvillus 
 (Fig. 3, 9), between them. 
 
 Of the two pairs of wings (Fig. 2, 17, 18), the first is attached 
 to the surface of the mesothorax, the second to the m eta- 
 thorax. The anterior pair is somewhat hardened, forming 
 protective covers for the more delicate posterior wings, which 
 are folded like a fan beneath them. The latter only are used 
 in flight. The wings are simple extensions of the body-wall, 
 and not jointed appendages like the legs. On the sides, just 
 beneath the posterior edge of the collar on the prothorax, is 
 a pair of breathing openings, or spiracles (not shown in the 
 figure). Two spiracles are placed just above the junction of 
 the second pair of legs (Fig. 2, 20), and the abdomen bears 
 eight pairs along the sides (Fig. 2, 21, 22). 
 
 The Abdomen. The first abdominal somite is much larger 
 
 o 
 
 than the others, though it does not form a complete ring, 
 owing to the space occupied by the cavities for the insertion 
 of the hind legs. Each side of this somite bears an oval spot 
 consisting of a thin skin stretched across a small cavity and 
 connected with a nerve, the whole forming an ear, or auditory 
 apparatus (Fig. 2, 19). The end of the abdomen in the female 
 is more tapering than in the male, and is furnished with two 
 pairs of blunt spines, which form an egg-laying instrument, or 
 ovipositor (Fig. 3, 36, 37). 
 
 The Digestive System. After this brief review of the main 
 features of the external anatomy of the locust, we turn our 
 attention to the organs of the interior. And first, owing to 
 its size and the ease with which its parts may be examined, 
 we may consider the digestive system. The function of the 
 digestive system of an animal is to prepare the food for use 
 by the different organs of the body. In the locust the organs 
 of digestion are the food-tube, or alimentary canal, and its 
 
6 GENERAL ZOOLOGY 
 
 accessory organs, the salivary glands (Fig. 3, 14) and gastric 
 cceca (gastric, pertaining to the stomach ; caeca, pi. of caecum, 
 a pouch or cavity open only at one end, Fig. 3, 1-5, 10). 
 
 The alimentary canal is a long tube extending through the 
 body and variously modified in the course of its extent. The 
 first division is the mouth, guarded on each side by the later- 
 ally moving mandibles. Between the mandibles, and arising 
 from the inner side of the labium, is a short brown, tongue- 
 like organ, the liypopharynx (Fig. 3, 12 ; Fig. 1, 3). At the base 
 of the hypopharynx opens the tube from the several pairs of 
 salivary glands. A portion of the slightly convex surface of 
 the inner side of the labrum is the epipharynx, the seat of the 
 sense of taste. 
 
 Beyond the mouth the alimentary canal continues as a short 
 curved oesophagus (Fig. 3, 13), which leads to a large crop, 
 armed with rows of spine-like teeth. Posterior to the crop 
 is a very small gizzard, also furnished with spines, opening 
 directly into a large, thin-walled stomach (Fig. 3, 17). At the 
 anterior end of the stomach are attached the six tubular 
 gastric cseca, closed at one end but opening into the stomach 
 at the other. Beyond the stomach the alimentary canal con- 
 tinues as a slightly coiled tube, the intestine (Fig. 3, 19), and 
 ends dorsally at the anal opening (Fig. 3, 20). 
 
 The functions of these different parts are as follows, The 
 food, after being crushed by the mandibles and moistened by 
 the saliva, enters the crop, where it is subjected to the action 
 not only of the saliva but also of a fluid from the gastric ceeca. 
 The " molasses " thrown out from the mouth as a defensive 
 fluid by the locust, when handled, consists of partially digested 
 food from the crop, mixed with the digestive fluids. When 
 sufficiently dissolved and changed chemica%, the food filters 
 through the spines of the gizzard into the stomach, where it 
 is further acted upon by another digestive fluid. The thin 
 walls of the stomach allow the particles of prepared food to 
 
THE COMMON KED-LEGGED LOCUST 7 
 
 pass through and mingle with the blood in the general body- 
 cavity. This process is called absorption. The anterior part 
 of the intestine is thin-walled, and absorption may take place 
 there and also in the caeca. The unused food-material is 
 removed from the body by means of the anal opening. 
 
 The Circulatory System. When the food has been acted 
 upon by the various digestive fluids, and so changed that it 
 may be used to supply the different organs with nourishment, 
 it is distributed over the body by the circulatory system. At 
 the same time certain waste matters are taken away and carried 
 to organs the function of which is to remove them from the 
 body. In the case of man and many other animals, the circu- 
 latory system is also the means by which oxygen is carried to 
 all the organs ; but, as we shall see in a moment, this work is 
 otherwise provided for in the locust. As soon as the prepared 
 food has been absorbed by the walls of the stomach and intes- 
 tine it mingles with the blood, which flows through the body- 
 cavity in sinuses (spaces between the various organs), though 
 not in definite blood-vessels. The blood is propelled by a 
 tubular, pulsating vessel, or heart (Fig. 3, 21), which extends 
 through the abdomen just beneath the dorsal surface. On 
 account of its position in the body it is often spoken of as 
 the dorsal vessel. The heart is prolonged anteriorly into a 
 tube leading to the head, and is partially divided by valves 
 into eight chambers, which permit the movement of the blood 
 only from the posterior to the anterior end. When the blood 
 has been passed out into the general body-cavity it returns 
 through a closed tube (ventral sinus) between the muscle 
 masses lying in the lower (ventral) part of the body, and 
 reenters the heart through side openings. 
 
 The Respiratory System. The function of the respiratory 
 system is to provide for a constant supply of oxygen for all 
 the organs of the body. This is accomplished by a system of 
 tubes, called tracheae, communicating with the surface by the 
 
8 GENERAL ZOOLOGY 
 
 spiracles of the thorax and abdomen. The trachese are con- 
 nected and form a network of tubes running to all parts of 
 the body, even out into the legs and wings. They are also 
 in connection with a system of large air-sacs (Fig. 3, 22, 23) 
 extending through the body. The tracheae are kept perma- 
 nently open by a spiral thickening of their chitinous lining, 
 so that air may enter freely at all times. The completeness 
 of the respiratory system in the locust is in striking contrast 
 to the undeveloped character of the circulatory system. 
 
 The Excretory System. The union of the oxygen taken in 
 during respiration with the carbon in the body produces car- 
 bon dioxide, a waste product. This leads us to consider the 
 organs which assist in the removal of materials which have 
 helped to build up the body-substance and have become so 
 changed chemically that they are no longer useful. Such 
 organs are termed organs of excretion. Besides carbon diox- 
 ide, important excretory products are water and various sub- 
 stances containing nitrogen, hence called nitrogenous wastes. 
 The two latter classes correspond to the material removed by 
 the kidneys of the higher animals. 
 
 Very little is known of the process of excretion in insects. 
 It has been generally believed that the carbon dioxide finds 
 its way to the surface through the trachese. In some cases it 
 probably escapes through the skin. Water and the nitroge- 
 nous wastes are removed by malpigJiian tubes (Fig. 3, 18), 
 which form so prominent an object when the body of the 
 locust is first opened. They ramify through the body-cavity 
 and open into the alimentary canal at the junction of the 
 stomach and intestine, their contents passing to the outside 
 with the undigested food in the intestine. This undigested 
 food is not an excretion, using the word in the sense defined 
 above, since it has never formed a part of the body-substance. 
 It has been suggested that as the chitinous covering of in- 
 sects is largely made up of carbon and nitrogen, the frequent 
 
10 GENEBAL ZOOLOGY 
 
 casting of the skin (molting) may be an act of excretion of 
 considerable importance. 
 
 The Nervous System. All the processes just described, 
 even the flow of blood and the secretion (formation) of the 
 digestive fluids, are under the control of the nervous system. 
 Through its organs of sense the locust is brought into touch 
 with the outside world ; by its control over the muscles, move- 
 ments are made. The nervous system of the locust consists 
 of a series of connected nerve centers, called ganglia (Fig. 3, 
 24, 28, 29), from which nerves are given off to the different 
 parts of the body. There are two kinds of nerves, sensory and 
 motor; the former carry messages from the various sense- 
 organs to the ganglia ; the latter carry impulses from the 
 ganglia, which result in the contraction of muscles and move- 
 ments of the various organs, or of the body as a whole. 
 
 The largest ganglion is in the head, and is generally called 
 the " brain," or, because of its position just above the oesoph- 
 agus, the supraoesophageal ganglion (Fig. 3, 24). From this 
 ganglion pass the nerves which go to the eyes, antennae, 
 and labrum. Two cords encircling the oesophagus pass to the 
 next ganglion, which, owing to its position just beneath the 
 oesophagus, is called the suboesopliageal ganglion (Fig. 3, 28). 
 This ganglion sends nerves to the mandibles and maxillse. 
 Both the supraoesophageal and the suboesophageal ganglia 
 are the seat of will in the locust, and preside over and 
 coordinate the various general movements of the locust's body. 
 It has been shown that an insect may live for months with 
 the anterior of these ganglia destroyed, if the other is not 
 injured. The insect will feed if food is placed to its mouth, 
 but it loses the power to go in search of food. Of the other 
 ganglia three are in the thorax and five are in the abdomen, 
 forming a median chain resting on the ventral surface of the 
 body-cavity. These ganglia are centers for movements and 
 respiration in the somites to which they belong. 
 
THE COMMON RED-LEGGED LOCUST 
 
 11 
 
 The Muscular System. All the muscles of the body are 
 supplied with microscopic nerves. The muscles are attached 
 to the hard covering of the body, and when stimulated by 
 the nervous system they contract, thus moving the part to 
 which they are attached. Though delicate in appearance the 
 muscles are in reality very strong, as may be understood 
 when the activity of the insect is considered. 
 
 The Reproductive System. As in most other animals, the 
 union of two dissimilar elements is necessary for the produc- 
 tion of a new locust. These elements are the very small, 
 active sperm-cells produced by the male, and the larger, pas- 
 sive egg-cell produced by the female. On the union of these 
 two cells the egg-cell is said to be fertilized and the growth 
 of a new individual is begun. Occupying a considerable part 
 of the posterior portion of the abdomen of the female are the 
 ovaries (Fig. 3, 30, 31), two sets of delicate tubular organs in 
 which the egg-cells are developed. These are connected with 
 the surface by the egg-tube, or oviduct (Fig. 3, 32). In the 
 male the sperm-cells are secreted in glands called spermaries, 
 
 FIG. 4. Rocky Mountain Locust Laying Eggs. About natural size. 
 (After Riley) 
 
 A, B, female laying eggs ; C, diagram showing the arrangement of eggs in the hole ; 
 JJ, mass of eggs removed from hole and part of covering taken away ; E, few 
 eggs separated 
 
12 
 
 GENERAL ZOOLOGY 
 
 FIG. 5. Development of Locust 
 
 A, P>, C, D, E, F, stages from nymph to adult, 
 enlarged: A X 6, B x 2, the others slightly 
 enlarged 
 (From Packard's Text-Book of Entomology') 
 
 which form a tubular mass in the 
 third, fourth, and fifth abdominal 
 somites. After fertilization the 
 eggs are covered on the way down 
 the egg-tube by a sticky substance 
 poured out from the cement or 
 colleterial gland (Fig. 3, 33). This 
 gland opens into a capacious 
 pouch (bursa copulatrix, Fig. 3, 34), 
 which rests on and opens directly 
 into the oviduct. 
 
 Development. The eggs of the 
 red-legged locust are laid in the 
 autumn in holes made by the 
 ovipositor of the female, in 
 the ground of fields, pastures, 
 and waysides. They differ in 
 no important respect from the 
 eggs of the Rocky Mountain 
 locust shown in Fig. 4. Each 
 hole contains from twenty to 
 thirty-five eggs. A secretion 
 from the gland already men- 
 tioned binds all the eggs in a 
 single hole into one 
 mass, and when the 
 number is completed 
 more fluid is poured 
 out, which hardens into 
 a firm covering. Here 
 they remain over the 
 winter and hatch out 
 into young locusts in 
 the spring, quite closely 
 
THE COMMON RED-LEGGED LOCUST 
 
 13 
 
 resembling the adult 
 except in absolute 
 and relative size of 
 parts and in the ab- 
 sence of wings. They 
 grow rapidly, molting 
 several times during 
 the summer, appear- 
 ing each time a little 
 larger and with more 
 fully developed wings. 
 While these changes 
 are going on the young 
 locust is called a 
 nympli (Fig. 5, AE). 
 When ready for the 
 last molt, which takes 
 place late in the 
 summer, the nymph 
 climbs up some grass 
 stem or similar ob- 
 ject, and, taking firm 
 hold, often with its 
 head pointing down- 
 ward, remains mo- 
 tionless for several 
 hours, till the skin 
 swells over the head 
 and thorax and finally 
 splits open along a 
 median dorsal line. 
 From this old skin 
 the new head, tho- 
 rax, legs, wings, and 
 
 FIG. 6. The Molting of Locust. Slightly 
 
 enlarged. (After Riley) 
 
 A, 13, C, D, E, successive stages in the process 
 of molting 
 
14 GENERAL ZOOLOGY 
 
 abdomen are slowly withdrawn while soft, expanding and 
 hardening within half or three quarters of an hour (Fig. 6). 
 It is now a perfect insect, or imago, of full size and with fully 
 developed wings. After the females have laid their eggs in 
 the fall most of the locusts die. 
 
 Relation to Environment. Red-legged locusts are found in 
 meadows, pastures, fields, and along roadsides, though most 
 abundant where the vegetation is succulent. Specimens from 
 low, damp ground are usually somewhat darker in color than 
 those from high, dry areas. Their food consists of the leaves 
 of grasses and other vegetation. The strength of the man- 
 dibles and the complexity of the digestive system fit them 
 admirably for a life of constant forage. Their color is, to a 
 certain extent, protective, for they are not easily seen among 
 the dried grasses of the summer. 
 
 Locusts have, when adult, a choice of three methods of 
 progression, walking, jumping, and flying. The many spines 
 pointing downward on the legs and the pulvilli between the 
 tarsal claws make climbing an easy matter. The complicated 
 system of air-sacs tends to reduce the weight of the body in 
 flight. By means of the air-sacs and wings the locust has 
 solved the problem of aerial locomotion. 
 
 The list of the locust's enemies is long and formidable, 
 even if man is not considered. Small animals, such as moles 
 and birds, especially the crow and blackbird, feed on the 
 eggs and young. Some species of wasps use the nymphs to 
 provision their nests, first stinging them to render them help- 
 less. They are also subject to a disease caused by a fungous 
 growth, and may often be found firmly attached to some grass- 
 blade to which they have clung before death. That they have 
 been able to maintain themselves in such large numbers in 
 spite of all their enemies marks them as successful competitors 
 in the struggle for existence. 
 
CHAPTER II 
 
 '^--:-r 
 
 THE ALLIES OF THE RED-LEGGED LOCUST : ORTHOPTERA 
 
 The poetry of nature is never dead : 
 
 When all the birds are faint with the hot sun, 
 
 And hide in cooling trees, a voice will run 
 
 From hedge to hedge about the new-mown mead : 
 
 That is the grasshopper's, he takes the lead 
 
 In summer luxury, he has never done 
 
 With his delights. KEATS. 
 
 Locusts. Though the common red-legged locust is widely 
 distributed throughout the United States, it has not attracted 
 so much attention as the Rocky Mountain locust, for its 
 effects on agriculture have not been so marked. The latter 
 has the remarkable habit of migrating from its habitat (see 
 map, p. 17) on the dry plains east of the Rocky Mountains, 
 destroying in a few hours the labors of the farmer for several 
 months. Not only are growing crops devoured, but every 
 green thing is attacked, leaving the country as bare as if a 
 fire had swept over it. It has been said that 'these swarms 
 occur at intervals of about eleven years. The locusts show a 
 tendency to become gregarious (having the habit of associat- 
 ing in groups) from the beginning of their life as nymphs, 
 but their migrations are not generally begun before they are 
 at least half grown. These hordes proved so destructive to 
 the agricultural district of the Middle West from 1873 to 
 1877 that a commission was appointed by the government 
 to study their habits and to report upon ways and means for 
 checking their devastations. Of late years this species has 
 not been so abundant or so destructive. Many machines have 
 been constructed to capture them. A recent method of fight- 
 ing them is to cultivate in a sweet solution a fungous growth 
 
 15 
 
16 GENERAL ZOOLOGY 
 
 which destroys them. Members of the swarm are then cap- 
 tured, dipped in the solution, and turned loose, thus spreading 
 the disease. The lesser locust has at various times caused con- 
 siderable damage to growing crops by appearing at different 
 points in the New England states. 
 
 There are several species of migratory locusts in the Old 
 World whose visitations in the past have been most destruc- 
 tive, especially in Egypt, Palestine, Syria, Asia Minor, China, 
 France, Russia, and Germany. They have appeared in almost 
 incredible numbers in certain years, so that a swarm has been 
 estimated to cover two thousand square miles of territory. 
 The prophet Joel has described the onslaught of locusts in 
 the lines beginning, 
 
 A day of darkness and of gloominess, a day of clouds and of thick dark- 
 ness, as the morning spread upon the mountains : a great people and a 
 strong; there hath not been ever the like, neither shall be any more after 
 it, even to the years of many generations. JOEL ir : 2. 
 
 It is easy to appreciate the fact that in thickly settled areas 
 famine and pestilence may follow the visitation of these in- 
 sects. Out of the twelve hundred or fifteen hundred species 
 of locusts in the world, only about twelve have the habit of 
 migration to any great extent, and these are mostly species 
 which live on large, elevated, open tracts of desert or semi- 
 desert character, where the climate is dry and hot, for ex- 
 ample, such regions as the steppes about the Caspian Sea. 
 Perhaps the determining factor in the migration is exces- 
 sive multiplication and the consequent need for new feeding- 
 ground. 
 
 Many locusts produce sounds by rubbing the inner edge 
 of the posterior femur against the outer edge of the first pair 
 of wings. It is supposed that this is done only by the males, 
 though it may be possible that the females produce sounds 
 which we are unable to hear. Some locusts produce a noise 
 in flight by the friction of the wings. 
 
17 
 
18 GENERAL ZOOLOGY 
 
 Locusts have been and are used to-day as food in various 
 parts of the East. The records on the bricks of Babylon and 
 Nineveh show that they were known in early times as food, 
 and they are mentioned among the clean meats in Leviticus 
 xi. 22. They are in common use among the Arabs and the 
 Bushmen ; our own Rocky Mountain locust has been eaten 
 and pronounced quite palatable. 
 
 Grasshoppers. The insects which so far we have been con- 
 sidering, while often spoken of as grasshoppers, are not true 
 
 FIG. 8. Katydid. Natural size 
 (From Hunter's Studies in Insect Life) 
 
 grasshoppers, though closely allied to them. The locusts 
 have short, rather stout, antennre, while the true grasshoppers 
 have thread-like antennae, much longer than the body. Per- 
 haps the most interesting of the grasshoppers are the katy- 
 dids (Fig. 8), large green insects of arboreal (tree-dwelling) 
 habits, found in the eastern and central United States. 
 They afford an illustration of protective resemblance, a term 
 which is used to cover those cases in which an animal pos- 
 sesses colors or shape which harmonize with its environment 
 (surroundings), or with some particular object in the environ- 
 ment, thus affording protection against enemies. In the case 
 of katydids the whole body is green and the wings are thin 
 and veined like a leaf. The well-known note from which the 
 name " katydid " is derived is produced only by the male, and 
 
THE ALLIES OF THE EED-LEGGED LOCUST 19 
 
 is made by rubbing the base of one of the first pair of wings 
 against the other anterior wing. An auditory apparatus is 
 found in both sexes at the base of the front tibise. 
 
 Some of the grasshoppers have taken to a cave life, and are 
 blind and wingless. Color has not been developed, and the 
 insects have the white appearance of plants grown in the 
 dark. The antennae and legs are elongated to an enormous 
 extent, and must be useful in an environment where much 
 depends on the sense of touch. 
 
 Crickets. The crickets (Fig. 9, A) resemble the grasshop- 
 pers in the possession of long, slender antennae, but differ 
 from them in having the anterior wings overlapping, instead 
 of meeting in a ridge along the median line of the back. 
 They are widely distributed over the earth, and are, as a 
 
 FIG. 9. Cricket 
 
 A, female, natural size. J5, under surface of right wing of male, enlarged : 1, rasp ; 
 2, position of scraper, only the scraper of left wing used ; 3, attachment of wing 
 
 rule, nocturnal in their habits. They feed mostly on vege- 
 table matter. Our native species live in the fields beneath 
 sticks and stones. Of late years the house-cricket of Europe 
 (Gryl'lus domes' tieus) has become common in the cities of the 
 eastern United States. This is the species famous in song 
 and story. Its well-known chirp is made only by the male. 
 The principal vein on the ventral surface of each anterior wing 
 is thickened into a rasp-like structure (Fig. 9, B, 1) ; on another 
 
20 GENERAL ZOOLOGY 
 
 part is a hardened portion called the scraper (Fig. 9, B, 2). The 
 noise is produced by raising the anterior wings and rubbing the 
 rasp of the right wing against the scraper of the left. Fig. 9 
 
 shows one of the 
 species common 
 in the eastern 
 United States. 
 
 The mole-crick- 
 ets ( Grryllotal f/ pa. 
 FIG. 10. Mole-Cricket. Slightly enlarged . 
 
 tig. 10) are bur- 
 rowing insects, which show interesting adaptations to sub- 
 terranean life. The fore legs are thickened and adapted to 
 burrowing. Roots are easily cut in two by means of a shear- 
 like motion of the joints of each front tarsus against the 
 teeth of the tibia of that leg. For this reason mole-crickets, 
 when numerous, are sometimes a serious pest. The female 
 mole-cricket watches over her eggs and, when they are hatched, 
 feeds the young till the first molt. Mole-crickets are found 
 both in America and Europe. 
 
 Cockroaches. The cockroaches are cosmopolitan forms, 
 some of which infest our houses, where they feed on both 
 animal and vegetable matter. They are dark-colored, flattened 
 insects, which depend upon their legs for escape, although 
 most of them possess wings. Their flattened bodies make it 
 easy for them to hide in crevices, whence they come out at 
 night to feed. The female carries her eggs about with her 
 in a large case till the young are nearly ready to appear. 
 It has been asserted of some species that the mother assists 
 the young in escaping from the egg-case. Just before hatch- 
 ing, the distance between the lateral surfaces of the young 
 cockroach is only one third of the diameter from the dorsal 
 to the ventral surface. Soon after hatching, it assumes the 
 dorso-ventral flattened form of the adult, an adaptation to 
 their life in concealed places. Fig. 11 shows the German 
 
THE ALLIES OF THE KED-LEGGED LOCUST 21 
 
 cockroach, or "croton-bug" (Phyllodro'mia german'icd), with 
 its egg-case ; and a larger species, the so-called Oriental 
 cockroach (Stiloyjyga orien'talis), though there is little evi- 
 dence to show its original home. 
 
 Walking-Sticks. The peculiar insects called walking-sticks 
 are also related to the locusts. Among them are some of 
 the most remarkable illustrations of protective resemblance 
 known in the animal kingdom. The common species in the 
 eastern United States (Diapherom 1 'era femora' to) is shown 
 in Fig. 12. The body and legs are elongated to such an 
 extent that when at rest the resemblance to a twig is most 
 
 FIG. 11. Cockroaches. Natural size 
 
 striking. The insect undergoes a seasonal change of color, 
 being brown when first hatched, turning green after feeding, 
 and changing to brown again as the season advances. It has 
 the power of replacing broken appendages at the next molt, 
 
22 
 
 GENERAL ZOOLOGY 
 
 the portion reappearing either as a short stump or as a 
 smaller appendage, complete except for the absence of one 
 tarsal joint. This walking-stick is a voracious feeder on the 
 leaves of trees ; it has been known to eat a piece of leaf an 
 inch long and a third of an inch wide in an hour. 
 
 Closely related to the walking-sticks are the peculiar East 
 Indian insects known as walking-leaves. In these insects 
 the anterior wings of the female are green and veined like a 
 
 leaf. The people in 
 the countries where 
 they are found be- 
 lieve that these 
 insects are really 
 transformed leaves. 
 The males are en- 
 tirely different from 
 the females, having 
 anterior wings 
 which have no leaf- 
 like appearance. 
 
 Mantids. The 
 ^ mantids are remark- 
 able for the de- 
 velopment of the 
 fore legs, which 
 are unusually large 
 and strong and 
 armed with stout 
 spines. The func- 
 tion of these legs is 
 
 to seize and hold living prey, which consists of other insects. 
 When lying in wait the fore legs are held up in the air, 
 but when an insect comes within reach they are extended 
 with swiftness and precision. The eggs of the mantids are 
 
 FIG. 12. Walking-Stick, x f 
 
THE ALLIES OF THE RED-LEGGED LOCUST 23 
 
 deposited in a mass of foam-like matter, which the female 
 discharges from the tip of the abdomen. This material soon 
 hardens and forms a protecting case for the eggs. The mantid 
 
 FIG. 13. Japanese Mantid. Natural size 
 
 shown with / I its egg-case in Fig. 13 is a Japanese species 
 (Tinode'ra sinen'sis), which has recently been intro- 
 
 duced in a few places in the eastern United States. 
 
 The color is brown and is to some extent protective, and 
 
 as this inconspicuous coloration may render it easier for the in- 
 sect to approach its prey or to escape notice while waiting for 
 food, it may be classed as an example of aggressive resemblance, 
 which term covers those cases where an animal, in resembling 
 its immediate environment, either in shape or color, or both, 
 is thought thereby to be assisted in attack on its prey. 
 
 Several species of mantids from India resemble different 
 flowers which are visited by insects, and seize upon such 
 
24 GENERAL ZOOLOGY 
 
 unwary visitors as do not detect the imposition. In this case 
 the resemblance is to an object attractive to the prey, and 
 may be spoken of as alluring coloration. Dr. J. Anderson 
 showed specimens of one of these insects to members of the 
 Asiatic Society of Bengal in 1877, and communicated infor- 
 mation concerning them as follows. " On looking at the 
 insects from above, they did not exhibit any very striking 
 features beyond the leaf-like expansion of the prothorax and 
 the foliaceous appendages to the limbs, both of which, like 
 the upper surface of the insect, are colored green ; but on 
 turning to the under surface the aspect is entirely different. 
 The leaf-like expansion of the prothorax, instead of being 
 green, is a clear, pale lavender violet, with a faint pink bloom 
 along the edges of the leaf, so that a portion of the insect 
 has the exact appearance of the corolla of a plant, a floral 
 simulation which is perfected by the presence of a dark, black- 
 ish-brown spot in the center over the prothorax, and which 
 mimics the opening to the tube of a corolla. A favorite posi- 
 tion of this insect is to hang head downwards among a mass 
 of green foliage ; and when it does so it generally remains 
 almost motionless, but at intervals evinces a swaying move- 
 ment, as of a flower touched by a gentle breeze." 
 
 Definition of Orthoptera (Gr. orthos, straight; pteron, wing). 
 All the insects mentioned in this chapter have the mouth-parts 
 adapted to biting, and most of them have two pairs of wings. 
 The posterior wings, when present, are folded lengthwise like 
 a fan beneath the hardened anterior wings, and are thus pro- 
 tected from injury. These insects agree in their mode of 
 growth, which is a gradual increase of size by successive molts, 
 without any abrupt change of form. The imagoes differ from 
 the nymphs chiefly by their larger size and the presence of wings. 
 On account of these common characteristics these insects are 
 united in a group, or order, called Ortliop' tera, in allusion to 
 the longitudinal folding of the posterior pair of wings. 
 
CHAPTER III 
 
 THE MAY-FLIES (PLECTOPTERA) AND THE DRAGON- 
 FLIES (ODONATA) 
 
 The sun comes forth and many reptiles spawn ; 
 
 He sets and each ephemeral insect then 
 
 Is gathered into death without a dawn, 
 
 And the immortal stars awake again. SHELLEY. 
 
 May-Flies. The May-flies (Fig. 14), which stand in litera- 
 ture as the type of brief and purposeless existence, are deli- 
 cately constructed, pale insects, with usually four finely 
 veined wings and two or three long white filaments project- 
 ing from the end of the abdomen. The eyes are compara- 
 tively large, but the mouth-parts are so reduced that no food 
 can be taken during adult life, which in most species lasts 
 only a few hours. May-flies appear in countless numbers in 
 late spring or early summer, dance about in the air at dusk 
 in swarms so dense that the atmosphere seems one mass of 
 moving forms, and, after laying their eggs, perish with the 
 day, forming a great food-supply for fishes and birds. 
 
 The eggs are laid in the water and hatch into nymphs 
 (Ephem'era, Fig. 14), which do not at all resemble the adult, 
 and are adapted to an aquatic existence by the presence, along 
 the sides of the abdomen, of outgrowths of the body-wall pene- 
 trated by tracheae. These outgrowths are called tracheal gills. 
 The delicate skin of which the gills are formed permits the 
 passage of oxygen from the surrounding water inward, and 
 allows the escape of carbon dioxide gas. The posterior divi- 
 sion of the heart (or an accessory chamber) is so arranged, 
 that it propels blood backward into the abdominal filaments, 
 so that they, too, act as an organ of respiration. The young 
 
 25 
 
GENERAL ZOOLOGY 
 
 feed on small aquatic animals, or on plants. After a year or 
 more of this life beneath the surface, during that time under- 
 going many molts, the nymph de- 
 velops rudimentary wings. From 
 the nymph issues a winged form 
 which may be called a subimago. 
 Within a very short time the skin 
 is again cast, even to a thin cover- 
 ing from the wings, and the true 
 imago comes forth. A molt in the 
 winged state is known nowhere 
 else among insects. Though the 
 reduced mouth-parts make it im- 
 possible for the adult May-fly 
 to take any food, the alimen- 
 tary canal is not useless. Air is 
 
 FIG. 14. Nymph and Imago of May-Fly. Natural size 
 
 taken in at the mouth, and the capacious stomach acts as a bal- 
 loon, being provided with valves so that the air cannot escape. 
 Definition of Plectoptera (Gr. plektos* twisted: pteron* 
 wing). The May-flies make up the order Plectop'tera. The 
 Plectoptera may be distinguished from other insects by the 
 reduced mouth-parts, the great disproportion in the size of 
 
THE MAY-FLIES AND THE DRAGON-FLIES 27 
 
 the anterior and posterior wings, and by the presence of 
 abdominal filaments. From the earliest nymph stage to the 
 imago there is quite a clearly marked though gradual change 
 of form, or metamorphosis. 
 
 To-day I saw the dragon-fly 
 
 Come from the wells where he did lie. 
 
 An inner impulse rent the veil 
 
 Of his old husk : from head to tail 
 
 Came out clear plates of sapphire mail. 
 
 He dried his wings : like gauze they grew ; 
 
 Thro' crofts and pastures wet with dew 
 
 A living flash of light he flew. TENNYSON. 
 
 Dragon-Flies. The dragon-flies (Libel'lula, Fig. 15) are 
 familiar insects found flying over the surface of still or run- 
 ning water. They feed on other insects, which they capture 
 on the wing. They are lovers of the sunshine, and are most 
 active in the brightest and hottest part of the day. The larger 
 kinds hawk freely over the surface of the water at some dis- 
 tance above it, often far out from the shore, where their range 
 of vision is unobstructed ; while the smaller and weaker kinds 
 keep closer to the shore and the protection of vegetation. All 
 are voracious feeders, destroying large quantities of flies and 
 mosquitoes. Many superstitions have become associated with 
 them in different parts of the country ; in the North it is 
 believed that they sew up the mouths and ears of children ; 
 in the South, that they bring dead snakes to life. It is, per- 
 haps, needless to say that they are harmless. The head is 
 made up almost entirely of the great, staring, compound 
 eyes, which shine like fire as the dragon-fly moves about. 
 The mouth has strong jaws, somewhat resembling the power- 
 ful mandibles of the locusts. The wings are large, with 
 many veins, and are moved by powerful muscles ; but the legs 
 are slender and small, as the dragon-flies are preeminently 
 creatures of the air. The long and slender abdomen is used 
 to balance the insect in its headlong flight. 
 
28 
 
 GENERAL ZOOLOGY 
 
 it 
 
 The eggs, generally attached to water plants, hatch into 
 dark-colored, flattened aquatic nymphs. The mouth-parts 
 are unique in structure. The second maxillae are enlarged 
 and armed with hooks at the extremity. This formidable 
 
 organ can be extended to seize 
 upon any insect within reach, and 
 when not so engaged it covers 
 the entire face like a mask, giv- 
 ing a peculiar and comical aspect 
 to a front view. The nymphs 
 breathe by means of tracheae, 
 which line the posterior portion 
 of the alimentary canal. When 
 water is drawn into the canal, 
 air is absorbed from it by this 
 
 FIG. 15. Metamorphosis of Dragon-Fly. Natural size 
 
THE MAY-FLIES AND THE DRAGON-FLIES 29 
 
 system of air-tubes, and water, deprived of its free oxygen, 
 can be ejected violently, thus forcing the nymph forward. 
 After successive molts the nymph develops rudiments of 
 wings, and finally crawls out of the water to some conven- 
 ient support, when the skin splits down the back and the 
 dragon-fly, with crumpled wings, slowly emerges. A short 
 time elapses before the body hardens and the wings expand, 
 and then the imago flies away to live its short adult life. 
 
 There are two quite distinct types of dragon-flies, both 
 widely distributed over the world. The form represented in 
 Fig. 15 is of comparatively robust build. The eyes touch 
 each other along the median line of the head. The posterior 
 wings are broader at the base than the anterior pair, and both 
 pairs are held horizontally when the insect is at rest. To this 
 type belong the best fliers of the group. The insects which 
 illustrate the other type, while they can easily enough be 
 recognized as dragon-flies, are of more slender build. Their 
 eyes are widely separated on opposite sides of the head. The 
 anterior and posterior wings are alike in size and shape, and 
 when not in use are folded against the abdomen. The flight 
 is less sustained and more erratic than with species of the 
 first type. Some of these dragon-flies, notably species from 
 the tropics, are most beautiful both in form and color. The 
 French call these insects " demoiselles," which we may trans- 
 late damsel-flies. 
 
 Definition of Odonata (Gr. odons (odont], a tooth). The 
 dragon-flies constitute the order Odona'ta, a word meaning 
 " toothed," perhaps in allusion to the teeth on the second 
 maxillae of the larvae. The Odonata are distinguished by the 
 biting mouth-parts and the four equal or nearly equal net- 
 veined wings. The metamorphosis is fully as well marked 
 as in the preceding order. 
 
CHAPTER IV 
 
 THE BUGS: HEMIPTERA 
 
 The shy cicada, whose noon-voice rings 
 So piercing shrill that it almost stings 
 
 The sense of hearing. ELIZABETH A. KERR. 
 
 Water-Bugs. In almost every pond and stream, not only 
 in the United States but scattered widely over almost the 
 
 whole world, are to be found 
 oval gray and black insects, 
 usually a little over a ceri- 
 ^^_ timeter long (about half an 
 inch). These are water-boat- 
 men (Corix'a, Fig. 16, B). They have 
 a long beak formed by the union and 
 lengthening of the second maxilla}, 
 inclosing at its base the bristle-like 
 mandibles and first maxillae. With 
 this they suck the body -fluids of other 
 water-creatures. They are adapted to 
 rapid locomotion in the water by means 
 of the lengthened and fringed middle 
 and hind legs. They breathe a thin 
 film of air, which is caught in the fine 
 hairs which cover the body, making 
 them look as if . incased in polished 
 metal. Slight movements of the legs 
 cause currents of water to pass over 
 this air-film, helping to purify it, and 
 rendering frequent visits to the surface 
 unnecessary. When at the surface air 
 30 
 
 FIG. 16. Back -Swimmers 
 and Water-Boatman. 
 Slightly enlarged 
 
 A, Notonecta, ventral view 
 -(swimming attitude); 
 A', Notonecta, dorsal sur- 
 face ; B, Corixa 
 
THE BUGS: HEMIPTERA 
 
 31 
 
 is taken into a cavity under the wings, where the spiracles 
 are placed, so that quite a supply is on hand at all times. 
 While these insects are thus adapted to water-life, they can 
 fly, and often leave their native ele- 
 ment, especially if it is in danger 
 of becoming dry. 
 
 Another widely distributed 
 group of insects resembling the 
 foregoing are the back-swimmers 
 (Notonec'ta, Fig. 16, 
 A, A'), which have 
 the curious habit ' 
 of swimming on 
 their backs, as 
 their common arid scientific 
 names denote. A favorite posi- 
 tion of these insects is to float with the 
 head down and the tip of the abdomen 
 protruding just enough to admit the 
 passage of air to chambers beneath the 
 wing-covers. The back-swimmers can 
 inflict a momentarily painful wound 
 
 with their sharp beaks. Search made 
 
 . . FIG. 17. Squash-Bug and 
 
 for these insects will reveal a variety of Young. Natural size 
 
 other beaked forms, some of which live 
 
 beneath the surface of water, while others skim swiftly over it. 
 Plant-Bugs. The squash-bug (An'asa tris'tis, Fig. 17), a 
 well-known enemy of squash and pumpkin vines, also pos- 
 sesses a beak, which is used to suck plant instead of animal 
 fluids. This bug is a little over two centimeters (nearly an 
 inch) long, and brownish black in color. It has the power, 
 in common with many other allied species, of pouring out an 
 evil-smelling secretion from two openings near the base of 
 the middle pair of legs, which probably renders it obnoxious 
 
32 
 
 GENERAL ZOOLOGY 
 
 to some creatures which might prey upon it. Observations 
 on the food of birds of the eastern United States seem to 
 dpi show that, so far at least as the birds are con- 
 cerned, these repellent odors are not in all cases 
 entirely effective, since many species of plant- 
 bugs are fed upon quite generally by birds. 
 
 Cicadas. An examination of the large, broad- 
 headed, triangular insects known as harvest- 
 flies, or cicadas, will show that they, too, agree 
 with the foregoing insects in the possession 
 of a sucking-beak. There are several species 
 in the United States, of which the best 
 known is the periodical cicada (Cica'da 
 septen'decim, Fig. 18), usually, but wrong- 
 ly, called the thirteen or seventeen year 
 " locust. 1 ' At the base of the abdomen of 
 the male is a " drum," 
 or sound-producing 
 organ, where a high- 
 pitched note is made 
 by the rapid 
 
 FIG. 18. Periodical Cicada, x 
 
THE BUGS: HEMIPTERA 33 
 
 vibration of tightly stretched membranes, somewhat in the 
 way sound may be produced by pushing up and down on 
 the bottom of a tin pan. This note, heard in the middle of 
 hot summer days, has been celebrated as the "song" of the 
 cicada since the time of the Greeks. 
 
 The female lays her eggs in slits, usually in the small 
 terminal twigs of trees, generally causing them to wither 
 and die. In a year in which these insects appear in large 
 numbers the trees look as if a fire had passed over them 
 and scorched the ends of all the twigs. The eggs hatch in 
 about six weeks, and the nymphs drop to the ground, into 
 which they dig, and for a long period of time, thirteen years 
 in the southern states and seventeen years in the North, 
 they lie in a cell feeding on the juices of the roots of trees. 
 Early in the summer of the thirteenth or seventeenth year, 
 they rise to the surface, and, clinging to some convenient 
 support, cast their last nymph skin to come out as winged 
 creatures for their few weeks of adult life. In some cases, 
 when the nymphs reach the surface, they build peculiar 
 cones of clay (Fig. 18) several inches in height, over the 
 mouths of their burrow's, entirely closing the top of the 
 cone. In the upper part of these they wait the period of 
 their final molt. The formation of these structures has been 
 explained by some as due to the prevalence of long-continued 
 wet weather at the time of the emergence ; by others, as 
 occasioned by heating of the ground in certain localities by 
 the sun, thus bringing the nymphs to the surface before their 
 time. 
 
 Aphids. Every one who has tried to keep plants indoors 
 must have noticed the small green, oval insects known as 
 plant-lice, or aphids. There are many species infesting dif- 
 ferent plants, upon the juices of which they feed. Some 
 attack the roots, but the greater number are found upon the 
 foliage. They are generally not more than three millimeters 
 
34 GENERAL ZOOLOGY 
 
 (about an eighth of an inch) in length, with a somewhat pear- 
 shaped body, and with or without wings. In most species 
 there is found projecting from the back of the sixth abdom- 
 inal somite a pair of slender tubes, which secrete a sticky, 
 waxen substance, which is probably protective in its nature. 
 Aphids are sought for by ants for the sake of a sweet sub- 
 stance called "honeydew," poured out from the alimentary 
 canal. We shall see later how certain species of ants have 
 taken to protecting aphids in order to secure a constant 
 supply of this food. 
 
 The life-history of some of the aphids is most remarkable. 
 An aphid colony in the summer may consist almost entirely 
 of wingless females, which have the power of producing gen- 
 eration after generation of living young without fertilization. 
 This form of reproduction is known as parthenogenesis. The 
 young so produced are females, and many of them are wing- 
 less, though winged females are produced which start colo- 
 nies in other places, sometimes on a different food-plant. 
 Both winged and wingless females are able to produce young 
 parthenogenetically within from ten to twenty days. This 
 kind of reproduction goes on till the approach of cold weather 
 or the failure of the food- supply, when males are produced. 
 After pairing, the female lays eggs which last through the 
 winter and hatch into females in the spring, which start a 
 new colony as already described. 
 
 One of the greatest enemies of the grape is an aphid 
 known as Phylloxe'ra vasta'trix, which has been the scourge 
 of many vineyards in France. It lives both on the roots and 
 on the leaves. Other species, called woolly aphids, have the 
 power of secreting a white downy substance, which entirely 
 covers their bodies. One of these, which lives in colonies, 
 making white masses on the alder, is known as the alder- 
 blight. This insect secretes honeydew, and is visited by 
 ants. 
 
THE BUGS: HEM1PTERA 
 
 35 
 
 Scale-Insects. Some of the greatest enemies to the horti- 
 culturist are included among the scale-insects, which infest 
 nearly all kinds of fruit-trees and many shade-trees. In some 
 species the body is scale-like in form ; in others (Mytilas'pis 
 
 FIG. 19. Scale-Insect. (After Howard, Year-book, United States 
 Department of Agriculture, 1894) 
 
 a, female, from beneath, showing eggs protected by scale, X 24; b, female, from 
 above, X 24; c, female scale on branch, natural size; d, male scale, X 12; 
 e, male scales on twig, natural size 
 
 porno 1 rum, Fig. 19), the female, which begins life as an active 
 insect, soon settles down, with the beak fixed in the tissues of 
 some plant, and develops a waxy scale as a secretion from the 
 skin of the back, beneath which she lies protected for the 
 remainder of her life. The male is entirely different in 
 
36 GENERAL ZOOLOGY 
 
 appearance and development. At first it resembles the female, 
 but it soon passes into a. short resting, m pupal stage, beneath 
 a protecting scale, from which it reappears as a two-winged 
 insect with rudimentary mouth-parts. In this form of meta- 
 morphosis the young differs greatly from the imago, and there 
 is a resting pupal stage before the emergence of the imago. 
 Following common usage, we may speak of this as a " com- 
 plete " metamorphosis. The young is called a larva. 
 
 There are more than eight hundred species of scale-insects 
 known, and it is certain that many more remain to be dis- 
 covered and described. Man is indebted to these insects for 
 a variety of products of greater or less value. One of the 
 scale-insects (Ooc'cus cac'ti), found on the cactus in Mexico, is 
 the source of the red coloring matter, cochineal ; to another 
 (Carte 'ria lac'ca), of India, we are indebted for lac. Several 
 species produce waxy substances in use in various countries 
 of the East. The white wax of one Chinese species, formerly 
 much prized, is said to be replaced now by the use of kero- 
 sene. The manna mentioned in the Book of Exodus is prob- 
 ably the secretion of a scale-insect. It is a sweet substance 
 used to-day by the Arabs as food. 
 
 Definition of Hemiptera (Gr. hemi, half; pteron, wing). 
 The insects mentioned in this chapter all agree in possessing 
 a sucking-beak. They are the insects to which the word 
 " bug " is strictly applicable. The order is called Hemip'tera, 
 the word referring to the fact that in some families the ante- 
 rior wings are hardened as a protection for about half their 
 length. Outside of the cicadas and scale-insects the Hemip- 
 tera develop without marked metamorphosis (see Fig. 17). 
 
CHAPTER V 
 THE BEETLES: COLEOPTERA 
 
 Now fades the glimmering landscape on the sight, 
 
 And all the air a solemn stillness holds ; 
 Save where the beetle wheels his drony flight 
 
 And drowsy tinklings lull the distant folds. 
 
 GRAY, Elegy in a Country Churchyard. 
 
 Tiger-Beetles and Ground-Beetles. The tiger-beetles (Cicin- 
 de'la, Fig. 20) will serve to introduce another type of insect. 
 Tiger-beetles are usually metallic, shining, bright-colored spe- 
 cies, about one and a half centimeters in length, with large 
 heads and prominent eyes, and are found on sandy roads or 
 beaches, flying about while the sun shines. Some of them are 
 bright red or green; some are brown or black, with white 
 markings ; while others are protectively colored, resembling 
 the sand on which they live. They run swiftly, and when 
 disturbed take flight, only to alight at a short distance, 
 often facing about so that they can better watch the pursuer. 
 The mouth-parts are all well-developed and distinct, as in 
 the locust. The mandibles are long, and toothed on the inner 
 edge, admirably fitted for seizing living prey. The posterior 
 wings are concealed by a pair of hardened wing-covers (ante- 
 rior wings), which meet in a median longitudinal line down 
 the back. The wing-covers are not used in flight, but serve 
 to protect the delicate wings beneath. 
 
 The larvse are misshapen, dirty-white grubs, living in holes 
 which they dig in sandy places. Two hooks on the dorsal 
 surface enable them to climb up and down in their holes, 
 which are sometimes thirty centimeters or more deep, and 
 prevent their being dragged out when they have hold of 
 
 37 
 
38 
 
 GENERAL ZOOLOGY 
 
 their prey. Here, with the earth-colored head even with the 
 surface, they lie in wait, seizing any passing insect with 
 their strong jaws. 
 
 Often there is found beneath stones in fields a small blue 
 oval insect, about two centimeters in length, which, when 
 handled, emits a puff of smoke-like gas with a strong odor, 
 
 and a quite audible noise, as of 
 the report of a tiny pop-gun. 
 This is the bombardier-beetle 
 (Brack 1 inus). Its secretion be- 
 longs to the class of repellent 
 odors, and may often render possible the escape 
 of its possessor before the enemy has had 
 time to recover. The bombardier is one of 
 the large family of ground-beetles which are 
 found beneath sticks and stones everywhere. 
 Ground-beetles are generally black in color ; 
 most of them capture living prey. Some have 
 taken to cave life and have become blind. 
 In such cases hairs possessing the sense 
 of touch are well developed on the body, so 
 FIG. 20. Tiger-Bee- that the beetles run as swiftly as if they 
 tie and Larva, possessed eyes. 
 
 Water-Beetles. The whirligig-beetles 
 (Dineu'tus, Fig. 21) are familiar, oval insects found in groups 
 
 FIG. 21. Whirligig-Beetles. Natural size 
 
THE BEETLES: COLEOPTERA 39 
 
 circling about on the surface of still water. They can see 
 both below and above the surface of the water, as the two 
 eyes are divided into four, and the parts separated so that 
 watch can be kept for danger from either direction. The 
 whirligigs are protected by a strong-smelling milky secretion 
 which probably renders them distasteful to fishes. They are 
 
 nor 
 
 FIG. 22. Diving Beetle. Slightly enlarged 
 
 able to dive to escape danger, carrying down with them a 
 small supply of air. 
 
 Beneath the surface of such ponds and pools as the whirli- 
 gig-beetles frequent are to be found different species of diving 
 beetles (Dytis'cm, Fig. 22), which have adaptations similar to 
 those mentioned among the aquatic Hemiptera. Thus in some 
 the spiracles, which in land insects are along the sides of the 
 
40 
 
 GENERAL ZOOLOGY 
 
 abdomen, are here placed beneath the edge of the wing- 
 covers on the back, and the space beneath the wing-covers 
 is used as an air-reservoir, which is replenished with pure 
 air by rising to the surface. In other species a thin coating 
 of air is carried on the under side of the abdomen. This 
 supply is obtained by pushing the head above water and 
 capturing a bubble of air with the antennoe, which are quickly 
 folded beneath the head, carrying the imprisoned bubble to 
 the under surface of the body. 
 
 Scavenger-Beetles. A useful part in the economy of nature 
 is played by the scavenger-beetles (Necroph' orus, Fig. 23), 
 large black, red-spotted insects, \vhich dig beneath the car- 
 casses of small animals, thus burying them beneath the 
 
 surface. The female 
 then lays her eggs in 
 the decaying material, 
 upon which the larva) 
 1 feed until ready to 
 transform. This exer- 
 tion removes the car- 
 cass from the field of 
 operations of other 
 creatures which might 
 feed upon it, if it were 
 left exposed, and thus 
 
 FIG. 23. Scavenger-Beetle. Slightly enlarged destroy the eggs, or 
 
 larvae. As these 
 
 beetles are protected by a fetid odor, their striking markings 
 are usually spoken of as an example of warning coloration, 
 a term applied to those appearances in animals which are 
 thought to be useful in notifying enemies of the presence of 
 something disagreeable or dangerous. 
 
 Lady-Beetles. The common and well-known insects vari- 
 ously called lady-beetles, lady-bugs, or lady-birds (CoccineVla, 
 
Tl 
 
 THE BEETLES: COLEOPTERA 41 
 
 Fig. 24), are hemispherical in shape and generally reddish or 
 yellowish in color, with black spots. Both the imagoes and 
 larvae of most species feed upon plant- 
 lice and other insects injurious to vege- 
 tation ; hence they are to be reckoned 
 among the insects useful to the farmer. 
 A few years ago, when the orange- 
 growing industry of California was 
 threatened with great loss, if not total 
 extinction, from the attacks of a scale- 
 insect, an Australian lady-beetle (Veda'- 
 lia) was introduced to feed upon it. 
 The success of the experiment was so 
 great that large sums have been saved 
 to the orange-growers. Another scale- F IG . 24. Lady-Beetle. 
 insect, the San Jose scale (Aspidio'tus 
 
 pernicio'sus), so called because it first appeared many years 
 ago in that city, has since spread widely over the country, 
 causing great damage to the orchard interests. Investiga- 
 tions set on foot by the Division of Entomology of the United 
 States Department of Agriculture located the original home 
 of the insect in China, and the discovery was made there 
 of a lady-beetle (Chiloc'orus sim'ilis) which preys upon it. 
 This lady-beetle has now been introduced and distributed to 
 infested regions, with every prospect of success. 
 
 The lady-beetles are protected by a yellow, odorous fluid 
 formed in the blood. ' When the insect is seized the fluid 
 oozes out from the ends of the femora. The bright colors 
 of these insects are usually cited as an example of warn- 
 ing coloration. 
 
 Click-beetles. The click-beetles are a well-known group, 
 generally brown in color and of elongate form. The species 
 are able to leap into the air when placed on their backs. 
 The mechanism which makes this possible consists of a spine 
 
42 
 
 GENERAL ZOOLOGY 
 
 projecting backward on the ventral surface of the prothorax, 
 and a corresponding cavity on the ventral surface of the 
 mesothorax. When the beetle falls upon its back, as often 
 happens from its habit of dropping to the ground as though 
 dead, the legs are so short that they are unable to help 
 much in regaining its position ; then the spine on the pro- 
 thorax is driven into the cavity of the mesothorax with 
 force sufficient to cause the base of the wing-covers to strike 
 against the surface and throw the beetle into the air. If it 
 lands wrong side up, the act is repeated until success crowns 
 its efforts. The larvae are called wireworms, and live in 
 decaying wood or attack the roots of vegetables. 
 
 Our largest species is called the eyed click-beetle (A'laus 
 ocula'tus, Fig. 25), on account of the oval, eye-like spots on 
 
 the back of the prothorax. These 
 spots have been thought to be of 
 the nature of terrifying organs. 
 Professor Needham of Lake Forest 
 University says: " If there be one 
 thing more than another of which 
 animals are suspicious, it is a 
 strange-looking eye. Nature has 
 taken advantage of this fact in 
 protecting some of the most 
 innocent little creatures by devel- 
 oping upon them spots that look 
 like sinister eyes." Several South 
 American and West Indian species 
 of click-beetles have the power 
 of emitting light from spots on 
 the side of the prothorax and 
 abdomen, and are used by the 
 natives as ornaments, being sewed in lace and worn on the 
 head. The light is the most brilliant and continuous of any 
 
 FIG. 25. Eyed Click-Beetle. 
 Slightly enlarged 
 
THE BEETLES: COLEOPTERA 
 
 43 
 
 luminous insect, though it is not given off when the insect is 
 at rest or feeding. 
 
 Fireflies. The power of giving off light is possessed by 
 the majority of the members of an allied group, the fireflies 
 (Photu'ris, Fig. 26), soft-bodied insects about two or three 
 centimeters in length, dull-colored, and with the prothorax 
 usually margined with red or yellow. The wing-covers are 
 much softer than in other 
 beetles. Fireflies are, for 
 the most part, nocturnal 
 in their habits, clinging 
 to the under side of leaves 
 during the day. They are 
 protected from the insect- 
 eating birds by a strong 
 odor which renders them 
 distasteful. The lumi- 
 nous spots are on various 
 abdominal somites, gen- 
 erally the last. Fireflies 
 appear in greatest num- 
 bers in the latitude of 
 the Middle Atlantic states 
 for a week or more in the 
 month of June. Many 
 attempts have been made 
 to account for the light 
 produced by the fireflies. 
 The light-giving organ 
 seems to consist of fat- 
 cells inclosed in a network of fine tracheae. These cells 
 apparently have the power, under nervous control, of secret- 
 ing a substance, possibly phosphureted hydrogen, which is 
 luminous when acted upon by the oxygen furnished by the 
 
 FIG. 26. Firefly. Slightly enlarged 
 
44 GENERAL ZOOLOGY 
 
 tracheae. The process is, therefore, a form of oxidation. It 
 is interesting to note that the efficiency of this apparatus as 
 a light-producing organ has been estimated at 100 per cent. 
 In such artificial illumination as a gas-jet, for example, only 
 about two per cent of the radiant energy consists of light-rays. 
 The function of the light of the fireflies is not understood. 
 
 Scarabs. Certain beetles of a quite different group have 
 long attracted the attention of observers by their curious 
 habit of forming and rolling about a pellet of manure for food 
 for themselves or their larvae. We have several species of 
 these beetles in the L T nited States, but the best known of the 
 
 FIG. 27. Sacred Beetle and Scarab in Stone, x 2 
 
 group is the sacred beetle of the Egyptians (Ateu'chus sa'cer, 
 Fig. 27), the Scarabceus of the ancients, figures of which are 
 found carved in stone on the monuments of ancient Egypt. 
 These beetles played an important part in the symbolism of 
 the Egyptians, to whom they typified the world and the sun, 
 - the former on account of their round pellets, the latter 
 on account of the projections on the head, which were likened 
 to the rays of the sun. 
 
 To the same group belong our common May -beetles or June- 
 beetles (Lachnoster'na, Fig. 28). These beetles live in the 
 ground in the larval stage, feeding on the roots of plants. 
 
THE BEETLES: COLEOPTERA 
 
 45 
 
 The larvae are the well-known white grubs often turned up 
 by the plow in the spring. The pupal stage is also passed 
 
 FIG. 28. Metamorphosis of June-Beetle. Natural size 
 
 in the ground. The imagoes feed on the leaves of trees, often 
 completely defoliating them. 
 
 Definition of Coleoptera (Gr. koleos, sheath ; pteron, wing). 
 The insects which we have considered in this chapter agree in 
 possessing biting mouth-parts and hardened sheaths to cover 
 the posterior wings. They are termed beetles, or Ooleop'tera. 
 The Coleoptera undergo a " complete " metamorphosis ; their 
 larvae are called grubs. 
 
CHAPTER VI 
 THE BUTTERFLIES AND MOTHS: LEPIDOPTERA 
 
 And what 's a butterfly ? At best 
 He 's but a caterpillar drest. JOHN GAY. 
 
 The Monarch Butterfly. One of the commonest and best 
 known of our butterflies is the monarch, or milkweed butter- 
 fly (Ano'sia plexip'pus, Fig. 30). It is a tawny-colored species 
 expanding about ten centimeters (four inches). The wings 
 have black veins, and the margins are black with white spots. 
 The colors are due to the presence of tiny scales, which cover 
 the surface regularly and overlap like the shingles on a roof. 
 Besides serving for the display of the colors, the scales also 
 strengthen the wings. The scales are in origin modified hairs, 
 like those which cover the rest of the body. The mouth-parts 
 are formed for sucking the nectar of flowers, and consist 
 mainly of a large tubular tongue, or proboscis, which is coiled 
 up beneath the head. The proboscis is formed from the length- 
 ening and union of the first maxillae. The mandibles are so 
 small as to be hardly visible. The anterior legs are so much 
 reduced in size that they cannot be used for walking, and the 
 butterfly is therefore practically four-legged. 
 
 The monarch passes the winter in the South, like our 
 migratory birds, and with approaching warm weather the dif- 
 ferent individuals slowly work their way northward, the 
 females laying eggs in different places in the course of the 
 journey. The eggs are pale green and are deposited singly 
 on the leaves of the different species of milkweed. In about 
 four weeks the eggs hatch into caterpillars, which immediately 
 proceed to devour the egg-shells. For the rest of their larval 
 
 46 
 
THE BUTTERFLIES AND MOTHS 
 
 47 
 
 existence the caterpillars are voracious feeders on the leaves 
 of the milkweed. They grow for two or three weeks, molting 
 several times as they increase in size, till they are conspicuous 
 objects, nearly five centimeters (two inches) long, prominently 
 banded with yellow and black (Fig. 29). When through feed- 
 ing, each larva spins a pad of silk on some convenient support, 
 and, molting once more, appears in a mummy-like pupal con- 
 dition (Fig. 29), attached by hooks at its extremity to the 
 pad of silk spun by the larva. In the pupal stage the milk- 
 weed butterfly is bright green with golden spots. To this, 
 and to some of the other 
 naked pupae of butterflies, 
 the name chrysalis is some- 
 times given. The insect re- 
 mains in the pupal stage 
 for ten or twelve days, 
 when the skin splits and 
 the butterfly comes out 
 with crumpled wings, which 
 soon expand and harden. 
 
 The monarch butterfly 
 possesses remarkable 
 powers of flight. Mr. 
 Scudder, in his Guide to 
 Butterflies, mentions that it has been seen at sea five hun- 
 dred miles from land, and that it has within thirty years 
 spread over nearly all the islands of the Pacific, and even 
 to Australia and Java. He says : " Undoubtedly carried in 
 the first place by trading or other vessels to the Hawaiian 
 Islands, and thence to Micronesia, it has unquestionably/oww 
 from island to island many hundreds of miles apart. It has 
 also appeared at various times in different places on the 
 seacoast of Europe ; here also probably transported acciden- 
 tally by vessels." 
 
 29. .Larva and Pupa of Monarch 
 Butterfly. Natural size 
 
 (From Hunter's Studies in Insect Life) 
 
48 GENERAL ZOOLOGY 
 
 It is asserted that these butterflies, although so brilliantly 
 colored and conspicuous, are not fed upon generally by birds 
 and other animals which might use them for food, owing to 
 their possessing a strong odor which renders them distasteful. 
 If this is the case, the distinctive coloration may be an advan- 
 tage rather than otherwise, making it easy for any animal 
 to distinguish them from edible species. The brilliant colors 
 are usually cited as an illustration of warning coloration. 
 
 The Viceroy Butterfly. Another butterfly of an entirely 
 different genus (see p. 95) and without any offensive odor, 
 the viceroy (Basilar'chia archip'pm, Fig. 30), closely resem- 
 bles the monarch. The viceroy belongs to a group of butter- 
 flies whose general body-coloration is blue and white, but 
 instead of the livery of its relatives it wears that of the mon- 
 arch. It offers the best-known illustration in North America 
 of what is called protective mimicry, a term applied to those 
 cases in the animal kingdom in which a group of animals 
 without disagreeable qualities resembles, to a greater or less 
 extent, animals provided with special means of defense. Pro- 
 tective mimicry will be seen to differ from warning coloration 
 in that the fe?n*er is believed to protect an animal by mark- 
 ing it as a source of real danger or unpleasantness; theT#fcter 
 is believed to protect by suggesting characters which have 
 no existence in fact. This explanation of the color of the 
 viceroy has lately been called in question, and observations 
 are wanting to show that the birds of the eastern United 
 States feed generally upon butterflies. Many cases of pro- 
 tective mimicry are known among the butterflies of Africa 
 and South America. By the use of the term it is not meant, 
 of course, that there is anything conscious in the mimicry. 
 
 The White Mountain Butterfly. Another butterfly of the 
 same group is the White Mountain butterfly (CEne'is semid'ea), 
 interesting on account of its peculiar distribution. It is found 
 only on the highest peaks of the White Mountains in New 
 
VIG. 30. Monarch. Viceroy, and Type Baailarrhin. Natural size 
 
 Upper figure, the monarch butterfly (Anosia plexippus) ; middle figure, the viceroy 
 butterfly (BasUarchia archippus) ; lower figure, another species of the genus 
 Bcurilarchia, to show the usual coloration of the genus 
 
THE BUTTERFLIES AND MOTHS 49 
 
 Hampshire and the Rocky Mountains in Colorado. As will 
 be seen later, the geological period immediately preceding the 
 present was an age of ice, in which the North American conti- 
 nent was covered by ice as far south as an irregular line drawn 
 through New York, Pennsylvania, Missouri, South Dakota, 
 and Oregon, and arctic conditions existed over the rest of 
 the continent. At this time these butterflies were probably 
 distributed over the country. As the ice slowly melted and 
 the climate became warmer, they found only on the summits 
 of these widely separated mountain ranges the conditions to 
 which they had been accustomed, all those occupying the 
 region between being driven to the northward or destroyed 
 by the heat. 
 
 Swallow-Tail Butterflies. The magnificent insects called 
 swallow-tail butterflies, widely distributed over the world, 
 have received their common name on account of the prolon- 
 gation of the posterior wings. They are especially interest- 
 ing to the naturalist, not only for the variety and beauty of 
 their colors and the elegance of their form, but also because 
 they often exhibit, within the limits of a single species, great 
 variation in color, size, and even in the shape of the wings. 
 The variation in form, size, and color between individuals of 
 the same species is spoken of as dimorphism (Gr. di, two ; 
 morphe, form), if the variations show two well-marked types ; 
 and as polymorphism (Gr. poly, many), if there are several 
 different variations. In many species the males differ greatly 
 from the females ; this is called sexual dimorphism. Many ex- 
 amples are known of broods of the same butterfly appearing 
 at two different seasons. These broods often differ widely in 
 size and color markings. This is known as seasonal dimor- 
 phism. In some cases seasonal dimorphism and polymorphism 
 seem to result from conditions of temperature. A swallow- 
 tail butterfly (Papil'io a'jax), which is widely distributed in the 
 eastern United States, has, in the latitude of West Virginia, 
 
50 
 
 GENERAL ZOOLOGY 
 
 three different forms, called the early spring, the late spring, 
 and the summer form. Both of the spring forms appear from 
 pupae which have lived through the winter. From the eggs 
 which the spring forms lay the summer form develops several 
 successive broods the same year. 
 
 Skippers. The skippers (Epargy'rem tit'yrus, Fig. 31) are, 
 like the butterflies, diurnal insects, and are found in fields 
 
 and along 
 woods ides, 
 where they 
 dart about 
 
 in a most erratic manner. They are 
 closely allied to the butterflies, but 
 differ from them in several details 
 of structure and habits. The butter- 
 flies (see Fig. 30) have club-shaped 
 antennae, while in the skippers the 
 antennae, though enlarged at the 
 end, are generally recurved, forming 
 a hook. The skippers have stouter 
 bodies than the butterflies, and most 
 of them hold the wings upright after 
 the fashion of the butterflies ; but 
 some hold only the anterior wings in this position. The larvse 
 of those species found in the United States can easily be dis- 
 tinguished from other caterpillars by the very large head and 
 strongly constricted neck (Fig. 31). They usually live in a 
 folded leaf, or in a nest of leaves, and pass the pupal stage in a 
 thin cocoon of silk spun by the caterpillars before changing. In 
 this latter respect, too, the skippers differ from the butterflies, 
 since the latter (as shown in Fig. 29) have a naked pupal stage. 
 
 FIG. 31. Metamorphosis of 
 Skipper. Natural size 
 
THE BUTTERFLIES AND MOTHS 51 
 
 Silkworm Moths. Allied to both butterflies and skippers 
 is the great group of moths, stout-bodied insects, the 
 antennse of which are usually feather-like or thread-like 
 (Figs. 32, 33, 34). Moths have the habit of holding the 
 wings horizontal when at rest. They are nocturnal or diur- 
 nal in their habits, though by far the larger number fly by 
 night. Most of them spin some kind of a cocoon in which 
 they pass the pupal stage. 
 
 We shall first consider the silkworm moths. Of these the 
 best known, as it is economically the most important, is 
 the Chinese silkworm moth (Bom 1 by x mo'ri). Cultivated in 
 China from very early times, the Chinese jealously guarded 
 the secrets of the manufacture of silk until, as the story goes, 
 in the middle of the sixth century two monks brought the 
 eggs to Constantinople by stealth, concealed in a hollow bam- 
 boo cane. The cultivation of the silkworm then spread rapidly 
 to those parts of Europe suited to its culture. It was intro- 
 duced into England in the fifteenth century, but the manu- 
 facture of silk was given no impetus till the arrival in 1585 
 of a body of Flemish weavers, who had fled from the Low 
 Countries on account of the struggle with Spain. One hun- 
 dred years later the revocation of the Edict of Nantes drove 
 a large body of skilled workmen from France to England, 
 Germany, and Switzerland, and the silk-manufacturing indus- 
 try developed still more in these three countries. From 1609 
 to the present day various efforts have been made to intro- 
 duce silk culture into the United States, the plan of bounties 
 and rewards to stimulate its growth having been tried by the 
 rulers in colonial days, and by several states since the war 
 of 1861-65. These artificial means have so far not met with 
 great success. In China the caterpillar thrives best on the 
 leaves of the white mulberry, but it has been found to do 
 well on the Osage orange, a tree widely distributed in the 
 south and west of the United States. 
 
52 GENERAL ZOOLOGY 
 
 The silk-glands extend through the body of the caterpil- 
 lar and open into the mouth. Toward the time of pupation 
 they increase in size and produce about four thousand yards 
 of material, which, on being exposed to the air, hardens and 
 becomes the silk of commerce. As there are two sets of these 
 glands, each silk filament is really double. Within this cocoon 
 of silk the larva casts its caterpillar skin and becomes a pupa. 
 In silk-culture the cocoons are placed in an oven to kill the 
 pupae, and the silk is softened by being placed in warm water. 
 Then, by means of a twig moved about among the cocoons, 
 loose ends of several of them are caught, united into one 
 thread, and wound on a reel, which is placed at a distance 
 from the hot water so that the silk may dry. This is the 
 raw silk of commerce. 
 
 We have several large moths in the United States, expand- 
 ing from ten to fifteen centimeters (four to six inches), whose 
 larvae spin silken cocoons, some of which have been utilized 
 to a limited extent by man. They are magnificent insects, 
 with broad wings beautifully colored, and with large feather- 
 like antennse. The larvae feed on the leaves of forest and 
 fruit trees, and are more or less armed with a variety of 
 colored spines and tubercles. The caterpillars, like other 
 larvse which feed upon plant food, are remarkable for the 
 amount of food which they consume and the great increase 
 in size in early life. The caterpillar of the American silk- 
 worm moth (Te'lea polyphe'mus), which weighs on hatching 
 one twentieth of a grain, increases to ten times its weight 
 within ten days, and to over four thousand times its weight 
 in fifty days. By this time it has consumed over one hundred 
 oak leaves, weighing almost three quarters of a pound, and 
 drunk nearly one half an ounce of water. The larvae of these 
 moths spin conspicuous brown cocoons, which can easily be 
 collected in the winter from the branches and leaves of trees 
 to which they are attached. In the spring the imagoes escape 
 
THE BUTTERFLIES AND MOTHS 
 
 53 
 
 from one end of the cocoons by cutting the silk with a pair of 
 stout spines, one on each side of the thorax, at the base of 
 the anterior wings. 
 
 Underwings. A very striking group of moths is the under- 
 wings (Catoc'ala, Fig. 32), which have the anterior wings in 
 sober tints of brown 
 or gray, but the pos- 
 terior wings black 
 with broad mark- 
 ings of red or yel- 
 low. When at rest, 
 as shown in the 
 figure, the posterior 
 wings are covered 
 and the moth tends 
 to be protectively 
 colored ; but when 
 in flight the broad, 
 contrasting colors 
 are conspicuous. It 
 is usual to account 
 for the coloration of 
 the anterior wings 
 by the principle of 
 
 protective resem- FIG. 32. Underwing at Rest. Reduced 
 
 blance. Some nat- 
 uralists have thought that the bright colors of the posterior 
 wings demand no other explanation than that they have 
 resulted from a natural tendency to bright colors ; while 
 others have suggested that they serve to call attention to a 
 non-vital part. 
 
 Hawk-Moths. The hawk-moths or sphinx-moths (Fig. 33) 
 are easily recognized by the stout conical body, long coiled 
 proboscis, narrow pointed wings, and the slender antennae. 
 
 > 
 
 f 
 
54 
 
 GENERAL ZOOLOGY 
 
 They are dressed, for the most part, 
 
 in quiet olive and brown tints, and fly J 
 
 by day. Their larvae are large, naked //. 
 
 4 
 
 caterpillars, often with a 
 curved horn near the pos- 
 terior extremity. They 
 have the habit of resting 
 with the head and front 
 of the body raised in 
 the air. In this attitude 
 they have been fancied 
 to resemble the Egyptian 
 sphinx. It has been 
 thought by some zoolo- 
 gists that this position is 
 assumed as a terrifying 
 attitude. The tobacco- 
 worm is the larva of the 
 
 FIG. 33. Metamorphosis of Sphinx-Moth. 
 Reduced 
 
THE BUTTERFLIES AND MOTHS 
 
 55 
 
 well-known species, Phlegethon'tim sex'ta (Fig. 33), found on 
 tomato, potato, and tobacco plants. The larva, though often 
 
 credited with poisoning people by sting- 
 ing them with the long curved caudal horn, 
 is in reality entirely harmless. The pupa 
 is remarkable for the long coiled proboscis- 
 case. 
 
 Tussock-Moths. The tussock-moths, 
 though few in number of species and incon- 
 spicuous in the adult stage, are compara- 
 tively well known from their conspicuous 
 larvse, which are clothed with white or 
 brightly colored tufts of hair. The white- 
 marked tussock-moth (NotoV ophus leuco- 
 stiy'ma, Fig. 34) is the commonest species 
 in the eastern United States. The head 
 and some body-spots are bright red. A 
 black stripe runs down the middle of the 
 back and yellow stripes occur on either 
 
 FIG. 34. Metamor- g^e. Long brushes of black hairs are 
 phosis of Tussock- . , -11-1 
 
 Moth. Natural size borne anteriorly and posteriorly, while 
 
 four dense clusters of white hairs stand 
 up prominently from just behind the head. The females are 
 wingless and look more like white grubs than moths. When 
 
56 
 
 GENERAL ZOOLOGY 
 
 they emerge from the cocoons the eggs are laid near by, often 
 on the cocoons. Fig. 34 shows the female in the act of 
 laying eggs in such a situation. 
 
 Observations on the food of birds of the eastern United 
 States seem to show that the spines, tubercles, and hairs, 
 with which many caterpillars are covered (compare Fig. 35, 
 the larva of the regal moth, Cithero'nia rega'lis), form very 
 efficient means of protection, at least from birds, since, 
 
 with the exception of the 
 
 [HI ' - , 
 
 cuckoo, no bird is known to 
 make a practice of feeding 
 on hairy caterpillars. Pro- 
 fessor Poulton of Oxford, 
 England, experimented with 
 a species of tussock-moth 
 from England to determine 
 the part the tufts of hair 
 play in the life-economy of 
 the caterpillar. He says : 
 " A caterpillar of the com- 
 mon vaporer moth (Oryg'ia 
 anti'qua) was introduced in- 
 to a lizard's cage, and when 
 attacked instantly assumed 
 the defensive attitude, with 
 the head tucked in and the 
 tussocks separated and ren- 
 dered as prominent as pos- 
 sible. An unwary lizard 
 seized the apparently convenient projection ; most of the 
 tussock came out in its mouth, and the caterpillar was not 
 troubled further. The lizard spent a long and evidently 
 most uncomfortable time in trying to get rid of its mouthful 
 of hairs." 
 
 FIG. 35. Larva of Regal Moth. 
 Reduced 
 
THE BUTTERFLIES AND MOTHS 57 
 
 Measuring- Worms. The measuring- worms (Fig. 36) are the 
 larva; of a group of medium-sized moths, which afford many 
 illustrations of protective re- 
 semblance. When some of 
 these larvae are at rest, stand- 
 ing out stiff from a twig, it is 
 difficult to believe them to be 
 caterpillars. Most of them 
 have three pairs of legs less 
 than other caterpillars, so that 
 a looping gait is the result, 
 whence the name, " measuring- 
 worms." They have the habit, 
 when disturbed, of dropping 
 to the ground on a silken 
 thread, which they spin as they 
 fall. 
 
 Definition of Lepidoptera 
 (Gr. lepis (lepidos), scale; 
 pteron, wing). The butterflies, 
 skippers, and moths, collec- 
 tively, are spoken of as Lepi- 
 dop'tera. The Lepidoptera 
 have four large wings covered 
 with scales, sucking mouth- 
 parts, and undergo a " com- 
 plete" metamorphosis. The 
 larvae, called caterpillars, with 
 few exceptions, feed upon the 
 leaves of plants. They pass a 
 greater length of time in the 
 pupal stage than the other 
 insects we have thus far con- FR; 36 Measuring _ Worms . Natural 
 sidered. size 
 
CHAPTER VII 
 
 THE FLIES: DIPTERA 
 
 . . . like small gnats and flies as thick as mist 
 On evening marshes. SIIKLLEY. 
 
 House-Flies and Flesh-Flies. The common house-fly (Mus'ca 
 domes' tica, Fig. 37) is a cosmopolitan insect. The eyes are 
 very large, occupying the whole side of the head; the an- 
 tennae are short and composed of only three joints, the third 
 
 bearing a bristle. 
 The mouth-parts 
 are formed for 
 sucking and lap- 
 ping. They consist 
 of a short tongue- 
 like proboscis, with 
 large oval flaps, or 
 lobes, on each side. 
 These flaps are 
 extensile, and are 
 roughened like a 
 file on the inner 
 surface, thus per- 
 mitting of their 
 use as a scraper, 
 by means of which the insect can lap up sweets or other food. 
 The proboscis is made up of the united maxillae. The thorax 
 is globular and bears but one pair of wings, though the rudi- 
 ments of others, called " balancers," can be seen in the form 
 of two little round objects, borne on slender stalks. These 
 
 58 
 
 FIG. 37. Metamorphosis of House-Fly. Enlarged 
 
THE FLIES: DIPTERA 59 
 
 balancers also act as organs of hearing. Two broad scales 
 are found on the sides of the thorax, just behind the wings. 
 The legs are fitted for running, and the pulvilli are large 
 and bear tubular hairs, which secrete a sticky fluid by means 
 of which the fly can walk on smooth surfaces, even when 
 upside down. 
 
 The eggs, over one hundred in number, are laid usually 
 in horse-manure, and hatch within a day into smooth white, 
 almost transparent, conical, footless larvae, called maggots. 
 They have rudimentary mouth-parts, consisting only of a 
 few small hooks. The larvse feed for about a week, growing 
 rapidly and molting twice within that time, and then pass 
 into an inactive pupal stage within the larval skin. In a week 
 more the perfect insect appears by making a circular hole 
 in one end of the pupal case by means of a large bladder- 
 like bulb, which swells out on the forehead and is later with- 
 drawn into the head. The life-history is thus completed 
 within about two weeks, and as the imagoes soon lay eggs, 
 there may be several generations in the course of the summer. 
 On the approach of cold weather most of them die, though 
 some hibernate in sheltered places. 
 
 The house-fly has always been considered a nuisance about 
 the house ; but lately a more serious charge has been laid at 
 its door, that of transporting on the pulvilli and proboscis 
 the germs of typhoid fever.. With the knowledge of its favorite 
 breeding-place it should be possible, by insisting on cleanli- 
 ness in stables, by the daily collection of manure and its dis- 
 posal in a closed place, or by treatment with chloride of lime, to 
 greatly mitigate, if not entirely destroy, this menace to health. 
 
 Equally well known are the blow-fly (Calliph'ora vomito'ria) 
 and the bluebottle (Lucil'ia cae'sar), which deposit their eggs 
 on fresh and decaying meat. These flies hatch within a day, 
 and the larvas greedily devour the decaying material, not 
 hesitating, when that task is finished, to devour each other. 
 
60 
 
 GENERAL ZOOLOGY 
 
 The famous tsetse fly of South Africa (Crlossi'na mor'sitans), 
 whose bite is almost certainly fatal to the ox, horse, and dog, 
 belongs to the same family as the species just mentioned. It 
 has been found almost impossible to build up certain sections 
 of South Africa, owing to the prevalence of this insect. An 
 English army surgeon has lately discovered that by its bite 
 it introduces disease germs from sick animals into the blood 
 of healthy ones. 
 
 Bot-Flies. The bot-flies are parasites in the larval stage ; 
 that is, they live in the bodies of other animals. There are 
 
 B D 
 
 FIG. 38. Metamorphosis of Horse Bot-Fly. (After Osborn, Bulletin No. -5, N.S., 
 United States Department of Agriculture, Division of Entomology) 
 
 A, egg on hair of horse (natural size) ; B, egg on hair of horse (enlarged) ; 
 C, young larva (enlarged) ; D, young larva (much enlarged) ; E, spines ; 
 F, full-grown larva (twice natural size) ; G, female (natural size) 
 
 nearly one hundred species known, infesting various animals, 
 living either under the skin, in the nostrils, or in the stomach. 
 The bot-fly of the horse (G-astroph'ilus e'qui, Fig. 38) attaches 
 its eggs singly by means of a sticky substance to the hairs of 
 the legs, where the larva is pretty sure to be swallowed when 
 the animal licks or bites its legs to remove the irritation. 
 
THE FLIES: DIPTERA 61 
 
 The larva then attaches itself to the lining of the stomach 
 by means of hooks, which encircle the mouth, and for nearly 
 a year feeds on the substance of the stomach-wall. The pupal 
 stage is passed in the earth, which is reached through the 
 alimentary canal. A few of these parasites do 110 particular 
 harm, but a large number may cause death. 
 
 The sheep bot-fly ( (Es'trus o'vis) in a similar manner attacks 
 the nostrils of sheep. The appearance of one of these flies 
 in a flock of sheep is sufficient to throw them into a state 
 of panic ; they run about with their noses between their 
 legs, or try to bury them in dust, to escape their tormentors. 
 The female bot-fly does not lay her eggs as do most other 
 insects, but retains them within her body till they hatch, 
 and then deposits the living young, that is to say, she is 
 viviparous. 
 
 Hover-Flies. Often a collector captures an insect flying 
 about flowers, which has the characteristic manner and yellow 
 and black colors of a wasp, but which has only two wings. 
 It is one of the hover-flies, many of which afford illustrations 
 of protective mimicry. Some species of Eris'talis (Fig. 45) 
 mimic the male honey-bee, and are therefore named drone- 
 flies ; others belonging to Volucel'la (Fig. 45) mimic bumble- 
 bees. The larvae of some feed upon aphids, and are therefore 
 beneficial to the farmer ; others inhabit pools of stagnant 
 water or decaying wood. Several are called rat-tailed larvae, 
 from the presence of a long tube projecting from the pos- 
 terior end of the body, which enables the larva to get air 
 when submerged. The larva of the drone-fly is of this type. 
 Other species are found in ants' nests. 
 
 Mosquitoes. The mosquitoes are a group widely distributed 
 over the tropical and temperate regions of both hemispheres. 
 In nearly all the species observed the mouth-parts of the 
 females only are fitted for piercing the skin of animals. 
 The males, if they feed at all, probably suck the fluids of 
 
GENERAL ZOOLOGY 
 
 plants ; in fact, both sexes in the past history of the race 
 were probably, and are still, to some extent, plant-feeders. 
 
 The common mos- 
 quito of the Missis- 
 sippi valley and the 
 East is Cu' lex pun' gens 
 (Fig. 39). The female 
 lays her eggs in irreg- 
 ular masses, contain- 
 ing over two hundred 
 eggs, on the surface 
 of the water early in 
 the morning. Within 
 a day they hatch, and 
 the larva? are the fa- 
 miliar, active creatures 
 known as "wrigglers." 
 The next to the last 
 Enlarged, somite bears a long 
 s., United respiratory tube 
 
 of Entomology) 
 
 A, egg-mass; -B, larva; C, pupa 
 
 FIG. 39. Development of Mosquito. 
 (After Howard, Bulletin No. 25, N 
 States Department of Agriculture, Division througb wh ; ch the 
 
 larva breathes air when 
 at the surface ; the last 
 somite is provided with four flaps (tracheal gills) which act 
 as organs of respiration when the larva is beneath the surface. 
 In addition to these methods of obtaining air, the skin is 
 capable of absorbing oxygen, and a network of trachea lines 
 the posterior part of the alimentary canal, so that oxygen 
 may be obtained from the water taken in at the anal opening. 
 The Iarva3 feed on small particles of decaying matter in the 
 water, thus being useful as scavengers. After several molts 
 and a life of about a week, if the weather is warm they then 
 pass into the pupal stage, breathing by means of two air- 
 tubes arising from the thorax. In about two days the pupal 
 
THE FLIES: DIPTERA 63 
 
 skin splits down the back and the imago works itself out of 
 its old skin, dries its wings, and flies away. Cold weather 
 retards these changes considerably. 
 
 Great interest attaches to the mosquitoes by reason of the 
 recent indictment that some species transmit malaria and 
 yellow fever. Malaria is carried by mosquitoes belonging to 
 the genus Anoph'eles, 
 the females of which 
 may be distinguished 
 from the females of 
 Culex by the greater 
 length of the palpi FlG - 40 - Resting Positions of Anopheles and 
 
 The males of both Culex ' Slightly enlarge(L < After Grassi) 
 genera can be distinguished from the females by their more 
 feathery antennae. Anopheles shows a tendency, especially 
 on horizontal surfaces, to alight with the hind end of the 
 body raised at a considerable angle to the surface ; Culex 
 holds the body parallel to the surface. In Anopheles the 
 body and beak are in the same plane no matter what the 
 position is ; Culex is humpbacked, with the beak pointing 
 downward. These various distinctions are well shown in 
 Fig. 40. The disease known as malaria is caused by the pres- 
 ence in the blood of a parasitic organism, one of the lowest 
 forms of animal life, known as Plasmo'dium mala' rice. Its rapid 
 development at certain stages produces the well-known fever 
 connected with the disease. The life-history of the organism 
 is described in Chapter XXI. The most extensive experi- 
 ments concerning the connection between the Anopheles 
 mosquito and malaria have been carried on by the British 
 Colonial Office and the British School of Tropical Medicine. 
 Two physicians, under the auspices of these institutions, estab- 
 lished themselves in the fever-infected Roman Campagna. 
 They took no special precaution against the disease, drinking 
 the water of the district and in other ways conforming to the 
 
64 GENERAL ZOOLOGY 
 
 customs of the people, save only that they did not allow them- 
 selves to be bitten by the Anopheles mosquito, which swarms 
 in that region at the close of day. They slept during the 
 night in a mosquito-proof house, and did not contract malaria. 
 Persons, on the other hand, with no traces of malaria, have 
 allowed themselves to be bitten, and thus contracted the 
 disease. It seems, from these and other experiments, that the 
 malarial parasite is injected into the blood with the saliva of 
 the insect, and it further appears that, in order to complete 
 the life-history of the parasite, it must enter the salivary 
 gland of the mosquito. Quinine is a specific, because it kills 
 the organism at a certain stage in its life-history. United 
 States army surgeons in Cuba have been instrumental in 
 clearing up the life-history of the yellow-fever germ, which 
 seems to be transmitted by mosquitoes of the genus Stegom'yia. 
 
 Many localities can be practically rid of these pests by the 
 drainage of the swamps or ponds in which they breed; by 
 the use of kerosene on the surface of such waters ; or by 
 the introduction of fish that feed on the larvse. Among the 
 fishes recommended are sunfish and sticklebacks. It must 
 be remembered that the insect will breed successfully in any 
 transient pool of water, or in any receptacle where water is 
 left standing long enough for the changes just described to 
 take place. Experiments are being conducted in the Middle 
 West with a fungous disease similar to that which destroys 
 large numbers of flies in the autumn. 
 
 Definition of Diptera (Gr. dipteros, two-winged). The in- 
 sects collectively called flies agree in the possession of two 
 wings, the place of the posterior pair being taken by the bal- 
 ancers, which may therefore be considered reduced wings. 
 The flies belong to the order Dip'tera. The Diptera have the 
 mouth-parts fitted for sucking or piercing. They undergo a 
 " complete " metamorphosis. The larvse are commonly known 
 as maggots. 
 
CHAPTER VIII 
 THE ANTS, BEES, AND WASPS : HYMENOPTERA 
 
 For so work the honey-bees, 
 Creatures that by a rule in nature teach 
 The art of order to a peopled kingdom. 
 
 SHAKESPEARE, King Henry V. 
 
 Social Wasps. The common brown wasps (Polis'tes, Fig. 41) 
 are interesting on account of their communal life in nests of 
 paper made from wood-pulp. The mouth-parts are fitted both 
 for biting hard substances and also for lapping the fluids of 
 plants. The mandibles are much the same as in such biting 
 insects as the locusts ; the first maxillae are elongate, sharp- 
 pointed, lance-like organs, and the second maxillse are modi- 
 fied into a flexible, tongue-like structure covered with hairs, 
 to which sweets adhere. There are four membranous, trans- 
 parent wings, with few veins. The female is provided with 
 a formidable sting, an important means of defense, 
 which is in origin a modified ovipositor. 
 
 Early in the spring a female Polistes, which has wintered 
 in a crevice, begins the construction of a nest in some suitable 
 place, either on the under side of a roof, especially in deserted 
 houses or barns, or on the ground beneath a stone. If there 
 are fences or barns in the region, she will very likely obtain 
 a supply of wood from them ; if not, from stumps and dead 
 trees. After being chewed by her and moistened by a secre- 
 tion from her mouth, this material is fashioned by the feet 
 and mandibles into circular cells, which become hexagonal 
 as their number is added to and the pressure increases. The 
 whole is waterproofed by a glutinous secretion, which is 
 said to be increased in amount in those cells which are most 
 
 65 
 
66 GENERAL ZOOLOGY 
 
 exposed to the weather. As soon as one cell is finished the 
 female lays an egg in it, and to her duty of enlarging and 
 strengthening the nest she soon lias to add the care of the 
 footless, worm-like larvae, which hatch in a few days. These 
 are fed with both plant and animal food, the former consist- 
 ing of nectar which has been swallowed and later regurgitated 
 (i.e. thrown back after being swallowed) ; the latter, of cater- 
 pillar meat chopped fine by the mandibles and worked into 
 a jelly-like mass. In about three weeks' time the first-born 
 larvae spin a silken lining and covering to the cell and pass 
 into an inactive pnpal stage. Three weeks later the first 
 imagoes appear, after having cut a circular opening in the 
 end of the cell. 
 
 These first imagoes differ somewhat from their mother, 
 and are really imperfectly developed females, called neuters, 
 or workers. They have the power, under certain conditions, 
 of laying eggs, but their eggs never produce true females. 
 Generally the workers attend strictly to the business of caring 
 for the young and repairing and enlarging the nest. They 
 assume care of the young at about the third day. 
 
