4 i Ny eresti setae oe ~~ Oa eth einen oie rade ae : es ass ay - aa) se aes ss Aes iT, ate wy ie en 3 Sore os — St. oy theres eaeese: gaat A yay tind Sera - ik: a Sts ‘arenas: sr 2 pei > 2, tor. fe ithi we — vi Tf: roe at a} “4 a eee i “ : , t ; ¢ \ oes eotire $e , we iyrater ayy ia toe “ ; » - Parts! et ee owen e re? +4 i wed es bs 1, } 5 bhek? rev $ ' yal. at ha LA Ae A we am ple. - ee —~ oe a ee ee + bi ‘4 ee ee u ice Vai: rw 44 ty Mh pea \ ¥ a eee COPYRIGHT DEPOSIT: ELEMENTS OF COMPARATIVE ZOOLOGY BY ts NGSLE ¥,, Sib. Professor of Zoology in Tufts College SAO DEM Pe LOIN LEVELS ED NEW YORK HENRY HOLT AND COMPANY 1904 [LIBRARY of CoNgRESS| Two Gopies neédved OV 4 1904 Copyrignt Entry 1G 0 of ‘a Noi Copyright, 1897, 1904, : BY HENRY HOLT AND COMPANY es (si Ca a Ce €CeE eG ROBERT DRUMMOND, PRINTER, NEW YORK | PREFACE TO THE SECOND EDITION. In preparing this edition many changes have been made; every page has been revised and some errors corrected. Several new illustrations have been added and directions for the study of other animals have been inserted. As in the first edition, greater prominence has been given to the vertebrate than to the non-vertebrate forms, since experience has shown that the work has been largely used as an introduction to or preparation for medical studies. The greatest change, however, has been in the separation of the laboratory work from the de- seriptive part of the text. Still, the pedagogica advan- tages of the former arrangement have been maintained by numerous cross-references, while the systematic portion has a continuity which was lacking in the former edition. In the illustrations care has been taken to figure noth- ing which is studied in the laboratory. Students have been known to copy drawings rather than to work the details out from the specimen. Turts CoLtLEeGE, Mass., June, 1904. PREFACE TO THE FIRST EDITION. THE present volume is intended as an introduction to the serious study of zoology. It embraces directions for laboratory work upon a selected series of animal types and a general account of related forms. Laboratory guides are somewhat numerous, but general outlines of zoology adapted to beg nners are few. By combining the two, it has been possible to emphasize the comparative side of the subject. A knowledge of isolated facts, no matter how extensive, is of little value in education, excepting as the powers of observation are trained in ascertaining those facts. Nature studies are truly educational only when the student is trained to correlate and classify facts. A considerable experience with students of different ages has resulted in the conviction that it is not sufficient to ask one to compare a grasshopper and a beetle, pointing out their resemb!ances and points of difference; leading questions must be asked. When the student has answered the questions under the headings ‘‘Comparisons’’ in the following pages, he has a tolerably complete statement of the principal characters of the larger groups of the animal kingdom. Several considerations have had weight in the selection of types to be studied in detail. In the first place, so far as possible, these should be such as are readily obtainable in any locality. But there are certain important groups, all the members of which are marine. The forms of these V vi PREFACE TO THE FIRST EDITION. which have been used can be purchased of dealers in laboratory supplies (see Introduction) at a cost of less than sixty cents per pupil. In the second place, the number of forms studied and the extent to which details of structure are worked out must be such that the work outlined can be done by students of average ability, in the time usually allotted to such work in the ordinary course. Especial care has been taken that time shall not be wasted in working out features of no morphological importance. Counting tail-feathers or fin-rays has no place in elementary zoology. Again, the work has been made largely macroscopic in character. Microscopes are expensive, and many institu- tions feel that they cannot afford to provide each student with one of these instruments. Then, too, there are enough important facts to be discovered with scalpel and hand-lens. Too many beginners have been lost among cell-theories and drowned in staining-fluids. These prop- erly come after the elements of the study have been mastered. In order of treatment the author has followed the se- quence which he believes productive of the best results- A strictly logical course would lead from the simple to the complex, but in practice this has not been found as valu- able as the order adopted here. A number of illustrations have been prepared especially for this work. Most of the others are credited to the author from which they are taken. It may interest some to know that Figures 39 and 123 were engraved for the second part of Agassiz and Gould’s “Principles of Zool- ogy,’’ which was never published. Turts CoLuecE, Mass., June 14, 1897. CONTENTS. PAGE Perv R ATO CO TDLIO NR ate Nes 2 eye ree Una, lino files ate Yon.’ Bee ge hoa if VEC PUNT STRANGE OI re scale Aeon, Oetkes of Cao tis hs Bane ae ak eee 2 MEGeKIal 1OE WISSCCLION) i>) 28.1. heen dinia a ee cyclen + EEC Te CCM OO KGit a eto seley ies Mian ttnn oe Selle aber any esa ete es wens 10 (fk TEsO UR 2 TUOTRST AN) 2 Ga ea a 15 iS) Oe Se a ea an aD ea a Re 1 DEN SOSLE oo: dele eae ont ce a eee i a 22 POMP AEISOMS RE ee -os cw. et Mer Soran ce ee Geno oF ko, oy eieney 30 TIED, yard cb eee eC ee eee ee pee 32 “PEC SOLE eke PEI as Se, a IR em 41 Won PATISONS emcees ery eb ee Sek wales ee 43 HU GINEE emp eeR Re foto estan Go RtiinS Wy any sysNd spaj'e-ni Stee Ei wag OR 44 SUAVE SG te chee Re Re Oe Bee RT ey ee Ve ae 47 TEN EG le So bets Re eae Re ae Ne re OI oe eR een Se 48 WGLMPALISONS ne sane ae a Me en ahe oe aes SR ee 52 Paria Pe ora aloha det ee Mersc ees UN a eas Sey wane 53 SS AAD AIS OM Stata cat x acc Ope tees sca chat a ex 0S oe ee Ras 64 Craps nor OWSbel ic a ara Gas Cad alst dha ns eg bates 6 67 SONS OWE RS Oak aI ace 73 ata AMISOHAS A ty Pah Ne MeN oe, ack Shc eo eee 75 Grasshopper. oc. 145% Dl che) Aare eee oe es 76 Conmipanisanss some ae Bena Se ee ek: 82 (OPE GRE ae SD SS ae rr Na Sas eG at nee ne en ee 84 5 UDG OURS Taye, RIN eG coos ka Vater Oat fe 85 TD NEG EPO Oh lat toc NE Un te a CERRO. Ue 86 ES COROTMINALS TOR. sare is th Syne ERIN S28 ooo See chet Ga 87 WomiparisOnS’: <0. 4s (cpr ee Ns Sc slisy ap) eins med 88 SICHUI SCO U fr a aU I OR URERIn kts, LO 2 Sn 89 vill CONTENTS. PAGE Buattertly si Vice) ee ee eens ee oS Ss 90 Comparisons..7.%) aca 2 «bes a!) fe ee ee 91 Barthworm. 2053 !.05 3k eeu soe Ge Seana elton ee 92 Comparisons. 200i 08 ee oe eee ee ele as 96 Clam! ek SO ee ae Oe NG vie ar 98 OV SUR, isso icin GAG Bole ae Ae ee er 102 Quid. = —<——— = Fic. 21.—Common white Jellyfish (Aurelia). After Agassiz. mark them off from the Hydrozoan jellyfishes (p. 166). While some are small, others become veritable giants, the large blue jellyfish of the New England coast sometimes measuring seven feet across, its tentacles streaming be- hind for a hundred feet as it swims through the water. Suspcuass IIJ.—CrenopHora. These forms, which are also called jellyfishes, differ from the other ecelenterates in several respects. The body is usually globular, instead of umbrella-shaped, and bears on the surface eight rows, like meridians (fig. 22, c) of vibratile organs, each row being composed of numerous series of cilia, arranged much like the teeth of a comb C@LENTERATA. 175 (ctenophora=comb-bearers). There is no proboscis, the wide mouth, with an ectodermal cesophagus, being at one pole of the body and leading to a digestive tract which hat NT cc aN tae SAAT NS AAEM ST SNS S aa Wy: VES SG Whee Brea Fic. 22.—Diagram of a Ctenophore. c, rows of combs; g, branches of digest- ive tract; 72, ‘‘intestine’”’; m, mouth; 0, csophagus; s, sensory plate; ¢, ten- tacle; tc, tentacle sheath; y, cesophageal vessel. branches again and again (g), so that at last a portion underlies each row of combs. There are no nettle-cells in these forms and there never occurs any alternation of 176 SYSTEMATIC ZOOLOGY. generations. The ctenophores are all marine, are per- fectly transparent and so delicate in structure that it is almost impossible to preserve them, some being torn by strong currents of water. They are among the most voracious of animals. As a rule few measure more than three or four inches in diameter. SUMMARY OF IMPORTANT Facts. 1. The CaLENTERATA and the Echinoderma were for- merly united as a group Radiata on account of their radiate structure. 2. The Ceelenterata have but a single opening to the digestive tract; there is no body-cavity; the body-wall is composed of ectoderm and entoderm with a supporting layer between them. 3. The nettle-cells are especially characteristic. 4, Reproduction is by eggs and by fission, or budding. 5. Some buds may become free and form medusze and there is frequently an alternation of generations. 6. The Coelenterata are divided into Hydrozoa and Scyphozoa. 7. The Hyprozoa lack an inturned cesophagus. They have frequently an alternation of fixed or polyp and free or medusa generations. 8. The Hydrozoa are divided into Hydride, Hydro- medusz, and Siphonophora. 9. The ScypHozoa have an inturned cesophagus; the digestive tract is subdivided by radial septa bearing mes- enterial filaments. 10. The Scyphozoa are divided into Actinozoa and Scyphomeduse. C@LENTERATA. 17 11. In the Actinozoa there is only the polyp condition Most of the species produce coral. #2. The Se yphomeduse are meduse, the young of which are polypoid in character. 13. The CTENOPHORA are ayesaarinnne they lack nettle-cells. Most characteristic are the eight meridional] rows of vibratile combs. Prytum III.—VERMES (Worms). Under this heading are included a large number of forms commonly known as worms, a group incapable of strict definition. In general it may be said that they have elongate bodies without internal skeleton, without jointed appendages, with a marked bilateral symmetry, and dis- tinct dorsal and ventral surfaces. Further than this we can hardly go in a definition which will at once include all worms and at the same time not include other forms. Indeed, it is probable that the group is not a natural one and that its members should not be associated together. Still in an elementary work it is best to follow a con- servative course and not confuse the beginning student with a number of phyla some of which contain but a few inconspicuous forms. Some worms are terrestrial, some aquatic, ‘and some live as parasites on or in other animals. Omitting a number of microscopic forms and small groups, we may divide the Vermes into four classes: Plathel- minthes, or flatworms; Nemathelminthes, or roundworms; Annelids, or segmented worms, and Molluscoidea. Cuass I.—PLATHELMINTHES (Fuatworms). In the flatworms the body is flattened, is without appen- dages or skeleton; the mouth when present is on the ven- tral surface and no vent occurs. There is no body-cavity aside from the digestive tract. Some are leaf-like, others are more elongate, and a very few are nearly cylindrical. The free-living and some of the parasites have an alimen- tary canal, but to this there is only a single opening, the 178 WORMS. 179 mouth. Aside from the digestive cavity, the body is solid throughout, there being no such body-cavity as occurs in the higher worms, the echinoderms and the vertebrates. The nervous system consists of a centre, or ‘brain,’ always in the dorsal front por- tion of the body, from which nerve-cords run to various parts, there being usually two long cords which run backwards in a nearly parallel direction. Eyes may be present on the dorsal surface near the brain. The capacity of reproduction by di- vision is very well developed in many species, especially in the non-parasitic groups. In these a sec- ond mouth will appear at about the middle of the body, then the body will constrict in front of the new mouth, and finally will divide into two worms. Not infrequently a new mouth will appear in each of the halves be- | fore the division is com- Fic. 23.—Process of di- Fie. 24.—A Tur- plete, so that we can visionin Microstomum. bellarian (Pla- : After Graff. m, m2, naria), enlarged. have a chain of four or eae eve cae even eight animals con- Pee nected together, and all the result of division of a single parent (fig. 23). Besides this reproduction by division, reproduction by means of eggs occurs. The Pla- thelminthes are divided into three orders—Turbellaria, Trematoda, and Cestoda. 180 SYSTEMATIC ZOOLOGY. OrpER |.—TuRBELLARIA. These are small free-living forms which occur in fresh (fig. 24) or salt water, and occasionally in moist earth. They are common in our ponds and streams, crawling slowly over the bottoms or upon submerged sticks and stones. They have a mouth and digestive tract, the latter rod-like, three or many branched. OrpER IJ.—TREMATODA. . Like the last, these have mouth and digestive tract, but they differ in being parasitic on or in other animals, and in having sucking-dises (from one to many) developed upon the body. Some of them become serious pests. One “form, the liver-fluke, produces the disease known as ‘liver-rot’ in sheep. Other forms occur in man, espe- cially in the tropics, being introduced in drinking-water. : They cause serious sickness. In the case of many trematodes the parasite must pass into two animals in order to complete its life-history, the process being frequently complicated by an alternation of genera- tions. Thus in the case of the liver- fluke, just mentioned, the eggs are laid by the fluke while still in the liver; they pass out through the bile-duct and intestine to the exterior, where they hatch a peculiar embryo on the grass. This bores into a snail, and by budding gives rise to other kinds of parasites, so | that from a single ege a large number chee. Rea of individuals may be produced. The Thowees? “#iter final stage in the snail is a tailed form, the cercaria, fig. 25, which escapes and getting on the grass is eaten by sheep, when it drops its WORMS. | 181 tail and changes into the adult fluke, which makes its way into the liver. In other cases the change is from snail to birds or to frogs, the host of the immature forms being usually a mollusc, that of the adult a vertebrate. OrpER III.—Crstopa (Tapeworms). The Cestodes are all parasitic in other animals. They differ from the Trematodes in the complete absence of mouth and digestive tract, since they absorb their nourish- ment through the skin. Usually they have ribbon-like bodies, and hence are commonly known as tapeworms (fig. 26). At the anterior end are the means of attachment (hooks or suckers) by which the animal at- taches itself to the lining of the intes- tine of its host, while usually the body becomes broken up into a series of joints or proglottids. There is con- tinually a formation of new proglot- tids near the ‘head,’ or scolex, while the older proglottids, loaded with eggs, drop off and are carried out with the waste of the digestive tract. These tapeworms obtain en- trance into the body in the food, man usually receiving his from raw or Tia, gehen hehe partially cooked beef or pork, and Ten eae eee more rarely from fish. The proglot- ee h, head en- tids and eggs, passing from the body, may fall where they may be eaten by cattle or swine. Inside their bodies they undergo partial development in the muscles, and then when taken into the human body they complete their development. Other vertebrates than man possess tapeworms. The cat gets hers from the mouse, ee 182 SYSTEMATIC ZOOLOGY. the dog his from cattle and rabbits, the sharks from other fish, ete. Ciuass IT—NEMATHELMINTHES. In these roundworms the body is long and cylindrical, and is covered with a firm, tough cuticle. Usually both mouth and vent are present, and the alimentary canal runs through a large body-cavity (ccelom), being con- nected with the body-walls only at the two ends. There is never any division of the body into segments. Some roundworms live freely in the water, some are parasitic in plants, and some infest animals. Among them are to be mentioned the vinegar and paste ‘eels,’ which are occasionally found in these substances. Here, too, belong the ‘horsehair-worms,’ which are 2a 2a frequently believed to be horsehairs con- Ss Veee verted into worms by soaking in water. Eas ce Eee These hairworms are at one period of their ES me lives parasitic in insects, especially in =a Ass ee= grasshoppers. Some of the roundworms 5 lead occur as parasites in man. The stomach- i : . ° worms and pinworms of children belong ez= to the roundworms, and these obtain S0/5E=| entrance to the human system only as Wiss the exceedingly minute eggs are taken 3 into the stomach by way of the mouth. (225 Worst of all the parasitic Nemathel- =] a RD PBD) ppp dua ) ) i i ym) ue M) My MY i POO He \ 2= A === minthes is the T'richina (fig. 27), which Fie. 27.—Triekina, When adult is scarcely an eighth of an encysted in human inch in length, and yet which not amire Be nEeu quently causes death. Man is usually in- fected with them by eating raw or partially cooked pork. In the pig they first appear in the alimentary canal, where WORMS. 183 tne mothers bring forth myriads of living young. These young burrow outwards into the muscles and there enclose themselves in a capsule, where they remain indefinitely. If this infested flesh be eaten raw, the capsule is dissolved by the stomach, the young are soon born, and they in turn wander through the muscles, and, when numerous, this boring into the flesh causes severe sickness, and even death. The worst epidemic of this disease, known as trichinosis, on record occurred near Emmersleben, Saxony, in 1884. From one pig three hundred and sixty-four persons were infected, and of these fifty-seven died w'thin a month. The moral which we have to learn from tape- worms and trichina is that our beef and pork should never be eaten raw, but should be cooked through. Crass IJJ].—ANNELIDA (SrcmMEentep Worms). The earthworm may be taken as a representative of this group, all the members of which have a marked external ringing or segmentation of the body. This seg- mentation also extends to the internal organs, so that the whole animal may be regarded as a complex of a number of essentially similar segments (also called somites or meta- meres). A little more detailed account of the structure may be given. The alimentary canal (fig. 28, 7) runs through the body like an axis, and is suspended by a longitudinal membrane, the mesentery (m) above and below, while at each constriction of the body a similar membrane, or septum (s) binds the canal to the body- wall. The result of this arrangement of septa and mesen- teries is to divide the body-cavity which surrounds the alimentary tract into a series of paired cavities, the celomic pouches (c), each pair corresponding to an exter- nal somite. The circulatory system consists chiefly of a 184 SYSTEMATIC ZOOLOGY. dorsal blood-vessel (d) in which the blood flows forward, and a ventral vessel (v) in which it flows in the opposite direction with pairs of vessels (cv), segmentally arranged, connecting the two. The nervous system is composed Fic. 28.—Diagram of trunk somites of an Annelid. am, muscles of aciculi; c, ccelom; cm, circular body muscles; cv, circular blood-vessels; d, dorsal blood- vessel; 2, intestine; /m, longitudinal body muscles; m, mesentery; n, ventral nerve cord; na, nephridium; ne, no, parts of parapodium; s, septum; sp, splanehnopleure; ¢, typhlosole. of a centre, or brain, above and in front of the mouth, from which a pair of nerve cords (ewsophageal commissures) pass on either side of the cesophagus to connect with a ventral nerve cord (n) which extends the length of the body beneath the alimentary canal, and which bears nervous enlargements, or ganglia, one pair in each somite. Thus it will be seen that the brain is dorsal, the rest of the nervous system ventral, to the alimentary canal; in other words, the digestive tract passes through the nervous system. The excretory system consists of a system of organs called nephridia (na). Typically there is a pair of these to each segment. Lach consists of a tube opening at one end by a funnel-shaped expansion, WORMS. 185 or nephrostome, into the ccelom, while at the other end it empties to the exterior. Usually the tube is much coiled and is enveloped in a network of small blood- vessels. The annelids are divisible into several groups or subclasses, only two of which need mention here. Supcuass J.—CHATOPODA. In these the body-cavities (coelomic pouches) are well marked, as in the earthworm, and each segment of the body bears small bristles (chwte or sete) which serve as locomotor organs. Usually the rings visible upon the external surface correspond to the somites. ORDER |1.—PoLYCHATA. In these the chetz are numerous in each segment and are usually borne on fleshy outgrowths (parapodia) from the sides of the body, which in many forms efficient swimming organs. The head (fig. 29) bears fleshy feelers, or tentacles, and eyes are commonly present. The Polychetes, of which there are numerous species, are almost entirely marine. For conven- lence they may be divided into two groups. In the ERRANTIA Fy. 29.—Head and anterior suemaumual is; Htied for a free » po.) C2 OF clam wom ie revs),an example of an errant life and frequently the mouth P= is provided with strong jaws, making them to the associated life terrible animals of prey. The other group, the Tust- COLA Or SEDENTARIA, live permanently in burrows from which the head, often furnished with numerous tentacles and gills, can be protruded. In life the tentacles are in SYSTEMATIC ZOOLOGY. 186 constant motion drawing small food particles to the mouth. As a result of this sedentary life the parapodia are often greatly reduced (fig. 30). Many of the Polychete are brightly colored and some are among the most beauti- ful objects in nature. In the development of many Polychetes there occurs a larval form known as the trochophore, which bears no eS, i SST yy s RS yy SO y KS =o = eS, e AY * = SS el = es= 2 Z\ Oss 5 = potest SI Ea oe a a Sy NY > x POL 0 NETS Fie. 30.—A Tubicolous Polychete (Amphitrite). At the upper end are the tentacles, and just below to the left the gills. resemblance to the adult. The body is oval or nearly spherical and bears one or more circles of cilia. The mouth is at one side, the vent terminal. This becomes transformed into the worm by elongation and segmentation The great interest connected with the at the hinder end. trochophore is that similar larvee occur in other groups, WORMS. 187 notably in the molluscs, thus showing a remote relation- ship between them. OrpER II1.—OLIGOCHATA. In the Oligochetes the parapodia are lacking, and the cheetze, which, as the name indicates, are few in number, project directly from the body-wall. Appendages of all kinds are usually entirely absent. A few of the group are marine, more occur in fresh water, but the great majority are terrestrial, and are familiarly known as ‘earthworms’ or ‘angleworms,’ the latter name being given from their use in baiting fish-hooks. The earthworms burrow in the soil, feeding upon decaying vegetable matter in the earth. They swallow earth and all, and come to the surface to deposit their well-known castings. In this way they work over the soil, and are of immense value to agriculture, as Darwin has shown in a most interesting volume on these lowly forms. Our earthworms are mod- erate in size, but in Africa, South America, and Australia giant earthworms, four to six feet in length and an inch in diameter, occur. Supciass Il.—Hirupiner1 (Leeches). The leeches have the body-segments ringed, so that one examining the outside would conclude that there were more segments than are really present. There are no bris- tles on the segments, but the hinder end always bears a sucking disc, while usually there is a second sucker around the mouth. The body-cavity is not distinct, for by the great development of the tissues it has been almost en- tirely obliterated. There are two great groups of leeches— those with jaws around the mouth, and those which lack jaws. 188 SYSTEMATIC ZOOLOGY. The jawless leeches are aquatic, and occur in fresh water; more rarely in the sea. They live largely upon fishes, feeding upon the mucus covering the body. The jawed leeches have three Jaws radiating from the mouth, and each jaw has its edge finely toothed. With these jaws they are IN N LE, LP. Aa FM isl Fic. 31.—Diagram of two Polyzoan individuals, one expanded, the other re- tracted into its cell (after Delage et Hérouard). a, anus; m, mouth sur- sounded by the tentacles; 0, operculum which closes the cell; r, retractor muscle. able to cut the skin of vertebrates, upon the blood of which they feed. This blood-sucking habit led to the use of leeches in medicine in those days when it was believed that if a man were sick his cure could be effected by still fur- ther weakening him. Most of the jawed leeches live in WORMS. 189 fresh water, but in the warmer parts of the Old World land leeches occur in the moist forests, and these form almost intolerable pests. Cuass IV.—MOLLUSCOIDEA. Under this heading are grouped a few forms, which in time past were considered as Molluses (see p. 193), but which are now known to have only superficial resem- blances to the clams, etc. There are two orders of these Molluscoids. OrpDER I.—Poxryzoa (Moss Animals). The Polyzoa are individually small, but by budding they form colonies of considerable size, the tentacles of the individuals giving the colony a mossy appearance, whence the name Bryozoa (moss animals) often given them. Fic. 32.—Diagram of a Brachiopod. 6, tentacles around mouth, m* 2, intes- tine; the shell black, the stalk to the right. These tentacles surround the mouth in a more or less modi- fied circle, and by them the animals obtain their food. The body is sac-like, and the alimentary canal is bent upon itself so that the vent is near the mouth. Many of the colonies secrete an external skeleton, which may be horny or calcareous. Most of the Polyzoa are marine, but a few occur in fresh water. 190 SYSTEMATIC ZOOLOGY. OrpDER IJ.—Bracutopopa (Lamp-shells). From the fact that the Brachiopoda possess a bivalve shell, these forms were formerly included among the molluscs near the clams. A little examination, however, shows that the resemblance between them is but slight. The two valves of the Brachiopod are unequal in size, and are dorsal and ventral, rather than right and left, as in the clams. Near the point where the two parts (valves) are hinged together there is usually an opening * in the larger valve through which a fleshy peduncle or stalk projects, ; by means of which the animal is fastened to some support. In- side the valves, which can be closed by muscles, are the prin- cipal organs. Near the mouth are found a number of delicate 3 ane tentacles (much like those of the Brachiopod. (Terebratulina “Polyzoa), the dis¢ whichyiieeas them being frequently rolled into a spiral. The alimentary canal is bent, but a vent is occasionally lacking. The Brachiopods are all marine. There are few in existing seas; but they are among the oldest inhabitants of the earth, for the shells are found fossil in great num- bers in all rocks from the earliest down to the present time. SuMMARY OF IMPORTANT F Acts. 1. The group of VERMES is not a natural one, but an association for convenience. Its members are bilaterally svmmetrical and have distinct dorsal and ventral sur- * In some the peduncle extends from between the valves instead of having a special opening. WORMS. 191 faces, but no general definition can be formulated for them. 2. The chief groups of Vermes are Plathelminthes, Ne- mathelminthes, Annelida, and Molluscoida. 3. The PLATHELMINTHES have no body-cavity and only one opening (mouth) to the digestive tract, when this is present. 4. The Plathelminthes are divided into Turbellaria, Trematoda, and Cestoda. 5. The Trematoda are parasitic on or in other ani- mals, often causing serious disease. They have a three- branched alimentary canal, and adhere to the host by suckers or hooks. 6. Many trematodes pass through two hosts and present also an alternation of generations in their life-history. 7. The Cestoda are all internal parasites and have lost the digestive system. 8. Many become broken up into proglottids, new pro- glottids forming in front while the older ones at the hinder end drop off when mature. 9. They frequently have an alternation of hosts. Man gets his cestode parasites (tapeworms) from the cow and pig. 10. The NEMATHELMINTHES have cylindrical bodies, and a complete alimentary canal (with mouth and anus) which runs through a large undivided body-cavity. il. They show no segmentation of the body and repro- duce solely by eggs. 12. They are largely parasites. The Trichina is one of the worst of human parasites, frequently causing death. 13. The ANNELIDA have segmented bodies with external ringing of the body and a division of the body-cavity into paired pouches. 192 SYSTEMATIC ZOOLOGY. 14. The nervous system consists of a brain and a pair of ganglia in cach somite. The cesophagus passes through the nervous system between brain and ventral cord. 15. The Annelida embrace the Chetopoda and the — Hirudinei. 16. The Chetopoda have well-developed body-cavity, and bristles on each segment, the bristles being frequently supported by fleshy parapodia. 17. The Hirudiner have reduced body-cavity and lack sete and parapodia. 18. The MouuuscorpEA were formerly regarded as mol- luses. They have a complete alimentary canal and a circle of tentacles surrounding the mouth. 19. The Molluscoidea are divided into Polyzoa and Brachiopoda. 20. The Polyzoa reproduce by eggs and by budding, the result of the latter being to produce large colonies. 21. The Brachiopoda have a bivalve shell, the two valves being dorsal and ventral. They are attached by a ped- uncle and reproduce solely by eggs. 22. The few existing Brachiopoda are marine. In past time they were far more numerous, and fossil brachio- pods are abundant in the older rocks. Poyruns LY —MOLEUSCA. Oysters, clams, snails, and cuttlefish may be taken as examples of the ten thousand different species which are known as molluscs. The name comes from the Latin mollis, soft, and alludes to the fact that, aside from the shell, the body has no conspicuous hard parts. This, how- ever, is a point of no real importance in classifying animals. Molluses vary greatly in appearance; but if we carefully compare the points which all possess in common, we can construct an ideal mollusc, from which any form may be derived by additions here and modifications there. Such a typical mollusc is described below (fig. 34). Fic. 34.