 This habit may be due primarily to imitation of the female, 
 whom the worker sees repeating the act while it is waiting 
 for the hardening of its tissues, or to the early development 
 of an instinctive tendency to perform the act (see p. 85). 
 Experiments performed by Dr. Enteman of the University 
 of Chicago, in which newly developed workers were given 
 bits of food at intervals before they had had any association 
 with others of their kind, seem to show that it is an instinct 
 which appears very early, but not at the same time with 
 all workers. When it does appear, owing to the presence of 
 food furnished by the female, the steps are, according to 
 Dr. Enteman, " first the crushing and molding, then a slow 
 walking around the nest with frequent pauses, and, if larvae 
 are present, the pinching off of the food bit by bit until all 
 
THE ANTS, BEES, AND WASPS 67 
 
 has been disposed of. If no larvse are present, if, for 
 instance, the young worker is living in an inverted tum- 
 bler and has never seen a larva, the various stages of the 
 process are the same." The instinct does not appear in per- 
 fection at first, for the same author notices that it takes a 
 young worker about three times as long to feed the larvae as 
 the female requires, and that a great deal of time is lost by 
 the new worker " in poking its head into the wrong cells 
 and running unnecessarily about over the face of the nest." 
 
 FIG. 41. Paper-Making Wasp and Nest. Natural size 
 
 The workers surely do not appreciate the character of their 
 task, for the observer just quoted has seen a young worker 
 gnaw a piece out of the body of a dead larva and offer it as 
 food to the mouth of the same larva; and, she continues, 
 " I once observed a neuter attack a live larva, and after she 
 had cut out and crushed a fair-sized piece of its body, come 
 back eight times in the course of her examination of the 
 cells of the nest, to this larva, which naturally had died in 
 the operation, and offer it this part of its own body, with the 
 evident expectation that it would be seized and eaten. .The 
 eighth time she dropped the piece on the face of the dead 
 larva and went away with an air of ' duty well done ' which 
 was comical to behold." 
 
68 GENERAL ZOOLOGY 
 
 From the time the workers take up the tasks of the nest 
 the female is left free to devote all her energies to laying 
 eggs, and the nest is rapidly made larger by the workers. 
 Toward September males and females appear from the cells, 
 which up to this time have produced only workers. The males 
 die soon after mating. On the approach of cold weather, the 
 workers also die, and only females remain to hibernate and 
 begin a new nest the next spring. 
 
 Another type of nest, in which the horizontal layers are 
 inclosed in a thin envelope, is made by the somewhat larger 
 and stouter-bodied wasps (Ves'pa, Fig. 45) commonly known as 
 " hornets." These wasps are generally conspicuously marked 
 with yellow, and their nests may be a foot and a half in 
 diameter. 
 
 The social wasps are the original paper-makers of the world. 
 The first suggestion as to the manufacture of paper by man 
 may have come from watching the work of these insects, 
 though the necessary steps may well have been taken without 
 such suggestion, as the use of the leaves of palms and the 
 bark of several trees is still common in China and India. It 
 is interesting to note that though the wasps were the original 
 inventors of paper, they have, in some cases, learned to take 
 advantage of man's present greater facilities for its manufac- 
 ture, thus saving themselves the trouble. In one case in 
 Missouri the wasps found the damp paper of bags, which 
 had been tied over grape-clusters in a vineyard to keep out 
 injurious insects, so much to their liking that they used it 
 freely instead of their own wood-pulp paper. 
 
 Solitary Wasps. Those wasps which are solitary in habit 
 make nests in various situations and of different materials, 
 and store them with food, generally insects and spiders, which 
 they often sting so as to paralyze but not to kill them. Each 
 species has its own method of providing food, and each keeps 
 pretty closely to the same material for nest-building. Thus 
 
THE ANTS, BEES, AND WASPS 
 
 69 
 
 the common mud-dauber (Pelopce'ua, Fig. 42), seen flying 
 about on sunny days over the muddy edges of puddles and 
 pools, builds its nests of clay and provisions them with 
 spiders. Each cell is filled with paralyzed spiders ; on top 
 
 FIG. 42. Mud-Dauber and Nest. Natural size 
 
 one egg is laid and the cell is sealed. When the larva hatches 
 it finds the requisite amount of food to carry it to the pupal 
 stage. These wasps are distinguished by the long pedicel, or 
 stalk, joining the thorax to the abdomen. 
 
 The digger-wasps of the West, which belong to the genus 
 Ammoph'ila (Fig. 43), make holes a little over a centimeter 
 
TO GENERAL ZOOLOGY 
 
 (about half an inch) in diameter and two or three centimeters 
 deep, in the hard, sun-baked earth, often choosing a place 
 beneath the protection of the leaf of some plant. These holes 
 they provision with caterpillars, which they sting in several 
 
 FIG. 43. Digger- Wasp using Pebble. Enlarged 
 (From Peckham's The Solitary Waspa) 
 
 places till they are paralyzed. In the process of provisioning 
 the nest some species close the opening with a pellet of 
 earth or with small stones, which they remove when they 
 return with a new caterpillar. Dr. and Mrs. Peckham, who 
 have studied these insects very carefully, say that this is, 
 however, not an invariable habit, some individuals leaving 
 the nest open while searching for more caterpillars. These 
 authors have this to say of the habits of one of these 
 insects. 
 
 " Just here must be told the story of one little wasp whose 
 individuality stands out in our minds more distinctly than 
 that of any of the others. We remember her as the most 
 fastidious and perfect little worker of the whole season, so 
 
THE ANTS, BEES, AND WASPS 
 
 71 
 
 nice was she in her adaptation of means to ends, so busy 
 and contented in her labor of love, and so pretty in her pride 
 over her completed work. In rilling up her nest she put 
 her head down into it and bit away the loose earth from the 
 sides, letting it fall to the bottom of the burrow, and then, 
 after a quantity had accumulated, jammed it down with her 
 head. Earth was then brought from the outside and pressed 
 in, and then more was bitten from the sides. When, at last, 
 the filling was level with the ground, she brought a quantity 
 of fine grains of dirt to the spot, and, picking up a small 
 pebble in her mandibles, used it as a hammer in pounding 
 them down with rapid strokes, thus 
 making this spot as hard and firm as 
 the surrounding surface. Before we 
 could recover from our astonishment 
 at this performance she dropped her 
 stone and was bringing more earth. 
 We then threw ourselves down on the 
 ground, that not a motion might be 
 lost, and in a moment we saw her pick 
 up the pebble and again pound the 
 earth into place with it, hammering 
 now here and now there, until all was 
 level. Once more the whole process 
 was repeated, and then the little crea- 
 ture, all unconscious of the commotion 
 that she had aroused in our minds, un- 
 conscious, indeed, of our very existence, 
 and intent only on doing her work and 
 doing it well, gave one final comprehen- 
 sive glance around and flew away." 
 
 A common North American species of solitary wasp 
 (Eume'nes frater'nus, Fig. 44) builds a pretty little jug- 
 shaped nest of clay or mud, which it attaches to vegetation 
 
 FIG. 44. Mason- Wasp and 
 
 Nest. Natural size 
 
72 GENERAL ZOOLOGY 
 
 and provisions with caterpillars. The young, when full- 
 grown, escape through a hole which they cut in the side of 
 the nest, as shown in the figure. 
 
 The Honey-Bee. The life-history of the honey-bee (A' pis 
 mellif'ica, Fig. 45) has been quite well understood for a long 
 time. This insect offers a most interesting illustration of a 
 society all the members of which act together for the good 
 of the community. In their community specialization of work 
 has been developed to a remarkable extent. The honey-bee, 
 originally a native of the eastern hemisphere, possibly from 
 the region along the eastern shore of the Mediterranean Sea, 
 has been domesticated from very early times for the sake of 
 its two important products, honey and wax. Escaped swarms 
 in this country have become the wild honey-bees, which nest 
 in hollow trees. In early summer a bee community in good 
 condition may contain from twenty-five to thirty-five thousand 
 workers, several hundred males, called drones, but only one 
 female, called the queen bee. The queen bee may be distin- 
 guished from the workers and drones by her larger size ; the 
 drones are stouter than the workers. 
 
 Upon the workers devolves most of the labor in connection 
 with the life of the community. They secrete the wax and 
 fashion it into the cells of which the home is composed. , 
 They bring water to the hives. They collect nectar from 
 flowers and later regurgitate it and ripen it into honey ; they 
 bring pollen to mix with nectar to make " bee-bread," and 
 gather propolis, a gummy substance from the bud-scales of 
 certain trees, especially the poplar, for filling crevices and 
 covering foreign objects which are too. big to remove from 
 the nest. When the young are hatched the workers act as 
 nurses and housekeepers for the community, feeding the 
 young and keeping the hive free from all substance which 
 might decay. In warm weather some of them may be seen 
 at the entrance and along the passageway, keeping the air in 
 
THE ANTS, BEES, AND WASPS 73 
 
 motion with their wings, thus setting up a current which 
 provides air and helps ripen the honey by evaporating the 
 water in it. Finally, as every one knows, they are the defend- 
 ers of the hive, and by their great numbers and formidable 
 stings they constitute a body-guard of no mean pretensions. 
 
 The name " queen bee " is misleading, if it suggests any con- 
 trol or management of the affairs of the hive. She is carefully 
 guarded by the workers, but that is on account of her impor- 
 tance to them as the only fertile female in the community, 
 though they can, as we shall see, produce other queens from 
 eggs which were destined for workers, if necessity arises. As 
 far as having any power to rule is concerned, she is, in reality, 
 ruled by the workers. It is her function to lay the eggs from 
 which all the other members develop. Those eggs destined 
 to become workers are laid in cells of ordinary size ; those 
 which are to become males are placed in slightly larger cells ; 
 while those which are to become queens, though differing in 
 no way at first from those which produce workers, are placed 
 in special " royal " cells, much larger and of an irregular 
 shape. They are, of course, few in number compared with 
 the others. 
 
 When the eggs hatch, all the larvae are fed for several 
 days on a jelly-like substance consisting of regurgitated 
 food mixed with a secretion from glands in the heads of 
 the workers and poured out from their mouths. After this 
 the workers and males receive "bee-bread," a mixture of 
 pollen and honey, while the young queens are continued on 
 their diet of elaborated material, " royal jelly," furnished by 
 the workers. When for any reason a hive loses its queen, the 
 workers proceed to break down the walls between three adja- 
 cent cells containing worker larvse, kill two of the occupants, 
 and bring the third to maturity as a queen by the use of royal 
 jelly. The first eggs laid in the spring produce workers ; the 
 males are produced from unfertilized eggs laid by the queen. 
 
74 GENERAL ZOOLOGY 
 
 When the larva is full grown no more food is supplied to it 
 and the cell is sealed with a waxen cover. Within this prison 
 the larva spins a cocoon and changes to a pupa. Within three 
 weeks from the laying of the egg the worker bee cuts a hole 
 in the covering of its cell and emerges. A queen is produced 
 in somewhat less time ; a drone requires slightly longer. 
 
 In late spring or early summer, as the colony has increased 
 in size, the time approaches for one of the new queens to 
 appear from the pupal stage. A peculiar noise may be heard, 
 made probably by the wings of the imprisoned queen. Part 
 of the ordinary work of the hive is neglected, and the old 
 queen rushes forth with a large number of the community, 
 generally alighting in a palpitating mass on some near-by 
 tree or other support. This is the " swarming" of the bees. 
 If provided with a new hive, they will generally settle down 
 quietly in their new home. Bees are particular as to the* 
 state of the weather at the time of swarming, appearing only 
 when the sky is clear. The workers carry a store of honey 
 in their crops, as if prepared for a long trip, which in a state 
 of nature may often have occurred before the bees could find 
 a hollow tree or crevice among rocks suitable for a home. 
 The swarming serves the purpose of lessening the chances 
 of a total extinction of the species, by increasing the number 
 of communities. 
 
 Meanwhile the new queen appears in the old hive, and 
 after a flight in the 'air with the drones, during which ferti- 
 lization occurs, she settles down to her duty of egg-laying. 
 This flight and the swarming are the only occasions upon 
 which the queen leaves the hive. The. number of swarms 
 thus given off varies with the size of the original community, 
 and seems to depend somewhat on climatic conditions. It is 
 not uncommon to have three swarms in a season. When the 
 community is to send out no more swarms, the queen is per- 
 mitted to sting the other young queens to death. If by any 
 
THE ANTS, BEES, AND WASPS T5 
 
 chance two queens meet, a conflict begins at once, and the 
 usual result is the death of one of them. This is often spoken 
 of as due to the jealousy of the queens, but it may have a 
 meaning in connection with the necessity the community is 
 under of sending out swarms to maintain a separate existence. 
 The sting of the queen is used only in these battles and 
 in slaying the young queens. At the end of the swarming 
 season the workers set upon the drones and kill them, casting 
 their dead bodies out of the hive. The queens live for several 
 years, depositing two or three thousand eggs a day during a 
 part of the season. The workers live, as a rule, less than two 
 months. 
 
 The wax of which the cells of the comb are composed is 
 secreted in the form of thin plates in " wax-pockets " beneath 
 some of the abdominal somites. While preparing this, full- 
 fed workers hang motionless to the cells in the upper part of 
 the hive, and in about twenty-four hours the wax appears. 
 This is removed by other workers and is used in construc- 
 tion. Honey is made for food for the young and for winter 
 consumption of the colony. The pollen of flowers is brought 
 to the hive in " pollen-baskets," clear spaces surrounded by 
 hairs on the outer side of the hind tibiae. The basal joints of 
 the hind tarsi are much enlarged, and are used as brushes 
 to gather the pollen. 
 
 Bumblebees and Guest-Bees. The bumblebees (Bom'bus, 
 Fig. 45) are social bees, having homes in fields, in deserted 
 mouse-nests and similar places. The nest is begun early in 
 the spring by a female which has wintered, and, as with the 
 social wasps, the burdens of the home are turned over to the 
 young workers when they emerge. Late in the season other 
 females and males appear, but there is no swarming as with 
 the honey-bee. On the approach of cold weather the workers 
 and males die. The honey made is strong-smelling, but much 
 sought after by boys in the country, perhaps as much for the 
 
76 
 
 GENERAL ZOOLOGY 
 
 danger connected with its capture as for the sake of the honey 
 itself. Boys in the West rob the bees by placing a gallon jug 
 partially filled with water in the vicinity of the nest and 
 thoroughly arousing the members of the community. The 
 boys make good their escape to a safe distance, and the bees, 
 perceiving the jug, fly to its open mouth, which echoes the 
 buzzing of their wings. Angered by the sound, some bees fly 
 
 Mimicked Forms, Insects with means of defense 
 The honey-bee A wasp A bumblebee 
 
 (Apis mellifica) (Vespa occidentalis) (lloinbus Howardii) 
 
 Mimicking Forms, Insects without means of defense 
 A fly A beetle A fly 
 
 (Eristalis latifrons) (Clytus niurginicollis) (Vohicella evecta) 
 
 FIG. 45. Mimicked and Mimicking Insects. Natural size. 
 
 From photographs 
 (From Hunter's Studies in Insect Life) 
 
 into the mouth of the jug, thus adding to the noise and 
 attracting others. It is said that with two disturbances of the 
 nest the worker bees can all be captured. 
 
 There are several bees called guest-bees (Psith'yrus), which 
 live in the nest of the bumblebees, apparently on good terms 
 
THE ANTS, BEES, AND WASPS 
 
 77 
 
 with them, though they do not, so far as known, perform 
 any useful function. Their eggs are laid with the eggs of 
 the bumblebees, and the larvae feed on the food which the 
 bumblebees provide for their own young. Some of the guest- 
 bees resemble their hosts quite closely ; others are different 
 in appearance, so that it cannot be said in all cases that the 
 bumblebees are deceived by the resemblance. One effect of 
 
 '- 
 
 FIG. 46. Leaf-Cutter 
 Bee and Nest. 
 Natural size 
 
 the dependence of 
 the guest -bees on 
 their hosts is seen 
 in the absence from 
 the hind legs of 
 the former of the 
 pollen-collecting 
 and pollen-carrying 
 organs, which have 
 probably been lost through disuse. It has been observed that 
 the bumblebees sometimes resent the introduction of one of 
 the guest-bees into their nest, though they may later become 
 accustomed to it and make no further trouble. 
 
 Solitary Bees. There are solitary bees, just as there are 
 solitary wasps. Their habits are very diverse ; some make 
 nests of mud or dig tunnels in the ground ; some are car- 
 penters, boring into wood ; and others are leaf-cutters, taking 
 circular pieces out of leaves, which they use to line their 
 
78 GENERAL ZOOLOGY 
 
 nests. Fig. 46 represents the work of one species, the leaf- 
 cutter bee (Megachi'le acu'ta), which makes long tunnels in 
 wood or in the ground. The eggs are laid singly on a paste 
 of nectar and pollen, which is placed carefully in a leaf-lined 
 cell and covered with a circular lid. Several such cells are 
 generally to be found in one nest. 
 
 Ants. Ants have long been considered models of industry. 
 In many respects some of the features of their life-history 
 are the most remarkable of anything in the insect-world. So 
 specialized have the members of the community become in 
 some cases that there are not only males and females, but 
 large and small workers (workers major and minor), and 
 soldiers for the defense of the colony. Ants build nests in 
 the ground, piling up the material taken out for their bur- 
 rows in the characteristic ant-hills ; or they make tunnels 
 in wood. Some inhabit the interior of thorns or the hollow 
 stems of grasses ; others live on certain trees, from which 
 they obtain all their food, forming a kind of body-guard by 
 defending the tree from the attacks of various enemies. The 
 food of ants is both animal and vegetable, the former consist- 
 ing of other insects, the latter of plant fluids. They are also 
 extremely fond of the sweet substance called " honeydew," 
 furnished by the aphids and some few other insects. 
 
 The eggs are, of course, extremely minute, and hatch into 
 footless larvao, which resemble those of the bees and wasps. 
 The workers take great care of the young, feeding them 
 and moving them about in conformity with changes in tem- 
 perature and amount of moisture. Among ants generally, 
 the workers feed not only the young but even give up food 
 to each other, when this is demanded by a stroke of the an- 
 tennae. The pupal stage is generally passed in silken cocoons. 
 These are the so-called " ant-eggs," which are the objects of 
 much solicitude when a nest is exposed. The imagoes are 
 unable to escape from the pupal case without the help of the 
 
THE ANTS, BEES, AND WASPS T9 
 
 workers. The males and females are at first winged, and 
 take flight in great numbers into the air on some warm day 
 in spring. At this time fertilization occurs. On their return 
 the males soon die, and the females, stripping off their wings, 
 become the mothers of colonies. The females can be distin- 
 guished from the workers by their larger size and the presence 
 of well-developed ocelli. 
 
 Many other insects, especially beetles, live habitually in the 
 nests of ants, and, in some cases at least, seem to perform some 
 useful function, acting as scavengers, for instance. These 
 cases, like that of the bumblebees and guest-bees, may be 
 cited as illustrations of commensalism (Lat. com ( = cum\ to- 
 gether ; mensa, table), an association of one species of animal 
 with another for support or advantage, but not as a parasite. 
 
 An illustration of cooperation between two different species 
 of animals is shown in certain ants and aphids. The corn-louse 
 ant '(La'sius) collects the eggs and young of a species of aphid 
 (A'plds mai'dis), which attacks the roots of corn in the Middle 
 States, and guards them throughout the winter in subterra- 
 nean burrows, so as to provide a constant supply of " honey- 
 dew." Some ants build a shelter of wood-pulp or mud over 
 colonies of aphids, which are crowded on a branch, from which 
 they derive their nourishment. These aphids are often spoken 
 of as the cows of the ants. In these cases the relation between 
 the ants and aphids is clearly of a more intimate character 
 than the association of the bumblebees and guest-bees; and 
 the advantages are mutual, for while the ants secure a con- 
 stant supply of food, the aphids receive care and a certain 
 amount of protection against their enemies. This association 
 is spoken of as symbiosis (Gr. syn, together ; bios, life). 
 
 An ant found in eastern Asia lives in shelters which it 
 forms on the leaves of trees by fastening the edges of the 
 leaves together. The imagoes have no sticky secretion for 
 this work, but the larvse have glands which furnish such a 
 
80 
 
 GENERAL ZOOLOGY 
 
 secretion for the purpose of spinning their cocoons. The 
 imagoes seize the larvae in their jaws, rubbing them backward 
 and forward over the edges of the leaves, when the sticky 
 
 FIG. 47. Tunnels of a Mexican Blind Ant 
 
 secretion is poured out and the edges of the leaves are drawn 
 together and kept there. 
 
 Fig. 47 shows the tunnels of a species of blind ant from 
 Mexico, on the trunk of a "wild fig." The tunnels serve as a 
 safe means of communication between the nest underground 
 and the leaves of the tree. 
 
 The honey-ant of Texas (Myrmecocys'tus mel'liger) has one 
 set of workers peculiarly modified to act as storage vessels 
 for sweets. The abdomens of these are distended with a store 
 of grape-sugar, till they are as large as a currant. These 
 workers cling to the roof of the nest, and in times of famine 
 can be drawn upon for food by the other workers. 
 
THE ANTS, BEES, AND WASPS 
 
 81 
 
 The agricultural ant (Myrmi'ca molefac'iens), of the same 
 region, clears large spaces, often several feet in diameter, 
 cutting down all vegetation growing thereon, and rears a 
 grain-bearing grass, storing its seeds in subterranean chambers. 
 Several kinds of ants have the habit of attacking other kinds 
 and carrying off their pupse. In one (Formi'ca sanguin'ea), a 
 small reddish species, the habit has become firmly fixed, and 
 periodical raids are made upon a larger black species, which 
 are afterwards raised in the nests of their captors. One ant 
 of a slave-making tendency, found in Europe (Polyer'gus 
 rufes'cens), has carried the habit so far that it has lost the 
 power of feeding and taking care of itself, depending entirely 
 on the exertions of its servants. The wars of ants have been 
 known for a long time, and many accounts are extant of the 
 fierceness of the struggle between opposing armies. 
 
 Gall-Flies and Ichneumon-Flies. The gall-flies form many 
 of the swellings on plants, known as galls. A common gall- 
 fly of the oak 
 (Amphib'olips) 
 is shown in Fig. 
 48. The gall is 
 caused by the 
 female laying 
 an egg in the 
 leaf- tissue, 
 which swells up 
 when the larva 
 hatches, owing, 
 
 perhaps, to the 
 
 FIG. 48. Gall-Fly . Natural size 
 presence of some 
 
 irritating substance. The young feed on the material of the 
 gall until they are ready to go into the pupal stage. Many 
 of these galls harbor also guest gall-flies, living with the 
 others as commensals. 
 
GENERAL ZOOLOGY 
 
 Closely allied to the gall-flies are the ichneumon-flies, one 
 of which, O'phion, is shown in Fig. 49. This species deposits 
 its eggs in the burrows of a wood-boring larva by means of its 
 long ovipositor, and the ichneumon larva on hatching moves 
 along in its burrow until it finds its host, when it fastens 
 itself to it and destroys it by sucking its blood. This carniv- 
 orous habit may be regarded as an approach to parasitism. 
 Many of the ichneumon-flies are true parasites in the larval 
 stage, the eggs being deposited on the skin or in the body 
 
 FIG. 49. Ichneumon-Fly. Natural size 
 
 of the caterpillars, upon the fluids of which the ichneumon 
 larva feeds. The pupal stage is generally passed within the 
 body of its victim. 
 
 Saw-Flies. The saw-flies differ from all the insects so far 
 discussed in this chapter in having the base of the abdomen 
 as broad as the thorax. The ovipositor of the female consists 
 of a pair of saws, which are used to make slits in the leaves 
 and stems of plants, in which she deposits her eggs. Fig. 50 
 shows the American saw-fly (Cim'bex america! no) , our largest 
 species. The larva looks like the caterpillar of a butterfly or 
 moth, but has more legs. It has the curious habit of coiling 
 the posterior end of its body about a branch, as shown in the 
 illustration. It forms a brown cocoon in which the winter is 
 passed in the ground. An Australian saw-fly is credited with 
 staying with its eggs till they hatch, afterwards brooding over 
 the young with outstretched legs, and protecting them by all 
 the means in her power. 
 
THE ANTS, BEES, AND WASPS 
 
 83 
 
 Definition of Hymenoptera (Gr. hymen, membrane ; pteron, 
 wing). The insects which we have been considering in this 
 chapter all agree in possessing mouth-parts adapted both to 
 
 FIG. 50. Metamorphosis of Saw-Fly. Natural size 
 
 biting and lapping, and four membranous wings with few 
 veins. The order is called Hymenop'tera. A structural pecul- 
 iarity is the union of the first abdominal somite to the thorax, 
 so tl]^t the division between what appears to be the thorax 
 and the abdomen comes after the first abdominal somite. 
 The Hymenoptera undergo " complete " metamorphosis. The 
 larvse are called maggots. 
 
CHAPTER IX 
 THE INSECTS : HEXAPODA 
 
 Though numberless these insect tribes of air, 
 Though numberless each tribe and species fair, 
 Who wing the moon, and brighten in the blaze, 
 Innumerous as the sands which bend the seas ; 
 These have their organs, arts, and arms, and tools, 
 And functions exercised by various rules. 
 
 H. BROOKE, Universal Beauty. 
 
 Definition of Hexapoda (Gr. hex, six; pom ('pod), foot). 
 The previous chapters have been devoted to entomology, that 
 branch of zoology which treats of insects. The insects belong 
 to the class Hexap'oda, the most numerous of all classes 
 of animals, comprising four fifths of the animal kingdom. 
 Insects are built externally upon the plan of a series of 
 somites, grouped in three regions and with segmented ap- 
 pendages on two of them, the head and thorax. Except 
 in very few cases, where this number is reduced, the imagoes 
 have six legs. Hexapods are found in every variety of situa- 
 tion, though they are, as a whole, adapted to life on the land 
 and in the air. A system of tracheae is universally present 
 in the imagoes, though the young of some species have tra- 
 cheal gills for breathing in the water. 
 
 The hard chitinous covering (exoskeleton) necessitates fre- 
 quent molts to provide for increase in size. The molts may 
 or may not be accompanied by metamorphosis. The most 
 marked change of form is seen in the Coleoptera, Lepidop- 
 tera, Hymenoptera, and Diptera. In the first three of these 
 orders, and in some Diptera, while the change in external 
 form is often considerable, most of the larval organs persist 
 
 84 
 
THE INSECTS: HEXAPODA 85 
 
 in the imago, even though they undergo considerable modi- 
 fication in the process of transformation. In that division of 
 the Diptera represented in our account of the order by the 
 house-flies, flesh-flies, bot-flies, and hover-flies, the change from 
 the larva to imago is so complete that nearly all the larval 
 organs are disintegrated and the organs of the imago are 
 built from separate masses of cells (imaginal disks or buds) 
 which alone escape destruction. The breaking-down of the 
 larval tissues is due to the activity of certain white blood-cells 
 called phagocytes (voracious cells). It has been suggested that 
 the escape of the imaginal disks from the general destruction 
 is due to the fact that these masses of cells alone remain func- 
 tional during the transition period between larva and imago. 
 
 All through the class a division of labor has been reached, 
 in which the young feed and build up the material for the 
 imagoes, which reproduce the species. 
 
 Instinct and Intelligence in Insects. Some of the most inter- 
 esting questions in zoology are those dealing with the various 
 reactions of animals to external objects, the general sub- 
 ject of the behavior of animals. Some actions we explain as 
 due to instinct, others we say are accompanied by intelligence, 
 and still others we believe to be governed by reason. There 
 is the widest possible difference of opinion among naturalists 
 as to the relative importance of each of these in the life of 
 the lower animals. Indeed, there is as yet little uniformity 
 in the definition of the terms themselves, so that in our dis- 
 cussion of this subject in the class of insects we shall follow 
 Professor Lloyd Morgan, of England, in his book, Animal 
 Behavior, by defining as instinctive those acts which are simi- 
 larly performed by all the members of a group of animals ; 
 which are, on their first occurrence, independent of experi- 
 ence ; and which tend, usually, to the well-being of the 
 individual and the preservation of the race. The act of the 
 newly hatched larva of the milkweed-butterfly in devouring 
 
86 GENERAL ZOOLOGY 
 
 its egg-shell would therefore be called instinctive, as would 
 the behavior of Pronuba in pollinating the yucca. 
 
 Dr. and Mrs. Peckham, in their work, The Solitary Wdsps, 
 from which we have quoted before, enumerate eight primary 
 instincts : 
 
 1. Stinging. 
 
 2. Taking a particular kind of food. 
 
 3. Method of attacking and capturing prey. 
 
 4. Method of carrying prey. 
 
 5. Preparing nest and capturing prey, or the reverse. 
 
 6. The mode of taking prey into the nest. 
 
 7. The general style or locality of nest. 
 
 8. The spinning or not spinning of a cocoon, and its specific form 
 when made. 
 
 Some instincts seem to be little more than direct responses 
 of the nervous system of the animal to external exciting 
 causes (see paragraph 011 reflex action, Chapter XVI, p. 208). 
 Thus it is well known that moths and some other night-flying 
 insects show a positive reaction toward light, which, under 
 certain conditions, may tend toward the destruction of the 
 insects, as may be seen about electric arc-lights in city parks 
 in summer. The blow-fly is attracted to the decaying meat 
 in which it lays its eggs by the chemical substances given 
 off, which are perceived by the fly's sense of smell. Experi- 
 ments on certain caterpillars seem to show that their life is 
 largely determined by their positive reaction to light, their 
 negative reaction to gravity, these two combining to compel 
 the caterpillars to crawl upward, and a contact reaction 
 with the convex terminal buds, tending to hold the cater- 
 pillar in place when at the end of twigs. When branches 
 were inverted and placed in a receptacle in which certain 
 caterpillars were, the latter remained at the top of the twigs, 
 though food was only a few inches away, showing that the 
 caterpillars were not normally attracted to their feeding-place 
 at the ends of twigs merely by the presence of food there. 
 
THE INSECTS: HEXAPODA 87 
 
 Actions which are due to the results of individually 
 acquired experience, and which are performed without reflec- 
 tion or deliberation as to the means to be employed, or knowl- 
 edge of the end to be reached, are termed intelligent actions 
 by Professor Morgan. The behavior of that particular Ammoph- 
 ila observed to make use of a stone to pound down the sand 
 over her nest may be called intelligent, using the word in 
 the sense just defined. The power possessed by the honey-bee, 
 bumblebees, and other Hymenoptera, of finding their way 
 back to the nest, often from a considerable distance, may be 
 dependent on a knowledge of the locality acquired in their 
 various trips. If so, it would be an example of an intelligent 
 action. Many of the habits of ants already described should 
 probably be included here. 
 
 The word " intelligent " is commonly used to cover another 
 and quite different class of activities, which demand separate 
 consideration. To those activities which are guided in accord- 
 ance with a plan which takes into consideration both the ques- 
 tion of means to be employed and the end to be reached 
 Professor Morgan applies the term " rational." Thus, a man 
 in attempting to cross a swollen brook will consider the pos- 
 sibility of leaping, w r ading, or swimming across; or he will 
 look about for material to make a bridge, noting the posi- 
 tion of stones which might serve for supports, and consider- 
 ing, perhaps, the possibility of piecing together two short 
 boards to make one board long enough for his purpose. When 
 action is finally taken it is the result of a carefully consid- 
 ered plan. An example of this class of actions cannot be 
 given from the insects, as we have at present no satisfactory 
 evidence that the behavior of any insect ever rises to the 
 rational plane. 
 
 In the discussion of this question it must not be forgotten 
 that instincts are not fixed and unalterable, but that they are 
 constantly being modified by new experiences. Therefore many 
 
88 GENERAL ZOOLOGY 
 
 of the actions of animals should not be classified as purely 
 instinctive or purely intelligent, for they may contain elements 
 of both factors. The words " instinctive " and " intelligent " 
 can only be used to denote an apparent preponderance of one 
 or the other factor. This is well illustrated by the observa- 
 tion Professor Morgan quotes from M. Fabre, who " describes 
 how a Sphex, one of the solitary wasps, instinctively draws its 
 prey, a grasshopper, into the burrow by its antennae. When 
 these were cut off the wasp pulled the grasshopper in by the 
 jaw appendages ; but when these were removed she seemed 
 incapable of further accommodation to the unusual circum- 
 stances." Here we see not only obedience to a strongly 
 marked instinctive tendency, but also some power to modify 
 the instinctive reaction. It seems strange to us that if the 
 wasp were capable of making this deviation from her instinc- 
 tive mode of procedure, she should not take the slight further 
 step of seizing upon the fore legs. 
 
 Another caution must also be stated. The distinctions 
 already made assume that we are able to determine the 
 mental states of animals ; but this is true only in a very gen- 
 eral way. We interpret the mental state of human beings 
 by inference from their actions, but with the lower animals 
 we have no positive means of knowing what mental state 
 accompanies any given action, since their physical organiza- 
 tion is so different from ours. And not only is this true, but 
 we also lack a language to express the facts we observe con- 
 cerning the mental life of the lower animals, since the words 
 we use have their meaning in connection with the facts of 
 human psychology. 
 
 Economic Importance of Insects. According to the report 
 of the Secretary of Agriculture for 1902, the fixed capital of 
 agriculture in the United States amounted in 1900 to twenty 
 billions of dollars, or four times the amount invested in 
 manufactures. More than half of the people of the United 
 
THE INSECTS: HEXAPODA 89 
 
 States live on farms. When it is considered that our crops 
 are attacked not by one but often by many different insects, 
 and that, according to the estimate of one of the state ento- 
 mologists of New York, there is no crop cultivated which 
 infesting insects do not diminish by at least one tenth, it is 
 plain that the economic relations of insects to agriculture are 
 extremely important. Nearly every order has its injurious 
 forms. Thus the Orthoptera has its locusts ; the Hemiptera, 
 the plant-bugs and aphids; the Coleoptera, the wireworms 
 and leaf-beetles ; the Diptera, 
 various flies ; while almost the 
 whole army of the larvae of the 
 Lepidoptera feed on plants. 
 
 The story of the introduction 
 and spread of the gypsy-moth 
 of Europe (Porthet'ria dis'par, FlG . 61 . Gypsy-Moth. Natural size. 
 Fig. 51) in Massachusetts, (After Howard, Bulletin No. ll,x.s., 
 teaches an important lesson. Umted States Department of Agri- 
 
 1 culture, Division of Entomology) 
 
 This insect, long well known 
 
 by European foresters as destructive, was probably introduced 
 in 1869 by a professor connected with Harvard Observa- 
 tory, who was interested in breeding silk-producing insects. 
 The larvae escaped into his garden at Medford, near Boston, 
 and though search was made for them, not all were found. 
 Nothing was heard from them for fifteen years, when they 
 began to be troublesome in gardens. By 1889 they had mul- 
 tiplied to such an extent that they attacked every green thing, 
 and the bare branches of trees in every direction gave evi- 
 dence of the extent of the devastations. In this year the 
 insect was identified. Up to that time it had been called 
 simply " the caterpillar." First the town of Medford, and 
 then the state, took up the matter, and the first state appro- 
 priation of twenty-five thousand dollars was passed. Since 
 that time additional appropriations have been called for, till 
 
90 GENERAL ZOOLOGY 
 
 seven hundred and seventy-five thousand dollars have been 
 spent in a territory comprising about two hundred square 
 miles. The end is not yet, for Dr. Howard, chief of the Divi- 
 sion of Entomology, United States Department of Agriculture, 
 in his report on The G-ypsy Moth in America, from whose paper 
 these facts have been taken, says that appropriations must con- 
 tinue for several years in order to exterminate the insects. 
 
 The Division of Entomology of the United States Depart- 
 ment of Agriculture has been the means of saving large sums 
 to the agricultural interests of the country by its various 
 activities, such as the importation from other countries of 
 beneficial species and its study of the habits of insects to 
 find the best method of attack. Many of the states maintain 
 boards of agriculture which employ entomologists. 
 
 The cotton-boll weevil (Anthon'omus yran'dis) has recently 
 become a serious menace to the cotton industry of the south- 
 ern states. The weevils are beetles possessing a long snout ; 
 this organ is often used by the female for piercing the tissues 
 of plants to deposit her eggs. Among the weevils are many 
 formidable enemies of the farmer. In this particular case 
 the cotton industry has in some places been threatened with 
 practical extinction. The Division of Entomology has been 
 unremitting in its effort to find means to check the ravages 
 of this weevil. 
 
 The relations recently discovered between some of the 
 Diptera and disease must not be overlooked in considering 
 the influence of insects on man, outside of his interests in 
 agriculture. 
 
 Among beneficial insects may be mentioned the parasitic 
 ichneumon-flies among the Hymenoptera, and the carnivo- 
 rous lady-beetles and many ground-beetles among the Cole- 
 optera. Comparatively few insects are directly useful to 
 man ; among such may be mentioned the silkworm, honey- 
 bee, cochineal-insect and lac-insect. 
 
THE INSECTS: HEXAPODA 
 
 91 
 
 Relations between Insects and Flowers. In order to make 
 seed, the flowering plants require to have the pollen furnished 
 by the stamens (Fig. 52, 1) carried to the pistil (Fig. 52, 2) of 
 the same kind of plant. The pollen is necessary to the ferti- 
 lization of the ovule (Fig. 52,3), which afterwards grows into 
 the seed. Continuous pollination of a plant by pollen which 
 it furnishes from its own stamens has been found to be detri- 
 mental to the vigor of the 
 seeds. We find in nature 
 many devices to insure 
 fertilization by pollen 
 from another plant of the 
 same kind, that is, by 
 cross-pollination. 
 
 Waite, Year-book, United States Depart- 
 ment of Agriculture, 1898) 
 
 1, stamen; 2, pistil; 3, ovule 
 
 Some plants have the 
 stamens and pistils so 
 placed in the flower that 
 no pollen can fall from 
 one to the other; some 
 ripen their stamens and 
 
 pistils at different times. FIG. 52. Diagram of Pear Flower. (After 
 Many have the stamens 
 and pistils on separate 
 plants, and a great num- 
 ber, though the stamens and pistils are close together, are 
 wholly or partially sterile to their own pollen, and " set " their 
 seeds only if the pistils receive pollen from the stamens of 
 another plant of the same species. This is the case with many 
 of the fruit trees. 
 
 The wind carries pollen for some plants which have their 
 stamens and pistils more or less exposed, but a great number 
 of plants, especially those with the most beautiful flowers, 
 depend on insects to bring about pollination. So far has 
 this dependence gone that, in many cases, plants have become 
 
92 
 
 GENERAL ZOOLOGY 
 
 unable to pollinate themselves. It is now clear that the 
 color, scent, nectar, and in many cases the form of flowers 
 have been developed in connection with their insect visitors. 
 The insects most concerned in the pollination of flowers are 
 flies, butterflies, wasps, and bees. 
 
 Some insects visit flowers for the sake of the nectar. Pol- 
 lination results from the insect brushing itself against the 
 pollen-bearing organs and subsequently rubbing this pollen 
 on to the pistil in a neighboring flower in the search for 
 nectar. But the case of Pronu'ba (Fig. 53) is somewhat 
 
 different. Pronuba is a 
 white moth a little over 
 a centimeter (about half 
 an inch) long, which 
 lives in the flower of 
 the yucca, or Spanish 
 bayonet, a familiar plant 
 of the dry southwestern 
 plains. During the day 
 the female remains 
 quiet, but at dusk (in 
 the breeding season) she 
 begins laying her eggs within the pistil of the flowers, among 
 the ovules, which, when the flower is fertilized, are to grow 
 into seeds. Upon these seeds the larva of the Pronuba will 
 feed. If this were all, there would be no peculiarity deserving 
 of mention; but the female goes a step farther and makes 
 sure of a supply of seeds for the larva by collecting pollen 
 from the stamens and thrusting it into .the pistil. The ad- 
 vantage to the larva is obvious, since its supply of food is 
 rendered certain ; the advantage to the plant probably lies in 
 the fact that not all the seeds thus provided for are eaten by 
 the larva before reaching maturity. This association may be 
 cited as an illustration of symbiosis. 
 
 FIG. 53. Pronuba Moth. Natural size. 
 (After Riley) 
 
THE INSECTS: HEXAPODA 93 
 
 Geographical Distribution of Insects. The map on page 17 
 shows the region of the United States occupied by the Rocky 
 Mountain locust. Within a portion of this area the species 
 is able to maintain itself permanently ; just outside of this 
 area are other regions which are only temporarily occupied, 
 as the great swarms forming periodically seek a new home. 
 That the species is able to maintain itself in one region and 
 not in another is due to its adaptation to a particular region 
 in the matter of food, temperature, climate, absence of over- 
 powering enemies, and other causes. Similar maps might be 
 drawn showing the geographical distribution of all the other 
 insects studied. In each case there would be found some 
 reason why a particular insect did not occupy a larger terri- 
 tory, since, generally, species tend by natural increase to 
 broaden their ranges till hindered by some barrier to their 
 farther advance. To land animals such barrier may be a 
 mountain range, a desert, or a large body of water. To a 
 desert-inhabiting species it might be a forest. To aquatic 
 animals, waterfalls or rapids are often insurmountable. 
 Temperature conditions are very definite in their effects 
 on the distribution of animal life. Food- supply is another 
 important factor. The ocean is a barrier to nearly all land 
 species. 
 
 The animal life of any region is known as its fauna. Though 
 insects are widely distributed over the earth, a study of the 
 different species shows that there are more or less well-marked 
 areas, each of which possesses its characteristic species. 
 Though much overlapping occurs, as might be expected in 
 the case of animals which can fly freely from place to place, 
 yet on the whole it is possible to separate fairly well-marked 
 regions, the climatic and other boundaries of which have 
 prevented any great intercommunication, thus producing 
 peculiar forms of life in each region. These regions may be 
 stated as follows. 
 
94 GENERAL ZOOLOGY 
 
 The Arctic realm includes all the land in the northern 
 hemisphere as far south as the northern limit of trees and 
 (so far as the insects are concerned) the tops of high moun- 
 tains in the temperate zone. It has already been noted that 
 the White Mountain butterfly (p. 48) belongs to this fauna. 
 The Eurasian realm comprises all of Europe south of the 
 Arctic realm ; Asia, north of the Himalayas and south of 
 the Arctic realm ; and Africa, north of the Desert of Sahara. 
 United with this, by many authors, is the North American 
 realm, embracing North America south of the Arctic realm 
 and north of Mexico. In past time land connection was 
 more complete than at present, and considerable migration 
 has taken place from one continent to the other. The South 
 American realm comprises that portion of the continent north 
 of Patagonia, and includes the West Indies, Central America, 
 the greater part of Mexico, and a portion of the most south- 
 erly part of Florida. This region has contributed many species 
 to our own fauna. South of this realm is another temperate 
 region in Patagonia, which corresponds in position to the 
 North American realm, but owing to its comparatively small 
 size it is not usually ranked among the great regions of the 
 earth. Its fauna is mainly derived from the South American. 
 Still farther south is an Antarctic region of eternal snow and 
 ice ; but little is known of the life of this region, and it may 
 be omitted from the list of the great faunal divisions. The 
 African realm includes all Africa south of the Desert of 
 Sahara. With this is often united the Indian realm, compris- 
 ing the Asian continent south of the Himalayas, and the 
 East Indies as far as the Strait of Lombok. The testimony 
 of geology is strong that these two realms were once con- 
 nected, though the water is now very deep and wide between 
 them. Madagascar is by some naturalists included within the 
 Indo-African realm ; by others, considered a separate region. 
 The last of the great faunal divisions is the Australian realm, 
 

 95 
 
 including Australia, Papua, Celebes, and Lombok, and neigh- 
 boring islands in the Pacific Ocean. It seems to have been 
 isolated from the other land masses for a considerable period ; 
 it is singularly deficient in the highest forms of life. Each of 
 the great faunal divisions is capable of subdivision, but into 
 the details of this we need not go. 
 
 Nomenclature and Classification of Insects. In order to 
 write intelligently about animals, it is necessary that natural- 
 ists should have some uniform system of naming, or nomen- 
 clature, since the common names of animals vary not only in 
 the different countries and languages but even in different 
 parts of the same country. It will be noticed that each insect, 
 when first spoken of in these chapters, is accompanied by a 
 scientific name printed in italics. Thus the Rocky Mountain 
 locust is Melanoplus spretus ; the common red-legged locust, 
 Melanoplus femur-rubrum ; the lesser locust, Melanoplus at- 
 lanis. These different kinds or species of locust differ in size, 
 color, and habitat, and they each receive a different specific 
 name, as spretus, femur-rubrum, and atlanis. They agree in other 
 characteristics, such as the general structure, size, and propor- 
 tion of their parts, and they are therefore placed in the same 
 group or genus, Melanoplus. The word " genus " is thus seen 
 to be a term of wider application than the word "species." 
 A genus may include one or several species. The generic and 
 specific names make up the complete scientific name of an 
 animal. The names are always taken from the Latin or Greek, 
 or are Latinized in form, so that they are understood by all 
 scientific men. They often refer to some striking character- 
 istic of the animal ; thus, Melanoplus means " black armor," in 
 allusion to the dark-colored exoskeleton. Sometimes the refer- 
 ence is to the locality where the animal is found, as atlanis, 
 referring to the Atlantic states ; sometimes the name is given 
 in honor of some student of animals, as Darwin'ii (see p. 343), 
 named after the naturalist, Charles Darwin. The scientific 
 
96 GENERAL ZOOLOGY 
 
 name first given to an animal, if accompanied by a descrip- 
 tion, is the name it must bear, and the species is known under 
 that name wherever found. This system of nomenclature was 
 introduced by Linnseus (see p. 443). 
 
 We must not overlook the fact that in the study of animals 
 we have to deal only with individuals. The words " species," 
 " genus," and the other words used beyond, are man's inven- 
 tion, for his convenience in scientific description. Individuals 
 which resemble each other in a large number of characters 
 and especially if the individuals are able to interbreed are 
 usually said to belong to the same species. The test of inter- 
 breeding, while of almost universal application, is not invari- 
 ably a means of distinguishing the species, since in some 
 cases two different species can produce offspring (called 
 hybrids), though the latter are usually not fertile, that is, 
 they are not themselves capable of producing young. 
 
 Often within the limits of a single species there are groups 
 of individuals which vary from the others in one or more 
 characters. Especially is this true of those species with a 
 wide range, including different climatic conditions. In such 
 cases the different forms which the species assumes are termed 
 varieties, and a varietal name is sometimes added to the 
 generic and specific names. We have already referred to the 
 seasonal variations of the black swallow-tail butterfly. 
 
 The different genera are arranged in groups, or classified, 
 according to their resemblances and differences. A number of 
 genera which show similar structural characteristics of more 
 general character than those used to constitute a genus make 
 up a family. Thus the locusts, not only of the genus Melano- 
 plm but also of all the other genera found in North Amer- 
 ica, together with the genera of the Old World, have short 
 antennae, in common with other characteristics, which cause 
 them to be placed in the locust family, Acrid'idce. Similarly, 
 the katydid and other green grasshoppers, with many meadow 
 
THE INSECTS: HEXAPODA 
 
 97 
 
 species, belong to the family of long-horn or true grass- 
 hoppers, Locust' idee. The crickets (GrryVlidce) and the cock- 
 roaches (Blat'tidce) are allied families. By common consent 
 family names end in -idee. Families are united to form orders, 
 and orders in turn make up classes. The largest and most 
 important of the orders which make 
 up the class Hexapoda have already 
 been discussed. As we shall see 
 later, the classes are united to form 
 phyla (sing., phylum), the primary 
 divisions of the animal kingdom. 
 
 Definition of Thysanura (Gr. 
 thysanos, fringe ; our a, tail). Of 
 the orders not mentioned in the 
 preceding chapters it will be neces- 
 sary to refer only to the Thysanu'ra, 
 or springtails. The springtails are 
 small, flattened, wingless insects, 
 with usually simple eyes, and ap- 
 pendages on some of the abdom- 
 inal somites. They are found under 
 stones, in damp places, or in human 
 dwellings. They develop from the 
 egg without metamorphosis. The 
 best-known species is the " silver- 
 fish," or " fish, moth " (Lepis'ma sac- 
 chari'na, Fig. 54), often seen in houses, where it sometimes 
 does damage to starched clothing or to the bindings of books. 
 
 Generalized and Specialized Forms. The Thysanura are espe- 
 cially interesting, since they probably more closely resemble 
 the ancestral type of insect than do any other living species. 
 The primitive or ancestral forms were probably naked, wing- 
 less hexapods, without strongly marked divisions into head, 
 thorax, and abdomen. Their legs were probably equal or 
 
 FIG. 54. Fishmoth. Enlarged. 
 (After Marlatt, Bulletin No. 4, 
 N.S., United States Depart- 
 ment of Agriculture, Division 
 of Entomology) 
 
98 GENERAL ZOOLOGY 
 
 nearly equal in size. The species probably developed from 
 the egg without metamorphosis. The lack of special adapta- 
 tions or modifications of the various organs marks the ances- 
 tral insects as generalized forms, as distinguished from their 
 more or less specialized descendants of to-day, in which the 
 organs have become modified to perform different functions. 
 Thus the greatly developed hind legs of the locusts are a 
 specialization in structure, fitting the insect to progress by 
 leaps as well as by walking. 
 
 Very different degrees of specialization often exist in the 
 organs of the same species ; thus the digestive system of 
 the locust is quite complex, while the separate prothorax is 
 a generalized character, which shows the locust to be allied 
 in this respect more closely to the primitive type than are 
 insects like the wasps, for example, where the three divisions 
 of the thorax are grouped in one mass. Within the limits of 
 every order there are different degrees of specialization, and 
 there are cases in every order where loss or decline of parts 
 (called degeneration) has been brought about through various 
 causes. Among the May-flies the mouth-parts of the imago 
 have become degenerate in connection with the short adult 
 life, which lasts only long enough for mating and the laying 
 of eggs for a new generation. In some scale-insects the female 
 becomes degenerate in connection with the quiescent life 
 beneath a protecting scale. She loses eyes, antennae, and legs, 
 becoming very little more than a bag capable of feeding and 
 reproducing. Parasitism also brings about degeneration. 
 
 From the study of the forms in which different organs 
 appear in the orders of insects (that is, from the study of 
 morphology, the science of form) the naturalist is able to say 
 which kinds of insects have, on the whole, become most spe- 
 cialized in structure, and those which have, on the whole, 
 varied least from the primitive generalized type. The evi- 
 dence from this source points to the fact that the more 
 
THE INSECTS: HEXAPODA 99 
 
 generalized of the orders which we have mentioned are the 
 Thysanura, Plectoptera, Odonata, Orthoptera, and Hemiptera. 
 These are the orders, it will be remembered, in which meta- 
 morphosis is either entirely wanting, or where, if present, 
 there is usually no well-marked pupal resting-stage. 
 
 In addition to morphology, another source of information 
 is the geological record of species, the fossil remains of 
 organisms preserved in the mud, clay, or sand at the bottom 
 of water. Wherever areas of land are uplifted, the atmos- 
 pheric agencies of wind and water begin their work of wear- 
 ing them down again. The worn materials in the form of 
 clay, sand, or mud, as may be seen to-day after a rain, find 
 their way in rivulets to lower ground, or into a river, which 
 deposits them still lower, finally even to the bottom of the sea. 
 When there, or in a temporary resting-place in some lake or 
 pond, the material forms a bed into which the remains of 
 animals may drop. Under favorable conditions their hard 
 parts are preserved in perfect form, but the substance in them 
 is replaced by minerals, and the entire mass is consolidated 
 into rock by heat and the pressure of other materials upon it. 
 Footprints may also be made in the soft mud at the edge of 
 ponds, and indelibly preserved in the rocks of later times. 
 
 The geologist has worked out in detail the order in which 
 the rock material of the world has been laid down. By study- 
 ing the fossil remains of living things the zoologist can 
 picture something of the life of each of the great epochs in the 
 earth's history, thpugh owing to the conditions of preserva- 
 tion, by far the greater part of the record has been lost. It is 
 as though we should try to get a connected idea of the history 
 of the United States from a book from which had been torn 
 the whole of the early voyages, much of the colonial period, 
 and many pages from the story of the Revolution, the Civil 
 War, and later history. Unfortunately the geological record 
 is especially incomplete with regard to the insects, so that it 
 
100 GENERAL ZOOLOGY 
 
 does not give us much help in this particular problem. How- 
 ever, of the remains of winged insects which have so far been 
 discovered, the earliest are those belonging to the orders 
 Orthoptera, Hemiptera, Plectoptera, and Odonata. 
 
 A third source of information comes from the study of the 
 earlier, or embryological, stages in the development of the 
 individual. According to von Baer, a Russo-German natural- 
 ist born in 1792, the more nearly alike two animals belonging 
 to the same phylum are, the greater will be the resemblance 
 in their embryological stages ; that is, the longer will the 
 animals continue to follow a similar line of development. 
 This is known as von Baer's law. Since his time the theory 
 has been advanced that each individual animal, being the 
 product of its ancestors, reproduces to a greater or less extent 
 the stages which have occurred in the history of the race. 
 According to this view the earlier stages in the history of 
 the individual represent adult stages in the life of the past. 
 This is known as the recapitulation theory. This principle 
 applied to the cockroaches (see p. 20), would indicate their 
 descent from ancestors which were more cylindrical than the 
 flattened forms of to-day. 
 
 The conclusions of embryology justify the general state- 
 ments just made, so that it is possible to assert that the orders 
 without strongly marked metamorphosis are, on the whole, the 
 " lower," or more generalized, insects ; while the orders with 
 marked (" complete") metamorphosis represent the "highest," 
 or most specialized, types of the class to-day. The sequence 
 in which the different orders of insects have been described 
 in these pages represents, on the whole, with the excep- 
 tion of the Thysanura, a gradually ascending series from the 
 more generalized forms to the highly specialized Lepidoptera, 
 Diptera, and Hymenoptera. 
 
CHAPTER X 
 THE DOCTRINE OF EVOLUTION 
 
 To the open ear it sings 
 
 Sweet the genesis of things, 
 
 Of tendency through countless ages, 
 
 Of star-dust and star pilgrimages, 
 
 Of rounded worlds, of space and time, 
 
 Of the old flood's subsiding slime, 
 
 Of chemic matter, force and form, 
 
 Of poles and powers, cold, wet, and warm. 
 
 EMERSOX, Wood Notes. 
 
 Definition of Evolution. The word " evolution," in its most 
 general sense, signifies a process of unfolding or develop- 
 ment, and it is in this sense that we speak of the evolution 
 of a plan or the evolution of history. In science, generally, 
 the word is used to express the process of development from 
 simplicity to complexity ; that is, in the words of the Century 
 Dictionary, " to a nicer and more elaborate means for reach- 
 ing definite ends, the process being regarded as of the nature 
 of a growth." In this sense we speak of the evolution of our 
 solar system from a mass of heated gaseous material (see 
 p. 293). In biology (the science which has to do with living 
 things, both plants and animals) the word is used not only 
 to signify the development of an individual organism from 
 the egg to maturity, but it serves to characterize a particular 
 view as to the derivation of all organisms by natural descent, 
 with modification of earlier and simpler forms of life. Biolo- 
 gists are generally agreed that all the many species of animals 
 and plants of to-day have come to their present form through 
 evolution, though the steps by which this evolution has been 
 accomplished are not thoroughly understood. A classification 
 
 101 
 
102 GENE.RAL ZOOLOGY 
 
 of animals is not a mere grouping of species which resemble 
 each other to a greater or less extent, but is rather an attempt 
 at a statement of the truth of evolution, aiming to express 
 the relationships existing between animals, as shown not only 
 in their present structure but also by their development from 
 egg to maturity, and their history through geological time. 
 
 While every species of animal tends to produce young 
 resembling itself, no two individuals of any species are ever 
 precisely alike. That the young of each species tend to 
 resemble their parents, we say is due to heredity ; that they 
 never exactly resemble them, we say is due to variation. Of 
 the causes underlying heredity and variation we know almost 
 nothing. We notice that in the course of time various forms 
 of life have appeared on the earth, and that on the whole 
 there has been a gradually increasing complexity in animal 
 structure through geological time, the more complex animals 
 following the simpler, as the environment has changed and 
 new conditions have arisen. Because of the incompleteness 
 of the knowledge of the evolution of life on the earth, we 
 can do little more than call attention to some of the second- 
 ary factors in evolution, without attempting to measure, ex- 
 cept in a rough way, their relative importance. 
 
 Natural Selection. With the principle of natural selection 
 are associated the names of Charles Darwin and Alfred Russel 
 Wallace, who independently stated it in papers published in 
 1858 (see p. 450). The principle had been recognized before, 
 but as stated by Darwin it was reenforced by such a wealth 
 of illustration that it compelled the attention of the scien- 
 tific world. 
 
 In introducing the discussion of natural selection, Darwin 
 makes use of the principle of artificial selection among domes- 
 ticated animals, that is, the selection by man of certain 
 individuals having peculiarities which he wishes to preserve. 
 These individuals are allowed to breed together, and, in the 
 
THE DOCTRINE OF EVOLUTION 103 
 
 next generation, those individuals varying in the direction 
 desired are again chosen for breeding. If the process is con- 
 tinued through several generations it may produce a race in 
 which the special characteristic desired is fixed. Artificial 
 selection is one of the means by which the different races of 
 domesticated animals and plants have been produced. 
 
 According to Darwin, something similar to this artificial 
 selection by man goes on in nature, producing the different 
 species of animals as we know them to-day. All organisms 
 tend to vary. Some variations, he says, are due to changes in 
 the conditions of life and to excess of food (these two under- 
 lying the great variability of domesticated animals) ; others 
 are due to the nature of the organism ; to the inherited 
 effect of habit and the use and disuse of parts ; or to rever- 
 sion to characters once possessed by ancestors. The varia- 
 tions. which occur are of two kinds, definite and indefinite. 
 Indefinite, or fluctuating, variations are those comparatively 
 slight differences which occur constantly among animals and 
 plants, so that of all the individuals of the same species, 
 no two are ever exactly alike. Definite variations are more 
 striking ; of these the an con ram is an example. This ani- 
 mal, born in Massachusetts in 1791, of an ordinary breed of 
 sheep, had a long back and short, crooked legs. From it, 
 by crossing, has been produced the ancon breed of sheep, 
 showing the same peculiarities as its progenitor. The breed 
 was highly prized for a time on account of the inability of 
 the animals to jump fences. Darwin lays most stress upon 
 the fluctuating variation as affording the material for natural 
 selection. * 
 
 In order to understand the principle of natural selection, we 
 must consider for a moment the struggle for existence. This 
 term is used by Darwin in " a large and metaphorical sense, 
 including dependence of one being on another, and including 
 (which is more important) not only the life of the individual 
 
104 
 
 GENERAL ZOOLOGY 
 
 but also success in leaving progeny." The struggle results 
 from the tendency of living things to increase more rapidly 
 than the means of subsistence. Professor 
 Jordan, of Leland Stanford Junior Uni- 
 versity, says, " If the eggs of a common 
 house-fly should develop, and each of its 
 progeny should find the food and tempera- 
 ture it needed, with no loss and no des- 
 truction, the people of a city in which this 
 might happen could not get away soon 
 enough to escape suffocation from a plague 
 of flies." Professor Thomson, of Edinburgh, 
 Scotland, gives this illustration: "A female 
 aphis, often producing one offspring per 
 hour for days together, might in a season 
 be the ancestor of a progeny of atomies 
 which would weigh down five hundred 
 
 FIG. 55. Caddice-Flies. Enlarged 
 
THE DOCTRINE OF EVOLUTION 105 
 
 millions of stout men." A similar rapid increase would be 
 noted on the part of any animal, were the various checks to 
 its multiplication removed. The struggle for life goes on 
 between different individuals of the same species, as in a 
 swarai of locusts ; between individuals of different species, 
 as with locusts and insect-eating birds, and with the con- 
 ditions of existence, such as temperature, winds, moisture, 
 and food-supply. 
 
 Owing to the struggle for existence, Darwin says: "Varia- 
 tions, however slight, and from whatever cause proceeding, 
 if they be in any degree profitable to the individuals of a 
 species, in their infinitely complex relations to other organic 
 beings and to their physical conditions of life, will tend to 
 the preservation of such individuals, and will generally be 
 inherited by the offspring. The offspring, also, will have a 
 better chance of surviving, for, of the many individuals of 
 any species which are periodically born, but a small number 
 can survive." 
 
 The caddice-flies are, in their immature stage, aquatic 
 larvae which build protective cases composed of grains of 
 sand, or bits of straw, or leaves (Fig. 55). These cases afford 
 concealment and protection to the young. Applying the prin- 
 ciple of natural selection here, it would be said that those 
 caddice-flies which varied in the direction of protective cases 
 have survived, and those which did not have been devoured 
 or otherwise destroyed ; hence a race of case-building cad- 
 dice flies is in existence to-day. Natural selection results in 
 "the survival of the fittest" for the environment, and the 
 principle is used to explain the degeneration due to parasi- 
 tism, as well as the development of increased complexity in 
 animal structure. 
 
 We have spoken of the conflict between individuals of the 
 same species for the necessities of existence, but many species, 
 individually rather weak, become successful competitors in 
 
106 GENERAL ZOOLOGY 
 
 the struggle for existence by mutual aid and cooperation. 
 Prince Kropotkin has recently called attention to cases of 
 mutual aid in the animal kingdom. He says : " As soon as 
 we study animals not in laboratories and museums only, 
 but in the forest and the prairie, in the steppe and the moun- 
 tain we at once perceive that though there is an immense 
 amount of warfare and extermination going on amidst vari- 
 ous species, and especially amidst various classes of animals, 
 there is, at the same time, as much, or perhaps even more, of 
 mutual support, mutual aid, and mutual defense amidst ani- 
 mals belonging to the same society. Sociability is as much a 
 law of nature as mutual struggle." Illustrations may be seen 
 in the complicated communities of the ants,Jbees, and wasps 
 among the insects ; others occur among the birds and fur- 
 bearing animals (see Chapters XXIX and XXXI). 
 
 Sexual Selection. The principle of sexual selection, also 
 formulated by Darwin, is an extension of the principle of 
 selection to account for the secondary sexual characters which 
 exist in many animals. In most insects, where there is sexual 
 dimorphism, the male, though usually smaller, is more brightly 
 colored ; it is armed or ornamented with spines, which the 
 female does not possess, or it has special sound-producing 
 'organs. In the common stag-beetle (Luca'nus, Fig. 56) the 
 mandibles of the male are of larger size than those of the 
 female. Among the birds, in those cases where the sexes are 
 differently colored, the males are usually more brilliant ; they 
 often have spurs, wattles, crests, or plumes, while the females 
 are without these structures, or have them in less degree. 
 It is only the male birds, too, which possess the gift of song. 
 Among the fur-bearers special characteristics, such as horns, 
 antlers, and tusks, often occur. These various secondary 
 sexual differences are ascribed by Darwin to sexual selection, 
 which "depends, not on a struggle for existence in relation 
 to other organic beings or to external conditions, but on a 
 
THE DOCTRINE OF EVOLUTION 107 
 
 struggle between the individuals of one sex, generally the 
 males, for the possession of the other sex. The result is not 
 death to the unsuccessful competitor, but few or no offspring. 
 Sexual selection is, therefore, less rigorous than natural selec- 
 tion. Generally the most vigorous males, those which are best 
 fitted for their place in nature, will leave most progeny. But 
 in many cases victory depends not so much on general vigor 
 
 FIG. 56. Stag-Beetle (male and female). Natural size 
 
 as on having special weapons confined to the male sex. A 
 hornless stag or spurless cock would have a poor chance 
 of leaving numerous offspring." The greater brilliancy of 
 many males is accounted for by ascribing it to the choice 
 by the females, through countless generations, of the most 
 brilliantly colored and attractive males. The song of male 
 birds is accounted for in a similar manner. 
 
 The Inheritance of Acquired Characters. Though Darwin 
 considered that species have arisen largely through the action 
 of natural selection on favorable variations, he admitted also 
 other factors in evolution, on which some naturalists to-day 
 lay great stress. It is a truism of our everyday life that the 
 use of an organ sooner or later affects its structure. Thus 
 the brawny arm of the blacksmith may be directly attributed 
 to the kind of work he does. There are many cases in the 
 animal kingdom where the characters of animals might be 
 interpreted as due to the use or disuse of organs. Among 
 the insects we may instance the enlarged fore legs of the 
 
108 GENERAL ZOOLOGY 
 
 mole-cricket and mantids, the enlarged hind legs of the locust, 
 and the absence of eyes in certain cave-inhabiting insects. 
 With this principle are associated the names of Erasmus 
 Darwin, grandfather of Charles Darwin, and the French 
 naturalist Lamarck (see p. 448). 
 
 The chief difficulty in the application of the principle of the 
 inheritance of acquired characters as a factor in evolution lies 
 in the fact that we have little or no evidence that the charac- 
 ters acquired by use or disuse during the life of an individual 
 are transmitted to its descendants, though some effort has 
 been made of late years to furnish this direct evidence. The 
 most important experiments along this line are those of Brown- 
 Sequard, a Franco- American physiologist (18191894). Pie 
 succeeded in producing epilepsy in guinea-pigs born of parents 
 which had been rendered epileptic by an injury to the spinal 
 cord. Exophthalmia (a disease characterized by abnormal 
 protrusion of the eyeball) was also transmitted through sev- 
 eral generations. Certain mutilations, produced by the ani- 
 mals eating off their hind-leg toes after the latter have been 
 rendered insensible to pain by cutting the nerve leading to 
 them, also seem in some cases to have been transmitted to the 
 descendants. The objection is made to these experiments 
 that they may show the result of a transmitted disease rather 
 than the inheritance of an acquired character. 
 
 The Direct Influence of the Environment. In connection 
 with the principle of the inheritance of characters acquired 
 through use or disuse, Lamarck held that the changes in the 
 environment directly brought about changes in the organism, 
 and that these changes were transmitted, to the descendants 
 (see p. 449). This and the preceding principle are therefore 
 often spoken of as Lamarckian factors in evolution, while 
 natural and sexual selection are termed Darwinian factors. 
 
 All organisms have to exist under certain conditions of 
 pressure either of liquids or gases; they are adapted to a 
 
THE DOCTRINE OF EVOLUTION 109 
 
 certain range of temperature, moisture, and light ; they require 
 more or less oxygen ; and they need a certain amount and 
 quality of food. As a general rule slight changes in these 
 various elements of the environment can be borne without 
 injury; greater changes may cause death. There are a num- 
 ber of cases in the animal kingdom where modifications in 
 the organism seem to be directly connected with environ- 
 mental changes, though it is not always easy to say what fac- 
 tor in the environment is responsible for the change. Thus it 
 has been stated that horses tend to decrease in size in north- 
 ern latitudes, on islands, and on mountains. Most of the 
 animals on islands are smaller than their continental relatives. 
 De Varigny, in his Experimental Evolution, says that, " In 
 the Canary Islands the oxen of one of the smaller islands are 
 much smaller than those of the others, although all belong to 
 the same breed; and the horses are also smaller, and the 
 indigenous inhabitants are in the same case, although belong- 
 ing to a tall race." The same author also cites the experi- 
 ments of Karl Semper, who stated that if the common 
 pond-snail of Europe is kept in small volumes of water, 
 less than five or six liters (a little over four or five quarts), 
 the animals do not attain their usual size, but remain more 
 or less dwarfed. The differences between the geographical 
 varieties of the gray squirrel are given on page 406. Among 
 the insects the influence of food in the production of the 
 queen bee, and the influence of temperature in the produc- 
 tion of the different broods of one of the swallow-tail butter- 
 flies have already been commented upon. It has also been 
 found that colored bodies in the vicinity affect the colors of 
 the pupae of certain butterflies (Fig. 57). Such color changes 
 are due to the susceptibility of the larva to surrounding colors 
 during a quiescent period before pupation. The experiments 
 on Arte'mia, described on page 148, may also be. referred to in 
 this connection. 
 
110 
 
 GENERAL ZOOLOGY 
 
 The difficulty in adopting this principle as an explanation 
 of the way in which evolution has taken place lies in the fact 
 
 already mentioned in 
 the discussion of 
 characters acquired 
 through use or dis- 
 use, that it is not 
 yet entirely clear that 
 changes occurring 
 during the lifetime 
 of the individual are 
 transmitted to the 
 next generation. 
 
 The Mutation 
 Theory. It will be re- 
 membered that Dar- 
 win laid stress upon 
 indefinite, or fluctu- 
 ating, variations as 
 furnishing the greater 
 part of the material 
 for selection. The mu- 
 FIG. 57. Pupse of Black Swallow-l^ai! Butterfly tation theorv stands 
 
 Showing influence of color of near-by object on the in sharp Contrast with 
 color of the pupa. Photographed from life. About .-, -, ,- ,, 
 
 three quarters natural size the Selection theory 
 
 (From Hunter's Studies in Insect Life) in emphasizing the 
 
 heredity transmission 
 
 of definite variations. With the mutation theory is particularly 
 associated the name of Hugo de Vries, a Dutch botanist living 
 in Amsterdam, Holland. He was led to express the princi- 
 ple from his studies of the variations of a species of even- 
 ing primrose introduced from America and found growing in 
 waste places in Hilversum, near Amsterdam. It should not 
 be overlooked that William Bateson, of Cambridge, England 
 
THE DOCTRINE OF EVOLUTION 111 
 
 (born 1861), emphasized the evolutionary importance of dis- 
 continuous variations (mutations) years before de Vries' work 
 appeared. One of the most recent general statements of the 
 principle is to be found in Evolution and Adaptation, by 
 Professor Thomas Hunt Morgan of Columbia University. 
 From his book most of the following statements have been 
 taken. 
 
 According to this principle new species have been pro- 
 duced by sudden and perfectly definite changes (mutations) 
 in the organism, though it is not necessary to assume that 
 these changes are always great. The theory makes no attempt 
 to account for the presence of mutations, but when they 
 occur it is a striking fact that the characters tend to be 
 transmitted to the descendants. De Vries is inclined to think 
 that there are periods of mutation when many and great 
 changes take place, and periods where comparatively little 
 change in the organism occurs. The same mutation may 
 occur time after time and in large numbers of individuals. 
 When a mutation appears its survival will depend on whether 
 it can find a place in nature where it can exist and leave 
 descendants. If the organism is well adapted to its environ- 
 ment, it will leave many descendants ; if it is poorly adapted, 
 it may barely succeed in existing. Useless or even slightly 
 injurious characters may appear, and if they do not too seri- 
 ously affect the perpetuation of the race, they may persist. 
 Since the mutations appear fully formed, there is no diffi- 
 culty in accounting for the early stages of an organ. Thus, 
 on the supposition of natural selection, it is difficult to see, 
 for example, how the first slight movement of the eye of the 
 flounder toward the upper side (see p. 320) could be a favor- 
 able variation, which it should be according to the selection 
 theory, in order to be preserved. Again, a difficulty in the 
 selection theory lies in the fact that the differences between 
 allied species consist largely in differences of unimportant 
 
112 GENERAL ZOOLOGY 
 
 organs, but this is the condition we should expect, according 
 to the mutation theory. 
 
 Professor Morgan brings his discussion to a close by a 
 statement contrasting the mutation theory with the selec- 
 tion theory, as follows : "Animals and plants are not changed 
 in this or in that part in order to become better adjusted 
 to a given environment, as the Darwinian theory postulates. 
 Species exist that are in some ways very poorly adapted to 
 the environment in which they must live. If competition 
 were as severe as the selection theory assumes, this imper- 
 fection would not exist. 
 
 " In other cases a structure may be more perfect than the 
 requirements of selection demand. We must admit, therefore, 
 that we cannot measure the organic world by the measure of 
 utility alone. If it be granted that selection is not a mold- 
 ing force in the organic world, we can more easily understand 
 how both less perfection and greater perfection may be present 
 than the demands of survival require. 
 
 " If we suppose that new mutations and 4 definitely ' inher- 
 ited variations suddenly appear, some of which will find an 
 environment to which they are more or less well fitted, we 
 can see ho^w evolution may have gone on without assuming 
 new species have been formed through a process of competi- 
 tion. Nature's supreme test is survival. She makes new 
 forms to bring them to this test through mutation, and does 
 not remodel old forms through a process of individual 
 selection." 
 
 MendePs Law of Heredity. Considerable attention has 
 lately been given to the experimental study of heredity and 
 variation by breeding animals and plants under close observa- 
 tion. Among the animals thus observed have been mice, 
 guinea-pigs, and rabbits. Little has been done along this 
 line with the insects. These experiments have been of great 
 interest in connection with what is known as Mendel's law. 
 
THE DOCTRINE OF EVOLUTION 113 
 
 Gregor Mendel was an Austrian monk, who experimented 
 with plants in his garden, and in 1865 communicated to the 
 Society of Naturalists at Briinn the substance of what has 
 since been described as " the greatest discovery in biology 
 since Darwin." As the result of later experiments the law 
 was rediscovered by Bateson. In our own country Professor 
 Castle, of Harvard University, has made observations on many 
 successive generations of guinea-pigs, mice, and rabbits. The 
 substance of most of the following statements has been taken 
 from his studies. 
 
 Mendel's law asserts that when mating occurs between two 
 animals differing in some character, the offspring (hybrids) 
 will frequently exhibit the characters of one parent only. 
 A particular character exhibited in that way is said to be 
 " dominant." If albino rabbits (white, with pink eyes) are 
 crossed with gray rabbits, all the offspring are gray, that color 
 being dominant. The character (in this case, whiteness) which 
 is not seen in the immediate offspring is said to be "recessive." 
 That the albinism (white character) is really present in the 
 second generation, although invisible, may be demonstrated 
 by permitting pairs of these hybrid rabbits to breed. The 
 principle may be called " the law of dominance." It does not 
 seem to be of universal application, as sometimes the young 
 have a character of their own. Thus, if a lop-eared rabbit is 
 bred with a short-eared rabbit, the young will have ears of 
 an intermediate length. There is no way of knowing what 
 the character of the young will be ; it can only be determined 
 by experiment. When once determined, however, the char- 
 acter is always the same for every hybrid, provided the par- 
 ents are of pure breeds. 
 
 The essential part of Mendel's discovery is this : that 
 the hybrids resulting from the crossing of animals, such as 
 white and gray rabbits already spoken of, whatever their own 
 character, will produce ripe germ-cells (reproductive cells, 
 
 a o 
 
114 GENERAL ZOOLOGY 
 
 see p. 210), which bear only the pure character of one 
 parent or the other, but never both ; and these will be pro- 
 duced in equal numbers. This is known as " the law of the 
 purity of the germ-cells." From this law follows the occur- 
 rence in the next and succeeding hybrid generations of a 
 definite number of forms in definite numerical proportions. 
 Thus in the third generation of rabbits, produced by the 
 breeding together of the progeny of the gray and the albino 
 rabbits already referred to, there are, in nearly every case, 
 three gray young to one albino. Results similar to these 
 were obtained by Professor Castle with mice and guinea- 
 pigs also. 
 
 The explanation of why a character may manifest itself in 
 the third generation, after being invisible in the second, is 
 to be found in the theory that characters of organisms are 
 transmitted from generation to generation only in the germ- 
 cells, and by extremely minute bodies, called chromosomes, 
 within these cells. The second generation is all gray, because 
 in the united germ-cells from male and female parents the 
 chromosomes which bear the gray character are more powerful 
 to express themselves in the appearance of the young which 
 is produced than are those chromosomes which bear the 
 albino character. However, the albino chromosomes are not 
 destroyed, but are carried along with the others and give 
 rise to other chromosomes of their own kind, until, in the 
 experiment of breeding two hybrids, there occurs the oppor- 
 tunity for one albino germ-cell from each of the two sexes 
 to unite and produce an albino young. The mathematical 
 chances of such an occurrence may be expressed in an alge- 
 braic formula in which D represents dominant germ-cells 
 (half the total number) and R represents recessive germ- 
 cells (half the total number). A D-cell may unite with 
 another Z>-cell, or it may unite with an It-cell. Similarly an 
 R-cell may unite with an A'-cell or with a D-cell, thus : 
 
THE DOCTRINE OF EVOLUTION 115 
 
 D and R 
 
 
 Of the three dominant individuals one is a pure dominant, 
 but it is impossible to say at first which one that is, except 
 by further breeding. The pure dominant, when bred with 
 another pure dominant, will produce only gray rabbits, and 
 these will produce gray rabbits generation after generation. 
 Albinos ^obtained in experiments like the one described will 
 breed true generation after generation, if mated with other 
 albinos. When one of the hybrid dominants, D(R), is mated 
 with a recessive animal, half the young are hybrid dominants 
 and half are recessives. Two hybrid^ mated will produce 
 young in the proportion of three gray to one albino, as in the 
 third generation. 
 
 Experiments to determine the dominant or recessive nature 
 of other characters, such as length of hair and smoothness of 
 coat, show that short hair in guinea-pigs dominates over long 
 hair, and a rough coat over a smooth coat. It is also true 
 that the various characters, so far as tested, are inherited 
 quite independently of one another. A smooth coat may be 
 associated with white hair or with pigmented hair in guinea- 
 pigs, and a rough coat also with white hair or with pigmented 
 hair. An experimenter, by controlling the combinations of a 
 number of characters, knowing which is dominant and which 
 recessive, may produce several distinct types of animals 
 within the same species. 
 
 If future experiments should support Mendel's law, we 
 should then be able to understand how it is that races sud- 
 denly spring into existence in nature and become established. 
 
CHAPTER XI 
 
 THE SPIDERS AND ALLIES (ARACHNIDA) AND THE CENTI- 
 PEDS AND MILLEPEDS (MYRIAPODA) 
 
 A noiseless, patient spider, 
 
 I marked where, on a little promontory, it stood isolated ; 
 Marked how, to explore the vacant, vast surrounding, 
 It launched forth filament, filament, filament out of itself ; 
 Ever unreaching them ever tirelessly speeding them. 
 
 WALT WHITMAN. 
 
 Spiders. Spiders have several of the anterior somites joined 
 into a single mass, the head-thorax, or cephalothorax(Fig.5S, 1), 
 followed by the nearly spherical abdomen (Fig. 58, 2). The 
 cephalothorax bears six pairs of appendages, two pairs 
 of the nature of jaws and four pairs of walking-legs (Fig. 
 58, 3). The mandibles (Fig. 58, 4), the first pair of jaws, are 
 appendages composed of two segments, of which the terminal 
 segment is sharp-pointed and hollow, for the passage of a 
 poisonous secretion from a gland placed partly in the head 
 and partly in the basal segment. The second pair of jaws, or 
 maxillce, bear jointed palpi (Fig. 58, 5), used for handling food. 
 On the front of the head are eight simple eyes ; compound 
 eyes and an ten use are wanting. 
 
 Two little slits on the under side of the abdomen open 
 into the breathing-organs (Fig. 58, 6), which consist of a pair 
 of sacs containing a number of thin plates, like the leaves of 
 a book, through which the blood passes for the exchange 
 of gases. Between the two slits are the external openings 
 of the reproductive organs (Fig. 58, 7). At the end of the 
 body are three pairs of spinnerets (Fig. 58, 0), consisting of 
 a number of little tubes leading from glands in the abdomen, 
 
 116 
 
THE ARACHNIDS AND THE MYRIAPODS 117 
 
 which secrete a viscous fluid that hardens into silk on 
 exposure to the air. Two trachece (Fig. 58, 8), which give off 
 branches to different parts of the abdomen, open just in front 
 of the spinnerets. 
 
 Many spiders build circular 
 webs of silk, in which they cap- 
 ture insects to suck their blood. 
 A common species of garden 
 spider (Argi'ope ripa'ria) is shown 
 in Fig. 59. The spider first spins 
 a line across the space where the 
 web is to be, and then attaches 
 near its center other threads, 
 which it carries to different points, 
 making the radiating foundation- 
 lines of the web. These lines are 
 all dry and inelastic. Concentric 
 spiral lines of an adhesive nature 
 are then added, the hind legs 
 being used to place the threads, 
 and an oval cover of silk is spun 
 in the center, beneath which, or FlG 5g External Anatomy of th 
 
 ' f* "I ~1 1 1 P j 1 "Til 
 
 Spider (Epeira vulgaris). 
 larged. (After Emerton) 
 
 ie 
 
 En- 
 
 in a folded leaf at the side, the 
 spider lurks in watch for its prey. 
 A zigzag band of white silk cross- 
 ing the center is usually added 
 to strengthen the web. When 
 an insect is captured the spider 
 rushes out, and if there is any 
 danger of the escape of the prey, it is deftly wound with 
 more silk till its struggles have ceased. If it proves to be a 
 wasp or other dangerous capture, or if it is too big to be 
 safely managed, it is often assisted to escape by cutting the 
 web, which is then repaired for another victim. 
 
 1, cephalothorax; 2, abdomen; 3, 
 fourth leg; 4, mandible; 5, palpus; 
 
 6, opening to breathing-organ ; 
 
 7, openings to reproductive 
 organs; 8, trachea;; 9, spinnerets 
 (3 pairs) ; 10, anus 
 
118 
 
 GENERAL ZOOLOGY 
 
 Like the click-beetles and many others of the Coleoptera, 
 this spider when alarmed has the habit of dropping to the 
 
 ground as if dead. It spins a 
 thread of silk as it drops ; when 
 
 FIG. 59. Garden-Spider and Web. 
 Reduced 
 
 the danger is over it is able by this means 
 to find its way back to the iveb. 
 
 The eggs are laid in the autumn in a sac of silk (Fig. 60), 
 which may contain from five hundred to two thousand eggs. 
 These eggs hatch early in the winter, and the young live in 
 the case through the cold weather, feeding on each other, so 
 that by spring a comparatively small number of spiders 
 
THE ARACHNIDS AND THE MYRIAPODS 119 
 
 emerge. By successive molts, without marked metamorphosis, 
 
 they reach their adult size. 
 
 The dark-colored, hairy spiders (Lyco'm) found under 
 
 sticks and stones usually build tubular nests in the ground, 
 
 which they line with silk. They do not 
 
 make a web to capture their prey, but 
 
 spring upon it as they run about in search 
 
 of food. The females may often be seen 
 
 dragging after them the large gray ball 
 
 which contains, at first, their eggs, and 
 
 afterwards the young. After a certain 
 
 time the young leave the silken case, and 
 
 for some time longer run about over the 
 body of the mother. 
 
 These spiders are 
 often called tarantulas, 
 but that name should be 
 restricted to the large, 
 hairy spiders of the 
 warm parts of the world, 
 which can be distinguished from all other 
 spiders by the fact that the terminal seg- 
 ment of the mandibles works vertically 
 instead of horizontally. Tarantulas are 
 
 universally dreaded in the countries where 
 FIG. 01. Trap-Door , , . . 
 
 Spider Burrow, the J g row to be of lar g e Slze > and the J are 
 showing Side Tube, believed to be very poisonous. The ability 
 Reduced. (After of ider to tl human skin 
 
 Emerton) \ 
 
 depends, of course, on its size and the 
 strength of its jaws ; the effect produced by the bite depends 
 not only on the amount of poison injected into the wound 
 but also on the age and mental and physical condition of 
 the person bitten. Though many stories of death by taran- 
 tula bites have been told, most of them are clearly untrue. 
 
 FIG. 60. Egg-Case of 
 the Garden-Spider. 
 Natural size. (After 
 Wilder) 
 
120 
 
 GENERAL ZOOLOGY 
 
 Persons have been bitten by them, and only temporary 
 pain and swelling have resulted, something like that which 
 
 follows the sting of a bee. 
 
 Among the most interesting of 
 the tarantula family are the trap- 
 door spiders of the western and 
 southern states, and of southern 
 Europe. They build burrows, 
 Avhich they line with silk, and 
 provide with a lid lined with silk, 
 attached by one edge to the mouth 
 _of the burrow. A European spe- 
 cies builds a nest with a side tube 
 (Fig. 61) into which it can retreat 
 
 Fio.62. .lumping-Spider. Enlarged. - i{ o f danger, closing a door 
 (After Peckham) ' 5 
 
 at the entrance ot this tube. 
 
 The jumping-spiders (As'tia vittata, Fig. 62) may be recog- 
 nized by the stout, hairy body and the square head. They are 
 usually conspicuously colored, and have bright, staring eyes. 
 They build no 
 webs to capture 
 their prey, but 
 spring upon it, 
 often from a 
 considerable 
 distance. These 
 spiders are 
 interesting on 
 account of the 
 remarkable an- 
 tics which the 
 males perform before the females. Dr. and Mrs. Peckham, 
 in their study of the habits of this group, say : " The fact 
 that the males vie with each other in making an elaborate 
 
 FIG. 63. Harvestman. Natural size 
 
THE ARACHNIDS AND THE MYRIAPODS 121 
 
 display not only of their grace and agility but also of their 
 beauty before the females, and that the females after atten- 
 tively watching the dances and tournaments which have been 
 executed for their gratification, select for their mates the 
 males that they found most pleasing, points strongly to the 
 conclusion that the great differences in color and in ornament 
 between these spiders are the result of sexual selection." 
 
 Harvestmen. The long-legged harvestmen, or daddy-long- 
 legs (Liolu'num, Fig. 63), are allied to the spiders. They 
 can be recognized by the eight extremely long legs, which are 
 thus developed as organs of touch, as well as for walking. 
 They are harmless creatures, found in damp and shady places ; 
 they feed on small insects, especially aphids. 
 
 Mites and Ticks. The mites and ticks are related to the 
 harvestmen and to spiders. They show less segmentation of 
 the body than the preceding groups. They are small, oval, 
 eight-legged forms. The mouth-parts are more or less united 
 to form a beak. Some are parasitic on other animals (Ixo'des, 
 Fig. 64) ; others, 
 like the common 
 red mite which in- 
 fests house-plants, t&^^&^S&.M- A 
 suck the fluids of 
 vegetation. One of 
 them produces the 
 disease known as 
 mange, among 
 
 dogs, horses, and FIG. 04. Cattle-Tick. Enlarged. (After Howard, 
 COWS. Year-book, Department of Agriculture, 1891) 
 
 Scorpions. The 
 scorpions have the 
 body plainly segmented. In the common scorpion (Bu'thus, 
 Fig. 65), found under sticks in our southern states, the 
 maxillae are greatly elongated, making a formidable-looking 
 
 A, parasite without food ; B, parasite rilled with blood 
 from host 
 
122 
 
 GENERAL ZOOLOGY 
 
 pair of claws. The abdomen is provided with a sting at its 
 extremity. The whip-scorpion (Thelyph'onus), also found in 
 
 similar situations in the South, 
 is another formidable -looking 
 creature, with immensely devel- 
 oped maxillse, which are used 
 to pull open decaying wood in 
 search of small insects, which 
 form its food. Its appearance 
 accounts for the dread it in- 
 spires, but there is no evidence 
 to show that it is harmful to 
 man. 
 
 Definition of Arachnida (Gr. 
 arachne, spider). All the forms 
 considered so far in this chapter 
 
 FIG. 65. Photograph of Scorpion, belong to the class Arach'nida. 
 Natural size. (American Museum The Arachnida a^ree in having 
 of Natural History) , , ., , fo . 4 
 
 the somites iused into two more 
 
 or less clearly marked regions, the cephalothorax and the 
 abdomen. There is no distinct head, as in insects. Eight 
 legs are present. The Arachnida undergo no well-marked 
 metamorphosis. 
 
 Centipeds. The common centiped (Litho'bius, Fig. 66) found 
 under the bark of trees is an elongate, flattened animal, 
 with long antennae, many somites, and a pair of legs on every 
 somite. There is a poison-gland in the base of the first pair 
 of legs, which is used to kill earthworms and insects, upon 
 which Lithobius feeds. The female is furnished with two 
 hooks at the end of the body close to the oviduct. When an 
 egg is laid it is seized by these hooks and rolled over till it 
 is completely covered with earth, which adheres to the egg 
 on account of a sticky substance with which it is covered. 
 It has been observed that if a male Lithobius perceives the 
 
THE ARACHNIDS AND THE MYRIAPODS 123 
 
 egg before it is disguised by the covering of earth, he 
 attempts to seize and devour it. 
 
 Centipeds are widely distributed over the world. In the 
 tropics they grow to be over thirty centimeters (one foot) 
 long. Some species are poisonous, even to man, and death 
 has been known to result from their bite. They are active 
 
 --rC* 
 
 FIG. 06. Centiped and Milleped. Reduced 
 
 creatures, and feed on living animals. The number of somites 
 varies from about nine to over two hundred. A pair of legs 
 is attached to each somite. The following lines were written 
 by Professor E. Ray Lankester, of England, after an attempt 
 to study the order in which the legs were moved. 
 
 A centipede was happy quite 
 
 Until a toad in fun 
 
 Said, " Pray, which leg moves after which ? " 
 
 This raised her doubts to such a pitch, 
 
 She fell exhausted in the ditch, 
 
 Not knowing how to run. 
 
124 GENERAL ZOOLOGY 
 
 Millepeds. Other elongate forms called millepeds (Spirob'- 
 olus. Fig. 66) may be distinguished from the centipeds by the 
 more cylindrical body. Millepeds also possess a greater num- 
 ber of legs than centipeds, each somite, with the exception of 
 several coming directly after the head, apparently bearing two 
 pairs of legs. They live in damp places and feed on living or 
 decaying vegetable matter ; they are entirely harmless. Many 
 have the power of coiling themselves up when disturbed. 
 The larvae, when first hatched, have few somites, and but 
 three pairs of legs. 
 
 Definition of Myriapoda (Gr. myria, many ; pous, foot). 
 The centipeds and millepeds are included in the class Myri- 
 ap'oda. Myriapods are distinguished from insects and arach- 
 nids by the greater number of somites and appendages. They 
 breathe through spiracles placed along the sides of the body. 
 After hatching from the egg, the young develop without any 
 marked metamorphosis. It is likely that centipeds and mille- 
 peds are not in reality as closely allied as might seem from 
 the external appearance. 
 
OF THF 
 
 UNIVERSITY j 
 
 OF ,>, 
 
 CHAPTER Xll 
 THE CRAYFISH 
 
 All night the crawfish deepens out her wells, 
 
 As shows the clay that freshly curbs them round. 
 
 J. P. IRVINE, Summer Drought. 
 
 Habitat and Distribution. Crayfishes, also called crawfishes, 
 are found in bodies of fresh water on every continent except 
 Africa, and in many of the large islands. The eastern 
 American species, Cam'barus af 'finis (Fig. 67), which grows to 
 the length of live or six inches, may be taken as an example 
 of the several genera and the m'any species which are known 
 by the common name crayfish. 
 
 External Plan of Structure. The body, except for the 
 ventral surface of the abdomen, is covered with a thick wall, 
 formed, like the covering of insects, from the hardening of a 
 secretion of the outer layer of the skin. Unlike the insects, 
 this protecting sheath is filled with carbonate of lime. The 
 body is divided into a cephalothorax and abdomen (Fig. 67, 1, 2), 
 as in the arachnids. There are no indications on the dorsal 
 surface of separate somites in the cephalothorax, but on the 
 ventral surface transverse grooves and paired appendages 
 indicate a division into thirteen somites. The abdomen 
 (Fig. 67, 2) plainly consists of seven somites, of which the 
 first six bear jointed appendages. The external plan upon 
 which the crayfish is formed is similar to that of the insects, 
 arachnids, and myriapods ; that is, a series of somites placed 
 one after the other, with all appendages jointed or segmented. 
 
 The Cephalothorax. The shell covering the dorsal and 
 lateral surfaces is distinct from the hard parts elsewhere on 
 the body, and is termed the carapace. At the anterior dorsal 
 
 125 
 
126 
 
THE CRAYFISH 127 
 
 end of the carapace there is a prominent beak, or rostrum 
 (Fig. 67, 3), beneath which, on either side, extends an eye 
 (Fig. ,67, 4), borne on a stalk. Study of the living crayfish 
 enables one to see how well the rostrum protects the stalked 
 movable eye. The eye is compound ; the manner in which 
 the image is formed is practically the same as in the insects. 
 Crayfishes have no simple eyes. 
 
 The cephalothorax bears at its anterior end six slender, 
 many-jointed feelers, the shortones calledawfew>m?e (Fig. 67,6), 
 the long ones, antennce (Fig. 67, 6). The four antennules are 
 really the two branches of a single pair of appendages coming 
 from a short stem which is attached to the body. On the 
 upper surface of one of the segments of this stem is a small 
 hole surrounded by a number of bristles. The hole opens into 
 a cavity which contains several small grains of sand placed 
 there by the crayfish itself after every molt. (The process of 
 molting is explained in Chapter XIII.) This organ, with 
 its nerve-connections, constitutes the " ear " of the crayfish 
 (Fig. 67, 7), the chief function of which is to help the ani- 
 mal to balance itself during locomotion. The technical name 
 otocyst is given to it. The antennae are the inner branch of a 
 pair of double-branched appendages, of which the outer branch 
 is short, flat, and triangular, and lies just below the eyes, where 
 it serves a protective function. It is called the squame. On 
 the lower, or basal, segment of the stem of this pair of append- 
 ages is a small, hard, round swelling, or papilla (Fig. 67, 8; 
 Fig. 68, II, l), on which is the opening from the "kidney," or 
 green-gland, shown in broken outline in Fig. 67. 
 
 About the mouth are six pairs of appendages. The first, 
 the hard mandibles (Fig. 67, 9), are adapted to crushing into 
 smaller bits the food seized by the large claws. Each mandi- 
 ble bears a short palpus (Fig. 68, III, 2). Next in the series 
 are the first and second maxillce (Fig. 68, IV, V) and the first, 
 second, and third maxillipeds (Fig. 68, VI, VII, VIII). The 
 
128 GENERAL ZOOLOGY 
 
 maxillipeds help to hold the food in place at the mouth ; the 
 maxillse also assist in this, and probably, with the upper 
 and lower lip and the wall of the mouth-cavity, are the seat 
 of the sense of taste. The second pair of maxilla} also act 
 as "gill-bailers " (Fig. 68, V, 3-4 ; Fig. 69, 1), which, by their 
 motion, help to maintain a current of water in the gill-chamber 
 (Fig. 69, 5), thus providing oxygen for respiration. In the 
 maxillipeds a basal stem, with two branches arising from it, 
 can be easily distinguished. The separation between head 
 and thorax is understood to come between the second maxillae 
 and the first maxillipeds, thus making five pairs of append- 
 ages in the head-region. 
 
 After the maxillipeds the next thoracic appendages are the 
 large claws, or chelipeds (Fig. 67, 11), composed of seven seg- 
 ments, of which the last two from the body, or distal two, 
 are adjusted to form a nipper, with which the animal captures 
 and holds even rapidly swimming fishes. The remaining 
 thoracic appendages are the four pairs of walking-legs (Fig. 67, 
 12 ; Fig. 68, XI, XII), also composed of seven segments, the first 
 two pairs with nippers at their ends, and the last two pairs 
 without nippers. The three pairs of maxillipeds, the one pair 
 of chelipeds, and the four pairs of walking-legs constitute the 
 eight pairs of appendages of the thorax. 
 
 The Abdomen. There are six pairs of appendages on the 
 abdomen. The first abdominal appendages of the female are^ 
 small, single, and thread-like ; in the male (Fig. 67, 13), they 
 are long and rigid, differing considerably from all the others 
 except the second pair (Fig. 67, 14). The second abdominal 
 appendage in the female is like the third. ' The third, fourth, 
 and fifth pairs, called swimmerets (Fig. 67, 15), are alike in 
 both sexes. The pair of appendages of the sixth somite 
 (Fig. 67, 16) are made up of broad flat branches jointed to 
 a short thick stem, and form, with the last somite, called 
 the telson '(which is without appendages), a strong tail-fin. 
 
4 XI 
 
 FIG. 68. Appendages of the Crayfish (Cambarus affinis), from the 
 
 left side. Natural size. 
 (I, II, III, etc., stand for the number of the somite in the animal's body) 
 
 1, protopodite; 2, eudopodite; 3, exopodite; 4, epipodite with gill-filaments; 
 5, gill with gill-filaments 
 
 129 
 
130 GENERAL ZOOLOGY 
 
 By doubling underneath it is capable of striking hard blows 
 against the water and forcing the crayfish suddenly backward. 
 A basal stem with two branches is to be clearly seen in all 
 the abdominal appendages except the first pair in the female. 
 
 Homology and Analogy. The fact that a stem and two 
 branches are apparent in several appendages which have been 
 mentioned, is important enough to deserve further discussion. 
 The simplest condition of the branched appendage is seen in 
 the third, fourth, and fifth abdominal appendages (Fig. 68, XVI). 
 If the branches are spread slightly, the form resembles the 
 capital letter Y. Taking a swimmeret as a model, the stem, 
 which is termed the protopodite (Fig. 68, XVI, 1), is seen to be 
 made up of a short basal segment, the coxopodite^ and a long 
 segment, the basipodite. Of the two branches, the one nearest 
 the median line of the body is the endopodite (Fig. 68, XVI, 2); 
 the outer is the exopodite (Fig. 68, XVI, 3). Wherever in the 
 series of appendages we find a stem and two branches, the 
 protopodite corresponds to the protopodite of all the other 
 appendages of the series, and so with the endopodites and 
 the exopodites. 
 
 The legs seem to be formed on a different plan, but we 
 know from the embryology (the science of the early stages 
 of development) of the crayfish that while the egg is still 
 unhatched the embryo has legs that have two branches (com- 
 pare larval lobster, Fig. 70), and that the outer and smaller 
 one disappears before the embryo hatches. The first and 
 second 'maxillae have the parts of a typical crayfish append- 
 age, divided as shown in Fig. 68, IV, V. The crushing part 
 of the mandible is thought to represent the coxopodite and 
 basipodite combined. The little palpus is the endopodite; 
 the exopodite is missing in the adult. 
 
 In this brief description of the appendages of the crayfish 
 two very important facts in morphology (the science of form) 
 have been suggested. One, the inherent similarity of structure 
 
THE CRAYFISH 131 
 
 of the parts of the appendages in a series ; the other, a diver- 
 gence in the forms of appendages because of adaptations to 
 different uses. Perhaps no fact in nature is better known 
 than the fact that organs are adapted in general form and in 
 special parts to perform particular functions. It is only when 
 we come to examine a series of organs like the appendages of 
 the crayfish that we obtain some insight into the very great 
 changes which must often take place before organs become 
 adapted to the performance of even slightly different func- 
 tions. Morphologists, realizing the extent of the principle of 
 adaptation, have been able to show that in a series of organs, 
 like the appendages of the crayfish, any part of an appendage, 
 as, for example, the endopodite, can be shown to correspond to 
 the endopodite in all the other appendages, no matter what 
 the superficial differences may be. 
 
 In referring to these corresponding parts we use the tech- 
 nical term " homologous parts." The protopodites of all the 
 appendages are structurally similar ; that is to say, they are 
 situated in the same relation to adjacent parts all through 
 the series. Likewise the legs and the antennse, being inner 
 branches (endopodites), and being jointed to the second seg- 
 ment of the appendages, are homologous parts. If such unlike 
 parts as the antenna; and the legs are homologous, it is, of 
 course, very clear that the legs and the chelipeds are homolo- 
 gous as whole endopodites, and also segment by segment from 
 the base to the tip. The crayfish appendages are examples of 
 serial homology ; in a broader sense, homology deals with 
 organs of all sorts that have a corresponding position and origin 
 in different animals. In connection with the study of homol- 
 ogy, the science of structurally similar parts, we find the word 
 " analogy " in frequent use. The difference between homolo- 
 gous parts and analogous parts is one easily made clear by 
 applying the terms to the present study. The legs of cray- 
 fishes are analogous parts, because their use is the same ; they 
 
132 GENERAL ZOOLOGY 
 
 are homologous parts because they are structurally similar. 
 The same is true, to take another case, of the swimmerets of 
 the third, fourth, and fifth abdominal somites ; but whereas the 
 antenna and the legs are homologous, they are not analogous, 
 because their functions are different. Ordinarily, zoologists 
 use the word " analogous " in a little different way from that 
 suggested above. Instead of being applied to structures in 
 the same animal, it is most commonly applied to organs of 
 similar function in different animals ; for example, the wings 
 of insects and birds, organs which have the same use but 
 are not homologous. 
 
 The Digestive System. The mouth (Fig. 67, 17) of the cray- 
 fish is located between the two mandibles. Reference to 
 Fig. 67, 18, will give an idea of the length of the oesoph- 
 agus and the position and relative size of the stomach 
 (Fig. 67, 19). The latter has two more or less clearly marked 
 ' regions, the anterior enlarged region and the posterior 
 funnel-shaped space. As the food passes into the anterior 
 portion the unbroken bits are caught between the contig- 
 uous grinding surfaces of three hard processes (Fig. 67, 20) 
 extending from the stomach-wall. These three "teeth" 
 one in the median dorsal line and two at the sides together 
 constitute the " gastric mill." Muscles attached to them and 
 to the inner surface of the carapace, by contracting, perform 
 the operation of grinding. The posterior part of the stomach 
 is filled with slender filaments which extend from the wall 
 out into the cavity (Fig. 67, 21). These filaments prevent the 
 unbroken particles of food from passing through into the 
 intestine, allowing only the thoroughly ground-up food to 
 do so. Absorption does not occur in either division of the 
 stomach /but in the intestine (Fig. 67, 24), which extends 
 straight 'from the stomach to the ventral surface of the tel- 
 son. A pair of digestive glands (Fig. 67, 23) lie one on either 
 side of the stomach and intestine. They open by tubes into 
 
THE CRAYFISH 
 
 133 
 
 the posterior division of the stomach, and have the combined 
 functions of digesting food and absorbing some of the prod- 
 ucts of digestion. 
 
 The Circulatory, Respiratory, and Excretory Systems. The 
 heart (Fig. 67, 26) is a muscular organ lying beneath the dor- 
 sal body-wall posterior to the stomach. The blood finds its 
 way into the heart through three pairs of openings furnished 
 with valves to prevent the escape of blood. When the heart 
 contracts the blood flows both forward and backward at the 
 
 FIG. 69. Gill-Chamber and Gills of the Crayfish (Cambarus affinis). 
 Slightly enlarged 
 
 1, gill-bailer on second maxilla; 2, first maxilliped; 3, second maxilliped with 
 first outer gill; 4, sixth outer gill; 5, last gill of inner series 
 
 same time, forward by five tubes and backward by two tubes, 
 called arteries (Fig. 67, 29, 30, 31). These arteries branch into 
 many smaller vessels with open ends ; from the open ends 
 the blood flows over the tissues of the body in sinuses, all of 
 which connect with a still larger median cavity, the ventral 
 sinus, lying along the ventral wall of the thorax and abdomen. 
 Branches from the median ventral sinus extend out into the 
 gills. The blood is carried back to the base of the gills by 
 parallel channels, and finally carried lip to the pericardial 
 sinus in which the heart lies. The set of delicate, plume-like 
 
134 GENERAL ZOOLOGY 
 
 gills (Fig. 69, 4) are attached to and near the basal joints of 
 the thoracic appendages, and extend dorsally into partially 
 closed chambers bounded by the body-wall on the inside and 
 the ventral extension of the carapace on the outside. Since 
 it is sometimes necessary for the crayfish to make journeys 
 from pond to pond in dry seasons, the gills are thus protected 
 from sudden drying. Water is drawn into and out of this 
 gill-cavity by means of the action of the gill-bailers on the 
 second maxillae already referred to (Fig. 68, V, 3-4 ; Fig. 69, 1). 
 The blood flowing into the gills from the ventral sinus gives up 
 its carbon dioxide waste and receives oxygen from the water. 
 
 The green-glands are prominent organs (Fig. 67, 8) in the 
 ventral region of the body-cavity in the head. A large artery 
 carries blood to them, and nitrogenous waste matter is sepa- 
 rated by them from the blood' and finds its way to the opening 
 on the basal segment of the antennae. 
 
 The Nervous and Muscular Systems. The "brain," the 
 supraoesopliageal ganglion, of the crayfish is a mass of nervous 
 tissue resulting from the aggregation of several pairs of ganglia 
 (Fig. 67, 33). Pairs of nerves may be traced to the eyes, the 
 antennas, and the antennules. Two slender connectives, simi- 
 lar to those described for the locust, extend from the brain, 
 encircle the oesophagus, and join the sulxxsopliageal ganglion 
 (Fig. 67, 34) posterior to the mouth. This ganglion, too, is 
 really a combination of several pairs of ganglia, which send 
 off the nerves to some of the head somites and to some of the 
 thoracic somites. There are five other ganglia in the thorax 
 joined to each other (first thoracic ganglion, Fig. 67, 35), and to 
 the six ganglia in the abdomen, by the double nerve-cord which 
 is a continuation of the connectives that encircle the oesophagus. 
 
 The muscles of the abdomen are arranged in a very com- 
 plicated fashion and are capable of powerful action. In all 
 parts of the body muscles are attached to the inner surface 
 of the exoskeleton. 
 
THE CRAYFISH 135 
 
 The Reproductive System. The male reproductive organ, 
 the spermary (Fig. 67, 37), and the female reproductive organ, 
 the ovary, lie just below the heart ; each consists of a three- 
 lobed organ. In the male a sperm-duct (Fig. 67, 38) leads from 
 either side of the spermary to an opening (Fig. 67, 39) on the 
 basal segment of either fourth walking-leg. In the female the 
 oviducts lead to similar openings on the second walking-leg. 
 
 Development. Cambarus affinis lays its eggs in the spring. 
 Most species of crayfishes lay their eggs then. The princi- 
 pal burrowing species, Cambarus diog'enes, lays its eggs in 
 April and they hatch in May, while a river species, Cambarus 
 immu'nis, lays its eggs in the fall and they hatch in the fol- 
 lowing spring. When the egg-lay ing season arrives the male 
 deposits spermatozoa in a shallow cup called the annulus, on 
 the ventral surface of the female, between the fourth pair of 
 legs. The mass of spermatozoa stays in the annulus till the 
 female lays her eggs. It is not certain how long the sper- 
 matozoa lie there before the eggs are laid. However, when 
 the eggs are discharged from the oviduct they pass back over 
 the mass of spermatozoa. Fertilization is accomplished when 
 a spermatozoon enters an egg. The fertilized eggs are carried 
 back and fastened to the swimmerets by a glutinous substance. 
 There the embryos develop, and the larvae, when they hatch, 
 remain clinging to the female's swimmerets by their cheli- 
 peds for some time, probably several weeks. 
 
 Relation to Environment. Crayfishes live in a great variety 
 of places. They are fresh- water animals, but one species has 
 also been found in the sea. As a rule, they crawl on the 
 bottom of rivers, brooks, and ponds, concealing themselves in 
 crevices or under protecting pieces of rock or submerged logs. 
 Several species make burrows in the soft earth of meadows. 
 The most widely distributed of these is Cambarus diogenes. 
 Species which live in ponds that are likely to dry up in the 
 summer, and also a few that live in rivers, leave the water 
 
136 GENERAL ZOOLOGY 
 
 in summer and burrow into the earth until they come to 
 water. At the bottom of their burrows, sometimes three feet 
 from the surface, they dig out a flask-shaped enlargement 
 and stay in it or near it till the next spring. The chimneys 
 made at the top of the " wells," referred to in the quotation 
 at the beginning of the chapter, are made by the burrowing 
 crayfish merely as an incident in getting rid of the mud 
 brought from below. Sometimes crayfishes stop up their bur- 
 rows completely. In that case they probably remain in a 
 dormant condition without food till spring returns. In the 
 bed of a pond or river where jutting stones abound cray- 
 fishes rest with the abdomen doubled beneath them and the 
 head toward the open. Boys often lure them from their 
 hiding-places with a piece of meat tied to the end of a 
 weighted string. The animal invariably seizes the meat in 
 a cheliped, and usually can be drawn to the surface before it 
 has time to " think " the matter over and let go. 
 
 The distribution of crayfishes is directly related to their 
 power of adapting themselves to conditions of considerable 
 variability. If a certain definite degree of temperature or of 
 clearness of water were required, they would be restricted to 
 a very limited area, and, indeed, it would be difficult for 
 them to maintain themselves at all. As it is, we find them 
 in drinkable water, in muddy water, in sulphur-laden water, 
 and in sea-water, but never in the water of streams or ponds 
 of a country devoid of limestone. This accounts for their 
 absence from the eastern part of New England, where the 
 rocks are largely of granite. 
 
 A striking example of adaptation to an unusual environ- 
 ment is found in the cave-dwelling crayfish, Oambarus pel- 
 lu'cidus. Professor Eigenmann of Indiana, Dr. O. P. Hay 
 of New York, and others have explored the caves of Indiana 
 and Kentucky for the purpose of studying the animals of 
 their subterranean rivers. The blind crayfish has small and 
 
THE CRAYFISH 137 
 
 abortive eyes, but its sense of touch is developed to a mar- 
 velous degree of delicacy. Dr. Hay says that although the 
 crayfishes may be resting quietly on the bottom of a rivulet, 
 it is impossible to capture them with a net. They feel the jar 
 in the water and dart backward with great accuracy to a pro- 
 tecting rock. In general appearance the blind crayfish differs 
 from others chiefly in having an exoskeleton which is so clear 
 that one may see the animal's stomach as a blue mass within, 
 and in being provided with antennae longer than the body. 
 
 Crayfishes are eaten by fish large enough to swallow them, 
 and they in turn catch small fish with great facility, and also 
 insect larvae, snails, tadpoles, and even frogs. They have 
 been known to prey upon each other, and also to eat dead 
 organic matter ; but as a rule they eat plant and animal food 
 in the fresh condition. 
 
 They are protected by their hard shells from the attacks of 
 passing fish. The color of the shell is more effective still, 
 since whatever the color of the bottom, it is closely imitated 
 in the distribution of color pigment in the shell. The usual 
 color is muddy greenish-black ; in ponds where the mud is 
 bluish, the shell is also blue. An account has been written 
 of the crayfishes found in Sandy Lake, Pennsylvania, where 
 the bottom is white marl and clay. All the crayfishes which 
 have been captured in the pond " vary in color from almost 
 pure white to pink, or in some cases to a delicate greenish 
 tint. They are practically invisible when at rest. The fisher- 
 men of the district capture them and use them for bait to 
 catch bass in other lakes where the bottom is of dark mud." 
 
 In America crayfishes seem to be used as food chiefly by 
 the French portion of our population. Possibly the rapid 
 depletion of the lobster fisheries may cause people generally 
 to turn to the lobster's nearest edible relative. In France the 
 crayfish industry is quite extensive, there being many farms 
 on which crayfishes are raised for the market. 
 
CHAPTER XIII 
 THE JOINTED-FOOT ANIMALS: ARTHROPODA 
 
 The Shelly Crawlers each returning year 
 
 Cast off their shells and new-made Armour wear. 
 
 OPPIAX, Ilalleutica. 
 
 THE ALLIES OF THE CRAYFISH : CRUSTACEA 
 
 The Lobster. Except for the considerable difference in 
 size, and the slight differences in the shape of the body, 
 the number of gills, and the structure of abdominal append- 
 ages, the description of the adult crayfish would serve for an 
 account of the structure of our common species of Ameri- 
 can lobster, Hom'arus america'nus. The lobster is found in 
 greatest numbers along the coast of Maine and the Canadian 
 maritime provinces. Toward the south the number gradu- 
 ally decreases to the Delaware breakwater, beyond which 
 they are very rare. In their days of greatest abundance 
 they grew to be about sixty centimeters (two feet) in length, 
 weighing twenty-five pounds, but with the increase in the 
 activity of the lobster-fishing industry they are now rarely to 
 be found weighing over two pounds. 
 
 The lobster lives on the bottom. It is protectively colored, 
 but it does not depend wholly upon that condition for escap- 
 ing the notice of its enemies. In shallow waters lobsters are 
 known to conceal themselves beneath masses of brown sea- 
 weed in pits and holes, and also to find safe retreat beneath 
 jutting ledges of rock, where they rest with the abdomen 
 doubled beneath, ready to dart out and seize passing prey in 
 their claws. We have no way of knowing the exact habits 
 of the animal when at its greatest depth (a hundred fathoms), 
 
 138 
 
THE JOINTED-FOOT ANIMALS 139 
 
 but since its enemies are probably quite as persistent there as 
 in the shallow water, every means of defense is likely to be 
 employed to the utmost. 
 
 The lobster is capable of swimming with great rapidity, 
 by suddenly doubling its flexible, muscular abdomen beneath 
 and shooting backward through the water. The habit does 
 not appear to be depended on except to enable them to escape 
 from impending danger. Their usual mode of progression is 
 by walking on the tips of the last four pairs of thoracic 
 appendages, the chelipeds being extended anteriorly, appar- 
 ently to expose as little of their bulk to the water as possible. 
 The swimmerets waving in rhythmic motion aid the animal 
 in its movement along the sea-bottom. 
 
 With all their appearance of armored strength, lobsters are 
 very sensitive to changed conditions in their environment. 
 When captured and detained in "pounds " (artificially inclosed 
 spaces), in shallow water, they will, on the approach of win- 
 ter, dig burrows in the sea-bottom and cover themselves all 
 but their eyes and antennae. There they remain in a dor- 
 mant condition until the returning warmth of spring affects 
 the temperature of the water. In their natural environment 
 they migrate to the deep waters in the autumn months and 
 remain there till spring. We know that they do not make 
 burrows and lie inactive in the deep waters, because fishermen 
 catch them in baited traps in all the winter months. In the 
 winter in our latitude deep waters are warmer than shallow 
 waters; in summer the shallow waters are warmer. Lobsters 
 are sensitive to even slight changes in temperature. In the 
 early summer they have been known to return to deep water 
 immediately on the occurrence of a storm in the atmosphere 
 above them. Another factor which must operate strongly in 
 determining the migration to the shore is the greater supply 
 of food there. Lobsters do not appear to migrate up and 
 down the coast. Hence, if all the lobsters in a certain bay 
 
140 GENERAL ZOOLOGY 
 
 and vicinity are caught, the chances are against that region 
 recovering its lost supply. 
 
 Slow, inactive animals living on the bottom fall an easy 
 prey to lobsters. When confined in pounds, lobsters even 
 dig up clams and crush the shells in their powerful crush- 
 ing claw, which is the thicker one of the two. Fish also are 
 caught, even where both captor and prey have perfect free- 
 dom of action. Those who have studied the habits of lobsters 
 closely believe that although the lobster is a scavenger in 
 the sea, it nevertheless prefers living food to dead organic 
 matter. Seaweeds form part of their food. The processes of 
 eating, swallowing, grinding in the stomach, and digestion are 
 exactly the same as in the crayfish. 
 
 Molting in the lobster, as in some other animals with a hard 
 exoskeleton, is an extremely important and critical event, 
 since the store of vitality is drawn upon in preparation for 
 the act of shedding the hard armor, and in fully restoring a 
 protective sheath. In the act of molting, the lobster does 
 not, as a rule, split the dorsal shell. The animal bends, mak- 
 ing a sharp angle at the junction of the cephalothorax and 
 the abdomen. The soft body at that point begins to withdraw 
 from the carapace. Getting out of the rigid shell is made pos- 
 sible by a preliminary process of taking up into the blood the 
 lime in the exoskeleton, along the median line of the carapace, 
 at the rostrum or beak, and at the narrow joints of the cheli- 
 ped and walking-appendages. The blood leaves the append- 
 ages and flows into the sinuses of the cephalothorax. The 
 withdrawal of the cephalothorax and its appendages soon fol- 
 lows, and lastly the abdomen is withdrawn from its old cover- 
 ing, and the soft, defenseless lobster conceals itself as quickly 
 as its weakened condition will permit. The volume and 
 weight rapidly become greater, due to the absorption of water. 
 Later, while the new shell formed beforehand under the old 
 one is becoming harder, the water previously absorbed is 
 
THE JOINTED-FOOT ANIMALS 
 
 141 
 
 replaced by true tissue. This periodic growth of the lobster 
 
 really begins before the act of molting takes place; in fact, 
 
 the physiological need for more room is what brings about the 
 
 act of getting rid of the old exoskeleton. The number of 
 
 molts an individual lobster may have depends, in a great 
 
 measure, upon the abundance of its food. Males molt more 
 
 frequently than females ; hence the largest lobsters are always 
 
 males. Very young lobsters molt more 
 
 frequently than those of the size we 
 
 find in the market. During the process 
 
 of molting it sometimes happens that 
 
 an appendage is broken off. In the 
 
 ordinary course of its life, also, the 
 
 lobster may lose a claw or an antenna. 
 
 It is regenerated in two or three molts 
 
 after the accident. The crayfish arid 
 
 many other animals closely related to 
 
 these two have the same power. 
 
 The female lobster lays her eggs 
 usually during the summer months. 
 The eggs remain attached to the swim- 
 mere ts until the next spring, when 
 the embryos hatch. The larval lobster 
 (Fig. 70) immediately floats to the sur- 
 face, and for several weeks swims about 
 there. Its length at first is about eight millimeters (one third of 
 an inch). In general appearance it resembles the adult lobster, 
 except that the large thoracic appendages are two-branched 
 and the abdomen has no appendages. After the sixth molt the 
 lobster, then about two thirds of an inch long, has lost the outer 
 branches of the legs, has gained abdominal appendages, and is 
 nearly like the adult in other respects. At about this time the 
 young lobster leaves the surface, goes to the bottom, and 
 makes its way to well-protected places near the shore. 
 
 FIG. 70. First Larval Stage 
 of American Lobster, 
 x 7. (After Herrick) 
 
142 GENERAL ZOOLOGY 
 
 The commercial value of the lobster is very great. As an 
 article of human food it is fast becoming a luxury. Consid- 
 ering its original abundance at times when a fifteen-pound 
 lobster could be bought at the fisheries as cheaply as a two- 
 pound lobster, that is, for two cents, we may well ask whether 
 it is not time for the ratification of treaties between the United 
 States and Canada to govern more effectively the activities 
 of persons engaged in supplying the market. The researches 
 of Professor Bumpus, Professor Herrick, and others, have 
 made it clear that a female lobster seldom lays eggs before 
 she is at least eight or nine inches long. Although she car- 
 ries about five thousand eggs the first time, two years later 
 she would lay many thousand more than that number. Be- 
 cause of the numberless enemies the young encounter, few 
 live to adult life from these thousands of eggs. Legislation 
 which permits lobsters to be caught before they are eight 
 inches long may ultimately be responsible for the extermi- 
 nation of the species. Sensible laws and increased facilities 
 for hatching lobsters in captivity and releasing them after the 
 first critical stages, would do much toward replenishing the 
 lobster fisheries. 
 
 The Common Prawn. Small animals which live at or near 
 the surface of the water are, if brightly colored, so small that 
 they are invisible ; if of visible size, they incline toward trans- 
 parency. The familiar prawn (Palccmone'tes vulga'ris, frontis- 
 piece), found abundantly among seaweeds near shore in sea 
 water and also in brackish and almost fresh water, is a good 
 example of a pelagic or surface-inhabiting animal of consider- 
 able size, which is so nearly transparent that it may be over- 
 looked unless it moves. The prawn, or, as it is frequently 
 called, the shrimp, is about t\vo inches long and resembles in 
 general form the lobster or the crayfish. The body is, how- 
 ever, more compressed (flattened from side to side), and more 
 strongly arched from head to tail. The carapace is thin but 
 
THE JOINTED-FOOT ANIMALS 143 
 
 tough and leathery, and covered with many reddish-brown 
 dots ; it is so transparent that the stomach and intestine can 
 be seen clearly while the animal is at rest. 
 
 The appendages show some interesting adaptations. The 
 antennas are as long as the body, very slender, and during 
 forward locomotion are constantly waving through the water. 
 One of the antennules on either side extends forward, and the 
 other backward, over the eye. At times, in sea-water aquaria, 
 the recurved antennule appears to be clearing the surface of 
 the eye of dirt. The cheliped is only about two thirds as 
 long as the first walking-leg ; it has the curious habit of 
 bending backward frequently at a middle joint like a knee. 
 The first walking-leg also has a nipper, and is much used 
 for grasping food. The remaining three appendages of the 
 thorax are about the length of the cheliped, and em.1 in a sin- 
 gle point. When at rest the prawn is usually found clinging 
 easily to the under surface of seaweeds. 
 
 Crabs. The species represented in Fig. 71 (Eupagu'rus 
 pollica'ris] is called the hermit-crab, probably because it lives 
 in a " house " by itself. The house consists of the shell of a 
 dead snail which may have been washed to the beach, or may 
 have rested on the bottom of the bay. The hermit-crab in its 
 early life is pelagic, but at a certain stage of its development 
 it sinks to the bottom, finds a snail-shell, and backs into it ; 
 from that time on, the general shape of the body and the 
 special modification of certain organs are determined by the 
 form of the snail-shell. The abdomen is soft, and all the abdom- 
 inal appendages except the terminal ones are misshapen and 
 useless. The terminal appendages extend laterally like flanges, 
 and prevent the body from being drawn forcibly from the 
 snail-shell by an enemy. The chelipeds are abnormally devel- 
 oped and, besides being of use in capturing prey, serve the 
 important function of closing the aperture of the shell in 
 times of danger. 
 
144 
 
 GENERAL ZOOLOGY 
 
 Hermit-crabs live in great abundance along gravelly beaches, 
 where they are useful scavengers of dead animals in the water. 
 In spite of the heavy houses which they carry, they move 
 about with surprising facility. As suggested by one observer, 
 they are wary, cunning, belligerent, and cowardly, making 
 great pretense of fighting, but on the first show of force by 
 an opponent they withdraw into their shells. 
 
 A small shore species more frequently seen never becomes 
 as large as Eupagurus pollicaris, which is a deep-water species. 
 All the species, however, when the individuals are young, 
 
 FIG. 71. Hermit-Crab and Blue Crab, x 
 
 choose small shells ; as they grow older and larger after each 
 molt, the unused space in the shell becomes less and less. 
 Naturalists have observed the action of hermit-crabs that have 
 become too large for the shell. The animal searches about for 
 a suitable larger shell, and when it finds one withdraws the 
 body from the old shell and extends it into the new. 
 
 The spider-crab (Libin'ia emargina'ta, frontispiece) stalks 
 slowly over the sea-bottom in shallow and deep water where 
 rocks and fixed plants and animals abound. It can neither 
 run nor swim, an inference which might be drawn from the 
 
THE JOINTED-FOOT ANIMALS 145 
 
 slender, stilt-like appearance of its legs. Having no means of 
 aggressive defense, it relies almost wholly on the fact that its 
 color is very much like its surroundings. The cephalothorax 
 is covered with coarse, hair-like, flexible spines, and the gen- 
 eral color is dull gray. Frequently we find on the back 
 small seaweeds, hydroids (p. 265), sea-anemones (p. 252), and 
 even rock-barnacles (p. 151), growing as they would on rock. 
 This protective resemblance appears to be very successful 
 from the point of view of the spider-crab, for they are in some 
 regions more abundant than any other kind of crab. In some 
 parts of Long Island Sound the spider-crabs are so numerous 
 that they get into the " lobster-pots " set by fishermen and 
 crowd them so that no inducement remains for the lobsters 
 to enter, much to the disgust of the fishermen. Along the 
 Atlantic coast this species grows to have chelipeds which 
 extend over one foot from tip to tip. The giant Japanese 
 spider-crab has chelipeds which extend over fifteen feet from 
 tip to tip, and has a body correspondingly large. 
 
 The edible crab, more frequently called by naturalists the 
 blue crab (Callinec'tes sap'idus, Fig. 71), is characterized by 
 having sharp lateral spines of large size, and by the last pair 
 of thoracic appendages being flattened and adapted to swim- 
 ming. The chelipeds are strong and fitted for cutting ; the 
 succeeding three pairs of appendages have no nippers, but 
 come to a point. 
 
 As is well known, the blue crab is caught in large num- 
 bers along the Atlantic and Gulf coasts for the markets in 
 the cities. The industry is of considerable value commer- 
 cially, and for that reason very general attention has been 
 given to the distribution and habits of this crab. They are 
 caught most easily soon after the molting, which takes place 
 in early summer, and are then called soft-shell crabs. It is 
 at this time also that they are considered most valuable as 
 food. 
 
146 
 
 GENERAL ZOOLOGY 
 
 The blue crab is not confined to the salt water, for it is 
 found frequently in rivers some distance from bays. Wherever 
 they are, they devour much of the organic waste that is carried 
 down to the sea. They are therefore important as scavengers. 
 The most noticeable feature in the structure of the fiddler- 
 crab (U'ca pugila'tor, Fig. 72) is the presence in the males of 
 a large cheliped. Sometimes it is the right one that is larger, 
 
 and sometimes the left one ; the 
 females have their chelipeds small 
 and of equal size. 
 The name " fiddler" 
 
 <^< ' 
 
 FIG. 72. Fiddler-Crab. Slightly reduced 
 
 is supposed 
 to have been 
 derived from the 
 fancied resemblance of 
 the large cheliped to a 
 fiddle, and of the small 
 one to a bow. 
 
 Fiddler-crabs live in 
 the mud and sand of salt-marshes along the Atlantic coast. 
 Sometimes on the higher ground where the sand is cleaner 
 and drier, and where vegetation is scant, these crabs may be 
 observed by the cautious visitor, as they glide quietly out 
 of their holes bearing pellets of sand and gravel under their 
 legs and cephalothorax, to deposit the burden a foot or more 
 away from their holes. The species shown in the picture has 
 been observed to carry on this process of excavation in the 
 
THE JOINTED-FOOT ANIMALS 147 
 
 brightest sunshine and at night. In feeding it seems to prefer 
 plants, living upon very small green algse which grow on the 
 moist sand. The male picks up these algse with its small 
 cheliped and passes them to its mouth, or collects them in 
 pellets to carry into its hole in the same way that it carries 
 pellets of sand out of it. 
 
 The Sow-Bug. The sow-bug, and a related species called 
 the pill-bug because of its habit of rolling up into a ball, are 
 found under stones, boards, logs, and in other dark, moist 
 places. They live on vegetable matter. The flattened con- 
 dition of the body reminds one of the cock- 
 roach and the cricket, which show the same 
 adjustment of the form of the body to the 
 necessities of their life. The species repre- 
 sented (Fig. 73) belongs to the genus Onis'cus. 
 
 The body has twenty somites, as have the 
 crayfish and all the forms described so far in 
 this chapter; five of these, with one thoracic 
 somite, are fused in the head-region ; seven 
 thoracic somites are free-moving, and of the 
 seven abdominal somites all are free-moving 
 except the last two. A pair of short, jointed ' ^ w 
 
 antennae and a pair of compound eyes with- 
 out stalks, i.e. sessile eyes (Lat. sedere, to sit), are the most 
 noticeable prgans of the head. They have a second pair of 
 antennae, which are rudimentary. The mouth-parts are small 
 and adapted to feeding on plant-food. The breathing organs 
 are gills, protected by flat, plate-like structures on the under 
 surface of the abdomen. The base of the legs of the female 
 bears other small plates, which, with the under surface of the 
 body, form a brood-pouch in which the eggs are carried and 
 the young developed. 
 
 Caprella. Probably one of the strangest looking free 
 forms to be found in the sea is the little brown Caprel'la 
 
148 
 
 GENERAL ZOOLOGY 
 
 geomet'rica (Fig. 74). Unless one should see it represented in 
 its natural environment, or actually find it there, the peculiar 
 slender form and the widely 
 separated groups of legs could 
 not be explained on the 
 ground of adaptation to its 
 environment. The artist has 
 shown the details of structure, 
 and also the general resem- 
 blance of the body and ap- 
 pendages to a portion of the 
 brown seaweed. The animal 
 is a little over a centimeter 
 long. The four flap-like ap- 
 pendages in the middle regions 
 . are gills. Caprella is 
 
 composed of twenty 
 
 somites. 
 
 
 FIG. 74. Caprella. x 2 
 
 Artemia. The genus Arte'mia is found in brackish water 
 (see larva, Fig. 78, p. 152). It is particularly interesting in 
 the light of experiments showing the direct influence of 
 the environment on an animal form. From 1871 to 1874 
 the Russian naturalist Schmankewitsch experimented with 
 Artemia. In one series of experiments he increased the 
 density of the brackish water in which they lived by add- 
 ing salt ; in another series he diluted the brackish water by 
 adding fresh water. After several generations of Artemia 
 had been produced under these conditions it was found that 
 
THE JOINTED-FOOT ANIMALS 
 
 149 
 
 the individuals in the water to which salt had been added 
 were of the form of a species hitherto supposed to be dis- 
 tinct, and bearing a different specific name. The individuals 
 in the water which had been gradually diluted approached 
 the form of an allied genus. Thus a mere chang'e of the 
 amount of salt in solution seems to have been responsible 
 for the different forms assumed by the descendants of the 
 same race. 
 
 Cyclops. Any fresh-water pond will afford millions of the 
 genus Cy'clops (Fig. 75), and the sea contains species of the 
 same genus in such numbers that they 
 with allied genera form a large part of the 
 food of many fishes, and even some species 
 of whales find in them an abundant food- 
 supply. Their powers of reproduction are 
 so enormous that it has been estimated that 
 the descendants of one Cyclops may num- 
 ber, in one year, 4,500,000,000 individuals. 
 Though microscopic in detailed structure, 
 on close observation it is easy to see them 
 darting spasmodically through the water 
 in aquaria. A single compound eye in the 
 middle of the head gives them their name, 
 in reference to the race of mythical giants 
 of Sicily. Two pairs of antennae, used in FlG - 
 locomotion, extend from the front of the 
 head. The legs are two-branched append- 
 ages, also used in swimming. One pair of antennse and 
 the legs are not shown in the figure. Two long appendages 
 extend from the end of the abdomen. The body consists 
 of fifteen somites, five in each of the three regions, head, 
 thorax, and abdomen. The female, in the summer season, car- 
 ries about with her two large brood-sacs of eggs which exten'd 
 diagonally out behind. 
 
 5. Cyclops. 
 Much enlarged. 
 (After Claus) 
 
150 
 
 GENERAL ZOOLOGY 
 
 Parasites. A large number of different forms resembling 
 Cyclops in many respects have adopted a parasitic life. 
 One of them is shown in Fig. 76 (Lernceoc'erci). They occur 
 on various hosts, but the greater number 
 of them are found on fishes. They live on 
 every part of the body, and in every degree 
 of commensalism and parasitism. Some live 
 in the alimentary canal, or in the gill-region, 
 feeding only on the food of the host ; some 
 temporarily seek their host for the body- 
 fluids, while others are permanent para- 
 sites, external or internal. In general, these 
 forms are spoken of as " fish-lice." To the 
 extent that they are dependent on a host, 
 the normal external structure tends to be 
 modified out of all resemblance to the type 
 represented by Cyclops. The somites lose 
 FIG. 76. Parasitic their distinctness, and the form of the body 
 Crustacean Much ig altered b protuberances of various kinds. 
 
 enlarged. (After > J 
 
 Von Nordmann) The mouth-parts become adapted as hold- 
 ing and sucking organs. As the external 
 organs degenerate, the tendency of certain internal organs is 
 also to become rudimentary. Some of these parasitic organ- 
 isms are so degenerate in form and structure that they have 
 lost all appearance of being animals at all. In many cases it 
 is the female only which is parasitic, the males leading a free 
 life and showing the normal structure of their race. As with 
 most parasites, immense numbers of eggs are produced, to 
 overcome the effect of the somewhat isolated positions they 
 occupy. Lernseocera is parasitic on the carp, a fish. The 
 form is considerably modified, but the egg-sacs signify its 
 relation to Cyclops. 
 
 Barnacles. Despite the great apparent difference between the 
 fixed, shell-bearing barnacles (Fig. 77) and the free-swimming 
 
THE JOINTED-FOOT ANIMALS 
 
 151 
 
 crabs and other forms discussed in this chapter, natural- 
 ists have shown that they are in reality closely allied both 
 in development and in structure. The species shown in the 
 accompanying figure is the rock-barnacle (Bal'anus balanoi 1 - 
 des), the most common barnacle along the North Atlantic 
 coast. In some places it literally incrusts the coast-rock 
 between tide lines with its hard, sharp-edged shell, composed 
 of carbonate of lime. The shell is usually a little over a 
 centimeter high, and narrower at the top than at the base. 
 Related species grow to be at least four centimeters high, and 
 
 FIG. 77. Rock-Barnacle. Reduced 
 
 one is found on the back of whales. At the top of the 
 rock-barnacle are two hard, movable valves, meeting in a 
 median line, which, on opening, expose long, feather-like 
 processes. These processes are, morphologically, divisions 
 of the feet. The animal lies on its dorsal surface within its 
 several-valved shell, and by rapid movement of the feet cre- 
 ates currents of water which bring to the mouth microscopic 
 animals and plants as food. When the feet are not scooping 
 in food the valves are closed, forming a most effective armor 
 for the parts beneath. 
 
152 
 
 GENERAL ZOOLOGY 
 
 Though the barnacle in its adult condition, as just described, 
 has nothing to fear, in early life the situation is quite differ- 
 ent, for it swims free at the surface of the water in the midst 
 of millions of the young of crabs and other animals. There 
 it is subject to the attacks of animals which might devour it, 
 and many young barnacles are undoubtedly destroyed. At 
 this time it would not be recognized as a barnacle by those 
 who have seen only the adult form. It is characterized by 
 having an unsegmented body, a long upper lip, single median 
 eye, as in Cyclops, and three pairs of jointed locomotor append- 
 ages. This larval form is called a nauplius, and resembles 
 Fig. 78. The barnacle nauplius stage undergoes further com- 
 plicated changes before it attaches itself by the head to some 
 solid object, as a rock, pile, or ship-bottom, when the swim- 
 ming appendages are absorbed and the shell and feathery 
 foot-processes are developed. 
 
 Definition of Crustacea (Lat. crusta, a shell). The crayfish 
 and the species mentioned thus far in this chapter belong 
 
 to the class Crusta'cea. They 
 are constructed on the plan 
 of a series of body-divisions 
 (somites) seldom exceeding 
 twenty in number. In gen- 
 eral, the somites are bilater- 
 ally symmetrical (uniform in 
 structure on either side the 
 median line). Each somite 
 usually has a pair of branched, 
 jointed appendages. As a 
 rule, two pairs of antennre 
 
 are present. A varying number of thoracic somites, in dif- 
 ferent members of the class, are fused to the head. The 
 exoskeleton contains chitin and carbonate of lime. Crustacea 
 are essentially aquatic in their habits and, with the exception 
 
 FIG. 78. Nauplius Stage of Artemia. 
 Much enlarged. (After Joly) 
 
THE JOINTED-FOOT ANIMALS 153 
 
 of the lowest forms, breathe through gills. Nine tenths of 
 the class are said to live in the ocean, some in fresh water, 
 and relatively few on land. 
 
 As in the insects, the hard exoskeleton necessitates fre- 
 quent molts to provide for growth, and also, as in that class, 
 growth is sometimes accompanied 
 by marked metamorphosis after 
 hatching. The lower forms, such 
 as Cyclops, the barnacles, and the 
 parasitic Crustacea, hatch as the 
 peculiar nauplius type of larva 
 already mentioned in the descrip- 
 tion of the rock-barnacle and illus- 
 trated in Fig. 78. FIG. 79. Zoea Stage of Crab. 
 
 In the higher Crustacea the Much enlarged: (After 
 .. . Emerton) 
 
 crabs pass the nauplius stage in 
 
 the egg and hatch in the zoea stage (Fig. 79). The lobster 
 passes the nauplius and the zoea stage in the egg, and hatches 
 in the my sis stage (Fig. 70). The crayfish passes all three 
 stages in the egg, and hatches practically in the form of the 
 adult, the young growing without subsequent metamorpho- 
 sis. It is important to note that the stages nauplius, zoea, and 
 mysis, in the development of the higher Crustacea, are practi- 
 cally identical with the adult form of certain other Crustacea 
 which are considered to be more primitive in organization. 
 The fact that the lower type form reappears in the develop- 
 ment of the higher is often cited as evidence in favor of the 
 recapitulation theory referred to in the chapter on insects. 
 
 THE TRILOBITES 
 
 Some of the most abundant of the forms in the earlier 
 periods of life on the earth were the Tri'lobites (Pha'cops 
 cauda'tus, Fig. 80), which are now considered to be closely 
 
154 
 
 GENERAL ZOOLOGY 
 
 allied to the Crustacea. They are named trilobite from the 
 apparent division of the body longitudinally into three parts. 
 The length of the body varied from one 
 inch to two feet. They are thought to 
 have lived in shallow Avaters along shores, 
 and through a long period of the earth's 
 history must have been a most character- 
 istic feature of the fauna of the world. 
 Of the many species of trilobites of which 
 we find fossils, not one remains at the 
 present day. 
 
 THE HORSESHOE CRABS: XIPHOSURA 
 
 FIG. 80. Trilobite The large, crab-like animal shown in 
 
 (From Report of Geolog- Fig. 81 is variously known as the horse- 
 
 ical Surve 
 Kingdom) 
 
 shoe crab, the king-crab, the horsefoot, 
 
 and by its scientific name, Lim'ulus poly- 
 phe'mus. The first and last common names are derived from 
 the shape of the cephalothorax. A pair of simple eyes is 
 placed near the median dorsal line ; a pair of large com- 
 pound eyes is on the sides of the cephalothorax. There are 
 five pairs of legs on the under surface of the cephalothorax. 
 Several pairs of plate-like gills are attached to the under 
 surface of the abdomen. The body is terminated by a long, 
 spear-shaped spine, which characteristic gives the group 
 its name, Xiphosu'ra (Gr. xiphos, sword; oura, tail). 
 
 Liniulus is found in sheltered bays and estuaries along our 
 eastern coast from Maine to Florida, and on the coasts of 
 the West Indies and Mexico. In places where it is most 
 abundant it is caught with rakes, killed, dried, and used 
 as a fertilizer. It is also used for baiting eels and other fishes. 
 Its practical extinction is threatened in many places. 
 
 The illustration shows the horseshoe crab almost buried 
 beneath the sand through which it is plowing in search of 
 
THE JOINTED-FOOT ANIMALS 
 
 155 
 
 worms. Sometimes they plow a few inches below the sur- 
 face. The older ones, thirty to forty centimeters in length 
 (twelve to sixteen inches), burrow in deeper water; small 
 ones may often be seen on sand-flats where the water is 
 only a few inches deep. At the time of high tides in May, 
 June, and July, the mature males and females, the latter 
 always the larger, leave the water and make their way up 
 the sandy shore to a point just below high-water mark. The 
 female digs a hole in the sand, deposits her eggs, and the 
 male follows and deposits the " milt," or spermatozoa, over 
 the eggs. Both animals then return to the deeper water, 
 and the retreating tide covers the eggs with sand. The young 
 
 Of, 
 
 FIG. 81. Horseshoe Crab 
 
 hatch in about four or five weeks, and make their way into 
 shallow water. When first hatched they resemble young 
 trilobites in form. 
 
 The horseshoe crab is a peculiar type. It shows many 
 points of similarity to both crustaceans and arachnids, par- 
 ticularly the scorpions, and it may be that the latter have 
 descended from these aquatic forms, which are an extremely 
 ancient stock. Some of the fossil allies of the horseshoe crab 
 grew to be five or six feet long. 
 
156 GENERAL ZOOLOGY 
 
 DEFINITION OF ARTHROPODA 
 
 The animals described so far in this book belong to the 
 phylum (see p. 97) Arthrop'oda (Gr. arthron, joint; pous (pod), 
 foot). All but a very few members of this phylum are in- 
 cluded in the four classes, Hexapoda, Arachnid a, Myriapoda, 
 and Crustacea. 
 
 The body of an arthropod is made up of bilaterally sym- 
 metrical somites arranged in a linear series. There is always 
 a head composed of from four to six fused or united somites. 
 The somites of the remainder of the body are grouped into 
 one region, the trunk (Myriapoda) ; or into two regions, thorax 
 and abdomen (Hexapoda, some Crustacea). The head is some- 
 times fused with the thorax, the abdomen being a distinct 
 region (Arachnida, some Crustacea). Appendages, wherever 
 present, are jointed or segmented, and occur as single pairs 
 on somites. The somites and appendages are covered with a 
 chitinous exoskeleton ; in some members of the phylum the 
 exoskeleton is very hard, and filled with carbonate of lime. 
 
 The digestive tract extends nearly straight through the 
 body from the anterior end to the posterior end. The blood, 
 which is colorless, is carried through the body in a partially 
 complete system of vessels with a tubular, or heart-like, pump- 
 ing organ in the dorsal region of the body-cavity. 
 
 Respiration takes place through gills (Crustacea), lung-like 
 sacs (Arachnida), or through an internal network of tubes 
 (tracheae) opening in two lateral series on the exterior of the 
 body (Myriapoda, Hexapoda, and some Arachnida). 
 
 The nervous system generally consists- of a "brain," dorsal 
 to the gullet, two connectives passing one on either side of 
 the gullet, and uniting below to form a ganglion, from which 
 a double nerve-cord extends along the ventral body-wall to 
 the posterior end. Sense-organs characteristic of the phylum 
 are segmented tactile organs, and simple and compound eyes. 
 
CHAPTER XIV 
 THE CLAM AND OTHER BIVALVES: PELECYPODA 
 
 And I then engaged myself, with the other merchants, in a pearl fishery 
 in which I employed many divers on my own account. 
 
 SINDBAD THE SAILOR, Arabian Nights. 
 
 THE LONG-NECK CLAM 
 
 Habitat and Distribution. The animal which is described 
 first in this chapter is commonly known as the long-neck 
 clam or the soft-shell clam. It is more accurately designated 
 by its scientific name, My 'a arena' ria (Fig. 82). As the spe- 
 cific name implies, the animal lives in the sand. It is found 
 in great abundance along our Atlantic coast, even as far north 
 as the Arctic regions. 
 
 External Structure. The shell of the clam has the same gen- 
 eral use as the carapace of the crayfish. In both animals these 
 hard external parts protect the organs within from injury, and 
 also afford surface for the attachment of muscles. The clam's 
 shell, however, is never molted. It grows continuously from 
 the time it begins existence, at the little rounded prominence 
 called the umbo (pi., umbones), or beak (Fig. 82, l). 
 
 Any one who has examined a dry shell of this kind can 
 tell which is the youngest portion of the shell. Probably he 
 will observe at the same time the little spoon-shaped piece 
 extending horizontally inward from one of the valves of the 
 shell. This projection is always on the left valve. It meets 
 a brown, rubber-like pad beneath the umbo of the right valve, 
 and is joined with it. As long as the two valves hold together 
 at this point, the pad, which is called the hinge-ligament, has 
 a tendency to separate the valves at an acute angle. In life 
 
 157 
 

 
 I ill! 
 
 mn 
 
 ^^G^ 2 
 
 i:sig 
 
 :?!&,- 
 
 o-^ .^ 
 
 S^^s;: 
 
 um 
 
 cfSsass 
 i-ss7i.| 
 
 3 .oo^ 
 
 Sbs'S"^ 
 
 ,00 SlS "tit ?i 
 
 s 
 
 s 
 
 158 
 
THE CLAM AND OTHER BIVALVES 
 
 159 
 
 two thick, short muscles (Fig. 82, 2,3; Fig. 83, 2 a) extend 
 across from valve to valve, and resist the spreading action 
 of the hinge-ligament. 
 
 The Mantle and the Mantle-Cavity. When the valves are 
 shut they inclose a considerable space besides the body 
 proper. Fig. 82 
 represents the 
 most important 
 organs as they 
 might lie in the 
 hollow of the 
 right valve. Fit- 
 ting close to the 
 inner surface 
 of the valves is 
 the mantle (Fig. 
 82,4). Except at 
 the edge, where 
 the mantle- folds 
 (halves) unite, the 
 mantle is quite 
 thin; its chief 
 use is to secrete 
 the calcareous 
 substance of 
 which the shell 
 
 is composed. The shell is deposited in three layers (Fig. 83, 
 3, 4, 5), the outer layer called the periostracum, the middle 
 layer called the prismatic layer, and the inner layer called the 
 nacreous or pearly layer. After the shell is formed at the edge 
 the thin part of the mantle-folds continues to deposit the 
 nacreous layer, which is sometimes called mother-of-pearl. 
 
 The mantle-folds inclose a mantle- cavity. An opening at the 
 anterior end of the mantle-cavity allows the foot (Fig. 82, 5), 
 
 FIG. 83. Mechanism for opening 
 Mussel-Shell 
 
 A, valves of mussel closed; B, valves of mussel open: 
 1, 2, hinge-ligament; 2 a , adductor muscle contracted; 
 2 b , adductor muscle relaxed ; 3, outer layer of shell ; 
 4, middle layer of shell; 5, inner (mother-of-pearl) 
 layer 
 
 (From Lang's Lehrbuch) 
 
160 GENERAL ZOOLOGY 
 
 the single locomotor organ, to be extended to the outside. 
 At the posterior end of the mantle-cavity is situated the 
 double-tubed siphon (Fig. 82, 6). Only the lower tube of 
 the siphon is connected directly with the mantle-cavity. 
 This siphon enables Mya to lie buried, anterior end down, 
 in the mud and sand, still maintaining communication with 
 the food-laden and air-laden water above. In large specimens 
 of this clam the siphon is over 25 cm. (10 in.) long. 
 
 The Digestive System. The ventral opening of the siphon 
 (Fig. 82, 7) is surrounded by many short tentacles which 
 guard the passage. An ingoing current is created in the 
 water by cilia on the gills. Ordinarily only microscopic food 
 passes through this incurrent opening of the siphon. In the 
 mantle-cavity the particles of food are carried forward over 
 the gills and along the mantle till they come within range 
 of the waving palps, or mouth-appendages (Fig. 82, 9). 
 
 The mouth-opening (Fig. 82, 10) is situated between the 
 four palps, and is very small. It has no organs of any kind 
 for seizing or chewing food ; none are needed. The food 
 once swallowed passes through the short oesophagus to the 
 stomach (Fig. 82, 11). Surrounding the stomach is the large, 
 paired digestive gland (Fig. 82, 12). which secretes the diges- 
 tive fluid. Situated in the end of the stomach, and in the 
 anterior end of the intestine, we find, in Mya arenaria, and 
 in many species related to it, an organ called the crystalline 
 style (Fig. 82, 14). In Mya this structure is three or four 
 inches long. It is soft and clear like thick, colorless jelly, 
 and lies in a long, thin-walled sac opening into the stomach. 
 
 Many theories have been advanced to account for the exist- 
 ence of the crystalline style. Recently (1901) the nature of 
 the structure was investigated by Professor Mitra, a physio- 
 logical chemist living in Calcutta, India. He has published 
 an account based on experimental evidence, which appears to 
 be satisfactory. His conclusion is that the crystalline style 
 
THE CLAM AND OTHER BIVALVES 161 
 
 of a certain fresh-water mussel (An'odon) is the condensed 
 secretion of the digestive gland ; its function is to convert 
 starch into sugar. After a period of feeding and subsequent 
 digestion the style disappears and is later formed anew. 
 
 The intestine (Fig. 82, 13) coils and twists in many planes 
 from the posterior end of the stomach to the point where it 
 penetrates the heart. The penetration of the heart by the 
 intestine is of common occurrence in the class to which Mya 
 belongs, but it occurs in no other class of animals. The part 
 of the alimentary canal from the heart to the anus (Fig. 82, 16) 
 is called the rectum (Fig. 82, 15). The rectum is inclosed 
 in a large, spindle-shaped organ (Fig. 82, 17) of unassigned 
 name and unknown function. 
 
 The Circulatory, Respiratory, and Excretory Systems. 
 When the food is absorbed by the wall of the intestine it 
 passes into small blood-spaces filled with colorless blood. 
 The blood with the contained food then passes into the 
 open ends of small blood-vessels. These blood-vessels lead 
 (in certain near relatives of Mya which have been studied 
 more fully) to a large blood-space below the pericardium 
 (Fig. 82, 18), the sac which incloses the heart. From the 
 blood-space (not shown in the figure) blood passes by vessels 
 to the nephridia (kidneys). The nephridia in Mya arenaria 
 lie one on either side near the heart. The anterior end of 
 the left nephridium is indicated at Fig. 82, 19. The rest of 
 the organ could not be shown in the drawing. 
 
 The nephridia are spongy, brownish organs of great com- 
 plexity. They are sometimes referred to under the name 
 "organs ofBojanus." The old-time anatomist, Bojanus, dis- 
 covered the structures,, but he made a most natural mistake 
 in thinking that they were the lungs of the animal, since they 
 look like lungs and lie very near the heart. Other anatomists 
 gave the name " organs of Bojanus," and later investigators 
 found that the organs were alike in structure and in function 
 
162 GENERAL ZOOLOGY 
 
 to the nephridia of simpler animals. Each nephridium of the 
 clam opens by one end into the pericardium. The other end 
 of each nephridium opens into the mantle-cavity just posterior 
 to the digestive gland. 
 
 As the blood-vessels in the nephridia divide into capilla- 
 ries, the nitrogenous waste of the body (uric acid) passes into 
 the nephridial tube and is carried out into the mantle-cavity. 
 The small blood-vessels, reuniting into large vessels, convey 
 the partially purified blood into a vessel that runs along the 
 line of attachment of -the gills. 
 
 There are four of these gills and they hang like double 
 curtains along the right and left sides of the body (Fig. 82, 20). 
 The oxygen coming into the mantle-cavity with the water, 
 through the incurrent tube of the siphon, passes over the 
 floating gills. They are thin and soft, arid are thus adapted 
 for the ready passage of oxygen to the blood-vessels inside. 
 
 In the blood the oxygen combines with Immocyanin, a 
 substance analogous to hemoglobin (see p. 203). At the same 
 time the waste carbon dioxide in the blood is given off to 
 the water in the mantle-cavity. The mantle-folds, as well 
 as the gills, take part in respiration. It is possible for them 
 to do so because of their rich supply of superficial blood- 
 vessels. 
 
 Returning from the gills and the mantle, the blood freed 
 of carbon dioxide is carried to the right (Fig. 82, 21) and left 
 auricles of the heart. These thin-walled, sac-like reservoirs 
 force the blood into the ventricle (Fig. 82, 22) of the heart 
 through valve-guarded openings on either side (Fig. 82, 23). 
 The heart contracts and forces the blood both forward and 
 backward through arteries. The anterior artery lies above 
 the intestine (Fig. 82, 24), and the posterior artery lies below 
 the rectum (Fig. 82, 25). Both arteries branch into smaller 
 arteries in all parts of the body. The blood flows from the 
 open ends of the smallest arteries into blood-spaces, from 
 
THE CLAM AND OTHER BIVALVES 163 
 
 which it is once more collected and carried to the purifying 
 organs in the manner already described. 
 
 The Excurrent Tube. Besides the rows of cilia which carry 
 food from the region of the in current tube to the mouth, 
 there are rows of cilia on the body and along the mid- 
 ventral line of the mantle, and it is known that these cilia 
 wave toward the incurrent tube. Food that has been rejected, 
 or waste that has accumulated, may be carried by the out- 
 waving cilia to the base of the incurrent tube. By muscular 
 contraction of the siphon at its base these substances may be 
 expelled through the tube. The dorsal tube of the siphon, 
 however, is the customary path of exit for substances that are 
 not used by the organism. All the undigested substances that 
 pass through the intestine must leave the animal by the dor- 
 sal tube. In addition, it is likely that wastes from the neph- 
 ridia, and from the gills and mantle, may pass from the 
 mantle-cavity through a slit-like opening (Fig. 82, 26) at the 
 base of the gills, and be carried out with the unused materials. 
 
 The Nervous System. Lying on the right and left sides of 
 the oesophagus, just posterior to the mouth, is a pair of cerebro- 
 pleural ganglia (Fig. 82, 27). They are joined by a cerebral 
 commissure running over the oesophagus. As the name of 
 the ganglia implies, there are two ganglia joined in each nerve- 
 mass. One pair controls the " head " region ; the other pair 
 controls the sides of the body near by. The cerebro-pleural 
 ganglia are joined to the pedal (foot) ganglion (Fig. 82, 28) 
 by two connectives, one on either side (Fig. 82, 29). The 
 pedal ganglion controls the movements of the foot. The vis- 
 ceral ganglion (Fig. 82, 30) is joined to the cerebro-pleural 
 ganglia by a pair of cerebro-visceral connectives (Fig. 82, 31). 
 The visceral ganglion controls the organs in the posterior 
 region of the body. 
 
 The Reproductive System. The pair of large glands (Fig. 
 82, 32), which in male and female clams contains spermatozoa 
 
164 
 
 GENERAL ZOOLOGY 
 
 3--- 
 
 or the eggs, lies in the midst of the coils of the intestine. 
 Each gland has a short, slender tube, with an external opening 
 (not shown) near the opening of the nephridium, just below 
 the attachment of the gills. 
 
 Development. The very early history of the } r oung Mya 
 arenaria has not been studied. We know, however, that 
 
 after a short period of 
 development and growth 
 young long-neck clams 
 I swim about on the sur- 
 
 face of the water. Soon 
 after the appearance of their shell 
 they sink to the bottom. If they are 
 fortunate enough to fall near the 
 shore-line, they anchor themselves 
 to a seaweed, or to a pebble, by a 
 tough, gelatinous thread (Fig. 84, 3) 
 which is secreted by a gland at the 
 5ck base of the foot (Fig. 84, l). This 
 thread is called the byssus. In cer- 
 tain mussels found in the sea the 
 byssus is a permanent and very com- 
 plicated organ of the adult, but in Mya arenaria it disappears 
 when the clam is about 5 millimeters (l- inch) long. At that 
 time the animal burrows into the mud and sand, where it 
 usually remains permanently. 
 
 Relation to Environment. The adult Mya arenaria lives 
 in soft mud and sand between high-tide line and a few feet 
 beyond low-tide line. The reason the -clam lives in that 
 situation is because food is most abundant there. Lying 
 almost helpless in its mold of mud, the long-neck clam is 
 rendered in a measure independent of conditions outside, as 
 long as the currents of water carry the bountiful supplies of 
 food over its burrow. 
 
 Clam. (After J. L. Kellogg) 
 
 1, foot; 2, siphon; 3, byssus- 
 thread; 4, pebbles 
 
THE CLAM AND OTHER BIVALVES 165 
 
 If a young clam escapes the danger of being carried out 
 to sea during its pelagic life, it is safe for a while when, on 
 sinking to the bottom, it anchors to some fixed or heavy ob- 
 ject with its byssus-thread. There it encounters dangers from 
 food-hunting fish. Still more dangerous are the storms that 
 carry waves of water far up the beach and leave to destruction 
 many kinds of animals that happen to be borne along. At 
 the same time countless young of the clams that escape being 
 carried out must be smothered by the shifting sand and mud. 
 
 As the adult stage approaches the dangers of existence 
 become less and less, until man himself interferes with the 
 natural balance of chances in the clam's life. In certain 
 parts of the Atlantic coast, especially in the vicinity of large 
 cities, the species is fast being exterminated. Although the 
 clam is not as highly esteemed as an article of human food 
 as its relative the oyster, it is nevertheless of great value. 
 Officers of the Bureau of Fisheries have considered the mat- 
 ter of restricting the digging of clams, and also various means 
 of tiding the young over the danger-points in their lives. 
 
 THE AMERICAN OYSTER 
 
 Habitat and Distribution. The American oyster (Os'trea 
 virginia'na, Fig. 85) is found in shallow to deep water along 
 the Atlantic coast from the Gulf of Mexico to Massachu- 
 setts Bay. As the artist has shown in the picture, the animal 
 lies attached to the bottom, frequently to another oyster-shell. 
 Although many oysters may live thus fastened to each other, 
 there is no organic connection between them. They some- 
 times form clumps so large and heavy that the basal ones 
 sink into the mud and die. The valves of the living ones 
 extend outward at any angle. When oysters are not crowded 
 iri the " bed," the usual method of living is the one shown 
 in the illustration. There the valves extend horizontally, 
 
166 
 
 GENERAL ZOOLOGY 
 
 and we can distinguish an upper and a lower valve. The 
 lower valve is always much larger and deeper than the upper 
 one. The lower one is the left valve. 
 
 Comparison with the Clam. The internal organs of Ostrea 
 virginiana and Mya arenaria are very much alike. The large, 
 dark-brown digestive gland, the coiled intestine, the three- 
 chambered heart, and the reproductive glands have a common 
 plan in the two species. A noticeable difference is the entire 
 absence of a foot in the oyster. Applying the principle of 
 adaptation, we can readily explain the absence of that organ. 
 The two animals are different also in the number of adduc- 
 tor muscles. In the clam there are two ; in the oyster only 
 one. The muscle-scar on the inner surface of the valves of 
 an oyster is a dark blotch. As the oyster grows from season 
 to season the location of the shell-closing muscle changes 
 
 FIG. 85. Group of Living Oysters. Reduced 
 
 to meet the necessity of performing its function most advan- 
 tageously. In a lot of a dozen oyster- valves the observer 
 may find several which indicate this change. In some valves 
 all trace of the change is concealed by the thick layer of 
 mother-of-pearl laid down by the mantle after the muscle 
 altered its position. 
 
THE CLAM AND OTHER BIVALVES 
 
 167 
 
 FIG. 86. Oyster Larva. Much 
 enlarged. (After Mcebius) 
 
 1, mouth; 2, stomach; 3, aims; 
 4, shell ; 5, adductor muscle ; 
 0, circle of cilia 
 
 Development. In the months of May, June, and July, in 
 the latitude of Baltimore, the male and female oysters send 
 out into the water their spermatozoa and their eggs. Pro- 
 fessor Brooks, of Johns Hopkins 
 University, estimates the number 
 of eggs which a female oyster 
 may yield in one season to be at 
 least nine million. "The number 
 of male cells," he says, " is great 
 beyond all powers of expression." 
 Of course we should expect that 
 in spite of the countless sperma- 
 tozoa, many eggs would never be 
 fertilized at all, on account of 
 their being carried away by un- 
 favorable currents. Eggs that are 
 not carried away fall to the bot- 
 tom naturally. Those eggs which are fertilized swim to 
 the surface as larvae after a few hours' development. There 
 surface-fish may, as Professor Brooks suggests, " gulp down 
 in a few seconds oysters equal in number to the population 
 of Baltimore." 
 
 Within one to six days after fertilization the oyster " fry " 
 (swimming larvae, Fig. 86) sink to the bottom again and affix 
 themselves by the margin of the left mantle-fold to whatever 
 solid object they happen to touch. At this time they are 
 about .3 mm. (^ in.) long. For a few weeks after beginning 
 their stationary life they are liable to be crunched to death 
 by voracious crabs, among others, the blue crab (Fig. 71). 
 
 Economic Importance. The largest and most important 
 " oyster-farms " along our coast are in Chesapeake Bay. 
 There and elsewhere the beds have been surveyed and leased 
 under laws of the states. So vast is the oyster-fishing industry 
 in this country that millions of dollars are paid annually by 
 
168 GENERAL ZOOLOGY 
 
 the markets of the large cities for these " esculent bivalves." 
 On the coasts of Holland, Belgium, and France far greater 
 care is taken of their species (Ostrea ed'ulis) than we take 
 of ours ; but the natural conditions here are superior to the 
 natural conditions there. 
 
 Relation to Environment. According to the investigations 
 of Professor Brooks, Professor Ryder, and others, oysters are 
 to be found most abundantly in the quiet, semistagnant water 
 of shallow inlets. Into such inlets slowly flowing creeks 
 enter, giving to the water of the inlet a brackish quality. 
 When food consisting of microscopic plants and animals is 
 carried to the oyster by the natural currents in the water, it 
 may enter at any point between the separate folds of the 
 mantle. Cilia on the inner surface of the mantle-folds, and 
 on the four gills, sweep the minute organisms forward to the 
 mouth, which lies near the hinge. The four palps aid in the 
 process. In brackish water the most important food-organism 
 of the oyster multiplies in vast invisible hordes. These 
 organisms are plants called diatoms. Diatoms live in the 
 soft mud at the bottom, and are carried by the water-currents 
 within range of the cilia in the oyster's mantle-folds. 
 
 In times of storm the home of the oysters' food may become 
 a source of great danger to them. Once covered with mud or 
 with shifting sand, the life of a bed of oysters is at an end. 
 At the mouths of rapidly flowing rivers no oysters are to be 
 found, chiefly because the silt (fine sediment) and the debris 
 of decaying plants are unfavorable to the growth of the animal. 
 
 Aside from the physical agencies which are favorable or un- 
 favorable to oysters, there are many animals which come into 
 definite and usually unfavorable relations to them. Only one 
 of these animals, so far as known, is anything but harmful 
 to the oyster. That one is a little crab, about 13 millimeters 
 (^ inch) wide, which spends its life in the mantle-cavity of 
 its messmate. Trie greatest enemy of the adult oyster is the 
 
THE CLAM AND OTHER BIVALVES 169 
 
 starfish (Fig. 118). There are various boring-snails, which 
 make round holes through one of the valves with their rasp- 
 ing-tongues and draw out what they need of the soft parts 
 (compare Fig. 99). Another enemy is the boring-sponge, 
 which, as it grows, makes holes in the valves by a secretion 
 which it produces. Like most other animals, the oyster has 
 its parasites. With all these facts before us, the statement 
 of Professor Mobius regarding the European oyster, that 
 each oyster when born has - - of a chance to survive 
 
 J 1145000 
 
 and reach adult age, seems well within reason. 
 
 THE SCALLOP 
 
 Habitat and Distribution. Of all the "shell-fish" that in- 
 habit the shallow waters of the Atlantic coast of our country, 
 none is more beautiful in color or in line than the common 
 scallop, Pec' ten irra'dians (Fig. 87). Scallops are abundant 
 among the eel-grass of shallow bays and inlets from the Gulf 
 of Mexico to Massachusetts Bay. Above the latter region 
 the waters are made colder by the Arctic currents. Pecten 
 irradians and many other species of sea-animals do not live 
 north of Cape Cod. There are, however, many species of ani- 
 mals that flourish best in the cold waters of Maine and the 
 maritime provinces of Canada. 
 
 Relation to Environment. The very young scallop holds to 
 some fixed object after the manner of a young soft-shell clam 
 (Fig. 84). The adult scallop has no byssus, and only the 
 rudiment of a foot. The scallop in the foreground of the 
 picture is in what we might call the attitude of rest. It has 
 released its single adductor muscle, which, we may say in 
 passing, is the only part of the animal sold for food. The 
 mantle-folds of the resting scallop expand, showing at the 
 margin slender tentacles and a variable number of delicate 
 cobalt-blue eyes. If a person causes a shadow to pass over 
 
170 
 
 GENERAL ZOOLOGY 
 
 the margin of the mantle, the mantle is withdrawn and some- 
 times the valves are closed. The same experiment may be 
 tried on the oyster with similar results, although the oyster 
 has no eyes at all. Invisible sense-organs in that animal 
 respond to the stimulus of light. 
 
 While feeding and breathing, the tentacles of the scallop 
 aid the cilia of the mantle, gills, and palps in conveying food 
 to the mouth. At such times the spores of various seaweeds 
 and the young of certain snails (Crepid'ula, on 
 scallop in foreground, Fig. 87) may find a surface 
 of attachment on one of the valves. These 
 organisms have an advantage over station- 
 ary individuals of the same species, 
 in being attached to a movable 
 support, for, when the scallop 
 swims about, the messmates are 
 carried to new and possibly 
 better stores of food. 
 
 If one were to reason from 
 the general appearance of the 
 scallop which part should go for- 
 ward when the animal swims, it 
 is verv likely that the conclusion 
 
 
 FIG. 87. Group of Living Scallops. 
 
THE CLAM AND OTHER BIVALVES 171 
 
 would be different from the actual performance. The attitude 
 of a swimming scallop is portrayed in the upper left-hand part 
 of the illustration. In the act of swimming the valves open 
 and close quickly, by the alternate action of the hinge-liga- 
 ment and the large adductor muscle. On closing, the valves 
 catch a quantity of water between the mantle-folds. The 
 water escapes under pressure from within, through a round 
 opening at either end of the straight flange of the hinge. 
 The resulting action of these jets of water backward, against 
 the body of water outside, is to force the larger and broader 
 end of the animal forward. Locomotion is not in a direct line, 
 but over a zigzag course. When the scallop ceases swimming 
 it immediately falls to the bottom. The animal is not what 
 one would call a skillful swimmer, although its movements 
 are very interesting to observe. 
 
 THE FRESH-WATER MUSSEL 
 
 Habitat and Distribution. In fresh waters generally, wher- 
 ever sufficient carbonate of lime is carried in solution, one 
 may find mussels living nearly covered in sand and mud. 
 The species represented in Fig. 88, U'nio complana'ta, is 
 distributed in the rivers and brooks of the entire country. 
 
 Comparison with Other Forms. The valves of the mussel are 
 equal, like those of the clam and the scallop. The valves of 
 the .fresh- water species are held together by a hinge-ligament, 
 aided by two pearl-covered ridges running parallel and fitting 
 into grooves. The mantle-folds are not united, as they are in 
 the clam. At two adjoining places in the posterior region the 
 rim of the mantle-folds is fringed with short tentacles. Dorsal 
 and ventral tubes are formed by the meeting of opposite edges 
 at the places where the tentacles occur. Food and oxygen are 
 carried in by the ventral tube, and undigested substances are 
 carried out by the dorsal tube. We may speak of the siphon 
 
172 
 
 GENERAL ZOOLOGY 
 
 of the mussel, but as a matter of strict accuracy the mussel 
 does not have a siphon, in the sense that the clam possesses 
 one. The foot of the mussel is large and muscular. It 
 enables the animal to plow its way through mud or even 
 through heavy gravel. The gills and the palps are practically 
 identical in structure in the mussel, the clam, the oyster, and 
 the scallop. The internal organs also have the same general 
 plan of structure in the four animals named. There are two 
 adductor muscles in the mussel. The sexes are separate. 
 
 FIG. 88. Living Fresh- Water Mussel. x| 
 
 Development. At least two genera of fresh-water mussels 
 carry their young in their gills, which are open dorsally on 
 the inside. Such an arrangement is necessary because the 
 currents in rivers all go one way, and would carry the help- 
 less young out to sea. At a certain stage the well-developed 
 larvae escape from the brood-pouch of the female mussel 
 and fall to the bottom. Fish " nosing " along the river-bed 
 touch the floating byssus-thread of the young mussel, which 
 at that stage is called the glochidium (Fig. 89). The thread 
 
THE CLAM AND OTHER BIVALVES 
 
 173 
 
 FIG. 89. Larva of Mussel. Much 
 enlarged. (After Balfour) 
 
 1, shell; 2, adductor muscle; 3, lar- 
 val hook ; 4, byssus-thread 
 
 (Fig. 89, 4) clings to the surface of the fish's gill or skin, and 
 the little hook (Fig. 89, 3) on the edge of either valve sinks 
 into the flesh. For several weeks the glochidium is trans- 
 ported on the fish, during which 
 time it may be carried into an- 
 other river, even by way of the 
 sea. When the end of fixed 
 development comes, the protect- 
 ing coat is dissolved and the 
 little mussel falls to the bottom 
 again. If this happens in a 
 favorable place, it burrows into 
 the mud and begins the life of 
 its adult kin. 
 
 Economic Importance. The dis- 
 tribution of fresh-water mussels has become a matter of con- 
 siderable economic importance, especially in the states of 
 Iowa and Illinois. Factories have been established there for 
 the purpose of making pearl buttons from the valves. True 
 pearls of fine quality have been found in many species of 
 mussels in all parts of the Mississippi valley. 
 
 The opinion has been held by many that if grains of sand 
 find lodgment between the mantle and the valve of a mussel 
 or an oyster, the mantle will surround the particle with 
 layers of pearl, like the substance normally secreted by the 
 species to line its valves, and thus form pearls. We have heard 
 stories of these valuable products being formed by pearl-oyster 
 fishermen, who inserted grains of sand between the valve 
 and the mantle of the famous pearl-oyster of the Arabian 
 Gulf, but we have no evidence that a grain of sand has ever 
 been found in a true pearl. Grains of sand only cause rough 
 spots in the layer of mother-of-pearl. 
 
 The investigations of Professor Jameson, of South Africa, in 
 1902, afford the first conclusive evidence regarding the origin 
 
174 
 
 GENERAL ZOOLOGY 
 
 of pearls in the common edible sea-water mussel, My'tilus 
 ed'ulis (in Fig. 126). A trematode parasitic worm (Fig. Ill) 
 in the larval stage creeps between the valve and the mantle- 
 fold. In its wanderings it starts to bore through the mantle- 
 fold. The tissue is soft, but the parasite may rest for a while 
 among the loosely connected cells. In that case it is imme- 
 diately surrounded by a minute fold of the outer epithelium 
 (surface-cells) of the mantle. About the trematode larva as 
 a center the epithelium (Fig. 90, 2) begins to secrete a sub- 
 stance which, on hardening, 
 becomes a pearl (Fig. 90, 5). 
 Before the hardening takes 
 place the larva may move to 
 some other part of the man- 
 tle-fold. Again it may be 
 the stimulus for producing a 
 pearl. 
 
 Examination of pearls 
 often reveals a small particle 
 of matter about which the 
 pearl was formed in layers. 
 Professor Jameson thinks the 
 substance at the center of 
 the pearls he has examined 
 
 is the body-waste, or excrement, of the parasite (Fig. 90, 0), 
 except in those pearls in which he has found the dead body 
 of the parasite itself. Even the temporary presence of the 
 parasite is a sufficient stimulus for the production of a pearl. 
 The pearl may get so large that it breaks through the outer 
 epithelium of the mantle-fold and becomes attached to the 
 valve itself. If the pearl breaks through the inner (ciliated) 
 epithelium (Fig. 90, 3) of the mantle-fold, it falls into the 
 mantle-cavity, and finally to the outside, which accounts for 
 the fact that pearls are often found in the sand. 
 
 FIG. 90. Section of Mantle-Fold of 
 Mussel showing how a Pearl is 
 formed. (After Jameson) 
 
 1, cells of mantle ; 2, external epithelium 
 of mantle ; .'$, internal (ciliated) epi- 
 thelium ; 4, position of shell ; 5, pearl ; 
 6, remains of parasite 
 
THE CLAM AND OTHER BIVALVES 175 
 
 Relation to Environment. The distribution of Unio com- 
 planata in the bed of a river is determined somewhat defi- 
 nitely by the position of the strongest current. It is well 
 known that in a crooked river the main current does not 
 follow the middle line of the stream, but sweeps from bank 
 to bank diagonally across the middle. The greater amount 
 of food is carried along by the swifter water, and hence, 
 unless the stream is too swift, the mussels find it advanta- 
 geous to range themselves along the line of the most abun- 
 dant food-supply. 
 
 Mussels are considered by some to be of great service to 
 man and other animals because of their habit of devouring 
 the decaying organic substances so abundant in rivers which 
 flow past large cities. There is good reason for believing, 
 however, that sewage is not the natural food of mussels, and 
 that they will flourish better in water of natural purity. In 
 fact, it has been positively determined that mussels do not 
 live near the mouth of a large sewer. 
 
 DEFINITION OF PELECYPODA 
 
 The four animals described in this chapter are representa- 
 tives of a class called by various authors Lamellibranch'ia, 
 Aceph'ala, or Pelecyp'oda (Gr. pelekys, hatchet ; pom (pod), 
 foot). They are also called bivalves because the shell is 
 in two pieces. Lamellibranchia signifies that the animals 
 have gills (branchige) which are thin, like plates (lamellae). 
 Acephala means " without a head." 
 
 Pelecypoda are usually bilaterally symmetrical animals with 
 an external skeleton composed of two more or less nearly 
 equal valves. They have no internal skeleton. The body is 
 without a head and is not divided into somites. There are 
 no segmented appendages. The mantle-folds surround the 
 body proper and secrete the shell substance. Locomotion is 
 
176 GENERAL ZOOLOGY 
 
 most frequently accomplished by a single muscular organ, 
 the hatchet-shaped foot. The valves are held together by a 
 hinge-ligament, aided sometimes by ridge-like processes fitting 
 into grooves. The valves are closed by one, or two, adductor 
 muscles. 
 
 Four palps surround the mouth and carry the food inward. 
 The oesophagus is short. The stomach receives the secre- 
 tion from a pair of digestive glands. The intestine coils 
 several times and ends posteriorly. The circulatory system 
 is nearly complete. There are two auricles and one ventricle 
 in the heart. The pair of glands of the reproductive system 
 in male and female individuals seems to differ only in micro- 
 scopic structure. In some species the sexes are separate. In 
 others the individuals are hermaphroditic ; that is, the male 
 and female sexual glands are present in the same animal. 
 
CHAPTER XV 
 ALLIES OF THE PELECYPODA : MOLLUSCA 
 
 The frugal snail, with forecast of repose, 
 Carries his house with him where'er he goes. 
 
 CHARLES LAMB. 
 
 The Pond-Snail. Any one of several genera and species of 
 snails that live in fresh water might be given the name 
 "pond-snail" with equal accuracy. The one represented in 
 Fig. 91 (Phy'sa heterostro'pha) is quite common not only in 
 ponds but in rivers as well. 
 
 Externally the most noticeable feature of the pond-snail 
 is its thin, spiral shell. This structure is made of the 
 same material as the shell of bivalves. A large portion of the 
 animal's body fills the " mouth " of the shell and extends 
 spirally toward the top. The direction of the spiral (or spire) 
 in Physa is left-handed, an unusual condition. The spire 
 of a left-handed shell, starting with the top toward the ob- 
 server, turns contrary to the movement of the hands of a 
 clock ; the spire of a right-handed shell turns with the hands 
 of a clock. Between the shell and the body-wall lies the 
 mantle, which throughout life continues the growth of the 
 shell in the characteristic spiral direction. 
 
 When the snail is disturbed it draws its shell down over 
 the entire body; but while feeding, as shown in the picture, 
 one can see the long, muscular foot, broad in front and 
 pointed behind. The anterior region of the body is the head, 
 more or less sharply marked off from what lies behind. The 
 mouth opens beneath an extensile upper lip. In the mouth 
 is a short, muscular tongue, on which grows a long but 
 minute ribbon of rasp-like teeth. The pond-snail uses this 
 
 177 
 
178 
 
 GENERAL ZOOLOGY 
 
 rasping-tongue, running it in and out, to tear into bits the 
 soft plant tissues on which it feeds. A most interesting 
 experience is to watch a pond-snail as it crawls slowly up 
 
 
 FIG. 91. Group of Living Pond-Snails. Natural size 
 
 the side of an aquarium, feeding on the microscopic plants 
 as it goes. At such times one can see the mouth open and 
 the tongue sweep gracefully out and in, with tiny, rhythmic 
 movements. 
 
ALLIES OF THE PELECYPODA: MOLLUSCA 179 
 
 The two tentacles are organs of touch. The eyes lie one 
 in front of either tentacle at its base. On the right side, 
 near the head, are the single openings of the intestine, the 
 nephridium, and the sexual glands. Also on the right side, 
 and partly beneath the edge of the shell, is an aperture 
 which opens and closes over a small hollow space in the 
 body. This space is the so-called "lung" of the pond-snail. 
 The lung is adapted to using the oxygen of the atmosphere. 
 Any one who owns an aquarium containing snails may ob- 
 serve them crawling up the side of the vessel on their way 
 to the surface. When they arrive there they remain for some 
 time, opening and closing the lung to the air. In aquaria 
 which have a supply of water-plants growing in them, the 
 pond-snail does not appear to go to the surface so often. It 
 is well known that plants give off oxygen. Some of this 
 oxygen held in the water may pass through the snail's skin, 
 which is thin and soft. The waste carbon dioxide of the snail 
 is discharged into the water, and may be used by water- 
 plants as raw food-material. 
 
 It is not uncommon to see a pond-snail crawling upside 
 down at the surface of the water. The explanation of this 
 curious phenomenon is the same as the explanation of how 
 they can get along on any kind of a surface. Just below the 
 mouth is the opening of a gland, which extends through the 
 middle of the foot near the lower surface. If we look closely 
 at the inverted snail, we can see the wall of this foot-gland 
 contracting with a wave-like movement in the act of sending 
 the secreted mucus (slime) forward to be poured out at the 
 opening. The mucus spreads out a short distance on the 
 water, or blade of water-plant, or submerged pebble, and 
 forms a bed over which the animal moves. 
 
 When the foot is extended in locomotion the pond-snail 
 weighs less than an equal volume of water. If the animal 
 releases its hold on an object at the bottom, it floats to the 
 
180 
 
 GENERAL ZOOLOGY 
 
 surface quickly. Conversely, if the animal voluntarily (or 
 under visible stimulus) releases its hold on the surface of 
 the water, it draws the entire body into the shell and quickly 
 
 falls to the bottom. In 
 the second instance the 
 weight of the snail's body 
 is greater than the weight 
 of an equal volume of 
 water. One might well 
 ask why the pond-snail 
 doesn't migrate up and 
 down in this way habit- 
 ually. We can only say 
 that perhaps the sudden 
 change of pressure from 
 a great to a less amount 
 in going up, and from a 
 small to a greater amount 
 in going down, is not so 
 favorable as a slower rate 
 FIG. 02. Mucus-Threads of Pond-Snail o f change would be. 
 (Limnoza) in Water. Reduced. (After 
 
 Kew) We find some confir- 
 
 mation of this theory in 
 
 the existence of vertical threads of mucus in snail aquaria 
 and in ponds (Fig. 92). A snail on leaving the bottom may 
 pour out mucus from its foot- gland in the usual way. The 
 mucus fastened at the bottom will *be paid out in the form 
 of a thread, as the animal floats upward, slowly held back by 
 this thread. When the snail gets to the surface the thread is 
 moored there in a patch of mucus. Each thread thus formed 
 becomes a permanent pathway, tending to increase in thick- 
 ness and in strength as the snail makes use. of it. 
 