—Transverse and longitudinal sections of a schematic Molluse. a, auri- cle; c, cerebral ganglia; d, digestive tract; f, foot; g, gill; h, heart; 7, intes- tine; J, liver m, mouth; n, nervous system; p, pedal ganglia; pc, pericar- um; s, stomach; v, vent (in left figure, ventricle). The body is saccular, and bilaterally symmetrical. There is, above, a conical visceral mass; below, a muscular joot; while from either side a fold of the body-wall extends outwards and downwards as a mantle. Between the 193 194 SYSTEMATIC ZOOLOGY. mantle and the body and foot is a mantle-chamber or, since it frequently contains the gills (branchiz), it is frequently called the branchial chamber. The outer surface of the mantle and the dorsal part of the body frequently have the power of secreting a shell composed, chiefly, of carbonate of lime. This shell in some forms becomes split along the median line, so that two halves or valves result. In most other forms the shell becomes coiled into a spiral, and when this occurs the primitive symmetry becomes lost in part. Shells increase in size during the life of the animal. The mantle is continually laying down new layers of shell inside of those first formed, hence the older parts are thicker than the newer portions. Then the mantle is larger when the new layers are secreted, so these project beyond the layers outside of them. As a consequence there occur on the outside lines of growth. In many ‘species there are colored bands or spots upon the mantle, and these parts secrete carbonate of hme similarly colored, the result being that the shell is corre- spondingly striped or spotted. Again, in some, the edge of the mantle is produced into finger-like lobes, etc., and these cause spines and the like upon the shell. Shells are frequently spoken of as the houses or homes in which the animals live. As will be seen from the above, the shells are as much a part of the animal as is the cara- pax of a lobster or the coral of a coral polyp. The oyster or snail can never leave its shell. In most molluscs folds of the skin extend from the body- wall into the mantle-chamber. These are the branchie or gills. Inside of them are blood-vessels, and through their thin walls the blood is brought into close connection with the oxygen dissolved in the water. In the common ter- MOLLUSCS. 195 restrial molluscs gills are absent, but the inside of the mantle-chamber is lined with a fine network of blood- vessels, so that the whole organ resembles somewhat a lung, and has received that name. In the course of the blood there is a oreat difference between a molluse and a fish. In the mollusc the blood returns at once from the gills to the heart, and is then forced by this organ to all parts of the body. The heart is situated in a chamber or pericardium * and consists of one or two (right and left) auricles which receive the blood, and a ventricle which pumps it to the body. In the squid and cuttlefish accessory or branchial hearts are added. These are placed at the bases of the gills and force the blood through these organs, from which it re- turns to the other or systemic heart, to go to all parts of the body. In all molluses except the Acephala the region of the mouth is provided with a lingual ribbon (fig. 35, called also radula and _ odontophore). This is a band of horny ma- terial, bearing on its free sur- face rows of hard and sharp teeth, so that the whole resem- bles a flexible file. It is sup- ported in such a way that it may be moved back and forth, v thus rasping the food. In sume gasteropeds it cam: even 1G 357% bit, of eninge be used in boring holes in the Te eee gs oe shells of other molluscs. This lingual ribbon is constantly growing at its deeper end, so that the loss by wear in front is continually made good. * This is the ccelom, greatly reduced in size. 196 SYSTEMATIC ZOOLOGY. The teeth on the ribbon vary in number and shape in different species. In some there are but three in a trans- verse row, while in others there may be over one hundred. In the ideal mollusc the alimentary canal goes straight through the body from mouth to vent. In nature it usually has some convolutions, increasing the amount of digestive surface. In the cephalopods and in most gas- teropods it becomes bent on itself, so that the vent is far in front, either upon the right side or even in the median line. In the gasteropods, when it is median, it is close to and dorsal to the mouth. In the cephalopods it is ventral. A large liver is always present. The nervous system (fig. 34, right) consists of at least three pairs of ganglia and the cords or commissures con- necting them, as well as the nerves going to the various parts. These ganglia are the cerebral, above the mouth; the pedal, primarily in the foot; and the visceral, farther back in the body. Both pedal and visceral ganglia are below the intestine; the pedal supplying the foot, the visceral the body and the mantle. To these three pairs others are frequently added. Sometimes the ganglia are widely separated, when the commissures are correspond- ingly lengthened; or they may be brought close together, with shortened connecting cords. Some molluses lack organs of special sense; others have eyes and ears. The ears are little sacs, usually near the pedal ganglion, but the eyes may have various positions. They may be on the sides of the head (squid), or on the sides or tips of tentacles arising from the head (snails), or scattered over the back (some slugs and chitons), or on the edges of the mantle (scallops), or on the end of the siphon (some clams). In some they are merely spots which have the power to distinguish between light and MOLLUSCS. 197 darkness, and from these all degrees of development may be found to the extreme in the squid, where these organs are scarcely inferior to those of vertebrates in structure. For kidneys the molluscs have one or two organs (nephridia) consisting of convoluted tubes opening at their inner end into the pericardium and communicating with the exterior at the other. In some the sexes are separate; in others, like our land-snails, both sexes are united in the same individual. Molluses reproduce exclusively by eggs, and in some there appears in development a trochophore-like larva which is regarded as indicating that these animals are related to the annelids (see p. 186). Molluscs are divided into five groups or classes: Amphineura, Gasteropoda, Scaphopoda, Acephala, and Cephalopoda. Cuass I1.—AMPHINEURA. Setting aside a few rare forms this division is represented by the Chitons (fig. 36). These are dis- tinguished from other molluscs by many points of anatomy, while ex- ternally they may be recognized by having oval, flattened bodies covered above by a shell composed of eight transverse plates which overlap, from in front backwards, like the shingles Fre. 36—Chiton squamosus. onaroof. All the species are marine. es ha aia: Cuass I].—GASTEROPODA. The gasteropods receive their name from the fact that the foot usually forms a large sole or creeping disc extend- ing along the ventral side of the body. There is a distinct 198 SYSTEMATIC ZOOLOGY. head, which usually bears sensory tentacles, and the eyes are commonly placed at the bases or on the tips of one pair of these structures. In some cases, as in most land- snails, these tentacles can be pulled back into the body in much the same way that one inverts the finger of a glove. In the majority of forms gills or branchie are developed in the mantle-chamber. In a few there is a pair of these organs, but in many one gill disappears, while in other species both true gills entirely disappear, and are either replaced by secondary gills developed on the back or in other regions; or the mantle-chamber may be richly lined with blood-vessels and thus be converted into an organ (lung) for breathing air. This is the case in all of our common land-snails. In all gasteropods a shell is present in the young, but in many it is lost before the animal becomes adult. It is never a bivalve structure, but is either conical, plate-like, or is coiled in a spiral. In some the spiral is flat, in others it may be elongate, and the turns may be either to the right or to the left, right-handed shells being in the great majority. In a large number of gasteropods a shell-like structure (operculum) is developed on the dorsal surface of the hinder part of the foot, and when the animal with- draws itself into the shell this operculum closes the open- ing like a door after all the soft parts are inside. Some of the peculiarities of the nervous system form the basis of the subdivision of the gasteropods. In one group (Euthyneura) the ganglia and the cords connecting them are much as in our diagram (fig. 34). In the other (Strep- toneura) the cords leading back from the brain become crossed so that the nerve which starts from the right side goes to a ganglion on the left, and vice versa. MOLLUSCS. 199 In all gasteropods a lingual ribbon (p. 195) is present, and this works against a plate or ‘jaw’ on the upper side of the mouth. The alimentary canal is rarely straight. Usually there are convolutions, and the whole is so bent upon itself that the vent is carried far forward, and may be placed upon the ‘neck’ just above the mouth. Some- times it, or the liver connected with it, becomes greatly branched. Suspcuass I.—STREPTONEURA. In these the nervous system is twisted; there is but a single pair of tentacles upon the head; and the gills are placed in front of the heart, a condition which leads many naturalists to call the group ‘Prosobranchs.’ OrpER I.—DIOTOCARDIA. In these forms the body retains its bilateral symmetry to a consider- able degree, and externally may ap- pear perfectly symmetrical. The name implies the existence of two auricles to the heart. In the limpets (fig. 37) the shell is a flattened cone; in the abalones it is somewhat ear-shaped and very weakly spiral, but in the top shells it is strongly spiral. The abalones alone have any economic value. Their shells, remarkable for ,., peed Ce fey ene) ae series: of “holes aniohem, jeslemals From Bin- are composed of a greenish mother- of-pearl, which is extensively used in inlaid work. 200 SYSTEMATIC ZOOLOGY. OrpER II.—MonorocarRpDIA. Here belong the great majority of marine snails, all of which agree in having but a single gill and a single auricle to the heart. Few of them have any economic interest aside from those which feed upon oysters and other valuable shell-fish. These injurious forms—com- monly known as ‘drills’—are able to bore holes through the shells of oysters, etc., by means of their lingual ribbons. Many, however, are great favorites with collectors, among them the strombs Si (fig. 388), cones, cowries, and olives. thee Sey. Some of the cones are noticeable from After Woodward. the fact that they have a poison-gland connected with the lingual ribbon. Some species, for- merly grouped as a distinct order of Heteropoda, are espe- cially modified for a life on the high seas. ‘Supciass I].—EuTHyNeurRA. In the Euthyneura the nervous system is without a twist, and the head almost always bears two pairs of tentacles. OrpDER I.—OPISTHOBRANCHIA. These forms are all marine, and have but two divisions to the heart—an auricle and a ventricle, the latter being in Fic. 39.—Naked mollusc (Doris), showing the gills, above to the right. front of the former. Some are provided with a spiral shell, while others — called Nudibranchs or naked mol- MOLLUSCS. 201 luses (fig. 39)—are without such protection in the adult, although shells are present in the young. In the nudi- branchs there are commonly developed gills upon the dor- sal surface, and in the living condition these forms are, from their bright colors, among the most attractive of molluses. Here, too, are forms (Pteropods) especially de- veloped for a life on the surface of the ocean, the foot being modified into a pair of wing-like structures. OrpDER IJ.—PULMONATA. The great majority of the land- and fresh-water snails and slugs belong here. In them gills have disap- peared, and the mantle-cavity has been modified into an organ (lung) for breathing air, the opening to which is to be seen on the right side of the body. Over six thousand species belong here, some (snails) having a well-developed spiral shell, while the slugs (fig. 40) are appar- ently shell-less; but in these slugs one can frequently find a rudimen- tary shell imbedded in the mantle. Cuass II].—_SCAPHOPODA (TOOTH-SHELLS). iimthese the manvle edves aretused "1: 70. Siuz Canes ‘ campestris). Ss, respir- below, forming a tube, and as a result aber Op eemee ; Hront b udwig’s Leunis. _ there is formed a tubular shell, open at both ends, in shape something like the tusk of an elephant. The foot is relatively large, and is adapted for digging in the sand in which these animals live. There is no distinct head, but the mouth is provided with a 202 SYSTEMATIC ZOOLOGY. lingual ribbon. In the anterior part of the mantle- cavity are a pair of bunches of long threads of unknown function; possibly they are sensory, possibly respiratory, in nature. All of the tooth-shells are marine. Crass 1V.—ACEPHALA. In the Acephala, as the name implies, there is no dis- tinct head. The body is flattened from side to side, and the two sides are almost exact repetitions of each other. On either side of the body there is a strong outgrowth of the body-wall, the mantle, which secretes on its outer sur- face the shell, which is divided in the median line so that two halves or valves result. Between the mantle folds and the body is the mantle-chamber, and into this on either side there usually hangs down a pair of leaf-like gills,* whence the name Lamellibranchs, often applied to the class. The muscular foot projects from the lower surface of the body. With these features the animal presents a marked resemblance to a book in which the valves represent the covers; the mantle, gills, body, and foot, seven leaves. Where the two valves are hinged together there is an elastic ligament which tends constantly to open the valves, which are closed by means of adductor muscles extending from one valve to the other. Usually there are two of these muscles—anterior and posterior—but the anterior of these may disappear. In some, as in the oyster, the mantle edges are free from each other throughout their extent; but not infrequently they become fused in places, leaving openings between. At the posterior end this fusion frequently results in the formation of two tubes or siphons connecting the mantle- * It is not necessary here to include the gill features of Cuspi- daria, Silenia, etc, MOLLUSCS. 203 cavity with the outer world (fig. 41). In some these siphons may be greatly developed as long tubes and Fie. 41.—Quahog (Venus mercenaria), with foot and siphons extended. then strong retractor muscles to draw them back are present. All of these muscles—adductors, retractors, etc. —leave their impress on the shell, so that the student, with the shell alone, may know of some of the structures of the soft parts (fig. 42). Water is drawn into the mantle-cavity by means of very minute hair-like structures (cilia) which cover the gills and other Fic. 42.—Inside of bivalve shell show- ing muscular impressions of a, an- terior adductor; p, posterior adduc- tor; s, siphonal muscle. parts. These cilia are in constant motion,* and thus currents of water are produced, flowing always in one * The teacher should demonstrate this ciliary action under the compound microscope, 204 SYSTEMATIC ZOOLOGY. direction. This water brings oxygen to the gills and, through them, to the blood. It also brings minute animals and plants. These are passed on to the labial palpi, fleshy folds, near the mouth,.which are similarly ciliated, and from these organs the cilia force the food into the mouth. In the nervous system we always find cerebral, pedal, and visceral ganglia, and frequently parietal gangha between the cerebral and the visceral, the first being above, the others beside or below, the alimentary canal. Ears are present, connected with the pedal ganglia; and eyes may be present, either upon the edges of the mantle or at the tips of the siphons. The alimentary canal is always provided with stomach and liver. Connected with the stomach a blind sac fre- quently occurs, and in this there may be a peculiar trans- parent rod, the crystalline style, of uncertain use. The intestine goes from the stomach first towards the foot, then mounts towards the hinge-line, and frequently passes through the ventricle of the heart. The heart consists of a single ventricle and usually two auricles, but sometimes there is but one of the latter. The heart is situated in a chamber (pericardium), which is connected with the exterior by means of a pair of con- voluted kidney tubules or nephridia (organ of Bojanus). A thoroughly satisfactory classification of the Acephala has not yet been worked out. Possibly the best is that based upon the structure of the gills, but a more convenient one for our purposes is based upon the presence or absence of a siphon. OrpDER |J.—ASIPHONIDA. The edges of the mantle free; no siphon present. Most prominent of this order are the oysters, These are all MOLLUSCS. 205 marine, species being found in all but the colder seas. In these forms the animals lie upon one side, and there results an inequality of the valves. On our east coasts oysters extend from the Gulf of Mexico to Cape Cod. Further north (except in the Gulf of St. Lawrence) they are not found native, but are ‘planted.’ The centre of the oyster industry is Baltimore. In 1894 the oyster- fishery of the United States amounted to over $16,000,000. and the Fie. 43.—Scallop (Pecten irradians). From Binney’s Gould. valves may be unequal or similar in shape. These mol- luses can swim freely by rapidly opening and closing the valves of the shell; and they are further noticeable from the fact that around the edge of the mantle are a series of rather complicated eyes. The ‘scallops’ of the markets are the adductor muscles of these molluses. In the pearl- oysters the inner layer of the shell has a pearly appear- ance, and these forms also produce, like some other mol- 206 SYSTEMATIC ZOOLOGY. luses, the precious pearls. These pearls are really the shell-forming secretions of the mollusc around some foreign body and they receive their beauty from the way in which the shell is deposited around the centre. Fresh- water mussels, to be referred to a few lines below, also form pearls of value. The shell of the pearl-oyster also has its value, for it furnishes the mother-of-pearl used for buttons, knife-handles, for inlaying, etc. The pearl- oysters occur in the Indian Ocean, and also in the Bay of Panama. The salt-water mussels (fig. 44) so abundant on the Fic. 44.—Salt-water mussel (Mytilus edulis). mud flats all along northern shores have a peculiar gland in the foot which secretes strong silky threads (byssus) by which these animals anchor themselves. The common species, which occurs both in Europe and New England, is called the edible mussel; but not infrequently severe “sickness follows its use as food. The fresh-water mussels or Unios are especially abundant in America, the Mis- sissipp1 basin being their centre. They are useless as food, owing to their strong taste. There are possibly a hundred species of these forms in America; over six hundred so-called species have been described. In their siphonal structure they form a transition to the next group. MOLLUSCS. 207 OrpDER IJ.—SIPHONATA. In these the margins of the mantle have grown together posteriorly into a double tube or siphon, and accordingly as this siphon is developed the Seay animal can burrow below the 2 surface and still obtain its nec- SY + : essary supplies of water and NON = Ne food; for these tubes can ~ SSNS zh oo reach the surface, and through = SSs3S = Se them there is a continual flow ASsy sy = wa of water—inward through the = XYs*sS; eS ventral, outwards through the 9 <8: RS a= 8 oS dorsal, passage (fig. 45). | SySesy [= : - < The great majority of bi- Cas =f ~~ valve molluscs belong here, but SS = S33 there are comparatively few of . => Sea general interest. The largest of all clams, the giant clam of the East Indies, with shell sometimes weighing over 300 pounds, belongs here, as do the quahog and the long clam, which are used as food. One of these forms, the Teredo or ship-worm, is a serious pest, as it bores in wood, destroying the piles of wharves, the bot- ENN toms of boats, etc. Their bur- 9 22285 ss SES NSs rows run to long distances, but P16, #57 Tons. clam are The dllstheir food and waver mist. )4 gon snow tae: cuments = be drawn in through the si- phons, One great inundation in Holland at the begin- SS VENA SSS 208 SYSTEMATIC ZOOLOGY. ning of the last century was directly due to the borings of these forms. ; Cuass V.—CEPHALOPODA (Saquip AND CUTTLEFISH). The Cephalopods derive their name from the fact that the circle of tentacles or arms around the mouth (i.e., on the head) was compared to the foot of other molluscs. Later investigations show that these tentacles represent but a part of the foot, the siphon also belonging to the same category. These same arms, which are either eight or ten in number, bear sucking organs by means of which these animals hold fast their prey. In the pearly nautilus only are the arms lacking, and here they are replaced by about a hundred smaller organs. The head, which is separated from the body by a distinct neck, bears a pair of eyes—simple in the nautilus, but al- most as complex as those of man in the other forms. In these more highly developed eyes there are retina, lens, iris, cornea, and cavities resembling those occupied by the aqueous and vitreous humors (see Vertebrates). Yet the resemblances are superficial; the structures are in reality totally different. The mantle is connected with the body in the region of the so-called back. Below, it encloses a good-sized mantle- cavity, open in front. It is very muscular, and the open- ing about the neck can be closed at will, so that the only connection between the mantle-chamber and the outside world is through the tube of the siphon. This is a tubular structure on the ventral surface, in no way homologous with the similarly named tubes of the Acephala. If one of these animals fill its mantle with water, close the neck opening, and then force out: the water by contracting the MOLLUSCS. 209 mantle, the water will stream from the siphon in a strong jet, which by its reaction forces the animal in the other direction. This apparatus forms with many, and especially with the squid, the chief organ of locomotion, and in these the tip of the siphon can be bent in any direction, so that the animal may go forwards, backwards, etc., according as it wishes. In the mantle-cavity are one or two (Nautilus) pairs of feather-like gills, and into the same chamber empty the ducts of the kidneys and reproductive organs, as well as the intestine, and the ink-sac connected with it. This last organ secretes a dark-colored fluid, which when dis- charged into the water makes a cloud, and thus the animal is enabled to escape unseen. From this ink the pigment sepia and some kinds of India ink are manufactured. Imbedded in the skin of the mantle are pigment spots or chromatophores, which are interesting from the fact that they can be enlarged or contracted by the nervous system. When enlarged they nearly touch each other, and thus give the body their general hue (red). When contracted they appear as minute black points, while the general body color (translucent white) then prevails. As a result we have in these animals a power of color-change far more striking than that of the chameleons. | Most living cephalopods have no external shell. Inside of the back, however, is a shell—the pen—which may be either feather-shaped and horny, or broader, thicker, and ealeareous. In this last condition it furnishes the ‘cuttle- bone’ so often given to cage-birds. The paper-nautilus has a shell which is formed only by the female; it is se- ereted, not by the mantle, but by one pair of the arms, and this shell is really a protection for the eggs. In the pearly nautilus, on the other hand, there is a true shell, 210 SYSTEMATIC ZOOLOGY. which is coiled in a spiral and is divided by partitions into a series of chambers, only the outer one being occu- pied by the animal (fig. 46). ‘Similarly chambered shells are very abundant among fossils. The mouth is armed with a pair of horny jaws shaped much like those of a parrot. These are very efficient in biting food; but any morsels taken into the mouth are subjected to further subdivision by means of the lingual ribbon, which is, as its name implies, a ribbon-like mem- brane, bearing on its surface numbers of minute teeth, whch rasp the food into fine shreds. The heart is situated in a pericardium and is systemic; that is, it pumps the blood returning from the gills to the various parts of the body. A peculiarity of the circulatory system is that in all, except the pearly nautilus, the vessel carrying blood to the gills develops a special pumping organ, the branchial heart. The various ganglia of the nervous system are (except the stellate ganglia) placed close together in the head, and from this centre nerves radiate to all parts of the body, those going to the tentacles being connected with each other by a circular cord. The stellate ganglia, of which there are two, are upon the anterior part of the mantle. The nerves which radiate from them control the motions of the mantle. The cephalopods are all marine. They are carnivorous, feeding upon fishes, etc., which they capture with their arms and hold fast by their numerous suckers. The larger forms might be no mean antagonist for man; but the monster described by Victor Hugo is without counter- part in nature. The cephalopods are divided into two orders, according to the number of gills. MOLLUSCS. 211 ORDER [.—TETRABRANCHIATA. In the Tetrabranchs there are two pairs of gills (7.e., four in all); the head bears numerous short tentacles without suckers, and the body is enclosed in a chambered shell. The pearly nautilus is the only living representative of this Fig. 46.—Female Nautilus, the shell laid open (from Ludwig’s Leunis). 1, man- tle; 2, dorsal lobes; 3, tentacles; 4, head fold; 5, eye; 6, siphon; 8, shell muscle; 9, living-chamber; 10, partitions between chambers; 11, siphuncle. group. It occurs in the East Indian seas, and, while the shells are very common, the animal is very rare in museums. In geological times allied forms were very abundant, and are known as Ammonites (with tightly coiled shells), and Orthoceratites (with straight shells), ete. OrpER IJ.—DIBRANCHIATA. These have two gills (one pair), and long, sucker-bearing arms. An ink-sac is always present. The order is sub- divided into the Ocropopa, in which there are eight arms (fig. 47), and the Drcapopa, in which the number is increased to ten by the addition of a pair of longer arms. In the Octopoda there is no internal shell, and the body 74 SYSTEMATIC ZOOLOGY. is saccular. Here belong the octopus, poulpes, etc., as well as the paper nautilus, which does not sail with its shell as a boat, and its broadened arms erect to catch the wind, as it is often said to do. The Decapoda include the squid, the sepia, and other forms. The smaller squid Fig. 47.—Octopus bairdit. From Verrill. One arm on the right side is modi- fied for purposes of reproduction. are abundant, and are caught in large numbers for bait in fishing for cod. Near Newfoundland; and in other parts of the world, giant squid are occasionally found, the largest one known having a body length of twenty feet. The length of the arms was not mentioned in the account. SUMMARY OF IMPORTANT FACTS. 1. The MOLLUSCA receive their name from the soft nature of the body, in which the body-cavity is greatly reduced. 2. They have a body from whick a foot depends below MOLLUSCS. 213 and a fleshy mantle fold on either side, enclosing a pair of branchial chambers between mantle and foot. 3. The mantle usually secretes a shell which increases in size during life, the stages e increase being shown by lines of growth. 4. The true branchiz project into the branchial chamber; they may be lost and replaced by other gills developed from other parts of the body. 5. A characteristic feature of all except me Acephala is the lingual ribbon. 6. The nervous system consists of at least three pairs of ganglia connected by nervous cords. 7. The reproduction is exclusively by eggs. A trocho- phore may occur in development. 8. The Mollusca are divided into Amphineura, Gastero- poda, Scaphopoda, Acephala, and Cephalopoda. 9. The AMPHINEURA have a very simple nervous sys- tem. In the Chitons, which belong here, there are eight plates of shell on the back. 10. The GastTERopopa have a distinct head with ten- tacles and a creeping foot. 11. The shell is unpaired, more or less conical, and fre- quently spirally coiled. It is occasionally lacking in the adult. 12. The Gasteropoda include the Diotocardia, Mono- tocardia, Opisthobranchia, and Pulmonata. 13. The ScaPpHopopa are primitive forms with tubular shell and no distinct head. 14. The AcmpHawa lack head and lingual ribbon, and have a bivalve shell. , 15. The edges of the two mantles may unite behind to form the siphon. 16. The foot is fleshy and more or less hatchet-shaped. é 214 SYSTEMATIC ZOOLOGY. 17. The Acephala may be divided into Asiphonida and Siphonata. , 18. The CrPpHALOPopA have no true foot, this being represented by the siphon and the tentacles around the mouth. 19. The shell, when present, is unpaired. When present it may be external or internal. 20. The ink-sac is peculiar to Cephalopoda. 21. The eyes are usually highly organized, and resemble those of vertebrates. 22. There are present special branchial hearts to force the blood to the gills, and a systemic heart to force it through the body. 23. The Cephalopoda are divided into Dibranchiata and Tetrabranchiata according to the number of gills. Paytum V.