 In the spring and summer months the pond-snail lays eggs 
 even in captivity. The sexual gland is hermaphroditic, hence 
 
ALLIES OF THE PELECYPODA : MOLLUSCA 181 
 
 every individual is likely to deposit eggs. The eggs may be 
 found on the branches of water-plants, or even on the per- 
 pendicular sides of a glass aquarium, imbedded in an ellip- 
 tical, clear, gelatinous mass from two millimeters to six 
 millimeters long. In each mass from five or six to twenty- 
 five eggs may be distinguished. 
 
 The Land-Snail. One of the commonest of the land-snails in 
 America is the one shown in Fig. 93 (He'lix nebulo'sa). 'Like 
 its many kindred species of the genus Helix, it lives in 
 moist, protected places during the day, and comes out to 
 feed at night. Frequently it leaves its hiding-place in cloudy, 
 damp, but not in rainy, 
 weather. 
 
 In general features, the 
 organs to be noted on the 
 exterior of this animal are 
 the same as in the pond- 
 snail. The openings of all 
 the internal organs 
 occur in the same 
 position in both 
 animals. There 
 are four tentacles 
 in Helix, an 
 upper, long pair 
 bearing the eyes, 
 and a lower, short 
 pair, which are 
 the organs of 
 touch. The edge of the mantle is thickened to form a collar. 
 
 In the fall of the year, about the time of frost, the land- 
 snail ceases to eat, becomes inactive, and makes preparation 
 for the winter's sleep, or hibernation. Crawling to the pro- 
 tected side of an object which has a smooth surface, the 
 
 FIG. 93. Living Land-Snail. Natural size 
 
182 GENERAL ZOOLOGY 
 
 animal withdraws into its shell, allowing the edge to fit 
 closely to the object. Then certain glands in the collar 
 secrete mucus, which flows from all sides over the under 
 surface of the foot, between it and the supporting surface. 
 
 When the membrane dries it has the appearance of stiff, 
 oiled paper of considerable toughness. It is called the epi- 
 phragin. It is supposed that the epiphragin aids in retaining 
 the body-heat during the four to six months of sleep. Metab- 
 olism (see p. 206) continues through all that time, but at a 
 much reduced rate. A very small hole is to be found in the 
 epiphragin, in one species of Helix at least, just below the 
 lung-aperture. Through this oxygen and carbon dioxide may 
 continue to pass. With the returning warmth of spring the 
 snail bursts the epiphragm and recommences active life. 
 
 The Garden-Slug. The particular species of garden-slug, 
 the habits of which are suggested in Fig. 94, is Li'max 
 max'imus. It is a native of Europe, not of America, and 
 since its introduction here has become a more unwelcome 
 guest in greenhouses than any other species of slug or snail. 
 As yet it is not widely distributed from the vicinity of 
 New York and Boston. 
 
 In brief terms we may describe a slug as a snail with a 
 rudimentary shell. The elliptical plate of muscle on the 
 dorsal surface of Limax is all that is left of the mantle. In 
 the process of degeneration, which we may well suppose has 
 occupied thousands of years, the mantle folded back over 
 the shell as the latter decreased in size. If we examine the 
 interior of the mantle, we find a thin, calcareous plate, which 
 is undoubtedly the rudimentary shell. 
 
 Aside from the difference in the size and form of the shell, 
 Limax maximus and Helix nebulosa are very much alike. 
 The body of Limax is straightened out, but the organs which 
 in Helix have openings on the right side of the body also 
 have openings on the right side in Limax. These are the 
 
ALLIES OF THE PELECYPODA : MOLLUSCA 183 
 
 generative opening just back of the right eye-stalk, the anus, 
 and the nephridial opening near the lung-aperture. The 
 garden-slug, like the snails, has a rasping-tongue. 
 
 If a person examines in daylight the under side of boxes or 
 bunches of straw that usually collect about a greenhouse, he 
 will find within the range 
 of the animal's distribution 
 many specimens with their 
 heads contracted to the 
 body, holding to the 
 
 surface of the 
 thing which 
 conceals them. Frequently 
 after a night's forage on the 
 tender parts of greenhouse plants, 
 they go no farther away than the 
 bottom of the flower-pot. Reliable 
 observers have marked specimens 
 and have found that these creatures return night after night 
 to a particularly succulent plant, such as the Amaryllis in the 
 picture. It is thought by some that their " sense of direction" 
 lies in the ability to smell their food-plant. Some authors 
 believe that the organ of smell lies at or near the end of 
 
 FIG. 94. Garden-Slug feeding 
 at Night, x i 
 
184 GENERAL ZOOLOGY 
 
 the eye-stalk; others are inclined to think that the animal 
 has a more definite organ of smell in the osphradium. This 
 organ occurs on the mantle-edge near the lung-aperture. 
 
 The ravages of Limax maximus are not serious, if the 
 florist does not allow refuse to collect about his buildings. 
 Many adopt the method of scattering ashes or cinders about 
 the plants to be especially protected. A slug crawling into 
 such an obstruction is stimulated by the dryness of the ashes, 
 or the roughness of the cinders, to secrete mucus from the 
 glands that occur in the skin. This mucus is like that which 
 is secreted from its foot-gland while crawling. Owing to the 
 unusual amount of mucus given off at such times, the animal 
 dies from exhaustion, and from suffocation by the drying of 
 its skin. 
 
 From the beginning of September to the end of November 
 Limax maximus lays its eggs in its place of hiding. The eggs 
 have about one half the diameter of dried peas. They are quite 
 spherical. The shell is translucent and is tough and membra- 
 nous. Twenty-five or thirty eggs are deposited at one time, 
 and left on the ground in a loose, agglutinated mass. The 
 embryos of the early eggs hatch within two or three weeks, 
 while eggs deposited late probably do not hatch until the 
 following spring. The garden-slug is hermaphroditic. The 
 eggs and spermatozoa in each individual mature at differ- 
 ent times, and consequently the union of two individuals is 
 necessary for the fertilization of the eggs. 
 
 Garden-slugs that live out-of-doors burrow into the ground 
 and curl up when the coldest weather comes. Those in green- 
 houses remain active throughout the year. 
 
 The Oyster-Drill. A few minutes' walk along almost any 
 pebbly beach between Florida and the Gulf of St. Lawrence 
 would afford a collector the opportunity of observing the sub- 
 ject of this description, the oyster-drill (Urosal'pinx cine'rea, 
 Fig. 99). In such a walk the artist discovered the unfortunate 
 
ALLIES OF THE PELECYPODA : MOLLUSCA 185 
 
 periwinkle at the left of the picture, with the oyster-drill of 
 the foreground engaged in devouring the soft parts of its 
 victim through the hole made in the thick shell. For the 
 purposes of illustration the oyster-drill was placed on another 
 periwinkle in the same position it occupied on the first when 
 discovered. In deep water the oyster-drill devotes itself to 
 the business which gave it the name it bears. There are 
 several other species of snails, however, which have the same 
 habit of boring through the oyster's valves and feeding on 
 the soft parts. 
 
 The oyster-drill has organs not found in the snails already 
 described in this chapter. In a little groove in the "mouth" 
 of the shell lies a small tube called the siphon, which carries 
 water to a gill-chamber, where the blood is supplied with 
 oxygen. Another organ is a horny plate growing on top of 
 the posterior end of the foot. When the foot is withdrawn 
 into the shell, the horny plate, which is called the operculum 
 (a lid, or cover), is drawn into the mouth of the shell. The 
 operculum is of great service to the animal in keeping out 
 unwelcome visitors. 
 
 The oyster-drill, in common with all other species of snails 
 that have their habitat on the seashore, possesses a very thick 
 shell, adapted to the severe conditions of life there. The 
 sand and pebbles are constantly shifting under the pressure 
 of the waves, and only those snails that have thick shells can 
 endure the conditions. 
 
 The Periwinkle. The periwinkle, a littoral (shore) species 
 (Littori'na litto'rea, Fig. 99), is a native of Europe. Its pres- 
 ence here is accounted for by the supposition that specimens 
 were accidentally thrown in with the gravel used for ballast 
 on ocean-going vessels, and thrown out again when the vessel 
 reached its port in America. The first specimens noticed in 
 America by conchologists (students of shells) were reported at 
 Halifax, Nova Scotia, in 1857. Since that time the periwinkle 
 
186 
 
 GENERAL ZOOLOGY 
 
 has been making its way down the coast. It may now be found 
 in southern waters. The new home in America seems to be 
 especially favorable for the periwinkle, for on the rocky coast 
 of New England there are so many of them that on first 
 impression there appears to be no other species. 
 
 The periwinkle depends on plant-food altogether. It is 
 reported that the oystermen of Whitstable, England, at the 
 mouth of the Thames River, collect these snails in large quan- 
 tities and throw them over the oyster-beds in order to be rid 
 of the excess growth of seaweeds. 
 
 On account of its great abundance the periwinkle is much 
 used as an article of human food in England and 011 the 
 Continent. It is one of the many species of snails and slugs 
 used as food, especially by the French people. 
 
 The Nudibranch. The strange-looking creature shown in 
 Fig. 95, Dendrono'tus arbor es'cens, is to be found on seaweeds 
 
 and under submerged 
 rocks along the North 
 Atlantic coast. 
 
 The general form of 
 a slug is, in this animal, 
 modified by the occur- 
 rence of tree-like proc- 
 esses growing on the 
 upper part of the body, 
 whence the generic and 
 
 specific names. These 
 
 Fio.96. Photograph of Living Nudibranch. gseg are oalled 
 
 Natural size 
 
 cer-ata, and to some 
 
 extent are used in respiration. Being thin, oxygen can pass 
 into the animal through them, and the waste carbon dioxide 
 can pass out. The group of animals to which they belong 
 is called Nudibran' chia, in reference to the fact that their 
 gills are naked. There is no indication of a rudimentary 
 
ALLIES OF THE PELECYPODA : MOLLUSCA 187 
 
 shell in Dendronotus, but the presence of other organs, 
 including the rasping-tongue, proves their relationship to the 
 garden-slug. 
 
 Nudibranchs deposit their eggs in protected places, fasten- 
 ing them with mucus against rocks and seaweeds. One may 
 recognize the egg-mass of Dendronotus by its salmon-pink 
 color and its coiled arrangement. 
 
 The color of this animal is rich brown ; the same colors 
 occur in its immediate environment. Quite as valuable as 
 the color-resemblance, in protecting the nudibranch against 
 ravenous fish, is the marked similarity of the cerata, in form, 
 to the delicate branches of certain seaweeds. The slowness of 
 the animal's movements must also aid it in escaping notice. 
 
 Definition of Gasteropoda (Gr. gaster, stomach ; pous 
 (2>od), foot). The class represented by the snails, the slug, 
 and the nudibranch is given the name Gr aster op' o da. The 
 class-name is only figuratively correct. The ventral surface, 
 not the stomach, is modified to form a locomotor organ, 
 the foot. 
 
 An important characteristic of the Gasteropoda is the 
 unsymmetrical arrangement of organs. With the exception 
 of the mouth and the opening of the mucus-gland, all the 
 openings of the body are on the right side, even in cases like 
 the slug and nudibranch, where the general form of the body 
 is bilaterally symmetrical. The asymmetry (lack of symme- 
 try) of the organs is directly connected with the existence 
 (present or past) of a shell. When a shell occurs it is com- 
 posed of one piece, and the characteristic form is spiral. A 
 shell-forming organ, the mantle, is usually present. 
 
 The body of Gasteropoda is not divided into somites, but 
 the head is slightly marked off from the rest of the animal, 
 and is provided with eyes and unsegmented tentacles. A 
 tongue-like organ bears a ribbon of minute teeth for tear- 
 ing food. 
 
188 GENERAL ZOOLOGY 
 
 The Squid. In the waters of the Grand Banks of New- 
 foundland and southward to Massachusetts the members of 
 a species of squid, Ommas'trephes illecebro'sa (Fig. 96), occur 
 in great numbers. They capture small fishes, and are them- 
 selves prey for cod and other large fishes. 
 
 The body of the squid is composed of a head and a slender, 
 conical portion, the former having a pair of large, movable 
 eyes (Fig. 96, G). Arising from the head-region are ten long, 
 club-shaped arms (Fig. 96, 1), corresponding morphologically 
 to the foot of the Pelecypoda and the Gasteropoda. Two of 
 the arms are longer than the other eight, but all are provided 
 on part of the inner surface with many sucking-disks, adapted 
 to holding the prey. The mouth has two horny jaws, resem- 
 bling in appearance the bill of a parrot turned upside down. 
 The tongue is adapted to rasping. 
 
 The conical portion of the body is the mantle (Fig. 96, 2), 
 highly modified by the existence of strong, muscular bands. 
 Part of the space within the muscular mantle is occupied by 
 the internal organs inclosed in a body-cavity. The remainder 
 of the space, the mantle-cavity itself, connects with the out- 
 side by a narrow opening (Fig. 96, 5), at either side of the 
 neck, and also by the siphon (Fig. 96, 4). A pair of feather- 
 shaped gills, one attached to either side of the body, lies in 
 the mantle-cavity. Imbedded in the tissue of the mantle, 
 on the side opposite the surface shown in the figure, there 
 is a long, pen-shaped structure composed of chitinous mate- 
 rial. This is supposed to be the homologue of the shell of 
 Pelecypoda and Gasteropoda. The sexes are separate. 
 
 In locomotion the squid contracts and relaxes the circular 
 muscles of the mantle, alternately decreasing and increasing 
 the volume of the mantle-cavity. During relaxation, water 
 enters the mantle-cavity at the sides by the neck, a valve 
 in the siphon being closed; in contraction the valves at 
 the side openings are closed and the water is discharged 
 
FIG. 96. Photograph of Squid, x - 
 1, teutacle; 2, mantle; 3, mantle-fin; 4, siphon; 5, incurrent opening ; 6, eye 
 
 189 
 
190 GENERAL ZOOLOGY 
 
 through the siphon. The siphon may be directed forward 
 or backward at will. If it is bent in the direction of the 
 arms, as it commonly is, the squid during strong contraction 
 of the mantle darts backward " with the speed of an arrow," 
 balanced and steered by the aid of the double mantle-fin 
 (Fig. 96, 3). 
 
 In the squid's most rapid locomotion the mantle-fins are 
 folded toward the body. In slower movements a wave-like 
 flapping of the fins supplements the jets from the siphon. 
 So skillfully manipulated are the mantle-fins, and the mantle- 
 point itself, in turning to one side or the other, and in going 
 up or down, that one marvels at the wonderful adaptations 
 of an animal that has its "steering-gear" in front, instead of 
 behind, its principal " engine." 
 
 While at rest on the bottom of an aquarium the squid ex- 
 tends its two long arms to the bottom, bent akimbo, appar- 
 ently to keep the siphon and the two lateral mantle-openings 
 away from the sand. The mantle forms the third point of 
 support in the resting attitude. Water may then be drawn 
 into the mantle-cavity, and expelled again, in the normal 
 process of respiration. 
 
 No more beautiful example of rapid color-change can be 
 witnessed than the one going on constantly in the skin of 
 captive squids. From bluish white the color may change on 
 the instant to mottled red or brown. The change may be 
 sudden and complete, or the colors may fluctuate repeatedly 
 from one shade to another and shimmer over the surface seem- 
 ingly as rapidly as the controlling nerves can act. Observers 
 who have been fortunate enough to come upon a " school " 
 of squids in a harbor have been puzzled by the sudden disap- 
 pearance of the animals. In times of danger the ability to 
 change color to resemble the environment must be of consid- 
 erable value to them in escaping the notice of enemies, as 
 well as useful in coming unseen into a school of small fish. 
 
ALLIES OF THE PELECYPODA : MOLLUSCA 191 
 
 Another and still more effective means of escaping from 
 the attack of a superior enemy is employed by the squid when 
 driven to its last resource. It has in its body-cavity a sac 
 which secretes a black, inky fluid. A tube from the ink-sac 
 passes to the siphon, and in the moment of need the sac and 
 the muscular mantle contract and force the black, confusing 
 fluid into the water. The squid then has a chance to escape. 
 
 The Chambered 
 Nautilus. Almost 
 the sole represent- 
 ative of a once 
 numerous race 
 living in the 
 depths of the sea, 
 the chambered 
 or pearly nautilus 
 (Nau'tilus pom- 
 pil'ius, Fig. 97) 
 now has a restrict- 
 ed distribution in 
 the vicinity of cer- 
 tain South Pacific 
 islands, such as 
 New Guinea and 
 the Philippines. Nautilus lives on the bottom, usually in 
 water from one hundred to seven hundred meters deep (three 
 hundred and twenty-five to twenty-three hundred feet). 
 
 The shell of Nautilus is divided into compartments by 
 cross-partitions. Each of these compartments represents a 
 space in which the animal lived at successive stages in its 
 growth. The chambers of the entire series are filled with air 
 and are connected by a slender tube called the siphuncle^ 
 borne in a thin-walled, calcareous tube (Fig. 97, 11 ). The 
 siphuncle is a part of the animal's body proper. A mantle 
 
 FIG. 97. Nautilus. Reduced. (After Ludwig) 
 
 1, mantle ; 2, dorsal fold of mantle ; 3, tentacles ; 4, head- 
 fold ; 5, eye ; 6, siphon ; 7, position of nidamental 
 gland ; 8, shell-muscle ; 9, living chamber ; 10, parti- 
 tions between chambers; 11, siphuncle with tube 
 
 (From Hertwig-Kingsley's General Zoology) 
 
192 GENERAL ZOOLOGY 
 
 lies within the outermost chamber of the shell and extends a 
 dorsal fold outward against the old part of the shell. When 
 the animal is contracted into the outer chamber a thick brown 
 hood conceals it from view. When the head is extended two 
 large eyes, about forty tentacles (arms), and a siphon are vis- 
 ible. The mouth is provided with a beak like that of the 
 squid, and with a rasping-tongue. Inside the mantle-cavity 
 there are four gills. There is no ink-sac. Another difference 
 between the chambered nautilus and the squid is the entire 
 absence in the former of the ability to change color. The 
 sexes are separate, as in the squid. 
 
 The food of the animal consists of deep-water bivalves. In 
 obtaining food Nautilus probably uses the tentacles. Although 
 these organs have no sucking-disks, as the squid has, the 
 inner edges of the tentacles appear to have the power of flat- 
 tening against an object and of holding it effectively. 
 
 Owing to the fact that Nautilus lives at great depths, we 
 know very little concerning its habits. Professor Willey, of 
 England, and Professor Dean, of Columbia University, have 
 studied the live Nautilus recently (1895 to 1901), and have 
 published reports on that subject. Nautilus is accustomed to 
 a great pressure of water and low temperature. When brought 
 to the surface in traps it could scarcely be expected to act 
 naturally. However, it seems reasonable to believe that the 
 method of locomotion would not be affected. It swims by 
 means of a jet of water from the siphon, and the convex sur- 
 face of the shell parts the water in its progress. 
 
 Oliver Wendell Holmes, in his poem, The Chambered Nau- 
 ?, thus refers to the phenomena of its growth : 
 
 Year after year beheld the silent toil 
 
 That spread his lustrous coil ; 
 
 Still, as the spiral grew, 
 He left the past year's dwelling for the new, 
 Stole with soft step its shining archway through, 
 
 Built up its idle door, 
 Stretched in his last-found home and knew the old no more. 
 
ALLIES OF THE PELECYPODA : MOLLUSCA 193 
 
 Fossil Relatives of Nautilus. Many millions of years ago, in 
 the early history of the earth, the most ancient of the imme- 
 diate ancestors of Nautilus lived. Paleon- 
 tologists (students of fossils) have given its 
 fossil (Fig. 98) the name Orthoc'eras (Gr. 
 orthos, straight; keras, horn). The strongest 
 evidence we have that Orthoceras is a rela- 
 tive of Nautilus is the series of chambers 
 joined by the siphuncle. We know nothing 
 of the structure of the soft parts of Orthoc- 
 eras, but paleontologists have made draw- 
 ings to show how Orthoceras probably 
 appeared. From the study of fossils in 
 later layers of the earth's crust we know 
 that the group of nautiloids (Nautilus-like 
 animals) grew to be of large size, and to 
 have their shells coiled more and more to 
 the close coil of the present-day Nautilus. 
 All of the hundreds of species of nautiloids, 
 except four species of Nautilus, disap- 
 peared as living things ages before man 
 came into existence upon the earth. 
 
 Definition of Cephalopoda (Gr. kephale, 
 head ; pous (pod), foot). Ommastrephes, 
 Nautilus, and Orthoceras, because of their 
 structural relationship, belong in a class 
 together, the Ceplialop'oda. 
 
 In this class the body has a distinct head. 
 No part shows indications of being divided 
 into somites. The head has two large eyes. 
 
 The mouth is surrounded by divisions of FIG. 98. Fossil Orthoc- 
 . P , eras. Reduced, 
 
 the primitive foot, called arms or tentacles. (After Blake) 
 
 These divisions of the foot either have 
 sucking-disks for holding on, or smooth surfaces which per- 
 form the same function. In the mouth there is a parrot-like 
 
194 
 
 GENERAL ZOOLOGY 
 
 beak and a rasping-tongue. A shell-forming mantle either 
 incloses the shell, as in the squid, or lies beneath it, as in 
 Nautilus and Orthoceras. 
 
 There are two gills in the mantle-cavity in the squid, and 
 four in Nautilus. A siphon is present in all the examples 
 described. The sexes are separate. 
 
 Definition of Mollusca (Lat. molluscus, soft). The phylum 
 Mollus'ca includes five classes. For the purpose of elemen- 
 tary study the most important ones are the Pelecypoda, the 
 Gasteropoda, and the Cephalopoda. 
 
 On the basis of the facts presented in this and the pre- 
 ceding chapter, we may formulate the following statement 
 concerning the phylum. Mollusca are soft-bodied animals 
 provided usually with a hard, calcareous, partly chitinous 
 shell, which in some forms occurs on the exterior, and in 
 others is partially or completely inclosed by a sheet of shell- 
 forming muscular tissue, the mantle. The body proper is 
 never divided into somites, and the appendages are never 
 segmented. 
 
 FIG. 99. Living Oyster-Drill and Periwinkle, x f 
 
CHAPTER XVI 
 THE EARTHWORM 
 
 I guess the pussy-willows now 
 Are creeping out on every bough 
 
 Along the brook ; and robins look 
 For early worms behind the plough. 
 
 HENRY VAN DYKE, An Angler's Wish. 
 
 Habitat and Distribution. The animal which is the subject 
 of this chapter is distributed widely throughout the world. 
 The more familiar species live in the soil, where their burrows 
 extend obliquely downward, sometimes many feet. One rather 
 common species, Alloloboph' ora fce'tida, marked by red and 
 dark bands of color, lives in manure heaps. When irritated 
 it gives off an offensive odor, whence its specific name. The 
 species best known in America is Lumbri'cus terres'tris. It is 
 found in small cylindrical burrows, which it makes in the soil 
 wherever it is not too dry or too sandy. In spite of the usual 
 habit of living in the earth, these animals can live for many 
 days in a body of water without great discomfort. Repre- 
 sentatives of the many species and the few genera of earth- 
 worms are found in practically all places from Arctic to 
 Antarctic regions, including isolated oceanic islands. 
 
 External Structure. T - external structure the body of the 
 earthworm is very simple. The anterior end is slender and 
 pointed when extended in life, and the posterior region is 
 flattened above as well as below. The somites of the anterior 
 region differ also from those in the posterior region in being 
 longer. There is no head, no thorax, and no abdomen. There 
 are no appendages except bristles, almost microscopic in size, 
 which occur in rows on the ventral surface of every somite 
 
 195 
 
196 GENERAL ZOOLOGY 
 
 except a few at the anterior end. The openings of the body 
 are themouth'&t the anterior end just beneath the prostomium 
 (lip), the anus at the posterior end, and various openings on 
 the ventral surface, which are connected with internal organs 
 to be described later. The earthworm has no eyes, yet it 
 knows of the existence of light, and shuns intense light; it 
 has no ears, but it becomes aware of the approach of an enemy 
 by the jar communicated through the soil. In the mature 
 earthworm a thick band, consisting of the thickened body- 
 wall, is visible at about one third the length of the animal 
 from the anterior end. This is called the ditellum. 
 
 PHYSIOLOGICAL PROCESSES 
 
 The internal anatomy of the earthworm seems, on reference 
 to Fig. 100, to be very complicated, but we shall find that 
 each system of organs has well-defined uses. From the study 
 of the internal organs represented here we shall learn some- 
 thing of the uses of internal organs in general; and we 
 shall endeavor to understand more fully the nature of physi- 
 ological processes, which have been briefly referred to in the 
 chapter on the locust. We have already become familiar with 
 the organs in which these processes take place under the 
 names digestive system, circulatory system, respiratory sys- 
 tem, excretory system, and the like. 
 
 Digestion. The first division of the digestive system of the 
 earthworm is the mouth (Fig. 100, 6), followed by the pharynx 
 (Fig. 100, 7), the latter having a very thick muscular wall. 
 The pharynx can be protruded slightly or retracted, and the 
 cavity enlarged by strands of muscle-fibers which extend to 
 the body-wall (Fig. 100, 9). Food, consisting of particles of 
 leaves, animal tissues, and even soil, is drawn into the pharynx 
 by the sucking action which takes place when the cavity of 
 the pharynx is enlarged. The food passes directly through 
 
. e N -~ 
 
 a s 1 ? a 8 a 
 
 PH E SH.^ bJD - 'V 
 ' 
 
 <VJ S 
 
198 GENERAL ZOOLOGY 
 
 the esophagus (Fig. 100, 10, 11). Before the ingested (swal- 
 lowed) food reaches the crop (Fig. 100, 12) the secretion, and 
 sometimes even hard particles from the calciferous glands 
 (Fig. 100, 15, 16), mixes with it and probably serves to neutral- 
 ize whatever acid may be present, and helps to maintain the 
 contents of the oesophagus in an alkaline condition, so that 
 the digestive fluid of the intestine (Fig. 100, 14), which is 
 alkaline in chemical nature, can act without interference. 
 The crop is a temporary reservoir for the food, and the gizzard 
 (Fig. 100, 13) is the only place in the entire digestive system 
 adapted for dividing large particles of food into minute pieces. 
 Earthworms are known to swallow small, rough pebbles, and 
 even sharp pieces of glass, for the purpose of using them in 
 the gizzard to grind into bits other particles which are swal- 
 lowed as food. The strong muscles in the wall of the gizzard, 
 by corseting, grind the contents together, and every particle 
 is worn smaller. 
 
 The process c LigestiOn in the earthworm begins " r hmi. 
 s on seizing food with its lip, the animal pours out a secretion 
 from glands 'iii "tire ^hurvnx. Digestion continues .as the food 
 is being drawn into the pharynx, ana Wiiiie on "its \va_> f h rough 
 the oesophagus. Experiments with the digestive fluid of etrth- 
 worms indicate that it has a chemical action on the thivt 
 principal classes of organic foods, namely, proteids, carfa 
 hydrates, and /ate. The proteids which the earthworm T 
 be likely to devour are bits of muscle of very small animals, 
 and protoplasm, the living cell-substance of both animals and 
 plants. The carbohydrates, such as the starch-granules or 
 the sugar of any vegetable cell, form a large portion of its 
 food, while fats are eaten probably in small quantities. 
 
 The digestive fluid of the earthworm resembles the digest- 
 ive fluid of the higher animals, not only in being capable of 
 acting on the three important classes of organic foods, but also 
 in containing some of the same special chemical compounds 
 
THE EARTHWORM 
 
 199 
 
 which have the digestive action. These are called ferments, or 
 enzymes. The peculiar quality of an enzyme is to cause a 
 chemical change in another substance without itself losing 
 any of its own properties. Thus, trypsin, the enzyme which 
 acts on proteids, can do so and still remain trypsin. Similarly, 
 the enzyme diastase acts upon starch, and steapsin upon fats. 
 
 Let us consider for a moment why 
 it is necessary for the earthworm, 
 or any animal, to secrete elaborate 
 chemical mixtures like digestive 
 fluids. If we were to examine the 
 alimentary canal of the earthworm, 
 we should find that there are no 
 openings leading from the canal to 
 the body-cavity which might permit 
 food to pass directly to different 
 organs. The wall of the canal is 
 thin, but it is made of cells which 
 are packed closely together. Water 
 will pass through this membrane 
 easily, but certain other substances, 
 although in a liquid state, will not 
 pass through so readily. Those solu- 
 
 f. ,.? j.1 ' u i 
 
 tions which pass through an animal- 
 membrane readily are called crystal- 
 
 7 . , ,. , r> i 
 
 loids; for example, solutions of salt or 
 sugar. Liquids which do not pass readily through an animal- 
 membrane are known as colloids; for example, solutions of 
 meat-juice or starch. The action of the digestive fluid is a 
 double one : it changes the state of the solid food physically, 
 by rendering it liquid ; it changes the state of organic foods 
 '(both solid and liquid) chemically, giving at the same time to 
 each of the altered food-substances a new physical property, 
 namely, that of being able to pass through the intestine-wall. 
 
 i- 101. Experiment show- 
 ing Osmosis 
 
 bottle; 2, water; 3, tube; 
 
 4> piece of sheep , s intest ine 
 containing salt-solution; 
 
 5, level of salt-solution 
 
200 GENERAL ZOOLOGY 
 
 For illustration, we may suppose that an earthworm has 
 swallowed a small piece of potato which contains a great deal 
 of starch. In the intestine the starch is changed physically by 
 being made liquid or partially so, and it is changed chemically 
 by the enzyme diastase into a sugar-compound. In the latter 
 state, what was once starch passes readily through the wall of 
 the intestine. A proteid substance like iVeat-juice cannot pass, 
 except in a slight degree, through the intestine until it has 
 been changed chemically ; this is done by the enzyme trypsin. 
 The changed substance is called a peptone. It is not likely 
 that earthworms in nature ever need to digest considerable 
 quantities of fat, but in experiments fats have been fed to 
 earthworms. Results followed similar to those obtained in 
 many other animals which usually consume fats. The enzyme 
 steapsiri separates the fats into compounds known as glycerin 
 and fatty acid. The fatty acids combine chemically with the 
 alkali in the digestive tract, resulting in compounds similar 
 to soap ; the process is therefore called saponification. When 
 the proteids are changed to peptones, the starch to sugar, and 
 the fats to glycerin and soaps, then these organic foods are 
 ready to pass with any inorganic foods, as, for example, 
 salt and water, through the' wall of the intestine. 
 
 Absorption. Digested food passes through the intestine- 
 wall and mixes with the body-fluids, in accordance with a 
 principle known in physics as osmosis (see Fig. 101). In the 
 experiment illustrated in the figure there is a salt-solution 
 in the sac made of sheep's intestine (Fig. 101, 4), and pure 
 water in the beaker outside. The experiment is supposed 
 to have been started with the salt water and the pure water 
 at the same level. Within a half-hour the level of the salt- 
 solution has risen several inches. Besides, some of the salt- 
 solution has passed through the membrane into the pure water. 
 It is one of the phenomena of osmosis that a greater amount 
 ^of liquid passes from the less dense to the more dense solution 
 
THE EARTHWORM 201 
 
 than in the contrary direction. If the pure water in the ex- 
 periment were replaced by a colloid-solution, then the pas- 
 sage of liquid would practically all be from the salt-solution 
 into the colloid-solution. 
 
 It is well known that a crystalloid, like salt or sugar, if 
 placed in a vessel of water, will soon diffuse through the water. 
 In doing so it exerts a certain amount of pressure. This is 
 called osmotic pressure. If a permeable membrane be inter- 
 posed between a solution of crystalloids and one of colloids, 
 both substances will exert some osmotic pressure, but by 
 far the greater amount is exerted by the crystalloid, because 
 of its greater facility in diffusing through water. Applying 
 the principle of osmosis to absorption in the intestine cf the 
 earthworm, we. have crystalloids in the cavity of the intes- 
 tine, a permeable though not porous membrane (the intestine- 
 wall), and colloids in the blood and body-cavity fluid. The 
 digested food diffuses through the intestine-wall because of 
 the pressure it exerts in seeking to mix with more water. 
 Food on passing to the blood is changed by the cells of 
 the intestine-wall from the crystalloid condition to a col- 
 loid, and is henceforth incapable of passing back through the 
 membrane. 
 
 Circulation. Whenever an animal body is too large or com- 
 plicated for the food to reach all the cells directly, we find 
 a circulatory system developed. The circulatory system of 
 the earthworm is complete, and rather complex. The dor- 
 sal blood-vessel (Fig. 100, 17) extends the length of the animal, 
 along the middle, between the body- wall and the alimentary 
 canal. The blood flows toward the anterior region in some- 
 what regular " pulses," carried along by waves of muscular 
 contraction in the wall of the blood-vessel itself. Between 
 the pharynx and the crop are situated five pairs of "hearts" 
 (Fig. 100, 19, 20). These short tubes receive most of the 
 blood that comes forward, take up the waves of contraction- 
 
202 GENERAL ZOOLOGY 
 
 sent along the dorsal vessel, and force the 'blood into theJ 
 ventral blood-vessel (Fig. 100, 22), which carries it posteriorly 
 in a regular flow. Below the ventral nerve-chain is the sub- 
 neural blood-vessel (Fig. 100, 23), in which the blood prob- 
 ably flows backward. The lateral blood-vessel (Fig. 100, 21), 
 with its connections, is limited to the region anterior to the 
 crop. Capillaries (fine blood-vessels joining larger ones) branch 
 in the wall of the intestine and connect in a very complicated 
 fashion with all the large vessels. Absorbed food passes into 
 the capillaries and is carried with the blood to the larger 
 blood-vessels, to be transported to all parts of the body. All 
 about the intestine, in the hollow spaces of the somites, tliei 
 is a large quantity of body-cavity fluid, which is very much 
 like the blood in the vessels, except that it is colorless. It is 
 thought that much of the absorbed food mixes with this 
 fluid. The outcome is the same with food carried by the regu- 
 lar circulatory system and with that taken up by the bod}-- 
 cavity fluid. 
 
 Assimilation. The food is transported by the blood in the 
 blood-vessels or in the bodj^-cavity to tissues, where some of 
 it is transformed into protoplasm. Just how this is done no 
 one has been able to discover, but it is known that the trans- 
 forming process, which is called assimilation, takes place in 
 tissues which are alive, for example, muscles and nerves. 
 We know that the building up of new protoplasm takes plac 
 in growth, when new cells are formed, and that it is also made 
 necessary on account of the slow and imperceptible destriu. 
 tion of the protoplasm in oxidation (see below). 
 
 It will be helpful at this point to know that of all the food 
 taken into the circulatory system of an animal but very little 
 except during growth, is actually made into protoplasm.^ 
 The carbohydrates and the fats that are absorbed, aiid those 
 that are made from proteids by the protoplasm, together with 
 some unassimilated proteids, are destroyed after they have 
 
THE EARTHWORM 203 
 
 been stored temporarily either in the lining of the body- 
 cavity, in the muscle-cells, or in the fat-cells. Protoplasm 
 itself breaks down, but to a less extent. 
 
 First Stage of Respiration. The earthworm has neither gills, 
 tracheae, nor lungs; still it can breathe quite as perfectly as the 
 animals which possess one or another of those organs. The 
 essential characteristic of a breathing organ is a thin, moist 
 membrane, with thin-walled capillary blood-vessels on one side 
 and air on the other. The outer skin of the earthworm is 
 thin and moist, and just beneath it are capillaries. While in 
 its burrow, or even in water, air comes in contact with the 
 skin, and its most important element, oxygen, passes through 
 and mixes with the blood. The second stage of respiration 
 comes after oxidation, in the series of events here described. 
 
 Oxidation. In the circulating blood there is a red-colored 
 Mibstance called haemoglobin. Oxygen combines chemically 
 with this, and the compound goes with the blood until it 
 reaches tissue-cells which have some food stored in them; 
 then the oxygen combines with the food, which may be car- 
 bohydrate, fat, or proteid. The chemical union of oxygen 
 with other elements is of the greatest importance in the life 
 of any plant or animal. A simple example of the result of 
 the chemical union of oxygen with another element may be 
 observed in the burning of coal. It is well known that coal 
 is composed chiefly of carbon. When a quantity of coal is 
 heated it begins to unite with oxygen from the air. During 
 this process four phenomena may be observed : first, the quan- 
 tity of oxygen in the room is reduced ; second, the quantity 
 of coal is reduced ; third, an invisible gas is formed ; and 
 fourth, heat and light are given off. 
 
 When oxygen unites chemically with carbon two kinds of 
 gas may be formed, either carbon monoxide or carbon dioxide, 
 or both. The union of a solid element with a gaseous one 
 to form a gaseous compound accounts for the fact that so 
 
204 GENERAL ZOOLOGY 
 
 great a mass of coal disappears in burning, leaving only the 
 mineral ash behind. We call the union of oxygen with an- 
 other element oxidation. 
 
 Forms of Energy. It is important to observe that as oxi- 
 dation takes place heat and light, which are called forms of 
 energy, are given off. Energy that is, the power to do work 
 can be transformed from one form to another ; for example, 
 the heat derived by oxidizing coal may be transformed into 
 mechanical energy like that of an engine, and the mechanical 
 energy may be changed into electricity, and the electricity 
 into mechanical energy again, or into heat and light. We 
 may regard the energy which is suddenly released upon the 
 oxidation of the carbon in the coal as having been stored there 
 by the sun millions of years ago, when the coal was the grow- 
 ing tissue of a tree. We may borrow from physics two other 
 terms which will help us in getting the notion of the states in 
 which energy may exist. Energy at rest as, for example, 
 chemical affinity (that is, the readiness of the carbon to com- 
 bine with oxygen) is called potential energy ; energy in action, 
 as heat, light, electricity, and motion, is called kinetic energy. 
 As we have already seen, potential energy may become kinetic 
 energy, and kinetic energy may become potential energy. 
 
 When the earthworm swallows a bit of leaf which passes 
 through all stages of digestion, absorption, circulation, and 
 food-storing, or assimilation, the form of the bit of leaf is 
 completely lost, and the chemical composition is also changed ; 
 but oxidation has not taken place, and hence the potential 
 energy transformed from the kinetic energy of the sun (heat 
 and light) when the leaf grew, remains unchanged until the 
 all-important phenomenon of oxidation occurs. 
 
 Carbohydrates, and especially fats, are capable of combin- 
 ing with a relatively large amount of oxygen, because of the 
 small proportion of that element in those compounds, and the 
 large proportion of carbon. Carbohydrates, chiefly glycogen, 
 
THE EARTHWORM 205 
 
 one of the many kinds of sugar in nature, are frequently made 
 from proteids by the protoplasm in the cells, and are stored 
 in the liver-cells of the higher animals, to be later transported 
 to their muscle-cells and stored in them until needed. In 
 animals that have no liver, as the earthworm, the glycogen 
 is stored in the cells of the lining of the body-cavity, and in 
 the muscles. A French physiologist, Chauveau, believes that 
 "the glycogen incorporated in the muscular tissue puts at 
 the service of the tissue the energy which it needs for its 
 work." This theory is valuable, because it enables us to see 
 how the energy (heat) released by the oxidation of the small 
 particles of glycogen in the muscle-cells may be transformed 
 into muscular energy without loss. Fats, made either from 
 carbohydrates or from proteid food by the protoplasm, or 
 stored directly in cells from the fatty acids absorbed through 
 the intestine, are reserve material, and are capable of supply- 
 ing energy when there is need of it. 
 
 Second Stage of Respiration. When carbohydrates and fats 
 are oxidized the resulting compounds are carbon dioxide and 
 water, as these foods contain only carbon, hydrogen, and 
 oxygen. Proteids are far more complex. All proteids con- 
 tain at least carbon, hydrogen, nitrogen, oxygen, sulphur, and 
 usually, in addition, phosphorus. When they are oxidized 
 many different compounds result. The best known of these 
 are uric acid, carbon dioxide, and water. All these com- 
 pounds are wastes. Carbon dioxide, whether derived from 
 carbohydrates, fats, or proteids, makes its way by the blood 
 to the skin-capillaries of the earthworm, and there passes 
 through the moist membrane to the air outside. The first 
 stage of respiration consists of the absorption of oxygen by 
 the blood-vessels of the skin ; the second stage is the excre- 
 tion of carbon dioxide from the same blood-vessels, through 
 the skin. The entire process of respiration consists simply 
 of an exchange of gases through a membrane. 
 
206 GENERAL ZOOLOGY 
 
 Metabolism. Before discussing the last of the series of 
 physiological processes, it will prove helpful to consider all 
 that has been said as being descriptive of processes that are 
 merely stages of the one great sum-process of living. In 
 scientific terminology we call this sum-process metabolism. 
 Considered as a single process, we recognize a series of events 
 during which things are coming into the body. These things 
 are in the course of making up a part of the body of the 
 organism ; this is called constructive metabolism, anabolic 
 metabolism, or simply anabolism (Gr. ana, up ; ballein, to 
 throw). Upon the occurrence of oxidation, food stored in 
 the muscle-cells, and protoplasm, when it is oxidized, are 
 broken up and reduced to simpler chemical compounds ; 
 this is destructive metabolism, katabolic metabolism, or katab- 
 olism (Gr. kata, down ; ballein, to throw). The products of 
 katabolic metabolism are the wastes of the organism. The 
 undigested food and the indigestible substances that pass 
 through the length of the intestine are not considered 
 wastes, a fact that has already been stated in the chapter 
 on the locust. 
 
 Excretion. The last of the stages of metabolism is excre- 
 tion. In the broadest sense of the term excretion includes 
 all those activities which result in ridding the body of wastes. 
 Carbon dioxide is given off only from the skin ; water prob- 
 ably in part from the skin ; uric acid and water are discharged 
 from pairs of small contorted funnel-shaped tubes in the lateral 
 portions of the cavity of the somites of the earthworm. These 
 excretory organs are called nephridia (Fig. 100, 25, 26). They 
 correspond in function to the kidneys of the higher animals. 
 Each nephridium has the mouth of its funnel extending 
 through a septum (Fig. 100, 4) into the cavity immediately 
 anterior to the somite which contains the greater portion of 
 the organ. The external opening of a nephridium is on the 
 ventral surface. 
 
THE EARTHWORM 207 
 
 The funnel-shaped end of a nephridium is provided with 
 cilia (hair-like structures) inside, which wave downward and 
 carry out such liquid waste products as collect in the body- 
 cavity. Blood-vessels, which break up into capillaries in the 
 wall of the nephridium, also carry a certain amount of waste. 
 The excess water and the nitrogenous waste in the blood 
 are separated in these capillaries ancTgo down the tube, to 
 be discharged at the external opening. The body-cavity fluid 
 is filled with small, free-moving cells, called amoebocytes. 
 They have the power of changing their form quickly by 
 extending irregular pointed processes from any part of the 
 cell-body. Owing to this power they can inclose any small 
 particle of solid matter. The amcebocytes dissolve solid par- 
 ticles that fall from the superficial cells of the intestine. 
 Frequently they make their way through the entire intestine- 
 wall, and are passed to the exterior with the contents of the 
 alimentary canal, carrying the waste products with them. 
 
 Nerve Control. In the preceding paragraphs we have been 
 considering the stages of metabolism, without making any 
 reference to the fact that no activity of internal or external 
 organs could take place in the body of the earthworm if it 
 were not for the controlling influence of the nervous system. 
 Ingestion, digestion, absorption, circulation, respiration, oxi- 
 dation, and excretion constitute a chain of processes, largely 
 because the nervous system, acting through the system of 
 muscles, especially in the digestive and the circulatory sys- 
 tems, causes them to take place according to a definite plan. 
 In order to understand how the nervous system of the earth- 
 worm may act, it will be necessary first to have some knowl- 
 edge of the structure of its nervous tissue. 
 
 The general plan of the nervous system of the earthworm 
 is similar to that of the locust and the crayfish, but Less 
 specialization is evident than in either of the other animals. 
 The " brain" (supraoesophageal ganglion, Fig. 100, 27) is a 
 
208 GENERAL ZOOLOGY 
 
 simple, very small, bilobed ganglion, joined by connectives 
 to a suboesophageal ganglion (Fig. 100, 28) ; from the latter a 
 pair of connectives extend along the ventral wall of the body- 
 cavity to the posterior end, with a ganglion (Fig. 100, 29) at 
 every somite. The brain and ventral nerve-chain constitute 
 the central nervous system. From each ganglion of the ven- 
 tral chain two pairs of nerves run out to the muscles of the 
 body-wall and the internal organs, and one pair begins in 
 the connective near by. The entire set of nerves leaving the 
 central nervous system constitutes the peripheral (surface) 
 nervous system. 
 
 If we were to trace one of the nerves outward from the cen- 
 tral nervous system as it penetrates the muscular tissue, we 
 should find that it divides into many very fine fibers. Certain 
 fibers can be traced to the end as they merge their substance 
 with a muscle-fiber. The nerve-fiber that is united to a 
 muscle-fiber (Fig. 102, 9) is a slender portion of a nerve-cell 
 (Fig. 102, 8), the nucleus (Fig. 102, 7) of which is in the 
 central nervous system (Fig. 102, 6). Nerve-cells of this t}^pe 
 are called motor nerve-cells. The fibers of many motor nerve- 
 cells lie parallel in every nerve. ' Mingled with them is 
 another type of nerve-cell which has its nucleus (Fig. 102,2) 
 at or near the skin of the animal, and the terminal portion of 
 its principal fiber (Fig. 102, 3, 4, 5) extending into the central 
 nervous system. Cells of this type are called sensory nerve-cells. 
 
 Reflex Action. In case an object touches one of the fine 
 sensory hairs on the skin (Fig. 102, l) of an earthworm, a 
 nervous impulse is sent along the sensory fiber to the ventral 
 nerve-chain. There the impulse is transferred to the short 
 branches of motor fibers, and by them ultimately to the prin- 
 cipal motor fiber (Fig. 102, 8). When the impulse reaches 
 the end of the nerve-fiber, the muscle-fiber (Fig. 102, 9) to 
 which it is attached contracts. When many sensory nerve- 
 cells are stimulated in this way, many motor cells will carry 
 
THE EARTHWORM 
 
 209 
 
 out the transferred impulse, the muscles will contract, and 
 the animal moves away. This kind of nerve-action is called 
 reflex action because, in a sense, the impulse is reflected back 
 from the ventral nerve-chain. 
 Reproduction. Every earth- 
 worm contains both spermaries 
 and ovaries. As explained on 
 page 176, animals which have 
 the male and female glands in 
 the same body are called her- 
 maphrodites. There are two 
 pairs of spermaries in the earth- 
 worm hidden by the three pairs 
 of seminal vesicles^indic'dted in 
 Fig. 100, 30, 31. The single pair 
 of ovaries (Fig. 100, 35) is very 
 small. Although each earth- 
 worm produces spermatozoa 
 and eggs, the eggs of one indi- 
 vidual are always fertilized by 
 the spermatozoa of another. 
 During the breeding season, 
 which extends through the 
 greater part of the year, earth- 
 worms occasionally meet be- 
 neath stones and logs, and affix 
 the ventral surfaces of their 
 bodies together by the anterior 
 thirds pointed in opposite directions, and each expels a quan- 
 tity of its spermatozoa which, are received in cavities of the 
 other, opening from the outside. These cavities (seminal 
 receptacles) are four in number, and are in the ninth and tenth 
 somites (Fig. 100, 33, 34). They retain the spermatozoa until 
 the eggs are ready to be laid. 
 
 FIG. 102. Reflex Action in the Earth- 
 worm. (Reconstructed from 
 drawings by Havet) 
 
 (The arrows indicate the path of the ner- 
 vous impulse) 
 
 1, cuticle of skin ; 2, sensory nerve- 
 ganglion ; .'$, sensory nerve-fiber ; 
 4, anterior branch of sensory nerve- 
 fiber ; 5, posterior branch of sensory 
 nerve-fiber ; 6, ventral nerve-cord ; 
 7, motor nerve-ganglion ; 8, motor 
 nerve-fiber; 9, longitudinal muscle- 
 fibers 
 
210 
 
 GENERAL ZOOLOGY 
 
 The presence of the thick band, the clitellum referred to on 
 page 196, indicates that the individual is sexually mature. 
 The clitellum is provided with glands on its ventral surface. 
 Just preceding the time of egg-laying these glands secrete 
 a thick mucus which forms a ring about the clitellum. Into 
 the space between this ring and the body is poured a milky 
 secretion which is food for the young earthworms. The ring of 
 mucus is then moved forward slowly. At the fourteenth somite 
 the eggs are caught up from the oviduct (Fig. 100, 36), which 
 
 ov 
 
 A B C 
 
 FIG. 103. Egg-capsule, Egg, and Spermatozoon, of Earthworm 
 
 A, egg-capsule. B, egg with nucleus: ov, eggs, about natural size. C, spermato- 
 zoon: n, nucleus; w, middle piece; t, tail 
 
 (From Sedgwick and Wilson's General Biology) 
 
 forces them out, at the time the ring passes. Farther forward 
 the spermatozoa that have been stored in the seminal recepta- 
 cles are received into the ring, and while the ring is making 
 its way forward, fertilization, which consists of the union of 
 the spermatozoon with the egg, takes place. At the anterior 
 end the ring begins to draw together at the ends, and when 
 this egg-capsule (Fig. 103, A) has been pushed off, it is a short, 
 spindle-shaped, tough-coated sac, about as large as a grain of 
 wheat, inside of which all the eggs are fertilized. Few of them, 
 however, reach the stage of young, free-moving earthworms. 
 
THE EARTHWORM 211 
 
 Egg-capsules are found buried in the soil and under stones 
 and boards and other protected places. They are often mis- 
 taken for seeds of some plant, which accounts for their iden- 
 tity being unknown to most people. 
 
 From the drawing we get an idea of the relative size of 
 the egg (Fig. 103, B) and the spermatozoon (Fig. 103, C). In 
 the case of animals which produce a large, yolk-filled egg, 
 e.g. birds, the difference in size between the egg and sper- 
 matozoon is far greater. The spermatozoon of all animals is 
 microscopic in size. 
 
 Maturation. The phenomena of fertilization in the egg of 
 the earthworm are not so well known as they are in a near 
 relative, the sandworm, Ne'reis (Fig. 107). The series of fig- 
 ures (Fig. 104, J, /?, C, D, E, F, maturation or egg-ripening 
 in Nereis) illustrates in a general way the phases through 
 which the eggs of animals pass before they begin to develop. 
 Fig. 104, A shows the egg fully grown and ready to receive 
 the spermatozoon. Among the things to be noted are the 
 egg-membrane and the nucleus containing the germinal spot. 
 Imbedded in the fine granular protoplasm (cytoplasm) about 
 the nucleus are the yolk-granules, destined to nourish the 
 developing embryo, and some large fat-globules. 
 
 At about the time of penetration of the egg by the sper- 
 matozoon (Fig. 104, B) the egg-nucleus begins to lose its out- 
 Une because of the encroachment of a spindle-shaped structure 
 ^ormetl from minute fibers in the cytoplasm. At either pole 
 of the spindle is an extremely small granule. These are 
 illed centrosomes (central bodies). They appear to dominate 
 the formation of the spindle and its movements after forma- 
 tion. The spindle draws from the egg-nucleus a definite 
 number of small, rod-like bodies called chromosomes (colored 
 odies). They are so called because in preparations of thin 
 ices of the egg these little bodies stain in certain dyes more 
 b illiantly than any other part. 
 
FIG. 104. Maturation and Fertilization in Nereis 
 
 A, egg with germinal spot; B, egg with first spindle forming, sperm-cell small ; 
 C, egg with first spindle at periphery, two sperm-centrosomes ; I), egg with 
 one polar cell formed, spindle with sperm-cell ; E, egg with second polar cell 
 formed, spindle from sperm-centrosomes ; f, first cleavage spindle, first 
 stage of embryo 
 
 (From Wilson's The Cell) 
 212 
 
THE EARTHWORM 213 
 
 After the chromosomes are arranged across the middle of 
 the spindle, the entire spindle moves end on toward the sur- 
 face of the egg. As it does so the chromosomes divide each 
 into halves and are drawn to the poles (Fig. 104, C). The 
 outer pole makes a prominence on the cell-wall, and soon a 
 little body is formed, the spindle dividing across the middle. 
 We 'observe that this little body is really a cell, because it 
 has a nucleus with chromosomes, a little cytoplasm, and a 
 wall about it. It is called the first polar cell. That portion 
 of the spindle which was left in the egg disappears, but the 
 little centrosome still exists. It soon divides into two, and 
 the parts, gradually separating, form a spindle between them. 
 The chromosomes are again arranged on the spindle. Then 
 the spindle (Fig. 104, D) swings around into the plane of 
 the first spindle. As the spindle moves toward the cell-wall 
 again the chromosomes divide as before. A second polar cell 
 is formed beneath or slightly to one side of the first. The 
 process of maturation is completed by this phase. 
 
 Fertilization. In the eggs of many animals the entrance 
 of the spermatozoon appears to be a stimulus for the begin- 
 ning of maturation. Whether the spermatozoon enters before 
 or after maturation has begun, it cannot take part in the 
 process of development until the second polar cell has been 
 formed. When this has taken place in Nereis, the egg-spindle 
 and the egg-centrosomes both disappear, leaving the egg- 
 chromosomes inclosed in a nuclear membrane. 
 
 The spermatozoon on entering the egg leaves the " tail " 
 outside, its locomotor function being at an end. The "head," 
 which is really the nucleus of the spermatozoon-cell, or sperm- 
 cell as we may now call it, becomes rounded and for a time 
 remains quiescent (Fig. 104, B). As indicated in Fig. 104, C, 
 the sperm-cell becomes larger, and is drawn toward the cen- 
 tral region of the egg by a centrosome, which we shall 
 call the sperm-centrosome, because it came into the egg with 
 
214 GENERAL ZOOLOGY 
 
 the sperm-nucleus. As the sperm-centrosome with its sperm- 
 aster (star-like arrangement of egg-cytoplasm fibers) is draw- 
 ing the sperm-nucleus inward, division of the centrosome 
 takes place and a spindle begins to form (Fig. 104, D). At 
 the same time the sperm-nucleus enlarges to the size of an 
 egg-nucleus. The new spindle with its enlarged sperm- 
 nucleus moves forward until it comes in contact with the 
 egg-nucleus (Fig. 104, j), which we remember has lost its 
 centrosome and spindle. 
 
 The fibers of the spindle penetrate the nuclear membranes 
 of both egg-nucleus and sperm-nucleus, and drag into the 
 middle plane of the spindle all the chromosomes, the same num- 
 ber from each nucleus. By this act fertilization is completed, 
 and the new individual begins its existence as an embryo. 
 
 Development. The spindle that is formed at the comple- 
 tion of fertilization is called the cleavage spindle. After the 
 chromosomes divide (Fig. 104, 7' 1 ), and are drawn toward 
 either pole, the young embryo cleaves or divides through the 
 middle, so that in each cell there is an equal amount of cyto- 
 plasm. There is also in each cell a nucleus containing chro- 
 mosomes, half of which came from the egg-nucleus and half 
 from the sperm-nucleus. Each of the two cells divides again, 
 making four cells. The polar cells disappear after a time. 
 
 In the eight-cell stage in the earthworm there is the begin- 
 ning of a cavity at the center of the small sphere. As the 
 number of cells increases the cavity becomes relatively larger, 
 although the diameter of the hollow sphere 'is no greater than 
 the diameter of an unfertilized egg. When the cavity reaches 
 its maximum relative size the cells are arranged in a single 
 layer just beneath the original egg-membrane. This is called 
 the blastula stage. In this stage, as seen in Fig. 105, B, a sec- 
 tion through the blastula shows that the upper cells are smaller 
 than the lower cells. The larger cells flatten and soon begin 
 to bend inward, as shown in Fig. 105, D. The effect of this 
 
THE EARTHWORM 
 
 215 
 
 is to decrease the blastula cavity and to make another cavity 
 with a wide opening to the outside (Fig. 105, _#, F). This is 
 the gastnda (little stomach) stage. It is appropriately called 
 so, because at this time the embryo first begins to take food 
 in the egg-capsule ; the food is digested in the cavity formed 
 from the outside. In the gastrula it is possible to distinguish 
 two layers of cells, both of which we know came originally 
 
 E 
 
 FIG. 105. Early Stages of Development of Earthworm. Much enlarged 
 
 A, blastula, surface view. B, blastula, section: s.c., blastula cavity ; m, first cell 
 of mesoderm. C, blastula, later stage. D, blastula, flattening of future 
 endodermal cells. E, gastrula, in side view : ec, ectoderm ; en, endoderm ; 
 s-s, line of section for F. F, gastrula, cross section : ar, archenteron 
 
 (From Sedgwick and Wilson's General Biology) 
 
 from a single layer; -these two layers are called ectoderm 
 (Fig. 105, E, ec) and endoderm (Fig. .105, E, en). 
 
 While the embryo is still in the blastula stage a single cell 
 (Fig. 105, B, m) can be identified as one which later develops 
 into a row of cells on either side, and finally into a mass of 
 tissue on either side, to which we give the name mesoderm 
 (Fig. 105, F). Many animals pass through these stages ; hence 
 the use of the terms ectoderm, endoderm, and mesoderm, as 
 
216 GENERAL ZOOLOGY 
 
 the primary germ-layers, has very great significance. Already 
 we can note many changes from the simple blastula condition 
 to the advanced gastrula. In discussing these and subsequent 
 changes, we shall use the word " differentiation," which means 
 literally " a becoming different." Differentiation increases 
 after the gastrula stage, and the embryo becomes longer and 
 larger, as organ after organ makes its appearance out of one 
 or the other of the three germ-layers. However small the 
 organs may be, the trained embryologist knows with a high 
 degree of certainty the origin and history of each one of them. 
 
 Before the gastrula has passed into a later stage we can 
 observe in sections cut like those in Figs. 105, C\ 1), E, F, that 
 the two large cells at the closed end of the gastrula, called 
 pole-cells, are giving rise by division to a row of mesodermal 
 cells. In the older portion of the two rows of mesodermal cells 
 cavities are beginning to appear (Fig. 106, A, I>). Fig. 106, ]> 
 shows how a gastrula of the same age appears in cross sec- 
 tion. Ectoderm and endoderm are separated at the lower 
 portion by a double layer of mesodermal cells, with a small 
 cavity between. The small cavities are the beginnings of the 
 sections of the body-cavity, found complete in the adult 
 earthworm. The cavity at the center of all is the archenteron 
 (Fig. 105, F, ar\ Fig. 106, B, ar), which means old or primi- 
 tive intestine. The mouth of the gastrula, which is called 
 the blastopore, becomes the mouth of the young earthworm. 
 At the opposite point a small opening appears ; this becomes 
 the anus of the young animal. Fig. 106, E, shows how a lon- 
 gitudinal section through a young earthworm would appear. 
 Development of the embryo to the form of the young is direct. 
 
 As the body-cavity increases in relative size the inner 
 layer of cells of the mesoderm becomes applied closely to the 
 wall of the intestine (Fig. 106, E, al) ; the outer layer of the 
 mesoderm becomes, from that time on, a part of the outer 
 wall of the body-cavity (Fig. 106, E, m 2 ). Fig. 106, C, D, n 
 
THE EARTHWORM 
 
 217 
 
 illustrates the development of the nervous system out of 
 the ectoderm. The organs and tissues of the earthworm which 
 originate from the germ-layers may be stated briefly as follows. 
 From the ectoderm come the outer skin and the nervous 
 system ; from the mesoderm develop the muscles, the blood- 
 vessels, the reproductive organs, arid probably the nephridia ; 
 from the endoderm comes the lining of the alimentary canal. 
 
 ec 
 
 an 
 
 FIG. 106. Late Stages of Development of Earthworm. Much enlarged 
 
 A, longitudinal section of gastrula, beginning of portions of body-cavity ; 7>, trans- 
 verse section of gastrula, same stage as A ; C, transverse section of gastrula, 
 body-cavity enlarging, mesoderm divided ; D, transverse section, inner por- 
 tion of mesoderm lying against endoderm, outer portion against ectoderm 
 E, longitudinal section of young earthworm, alimentary canal fully formed 
 ar, archenteron ; an, anus ; al, alimentary canal ; ec, ectoderm ; en, entoderm 
 coe, body-cavity (coelom) ; m, pole-cells of mesoderm ; m 2 , mesoderm 
 mh, mouth; n, ventral nerve-chain; s, cavity of somite; s.m, outer layer of 
 mesoderm ; spl. in, inner layer of mesoderm 
 
 (From Sedgwick and Wilson's General Biology} 
 
218 GENERAL ZOOLOGY 
 
 RELATION TO ENVIRONMENT 
 
 We could find no better animal to show how an organ- 
 ism may be adapted to its environment than the earthworm. 
 In the first place, the slender, rounded body with its pointed 
 anterior end is the best possible form for progression through 
 a dense medium, the substance of which is usually displaced 
 by muscular energy. The appendages, which in none of 
 the earthworm's relatives are hard enough to be used for 
 digging, are here reduced to the minimum, only the tips of 
 bristles remaining. The animal is thus not impeded by 
 useless organs. The smooth skin is thin, and is kept moist 
 for use as a breathing-surface. Branched gills, such as are 
 developed on many relatives of the earthworm that live 
 in the sea, would in the earthworm be superfluous, and 
 much in the way. Reasons that explain the presence of 
 eyes in animals which live in the atmosphere, or in the 
 water, lead to the explanation of the absence of eyes in 
 the earthworm. 
 
 It is a wonderful fact that the earthworm has no eyes and 
 still is able to distinguish light from darkness ; for, except in 
 the time of a rainstorm or in case of disease, it never leaves 
 its burrow in the daytime. By means of the very simple 
 sense-organs in the skin the earthworm can distinguish dif- 
 ferent intensities of light. It was found recently (1902), 
 during experiments carried on at Harvard University, that 
 earthworms not only appear to know the direction from 
 which light comes, but that they crawl away from light of 
 high intensity and crawl toward light of low intensity. Of 
 course, in the experiment, they did this without reference 
 to the matter of food. In nature, earthworms come out at 
 night, in the warm seasons, probably in response to the 
 stimulus of a low intensity of light, but also for the purpose 
 of obtaining food. 
 
THE EARTHWORM 219 
 
 Earthworms are sensitive to changes in temperature, al- 
 though when in otherwise favorable situations they will 
 endure a rise from 18 C. to 28 C. (64.4 F. to 82.4 F.) with- 
 out changing their position, a fact determined by some 
 experiments carried on at Bryn Mawr College. When earth- 
 worms rest in the daytime, just below the mouth of their 
 burrows, they do so probably as the result of at least four 
 stimuli, light, heat, fresh air, and moisture. If certain of 
 these stimuli were taken away, or even changed in degree, 
 the earthworm would undoubtedly move. 
 
 For example, if the moisture of the ground should become 
 lessened by continued dry weather, the animal would have to 
 forego the fresh air and retreat in order to prevent its skin 
 from drying, which would shut off respiration altogether. If 
 moisture becomes too great, as in a rain-storm, the burrows 
 are filled with water, and most of the oxygen in the narrow, 
 close quarters is driven out and the rest is soon used up. 
 The earthworm is then compelled, if it has been resting near 
 the surface, to leave its burrow and crawl about. This it 
 may do in protected places without serious results, since the 
 heat at such times cannot have its drying effect on the skin. 
 When the storm is over, those that are not caught up by 
 birds or trampled under foot by large animals can make their 
 way into the soil again. When earthworms are engaged in 
 boring through the soil, the air in their burrows is in circula- 
 tion, and even though the amount of oxygen may be small, 
 it appears to be sufficient to release the necessary amount of 
 energy for their work. 
 
 When animals become adapted in structure and habit to 
 their environment, the result is a definite food-supply and 
 protection to themselves and their race. Certainly the food- 
 supply of earthworms is assured to them, for besides the leaves 
 which they drag into their burrows, they are known to devour 
 the soil itself, taking it into their mouths as they burrow 
 
220 GENERAL ZOOLOGY 
 
 along. Black soil called humus is made up of the usual soil- 
 minerals, mixed with a large amount of decaying vegetable 
 matter and some animal matter. Completely decayed organic 
 matter is that which has returned to its original inorganic, 
 mineral state. The partially decayed organic matter can still 
 be used as tissue-building and energy-producing food ; it is 
 this which the earthworms get in the soil they swallow. 
 
 It is one of the habits of earthworms to come to the sur- 
 face at night to void the indigestible contents of the intestine. 
 The coiled, worm-shaped " castings " are familiar to any one 
 who has noticed the ground where the grass is thin, even by 
 the sides of much-used pavements in cities. The soil in the 
 castings is usually brought from depths varying from a very 
 few inches to as great a depth as five feet. Observations 
 made by Darwin, extending over a period of more than forty 
 years, during which time he also collected facts from all parts 
 of the world and published in a book entitled, The Forma- 
 tion of Vegetable Mould through the Action of Worms, are 
 extremely valuable to us now, in showing how small agencies 
 acting over wide areas, through ages or even years of time, 
 can yield tremendous results. 
 
 If every active earthworm voids its castings at the surface, 
 fallen leaves, sticks, and other bits of organic objects will in 
 a short time be covered with a thin coating of earth brought 
 up from beneath. The humus acids present at all times in 
 the soil attack and disintegrate the organic matter, thus en- 
 riching the soil with the minerals which the growth of exten- 
 sive crops may have deprived it of. Darwin determined the 
 rate at which objects once upon the surface gradually sink 
 to lower depths. Layers of cinders, chalk, stone, etc., were 
 strewn upon small fields, and trenches were dug from year 
 to year to ascertain the progress of the earthworms' activity. 
 In fields of ordinary fertility, having an average supply of 
 worms, the amount of earth brought to the surface and spread 
 
THE EARTHWORM 221 
 
 out more or less evenly is one fifth of an inch a year. In the 
 course of comparatively few years this is sufficient to conceal 
 from sight objects of considerable size. Indeed, Darwin wit- 
 nessed a sterile, stony field with flints " as large as a child's 
 head " transformed into a fertile, grass-covered pasture, " so 
 that after thirty years (1871) a horse could gallop over the 
 compact turf from one end of the field to the other, and not 
 strike a single stone with its shoes. This was certainly the 
 work of worms, for, though castings were not frequent for 
 several years, yet some were thrown up month after month, 
 and these gradually increased in numbers as the pasture 
 improved." 
 
 Estimates which Darwin based on careful observations 
 indicate that over fifty thousand earthworms find plenty of 
 working-room in an acre of ground, and that these bring 
 to the surface annually from fourteen to eighteen tons of 
 earth. 
 
CHAPTER XVII 
 ALLIES OF THE EARTHWORM: VERMES 
 
 Sinuous, glittering worm of the sea, 
 Wondrous in sheen of ruby and green. 
 
 The Sandworm. One of the commonest of the animals liv- 
 ing in the mud and sand at tide-level in protected bays and 
 inlets of all the oceans is the sandworm, known more defi- 
 nitely by its scientific name Ne'reis vi'rens (Fig. 107). It lives 
 
 FIG. 107. Livin Sandworm. Reduced 
 
 in burrows lined with a thick mucus, which unites the grains 
 of sand into a tough, black tube. The depth of these burrows 
 depends on the length of the animal, which is sometimes as 
 great as two feet. Like the earthworm, they often rest with 
 the head near the opening during the day; sometimes at night 
 
 222 
 
ALLIES OF THE EARTHWORM 
 
 223 
 
 they leave their burrows to swim at the surface. It is likely, 
 however, that in most cases they do not withdraw the entire 
 body from the burrow, but reach out in all directions for prey 
 that comes near them. When driven from their burrows in 
 the daytime they swim away, and at that time look very 
 beautiful, as the couplet above suggests. Nereis has two 
 horny jaws, sharp- 
 pointed, and bend- 
 ing to meet at the 
 tips. The jaws are 
 concealed by the 
 infolded pharynx 
 when not in use. 
 When about to 
 seize its prey, which 
 consists chiefly of 
 small, live sea-ani- 
 mals, the sandworm 
 suddenly everts the 
 pharynx, and the 
 jaws, thus freed, at 
 once spread hori- 
 zontally and seize 
 the victim. 
 
 Comparison of 
 the external appear- 
 ance of the sand- 
 worm with that of 
 the earthworm brings out some points of difference, as well 
 as some points of similarity. We observe the same division 
 into somites of approximately uniform structure throughout 
 the body. Fully developed locomotor organs, and a distinct 
 head with eyes and tactile sense-organs, serve to adapt Nereis 
 to the necessities of its environment. 
 
 EIG. 108. Photograph of Tube- Worm. Slightly 
 
 reduced 
 1, thread-like gills; 2, tentacles 
 
224 
 
 GENERAL ZOOLOGY 
 
 
 The Tube-Worm. The name " tube-worm " applies equally 
 well to many genera of slender animals that live continuously 
 in tubes of mud, sand, or limy secretions (Ser'pula, in Fig. 77) 
 in the sea. In an animal remaining fixed in the sand, like 
 Amphitri'te orna'ta (Fig. 108), it would seem to be economy in 
 animal architecture not to have broad swimming appendages 
 like those of its relative, Nereis. On the same principle we 
 observe that gills (Fig. 108, l) occur only at the anterior end 
 
 where they may obtain oxygen from 
 the circulating water above the 
 animal. To counterbalance the dis- 
 advantage of a fixed habitat, Am- 
 phitrite has many long tentacles 
 (Fig. 108, 2) which extend out over 
 an area sometimes of three square 
 feet. These tentacles are covered 
 with scattered fine bristles and 
 with many cilia; the cilia are 
 waving constantly toward the ani- 
 mal's mouth, carrying in the micro- 
 scopic food present 
 in the water. At 
 the same time the 
 bristles, aided by 
 mucus which is se- 
 creted from glands 
 on the tentacles, 
 catch up grains of 
 sand. These are 
 added to the little 
 hummock that con- 
 ceals the mouth of Arnphitrite's permanent home. 
 
 The Leech. Most species of leeches are known to be tem- 
 porary parasites on other animals, but Placobdel'la rugo'sa 
 
 FIG. 109. Leech. Slightly reduced 
 
ALLIES OF THE EARTHWORM 225 
 
 (Fig. 109) feeds on plants that grow among stones and sticks 
 at the bottom of brooks. It is about two inches long and 
 broader near the posterior end than elsewhere. The anterior 
 and posterior sucking-disks on the ventral surface are used 
 for holding on to a support, and for locomotion. Placobdella 
 "loops" itself along, but it cannot swim, as some other species 
 of leech can, although no leeches have appendages. 
 
 The body of the leech is divided into thirty-three somites, 
 and these are superficially divided into two and sometimes 
 three rings. Two eyes lie close together on the dorsal surface 
 of the third somite. The mouth is on the ventral surface near 
 the anterior sucking-disk. The pharynx can be rolled out as 
 in Nereis. The color of Placobdella is described by Professor 
 Moore, of the University of Pennsylvania, as a " pepper-and- 
 salt mixture of various light and dark browns, yellows, and 
 greens." Around the margin are light-colored patches. 
 
 Leeches are hermaphroditic. Placobdella rugosa carries its 
 eggs in a gelatinous mass on the ventral surface. When the 
 young hatch they live for several weeks attached by the pos- 
 terior sucker to the parent, as shown in the picture. 
 
 Definition of Annulata (Lat. ^anmdus, a ring). The earth^ 
 worm, sandworm, tube-worm, and leech have certain charac- 
 ters in common. The body is divided into somites of nearly 
 uniform shape, the characteristic form being a ring. From that 
 resemblance the name of the phylum Annula'ta, also called 
 Anneli'da, is derived. 
 
 Two classes are represented by these four animals: the 
 Chcetop'oda (bristle-footed), by Lumbricus, Nereis, and Am- 
 phitrite ; and the Hirudin'ea (Lat. hirudo, leech), by Placob- 
 della. 
 
 The Flatworm. On the lower surface of submerged stones, 
 near the margin of ponds, there are many little black, or white, 
 flatworms. The most of these belong to a genus called Pla- 
 na'ria. Quite often a larger specimen (10 mm. to 15 mm.) is 
 
226 
 
 GENERAL ZOOLOGY 
 
 FIG. 110. Flat- 
 worm, x 10 
 
 found among the others. This is most likely to belong to the 
 species Dendrocoe'lum lac'teum (Fig. 110). It is nearly color- 
 less except for a clouded middle region. Upon 
 examination with a simple lens an observer may 
 distinguish the organs of the interior with 
 remarkable clearness. The mouth is in the 
 middle of the under surface. It is at the end 
 of a short proboscis (the pharynx) which may 
 be rolled inside out. Microscopic food entering 
 the mouth may pass forward through a slender 
 tube, and into all of the many branches, or it 
 may pass backward by two tubes and into their 
 branches. Since every part of the body has its 
 branch from the digestive tubes, the animal 
 does not need a blood-system. At the anterior 
 end beneath, there is a shallow sucker for hold- 
 ing on to stones or plants. Above there is a 
 pair of small eyes of very simple structure. The body is not 
 divided into somites. Each individual is hermaphroditic. 
 
 The class to which Dendrocoelum lacteum belongs is called 
 Turbella'ria (Lat. turbo, a whirling, referring to the move- 
 ment of water about the mouth). 
 
 The Trematode. Animals of the appearance of Dis'tomum 
 somater'ice (Fig. Ill) are not often seen, because they are 
 parasitic in the bodies of other animals. This species infests 
 the bodies of mussels, and as already stated, is now believed to 
 be the indirect cause of pearls being found in those animals 
 (see p. 174). The figure represents the parasite in a stage 
 which is nearly adult. 
 
 The ventral surface of the body has two sucking-disks, one 
 at the anterior end (Fig. Ill, 1) and one near the middle (Fig. 
 Ill, 5). They are for holding on. The mouth is at the cen- 
 ter of the anterior disk, and is connected by a short tube with 
 a wide pharynx (Fig. Ill, 2). The gullet is divided into a 
 
ALLIES OF THE EARTHWORM 
 
 227 
 
 right and left branch which open into sacs (Fig. Ill, 3). Food 
 taken into these sacs passes by osmosis into the tissues. The 
 granular masses (Fig. Ill, 4) are the excretory organs. In this 
 stage the ovaries and spermaries are not developed ; these 
 organs occur together in each adult. The body is not divided 
 into somites. 
 
 The life-history of these parasites is usually very com- 
 plicated. Professor H. L. Jameson believes that Distomum 
 somaterise begins its life in a clam 
 found on the coast of France. At a 
 certain stage the young leave the 
 clam and make their way into the 
 mussel, Mytilus edulis (see Fig. 126). 
 The mussels are eaten by the black 
 scoter, a sea-duck, and in the body 
 of the bird the eggs of the parasite 
 are produced and sent out. By some 
 chance the larvse enter the clam, 
 and thus complete the cycle of devel- 
 opment. 
 
 The class to which this parasite be- 
 longs is called Tremato'da (Gr. trema, 
 hole ; eidos, form, referring to appear- 
 ance of suckers). 
 
 The Tapeworm. The best-known 
 tapeworm is the one that is sometimes 
 found to inhabit the intestine of man, 
 Tce'nia sagina'ta (Fig. 112). This parasite frequently grows to 
 the length of many feet. The figure seems to show that the 
 body is divided into somites, but these divisions are not con- 
 sidered true somites. The head of the animal is, except for 
 the narrow neck behind it, the smallest portion of the body ; 
 the posterior portion is the oldest part of the parasite, except 
 the head itself. New somite-like divisions of the body form 
 
 FIG. 111. Treinatode. 
 Much enlarged. (After 
 Jameson) 
 
 1, anterior sucking-disk, 
 and mouth ; 2, pharynx ; 
 3, digestive sac; 4, excre- 
 tory organs ; 5, posterior 
 sucking-disk 
 
228 
 
 GENERAL ZOOLOGY 
 
 just behind the head, and as they grow older and larger are 
 pushed backward by newer ones. The tapeworm is an inter- 
 esting example of a parasite that has become so completely 
 dependent on its host that one of the most important systems 
 of the body has totally disappeared, namely the digestive 
 system. The parasite maintains its hold on the inner wall of 
 the intestine by four sucking-disks on the head ; the body floats 
 free in the intestine, and food can be absorbed from all sides. 
 Every tapeworm has in each division both 
 eggs and spermatozoa. The spermatozoa ferti- 
 lize the eggs in the same division. When the 
 embryos reach a certain stage, a few terminal 
 divisions of the adult separate from the 
 rest, and pass out with the undigested 
 portion of the person's food. Sometimes 
 the embryos, inclosed in their thick mem- 
 branes, are swallowed by cattle while 
 drinking at pools. In the intestine the 
 membrane of the embryo is dis- 
 solved, and the freed larva bores 
 its way through the wall of the 
 intestine, and finally comes to 
 rest in the muscular tissue. It 
 remains there until the muscle 
 is consumed in a partially raw 
 state by man ; then in his intestine 
 the young animal develops into 
 the adult, mature tapeworm. An- 
 other species of tapeworm (Tcvnia 
 so'lium), found in human beings, 
 comes from uncooked pork. 
 
 FIG. 112. Tapeworm. Left-hand 
 drawing, reduced ; right-hand 
 drawing, enlarged. (After 
 Leuckart) 
 
 Tapeworms are not necessarily fatal. The annoyance is con- 
 siderable, however, until, by a period of fasting jgid medical 
 treatment, the life of the head of the parasite is destroyed. 
 
ALLIES OF THE EARTHWORM 
 
 229 
 
 The class to which the tapeworms belong is called Ccsto'da 
 (Gr. kestos, girdle; eidos, form). 
 
 Definition of Platyhelminthes (Gr. platys, flat ; helmins, 
 worm). The three classes, Turbellaria, Trematoda, and Ces- 
 toda, constitute the phylum Platyhel- 
 min'thes. The members of this phylum 
 are worms with flattened bodies, that 
 are not divided into somites. All the 
 species are hermaphroditic. 
 
 Trichina. Trichi'na spira'lis (Fig. 
 113, 1) is one of the most dangerous 
 of parasites. Like the tapeworm it 
 requires two hosts to complete its de- 
 velopment. The adult Trichina may 
 be found in the intestine of a pig, rat, 
 or of man. The female Trichina, about 
 3 mm. (| in.) long, brings forth its young 
 alive ; the young ones bore their way 
 through the intestine and along the thin 
 
 connective tissue of the trunk or legs. 
 
 rr(1 ,, , . FIG. 113. Trichina. Much 
 
 Ihere they come to rest, and inclose enlarged. (After 
 
 themselves in a thick, tough membrane 
 or cyst (Fig. 113, 2), remaining encysted 
 until the muscle is eaten by another 
 animal. Then the cyst dissolves, per- 
 mitting the young and still undeveloped Trichina to grow and 
 reach maturity in the intestine of the second host. If the 
 first host is the pig, the second host may be the human being. 
 The danger to the human being comes while the young 
 are making their way into the muscular tissue. The boring 
 of thousands and sometimes millions of these larval parasites 
 in the muscles disintegrates the tissue and causes a fever, 
 which is very frequently fatal. A simple preventive remedy, 
 which every one should apply, is to see that all pork eaten 
 
 Leuckart) 
 
 1, parasite; 2, membrane 
 of cyst; 3, muscle-fiber 
 of pig 
 
230 
 
 GENERAL ZOOLOGY 
 
 is well cooked. The Bureau of Animal Industry, United 
 States Department of Agriculture, has officials at all the 
 large packing institutions, who examine microscopically for 
 Trichina and tapeworm larvse some of the muscle of every 
 animal killed. 
 
 Trichina belongs to the class Nemato'da (Gr. nema, thread ; 
 eidoB, form) and the phylum Nemathelmin'thes (Gr. nema, 
 thread ; helmins, worm). 
 
 The Rotifer. Sometimes when we examine with the com- 
 pound microscope the contents of a small drop of stagnant 
 water, we find very small, conical- 
 shaped animals (Fig. 114), with two 
 spines at the end of a short tail, 
 "looping" across the field of vision 
 with considerable vigor. Occasionally 
 they cease the inch-worm method of 
 getting along, and whirl away by 
 means of one or two circular rows of 
 cilia (Fig. 114, l) at the broad, ante- 
 rior end. These animals are called 
 rotifers. A common species is Brachi- 
 o'nus urceola'ris. In length they are 
 about .3 mm. (^ in.). Although very 
 small, they possess a complete diges- 
 tive system, with mouth, pharynx, 
 grinding-apparatus, stomach, diges- 
 tive gland, intestine and anus, an 
 excretory system (no circulatory 
 system), nervous .system, sense-organs, 
 and reproductive system. The indi- 
 viduals are male or female, but the 
 male is to be found only in the fall of the year, and even 
 then rarely. It is about one fourth as large as the female. 
 In some species of rotifers the male is unknown. 
 
 FIG. 114. Rotifer. Much 
 enlarged. (After Weber) 
 
 1, cilia ; 2, nerve-ganglion ; 
 3, eggs forming ; 4, eggs 
 formed; 5, excretory 
 organs, n e p h r i d i a ; 
 6, terminal spines 
 
ALLIES OF THE EARTHWORM 231 
 
 There may be more than one generation of females produced 
 in the spring and summer from large eggs, which undergo 
 development while attached near the tail of the parent (Fig. 
 114, 4). These eggs develop parthenogenetically (see p. 34). 
 The large eggs always produce females. Under certain con- 
 ditions some small eggs are formed. These develop with- 
 out fertilization into males. In the autumn the females form 
 " winter eggs," which are fertilized by spermatozoa from the 
 males. The fertilized eggs lie dormant through the winter 
 and develop into females in the spring. 
 
 Members of the class to which Brachionus belongs (class 
 Motif era) are found in bodies of water, both salt and fresh, 
 all over the world. Certain species live in swamps, others at 
 the bottom of deep water, others still at the surface. No 
 matter how great the distance, the same species appears to 
 be present in situations that have approximately identical 
 conditions. This is accounted for partly by the fact that the 
 eggs will endure drying in the mud, and in that condition 
 may be scattered over wide areas by being carried on the 
 feet of birds, or by being blown about by the wind. Thus 
 they have the opportunity of developing in places exactly 
 suited to them. The phylum is called Trochelmin'thes (Gr. 
 troches, wheel; helmins^ worm). 
 
 Plumatella. There are many animals which, in their habit 
 of living attached to some object throughout life, resemble 
 plants. Some of them live in a mass composed of many 
 individuals, so closely connected with one another that we 
 give the name "colony "to the entire collection. In the case 
 of Plumatel'la re' pens (Fig. 115) the individual zooids (mem- 
 bers of the compound organism) are connected by a system 
 of branching, but the vital organs of each are not connected 
 with those of any other zooid. A colony of Plumatella grows 
 in a small, roughly branched mass around a dead submerged 
 twig in fresh-water ponds. 
 
232 
 
 GENERAL ZOOLOGY 
 
 Each zooid is microscopic in size, but, as in the rotifers, 
 we can identify definite and rather highly organized internal 
 
 organs. The mouth 
 is surrounded by a 
 circle of tentacles 
 that have the func- 
 tion of creating cur- 
 rents in the water, 
 on which food and 
 oxygen are carried 
 to the animal. The 
 circle of tentacles 
 is called the lopho- 
 phore (Fig. 115, 1). 
 From the mouth 
 the food passes 
 by a short gullet 
 (Fig. 115, 3) to the 
 stomach. The in- 
 testine is bent on 
 the stomach in 
 such a way that it 
 opens on the ex- 
 terior (Fig. 115, 4), 
 just outside the 
 circle of tentacles, 
 giving the whole 
 FIG. 115. Plumatella. Upper portion of figure alimentary canal 
 much enlarged; lower portion, slightly enlarged, something" of the 
 (After Allman) 
 
 appearance of the 
 
 letter I). Other 
 organs are a gan- 
 glion between the mouth and the anus, a pair of nephridia for 
 excretion, an ovary and a spermary, muscles which withdraw 
 
 1, lophophore ; 2, chitinous sheath; 3, gullet; 4, anus; 
 5, statoblast 
 
ALLIES OF THE EARTHWORM 
 
 233 
 
 the body into the chitinous sheath (Fig. 115, 2), and other 
 muscles to extend the body again. Plumatella reproduces 
 by eggs and spermatozoa, by budding, and by statoblasts 
 (Fig. 115, 5). Statoblasts are internal buds developed from 
 cells lying upon the retractor muscle, and are covered with a 
 chitinous shell. In case the colony freezes in winter, or the 
 pond dries up, the statoblasts remain alive, and on the return 
 of favorable conditions start a new generation. 
 
 The class of which Plumatella is an example is called 
 sometimes Polyzo'a, and sometimes Bryozo'a. Most of the 
 members of the class live in the sea as mat-like or moss-like 
 fixed colonies. On account of their brownish color and deli- 
 cate texture some of these colonies are fre- 
 quently mistaken for brown seaweeds. 
 
 The Brachiopod. The first impression that 
 the casual observer has of the animal repre- 
 sented in Fig. 116 (Lin'gula lepid'ula) is that 
 he is looking at some kind of a clam, 
 an impression given by the two calcareous 
 valves which inclose the body proper ; but 
 the brachiopod is not a clam. It lives at the 
 bottom of bays, and is found most abundantly 
 in the waters of Japan. It has a shell from 
 one half inch to one inch in length, and a 
 stalk called the peduncle, two or three times FIG. 116. Brachi- 
 as long. Professor E. S. Morse, of Salem, P d - Natural 
 Massachusetts, has witnessed the activities 
 of various species of these animals, and has 
 written interestingly 6f their habits. When undisturbed in 
 a sea-water aquarium, Crlottid'ia pyramida'ta (Fig. 117) lies 
 with part of its body above the sand. The valves open 
 slightly, and the bristles, extending from between the valves, 
 are grouped roughly into three tubes. The lophophore makes 
 a waving motion which sets up currents in the water, as 
 
 size. (After 
 Morse) 
 
234 GENERAL ZOOLOGY 
 
 shown by the arrows. Through two of these improvised tubes 
 solid (microscopic) food is carried in ; through the middle one 
 the unused particles and the excreted wastes of the body are 
 sent away. The bristles are useful in affording a surface 
 for microscopic organisms to grow, which later become food 
 
 for their larger table-mate ; the 
 bristles are also useful in pre- 
 venting sand from entering the 
 cavity between the valves. 
 
 The internal organs are very 
 much the same as in Pluma- 
 tella. In fact, 
 the nearest liv- 
 ing relatives of 
 Lingula and its 
 
 close allies, the 
 FIG. 117. Brachiopod. Enlarged. (After Morse) 
 
 members of the 
 
 class Brachiop'oda, are thought to be the class Polyzoa. 
 Brachiopods are among the oldest of animal groups. The 
 valves of ancient brachiopods found in strata of rock indi- 
 cate that the class, many millions of years ago, was far more 
 abundant than it is now, and also that the structure of the 
 animals has changed little in all that time. 
 
 O 
 
 The phylum represented by Plumatella and Lingula is 
 known by the name Molluscoi' da, because of their formerly 
 supposed relationship to the Mollusca. 
 
 Definition of Vermes (Lat. vermis, a worm). The task of 
 summing up the characteristics of the Arthropoda was a 
 comparatively simple one, but the " worms" comprise such 
 a varied lot of widely different forms, that no important set 
 of structural characteristics can be found that tends to unite 
 them into a clearly defined group. The old systems of classi- 
 fication employed the term " Ver'mes " as the name of a sub- 
 kingdom, to include all those animals that had a long, slender, 
 
ALLIES OF THE EARTHWORM 235 
 
 worm-like form. Many animals that have such a form have 
 been taken out of that branch of the system and placed in 
 another group, because their discovered relationship required 
 it. On the other hand, animals like the brachiopods and the 
 polyzoans were once classed with clams, mussels, and snails, 
 because all possessed a shell ; they are now thought to be 
 more nearly related to animals like the earthworm and other 
 annelids than they are to the clams. 
 
 So true is it that no single characteristic of structure can 
 be found that tends to unite the organisms classed as worms 
 into a well-defined group, that systematists are accustomed 
 to say that Vermes include all animals that are not clearly 
 members of some other large group. This does not indicate 
 any imperfection in the bodily structure of the members of 
 the group ; it means that our knowledge of animal morphol- 
 ogy is broken and incomplete, partly from lack of complete 
 investigation, but chiefly because some organisms that must 
 have filled up the "gaps" in the chain of relationships have 
 disappeared entirely, leaving no trace even in fossils. The 
 little basis we have for grouping all the forms discussed in 
 Chapters XVI and XVII into the group Vermes is found in 
 the tendency of the body to show a greater or a less degree 
 of metamerism (division into somites), either in the adult or 
 in the embryo. In these somites the characteristic excretory 
 organ, the nephridium, most highly developed in Nereis and 
 Lumbricus, is nearly always present. In some of the mem- 
 bers of the group several pairs of nephridia occur with no 
 other evidence of metamerism. Whenever appendages occur 
 among Vermes they are never jointed, as they are in Arthrop- 
 oda. Perhaps the strongest indication of relationship exist- 
 ing between widely differing members of the groups, as, for 
 example, Annulata and Molluscoida, is to be found in the 
 great similarity of a certain stage of the free-swimming larvse 
 of the two phyla. 
 
CHAPTER XVIII 
 THE STARFISH AND SOME ALLIES: ECHINODERMA 
 
 Let the mere star-fish in his vault 
 
 Crawl in a wash of weed, indeed, 
 Rose-jacynth to the finger-tips. 
 
 ROBERT BROWNING. 
 
 THE STARFISH 
 
 Habitat and Distribution. The purple starfish (Aste'rias 
 vulya'ris, Fig. 118) is found most abundantly north of Cape 
 Cod in tide-pools on rocky shores, and in deep water near 
 the shore. It is only in the warmer season, however, that one 
 may witness a scene like that portrayed in the illustration. 
 When the winter storms come on, starfishes and 'many other 
 tide-pool animals that are not fixed permanently migrate to 
 the deeper water, in order to be in more protected places. 
 
 External Structure. Up to this chapter we have been giv- 
 ing our attention to animals that have a perfect, or slightly 
 modified, bilateral symmetry. The starfish evidently has a 
 plan of structure for which we must find some other name. 
 In a specimen we observe five arms extending from a central 
 region. The position of the arms with reference to the cen- 
 tral region or disk is practically the same as the position of 
 radii in a circle. Hence we say that the starfish is radially 
 symmetrical. We find it necessary also to change a few 
 terms of location. In the picture of the tide-pool study we 
 are looking down upon the aboral surface of the three star- 
 fishes. The opposite side has the mouth at the center, and 
 for that reason is called the oral surface. 
 
 The aboral surface and part of the oral surface of Asterias 
 is thickly set with calcareous spines that arise from small 
 
 236 
 
FIG. 118. Tide-Pool Study of Starfishes, East Point, Nahant, Mass. 
 
 237 
 
238 
 
 GENERAL ZOOLOGY 
 
 plates of the same material just within the skin. The spines 
 of the oral surface are longer and more pointed than those of 
 the aboral surface. By examining the aboral spines with a 
 hand-lens one can make out a circle of very minute struc- 
 tures surrounding the base. Each of these structures consists 
 
 12 
 
 10 
 
 FIG. 119. Dissection of 
 the Starfish (Asterias 
 vulgaris). Aboral view. 
 Slightly reduced 
 
 stomach-pouch ; 2, tube of 
 pyloric caeca; 3, pyloric 
 caecum; 4, pyloric csecum, 
 
 cross section ; 5, intestinal 
 creca: 0,anus; 7, retractor 
 muscle of stomach ; 8,-sieve- 
 plate ; 9, ampulla ; 10, tube- 
 foot; 11, ambulacral 
 plates; 12, reproductive 
 gland; 13, reproductive 
 gland, cross section; 
 14, position of eye ; 15, re- 
 generating ray 
 
 of a short stalk supporting two branches that open and close 
 like nippers. These short stalks with their branches are 
 called pedicellarioe. Their use is unknown, but they may 
 rid the aboral surface of undesirable matter. 
 
 Along the middle of the oral surface of each arm there is a 
 groove which begins at the mouth and ends near the tip. The 
 roof of the groove is formed by two series of flat, calcareous 
 
THE STARFISH AND SOME ALLIES 
 
 239 
 
 plates setting together like the rafters of a frame house. 
 Between the plates four rows of slender, flexible tube-feet 
 (Fig. 120, ab) extend to the outside. The groove is called 
 the ambulacral groove, because it protects the ambulacral 
 organs (Lat. ambulare, to walk). A few of the ambulacral 
 organs (tube-feet) near the tips of the arms are sense-organs 
 for "smelling" food. The remainder are the organs of loco- 
 motion. At the very end of each arm there is a small red 
 eye protected by a circle of spines. 
 
 The Water-Vascular System. On the aboral surface at one 
 of the angles between the arms lies a lens-shaped structure 
 (Fig. 11 9, 8; Fig.l20,w; Fig. 
 121, 10). This is the sieve- 
 plate, sometimes known by 
 the name madreporic body. 
 The plate is perforated with 
 fine holes through which sea- 
 water passes to the stone-canal 
 (Fig. 120, s ; Fig. 121, 11). 
 Near the mouth the stone- 
 canal joins the ring-canal 
 (Fig. 120, r; Fig. 121, 12), 
 which in turn joins five 
 radial canals (Fig. 120, c\ Fig. 
 121, 13) that extend through 
 the middle of the roof of the 
 ambulacral groove. Many 
 short tubes branch off in pairs 
 from the radial canals and 
 join the tube-feet. At the 
 exposed end of a tube-foot is 
 a sucking-disk ; at the inner end is a bulb-shaped expansion, 
 the ampulla (Fig. 119, 9 ; Fig. 120, a ; Fig. 121, 14). From the 
 sieve-plate to the tube-feet there is a continuous cavity, and 
 
 FIG. 120. Ambulacral System of 
 Starfish 
 
 a, ampullae; ab, tube-feet; c, radial 
 canal ; m, sieve-plate ; ?^, radial nerve ; 
 p, Poliau vesicle ; r, ring-canal, with 
 nerve-ring beneath ; ,s, stone-canal ; 
 t, Tiedemann's vesicle 
 
 (From Hertwig-Kingsley's Manual of 
 Zoology) 
 
240 GENEPxAL ZOOLOGY 
 
 because of the fact that water passes through the entire set 
 of tubes it is called the water-vascular system. 
 
 This set of organs is a mechanism which enables the star- 
 fish to move. The stone-canal being inclosed in a sheath of 
 calcareous substance has a constant diameter, and so have the 
 ring-canal and the radial canals ; but the ampullse and the 
 tube-feet are not inclosed by an unyielding cover, and hence 
 they can increase and decrease the volume of their contin- 
 uous cavity. Preparation for locomotion is made when the 
 ampulla by contracting causes the water to close a valve at 
 the branch from the radial canal, and then forces the contained 
 .vater into the cavity of the tube-foot. Simultaneously with 
 the act of forcing water into the tube-feet, circular muscle- 
 libers in those organs contract and cause the water to extend 
 them to their greatest length. Next, the sucking-disks fasten 
 to some object, it may be even a smooth surface like the glass 
 side of an aquarium tank. The longitudinal muscle-fibers 
 in the tube-feet then contract and drive the contained water 
 back to the ampullae. When the hundreds of tube-feet in the 
 advancing arms of a starfish are contracting to pull the body 
 along and extending to renew their hold, the arms themselves, 
 turned up a little on the tips, remain in a more or less set 
 attitude, although they may bend now and then to pass an ob- 
 struction. When it is necessary the animal can bend its arms 
 and central disk, and pass through seemingly impossible holes. 
 
 The Digestive System. The mouth (Fig. 121, 1) is a circular 
 opening surrounded by a thin, circular membrane, the lip. 
 There is ho oesophagus, for the stomach (Fig. 121, 2) begins 
 at the mouth and occupies the greater portion of the central 
 disk, besides extending two short pouches (Fig. 119, l ; Fig. 
 121, 3) into every arm. At the aboral end of the stomach five 
 tubes branch off (Fig. 119, 2; Fig. 121, 5) and are divided 
 again into ten pyloric cceca (Fig. 119, 3; Fig. 121, 6). The 
 cavities of these organs are continuous with the cavity of the 
 
THE STARFISH AND SOME ALLIES 241 
 
 stomach. The function of the pyloric caeca is digestive ; 
 they secrete a fluid analogous to the digestive fluid of the 
 earthworm and the clam. The short intestine sends off two 
 branches, which again divide. These branches are called the 
 intestinal cceca (Fig. 119, 5; Fig. 121, 7). Their function is 
 to increase the absorbing surface of the intestine. The intes- 
 tine ends at the anus (Fig. 119, 6; Fig. 121, 8), which lies 
 near the center of the aboral surface. 
 
 Asterias feeds on oysters, mussels, clams, and snails. Many 
 fanciful theories have been proposed in the effort to explain 
 
 16 / 12 2 // 9 3 14 IS 13 
 
 FIG. 121. Dissection of the Starfish (Asterias vulgaris), oral-aboral section. 
 Slightly reduced 
 
 1, mouth; 2, stomach; 3, stomach-pouch ; 4, interradial pouch of intestine ; 5, cav- 
 ity of pyloric caecum ; 6, pyloric caecum ; 7, intestinal caecum ; 8, anus ; 9, re- 
 tractor muscle of stomach; 10, sieve-plate; 11, stone-canal; 12, ring-canal; 
 13, radial canal ; 14, ampulla^ 15, tube-foot ; 16, nerve-ring ; 17, radial nerve ; 
 18, reproductive gland ; 19, calcareous plate 
 
 how the starfish is able to get at the soft parts of animals 
 with thick, heavy shells. The method employed is totally dif- 
 ferent from that which any one seems to have imagined before 
 Professor Schiemenz, of Germany, discovered it in 1896. His 
 published results were corroborated by Professor Mead, of 
 Brown University, in 1899. By referring to Fig. 118, at the 
 lower end of the illustration, we can see the attitude of 
 Asterias when it has captured a sea-mussel. While crawling 
 along the bottom the hungry starfish " smells " its prey by 
 means of the tube-feet at the tip of the arms. It then moves 
 
242 GENERAL ZOOLOGY 
 
 in the direction of the mussel and arches itself over the shell, 
 touching the bottom all around with the tips of its arms. 
 Next it turns the mussel about, until the hinge-ligament rests 
 on the bottom and the free edges of the closed valves lie just 
 beneath the captor's mouth. Then the starfish takes a firm 
 hold on the bottom with the tube-feet of the outer portion 
 of its arms, and simultaneously applies the suckers of the 
 remaining tube-feet to both valves of the mussel. 
 
 Then the struggle begins. The mussel has long before closed 
 its valves tightly by means of its tAvo strong adductor muscles, 
 and the only way the starfish can get at the soft parts is to 
 force the valves open. This it does by a long-continued, steady 
 pull on the surface of the valves, with two sets of tube-feet 
 drawing in opposite directions. The mussel has great momen- 
 tary strength, but it seems to be as difficult for it to keep 
 up the strain as it is for a man to hold out his arm several 
 minutes at a time. A single tube-foot of the starfish is very 
 weak, and the combined strength of all its tube-feet measures 
 less than the momentary strength of a mussel. But the star- 
 fish can exert much less than its full strength, and open the 
 valves of a mussel within from fifteen to thirty minutes. 
 
 As soon as the valves of the mussel are open a few milli- 
 meters the starfish contracts certain muscles in its body-cavity, 
 which bring the stomach down toward the oral surface and 
 cause it to pass through the mouth-opening, turning inside 
 out on its way. The everted stomach is applied to the soft 
 body of the mussel, and digestion and absorption begin im- 
 mediately. With slight variations this is the method which 
 starfishes employ in opening and digesting oysters, snails, and 
 other mollusks. 
 
 The Circulatory, Respiratory, and Excretory Systems. The 
 circulatory system is too small to be indicated in drawings 
 on the scale of the dissection drawings. A circular blood-vessel 
 4ies just below the ring-canal of the water-vascular system, 
 
THE STARFISH AND SOME ALLIES 243 
 
 and sends a branch into each arm below the radial canal. The 
 body-cavity is filled with a fluid similar to the blood, which 
 is colorless. The system of blood-vessels is not complete. 
 
 The body gets much of the oxygen it needs by way of the 
 water-vascular system. The remainder conies in through the 
 many short-branched gills, that cover the aboral surface be- 
 tween the spines like the pile of a soft mat. The gills open 
 into the body-cavity at their bases. Carbon dioxide passes 
 through the same organs which bring in the oxygen. 
 
 The diagram shows nine bulb-like organs on the outer 
 margin of the ring-canal. These are called the Polian vesicles 
 (Fig. 120, p). The small glandular bodies, Tiedemanns vesi- 
 cles (Fig. 120, ), which join the Polian vesicles are thought 
 to have the function of producing amoebocyte-cells, described 
 on page 207. The cells on escaping into the body-cavity 
 consume the waste substance of metabolism, and make their 
 way through the body-wall, perishing on the outside. Asterias 
 has no definite organs of excretion, like kidneys or nephridia. 
 
 The Nervous System. If an observer takes a live starfish, 
 and parts the tube-feet in an arm so that the animal's skin is 
 exposed between the second and third of the four rows, he 
 may see the dead- white, radial nerve-cord extending along just 
 beneath the skin (Fig. 121, 17). Fig. 120 shows the position 
 of the nerve-ring just beneath the ring-canal. The circular 
 blood-vessel lies between the ring-canal and the nerve-ring. 
 
 Reproduction and Development. The sexes of Asterias vul- 
 garis are separate, but externally there is no difference 
 between them. At the time the dissections were made for 
 the drawings, the sexual glands in the specimens were small 
 (Fig. 119, 12; Fig. 121, 18). As the first of June approaches, 
 the ten sexual glands increase in size until they occupy all the 
 available space in the body-cavity of the arms. The ovaries 
 of the females, when they contain ripe eggs, are bright orange 
 in color ; the spermaries of the males are light cream color. 
 
244 GENERAL ZOOLOGY 
 
 From about the first to the middle of July, in the latitude of 
 Boston, the sexual cells are sent out into the water through 
 ten small holes on the aboral surface, two at each angle 
 between the arms all around. The egg-cells are fertilized by 
 the sperm-cells in the water, and within a few hours the 
 young starfish in the Uastula stage (see p. 214) is swimming 
 about at the surface by the aid of cilia. The manner of 
 development after the yastrula stage (see p. 215) is quite 
 different from the plan described for the earthworm. The 
 most striking incident in the development of a starfish is the 
 change that takes place after about three weeks of life as a 
 pelagic bilaterally symmetrical larva, when it settles toward 
 the bottom and fastens temporarily to a seaweed. On the 
 posterior region a star-shaped bud is formed, which becomes 
 the adult starfish. As the bud grows it draws into itself the 
 larva which gave rise to it. The starfish attains the stage of 
 sexual maturity within a year. 
 
 Regeneration. It is not unusual to find in a lot of star- 
 fishes dredged from the bottom, many specimens that have 
 one or more arms shorter than the others (Fig. 119, 15). 
 This means that some accident has befallen the irregular 
 specimens, and that new arms are being formed to take 
 the place of those that were lost. It has been found that a 
 starfish deprived of all its arms will, under favorable circum- 
 stances, reform all five ; but one that has suffered an injury 
 as extensive as a cut through the entire disk probably never 
 survives. 
 
 THE BASKET-FISH 
 
 Occasionally fishermen bring up on their hooks from the 
 deep waters of sounds specimens of the basket-fish, Astroph'- 
 yton agassiz'ii (Fig. 122). It is very difficult to keep them 
 alive long on account of the change from the great pressure 
 and the low temperature of their habitat. 
 
THE STARFISH AND SOME ALLIES 245 
 
 The central disk is more distinct in the basket-fish than in 
 the starfish. The five arms, instead of being single, divide 
 and redivide many times. The sieve-plate lies on the oral 
 surface. There is only one opening to the .digestive system, 
 the mouth. The tube-feet do not extend to the outside, 
 hence they are not used for locomotion, that activity being 
 accomplished by the branched arms, controlled inside by mus- 
 cles. Respiration takes place through little pockets which 
 open into the central disk from below. 
 
 Only in the rarest instances is it possible to learn anything 
 of the activities of the basket-fish. Mr. A. Agassiz and Mrs. 
 E. C. Agassiz give an interesting account of it in Seaside 
 
 ni. 122. Photograph of Basket-Fish, x \ 
 
246 
 
 GENERAL ZOOLOGY 
 
 Studies in Natural History. They say: " In moving, the ani- 
 mal lifts itself on the extreme end of these branches, standing, 
 
 as it were, on tiptoe, so that the 
 ramifications of the arms form a 
 kind of trelliswork all around it, 
 reaching to the ground, while the 
 disk forms a roof. In this living 
 house with latticed walls small 
 fishes and other animals are occa- 
 sionally seen to take shelter ; but 
 woe to the little shrimp or fish 
 who seeks a refuge there, if he be 
 of such a size as to offer his host 
 a tempting mouthful ; he will fare 
 as did the fly who accepted the 
 invitation of the spider." 
 
 THE SEA-LILY 
 
 At the present day we find here 
 and there in the comparatively 
 warm, deep waters of the ocean, 
 animals like that shown in Fig. 
 123 (Pentacri'nus bla'kei). In 
 past geological eras the class -to 
 which the sea-lily belongs was far 
 more widely distributed than it 
 is now. Members of the genus 
 Pentacrinus may be obtained by 
 dredging in the deep waters about 
 Porto Rico, and in the South 
 Pacific and the Indian oceans. 
 The sea-lily is a relative of the starfish and the basket-fish. 
 The central disk and the radial arrangement of the arms make 
 
 FIG. 123. Sea-Lily. Reduced 
 (From Report of H. M. S. Challenger) 
 
THE STARFISH AND SOME ALLIES 247 
 
 the resemblance striking. In Pentacrinus blakei the number 
 of arms varies ; it may be as great as twenty. The sea-lily 
 is different from the starfish and the basket-fish, in having a 
 long stalk which grows from the center of the aboral surface 
 and sends root-like branches in among the rocks at the bottom. 
 The mouth and the arms lie on the oral surface, which is 
 uppermost. A water-vascular system is present, but it is of 
 no service to the animal in locomotion. 
 
 Movement in Pentacrinus is limited to the arms. A related 
 genus, Comat'ulus, found off the North Atlantic coast, is fixed 
 by a stalk when young, and free in its adult stage, moving 
 about then like a basket-fish. Food is brought to the mouth 
 of Pentacrinus by the wave-like action of cilia on the inner 
 edge of all the arms. 
 
 THE SEA-URCHIN 
 
 Practically any tide-pool along the North Atlantic coast that 
 affords specimens of starfish will harbor several sea-urchins. 
 The geographical distribution of the species Strongylocentro'- 
 tus drobachien'sis (Fig. 124) is very wide. It is found on the 
 coast of Great Britain and Norway, along the North Atlan- 
 tic coast, and also on the North Pacific coast, in all these 
 regions from tide-water down to several hundred fathoms. 
 
 Deprived of its spines a sea-urchin suggests, as Professor 
 W. F. Ganong aptly says, " an old-fashioned door-knob." It is 
 flattened on the oral surface and curved above into a rounded 
 dome. From the center of the dome one may trace downward 
 twenty radiating rows of calcareous plates, fitting against one 
 another closely. Five pairs of these plates radiating at equal 
 angles have many fine holes for the tube-feet ; five other 
 pairs of plates lie in the spaces between the regions of tube- 
 feet. All over the aboral surface and over most of the oral 
 surface, the plates bear short, rounded knobs on which the 
 
248 
 
 GENERAL ZOOLOGY 
 
 spines fit, and form a ball-and-socket joint. On each tube- 
 foot area at the point nearest the center of the aboral surface 
 lies an eye ; and between every two eyes there is an opening 
 for the eggs, or spermatozoa, to emerge. A sieve-plate lies 
 in one of the spaces between two eyes. The mouth has five 
 sharp teeth which meet together in a point. The breathing 
 organs are located on the oral surface around the mouth. 
 
 Considering the 
 structure of the 
 animal, one could 
 be almost posi- 
 tive that the sea- 
 urchin does not 
 get its food after 
 the manner of the 
 starfish. It feeds 
 on both animal 
 and plant sub- 
 stance. Small ani- 
 mals are captured 
 by the tube-feet. 
 The tube-feet may 
 be extended to a 
 distance equal to 
 half the diameter 
 of the body ; they 
 affix by the sucking-disk to some small creature and draw it 
 to the mouth. All food is then ground into bits by the five 
 sharp teeth before being swallowed. 
 
 A sea-urchin when taken from the water and placed in a 
 person's hand causes a gentle tickling of the skin. This 
 it does with its movable spir>es. The spines may be of use 
 as levers in pushing the body along, but locomotion in a 
 definite direction is accomplished by the tube-feet on the 
 
 FIG. 124. Photograph of Sea-Urchin. Slightly 
 reduced 
 
THE STARFISH AND SOME ALLIES 249 
 
 oral surface, aided by some of those on the aboral surface, 
 all extending and contracting much as in the starfish. The 
 uppermost tube-feet are used as tentacles for feeling, and it 
 may be for smelling also. The fact that sea-urchins collect 
 in numbers about the body of a large dead animal in the 
 water, indicates that they have the sense of smell. 
 
 In certain parts of our eastern coast, members of the genus 
 Strongylocentrotus live in cavities in the rock, which are 
 excavated by the animals themselves. A related species living 
 on the coast of California burrows a hole in the solid rock deep 
 enough to conceal itself entirely. No one knows positively 
 how the burrowing is done. Probably three factors take part 
 to a varying degree, gnawing by the teeth, slow grinding 
 by voluntary movement of the spines, and incessant slight 
 turnings of the whole body by the waves. 
 
 THE SEA-CUCUMBER 
 
 Sea-cucumbers of various species are found in every ocean. 
 The species represented in Fig. 125 (Cucuma'ria chronhjel'mi) 
 is found in Puget Sound, Washington. It lives on the 
 bottom. 
 
 The animals are about four inches long. The body is cylin- 
 drical, but without calcareous plates that touch one another 
 and keep the form constant. The only trace of a skeleton 
 comparable to that of the sea-urchin consists of scattered bits 
 of calcareous secretions of definite form beneath the skin. Al- 
 though the sea-cucumber is radially symmetrical, having the 
 five double rows of tube-feet along the cylinder, we can speak 
 of the anterior and posterior ends, because the animal lies flat. 
 
 The anterior region is the oral region. At the centej; we 
 observe the round mouth, about which are the ten branching 
 tentacles. Internally there is a water-vascular system with 
 a ring-canal and radial canals. In respiration water is drawn 
 
250 GENERAL ZOOLOGY 
 
 into the intestine at the aboral end, and an exchange of gases 
 takes place through internal gills that join the intestine. 
 
 The tentacles in the picture are not extended in the usual 
 radial direction. The reason is that when photographed the 
 
 
 LA 
 
 , A 
 
 T* 
 
 FIG. 125. Photograph of Living Sea-Cucumber. Natural size 
 
 animal was using its tentacles as well as its tube-feet to crawl 
 along the bottom of a dish of sea-water. When the animal is 
 at rest, the tentacles are probably used to capture small 
 animals, and to pass them to the mouth. 
 
 Relatives of Cucumaria have been known by observers 
 to disgorge the entire set of internal organs through the 
 
THE STARFISH AND SOME ALLIES 251 
 
 mouth-opening. In captivity they appear to do this when 
 placed in unfavorable situations. It is not so remarkable that 
 they should lose their internal organs, as it is that they should 
 regenerate them all again as perfect as ever. If sea-cucum- 
 bers throw out their internal organs in nature, it would 
 appear to be a very expensive process. Since they do per- 
 form this action, in nature as well as in captivity, there must 
 be some reason for it. The only reason that suggests itself is 
 based on the fact that fish prey upon sea-cucumbers. The 
 sea-cucumber is a slow-moving animal, and once seen by a 
 roving fish the chances of escape under ordinary circumstances 
 would be few indeed. If the prospective victim when dis- 
 turbed were to eject its internal organs into the water, the 
 fish, true to the instinct of its kind, would gobble up the 
 swiftly moving object, and probably go away satisfied. 
 
 Sea-cucumbers are prepared and used as food by the Chinese, 
 and it is reported that the Siwash Indians of the northwest 
 of the United States eat them, and sea-urchins also. 
 
 DEFINITION OF ECHINODERMA 
 
 Each of the five animals described in this chapter represents 
 one of the five classes that make up the phylum Echino- 
 der'ma (Gr. ecliinos, hedgehog ; derma, skin). The five classes 
 represented are Asteroi'dea, by Asterias; Ophiuroi' dea, by 
 Astrophyton; Crinoi'dea, by Pentacrinus ; Uchinoi'dea, by 
 Strongylocentrotus ; and Holothuroi'dea, by Cucumaria. 
 
 The most important characteristics of the phylum are the 
 radial symmetry of the body (the importance of this character 
 is denied by some zoologists); the occurrence of repeated 
 divisions or organs of the body to the number of five, or 
 in multiples of five ; and the existence of a water-vascular 
 system. No other phylum has parts occurring in fives, and 
 none other has a water-vascular system. 
 
CHAPTER XIX 
 THE SEA- ANEMONE AND SOME ALLIES: OELENTERA 
 
 To-day the many-hued anemone 
 Waving, expands within the rock-pools green, 
 And swift, transparent creatures of the sea 
 Dart throu' the feathery sea-fronds scarcely seen. 
 
 SIR LEWIS MORRIS. 
 
 The Sea-Anemone. The best-known sea-anemone of the 
 North Atlantic coast is Metrid'ium margina'tum (Figs. 126, 
 128, and 129). Although this species is usually found in tide- 
 pools, it also lives attached to the piles of wharves in har- 
 bors where the impurities of the water are not too great. 
 The picture of the tide-pool shows sea-anemones in various 
 attitudes. Metridium has the power of moving, by creeping 
 along on its base, but it seldom changes its place of attach- 
 ment, even in the coldest weather. 
 
 The form of Metridium is nearly cylindrical. The base, 
 which is the aboral surface of the animal, widens irregularly 
 to fit the surface of attachment, thus enabling the body to 
 maintain its hold by expelling the water from beneath the 
 disk. The oral end of the column-shaped body expands into 
 a crown of many small, slender tentacles. At the middle of 
 the oral surface is the mouth. The skin of the body is soft, 
 but rather tough. An animal with the general plan of struc- 
 ture of. the sea-anemone is called & polyp.. 
 
 The food of the sea-anemone consists in general of many 
 kinds of microscopic pelagic organisms. The capture of 
 prey is accomplished by a method peculiar to the phylum to 
 which Metridium belongs. All over the tentacles are number- 
 less microscopic cells containing nettling -capsules (compare 
 
 252 
 

 FIG. 126. Tide-Pool Study of Sea-Anemones, East Point, Nahant, Mass. 
 
 253 
 
254 
 
 GENERAL ZOOLOGY 
 
 Fig. 127, Hy'dra, see p. 263). When any small animal strikes 
 against the minute bristle (Fig. 127, A, 3) that arises from the 
 external surface of one of these cells, the 
 capsule breaks, and a slender, hollow 
 thread or filament (Fig. 127, B, 4) shoots 
 out; reversing itself from the base, like 
 the pharynx of the sand worm, and pierces 
 the skin of the creature. In the capsule 
 there is some fluid which is discharged 
 through the filament and poured into the 
 wound. The effect of the fluid is to be- 
 numb the victim. 
 
 A sea-anemoHe resting in the attitude 
 of the one shown in Fig. 128 could not 
 swallow anything, even after the victim 
 had been overcome. The reason is that 
 the minute cilia which cover the tentacles 
 wave outward at all times. As long as 
 particles of wasfe and other undesirable 
 
 FIG. 127. Nettle-Cells substances fall within range of the cilia, 
 of Hydra. Much,! ,-,1 -, > 
 
 enlarged. (After they are swept out of the way ; but when- 
 
 ever small animals come within range of 
 the cilia, and are paralyzed by the net- 
 tling filaments, the tentacles bend over 
 with their tips pointing toward the 
 mouth. The normal action of the cilia 
 
 Schneider) 
 
 A, nettle-cell, with un- 
 discharged nettling 
 capsule; B, nettle- 
 cell, with discharged 
 nettling capsule : 
 
 1, nettling capsule ; 
 
 2, nucleus of nettle- now sweeps the helpless creatures toward 
 cell: 3, bristle of ,! , ,1 A -n ,-, 
 nettle-cell ; 4, hollow the sea-anemone s mouth. All over the 
 
 filament of nettling thick, grooved lip there are more cilia. 
 The cilia at the opposite ends of the 
 
 mouth lie in a deep, wide groove called the sipTionoglyphe 
 (Fig. 129, 3). Here the cilia always wave inward. At the 
 sides of the mouth the cilia wave outward except when food 
 is dropped on them by the cilia of the tentacles ; then they 
 
THE SEA-ANEMONE AND SOME ALLIES 255 
 
 reverse their action, and all the mouth-cilia unite in sweeping 
 the food down the gullet. These observations were made by 
 Professor G. H. Parker, of Harvard University, in 1896. 
 
 The mouth opens to receive the food, which is sometimes 
 quite large, and the gullet (Fig. 129, 4) passes it down by 
 ciliary action aided by muscular activity in the gullet-wall. 
 
 FIG. 128. Photograph of Living Sea-Anemone. Natural size 
 
 At the inner end (Fig. 129, 5) of the gullet, food passes into 
 a large space which extends radially between mesenteries (par- 
 titions) (Fig. 129, 12, 13) to the body- wall. Thus there is no 
 distinct alimentary canal separate from a body-cavity. This 
 fact shows the sea-anemone to be a less specialized animal, 
 and hence a lower form, than any we have yet studied. Those 
 
256 
 
 GENERAL ZOOLOGY 
 
 animals that do not have a body-cavity and an alimentary 
 canal have but one cavity to take their place ; this cavity is 
 
 FIG. 129. Dissection of the Sea-Anemone (Metridium marginatum). 
 Natural size 
 
 1, intermediate zone; 2, lip; 3, siphonoglyphe ; 4, gullet; 5, inner end of gullet; 
 6, edge of mesentery ; 7, cavity of a tentacle ; 8, inner ostium ; 9, outer ostium ; 
 10, primary mesentery; 11, muscle-plate on primary mesentery; 12, abnor- 
 mal tertiary mesentery ; 13, secondary mesentery ,- 14, tertiary mesentery ; 
 15, quaternary mesentery; 16, reproductive gland; 17, mesenterial filament; 
 18, opening for mesenterial filament. 
 
 called the gastrovascular cavity, because in the same space 
 food is digested and carried about. The fact that food and 
 oxygen can pass into any portion of the body, even into 
 
THE SEA-ANEMONE AND SOME ALLIES 257 
 
 ollow tentacles (Fig. 129, 7), accounts for the absence of a 
 circulatory system, which usually serves the purpose of trans- 
 porting oxygen, digested food, and also waste products from 
 part to part in the animal body. Likewise we find no gills 
 or nephridia, for probably all the waste products of metab- 
 olism are sent from the cells into the gastrovascular cavity 
 and ultimately to the outside. The absence of all these spe- 
 cial organs is further indication of a low and simple type of 
 organism. 
 
 There are usually six pairs of principal mesenteries in 
 Metridium marginatum. They are thin, radial partitions 
 extending from the gullet outward and downward to the 
 body-wall. These six pairs are called the primary mesen- 
 teries (Fig. 129, 10, 11). In the arcs between the sets of pri- 
 mary mesenteries there are secondary mesenteries, also in 
 pairs (Fig. 129, 13), arising from the body-wall and extend- 
 ing part way toward the gullet. The tertiary mesenteries 
 (Fig. 129, 14) and the quaternary mesenteries (Fig. 129, 15) 
 extend shorter distances into the gastrovascular cavity, but all 
 unite with the body-wall of the oral and the aboral ends, and 
 in the latter place meet at the center. Occasionally a mesen- 
 tery grows beyond the usual width and becomes attached to 
 the gullet, as in Fig. 129, 12. Every mesentery has a longitu- 
 dinal muscle-band (Fig. 129, 11) on one side near its free or 
 inner edge. In all but two pairs of mesenteries the muscle- 
 bands face each other. The four primary mesenteries which 
 are directed toward the siphonoglyphes have their muscle- 
 bands on the outside. At the oral end there are two circles 
 of openings called ostia (Fig. 129, 8, 9). They perforate all 
 the primary mesenteries and bring the radial chambers into 
 communication at that end. 
 
 At the free edge of the widest mesenteries below the end 
 of the gullet there are to be found coiled masses which are 
 composed chiefly of mesenterial filaments (Fig. 129, 17, 18). 
 
258 GENERAL ZOOLOGY 
 
 These filaments are thickly set with microscopic nettle-cells, 
 like those shown in Fig. 127. When the animal is dis- 
 turbed greatly, the mesenterial filaments stream out through 
 the mouth and through small invisible openings in the body- 
 wall. It is likely that the most frequent use of the mesen- 
 terial filaments is in defense. 
 
 The egg-cells and the sperm-cells of Metridium are found 
 in separate individuals, and adjacent to the mesenterial fila- 
 ments (Fig. 129, 16). The development of Metridium has not 
 been studied, but in kindred species embryologists have found 
 that the eggs are fertilized while they are still in the mes- 
 enteries. At a certain stage of development the embryo is 
 freed. It passes out through the mouth of the female, swims 
 awhile by cilia, and finally settles and continues life after 
 the manner of the adult. Reproduction takes place probably 
 most frequently by budding (the formation of small individ- 
 uals on the edge of the aboral surface), and, rarely, by longi- 
 tudinal division into halves. 
 
 Wherever the sea-anemone lives, in tide-pools, on piles of 
 wharves, on rubble beaches, or in the deeper waters of bays, 
 it has to contend with whatever unfavorable conditions char- 
 acterize the place. The periodic fall of the tide leaves some 
 individuals exposed to the drying effect of the air. They meet 
 the conditions by contracting the organs of the oral end, and 
 exposing as little surface as possible to the air (Fig. 126). 
 On account of their tough skin, their nettle-cells, and their 
 ability to hold to a fixed support, it is not likely that adult sea- 
 anemones are ever attacked by fishes or other ravenous animals. 
 We cannot tell how many of the pelagic young sea-anemones 
 are lost by being swept upon the beach, or how many are car- 
 ried far out into the ocean, or swallowed by larger animals. 
 Undoubtedly the number is very great. 
 
 The protection insured to the adult sea-anemone by its 
 tough skin and its nettle-cells is considerable, and we find no 
 
THE SEA-ANEMONE AND SOME ALLIES 259 
 
 relation between the color of the animal and the c'olor of the 
 objects in the environment. In the same situation one may 
 find all variations of uniform or mingled shades, from light 
 yellow to dark brown, a fact which of itself would indicate 
 that the animal does not depend on color-resemblance for 
 protection. 
 
 The Coral Polyp. The only coral polyp of the North 
 Atlantic coast is Astran'gia da'nce (Fig. 130). It occurs in 
 colonies of many individuals and incrusts rocks or pebbles 
 
 FIG. 130. Colony of Coral Polyps. Enlarged 
 
 in shallow water, near the shore line from Massachusetts to 
 North Carolina. 
 
 A polyp of Astrangia is about one eighth of an inch in 
 diameter and of variable length. It bears a very obvious 
 resemblance to a sea-anemone. The columnar form, the flat- 
 tened aboral surface resting on a support, and the oral end 
 with its crown of tentacles, prove the relationship. Besides, 
 examination of the interior reveals the presence of mesenteries 
 arranged very much as in Metridium. One important struc- 
 ture of Astrangia, however, is never found in the sea-anemone, 
 and that is the carbonate of lime " skeleton." This structure 
 
260 GENERAL ZOOLOGY 
 
 at the base of the polyp is more definitely referred to under 
 the name corallite, for it is not a true skeleton. Several coral- 
 lites are shown in the lower portion of the figure. The hard, 
 radial plates repeat the number of pairs of mesenteries of the 
 polyp, since each plate is formed between the members of 
 pairs of mesenteries. 
 
 The aboral surface of the polyp is molded over the corallite 
 so that the soft tissue of the animal extends down between 
 the radial plates, and also over the circumference. Although 
 the polyp may be said to fit into the corallite, it is the real 
 cause of the existence of the corallite. 
 
 The substance of the corallite is formed by the crystalli- 
 zation of carbonate of lime in the epidermal cells of the polyp. 
 Crystallization takes place in the outermost cells, and as the 
 substance in them hardens newer cells are formed just within, 
 and in these the process of crystallization continues. Thus it 
 is that as the coral polyp grows, it actually pushes itself far- 
 ther and farther away from the surface to which it became 
 attached at the beginning of its fixed life. Astrangia has a 
 characteristic method of forming a colony. The height of a 
 corallite does not exceed a half-inch. The colony increases 
 by budding from the older polyps at their bases. The result 
 is a low mass of corallites that seldom exceeds an area of four 
 inches square. 
 
 Definition of Actinozoa (Gr. aktis (aktiri), ray ; zoon, ani- 
 mal). The members of the class Actinozo'a are alike in having 
 a soft, generally cylindrical body. The plan of structure is 
 bilaterally symmetrical, as indicated in the arrangement of 
 mesenteries in the gastrovascular cavity, it being possible to 
 pass a line lengthwise through the mouth to opposite siphono- 
 glyphes, and separate one half the mesenteries from the other 
 half. Superficially, however, as indicated by the arrangement 
 of the tentacles, there is radial symmetry. Into the single, 
 partially divided gastrovascular cavity the mouth opens, and 
 
THE SEA-ANEMONE AND SOME ALLIES 261 
 
 through it food enters and unused particles are discharged. 
 Nettling-capsules, which are the organs of offense and defense, 
 are at the surface of the tentacles and on the mesenterial 
 filaments. 
 
 Coral Islands. Ever since Charles Darwin from 1831 to 
 1836 made his famous journey around the world in H.M.S. 
 Beagle, scientific explorers have engaged from time to time 
 in the study of the life and structure of coral reefs and 
 islands. We know from their researches that coral reefs are 
 formed of great masses of carbonate of lime, largely as the 
 result of the secretion of that substance by polyps. 
 
 Just as with other organisms, reef-forming polyps flour- 
 ish wherever they become adapted to external conditions. 
 The food they need is probably abundant anywhere in the 
 seas, but they cannot endure the temperature common to 
 regions outside the torrid zone. They can live in situations 
 where the tide recedes from them for two or three hours, 
 or in depths as great as fifty fathoms (300 feet), but the most 
 general limit of depth for the greatest number of species is 
 about twenty fathoms. A condition which checks their dis- 
 tribution near large bodies of land is the presence of silt, as 
 in the fresh water that flows from the mouths of rivers. 
 Fresh water itself when free from impurities is not especially 
 detrimental to the growth of coral polyps. The most famous 
 coral formations are found in the region of the Bahama Islands, 
 in the Great Barrier Reef of Australia, in the Fiji Islands of 
 the South Pacific Ocean, and in the Maldive Islands of the 
 Indian Ocean. 
 
 When conditions permit, young coral polyps attach them- 
 selves to the sea-bottom near a body of land, and by the 
 process of secreting carbonate of lime, as described for 
 Astrangia, extend upward toward the surface in the form of 
 a long, narrow ridge skirting the land. When the ridge is 
 so near the land that it leaves no channel, it is called a 
 
262 GENERAL ZOOLOGY 
 
 fringing reef. If by subsequent changes, or as originally 
 formed, a navigable channel lies between the ridge and the 
 land, it is called a barrier reef. If the formation surrounds 
 a body of water, which it nearly or completely cuts off from 
 the sea, it is .called an atoll. The most remarkable examples 
 of atolls are the Maldive Islands. 
 
 Two important theories have been advanced to account 
 for the historical connection which in many cases is thought 
 to exist between fringing reefs, barrier reefs, and atolls. 
 Darwin believed that an atoll begins as a fringing reef sur- 
 rounding an oceanic island, which may be of volcanic or other 
 origin, and that as the island sinks from internal causes, the 
 coral polyps build up carbonate of lime as long as they are 
 within their range of favorable depth. The reef that at first 
 was a fringing reef becomes a barrier reef, on account of the 
 increase in distance between it and the decreasing area of 
 sinking land. At last the top of the island disappears beneath 
 the water, and the atoll remains. Professor J. D. Dana, and 
 others, have published evidence in support of Darwin's sub- 
 sidence theory, but the erosion theory suggested by Dr. John 
 Murray, leader of the exploring expedition of H.M.S. 
 Challenger (1850), has probably more adherents at the present 
 day. The erosion theory has been modified and extended, 
 chiefly by Dr. Alexander Agassiz. According to this theory 
 coral polyps may form a fringing reef about an oceanic island. 
 The reef continues to grow, while the soil or rock of the 
 island is carried away by rains and by rivers. The solution of 
 the soil and rock is caused by the temporary chemical union 
 of these substances with carbon dioxide derived from dead 
 animals and plants. The idea is that in the course of a few 
 centuries an entire island could be worn away, and the atoll 
 left with its lagoon of Avater partially connected with the sea. 
 
 Dr. Murray suggested also the probability of atolls being 
 formed without the preliminary stages of fringing and barrier 
 
THE SEA-ANEMONE AND SOME ALLIES 263 
 
 reefs. If coral polyps were to attach to a submerged plateau 
 not too deep for them to live on, the small colony would grow 
 upward and extend itself radially, something like the flaring 
 sides of a shallow wash-basin. As the mass grows larger the 
 polyps at the center would be killed by the detritus collecting 
 from the broken pieces of- coral rock at the wave-beaten 
 margin, and the rock already formed at the center would be 
 worn and scooped out by erosion with coral sand. 
 
 Coral atolls are imperishable bulwarks against the sea, and 
 in some cases have formed the beginning of strips of land 
 sufficiently wide for wild races of men to live upon. 
 
 The Fresh-Water Polyp. There are but tw r o species of 
 fresh- water polyps that are at all common, and these are so 
 small that the casual observer would seldom be aware of their 
 existence, even though they were abundant in his aquarium. 
 The two species are Hy'dra vir'idis (Fig. 131), the green 
 hydra, and Hydra fus'ca, the brown hydra. 
 
 Hydra viridis lives among green fresh-water plants in 
 places where there is abundant sunlight. At rest it holds to 
 a plant with its aboral surface, the remainder of the body 
 floating outward or downward very much like the sea-anemone. 
 The body, which, is cylindrical in form, is about 3 mm. 
 (^ inch) long and .4 mm. (^ inch) in diameter. A little prac- 
 tice will enable a person to distinguish one in an aquarium, 
 for specimens frequently leave the green plants and crawl 
 up the side of the glass nearest the light. They can move 
 either by a slow, creeping movement on the aboral surface, 
 or by the process of " looping," like an inchworm. Hydras 
 exist for a long time in an aquarium, provided there is an 
 abundance of their food-animals, which are usually small 
 Crustacea. The most common of these is a fresh-water spe- 
 cies of Cyclops (resembling Fig. 75), which they benumb 
 with their nettling-threads, and carry to the mouth with their 
 tentacles. 
 
264 
 
 GENERAL ZOOLOGY 
 
 The number of tentacles a specimen of Hydra viridis may 
 have depends upon its size, and also upon its age. The small 
 
 individuals are gener- 
 ally the youngest; 
 these have four tenta- 
 cles. The larger, older 
 ones gain in the num- 
 ber of tentacles, up to 
 the extreme number of 
 eleven; but there is a 
 greater per cent of in- 
 dividuals with six ten- 
 tacles than with any 
 other number. 
 
 Internally, Hydra is 
 the simplest animal 
 we have studied. The 
 mouth (Fig. 131, 1) 
 opens into a cylindrical 
 cavity (Fig. 131, 7) with 
 no indication of gullet, 
 or radial partitions. 
 
 FIG. 131. Fresh- Water Polyp. Longitudinal The cavity extends by 
 
 slender tubes out into 
 each tentacle, and in all 
 
 ,gastrovascular cavity ; 8, spermatozoa form- parts Only two layers 
 
 of cells separate it from 
 the water outside. The 
 inner one of these two layers is the endoderm (Fig. 131, 6), 
 and the outer one, the ectoderm (Fig. 131, 5). Cells of the 
 endoderm secrete fluid for digesting food, and even take up 
 small particles of food, digesting them inside the cell-sub- 
 stance. The ectodermal cells are modified into nettle-cells, 
 nerve-cells, muscle-cells, and general surface-cells. 
 
 9 
 
 section. Much enlarged 
 
 1, mouth; 2, tentacle; 3, forming bud; 4, older 
 bud ; 5, ectodermal cells ; 6, endodermal cells ; 
 
 ing ; 9, egg forming 
 
 (From Parker's Elementary Rioloyy} 
 
THE SEA-ANEMONE AND SOME ALLIES 265 
 
 -3 
 
 Reproduction may take place by the sexual method, or by 
 budding. Eggs (Fig. 131, 9) are developed in the ectoderm 
 near the aboral end. In the same 
 individual spermatozoa (Fig. 
 131, 8) are formed in the ectoderm 
 nearer the oral end, and these on 
 escaping fertilize the eggs, which 
 remain in the ectoderm for some 
 time as embryos. Then the em- 
 bryos separate from the parent, 
 and after swimming about for a 
 variable period develop into 
 organisms like the parent. Non- 
 sexual reproduction is the more 
 frequent method, however. Buds 
 involving both ectoderm and 
 endoderm form on the side of the 
 body (Fig. 131, 3, 4) ; four tenta- 
 cles appear, the mouth forms, and 
 the base of the bud constricts, 
 setting the young Hydra free to 
 begin its own career. 
 
 Hydroids and Medusae. There 
 is a large group of animals closely 
 allied to Hydra, that live in the 
 sea. A portion of one of them, 
 Bougainvitfliafrutieo'sa, is shown 
 in Fig. 132. It looks very much 
 like a plant, owing to its habit of 
 branching. The colony may con- 
 tain many polyps, each of which 
 
 is connected indirectly with every other by means of the 
 continuous body-wall. At the base of the colony, root-like 
 branches from a stem-like structure cling to floating timbers 
 
 FIG. 132. Hydroid. Much en- 
 larged. (After Allman) 
 
 1, tentacles; 2, 3, 4, stages in the 
 formation of medusa 
 
266 
 
 GENERAL ZOOLOGY 
 
 or buoys. Although the colony reaches the height of two 
 inches, the individual polyps are microscopic in size. Each 
 polyp has about fourteen tentacles amply provided with net- 
 tling capsules, which aid in capturing small pelagic animals. 
 The mouth is at the center of the circles of tentacles 
 (Fig. 132, l) ; it opens directly into the gastrovascular cavity. 
 As the branches are terminated by feeding polyps, the cells 
 
 of the branches are probably supplied 
 with food by the polyps nearest at 
 hand. 
 
 Reproduction in Bougainvillia may 
 be a mere increase in the number of 
 polyps by a process of budding similar 
 to that described for Hydra. Occa- 
 2 sionally, however, a bud develops into 
 a structure totally different from an 
 ordinary polyp, and after a series of 
 stages indicated in Fig. 132, 2, 3, 4, 
 finally becomes separated from the 
 colony and floats away as a free- 
 swim mi 11 g individual (Fig. 133). 
 
 FIG. 133. Medusa. Much This is callecl the ^edltsa stage of 
 
 enlarged. (After Allman) the animal. The medusa has some- 
 
 i, bell; 2, tentacle; .3, maim- thing like the shape of an umbrella. 
 
 The mouth is located at the end of 
 the pendent manubrium (Fig. 133, 3). 
 The gastrovascular cavity sends out four slender tubes (Fig. 
 133, 4) radially to the perimeter, where a circular canal joins 
 them. Tentacles (Fig. 133, 2) stream downward from the mar- 
 gin, and at their bases are minute sense-organs (Fig. 133, 5). 
 There are male and female medusas. The ovaries and the 
 spermaries of Bougainvillia are located in the manubrium. 
 When the eggs and spermatozoa are ripe, they pass out 
 through the mouth, and fertilization takes place in the water 
 
 brium; 4, radial tubes; 
 5, sense-organs 
 
THE SEA-ANEMONE AND SOME ALLIES 267 
 
 outside. The embryo swims about for awhile and then set- 
 tles to some fixed or floating object, attaches itself, and soon 
 another colony of the hydroid (hydra-like) stage is developed 
 by budding. The life-history of Bougainvillia illustrates 
 alternation of generations. The fixed, colonial, non-sexual, 
 hydroid stage alternates with the free-swimming, single, 
 sexual, medusa stage, and together they complete the life- 
 cycle. 
 
 Definition of Hydrozoa (Gr. Hydra, the fabulous monster; 
 zoa, animals). The class Hydrozo'a includes the genus Hydra 
 and many thousands of species of hydroids. The life-history 
 described for Bougainvillia by no means applies to all spe- 
 cies of hydroids, but it is as characteristic as any. Hydrozoa 
 are small animals occuring singly and in colonies. There is 
 but one cavity in the body, and that is continuous with the 
 mouth-opening. There are but two layers of cells, the ecto- 
 derm and the endoderm. In some members of the class the 
 two layers are separated by a jelly-like mass secreted by the 
 cells. The body is radially symmetrical. Tentacles with net- 
 tling-capsules in their ectodermal cells are the organs of 
 offense and defense. 
 
 The Jellyfish. Although the name " jellyfish " is sometimes 
 applied to the medusae of the class Hydrozoa, it is more com- 
 monly given to the larger, saucer-shaped or bell-shaped animals 
 that swim at or near the surface in harbors and bays of all 
 lands. The species most frequently found from Massachusetts 
 southward is Aure'lia flavid'ula (Fig. 134). This jellyfish 
 reaches the diameter of fifteen inches. 
 
 In various details of structure Aurelia resembles the 
 medusa of certain hydroids, and also the sea-anemones, the 
 coral polyp, and the fresh-water polyp. The mouth opens at 
 the center of the under surface into a large cavity which 
 branches freely into many tubes running to the circumference, 
 where they join the circular canal. Between the ectoderm 
 
268 GENERAL ZOOLOGY 
 
 covering the body, and the endoderm lining the gastrovascu- 
 lar cavity, is a great mass of jelly secreted by the cells of the 
 two layers. Hanging from about the mouth are four broad 
 ribbon-like appendages called u lips." These and the delicate 
 fringe of tentacles at the rim of the bell are covered with 
 nettle-cells. Nettle-cells are found also on the mesenterial 
 filaments which lie in the radial canals. 
 
 FIG. 134. Photograph of Jellyfish. Reduced 
 
 A very noticeable detail of structure that one observes in 
 watching these animals in the water, especially in the late 
 summer, is the set of four partial rings about the center, 
 yellowish in color in the males and reddish in the females. 
 These rings are the sexual glands. They are sacs which con- 
 tain the eggs or spermatozoa until these cells are ready to be 
 discharged through the radial canals and the mouth. On the 
 rim of the bell, at eight equidistant points, are small, rounded 
 
THE SEA-ANEMONE AND SOME ALLIES 269 
 
 sense-organs, which have the function of controlling, through 
 the nervous and muscular systems, the direction of movement 
 of the jellyfish. The most important muscle is a circular 
 band near the rim. The nerve-cells are grouped near the 
 sense-organs, and connect the latter with the muscle-band. 
 When the circular muscle contracts, the bell becomes more 
 convex, and the resulting action of the water in the hollow 
 of the bell against the water outside, sends the animal along 
 in a slow, periodic, pulsating movement. 
 
 The development of Aurelia is very different from that of 
 the hydro ids. The simple, free-swimming larva of Aurelia 
 sinks to the bottom, attaches itself to some fixed object, 
 and takes on a form resembling Hydra. The formation of 
 circular grooves below the tentacles develops a series of saucer- 
 like divisions, one within another. These separate and, swim- 
 ming away with the convex, aboral surface uppermost, grow 
 into the adult form. The fixed stage is comparable with the 
 hydroid generation of Hydrozoa. 
 
 Aurelia is but slightly more dense than the sea-water itself. 
 According to one authority there is less than one eighth of one 
 per cent of proteid material present. Thus over ninety-nine 
 per cent is water. The small amount of proteid material in 
 the body of Aurelia makes it very unlikely that many animals 
 depend on them for food. After a storm in summer great 
 numbers of Aurelise may be found on the shore. In a few 
 hours only scattered films are left on the sand to show where 
 the animals lay. The destruction of many Aureliao is to be 
 expected because of their general helplessness, but annihila- 
 tion of the species is prevented by the enormous number of 
 young produced. 
 
 The great fecundity of Aurelia and its giant relative Cya'nea 
 which sometimes grows to a diameter of eight feet, might 
 threaten to fill the ocean with their bodies, were it not for 
 the fact that neither lives over the winter. The young start 
 
270 
 
 GENERAL ZOOLOGY 
 
 their development in the autumn and complete it in the 
 spring. It is a self-evident fact, in this instance at least, 
 that death is a benefit, not only to all other forms of sea life, 
 but even to the race of Aurelia itself. The adults swallow 
 everything that can be taken into the mouth, but probably 
 their most abundant food is small pelagic Crustacea similar 
 to Cyclops (Fig. 75). 
 
 The class of which Aurelia flavidula is a representative is 
 called Scyphozo'a (Gr. skyphos, cup ; zoa, animals). 
 
 FIG. 135. Photograph of Comb-Jelly. Enlarged 
 
 The Comb-Jelly. The species of "comb-jelly," or "sea- 
 walnut," shown in Fig. 135 (Pleurobrach'ia rlwdodac'tyla), 
 is found in the colder seasons floating at the surface along 
 the North Atlantic coast. It is about as large as a hazelnut, 
 but greater in diameter vertically than tranversely. 
 
THE SEA-ANEMONE AND SOME ALLIES 271 
 
 The body of the comb-jelly is soft like that of the jellyfish, 
 but the plan of structure and the organs are somewhat differ- 
 ent. There are eight meridional bands of comb-like struc- 
 tures, which serve the animal as locomotor organs. During 
 locomotion these combs move vigorously, and in such a way 
 that beautiful iridescent effects are produced by them. 
 Near the lower end, as shown in the figure, there are two 
 fringed tentacles with such wonderful powers of extension 
 that from a mass no larger than a pin-head they can extend 
 over a foot. The tentacles have minute adhesive cells which 
 are thought to be .modifications of nettling-capsules, or struc- 
 tures which take the place of them. By means of the adhe- 
 sive cells the tentacles hold small animals and pass them to 
 the mouth. As the animal swims the tentacles are below 
 and the mouth above. A funnel-shaped space at the upper 
 end carries the food into the mouth. The gastro vascular 
 cavity extends into two lateral pouches from which two 
 branches arise, making four; each of the four branch-tubes 
 gives rise to two, making eight altogether. Each of the eight 
 branch-tubes joins a meridional tube which lies just beneath 
 the bands of combs. Food carried in at the mouth can thus 
 pass to any portion of the body. At the end opposite the 
 mouth there is a small sense-organ, which is the center of 
 the animal's nervous system. Every comb-jelly contains both 
 egg-cells and sperm-cells. The eggs are fertilized outside the 
 body, and the young larvae swim free and gradually develop 
 into the adult form. The comb-jelly produces a phosphor- 
 escent light when disturbed. 
 
 The class of which Pleurobrachia rhododactyla is a repre- 
 sentative is called Ctenoph'ora (Gr. Jcteis (Jcten), comb; phero, 
 bear). 
 
 Definition of Coelentera (Gr. koilos, hollow ; enteros, intes- 
 tine). Arranged in the order of their increasing degree of 
 specialization, the four classes that make up the phylum 
 
272 GENERAL ZOOLOGY 
 
 Coelen'tera are Hydrozoa, Scyphozoa, Actinozoa, and Cte- 
 nophora. The classes constitute a fairly distinct phylum by 
 including animals with radially symmetrical bodies (at least 
 in external appearance) in which there is but one cavity. 
 This cavity, joining the mouth-opening, is the digestive 
 cavity, and is not separated from a body-cavity, as in higher 
 animals (whence the derivation of the name of the phylum). 
 The body develops from an embryo that has two germ-layers, 
 - the ectoderm and the endoderm. In this particular it is 
 different from every phylum of animals heretofore described. 
 The characteristic organs of offense and defense are the net- 
 tling-capsules. By some authorities the Ctenophora are 
 separated into a phylum by themselves, partly because they 
 do not possess nettling-capsules. 
 
THE FRESH- WATER SPONGE AND SOME ALLIES : PORIFERA 
 
 The unending shapes of plants, the rainbow's varied hues, 
 All these, the lowly sponge on ocean's bed renews. 
 
 The Fresh-Water Sponge. The sponge illustrated in Fig. 
 136 (Heteromeye'nia ry'deri) is found quite generally in ponds 
 and quiet brooks, at least as far west as the Mississippi River. 
 It grows on the under side of overhanging submerged rocks, 
 and on dead sticks and leaves. The largest specimens are 
 not usually more than one inch across. Each mass of sponge 
 clings flat against the supporting substance, and seldom is 
 more than one eighth of an inch thick. The sponge yields 
 slightly on being pressed with the finger. The surface looks 
 rough, but to the touch it is smooth. The color is grayish; 
 occasionally specimens are found with a part or all of the 
 mass green. This is due to the presence of a green alga 
 growing in the sponge. 
 
 The first thing that attracts one's attention in the drawings 
 of the fresh-water sponge is the many small, circular holes, 
 oscula (sing, osculum, a little mouth), scattered over the surface. 
 They are openings through which the waste, the unused food, 
 and water are expelled from the sponge. Everywhere between 
 the oscula are numerous very small holes, dermal pores (com- 
 pare Fig. 137, 5), which open into quite large subdermal cham- 
 bers. Leading from the subdermal chambers are short canals 
 called incur rent canals. These lead to cavities lying deeper 
 in the sponge, the ampullce (Fig. 137, c), which are lined 
 with cells that bear flagella (lashes). These cells are called 
 collar-cells, on account of their having a collar-like membrane 
 
 273 
 
274 
 
 GENERAL ZOOLOGY 
 
 around the base of the flagellum. The flagella wave inward 
 and cause a current of water to flow into the sponge through 
 the minute dermal pores and along the incurrent canals, 
 past the collar-cells into the excurrent canals. Water passes 
 
 FIG. 136. Fresh-Water Sponge. Upper 
 portion of figure natural size; lower 
 portion enlarged 
 
 from the excurrent canals 
 into the cloaca, a large 
 chamber just below the os- 
 culum, and thence flows 
 out of the sponge through the osculum (Fig. 137, d). 
 
 Food consisting of microscopic plants and animals is drawn 
 in at the dermal pores and carried along by the current. 
 Very small particles are taken into certain cells along the 
 canals and digested there, as in the endodermal cells of Hydra. 
 Larger particles are surrounded by ivandering cells and 
 digested little by little. Digested food passes by osmosis to 
 all the cells of the sponge. 
 
FRESH-WATER SPONGE AND SOME ALLIES 275 
 
 The fresh-water sponge has no special digestive organs, 
 no circulatory system, respiratory system, muscular system, 
 nervous system, nor sense-organs. Food and oxygen are 
 carried in together, and oxidation takes place freely because 
 oxygen can go anywhere within the sponge. The oscula 
 sometimes contract when the sponge is disturbed, but this 
 action takes place because of the power of contracting which 
 is possessed by certain cells that are not true muscle-cells. 
 There are, however, two important systems of organs pos- 
 sessed by the fresh- 
 water sponge: a set 
 of structures which 
 constitute the skele- 
 ton, and special 
 cells for reproduc- 
 tion. The substance 
 
 'V 1NX ^^^^yJ^^ 
 
 which serves as a ^ --c 
 
 skeleton supporting FIG. 137. Section of Fresh- Water Sponge (Spon- 
 the soft, protoplas- 
 mic cells, is made 
 up of microscopic 
 spicules (compare Fig. 139) of various forms, and of very hard 
 material called silica. These spicules, interlacing a-nd cross- 
 ing one another, give a very firm texture to organisms that 
 would otherwise be formless and slimy. 
 
 Certain cells along the canals develop eggs and sperma- 
 tozoa. Each sponge-mass is capable of producing both kinds 
 of cells, but not at the same time. While some masses are 
 producing eggs, others in the same pond or brook are pro- 
 ducing spermatozoa. The eggs are retained in position on the 
 canals, while from other specimens the spermatozoa escape and 
 swim out into the water, to be drawn later, quite by accident, 
 into the incurrent canals of sponges with eggs. The eggs are 
 fertilized and immediately begin the process of development. 
 
 a, surface; 
 
 Much enlarged (After Huxley) 
 
 , dermal pores ; c, ampullae, lined with 
 collar-cells ; d, osculum 
 
276 
 
 GENERAL ZOOLOGY 
 
 When the embryo has reached the blastula stage it is set free, 
 and swims out through the osculum. The larva, in SpongiVla, 
 another fresh-water sponge, and probably in Heteromeyenia 
 as well, is shaped like a hen's egg, but is very small and is 
 covered with collar-cells bearing flagella, which are the organs 
 of locomotion for the few hours of free life Avhich the larva 
 has. When it comes to rest it attaches itself by the broad 
 end, and grows into the form of the adult. 
 
 Fresh-water sponges reproduce also by means of special 
 organs called gemmules, which are about one-fiftieth of an inch 
 in diameter (Figs. 136 and 138). These structures are pro- 
 duced in the sponge-mass toward the end of August. Their 
 use is to carry the species over the unfavorable season after the 
 destruction of the parent sponge, which usually takes place in 
 the fall. They are admirably protected by the three layers of 
 material which form the horny covering. The double-headed 
 spicules give stiffness to the whole gemmule. Inside is a mass 
 
 of cells containing food-material; 
 these cells remain in a state of 
 inactivity until the return of 
 favorable conditions. Then the 
 contents of the gemmule forces 
 itself through the thinly covered 
 pore, and soon forms a minute 
 sponge with incurrent canals 
 and a single osculum, which, as 
 Professor Potts says, " puffs out 
 material after the manner of a 
 miniature volcano." 
 By far the greater number of species of marine sponges, 
 and all fresh-water sponges, are composite in character. In 
 hydroids it is easy to distinguish one individual of a colony 
 from another, but in fresh-water sponges the only clew one 
 can get to the number of individuals is that furnished by the 
 
 
 FIG. 138. Gemmule of Fresh- 
 Water Sponge. Much enlarged. 
 (After Evans) 
 
FRESH-WATER SPONGE AND SOME ALLIES 277 
 
 number of oscula. The evidence obtained through studying 
 the embryology of sponges indicates that each osculum marks 
 the position of an individual, and that the adult form results 
 from the fusion of numerous individuals originally distinct. 
 Internally, however, there is no sepa- 
 ration between individuals, their 
 chambers being continuous. 
 
 Sycon. Some sponges that live in 
 the sea are simple ; that is, they con- 
 sist of a single individual. A sponge 
 of this kind is Sy'con (Fig. 139). The 
 free end has a single osculum. All 
 over the body elsewhere are minute 
 dermal pores leading into in current 
 canals, alternating in the substance 
 of the body-wall with radial canals. 
 Food and water entering the incur- 
 rent canals by dermal pores are 
 carried into the adjacent radial canals 
 by short canals. From the radial 
 canals the water passes into the large 
 cloaca. Waste and extra water are 
 discharged through the osculum. The spicules are composed 
 of carbonate of lime. 
 
 The Bath-Sponge. The best known of all species of sponges 
 is, of course, the bath-sponge (Euspon'gia officina'lis). It is a 
 composite sponge of great complexity, but usually the oscula, 
 looking like chimneys, stand out so clearly that one may deter- 
 mine the number of individuals present in a mass. Varieties of 
 this sponge are found in the deep waters about the Bahama 
 Islands and in the Mediterranean Sea, especially on the coast 
 of the Turkish dominions. 
 
 The bath-sponge grows attached to rocks in water of a few 
 fathoms' depth. Divers cut the masses at the base and later 
 
 FIG. 139. Sycon and Spic- 
 ules. Sponge enlarged; 
 spicules much enlarged. 
 (After Grentzenberg) 
 
278 GENERAL ZOOLOGY 
 
 throw them upon the beach, where the soft portion rots and 
 dries. Then the remainder, which is the skeleton, is cleaned 
 and made ready for the market. These sponges are valuable 
 for the uses of man on account of the softness of the whole 
 skeleton and the tenacity of its substance. The skeleton is 
 composed of tough, anastomosing fibers of horny material 
 instead of spicules of silica, as in Heteromeyenia, or of car- 
 bonate of lime, as in Sycon. 
 
 Relation to Environment. Perhaps no group of animals has 
 so wide a distribution in water as sponges. In fresh water, 
 and in the sea from the very margin of low tide to the greatest 
 depth of ocean yet explored, and in all zones, various species 
 of sponges are found. They live in every conceivable situa- 
 tion, adapting themselves in form of mass to the particular 
 place in which they grow. Branched species, like Microci'ona 
 prolifera^ in the frontispiece, vary much in form and arrange- 
 ment of branch. Incrusting species on rocks, as in the fron- 
 tispiece, and as shown growing about barnacles, Fig. 77, 
 follow every turn of the supporting substance. One species 
 of Clio'na grows on shells of mollusks, and through the 
 agency of a secretion of its protoplasm consumes the sub- 
 stance of the shell and grows to fill the space thus made. 
 In regions where the ocean-bottom is muddy, sponges grow 
 stalks that keep the mass away from the mud, which if 
 stirred up would smother the colony. 
 
 Many marine sponges being thick and massive, and of loose 
 texture, like the sulphur sponges, are very convenient har- 
 bors of refuge for myriads of small animals, chiefly Crustacea 
 and worms. Undoubtedly the odor of living sponges, described 
 by one investigator as resembling garlic, drives away fishes 
 and other ravenous animals of large size that might feed on 
 the little guests, or even on the sponge itself. 
 
 Definition of Porifera (Lat. porns, pore ; ferre, to bear). 
 By most investigators the sponges are considered a distinct 
 
FRESH-WATER SPONGE AND SOME ALLIES 279 
 
 phylum Porif'era, including only a single class. It is evident 
 that the Porifera are lower in organization than the Ccelen- 
 tera, for the members of the phylum do not show indications 
 of muscle-cells, of nerve-cells, or of sense-organs. Neither are 
 there special organs of offense. Protection is afforded by the 
 spicules and the characteristic odor. Sponges are the lowest 
 animals which reproduce by eggs and spermatozoa. In devel- 
 opment two germ-layers are present, ectoderm and endoderm, 
 and a middle undifferentiated layer called the mesoglwa. 
 
CHAPTER XXI 
 AMOEBA AND SOME ALLIES: PROTOZOA 
 
 Gradual, from these what numerous kinds descend, 
 Evading even the microscopic eye ! 
 Full nature swarms with life, one wondrous mass 
 Of animals, or atoms organized. 
 
 JAMES THOMSON, Summer. 
 
 Amoeba. The amoeba (Amce'ba pro' tens, Fig. 140) is com- 
 mon in stagnant water of all lands, but it is so minute 
 that it is impossible to be sure of its presence in a given 
 place until examination has been made with a compound 
 microscope. 
 
 One of the best ways to find large specimens of the 
 amoeba is to remove carefully from the bottom of a well- 
 stocked fresh-water aquarium a few dead leaves. A medi- 
 cine-dropper full of material from the surface of one of the 
 leaves may yield several specimens. A short time after a few 
 drops of the water have been mounted on a glass slide the 
 Amoebae will exhibit the characteristic structure and activities. 
 The usual diameter of an amoeba is about .5 mm. (^ inch). 
 
 The beginner in microscopy is very likely to overlook an 
 amoeba altogether, or to think in his anxiety that every little 
 irregular clear spot in the field of his microscope-objective 
 is one. The active amoeba is never the same in appearance in 
 consecutive moments. The outline, at all times irregular in 
 locomotion, constantly becomes more or less so, by the increase 
 or decrease in prominence of little processes called pseudo- 
 podia (false feet), which extend in one or several directions. 
 
 Amoeba is a complete organism, although it is composed of 
 a single cell. The substance of the cell is protoplasm, that 
 
AMCEBA AND SOME ALLIES: PROTOZOA 281 
 
 complicated substance without which life cannot exist. The 
 principal organ of the cell is the nucleus, composed of pro- 
 toplasm more dense than that which surrounds the nucleus. 
 Frequently zoologists distinguish the protoplasm of the 
 nucleus, nudeoplasm, from that of the cell-body or cytoplasm. 
 The nucleus is usually quite difficult to see unless the amoeba 
 is killed by chemicals and 
 
 its protoplasm "fixed" and ^-,. ^|fcj 
 
 stained. The cytoplasm is ^ : 9j^^^ 
 
 finely granular all through, VSIflfli 
 
 except for a thin layer on lii|Sfe:>....--;:"-'- N I.SSR! 
 
 the surface, which is always /^ip-fSSSS^F'S-v;-;:? 4lS*l-/ 
 
 clear and without granules. Sk ^^~ : ^^SS^S?Q' 
 
 The granular part of the ^^S^ 
 
 cytoplasm is called endo- 
 
 plasm, and the non-granular 
 
 sheath the ectoplasm. FlG - 14(X Amceba ' Much enlar ed 
 
 During locomotion the < From Sedgwick and Wilson's General 
 . , , Biology) 
 
 pseudopodia are first formed 
 
 of the ectoplasm, the endoplasm following immediately and 
 continually in the same direction that the ectoplasm takes. 
 The method of locomotion in Amoeba, as stated by Professor 
 H. S. Jennings, of the University of Pennsylvania, is as 
 follows. " Locomotion in Amoeba is a process that may be 
 compared with rolling, the upper and lower surfaces contin- 
 ually interchanging positions. This is shown by observation 
 of the movements of particles attached to the outer surface 
 or imbedded in the ectosarc [ectoplasm] of the animal. Such 
 attached particles move forward on the upper surface and 
 over the anterior edge, remain quiet on the under surface 
 till the body of the amoeba has passed, then pass upward at 
 the posterior end, and forward on the upper surface again. 
 Single particles may thus be observed to make many com- 
 plete revolutions." 
 
282 GENERAL ZOOLOGY 
 
 When the advancing pseudopodia come in contact with a 
 minute unicellular organism, the object may be enveloped; if 
 so, it gradually sinks into the cytoplasm, the amoeba mean- 
 time continuing its rolling locomotion; if the object is useless 
 for food, the amoeba simply rolls over it, leaving it behind. 
 Food is taken in with a small amount of water which forms 
 a surrounding bubble or vacuole. This food-vacuole is carried 
 about in the endoplasm and slowly disappears in the process 
 of digestion, which goes on quite as effectively in the amoeba 
 as in any of the higher animals. The indigestible particles of 
 the food are left behind as the amoeba rolls along. 
 
 All the other phases of metabolism go on as in many-cell 
 animals, except that in the amoeba everything must be done 
 in the one cell. The oxygen which the animal needs probably 
 comes in through the general surface of the ectoplasm by 
 osmosis. Oxidation and the release of energy take place, as 
 is manifested in locomotion. The waste of the body is prob- 
 ably partly expelled by the contractile vacuole. This organ 
 may be observed in that portion of the ectoplasm which is 
 behind in locomotion. The products of metabolism when 
 brought into that region form a sphere of liquid which, as 
 it increases in size, is carried back from the region of the 
 nucleus to the point where it contracts and bursts on the 
 surface. 
 
 Reproduction in Amoeba is accomplished by the nucleus 
 and the protoplasm dividing into equal portions, the two new 
 cells separating immediately and growing to the size of the 
 original one. This kind of reproduction is considered by 
 many zoologists to be a phase of growth. The cell, by feed- 
 ing, becomes so large that the surface through which food and 
 oxygen pass is not great enough to supply the more rapidly 
 increasing volume of cytoplasm. When division takes place, 
 masses are produced which have enough surface to supply the 
 interior with material for growth and other forms of energy. 
 
AMCEBA AND SOME ALLIES: PROTOZOA 283 
 
 Under certain conditions of the environment the amoeba 
 ceases moving about; it takes on the form of a ball, and 
 incloses itself in a membrane or cyst. The encysted amoeba 
 remains in that state until the return of favorable conditions 
 in its habitat. 
 
 Euglena. A relative of Amoeba, found in the same situ- 
 ations, is Eugle'na vir'idis (Fig. 141) ; it also is composed of 
 one cell. Euglena has a more fixed arrangement of parts 
 than Amoeba. There is a blunt anterior end with a short, 
 funnel-shaped mouth to carry food into the cytoplasm. Out 
 of the mouth extends a long lash, which by its whip-like 
 vibrations carries the animal through the water, and at 
 the same time sends food back to the mouth. Behind the 
 mouth is a small red eye-spot, which lies beside a clear 
 space. This clear space has been found to be sensitive to 
 light. The nucleus is near the middle of the body, and 
 can be seen easily in the living animal, although 
 the cytoplasm immediately about it is colored 
 quite green with 
 chlorophyll, a 
 coloring matter 
 found in the 
 
 green parts of FlG 141 Euglena. Much enlarged. (After Saville Kent) 
 plants. 
 
 Many biologists believe that Euglena is indeed a plant 
 because, through the agency of its chlorophyll, it can use car- 
 bon dioxide as a raw food-material, retaining the carbon and 
 giving off oxygen when the organism is in the light. This 
 creature illustrates the fact that it is impossible to classify 
 all organisms as plants or animals. 
 
 As a rule Euglena moves with the lash forward, but the 
 animal can turn in any direction, and can even change 
 the shape of its body considerably, but it does not form 
 pseudopodia. Sometimes when being experimented 011 with 
 
284 GENERAL ZOOLOGY 
 
 substances which it does not like, Euglena ceases moving, 
 contracts into a ball, and encysts itself, just as it does in 
 nature when it is surrounded by unfavorable conditions. 
 
 The Malarial Parasite. Many one-cell animals are parasitic. 
 One of the most studied in recent years is the malarial para- 
 site of man (Plasmo'dium mala' rice, Fig. 142). The life-history 
 of this organism is long and complicated, but we can get a fair 
 understanding of its principal phases without discussing the 
 minutest details. 
 
 In its simplest form the animal resembles an extremely 
 small amoeba. In that stage it is found in the red corpuscles 
 of human blood. There the parasite increases in size until it 
 almost fills the corpuscle (Fig. 142, 4) ; then it divides into 
 small bodies called spores (Fig. 142, 5a v ). The process of 
 spore-formation causes the chill that accompanies malaria. 
 When the spores burst from their spore-case (Fig. 142, 5a VI ) 
 and from the blood-corpuscles, a quantity of poisonous mate- 
 rial (represented by black dots in Fig. 142, 5 YI ) is released 
 and mingles with the liquid of the blood. This poisonous 
 material induces the fever which always follows the chill. 
 The released spores may enter red corpuscles again, and in 
 forty-eight hours in one type of malaria, and seventy-two 
 hours in another, form spores once more. 
 
 Some of the amoebulce (amoeba-like stages) of the parasite 
 have a different history. While most of them in the red cor- 
 puscles of a person go on reproducing non-sexually, as just 
 described, some develop into a form which, by comparison 
 with higher animals, we call the female cell (Fig. 142, 5c n ), 
 and others into male cells (Fig. 142, 5Z> n *). If now the person 
 be exposed to the bite of a mosquito of the genus Anopheles 
 (see p. 63), the male and female cells of Plasmodium each 
 reach their full development in the human red blood-corpus- 
 cles, as these rest in the stomach of the mosquito. Leaving 
 the corpuscles, the two cells unite to form a worm-like cell 
 
11 
 
 13 
 
 SCHEMA 
 
 FIG. 142. Life-Cycle of Malarial Parasite. (After Grassi) 
 
 285 
 
286 GENERAL ZOOLOGY 
 
 (Fig. 142, 6), which penetrates to the outer wall of the stomach 
 of the mosquito, where it increases in size to form a large 
 sphere (Fig. 142, 12). In a short time the sphere subdivides 
 into countless extremely minute blasts (Fig. 142, 17, l). These 
 make their way through the body-cavity of the mosquito to 
 the salivary glands. Penetrating to the interior of those 
 glands, the blasts enter the ducts, and are carried outward 
 and down the insect's proboscis by the saliva when the 
 mosquito bites another person. Then in the human blood 
 the blasts enter the red corpuscles and become amcebulce, 
 thus completing a cycle. 
 
 Prominent among the scientific men who since 1896 have 
 discovered the facts of the life-history of the malarial para- 
 site are Dr. Ross, of India, and Professor Grassi, of Italy. 
 Upon their discoveries, and those of others, are based the 
 numerous operations against the mosquito in the vicinity of 
 large cities. 
 
 Paramoecium. Perhaps no member of the phylum under 
 discussion in this chapter has been observed by more 
 students than has the slipper-animalcule, Paramce'cium cau- 
 da'tum (Fig. 143 A, B) ; and no member of its phylum has 
 been so frequently made the basis of scientific discussions of 
 cell-structure and cell-physiology. Paramoecium lives in stag- 
 nant pools of fresh water in all lands. Specimens may be 
 obtained in countless numbers by placing a quantity of hay 
 in a jar of ordinary water and leaving it to stand for a few 
 weeks. The bacteria developed in the decaying hay furnish 
 an inexhaustible food-supply for the animals. 
 
 As in Amoeba, Euglena, and Plasmodium, the entire body 
 of Paramoecium is a single cell. The cell when moving 
 freely has a definite shape, although it changes constantly in 
 outline, owing to the fact that the irregularities in the body 
 are whirled into view as the animal swims along in a slender 
 spiral path. 
 
AMCEBA AND SOME ALLIES: PROTOZOA 287 
 
 Paramoecium is about .2 mm. (^ inch) in length. T<he 
 anterior end is rounded and the posterior end pointed. 
 Right and left sides are, as indicated in the figures, deter- 
 mined by the position of the mouth (Fig. 143, 2), which is 
 on a surface called ventral. 
 The entire surface of the 
 ectoplasm is covered with 
 great numbers of short, 
 hair-like structures, called 
 cilia (Fig. 143, l). The cilia 
 are the organs of locomo- 
 tion. Their customary 
 manner of working is to 
 wave backward toward the 
 posterior end, propelling 
 the animal forward, but 
 they may also wave so as 6-:-. 
 to send the body along 
 with the pointed end for- 
 ward. A few cilia j5pm- 
 what longer than the 
 Others lie in the groove FIG. 143. Paramoecium. Much enlarged 
 that leads diagonally across 
 the ventral surface to the 
 mouth. Their function *is 
 
 B 
 
 A, left side; B, ventral surface; 1, cilia; 
 2, mouth; 3, gullet; 4, food-vacuole 
 forming; 5, food-vacuole in cytoplasm; 
 6, anus; 7, contractile vacuole ; 8, mac- 
 ronucleus ; 9, micronucleus 
 
 (From Sedgwick and Wilson's General 
 Biology) 
 
 to carry the food down the 
 short gullet into the endo- 
 plasm. 
 
 The endoplasm, which, as already explained, is that por- 
 tion of the cytoplasm lying between the nucleus and the out- 
 side layer of ectoplasm, is soft and semifluid. Food is passed 
 into it by the gullet (Fig. 143, 3), and immediately begins to 
 float away from that point, surrounded by a little drop of 
 water. These masses are called food-vacuoles (Fig. 143, 4, 5). 
 
288 
 
 GENERAL ZOOLOGY 
 
 While the current in the cell-protoplasm is carrying the food- 
 vacuoles around, digestive fluid formed by the protoplasm 
 is breaking up the food, liquefying, and changing it chem- 
 ically for the process of assimilation or building up into pro- 
 toplasm. The indigestible particles are discharged from the 
 cell by a small opening, the anus (Fig. 143, 6). The waste 
 derived from the food and protoplasm that is used up in the 
 work of the animal is probably discharged in the form of 
 liquid from two special organs, one 
 near either end at the dorsal surface. 
 These are contractile vacuoles (Fig. 
 143, 7). It is supposed that the liquid 
 waste when formed, flows through the 
 protoplasm along somewhat definite 
 channels, to the point where it collects 
 in a gradually increasing vacuole. 
 Soon the maximum size is attained, 
 and the vacuole bursts at the surface, 
 the waste pouring into the water out- 
 side. The two contractile vacuoles 
 alternate in contracting. 
 
 Paramcecium has two nuclei ; the 
 large one is called the macrvnucleus 
 (Fig. 143, 8), and the small one the 
 micro nucleus (Fig. 143, 9). The macro- 
 nucleus is thought to be the seat of 
 the general activities of the cell, while 
 the micronucleus is the seat of the 
 important process of reproduction. 
 
 The theory that reproduction by divi- 
 sion is a phase of growth was stated in 
 
 the description of Amoeba. Paramoecium also divides into 
 two equivalent cells (Fig. 144), with half the macronucleus 
 and half the micronucleus in each, probably because the 
 
 FIG. 144. Paramoecium 
 dividing. Much en- 
 larged 
 
 1, mouth and gullet; 
 2, macronucleus divid- 
 ing; 3, micronucleus 
 dividing 
 
 (From Sedgwick and Wil- 
 son's General Biology) 
 
AMCEBA AND SOME ALLIES: PROTOZOA 289 
 
 volume of the cell becomes too great to be kept alive by the 
 organs of the relatively decreasing surface. As many as 
 three or four generations of Paramoe- 
 cia may be produced in a single day. 
 The frequency of division of the cell 
 depends upon the kind and abun- 
 dance of food obtainable, and also upon 
 a process known as conjugation (Fig. 
 145). This complicated process was 
 worked out in great detail in 1888 by 
 Maupas, a French librarian, who in his 
 spare time studied the life-history of 
 Paramoecium and other unicellular 
 organisms. 
 
 In conjugation two Paramoecia unite 
 temporarily in the manner indicated in 
 the figure. A fraction of the micro- 
 nucleus of each passes through the 
 two contiguous layers of ectoplasm 
 and unites with a similar fraction in 
 the other animal. When this and cer- 
 tain other less essential phenomena 
 have taken place, the individuals sep- 
 arate and continue the process of transverse division, but 
 with greater frequency than before. Maupas interpreted 
 conjugation as a process of rejuvenescence, or renewing the 
 youth, through which these organisms, being exhausted by a 
 long series of divisions, could regain their vitality, thus pre- 
 venting the extermination of the race. It has been pointed 
 out by some zoologists that conjugation in unicellular organ- 
 isms has many points of resemblance with the union of egg 
 and spermatozoon in the higher animals. We may therefore 
 speak of conjugation as sexual reproduction, to distinguish it 
 from the non-sexual reproduction by division. 
 
 FIG. 145. Paramoecia con- 
 jugating. Much en- 
 larged. (After Saville 
 Kent) 
 
290 GENERAL ZOOLOGY 
 
 Some interesting experiments bearing on the problem of 
 conjugation in Paramoecium were carried out in the years 
 1901 and 1902 by Professor G. N. Calkins, of Columbia 
 University. He found that as the generations approached 
 ninety to one hundred and seventy in number, the individuals 
 become smaller in size and appear to lose some property in 
 their protoplasm. He was able to " renew the youth " of his 
 series of animals by artificial means, twice by change of 
 food, once by mechanical agitation, and once by a rise in 
 temperature. After each stimulation the Paramcecia divided 
 frequently, and in other respects imitated the phenomena 
 subsequent to conjugation. 
 
 Results strikingly similar to these have been obtained by 
 Professor Jacques Loeb, of the University of California, in 
 stimulating by mechanical and chemical means the eggs of 
 sea-urchins to develop to advanced stages. The term " artifi- 
 cial parthenogenesis " (see parthenogenesis, p. 34) has been 
 used in describing the results obtained by Professor Loeb. 
 It is interesting to notice in connection with these experiments 
 that in the eggs of sea-urchins stimulated to develop naturally 
 by the spermatozoon, and artificially by mechanical and chem- 
 ical means, and in Paramcecium stimulated to frequent divi- 
 sion naturally by conjugation, and artificially by mechanical 
 and chemical means, we have a result the identity of which 
 can be expressed under the name rejuvenescence. Although 
 these experiments have value in interpreting the phenomena 
 of reproduction, it is well to keep in mind the fact that the 
 artificial method fails after a few cycles in Paramoecium, and 
 before the end of the larval period in the sea-urchin. 
 
 When the water in which Paramoecia live shows indica- 
 tions of drying up, the animals encyst themselves by secret- 
 ing a film of gelatinous substance from their ectoplasm. The 
 encysted animal retains its usual form, and remains inactive 
 until it is brought into water again. 
 
AMCEBA AND SOME ALLIES: PROTOZOA 291 
 
 Unicellular organisms have long been objects of profound 
 study for biologists and psychologists. The biologists recog- 
 nize in them the morphological unit of structure, identical in 
 important details with the unit of structure in the tissues of 
 all animals as well as all plants, but differing from the tissue- 
 cells in the fact that the latter have only one chief function 
 to perform, whereas unicellular organisms carry out all the 
 processes of living in one small bit of protoplasm, the single 
 cell. Psychologists look to these organisms for the beginning 
 of that phase of mind called consciousness, one evidence of 
 which we see in the ability of ourselves and other animals to 
 choose a course of action. As a matter of fact, we have no 
 way of knowing whether unicellular organisms are conscious 
 or not. According to Professor Jennings, these organisms, 
 as well as others, manifest complicated internal physiological 
 processes. Any external agents, as, for example, oxygen, heat, 
 or food, which bear relation to the internal physiological 
 processes, are concerned in the activities of the organism. If 
 a Paramoecium comes to a place where oxygen is scarce, it 
 will make a series of trial trips in various directions, until the 
 internal demand for oxygen is satisfied. As the result of 
 the needs of the organism, it is constantly on the move, but 
 we cannot say that these movements are conscious efforts. 
 
 Definition of Protozoa (Gr. protos, first ; zoon, animal). 
 The four members of the phylum described in this chapter 
 were selected as representatives of the four classes that make 
 up the phylum : Amoeba proteus, of the class Sarcodi'na ; 
 Euglena viridis, class MastigopJi' ora ; Plasmodium malarise, 
 class Sporozo'a; and Paramoecium caudatum, class Infuso'ria. 
 
 Although in each class the genera differ widely, all the 
 members of the four classes agree in being composed of 
 single cells. Nearly all species are microscopic in size. 
 
 Reproduction is brought about by division of the cell, and 
 never by eggs and spermatozoa. 
 
CHAPTER XXII 
 
 THE EVOLUTION OF INVERTEBRATES AND THE ANCESTRY 
 OF THE VERTEBRATES 
 
 I wrote the past in characters 
 Of rock and fire the scroll, 
 The building in the coral sea, 
 The planting of the coal. 
 
 EMERSON, Song of Nature. 
 
 Vertebrates and Invertebrates. However various in form 
 and structure the members of the phyla thus far discussed 
 are, they have in common at least this negative character, 
 that in none of them has a backbone been developed. For 
 this reason they are collectively termed Invertebrates (Lat. 
 in, not ; vertebratm, vertebrate) ; the animals which have a 
 backbone are called Vertebrates. It will be worth our while, 
 before beginning the study of the latter, to consider some 
 general questions of interest in connection with the evolution 
 of the invertebrate phyla, and then to describe briefly some 
 peculiar forms which appear to stand between the inverte- 
 brates and the vertebrates. These intermediate forms, or their 
 ancestors, may be the immediate ancestors of the vertebrates. 
 
 THE EVOLUTION OF THE INVERTEBRATES 
 
 Sources of Information. There are, as we have seen in 
 the chapter on insects, three sources of information which the 
 zoologist may draw upon, in his endeavor to discover the rela- 
 tionship which the animals of the past and the present evi- 
 dently bear to each other, throughout the long series from 
 the lowest to the highest. These sources of information are 
 the geological record of species, comparative anatomy or 
 
 292 
 
THE EVOLUTION OF INVERTEBRATES 293 
 
 morphology, and the embryological stages in the develop- 
 ment of the individual. We shall consider first the record of 
 geology, and in order to do this intelligently we shall have 
 to begin far back, for perhaps more than any other science, 
 geology requires of the mind of man vast sweeps of the 
 imagination to form even faint conceptions of the illimitable 
 processes that have brought the earth to its present state. 
 Scarcely less awe-inspiring is the contemplation of the changes 
 that must have taken place in living things, since life began/ 
 in the ocean and on the land. Great as the time and changesl! 
 were before the earth had life upon it, greater still may be^ 
 the time that the processes of evolution have required to I 
 develop all the forms of life in their complexity. 
 