—ARTHROPODA. The word Arthropoda means ‘jointed foot,’ and is very characteristic of all that immense series of forms which, like the grasshopper and the crayfish, have an external skeleton which only permits of motion by a thinning or jointing at intervals. In this way both body and limbs have this jointed appearance, but with the body this joint- ing or segmentation of the external surface is associated with features of internal structure which must have a moment’s attention. This external jointing of the body divides it into a series of essentially similar rings, somites, or metameres, and in each of these we find parts of all the internal organs. That is, the segmentation is not con- fined to the external surface, but is characteristic of all parts. In an ideal arthropod each of these segments would be an exact repetition of its fellows, much as they are in the annelids (p. 183), but in nature we find that certain segments or parts of certain segments become over-devel- oped (hypertrophied), and this produces an under-develop- ment (tendency towards atrophy) in others. Thus every segment in our ideal arthropod would bear a pair of jointed appendages, but these are frequently atrophied on some of the segments. Again, there is a tendency in some regions, and especially in the head, for a more or less complete fusion of segments, so that the number can 215 216 SYSTEMATIC ZOOLOGY. only be ascertained by the appendages or by the features presented in development. Usually these segments can be grouped in regions, of which, at most, three can be distinguished: in front the head; next, the thorax; and behind, the abdomen (fig. 48). The head is largely concerned in the taking of food, Fic. 48:—Diagram of grasshopper showing the body divided into the three regions: head, thorax, and abdomen. and is usually the seat of the special senses. The thorax is the locomotor region, while in the abdomen the primi- tive segmentation is most marked. Through the body as an axis runs the alimentary canal, the mouth being on the under surface of the head, while the vent is at the tip of the abdomen. Above the diges- tive tract lies the heart, which in many forms has a chamber in each of several somites of the body; that is, the heart is segmented. On the floor of the body, below the alimentary canal, is the nervous system, which ex- hibits this segmentation in a more marked degree. In. each segment there is a paired enlargement or ganglion from which nerves go to the various organs of the seg- ment. These ganglia of the successive segments are con- nected with each other by a double nerve-cord, so that all are in communication with each other. At the front end of the body one of these nerve-cords passes on one side of the cesophagus, the other on the other, and above it they unite with a large compound ganglion, the so- called brain. In this way a part of the nervous system ARTHROPODS. 217 is brought above the alimentary canal, while the rest lies below. In other words, the digestive tract passes through the nervous system, a condition which is common in the non-vertebrate animals, the structure in the arthro- pods closely paralleling that in the annelids. : Two kinds of eyes occur in the Arthropoda, the simple or ocella and the compound, each with an apparatus (lens) to concentrate the light and a retina for its recog- nition. As the name implies, the compound eye consists of a number of simple eyes closely united together, the whole forming a visual apparatus, each element of which sees a part of the object, the whole visual impression thus resembling a mosaic. The organs of respiration are never connected with the alimentary canal, but are always developments of the surface (ectoderm) of the body. They are of two kinds: gills or branchiz in aquatic forms and traches or air- tubes in the forms which do not live in the water. Gills in the arthropods are outgrowths of the body-wall, usually much folded or divided to afford additional surface, and in these are blood-vessels. In the case of gills, then, we may say that the blood is brought to the oxygen dissolved in the water for that exchange of gases (carbon dioxide and oxygen) upon which respiration depends. With trachee, on the other hand, the respiratory surface is obtained by a forcing of the external surface into the deeper parts, much as one might invert the finger of a glove into the palmar region. In the tubes thus formed air can enter, and thus the oxygen is brought to the blood and other tissues of the body. It is interesting to note that the more the traches are developed, the more the circulatory organs are reduced. The ‘lungs’ of the arachnid are to be regarded as modified gills. 218 SYSTEMATIC ZOOLOGY. The excretory organs of the arthropod are formed upon two plans. In the one (Crustacea and Acerata) we have a few organs, like the green gland and the shell gland, which are apparently to be regarded as comparable to the nephridia of the annelids (p. 184). The other type, the Malpighian tubes (Arachnida and Insecta) are con- nected with the alimentary tract. The Arthropoda are by far the largest group of animals, the number of forms living to-day being estimated from half a million to a million or more. The Arthropoda are subdivided into three groups or classes: Crustacea, Acerata, and Insecta, and besides these a few forms of uncertain position. Cuass I.—CRUSTACEA. The crayfish and sow-bug may be taken as types of the Crustacea, or crab-like forms. All have two pairs of appendages (antenne) in front of the mouth; they have a varying number of segments at the front of the body, covered by a common shell or carapaz, and, excepting gill-less microscopic forms, they all breathe by means of gills attached to some of the feet. The number of segments in the body varies; in the higher groups it is constantly twenty, but in the lower it may fall far short of, or far exceed, that number. The regions also vary in extent and cannot be compared throughout the eroup. Taking the segments connected with the senses | and with eating as constituting the head, this region may contain as few as five or as many as eight segments. Not infrequently the head and the next region of the body are united so that they are called a cephalothorax. The abdo- men is usually well developed, but it may be reduced to a CRUSTACEA. 219 mere stump, as in the barnacles. Any of the segments except the last one may bear appendages. The append- ages most commonly present are the two pairs of antenne in front of the mouth, next those concerned in eating and grouped as ‘mouth-parts.’ Of these there are always a pair of biting-jaws or mandibles, then two pairs of acces- sory jaws or maxille, and lastly a varying number of ‘jaw-feet’ or maxiliipeds. Behind these there may be the walking-feet upon the thorax and the swimming-feet upon. the abdomen. If these appendages be studied in the adult of some species or in the young of all, they are found each to con- sist of a basal joint, bearing two jointed branches, the exopod and endopod. With growth of the animal the exopod frequently disappears. The gills by which most Crustacea breathe are thin out- growths of the body, usually closely connected with some of the appendages, either of the thorax or of the abdomen. In shape they may be plates or plumes or sacs, but all are traversed by blood-vessels so that the blood is brought in close proximity to the water. In some cases these gills hang freely into the water, in others they are placed in special gill-chambers, and then there is an arrangement of parts for pumping fresh water over them. In the ter- restrial Crustacea these gills still serve as breathing- organs, as in the sow-bugs, and are constantly kept moist. In some of the lower Crustacea there are no special organs of respiration, the thin walls of the body affording suffi- cient surface for the purpose. The alimentary canal is nearly straight, and there is usually a chewing-stomach in which the food is ground. by hard teeth in the walls, and beyond this there is fre- quently a straining-stomach. A large so-called liver is 220 SYSTEMATIC ZOOLOGY. always present, pouring digestive juices into the alimentary canal behind the stomach. The eyes are either simple or compound. In the simple eyes there is a single lens for the whole structure, while the compound eyes are com- posed of many separate eyes, each with its own lens. In some cases the compound eyes are placed on jointed stalks, at others they are on the walls of the head. Ears have been found in some forms. Usually they are sacs in the base of the antennule, but in the opossum-shrimps they occur near the end of the abdomen. The hairs which occur over the body are organs of touch, and probably some of them around the mouth and on the antenne serve as organs of taste and smell as well. A heart is lacking in a few forms. When present it is dorsal in position, but may be either in thorax or abdo- men. It may be a long tube with several chambers, or a short thick muscular organ without divisions. ‘The blood returning from the gills enters the heart and is forced thence to all parts of the body, a condition quite different from what is found in the fish. It does not flow throughout its course in closed vessels, but escapes from them and comes into large spaces (lacune) between the various organs and muscles, and from the largest of these lacune, near the floor of the body, it again goes to the gills. In the Crustacea the excretory organs (nephridia) open to the exterior entirely independently of the alimentary canal. In the higher Crustacea (crayfish, etc.) these nephridia are known as ‘green glands’ and open at the base of the antennz (second segment of the body); in the lower Crustacea they are called ‘shell-glands’ and open at the base of the second maxille (fifth segment). The sexes are separate in all except the barnacles, and CRUSTACEA. 221 the ducts of the reproductive organs open to the exterior in the thoracic region, never in the abdomen. In almost. all forms the eggs are carried about by the mother until they are hatched. In almost all the lower Crustacea the young escapes from the egg in a very immature condition, known as a Nauplius (fig. 49), a name given years ago under the be- lief that it was an adult. The nauplius has an unsegmented body, a single median eye, and ‘ Fic. 49.—Nauplius stage of fairy- only three pairs of appendages shrimp (Branchipus). After —antennule, antenne, and ee mandibles—the antennulze being solely sensory, while antennse and mandibles are used in ‘both swimming and eating. In the higher Crustacea the nauplius stage is passed in the egg, and the young hatches in a more ad- vanced condition—sometimes closely like the adult in all except size. Growth is allowed for by frequent molts of the external cuticle of the body. Over 10,000 species of Crustacea are known, almost all of them aquatic, and the majority marine. Only a few, like the sow-bugs and land-crabs, live on the land. CP ee oh LA; ZA ZA ra \f VERTEBRATES. 303 In the sharks this ear-sac is placed behind and medial to the spiracle (p. 308). In the higher vertebrates the spiracle becomes closed on the outside, but the rest of the structure remains, and is known as the Eustachian tube, and as its outer end comes between the ear and the external world, one or more bones usually extend across the tube to convey the sound-waves to the sac. This forms the middle ear. In the frogs the outer end of the Eustachian tube is closed by the large tympanic membrane on the side of the neck. In the higher vertebrates an external ear occurs. This consists of a tube leading inward to the tympanic mem- brane, and to this tube are frequently added structures to catch and reflect the sound-waves into the tube. It should be mentioned that the ear is more than an organ of hearing; it is also an organ for maintaining the balance, for if the ear or the auditory nerve be injured the animal can no longer maintain its equilibrium. The eye (fig. 113) is built on the plan of a photographic camera. The essential parts are a lens which brings the rays of light to a focus on the retina, and means for causing the image on the retina to stimulate the optic nerve. To these are added various accessory structures for protection, for regulating the amount of the light, etc. In the lower forms eyelids are absent, but higher in the scale folds of flesh are developed which can close over the organ. Many ani- mals have three of these eyelids, two working. vertically, the third, the nictitating membrane, drawn from the inner angle of the eye over the transparent cornea. This nictitat- ing membrane occurs in the eye of man as a small fold (semi-lunar fold), which has entirely lost its primitive protective function. Over the whole globe of the eye is a tough layer, the 304 SYSTEMATIC ZOOLOGY. sclerotic coat, which is usually white (the white of the eye is part of it), and which may be cartilaginous or may even have bone deposited in it, as in many reptiles and birds. In front this layer becomes perfectly transparent, and is there known as the cornea. Inside of the sclerotic is found a densely black layer (choroid), and still within this the transparent retina, the outer portion of which is Fic. 113.—Diagram of vertebrateeye. c, choroids ¢, iris; /,lens; n, optic nerve; 7, retina; s, sclerotic. imbedded in the choroid. In front the choroid is con- tinued into the iris, a circular muscle with an aperture, the pupil, in its centre. This iris, which is colored, regu- lates by its enlargement and contraction the amount of light which is admitted to the visual parts of the eye. Back of the iris, and held in position by a circular muscle and ligament, is the transparent lens. In front of this lens is a watery fluid (aqueous humor), while behind it and between it and the retina is the somewhat denser vitreous humor. The optic nerve enters the eye from behind, passing VERTEBRATES. 309 through sclerotic, choroid, and retina, and is then distrib- uted over the inner surface of the latter layer. The eyeball is moved by six muscles, which are essentially alike in all vertebrates. Four of these are straight or rectus muscles, two are oblique. These muscles are con- trolled by the three eye-muscle nerves (p. 300). The alimentary canal runs through the body from mouth to vent. In it several parts can be distinguished. The mouth, at or near the anterior end, is without fleshy lips, except in the mammals. The mouth is fre- quently armed with teeth, and even in those groups, like the turtles and the birds, where teeth are absent the germs occur in the young, a fact which points to the descent of these from toothed ancestors. The tongue is formed as a fold of the floor of the mouth, and is usually supported by a skeleton (hyoid bone, p. 294) derived from the first or first and second visceral arches. In some it is without powers of motion, but - frequently it is very mobile. Usually it is attached behind, the front margin being free, but in many Am- phibia it is attached in front and folded back in the mouth. The mouth-cavity 1s succeeded by the pharynz, a re- gion concerned in respiration and distinguished by contain- ing the respiratory openings (internal nostrils, gill-slits, glottis). Behind the pharyngeal region is the digestive tract proper. In some vertebrates it 1s scarcely possible to dis- tinguish regions in it, but in most cases several distinct portions occur. Those usually to be recognized are the following: The pharynx communicates with the gullet or esopha- gus, a muscular tube which frequently serves only to carry food back to the stomach, On the other hand, a 306 SYSTEMATIC ZOOLOGY part of this tube may be expanded into a glandular food- reservoir or crop (birds). In some fishes and Amphibia the stomach is hardly differentiated from the cesophagus, but in other forms it is well developed, with muscular and glandular walls. It may even be divided into several portions. Thus in Z = ANG Fic. 114.—Diagram of the digestive tract of a mammal. b, brain; d, dia- phragm; h, heart; 7, intestine; k, kidney; l, liver; 0, cesophagus; p, pane- creas; s, stomach; sp, spleen; v, vent. birds (fig. 147) we frequently find two parts, one chiefly glandular, while the other (gizzard) is extremely muscu- lar. In the ruminants (p. 385) the specialization is carried farther, and we find four divisions to the or- gan. While some absorption ot food takes place in the stom- ach, the intestine is the chief absorptive portion of the alimentary canal. In some vertebrates it is short and straight, in others long and convoluted, there being usu- ally a correlation between length of intestine and the character of the food, this region being longer in the vegetable feeders. Increased absorptive surface is ob- tained in several ways, in addition to lengthening of the intestine. In the lower Ichthyopsida this is accomplished VERTEBRATES. 307 by the development of an extensive internal fold (spiral valve). In others there are numerous small longitudinal folds, while in the highest vertebrates transverse folds occur on which are minute finger-like outgrowths (vill). In the lower vertebrates the hinder part of the intestine receives the ducts of the excretory and reproductive organs, and at such times is called a cloaca. In the mammals, the monotremes excepted, no cloaca is form- ed. The vent is on the lower surface, in the median line. There are several accessory structures connected with the alimentary canal. Thus frequently salivary glands are present, emptying into the mouth. Behind the stomach the ducts of the liver and pancreas pour in their secretions, while in many fishes well-developed pyloric ceca occur, just behind the stomach, which have a diges- tive function. The digestive organs are supported in the body-cavity by a thin membrane (mesentery) which bears blood- vessels, etc., and which is attached to the dorsal wall of the body-cavity. This mesentery in reality is but the continuation of the lining (peritoneum) of the body- cavity. Vertebrates respire in three ways: by gills, by lungs, and by the skin. Gills arise first as outpushings or pouches in the sides of the pharynx, and then these break through to the exterior, giving rise to gill-slits or clefts, through which water taken in at the mouth can pass out. On the sides of these clefts the gills proper are developed. These are thin-walled leaves or filaments with a rich blood- supply, and through these thin walls there is an exchange of dissolved gases (oxygen and carbon dioxide) between the water and the blood. 308 SYSTEMATIC ZOOLOGY. in the septa between the gill-slits are the gill-arches or cartilages (p. 294); and from the septa there grow out, in the larval Amphibia, fleshy fringes, the external gills. Fic. 115.—Relations of gills, as etc., in a shark (left) and a teleost right). In most Amphibia these external gills are later absorbed and replaced by internal gills, which in turn may disap- pear upon the assumption of an aerial respiration. The number of these clefts varies between four and eight (more in some cyclostomes), but in all gnathostomes the anterior cleft has largely lost its respiratory function. In the sharks it becomes modified into the spiracular cleft; in the higher vertebrates it enters into the struc- ture of the ear, giving rise to the cavity of the drum and to the Eustachian tube (p. 303). In the sharks (fig. 115) each cleft opens separately to the exterior; but in ganoids and teleosts the hyoid sep- tum gives rise to a fold (operculum) or gill-cover, which grows back over the external openings, so that there is VERTEBRATES. 309 apparently but a single slit externally. A little con- sideration will show that there is little real modification. In the anu- rous Amphibia a similar fold is found, but this unites again with the body-wall behind the gills, thus enclosing the external openings in an atrium, with but a single open- ype ht ing to the exterior (p. 337). Inthe , LEG Sauropsida and mammals (fig. 116) ~"' Hy, gill-pouches are formed in the em- Fic. 116.—Human embryo (after Hertwig), with bryo, but according to recent observ- the floor of mouth and throat removed, to show ers these never break through, so the rudimentary gill- ; slits, g. Jl, lung; n, nos- that no real clefts are formed. With tril, still connected with growth all but the first pair of these a pouches disappear, the first persisting as the Eustachian tube. In all vertebrates above fishes, gills are supplemented (Amphibia) or replaced by lungs. These are paired sacs richly supplied with blood-vessels, and connected with the external world by means of a tube (windpipe or trachea) which opens by the glottis upon the floor of the pharynx. The trachea is usually strengthened by the development of cartilages in its wall, some of which may become large, as in the case of the human ‘Adam’s apple.’ The lungs themselves may be simple sacs, but usually they become greatly folded, thus increasing the respiratory surface. In the Amphibia, which lack diaphragm and ribs, air is forced into the lungs by swallowing; in the reptiles and birds it is drawn in by means of the muscles (zntercostals) between the ribs; in the mammals the intercostals are reinforced by a transverse muscle (diaphragm) (fig. 114) which erosses the body-cavity. This is dome-shaped, convex 310 SYSTEMATIC ZOOLOGY. above, becoming flatter by contraction and thus enlarging the cavity (thoracic cavity) which les in front of it. In the ganoids and bony fishes exists a structure, the swim-bladder or air-bladder, which is usually thought to represent the lungs. In the lower teleosts (Physostomi) it is connected with the alimentary canal by a duct open- ing on the dorsal wall of the pharynx, but in others (Physo- clisti) this duct closes long before the adult condition is reached. In the lung-fishes, on the other hand, the structure is double and its duct ventral. Connected with the respiratory system are two glands of problematical function. One of these, the thyroid, is formed from the floor of the pharynx. The other (the thymus) arises from the gill-pouches, and in the higher vertebrates disappears in adult life. In the calf it forms the ‘neck sweetbread.’ Both these glands are without ducts, and the part they play is obscure, but since when the thyroid is diseased it produces serious illness, it is apparent that it is very important in the economy. In the circulatory system three parts may be recognized: (1) a central propelling organ, the heart; (2) arteries, carrying the blood away from the heart; and (8) veins bringing it back. Between arteries and veins are inter- posed minute tubes, the capillaries. The heart is a muscular organ, enclosed in a special sac of the body-cavity, the pericardium. In the heart can always be distinguished a receptive portion (auricle), which receives the blood as it comes from the veins, and passes it on to the true propelling organ, the ventricle. This latter has strong muscular walls, and when it contracts, the blood, prevented by a valve from returning to the auricle, is forced out through the artery (ventral aorta) connected with the ventricle. VERTEBRATES. 311 In all fishes there is but a single atricle and a single ven- tricle, but when lungs appear, as in the Amphibia, the auricle becomes divided, and now one half (the right) receives the blood from the body, while the left auricle takes the blood returning from the lungs. These both pour the blood into the single ventricle. In the reptiles we find the beginning of a division of the ventricle, which becomes complete in the crocodiles and continues in birds and mammals (fig. 118). In these forms the left auricle pours its blood into the left ventricle, while the same relations exist between the auricle and ventricle of the right side. In the fishes the blood leaves the ventricle by an arterial trunk, in which, when best developed, we can distinguish a conus with valves inside to prevent the blood flowing back into the ventricle; or a bulbus, without valves, and in front of these the ventral aorta. From this lateral ves- sels ‘(afferent branchial arteries) are given off, and these pass up through the branchial septa. Consequently the number of these arteries depends primarily upon the num- ber of gill-clefts. In the septa the arteries break up into capillaries which pass through the gills, and collect in efferent branchial arteries which pass above the pharynx. Here they unite and give rise to the main trunk, the dorsal aorta, which runs, above the alimentary canal, through the body, giving off vessels to all parts, see fig. A: From these vessels the blood passes through the capil- laries and is collected in veins which bring it back to the heart to repeat the circuit. In this circulation the blood changes in its character. When it enters the heart it bears nourishment obtained from the alimentary canal, and waste from al! parts of the body. Its color is a dark 312 SYSTEMATIC ZOOLOGY. purplish red. In its passage through the gills it rids itself of one kind of waste (carbon dioxide) and absorbs oxygen from the water. This exchange is accompanied by a’ cx }) Fic. 117.—Diagram of the arterial arches and their modifications in various vertebrates (after Boas). The primitive arches are outlined; those which are functional in the adult are black. A, embryonic condition; B, Ceratodus (fish); C, Salamandra; D, Triton; E, frog; F, lizard; G, bird; H, mammal; C, carotid artery; DB, ductus Botallii; DO, dorsal aorta; HC, external carotid; IC, internal carotid; P, pulmonary artery; SC, subclavian artery; VO, ven- tral aorta; 1-6, primitive arches. change of color to bright red. The other waste is gotten rid of in the kidneys. In the capillaries of the body it gives up its oxygen and nourishment to the surrounding VERTEBRATES. 313 parts, and becomes loaded anew with carbon dioxide and other waste, changing color again to the dark red. From this account it will be seen that in the fish only blood charged with impurities passes through the heart. From the arrangement of blood-vessels found in the fishes (sharks) all the conditions found in the higher verte- brates may be derived, simply by enlarging some vessels and suppressing others. Some of the changes involved may be made out from the diagrams (fig. 117) in compari- son with your dissections, the explanatory statement being made that in embryo birds and mammals paired branchial arteries occur, while in the adult this symmetry is largely lost. One point particularly to be mentioned is that with the development of lungs, pulmonary arteries going to these organs are developed from the hinder pair of branchial arteries (fig. 117, B-E, P). When the gills are lost and the lungs function as respi- ratory organs, the conditions of the circulation are changed. The blood, in leaving the heart, passes partly to the various parts of the body, partly to the lungs. . That going to the latter organ loses its carbon dioxide, and takes up oxygen and changes to bright red. It now returns along with blood from other parts to the heart, which therefore now receives both lght and dark blood and forces the same out again. But when the lungs are developed the auricle of the heart divides, and one auricle receives the dark, the other the light blood, both emptying their contents in turn (in frogs and reptiles) into the single ventricle. It was therefore formerly thought that the blood sent out through the ventral aorta must necessarily be mixed; but this is not the case with the frog. By means of a peculiar valve the red blood is sent to the body, the dark blood to the lungs. 314 SYSTEMATIC ZOOLOGY. As has already been mentioned, in crocodiles, birds, and mammals the ventricle is also divided, and hence one half of the heart contains only bright, the other only dark, blood. The division is also car ied farther, for the last arch (going to the lungs) becomes connected with the half of the heart which receives the dark b ood, while the rest of the arches are similarly related to the other half of the heart (fig. 118). The blood itself should have a moment’s attention. It consists of a fluid (plasma) in which float myri- — ads of minute solid bodies (corpus- cles). The plasma is a pale yellow in color, the red of the blood being due to certain of the corpuscles, which are therefore known as the red corpuscles. Other corpuscles Fic. 118.—Diagram of the circulation in a mam- mal. The arrows show the direction of the flow; the vessels carrying red blood are shown white, those carrying dark blood, shaded. a, au- ricles;1, lung; lv, liver; p, portal vein bringing the blood from the in- are colorless, and are called white corpuscles or leucocytes. The red corpuscles carry the oxygen and carbon dioxide, the plasma the nourishment and the other waste. testine; v, ventricle. : ; : The plasma is further peculiar in that when withdrawn from the veins it soon solidifies or ‘clots.’ The excretory organs (kidneys or nephridia) are very complicated structures. In a few words, they may be described as a pair of organs lying in the dorsal wall of the body-cavity close to the median line. Hach kidney is richly supplied with blood, and it extracts from this CYCLOSTOMES. 315 fluid the nitrogenous waste and pours it into an excretory or urinary duct which empties behind, near the anus. The reproductive system is closely related to the excre- tory organs. In all except a few fishes the sexes are sepa- rate. In the females, eggs are formed in specicl structures, the ovaries, and when ripe the eggs are passed out to the exterior by means of a tube (oviduct) developed from the urinary duct. This passage may be rapid, or the egg may remain for a time in the oviduct and there undergo its development, as is the case in certain members of all groups of vertebrates except birds. In the male, corresponding to the ovaries in position, etc., are the testes, which produce the male reproductive element, which is also carried off by.a part of the primitive excretory duct. All vertebrates produce eggs, but these vary consider- ably in size. In the mammals the diameter is about +4, of an inch, the ostrich lays an egg about 5 inches in diam- eter, while the egg of #piornis, one of the extinct birds of Madagascar, was equal in size to 150 hen’s eggs. The Vertebrates are divided into Cyclostomes and Gnathostomes. 3 Series 1.—CYCLOSTOMATA. The Cyclostomes include a few eel-like forms, commonly known as lampreys and hagfishes. These differ from the other Vertebrates in many points, some of which are mentioned here. Bone is entirely lacking, and cartilage is feebly developed. Vertebre are scarcely recognizable, and there are no traces of paired fins, although dorsal and caudal fins may occur. The mouth, as the name Cyclo- stome implies, is circular, but is incapable of closure like 316 SYSTEMATIC ZOOLOGY. that of other vertebrates, since movable jaws are lacking. Inside of the mouth are horny teeth (few in the hagfishes, many in the lampreys), but these are chiefly used for holding, not for biting or crushing. The tongue is very large. ; There is but a single nostril on top of the head. The gills are placed not in simple slits, but in large pouches on the sides of the neck (hence the name, Marsipobranchs, often given the group), and these pouches may either open separately to the exterior or by means of a tube which leads to a single opening. The number of gill- pouches ranges between six and fourteen on either side. The Cyclostomes are subdivided into two groups, accord- Fic. 119.—Lamprey (Petromyzon marinus). After Goode. ingly as the nostril communicates with the throat or not. As examples of the first, the hagfishes may be cited. These are all marine, and are capable of secreting a large amount of mucus from their bodies, so that a few hagfish in a pail will convert the water into a jelly-hke mass. These fishes are parasites, and work their way into vari- ous fishes, like the cod, and when once inside they eat up - all the flesh and viscera, leaving nothing except the skin and bones. The second group is represented by the lampreys. Some of these are marine, others live in fresh water, while many of the marine forms ascend streams in spring to lay their FISHES. 317 eggs. By means of their circular mouths, horny teeth, and sucking tongues, the lampreys attach themselves. to fishes, from which they suck the mucus and frequently the blood. In some places the large sea-lampreys are regarded as delicacies, but usually they are not esteemed as food. Serigrs I].—GNATHOSTOMATA. This group, the name of which means jaw-mouth, includes the great majority of vertebrates in which true jaws, capable of closure, occur. The skeleton, sometimes of cartilage, sometimes of bone, is a true support to the body; usually paired limbs are present, and there are a pair of nostrils. The preceding general account of the Vertebrata (pp. 290 to 315) applies especially to the gnathostomes. The group is subdivided into Ichthyop- sida, Sauropsida, and Mammalia. GraDE J.—ICHTHYOPSIDA (FIsH-LIkzE Forms). Under this name are grouped fishes and batrachians, since they are alike in certain important respects. Thus they have, either as larve or adults, functional gills, they have lateral-line organs, they have median fins, and the blood is cold. Besides these there are several other points of union, notably in the development, especially promi- nent being the absence of two embryonic structures, the amnion and allantois, which occur in higher forms. The Ichthyopsida are divided into two classes: Pisces and Amphibia. Ciass I.—PISCES (Fisuus). The forms to which the name Fishes is usually applied have a body adapted in shape and structure for an aquatic life. It is usually covered with scales, which lie between 318 SYSTEMATIC ZOOLOGY. the two layers (coriwm and epide mis) of the skin, the lat- ter extending over them. ‘These scales may be of four - kinds, the placoid, ctenoid, cycloid, and ganoid. Placoid scales are hard plates, in structure much like teeth, with usually a spine projecting backwards from the surface. Cycloid scales are much softer, more or less circular in outline, and with no projecting spine. Ctenoid scales differ from cycloid in having the free edge of the scale toothed somewhat lke a comb. Ganovrd scales are either rhomboid or circular in outline and are covered externally with a peculiar enamel layer. At one time fishes were classified according to the scales, but this was found to be unnatural. The fins are adapted to fanning the water, being broad plates with an internal stiffening skeleton. Usually both anterior and posterior paired fins are present, and these are supported on skeletal girdles (pectoral in front, pelvic behind), which extend across the body beneath, but which have no connection with the vertebral column, nor with any structure like a breast-bone. The pectoral, however, is frequently joined to the skull. The paired fins are largely organs of balancing and of directing the body upwards or downwards; the caudal is the chief swimming- organ. The caudal fin presents three interesting con- ditions. In all fishes it is at first dvphycercal (fig. 120, A); that is, the vertebral column runs out in a straight line, dividing the fin into equal and symmetrical halves. This condition is retained in a few forms. In others, with growth, the vertebral axis becomes bent upwards, and a secondary lower lobe is developed which, as it is smaller than the other, gives the heterocercal condition (fig. 120, B). This condition is permanent in the Selachiu and most ganoids, but in the bony fishes the lower lobe grows out equal to the other, and the tail becomes homocercal, FISHES. 319 although the skeleton shows a bent back-bone (fig. 120, C,D). iy H : fH felt i | eat pe : Mal v ne = Vi 1 Cleoeldal S —— s So a ey if a Yee 7 ESS a Sg DP =a N S 7 RA SRS = OT SS === Sat SS = WEISS \ SS rithet na Via NAN. aa HEH HF \ wit a ‘ Mi wi if ae na AN iH ui a 09. Wy \\ “aN Y/ WN \ Na Ni Ni ZL 0 oa mma ey, yeaa A ee LE ITZ Wee Raa Lay Oh ee A\ 5 AM \\\ 15 \X 5 UR NW ZS7/- B, hetero- Fie. 120.—Different forms of tails of fishes. A Sieve stale cercal; C, D, homocercal. (From Zittel.) There are two nasal sacs, although frequently four nostrils are present, the four arising by a closure of the two primitive openings in the middle. Inside the sac is 320 SYSTEMATIC ZOOLOGY. the folded olfactory membrane. In no case is there any connection of the nasal cavities with the mouth or throat, although it is interesting to note that in the skates a groove leads backward from each nostril to the mouth, recalling the way in which the internal nostrils are formed in the young of the higher vertebrates. | The gill-slits start-as paired outpushings from the throat, which later break through to the exterior. These may all retain their separate external openings, or they may be covered up by a fold from the back side of the head grow- ing over them and forming an operculum. (See also p. 308). Water taken in through the mouth is forced out through these slits, and is thus brought in close contact with the thin-walled gills lining their sides. In many forms an air-bladder occurs. This arises as an outgrowth from the dorsal wall of the cesophagus or gullet, and in many this connection persists throughout life (Physostom1), but in others the duct is closed later. The bladder serves as a hydrostatic apparatus, and when it is expanded the specific gravity of the fish is lessened and the animal can rise, while when it is compressed the animal sinks. In some forms the bladder is used in pro- ducing a noise. In all fishes the heart, situated in a pene chamber, consists of two portions: an auricle, which receives the blood returning from the body, and a ventricle, which | forces it forward through the gills to all parts of the animal. In leaving the heart proper the blood first passes through an arterial cone or an arterial bulb (fig. 121). These differ in this: the arterial cone is really an outgrowth of the heart, and contains, on its interior, valves to prevent the flow of the blood back into the ventricle; the arterial bulb, on the other hand, is merely a muscular thickening FISHES. 321 of the ventral aorta, and contains no valves. After pass- ing through the afferent and efferent branchial arteries (p. 311) the blood is collected in the dorsal aorta and thence distributed to the body. - The blood, returning to the heart, bears with it the waste from all parts of the body, and prominent among this is carbonic dioxide; in short, it is what physiologists Fic. 121.—Types of Fish-hearts. a, auricle; 6, bulbus; c, conus; v, ventricle. call venous blood. This is forced forward, through the ventral aorta and the branchial arteries, to the gills. Through the thin walls of these it comes in close connec- tion with the water, and the carbonic dioxide is given off, while oxygen, from the air dissolved in water, is taken into the blood, which thus becomes arterial blood, and is distributed to all parts of the system through the dorsal aorta and other vessels. Hence, as will readily be under- stood, the heart of the fishes, in contrast to that of all other vertebrates, receives only venous blood. It is interesting to note why a fish dies when taken from the water. It is simply because it cannot obtain air enough. When the fish is in the water the gills are floated out so that all parts of them are exposed to the stream 322 SYSTEMATIC ZOOLOGY. passing through the gill-slits. When the fish is out these delicate filaments mat together, reducing the surface for breathing; and then, too, the gills soon become dry, and then are less favorable for the exchange of carbonic dioxide and oxygen. Among the peculiarities of the skull are the numbers of branchial arches and the ease with which these, the oper- cular structures, and bones of the face can be separated from the cranium (p. 293). In the Selachii these, like the rest of the skeleton, are composed of cartilage. In the Teleosts this is largely replaced by bone. Another peculiarity is that the lower jaw does not directly join (articulate with) the skull, but certain parts intervene between the two, forming what is known as a suspensory apparatus (see p. 294). The group of Pisces is divided into four subclasses: Elasmobranchii, Ganoidei, Teleostei, and Dipnoi. SuscLass I.—ELASMOBRANCHII (Selachii, Sharks, and Skates). These forms, of which the dogfish is an example, are, with few exceptions, marine. They are sharply marked off from all other fishes by several characters. The skeleton is entirely of cartilage, no bones being developed; the body is usually covered with placoid scales (p. 318); the gill-slits (five to seven in number) open separately to the exterior, except in the Holocephali, and no operculum is developed; the heart has an arterial cone, and the intes- tine is provided with a spiral valve. There is usually a spiracle, and the air-bladder is always lackmg. The mouth and nostrils are usually on the ventral surface. The Elasmobranchs are, on the whole, the most primitive of the jawed vertebrates and hence they have been studied FISHES. 323 to a great extent, since no other forms give such a clear understanding of the characters of the group. Of the several orders, only the Squali, Raisw, and Holocepha need mention here. OrpER I.—SqQuati (Sharks). In the sharks the body is more or less cylindrical, and the gill-slits open upon the sides of the neck. About 150 ce asia be Sat PEST Bee on oar eee Fie. 122.—Sawfish Fic. 123.—Common Skate (Raia erinacea). (Pristis pectinatus). After Goode. species are known, some, like the dogfish, being small, others reaching an enormous size. Those species which o24 - SYSTEMATIC ZOOLOGY. feed on fish and the like have sharp cutting teeth, and these are arranged in rows, one behind another, so that only one row is in use at a time, the other serving as a reserve supply if one of the front row be lost. In other sharks, which feed on shell-fish, the teeth are flattened plates, the whole forming a mill for crushing the shells. Most of the species are much lke the dogfish in their general appearance, but there are strange forms. Thus in the hammer-head sharks the sides of the front of the head are drawn out like a mallet, the eyes being on the outer ends of the lobes. In the sawfishes the snout is drawn out in a long beak, either edge of which is armed with sharp teeth. OrpDER II.—Ra1# (Skates, Rays). In the skates and rays the body is usually flattened, and the gill-slits are on the under surface. In most forms the body is sharply marked off from the tail, but in those saw- fishes which belong to this order the body is shark-like. The width of body in the true skates is partly due to the fact that the pectoral fins are enclosed in it, the whole making a disk, rounded or four-sided in outline. Most of them are bottom feeders, living upon shell-fish, and hence have flattened pavement-teeth. The torpedoes are remark- able for their electrical powers. In them certain muscles on the sides of the head are metamorphosed into an elec- trical battery, the discharge of which is under control of the will. The current is strong enough to kill small animals which come into contact with the creature. . The largest of the skates are the huge tropical devil-fish, which reach a length of twelve or more feet and a weight of 1200 pounds. FISHES. 320 OrpeER III.—HoLocEPHALt. A group of less than ten species of strange marine car- tilaginous fishes in which the upper jaw is firmly united to the cranium, the gills are covered by a flap of skin, like an operculum, and a spiracle is lacking, compose this order. Fic. 124.—Chimera monsirosa. Mouth and nostrils are ventral, as in the sharks. The name Chimera, given to some forms, emphasizes their strange appearance. Little is known of their habits. Supcuass IJ].—GANOIDEI. These are remnants of a group once very abundant on the world’s surface, but now showing less than fifty living species in the whole world, and most of these in North America. Some of them are much lke Selachians, others like Teleosts, and still others go off towards the Dipnoi. The skeleton is bony or cartilaginous; the body may be covered with ganoid or cycloid scales, or with bony plates, or it may be naked; the tail either homo- or heterocercal; the gills are covered with an operculum. The heart is provided with an arterial cone, and the intestine has a spiral valve. A swim-bladder occurs, and this has its duct, which, in one form, empties into the ventral side of the cesophagus. With this confusing mixture of characters 326 SYSTEMATIC ZOOLOGY. it is not strange that many naturalists have split up the group and distributed its members among the other sub- classes. Fig. 125.—Common Sturgeon (Acipenser sturio). After Goode. To it belong the sturgeons (fig. 125), the most sharklike of all, some of which live in fresh water, while the marine forms ascend the rivers to lay their eggs. From their ovaries are made caviare, while their swim-bladders fur- nish the isinglass, now so largely supplanted in domestic economy by gelatine. Though some attain an enormous size, all feed upon small animals, worms, insect larve, etc., which they find in the mud. The garpikes (fig. 126), YS ACeSSe SS ST SSSR Fic. 126.—Garpike (Lepidosteus osseus). After Tenney. with their strongly armored bodies, which also belong here, on the other hand, are very voracious. The bowfin of the United States is the most like Teleosts of all the ganoids. : Suscuass JIJ.—TrELroster (Bony Fishes). The great majority of the forms which we ordinarily call fishes belong to the group of Teleosts or bony fishes, so called from the abundant bony matter in the skeleton. In all, the mouth is at the tip of the snout, the nostrils on the FISHES. 327 upper surface, and the caudal fin, though heterocercal in the young, is homocercal in the adult.* The skull is cov- ered with numerous bony plates, and the body is covered with either cycloid or ctenoid scales. Sometimes (trout) scales are apparently lacking, but this apparent absence may be due to their small size and their being buried in the skin. The gills are covered by an operculum. Of the internal features which characterize the group may be mentioned the absence of a spiral valve in the intestine, the presence of an arterial bulb in the heart, and, very frequently, of a swim-bladder. The ten thousand species of bony fishes are variously subdivided by naturalists accordingly as different structures are made the basis of classification. One of the simplest of these schemes recognizes six subdivisions or orders, and is adopted here. To which does the specimen you studied belong? ORDER I.—PHYSOSTOMI. Bony fishes in which the gill-filaments are arranged on the branchial arches like the teeth of a comb; with the premaxillary and maxillary bones movable (p. 24); the dorsal, anal, and ventral fins supported only by soft rays (p. 23); the ventral fins, when present, placed near the vent. An air-bladder is almost always present and retains its connection with the throat throughout life (p. 310). The scales are usually cycloid (p. 318). Most of the species belong in fresh water. The catfishes and horned pout, with long filaments or barbels about the mouth, belong here. In our eastern waters the species are small, but in the Mississippi basin * In a very few the tail remains diphycercal throughout life. 028 SYSTEMATIC ZOOLOGY. large species occur, some weighing 100 pounds or more. Many more species occur in the tropics of Africa and America, and some of these have the scales greatly devel- oped so that they form a bony armor. One African species, like the electrical eel and the torpedo, can give a sharp electrical shock. The carp and minnows abound in fresh water, but, excepting as they furnish food for other fishes, they are of little importance; the carp of Europe having a slight value as food for man. The goldfishes of Chinese origin also belong here. Much more valuable is the group of trout and salmon, which are among the most important of food-fishes. As a rule these have a soft fin behind the rayed dorsal. The salmon, of which there are one species on the Atlantic Fic. 127.—Atlantic salmon (Salmo salar). After Goode. (fig. 127) and four on the Pacific coast, live in the sea and enter the rivers to lay their eggs. The whitefish of the lakes are closely allied forms. The blindfish of Mammoth Cave should be mentioned here. In this form a life in total darkness has resulted in the degeneration of the eyes, which are buried -beneath the skin. The savage, swift-swimming pike, pickerel, and muska- longe, the latter reaching a length of eight feet, are, with one exception, confined to America. They are noted for FISHES. 029 their voracity, and have been termed ‘‘mere machines for the assimilation of other organisms.”’ Among the marine members of the order are the her- ring (fig. 128), shad, menhaden, fishes of great importance to man, both as food and for the oil and fertilizers which Fig. 128.—Herring (Clupea harengus). are made from them. They occur in large schools, and afford food for numerous predaceous fishes. Differing from the forms already mentioned are those which may be grouped together as eels, fishes with elongate bodies and without ventral fins. Most of the species are marine, and those which live in fresh water go to the sea to spawn. All are voracious creatures, and one South American species has marked electrical powers. OrpER IJ.—ANACANTHINI. These have the gills comb-like (p. 327) ; the dorsal, anal, and ventral fins without spines; the ventral fins, when present, placed far forward between the pectorals; the swim-bladder without connection with the gullet; and the scales either ctenoid or cycloid. Mostly marine. But few of these forms need mention. Most important of all are the cod (fig. 129) and haddock, which stand beyond all others as food-fishes. They occur in the north- SYSTEMATIC ZOOLOGY. 330 ern parts of both oceans, and find their favorite feeding- grounds on those shallow spots The known as ‘banks.’ Grand Banks of Newfoundland are constantly visited by fishermen from Europe and Amer and have aptly been d 1ca SS After Storer. Fie. 129.—Cod (Gadus morrhua). ing every d to be the richest banks in the world, honor draft upon them. sal Allied to the cod is the strange group of flatfishes, the halibut, flounders (fig. 130), turbot, and the like. In After Goode. ro Fic. 130.—Winter Flounder (Pseudopleuronectes americanus). early life these are symmetrical like other fishes, but as de, and then the n one sl they grow older they turn over o FISHES. dol eye of that side migrates to the upper surface, twisting the bones of the skull in its progress. Henceforth the fish lives constantly in this peculiar position, the side of the body turned downward being white, the other colored. The halibut, occurring in all northern seas, are among the largest fishes, occasionally weighing 350 to 400 pounds. OrpeR IIJ.—AcANTHOPTERI (Spiny-finned Fishes). In this, the largest order of bony fishes, the gills are comb-like, the jaw-bones are movable (p. 24), and the dorsal, anal, and ventral fins have spiny rays in front. In some there is a swim-bladder, but it is without connection with the gullet. Among the strange modifications in the group are the suck-fish or Remoras (fig. 131), in which Fic. 131.—Remora (Remoranein brachyptera). After Goode. The sucker is shown on the top of the head. part of the dorsal fin is modified into a sucker, by which they attach themselves to other fishes or floating objects, and are thus carried about. In the swordfishes the bones of the upper jaw are modi- fied into a long, stiff sword terminating the snout, and used as a weapon of offence and defence. The largest species reaches a length of fifteen feet. In other points of structure the swordfish are much like the mackerels, (fig. 182), pompanos, and bluefish, so well known as food- fish. Of these the largest is the tunny or horse-mack- erel, which sometimes weighs 1500 pounds. 332 SYSTEMATIC ZOOLOGY. In another group of perch-like forms the spines of the fins are more developed. Here belong the perch, sea- bass, and porgies, the sheepshead and fresh-water sunfish, the sculpins, and a long series too numerous to mention. Fic. 132.—Mackerel (Scomber scombrus). ORDER IV.—PHARYNGOGNATHI. These are Acanthopteri in which the last branchial arches are fused into a single bone, which thus resembles an additional jaw in the throat, whence the name (pharynx- Fic. 133.—Cunner (Ctenolabrus ceruleus). After Goode. jaw). All of the species are marine, and with few excep- tions they are tropical. On our east coast are found the cunner (fig. 133) and tautog; on the Pacific occurs a group of surf-fishes (Embiotocide), remarkable for bring- ing forth living young. FISHES. 303 ORDER V.—PLECTOGNATHI. In this group of peculiar forms, almost all of which are marine, the upper jaws are immovably united to the skull. Some are naked, others have the skin covered with spines or bony plates. The spiny forms (swellfish—fig. 134) can Fic. 134,—Swellfish (Chilomycterus geometricus). After Goode. erect the spines by swelling out the body, and thus gain additional protection. In the trunkfishes the bony plates unite to form a solid box. In the sunfishes of the ocean (fig. 1385), which may weigh 1800 pounds, the body is almost circular in outline, and has a distinctly chopped- off appearance. As a whole, the order bears most re- semblance to the Acanthopteri. None are of the slightest economic importance. ORDER VI.—LOPHOBRANCHII. These are the most aberrant of bony fishes. The gills, as the name implies, are tufted, and composed of small rounded lobes packed in the gill-chamber. The oper- cular apparatus is reduced to a simple plate, the small, toothless mouth is at the end of a long snout, the skin is covered with bony plates arranged in rings around the 304 SYSTEMATIC ZOOLOGY. body. ‘The species, which are all small, are known, from their fanciful shapes, as pipefishes and sea-horses (fig. 136). Fic. 135.—Sunfish (Mola rotunda). After Putnam. Many have a remarkable peculiarity in breeding habits, in that the young are carried for a time in a pouch beneath the tail of the male. Suscitass I1V.—Dripno1 (Lung-fishes). Four species, one from Australia, one from Africa, and two from South America, are the sole living representa- FISHES. 3390 tives of this group, which, however, occurs as fossils in very old rocks. They have scaly bodies, diphycercal tail, Fig. 136.—Sea-horse (Hippocampus heptagonus). After Goode. Fic. 137.—African lung-fish (Protopterus annectens). After Boas. spiral valve, and a swim-bladder which is used as a lung. Both pectoral and ventral fins are present, and these are 330 SYSTEMATIC ZOOLOGY. supported by a peculiar skeleton, while the skull shows many strange features. The lung-fishes present many points of interest for the naturalist. By many they are supposed to be nearest to the line from which the Amphibia have sprung. ; Crass I.—AMPHIBIA (BATRACHIA). The frog may serve as a type of the Amphibia, which, so far as living representatives are concerned, are marked off from the fishes by a number of important characters. With very few exceptions the Amphibia pass at least a part of their life in the water, and many, in reaching the adult condition, pass through great changes in structure (all are familiar with the metamorphosis of the tadpole ~ into the frog), so that, in considering the group, the char- acters of both larva and adult must be taken into account. In all the skin is very glandular and in all, except the tropical group of blindworms, scales are lacking, and, ex- cepting again these same limbless forms, fins have given place to legs, much like the limbs of man, and like them ending typically with five digits. In the larve of all there is a tail, and some (salamanders and newts) retain this structure during life, while in others, as in the frog, it is absorbed (not dropped off) during growth. The lar- val tail bears a median fin, but this is never divided into dorsal, caudal, and anal, and it differs further from the fins of fishes in having no internal skeleton. Of internal features those most distinctive are the skeleton of the limbs, unlike that occurring in any fish; the union of the pelvic girdle with the back-bone; the existence of an Eustachian tube in connection with the ear; the connection of the nostrils with the cavity of the mouth; and the presence of two auricies in the heart. AMPHIBIANS. 337 In the larvee respiration takes place by gills, recalling those of fishes; and in a few forms these are retained during life. Besides gills, all, in the adult condition, develop lungs,* which grow out from the pharynx, and always re- tain their connection with it by means of a windpipe (tra- chea) opening upon its floor (compare p. 310). The gills are fewer in number than in any fish, and only three or four gill-slits are formed. Between these slits are devel- oped external gills (fig. 138). Later the slits are closed Fic. 138.—Larval stage of a salamander with external gills. From Hertwig. in those salamanders which lose the gills, by the growing together of the slits. In the frogs the process is preceded by the formation of an opercular fold (compare fishes) in Se Sais ™. —P | Fic. 139.—Side view of tadpole. e, eye; g, gill-opening; J, hind leg; m, mouth; n, nostril; v, vent. front of the gill region on either side. These folds grow back over the gill-slits, those of the two sides fusing below the throat and uniting with the wall of the body above * It has recently been shown that some of the North American salamanders never develop lungs, but respire solely through the skin. 338 SYSTEMATIC ZOOLOGY. and behind the gills, thus forming a large chamber outside the gills which is connected with the exterior by a small opening on the left side,* through which the water used in breathing passes. In the larva the heart is two-chambered, and the blood, passing forward from it, traverses afferent and efferent branchial arteries, as in fishes, and is collected, as in those forms, in a dorsal aorta. With the loss of gills and the development of lungs the gill circulation changes. The first arterial arch becomes converted into the carotid artery, supplying the head; the second, the aortic arch, connects the heart with the dorsal aorta; the third dwindles and usually disappears; while the fourth, the pulmonary artery, carries blood to the lungs and skin. As will be seen, the embryonic circulation is like that of the fishes, but the different condition in the adult is brought about not so much by new formations as by modifications of pre-existing structures. Compare in this connection the diagrams on page 312. In the larva the heart pumps only venous blood, as in the fish. With the development of lungs and the division of the single auricle into two, different conditions occur. Blood from the body (venous) is poured into the right auricle, and blood from the lungs (arterial, because in the lungs it comes into contact with the air) into the left. From the auricles the blood goes to the single ventricle, and thence through the arterial trunk to head, body, and lungs. So at first sight it would appear as if all parts must receive a mixture of arterial and venous blood, but this is not exactly the case. By means which cannot be described here the purest arterial blood goes to the * Right and left openings occur in two tropical toads (Aglossa). A few forms have a median opening. AMPHIBIANS. 339 head, the next to the aorta, while the venous blood is sent to the lungs. In the larvee of the frogs and toads the mouth is small and the horny jaws are adapted to scraping small plants from submerged objects. Correlated with this vegetable food is an extreme length of intestine, it being a notice- able fact that herbivorous animals require a longer diges- tive tract than carnivorous forms. In the larve there is also a well-developed lateral-line system (p. 300), and this persists to some extent in the adult of the aquatic salamanders, though disappearing in all other forms. The vertebral column varies greatly in length, and in all except the footless forms it can be divided into neck (cer- vical), breast (thoracic), sacral, and caudal or tail regions, the sacral being that which connects with the pelvic girdle. In some the bodies of the vertebrae are amphicce- lous (p. 292); in most salamanders they are opisthoccelous (rounded in front, hollow behind), while in the frogs and toads they are proccelous (hollow in front). The trans- verse processes of the vertebre are different from anything in fishes in that they arise from the neural arch and not from the centrum. In some forms the ends of these processes are jointed, and from this and other facts they must be regarded as in part equivalent to ribs. It is to be noticed that these ribs never reach the sternum (p. 293), which, by the way, is a structure lacking in all fishes. A noticeable feature in the Amphibia is the metamor- phosis during growth, the chief features of which have already been mentioned (p. 337), the result being that the adult differs very considerably from the young. All living Amphibia live either in fresh water or on the land; none occur in salt water. The existing forms are 340 SYSTEMATIC ZOOLOGY. comparatively small, the largest being the giant sala- mander of Japan, which may be three to four feet in length. Existing Amphibia are conveniently divided into three groups or orders: Cecilia, Urodela, and Anura. OrpER I.