 The Nebular Hypothesis. The earth is one of a number of 
 bodies called planets, which revolve about a central heated 
 body, the sun. The planets, with their attendant moons or 
 satellites, and a number of smaller bodies revolving about the 
 sun in the same direction and nearly in the same plane, con- 
 stitute our solar system. The nebular hypothesis is a theory 
 which involves the suggestion of a common origin for all 
 members of the solar system from a mass of heated gaseous 
 material (Lat. nebula, cloud) in motion, which is supposed to 
 have occupied all the space between the central sun and the 
 orbit of the outermost planet. In the process of cooling and 
 condensation rings of matter were formed, which later broke 
 up into the different planets. 
 
 Archaean Time. The earliest period of the earth's geological 
 history is termed the Archaean Era (Gr. archaios, ancient). 
 At first all the substances, including the water which now 
 covers three quarters of the earth's surface, were held sus- 
 pended in the atmosphere, owing to the high temperature. 
 Later there came a time when the waters condensed, and the 
 surface, cooled still further, permitted the water to cover 
 the rocks of the early crust entirely or in part. Stupendous 
 
294 
 
 GENERAL ZOOLOGY 
 
 volcanic upheavals must have been frequent as fire and water 
 struggled for the mastery. During this time, of course, no 
 life was possible. As the crust continued to cool it was 
 upheaved and formed land. When the waters had cooled 
 sufficiently to permit of it, life appeared, but in what form 
 
 FIG. 146. North America in the Archsean Era 
 (From Dana's Manual of Geology) 
 
 we do not know. It is thought that this early life may have 
 been plant rather than animal in its nature, since plants 
 to-day, with the exception of the fungi (mushrooms, bacteria, 
 etc.), feed upon mineral matter, while animals require plant 
 or animal food. As regards the temperature at which life 
 became possible, it is known that plants live now in the hot 
 springs of the West in water reaching 180 F. 
 
THE EVOLUTION OF INVERTEBRATES 
 
 295 
 
 There is very little direct evidence to indicate the charac- 
 ter of the life in the Archaean era, but in all probability it 
 was of the simplest structure, like some of the single-cell 
 organisms of to-day. Although fossil remains of that time are 
 wanting, beds of limestone and graphite formed then, point 
 to the existence of life, for similar beds formed in later eras 
 are known to have been made through the agency of organ- 
 
 FIG. 147. North America toward the Close of the Age of Invertebrates 
 (From Dana's Manual of Geology] 
 
 isms (polyps, mollusks, etc., and plants). Fig. 146 shows the 
 North American continent as it probably existed at the close, 
 of the Archaean era. The main body of land was a V-shaped 
 mass lying north of the present Great Lakes and the St. 
 Lawrence River. Archaean islands lay in the position of parts 
 of subsequent eastern and western highlands. 
 
 The Age of Invertebrates. Following the Archaean era, 
 several succeeding geological periods may be, for our purpose, 
 
296 GENERAL ZOOLOGY 
 
 grouped under the general term, Age of Invertebrates, from 
 the predominance of these forms of life. The era was 
 very long, undoubtedly to be reckoned in millions of years. 
 We have no knowledge of the exact time that the different 
 species appeared, nor of the exact length of time they existed. 
 Neither do we know from actual specimens all the stages of 
 evolution through which the early forms of life may have 
 passed in coming to the form and structure in which we 
 know their kin to-day, for the intermediate types have been 
 lost on account of one catastrophe or another in the history 
 of the world. 
 
 In the beginning of the era, life was marine, as far as fossil 
 records indicate. The earliest fossils are of sponges, corals, 
 sea-lilies or crinoids (see p. 246), worms, brachiopods (see 
 p. 233), mollusks, and trilobites (see p. 153). Subsequently 
 land animals made their appearance in forms like the arach- 
 nids and the insects. Before the close of the era a class of 
 vertebrate animals, the fishes, had come into existence. The 
 accompanying map (Fig. 147) will give an idea of the probable 
 growth of the land area of North America during the period. 
 
 Evidence from Embryology and Morphology. Frequently 
 the only way the zoologist may know of the kinship of cer- 
 tain groups is by studying their early stages of development. 
 Since all the animals composed of more than one cell repro- 
 duce at one time or another by means of eggs and sperma- 
 tozoa, we see that all animals, however great the differences 
 between the adults may be, are alike in being composed of 
 one cell at the beginning of development. But in some ani- 
 mals the number and complexity of the changes intervening 
 between the egg stage and the adult stage are few and sim- 
 ple in comparison with the changes taking place in others. 
 All those animals which have few organs show relatively 
 few changes in development, in comparison with those 
 animals which have numerous, complicated organs. Hydra, 
 
THE EVOLUTION OF INVERTEBRATES 297 
 
 for example, as morphology shows, is a very simple form com- 
 pared with the earthworm. Not only has Hydra fewer organs 
 than the earthworm, but reference to the study of develop- 
 ment of the latter will show that the two layers of cells 
 which constitute the entire animal Hydra represent a very 
 early stage in the development of the earthworm. 
 
 There is an additional point of value to be observed in 
 the comparison of Hydra and the earthworm. There are two 
 phyla of animals that in development have two germ-layers, 
 Porifera and Coelentera. All the others (except the Protozoa) 
 have three germ-layers. The third germ-layer, the mesoderm, 
 offers a beginning place for organs not developed in the 
 ectoderm and endoderm, and groups of animals possessing it 
 develop more kinds of organs than those which do not have 
 it ; that is to say, they show greater differentiation. 
 
 If we were to begin at once to arrange all animals in a 
 regular graded series, on the basis of what we learn from 
 morphology and from embryology, we should have a difficult 
 task. The number of facts that it is necessary to know is so 
 considerable that even to-day systematic zoologists are not 
 agreed on important details of grouping animals in a com- 
 plete system of classification. Besides, the doctrine of evolu- 
 tion takes into account the fact that the phyla of animals 
 have not developed in a direct line, but as branches from a 
 previously existing stem. The whole system of animals 
 might be represented graphically by a series of stem and 
 branches resembling a tree ; but whereas in a tree we can 
 trace down one branch and out any other, in the diagram 
 suggested some of the branches would not be connected with 
 the stem at all, because the organisms which would stand in 
 the connecting places have disappeared both in living and 
 in fossil form. 
 
 However, we can see very clearly that the Protozoa being 
 composed of a single cell are the lowest of all animals ; and 
 
298 GENERAL ZOOLOGY 
 
 that the Porifera, with their structure showing no sign of 
 digestive organs, muscle-cells, nerve-cells, or sense-organs, are 
 the simplest of the many-cell animals (Metazoa). Of course 
 we do not place the Porifera next above the Protozoa until 
 we have weighed the facts by comparing their structure with 
 the only other phylum that has two germ-layers. The Cce- 
 lentera have, as we recall, a gastrovascular cavity, simple 
 muscle-cells, nerve-cells, and sense-organs. 
 
 An attempt to classify the animals that have three germ- 
 layers in development immediately brings us into difficulties. 
 Formerly it was the custom to place the Echinoderma near 
 the Ccelentera because of their radiate plan of structure, but 
 now the radial symmetry is not generally considered a factor 
 of great significance. The old group of Venues has been thor- 
 oughly studied in recent years, and, as indicated in Chapter 
 XVII, it has been subdivided into five phyla by some of the 
 best-known authorities. In the order of their increasing com- 
 plexity, the phyla are Platyhelminthes, Nemathelminthes, 
 Trochelmiiithes, Molluscoida, and Annulata. They are all 
 bilaterally symmetrical animals, but only the last phylum has 
 the body divided into somites. Because of this and other 
 facts, the order of classification is modified by the English 
 zoologists Parker and Haswell by placing the Echinoderma 
 between the Molluscoida and the Annulata. The Echino- 
 derma have an alimentary canal separated from the body- 
 cavity, digestive glands, a fairly well-defined blood-system, 
 an elaborate water-vascular system, and a definite nervous 
 system. For these reasons they are entitled to rank next to 
 the Annulata. All members of the Annulata have the body 
 divided into somites with unsegmented appendages. The 
 body has a distinct alimentary canal, a complete blood-system, 
 and a more complicated nervous system than is found in any 
 of the phyla already mentioned. The system of nephridia also 
 is more extended, one pair being present in every somite. 
 
THE EVOLUTION OF INVERTEBRATES 299 
 
 The phylum Arthropoda is pretty clearly distinct from 
 other phyla. Its advance over the Annulata consists in the 
 tendency of the somites to be fewer and more definite in 
 number. The somites are grouped in two or three regions; 
 in certain regions the somites are fused, an indication of still 
 greater differentiation. All the appendages are segmented. 
 The dorsal blood-vessel is more differentiated than other 
 parts of the circulatory system, and in some classes it is a 
 clearly defined one-chambered heart. Sense-organs, especially 
 eyes, reach a condition of great complexity in comparison 
 with what is found in lower phyla. 
 
 If division into somites is an indication of advance, the 
 loss of it would seem to be an indication of degeneration, but 
 we have no proof that the ancestors of the Mollusca had 
 bodies which showed metamerism. Their development was 
 evidently in a different direction from that of the Annulata 
 and the Arthropoda. The factors which seem to place Mol- 
 lusca higher in the system are greater centralization of the 
 nervous system in a miniature "brain," and the possession 
 of a three-chambered heart, two auricles and one ventricle. 
 
 INVERTEBRATE PHYLA AND CLASSES 
 
 The subjoined list of the classes discussed in the first 
 twenty-one chapters will be of service in recalling the rela- 
 tive position of the phyla in the system of classification. 
 
 I. PROTOZOA 
 
 Class 1. Sarcodina; example, Amoeba protens. 
 Class 2. Mastigophora ; example, Euglena viridis. 
 Class 3. Sporozoa; example, Plasmodium malariae. 
 Class 4. Infusoria ; example, Paramoecium caudatum. 
 
 II. PORIFERA 
 
 Class 1. Porifera; example, Heteromeyenia ryderi. 
 
300 GENERAL ZOOLOGY 
 
 ITT. C<ELENTERA 
 
 Class 1. Hydrozoa ; example, Hydra viridis. 
 Class 2. Scyphozoa ; example, Aurelia flavidula. 
 Class 3. Actinozoa ; example, Metridium raarginatum. 
 Class 4. Ctenophora ; example, Pleurobrachia rhododactyla. 
 
 IV. PLATYHELMINTHES 
 
 Class 1. Turbellaria ; example, Dendrocoelum lacteum. 
 Class 2. Trematoda; example, Distomum somaterise. 
 Class 3. Cestoda ; example, Taenia saginata. 
 
 V. NEMATHELMINTHES 
 Class 1. Nematoda; example, Trichina spiralis. 
 
 YT. TROCIIELMINTHES 
 
 Class 1. Rotifera ; example, Brachionus urceolaris. 
 
 YTT. MOLLUSCOIDA 
 
 Class 1. Polyzoa ; example, Plumatella repens. 
 Class 2. Brachiopoda ; example, Lingula lepidula. 
 
 YTIT. ECHINODERMA 
 
 Class 1. Asteroidea ; example, Asterias vulgaris. 
 
 Class 2. Ophiuroidea ; example, Astrophyton agassizii. 
 
 Class 3. Echinoidea : example, Strongylocentrotus drobachiensis. 
 
 Class 4. Holothuroidea ; example, Cucumaria chronhjelmi. 
 
 Class 5. Crinoidea; example, Pentacrinus blakei. 
 
 IX. ANNULATA 
 
 Class 1. Chsetopoda; example, Lumbricus terrestris. 
 Class 2. Hirudinea ; example, Placobdella rugosa. 
 
 X. ARTHROPODA 
 
 Class 1. Crustacea; example, Cambarus affinis. 
 Class 2. Xiphosura; example, Limulus polyphemus. 
 Class 3. Arachnida ; example, Argiope riparia. 
 Class 4. Myriapoda; example, Lithe-bins americanus. 
 Class 5. Hexapoda ; example, Melanoplus femur-rubrum. 
 
THE EVOLUTION OF INVERTEBRATES 
 
 XI. MOLLUSCA 
 
 Class 1. Pelecypoda ; example, Mya arenaria. 
 Class 2. Gasteropoda ; example, Helix nebulosa. 
 Class 3. Cephalopoda; example, Nautilus pompilius. 
 
 301 
 
 PROBABLE ANCESTORS OF THE VERTEBRATES 
 
 The Lancelet. It is always important to find, if possible, 
 connecting links between large and seemingly distinct groups 
 of animals. The words " invertebrate " and " vertebrate " 
 were once thought to be terms which together included all 
 animals ; but zoologists have discovered several animals 
 which are neither vertebrate nor invertebrate in the usual 
 sense of the words. 
 
 The first of the three animals to be described in this sec- 
 tion of the chapter is a vertebrate of a very simple type. 
 
 FIG. 148. The Lancelet. x 2. (After Kowalevsky) 
 
 1, mouth; 2, gill-slits; 3, atrium; 4, atrial pore; 5, intestine; 6, anus; 7, noto- 
 chord; 8, nerve-cord 
 
 The lancelet (Amphiox'us lanceola'tus, Fig. 148) is a fish-like 
 animal about two inches long. It lives almost imbedded in 
 the sand at the sea-bottom in Chesapeake Bay and in other 
 warm ocean waters. 
 
 The mouth (Fig. 148, 1) of the lancelet opens into a long 
 pharynx, which has many pairs of gill-slits (Fig. 148, 2). 
 When water and food pass in at the mouth, the water passes 
 through the gill-slits, giving up oxygen to the blood in the 
 gills, and then passes into a chamber partially surrounding 
 the pharynx, called the atrium (Fig. 148, 3), and to the 
 
302 
 
 GENERAL ZOOLOGY 
 
 outside by the atrial pore (Fig. 148, 4) ; the food goes down 
 the intestine (Fig. 148, 5). 
 
 Immediately above the intestine is the structure which 
 corresponds in position to the backbone of higher animals ; 
 it is called the notochord (Fig. 148, 7). The notochord is soft 
 throughout life, but it is sufficiently strong to act as a support- 
 
 B ' 
 
 FIG. 149. Photograph of Living Tunicates. Natural size 
 A, Styela stimpsoni ; Z>, Cynthia haustor 
 
 ing skeleton for the body. Parallel with the notochord and 
 above it, is the spinal cord (Fig. 148, 8) lying near the dorsal 
 wall. The characteristics of structure which make Amphioxus 
 a vertebrate are the presence of gill-slits, a notochord above 
 the intestine, and a spinal cord dorsal to the notochord. 
 
 The Sea-Squirt. As far as outward appearance indicates the 
 sea-squirts, Sty'ela stimpson'i and Cyn'thia, haus'tor (Fig. 149, 
 
THE EVOLUTION OF INVERTEBRATES 
 
 303 
 
 A and Z?), have nothing in common with vertebrates. Sea- 
 squirts live attached to rocks and wharves, and once attached 
 never leave the place. The body 
 is covered with a tough coat or 
 tunic, which gives the class its 
 name, Tunica 1 ta. The food and 
 oxygen are drawn through the 
 opening in the upper tube, and 
 the excess water and wastes are 
 discharged by the lower tube. 
 There is a pharynx Avith gill- 
 openings, and a nervous system, 
 but there is no indication of a 
 notochord. 
 
 The adult tunicate exhibits 
 a lower degree of organization 
 than the larva. The larva (Fig. 
 150) has very much the form 
 of a frog-tadpole, and it swims 
 about. Its locomotor organ is a 
 fin-like tail (Fig. 150, 12). As 
 long as the animal remains a 
 larva it has structures which 
 indicate vertebrate relationship. 
 Extending through the middle 
 of the tail is a notochord (Fig. 
 150, 6), which is evidently a sup- 
 porting organ. Dorsal to the 
 notochord is the nerve-cord (Fig. 
 150, 7). Below the notochord is 
 the alimentary canal (Fig. 150, 3), and near by are the begin- 
 nings of the gills, with openings (Fig. 150, 2) which, however, 
 are not gill-slits. When the larva reaches a certain stage of 
 development, it fastens itself by adhesive papilla? (Fig. 150, 11) 
 
 11 
 
 FIG. 150. Larva of Tunicate. 
 Much enlarged. (After Herd- 
 in an) 
 
 1, incurrent opening ; 2, gill-open- 
 ings ; 3, intestine ; 4, anus ; 5, ex- 
 current opening ; 6, notochord ; 
 7, nerve-cord ; 8, eye ; 9, otocyst ; 
 10, endostyle; 11, adhesive pa- 
 pillae; 12, portion of tail 
 
304 
 
 GENERAL ZOOLOGY 
 
 to some fixed object. Then begins the process of degener- 
 ation of all distinctly vertebrate structures ; the tail is 
 absorbed, the notochord also disappears, and the nerve-cord 
 changes form. If it were not for what is known of the 
 
 larva, the vertebrate relationship of 
 tunicates would never be suspected. 
 The Acorn-Tongue Worm. Some 
 zoologists have supposed that the 
 ancestors of the vertebrates were 
 worm-like animals. The reasons for 
 that supposition are based chiefly on 
 3 the structure of the acorn-tongue 
 worm, Balanoglos'sus (Fig. 151). This 
 animal is found in the sand of sea- 
 shores. It has a proboscis (Fig. 151, l) 
 with a collar-like band (Fig. 151, 2) at 
 the base, both Organs together some- 
 what resembling an acorn in its cup. 
 The mouth, at the base of the 
 proboscis, opens into a pharynx from 
 which many pairs of gill-slits (Fig. 
 151, 3) open to the exterior. There is 
 a dorsal nerve-cord and a ventral nerve- 
 FIG. 151. Acorn-Tongue cord. A notochord-like structure has 
 Worm. Enlarged. (After ^ f d extending into the middle 
 A. Agassiz) & . 
 
 ot the proboscis. Many zoologists 
 
 1, proboscis ; 2, collar ; 3, gill- , , , . * , , . 
 
 slits express doubt concerning this organ, 
 
 and no investigator seems to be posi- 
 tive of its notochordal structure. If* the .main nerve-cords 
 were limited to one above the intestine, that would clearly 
 be a vertebrate characteristic ; but with one above and one 
 below, it is neither definitely vertebrate or invertebrate, and 
 hence possibly an intermediate form. The gill-slits have the 
 position and form of those in Amphioxus. 
 
CHAPTER XXIII 
 THE YELLOW PERCH 
 
 Give me some observations and directions concerning the Pearch for they 
 say he is both a very good and a bold biting fish, and I would fain learne 
 to fish for him. IZAAK WALTON, The Complete Angler. 
 
 Habitat and Distribution. Brilliant in coloration, abundant 
 and easy of capture, and possessing a firm, white flesh of 
 delicate flavor, it is no wonder that the yellow perch (Per'ca 
 flaves'cens, Fig. 152) is one of the best known of the fresh- 
 
 FIG. 152. Photograph of Yellow Perch. Reduced 
 (From Jordan and Evermann's American Food and Game Fishes) 
 
 water fishes of the United States. Though found in streams, 
 especially in those with quiet reaches of water, the yellow 
 perch is more truly a creature of ponds and lakes. There it 
 prefers a pebbly or sandy bottom. Its range extends from 
 Labrador to Georgia in the fresh-water rivers and the lakes 
 
 305 
 
306 GENERAL ZOOLOGY 
 
 along the Atlantic coast, and westward in the region of the 
 Great Lakes and upper Mississippi valley. Though origi- 
 nally absent from the far West, it has recently been intro-- 
 duced with success into the lakes of Washington, Oregon, 
 and California. In structure and habits our yellow perch 
 very closely resembles the perch of Europe, referred to in the 
 quotation at the head of this chapter, and by some authors 
 it is considered to be identical with the latter species. 
 
 External Structure. The body of the perch is elongate, 
 slightly compressed from side to side, and tapers toward both 
 ends. Three divisions are apparent, the head, trunk, and tail; 
 several appendages, the fins, are attached to the body. The 
 covering is a smooth skin, containing pigment cells, to which 
 the colors are due, and glands which secrete mucus. Within 
 pouches in this skin are transparent scales, which overlap, 
 like the shingles on the roof of a house, and form a coat of 
 mail, incasing the fish from head to tail. Along a clearly 
 defined lateral line the scales are somewhat modified, and 
 beneath them are sense-organs the functions of which have 
 been variously stated. Professor G. H. Parker considers that 
 these organs are sensitive to mechanical jars of a low rate of 
 frequency, thus standing between organs of touch proper, and 
 those of hearing. 
 
 At the anterior end of the head are the jaws, armed with 
 teeth for seizing food. The eyes have no eyelids. Just in 
 front of the eyes are the nostrils, two on either side. They 
 have no communication with the mouth. Behind the eyes, on 
 each side of the body, is a movable flap called the operculum, 
 beneath which are the red comb-like gills.. 
 
 There are five fins, three unpaired and two in pairs. Of the 
 unpaired fins those on the back are called the dorsal fins, the 
 one on the under side the anal fin, and the one at the tail 
 the caudal fin. The more anterior of the paired fins are the 
 pectoral fins ; the more posterior and lower, the ventral or 
 
THE YELLOW PERCH 307 
 
 pelvic fins. The fins are supported by Jin-rays of two sorts, 
 the one hard, unsegmented, and unbranched (Fig. 153,1); the 
 other soft, segmented, and branched (Fig. 153, 2). 
 
 The Digestive System. The mouth is large. Teeth are borne 
 not only on the jaws but also on the roof of the mouth 
 (Fig. 153, 6, 7, 9). On the ventral surface of the mouth is a 
 rather large, fleshy tongue (Fig. 153, 8). Behind the tongue 
 is the pharynx (Fig. 153, 10), with gill-slits on both sides, 
 which allow water from the mouth to pass into the gill-cham- 
 ber. From the pharynx a short oesophagus leads to the stomach 
 (Fig. 153, 14). Several pyloric cceca (Fig. 153, 15) open into 
 the intestine (Fig. 153, 16), increasing its absorbing and secret- 
 ing surface. The intestine ends ventrally at the anal opening 
 anterior to the anal fin (Fig. 153, 4). The liver-secretion, 
 called bile, is stored in a gall-bladder (Fig. 153, 12) attached 
 to the posterior surface of the liver (Fig. 153, 11), and finds 
 its way into the alimentary canal through the bile-duct (Fig. 
 153, 13). Close to the alimentary canal, but not opening into 
 it, is a bright red organ called the spleen (Fig. 153, 20), the 
 function of which is not positively known. 
 
 The Circulatory, Respiratory, and Excretory Systems. The 
 heart is placed in a large pericardial cavity, the posterior wall 
 of which forms a thin membrane separating the heart from the 
 other organs of the body-cavity. Two divisions to the heart 
 may be clearly distinguished, an auricle (Fig. 153, 21) and a 
 ventricle (Fig. 153, 22). The blood, driven from the heart by 
 the contraction of the ventricle, is forced through an artery 
 (the aorta] with a bulbous base (bulbus aorta;, Fig. 153, 23) to 
 the gills, where it is aerated. After aeration the blood is 
 collected into a dorsal artery, which carries it through the 
 bodjr, giving off branches to the various organs. In the 
 capillaries of the different organs it gives up its oxygen, col- 
 lects waste products, and makes its way through the veins 
 to the auricle, whence it enters the ventricle to repeat its 
 
308 GENERAL ZOOLOGY 
 
 circulation. Valves in the heart and in the course of the venous 
 circulation prevent the backward flow of the blood. In addi- 
 tion to the blood, a white fluid (lymph) circulates through 
 the body in vessels called lymphatics. The function of the 
 lymph is supplementary to that of the blood. 
 
 The principal organs of respiration are the gills, eight in 
 number, four on either side. Each gill consists of a bony 
 arch, on the anterior surface of which are teeth-like gill- 
 rakers ; on the posterior surface are the delicate gill-filaments. 
 In this position the filaments are constantly bathed by a cur- 
 rent of water, which passes from the mouth-cavity out beneath 
 the operculum. In the dorsal part of the body-cavity is a 
 large air-bladder (Fig. 153, 19). In the lining of the wall of 
 the air-bladder is a network of blood-vessels, grouped into 
 gland-like " red bodies." By the absorption and formation 
 of gas by these blood-vessels the weight of the fish can be 
 maintained nearly equal to that of the water it displaces. 
 The air-bladder is probably useful also as a reservoir of air, 
 for it has been found that in a perch suffocated in stagnant 
 water the oxygen in the air-bladder, which normally amounts 
 to about one fifth of the volume of the inclosed gas, had 
 been entirely absorbed and replaced by carbon dioxide and 
 nitrogen. In some fishes the air-bladder communicates with 
 the alimentary canal by means of a tube called the pneumatic 
 duct. In the perch this duct is present in early life, but it 
 soon closes, remaining, however, as a fibrous cord (Fig. 153, 18). 
 
 The perch, like other fishes, is usually spoken of as cold- 
 blooded, since its body-temperature is little above that of the 
 surrounding medium. Compared with the higher vertebrates, 
 the birds, for example, very little oxygen is required for 
 respiration, and the circulation is comparatively slow. 
 
 The principal organs of excretion are the M^j/s(Fig.l53,24), 
 placed just above the air-bladder and below the back-bone. 
 From the kidneys two tubes, the ureters (Fig. 153, 25), lead, 
 
309 
 
310 GENERAL ZOOLOGY 
 
 after union, to the urinary bladder (Fig. 153, 26). The con- 
 tents of the urinary bladder are carried to the surface of the 
 body at the urinogenital opening (Fig. 153, 37), just posterior 
 to the anal opening. 
 
 The Skeletal System. So far in our study of the animal 
 kingdom the skeletal, or protecting and supporting, parts have 
 been found chiefly on the outside ; in the fish there is a well- 
 developed internal skeleton formed of bones composed largely 
 of phosphate of lime. Running from head to tail through the 
 body is the back-bone or vertebral column, consisting of a 
 number of separate bones called vertebrae (Fig. 153, 27), and 
 continued into a brain-case or cranium (Fig. 153, 28) at the 
 anterior end. Bones also form the foundation of the upper 
 and lower jaws, and support the gills and tongue. Attached 
 to the back-bone are a number of ribs which inclose and pro- 
 tect the organs of the body-cavity. A row of small bones 
 (interspinals, Fig. 153, 29) supports the unpaired fins. The 
 pectoral and ventral fins are each supported by a framework 
 of bones forming respectively a shoulder-girdle and a hip or 
 pelvic girdle. 
 
 The Nervous and Muscular Systems. Four divisions are quite 
 clearly marked in the brain, the cerebrum (Fig. 153, 32); 
 the two large rounded optic lobes (Fig. 153, 33) ; the medially 
 and dorsally placed cerebellum (Fig. 153, 34) ; and the medulla 
 oblongata, the latter tapering posteriorly into the spinal cord 
 (see Fig. 153, where the medulla is shown though not num- 
 bered). Anteriorly the brain is prolonged into the olfactory 
 tracts (Fig. 153, 30), which communicate with the nostrils ; 
 nerves extend to the different sense-organs and to the various 
 parts of the body. 
 
 The ears of. the perch consist of two closed cavities on 
 opposite sides of the cranium, containing concretions of car- 
 bonate of lime, called otoliths, or ear-stones. There has been 
 some question in the past as to whether fishes could hear, 
 
THE YELLOW PERCH 
 
 311 
 
 but recent experiments seem to show that some, at least, are 
 capable of appreciating sound- vibrations. The ears also serve 
 as organs of equilibration, by aid of which the fish is able to 
 maintain its balance. The sense of touch is located in the 
 skin generally, and in the lateral-line organs. The sense of 
 taste is not greatly developed in the perch, and the eyes 
 are not adapted for vision at any great 
 distance. The organ of smell of fishes is 
 peculiar among vertebrates in that it has 
 no connection with the respiratory system. 
 
 The muscular system con- 
 sists principally of a long, 
 thick muscle on either side, 
 stretching from head to tail. 
 In the young fish this muscle 
 is divided into muscular seg- 
 ments extending vertically 
 and corresponding in number 
 with the vertebrae. As the 
 young fish begins active exist- 
 ence the muscle-segments are Fi. 154. Eggs of Perch before and 
 bent and twisted so that for 
 a portion of their extent they 
 seem to run zigzag. 
 
 The Reproductive System. Both the ovary of the female 
 (Fig. 153, 36) and the spermaries of the male are of large size 
 in the mature perch. They open on to the surface at the 
 urinogenital opening (Fig. 153, 37). 
 
 Development. Early in the spring the adult perch, which 
 have spent the winter in the deepest waters of ponds or lakes, 
 often without feeding very much, draw toward the shore. 
 The colors, especially on the males, begin to brighten, till an 
 adult perch in the full glory of his breeding colors is one 
 of the most beautiful objects in his domain. The time of 
 
 after Egg-Laying. Reduced 
 
 (From Bulletin United States Fish Com- 
 mission) 
 
312 GENERAL ZOOLOGY 
 
 spawning varies with the climate ; in the South it begins as 
 early as March ; in New England, in May. The eggs are laid 
 in shallow water in a ribbon-like mass, which, after absorption 
 of water, is sometimes six or seven feet long and two inches 
 in diameter. This great mass, which contains thousands of 
 eggs (over a hundred thousand have been counted irr a two- 
 pound perch), is fertilized by the male emitting his sperm 
 (milt) over it. The eggs form a large part of the food of 
 other fishes and aquatic birds, and were it not for their great 
 numbers few would ever hatch. In from two to four weeks, 
 depending on the temperature, the young perch hatches from 
 the egg, at first with the yolk-sac attached to the ventral sur- 
 face (compare Fig. 155). After absorption of the yolk-sac, 
 
 which soon occurs, the young 
 perch differs from the adult 
 chiefly in its smaller size and 
 lighter color, and in the rela- 
 tively greater size of head 
 FIG. 155. Young Sturgeon with Yolk- -, n .^ ,, 
 
 Sac. Enlarged. (After Ryder) and e y es as compared With the 
 
 rest of the body. 
 
 Relation to Environment. The whole organization of the 
 perch marks it at once as one of the predatory type of ani- 
 mals, those which hunt their food and depend upon their 
 superior strength or agility to obtain it. As Izaak Walton 
 long ago said of its European relative, the yellow perch is 
 " one of the fishes of prey that, like the Pike and Trout, car- 
 ries his teeth in his mouth, not in his throat, and dare venture 
 to kill and devour another fish." The shape of the body is pre- 
 cisely that which offers least resistance to motion in the water. 
 The strong lateral muscles afford an economical method of 
 applying power for propulsion to the caudal fin, which, by a 
 slight lateral motion, drives the fish forcibly forward. Lateral 
 and median fins assist in maintaining equilibrium, in steering, 
 and in raising and lowering the fish in the water. 
 
THE YELLOW PERCH 313 
 
 The colors of most fishes are protective in their nature, 
 and the perch is no exception to this general rule. From 
 above, the olivaceous back is with difficulty distinguished 
 from the water itself or the bottom below ; from beneath, the 
 white under parts are colored like the surface of the water 
 or the atmosphere above. The mottled sides also serve to 
 render the perch less conspicuous in an environment of lights 
 and shadows among weeds and rocks on the bottom. It has 
 been noted that in some instances where perch live both in 
 a large lake and in its tributaries, as in Lake Michigan and 
 the rivers which flow into it, the lake fish have a tendency to 
 lighter general coloration and to disappearance of the dark 
 vertical bands. It has been suggested that this difference in 
 color is due, in part at least, to the smaller amount of light, 
 combined with the absence of dark lurking-places. 
 
 The study of the mental organization of the perch is beset 
 with many difficulties, though it is of the greatest interest 
 for the light it may throw on problems connected with the 
 mental life of the higher animals; for the perch is a member 
 of the class of fishes, one of the oldest and most generalized 
 of the vertebrates, to which division man himself belongs. 
 Perch are able to learn, and they profit by experience, even 
 though the line along which education can take place is very 
 narrow. In order to test their capacity to learn, two adult 
 perch were kept in an aquarium in which a glass partition 
 was placed several times a week for a period of about a 
 month. Live minnows were introduced on the opposite side 
 of the partition at the times of experimentation. Of course 
 the perch bumped their noses against the glass in a vain 
 attempt to get at the food temptingly displayed at so short 
 a distance. After they had become accustomed to this reac- 
 tion, whenever they made a movement in the direction of 
 the minnows, the glass partition was removed, and they 
 were watched to see if by their actions they seemed to recall 
 
314 GENERAL ZOOLOGY 
 
 the effect which had invariably followed a movement in the 
 direction of the minnows. On the whole, the observer con- 
 cluded that the perch showed strong symptoms of having 
 learned to appreciate the presence of an obstacle, for neither 
 fish made a move in the direction of the minnows when the 
 partition was first removed. The same observer noted that 
 perch are very imitative, a series of motions on the part of 
 one being very likely to be performed by others. This is prob- 
 ably of use in connection with their gregarious life, where 
 the " school " is kept together by each fish watching and fol- 
 lowing the others. 
 
 Sight is probably the best developed sense, though, as 
 already stated, the eyes are not adapted to vision at a great 
 distance. To test the power of sight discrimination, the ob- 
 server quoted above dropped into the aquarium pieces of 
 wireworms (larvae of click-beetles) alternately with similar bits 
 of earthworms. Nearly every time one or more of the bits 
 of wireworm were seized by the perch, only to be dropped 
 a moment later. The fishes did not seem to make any per- 
 manent association between the appearance of the wireworm 
 and its inedible character. 
 
 Perhaps the clearest way to picture the limitations in 
 the mental organization of a fish is to sum up, as Professor 
 Sanford does, some characters in which the fish differs from 
 man. "No fish is ever conscious of himself; he never thinks 
 of himself as doing this or that, or feeling in this way or that 
 way. The whole direction of his mind is outward. He has 
 no language and so cannot think in verbal terms ; he never 
 names anything ; he never talks to himself. As Huxley says 
 of the crayfish, he i has nothing to say to himself or any one 
 else.' He does not reflect; he makes no generalizations. All 
 his thinking is in the present and in concrete terms. He has 
 no voluntary attention, no volition in the true sense, no self- 
 control." 
 
THE YELLOW PERCH 315 
 
 The food of the young perch at first consists entirely of 
 small, delicate crustaceans, such as Cyclops and its allies; 
 from the time the perch are about an inch and a half in length 
 they begin to add insects to the bill of fare. Adult perch have 
 a still more varied diet, consisting of the larger crustaceans, 
 mollusks, and other fishes. The young are gregarious, and 
 those of about the same size tend to keep together, so that 
 every farmer boy knows his chances of catching "a big one" 
 are small indeed when he has his hook in a swarm of little 
 fishes. He has, however, this consolation, that the supply 
 of the one size is likely to last ; for 
 
 Perch, like the Tartar clans, in troops remove, 
 And, urged by famine or by pleasure, rove ; 
 But if one prisoner, as in war, you seize, 
 You '11 prosper, master of the camp, with ease 
 For, like the wicked, unalarmed they view 
 Their fellows perish, and their path pursue. 
 
 OPPIAN, Halieutica. 
 
CHAPTER XXIV 
 THE ALLIES OF THE PERCH : PISCES 
 
 Halcyon prophecies come to pass 
 In the haunts of bream and bass. 
 
 MAURICE THOMPSON. 
 
 Definition of Pisces (L&t. piscia, a fish). The perch is a mem- 
 ber of the class Pis'ces. Fishes are cold-blooded vertebrates, 
 adapted to life in the water. In the lower forms the notochord 
 persists as a continuous rod; in the higher fishes it is replaced 
 by the vertebra. The body is covered with a skin, in which 
 are numerous mucus-glands. Scales are usually present, set 
 in pouches in the skin. In the great majority of forms gills are 
 the only organs of respiration. Locomotion is usually effected 
 by means of fins. With very few exceptions, fishes lay eggs 
 from which the young are hatched ; that is, they are oviparous. 
 
 There is a remarkable uniformity of type in the class when 
 the number of species (about fifteen thousand) and the length 
 of time they have been in existence is considered. Professor 
 Dean, of Columbia University, says : " The evolution of fishes 
 has been confined to a noteworthy degree within rigid and 
 unshifting bounds ; their living medium, with its mechan- 
 ical effects upon fish forms and structures, has for ages been 
 almost constant in its conditions ; its changes of temperature 
 and currents have rarely been more than of local impor- 
 tance, and have influenced but little the survival of genera 
 and species widely distributed ; its changes, moreover, in the 
 normal supply of food organisms cannot be looked upon as 
 noteworthy." 
 
 We shall consider three of the four groups into which the 
 fishes are usually divided. 
 
 316 
 
THE ALLIES OF THE PERCH: PISCES 317 
 
 Sharks and Rays. The sharks and rays, or Elasmobran'chii 
 (Gr. elasmos, plate ; branchia, gills), are fishes with a cartilagi- 
 nous skeleton and with gills which communicate with the 
 surface by several openings, instead of being covered by an 
 operculum, as in the perch. The skin is roughened by small 
 tubercles, which, when closely set, form shagreen, used in 
 the arts for polishing woods and for ornamental work. The 
 tail is usually unequally lobed, the dorsal division being the 
 larger. 
 
 The sharks (Fig. 156) are, with the exception of one species 
 found in Lake Nicaragua, marine animals, and are developed 
 
 FIG. 156. Photograph of Shark. (American Museum of Natural History) 
 
 to the greatest extent in the tropics. The rays, or skates, are 
 more flattened forms, adapted to a life on the bottom of the 
 sea, which they often resemble in color. Fig. 157 shows a 
 species common on the North Atlantic coast, which grows to 
 be about two feet in length. The most famous of the rays 
 are the torpedoes, so called from their power of giving an 
 electric shock. About fifteen species of torpedoes are known, 
 of which one is sometimes found on the eastern coast of the 
 United States. 
 
 Bony Fishes. The bony fishes, or Teleos'tomi (Gr. teleos, com- 
 plete or perfect ; stoma, mouth), in the higher forms, of which 
 the perch is an example, have the skeleton ossified (converted 
 into bone) and the body usually covered with scales ; in the 
 
318 GENERAL ZOOLOGY 
 
 lower forms the body may be covered with bony plates, and 
 the skeleton may be hardly more ossified than in the group 
 which has just been considered. In all teleostomes, however, 
 the gills open beneath a protecting operculum. The order 
 comprises ninety-five per cent of all known fishes. 
 
 FIG. 157. Photograph of Skate 
 
 The garpikes of American waters illustrate one type of 
 body-covering, consisting of bony, enameled, closely set 
 plates, which form a complete coat of armor. The sturgeons 
 (Fig. 158) illustrate another type in which the armor is 
 greatly reduced, the teeth absent, and the animals adapted to 
 bottom-feeding by the development of a beak, and by barbels 
 for feeling for their food in the mud. Sturgeons are found in 
 
THE ALLIES OF THE PERCH: PISCES 319 
 
 Europe as well as in the United States and Canada. One of 
 the European species grows to be over twenty feet long. 
 
 The remaining bony fishes have fully ossified skeletons. 
 The eels are forms in which the body is greatly elongated 
 and the scales reduced to almost invisible rudiments. Loco- 
 motion is effected by snake-like movements of the body. 
 The common eel (Angml'la chrys'ypa) of North America is 
 found along the Atlantic coast from Newfoundland to Central 
 America, and in most streams and ponds in the eastern states 
 
 Fi<;. 158. Photograph of Sturgeon 
 (From Jordan and Evermann's American Food and Game Fishes) 
 
 which are accessible from the sea. The young are hatched 
 on mud-banks in the Atlantic Ocean, often near the mouth 
 of a river. The eggs are laid in the fall, and the young, at 
 the beginning of the second spring, find their way in count- 
 less numbers up the various streams, where they complete 
 their development and return to the sea to spawn. After 
 providing for the new generation the adult eels die, never 
 returning to fresh water. The number of young produced 
 has been estimated, in the case of an eel thirty-two inches 
 long, to be 10,700,000. Eels may grow to be four feet long. 
 
320 
 
 GENERAL ZOOLOGY 
 
 The Atlantic salmon (Sal 1 mo sa'lar) is a well-known food- 
 fish found on the coasts of both Europe and America. Unlike 
 the eel, the salmon spends most of its life in the sea, visiting 
 the fresh water, however, to spawn, in this ascent leaping 
 waterfalls which may be in its way. Leaps of over twelve 
 feet have been recorded. Several allied species of salmon 
 are extensively canned on the Pacific coast. 
 
 The flatfishes (including among other fishes the flounders 
 and halibuts) are a family of compressed fishes, dark on one 
 side and light on the other, which lie on the light side on 
 
 FIG. 159. Flatfish 
 (From Report of Fur-Seal Investigations) 
 
 the bottom of the sea (Fig. 159). When thus placed the 
 dark surface is protectively colored and the eyes are both on 
 the upper side, which is sometimes the right side and some- 
 times the left side of the body. When they are hatched they 
 have an eye on either side and they swim like other fishes, 
 though with a slight leaning to one side, which becomes more 
 and more marked as they develop, till they finally turn entirely 
 over. The eye on the light side has meanwhile worked its 
 way slowly round on to the dark side, where it remains with 
 its fellow, looking upward when the fish lies on the bottom. 
 
THE ALLIES OF THE PERCH: PISCES 
 
 321 
 
 The absence of coloring matter on the side which is in con- 
 tact with the bottom seems to be due to the fact that little 
 or no light reaches it, for when a number of young floun- 
 ders were placed, under experimentation by Professor Cun- 
 ningham of England, so that the under side was illuminated 
 
 by a mirror for four months, 
 nearly all the specimens devel- 
 oped pigment on the skin of 
 that surface. 
 
 The sunfishes are interesting on account of 
 their nest-building habits. They scoop out a space, 
 sometimes three feet across, in the clear sand or 
 gravel in shallow water. Here the eggs are laid, 
 f i^j anc ^ ^ nen g uar( l e d ty both parents, their pug- 
 \ lit? nacity keeping larger fishes at a distance. 
 
 VlfL^ 5 ^ Lung-Fishes. The lung-fishes (Fig. 160), or 
 Dip'noi (Gr. di, two ; pneo, breathe), are fishes 
 with an almost entirely cartilaginous skeleton, 
 and the body is covered with scales instead 
 of with tubercles. The gills are covered by an 
 operculum, and the tail tapers to a point. The 
 structural character of the greatest interest is. 
 suggested in their common name; in place of 
 the air-bladder there is a true lung, or pair 
 of lungs, opening from the ventral side of the 
 alimentary canal. Dipnoans differ from other 
 
 fisheS ' t0 ' in the fact that the heart is incom " 
 pletely divided into three chambers. These ani- 
 
 mals are interesting as the possible ancestors 
 of the toads, frogs, and their allies, which we shall consider 
 later. Though numerous in earlier times, there are but three 
 genera now in existence, one each in the rivers of Queens- 
 land (in Australia), Brazil, and tropical Africa. " The 
 Australian species inhabits rivers which at certain seasons 
 
 Dean) 
 
 Aftfr 
 
322 GENERAL ZOOLOGY 
 
 become fetid with decaying vegetation, and during the time 
 it breathes air." The African and South American species 
 " bury themselves in mud during the dry season, a necessary 
 precaution, since they inhabit swamps which dry up." 
 
 Economic Importance of Fishes. The value to a people of 
 an abundant and cheap fish-supply cannot be overestimated. 
 Recognizing its importance, the United States government 
 has long maintained a Commission of Fish and Fisheries 
 (the name of which has been changed recently to Bureau of 
 Fisheries), which has been active along both practical and 
 scientific lines. Among the subjects which are considered 
 by the bureau are the resources of our inland and coastal 
 waters, the geographical distribution of the economically im- 
 portant fishes inhabiting them, and the study of the natural 
 history of fishes, their enemies, diseases, and the remedies 
 therefor. It has also made statistical researches into the con- 
 dition and commercial value of the fishing industries of the 
 United States, and the methods employed in these industries ; 
 and, perhaps the most important of all, it has carried on the 
 artificial propagation and distribution of valuable species. 
 Thus, during the year ending June 30, 1901, 1,173,833,400 
 fishes and eggs were distributed to different parts of the 
 United States, the principal species being shad, salmon, lake- 
 trout, whitefish, pike, perch, lake-herring, cod, and flatfish. 
 In this way many bodies of water have been restocked after 
 indiscriminate destruction. 
 
 Geographical Distribution of Fishes. A simple and seem- 
 ingly natural classification of fishes, as regards their hab- 
 itat, is a division into fresh-water and marine forms ; and this 
 will serve our purpose if it be remembered that there has 
 been much interchange of species between the two media. 
 In general, the truly fresh-water species of the world vary 
 in connection with the great faunal regions mentioned on 
 page 94. In the North American and Eurasian realms some 
 
THE ALLIES OF THE PERCH: PISCES 
 
 323 
 
 important fresh-water families are the sunfishes (Centrar'chidce), 
 the perches (Per'cidce), and the catfishes (Silur'idce). Many of 
 the salmon and trout are inhabitants of fresh water, though 
 some of the larger species are marine, visiting fresh water 
 only to lay their eggs. The peculiar distribution of the few 
 lung-fishes which have survived the vicissitudes of geological 
 time has already been mentioned. When allied species of 
 animals are widely scattered over the globe in small separated 
 areas, the distribution 
 is spoken of as dis- 
 continuous. 
 
 There are three 
 common divisions of 
 the ocean fauna, - 
 the littoral or shore 
 fauna, the pelagic or 
 open-sea fauna, and 
 the abysmal or deep- 
 sea fauna. The shore 
 fishes never venture 
 far into the open sea. 
 Among them are to 
 be included the large 
 
 members of the salmon family already referred to. The pelagic 
 fishes are mostly hunters of other animals in the sea and are 
 strong swimmers, as befits their environment. Typical fishes 
 of this type are many of the sharks. 
 
 The most peculiar forms belong to the deep-sea fauna. 
 There, of course, the conditions are unusual; life must be 
 adapted to an enormous pressure, to a low temperature (not 
 far above freezing), and to absolute darkness, except where 
 it is lit up by some phosphorescent animal. Hence the fishes 
 found in the deep waters are most bizarre, characterized by 
 uniformity of color-pattern, often black, though brighter 
 
 FIG. 161. Deep-Sea Fish 
 (From Gunther's Fishes) 
 
GENERAL ZOOLOGY 
 
 colors are sometimes developed; by modifications of the 
 eyes, either very large in proportion to the size of the fish, 
 or entirely absent; by the development of tactile and phos- 
 phorescent organs; and by hypertrophy (increase of size) of 
 mouth, jaws, and stomach, which enables the fish to swallow 
 an animal larger than itself. Fig. 161 shows one of these 
 species. 
 
 Geological Development of Fishes. We left the geological 
 history of the development of animal life on the earth at the 
 
 FIG. 162. Devonian Fishes 
 
 end of the Age of Invertebrates. A glance at the map on 
 page 295 will serve to recall the appearance of our continent 
 at that time. In North America the Age of Invertebrates 
 passed slowly and quietly into the Devonian Period, or Age 
 of Fishes. Though numerous kinds of invertebrates already 
 in existence rose into prominence, or passed away to give 
 place to new forms, the chief interest centers about the 
 fishes. Geology gives us no hint concerning the remote an- 
 cffctry of the class. The earliest fossil fishes, which belong 
 
THE ALLIES OF THE PERCH: PISCES 325 
 
 to the latter part of the Age of Invertebrates, are represen- 
 tatives of the sharks and rays, lung-fishes, and, among the 
 bony fishes, forms related to the garpikes of to-day. Thus 
 all the great groups of fishes were in existence very early, 
 with the single exception of the most specialized bony fishes, 
 of which the perch is an example. Fig. 162 shows two spe- 
 cies of Devonian fishes. 
 
 The earliest fossil remains of the sharks and rays are frag- 
 ments of teeth and spines, for the skeleton was not fully 
 ossified and no coat of mail was developed. The shark-like 
 forms rose to great prominence in the course of the Age 
 of Fishes, a little later becoming the predominant type of 
 fishes, of which our species to-day are but the scattered rem- 
 nants. The sharks are especially interesting in that they 
 probably represent most nearly the ancestral condition of 
 all fishes, and hence of all animals with a back-bone. The 
 rays are more modern descendants of the group, adapted to 
 life on the bottom. 
 
 The lung-fishes were also a dominant group very early in 
 the period. By the end of the next succeeding age they had 
 practically disappeared, leaving, as has been noted, but few 
 descendants to-day. Some of them, which have been found 
 in the rocks of Ohio, were giants among fishes ; they were 
 covered with great plates, at least anteriorly, and ranged in 
 length from ten to twenty-five feet. 
 
 Among the gar-forms there are many well-preserved speci- 
 mens, owing to the fact that these fishes were incased in a 
 complete coat of mail formed of closely interlocking bony 
 plates, such as those found in the gaipike and, in vestigial 
 form, in the sturgeon of to-day. 
 
 The other bony fishes, forming ninety-five per cent of all 
 the species of fishes to-day, may well be called modern fishes, 
 since they did not make their appearance till long afterwards, 
 in the Age of Reptiles. 
 
326 GENERAL ZOOLOGY 
 
 The question of the ancestry of the fishes is one of the 
 most interesting problems of zoology. Though, as we have 
 seen, geology fails to answer that question, and probably 
 never will be able to answer it, on account of the presum- 
 ably soft character of the ancestral type ; still, by considering 
 what has been learned from geology, in connection with the 
 facts of embryology, it will be possible to trace the evolu- 
 tion of certain organs. 
 Thus the scales, which 
 form so characteristic 
 
 a covering of most 
 FIG. 163. Dermal Fold of Fish. (After fighes to . day? can be 
 
 Wiedersheim) . . 
 
 traced to their origin 
 
 in limy tubercles, like those forming the shagreen of sharks. 
 Teeth originated from the same structures along the margin 
 of the mouth. The fins are looked upon by some ichthyol- 
 ogists (students of fishes) as remnants of a once continuous 
 fold of skin (Fig. 163) ; others regard these structures as 
 having originated from external gills, or from modified gill- 
 arches. Gills first arose as slits in the wall of the alimentary 
 canal, and the air-bladder is a branch of the same structure. 
 
 The land area of North America did not greatly change 
 throughout the Age of Fishes, though a gradual increase in 
 size is to be noted, preparing the way for a greater develop- 
 ment of land animals and plants, to which reference will be 
 made after some study of the frog and its allies in the follow- 
 ing chapters. 
 
CHAPTER XXV 
 THE GREEN FROG 
 
 Cardanus undertakes to give reason for the raining of Frogs ; but if it 
 were in my power, it should rain nothing but Water Frogs, for those, I think, 
 are not venomous. IZAAK WALTON, The Complete Angler. 
 
 Habitat and Distribution. The green frog (Ra'na dam'itans) 
 is one of the commonest species of frogs in the eastern United 
 States. It frequents the neighborhood of springs and meadow 
 
 FIG. 164. Photograph of Bullfrog. Reduced 
 
 brooks, and may be distinguished from its larger relative, the 
 bullfrog (Rana catesbia'na, Fig. 164), by the presence of two 
 glandular folds of skin along the sides of the back. 
 
 External Structure. The body is divisible into a head and 
 trunk ; there is no visible tail. The body-covering is a soft, 
 
 327 
 
328 GENERAL ZOOLOGY 
 
 smooth skin without scales, abundantly supplied with mucus- 
 glands. There are four appendages, the limbs, the anterior 
 of which are divisible into upper arm, forearm, and hand; the 
 posterior, into thigh, lower leg, and foot. The hand ends in 
 four short fingers; the foot, in five toes, joined by a web. Both 
 fingers and toes are often spoken of as digits. The eyes are 
 situated prominently on the top of the head, and possess, 
 in addition to an upper eyelid, a thin fold of skin called 
 the nictitating membrane, which can be drawn across the eye- 
 ball from below. There is no true lower eyelid. In front of 
 the eyes, near the anterior end of the head, are the external 
 openings of the nostrils; posterior to the eyes are smooth, 
 round spots, the tympanic membranes, the outer portions of 
 the frog's ears. 
 
 The Digestive System. The wide mouth-cavity (Fig. 165, 1) 
 narrows into the short, straight oesophagus (Fig. 165, 6). 
 Conical teeth are placed along the edge of the upper jaw 
 (Fig. 165, 2) and on the roof of the mouth. A thick, fleshy 
 tongue (Fig. 165, 3), notched posteriorly, is attached by its 
 anterior margin to the ventral surface of the mouth-cavity. 
 The tongue can be thrust out suddenly for quite a distance 
 to capture food, which consists largely of insects, worms, and 
 mollusks. Two openings lead from the mouth to the nostrils 
 (Fig. 165, 4), and two openings (the Eustachian tubes, Fig. 
 165, 5) communicate with the ears. The stomach (Fig. 165, 7) 
 is a thick-walled sac tapering gradually into the coiled small 
 intestine (Fig. 165, 8). Beyond the small intestine the ali- 
 mentary canal suddenly increases in diameter, forming the 
 large intestine or rectum (Fig. 165, 9), which passes without 
 change of diameter into the terminal cloaca (Fig. 165, 10), 
 communicating with the surface at the cloacal opening (Fig. 
 165, 11). Between the lobes of the liver (Fig. 165, 13) lies a 
 large gall-bladder (Fig. 165, 14). A pancreas (Fig. 165, 15) 
 and a spleen (Fig. 165, 16) are present. 
 
329 
 
330 GENERAL ZOOLOGY 
 
 The Circulatory, Respiratory, and Excretory Systems. The 
 heart inclosed in its sac, the pericardium (Fig. 165, 17), has 
 one chamber more than the heart of the perch, by the divi- 
 sion of the auricle into two parts, a right and left auricle 
 (Fig. 165, 20, 18). The blood is aerated in the lungs (Fig. 165, 
 25, 26), the walls of which are traversed by the capillaries of 
 the blood-system. The lungs communicate with the exterior 
 by means of the windpipe or trachea (Fig. 165, 24), opening 
 into the mouth by a narrow slit, the glottis (Fig. 165, 23). 
 
 Owing to the additional chamber in the heart and the 
 presence of lungs, the course of circulation in the frog is 
 somewhat different from that in the perch. The aerated 
 blood returned from the lungs by the pulmonary veins is 
 poured into the left auricle ; the non-aerated blood from all 
 over the body is returned to the right auricle. The auricles 
 contract at the same instant, forcing both venous and arterial 
 blood into the ventricle (Fig. 165, 19), which in turn con- 
 tracts before there has been much mixing of the two kinds 
 of blood, emptying its contents into the arterial circulation, 
 the beginnings of which are shown in Fig. 165, 21 and 22. 
 As the arterial system takes its rise from the right side 
 of the ventricle, the first blood to enter the arteries is non- 
 aerated. Owing to the less pressure in the arteries which 
 supply the lungs and skin, and the presence of valves which 
 cut the blood off from easily entering the arteries that supply 
 the head and body, most of the non-aerated blood goes to the 
 lungs and skin. The blood which follows is a mixture of 
 aerated and non-aerated blood, and the pressure being raised 
 by the presence of non-aerated' blood in .the capillaries of the 
 lungs and skin, this blood forces the valves aside and makes 
 its way to the different parts of the body, except the head. 
 In the course of the artery leading to the head is a structure 
 (the carotid gland) which temporarily obstructs the flow of 
 blood till the body-arteries have become filled ; and the supply 
 
THE GREEN FROG 331 
 
 of mixed blood having become exhausted, the head receives 
 only aerated blood. The impure blood from the organs of the 
 body-cavity and from the hind legs returns either through 
 the liver or the kidneys ; while that from the head, the fore 
 limbs, and from the skin and muscles generally, is poured 
 directly into the right auricle. 
 
 The frog breathes with the mouth closed. By depressing 
 the tongue, air is drawn into the mouth-cavity through the 
 nostrils. When the tongue is raised the nostrils close by 
 valves and the air is forced into the lungs. Considerable 
 exchange of gases takes place through the soft, moist skin, 
 which is well supplied with blood-vessels (Fig. 165, 28). 
 
 The lymphatic system is well-developed in the frog, and 
 the lymph is assisted in its circulation by two pairs of 
 lymph-hearts, one at the posterior end of the body, and one 
 in the region of the shoulders. The pulsations of the pos- 
 terior lymphs-hearts can be observed externally in the living 
 frog. 
 
 The kidneys (Fig. 165, 29) are a pair of oval, dark-red 
 bodies lying in the dorsal part of the body-cavity. The ureters 
 (Fig. 165, 30) open from them into the cloaca (Fig. 165, 31). 
 The urinary bladder (Fig. 165, 32) is a large, thin-walled sac 
 projecting ventrally from the cloaca, and is a very different 
 organ from the urinary bladder of the perch, which is a dila- 
 tation of the ureter. The function of the two organs is, how- 
 ever, the same, that of receiving the liquid nitrogenous waste 
 from the kidneys. 
 
 The Skeletal System. In general, the skeleton of the frog 
 is built upon the plan seen in the perch, but its appendages 
 are considerably more specialized. The skull (Fig. 166, 1) 
 is flattened and the cranium articulates with the first verte- 
 bra by two surfaces, or condoles. The vertebral column consists 
 of nine vertebrae, terminated by a long bone called the urostyle 
 (tail-bone) (Fig. 166, 3). 
 
3 
 
 11 
 
 FIG. 106. Skeleton of Frog. Natural size. (After Duges) 
 
 1, skull; 2, vertebral column; 3, urostyle; 4, scapula; 5, hmnerus; 6, radius and 
 ulna; 7, carpus; 8, metacarpals ; 1), phalanges of fore leg; 10, pelvic girdle; 
 11, femur; 12, tibia and fibula; 13, tarsus; 14, metatarsals ; 15, phalanges of 
 hind leg ; 16, rudimentary toe 
 
 332 
 
THE GREEN FROG 333 
 
 The bones of the arms are attached to a shoulder-girdle 
 consisting of the shoulder-blades or scapulas (Fig. 166, 4), two 
 coracoids, and two collar-bones or clavicles. A broad breast- 
 bone (sternum) extends a short distance along the median 
 ventral line. Each of the anterior limbs contains one bone in 
 the upper arm, called the humerus (Fig. 166, 5); one bone 
 in the forearm, composed of two bones united, the radius 
 and ulna (Fig. 166, 6) ; six bones in the wrist-region, or car- 
 pus (Fig. 166, 7); four complete sets of bones in the palm 
 (metacarpals, Fig. 166, 8) ; and four complete sets of finger- 
 bones (phalanges, Fig. 166, 9). The metacarpals arid phalanges 
 of the inner digit are rudimentary. 
 
 The leg-bones are attached to the vertebral column by 
 means of a hip 01 pelvic girdle (Fig. 166, 10), of peculiar shape. 
 The skeleton of each leg consists of one bone in the upper, leg, 
 the femur (Fig. 166, 11); one bone in the lower leg, formed 
 from two bones united, the tibia and fibula (Fig. 166, 12) ; five 
 bones in the ankle-region, or tarsus (Fig. 166, 13) ; and five 
 complete sets of phalanges (Fig. 166, 15). A sixth rudimen- 
 tary digit is also present (Fig. 166, 16), consisting of one 
 metacarpal bone and two phalanges. 
 
 The Nervous and Muscular Systems. The nervous system 
 is similar in general plan to that of the perch. The brain has 
 large cerebral hemispheres (cerebrum, Fig. 165, 43), each of 
 which is prolonged anteriorly into an olfactory lobe (Fig. 
 165, 42). The optic lobes (Fig. 165, 44) are also large, but the 
 cerebellum (Fig. 165, 45) is small. Behind the cerebellum is 
 the medulla oUongata (Fig. 165, 40), at the posterior end of 
 which the spinal cord (Fig. 165, 47) arises. The nerves are not 
 shown in the dissection. The muscles are arranged in bands 
 or spindle-shaped masses instead of in segments, and the frog 
 is capable of much more complex movements than the perch. 
 
 The Reproductive System. The spermaries of the male 
 frog (Fig. 165, 49) are bean-shaped bodies lying beneath the 
 
334 GENERAL ZOOLOGY 
 
 kidneys, to which they are attached. The ovaries of the female 
 frog when mature fill up a large portion of the body-cavity. 
 Attached to the anterior end of the spermaries and ovaries 
 are the fat-bodies (Fig. 165, 34), lobed organs which attain 
 their fullest development in the spring. These organs are 
 believed to be of use as storehouses of reserve material, ren- 
 dering possible the formation of large numbers of sperma- 
 tozoa, or eggs, without complete exhaustion of the animal. 
 After the spawning season the fat-bodies decrease in size. 
 
 Development. The eggs of frogs (Fig. 167, 1, 2, 3) are laid 
 early in the spring in shallow water in large, jelly-like masses. 
 They are fertilized by the male as they leave the body of the 
 female. Within a week or ten days they hatch, the time 
 required depending largely upon the temperature of the water. 
 At first the young is blind, and is without gills or a mouth; it 
 fastens itself to weeds and other objects in the water by means 
 of a crescent-shaped, adhesive apparatus at the anterior end 
 (Fig. 167, 4). Certain areas of the body are covered with 
 cilia, by the vibration of which the animal is able, even with- 
 out using its tail, to go forward in the water. Eyes, external 
 gills, and a mouth provided with horny jaws soon appear, 
 and the young, now the familiar tadpole, begins to feed on 
 plant food (Fig. 167, 5). The -alimentary canal is long and 
 coiled, as it usually is in animals which feed upon plant 
 material. The heart has two chambers. 
 
 As the tadpole increases in size (Fig. 167, 6) the first or 
 primary gills are replaced by secondary gills, which soon be- 
 come covered with a fold of skin, the operculum. The growth 
 of the operculum continues till the gill-openings are covered, 
 leaving a small hole usually on the left side. In this fish-like 
 condition the tadpole continues through the summer, and on 
 the approach of cold weather buries itself in the mud, where 
 it hibernates. In some species of frogs the tadpole develops 
 into the adult form in the course of a single season. 
 
FIG. 167. Development of Frog 
 
 1, 2, 3, eggs; 4, young immediately after hatching; 5, tadpole with external gills 
 6, 7, 8, 9, 10, and 11, further stages of development; 12, frog 
 
 (From Baskett's Story of the Amphibians and Reptiles) 
 335 
 
336 GENERAL ZOOLOGY 
 
 If the adult condition has not been reached, the tadpole 
 continues its growth the following summer. The hind legs 
 appear (Fig. 167, 7, 8), and grow to be about an inch long, 
 when the fore legs suddenly appear (Fig. 167, 9, 10). The 
 front legs are really formed as early as the hind legs, but they 
 are kept beneath the skin for a while. The broad and com- 
 pressed tail, which forms the tadpole's chief organ of loco- 
 motion, is gradually absorbed, and the young frog finally hops 
 out on land with only a stump of a tail remaining (Fig. 167, 11). 
 By the time these changes have taken place externally, im- 
 portant changes have gone on inside : the gills have been 
 replaced by lungs ; one of the chambers of the heart has been 
 divided; the intestine has become shorter, fitting the frog 
 better for an animal-diet; and the horny jaws have given 
 place to a wide mouth with teeth. This metamorphosis is 
 retarded by cold, and accelerated by rest and freedom from 
 disturbance of the water. The frog (Fig. 167, 12) grows for 
 several years without further metamorphosis, except the 
 gradual disappearance of the stump of the tail. Through- 
 out life the outer skin is cast periodically in a single piece 
 and immediately devoured. 
 
 Relation to Environment. The dark-green and brown colors 
 of the upper surface afford considerable protection among the 
 water-plants and along the muddy or grassy margins of ponds 
 and streams, and the white under surface may be similarly 
 useful in the water. 
 
 The green frog is a voracious feeder, and varies its diet 
 with almost every kind of small creature which comes its 
 way, not hesitating in the least to devour smaller individuals 
 of its own kind. Usually only moving objects are seized, and 
 it has been said that the frog may starve to death in the 
 midst of an abundance of food if there is no movement to 
 attract its attention. The eyes are situated high on the top of 
 the head, where they maintain a wide survey. Every boy in 
 
THE GREEN FROG 337 
 
 the country knows of the difficulty of approaching these alert 
 creatures, and he knows, too, how to capture them by dang- 
 ling a hook with a piece of red flannel in front of them. 
 Even if well fed the frog seems to find the moving object irre- 
 sistible, and seizes it with wide-open mouth. The tongue is 
 covered with a sticky substance, and can be swiftly extended 
 with unerring aim to a distance of several inches. 
 
 While the frog depends very largely on the sense of sight 
 to warn it of approaching enemies or enable it to distin- 
 guish food, the sense of hearing is also of considerable value. 
 Dr. R. M. Yerkes, of Harvard University, who has studied 
 the sense of hearing in frogs both in the laboratory and in 
 the field, says that he is convinced that sounds which are of 
 importance in the life of the animal, as the splash made by 
 a frog jumping into the water, are not only heard, but that 
 such sounds serve to put other frogs on their guard. The 
 croaking of male frogs in the spring is undoubtedly heard 
 by the female, and serves to make mating more certain. 
 
 The observer just quoted does not give the green frog 
 credit for much intelligence, as his experiments seem to 
 show that nearly all the frog's actions are repeated with 
 machine-like accuracy, and new habits are learned very 
 slowly. He is inclined to think that even the perch learns 
 more rapidly than the frog. He also notes that the frog is 
 very timid, and that fright tends to lengthen the process of 
 learning. 
 
 When suddenly touched, the frog may do one of several 
 things: it may jump, using the strong hind legs sometimes 
 with force enough to carry it several feet ; it may remain 
 perfectly quiet ; or it may crouch with its head close to 
 the ground, at the same time puffing itself out. This last 
 action, Dr. Yerkes has noticed, more often takes place when 
 the animal is touched in front, and is probably useful to 
 render seizure difficult, or to prevent it altogether. If the frog 
 
338 GENERAL ZOOLOGY 
 
 leaps away, it is usually into the water with a loud "plunk." 
 A few swift strokes of the hind legs serve to carry the ani- 
 mal to shelter beneath protecting debris in the water. There 
 it is able to remain for a considerable period without the 
 necessity of rising to the surface for oxygen, owing to the 
 low state of all the life-processes. The frog has numerous 
 enemies, among which are owls, hawks, and herons, many 
 snakes and other reptiles, and several fur-bearing creatures 
 which come to the water in search of food. 
 
 During the winter green frogs, like some other frogs, 
 hibernate in the mud at the bottom of pools. With return- 
 ing spring they congregate to lay their eggs, and the males 
 may then be heard calling to the females in an unmusical 
 u chung," "chung," which is not as familiar a sound, per- 
 haps, as the bass voice of the bullfrog or the high-pitched, 
 insistent note of the spring " peepers " (p. 344). After provid- 
 ing for the reproduction of the species, the green frog spends 
 the rest of the summer in its rather solitary life on the bank 
 of some stream or spring-hole. 
 
CHAPTER XXVI 
 THE ALLIES OF THE FROG : AMPHIBIA 
 
 Blue dusk, that brings the dewy hours, 
 Brings thee, of graceless form in sooth 
 
 Dark stumbler at the roots of flowers, 
 Flaccid, inert, uncouth. 
 
 EDGAR FAWCETT, A Toad. 
 
 Definition of Amphibia (Gr. amphibios, capable of living in 
 both air and water). The frog belongs to the class Amphib'ia, 
 to which belong also the toads, newts, and salamanders. Am- 
 phibians are cold-blooded vertebrates covered with a smooth 
 or rough, moist skin, in which are numerous mucus-glands. 
 In the immature state amphibians are adapted to a life in 
 the water, and breathe by gills ; when adult the gills are in 
 the majority of cases absorbed, and the animals breathe by 
 lungs. Four limbs are usually present. Nearly all amphibians 
 are oviparous. 
 
 Two out of the three orders into which the class is divided 
 will be discussed here. One of these orders includes the sal- 
 amanders and newts, the other the toads and frogs. 
 
 Salamanders and Newts. The Urode'la (Gr. oura, tail; delos, 
 conspicuous) are elongate forms, with rounded or compressed 
 tail. They are often, but erroneously, called lizards, and 
 resemble the latter only in external form. The eggs are laid 
 usually in the water in strings, or in large masses resembling 
 frogs' eggs, or singly, attached to the leaves of water-plants. 
 Salamanders and newts hatch as tadpoles, which develop into 
 the adult form without a strongly marked metamorphosis. The 
 young of our common eastern species may be distinguished 
 from the tadpoles of the toad, and from those of our vari- 
 ous species of frogs, by their more elongate form, and by 
 
340 
 
 GENERAL ZOOLOGY 
 
 the presence, usually, of two short, rod-like organs, called 
 " balancers," which project from the anterior end of the body 
 near the mouth. The balancers may serve as sense-organs of 
 touch, or as adhesive disks, in addition to 
 the use suggested by their name. The gills 
 are usually visible externally for a longer 
 period than is the case with the toad and 
 the frogs. Some species retain their gills 
 throughout life, though the lungs are also 
 functional ; in others, though the gills are 
 absorbed in adult life, the gill-openings are 
 retained ; in still others all traces of gills 
 and gill-slits disappear; and, finally, a few 
 species lose their lungs also, when mature, 
 depending entirely upon the skin for res- 
 piration. 
 
 Of the five species which retain their gills 
 throughout life, three are found in the sur- 
 face-waters of the eastern and southeastern 
 United States, and one in the subterranean waters of Austria 
 and Texas respectively. Both the cave-inhabiting species live 
 in absolute darkness, far below the surface of the earth, and 
 are colorless and blind. The white skin is sensitive to light, 
 and has been changed to a black color after several months of 
 exposure under ordinary conditions. Fig. 168 shows the Texan 
 cave salamander (TypJdomoVge rath'buni) from an artesian well 
 one hundred and eighty-one feet below the surface. 
 
 The genus Amblydtoma includes some of the largest of 
 our species, known by the common name of blunt-nosed sal- 
 amanders. The color is black, spotted with yellow. As these 
 salamanders are protected by an acrid secretion from the 
 mucus-glands of the skin, the conspicuous colors are possi- 
 bly to be interpreted as warning coloration. The adults live 
 in damp places and lay eggs in the water in large masses 
 
 FIG. 168. Cave Sala- 
 mander. Slightly 
 Reduced. (After 
 Eigenmann) 
 
THE ALLIES OF THE FROG: AMPHIBIA 341 
 
 resembling frogs' eggs, though the jelly-like mass which sur- 
 rounds them is more opaque. The young keep their gills for 
 a considerable period, and one species, called the axolotl 
 (Amblystoma tigri'num, Fig. 169), found from New York to 
 California and Mexico, may even breed in the gill-bearing 
 larval stage. These immature forms live in the water, grow- 
 ing to be eight or nine inches long, or, in exceptional cases, 
 even larger, and may continue in this condition for years, with- 
 out ever changing to the adult form. An observer who has 
 
 FIG. 169. Photograph of Young Axolotl. Reduced. (By H. V. Letkemann) 
 
 had opportunity to study axolotls in their native habitat says 
 that the change to the adult condition is hastened by abun- 
 dance of food, and by the partial drying up of the water and 
 consequent increase in temperature of the water which remains. 
 Like some other amphibians these salamanders can regen- 
 erate lost limbs. This, according to Professor Gadow, of Cam- 
 bridge, England, takes place more certainly and quickly the 
 younger the animal is. In one case quoted by this authority 
 
342 
 
 GENERAL ZOOLOGY 
 
 the hand of an axolotl ten years old was removed, and it 
 was replaced within twelve weeks. Often more than the 
 usual number of digits is replaced ; this tendency is greatest 
 in those cases where the limb is cut off close to the body. 
 
 The Alpine salamander (Salaman'dra a'tra), found in moist 
 places two thousand feet in altitude, especially near water- 
 falls, in the Alps of Europe, is remarkable for its breeding- 
 habits. Only two young are produced at a time, and these 
 are born alive at an advanced stage of development. During 
 
 FIG. 170. Development of Newt. Reduced. (After Gage) 
 
 A, Egg on water-plant; Ji, larva (in August); C, young, in autumn; D, about 
 two years old ; E, adult 
 
 the time they are within the mother's body they are nour- 
 ished by the nutritive matter from several eggs, which only 
 partially develop. 
 
 The newts, or tritons, are carnivorous salamanders which 
 are more or less aquatic in their habits when adult, or, at 
 least, during the breeding-season, at which time also the colors 
 of the males in some species become brighter, and a crest is 
 developed along the back. The common species of the eastern 
 United States (Diemy c' tylus virides' cens, Fig. 170) is olive- 
 green or reddish in color, with a compressed tail and a row of 
 small orange-colored spots along the right and left sides of 
 the body. It grows to the length of three and a half inches. 
 The eggs (Fig. 170, A) are laid during April, May, or June, 
 usually in the axils of leaves of water-plants, and the leaves 
 are drawn together and made into a compact mass by a 
 
THE ALLIES OF THE FROG: AMPHIBIA 343 
 
 secretion from the oviduct. As a general rule one egg is laid at 
 a time ; occasionally two are inclosed in the same mass. The 
 young hatch in from twenty to thirty-five days, depending 
 on the temperature. In August they resemble Fig. 170, B. 
 Late in the fall they leave the water and live on land in 
 damp places beneath logs and leaves in the woods. They 
 are then of a beautiful red color and have a cylindrical tail 
 (Fig. 170, C). Several years are required to produce the 
 aquatic adult form (Fig. 170, E). 
 
 Toads and Frogs. The members of the order Anu'ra (Gr. an, 
 without; oura, tail) undergo a well-marked metamorphosis. 
 They are tadpoles at first, and later change to the adult 
 condition by the absorption of the tail and the development 
 of legs. 
 
 Many examples of peculiar breeding-habits are known. 
 The female of a Brazilian species of tree-frog (Hy'la fa'ber) 
 lays her eggs within a circular wall of mud which she con- 
 structs on the bottom of a shallow pool of water. Within 
 this nursery the tadpoles develop, unless liberated by the 
 rain or other accident. Several species lay their eggs on the 
 leaves of trees above the water, into which the young fall 
 when hatched. The male of the obstetrical toad of Europe 
 (Al'ytes obstet'ricus) winds the eggs around his legs, and, seek- 
 ing a safe place, guards them till they hatch. In a South 
 American species, the famous Surinam toad (Pi 1 pa ameri- 
 ca'na), the eggs are spread by the male over the back of the 
 female, where each egg becomes covered with a growth of 
 skin, forming a pouch with a lid. Here development goes 
 on, and the entire metamorphosis takes place within the 
 egg. In a Chilian species (Rhinoder'ma Darwin'ii) the eggs 
 are transferred by the male to vocal sacs at the side of the 
 mouth, which become greatly developed at the breeding- 
 season. Metamorphosis takes place within these sacs, and 
 the young escape in the adult condition. In half a dozen 
 
344 
 
 GENERAL ZOOLOGY 
 
 species of tree-frogs from South America (Nototre'ma) the 
 females possess dorsal pouches in which the eggs are placed. 
 The young appear either as tadpoles or as perfect frogs. 
 
 The tree-frogs or tree-toads are forms adapted to an arbo- 
 real existence. They possess soft pads on the end of the 
 
 digits. Many of 
 them, like our 
 common tree-toad 
 (Hyla versic'olor, 
 Fig. 171), are pro- 
 tectively colored, 
 and have the 
 power of chan- 
 ging their color 
 through various 
 shades of gray and 
 green. A South 
 American species 
 is conspicuously 
 marked with red 
 and blue. Experi- 
 ments seem to 
 show that it is so 
 well protected by 
 an acrid secretion 
 that it is not fed 
 
 upon by birds, which might otherwise devour it. Several of 
 our smaller species of tree-toads, called " peepers " in the 
 country, give utterance to shrill notes, which are among the 
 first sounds of spring. In that season they seek the ponds to 
 mate and lay their eggs. 
 
 The common toad (Bu'fo lentigino'sus) is one of the farmers' 
 most valuable allies in the destruction of injurious insects. 
 Despite the prejudice which its appearance still excites among 
 
 Fi<;. 171. Photograph of Tree-Frog. Reduced 
 
THE ALLIES OF THE FROG: AMPHIBIA 345 
 
 those who do not understand it, the animal is a most inter- 
 esting object for study. There is no truth in the oft-repeated 
 statements of its poisonous qualities, except in so far as the 
 acrid secretion of the skin, which is a protection to many 
 amphibians, might be injurious if it gets on sensitive sur- 
 faces, such as the lining of the eyelids. The dark-colored 
 eggs are laid in long strings, like a string of beads, in shal- 
 low water, usually in April, in the latitude of New York. 
 They hatch in two or three weeks into small black tadpoles, 
 which pass through their transformation within about two 
 months. 
 
 Geological Development of Amphibians. As time passed on 
 from the Age of Fishes a large portion of the great interior 
 sea of North America, shown on the map, page 295, became 
 a region of swamps, though many times depressed and exposed 
 to the inroads of the sea. These conditions brought about the 
 formation of the great coal-beds of the continent, alternating 
 with beds of shale, sandstone, and clay. When the land was 
 above the surface of the 
 water, vegetation flour- 
 ished in more than tropi- 
 cal luxuriance ; when the 
 land was depressed, the 
 
 ocean-waters rolled in 
 
 FIG. 172. Skull of Labyrmthodont 
 
 and destroyed the life of 
 
 the land. The swamps of that time are the coal-beds of 
 to-day, and the period is known as the Carboniferous Age 
 or Age of Coal Plants. Though fishes and many invertebrate 
 forms were abundant, progress had been made over pre- 
 ceding periods in the development of back-boned creatures 
 adapted to breathing air. These were amphibians, and from 
 the prevalence of species of this order the period is often called 
 the Age of Amphibians. There were snake-like forms without 
 limbs, and forms with every degree of limb-development. 
 
346 
 
 GENERAL ZOOLOGY 
 
 Some species grew to be as large as alligators. Their skulls 
 (Fig. 172) were solidly roofed over with bone. Their teeth, 
 in many cases, showed complicated foldings of the enamel ; 
 hence they have been called labyrinthodonts, i.e. labyrinth- 
 toothed (Fig. 173). There is little doubt that the labyrinth- 
 odonts descended from the fishes. Anurans and urodeles did 
 not appear till later. Both are probably descended from the 
 labyrinthodonts, each by its own line of ancestry. 
 
 The close of the 
 Age of Amphibi- 
 ans is marked by a 
 great change in the 
 topography of North 
 America, for it was 
 
 Appalachian system 
 of mountain ranges 
 was uplifted. This 
 brought a great area 
 of land in eastern 
 North America above 
 FIG. 173. Section of Tooth of Labyrinthodont ^e l eve l o f the sea, 
 
 (From Baskett's Story of the Amphibians and as jg shown on the 
 Reptiles) . _ . x ^ T 
 
 map (Fig. 174). No 
 
 species of animal of earlier time is known to have existed 
 after this upheaval. The causes underlying the culmination 
 and decline of so many species at this time are not thor- 
 oughly understood. They are probably connected with the 
 changes already spoken of, with the decline in the temper- 
 ature, and with the slow removal of carbon dioxide from 
 the atmosphere. 
 
 Paleozoic Time : Era of the Ancient Forms of Life. The 
 geological periods so far considered since the close of Archrean 
 Time (see pp. 295, 324, and 345) are usually grouped under 
 
THE ALLIES OF THE FROG: AMPHIBIA 347 
 
 the general heading of Paleozoic Time, or the Era of the 
 Ancient Forms of Life. The paleozoic invertebrate world 
 was peculiar in its corals, crinoids (p. 246), trilobites (p. 153), 
 brachiopods (p. 233), mollusks of the orthoceras-type (p. 193), 
 and in its insects, which were largely of those groups which 
 develop without metamorphosis. Among the vertebrates, 
 the fishes represented were sharks and rays, gar-forms and 
 
 FIG. 174. North America after the Appalachian Revolution 
 (From Dana's Manual of Geology) 
 
 lung-fishes. The Appalachian revolution wiped the trilobites 
 entirely out of existence ; the corals and orthoceras-forms 
 disappeared soon after, with but? few exceptions ; the brachio- 
 pods were much diminished in numbers ; and the insects 
 which developed without strongly marked metamorphosis 
 after hatching dwindled away before the rapid rise of forms 
 which underwent a complete metamorphosis. The sharks, 
 rays, gars, and lung-fishes of the era became extinct as the 
 higher bony fishes began to people the sea. 
 
CHAPTER XXVII 
 THE PINE-LIZARD AND ITS ALLIES : REPTILIA 
 
 I only know thee humble, bold, 
 Haughty, with miseries untold, 
 And the old curse that left thee cold, 
 And drove thee ever to the sun 
 On blistering rocks. 
 
 BRET HARTE, The Rattlesnake. 
 
 THE PlNE-LlZARD 
 
 Habitat and Distribution. The pine-lizard (Scelop'orus un- 
 dula'tus, Fig. 175), or swift as it is often called, is found in 
 the eastern United States as far north as Michigan, prefer- 
 ring the more sandy areas covered with pine. It is a graceful 
 little creature about seven inches long, gray in color above, 
 with faint undulating black stripes, and silvery white below. 
 The male is ornamented with lustrous patches of blue or 
 green, edged with black on the sides of the throat and under 
 surface of the body. Old fences which border pine-lands are 
 favorite resorts, and here it pursues and captures countless 
 insects. Like others of its kind this lizard loves the sun, and 
 is to be found active only in the hottest part of the day. 
 During the cold weather it hibernates, at least in the northern 
 part of its range. 
 
 External Structure. The body is elongate in form, resem- 
 bling that of the salamanders, but the skin is covered with 
 scales instead of being smooth, and there are no mucus-glands. 
 The digits of the four legs are long and slender, and have 
 sharp claws, which are admirably fitted for clinging to in- 
 equalities in the bark of trees. The gray color of the back is 
 protective when the lizard is at rest, and its movements are 
 
 348 
 
PINE-LIZARD AND ITS ALLIES: REPTILIA 349 
 
 so quick that it is difficult for the eye to follow them. When 
 alarmed the scales can be raised, the throat patches swollen, 
 and the head elevated. The harmless little creature then 
 looks quite formidable. In order to provide for growth the 
 scaly skin is cast periodically. 
 
 Internal Structure. The internal structure is, in general, 
 similar to that of the amphibians, but in several respects it 
 
 FIG. 175. Pine-Lizard. Reduced 
 
 indicates a higher type of animal. Thus, the lizard 
 breathes by lungs at all periods of its life. The 
 heart has a longitudinal partition extending par- 
 tially through the posterior chamber (Fig. 176, 19), 
 so that there is an incomplete separation into right 
 and left ventricles. As in the frog, the left auricle (Fig. 176, 18) 
 receives aerated blood returned from the lungs (Fig. 176, 30) 
 by the pulmonary veins (Fig. 176, 24) and the right auricle 
 receives the blood from the rest of the body (Fig. 176, 25). 
 From the right side of the ventricle arises the pulmonary 
 artery (Fig. 176, 23) ; from the left side are given off the 
 branches of the artery supplying the head and body generally 
 (Fig. 176, 20, 21, 22). When both auricles contract, the venous 
 blood in the right auricle tends to keep to that side of the 
 heart, and, by the aid of the incomplete partition, is forced 
 into the pulmonary artery; the arterial blood from the left 
 
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 350 
 
PINE-LIZARD AND ITS ALLIES: REPTILIA 351 
 
 auricle, with some admixture of venous blood, is driven to 
 the arterial branches supplying the head and body generally. 
 The nervous system, especially the brain, is also more highly 
 differentiated than in the amphibians, and the bones are more 
 completely ossified. A skeletal difference is the articulation 
 of the cranium to the first vertebra by means of a single con- 
 dyle. A study of Fig. 176 will make clear the relation of the 
 most important organs. 
 
 Development. The female pine-lizard lays her eggs in the 
 ground, a short distance below the surface ; ten or fifteen 
 eggs are deposited in each lot. The eggs are oblong in shape, 
 from fourteen to eighteen millimeters (a little over half an 
 inch) in length, and are roughened on the surface, causing 
 dirt to adhere to them. One lot brought to an observer in 
 North Carolina late in the month of June had been plowed 
 up. The eggs increased in size as the embryo developed, 
 finally hatching in about two months. The young resemble 
 the adult quite closely in everything but size. They are able 
 to take care of themselves from the first. 
 
 THE ALLIES OF THE PINE-LIZARD: REPTILIA 
 
 Definition of Reptilia. The pine-lizard will serve as an 
 example of the class Reptil'ia (Lat. repere, to creep), which 
 includes also snakes, turtles, tortoises, alligators, and croco- 
 diles. Reptiles are cold-blooded vertebrates covered with 
 scales or plates ; they breathe by lungs throughout their life. 
 A few reptiles are viviparous, but most of them lay eggs, 
 from which the young hatch in the form of the adult. 
 
 Four out of the five groups into which the class may be 
 divided, are here considered. 
 
 Lizards. Most of the Lacertil'ia (Lat. lacerta, a lizard) are, 
 like the pine-lizard, elongate reptiles with four limbs and 
 movable eyelids. A few families have, however, lost one or 
 
352 
 
 GENERAL ZOOLOGY 
 
 both pairs of limbs in connection with their adoption of a 
 burrowing life, and the eyes have disappeared beneath the 
 
 FIG. 177. Photograph of Legless Lizard 
 
 skin. The covering of scales, so characteristic of reptiles, has 
 also in some cases become much reduced. Legless lizards 
 
 FIG. 178. Photograph of Mexican Iguana 
 
 (Fig. 177) may be distinguished from the snakes, which they 
 resemble, by the fact that they are incapable of opening the 
 mouth to so great an extent as snakes are. 
 
PINE-LIZARD AND ITS ALLIES: REPTILIA 353 
 
 Many lizards possess the power, when seized suddenly, of 
 snapping off the tail, which may be left in possession of the 
 captor, while the creature hurries away to safety. Fig. 179 
 shows a Mexican species of iguana which had thus responded 
 to the efforts of the photographer to take its picture. The same 
 animal before mutilation is shown in Fig, 178. The .tail is 
 usually reproduced, at least so far as the flesh and skin are 
 
 FIG. 179. Photograph of Mexican Iguana with Broken Tail 
 
 concerned ; new vertebrae are not developed. The pattern 
 of the scales on the newer portion is usually simpler, some- 
 times apparently reverting to an ancestral type. 
 
 The chameleons (Chame'leo) of the Old World are famous 
 for their color changes, but the power is possessed to a greater 
 or less extent by nearly all lizards. It is accomplished by the 
 shifting of pigment granules in cells in the deeper layers of 
 the skin, toward or away from the colorless outer skin. The 
 movement of the granules, though affected by external con- 
 ditions, such as color and temperature of surrounding objects, 
 is said to be largely under the control of the animal. 
 
 Snakes. The snakes, which belong to the class Ophid'ia 
 (Gr. ophis, a serpent), are usually very easily distinguished 
 
354 
 
 GENERAL ZOOLOGY 
 
 13 
 
 externally by the absence of eyelids and limbs, although 
 rudimentary hind legs are to be found in a few forms, such 
 as the pythons of Asia, Africa, and Australia. Teeth are 
 
 present in all ophidians, 
 
 ...^^y;^ ^ *- 
 
 and are of two types, 
 the ordinary teeth, used 
 for seizing food, and the 
 poison-fangs, which are 
 perforated, forming a 
 passage for the poison 
 secreted in a gland at 
 their base. Both kinds 
 of teeth are shown in the 
 illustration of the skull 
 of the rattlesnake (Fig. 
 180), which shows also the 
 gland where the poison is 
 secreted (Fig. 180, 9), and 
 the reserve fangs (Fig. 
 180, 11) which replace the 
 first pair when the former 
 are broken or shed. In the 
 non-poisonous species the 
 number of teeth is much 
 greater than in the rattle- 
 snake. 
 
 The tongue of a snake 
 is a long, slender, forked 
 structure, used principally 
 as an organ of touch. The 
 lower jaw is joined to the upper jaw in such a way (see Fig. 
 180) as to admit of so much freedom of movement that the 
 snake's mouth can be opened wide enough to swallow animals 
 greater in diameter than itself. The passage of food into the 
 
 Fir.. 180. Skull of Rattlesnake, showing 
 Poison-Fangs 
 
 1, 2, bones of cranium; 3, prefrontal bone; 
 4, quadrate bone; 5, maxillary bone; 
 6, fang ; 7, bones of lower jaw ; 8, tip of 
 snout ; 9, poison-gland ; 10, poison-duct ; 
 11, reserve fangs ; 12, tip of fang ; 13, tem- 
 poral muscle 
 
 (From Baskett's Story of the Amphibians 
 and Reptiles) 
 
PINE-LIZARD AND ITS ALLIES: REPTILIA 355 
 
 oesophagus is facilitated by an abundant secretion from sali- 
 vary glands, and escape of the prey is prevented by the sharp, 
 backward-pointing teeth in both jaws. The union of the two 
 sides of the lower jaw in front is so loosely made by a carti- 
 laginous connection that each side of the jaw can be pushed 
 forward independently, thus getting a fresh hold on the food- 
 mass. Some of the larger snakes, as the pythons and boas, 
 kill their prey by constriction ; the non-poisonous kinds may 
 swallow theirs alive ; the poisonous species generally kill the 
 animal, unless it be a small one. Snakes progress by means 
 of muscles attached to the ribs and scales of the under side. 
 These scales have a free posterior edge, which can be inserted 
 into rough places in the surface of the ground. 
 
 The poisonous snakes of the United States are the prettily 
 colored beadsnake (E'laps ful'vius) and the water-moccasin 
 (Agkis'trodon 
 pisciv'orus) of 
 the southern 
 states ; the 
 copperhead 
 (Agkistrodon 
 contor'trix], 
 found from 
 New England 
 to Wisconsin 
 and southward; 
 and more than 
 a dozen species 
 of rattlesnakes 
 
 FIG. 181. Photograph of .Rattlesnake 
 
 (Fig. 181), found mostly in the arid regions of the West 
 and Southwest. The use of the peculiar horny appendage 
 at the end of the tail of the rattlesnake has occasioned 
 much discussion. By some it has been thought to be a 
 means of terrifying its prey, so that escape may be rendered 
 
356 
 
 GENERAL ZOOLOGY 
 
 impossible ; by others it has been regarded as a sex-call for 
 its mate, or even as a lure for birds. Many naturalists con- 
 sider that its function is similar to that of the yellow and 
 black coloration of wasps, or the distinctive red markings of 
 poisonous spiders, features which serve to mark the pos- 
 sessor as having unusual means of defense. By the mere 
 
 FIG. 182. Photograph of Blacksnakes 
 
 fact of this advertisement it is thought many conflicts are 
 avoided which might prove disastrous to the rattlesnake, 
 even if the attacker were killed in the contest. As it is, 
 an animal must have some confidence in its powers, if it 
 disregards the warning rattle and tries conclusions with 
 the owner. A diamond-back rattlesnake in captivity in the 
 New York Zoological Park grew a new "button" to the 
 rattle every three months, on each occasion of shedding 
 its skin. 
 
PINE-LIZARD AND ITS ALLIES: REPTILIA 357 
 
 Of the non-poisonous snakes of. this country the little 
 green snake (Cy'elophis verna'lis) is one of the 'most interest- 
 ing and beautiful. When kept in confinement it is a harmless 
 and interesting pet. As much cannot be said for our water- 
 snakes (Tropidono'tus), which are of irritable disposition and 
 disposed to strike when handled. Blacksnakes (Basca'nion, 
 Fig. 182) have been kept in captivity and handled freely after 
 they have become accustomed to their new surroundings. 
 
 Turtles and Tortoises. The turtles and tortoises, Chelo'nia 
 (Gr. chelone, a tortoise), are externally the best protected of 
 all the reptiles, being incased in a shell formed of plates 
 firmly fixed to the vertebrae and ribs. Chelonians have no 
 teeth, but the rim of the jaws is covered with a horny skin. 
 The limbs are sometimes modified into flippers for locomo- 
 tion in the water ; to such species the name " turtle " is com- 
 monly applied. The tortoises are land and fresh-water species, 
 with claws on the digits. 
 
 Of the turtles, the green turtle (Ohelo'ne my' das) of the 
 warmer portion of the Atlantic, Indian, and Pacific oceans, 
 and the hawkbill (Ohelone imbrica'ta), also widely distributed 
 in warm ocean-waters, are economically important, the first 
 as -an article of food, the second as the source of tortoise-shell. 
 These turtles lay their eggs in immense numbers on sandy 
 beaches in holes dug for the purpose by the female. As 
 many as two hundred eggs may be laid by a single female. 
 Within about six weeks they hatch, having been incubated 
 by the heat of the sun. These turtles are captured by the 
 natives of different parts of the world, by diving or by nets or 
 harpoons. A peculiar method of capturing them is followed 
 by natives of such widely separated regions as Torres Strait, 
 Madagascar, and Cuba. This method consists in utilizing 
 the services of the sucking-fish (Echene'u), a commensal fish 
 provided with a sucker-like attachment on the top of the 
 head, by means of which it is borne from place to place by 
 
358 GENERAL ZOOLOGY 
 
 larger fishes, especially sharks and swordfishes, leaving its 
 host occasionally to procure food. A string is attached to 
 one of these sucking-fishes, which is then liberated in the 
 vicinity of turtles, where it soon attaches itself to the under 
 
 FIG. 183. Photograph of Box-Tortoise 
 
 surface of the shell, holding on so tenaciously that the turtle 
 can be drawn gently to the surface. The method was noticed 
 by Columbus or one of his companions, and was described in 
 1671, in Ogilby's America, as follows: " Somewhat further he 
 [Columbus] saw very strange Fishes, especially of the G-uaican, 
 not unlike an Eel, but with an extraordinary great Head, over 
 which hangs a skin like a bag. This Fish is the Natives Fisher, 
 for having a Line or handsom Cord fastned about him, so 
 soon as a Turtel, or any other of his Prey, comes above 
 Water, they give him Line ; whereupon the Gruaican, like 
 an Arrow out of a Bowe, shoots toward the other Fish, and 
 then gathering the Mouth of the Bag on his Head like a 
 Purse-net, holds them so fast that he lets not loose till hal'd 
 up out of the Water." 
 
 A common species of tortoise in the eastern LTnited States 
 is the box-tortoise (Cistu'do, Fig. 183). These tortoises have 
 
PINE-LIZARD AND ITS ALLIES: REPTILIA 359 
 
 a very convex upper shell ; the lower portion is provided 
 with a transverse hinge, which makes it possible for the 
 animal to bring the two parts of the shell closely together, 
 thus forming a box, within which are concealed head, neck, 
 legs, and tail. A remarkable sex-dimorphism occurs ; the 
 eyes of the male are red, those of the female, brown. More 
 flattened species, like the painted tortoise (Chrys'emys) and 
 the spotted tortoise (Nan'emys), are better adapted to an 
 aquatic existence. 
 
 Alligators and Crocodiles. The large reptiles known as alli- 
 gators and crocodiles belong to the Crocodil'ia (Lat. crocodilus, 
 crocodile). The heart in the crocodilians is highly specialized, 
 having four separate chambers by the complete separation of 
 the two ventricles. Alligators (Fig. 184) differ from croco- 
 diles in having the canine teeth of the lower jaw fitting into 
 pits in the upper jaw ; in the crocodiles they fit into notches 
 in the side of the jaw. A species of each kind is found in 
 
 FIG. 184. Photograph of Alligator 
 
 Florida, though both have been sought so eagerly for the 
 teeth and skin that they are now found only in the more 
 inaccessible places. Crocodilians are also found in China, 
 Africa, southern Asia, and South America. They frequent 
 the edge of rivers, ponds, and lakes, lying in wait for their 
 
360 
 
 GENERAL ZOOLOGY 
 
 prey with only the tip of the snout exposed, or concealed in 
 the vegetation at the edge of the water. They feed at night, 
 and during the day bask in the sun on sand-banks or on logs. 
 Geological Development of Reptiles. We have seen (p. 345) 
 that during the Age of Amphibians a great part of the 
 interior of North America was one vast swamp, in which 
 stretches of black water alternated with drier areas covered 
 with the characteristic vegetation of the period, the whole 
 bathed in the heat of a tropical climate. Under conditions 
 similar to these the reptiles first came into existence in the 
 latter part of the Carboniferous Age. They developed in num- 
 bers, size, and form, and became in the succeeding period so 
 characteristic a part of the world's fauna that the age is 
 named, from them, the Age of Reptiles. This forms the third 
 great division of geological time, called Mesozoic Time, or the 
 
 FIG. 185. Ceratosaurus 
 
 Era of the Mediceval Forms of Life. In North America the 
 era began with the upheaval of the Appalachian system of 
 mountain ranges, as stated on page 347. During a part of 
 the era great areas in the south and west were submerged 
 beneath the ocean. 
 
PINE-LIZARD AND ITS ALLIES: REPTILIA 361 
 
 Fossil remains of the latter part of the Carboniferous Age 
 link the reptiles with the amphibians, so that it is likely that 
 the former are descended from a labyrinthodont ancestry. 
 Some of the reptiles possessed certain skeletal characteristics 
 
 FIG. 186. Photograph of Model of Triceratops 
 (American Museum of Natural History) 
 
 of the fur-bearing animals, arid they are called theromorphs 
 (beast-formed) on that account. 
 
 On land many species of dinosaurs (terrible lizard) were 
 found; some of them were the largest animals ever devel- 
 oped on the earth, reaching, in one case, the possible length 
 of sixty or seventy feet and the height of nearly twenty 
 feet. This animal was so great in bulk that it is consid- 
 ered hardly possible for it to have supported such a vast 
 amount of flesh on land, and it is therefore thought that it 
 was aquatic or semiaquatic in its habits. Some of the dino- 
 saurs, as Ceratosau'rus (Fig. 185), were particularly fitted to 
 walk on their hind legs, using the tail as a support. Mem- 
 bers of this genus grew to be seventeen feet in height. 
 Hundreds of the footprints of dinosaurs have been found in 
 the sandstone of the Connecticut valley. Fig. 186 shows a 
 well-known dinosaur, Tricer 1 'atops, with formidable armature. 
 
362 
 
 GENERAL ZOOLOGY 
 
 One species reached a length of more than twenty feet, and 
 stood eight feet high. 
 
 Some of the ancient reptiles (the flying lizards, or ptero- 
 saurs, Fig. 187) were capable of flight by means of skin 
 stretched between the front and hind limbs and tail. Most 
 of the bones were hollow and the skull was quite bird-like. 
 Whether these characteristics can be taken to mean that 
 
 the birds have de- 
 scended from these 
 flying reptiles is 
 doubtful, though it 
 has been asserted 
 by some paleontolo- 
 gists. It is perhaps 
 more likely that 
 these common 
 characteristics were 
 evolved to meet 
 similar conditions 
 in two different 
 groups, and that we 
 must look farther 
 back to find the an- 
 cestors of the birds. 
 Reptiles which are 
 apparently related 
 to the alligators and crocodiles, and to the turtles and tor- 
 toises, have also been found in the rocks of this period, so 
 that these groups are very ancient. Most of the lizards and 
 snakes belong to a later day, 
 
 At the close of the Age of Reptiles a great upheaval of 
 land occurred in the west, forming the Rocky Mountain sys- 
 tem. After that disturbance, which ranks in importance with 
 the uplift at the close of Paleozoic Time, practically the 
 
 FIG. 187. Restorations of Pterosaurs 
 (From Seeley's Dragons of the Air) 
 
PINE-LIZARD AND ITS ALLIES: REPTILIA 363 
 
 whole of our continent, with the exception of a strip along 
 the South Atlantic and Gulf coasts, was above the level of 
 the sea (Fig. 188). During the Age of Reptiles a tropical 
 climate extended far toward the poles, but with the upheaval 
 of the great land-masses a gradual lowering of the temper- 
 
 FIG. 188. North America after the Mesozoic Upheaval 
 (From Dana's Manual of Geology) 
 
 ature took place, which affected the vegetation. In connec- 
 tion with these changes occurred a wide-spread destruction 
 of species, similar to that which took place at the close of 
 Paleozoic Time. Professor Dana says that no American spe- 
 cies of vertebrate and no marine invertebrate is known to 
 have lived both before and after the Mesozoic upheaval. 
 
CHAPTER XXVIII 
 THE DOMESTIC PIGEON 
 
 A hundred wings are dropt as soft as one. 
 Now ye are lighted lovely to my sight 
 The fearful circle of your gentle flight, 
 Rapid and mute, and drawing homeward soon ; 
 And then the sober chiding of your tone 
 As there ye sit from your own roof arraigning 
 My trespass on your haunts, so boldly done, 
 Sounds like a solemn and a just complaining ! 
 
 CHARLES TENNYSON TURNER, On Startling Some Pigeons. 
 
 Habitat and Distribution. The domestic pigeon is known 
 under many varieties, all of which, it is now believed, have 
 been bred by artificial selection from the rock-dove (Colum'ba 
 liv'ia, Fig. 189), a bird widely distributed throughout the 
 European north-temperate realm. In its wild state the rock- 
 dove nests in the crevices of rocks, usually along seacoasts. 
 The different domesticated varieties have been still more 
 widely scattered over the earth through man's influence. 
 
 External Structure. In the pigeon we can distinguish a 
 head, neck, trunk, and tail. All over the body the skin is 
 closely set with feathers. There are two pairs of appendages : 
 the anterior, or wings, are used for flight, and the posterior, 
 the legs, for support. The wings consist of an upper arm, fore- 
 arm, and hand, as in the amphibians and reptiles, though the 
 digits are joined together and reduced in number (Fig. 191, 
 1,2; a third is shown, though not numbered). The legs (Fig. 
 191, 3) also show divisions similar to the hind legs of amphib- 
 ians and reptiles, i.e. thigh, lower leg, and/t>0, the latter being 
 covered with scales and ending in four toes, which bear claws 
 resembling those of the lizard. 
 
 364 
 
THE DOMESTIC PIGEON 365 
 
 The mouth is inclosed by a toothless, horny beak, above 
 which are situated the two nostrils, set in a mass of soft, fleshy 
 skin called the cere (Fig. 191, 5). The eyes are large, and 
 have an upper and a lower eyelid and a nictitating membrane. 
 The external openings to the ears are a little behind and 
 
 FIG. 189. Photograph of Rock-Dove 
 
 below the eyes, and are surrounded with specially modified 
 feathers. At the base of the tail on the dorsal surface is a 
 gland (Fig. 191, 4) which secretes an oil for keeping the 
 feathers in good condition. 
 
 The feathers are not scattered uniformly over the body, 
 but are arranged in definite tracts separated by areas in 
 which grow only a few hair-like feathers. As an example 
 
366 
 
 GENERAL ZOOLOGY 
 
 of a fully developed feather we may choose one of the con- 
 tour-feathers (Fig. 190, A) which form the main body-covering. 
 It consists of a hollow base, the quill (Fig. 190, A, l), from 
 which arises an expanded portion called the vane. Through 
 the center of the vane runs the rachis (Fig. 190, A, 2), which 
 gives off branches called barbs. From the barbs run inter- 
 locking structures 
 (barbules), bearing 
 hooks which serve 
 to bind the vane 
 into one continu- 
 ous surface. At 
 the junction of 
 quill and rachis on 
 the under surface 
 of the feather a 
 tuft of down, the 
 after shaft (Fig. 
 190, A, 3), is often 
 found. The wings 
 and tail bear 
 feathers which are 
 contour-feathers 
 of large size and 
 
 with very firm 
 FIG. 190. Kinds of Feathers of Pigeon J , 
 
 vanes. Scattered 
 
 A, contour-feather: 1, quill ; 2, rachis; 3, aftershaft. aTnonp , thp pfm 
 fl.filoplume; C, down-feather * among 
 
 tour-feathers are 
 
 down-feathers (Fig. 190, C f ), with which the nestling pigeon 
 was covered, and hair-like feathers, orfiloplumes (Fig. 190, B). 
 Down-feathers differ from contour-feathers in having no 
 barbules, so that the barbs are not held together, but 
 make a fluffy mass. Filoplumes bfrye only a main axis with 
 few barbs. 
 
THE DOMESTIC PIGEON 367 
 
 The Digestive System. The mouth is without teeth. Sali- 
 vary glands opening into the mouth furnish a fluid which 
 assists in swallowing the food. There is a large tongue 
 (Fig. 191, 7), pointed at its anterior end. From the pharynx 
 there are openings (Fig. 191, 6) to the nostrils and to the 
 ears, as in reptiles and amphibians. A short oesophagus 
 (Fig. 191, 8, 10) leads to a large crop (Fig. 191, 9), in which 
 the food, consisting largely of grain, is somewhat softened 
 before passing into the glandular stomach (Fig. 191, 11) behind 
 it. Glands in the lining walls of the stomach pour out a 
 digestive fluid which serves to further soften the food, 
 which then enters the gizzard (Fig. 191, 12), an organ with 
 a yellow, horny lining surrounded by a thick mass of muscle. 
 The gizzard contains small stones swallowed for the purpose 
 of assisting in grinding the food ; this process is accomplished 
 by movements of the muscular walls. Beyond the gizzard 
 the small intestine (Fig. 191, 13) forms a loop inclosing the 
 pancreas (Fig. 191, 17), which discharges its secretion into 
 the intestine through three ducts, one of which is shown in 
 Fig. 191, 18. The liver (Fig. 191, 14) is large and opens into 
 the intestine by two bile-ducts (Fig. 191, 15, 16). At the pos- 
 terior end the intestine (rectum) passes without change of 
 diameter into the cloaca (Fig. 191, 20). The junction between 
 the rectum and cloaca is marked by the presence of two cceca 
 (Fig. 191, 19). The spleen (Fig. 191, 21) is bright red, and is 
 attached to the walls of the glandular stomach. 
 
 The Circulatory, Respiratory, and Excretory Systems. The 
 heart is a large, four-chambered organ inclosed in the peri- 
 cardium (Fig. 191, 22). It consists of two auricles and two 
 ventricles, the latter separated by a complete partition, as in 
 the crocodilians. The circulation is double, and the aerated 
 and non-aerated blood come nowhere in contact, except in 
 the capillaries. The blood is sent to the lungs from the right 
 ventricle, through the pulmonary artery (Fig. 191, 29). Freed 
 
THE DOMESTIC PIGEON 369 
 
 of its carbon dioxide, the blood returns through the pulmonary 
 vein (Fig. 191, 30) to the left auricle (Fig. 191, 23), whence it 
 passes to the left ventricle (Fig. 191, 24) and thence into the 
 aorta (Fig. 191, 25), which distributes it to all parts of the 
 body. The blood from the body returns to the right auricle, 
 whence it enters the right ventricle, completing its circuit. 
 Lymph circulates through the body of the pigeon in vessels 
 of the lymphatic system. 
 
 The organs of respiration are the larynx, which opens out 
 co the pharynx by a slit-like glottis (Fig. 191, 31) ; the trachea 
 (Fig. 191, 32); the bronchial tubes, which ramify through the 
 tissue of the lungs, and the lungs themselves (Fig. 191, 34). 
 The trachea is kept open by rings of cartilage in its wall. 
 At the junction of the bronchial tubes and trachea is a slight 
 enlargement, forming the syrinx (Fig. 191, 33), the organ of 
 voice. The well-known sounds are produced by the vibra- 
 tion of a fold of membrane at this place. Many of the bones 
 are hollow, and there is a system of air-sacs scattered through 
 the body and communicating with the bronchial tubes. By 
 these means the air available for respiration is greatly increased 
 and the weight of the body is lessened. Breathing is accom- 
 plished by movements of the muscles of the thoracic region, 
 by which air is driven almost completely out of the lungs at 
 each expiration. The aeration of the blood is very complete, 
 and a high temperature, 37 C. (100 F.) is maintained. 
 
 The kidneys (Fig. 191, 35) are dark, three-lobed organs 
 fitting closely into cavities beneath the back-bone. The ureters 
 (Fig. 191, 36) open into the cloaca (Fig. 191, 37). 
 
 The Skeletal System. The skull (Fig. 192, l) is large, with 
 a comparatively large, rounded cranium (Fig. 192, 2). The 
 articulation of the cranium with the first vertebra is made 
 by a single condyle, as in the reptiles. The vertebrae of the 
 neck or cervical region (Fig. 192, 5) are free; those of the 
 thoracic region (Fig. 192, 6), pelvic region (Fig. 192, 7), and 
 
370 
 
 GENERAL ZOOLOGY 
 
 caudal region (Fig. 192, 8) are more or less united. There 
 are several pairs of ribs (Fig. 192, 13). The caudal vertebra 
 are terminated by a peculiar bone called, from its shape, 
 the plowshare bone (Fig. 192, 9). The shoulder-girdle is 
 
 l j 
 
 18 
 
 17 
 
 -5 
 
 16 
 
 15 10 
 
 19 
 
 20 21 22 
 
 7 
 
 14---- 
 
 23 
 
 2? 26- , 
 
 FK 
 
 Skeleton of Pigeon. Reduced 
 
 skull; 2, cranium; 3, upper mandible; 4, lower mandible; 5, cervical (neck) 
 vertebra;; 0, thoracic region; 7, pelvic region; 8, caudal region; 9, plow- 
 share bone ; 10, scapula ; 11, coracoid ; 12, keel of sternum ; 13, ribs ; 14, clav- 
 icles (wish-bone); 15, humerus ; 10, radius; 17, ulna; 18, thumb; 19, wrist 
 and hand bones (carpometacarpus) ; 20, bone of third finger; 21, bone of 
 second finger; 22, end bone of second finger; 23, femur; 24, tibiotarsus; 
 25, fibula ; 20, ankle and foot (tarsometatarsus) ; 27, bone of first toe ; 28, bone 
 of second toe 
 
THE DOMESTIC PIGEON 371 
 
 composed of a pair of narrow scapulas (Fig. 192, 10), to 
 which are attached two coracoids (Fig. 192, ll), connecting 
 the scapulas and the sternum, and a V-shaped bone, the wish- 
 bone, formed from the union of the two clavicles (Fig. 192, 14). 
 A greatly enlarged sternum with a prominent ridge or keel 
 (Fig. 192, 12) serves as a surface for attachment of the mus- 
 cles of flight. The hip-girdle is united to the vertebrae of 
 the pelvic region (Fig. 192, 7). A study of Fig. 192 and com- 
 parison with the skeleton of the frog (Fig. 165) will make 
 clear in what respects the appendages are different. 
 
 The Nervous and Muscular Systems. The brain is larger 
 in the pigeon, in proportion to the size of the animal, than 
 in the amphibians and reptiles. The cerebrum (Fig. 191, 44) 
 and the cerebellum (Fig. 191, 46) are especially large. One 
 of the principal functions of the cerebellum is to control the 
 muscles which bring about the balancing of the body. It is 
 apparent that this is of greater importance in the birds and 
 fishes than in the broader-bodied amphibians and reptiles. 
 The optic lobes (Fig. 191, 45), pressed to one side by the large 
 cerebrum, are also well-marked, in correlation with the 
 unusually large eyes and the dependence of the pigeon on 
 the sense of sight. The, olfactory lobes (Fig. 191, 42) are rela- 
 tively small, and the sense of smell is not at all keen. The 
 medulla (Fig. 191, 47) is bent downwards, as in the reptiles. 
 
 The muscular system shows many adaptations to the aerial 
 life of the pigeon. The great mass of muscle by which the 
 downward stroke of the wings is accomplished, occupies 
 almost all the space on the prominent, keeled breast-bone. 
 Its position, low down on the body, makes overturning in 
 the air almost an impossibility. The muscle which raises the 
 wing is also situated beneath the breast-bone, and is inserted 
 on the dorsal surface of the humerus by a tendon which 
 passes through an opening at the shoulder. The tendon thus 
 acts as a pulley in raising the wing. The muscles which 
 
372 GENERAL ZOOLOGY 
 
 bend the toes in perching are so arranged that the mere 
 weight of the bird keeps them contracted, so that even when 
 the pigeon is asleep the toes firmly grasp the perch. 
 
 The Reproductive System. The spermaries (Fig. 191,49) 
 are oval bodies attached to the kidneys. The ovary of the 
 right side is not developed, but the left ovary is a large organ 
 situated near the kidneys. 
 
 Development. Unlike most of our domestic animals, pigeons 
 choose their mates for life. After fertilization the ova or 
 " yolks " pass down the oviduct and are covered with secre- 
 tions from glands in different regions, first with the white, 
 or albumen, then with a thin membrane, and lastly with a 
 white, limy shell. The eggs are laid in a roughly made nest, 
 and are incubated by both parents in turn for about two 
 weeks, when they hatch. The young bird breaks through 
 the shell by means of a hard structure on the tip of its beak, 
 and makes its appearance covered with a fine down. It is 
 interesting to note in this connection that Darwin says that 
 some of the short-beaked tumbler pigeons, which have been 
 developed by artificial selection, have beaks so short that they 
 are unable to get out of the shell alone, and require therefore 
 to have the help of the pigeon-fanciers. For a few days after 
 hatching the young bird is fed by both parents with a milky 
 secretion afforded by the crop, and called " pigeon's milk." 
 
 At first the young are deaf and the eyes are closed, but 
 both sight and hearing are acquired within a few days. 
 Professor T. Wesley Mills of McGill University, Montreal, has 
 found that in newly hatched pigeons the sensibility to touch 
 and pain is very noticeable, and that they are extremely sen- 
 sitive to heat and cold. The young birds rapidly acquire the 
 power to make coordinated or connected muscular movements, 
 and in a few days the voice develops. The independent life 
 of the pigeon, in some cases Professor Mills observed, began 
 about the thirty-fourth day after hatching. 
 
THE DOMESTIC PIGEON 373 
 
 Relation to Environment. The oval form of the pigeon is 
 well adapted to cleaving the air, and the feathers form a light 
 waterproof covering which serves to retain the body-heat in 
 the rapid flights in the cold atmosphere. A bird has been 
 termed " an ocean greyhound in miniature," and the compar- 
 ison is not inapt for a creature which possesses such powers 
 of flight and maintains so high a temperature. " It is worthy 
 of notice," say Parker and Haswell, " that birds agree with 
 insects, the only other typically aerial class, in having the 
 inspired air distributed all over the body, so that the aeration 
 of the blood is not confined to the limited area of an ordinary 
 respiratory organ." Other important structural peculiarities 
 are the light, toothless beak, and the small number of digits 
 in the anterior extremities. Still other characters have been 
 referred to in the discussion of the internal anatomy. 
 
 The many varieties of the domestic pigeon afforded Darwin 
 much material for his book, The Variations of Animals and 
 Plants under Domestication. From their study he obtained 
 many of the conclusions which led to the statement of the 
 principle of natural selection. These domestic varieties differ 
 among themselves in appearance far more than many species 
 in nature. Some well-known varieties are the pouters, fan- 
 tails, tumblers, and carriers. The pouters are large birds with 
 elongate body and legs, and often with inflated crop and 
 oesophagus. The fan tails are known by the extraordinary 
 development of tail-feathers. The tumblers have the remark- 
 able habit of turning somersaults backward in the air from a 
 considerable height nearly to the ground. The carriers have 
 the " homing faculty " developed to such an extent that they 
 are useful as messengers. Though shut within a basket and 
 removed long distances from their home, they have been able 
 to find their way back. Carriers have been used by man for 
 many centuries, notably within recent times at the siege of 
 Paris and in the Russo-Japanese War. 
 
CHAPTER XXIX 
 THE ALLIES OF THE PIGEON: AVES 
 
 Robins and mocking-birds that all day long 
 
 Athwart straight sunshine weave cross-threads of song. 
 
 SYDNEY LANIER. 
 
 Definition of Aves (Lat. avis, a bird). The pigeon is a rep- 
 resentative of the class A'ves. Birds are warm-blooded verte- 
 brates adapted as a class to an aerial existence. They are 
 covered with feathers, which are, in their origin, modified 
 scales. Birds breathe by lungs. The young are always 
 hatched from eggs in a form closely resembling the parent. 
 There is remarkable uniformity of structure in the class, 
 making classification extremely difficult. 
 
 The following groups, which are some of the most impor- 
 tant of the many divisions into which birds have been divided, 
 are not all entitled to rank as separate orders, though often 
 treated as orders. 
 
 The Ostrich and Allies. The group Struthio'nes (Gr. struthion, 
 ostrich) contains the ostrich of Africa, the rheas or South 
 American ostriches, and the emus and cassowaries of Aus- 
 tralia, New Guinea, and adjacent islands. They are all large 
 birds with rudimentary wings, and with only two or three 
 toes on each foot. They have no ridge or keel on the sternum, 
 a structure which in most birds serves as an attachment for 
 the muscles of flight ; hence the struthious birds cannot 
 fly, though there is evidence that they have descended from 
 ancestors that had functional wings. The legs are large, 
 and the birds run with great speed. Most of them live in 
 open desert places, though cassowaries inhabit forest regions. 
 The eggs are laid in a deep depression in the sand, or in a 
 
 374 
 
THE ALLIES OF THE PIGEON: AVES 375 
 
 rough nest in the case of the cassowary. The ostrich is 
 the best known of the group, largely on account of the 
 beautiful wing and tail plumes, which have been used for 
 ornaments from very early times. Ostriches are now raised 
 for the sake of the plumes on " farms " in California and 
 South Africa. 
 
 Diving Birds. The group Pygop'odes (Gr. pyge, the rump ; 
 pous (pod), foot) includes various species of water-birds with 
 
 FIG. 193. Photograph of Tern on Nest 
 
 webbed or lobed toes. Their scientific name refers to the 
 fact that the legs are placed very far back, so that when 
 standing an erect position is assumed. The tail is very short. 
 The beak is sharp and pointed and fitted for spearing fishes, 
 which constitute a large part of their food. They are expert 
 divers and can swim under water with only the tip of the bill 
 exposed. The nest is generally nothing more than a floating 
 mass of decaying vegetation, attached perhaps to some reeds 
 in shallow water. Our northern lakes and ponds are often 
 visited by the loon, a characteristic diving bird. 
 
376 GENERAL ZOOLOGY 
 
 Gulls and Terns. The group Longipen'nes (Lat. longus, 
 long ; penna, feather) includes long-winged water-birds with 
 sharply pointed or hooked beaks. The colors are usually gray 
 above and lighter below. The three front toes are connected 
 by a web. These birds are strong and graceful fliers, and 
 spend much of their time on the wing. All the members of 
 the group are gregarious, occupying nesting sites on sandy 
 beaches, in marshes, or on rocky shores. They obtain the 
 greater part of their food from the ocean, and are useful as 
 scavengers. Terns (Fig. 193) may be distinguished from 
 gulls by their usually deeply forked tail and straight bill. 
 Gulls are generally pelagic, and they often follow ships for 
 the sake of the refuse thrown overboard ; terns frequent 
 the shores of both fresh and salt water. Owing to the 
 forked tail and graceful flight, the terns are often called 
 sea-swallows. 
 
 Petrels and Allies. The petrels and their allies are strong- 
 winged pelagic birds, many of which externally resemble the 
 gulls and terns. They may be distinguished from other water- 
 birds by the nostrils, which are inclosed in tubes lying on 
 the dorsal or lateral surface of the upper mandible ; hence 
 their scientific name, Tubina'res (Lat. tubus, tube ; naris, 
 nostril). The beak is usually strongly and sharply hooked. 
 The food consists of fishes and other small animals which 
 live near the surface of the ocean. The birds often follow 
 ships, like the gulls, to pick up refuse. They occupy various 
 nesting sites along shores. The wandering albatross (Dio- 
 mede'a ex'ulans) of southern oceans is the best-known species. 
 It is the largest of sea-birds, measuring over twelve feet 
 between the tips of the wings. One of the traditions among 
 sailors concerning the albatross is referred to in Coleridge's 
 Ancient Mariner. Other members of the group, called stormy 
 petrels and Mother Carey's chickens, are also regarded by 
 many sailors with superstitious dread. 
 
THE ALLIES OF THE PIGEON: AVES 377 
 
 Pelicans and Allies. The members of the group Steganop'- 
 odes (Gr. steganos, covered; pous (pod), foot) differ from 
 all other web-footed birds in that all four toes are con- 
 nected by a web (Fig. 195). They are aquatic, usually marine 
 birds, and feed mainly on fishes. To this group belong the 
 pelicans (Fig. 194), remarkable for the pouch beneath the 
 bill, which is used as a scoop to capture food or as a storage 
 
 FIG. 194. Photograph of White Pelican 
 
 reservoir. There are about a dozen species of pelicans distrib- 
 uted over the world, of which two species, the brown and the 
 white pelican, occur within the limits of the United States. 
 White pelicans (Fig. 194) have the habit of surrounding 
 schools of small fishes and driving them with loud beatings 
 of wings into shallower water, where they can be scooped up 
 in the great pouch and devoured at leisure. The figure shows 
 the peculiar horny outgrowth which appears on the bill of 
 the male at the breeding-season. 
 
 Ducks, Geese, and Swans. The group An' seres (Lat. anser, 
 goose) is made up of water-birds which have the three front 
 toes webbed and the tail comparatively well-developed. The 
 
378 
 
 GENERAL ZOOLOGY 
 
 FIG. 195. Foot of Pelican 
 
 ducks, geese, and swans are included here. The bill is usually 
 flattened and is furnished with transverse tooth-like ridges 
 
 on both upper and lower mandibles. 
 In the species which frequent rivers 
 and ponds, feeding largely on vege- 
 table food or on small mollusks, 
 crustaceans, and larvse of insects, 
 these ridges act as a strainer 
 through which the water runs off 
 when the bill is closed, leaving the 
 
 rL Vm ^ 00( * Behind; in the harbor and 
 
 1 i TO sea-haunting, fish-eating species the 
 
 ridges are useful in holding the 
 slippery food. The nest is usually 
 placed on the ground near the water. 
 Several of the swans have the 
 trachea greatly lengthened and 
 looped through the hollow sternum (Fig. 196). By this means 
 they produce their loud whistling or trumpeting note. Wild 
 geese have long excited interest on account of their peculiar 
 manner of migrat- 
 ing in a flock ar- 
 ranged in a long, 
 V-shaped group, 
 keeping up the 
 continual, sono- 
 rous "honk, honk." 
 Among the geese 
 
 and swans the 
 
 FIG. 196. Trachea of Trumpeter Swan 
 sexes are usually 
 
 alike, but in many of the ducks the male is specially orna- 
 mented with brilliantly colored plumage. Well-known species 
 of ducks are the canvasback duck, dear to the epicure ; and 
 the mallard, the ancestor of the common domesticated duck. 
 
THE ALLIES OF THE PIGEON: AVES 
 
 379 
 
 Herons, Storks, and Allies. The birds of the group Hero- 
 dio'nes (Or. erodios, heron), often spoken of as wading birds, 
 are long-legged species, with four toes placed on about the 
 same level, and slightly or not at all webbed. The bill and 
 neck are long and slender. Crests and decorative plumes 
 often ornament the head and neck. Herons haunt the edge 
 
 FIG. 197. Photograph of Egrets 
 
 of ponds, lakes, and rivers, where they feed on fishes and 
 frogs, which they capture with their long, sharp beaks. 
 They nest in great colonies, usually in trees. The nests 
 are clumsy affairs made of sticks in an untidy mass. One 
 of our largest species is the great blue heron which stands 
 nearly five feet high. Several herons, called egrets (Fig. 197), 
 which have the misfortune to grow beautiful dorsal plumes, 
 or " aigrettes," at the breeding-season, have been practically 
 exterminated by man for the sake of their plumes for women's 
 hats. These birds were formerly common in Florida and along 
 
380 GENERAL ZOOLOGY 
 
 the Gulf coast. Storks are natives of the Old World, fre- 
 quenting wooded regions or open country. The white stork 
 has been tamed in some countries, where it frequently occu- 
 pies nesting sites on houses. 
 
 Cranes and Allies. Though superficially like the herons, in 
 that they have a long bill, neck, and legs, the cranes and 
 their allies may nevertheless be distinguished from the herons 
 by the elevation of the hind toe above the level of the others. 
 The cranes are scattered widely over the globe, though we 
 have but three species in North America. They frequent 
 marshes and open plains (their scientific name, Paludic'olce, 
 means marsh-inhabitant), and feed on both vegetable and ani- 
 mal food, the latter consisting largely of small reptiles and 
 amphibians. " Erect and tall, they may be seen striding 
 swiftly along with head thrown back, or strutting around 
 their mates; while in spring they often stand in rows and 
 proceed. to stalk about in single file, or dance to meet one 
 another with nodding heads, necks advanced, and wings 
 widely outspread. Thereafter they bow toward the ground, 
 jump in the air, and perform graceful antics of all descrip- 
 tions. The chosen spot for these dances is commonly near 
 water. The male courts his spouse in somewhat similar 
 fashion, and twigs or feathers are often tossed in the air in 
 sport, to be caught again ere they touch the ground" (Cam- 
 bridge Natural History, Vol. IX). 
 
 Snipes, Sandpipers, Plovers, and Allies. The well-known 
 shore-birds, included in the group Limic'olce, usually have 
 long, slender legs, with the hind toe, when present, elevated 
 above the others. The scientific name refers to their habitat, 
 (Lat. limus, mud ; colere, to dwell). The bill is usually long 
 and slender and more or less soft, especially at the tip. With 
 their bills these birds probe the mud and sand of pond and 
 river margins and the seacoast for their food, which consists 
 of small crustaceans, worms, and mollusks. The plumage is 
 
THE ALLIES OF THE PIGEON : AVES 
 
 381 
 
 usually brown or gray, with some white intermixed. During 
 the breeding-season many species give utterance to more or 
 less musical cries. At other seasons a number of species 
 have shrill call-notes or whistles. The eggs are usually laid 
 on the sand in a hollow scraped for the purpose. They are 
 very often protectively colored. Like the domestic fowl, the 
 young are able to take care of themselves from the very first. 
 Their nestling plumage is also protectively colored. 
 
 One of the best known is the woodcock, which frequents 
 low, moist, wooded regions. The tip of the upper mandible 
 can be moved upward, so that it is of use in feeling for and 
 seizing worms in the ground. The Wilson's snipe of fresh- 
 water meadows and swamps, and the upland plover of higher 
 and drier pastures, are other familiar species. 
 
 Grouse, Quail, Turkeys, Pheasants, and Allies. The galli- 
 naceous birds, G-alli'nce (Lat. gallina, hen), commonly known 
 as scratching birds, 
 have a stout, convex 
 beak fitted for seizing 
 and crushing seeds, 
 which form a large 
 part of their food ; the 
 wings are short and 
 rounded, and the short, 
 stout legs have strong 
 toes adapted to scratch- 
 ing. Nearly all species 
 are terrestrial in habit. 
 Here are included the 
 larger part of the game- 
 birds of the world. By far the best known of the group is 
 our domestic fowl, of many races, all of which are descended 
 from the red jungle-fowl (Gal'lus banki'vus, Figs. 198, 199) 
 of India, Sumatra, Celebes, and the Philippines. 
 
 FIG. 198. Photograph of Jungle-Fowl 
 
382 
 
 GENERAL ZOOLOGY 
 
 FIG. 199. Young of Jungle-Fowl 
 
 The best known of the grouse in the eastern United States 
 is the ruffed grouse (Bona'sa umbel' lus), usually, but wrongly, 
 called " partridge " in New England. It is about the size of 
 
 the domestic fowl, and has pro- 
 nounced black ruffs on the sides 
 of the neck. The male produces 
 a loud drumming sound by beat- 
 ing the air rapidly with the wings. 
 The sound is a call to the female, 
 though it is indulged in occa- 
 sionally at other seasons than in 
 the spring. The quail-like bob- 
 white (Coli'nus Virginia' nus) is 
 also, but erroneously, called "par- 
 tridge " in the southern states. It is a smaller bird than the 
 ruffed grouse, reddish brown in color, and without the ruff 
 about the neck. Neither of these birds should be called 
 "partridge," since that name is already in use for Eurasian 
 species of gallinaceous birds. The same statement is true of 
 the term " quail," which is often applied to our bob- white. 
 The pheasants are magnificently colored birds, native to 
 southeastern Asia and adjacent islands. 
 
 Pigeons and Doves. The Colum'bce (Lat. columba, a dove) 
 are closely related to the gallinaceous birds, but the nostrils 
 open into a fleshy cere. We have in the eastern United 
 States several species of wild doves, and the passenger-pigeon 
 (Ectopis'tes migrato'rius}. The latter were formerly present in 
 immense numbers in the wooded regions of the eastern United 
 States. In the early years of the eighteenth century flocks 
 were seen that stretched far across the sky, and which 
 required hours to pass a given point. Farmers were in some 
 places obliged to watch their fields constantly to prevent the 
 birds from picking up the sowed grain. The birds nested in 
 great colonies of thousands, sometimes as many as forty nests 
 
THE ALLIES OF THE PIGEON: AVES 
 
 383 
 
 FIG. 200. Head of Golden Eagle 
 
 in a single tree. Owing to the increased demand for both 
 young and adults as food they were slaughtered indiscrimi- 
 nately and have since 
 been nearly extermi- 
 nated. 
 
 Hawks, Eagles, 
 Owls, and Vultures. 
 The Rapto'res (Lat. 
 raptor, robber) are 
 generally spoken of 
 as birds of prey, 
 though the term is 
 equally applicable to 
 some members of 
 other groups, the 
 gulls among the long-winged swimmers, for example. The 
 beak is stout, strong, and sharply hooked (Fig. 200); the toes, 
 
 arranged three in front and one 
 behind, are provided with strong, 
 sharp, curved claws (Fig. 201) 
 with which to seize their living 
 prey, except in the vultures, 
 which feed on carrion. The 
 Raptores possess great powers 
 of flight. The female is larger 
 than the male. The nests are 
 generally bulky structures, com- 
 posed of sticks and placed in 
 tall trees or on rocky cliffs. 
 
 The red-tailed and the 
 red-shouldered hawks are gener- 
 ally termed " hen-hawks " or " chicken-hawks " by farmers. 
 Though they occasionally levy tribute on the chicken-yard, 
 their propensities in this direction are not so marked as is the 
 
 FIG. 201. Claw of Golden Eagle 
 
384 
 
 GENERAL ZOOLOGY 
 
 case with some of the other hawks which do not sail so con- 
 spicuously in the air. Hen-hawks undoubtedly do more good 
 than harm by destroying large numbers of mice and other 
 small mammals. The vultures are, generally speaking, scav- 
 engers, or they may attack weak and disabled animals. The 
 black vulture and the turkey-buzzard are invaluable as scav- 
 engers in the southern states. They have been protected for 
 
 this reason, and have 
 become very tame in 
 many places. The 
 owls (Fig. 202) are 
 adapted to nocturnal 
 life. The plumage is 
 soft, making possible 
 a noiseless flight ; the 
 eyes are large, and 
 placed so that they 
 look forward. 
 
 Parrots and Cock- 
 atoos. The Pait'taci 
 (Gr. psittakos, parrot) 
 are generally birds of 
 
 Colors ' with a 
 
 u. 202. Photograph of Barred Owl 
 
 very stout, strongly 
 
 hooked beak, which is used for climbing, as well as for 
 crushing seeds. They have four toes, arranged two in front 
 and two behind, with strong, curved claws. Most species 
 inhabit forests ; they are all good climbers. A great many 
 species can learn to talk, but the red-tailed gray parrot of 
 Africa is considered the best talker. The cockatoos (Fig. 
 203) are often ornamented with crest-feathers of various 
 colors. They are restricted to Australia, Tasmania, and 
 the Philippines. A New Zealand parrot, the kea (Nes'tor 
 notab'ilis), has of late years become carnivorous in its habits, 
 
THE ALLIES OF THE PIGEON : AVES 
 
 385 
 
 alighting on the backs of live sheep and digging deep into 
 the flesh for the fat surrounding the kidneys. " The pro- 
 pensity is said to have originated from the bird pecking 
 at sheepskins hanging outside country stations." We have 
 only one member of the group in the United States, the 
 Carolina paroquet, and that has been almost exterminated. 
 
 Woodpeckers. The group Pi'ci (Lat. picus, a woodpecker) 
 forms a well-marked 
 assemblage of climb- 
 ing birds, with two 
 toes in front and 
 two behind (except 
 in the three.-toed 
 woodpeckers). 
 
 Woodpeckers have 
 a strong, straight bill, 
 with which they dig 
 into wood for insects, 
 and a long, barbed 
 tongue, spear-pointed 
 at the end, which 
 enables them to 
 draw their food from 
 beneath the bark of 
 trees. The tail-feathers are usually stiff and pointed, and 
 form a support to rest on while the bird is engaged in 
 feeding. The usual coloration in the group is black and 
 white, but red often appears on the head. The nests are 
 made in holes in trees, and the eggs are white in color. 
 By far the greater number of the woodpeckers are beneficial 
 to the farmer, but the yellow-bellied woodpecker, or sap- 
 sucker (Spliyrapi' cus va'rius, Fig. 204), girdles trees with 
 numerous small holes to get at the sap beneath the bark. 
 The golden- winged woodpeckers (Colap'tes) have lost some 
 
 FIG. 203. Photograph of Cockatoo 
 
386 
 
 GENERAL ZOOLOGY 
 
 of the habits of the family, and have descended to picking 
 
 up part of their food on the ground of fields and pastures. 
 
 Perching or Singing Birds. The passerine type (Lat. passer, 
 
 sparrow) is exemplified in more than half the birds of the 
 
 FIG. 204. Photograph of Yellow-Bellied Woodpeckers 
 (American Museum of Natural History) 
 
 world. The characteristics which serve to distinguish the 
 Pas' seres, or perching birds, from other groups are the pres- 
 ence of four toes without webs, placed at the same level, 
 three in front and one behind. The perchers are birds of 
 
THE ALLIES OF THE PIGEON : AVES 
 
 387 
 
 small or medium size. Among them are included all our 
 well-known songsters. The nesting-habits are various, but a 
 
 FIG. 205. Nest of Catbird 
 
 great number build complicated and often beautiful nests 
 (Fig. 205) in which to rear their young. The young when 
 hatched are 
 always in a 
 helpless condi- 
 tion, requiring 
 the care of the 
 parent for a 
 time (compare 
 Figs. 206 and 
 199). The sexes 
 may be alike, or 
 the male may 
 
 FIG. 206. Youns; of Catbird 
 
 be specially 
 
 ornamented. 
 
 The bright colors of the male are generally believed to be 
 
 due to sexual selection, and his ability to sing is accounted 
 
388 
 
 GENERAL ZOOLOGY 
 
 for in a similar manner. It is worthy of notice that in those 
 cases where song has been developed, bright colors are usu- 
 ally absent. The perching birds are the familiar birds of 
 forest, field, and garden, and are those with which the young 
 student will naturally begin his study in the field. They are 
 so numerous that very few can be referred to here. 
 
 The flycatchers (Tymn'nidm, Fig. 207) are pert little birds 
 with a slightly hooked bill, provided with bristles at its base. 
 From some convenient perch they watch for insects, which 
 
 
 FIG. 207. Photograph of Mounted Group of Flycatchers 
 (American Museum of Natural History) 
 
 they snap at on the wing, returning to the perch after each 
 flight. The bristles at the base of the bill serve to entangle 
 insects and make their capture more certain. The brightly 
 colored wood- warblers (Mniotil'tidce), as Mr. Chapman says, 
 " at once the delight and the despair of field students," are 
 also insect-eaters, getting their food almost exclusively from 
 the leaves or bark of trees, though some capture it on the 
 wing, after the manner of the flycatchers. 
 
 The vireos (Vir eon' idee) are to be found in much the same 
 places as many of the wood-warblers, industriously picking 
 insects from the leaves of trees, or from crevices in the bark. 
 
THE ALLIES OF THE PIGEON: AVES 389 
 
 Vireos are small, greenish-colored birds, which build cup- 
 shaped, hanging nests of plant-fibers, lined with pine-needles 
 and similar material. The white-eyed vireo has the habit of 
 often weaving a piece of newspaper into the structure of its 
 nest ; hence it is called " the politician " in some parts of the 
 country. A cast snake's skin is also a favorite object for this 
 purpose. 
 
 Our familiar crow and our almost equally familiar blue jay 
 are members of the family Cor'vidce. The family is considered 
 by ornithologists to be unusually intelligent, and by some is 
 even considered the highest bird-group. Closely allied to the 
 crows and jays are the blackbirds and orioles (Icter'idce). In 
 this family is the cowbird, which has the habit of laying its 
 eggs in the nests of other birds, which are usually smaller 
 than itself, and of leaving the egg to be hatched by its foster- 
 parent. A South American cowbird lays its eggs in the nest 
 of another species of cowbird, which does not possess this 
 parasitic habit fully developed, since it sometimes builds its 
 own nest and sometimes lays its eggs in the nests of other 
 birds. The orioles are remarkable for their elaborately inter- 
 woven hanging nests, much deeper than the somewhat similar 
 hanging nests of the vireos. 
 
 The finches and sparrows (Fringil'lidoe) are the largest 
 family of birds. However varied the members of this group 
 are in form and color, they agree, usually, in the possession 
 of a stout, conical bill, adapted to crushing seeds. The 
 European house-sparrow, often called the English sparrow 
 (Pas'ser domes'ticus), is probably well known to dwellers in 
 nearly every town and city in the United States. Intro- 
 duced from Europe into this country in the neighborhood of 
 Brooklyn, in 1851 and 1852, the house-sparrow has since 
 spread so widely that it may now be said that its conquest 
 of the centers of population in our country is almost com- 
 plete. It has made itself at home in our city streets, and 
 
390 GENERAL ZOOLOGY 
 
 has managed to pick up a living where another bird would 
 starve to death. Most of the sparrows belong to the fields 
 and hedges, where their brownish coloration serves to make 
 them inconspicuous. 
 
 Our American robin belongs to the family of thrashes 
 (Tur'didcu). Though not a gifted songster, like some of its 
 near relatives, the robin is dear to all dwellers in the country. 
 With the bluebird and the song-sparrow it shares the honor 
 of being spring's harbinger among the birds in eastern North 
 America. Its habits, song, and call-notes offer an interesting 
 subject for study. 
 
 Migration of Birds. The phenomena of migration are espe- 
 cially noteworthy among birds, and the birds of a region may 
 be roughly classified in connection with this habit. Those 
 species which remain in a region all the year are spoken of 
 as permanent residents of that region. They may be more 
 or less migratory as individuals ; that is, the birds seen in 
 the summer may not be the same individuals that appear 
 in the autumn or winter. The great majority of the birds 
 of the northern hemisphere leave in the autumn to pass the 
 winter in the south, returning in great bird waves in the 
 spring. These birds are the summer residents of the region. 
 The summer residents of the eastern United States may 
 pass the winter in the southern states, or they may (like the 
 bobolink) go as far as Brazil. When the great hordes of the 
 summer residents have passed to the south, other birds come 
 down from the north; these are ivinter visitants. Often a 
 bird loses its way, or is blown out of its regular line of travel 
 to other regions ; such birds are accidental visitants to those 
 regions. 
 
 The great migratory movements of birds are fairly regular 
 year after year, and they are participated in by thousands 
 upon thousands of individuals. When the appropriate time 
 comes each species gathers in large flocks, or the individuals 
 
THE ALLIES OF THE PIGEON : AVES 391 
 
 separately move off on their long trip. The larger birds, with 
 special means of defense, as the large hawks and cranes or 
 those species with untiring flight, as the ducks, choose day- 
 light in which to travel. Some of the smaller birds which 
 are also rapid and untiring fliers, like the swallows, also 
 carry on their migrations during the day, but most of the 
 smaller birds migrate at night. A foggy night causes the 
 death of large numbers of birds ; over fifteen hundred indi- 
 viduals have been picked up at the foot of Bartholdi Statue 
 in New York Harbor after a dark night in the migration 
 period. Attracted by the bright light the birds had dashed 
 against the glass in their swift flight. Birds are exposed to 
 other dangers on their migration-flight. They are fed upon 
 by other animals, and many perish from fatigue, or are blown 
 out to sea, where they fall exhausted into the water. 
 
 It is not thoroughly understood how birds find their way 
 over such great stretches of territory. The " fly-lines " of 
 some swallows are ten thousand miles long. The golden 
 plover breeds in arctic America and winters in Patagonia. 
 By some ornithologists (students of birds) the ability to 
 travel these great distances is ascribed to the possession of 
 a sixth sense, that of direction, which seems to be pos- 
 sessed by some other animals and by savage man. It is 
 supposed that somehow the nervous system registers the 
 ground passed over. Observations by American ornitholo- 
 gists seem to show that the old birds lead the way. Some 
 birds keep up a continual calling to each other, which may 
 help to keep the members of the flock together. In following 
 their migration-routes birds have undoubtedly been helped in 
 some cases by the rivers and coast-lines, and in Europe there 
 are cases where the fly-lines mark submerged coast-lines which 
 the birds followed when the land was above the water. There 
 is such a line between England and the continent, and another 
 across the Mediterranean Sea. 
 
392 GENERAL ZOOLOGY 
 
 The causes which underlie these great movements cannot 
 yet be stated with absolute certainty. The southerly migra- 
 tion is probably to be associated in general with the failure 
 of the food-supply and the decrease in temperature. It has 
 been stated that the return to the north is due to the desire 
 of the birds to regain their old home, or to their desire for 
 seclusion during the breeding-season. The origin of the 
 habit has undoubtedly to be looked for in the geological 
 history of the world. During the Glacial Epoch (see p. 431) 
 a great part of the northern hemisphere was shrouded in a 
 mass of ice, which came down from the north upon a region 
 which was then almost tropical *ink its climate. With the 
 onward advance of the ice, the birds, like all other forms of 
 life, were driven south, returning whenever the melting of 
 the ice permitted. Geology tells of many periods of alter- 
 nate progression and regression of the ice-sheet, with accom- 
 panying changes of climate. We have already spoken of the 
 discontinuous distribution of the White Mountain butterfly 
 (see p. 48) as dating from this period. It may well be that 
 the northerly and southerly movements then begun among 
 the birds have been continued till to-day. 
 
 Economic Importance of Birds. Leaving out of considera- 
 tion their value to man as a source of food, birds are chiefly 
 important economically in connection with their destruction 
 of insects injurious to vegetation. Of course not all birds 
 are beneficial in this respect ; whether they are beneficial or 
 injurious depends largely on the character of their food. 
 What we know of the food of birds has come not only from 
 the observation of the birds in the field but also from the 
 examination of the contents of their stomachs. The Division 
 of Biological Survey of the Department of Agriculture has 
 performed a most useful task in collecting, tabulating, and 
 publishing observations from all parts of the country, and 
 has recently supplemented this general work by a study of 
 
THE ALLIES OF THE PIGEON: AVES 393 
 
 the economic conditions of a single area. The tract chosen 
 was a farm of about two hundred and thirty acres on the 
 Potomac River in Maryland, just opposite Mount Vernon. 
 Here observations were made on the bird and insect life of the 
 farm, with the view of determining not only what the birds 
 really did eat but also what food was available for them at 
 different seasons. So, too, the vertebrate life of the farm, 
 the mice, poultry, and game, which form a part of the food 
 of some birds; the fruit, both wild and cultivated; the grain 
 and the weeds of the region, and the crops that were planted ; 
 all these were considered in the investigation. Besides obser- 
 vations on the living birdsJflhe stomachs of six hundred and 
 forty-five specimens were examined. As in other investiga- 
 tions along the same line, it was found that the largest con- 
 sumption of insects is to be credited not to the adult but to 
 the nestling. As several broods are raised by many birds 
 each year, and each young bird requires at first considerably 
 more than its own weight of food in a day, the number of 
 insects destroyed in this way is almost incalculable. Of course 
 some beneficial insects are included in this list, but it has 
 been found that those insects which are to be classed as cer- 
 tainly useful, as some of the bees, wasps, and beetles, which 
 prey on pests, make up a very small proportion of the food. 
 The diagram (Fig. 208) shows the proportion of different sorts 
 of food in the young and the adult of the common crow. 
 
 Some of the conclusions of Dr. Judd, who studied this region 
 for the Biological Survey, are that " the English sparrow, the 
 sharp-shinned and Cooper hawks, and the great horned owl 
 are, as everywhere, inimical to the farmers' interests and 
 should be killed at every opportunity. The sapsucker punc- 
 tures orchard trees extensively and should be shot. The 
 study of the crow is unfavorable in results so far as these 
 particular farms are concerned, partly because of special con- 
 ditions. Its work in removing carrion and destroying insects 
 
GENERAL ZOOLOGY 
 
 is serviceable, but it does so much damage to game, poultry, 
 fruit, and grain that it more than counterbalances the good, 
 and 'should be reduced in numbers. The crow-blackbird 
 appears to be purely beneficial to these farms during the 
 
 7 days or less 
 
 1 to 2 weeks old 
 
 BEETLES ^VERTEBRATES 
 
 3 weeks and older adult 
 
 FIG. 208. Diagram of Crow-Food 
 (From Judd's Birds of a Maryland Farm) 
 
 breeding-season, and feeds extensively on weed-seed during 
 migration, but at the latter time it is very injurious to grain. 
 The remaining species probably do more good than harm and, 
 except under unusual conditions, should receive encourage- 
 ment by the owners of the farms. Certain species, such as 
 
THE ALLIES OF THE PIGEON: AVES 395 
 
 flycatchers, swallows, and warblers, prey to some extent upon 
 useful parasitic insects ; but on the whole the habits of these 
 insectivorous birds are productive of considerable good to 
 man. Together with the vireos, cuckoos, and woodpeckers 
 (exclusive of the sapsuckers), they are the most valuable con- 
 servators of foliage on the farms. The quail, meadow-lark, 
 orchard-oriole, mocking-bird, house-wren, grasshopper-sparrow, 
 and chipping sparrow feed on insects of the cultivated fields, 
 particularly during the breeding-season, when the nestlings 
 of practically all species eat enormous numbers of caterpillars 
 and grasshoppers." 
 
 Bird-Protection. The first steps toward bird-protection 
 were taken at the instance of the sportsmen, in whose inter- 
 est laws were passed prohibiting the destruction of game- 
 birds except at stated seasons of the year. These laws were 
 in the interest, too, of the hunter who shot for the market, 
 since they secured for the birds freedom from the molesta- 
 tion of man during the period of bringing up their young, 
 without which protection their extinction would, in many 
 cases, have been only a matter of time. Of late years great 
 interest has been aroused in ornithology, and the value of 
 birds to agriculture or as scavengers has been more generally 
 recognized. People generally have begun to take pleasure 
 in having birds about, for their beauty of form, or color, or 
 movement, and for their song, so that an aesthetic argument 
 has been added to the others. The separate states have 
 shown the effect of this general awakening by the improve- 
 ment of old laws or the passage of new ones for the protec- 
 tion of the insectivorous song-birds and other birds which 
 have not been proven to be directly injurious. The Audubon 
 societies of the country and the Committee on Bird Pro- 
 tection of the American Ornithologists Union were helpful 
 in arousing a public sentiment which made possible in May, 
 1900, the passage by the federal government of an act "to 
 
396 
 
 GENERAL ZOOLOGY 
 
 aid in the restoration of such birds in those parts of the 
 United States adapted thereto where the same have become 
 scarce or extinct, and also to regulate the introduction of 
 American or foreign birds or animals in localities where they 
 have not heretofore existed." By its provision the preserva- 
 tion of birds is placed under the jurisdiction of the Depart- 
 ment of Agriculture. The importation of foreign wild birds 
 is forbidden without permits from the department, and in- 
 terstate traffic in birds killed in violation of state laws is 
 prohibited. This is the most sweeping act of legislation in 
 favor of birds ever attempted, and it is confidently expected 
 to give them a great measure of protection. As one result of 
 the interest in the study of birds in the schools several states 
 have set apart a Bird Day, which is observed after the fashion 
 
 of Arbor Day, and oftentimes 
 in connection with it. The first 
 Bird Day was observed in Penn- 
 \/> m, sylvania, May 4, 1894. 
 
 Geological Development of 
 Birds. The earliest remains of 
 birds of which we have any 
 knowledge come from the Age 
 of Reptiles. The oldest of 
 these remains is the famous 
 fossil known as Archwop'teryx 
 (Fig. 209), two specimens of 
 which have been found in 
 Bavaria. The ancestry of all known birds is therefore to be 
 traced back, at least so far as our knowledge goes, to these 
 two specimens. Archseopteryx was a land bird about the size 
 of a crow, probably arboreal in its habits, though not neces- 
 sarily a good flier. It had true feathers, but it was very 
 different from the birds of to-day in that it possessed teeth 
 and a long, lizard-like tail of about twenty vertebra*. These 
 
 FIG. 209. Archseopteryx. (After 
 Pycraft) 
 
THE ALLIES OF THE PIGEON: AVES 397 
 
 last characteristics are strikingly reptilian, and such considera- 
 tions point to the fact that the birds developed from the rep- 
 tiles. As the development was undoubtedly gradual, we should 
 expect to find forms possessing the characters of both groups. 
 
 Many bird-remains have been found, especially in the rocks 
 on the eastern slope of the Rocky Mountains, in Kansas and 
 Colorado, which belong to species which lived later in the 
 period. These birds are of at least two different types, dif- 
 fering in the arrangement of the teeth. One group had the 
 teeth set in separate sockets ; the other had the teeth in 
 grooves. Some of the birds found in the rocks of this age 
 in New Jersey seem to have been toothless, like birds to-day. 
 It is interesting to note that even thus early the bird type 
 had become quite well advanced, having lost not only the 
 teeth but also the long tail of earlier forms. The time of this 
 period was great enough to permit the development of species 
 of birds with highly developed wings, as well as others with 
 degenerate wings. 
 
 In the next succeeding period, to which we shall refer at 
 the close of a later chapter, the birds were all toothless and 
 related to those of to-day. There were woodpeckers, parrots, 
 swallows, cranes, and many others. 
 
CHAPTER XXX 
 THE GRAY SQUIRREL 
 
 Up the oak-tree, close beside him, 
 Sprang the squirrel, Adjidaumo, 
 In and out among the branches 
 Coughed and chattered from the oak-tree. 
 
 LONGFELLOW, The Song of Hiawatha. 
 
 Habitat and Distribution. The gray squirrel (Sciu'rus caro- 
 linen'sis, Fig. 210) \vas formerly found all over the wooded 
 region of the eastern United States, and still exists, though 
 in much diminished numbers, wherever its numerous enemies 
 permit. It does not extend farther west than Minnesota and 
 Wisconsin. It prefers those regions where hardwood trees 
 grow, seldom being found in the depths of coniferous forests. 
 
 External Structure. The elongate body is covered with a 
 skin bearing soft hair, and is clearly divisible into a head, 
 neck, trunk, and tail. There are four appendages, the legs. 
 The fore legs are used in grasping objects and bringing them 
 up to the mouth, and the hind legs for making the long leaps 
 so characteristic of the squirrel's method of progression in 
 trees. Both pairs of legs show the divisions which we have 
 already noted in the amphibians, reptiles, and birds, and they 
 are provided at the end with digits ending in horny claws. 
 The nostrils (Fig. 213, 2) are situated at the anterior extrem- 
 ity, just above the mouth. The eyes are large, and furnished 
 with an upper and lower eyelid and a nictitating membrane. 
 About the mouth and eyes are long, sensitive hairs called 
 vibrissce. At the back of the head are movable flaps of skin 
 (pinnw, Fig. 213, l), placed at the opening of the ears. The 
 long and bushy tail is useful in a number of ways : it is an 
 
THE GRAY SQUIRREL 
 
 399 
 
 ornament ; it is useful as a balancing organ in the long leaps 
 from branch to branch ; and it serves to keep the squirrel 
 warm in its nest in cold weather. 
 
 The Digestive System. The mouth is provided with fleshy 
 lips, which assist in seizing and holding food. On the ventral 
 
 FIG. 210. Photograph of Gray Squirrel 
 
 surface of the mouth rests a large, fleshy tongue (Fig. 213, 5), 
 with numerous nerve-endings of the organ of taste (papillae) 
 scattered over the surface. Two kinds of teeth are present. 
 The front teeth, called incisors (Fig. 213, 4), are long, sharp, 
 and chisel-shaped, and are fitted for gnawing; those in the 
 back of the jaw, separated from the incisors by quite a space, 
 
400 GENERAL ZOOLOGY 
 
 are shorter, broader, and flattened on top, and are fitted for 
 grinding (Fig. 211). The incisors are four in number, two 
 in each jaw; the grinding-teeth in an adult squirrel may 
 
 be eighteen in 
 number, -- four 
 on either side 
 of the lower jaw 
 and five on either 
 side of the upper 
 jaw. Of the 
 grinding-teeth 
 the last three 
 on either side 
 in both jaws are 
 termed molars, 
 
 the others pre- 
 FIG. 211. Skull of Squirrel , ~ f 
 
 molars. One 01 
 
 the premolars in the upper jaw is very likely to be minute, or 
 even missing, having been shed in early life. The complete 
 dentition can be expressed in a simple formula, using letters 
 to stand for the names of the teeth, and placing the lower 
 jaw below the line, thus : 
 
 .2 4 6 12 . 
 
 i -i pm '-a m '6 SB i6 s 
 
 or, because each side of each jaw is similar to the other, 
 .1 236 
 
 A tooth contains & pulp-cavity (Fig. 212, 4) supplied with 
 blood-vessels and nerves, and surrounded by a mass of firmer 
 tissue, or dentine (Fig. 212, 3), which makes up the bulk of the 
 tooth. The dentine is usually covered, where the tooth pro- 
 jects from the gum, with a very hard, smooth substance called 
 
THE GRAY SQUIRREL 
 
 401 
 
 enamel (Fig. 212, l) ; below there is a bony substance, the 
 cement (Fig. 212, 2), surrounding the root of the tooth. In 
 the molar teeth of the squirrel the pulp-cavity, which is at 
 first open at the base, as in the case of man (shown in Fig. 
 212, B), becomes inclosed and develops a root (see Fig. 212, C), 
 after which all growth of the 
 tooth stops. In the incisors 
 of the squirrel the pulp-cav- 
 ity persists throughout life, 
 remaining open so that the 
 tooth continues to grow as 
 fast as it is worn away. The 
 enamel is confined to the 
 front surface of the incisors, 
 so that when the tooth is 
 used on hard substances the 
 softer dentine wears away 
 more quickly and the tooth 
 becomes sharper the more it 
 is used. 
 
 In most fur-bearing animals 
 the lower jaw is articulated to 
 the upper by means of trans- 
 verse condyles, but in the 
 squirrel and its allies the 
 condyles are parallel with 
 the long diameter of the head, 
 thus allowing some backward (From Flower and Ly d e kker's Mammals) 
 and forward motion of the 
 
 lower jaw. The advantages of these special adaptations of 
 the structure of teeth and jaws to the life of a gnawing 
 animal like the squirrel are obvious. 
 
 The ducts of four pairs of salivary glands open into the 
 mouth. A muscular flap, called the soft palate, to distinguish 
 
 D 
 
 FIG. 212. Sections of Teeth 
 
 incisor or tusk of elephant ; .B, 
 human incisor during development; 
 C, human incisor completely 
 formed ; D, human molar; E, molar 
 of ox ; 1, enamel ; 2, cement; 3, den- 
 tine ; 4, pulp-cavity 
 

 ' 
 
 23^ 8 ^"a 
 
 *> fela!* 8 . 
 
 x 8 !! a 
 ^5g&J 
 
 ^^ **! i CV. 2 i O O 
 
 
 -o ^> - -^-o...*. 
 
 8 #&.-& 
 
 
 ' 
 
 Q ^- c=c^3i-?:-"o 
 
 ^ 2 ^s-al^gs-o 
 
 & -2i^t-" L 5 
 
 
 
 
 402 
 
THE GRAY SQUIRREL 403 
 
 it from the roof of the mouth, or hard palate, separates the 
 mouth from the pharynx (Fig. 213, 6). Imbedded in the soft 
 tissues of the soft palate are the tonsils, two small oval bodies 
 the function of which is unknown. The nostrils open pos- 
 teriorly (Fig. 213, 3) into the pharynx. The Eustachian tubes 
 from the ears enter the pharynx at the sides. 
 
 A short, straight oesophagus (Fig. 213, 7, 8) leads to the 
 sac-like stomach (Fig. 213, 9), passing through a muscular 
 partition called the diaphragm (Fig. 213, 19), which separates 
 the heart and lungs in the thoracic cavity from the organs 
 of the abdominal cavity. In the first 
 fold of the intestine is the pancreas 
 (Fig. 213, 13), an extended mass of 
 spongy tissue roughly suggesting a 
 bunch of grapes. The liver (Fig. 
 213, 11) is large and is divided into 
 several lobes. The intestine is very 
 long and much coiled. A clearly 
 marked anterior portion, the small 
 intestine (Fig. 213, 10), can be distin- 
 guished from the posterior portion, or FlG - 214 - Caecum and Ver- 
 rectum (Fig. 213, 14). At the junction miform A PP eildix of the 
 
 . , , n . , /. . Squirrel 
 
 of the small intestine and rectum is 
 
 the cwcum (Fig. 214), from which projects a closed finger-like 
 appendix vermiformis. 
 
 Ductless Glands. Several glands, called ductless glands 
 (owing to the absence of a duct leading from them), are 
 present in vertebrates. With the single exception of the 
 spleen (mentioned in each case in the course of the statements 
 concerning the digestive system) they have not been referred 
 to in our brief discussion of the internal anatomy of the 
 classes of vertebrates, but as they show plainly in the squirrel, 
 attention may be called to them at this time. They are, 
 besides the spleen (Fig. 213, 15), the adrenal capsules (Fig. 213, 16), 
 
404 GENERAL ZOOLOGY 
 
 just anterior to the kidneys, the thymus (Fig. 213, 17), and the 
 thyroid gland (Fig. 213, 18). Their functions are not thor- 
 oughly understood. 
 
 The Circulatory, Respiratory, and Excretory Systems. The 
 heart is inclosed in a pericardium (Fig. 213, 20), and is of the 
 four-chambered type found in the birds. There is a complete 
 double circulation of the blood in the squirrel, as in birds. 
 The lymphatic vessels of the abdomen, called lacteals, which 
 carry from the intestine the absorbed fatty materials of food, 
 unite to form a thoracic duct, which extends anteriorly and 
 empties into the venous system near the heart. 
 
 At the anterior end of the larynx is a cartilaginous flap 
 called the epiglottis (Fig. 213, 30). The lungs (Fig. 213, 32) 
 are larger and more extensible than in the birds, and hang 
 free in the thoracic cavity. Respiration is effected mainly by 
 movements of the diaphragm and the ribs, thus altering the 
 size of the thoracic cavity and causing air to enter and to 
 leave the lungs. 
 
 The kidneys (Fig. 21.3, 33) are almond-shaped bodies in the 
 dorsal part of the abdominal cavity. The ureters (Fig. 213, 34) 
 lead from them to the urinary bladder (Fig. 213, 35), whence 
 the waste products are carried to the surface by the urethra 
 
 (Fig. 213, 36, 37). 
 
 The Skeletal System. The skeleton is, in general, built 
 upon the plan with which we have become familiar in the 
 study of the frog, the lizard, and the pigeon. The cranium 
 (Fig. 213, 38) is articulated to the vertebra by two condyles, 
 as in the amphibians. All the vertebra (Fig. 213, 40), except 
 those in the pelvic region, are free. 
 
 The Nervous and Muscular Systems. The nervous system 
 is similar to that of the bird, but the cerebrum (Fig. 213, 44) 
 is considerably more differentiated. The muscles, especially 
 those in the hind legs, form a complex system adapted to 
 strong and rapid movement. 
 
THE GRAY SQUIRREL 405 
 
 The Reproductive System. The organs of reproduction in 
 the male consist of oval spermaries (Fig. 213, 48) and & penis 
 (Fig. 213, 54) ; in the female, of ovaries with their oviducts. 
 
 Development. The squirrel is viviparous. The ovum pro- 
 duced in the ovary passes into the oviduct, where it becomes 
 fertilized, and in that portion of the oviduct called the uterus 
 it develops into the young squirrel. The young is born in a 
 condition resembling the adult, though the hair is not com- 
 letely formed and the eyes are closed. In the southern states 
 the first of two or three litters appears early in March, and 
 four young are usually produced at a birth. The nest is 
 usually in a hollow tree in the colder portions of its range, 
 and exposed on the branches in the warmer regions. The 
 female keeps the male away from the young during their 
 period of infancy, and feeds them on milk, which is secreted 
 by the mammary glands on her ventral surface. 
 
 Relation to Environment. When the young have been 
 reared, the winter nest in a hollow tree is usually deserted 
 for a structure of leaves and twigs built high among the 
 branches of a tree. This outside nest is occupied (at least in 
 the colder regions) throughout the summer. 
 
 The food of the squirrel in the spring consists largely of 
 buds, especially of the maple and elm. In the summer, fungi 
 and berries are added to the bill of fare, and in the fall nuts 
 form a large part of the diet. The gray squirrel has been 
 accused of varying its vegetable diet with such animal food 
 as the young and the eggs of song-birds, but it is probably 
 not as frequent an offender as the red squirrel, whose bad 
 habits in this respect are well known. The nuts of autumn 
 are gathered and stored in secret places beneath stumps and 
 in hollow trees, and many are separately buried in the ground. 
 Some observers are inclined to think that their sense of smell 
 guides them to the buried food, though it is doubtful if these 
 individual hoards are always located again. 
 
406 GENERAL ZOOLOGY 
 
 When winter comes on, gray squirrels are likely to be 
 later in rising in the morning, preferring to come out in the 
 warmest part of the day, and on some inclement days they 
 may not venture forth at all. There is no evidence, however, 
 that they truly hibernate. 
 
 Gray squirrels have been known to travel in bands from 
 place to place. Of late years, either on account of their 
 much diminished numbers or because of change in the food- 
 supply, we see little of the great migrations which formerly 
 occurred. Many such visitations have been recorded. Penn- 
 sylvania was overrun with squirrels in 1749, and a bounty of 
 threepence a head was offered for their destruction. It is 
 estimated that about six hundred and forty thousand squirrels 
 were killed at that time. In their migrations bodies of water 
 were crossed by swimming, though ordinarily squirrels are 
 not lovers of water. The cause of the migrations is probably 
 to be looked for in connection with the scarcity of the food- 
 supply. 
 
 The general color of .the gray squirrel's fur is protective, 
 and the animal has the habit of flattening itself on the upper 
 side of a horizontal branch, so that it is invisible from below. 
 Of their enemies, the hawks probably give them most trouble. 
 It is said that the red-tailed hawks hunt them in pairs, thus 
 making futile their habit of dodging to the far side of a 
 branch. 
 
 Spread over a large area from Maine to Minnesota and 
 south as far as Florida, it is to be expected that the different 
 individuals will vary considerably. In general, it is found 
 that the colors increase in intensity southward and in regions 
 of copious rainfall, while the legs, tail, and ears show a tend- 
 ency to increase in length. In all parts of their range indi- 
 viduals are sometimes born in which the normal coloring- 
 matter of the hairs is replaced by black pigment, and others 
 in which the pigment is lacking, leaving the fur white. 
 
THE GRAY SQUIRREL 407 
 
 The black individuals are examples of melanism; the white, 
 of albinism. Both conditions are quite common among 
 squirrels. 
 
 The calls of the gray squirrels to each other may often be 
 .heard in the woods, especially in the fall. The " barking," as 
 it is termed, consists of a series of notes ending in a longer 
 snarl. It expresses anger, alarm, or warning. Gray squirrels 
 have sometimes been encouraged to make their homes in city 
 parks, where they soon learn to accept and finally to be 
 largely dependent on contributions of food from human 
 visitors. 
 
CHAPTER XXXI 
 THE ALLIES OF THE SQUIRREL : MAMMALIA 
 
 They say, 
 
 The solid earth whereon we tread 
 In tracts of fluent heat began, 
 
 And grew to seeming random forms, 
 The seeming prey of cyclic storms, 
 Till at the last arose the man. 
 
 TENNYSON, In Memoriam. 
 
 Definition of Mammalia (Lat. mamma, breast). The squir- 
 rel serves to introduce the Mamma'lia, the highest class of 
 the animal kingdom. Mammals are warm-blooded verte- 
 brates covered with hair. Generally two pairs of appendages 
 are present, the anterior of which are never absent in any 
 member of the class. Mammals breathe by lungs. Teeth are 
 almost invariably present, in the majority of cases occurring 
 in two sets. Mammals bring forth their young alive and feed 
 them on milk, except in the very few cases to be referred to 
 under the Monotremata below. 
 
 The principal orders into which the class is divided are 
 mentioned in the following pages. 
 
 The Duckbill and Allies. The duckbill (OrnitJiorJiyn' chus 
 anati'nm, Fig. 215) and two or three species of spiny ant- 
 eater (Echid'na), mammals of the size of a rabbit and found 
 only in Australia, Tasmania, and New Guinea, have many 
 special characteristics. The name Monotrem'ata is given to 
 them in reference to the fact that these mammals possess but 
 a single opening (cloaca) through which the contents of the 
 intestine and the urinary and reproductive products pass 
 outward, as in the case of amphibians, birds, and reptiles. 
 Monotremes also stand alone among mammals in the fact 
 
 408 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 409 
 
 that they lay eggs inclosed in a white, flexible shell, remind- 
 ing one of the egg of a reptile. The duckbill gets its name 
 from its peculiar duck-like beak, which is toothless when the 
 animal is full grown, the teeth being shed after they have 
 been used for a while. The male has a hollow spur on the 
 heel, which is connected with a poison-gland in the thigh. 
 The duckbill is semiaquatic, and lives in burrows in the 
 
 FIG. 215. Duckbill 
 (From Lydekker's Geographical History of Mammals) 
 
 banks of ponds and streams. Its food consists of mollusks, 
 small insects, worms, and crustaceans. Spiny ant-eaters are 
 inhabitants of elevated rocky districts and feed on ants. 
 They are protected by a covering of spines intermixed with 
 the hairs. 
 
 Kangaroos, Opossums, and Allies. The order Marsupia'lia 
 (Lat. marsupium, a pouch) contains a large number of spe- 
 cies, almost all of which are confined to Australia and the 
 
410 
 
 GENERAL ZOOLOGY 
 
 surrounding islands. The mammals comprising it are of vari- 
 ous external form, but the females of nearly all species have 
 an abdominal fold of skin forming a pouch into which the 
 almost helpless young are placed by the mother when born ; 
 they are then carried about with her until they are able to 
 take care of themselves. The kangaroos vary from the size 
 of a rabbit to that of a sheep. The hind legs are developed 
 for jumping. The Virginian opossum (Didel'pJiys Virginia 'na, 
 
 FIG. 210. Photograph of Opossum 
 
 Fig. 216) of our southern and middle Atlantic states is the 
 most northern member of the opossum group, many species of 
 which are found in South and Central America. It has the 
 habit of feigning death when in danger 'of capture, hence the 
 expression, " playing 'possum." 
 
 Fossils from the rocks of the latter part of the Age of Rep- 
 tiles show that marsupials were widely distributed over the 
 earth at that time. Then came the separation of the Austra- 
 lian continent from the land to the north, isolating the mar- 
 supial fauna from the larger and more diversified land areas. 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 411 
 
 The Australian fauna evolved along various lines, produ- 
 cing herbivorous, insectivorous, and carnivorous forms which 
 resemble in outward appearance the members of the higher 
 orders, though they are in reality marsupial in structure. 
 Over, the rest of the world, witli the exception of America, 
 the marsupials were entirely destroyed and their places taken 
 by more highly specialized types. Marsupials retained a foot- 
 hold in South America owing to the absence of overpowering 
 enemies, and on account of their adaptation to climatic and 
 
 FIG. 217. Photograph of Armadillo 
 
 general environmental conditions. They afford an illustration 
 of discontinuous distribution. 
 
 Sloths, Armadillos, and Allies. Both terrestrial and arboreal 
 animals are included in the order Edenta'ta (Lat. e, out; dens, 
 tooth). Edentates have incompletely developed teeth, or if 
 the teeth are well developed, they are of simple structure; 
 true incisors are never present. Many members of the order 
 have a covering of scales formed from the hardening of the 
 skin. 
 
 The armadillos (Fig. 217) are terrestrial American forms 
 which are protected by the scaly covering just referred to. 
 The tail and head are generally exposed, but the animals can 
 
412 GENERAL ZOOLOGY 
 
 roll themselves into a ball, thus offering a hard surface in 
 every direction. 
 
 The sloths of South and Central America are nocturnal, 
 arboreal animals; their natural attitude during the day is 
 hanging from a branch back downward. The hair is gray, 
 but in some species it offers a lodgment for a green alga, a 
 plant of low organization, which gives the hair a green tinge 
 like that of the masses of vegetation of the tropical forest. 
 Sloths rarely descend from the branches of trees. 
 
 Whales, Dolphins, Porpoises, and Allies. The whales, dol- 
 phins, and porpoises are true mammals, though so adapted 
 to their aquatic life that they seem, on superficial examina- 
 tion, to be fishes. The name of the order, Ceta'cea, is derived 
 from the Latin cetus, a whale. 
 
 Flower and Lydekker, in their Mammals, thus review the 
 principal peculiarities of the group : " The external fish-like 
 form is perfectly suited for swimming through the water ; 
 the tail, however, is not placed vertically as in fishes, but 
 horizontally, a position which accords better with the con- 
 stant necessity for rising to the surface for the purpose of 
 breathing. The hairy covering characteristic of all mammals, 
 which, if present, might interfere with rapidity of movement 
 through the water, is reduced to the merest rudiments, a few 
 short bristles about the chin or upper lip, which are often 
 present only in very young animals ; and the function of 
 keeping the body warm is performed by the ' blubber.' The 
 fore limbs, though functionally reduced to mere paddles, 
 with no power of motion except at the shoulder-joint, have 
 beneath their smooth and continuous covering all the bones, 
 joints, and even most of the muscles, nerves, and arteries of 
 the human arm and hand ; the rudiments of hind legs, found 
 buried deep in the interior of the animal, apparently sub- 
 serve no useful purpose, but point an instructive lesson to 
 those who are able to read it." 
 
OF THf 
 
 UNIVERSITY 
 
 THE ALLIES OS\THE SQUIRR^t: MAMMALIA 413 
 
 Cetaceans are found in al seas, and feed on fishes, crus- 
 taceans, and the smaller floating animal life of the ocean gen- 
 erally. They vary from four to eighty feet in length, some 
 of the whales being the largest of existing animals. There is 
 every reason to believe that the group is descended from land- 
 mammals. The whalebone-whales are species without teeth, 
 but with a development of baleen or whalebone in the upper 
 jaw, which acts as a strainer. By means of the closely set, 
 flexible strips of whalebone the small animals on which they 
 feed are retained, while the water is forced out. Several 
 species are found in the Atlantic and Pacific oceans. The 
 sperm-whale (Physe'ter macroceph' alus) has a square head, 
 
 FIG. 218. Narwhal. (After Cuvier) 
 
 within which is a cavity containing oil, which on being refined 
 yields spermaceti. The narwhal (Mon'odon monoc'eros, Fig. 218) 
 is a smaller species, the males of which possess a single abnor- 
 mally developed incisor tooth, usually on the left side, which 
 grows into a tusk six or eight feet in length. 
 
 Hoofed Mammals. The great assemblage of animals called 
 Ungula'ta (Lat. unguis, a nail) includes the hippopotami, 
 pigs, camels, deer, the giraffes, antelopes, oxen, goats, sheep, 
 rhinoceroses, horses, and elephants. All these mammals have 
 the toes ending in either a blunt nail or a fully developed 
 hoof, both of which structures are formed from the thicken- 
 ing of the skin of the toes. In ungulates like the cow and 
 sheep there are two divisions in the hoof, and the animals 
 really walk on the tip of the third and fourth digits, the others 
 being much reduced in size. In the horse and its allies this 
 reduction has gone much farther, so that the tip only of the 
 
414 GENERAL ZOOLOGY 
 
 third digit is used for support. The elephants have five toes, 
 each incased in a short nail. The two living species of ele- 
 phants would undoubtedly be removed to a separate order if 
 
 fossil forms had not been 
 discovered possessing 
 characters intermediate 
 between these mammals 
 and other ungulates. 
 
 Ungulates are adapted 
 to a terrestrial life and 
 feed almost entirely on 
 vegetable food. Four 
 kinds of teeth are pres- 
 FIG. 219. Skull of Peccary, showing teeth ^ __ incisors> can i nes , 
 
 premolars, and molars. The first kind and the last two kinds 
 will be recognized from the study of the squirrel; the canines, 
 so named because they are well -developed in the dog (Lat. 
 cam's, a dog), fill the space between the incisors and premolars. 
 The canines are often elongated to form tusks for defense or 
 for obtaining food (see Fig. 219) ; the incisors serve to crop 
 the herbage ; the molars and premolars are flattened for 
 grinding. 
 
 Horns for defense have been developed in many species 
 of ungulates. They are of various sorts. The rhinoceroses 
 (Fig. 220) have one or more median horns, which are com- 
 posed of a thickened and hardened portion of the skin and 
 hair, covering a short protuberance of the skull. In the 
 giraffes there are one or two pairs of horns consisting of a 
 layer of skin over bony processes of the skull. Neither in 
 the rhinoceros nor the giraffe are the horns ever shed. In the 
 North American pronghorn antelope (Antiloca'pra america'na) 
 the horns are branched and consist of a hardened and thick- 
 ened skin on a bony core. The thickened skin is shed peri- 
 odically but the core is retained. The horns in true antelopes 
 
THE ALLIES OF THE SQUIRREL : MAMMALIA 415 
 
 and in oxen, sheep, and goats, are of similar structure. They 
 are usually found in both sexes and are never shed. In the 
 deer family (Fig. 221) the horns, called antlers, consist of 
 outgrowths of bone covered each year during the period of 
 growth with a sensitive skin called " the velvet." When 
 the annual growth is completed the supply of blood to the 
 antlers ceases and the velvet peels off, leaving the bone bare. 
 After a time the antlers separate from the skull and are shed. 
 In most deer this takes place annually. In some members of 
 the family the antlers remain simple throughout life ; in 
 
 Fi<;. 220. Head of Rhinoceros 
 (American Museum of Natural History) 
 
 others they become much branched in successive annual 
 growths (Fig. 221). It is interesting to note that, in a broad 
 way, this was the order of development of antlers in geo- 
 logical time, the earliest deer of which we have any knowl- 
 edge being without them. Horns and antlers are used in the 
 battles of the males for the possession of the females, as well 
 as for defense of themselves and their band. The presence 
 
416 
 
 GENERAL ZOOLOGY 
 
 FIG. 221. Series of Antlers 
 
 (American Museum of Natural 
 History) 
 
 of these organs is usually ascribed 
 to the action of sexual selection. 
 
 A large number of the ungulates 
 have learned the advantage of 
 cooperation, and live in herds, which 
 possess an organized power of resist- 
 ance far greater than any individual 
 has. In many cases, especially among 
 the deer, scent-glands are developed 
 on the head below the eyes, and as 
 the sense of smell is extremely acute, 
 notice of the presence of other mem- 
 bers of the herd is given by the odor 
 of the secretion from these glands. 
 Often the tail and rump are con- 
 spicuously marked with white, show- 
 ing plainly when the animal is in 
 flight, and probably serving as a 
 recognition or signaling mark. 
 
 The structural peculiarities 
 already referred to form the basis for 
 separating the ungulates into three 
 divisions, those with an even num- 
 ber of toes, as the cow ; those with 
 an odd number of toes (one or three), 
 as the rhinoceros and horse ; and 
 the long-nosed forms (Proboscid'ea), 
 including the elephants. Of the 
 even-toed ungulates the families of 
 camels (Camel'idce), deer (Cer'vidce) 
 and antelopes, goats, sheep, and 
 oxen (Bo'vidw), have the stomach 
 (Fig. 222) divided into a digestive 
 and a non-digestive or storage region, 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 417 
 
 forming a complex organ of several compartments. The food 
 is taken into the first two of these divisions, the reticulum or 
 honeycomb bag, and the rumen or paunch, where it remains 
 till the animal has finished grazing and has leisure for its 
 digestion. The food is then raised to the mouth in a some- 
 what softened condition and is there ground between the 
 molar teeth and moistened with saliva, after which it is again 
 swallowed, this time into the psalterium, or manyplies, so 
 called from the numerous folds in its lining membrane. The 
 food slowly filters through the 
 manyplies into the true digestive 
 stomach, or abomasum. This habit 
 of chewing the cud has suggested 
 the name of 
 ruminants (Lat. 
 rumen, throat) 
 for these ungu- 
 lates. 
 
 Though zoolo- 
 gists do not feel 
 certain as to the 
 ancestry of the 
 domestic horse 
 (E'quus cabal'lus), a recently discovered animal (Equus 
 przewal'skii, Fig. 223) of the sandy deserts of Central Asia 
 may be its progenitor. The interesting story of the geological 
 development of the horse is told farther on (p. 428). 
 
 Of the Proboscidea the elephants alone require mention. 
 There are two existing species, the Asiatic (El'ephas in'di- 
 cus) and the African elephant (Elephas africa'nus). The latter 
 can be distinguished from the former by its very large ears. 
 The Asiatic species has long been domesticated and many 
 stories are told of its intelligence. The African species 
 was used by the Romans in battle and circus games, but in 
 
 FIG. 222. Diagram of Stomach of Ruminant. (After 
 
 Wiedersheim) 
 (Arrows and dotted lines show the course of the food) 
 
418 
 
 GENERAL ZOOLOGY 
 
 modern times these animals have been hunted so persist- 
 ently for their ivory that there is danger of their being ex- 
 terminated. Steps are now being taken to prevent their 
 complete destruction. 
 