—CaciLia (Blindworms). These are legless, worm-like Amphibia found in the tropics of both hemispheres. They have a rudimentary tail, degenerate eyes, and the larvee, so far as known, have three pairs of gills. Some species form an exception to all living Amphibia in having scales in the skin. While highly modified in some respects, in others they are the lowest in position. They live a burrowing life, feeding upon earth- worms, insects, etc., found in the soil. OrpER II.—UrRopE.a (Salamanders, Newts, etc.). These forms retain the tail throughout life, and have the extremities weakly developed, fitted for creeping rather than jumping. Some live in the water throughout life, while others, as adults, are to be sought in moist places. Fic. 140.—Salamander (Plethodon). In some forms the external gills are retained permanently. The order belongs almost exclusively to the northern hemisphere, and is especially well developed in America. Allied to the Urodelans and Ceecilians are some enormous AMPHIBIANS. 341 fossils, grouped under the name STEGOCEPHALI, some of which had skulls five feet or more in length. OrpeErR IJ].—Anura (Frogs and Toads). These, in the adult condition lack a tail, and have appen- dages fitted for leaping. The lower jaw is without teeth. The larvee are always tailed, and have at first external gills. Frogs (Ranidz) and toads (Bufonide) differ in that frogs have a smooth skin, and teeth in the upper jaw; toads have a warty skin (caused by numerous glands) and no teeth. Tree-toads (Hylide) are more frog-like, but they have sucking discs on the ends of the toes, by means of which they are adapted to a life in trees. Another group (Aglossa) occurs in the tropics, in which the tongue is absent. Some of the Anura have strange breeding habits. Thus in the European Alytes the male wraps the long string of eggs about his body and carries them there until they hatch. In Nototrema of South America the skin of the back forms a pouch, in which the eggs are carried; while in the Surinam toad (Pipa) the skin of the back becomes very much thickened, leaving little cups, in each of which an egg is placed, and here the young are hatched out. Another interesting form is the flying tree-toad of the East Indies, in which the feet with the web between the toes become greatly enlarged, forming large discs, upon which the animal sails, much as does a flying squirrel upon its lateral folds of skin. 342 SYSTEMATIC ZOOLOGY. GraDE IJ].—SAUROPSIDA. Although we naturally associate the birds with the warm-blooded, hair-bearing mammals, they are structur- ally far nearer the reptiles; hence the group which con- tains the reptiles and birds is called Sauropsida, which means lizard-like. The Sauropsida are distinguished from the Ichthyopsida (p. 317) by the fact that at no stage of development are functional gills present, and there is never a metamorphosis. Scales, which are always present, lie not between the two layers of the skin (see p. 318) but are composed of the outer layer. The eggs are always very large and in their development two structures, the amnion and allantois, always occur. The sternum, when present, is always connected with the ribs. From the mammals they are marked off by the absence of hair, the position of the quadrate as the suspensor of the lower jaw (p. 294), the articulation of the skull to the vertebral column by a single condyle, by the large eggs, and by the existence of a cloaca, 2 common tube into which the di- gestive, excretory, and reproductive organs empty. There are two classes of Sauropsida, Reptilia and Aves. Cuass I.—REPTILIA (ReEpriss). The living reptiles closely simulate the Batrachia, and in fact the frogs, toads, and salamanders are reptiles in popular parlance. The short-bodied turtles are paralleled by the frogs, the lizards by the salamanders, and the snakes by the blindworms. Yet the differences between the two groups are many and important. REPTILES. 343 The body is more or less completely covered with scales, and the toes, when present, bear claws. The scales differ from those of fishes in being outside of the outer layer of the skin. These scales differ much in ar- rangement, etc. The large plates covering the carapace of the tur- tle are but enlarged scales, while the bony armor of the alligator is composed of scales, rendered more protective by the development of bone in the deeper layer of the skin. In the snakes the scaly covering is periodically shed. By the greater development of the neck the heart is carried back to a greater distance from the head than in the Batrachia. In all except the alligators the heart is three-chambered, and in these the ventricle is incompletely di- vided into two. There are two aortic arches (fig. 141), but the left one, which also supplies the stomach, is smaller where it joins its fellow to form the dorsal aorta. Fic. 141.—Arterial Circulation of Turtle. a, right aortic arch; 6, bronchus; /, artery to fore limb; h, artery to hind limb; p, pulmonary artery; 7, renal arteries; s, arteries to stomach; ¢, trachea; 1, 2, 4, persisting aortic arches. Compare with fig. 117, £. The blood is ‘cold,’ or rather it is variable in temperature, varying with that of the air or water in which the animal lives. The brain is small, no part being extremely developed, and the optic lobes touch, or may touch, each other in the median line. In snakes, lizards, and turtles the cerebel- lum is small; in the alligators it is larger. 344 SYSTEMATIC ZOOLOGY. The vertebree are usually proccelous, and the vertebral column ‘is divisible into the regions of neck (ribless), thorax (with ribs), lumbar (ribless), sacrum (usually two vertebre which connect with the pelvis), and tail; but in snakes these distinctions fail, and only trunk and tail ver- tebree are recognizable. A breast-bone is present in Fic. 142.—Brain of Snake. c, cerebrum; cl, cerebellum; o, optic lobes; I, olfactory nerve; II, optic nerve. lizards and alligators, but none occurs in turtles or snakes. The skull articulates with the vertebral centrum by a single surface (condyle). The hinder angle of the lower jaw is connected with the skull by the quadrate bone, which may be free (fig. 143), or firmly united to the skull; and the Fie. 143.—Skull of Garter-snake (Hutenia sirtalis), showing the attachment oe the ee jaw to the skull by means of the quadrate bone, g. (Slightly enlarged. premaxillary and maxillary bones are firmly united to the rest of the skull. Teeth are usually present, and in the alligators these are inserted in sockets. The shoulder- girdle (lacking in snakes) is much like that of frogs, the clavicle, however, being absent in alligators. The pelvis REPTILES. 345 is lacking in most snakes, being represented by two bones in the boas. The feet, when present, are usually of the normal type, the bones of the forearm (ulna and radius) and of the shank (tibia and fibula) being separate, and the toes, five in number, provided with claws. In the embryo, gill-slits are partially developed, but no functional gills occur. The lungs are well developed; the left one being reduced or absent in the snakes and snake- like lizards. Respiration is effected by means of the ribs, except in the turtles, and there by a special muscle. Both ovaries are developed. The eggs are large, and, in those reptiles which lay eggs, are covered with a limy shell. A few snakes and lizards bring forth living young. Reptiles are most abundant in the tropics, and are lacking in cold regions. They are mostly flesh-eaters, some living on insects, others on larger forms. Some live on land, some in fresh water, and some in the sea. All living forms can be arranged in four orders, Lacertilia, Ophidia, Testudinata, and Crocodilia. OrpER I.—LacrErTILIA (Lizards), In these the quadrate bone is movable, but the under jaw cannot be displaced (cj. Snakes). Legs are usually present, but either or both pairs may disappear. When the legs are absent the body is exceedingly snake-like, but these forms, like all other lizards, may be distin- guished at once from the true snakes by the presence of small scales on the belly. Only one lizard, the ‘Gila monster’ of Arizona, has the reputation of being poison- ous, but in former times many, like the basilisk, were fabled to have most deadly powers. Among the more interesting forms are the ‘glass snakes,’ so called from 346 SYSTEMATIC ZOOLOGY. the ease with which the tail breaks; the ‘horned toads,’ which are not toads, but true lizards; and the chameleons, with their wonderful powers of color change, a capacity ae Fia. 144.—Green Lizard (Anolis). From Litken. which is shared to a less degree by other forms. Among others by the Anoles (fig. 144) which are abundant in the southern states. REPTILES. 347 OrpDER I].—Opuipia (Snakes). These are like the lizards in the movable quadrate, but they differ in the absence of limbs and of sternum, the presence of broad scales (scutelle) on the belly, and in the fact that the lower jaw is connected with the cranium by elastic ligaments, so that it can be displaced in swallowing food. Many snakes are poisonous, the poison being con- —— Oe LR Sa > Fie. 145.—Dissection of head of Rattlesnake. /, poison-fangs; p, poison-sac. veyed into the wound by specialized teeth, the so-called poison-fangs, which are either grooved or are tubular, the grooved teeth being capable of being folded back when not in use, the others being permanently erect. The rattle- snakes (fig. 145) and moccasins belong to the former group. The largest snakes, the pythons of India and Africa and the boas and anacondas of South America, kill their prey by crushing, as do most of the smaller snakes—our black-snakes, for example. Some snakes are protected against their enemies by their colors, which render them inconspicuous in their usual haunts; others by the nauseous smell which is pro- 348 SYSTEMATIC ZOOLOGY. duced by certain glands in the skin: still others by their | poison-glands. Most of the snakes are terrestrial, but some, like our water-snakes, take to the water, while in the Indian Ocean are found truly aquatic snakes, which never go on land and which bring forth living young. These sea-snakes are very poisonous. The rattlesnakes are the best known poisonous forms in the United States. In these the rattle is formed by bits of dry skin, which are not lost at the time when the snake sheds the rest of its covering. In this way a new joint is added to the rattle at each molt, and so the whole becomes an approxi- mate index of age. OrperR IIJ.—Trstupinata (Turtles). The turtles and tortoises are characterized by their short bodies, enclosed in a bony shell or box; by the absence of teeth; and by the union of the quadrate bone with the cranium. The shell, with its two parts, a dorsal carapace and a ventral plastron, is composed of an outer layer of horny plates (modified scales) and a deeper bony layer with which ribs and vertebree are more or less com- pletely united. Into this protective case the head, tail, and legs may usually be retracted, and in the box-tortoises a hinge in the plastron allows the closure of the openings. Some turtles are vegetarians, others are carnivorous. — Some live on land some in fresh water and some in the sea. The largest of existing species are the giant land- tortoises of the Galapagos Islands and Mozambique, and the leather-back and the loggerhead turtles of tropical seas. Tortoise-shell, before the days of celluloid, was furnished by the dorsal plates of the large tortoise-shell turtle of REPTILES. 349 tropical seas. These plates have the peculiarity that they can be united by heat, so that pieces of any desired size may be obtained. While many turtles are most inoffensive creatures, others, like our snapping-turtles and our soft-shell turtles, are ferocious, the young snapper showing its temper as soon as it is hatched frc m the egg. OrpER IV.—Crocopiuia (Crocodiles and Alligators). These forms have the highest development of brain and heart of any of the reptiles, the heart being incompletely four-chambered. In general shape they are closely like the lizards, but in bony and other structural features they are greatly different, among these being the immovable quadrate. Crocodiles and alligators are distinguished from each other by the fact that the former have fully webbed feet and more slender snouts. The gavials of the rivers Fig. 146.—Restoration of Ichthyosaur (modified from Fraas). of India have the snout even more slender. The alli- gators are-confined to the New World, while the crocodiles occur in both hemispheres. The fossil reptiles show a greater range of forms than the living species. The Ichthyosaurs represented the whales among the reptiles of former times, while the Plesio- saurs, also swimming forms, had extremely long necks. The Dinosaurs were like the birds in many structural features, although they lacked powers of flight and were terrestrial or aquatic. Some were enormous in size, hav- 350 SYSTEMATIC ZOOLOGY. ing thigh-bones nine feet in length and vertebre five feet across. The Pterodactyls were flying reptiles with wings like those of the bats, except that the wing-membrane was supported by a single finger. Cuass II.—AVES (Brrps). No one can have the slightest question as to whether a certain animal is a bird or not. The feathers, the fore- limbs fitted for flight, and the horny, toothless beak are characteristic of all living forms. Feathers arise from the outer layer or epidermis of the skin, and each has its tip inserted in a pit or follicle in the integument. Feathers vary considerably. Most promi- nent are the large, strongly built contour feathers, which give the animal its general shape. Beneath these are the down and the pin-feathers. Feathers are not uniformly dis- tributed over the body, but are gathered in feather tracts, the arrangement of which varies in different birds. The feathers are not permanent structures, but they are molted or shed and replaced by a new growth, this taking place usually once a year. In connection with the feathers should be mentioned the oil-glands (the only glands in the skin of birds) upon the tail, the secretion of which is used in preening the feathers. In their origin feathers are much like the scales found on the feet, and are probably modifications of such struc- tures. The scales on the feet may be small or broad, both kinds sometimes occurring on the same foot. The spur of the cock is but an extremely developed scale with a bony core. These scales, like those of reptiles, differ from those of fishes in that they are developed on the outside of the outer layer of the skin (compare p. 318). The toes are BIRDS. 351 terminated by claws; short in the terrestrial, longer in the arboreal, forms. Claws occur in some cases, espe- cially in young birds, upon the wings. In all living birds teeth are ab- sent, and even in the embryos but the slightest trace of their former existence can be found. In certain fossil birds well-developed teeth oc- cur (fig. 150). The tongue is usu- ally slender, stiff, and horny, and in some forms (woodpeckers, etc.) it is very extensible. The cesophagus is long, and frequently a part of it in the neck is swollen out to form a reservoir of food, or crop. The stomach is divided into two parts. The first of these (proventriculus), which is glandular, appears much like an enlargement of the gullet. The second or muscular stomach (gizzard) is a veritable chewing organ. It is most developed in the grain or seed-eating birds, and in these often contains small stones to assist in grinding the food. The lungs are especially well de- veloped, and a peculiarity is that connected with them are air-sacs Fic. 147.—Alimentary tract of an eagle. c, crop; m, muscular stom- ach (gizzard); 7, intes- tine; p, glandular stom- ach (proventriculus); ¢, trachea; v, vent. which extend among the other viscera and even into some of the bones, as those of the wing.* These air-sacs serve * A similar pneumaticity occurred in the bones of some of the fossil reptiles (Dinosaurs, p. 349). 352 SYSTEMATIC ZOOLOGY. to increase the respiratory surface, and also to lessen the specific gravity of the bird. They are also possibly of use in changing the position of the centre of gravity during flight. | The heart has four chambers, the single ventricle of lower forms being divided into right and left ventricles. The large blood-vessels which lead from the heart are, in the embryo, much like those of the fish; but with develop- ment some parts are altered and others suppressed (fig. 117, D), so that the result is more modified than in the forms already discussed. Thus the left half of the third arch, except for an artery (subclavian) going to the wing of that side, has entirely disappeared, while the right half, here called the arch of the aorta, connects the left ventricle with the dorsal aorta. From this the first and third arches, modified into carotids, seem to arise. The second arch is completely suppressed, while the sixth arch, arising from the right ventricle, carries the blood to the lungs and forms the pulmonary artery. In returning from the body the venous blood is emptied into the right auricle and passes thence, through the right ventricle, to the lungs for aeration; while that from the lungs goes to the other side of the heart, and thence to all parts of the body. Hence there is here no mixing of arterial and venous blood in the heart. In the reproductive organs a constant feature is the suppression of the right ovary, a rudiment of it existing in a few forms. In the breeding-season the oviduct is very large, and from its walls are secreted the white and the shell of the egg. The eggs are large, and are always enclosed in a limy shell. There is quite a difference in the condition in which the young hatch from the egg. Some are nearly naked and very helpless (alirices), while others BIRDS. 353 are thickly clothed with down and are able to run and to feed themselves (precoces). The brain is large, and, in comparison with the lower forms already studied, is noticeable for the great develop- ment of the cerebrum and cerebel- lum, which by their growth have forced the optic lobes apart and have covered over the ’twixt-brain. The eye is peculiar in that it de- parts widely from the spherical form, being obtusely conical in front, and in that a circle of bones is usu- ally developed in this conical por- tion. There is a tube (ezternal meatus) developed leading from the side of the head in to the ear, and this is surrounded by a ring of regu- larly arranged feathers. Frc. 148.—Brain of Bird. In the skeleton, division into neck, thoracic, sacral, and caudal vertebre occurs. The number of neck vertebre varies from eight to twenty-four. The sacrals are notice- able for their number, and really embrace, besides the true sacrals, some of the lumbars and caudals, which become united with the pelvis. The anterior caudal vertebre are free, but the last six or eight are coalesced into the pygostyle or plowshare bone. The bodies of the vertebree in living birds are saddle-shaped, that is, concave vertically, convex transversely behind, the conditions being reversed on the anterior faces. The cervical vertebr bear short ribs, free in the young but firmly united in the adult. Each of the true ribs has a small plate (wncinate process) on the posterior margin, which connects it with the rib behind The breast-bcne (sternum) is large and broad, and in 354 SYSTEMATIC ZOOLOGY. flying birds possesses a strong ridge or keel (carina) below, to which the muscles of flight are attached. In some flightless birds the keel is lacking. The skull is noticeable from the great extent of the fusion of the separate bones; for the single condyle for articulation with the neck and for the suspension of - the lower jaw by means of a movable quadrate bone, as in the lizards, snakes, etc. The shoulder-girdle consists of scapula, coracoid, and clavicles, the latter noticeable for their union into a V- shaped ‘wish-bone’ or jurcula. In the wing the reduction in bones of the wrist and hand is remarkable. The bones of the wrist are all united into two, while the three fingers Fic. 149.—Skull of quail. gq, quadrate bone. which remain have few joints and are partly united. In the hind limb the fibula is short, but especially noticeable is the great lengthening of two of the ankle-bones, the result being that the heel is elevated some distance from the ground. Birds are grouped in three divisions or subclasses, Saururze, Odontornithes, and Ornithure, the first two of which are extinct; the third contains the ten thousand known species of living forms. BIRDS. 355 SupcLass I.—Saurur# (Tailed Birds). These forms, found fossil in the lithographic stone of Bavaria, had tails of extreme length, the feathers being arranged on either side of the long tail vertebre; and they —————— Be f fs Vt <9 Wy Pp FBC? Fie. 150.—Skeleton of wingless toothed bird (slesperornis). From Marsh. had teeth in the jaws. Only two specimens are known, the smaller being about the size of a crow, the other some- what larger. They are called Archeopteryz. 356 SYSTEMATIC ZOOLOGY. Supcuiass II].—OpontTornITHES (Toothed Birds). These forms, which have been found only in American rocks, are more like modern birds than is Archeopteryz, but they differ from all existing birds in having teeth. They had normal tails, and one form (Hesperornis, fig. 150) apparently was wingless, only a rudimentary humerus persisting. Some of these toothed birds were about as large as a pigeon; one was about three feet in height. Suspc ass II].—OrnirHura (Modern Birds). In all living birds teeth are lacking and the tail is re- duced; and, excepting a few forms, all have well-developed wings. The recent subdivisions of the subclass are based upon characters not readily grasped by elementary stu- dents, so we must content ourselves with a classification founded on external features. The student should, how- ever, remember that the so-called orders are in no wise equivalent to orders in other groups of animals. % OrpER I.—Strutuit (Ostriches). The ostrich-like birds have long running legs, and wings so reduced as to be useless in flight, and with this the keel of the sternum (p. 354) has disappeared. The foot con- tains usually three, occasionally but two, toes. These birds are mostly large, and embrace the true ostriches of Africa, so valuable for their feathers; the South American _nandus, the feathers of which are used for feather dusters; the emeus and cassowaries of Australia, and the nearly wingless kiwi of Australia. 357 BIRDS. OrpeER II].—Rasores (Scratching Birds). These, like all the remaining birds, have a keeled sternum. They have a weakly curved beak, feet well fitted for run- th three toes in front, and a fourth at a higher ning, Wl From Liitken. Fie. 151.—South American ostrich or nandu (Rhea americana). level behind. Here belong the grouse, the pheasants, and the domestic fowl and turkeys, as well as a considerable number of tropical forms. ir ll the Sun a) Our common hens numberless varieties, are descendants of the wild fowl of India. The turkeys are natives of America. 358 SYSTEMATIC ZOOLOGY. OrveER III.—Natatorres (Swimming Birds). In these the short legs end in feet adapted for swimming by having a web between the anterior toes. The body varies greatly in shape. In the penguins (fig. 152) the wings have lost the powers of flight, the wing-feathers being short and scale-like. On the other hand, they are aii". + “l Fig. 152.—Penguin (A ptenodytes longirostris). From Liitken. strong swimmers, and the loons almost equal them in this respect. The other extreme is reached in those strong fliers, the albatross, tropic birds, gulls, ete. More useful to man are the ducks and geese, while the swans, auks, and cormorants must be mentioned as members of the order. BIRDS. 309 Orper IV.—GRALLATORES (Wading Birds). The wading birds have long legs, the tarsal region being extremely long, and the shank partly naked. Correlated with length of leg is length of neck. Here belong a long series of forms, some of which, like the snipe, are of value Fig. 153.—Wilson’s Snipe (Gallinago wilsoni). After Wilson. to man as game-birds; while others, like the cranes, herons, storks, etc., have less importance. Some, like the ibis and the flamingo, are brightly colored, while marabou and egret furnish feathers for human adornment. In all the foregoing groups of birds the hinder toe is, as a rule, small and of little use. In all that follow it is usually well developed. OrpER V.—Raprorss (Birds of Prey). The owls, hawks, eagles, and their allies are characterized by short, stout, curved beaks, strong feet and large wings; all structures admirably adapted to the capture of prey 360 SYSTEMATIC ZOOLOGY. and the tearing of flesh. Some, like the eagles, hawks, and vultures, are strong fliers with excellent powers of sight; the owls, on the other hand, are more dependent upon catching their prey by stealth; and their eyes are adapted to their nocturnal habits. The buzzards and vul- tures depend upon decaying flesh for their food, and their value as scavengers leads to their protection by law in the regions where they occur. In the birds of prey, like all that have preceded them in this account, the young, when hatched, are covered with feathers (usually down feathers), and have their powers well developed. In all the remaining orders the young are helpless and nearly naked when they escape from the shell. | | OrpER VI.—CoLuUMBIN” (Pigeons). The pigeons stand nearest to the Rasores from which, however, they differ in the weaker legs, the large pointed wings, and the fleshy membrane at the base of the beak, pierced for the nostrils. The five hundred different kinds of pigeons show little variety in form. Our domestic pigeons, with their wonderful variations, have descended from the rock-pigeon of Europe. The extinct dodo of the islands east of Africa was a flightless pigeon of large size. The species died out some two hundred years ago. OrpER VII.—Scansores (Climbing Birds). These birds have the feet adapted for climbing, two of the toes being directed forwards and two backwards. Some, like the toucans, have enormous bills, others have the beak of moderate size. Here belong the cuckoos, with their reprehensible egg-laying habits, and the well- BIRDS. 361 known woodpeckers. The large group of parrots also belong to the group of climbing birds. In these last the Fic. 154.—Carolina Paroquet (Conurus carolinensis). After Wilson. tongue is fleshy, and the feet are very efficient organs of prehension. OrpEeR VIII.—Passeres (Perching Birds). In these the feet have three toes in front, one directed backward and all on a level, and no naked skin on the beak. They are usually subdivided into the Clamatores or crying birds, and the Oscines or singing birds, the latter having a complicated muscular apparatus in connection with the vocal organs. To the Clamatores belong the Asiatic hornbills, which recall the American toucans; the kingfishers, with their large strong beaks; and those gems 362 SYSTEMATIC ZOOLOGY. of bird-life, the humming-birds. To the Oscines belong an enormous series of feathered songsters, the mere enume- Fig. 155.—Bird of Paradise (Paradisea apoda). After Levaillant. ration of which would take a volume the size of the present one, the whole series reaching its apex in that pestilential MAMMALS. 363 immigrant, the English sparrow. Among these singing birds are some which, like the crows, are not noted for Fig. 156.—Winter Wren. From Coues. their musical abilities, and their near relatives, the birds of paradise. We can only mention, in addition, the star- lings, flyeatchers, wrens, orioles, warblers, and thrushes, forms which make our woods and fields vocal and beautiful. GraDE IJJ].—MAMMALIA (Mammats). The name Mammalia is applied to all those forms which, like the mouse, cow, and man, have warm blood, a body covered with hair, and which bring forth living young, nourished during the early stages by milk secreted by the mother. These characters at once distinguish any mam- mal from any other animal, but other features of equal or greater importance occur. Hair occurs in the young of all mammals, and is usually found also in the adult; but in the case of the whales it is absent in the fully grown animal, and even in the young it is only found near the mouth. Hair is a product of the outer or epidermal layer of the skin. At places this layer 364 SYSTEMATIC ZOOLOGY. dips down into the deeper layer (derma), forming a pit or follicle from the bottom of which the hair grows, continual additions being made at this point, commonly known as the ‘root.’ The hair itself is a solid column, varying con- siderably in shape in differént animals, from the delicate fur of the fur-seal, to the bristles of the pig or the spines of the porcupine. There are usually glands present which open into the follicle and which secrete a fluid, the object of which is to keep the hair moist; and besides, each follicle is provided with muscles which serve to erect the hair at times of fright (as in cats and dogs) or in cold weather. Closely related to hair are nails, claws, hoofs, and horns.* In fact these structures must be regarded as hairs united throughout their length. At other times a similar con- solidation of hair gives rise to protective scales covering the body, as in the case of the pangolins (fig. 163). The bodies of the vertebre usually have flat faces, and the vertebral column in most forms can be divided into five regions—cervical, thoracic, lumbar, sacral, and caudal. The cervical vertebve bear no free ribs, and, except in three tropical species, they are constantly seven in number, the long-necked giraffe and the short-necked whale having the same number of cervicals. The thoracic vertebre are more variable in number. They bear ribs, some of which extend downward and unite with the breast-bone or sternum. Between the thoracic and pelvic regions occur the ribless lumbar vertebre, while the sacral vertebre are those which unite with the pelvic bones. The caudal vertebrae are found in the tail. In the whales only cervi- cal and thoracic vertebre can be distinguished, since the * Here are intended such horns as those of the cow, sheep, antelope, and rhinoceros; the horns of the deer are true bone. MAMMALS. 