 Gnawing Mammals. The Roden'tia (Lat. rodere, to gnaw) 
 are the most numerous in point of species and are the most 
 widely distributed of all the mammals. Here belong the 
 
 FIG. 223. Photograph of Frzewalsky's Horse 
 
 hares, guinea-pigs, porcupines, mice, rats, beaver, woodchuck, 
 prairie-dog, and squirrels. Rodents are distinguished by the 
 absence of canine teeth and the presence of chisel-shaped 
 incisors, which grow from persistent pulps (see Fig. 212). 
 They are mostly terrestrial animals, though a few, like the 
 beaver, are modified for an aquatic existence, and others, like 
 the squirrels, for life in the trees. 
 
 The hares are distinguished from all other rodents by the 
 presence of a second pair of incisor teeth behind the first pair 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 419 
 
 in the upper jaw. Well-known American species are the 
 cottontail, or gray rabbit, of the East (Le'pus florida'nus), the 
 varying hare (Lepus america'nus) of the North, and the north- 
 ern jack-rabbit (Lepus campes'tris) of the West. The cottontail 
 is so named from the white tail, which is plainly shown in 
 flight and probably serves as a signaling or recognition mark. 
 The varying hare is a larger and more northern species which 
 takes on a white coat of fur in winter. The northern jack- 
 rabbit also changes to white in the northern part of its range ; 
 farther south the change is only partial or entirely wanting. 
 The domestic rabbit is descended from the common rabbit of 
 the Mediterranean basin (Lepus cunic'ulus). 
 
 The porcupine (Erethi'zon dorsa'tus) is a sluggish, stupid 
 animal, which, having spines for protection, relies on them 
 to such an extent that it hunts its food in the daytime, 
 a habit which most rodents have had to give up (if they 
 ever possessed it) on account of their lack of protection and 
 means of defense against numerous enemies. The squirrels 
 have solved the problem in another way by the development 
 of extreme watchfulness. There is no truth in the oft- 
 repeated statement that the porcupine can shoot its quills, 
 the fact being that, as they are loosely attached, they are 
 likely to come out on slight pressure. 
 
 So much has been written on the beaver and its works 
 that its habit of felling trees for its dam or for food, its win- 
 ter storage of branches or twigs beneath the ice, and the 
 habits developed in connection with its communal life are 
 pretty well known to everybody. In the communal life of 
 the beaver, as among the bees and wasps, instinctive actions 
 are performed with a high degree of perfection. The beaver 
 also has capabilities of meeting new conditions, and it has 
 been credited with a considerable degree of intelligence. 
 It has been hunted so persistently for its fur and scent- 
 bags that it is now almost extinct. The few remaining 
 
420 GENERAL ZOOLOGY 
 
 individuals scattered in isolated colonies seldom dare to raise 
 lodges, but have to be content with a home in the bank of 
 some stream. 
 
 Flesh-Eating Mammals. The carnivorous mammals, Car- 
 niv'ora (Lat. caro, flesh ; vorare, to devour), are the flesh-eaters 
 par excellence. The incisor teeth are small and sharp ; the 
 canines are generally long, strong, and conical, fitted for 
 tearing ; and the pre molars and molars are raised into more 
 or less sharp ridges. The toes are sheathed in claws, often 
 fitted for grasping, and in one family, the cats, are capable 
 of being retracted and thus kept sharp by being saved from 
 constant friction. The group has divided along two main 
 lines of development, one adapted to terrestrial, the other to 
 aquatic life. To the first belong the family of cats (Fe'lidoe), 
 including the lion, tiger, leopard, lynx, jaguar, and puma ; 
 the hyenas (Hycen'idce) ; the dogs, wolves, and foxes ( Oan'- 
 idov)' 9 the bears ( Ur'sidcc) ; and the raccoons (Procyon'idce). 
 To the second division belong the seals and walruses. 
 
 The jaguar is a South American cat resembling in general 
 appearance the leopard of Africa, and, like it, an inhabitant 
 of wooded regions, where it spends much of its time in trees. 
 The irregular markings resemble in a general way the pat- 
 terns of light and shade beneath the leaves of a forest. The 
 markings are usually spoken of as an illustration of aggres- 
 sive resemblance. The dun-colored lion and the gayly striped 
 tiger are mentioned as similar examples, the one resembling 
 the brown of desert places and the other the vertical shadows 
 of reeds and grasses in tropical jungles. The origin of our 
 domestic cat and dog, like that of some of our other domestic 
 animals, is uncertain, but it is generally believed that the cat 
 is descended from the Egyptian or Caff re cat (Fe'lis caf'frd}, 
 an African and Asiatic species domesticated by the Egyptians 
 and held in veneration by them ; the dog is variously thought 
 to be the descendant of some wild species now extinct, or of 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 421 
 
 one of several wolves or jackals, or a mixture of several 
 species. The great length of time since the dog first became 
 the companion of man, and the numerous races which have 
 arisen, render the question extremely complicated. 
 
 Of our smaller wild carnivores none is more generally 
 known and feared than the skunk (Mephi'tis), of which there 
 are many species in the United States. Their powerful means 
 of defense is a pair of glands secreting a strong-smelling fluid, 
 which they are able to eject for a distance of several feet. 
 Though they are destroyed by the farmer for robbing his 
 hen-roosts, they are on the whole beneficial, as they feed 
 largely on injurious insects. Those who have observed them 
 most say that they make interesting and cleanly pets, even 
 without the removal of the scent-glands, and that they are 
 not prone to defend themselves except under great provoca- 
 tion. The presence of this means of defense has had its effect 
 upon the skunk's character, insomuch that if a person comes 
 upon it in the daytime it is likely to make no special effort 
 to escape, but goes about its business leisurely, secure in the 
 confidence that it will not be molested. The eastern species 
 are black animals about the size of a cat, with prominent white 
 stripes down the back and a white patch on the forehead. The 
 white markings on the black ground are usually cited as an 
 example of warning coloration. It has been asserted that it is 
 advantageous to the skunk to be thus marked, for if it had 
 a uniform black color, it might be mistaken in the uncertain 
 light for other night-prowlers and be pounced upon and killed 
 by an enemy before it had an opportunity to use its peculiar 
 method of defense. 
 
 Among the aquatic carnivorous forms the Alaskan fur-seal 
 (Callota'ria alasca'nus) has been the subject of international 
 discussion on account of the value of its fur as an article of 
 commerce. This is a truly migratory species of mammal, 
 bringing up its young on the Pribilof or Fur-Seal Islands in 
 
422 GENERAL ZOOLOGY 
 
 the summer, and going far to sea in the winter. The males 
 do not reach their full size and strength till about the seventh 
 year, and until that age the young males herd by themselves, 
 being forbidden the general herd by the older males. The 
 females mature in two years. Early in May the full-grown 
 males appear at the islands, and the females a few weeks after- 
 ward. Each male immediately collects as many females as 
 he can guard, and battles are frequent before the groups are 
 made up. The old males begin to leave the beaches about 
 the middle of July. Seal-hunters are restricted in their oper- 
 ations to killing the young males of three years of age 
 and upwards. This restriction tends to prevent the extermi- 
 nation of the species. The fur is most valuable between the 
 ages of three and seven years. 
 
 Insect-Eating Mammals. The insect-eating mammals, Insec- 
 tiv'ora, are usually of small size. The teeth are sharp and 
 numerous, and the molars have sharp points for crushing the 
 bodies of insects. The eyes are often small and hidden in 
 the fur, especially in the forms which, like the moles and 
 shrews, burrow in the ground. The star-nosed mole (Con- 
 dylu'ra crista'ta) is a common American species living in 
 peat-swamps and rich land near ponds and streams. They 
 make great burrows, and the earth thrown up may sometimes 
 make a pile a foot or more in diameter. The name is given 
 from a fleshy filamentous appendage on the nostrils, which 
 is probably used as an organ of touch. Some of the shrews 
 are the smallest mammals known. They generally live in 
 burrows like the moles. They somewhat resemble mice, from 
 which they can be distinguished by the different plan of 
 the teeth. 
 
 Bats. The Chirop'tera (Gr. cheir, hand ; pteron, wing) are 
 marked off from all other mammals by the possession of 
 wings, which are formed of skin stretched over the bones of 
 the arm, and including also the legs and sometimes the tail. 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 423 
 
 So well adapted for aerial locomotion have the bats (Fig. 
 224) become that progress on the ground is almost impossible. 
 .The sense of touch is greatly developed not only on the 
 muzzle but on the wings 
 as well, so that the animals 
 are able to avoid obstacles 
 in their nocturnal flights. 
 During the day bats hang 
 themselves up by their legs 
 to sleep in caves and in 
 hollow trees. Some species 
 feed on insects, others on 
 fruit, and some, the vampire 
 bats of Central and South 
 America, feed on blood. 
 The latter have the teeth 
 peculiarly adapted to cut- 
 ting, the skin of animals. 
 The (Bsophagus is so nar- 
 row that no solid matter 
 can pass down it. 
 
 Primates. The Prima'tes 
 (Lat. primus, first) include 
 the monkeys, apes, and 
 ,man. The teeth are gener- 
 ally adapted to a diet of 
 
 FIG. 224. Photograph of Bat 
 
 both plant and animal food ; the five toes and fingers are sepa- 
 rate and are usually provided with nails; the thumb is oppos- 
 able to the other digits, and the eyes are directed forward. 
 
 The spider-monkeys (At'eles, Fig. 225) of South and Cen- 
 tral America are representative forms of the New World 
 monkeys. They have a long tail, which serves as an organ 
 of prehension. The most man-like of the monkeys are the 
 orang-utan (Sim'ia sat'yrus) of Borneo and Sumatra, and the 
 
424 
 
 GENERAL ZOOLOGY 
 
 gorilla (Croril'la goril'la) and chimpanzee (Anthropopithe'cus 
 troglod'ytes) of equatorial Africa. Of these the chimpanzee 
 is the most gentle in disposition and the most intelligent. 
 All these monkeys lead a more or less arboreal life and build 
 nests in trees, where the young are produced. 
 
 FIG. 225. Photograph of Spider-Monkey 
 (American Museum of Natural History) 
 
 That man belongs zoologically in the same group with the 
 monkeys is now universally admitted, for in the structural 
 characters upon which classification largely depends, as Prc 
 fessor Huxley pointed out many years ago, he differs less 
 from the apes, which resemble him most, than they do from 
 other monkeys. The principal anatomical characters are the 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 425 
 
 possession 'of a relatively larger brain-case and less-developed 
 canine teeth, the adaptation of the vertebral column to an erect 
 posture, the greater length of the lower as compared with the 
 upper extremities, and absence of the power to oppose the 
 great toe to the other toes. Some of these differences seemed 
 to have been bridged over by the discovery in 1891-1892 of 
 the fossil remains of an ape-like -man, or man-like ape (Pithe- 
 canthro'pus erec'tus), from the island of Java. These remains 
 point to the existence of an animal about five and a half feet 
 high, with a skull whose profile is " roughly midway between 
 the skull of a young chimpanzee and the lowest human skull," 
 and whose brain-capacity was nearly equal to that of some 
 savage races of to-day. It is now generally admitted that there 
 is but one species of man in the world (Ho 1 mo sa'piens), and 
 the tendency is to group all the different varieties into three 
 races, the Caucasian of Europe, the Mongolian of Asia, 
 and the Ethiopian of Africa. 
 
 Instinct and Intelligence in Mammals. There are some who 
 ascribe to the birds and to the mammals below man mental 
 attributes, including a power of reasoning, differing from the 
 attributes of man not so much in kind as in degree. Some 
 writers separate man quite distinctly in this regard from 
 the lower animals. Careful observation and experiment with 
 animals under conditions as nearly natural as possible is 
 needed before a final answer can be given to questions which 
 are beset with the same difficulties that we have noted in con- 
 nection with the study of instinct and intelligence in insects. 
 
 In order to test whether dogs and cats exhibit any power 
 of reasoning, Professor Thorndike, of Columbia University, 
 experimented upon these animals by inclosing them when 
 hungry in boxes which could be opened by operating some 
 simple mechanism, such as pulling a wire loop or turning a 
 wooden button. Freedom and food outside were the motives 
 to escape. The experiments showed that in all cases the 
 
426 GENERAL ZOOLOGY 
 
 animal instinctively clawed at the side of the box, in the 
 course of which series of movements the door would usually 
 be opened sooner or later. If the animal was replaced in the 
 box again and again, the number of useless clawing actions 
 gradually decreased, till finally the mechanism was operated 
 as soon as the animal was put in the box. If the animal could 
 reason, it would be expected that the box would be opened at 
 once after its first successful attempt; so Professor Thorndike 
 says : " This sort of history is not the history of a reasoning 
 animal. It is the history of an animal who meets a certain 
 situation with a series of instinctive acts ; included without 
 design among these acts is one which brings freedom and food." 
 
 With this general conclusion Professor C. Lloyd Morgan, 
 in his Animal Behavior, agrees. This author says: "As at 
 present advised, therefore, I see no reason for withdrawing 
 from the position provisionally taken up. The utilization of 
 chance experience, without the framing and application of 
 an organized scheme of knowledge, appears to be the pre- 
 dominant method of animal intelligence." 
 
 In their mental attributes monkeys seem to occupy an 
 intermediate position between man and the lower mammals. 
 Some of the observations made on this subject have been 
 thus summed by Professor R. Ramsay Wright, of Toronto 
 University. " Sympathy has been observed in many forms. 
 The female gorilla has been said to die of grief when the 
 young is taken away ; orangs have come in a body to beg for 
 the corpse of a dead companion, gibbons for a wounded com- 
 rade. A female gibbon has been observed to wash the face 
 of her young, a Cebus to brush off flies from the face of hers 
 while sleeping, and all monkeys assist each other with the 
 utmost zeal in the search for intruders in their hair. They 
 have been noticed to feed each other, to carry food to sick 
 monkeys, and to adopt orphans. More remarkable than all, 
 a monkey has been seen to throw a rope to a comrade who 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 427 
 
 had fallen overboard. That all monkeys are fond of play, 
 especially when young, is notorious ; they have a keen sense 
 of the ludicrous and enjoy exciting laughter, but they resent 
 being jeered at and may revenge themselves, as in the case 
 of a Cape baboon, who bespattered with mud an officer in 
 his dress uniform who had offended him." 
 
 Professor Thorndike closes an article in the Popular Science 
 Monthly for July, 1901, in a way which serves to bring out 
 the intermediate position of the monkeys between man and 
 the lower mammals. He says : " In their method of learning, 
 although monkeys do not reach the human stage of a rich 
 life of ideas, yet they carry the animal method of learning, 
 by the selection of impulses and association of them with 
 different sense-impressions, to a point beyond that reached 
 by any other of the lower animals. In this, too, they resem- 
 ble man ; for he differs from the lower animals not only in 
 the possession of a new sort of intelligence but also in the 
 tremendous extension of that sort which he has in common 
 with them. A fish learns slowly a few simple habits. Man 
 learns quickly an infinitude of habits that may be highly 
 complex. Dogs and cats learn more than the fish, while 
 monkeys learn more than they. In the number of things he 
 learns, the complex habits he can form, the variety of lines 
 along which he can learn them, and in their permanence 
 when once formed, the monkey justifies his inclusion with 
 man in a separate mental genus." 
 
 Economic Importance of Mammals. The mammals come 
 into more intimate relations with man than any other group 
 of animals. From them he gets materials for dress, wool, 
 leather, and furs ; food in the shape of butter, cheese, and 
 meat of different kinds. They are his beasts of burden the 
 world over, and they furnish a long line of miscellaneous 
 products such as horn, bone, ivory, perfumes, whalebone, 
 oils, fats, and material for fertilizers. 
 
428 GENERAL ZOOLOGY 
 
 Geological Development of Mammals. With the upheaval 
 of the Rocky Mountain system at the close of Mesozoic 
 time the North American continent assumed practically its 
 present outline, with the exception of a strip along the south- 
 eastern coast, which was still beneath the level of the ocean 
 (see map, p. 363). In connection with this disturbance of 
 level and the accompanying climatic changes the great rep- 
 tiles so characteristic of the period became extinct and left 
 the field clear for the development of the mammals. The 
 succeeding period is therefore called the Age of Mammals. 
 As we have already seen, representatives of each group of 
 animals have appeared before the age which bears its name, 
 so the first mammals of which we have any knowledge are 
 to be credited to the Age of Reptiles. They were nearly all 
 of small size and allied to the marsupials and monotremes 
 of to-day, groups which we have noticed as being the 
 lowest of the class. 
 
 During the Age of Mammals there were extensive areas 
 of fresh- water lakes in western North America, shown by the 
 shaded areas on the map on page 363. It is from these deposits 
 that much of our information regarding the early mammals 
 of America has been obtained. The American Museum of 
 Natural History in New York City has on exhibition a large 
 series of fossils from this region. Many of the specimens 
 discovered are of generalized structure; that is, they possess 
 the characteristics of several different groups of to-day, with- 
 out much special adaptation or modification to a particular 
 kind of life or food. It is among such animals that we must 
 look for the ancestors of the species of to-day, for no species 
 of mammal which was in existence in the Age of Mammals 
 has lasted through to the present time. 
 
 Of no other animal have we so complete and satisfactory 
 a geological record as in the case of the horse. From fossil 
 remains found in the western part of the United States we 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 429 
 
 are able to trace its evolution from an ancestor (ProtoroTiip 1 - 
 pus, Fig. 226) a little larger than a cat, with four toes on 
 the front feet and three on the hind feet. The figure of 
 Protorohippus is photographed from a water-color by Mr. 
 Charles II. Knight, based on skeletal material at the Amer- 
 ican Museum of Natural History. The markings are drawn 
 as they are supposed to have existed on the animal. There is 
 
 FIG. 226. Protorohippus 
 (American Museum of Natural History) 
 
 reason to believe that the undiscovered ancestors of this early 
 form had five toes on each foot. The transition to the horse 
 of to-day has been accomplished by a gradual increase of size, 
 a reduction in the number of toes, and a reduction in number 
 and an increase of complexity in the teeth. The main steps 
 in the evolution of the bones of the feet are shown in Fig. 227. 
 The changes in the limbs are in the nature of adaptations 
 fitting the animal for rapid locomotion over level, grassy 
 
430 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 431 
 
 areas. The increased complexity of the teeth makes them 
 more efficient grinding-organs. In the latter part of the Age 
 of Mammals North America was broadly connected with Asia, 
 and the horse is known to have inhabited plains of all the 
 continents excepting Australia. After the horse had reached 
 practically its present state of development (in the early part 
 of the next succeeding period, the Age of Man) it seems to 
 have disappeared entirely from America, owing to causes not 
 thoroughly understood, though generally ascribed to the 
 oncoming cold of the Glacial Epoch. The horse persisted, 
 however, in Europe, and was one of the animals which prim- 
 itive man domesticated. The various uses to which the horse 
 could be put were gradually learned by man, for Professor 
 Osborn, of the American Museum of Natural History, says 
 there is " abundant proof that man first hunted and ate, then 
 drove, and finally rode the animal." It was reintroduced into 
 America by the Spaniards at the time of their conquest, and 
 soon ran wild. 
 
 The carnivores were early represented by generalized 
 types, and later by dogs and saber-toothed cats. The latter 
 get their name from their lengthened canine teeth. Insec- 
 tivorous mammals, rodents, bats, ungulates of many kinds, 
 and even the primates also occurred, and in the waters of the 
 oceans were found cetaceans of different species. 
 
 The Age of Mammals began in North America with a 
 warm climate, as in the case of previous periods, but toward 
 its close frigid conditions began to prevail, probably due to 
 the gradual elevation of the continental land-mass. The on- 
 coming cold produced in the northern part of both America 
 and the Eurasian land-mass conditions so severe that to the 
 period the name Glacial Epoch is given. During its contin- 
 uance all of North America north of a line drawn from 
 New York through Pennsylvania, Indiana, Missouri, South 
 Dakota, Montana, and Oregon, was covered at different times 
 
432 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 433 
 
 with a layer of ice, which in certain regions grew to be a 
 mile thick over the land, destroying all life or forcing it to 
 migrate southward to escape the rigors of the climate. As 
 there were several invasions and retreats of the ice, there 
 may be said to have been several glacial epochs, separated 
 by long periods of warmer weather, when the animal and 
 plant life could slowly work its way back on the edge of 
 the retreating glaciers. There is a peculiar interest to this 
 period, inasmuch as it introduces the last of the great geo- 
 logical eras, the Quaternary Period, or the Age of Man. 
 
 A conspicuous feature of the mammalian life of the Age 
 of Man was the great size of many of the species. After the 
 opening glacial epoch the climate became mild again, and 
 this seems to have favored the development of abundant 
 vegetation and great mammalian forms. One of the largest 
 and most widely distributed species was the Mammoth 
 (EVephas primige'nius, Fig. 228), a proboscidean larger than 
 the elephant of to-day and covered with a thick coat of 
 hair, an adaptation to cold temperate regions. Its remains 
 have been found frozen in the ice of Siberia, the hair and 
 flesh perfectly preserved. Early man knew of this great 
 mammal, for a drawing of the creature is in existence, 
 made on a piece of its own tusk (Fig. 229). The mastodons 
 were somewhat similar to the mammoths, but fitted on the 
 whole for a warmer climate. There are over thirty species 
 of mastodons known, of nearly world-wide distribution. 
 They have become extinct within so short a time, geologi- 
 cally speaking, that traditions of their existence as living 
 animals occur among men. 
 
 The remains of giant edentates have been found in South 
 America. Recent discoveries seem to show that some of them 
 were living within the period of man on that continent, for 
 some of the tribes of South American Indians have traditions 
 respecting these monsters. In Europe and Asia there were 
 
434 
 
 GENERAL ZOOLOGY 
 
 lions, hyenas, bears, rhinoceroses, and gigantic ungulates. In 
 Australia, as will be expected from what has been said of the 
 distribution of the group, there were marsupials of various 
 species. 
 
 But the great interest of the Quaternary Period centers 
 about man. If it is not yet possible to prove to the satisfac- 
 tion of every one the existence of man in the Glacial Epoch 
 in North America, it is certain that he was in existence in 
 Europe at that time. It would be interesting to know, if 
 possible, how far distant we should place this period, and 
 
 FIG. 229. Primeval Drawing of Mammoth on Mammoth Tusk 
 (From Lucas' Animals of the Past) 
 
 where man first appeared on the earth, but to neither of these 
 questions can any satisfactory answer be given. Regarding 
 the time, estimates have been made in various ways, reaching 
 conclusions which vary greatly. A conservative estimate is 
 that the Glacial Epoch began two million four hundred thou- 
 sand years ago and ended eighty thousand years ago. Regard- 
 ing the place of man's origin, it has been asserted that his 
 earliest home was Africa, because the great apes, which most 
 resemble him, live there to-day ; or that it was somewhere in 
 equatorial regions, where the vegetation is abundant and the 
 climate quite similar throughout the year ; others claim that 
 it was on some of the high plains of the temperate zone, like 
 
THE ALLIES OF THE SQUIRREL: MAMMALIA 435 
 
 those of Persia and Tibet. After all, the study of the condi- 
 tions under which he lived is a more important subject than 
 the discussion of either the time or place of his origin. 
 
 Primitive man was a savage, living in caves. His princi- 
 pal means of defense, in addition to those with which nature 
 had provided him, were a stone picked from the ground or a 
 bough broken from a tree. At an early stage in his develop- 
 ment he learned the use of fire, made clothing of the skins of 
 wild beasts to keep himself warm, and fashioned rude imple- 
 ments out of bone, shell, horn, wood, and stone. In those 
 places where such easily worked metals as copper and zinc 
 were accessible man early learned their use and made from 
 them implements of bronze, a compound of the two metals. 
 From a hunting existence arose the nomadic or wandering 
 life, with property in the shape of herds of domesticated or 
 semidomesticated animals, and the more fixed agricultural 
 condition in which the main dependence for food was on the 
 products of the field. We see people to-day in each of these 
 conditions of existence. Along with the advance in the mode 
 of life has gone a mental and moral evolution as man's con- 
 quest of nature has been pushed through wider and wider 
 fields. 
 
CHAPTER XXXII 
 THE HISTORICAL DEVELOPMENT OF ZOOLOGY 
 
 The present generation finds itself the heir of a vast patrimony of science ; 
 and it must needs concern us to know the steps by which these possessions 
 were acquired, and the documents by which they are secured to us and our 
 heirs forever. WHEWELL, History of the Inductive Sciences. 
 
 Divisions of the Science of Zoology. Zoology is the science 
 that treats of animals. It is a sister science of botany, which 
 deals with the plant world. Both botany and zoology are 
 branches of biology, the science which has to do with living 
 things. The various ways in which animals may be consid- 
 ered by man give rise to the different divisions of the science 
 of zoology. Thus the study of the structure of the organs of 
 animals is comparative anatomy, or morphology ; the study 
 of the functions of the organs (such as nutrition, growth, and 
 reproduction) is comparative physiology. The consideration 
 of the mental phenomena of animals is the field of compara- 
 tive psychology. The geographical distribution of animals deals 
 with the fauna of the different land-areas ; the geological dis- 
 tribution (paleontology), with the animal life of past eras. The 
 study of the relations of animals to each other, to plants, 
 and to their inorganic environment, is ecology. Under the 
 name of bionomics, Professor E. Ray Lankester has defined 
 this as " the lore of the farmer, gardener, sportsman, and 
 field naturalist." To show the blood-relationships of the dif- 
 ferent members of the kingdom, animals are arranged in 
 groups, or classified ; this division of the subject is system- 
 atic zoology. The consideration of the uses of animals to man 
 is the field of economic zoology. Finally, the inquiry after 
 the causes of the various phenomena of nature is etiology. 
 
 436 
 
HISTORICAL DEVELOPMENT OF ZOOLOGY 437 
 
 Zoologists are, of course, interested to understand, as far as 
 they can, the phenomena exhibited by the animal kingdom. 
 We have called attention to some of these efforts at explana- 
 tion in Chapter X. 
 
 It will serve to give us the historical perspective which 
 will enable us to better appreciate the great mass of informa- 
 tion available for us to-day, if we pass in brief review the 
 main steps in the development of this body of knowledge. 
 We shall gain thereby some insight into the method of scien- 
 tific research, and shall be helped to see the limitations of 
 our knowledge and to appreciate the problems which are 
 now pressing for solution. 
 
 Zoology among the Greeks and Romans. In our survey we 
 need not go farther back than the time of the Greeks, for it 
 was there, though in no systematic form, that the beginnings 
 of modern zoology were laid. The Greeks' knowledge of 
 animals grew from humble beginnings in an early prehistoric 
 period, and reached its culmination in the philosopher Aris- 
 totle (384-322 B.C., Fig. 230). Though the Greeks early 
 showed a lively scientific curiosity and a desire to explain 
 the world of matter and life by ascribing phenomena to natu- 
 ral causes, they generally failed to appreciate the necessity 
 for careful observation of a long series of individual facts 
 before proceeding to explain those facts by reference to a 
 general law. 
 
 Aristotle's name is the greatest among Greek scientists 
 partly because he appreciated this need. He laid great stress 
 upon the importance of what is called the inductive method 
 in the pursuit of scientific knowledge. This method demands, 
 first, careful observation of a wide range of facts ; second, the 
 study of those facts with reference to each other, to bring 
 out the essential and to eliminate the nonessential elements ; 
 and finally, the explanation of the facts observed, by a. state- 
 ment of the law involved. Aristotle protested against the 
 
438 
 
 GENERAL ZOOLOGY 
 
 separation of theory and fact, which invariably occurs when 
 theories are not put to the test of agreement with the 
 facts. "We must not," he said, "accept a general prin- 
 ciple from logic only, but must prove its application to 
 each fact; for it is in facts that we must seek general prin- 
 ciples, and these must always accord with facts." Though 
 
 so clearly stated, the 
 principle was forgot- 
 ten by the world until 
 it was restated by 
 Francis Bacon (1561- 
 
 M '^^^i Ilk I 626 ) in the seven- 
 
 J|| II teenth century. To be 
 
 B sure, the English Fran- 
 
 ciscan monk, Roger 
 
 Bacon (1214-1292), 
 appreciated the neces- 
 
 BP|M mj sity of observation in 
 
 ^r^'^-mfm nature, and himself 
 JjHl if applied the inductive 
 
 ^B ; jf I al^r method in some of his 
 
 m dr / Ji work, but the time was 
 
 not then ripe for a 
 general appreciation of 
 the importance of the 
 principle. 
 
 Aristotle also owes his preeminence over other Greek 
 writers on natural history to the variety and extent of his 
 own observations, to his voluminous collection of the obser- 
 vations and statements of others, and to his theories of life, 
 which are curiously anticipatory of some features of modern 
 evolutionary views. To refer first to his own observations, 
 it has been computed from Aristotle's works that he was 
 more or less acquainted with over five hundred species of 
 
 FIG. 230. Aristotle 
 
HISTORICAL DEVELOPMENT OF ZOOLOGY 439 
 
 animals, though he was unable to classify them except in a 
 superficial way. His lack of an exact knowledge of anatomy 
 rendered anything like a natural classification impossible. 
 He was, however, familiar with the external appearance of 
 many organs and was able to note the adaptation of organs 
 to different functions. His writings consist not only of his 
 own observations but also of statements about animals taken 
 from every source, and many of these, it must be confessed, 
 seem to us of to-day so plainly untrue and impossible of 
 belief that it is difficult for us to understand how they 
 could have been credited by the philosopher whose vision 
 extended so widely. However, Aristotle's History of Ani- 
 mals was the source, as we^shall see, from which, for many 
 centuries, much of the natural-history lore of Europe was 
 drawn. The question concerning a disputed point, then, 
 was not, What do the facts say? but, What is written in 
 Aristotle ? 
 
 It has just been said that Aristotle held views suggestive 
 of those of modern evolutionists. Though he could not .have 
 had a sufficient basis of facts from which to draw conclu- 
 sions, he yet conceived of a complete gradation in nature, 
 beginning with the inorganic world, passing through the 
 plants to animals, and ending with man. Like others of his 
 time, Aristotle believed in the development of living from 
 non-living matter (spontaneous generation), and he pictured 
 the change as taking place directly, even with some of the 
 higher animals. With much that is false and mistaken, enough 
 of value and brilliancy remains in -the work of Aristotle to 
 entitle him to be called the founder of zoology. 
 
 Passing mention should be made of one other Greek, 
 the philosopher and physician Galen (born A.D. 130). He 
 deserves credit for being the first to insist that medicine 
 must rest on a knowledge of anatomy and physiology. Dis- 
 section of the human body being forbidden, he examined the 
 
440 GENERAL ZOOLOGY 
 
 bodies of monkeys and swine as being near to man in struc- 
 ture. His work represents the highest attainments of Greek 
 medicine. 
 
 The genius of Rome was not manifested along the line of 
 biology, and there is in the whole course of Roman history 
 no really great name in this science. We may mention, how- 
 ever, the Roman naturalist Pliny (born A.D. 23), who lost 
 his life while attempting to approach Vesuvius during the 
 great eruption in A.D. 79, which overwhelmed the cities of 
 Herculaneum and Pompeii. Pliny was not so much an origi- 
 nal observer as a voluminous writer and collector of the opin- 
 ions of others. His books are a great storehouse of the facts 
 and fancies of antiquity. 
 
 The Middle Ages. History tells how Greece was conquered 
 by Rome, to what height Rome attained, and how the down- 
 fall of the Western Roman Empire in A.D. 476 brought to a 
 close the ancient history of Europe and ushered in a new 
 civilization built on the ruins of the old. The period from 
 the fifth to the sixteenth century is usually spoken of as the 
 Middle Ages. In the early part of this period (from the fifth 
 to the eleventh century, often called the Dark Ages) the 
 many wars left little time for the pursuit of science. The 
 habit of observing natural phenomena and the desire to seek 
 an explanation had given place to a slavish acceptance of the 
 statements of others. Blind adherence to authority reigned 
 everywhere. In all this time no new fact of importance ap- 
 pears in the history of our science ; no great original student 
 of the subject was born. 
 
 While Europe was in this condition of darkness the Ara- 
 bians, originally a shepherd race, stirred to national life by 
 their prophet, Mohammed (born A.D. 570 or 571), began a 
 long series of wars, which resulted in the conquest of a large 
 part of western Asia and northern Africa. They even pushed 
 their way into Europe, conquering the whole of the peninsula 
 
HISTORICAL DEVELOPMENT OF ZOOLOGY 441 
 
 of Spain, with the exception of a few mountainous districts 
 in the north. During the period of their greatest power the 
 Arabians alone, of all the races of Europe, kept alive the 
 spirit of science. They preserved many classical works from 
 destruction, especially those of medicine, by translating them 
 into Arabic. The power of the Arabians came to an end in 
 Europe in 1491, when Granada, their last stronghold, was 
 torn from their grasp by Ferdinand and Isabella. 
 
 During the closing centuries of the Middle Ages many 
 events prepared the way for the new interest in science 
 characteristic of the sixteenth and seventeenth centuries. 
 The many political adjustments of the period molded the 
 nations of Europe into much the same form as we know them 
 to-day. The application of the mariner's compass to naviga- 
 tion made voyages to new lands possible. America was dis- 
 covered by Columbus ; Magellan's ship sailed round the 
 world. As a result of the general intellectual awakening 
 the bonds of authority were weakened and men began to 
 think for themselves. Printing was invented, and then fol- 
 lowed a wide dispersion of the knowledge of the ancients. 
 Universities were founded, to which flocked students from 
 all over Europe, eager to drink in the new learning. 
 
 Zoology of the Sixteenth Century. With the sixteenth 
 century we are fairly adrift on the stream of modern science. 
 One of the earliest investigators was Andreas Vesalius, born 
 in 1514 at Brussels. He became interested in anatomy while 
 only a boy and studied the human body from dissections, 
 though often experiencing considerable difficulty in getting 
 material. In 1540 he became professor of anatomy in the 
 University of Padua, in northern Italy, and two years later, 
 when twenty-eight years of age, he published his Great Anat- 
 omy, illustrated with woodcuts by the best Italian artists of 
 his time. Having had the advantage of making dissections, 
 he was able to point out errors in the work of Galen, who 
 
442 GENERAL ZOOLOGY 
 
 had been forced to study the lower forms. With Vesalius 
 and his contemporaries modern anatomy may be said to have 
 begun. 
 
 Konrad von Gesner (1516-1565), born at Zurich, Switzer- 
 land, had a wide interest in natural history. He was a poor 
 boy, left an orphan, and his early life was one constant strug- 
 gle with poverty. Conquering all difficulties, so great was 
 his enthusiasm for science, he rose to be professor of natural 
 history in his native city. He made collections of animals 
 and plants, and published (15511558) a great History of Ani- 
 mals, in which he described all the animals then known, with 
 statements concerning their structure and habits, some details 
 of their physiology, and their economic importance. This 
 was the first comprehensive work on natural history since 
 the time of Aristotle. 
 
 Zoology of the Seventeenth Century. To William Harvey 
 (1578-1657), an Englishman who studied at Padua under a 
 pupil of Vesalius, we are indebted for the first accurate state- 
 ment of the circulation of the blood in man. Galen had shown 
 the existence of blood in the arteries, and Harvey's professor 
 at Padua had confirmed the existence of the valves in the 
 course of the venous circulation, pointed out by a still earlier 
 investigator ; but it was left to Harvey's painstaking observa- 
 tions to follow the course of the blood from the heart to the 
 lungs, from the lungs back to the heart, and thence all over 
 the body. Harvey's discovery was made in 1614 and pub- 
 lished in 1628, after his return to London, where he practiced 
 as a physician. Like many another discovery in science, it 
 at first aroused hostile criticism. From this period the rise 
 of animal physiology may be dated. Harvey also studied the 
 development of the chick in the egg, arid may be said to be 
 the founder of modern embryology. Of course he did not 
 understand the egg as well as we understand it to-day, since 
 he believed in spontaneous generation. 
 
HISTORICAL DEVELOPMENT OF ZOOLOGY 443 
 
 In the early part of the seventeenth century (1609) Galileo 
 used the telescope, bringing distant worlds within our nearer 
 view. AVhat the telescope was to astronomy the microscope 
 was to zoology. The invention of the microscope, about 1600, 
 is usually credited to Zacharias Janssen, a Dutch spectacle- 
 maker; it was used in the study of animals by Malpighi 
 (1628-1694), an Italian 
 anatomist, about 1661. 
 Among other subjects 
 he studied the capillary 
 circulation, which Avas 
 beyond the power of 
 Harvey with only his 
 simple lens. In Eng- 
 land the labors of John 
 Ray (1628-1705) added 
 greatly to our knowl- 
 edge of animals. Ray 
 was the first to define 
 the use of the word 
 " species." He laid the 
 foundations of system- 
 atic zoology. 
 
 Zoology of the Eight- 
 eenth Century. To 
 Linnaeus (1707-1778, 
 Fig. 231) is due the 
 credit for the invention of the binomial nomenclature. Before 
 this time there had been the greatest confusion among natu- 
 ralists as to the names of animals and plants. Not only were 
 the names themselves cumbersome, but there was no uni- 
 formity in their use. Linnasus also saw the need of groups 
 higher than species, and he put classification on a more exact 
 basis by recognizing and defining six classes of animals, 
 
 FIG. 231. Linnaeus 
 
444 GENERAL ZOOLOGY 
 
 mammals, birds, amphibians (including reptiles), fishes, insects 
 (including all arthropods), and Vermes (including mollusks, 
 worms, echinoderms, coelenterates, and protozoans). He be- 
 lieved in the fixity of species, teaching at first that there are 
 as many species of animals as were created in the beginning. 
 Subsequent editions of his System of Nature (first published 
 as a pamphlet in 1735) showed slight modifications of this 
 view, but on the whole his influence was in behalf of the idea 
 of the fixity of species. 
 
 Buffoii (1707-1788) was destined to exert as great an 
 influence on zoology as did Linnaeus, but in a different field. 
 Buffon's studies were widely extended over nature. His 
 Natural History is a popular account of the animal kingdom 
 most interestingly written. It was read very generally and 
 did much to popularize the subject. Buffon was one of the 
 first to attempt an explanation of the facts of the geograph- 
 ical distribution of animals, and he is considered the first of 
 the great pioneers of modern evolution. Professor Osborn, 
 in his history of the development of the evolution idea, From 
 the G-reeks to Darwin, says: " It is interesting to contrast these 
 two great men [Linnaeus and Buffon], one the founder of the 
 view of classification- as a fixed system of the divine order 
 of things, and the ne plus ultra of botany and zoology; the 
 other the founder of the directly opposed view of classifica- 
 tion as an invention of man, and of the laws governing the 
 relation of animals to their environment as the chief end of 
 science." As might be expected at this period Buffon was 
 not an unqualified evolutionist but wavered between views 
 such as Linnaeus held and a belief in the mutability (liability 
 to change) of species. 
 
 One of the earliest writers in the field which we have termed 
 ecology or bionomics was the English clergyman, Gilbert 
 White (1720-1793), the author of The Natural 'History 
 and Antiquities of Selborne. Though, as Professor J. Arthur 
 
HISTORICAL DEVELOPMENT OF ZOOLOGY 445 
 
 Thomson points out, White was " the prototype of the better 
 class of modern amateurs," still the out-of-door study of ani- 
 mals "rarely attained either dignity or definiteness until 
 Darwin demonstrated its importance." 
 
 Animal electricity was discovered by Galvani (1737-1798), 
 professor of anatomy at Bologna. His attention is said to 
 have been called to the subject by his wife. She was prepar- 
 ing frogs' legs for the table near an electric machine in opera- 
 tion, and noticed that when the legs were touched by the 
 knife they twitched violently. 
 
 Zoology of the Nineteenth Century. The science of zoology 
 developed so rapidly from the beginning of the eighteenth 
 century that it will be impossible now to do more than call 
 attention to a very few of the most important discoveries and 
 the men to whom they are accredited. A dominating figure 
 in the early part of the nineteenth century was Georges Cuvier 
 (1769-1832), a French naturalist whose influence was exerted 
 along many different lines. By his studies of fossils, recog- 
 nizing them as the remains of animals of past times, and 
 related to the animals of to-day, he founded paleontology. 
 He also stated the principle of the correlation of parts, 
 a conception which pictures the animal as a unit rather 
 than a fortuitous collection of separate parts. While he un- 
 doubtedly carried the principle beyond its legitimate limits, 
 there can be no question as to its important influence on 
 the history of zoology. Cuvier recognized the importance 
 of anatomical structure as a basis for classification. He also 
 knew a second basis in paleontology, a fact just referred to. 
 Cuvier divided the animal kingdom into four groups, Ver- 
 tebrata, Mollusca, Articulata, and Radiata. 
 
 During the nineteenth century important discoveries paved 
 the way for a better understanding of the minute structure 
 of the animal body and the physiology of its units of struc- 
 ture, the cells. In 1838 Schleiden showed that plants were 
 
446 GENERAL ZOOLOGY 
 
 made up of very small parts called cells, and the next year 
 Schwann made a similar discovery with respect to the animal 
 body, thus laying the foundations for the " cell-theory." The 
 main propositions involved in the cell-theory, as stated by 
 Professor Thomson, are, first, that all organisms are either 
 built up of single cells or combinations of such cells ; second, 
 that all organisms begin life as a single cell, which, in the 
 case of the many-cell organisms, gives rise to a more or less 
 complex body ; and third, that the function of a multicellu- 
 lar organism can be expressed in terms of the activities of 
 its component cells. Though the third proposition may now 
 require some modification, the cell-theory proved an invalu- 
 able unifying conception in biology. In 1846 the word "pro- 
 toplasm," originally used in a different sense, was applied by 
 von Mohl to the substance inclosed by the cell-wall in plants ; 
 and in 1861 Max Schultze established the essential identity of 
 protoplasm with the life-substanoe in the animal cell, which 
 had been called sarcode. Embryology was broadened through 
 the influence of von Baer (1792-1876), who, in 1827, de- 
 scribed the primary germ-layers in the vertebrate embryo. We 
 owe the appreciation of the importance of the embryological 
 basis of classification to von Baer. 
 
 The nineteenth century was prolific in experiments to test 
 whether there could be spontaneous generation of organisms, 
 and a war of discussion was waged between those who sup- 
 ported the idea and those whose experiments seemed to show 
 that all the living organisms experimented upon came from 
 preexisting life. The experiments of Francesco Redi (1626- 
 1697) in the seventeenth century had shown that maggots 
 did not appear in decaying meat if flies were prevented from 
 having access to it, and the discussion took a new turn 
 about the possibility of the spontaneous generation of the 
 animalcules (such minute animals as the infusorians and roti- 
 fers). Some of the earlier experimenters did not succeed in 
 
HISTORICAL DEVELOPMENT OF ZOOLOGY 447 
 
 reaching the truth on account of their carelessness in opera- 
 tion, but it was finally shown that no animalcules appeared 
 in water which had been boiled thoroughly and sealed so that 
 no germs could enter. The final conclusive experiments 
 were those of Pasteur (1822-1895) about 1860, and those 
 of Tyndall (1820- 
 1893) a few years 
 later. 
 
 An important step 
 in paleontology was 
 made when Boucher 
 de Perthes, in 1836, 
 found flint axes in 
 northern France so 
 far beneath the sur- 
 face of the ground 
 that it pointed to- 
 ward a greater an- 
 tiquity for man than 
 had hitherto been 
 believed. Though 
 combated by many, 
 the truth finally 
 
 prevailed, and 
 
 , FIG. 232. Louis Agassiz 
 
 man s presence in 
 
 Europe was proven at least as far back as glacial times. 
 Louis Agassiz (1807-1873, Fig. 232) is famous both as an 
 investigator along many different lines and as an inspiring 
 teacher. He was born in Switzerland, near Lake Neuchatel, 
 and after study in Europe came to America at the height 
 of his reputation in 1846, where he remained during the rest 
 of his life. He became connected with Harvard University 
 in 1847, and the Museum of Comparative Zoology at Cam- 
 bridge, Massachusetts, is a monument to his enthusiasm and 
 
448 GENERAL ZOOLOGY 
 
 devotion. Agassiz' researches cover a wide field, but per- 
 haps his most important contribution to zoology is his work 
 on fossil fishes. It is interesting to note that he was the last 
 great zoologist to hold out against the evolutionary views 
 which came in with the epoch-making work of Charles 
 Darwin. 
 
 We must go back for a moment to consider the beginning 
 of the evolutionary views, which, as we have said on page 101, 
 are accepted in some form by practically all scientific men 
 to-day. Professor Osborn in the volume referred to in 
 the discussion of Buffon says that the Greek philosopher 
 Empedocles, of Agrigentum (495-435 B.C.), may justly be 
 called the father of the evolution idea, since he conceived of 
 animals and plants as arising through the fortuitous play of 
 the great forces of nature, love and hate, on the four elements, 
 fire, water, earth, and air. First appeared the plants; later, 
 after many trials, the animals, the latter not as complete 
 individuals but as parts of individuals. From the chance 
 meeting of parts came monstrous forms incapable of propa- 
 gation. After ceaseless trials Nature produced the fit and 
 perpetual tribes. Here is the germ, according to Professor 
 Osborn, of the survival of the fittest or of natural selection. 
 
 Aristotle's conception has already been referred to. In one 
 form or another, evolutionary views were put forward by 
 philosophers and naturalists during the long period which 
 intervened between Greek thought and the time of Buffon. 
 These views, while interesting historically, need not detain 
 us now, nor can we stop to outline further Buffon's influence 
 on evolutionary thought. We must pass at once to the great 
 figure of Lamarck (1744-1829). We have already mentioned 
 (Chapter X, p. 108) the two factors of evolution with which 
 the name of Lamarck is associated, and have noted the fact 
 that Erasmus Darwin (1737-1802), grandfather of Charles 
 Darwin, seems to have anticipated Lamarck's views in part. 
 
HISTORICAL DEVELOPMENT OF ZOOLOGY 449 
 
 Lamarck's four propositions are as follows : 
 
 First Law. Life by its own activities tends continually to increase 
 the volume of every body that possesses it, and to increase the size of 
 all the parts up to a limit which it itself imposes. 
 
 Second Law. The production of a new organ or part results from a 
 new need, which continues to be felt, and from the new movement which 
 this need originates and 
 sustains. 
 
 Third Law. The de- 
 velopment of organs and 
 their power of action are 
 always in direct relation 
 to the employment of 
 these organs. 
 
 Fourth Law. All that 
 has been acquired or 
 changed in the structure 
 of individuals during 
 their life is preserved by 
 generation and trans- 
 mitted to new individuals 
 which have undergone 
 these changes. 
 
 Discussion of the 
 validity of these prin- 
 ciples still continues. 
 
 Though Lamarck's 
 
 . PT FIG. 233. Charles Darwin 
 
 influence can be 
 
 traced in his contemporaries and those who followed him, it 
 does not seem that he directly affected the far more important 
 work of Darwin. 
 
 Without doubt biology owes a greater debt to Charles 
 Darwin (1809-1882, Fig. 233) than to any other man. He 
 compelled the attention of men in a way and to an extent 
 unsurpassed by any other writer. His labors were directed 
 not alone towards stating the doctrine of descent with 
 modification and marshaling evidence to its support, but 
 
450 GENERAL ZOOLOGY 
 
 he promulgated the theory of natural selection as the main 
 though not the chief factor in evolution. His work was a 
 triumph for the inductive method, for never before had such 
 an array of facts been collected and presented. The battle 
 was first fought over the fixity of species, till belief in that 
 theory no longer became possible. Then investigators sprung 
 up on every side, stimulated by the brilliancy and simplicity 
 of natural selection (to which Darwin afterwards added sexual 
 selection), or anxious to disprove its validity as a factor in 
 evolution. 
 
 When twenty-two years of age Darwin sailed on H.M.S. 
 Beagle on a voyage to South America and around the world. 
 He returned to England, his interest in natural history 
 strengthened and the problems of life outlining themselves 
 to him. This voyage was the beginning of the collection 
 of that vast store of facts which were afterward organized 
 and used with such effect. For over twenty years he worked 
 getting together facts which had to do with the variation of 
 animals and plants, and thinking on the general problem. 
 And now occurred one of the most remarkable coincidences in 
 the whole history of science. While Darwin was elaborating 
 his views on the mutability of species Alfred Russel Wallace 
 (born 1822), an English naturalist then in the Malay Archi- 
 pelago, arrived at practically the same conclusion that Dar- 
 win had reached. By the aid of friends it was arranged that 
 publication should be simultaneously made, and therefore in 
 the Journal of the Linncean Society of London of June 30, 
 1858, we find two papers of transcendent interest. The one 
 by Darwin consists of portions of manuscript written in 1839 
 and 1844, entitled On the Variation of Organic Beings in a 
 State of Nature; on the Natural Means of Selection ; on the 
 Comparison of Domestic Races and True Species. Wallace's 
 paper is On the Tendency of Varieties to depart indefinitely 
 from the Original Type. A year afterward appeared Darwin's 
 
HISTORICAL DEVELOPMENT OF ZOOLOGY 451 
 
 Origin of Species, in which the theory of natural selection was 
 elaborated. The main features of the theory have already 
 been outlined in Chapter X. Darwin was a prolific writer; 
 some of his books are On the Variations of Animals and Plants 
 under Domestication, The Descent of Man, and The Expres- 
 sions of the Emotions in Man and the Lower Animals. In all 
 of these natural selection is applied. 
 
 Among the contemporaries who aided Darwin in his work, 
 and who were in turn influenced by him, may be mentioned 
 the names of Herbert Spencer (1820-1903), the philosopher 
 and author of the Principles of Biology; Ernst Haeckel (born 
 1834), the brilliant author of General Morphology ; Thomas 
 H. Huxley (18251895), a great teacher and popularize! 1 of 
 zoology, and author of important works ; and, finally, August 
 Weismann (born 1834), who aroused skepticism as to the 
 hereditary transmission of acquired characters, and who has 
 made important supplementary contributions to the theory 
 of natural selection. 
 
 It is impossible to overestimate the influence of the selec- 
 tion theory in the progress of modern zoology. It has thrown 
 new light on all fields of activity, so that it may be said that 
 a new science of zoology has arisen. The importance of care- 
 ful experiment has been appreciated as never before. A host 
 of investigators have sprung up, whom to merely mention 
 would transcend the limits of this work. The work of a very 
 few men has been referred to in the preceding chapters, in the 
 effort to give some picture of the state of the science of 
 zoology to-day. Everywhere zoologists are endeavoring to 
 learn the truth about animals, trying to understand better 
 the problem of animal life, and the greatest problem of all, 
 towards which the solution of all others is directed, the 
 problem of man and his relation to the universe. 
 
INDEX 
 
 Abomasum, 417 
 
 Aboral surface, 236 
 
 Absorption, 200 
 
 Acephala, 175 
 
 Acquired characters, inheritance of, 
 107 
 
 Actinozoa, 260 
 
 Adhesive papillae, 303 
 
 Adrenal capsules, 403 
 
 Aftershaft, 366 
 
 AGASSIZ, ALEXANDER, on formation 
 of coral islands, 262 ; on habits of 
 basket-fish, 245 
 
 AGASSIZ, MRS. E. C., on habits of 
 basket-fish, 245 
 
 AGASSIZ, Louis, 447 
 
 Age of Amphibians, 345, 346, 361 ; 
 of Coal Plants, 345, 346, 361 ; of 
 Fishes, 324 ; of Invertebrates, 295, 
 324; of Mammals, 428, 431; of 
 Man, 431, 433, 434 ; of Reptiles, 
 360, 362, 396, 410, 428 
 
 Aggressive resemblance, 23 
 
 Albatross, wandering, 376 
 
 Albinism, 407 . 
 
 Alder-blight, 34 
 
 Alligators, 359 
 
 Alluring coloration, 24 
 
 Alternation of generations, 267 
 
 Amblystoma, 340 
 
 Amoeba, 280 
 
 Amoebocytes, 207 
 
 Arncebulae, 284 
 
 Amphibians, age of, 345, 346, 361 ; 
 definition of, 339 ; geological de- 
 velopment of, 345 
 
 Ampullae, 239, 273 
 
 Analogy, 130 
 
 Anatomy, comparative, 436 
 
 ANDERSON, DR. J., on colors of 
 mantids, 24 
 
 Annelida, 225 
 
 Annulata, 225, 298 
 
 Annulus, 135 
 
 Ant-eater, spiny, 408 
 
 Antelopes, 413, 416 ; pronghorn, 
 414 
 
 Antennae, 2, 127 
 
 Antennule, 127 
 
 Antlers, 415 
 
 Ants, 78; agricultural, 81; corn- 
 louse, 79; honey, 80 
 
 Anura, 343 
 
 Apes, 423 
 
 Aphids, 33, 104 ; woolly, 34 
 
 Appendix vermiformis, 403 
 
 Arachnida, 122, 156 
 
 Archaean Time, 293 
 
 Archaeopteryx, 396 
 
 Archenteron, 216 
 
 ARISTOTLE, 437 
 
 Armadillos, 411 
 
 Artemia, 148 
 
 Arthropoda, 156, 299 
 
 Assimilation, 202 
 
 Asteroidea, 251 
 
 Asymmetry, 187 
 
 Atoll, 262 
 
 Atrial pore, 302 
 
 Atrium, 301 
 
 Aves, 374 
 
 Axolotl, 341 
 
 Baboon, Cape, 427 
 Back-swimmers, 31 
 BACON, FRANCIS, 438 
 BACON, ROGER, 438 
 BAER, KARL ERNST VON, 446 
 Barbs, 366 
 Barbules, 366 
 Barnacles, 150, 153 
 Basipodite, 130 
 Basket-fish, 244 
 BATESON, WILLIAM, 110 
 Bats, 422, 431 ; vampire, 423 
 Beadsnake, 355 
 Bear, 420, 434 
 Beaver, 418, 419 
 
 Bees, guest, 76 ; honey, 72 ; leaf-cut- 
 ter, 78; solitary, 77 
 
 453 
 
454 
 
 GENERAL ZOOLOGY 
 
 Beetles, 45 ; bombardier, 38 ; click, 
 41 ; diving, 39 ; ground, 37 ; June, 
 44 ; lady, 40 ; May, 44 ; scavenger, 
 40; stag, 106; tiger, 37; water, 
 38; whirligig, 38 
 
 Biological Survey, 392 
 
 Biology, 101, 436 
 
 Bionomics, 436 
 
 Bird Day, 396 
 
 Birds, definition of, 374 ; diving, 375; 
 economic importance of, 392 ; gal- 
 linaceous, 381 ; geological devel- 
 opment of, 396; migration of, 
 390 ; mocking, 395 ; of prey, 383 ; 
 perching, 386; shore, 380; sing- 
 ing, 386 
 
 Blackbird, crow, 394 
 
 Blacksnake, 357 
 
 Blastopore, 216 
 
 Blasts, 286 
 
 Blastula, 214, 244 
 
 Bluebird, 390 
 
 Blue jay, 389 
 
 Bob-white, 382 
 
 BOJANUS, PKOFESSOR, on nephridia 
 of mollusks, 161 
 
 Botany, 436 
 
 BOUCHER DE PERTHES, 447 
 
 Bovidse, 416 
 
 Brachiopoda, 234 
 
 Brachiopods, 233, 296, 347 
 
 BROOKS, PROFESSOR, on early stages 
 of oyster, 167 ; on environment of 
 oyster, 168 
 
 BROWN-SEQUARD, on guinea-pigs, 
 108 
 
 Bryozoa, 233 
 
 Budding, 258 
 
 BUFFON, 444 
 
 Bugs, 36; squash, 31; plant, 31; 
 water, 30 
 
 Bumblebees, 75 
 
 BUMPCS, PROFESSOR H. C., on egg- 
 laying of lobster, 142 
 
 Bureau of Animal Industry, work 
 of, 230 
 
 Bureau of Fisheries, work of, 322 
 
 Bursa copulatrix, 12 
 
 Butterfly, milkweed, 46; monarch, 
 46 ; swallow-tail, 49 ; viceroy, 48 ; 
 White Mountain, 48 
 
 Buzzard, turkey, 384 
 
 Byssus, 164 
 
 Caddice-flies, 105 
 
 Cseca, intestinal, 241 ; pyloric, 240 
 
 Caecum, 403 
 
 CALKINS, PROFESSOR G. N., on ex- 
 periments with rejuvenescence in 
 Paramcecium, 290 
 
 Camels, 413, 416 
 
 Canal, radial, 239, 268; ring, 239; 
 stone, 239 ; excurrent, 274 ; incur- 
 rent, 273. 
 
 Canidse, 420 
 
 Canines, 414 
 
 Capillaries, 202 
 
 Caprella, 147 
 
 Carapace, 125 
 
 Carbohydrates, 198 
 
 Carboniferous Age, 345, 346, 361 
 
 Carnivora, 420 
 
 Cassowaries, 374 
 
 CASTLE, PROFESSOR W. E., on Men- 
 del's law, 113 
 
 Cats, 420, 425 ; caff re, 420 ; Egyptian, 
 420 ; saber-toothed, 431 
 
 Cavity, gastrovascular, 256 ; mantle, 
 159 
 
 Cells, collar, 273; polar, 213; pole, 
 216 ; wandering, 274 
 
 Cement, 401 
 
 Centipeds, 122 
 
 Centrosomes, 211 
 
 Cephalopoda, 193, 194 
 
 Cephalothorax, 125 
 
 Cerata, 186 
 
 Ceratosaurus, 361 
 
 Cervidae, 416 
 
 Cestoda, 229 
 
 Cetacea, 412 
 
 Chsetopoda, 225 
 
 Chameleons, 353 
 
 Cheliped, 128 
 
 Chelonia, 357 
 
 Chimpanzee, 424 
 
 Chiroptera, 422 
 
 Chitin, 2 
 
 Chromosomes, 114, 211 
 
 Chrysalis, 47 
 
 Cicadas, 32; periodical, 32 
 
 Cilia, 207, 287 
 
 Circulation, 201 
 
 Clam, long-neck, 157 ; soft-shell, 
 157 
 
 Cleavage spindle, 214 
 
 Clitellum, 196 
 
INDEX 
 
 455 
 
 Cochineal insects, 36 
 
 Cockatoos, 384 
 
 Cockroaches, 2*0, 100 
 
 Cocoon, 51 
 
 Ccelentera, 271, 297 
 
 Coleoptera, 43 
 
 Colleterial gland, 12 
 
 Colloids, 199 
 
 Coloration, alluring, 24 ; warning, 
 40 
 
 Columbse, 382 
 
 Comb-jelly, 270 
 
 Comrnensalism, 79 
 
 Commissure, cerebral, 163 
 
 Conchologists, 185 
 
 Conjugation, 289 
 
 Connectives, cerebro-visceral, 163 
 
 Coral islands, 261 ; polyp, 259 
 
 Corallite, 260 
 
 Corals, 296, 347 
 
 Corvidee, 389 
 
 Cow, 413, 416 
 
 Cow-bird, 389 
 
 Coxopodite, 130 
 
 Crabs, blue, 145; fiddler, 146; her- 
 mit, 143; horseshoe, 154; spider, 
 144 
 
 Cranes, 380, 391, 397 
 
 Crinoidea, 251 
 
 Crinoids, 246, 296, 347 
 
 Crocodiles, 359 
 
 Crop, 198, 367 
 
 Crow, 389, 393 
 
 Crustacea, 152, 156 
 
 Crustaceans, parasitic, 150, 153 
 
 Crystalline style, 160 
 
 Crystalloids, 199 
 
 Ctenophora, 271 
 
 Cuckoos, 395 
 
 CUNNINGHAM, PROFESSOR, on color 
 of flounders, 321 
 
 CUVIER, GEORGES, 445 
 
 Cyclops, 149, 153, 263 
 
 Cytoplasm, 211, 281 
 
 DANA, PROFESSOR J. D., on forma- 
 tion of coral islands, 262 ; on geo- 
 logical distribution of animals, 363 
 
 DARWIN, CHARLES, 449; on forma- 
 tion of coral islands, 262 ; on 
 habits of earthworms, 220; on 
 natural selection, 102 ; on. pigeons, 
 373; on sexual selection, 106 
 
 DARWIN, ERASMUS, 108, 448 
 
 DEAN, PROFESSOR B., on evolution of 
 fishes, 316 ; on habits of Nautilus, 
 192 
 
 Deer, 413, 415, 416 
 
 Degeneration, 98 
 
 Dentine, 400 
 
 Dermal pores, 273 
 
 DE VARIGNY, on evolution, 109 
 
 Devonian Period, 324 
 
 DE VRIES, HUGO, on the mutation 
 theory, 110 
 
 Diaphragm, 403 
 
 Diastase, 199 
 
 Differentiation, 216, 297 
 
 Dimorphism, 49 
 
 Dinosaurs, 361 
 
 Dipnoans, 321 
 
 Diptera, 64, 100 
 
 Direct influence of environment, 108 
 
 Discontinuous distribution, 323 
 
 Distribution, geographical, 436; geo- 
 logical, 436 
 
 Dogs, 420, 425 
 
 Dolphins, 412 
 
 Doves, 382 ; rock, 364 ; wild, 382 
 
 Dragon-flies, 27 
 
 Drones, 72 
 
 Duckbill, 408 
 
 Ducks, 378, 391 ; canvasback, 378 ; 
 mallard, 378 ; domestic, 378 
 
 Eagle, 383 
 
 Earthworm, 297 
 
 Echeneis, 357 
 
 Echinoderma, 251, 298 
 
 Echinoidea, 251 
 
 Ecology, animal, 436 
 
 Ectoderm, 215, 264 
 
 Ectoplasm, 281 
 
 Edentates, 411, 433 
 
 Eels, 319 
 
 Egg, 209 
 
 Egrets, 379 
 
 EIGENMANN, PROFESSOR, on blind 
 
 crayfishes, 136 
 Elasmobranchii, 317 
 Elephants, 413, 414; African, 417 ; 
 
 Asiatic, 417 
 Embryo, 214 
 Embryology, 130 
 EMPEDOCLES, 448 
 Emus, 374 
 
456 
 
 GENERAL ZOOLOGY 
 
 Enamel, 401 
 
 Endoderm, 215, 264 
 
 Endoplasm, 281 
 
 Endopodite, 130 
 
 Energy, 204 
 
 ENTEMAN, DR., on paper-making 
 
 wasps, 66 
 Entomology, 84 
 Environment, direct influence of, 
 
 108 
 
 Enzymes, 199 
 Epiglottis, 404 
 Epipharynx, 6 
 Epiphragrn, 182 
 Epithelium, 174 
 Epoch, Glacial, 392, 431 
 Era of the ancient forms of life, 
 
 346; of the mediaeval forms of life, 
 
 360 
 
 Erosion theory, 262 
 Etiology, 436 
 Euglena, 283 
 Evolution, 101 
 Excretion, 206 
 ^Exopodite, 130 
 Exoskeleton, 84 
 
 FABRE, M., on instinctive acts of 
 Sphex, 88 
 
 Facets, 2 
 
 Family, 96 
 
 Fat-bodies, 334 
 
 Fats, 198 
 
 Fatty acids, 200 
 
 Fauna, 93 
 
 Fauna areas, 94 
 
 Feathers, contour, 366 ; down, 366 
 
 Felidse, 420 
 
 Femur, 3, 333 
 
 Ferments, 199 
 
 Fertilization, 213 
 
 Filoplume, 366 
 
 Finches, 389 . 
 
 Fireflies, 43 
 
 Fishes, Age of, 324 ; bony, 317 ; deep- 
 sea, 323 ; definition of, 316 ; eco- 
 nomic importance of, 322 ; geo- 
 graphical distribution of, 322 ; 
 geological development of, 324 ; 
 lung, 321, 325, 347 ; sucking, 357 
 
 Flagella, 273 
 
 Flatfishes, 320 
 
 Flatworm, 225 
 
 Flies, blow, 59 ; bot, 60 ; bluebottle, 59 ; 
 
 house, 58, 104 ; hover, 61 ; tsetse, 60 
 Flounders, 320 
 FLOWER and LYDEKKER, on whales, 
 
 412 
 
 Flycatchers, 388, 395 
 Fowl, domestic, 381 ; jungle, 381 
 Fox, 420 
 Fringillidse, 389 
 Frogs, 343 ; bull, 327 ; green, 327 
 
 GALEN, 439, 442 
 
 Gall-flies, 81 ; guest, 81 ; oak, 81 
 
 Gallinse, 381 
 
 GALVANI, 445 
 
 Ganglia, cerebro-pleural, 163 
 
 Ganglion, pedal, 163 ; visceral, 163 
 
 GANONG, PROFESSOR W. F., on form 
 of sea-urchins, 247 
 
 Garpike, 318, 325, 347 
 
 Gasteropoda, 187, 194 
 
 Gastrula, 215, 244 
 
 Geese, 378 
 
 Gemmules, 276 
 
 Generalized forms, 98 
 
 Generation, spontaneous, 439 
 
 Genus, 95 
 
 Geological development of amphibi- 
 ans, 345 ; of birds, 396 ; of fishes, 
 324 ; of insects, 99 ; of inverte- 
 brates, 295 ; of mammals, 428 
 
 Germinal spot, 211 
 
 Germ-layers, 216 
 
 GESNER, KONRAD VON, 442 
 
 Gibbon, 426 
 
 Gill-bailer, 128 
 
 Gill-chamber, 128 
 
 Gill-slits, 301 
 
 Giraffe, 413 
 
 Glacial Epoch, 392, 431 
 
 Gland, foot, 179 ; green, 134 ; cal- 
 ciferous, 198 
 
 Glochidium, 172 
 
 Glycerin, 200 
 
 Glycogen, 204 
 
 Goat, 413, 415, 416 
 
 Gorilla, 424, 426 
 
 Grasshoppers, 18 
 
 GRASSI, PROFESSOR, on life-history 
 of malarial parasite, 286 
 
 Grouse, ruffed, 382 
 
 Guinea-pig, 418 
 
 Gulls, 376, 383 
 
INDEX 
 
 457 
 
 HAECKEL, ERNST, 451 
 Haeniocyanin, 102 
 
 Haemoglobin, 102, 203 
 
 Halibut, 320 
 
 Hares, 418 ; varying, 419 
 
 Harvest-flies, 32 
 
 Harvestmen, 121 
 
 HARVEY, WILLIAM, 442 
 
 Hawks, 383, 391 ; chicken, 383 ; 
 cooper, 393 ; hen, 383 ; red- 
 shouldered, 383 ; red-tailed, 383, 
 400 ; sharp-shinned, 393 
 
 HAY, DR. O. P., on blind crayfishes, 
 136 
 
 Hemiptera, 30, 99, 100 
 
 Heredity, 102, 112 ; Mendel's law 
 of, 112 
 
 Hermaphrodite, 170 
 
 Herod iones, 379 
 
 Herons, 379 ; great blue, 380 
 
 HERRICK, PROFESSOR F. H., on egg- 
 laying of lobster, 143 
 
 Hexapoda, 84, 150 
 
 Hinge-ligament, 157 
 
 Hippopotami, 413 
 
 Hirudinea, 225 
 
 Holothuroidea, 251 
 
 Homing faculty, 373 
 
 Ilomology, 130 
 
 Honeydew, 34 
 
 Hornets, 68 
 
 Horse, domestic, 413, 410,. 417, 428, 
 431 
 
 HOWARD, DR. L. O., on the gypsy 
 moth, 90 
 
 HUXLEY, THOMAS H., 451 
 
 Hysenidse, 420 
 
 Hybrids, 96 
 
 Hydra, 296 ; brown, 263 ; green, 263 
 
 Hydroids, 265 
 
 Hydrozoa, 267 
 
 Hyenas, 420, 434 
 
 Hyla, 338, 343, 344 
 
 Hymenoptera, 83, 100 
 
 Hypopharynx, 6 
 
 Ichneumon-flies, 82 
 Ichthyologists, 326 
 Icteridse, 389 
 Iguana, Mexican, 353 
 Imago, 14 
 Incisors, 399 
 Infusoria, 291 
 
 Insectivora, 422 
 
 Insects, 347 ; instinct and intelligence 
 in, 85 
 
 Invertebrate phyla and classes, 299 ; 
 
 Invertebrates, Age of, 295, 324 ; evo- 
 lution of, 292 
 
 Jackals, 421 
 
 Jaguar, 420 
 
 JAMESON, PROFESSOR H. L., on life- 
 history of trematode worm, 227; on 
 the formation of pearls, 173 
 
 Jay, 389 
 
 Jellyfish, 267 
 
 JENNINGS, PROFESSOR H. S.,on loco- 
 motion of amoeba, 281 ; on activi- 
 ties of Protozoa, 291 
 
 JORDAN, PROFESSOR, on rapid devel- 
 opment of the house-fly, 104 
 
 JUDD, DR., on food of birds, 393 
 
 Labium, 2 
 
 Labrum, 2 
 
 Labyrinthodonts, 346 
 
 Lacertilia, 351 
 
 Lac-insect, 36 
 
 Lacteals, 404 
 
 LAMARCK, 107, 448 
 
 Lamellibranchia, 175 
 
 LANCASTER, PROFESSOR E. RAY, on 
 bionomics, 436 
 
 Lancelet, 301 
 
 Lark, meadow, 395 
 
 Larva, 36 
 
 Lateral line, 306 
 
 Leech, 224 
 
 Leopard, 420 
 
 Lepidoptera, 57, 100 
 
 Lice, fish, 150 ; plant, 33 
 
 Limicolse, 380 
 
 LINNJEUS, 96, 443 
 
 Lion, 420, 434 
 
 Lizards, 351 ; legless, 352 ; flying, 
 362 ; pine, 348 
 
 Lobster, 138 
 
 Locusts, 15 ; common red-legged, 1 ; 
 lesser, 1, 16; Rocky Mountain, 1, 
 15, 93; seventeen-year, 32; thir- 
 teen-year, 32 
 
 LOEH, PROFESSOR JACQUES, on artifi- 
 cial parthenogenesis, 290 
 
 Longipennes, 376 
 
 Loon, 375 
 
458 
 
 GENERAL ZOOLOGY 
 
 Lophophore, 232, 233 
 Lymph-hearts, 331 
 Lynx, 420 
 
 Macronucleus, 288 
 
 Madreporic body, 239 
 
 Maggots, 59 
 
 Malarial parasite, 284 
 
 MALPIGHI, 443 
 
 Malpighian tubes, 8 
 
 Mammals, Age of, 428, 431 ; carniv- 
 orous, 420 ; definition of, 408 ; eco- 
 nomic importance of, 427 ; flesh- 
 eating, 420, 431 ; gnawing, 418 ; 
 hoofed, 413, 416, 431, 434 ; insect- 
 eating, 422, 431 ; instinct and in- 
 telligence in, 425 
 
 Mammary glands, 405 
 
 Mammoth, 433 
 
 Man, 423, 424; Age of, 431, 433, 
 434 ; races of, 425 
 
 Manna, 36 
 
 Mantids, 22 
 
 Mantle, 159 
 
 Mantle-fold, 159 
 
 Manubrium, 266 
 
 Many plies, 417 
 
 Marsupials, 409, 434 
 
 Mastigophora, 291 
 
 Mastodon, 433 
 
 Maturation, 211 
 
 MAUPAS, on conjugation in Paramce- 
 cium, 289 
 
 Maxillae, 2, 116, 127 
 
 Maxilliped, 127 
 
 May-flies, 25, 98 
 
 MEAD, PROFESSOR, on food-getting 
 habits of starfish, 241 
 
 Measuring-worm, 57 
 
 Medusae, 265 
 
 Melanism, 407 
 
 Melanoplus, 95 
 
 MENDEL, GREGOR, 113 
 
 Mendel's law, 112 
 
 Mesenteries, 255 
 
 Mesoderm, 215 
 
 Mesoglcea, 279 
 
 Mesothorax, 3 
 
 Mesozoic Time, 360 
 
 Mesozoic upheaval, 363 
 
 Metabolism, 206 
 
 Metamerism, 235 
 
 Metamorphosis, 27 
 
 Metathorax, 3 
 
 Metazoa, 298 
 
 Method, inductive, 437 
 
 Mice, 418 
 
 Micronucleus, 288 
 
 Middle Ages, 440 
 
 Migration of birds, 390 
 
 Millepeds, 124 
 
 Milt, 155 
 
 Mimicry, protective, 48 
 
 Mites, 121 
 
 MITRA, PROFESSOR, on function of 
 
 crystalline style, 160 
 Mniotiltidse, 388 
 MO'BIUS, PROFESSOR, on oyster's 
 
 chances of living, 169 
 Mocking-bird, 395 
 MOHAMMED, 440 
 MOHL, HUGO VON, 446 
 Molars, 400 
 Mole, star-nosed, 422 
 Mollusca, 194, 299 
 Molluscoida, 234, 298 
 Mollusks, 296 
 Molting, 140 
 
 Monkeys, 423, 426, 427 ; spider, 423 
 Monotrernata, 408 
 MOORE, PROFESSOR, on coloration of 
 
 leech, 225 
 MORGAN, PROFESSOR C. LLOYD, on 
 
 instinct and intelligence, 85 ; on 
 
 intelligence of mammals, 426 ; on 
 
 rational acts, 87 
 MORGAN, PROFESSOR THOMAS HUNT, 
 
 on mutation theory, 111 
 Morphology, 98, 130, 436 
 MORSE, PROFESSOR E. S., on habits 
 
 of brachiopods, 233 
 Mosquito, 61, 284 
 Mother Carey's chickens, 376 
 Mother-of-pearl, 166 
 Moths, 51 ; American silkworm, 52 ; 
 
 Chinese silkworm, 51 ; gypsy, 89 ; 
 
 hawk, 53; regal, 56; silkworm, 
 
 51 ; sphinx, 53 ; tussock, 55 ; un- 
 
 derwing, 53 ; vaporer, 56 
 Mucus, 179 
 MURRAY, DR. JOHN, on formation of 
 
 coral islands, 262 
 Mussel, 171 
 Mutation theory, 110 
 Myriapoda, 124, 156 
 My sis, 153 
 
\ __ 
 
 INDEX 
 
 459 
 
 Nacreous layer, 159 
 Narwhal, 418 
 Nauplius, 152 
 Nautiloids, 193 
 Nautilus, 191 
 Nebular hypothesis, 293 
 Nemathelminthes, 230, 298 
 Neinatoda, 230 
 Nephridia, 161, 206 
 Nerve control, 207 
 Nerve-cell, motor, 208 ; sensory, 208 
 Nerve-cord, 303 
 
 Nervous system, central, 208 ; periph- 
 eral, 208 
 Nettle-cells, 258 
 Nettling-capsules, 252 
 Newts, 339, 342 
 Nitrogenous waste, 162 
 Notochord, 302 
 Nototrerna, 344 
 Nucleoplasm, 281 
 Nucleus, 211, 281 
 Nudibranch, 186 
 Nymph, 13 
 
 Odonata, 29, 99, 100 
 
 Operculum, 185, 306, 334 
 
 Ophidia, 353 
 
 Ophiuroidea, 251 
 
 Opossums, 409, 410 ; Virginian, 410 
 
 Oral surface, 236 
 
 Orang-utan, 423, 426 
 
 Orders, 97 
 
 Organs, of Bojanus, 161 ; terrifying, 
 42 
 
 Orioles, 389 ; orchard, 395 
 
 Ornithologists, 391 
 
 Orthoceras, 367 
 
 Orthoptera, 24, 99, 100 
 
 OSBORN, PROFESSOR, on Linnaeus and 
 Buffon, 444 ; on Empedocles, 448 
 
 Oscula, 273 
 
 Osmosis, 200 
 
 Osphradium, 184 
 
 Ostia, 257 
 
 Ostrich, African, 374 ; South Ameri- 
 can, 374 
 
 Otocyst, 127 
 
 Otoliths, 310 
 
 Oviduct, 210 
 
 Oviparous, 316 
 
 Owls, 383, 386 ; great horned, 393 
 
 Oxen, 413, 415, 416 
 
 Oxidation, 203 
 
 Oyster, 165 ; -beds, 186 ; -drill, 184 ; 
 -farm, 167 ; fry, 167 ; pearl, 173 
 
 Palate, soft, 401 ; hard, 403 
 
 Paleontologists, 193 
 
 Paleontology, 436 
 
 Paleozoic Time, 346 
 
 Paramcecium, 286 
 
 Parasites, 60 
 
 PARKER, PROFESSOR G. H., on feed- 
 ing habits of sea-anemone, 254 
 
 PARKER and HASWELL, on birds, 
 373 ; on classification, 298 
 
 Parrots, 397 ; gray, 384 
 
 Parthenogenesis, 34 ; artificial, 290 
 
 Partridge, 382 
 
 Passeres, 386 
 
 PASTEUR, 447 
 
 Paunch, 417 
 
 Pearls, formation of, 173 
 
 PECKHAM, DR. and MRS., on the 
 digger-wasp, 70 ; on instinctive 
 acts in wasps, 86 ; on jumping- 
 spiders, 120 
 
 Pedicellarise, 238 
 
 Peduncle, 233 
 
 Pelecypoda, 175, 194 
 
 Pelican, white, 377 
 
 Peptone, 200 
 
 Perch, yellow, 305 
 
 Perching birds, 386 
 
 Pericardial sinus, 133 
 
 Pericardium, 159 
 
 Periwinkle, 185 
 
 Petrels, stormy, 376 
 
 Phagocytes, 85 
 
 Pheasants. 381 
 
 Phyla, 97 
 
 Phylloxera, 34 
 
 Physiological processes, 196 
 
 Physiology, comparative, 431 
 
 Pici, 385 
 
 Pigeons, carrier, 373 ; domestic, 364 ; 
 fantail, 373 ; passenger, 382 ; 
 pouter, 373 ; tumbler, 372, 373 
 
 Pigs, 413 
 
 Pill-bug, 147 
 
 Pinnae, 398 
 
 Pisces, 316 
 
 Platyhelminthes, 229, 298 
 
 Plectoptera, 26, 99, 100 
 
 PLINY. 440 
 
460 
 
 GENERAL ZOOLOGY 
 
 Plovers, 380 ; golden, 391 ; upland, 
 
 381 
 
 Plowshare bone, 370 
 Plumatella, 231 
 Polian vesicles, 243 
 Pollination, 1)1 
 Polymorphism, 49 
 Polyp, 252 ; fresh-water, 203 
 Polyzoa, 233 
 Porcupine, 418, 419 
 Porifera, 278, 297 
 Porpoise, 412 
 POTTS, PROFESSOR, on habits of 
 
 sponge, 276 
 POULTON, PROFE.SSOR, on the vaporer- 
 
 moth, 56 
 Prawn, 142 
 Premolars, 400 
 Primates, 423 
 Prismatic layer, 159 
 Proboscidea, 416 
 Proboscis, 46, 304 
 Procyonidse, 420 
 Pronuba, 92 
 Prostomium, 196 
 Protective mimicry, 48 
 Protective resemblance, 18 
 Proteids, 198 
 Prothorax, 3 
 
 Protoplasm, 202, 205, 211, 280 
 Protopodite, 1: : 10 
 Protorohippus, 428 
 Protozoa, 291 
 Psalterium, 417 
 Pseudopodia, 280 
 Psittaci, 384 
 
 Psychology, comparative, 436 
 Pterosaurs, 362 
 Pulp-cavity, 400 
 Pulvillus, 4 
 Puma, 420 
 Pupa, 36 
 Pygopodes, 375 
 
 Quail, 381, 382, 395 
 
 Quaternary Period, 431, 433, 434 
 
 Rabbit, cottontail, 419; domestic, 
 
 419; gray, 419; jack, 419 
 "Raccoon, 420 
 Rachis, 366 
 Raptores, 383 
 
 Rasping-tongue, 169, 177 
 
 Rational acts, 87 
 
 Hats, 418 
 
 Rattlesnake, 354, 355 
 
 RAY, JOHN, 443 
 
 Rays, 317, 347 
 
 RE DI, FRANCESCO, 446 
 
 Reef, barrier, 262; fringing, 262; 
 coral, 261 
 
 Reflex action, 208 
 
 Regeneration, 244 
 
 Rejuvenescence, 289 
 
 Repellent odors, 32 
 
 Reproduction, by artificial parthe- 
 nogenesis, 290 ; by budding, 258 ; 
 by conjugation, 289; by eggs and 
 spermatozoa, 209 : by equal divi- 
 sion, 282, 288 ; by gemmules, 276; 
 by parthenogenesis, 34 ; by spores, 
 284 ; by statoblasts, 233 
 
 Reptiles, Age of, 360, 362, 396, 410, 
 428 ; definition of, 351 ; geological 
 development of, 360 
 
 Resemblance, protective, 18 
 
 Respiration, 203 
 
 Reticulum, 417 
 
 Rheas, 374 
 
 Rhinoceros, 413, 414, 416, 434 
 
 Rhinoderma, 343 
 
 Robin, American, 390 
 
 Rodents, 418, 431 
 
 Ross, DR. , on life-history of malarial 
 parasites, 286 
 
 Rostrum, 127 
 
 Rotifer, 230 
 
 Rotifera, 231 
 
 Rumen, 417 
 
 Ruminants, 417 
 
 RYDER, PROFESSOR, on environment 
 of oyster, 168 
 
 Salamanders, 339; Alpine, 342; 
 blunt-nose, 340 ; Texan cave, 340 
 Salmon, Atlantic, 320 
 Sandpipers, 380 
 Sand worm, 222 
 Saponification, 200 
 Sapsucker, 385, 393 
 Sarcodina, 291 
 Saw-flies, 82 
 
 Scale-insects, 35, 98 ; San Jose, 41 
 Scallop, 169 
 Scarabs, 44 
 
INDEX 
 
 461 
 
 SCHIEMENZ, PROFESSOR, on food-get- 
 ting habits of starfish, 241 
 
 SCHLEIDEN, M. K., 445 
 
 SCHULTZE, MAX, 446 
 
 SCHWANN, THEODOK, 446 
 
 Scorpions, 121 
 
 SCUDDER, H. S., on the distribution 
 of the monarch butterfly, 47 
 
 Scyphozoa, 270 
 
 Sea-anemone, 240; -lily, 246, 296, 
 347 ; -squirt, 302 ; -urchin, 247 ; 
 -walnut, 270 
 
 Seal, Alaskan fur, 421 
 
 Selection, artificial, 102 ; natural, 
 102; sexual, 106 
 
 Seminal receptacles, 209 ; vesicles, 
 209 
 
 SEMPER, KARL, on the pond-snail, 
 109 
 
 Serpula, 224 
 
 Shark, 317, 325, 347 
 
 Sheep, 413, 415, 416 
 
 Shell-fish, 169 
 
 Sieve-plate, 239 
 
 Siphon, 160 
 
 Siphonoglyphe, 254 
 
 Siphuncle, 191 
 
 Skate, 317 
 
 Skipper, 50 
 
 Skunk, 421 
 
 Slipper-animalcule, 286 
 
 Sloth, 412 
 
 Slug, garden, 182 
 
 Snail, land, 181 ; pond, 177 
 
 Snakes, 353 ; copperhead, 355 ; green, 
 357 ; water, 357 
 
 Snipe, Wilson's, 381 
 
 Somites, 2 
 
 Sow-bug, 147 
 
 Sparrows, 389 ; chipping, 395 ; Eng- 
 lish, 389, 393; grasshopper, 395 ; 
 house, 389 ; song, 390 
 
 Specialized forms, 89 
 
 Species, 95 
 
 SPENCER, HERBERT, 451 
 
 Spermatozoon, 209 
 
 Spicules, 275 
 
 Spiders, 116; garden, 117 ; jumping, 
 120; trap-door, 120 
 
 Spinal cord, 302 
 
 Spinnerets, 116 
 
 Sponges, 296; bath, 277; fresh- 
 water, 273 
 
 Spores, 284 
 
 Sporozoa, 291 
 
 Spring-tails, 97 
 
 Squame, 127 
 
 Squid, 188 
 
 Squirrels, 418, 419; gray, 398; red, 
 
 405 
 
 Statoblasts, 233 
 Steapsiu, 199 
 Stork, white, 380 
 Struthiones, 374 
 Sturgeon, 318 
 Subimago, 26 
 Subsidence theory, 262 
 Sucking-disk, 188, 239 
 Sunfishes, 321 
 Swallow, 391, 395, 397 
 Swan, trumpeter, 378 
 Swimmeret, 128 
 Sycon, 277 
 Symbiosis, 79 
 Symmetry, bilateral, 152; radial, 
 
 236, 298 
 System, water-vascular, 239 
 
 Tadpole, 334 
 
 Tapeworm, 227 
 
 Tarantula, 119 
 
 Tarsus, 4 
 
 Teleostomi, 317 
 
 Telson, 128 
 
 Terns, 376 
 
 Terrifying organs, 42 
 
 Theromorphs, 361 
 
 THOMSON, PROFESSOR, on the cell 
 theory, 446 ; on rapid development 
 of aphis, 104 
 
 Thoracic duc, 404 
 
 TIIORNDIKE, PROFESSOR, on intelli- 
 gence of animals, 426, 427 
 
 Thrushes, 390 
 
 Thymus gland, 404 
 
 Thyroid gland, 404 
 
 Thysanura, 97, 99 
 
 Tibia, 4, 333 
 
 Ticks, 121 
 
 Tiedemann's vesicle, 243 
 
 Tiger, 420 
 
 Toads, 343; common, 344; obstet- 
 rical, 343 ; Surinam, 343 
 
 Tobacco-worm, 54 
 
 Tonsils, 403 
 
 Torpedoes, 317 
 
462 
 
 GENERAL ZOOLOGY 
 
 Tortoises, 357; box, 35*8; painted, 359 
 Tracheal gills, 25 
 Tree-frogs, 344 ; Brazilian, 343 
 Tree-toads, 344 . 
 Trematoda, 227, 229 
 Trematode, 174, 226 
 Triceratops, 361 
 Trichina, 229 
 Trilobites, 153, 296, 347 
 Trocheiniintb.es, 231, 298 
 Trypsin, 199 
 Tube-feet, 239 
 Tubinares, 376 
 Tunicata, 303 
 Turbellaria, 226, 229 
 Turdidse, 390 
 Turkey-buzzard, 384 
 Turkeys, 381 
 
 Turtles, 357 ; green, 357 ; hawk- 
 bill, 357 
 
 TYNDALL, JOHN, 447 
 Tyrannidse, 388 
 
 Umbo, 157 
 
 Ungulates, 413, 431, 434 ; even-toed, 
 
 416; odd-toed, 416 
 Urethra, 404 
 Uric acid, 162 
 Urodela, 339 
 Urostyle, 331 
 Ursidse, 420 
 Uterus, 405 
 
 Vacuoles, contractile, 282, 288 
 Vacuoles, food, 287 
 Vane, 366 
 Varieties, 96 
 Venues, 234 
 Vertebrates, 292, 301 
 VESALIUS, ANDREAS, 441 
 Vireos, 388, 389, 395; white-eyed, 
 389 
 
 VON BAER'S law, 100 
 Vultures, 383 ; black, 384 
 
 Walking-leaves, 22 ; -sticks, 22 
 
 WALLACE, ALFRED RUSSEL, 102, 450 
 
 Warblers, wood, 388, 395 
 
 Warning coloration, 40 
 
 Wasps, digger, 69 ; mud-dauber, 69 ; 
 social, 65 ; solitary, 68 
 
 Water-boatmen, 30 
 
 Water-moccasin, 355 
 
 Weevils, 90 ; cotton-boll, 90 
 
 WEISMANN, AUGUST, 451 
 
 Whale, sperm, 413; whalebone, 413 
 
 Whip-scorpion, 122 
 
 WHITE, GILBERT, 444 
 
 WILLEY, PROFESSOR, on habits of 
 Nautilus, 192 
 
 Wolves, 420 
 
 Woodchuck, 418 
 
 Woodcock, 381 
 
 Woodpeckers, 385, 395, 397 ; golden- 
 winged, 385; sap-sucking, 385, 
 393; three-toed, 385; yellow-bel- 
 lied, 385 
 
 Worm, acorn-tongue, 304 ; tube, 224 
 
 Wren, house, 395 
 
 AVRIGHT, PROFESSOR R. RAMSAY, on 
 intelligence of monkeys, 426 
 
 Xiphosura,154 
 
 Zoea, 153 
 
 Zooid, 231 
 
 Zoology, among the Greeks and 
 Romans, 437 ; definition of, 436 ; 
 definition of economic, 436; of 
 the sixteenth century, 441 ; of the 
 seventeenth century, 442; of the 
 eighteenth century, 443; of the 
 nineteenth century, 445; system- 
 atic, 436 
 

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