365 absence of a pelvis in these forms allows no line to be drawn between lumbar, sacral, and caudal regions. In the skull there is a tendency for bones which are distinct in the fishes and reptiles to fuse with each other, so that the number of distinct elements is considerably reduced. The skull is borne on the first cervical vertebra (atlas) upon which it slides by means of two rounded sur- faces or condyles. The lower jaw articulates directly with the skull, and is never suspended by a quadrate bone, as in all other classes of vertebrates, the cyclostomes excepted. Fie. 157.—Brain of dog. (After Wiedersheim.) II-XII, the cranial nerves (see page 299). The fore limbs are always present; the hind limbs are absent in the whales and manatees, being represented in a few forms by one or two bones imbedded in the muscles of the trunk. Except in the Monotremes (p. 369), the cora- coid does not occur as a distinct bone, but as a small prominence joined to the shoulder-blade (scapula), while in many the collar-bone (clavicle) also is lacking. The feet have typically five toes, but not infrequently this number is reduced by a disappearance of the outer digits, the reduction reaching its extreme in the cow, which has but two, and the horse, which walks upon the tip of its middle toe. 366 SYSTEMATIC ZOOLOGY. The most marked characteristic of the nervous system is the great relative increase in size of the cerebrum, and, to a less extent, of the cerebellum; the optic lobes and the medulla, so prominent in the lower forms, being over- shadowed by these parts. The cerebrum is the seat of intelligence, and this increase in size is correlated with the higher mental powers of the mammals. Microscopic study of the brain shows that this organ is composed of two different portions, called, according to their colors, white and gray, and that the gray matter is the true brain substance, while the white is composed of nerve-cords to transmit nerve impulses. The gray matter is on the outside of the cerebrum, hence the larger the brain the more surface it has, and consequently the more gray matter it can have. In the higher mammals the amount of surface of the cerebrum is greatly increased by folds or convolutions, and the extent and complexity of these convolutions correspond well with the intelligence of the form. In the eyes the nictitating membrane or ‘third eyelid’ of the birds is reduced to a small fold at the inner angle of the eye (p. 303). Except in the whales, and some seals, moles, etc., external ears are developed, while the internal parts of the ear become considerably modified. Thus the quadrate and one other bone pass in to the middle ear, where they, together with a third bone (stapes), form a chain to convey sound-waves to the sensory portions. In the inner or sensory portion a spiral outgrowth, the cochlea, occurs (fig. 112), and in this is a most wonderfully intricate sensory apparatus—the organ of Corti—the func- tions of which are as yet uncertain. The mouth is usually provided with fleshy lips, and all mammals, except monotremes, some edentates and whales, MAMMALS. 367 have teeth. These teeth are always confined to the edges of the jaws (cf. Fishes, p. 24), being in- serted by one or more roots into sockets in the bone. Some mammals have but a single set of teeth through- out life, but the majority havea first or milk dentition, which is soon lost and re- placed by a permanent den- tition. Occasionally, as in Fie. 158.—Milk (shaded) and perma- imeperm-whale, ete. allthe nent dentitions (quibne! oj tne eat. Poeri@arenctmilir im shape, qoler | “the totsprs (to left) not but usually several different kinds occur, the extreme being reached when four types are present—incisors, canines, premolars, and molars. The incrsors have but a single root, and are found in the premaxillary bone and in the corresponding position in the lower jaw. The first teeth in the maxillary, if single- rooted and pointed, are called canines; and behind these come the molars, with two or more roots. These in turn are subdivided into premolars (the bicuspids of the dentist), which appear in both milk and permanent dentitions, and molars proper, which occur only in the permanent set. The number of teeth and their arrangement vary con- siderably in different mammals, and the characters which they furnish are of great value in grouping the various species. To express these characteristics briefly a dental jormula has been introduced, in which the different kinds _ of teeth are indicated by initials, while the number in each half of either jaw is represented by a figure above or below a horizontal line. Thus the permanent dentition of 368 SYSTEMATIC ZOOLOGY. man is expressed thus: 73, 14, pm%, m3; which indi- cates that in man there are two incisors, one canine, two premolars, and three molars in each half of each jaw. The pig has, 73, ct, pm}, m%; the cow, 78, ct, pm, mi, incisors and canines being absent from the upper jaw. The body-cavity is divided by a transverse muscular partition, the diaphragm (p. 309), into two chambers—an anterior pleural cavity containing the heart * and lungs, and a posterior peritoneal cavity in which are situated the stomach, liver, intestine, etc. The heart, placed a little to the left of the median line, is four-chambered, having, like that of the birds, two auricles and two ventricles. Of these the auricle and ven- tricle of the right side receive the blood from the body and send it to the lungs, while those of the left side take the biood as it comes from the lungs and send it through the aorta to all parts of the body. The aorta, which bends backward and to the left, represents the left arch of the fourth pair of the primitive branchial vessels, the right of the same pair being partially represented in the artery (subclavian), which carries the blood to the right fore limb —a, condition just the reverse of what occurs in the birds. The sixth pair of arches form part of the arteries (pulmo- naries) which convey blood from the heart to the lungs. The blood of the mammals differs from that of all other fo ms in that the red corpuscles (p. 314) are usually cir- cular in outline and are not nucleated. The monotremes form the only exceptions to the state- ment that the mammals bring forth living young. They lay eggs, one species having the eggs about the size of a pigeon; but the young which are hatched from these eggs * The heart, inside the pericardium, is not actually inside the pleural cavity, which really contains the lungs alone. MAMMALS. 369 are nourished by milk secreted by the mother, as in the case with all other mammals. The Mammalia are divisible into two classes: Mono- tremata and Eutheria. Ciass I.—MONOTREMATA. This class contains three or four species of animals which are found only in Australia and its immediate neighborhood. They present resemblances to the birds, or, better, to the reptiles, in the following points in all of Fie. 159.—Duckbill (Ornithorhynchus paradoxus). From Liitken. which they differ from the other mammals: They lay egos; they have well-developed coracoid bones; the bones of the skull are fused, as in birds, and reproductive and excretory organs empty into the posterior portion (cloaca) of the intestine, and thence pass by a common opening to the exterior. The monotremes include the duckbill (fig. 159) and the spiny ant-eaters. The duckbill is an aquatic animal, and receives its common name from the fact that it has a 370 SYSTEMATIC ZOOLOGY. horny bill much like that of the duck. It lives in burrows in the banks of streams, and feeds on beetles, shrimps, etc., which it catches in the water and crushes with its horny teeth, its true teeth being lost at an early age. The spiny ant-eaters resemble the duckbill in their burrowing _ habits, but they live exclusively on the land, where they feed on ants. They are, like the true ant-eaters (p. 374), entirely toothless, and receive the adjective spiny of their common name from the fact that their hair takes the shape of long stout spines, recalling those of the porcupines. Cuiass Il.—EUTHERIA. This division contains the great majority of the mam- mals and is characterized by the following features: The alimentary canal opens to the exterior distinct from the reproductive and excretory organs, the sutures of the skull are well marked and the coracoid bone is reduced and fused with the shoulder-blade, forming the coracoid process of human anatomy. The Eutheria are divided into twelve orders: Marsupialia, Edentata, Rodentia, Insectivora, Chiroptera, Cetacea, Sirenia, Proboscidea, Hyracoidea, Ungulata, Carnivora, and Primates. ORDER I.—MARSUPIALIA. This order receives its name from the fact that in the female a curious pouch or marsupium is developed on the lower surface of the body, in which the young are placed by the mother immediately after birth, and where they remain until able to take care of themselves. This pouch is supported by a pair of bones which extend for- ward from the pelvis—the marsupial bones (fig. 160)— and these, as well as a peculiar inbending of the angle of MAMMALS. 371 the lower jaw, serve at once to distinguish any marsupial skeleton. The living marsupials have a peculiar distribu- tion: they are restricted to warmer America and the chain of islands extending from Australia to the Celebes. Fossil forms are found in Europe as well. The North American species are all opossums—forms with prehensile tails which have given rise to the expres- sion ‘playing ’possum,’ from their habit of feigning death Fic. 160.—Pelvis of Opossum. (After Minot.) M, marsupial bone; 21, ilium; 7s, ischium; p, pubis. Bachman. when disturbed. Their food is chiefly insects, but birds, eges, ete., are not despised. Australia is the real home of the marsupials; indeed, at the time of its discovery this continental island contained only marsupials, if we except mice and the dingo, or native dog. In this region are found forms which recall animals of different groups occurring in other parts of the world. Thus the wombat resembles in size and teeth the beaver; the thylacines in habits and in form are dog-like, while the phalangers in size and appearance arc like the flying squirrels, and, like those animals, they have that same fold of skin which enables them to glide through the O12 SYSTEMATIC ZOOLOGY. air from tree to tree. Most familar of all the Australian forms are the large grass-eating kangaroos, in which the fore legs have become almost useless for locomotion, the animal jumping with its hind legs, and, when resting, supporting itself upon these members and its enormously developed tail. There are also fossil marsupials in Aus- tralia, some of them of enormous size. Thus Thylacoleo was as large as a lion, while Diprotodon had a skull three feet in length and a thigh-bone two feet from tip to tip. The remaining orders of mammals were formerly placed, in contrast to the Marsupials, as a distinct group, Placen- talia, from the fact that they are not born until their internal organization has been well advanced; and in order that they may be supplied with nourishment a peculiar vascular structure is formed,—the placenta,— by means of which blood is brought to the growing em- bryo. It has, however, been ascertained recently that some of the Marsupials also have a placenta, and with this discovery the line of course breaks down. j OrpER IJ.—EDENTATA. The edentates, the lowest of the placental mammals, receive their name from the fact that incisor teeth are always lacking, while in the ant-eaters no teeth occur. The feet are armed with strong claws. The group is a tropical one, and has its greatest representation in Amer- ica. Here belong the armadillos, in which the deeper layer of the skin becomes converted into bone, forming an armor over the body. In the fossil Glyptodon this armor formed one solid piece, enclosing the trunk much like the armor of a turtle; but in the living forms it becomes MAMMALS. 373 broken into several transverse bands, which move upon each other, so that the animal can coil itself into a ball. The sloths are larger forms which, back downward, crawl with the slowest motions along the branches of the trees, holding themselves by their hook-like claws. Upon the ground they walk with difficulty, their long claws being in the way. In geological times there were forms Ml) — — NER Fig. 163.—Pangolin (Manis longicaudata). From Monteiro. allied to the sloths, but of much larger size. One, the Megatherium of South America, had a skeleton 18 feet in length. Another form, Mylodon, found in North America 3v4 SYSTEMATIC ZOOLOGY. receives interest from the fact that it was first described by Thomas Jefferson. The ant-eaters are true edentates in that they are wholly without teeth. As their name implies, ants form the chief part of their food; their claws are well adapted for digging into the nests, the tongue is very long and extensible, while the salivary glands pour out a thick, sticky secretion which fastens the ants to the tongue. The true ant-eaters are natives of South America, but in Africa and India are allied forms with teeth, which also feed upon ants. Among these are the pangolins (fig. 163) in which the whole upper surface of the body is covered with scales, arranged somewhat like those of a pine-cone. These scales, as already mentioned (p. 364), are to be regarded as modified hair. Orver II.—Ropenrt1a (The Gnawers). The rodents are the gnawers, the well-known abilities of rats, mice, and beavers in this direction being shared by all members of the order. They have no canine teeth; Fie. 164.—Skull of muskrat (enlarged), showing the gnawing incisors and absence of canines. the molars are usually 3, while the incisors vary between 3, 4, and §. These incisors demand a moment’s attention. These teeth have persistent pulps, 1e., they continue to erow throughout life. As fast as they wear away they MAMMALS. 375 are renewed from below. In each incisor two parts can be distinguished: the anterior face of the tooth is covered with a very hard layer (enamel), while the posterior sur- face is composed of a much softer dentine. This dentine wears away much faster than the enamel, and the result is that the teeth are constantly kept at a chisel-edge. Lowest of the rodents come those forms familiarly known as hares and rabbits, with disproportional hind legs and long ears. The distinction between the two— hares and rabbits—is very slight, the true rabbit being a native of southern Europe. All the rest are hares. In America, however, the term rabbit is usually restricted to the small burrowing forms. The porcupines, with some of their hair changed to long sharp spines,—efficient weapons of defence,—come next. These occur in both hemispheres, but the American forms are mostly arboreal, while those of the Old Worid burrow. Allied to them in structure, but differing in fur, are the chinchilla and the coypu of South America, the latter fur- nishing the well-known ‘nutria fur.’ The same country furnishes the stupid, so-called guinea-pigs,—whose young shed their milk-teeth before birth,—and the giants of rodents, the capybara, with a body four feet in length. Rats and mice are the great pests of the order. Our common brown rat is a recent immigrant. The early set- tlers brought with them the black rat, the brown rat being then unknown in western Europe, but about 1720-30 the latter came west from the Volga region, and gradually spread all over western Europe and then over America, the black rat disappearing before the invader. There are many rat-like forms, among them the lemmings of the Arctic regions, vast hordes of which occasionally overrun Norway; the dormice, which hibernate in winter; the 3/6 SYSTEMATIC ZOOLOGY... gophers and pocket-rats, which burrow through the soil in the western states; the familiar muskrat, and the less familiar Jumping mice, which resemble the kangaroos in their locomotion. Another series of rodents contains the beaver, common to the Old World and the New, which furnishes furs of great value. These live most of their lives in the water, building dams so that they may always have plenty of it; while their near relatives, the woodchucks, and their western representatives, the prairie-dogs, have no such de- pendence upon water. Highest of all the rodents are the ground-squirrels, the true squirrels, and the flying squirrels. Orper IV.—INsEctivora (Insect-eaters). These are small mammals, in which all four types of teeth are developed, and which are marked off from all other orders by characters rather difficult of expression. As their name implies, they feed largely upon insects, but worms and other small animals are not despised. The species are largely tropical, but the shrews and moles are found in cooler climates. Most of the species are noctur- nal and burrowing animals, consequently their eyes are small and degenerate while their fore legs are adapted for digging. | ORDER V.—CHIROPTERA (Bats). The bats are the only mammals which truly fly. In the case of the flying squirrel and the rest, the animals glide through the air on the plane formed by the lower surface of the body, the tail, and the broad membrane which extends between the limbs; and they can never ascend to the level from which the flight started. With the bats, MAMMATS. i oud. on the other hand, there are no such limitations to the flight. The wing in the bats consists of a very thin mem- brane supported upon a framework composed of the body and the bones of the fore limbs. These latter are elon- gated, four of the fingers excessively so (fig. 165); and \ ! \ Fic. 165.—Skeleton of bat. between these fingers and extending back to the body and the hind limbs is the web of the wing. The thumb, how- ever, is not involved in the wing, but forms a claw of great use in supporting the body, although when at rest they usually hang, head downwards, by the five claws of the hind feet. The jaws are provided with incisors, canines, premolars, and molars. Bats are social animals, occur- ring in large numbers in caves, deserted buildings, and the like, where they spend the day, and it is remarkable that these colonies are usually entirely male or female. In a rough way the bats may be divided into fruit-eating and insect-eating forms, their habits being correlated with 378 SYSTEMATIC ZOOLOGY. peculiarities of structure. To the fruit-eating species belong the large bats of the East Indies known as flying foxes. All of our bats are insect-eating. Some of the South American bats (not the one called the vampyre by Linné) are known to suck the blood of other mammals. In the five orders Marsupials, Edentates, Rodents, In- sectivores, and Bats the surface of the cerebrum is smooth; in all the remaining orders it is at least fissured, and in most it is convoluted (see fig. 157), this increase in sur- face reaching its greatest development in man. Since this line of division corresponds in a way with the intelli- gence of the forms (see p. 366), the five orders already mentioned are grouped together as Ineducabilia; the others are associated as Educabilia. OrpDER V.—CrETaAcEA (Whales). The whales have a fish-like body, the resemblance being frequently heightened by the development of a dorsal fin; and yet in all points of structure they are mammals. The Fic. 166.—Pigmy whale (Kogia floweri). From Gill. anterior limbs contain the same bones (except that the number of joints in the fingers may be increased) as do our own, but the whole has been modified into a ‘flipper’ for use in swimming. The hind limbs are absent exter- nally, but imbedded in the flesh on either side is a bone, MAMMALS. ol9 variously interpreted as a part of the pelvis or as the bone of the thigh. The body terminates in a bilobed caudal fin (‘flukes’), but this, instead of being vertical, as in the fish, is horizontal. All of the whales have teeth in the young stages; some retain them through life, while others lose them long before maturity, sometimes even before birth. The stomach is remarkable for having several (4-7) chambers, this complication recalling the condition in the cow (see p. 385). According to the presence or absence of teeth the living whales are divided into two groups. In some of the toothed whales but two teeth are present; others may have a large number; and usually these cannot be well distributed among incisors, canines, etc., as all are essen- tially alike in size and shape. In the male narwal, how- ever, one of the upper teeth on one side (apparently a canine) grows straight forward into a long twisted spear eight or nine feet in length, while the other teeth disap- pear at an early age. The killer-whales are compara- tively small, but are among the most voracious of mam- mals, not hesitating to attack the largest whales. Here also belong the blackfish, porpoises, and dolphins. The sperm-whales are larger, and have no teeth in the upper jaw, while the lower jaw is abundantly supplied. They derive their common name from the spermaceti which they produce. This is a solid granular substance found in the ‘case,’ a cavity occurring on the right side of the front of the head between the skin and the skull. The sperm-whales also produce the substance known as am- bergris used in perfumery. This is a concretion formed in the intestine and is found floating on the surface of the sea. It is worth about $20 a pound. The toothless whales are also known as whalebone whales, 380 SYSTEMATIC ZOOLOGY. from the fact that they bear upon the lower sides of the upper jaw hundreds of long parallel plates of so-called whalebone or baleen. These plates are fringed at the end, and the whole apparatus forms an efficient strainer, used in separating the small animals upon which these whales feed from the surrounding water. Fig 167, Seaton thoueh thehend Tt js among these whalebone showing how the plates of baleen : (w) are arranged on either side of whales that the giants among the mouth-cavity (mm) Thevtre’ mammals Occur. acim whales of the Arctic seas reach a length of sixty feet, the razor-back whales are still larger, while the sulphur bottoms and silver bottoms (so called on account of the color of the lower surface) attain a length of from 90 to 95 feet. OrDER VIIJ.—SIRENIA (Sea-cows). These are whale-like animals, with the same flippers and the same horizontal tai!, but they differ from the whales in the possession of an evident neck, and of sparse hair or bristles all over the body. Besides these features all, except the extinct Rytvna, have flat-crowned molar teeth. The living forms are very few. fytina, which lived near Bering Strait, was exterminated in the last century. The dugong is the representative of these forms in the Indian Ocean, while the three species of manatees come, one from Africa, the other two from the eastern coasts of America (fig. 168). All the sea-cows are vegetable feeders, living upon seaweed or, in the case of the manatees, upon the plants found in fresh-water streams as well, MAMMALS. 381 = ORDER VIII.—Proposcipi1a (Elephants). The elephants are the giants among the land mammals. They have five toes, each encased in its own hoof; they EN \\ y} ; \Y iN ae ie D Ze NE aN SRS Fic. 168.—A manatee (T’richechus americanus) feeding. After Elliott. have no incisors in the lower jaw, while the pair in the upper jaw are developed into large tusks. Canines are lacking, but there are seven molars in each half of each 382 SYSTEMATIC ZOOLOGY. jaw. These molars are flat-crowned. the surface of the crown being crossed by several ridges of harder enamel. Only two, or at most three, of these molars are in use at once, but as the old ones wear out they drop out at the front of the jaw, and are replaced by new ones from behind until the seven are gone. The skull is enormous, but it is comparatively light on account of the numerous cavities in the bone. Most striking of all is the proboscis, which is merely an enormously developed nose, with capacities which only one who has studied an elephant can realize. The skin is almost entirely naked, hairs being scarce, and on the tail taking the shape of long wiry bristles. To-day two species of elephants exist, one having its home in India, the other in Africa. In the later geological ages there were several others, one, the mammoth, having lived in America and others in Europe. Towards the end of the eighteenth century remains of hairy elephants— even the flesh being preserved—were found imbedded in the ice in northern Siberia. Another has recently been found equally well preserved. Allied to the elephants were the somewhat larger mastodons, in which the molar teeth bore conical cusps, while the tusks were frequently enor- mous. Some mastodons had incisors in the lower jaw as well. OrpDER IX.—HyrRacorpEA (Coneys). This order contains but two or three species, distributed from Syria south into Africa. In having long curved incisors and absence of canines they recall the rodents; in other points their structure is like that of the rhinoceros, while the foot-pads on their feet recall those of the cat or dog. The Hyrax of Syria is probably the coney of the Old Testament. MAMMALS. 383 Orper X.—Uneutata (Hoofed Animals). To this order belong the great majority of important mammals. They are herbivorous, usually of large size, and lack collar-bones. The feet are used solely in walking, and not in prehension, each toe having its tip enclosed in a horny hoof, and in living forms there are never more than four toes developed on a foot. The living ungulates are arranged in two series, according to the number—even or odd—of toes upon their hind feet. The odd-toed forms are called PrRISsopACTYLA, the even-toed are ARTIODACTYLA. To the perissodactyls belong, of living forms, the tapirs, rhinoceroses, and horses. The tapirs live in the forest regions of the tropics of both continents. They have a hog-like body, large prehensile upper lip; teeth, 73, c}, pms, m3; while their fore feet have four toes, the hind feet three. Yet, although the fore feet have an even number of toes, these are not symmetrically arranged, 084 SYSTEMATIC ZOOLOGY. as in artiodactyl forms, the pig for example, but one (third) is enlarged and bears most of the weight of the body. The rhinoceroses have three toes on each foot; the skin is extremely thick;* the snout bears one or two well- developed horns, in which there is no bony core; and canine teeth are not developed even in the young. There are six species known, those occurring in Africa having two horns, while in the East Indies are both one- and two- horned forms. , / | In the horses the reduction of toes has gone still farther, there being but one (the middle or third) in each foot. In the skeleton, however, traces of two more can be found in the ‘splint-bones,’ two small bones occurring alongside the large ‘cannon- bone’ (fig. 170). All of the existing horse- like forms have the teeth 23, ct, p%, m3, and all are natives of the Old World, none existing in America at the time of its dis- covery. All evidence goes to show that the home of the domestic horse was in cen- tral Asia, and indeed four different species of horse run wild there to-day. The asses have their céntre around the eastern end of the Mediterranean, while the zebras or striped horses are all African. In geological Fic.170._Foot time, however, America had horses, and of horse, the fossils in our western states give the showing the epuint Pones history of the race from small forms about er toes) the size of a fox, and with three toes behind Boe and four in front; later, those as large as a sheep, with three functional toes in each foot; and still * The elephants and rhinoceroses were formerly united as a group called Pachydermata on account of the very thick skin. MAMMALS. | 385 later, three-toed forms as large as a donkey. In domesti- cation horses vary extremely in size as in other respects. Lowest of the artiodactyls, or even-toed ungulates, come the two species of hippopotamus, in which there are four toes, large canine teeth, and a huge, clumsy body, some- times fourteen feet in length. In the pigs the canines are still large, and the toes are four in number, but the outer ones are lifted above the ground so that they are useless as organs of locomotion. Our domestic swine have descended from the wild boars of Europe. In the warmer parts of America the peccaries represent the group. The hippopotamus and the pigs have the axis of the foot passing up between the middle toes; in other words, they have cloven hoofs. In all other artiodactyls the cloven hoof occurs, and be- sides, they chew the cud, and hence they are asso- ciated as a group of rumi- nants. The stomach is di- vided into four chambers, and when a cow, for instance, feeds, it swallows the SUAS 6 are. 171.—Diagram of the stomach sumeu chewing the Th Ge mane ie. doled tne passes down to the first stomach and thence to the second. In these it becomes mixed with digestive fluids and softened. It is then brought up in the mouth, thoroughly chewed, and again swallowed. This time it passes into the third stomach, and from this into the fourth, and so into the intestine. To the ruminants belong the most valuable domesti- cated animals. In South America are found the llamas and alpacas, which were the cattle and beasts of burden 4 é 386 SYSTEMATIC ZOOLOGY. of the ancient Peruvians; while in Asia and Africa the camels, in part, take their place. Two kinds of camels occur, one with one and the other with two humps upon the back. These humps are merely large masses of fat. Some fifty years ago the United States Government intro- duced some camels into our southwestern territory, and the descendants of these are still to be found in Arizona. We associate together under the common name of deer all those ruminants which have horns consisting of solid bone. These horns are annually shed and grow out anew each year, usually increasing in size with the age of the - animal. When first formed the horns are covered with a thin skin with short hairs. The horns in this condition are said to be ‘in the velvet.’ When the horn is fully formed the skin dies and is worn off. In some deer horns are borne only by the male, but sometimes both sexes, as with the reindeer, are provided with them. The long- necked giraffes are closely related to the deer. In other ruminants the horns are never shed. In these the horns consist of a central core of bone, covered on the outside with a horny structure—in reality modified hair (p. 364). Here belong our domestic cattle, which are believed to have arisen from four different species, which formerly were wild in Europe. This wild stock is almost extinct. One of these forms at least was closely similar to our American bison, which has so nearly approached ex- tinetion from the desire for ‘buffalo’ robes. The true buffalo are all natives of the Old World, and occupy a position between the ancestors of domestic cattle and the long series of forms grouped together as antelope, most of which belong to Africa, but which are represented in America by the prong-horned antelope of our western states (fig. 172) which forms the sole exception to the MAMMALS. 387 statement that the antelopes do not shed their horns. Other members of the same group with permanent horns are the sheep and the goats, the series ending with the so-called musk-ox of the arctic regions, a form nearer the goats than to the domestic cattle in its structure. As a whole, we may say that in points in structure— especially in the characters of feet.and teeth—the group of ungulates is among the most specialized of the mam- Fic. 172.—Prong-horned antelope (Antilocapra americana). malia, the whales, bats, seals, and possibly the elephants alone excelling them in this respect. ORDER X.—CARNIVORA (Beasts of Prey). The beasts of prey are specialized in the direction of flesh-eating. Their bones are slender, but strong; their feet (usually five-toed) are furnished with claws; while on the top of the skull is a crest for the attachment of the 388 SYSTEMATIC ZOOLOGY. strong muscles of the jaws. All four kinds of teeth are present, and one of the molars or premolars is flattened vertically, so that, meeting its fellows of the opposite jaw, it cuts like a pair of shears. In the lower mammals we . find the lower jaw so hinged upon the skull that it can move back and forth in grinding the food. In the car- nivores, on the other hand, no such motion is possible. The carnivores are divided into two groups, one embrac- ing the typical land-inhabiting forms; the other, which includes the walrus and the seals, is modified for an aquatic life; the differences being most marked in the structure of the appendages. In the first group the legs are elongate and the toes are distinct, whence the name FISsIPEDIA; while in the other division (PINNIPEDIA) the legs are shortened, the fingers are webbed, and the feet are thus effective paddles. Lowest of the Fissipedia are the bears and their allies, in which the whole sole of the foot is applied to the ground in walking, and hence are cailed plantigrade, in opposition to those digitigrade forms, like the cat and dog, which walk upon the tips of their toes. The bears are widely dis- tributed over the earth, America having at least three species. The raccoon is distributed throughout the United States, and in tropical America is represented by that exceedingly interesting animal, the coati. Another group of carnivores includes the otters, mink, ermine, sable, and marten—all of which are valuable for the furs which they afford,—as well as the weasels and ferrets, and the well-known skunks. These are partly plantigrade, partly digitigrade. The dogs, foxes, wolves, and jackals are all digitigrade. They have the teeth, 73, c+, pm4, m2? or %. Foxes and wolves are wild, and many believe that our domestic dogs MAMMALS. 389 have descended from some wolf stock; but others think that dogs and wolves are distinct, and even that our com- mon dogs represent several originally distinct kinds or species. The hyenas are intermediate between the cats and dogs in many respects. They have the back teeth fitted for ' Fig. 173.—The harbor seal (Phoca vitulina). After Elliott. crushing. In the cats, of which there are more than fifty species, the teeth are usually 23, c+, pm3, m4, while the claws are retractile into sheaths. Our domestic cat appar- ently had its origin in Egypt, while ancient Greece and Rome lacked our familiar puss, its place being taken by domesticated martens. Among the cats the tiger, lion, panther, leopard, and puma rank first, and with them are associated the wildeats and lynxes. In external form the Pinnipedia (seals and walruses) have little resemblance to the other carnivores, but in structure, 390 SYSTEMATIC ZOOLOGY. and especially in their skulls, there is great resemblance to the bears and otters in particu ar. As has been said, their feet are modified into paddles, and only the distal region is distinct from the body. Lowest are the large walruses, of which there are two species in northern seas, in which the upper canines are enormously developed. They can use their hind feet in walking. The eared seals are so- called because they have small external ears. The largest of these are the sea-lions, but the most valuable are the fur seals, of which two species are known. The one which occurs in the southern hemisphere has been almost exterminated, while the Alaskan species is rapidly follow- ing the same road. The true seals lack all external ears, and since their skins are less va uable, a longer lease of life seems assured them. They occur on all shores, and from their fish-eating habits are frequently a nuisance to fishermen. ORDER XI.—PRIMATES. The term Primates is given to that group which includes the monkeys, apes, and man, from the fact that they are the first or highest group in the animal kingdom. Collar- bones are always present; the feet are very primitive, and the fingers and toes are armed with nails, claws but rarely occurring. Intelligence, not structure, assigns them the leading place. Lowest come the group of lemurs or ‘half apes,’ which have their metropolis in Madagascar, but have relatives in Africa and in the East Indies. They are largely nocturnal, and eat fruit or insects or other small animals. They are noticeable from the fact that the second finger is pro- vided with a claw. MAMMALS. 391 The marmosets are small squirrel-like forms found in South America. They are provided with claws on all digits except the great toe, and the tail is incapable of grasping, while the thumb is scarcely capable of being opposed to the fingers. _ The remaining American monkeys—the howlers, sapa- jous, spider-monkeys, and the like—have a broad septum Fie. 174.—Chimpanzee (Troglodytes niger). After Brehm. of the nose, causing the nostrils to be wide apart; the thumb is scarcely opposable, and in some is lacking; while the teeth differ from those of the Old World monkeys, and of man, in having pm3. Many have a prehensile tail. The Old World monkeys have the nostrils closer together, the thumb as well as the great toe is opposable, and the tail never takes the place of a fifth hand. In their teeth they resemble man: 1%, c+, pm3, m8. The baboons, distributed across Asia and Africa, have large cheek 092 SYSTEMATIC ZOOLOGY. pouches for the storage of food, etc., and naked callous patches on which they sit. Some have long tails, others no tails at all. The macaques and mangabeys are allied Asiatic forms. In the anthropoid apes tail, cheek-pouches, and callous spots are lacking; as the name indicates, they are man- like. There are three of these. The orang-utan (the name is Malay for Man of the Woods) lives in Borneo and Sumatra. The chimpanzee and the gorilla are African: Each of these has certain points in which it is more lke man than are the others. The highest mammal is man, who differs from the other primates less in structure than in intelligence. SUMMARY OF IMPORTANT FACTS. 1. The CHORDATA possess a notochord, gill slits, and a central nervous system entirely on one side of the diges- tive tract. Ro 2. To the Chordata belong the Tunicata, Leptocardii, and Vertebrata. 3. The TUNICATA are marine; in most species the noto- chord exists only in the tadpole-like young. Many species reproduce by budding. 4. The LEPTOCARDII are fish-like, but differ from the true fishes in lack of skull, vertebrae, and heart. They are marine, small, and transparent. 5. The VERTEBRATA have skull and vertebral column, and usually paired appendages. They breathe by gills or by lungs, both connected with the digestive tract. 6. The brain consists of five divisions: cerebrum, ’twixt- brain, optic lobes, cerebellum, and medulla oblongata. 7. The heart is ventral in position; it consists of an MAMMALS. == 393 auricle and a ventricle. In air-breathing vertebrates the auricle is, and the ventricle may be, divided. 8. The sexes are usually separate, and reproduction by budding, etc., is unknown. 9. The Vertebrata are divided into the Cyclostomata and the Gnathostomata. 10. The Cyctostomata lack true jaws and paired ap- pendages; they have a single nostril. Some are parasitic. 11. The GNaTHosToMATA have true jaws and paired nostrils. They are subdivided into Pisces, Amphibia, Reptilia, Aves, and Mammalia. 12. The Pisces or Fishes have median and usually paired fins; they usually have scales; they breathe by gills and have a two-chambered heart. 13. The Pisces are divided into Elasmobranchii, Ga- noidei, Teleostei, and Dipnoi. 14. The Amphibia usually have true feet; they have lungs, and in the young gills as well. A metamorphosis is common. The heart is three-chambered. 15. The Amphibia are divided into the Cecilia, Urodela, and Anura. 16. Pisces and Amphibia are called Ichthyopsida on account of their gills and their aquatic life. 17. Reptilia have external scales and a three- or four- chambered heart; they lack functional gills at all times. 18. Recent Reptiles are grouped as Lacertilia, Ophidia, Testudinata, and Crocodilia. 19. Aves or Birds are characterized by the presence of feathers, a four-chambered heart, warm-blood, and wings. 20. Birds and Reptiles are grouped as Sauropsida on account of the single occipital condyle, the similar scales and the large eggs. 394 SYSTEMATIC ZOOLOGY. 21. The Mammalia have hairy skin, a four-chambered heart, warm blood, and two occipital condyles. : 22. The young are nourished by milk furnished by the mother. 23. The teeth have roots, and usually several kinds of teeth are recognizable. 24. The Mammals are divided into Monotremata and Kutheria. GENERAL ZOOLOGY. The foregoing pages have been largely devoted to the study of the structure of animals and the various degrees of structural resemblances which they bear to each other as expressed by classification. Animals, however, pre- sent other points for consideration, and some of these may be referred to here. COMPARATIVE PHYSIOLOGY. An animal must be regarded as a mechanism, but our knowledge of a machine is not complete when we know its structure; we must also understand the way the differ- ent parts perform their work. The study of the st: ucture of an animal is the province of anatomy, while that branch of science which deals with the action of the various parts and the working of the whole is called physiology. It is a far more difficult task to ascertain from the speci- mens themselves the function of the parts and the way that they act, than it is to make out the details of struct- ure, and so a general summary is given here. Every machine, in order that it may perform work, must be supplied with energy, and the animal obtains this energy by the slow combustion (oxidation) of food or food products, Just as the steam-engine gets its energy 395 396 GENERAL ZOOLOGY. from the rapid combustion of coal. In the case of a steam- engine an engineer supplies the fuel, regulates the action. of the parts, and disposes of the waste. The animal must be its own engineer. It must have the means of obtaining fuel (food), of putting it in such position that the energy produced by its oxidation can be utilized to its fullest extent, and all waste can be properly disposed of. This has led, in the first place, to the formation of a digestive tract, in which the food is put in such shape as to be most advantageously used by the organism. In the lowest animals (lowest Protozoa) we find that the whole body (cell) serves as a digestive tract, and that food can be taken in at any point on the surface. A little higher (p. 162) an organ which we must call a mouth is formed in the body, and this opening for the taking in (ingestion) of food is found in all higher animals, except a few parasites which, living on liquid food, need no such opening. With larger animals a definite digestive cavity or canal is formed, the lining of which has certain definite work to perform. Most articles of food are insoluble as taken into the body; a bit of meat or starch can be soaked indefinitely in pure water or may even be boiled for days without passing into solution. In the digestive tract juices are produced which alter these substances so that they can be dissolved; and it is only when they are in solution that they can pass through the walls of the alimentary canal to those parts where they are to be utilized. In the lower animals all parts of the digestive tract seem able to act at once as formers of digestive fluids, and in taking up of the dissolved food, but as we pass higher in the scale-complications of various kinds are introduced. In the first place, we find certain organs, like the salivary PHYSIOLOGY. 397 glands,. stomach, pancreas, and liver, set apart for the secretion of digestive fluids, and even in animals as low as the sea-anemone the mesenterial filaments (p. 169) appear to have the same power. On the other hand, the other portions, while they may secrete, are pre-eminently the regions for the absorption of the liquefied food. An- other complication is this: A given amount of surface can absorb only so much in a given time; so as to obtain the necessary amount of food the surface must be increased. This explains in part the folding of the wall of the digestive tract in the sea-anemone, as well as the lengthening and coiling of the intestine in tadpole and rat, and the spiral valve in the shark. In many vertebrates the surface is still further increased by numerous minute foldings and outpushings of the lining of the intestine which, though so small as to be invisible to the naked eye, still more than double the surface. , With most food there are certain portions: which are indigestible. These of course must be eliminated. In the Coelenterates and flatworms the only opening through which they can pass out is the same one by which they entered, and so this opening, usually called the mouth, serves at once as mouth and vent. In the higher forms the alimentary canal becomes a complete tube with two distinct openings, one—the mouth—for the taking in of food, the other—anus or vent—for the ejection of non- nutritious portions. After its solution the food (nourishment) must be trans- ferred to the parts which are to do the work. In the Protozoa the same parts which digest do the work. In the sea-anemone and flatworms the pouching of the diges- tive tract (figs. 17, 24) renders the transfer easy, for the pouches extend to all parts, Above these forms we find 398 GENERAL ZOOLOGY. circulatory organs present, one of the functions of which is the carrying of the dissolved food from the digestive tract to the working parts. These circulatory organs are tubes through which the fluid flows, but a flow can only be produced by some mechanism which shall propel the fluid. In most cases this is effected by muscles in the walls of the vessels, which by waves of contraction force the fluid along. In the lower worms and even in Amphwoxus (p. 289) all of the vessels are markedly con- tractile and no part has supremacy over another. As we go higher in the scale the tendency is constantly towards a concentration of these pumping muscles in one region, and thus a heart results. So far we have traced the fuel to the working parts. In order to do work the fuel must be oxidized, and this means that oxygen must also be brought to these parts. This oxygen 1s found either in the air or dissolved in the water in which the animal lives. In the Ccelenterates, flatworms, and many other forms, the general surface of the body is sufficient for the absorption of the oxygen, but where the animal is larger and needs more oxygen special provisions are needed. A very simple condition, physiologically, is found in the insects, where air-tubes (tracheze, p. 239) extend inwards from the outside, their fine branches reaching to every part of the body. Air is drawn into these tubes by an enlargement of the body by suitable muscles, and then, when the oxygen is absorbed, contraction forces out the remainder. This breathing process can be seen by watch- ing the abdomen of a grasshopper or a wasp. So far the circulating fluid is largely nutrient in character, as it carries only the food (and some of the waste). In many crustacea, in molluscs, worms, and vertebrates, PHYSIOLOGY. 399 the conditions are more complicated. In these the nutri- ent fluid is also the bearer of the oxygen; and, in order that the fluid may obtain this element specialized portions are developed, where the circulatory fluid may come into close relationship with the water (gills) or the air (lungs). In some (see the figure of Doris, p. 200) the gills project freely into the water, and there is no need of special appa- ratus for changing this fluid. In other forms the gilis are protected by enclosure in a branchial chamber, and then the water containing the oxygen must be brought here. In the oyster and clam this 1s effected by numerous minute hair-like structures (cilia) which by their constant motion draw water over the gills. The squid gets its supply by enlarging and contracting its mantle-cavity, the crayfish by pumping water over the gills by means of its ‘gill-bailer’ (p. 69), and the fish and tadpole by taking water into the mouth and forcing it out through the gill-slits. The lungs of the higher vertebrates possess a resemblance to the trachese of the insects in that air is drawn into them; but here the similarity ceases, for in the vertebrates the air is brought from the lungs to the working parts by the intervention of the nutrient fluid (blood). The methods by which air is drawn into the lungs vary. The frog swallows the air by aid of the muscles extending across the throat between the halves of the lower jaw, and that this swallowing is the only way of forcing air into the lungs is shown by the fact that if the mouth be kept from closing the animal will suffocate.* ~In the Sauropsida the muscles between the ribs and those forming the walls of the abdomen are concerned in the inspiration and expiration of air; while in mammals the * The skin is a very important organ in the respiration of the Batrachia (see p. 337). 400 ‘GENERAL ZOOLOGY. muscular partition (diaphragm) which divides the body- cavity becomes an efficient organ in the process (see p. 309). We naturally think of work in terms of motion, and in the case of an animal the contraction of a muscle or the movement of a part or the whole of the body naturally suggest themselves as examples. These, however, are but a part of the work which the animal does. The per- formance of any function of the body is really work. When a gland secretes, a nerve acts, an intestine absorbs, or the mind carries on its operations, the expenditure of energy is called for just as in the contraction of a muscle. So all parts must have both food and oxygen. When coal is burned in an engine, besides energy there is a production of waste. A part of this waste passes off in a gaseous condition as water vapor and part as ashes. When any part of the animal body works there is a similar formation of waste, and the carbon dioxide and water vapor are carried away by the same structures (tracheze in the insects, blood-vessels and gills or lungs in many other forms) which brought the oxygen to the parts. The animal, unlike the engine, needs also for its fuel substances known to the chemist as nitrogenous food (proteids) and the combustion of this produces, besides the carbon dioxide and water, nitrogenous waste, and this, in all of the higher animals, is eliminated by means of organs which can be grouped under the common name of excretory organs. Here are to be placed not only those structures specifically called kidneys in the fore- going pages, but also the green gland of the crayfish, the Malpighian tubes of insects, the nephridia of the earth- worm, and the organ of Bojanus in the clam. Even the contractile vacuole of the Protozoa seems to be an organ for the excretion of nitrogenous waste. : PHYSIOLOGY. 401 We have seen that the fluid propelled by the heart may have a large series of different purposes to fulfil. It must carry nourishment from the digestive tract to the different parts of the body; it has to carry oxygen from the gills and lungs to these various structures, and to carry the carbon dioxide and water produced by work to the same lungs and gills, while the nitrogenous waste must be carried to the excretory organs. The fluid which does all this is the blood. It isfurther to be noted that the flow of the blood, un- like that of the air in the trachez of insects or the lungs of vertebrates, is not tidal, but forms a complete circula- tion, entering the heart by different vessels and different openings than those by which it leaves that organ. There are other aspects of animal physiology to be re- viewed. ‘The animal needs to be aware of the presence of food and of the proximity of things injurious to it. This implies the formation of a sensory system, and naturally this system must be on the outside of the body, for from without come both food and danger. The knowledge of the presence of good or of evil would be of little value to the animal were it without ability to avail itself of this knowl- edge. Hence this sensory system is connected with a nervous system, which directs and controls the actions of the animal. In the lower animals most parts of this nervous system are on the surface, but as this superficial position is dangerous to such an important structure, we find in all the higher animals that the nerve centres or ganglia become removed to a deeper position, which necessitates the development of nerve-cords to connect them with the sensory system and with the muscles and other parts. It is interesting that in all animals, even in man, no matter how deeply situated or how thoroughly 402 GENERAL ZOOLOGY. protected it may be in the adult, the central nervous system arises from the outer surface (ectoderm, p. 155) and secondarily attains its permanent position. Since most animals must search for their food, we find that except in the lower forms, one end becomes adapted for always going in front, and in this way a head has come into existence, and here are situated the brain and the most important sensory organs, as well as the mouth, since this part of the body first comes into the neighborhood of substances useful as food or likely to be injurious to the animal. Further, it is probable that this same loco- motion has resulted in bilaterality of the body, which is so marked in all animals except the Ccelenterata and sponges. Locomotion implies motion of the parts, and when resolved to its ultimate all motion is to be referred back to the contractility of protoplasm (p. 139). In the lower Protozoa (Ameba, p. 148) all parts of the protoplasm (cell) are equally contractile, but from this point onward specialization sets in. In some there occurs the develop- ment of special vibratile organs—cilia and flagella— moved by contraction of the protoplasm in them or at their bases. Cilia and flagella occur in most groups where a slow motion is needed. Cilia occurs even in man in the trachea, and doubtfully in the tubules of the kidney, while the tail of the spermatozoan is but a flagellum. Another type of modification is the conversion of a part of the protoplasm of the cell into muscular substance which contracts under stimulus. Traces of this appear even in the Protozoa (Stentor, p. 146), and it is abundant in all other groups except sponges. Cilia are apparently automatic in action and while in a few instances they may be regulated by something like nerves, they are not stimu- lated by them. Muscles, however, are quiescent unless MORPHOLOGY. 403 stimulated, and this stimulation is usually and normally effected (how is not known) by nervous impulse. Another physiological peculiarity which needs mention is the power of the cells to take only those substances which they need from the circulating fluids and to build them up into compounds for use in the cell itself, as in the case of muscle- and nerve-cells, for use in other parts of the organism, as in the case of the liver and pancreatic cells or for elimination from the body (kidneys, sweat glands, etc.). So far we have treated of the animal as an automatic self-regulating machine, but in one respect it differs from all machines of human production. No amount of fuel put under the boiler of a steam-engine will cause this mechanism to increase in size or to give rise to other bits of mechanism like itself. The animal machine grows by the taking in of food, and like the steam-engine, it wears out. It, however, has the power of reproducing the kind, by the formation of small parts (either buds or eggs), which eventually grow into animals like the parent which produced them, and thus the species is perpetuated, the young taking the place of the generation which has worn itself out. GENERAL MORPHOLOGY. We are now in position to review some of the facts already discovered in the laboratory or described in the accompanying text, to add to them, and to draw some general conclusions. Excepting sponges and some Protozoa, each and every animal can be placed under one of two heads. In the 404 GENERAL ZOOLOGY. one, the body is bilaterally symmetrical. In it we can recognize anterior and posterior; dorsal and ventral; light and left. Under the other we place those forms in which these features do not exist; there is no right and left, but the parts are radially arranged around an axis, like the spokes around the axle of a wheel. To this latter group belong the ccelenterates; to the first, all other divisions reviewed in this volume. Even the Hchino- derms belong to the bilateral type, for their development (fig. 90) shows that in the early stages they have not a trace of radial symmetry, but only acquire it later in life. In the bilateral animals, in turn, two types can be recognized: the segmented and the unsegmented. The - segmented forms show their peculiarities in the most striking manner in some of the Annelids, like the earth- worm. In these the body is made up of a series of rings or segments, each essentially like its fellow, and each containing a portion of all systems of organs—muscular, nervous, circulatory, digestive, excretory, etc. In the arthropods this segmentation again appears, but here there are tendencies in two directions: towards a fusion of segments, and towards an increase of one segment at the expense of another. In annelids and arthropods this segmentation is visible externally; in the vertebrates it is not so plainly shown, but it nevertheless exists. The trunk muscles (see p. 17) are thus arranged; the spinal nerves and the vertebrae correspond to the muscle seg- ments, as do also certain blood-vessels (intercostals), while in their early history the kidneys are segmentally arranged. On the other hand, the lower worms show no traces of segmentation, while the molluscs show it to a very slight MORPHOLOGY. 405 extent.* In: the echinoderms there is a repetition of ambulacra and ambulacral plates, but this is supposed to be different in its origin from that in the segmented animals. : Study of different animals further reveals the fact tha in some there is no cavity inside the body aside from that. of the digestive tract (sponges, ccelenterates), while in all others there are more or less well-marked cavities between the alimentary canal and the body-wall. Further and more detailed studies lead to the conclusion that there may be at least three different categories of cavities in the body, those of the excretory organs, those of the circu- latory organs, and a third, the celom, sometimes small and containing only the reproductive glands, sometimes large, as in the vertebrates, and including not only the reproductive organs, but other structures as well. So the term ‘body-cavity,’ often used, is inexact. The body- cavity of a lobster, for example, is merely an expansion of the circulatory system and has no relation to the body- cavity of the fish or frog, which is a true cceelom. Thus the large cavity of the echinoderm and that of the am- bulacral system, the pericardium of the mollusc, the paired ‘body-cavities’ of the annelids, the cavities of the reproductive organs of the arthropods, and the pleuro- peritoneal and pericardial cavities of vertebrates are all cceloms. All animals reproduce sexually, as mentioned on p. 141, but besides this sexual reproduction, many animals pos- sess the power of reproducing asexually. In these cases the animal may divide into two (fission), or a small por- * The gills, kidneys, and heart of the Chitons (p. 197) and the Nautilus (p. 211) are supposed to present indications of segmenta- tion. 406 GENERAL ZOOLOGY. tion may protrude as a bud which will eventually produce an individual more or less like the parent (gemmation). This asexual reproduction is very common among the Coelenterates, but it may also occur among the lower - worms (p. 179), the Polyzoa, the tunicates, etc. In many instances this asexual reproduction does not result in the formation of distinct and separate animals, but buds and parents may remain somewhat intimately connected with each other, the result being the formation of what are known as colonies, of which Pennaria may be taken as a type. Here we are met with a difficulty in the use of terms. We have spoken heretofore of 7- dividuals; but is each hydranth in a colony of Pennaria an individual, or is the colony itself to be so regarded, the hydranths being regarded as organs? In many cases this reproduction by budding results in the formation of parts very different from each other. Thus in the hydroid (fig. 175) abundant on shells in- habited by hermit-crabs, the colony consists of three different kinds of hydranths: (1) the feeding hydranths (/) which take nourishment for the whole colony; (2) the protective hydranths (p) which lack mouths, but which are richly provided with nettle-cells; and (8) the repro- ductive hydranths (7), the sole function of which is the reproduction of the species. In the Siphonophores this differentiation is carried still farther (p. 168), for here seven different forms may be developed, and here we notice a marked fact in colonial conditions. The more different the members of the colony become the more it conveys the impression of being a single animal instead of an aggregate. When there are but two different forms in the history of the species it is called dimorphic (from the Greek mean- MORPHOLOGY. 407 ing two forms); if more than two, the species is polymor- phic, no matter whether the forms are colonial or whether they lead distinct lives. Besides the di- or polymorphism produced by budding, Fia. 175.—Part of a colony of the hydroid, Hydractinia, an illustration of poly- morphism. /, feeding individuals; p, protective individuals; r, reproduc- tive individual. similar conditions may arise in other ways. Thus fre- quently we find serwal dimorphism, in which the male and female of the same species are greatly different in their appearance. An example of this is familiar in the can- kerworm-moths, the male of which is winged, the female wingless. More striking cases are furnished by many Crustacea where the female has become so aberrant that in the adult all arthropod features may have disappeared (fig. 176). 7 408 GENERAL ZOOLOGY. Again, we have to recognize a seasonal dimorphism. Thus certain butterflies produce several broods in a year. Those of the summer broods are so different from those which come from cocoons which have passed through the winter, that without Fra. 176. Male (m) and female (f) following through the whole of one of the ipod, crustacee, 42 history the _ relationships morphism. ete would not be suspected. Closely connected with this polymorphism is the phe- nomenon of alternation of generations, of which instances are abundant in some groups of the animal kingdom (p. 167). Thus in the butterflies just mentioned, from the eggs of the winter-brood individuals are produced (the summer brood), presenting far different appearances from the parents, while the eggs of the summer brood produce in turn the winter brood. Again, in certain gall-wasps the difference between two generations is so great—both in appearance and in habits—that they would never be regarded as belonging to the same species, or even to the same genus, were it not that the whole his- tory had been followed, so that it was ascertained that each generation resembles, not its parents, but its grand- parents. Another and a more complicated example is furnished by the liver-fluke (p. 180). Many animals in the course of their development pass through a metamorphosis, which is not to be confused with polymorphism. In forms where a metamorphosis occurs the young (the larva), as it hatches from the egg, is greatly different from the parent, but by successive changes of form it at last reaches the adult condition in which it DISTRIBUTION 409 resembles closely the parent. ‘these metamorphoses at times give us clues as to the past history of the group. Thus the larve of Echinoderms (p. 273) and the tadpoles of the Anura (p. 337) point to the fact that the first group has descended from markedly bilateral ancestors, and that the radiate condition of the adult has been secondarily acquired; while the history of the frog is evidence that these amphibians have sprung from tailed water-breathing ancestors. In the insects, on the other hand, the larval and pupal stages have far less significance, but have apparently been introduced into the history the better to adapt these forms to the various conditions of their exist- ence (p. 242). GEOGRAPHICAL DISTRIBUTION. The most superficial observation shows that the differ- ent regions of the earth are inhabited by different animals, and the same, though not so evident, is true of the sea. The animals found in a given region constitute its fauna, and the study of these faunz and the causes underlying them is one of the most interesting branches of zoology. From detailed studies of the distribution of the higher vertebrates most zoologists have come to recognize six primary land regions: (1) The Palearctic, including Europe and the southern shore of the Mediterranean, and Asia south to the Himalayas; (2) the Ethiopian, including Africa south of the Sahara; (8) the Oriental, including southern Asia and the islands as far east as Celebes, (4) the Nearctic, embracing North America south to about the Mexican boundary; (5) the Neotropical, consisting of the rest of the American continent; and (6) the Aus- tralian, composed of Australia, the islands of the Pacrfic, > 410 GHNERAL ZOOLOGY. and the eastern Malay archipelago. These regions are not all equivalent. The Australian is most markedly separated from the rest, while the Nearctic and the Pale- | arctic are closely similar; indeed, are often united as a Holarctic region. The Australian region is characterized by the mono- tremes and by the great abundance of the Marsupials, te ad we a TS a i. = gees eb, deer: ae Smee, ie anne? se ttt ie AGEAYGEEE | : = - Fig. 177.—Main geographical regions of the earth. Horizontal lines Pale- arctic; vertical lines, Nearctic; coarse oblique, Ethiopian; fine oblique, Neotropical; Cross- -lined, Oriental: dotted, Australian. forms which occur nowhere else, except a few species in America. The absence of all other mammals, except those which might have drifted there or have accom- panied man, is noticeable. The Neotropical region contains the platyrrhine apes, numerous rodents and edentates, and has an almost entire absence of insectivores. The llamas and alpacas are noticeable, while numerous families of birds, among them the humming-birds and the toucans, are characteristic. The Ethiopian region is marked by the presence of the DISTRIBUTION. 411 hippopotamus and giraffes, the numerous Antilopes, and the gorilla and chimpanzee, while a part of it—Madagascar, often set off as a Malagassy region—is the great home of the lemurs. The lemurs, elephants, and rhinoceroses, which also occur in Africa, are found in the Oriental region, which has besides the orang-utan and the gibbons. The mon- keys of this and the Ethiopian region belong to the Catarrhine division. The Palearctic region abuts against the Oriental, Ethi- opian, and Nearctic regions, and members of each extend into it so that it is not so sharply marked as the rest. Indeed, it is characterized more by what it lacks than by what it contains. Among the more striking members of the fauna are the chamois, the horses, and the great num- ber of deer. The Nearctic region is characterized by the presence of _the pronghorn antelope, the sewellel, the star-nose mole, and Rocky Mountain goat, as well as by the great num- bers of tailed amphibians and ganoids. It is capable of subdivision into an Arctic region, essentially similar to that of the Palearctic, an eastern region, including most of the United States east of the Rocky Mountains, a Pacific region, and a Sonoran region, which merges into the Neotropical of Mexico. In the oceans similar divisions may be made, but only a few of the broader features need mention here. The Arctic, the temperate, and the tropical seas each have their peculiar and characteristic faune, the temperate and tropical regions being subdivided by the continents into Pacific and Atlantic areas. Again there is an eastern and a western Atlantic and similar Pacific areas. The boundaries between these are less marked than in the 412 GENERAL ZOOLOGY. regions on land, but on our Atlantic coast we can set the boundaries at approximately Cape Cod and Cape Hat- teras; the Arctic fauna extending down to the former; | the tropical, though not so distinctly, up to the latter promontory. Besides these coast areas there exists a pelagic fauna composed of animals which live on the surface of the high seas, and another abyssal fauna con- taining those in the greater depths (500 fathoms and more) of the sea. These different faunz suggest numerous problems, only one or two of which can be alluded to here. In part the differences between them are easily explicable upon climatic grounds, but there are numerous others which are not solved so easily. Why are the Marsupials re- stricted to America and the Australian region? Why are all the ostrich-like birds, except the ostrich itself, confined to the southern hemisphere? How is the pe- culiar distribution of the Dipnoan fishes (p. 334) to be explained? Clearly these are not the result of climate. Not all these questions have been answered, but the solu- tion of many is found in the study of the past history of the earth when it is found that once North America and the Old World were connected and that once Marsupials, for instance, occurred in Europe as well. A knowledge of this past history shows that the later the connection between two regions of like climatic conditions the more close their faunze are related to each other, while those which have been separated for a greater length of time are much more distinct, for their inhabitants have had a longer opportunity to develop in their own lines. DISTRIBUTION. 413 GEOLOGICAL DISTRIBUTION. Geographical distribution treats of the distribution of animals in space; there is also a distribution in time. The animals of past ages have left their record in the rocks, and a study of these fossils shows that in the past the ani- mals in any region were more or less different from those in the same region to-day. Thus at the time of its dis- covery America contained no elephants, camels, horses, or rhinoceroses, yet the rocks of our western states have revealed the skeletons of all of these animals. Geologists have classified the rocks according to their age, and by studying the fossils which they contain we get not only an idea of the changes in a region, but also of the progress of life on the earth as a whole. Going from the older to the newer rocks the following are the main subdivisions of time recognized by geologists - the characteristic animals contained in each. I. Azoic oR ARCHAAN AGE. No fossils are certainly known from this age. II. Pautmozoic AGE. Divided into (1) Cambrian, (2) Silurian, (3) Devonian, (4) Carboniferous, and (5) Permian periods. In the Cambrian rocks only invertebrates occur: Brachiopoda, trilobites, molluses, and echinoderms prevail. Corals and fishes appear in the Silurian, amphibia in the Carbonifer- ous, reptiles in the Permian. 414 GENERAL ZOOLOGY. III. Mesozoic AGE. Divided into (1) Triassic, (2) Jurassic, and (3) Cretaceous periods. This was the age of reptiles, the group reaching its culmination in the Cretaceous, some of the species being of gigantic size. The mammals appear in the Triassic, but they are few in number and are rare in the other Mesozoic rocks. The earliest known birds are in the Jurassic. IV. Ca@nozotic AGE. Divided into (1) Eocene, (2) Miocene, (3) Pliocene, (4) Pleistocene, and (5) Recent periods. The first three periods are grouped as the Tertiary the other two as the Quaternary divisions. The Cenozoic is pre-eminently the age of mammals. EVOLUTION. It was long thought that the million or more different species of animals on the earth (and the same is true of plants) were specially created and placed in conditions best adapted for them, but with deeper knowledge this view has now become obsolete. At the beginning of the last century (1809) Lamarck advanced the view that the living species had come into being by modification of pre-existing forms. The time was not ready for this view; the facts had not been accumulated to support it and so it was forgotten, until, in 1859, Darwin published his “Origin of Species,’’ which put the theory of evolution upon a firm basis, and which since that time has influenced almost every line of human thought, and has been accepted by every zoologist, in its broader features, although there EVOLUTION. 415 are details which are still in dispute. Some of the factors may be outlined here. Fertility and the Struggle for Existence—Animals tend to multiply in a geometrical ratio, the number of individuals in any generation being the number in the preceding multiplied by the number of young produced. This rapidly results in enormous numbers. Thus Darwin has estimated that the progeny of a single pair of elephants, the slowest breeders among animals, would number 19,000,000 in about 750 years. In other animals the rate is far more rapid. The dogfish (Acanthias) breeds at the age of two years and produces, on the average, six young at a birth. The English sparrow breeds four times a year, laying six eges in a clutch. The full-grown codfish produces over a million eggs a year. With many lower animals the rate of increase is even greater. Maupas states that if the Protozoan he studied were to continue to reproduce at ‘its most rapid rate, the result, in thirty-eight days, would be a mass of Protozoa equalling the sun in size. We know, however, that there is no such actual increase in the number of individuals. In fact, from year to year the number of any species varies but little. In other words, the great majority of eggs or young pro- duced fail to come to maturity, but die at an early age. Only a small minority survives. There is constantly a struggle for existence with every species, and it is evident that, in the long run, only those best fitted for their sur- roundings will survive, while those less fit will perish. In fact, even a very slight difference may determine the fate of the individual. This struggle may be between (1) individuals of the same species; (2) between different species which prey upon or serve as food for each other; 416 GENERAL ZOOLOGY. or (3) between the individual and its environment. In what way is difference in fitness brought about? Variation.—Animals and plants are continually vary- ‘ing. Children of the same parents differ from their father and mother and from each other in size, features, color of eyes and hair, as well as in mental characteristics. The differences may be slight, but still they are notice- able. So, too, the chickens of a brood, the kittens of a litter, the caterpillars from an egg cluster are not exact repetitions of one another, but each has its own indi- viduality. The same is true of every animal and every plant. These variations between the individuals of a species would naturally be in different directions. Some individ-. uals would differ from the rest in such a way as to fit them better for their surroundings. They might have keener senses or quicker motions and thus be better adapted to obtain their food or to escape their enemies, On the other hand others might vary in such a way as to be handicapped in the struggle for existence. In such a severe contest as is going on, where only a small fraction of a generation can survive, any advantage, however slight, may decide the question of life or death. It logically follows that in the long run only those whose variations have been in a beneficial direction will arrive at maturity, and that only those which have thus varied to some ex- tent, however slight, from their ancestors, will produce the next generation. There may be two kinds of variation. In the first the modifications from the ancestor may arise from the germ-cells (eggs and spermatozoa) and be in no way de- pendent upon external conditions. Thus the markings of a litter of kittens the differences between twins, are EVOLUTION. 417 readily seen to be independent of any variation in con- ditions and can only be explained by differences in the germ-cells from which they arise. Such modifications are called congenital variations. The second, or so-called acquired variations, depend upon external conditions. Two plants from the same lot of seeds will present con- siderable differences provided one be well fed while the other is placed in soil deficient in nutrition. So, too, use and disuse of parts, differences of temperature, of moist- ure, etc., will produce variations. Another and an important factor is heredity. Certain of these variations will be inherited. The congenital varia- tions certainly are; there is a question as to the trans- missibility of those which are called acquired.. Now, with constant variations in different directions, the con- stant elimination of the unfit, and the inheritance of those variations which have been of benefit, the appear- ance of the species will gradually change; and since different kinds of beneficial variation may occur, the result will be to split the originally homogeneous species into races. A continuation of the process will produce such divergences that the resulting forms must be regarded as distinct species, genera, and higher groups. The process is aided by other factors. If the varying forms be in such position that they can interbreed, there will be a constant tendency towards the disappearance of the variation. But if they be isolated, the chances of a favorable variation being perpetuated will be greatly increased. Such isolation is brought about when birds, blown out to sea, have colonized a distant island, or where, as has frequently happened, the sea divides an area of land inhabited by a species into two distinct tracts. As a rule this evolution is progressive, the new forms 418 GENERAL ZOOLOGY. are higher and more differentiated than their ancestors, but occasionally—and usually the result of parasitism— degeneration occurs and organs not needed for the para- sitic life gradually disappear. Almost all phases of this can be seen in the parasitic crustacea (p. 222) from forms where the degeneration has just begun to those in which, in the adult female, every crustacean feature has disap- peared and the position of the species in the class is only recognized from the young. In the cestode worms (p. 181) degeneration has gone even further and the ancestral features have been lost from the development. Carrying these ideas of evolution to their logical con- clusion, it follows that all the millions of species now on the earth, or which have lived on it in the past, have arisen from a few original forms, and that these ancestors must have been very primitive in their structure. The farther back the divergence between two forms took place the wider are the groups apart, while those more closely allied must have separated in more recent times. It also follows that our systems of classification should aim to express the lines and degrees of blood-relationship, like a genealogical tree. A third conclusion is that the totality of organization is an adaptation to the surroundings, and hence not infrequently similarities between two species in certain matters of detail are to be explained, not as inheritances from a common ancestor, but ‘as having arisen independently in response to external conditions. The theory of evolution explains many things otherwise inexplicable. It tells us why there has been a regular succession of animals in the past, as revealed to us in the rocks, where we find a gradual progress from the simple to the complex. It explains the peculiarities of geo- graphical distribution when taken in connection with EVOLUTION. 419 what we know of the past and present relations of land and sea areas. It gives a meaning to many of the facts of embryology, such as the occurrence in the young of the human being of branchial arteries similar in number and relations to those of the fish, the larger part of which disappear in the adult. In short, evolution gives to biological study and to our conceptions of nature a depth — which nothing else can supply. INDEX. Abalone, 199 Abdomen of arthropods, 217 Abducens nerve, 300 Aboral, 110, 276 Abyssal fauna, 412 Acanthias, dissection of, 15 Acanthoderus, 245 Acanthopteri, 331 Acarina, 234 Accessorius nerve, 300 Acephala, 202 Acerata, 231 Acetabulum, 38 Acipenser, 326 Acmeza, 199 Acorn barnacle, 224 Acquired variations, 417 Actinozoa, 171 Adambulacral areas, 275 Adam’s apple, 309 Adductor muscles, 99 Adrenal gland, 34 Afferent arteries, 18, 27, 311 Afferent nerves, 298 Aglossa, 341 Air-bladder, 26, 310, 320 Air-saes, 50, 351 Ala spuria, 49 Albatross, 358 Alcohol, 5 Alligators, 349 Alpaca, 385 Alternation of generations, 167, 408 Altrices, 352 Alum cochineal, 9 Alytes, 341 Ambergris, 379 Ambulacra, 110, 274 Ambulacral areas, 113, 115, 275 Ambulacral groove, 113 Ambulacral plates, 113 Ambulacral pores, 113 Ambulacral system, 274 Ametabola, 241 Ammonites, 211 Ameeba, 148 Amoeba, study of, 132 Amphibia, 336 Amphiccelous, 27, 292 Amphioxus, 289 Amphineura, 197 Amphipoda, 230 Amphitrite, 186 Ampulle, 111, 117, 275 Ampulle of sponge, 130, 159 Anacanthini, 329 Anaconda, 347 Anal area, 116 Anal cereus, 77 Anal fin, 16, 23 Anal plates, 116 Analogy, 144 Angle-worms, 187 Angulare, 39 Animal Kingdom, 137 Animals and Plants, 137 Annelida, 183 Anodonta, 98 Anolis, 346 Anomura, 226, 227 Ant-eaters, 372, 374 421 422 Antelope, 386 Antenne, 69, 79, 219 Antennulz, 69 Antilocapra, 387 Ant-lion, 248 Ants, 255 Ants, white, 247 Anura, 341 Aorta, 18 Aortic arch, 35, 58 Apes, 390 Aphides, 260 Apoda, 284 Aptenodytes, 358 Apus, 222 Aqueous humor, 304 Arachnida, 232 Araneida, 233 Arbacia, 115 Arbor vite, 62 Archean age, 413 Archeopteryx, 355 Arch, aortic, 35 Arch, branchial, 19, 24 Arch, hzemal, 20, 27 Arch, hyoid, 19 Arch, neural, 20 Arch, pelvic, 37 Arctic region, 411 Argynnis, 266 Aristotle’s lantern, 117, 281 Armadillos, 372 Army-worm, 262 Arterial blood, 321 Arterial bulb, 26 Arterial trunk, 311 Arthrobranchiz, 69 Arthropoda, 215 Artiodactyla, 383, 385 Ascon, 158 Asexual reproduction, 405 Asiphonida, 204 Asses, 384 Assimilation, 139, 396 Asterias, 110 Asteroidea, 276 Atlas, 38, 365 Atrium, 309 Atrophy, 70, 215 INDEX. Auditory nerve, 21 Auks, 358 Aurelia, 174 Auricle, 18, 26, 59, 310 Australian region, 409, 410 Aves, 350 Axial skeleton, 290 Azoic age, 413 * Baboon, 391 Back-bone, 290 Bacon-beetle, 251 Balancers, 237, 267 Baleen, 380 Barnacles, 224 Basilisk, 345 Basiopod, 67 Basket-fish, 279 Bath-sponge, 130 Bats, 376 Beach-flea, 230 Bean-weevil, 253 Bears, 388 Beaver, 376 Bedbug, 258 Bee-moth, 264 Bee, study of, 87 Bees, 256 Beetles, 250 Bicuspids, 367 Bilateral symmetry, 404 Bile-duct, 56 Biloculina, 148 Bird, dissection of, 48 Birds, 350 Birds of Paradise, 363 Bison, 386 Blackfish, 379 Black-snake, 347 Blindfish, 328 Blindworms, 340 Blister-beetle, 253 Blood, 314 Blood-corpuscles, 35 Blow-fly, 268 Bluefish, 331 Boa, 347 Body-cavity, 17, 25, 405 Body-layers, 154 INDEX. Bojanus, organ of, 100, 204 Bombycid moths, 265 Bony-fish, dissection of, 22 Bony fishes, 326 Borax carmine, 9 Bot-fly, 268 Bowfin, 326 Brachial plexus, 63 Brachiocephalic artery, 58 Brachiopoda, 190 Brachyura 226, 228 Brain of vertebrates, 298 Branchie of lobster, 69 Branchiz of molluses, 194 Branchiz of starfish, 111 Branchial apparatus, 24 Branchial arch, 19, 24 Branchial arteries, 18, 311 Branchial chamber, 194 Branchial clefts, 16 Branchial heart, 105, 195 Branchial tree, 112, 277 Branchiostegal membrane, 24 Branchiostegal rays, 24 Branchipus, 221, 222 Bristletails, 243 Brittle-stars, 278 Brood-pouch, 73 Bruchus, 253 Bryozoa, 189 Buccal mass, 106 Budding, 406 Buffalo, 386 Buffalo-bug, 251 Bufonide, 341 Bugs, 257 Duibus, 311, 321 Buthus, 232 Butterflies, 261, 265 Butterfly, study of, 90 Buzzards, 360 Byssus, 206 Cabbage butterflies, 266 Caddis-fly, 248 Ceecilia, 340 Cecum of rat, 54 Czenozoic age, 414 Calcarea, 160 Calcareous sponge, 130 Calyx, 279 Cambrian period, 413 Camel, 386 Cancer, 229 Canine teeth, 367 Canker-worms, 264 Cannon-bone, 384 Capillaries, 310 Capybara, 375 Carapax, 44, 69, 218, 318 Carboniferous period, 413 Cardiac part of stomach starfish, 276 Carina, 354 Carmine, 261 Carnivora, 387 Carotid artery, 19, 59 Carp, 328 Carpals, 297 Carpus, 38 Carrion-beetles, 251 Case-fly, 248 Cassowary, 356 Caterpillar, 261 Caterpillar-hunters, 251 Catfishes, 327 Cats, 388 Cattle, 386 Caudal fin, 16, 23, 318 Caudal region, 292 Caviare, 326 Cecropia-moth, 265 Cell organs, 145 Cells, 140, 156 Centipedes, 235 Centrosome, 141 Centrum, 27, 291 Cephalopoda, 208 Cephalothorax, 67 Cercaria, 180 Cerebellum, 20, 28, 299 Cerebral ganglia, 100 Cerebral hemispheres, 28 Cerebrum, 20, 28, 299 Cervical region, 292 Cervical suture, 70 Cestoda, 181 Cetacea, 378 423 of 424 Chet, 92, 185 Cheetopoda, 185 Chameleon, 346 Chele, 68 Chilomonas, 150 Chilomycterus, 333 Chilopoda, 235 Chimera, 325 Chimpanzee, 392 Chinch-bug, 258 Chinchilla, 375 Chiroptera, 376 Chiton, 197 Chloragogue organ, 94 Chordata, 286 Choroid, 304. Chromatophores, 103, 209 Chrysalis, 262 Cicada, 259 Cilia, 134, 145, 149 Circulation, 311, 397 Cirripedia, 224 Clam, dissection of, 98 Clams, 207 Clamatores, 361 Clam-worm, 185 Class, 143 Classification, 142 Clava, 125 Clavicle, 37, 296 Clitellum, 92 Cloaca, 130, 159, 307, 342 Cloacal chamber, 100, 287 Clothes-moth, 264 Clupea, 329 Clypeastroidea, 281 Clypeus, 79 Coati, 388 Coccide, 261 Cochineal, 261 Cockroaches, 243, 245 Cod, 329 Codling-moth, 264 Coelenterata, 162 Ceeliae axis, 18, 55 Coelom, 17, 25, 274, 405 Ccelomic pouches, 183 Coleoptera, 250 Colon, 54 INDEX. Colonies, 164, 406 Colorado potato-beetle, 252 Colors, conventional, 4 Columbine, 3C0 Comatula, 279 Commissures, 71 Compound eyes, 70, 78, 217 Condyles, 365 Cone-shells, 200 Coney, 382 Congenital variations, 417 Conjugation, 142, 150 Connective tissue, 54 Contractile vacuole, 133, 146 Conurus, 361 Conus, 311, 321 Conventional colors, 4 Convergent evolution, 418 Copepoda, 222 Coracoid, 37, 296 Coracoid process, 370 Coral. 172,178 Corium, 318 Cormorants, 358 Cornea, 107, 304 Corpora restiformia, 20 Corpus callosum, 62 Corpuscles of blood, 314 Corydalis, 249 Cowries, 200 Coypu, 375 Coxa, 77 Crabs, 228 Cranes, 359 Crangon, 227 Cranium, 293 Cranium of fish, 29 Cranium of frog, 38 | Crayfish, dissection of, 67 _ Cretaceous period, 414 _ Cricket, study of, 84 Crickets, 243, 246 Crinoidea, 279 Crocodilia, 349 Crop, 50, 81, 305, 351 Croton bug, 245 Crows, 363 Crustacea, 218 Ctenoid seale, 23, 318 Ctenolabrus, 332 Ctenophora, 174 Cuckoos, 360 Cucumaria, 283 Cucumber-beetles, 252 Cunner, 332 Cuttle-bone, 209 Cycloid scale, 23, 318 clops, 223 Cyclostomata, 315 Cypris, 224 Cytology, 140 Cytopharynx, 134 Cytostome, 134 Crystalline style, 101, 204 Dactylocalyx, 160 Daddy-longlegs, 234 Dasypus, 373 Day-flies, 247 Dealers in material, 5 Decalcifying fluid, 8 Decapoda, 211, 226 Deer, 386 Degeneration, 418 Dental formula, 368 Dentary bone, 24, 39 Dentine, 375 Derma, 363 Dermal tooth, 17 Devil-fish, 324 Devonian period, 413 Diaphragm, 56, 309 Diastole, 134 Dibranchiata, 211 Didelphys, 371 Diencephalon, 299 Differentiation, 145 Difflugia, 148 Digestion, 396 Digger-wasps, 255 Digit, 38 Digitigrade, 388 Dimorphism, 406 Dinosaurs, 349 Diotocardia, 199 Diplopoda, 235 Diphycercal, 318 Dipnoi, 334 INDEX. 425 Diprotodon, 372 Diptera, 267 Directives, 122 Dissecting-pan, 3 Dissipiments, 93 Distribution, geographical, 409 Distribution, geological, 413 Dobson, 248 Dodo, 360 Dog-day locust, 259 Dogfish, dissection of, 15 Dogs, 388 Dolphin, 379 Doris, 200 Dormice, 375 Dorsal aorta, 18 Dorsal fin, 16, 23 Doryphora, 241 Dragon-flies, 246 Dragon-fly, study of, 86 Drills, 200 Duckbill, 369 Ducks, 358 Dugong, 380 Dura mater, 61 Eagles, 359 Ear, 69, 302 Earthworm, dissection of, 92 Earthworms, 187 Eastern region, 411 Echinarachnius, 282 Echinoderma, 273 Echinoidea, 280 Ectoderm, 125, 154 Ectosare, 132 Edentata,.372 Educabilia, 378 Eels, 329 Efferent arteries, 19, 27, 311 Efferent nerves, 298 Egg, 126, 141 Keret, 359 Elasmobranchii, 322 Hlectric-light bugs, 258 Elephants, 381 Elytra, 238, 250 Embiotocide, 332 Emeu 356 426 3 INDEX. Enamel, 375 Endopod, 67, 219 Endosare, 132 Energy, source of, 395 English sparrow, 363 Entoderm, 125, 154 Entomostraca, 222 Entosare, 132 Eocene period, 414 Epeira, 233 Epicranium, 78 Epidermis, 318 > Kpiglottis, 60 Hpencephalon, 299 Ermine, 388 Errantia, 185 Ethiopian region, 409, 410 Kupagurus, 228 Eustachian tube, 33, 303 Eutheria, 370 Euthyneura, 198, 200 Everyx, 265 Evolution, 414 Excretion, 400 Excretory organs of vertebrates, 314 Excurrent canals, 130 Exoccipital bones, 38 Exopod, 67, 219 External meatus, 353 Exumbrella, 127 Eye-muscles, 305 HKyes of arthropods, 217 Eyes of fish, 23 Eyes of molluscs, 196 Hyes of vertebrates, 303 Eyes, simple and compound, 217 Face, 293 Facial nerve, 21, 300 Fairy shrimp, 221, 222 False diaphragm, 26 Family, 143 _ Fat body of grasshopper, 80 Feather tracts, 49, 350 Feathers, 350 Feathers, kinds of, 48 Femur, 38, 77, 297 Ferrets, 388 Fertility, 415 Fertilization, 142 Fibula, 45, 297 Fins, 16, 23, 318 Firefly, 251 Fishes, 317 Fish-lice, 222 Fission, 405 Fissipedia, 388 Flagella, 149 Flagellata, 151 Flamingo, 359 Flatfish, 330 Flatworms, 178 Flies, 267 Flipper, 378 Flounders, 330 Fluke, liver, 180 Flukes of whale, 379 Fly-catchers, 363 Flying foxes, 378 Food vacuole, 133 Foot of molluse, 193 Foramen magnum, 38 Foraminifera, 148 Formol, 6 Four-legged butterflies, 266 Fowl, 357 Foxes, 388 Frog, dissection of, 32 Frogs, 341 Fronto-parietals, 38 Furcula, 51, 297, 354 Gadus, 330 Gall-bladder of fish, 25 Gall-bladder of rat, 56 Gall-flies, 254 Gallinago, 359 Gammarus, 230 Ganglia, 71, 184 Ganglion, 36 Ganoid scales, 318 Ganoidei, 325 Garpikes, 326 Gastral cavity, 127 Gastric artery, 55 Gastric ceca, 80 Gastric vein, 55 INDEX. 427 Gastropoda, 197 Grouse, 357 Gavials, 349 Guinea-pigs, 375 Geese, 358 Gullet, 305 Gemmation, 406 Gulls, 358 Generations, alternation of, 167, 408 Haddock, 329 Genital plates, 116 Hemal arch, 20, 27, 291 Genus, 143 Heemal process, 27 Geographical distribution, 409 Hezemal spine, 27 Geological distribution, 413 Hagfish, 315 Geometrid moths, 264 | Hair, 363 Geophilus, 235 Hairworms, 182 Gila monster, 345 Half-apes, 390 Gill-arches, 294 Halibut, 330 Gill-bailer, 69 Haliomma, 149 Gill-bars, 294 Hares, 375 Gill-chamber of lobster, €9 Harvestmen, 234 Gill-clefts, 24 Haustellate, 240 Gill-cover, 24, 308 Hawk-moths, 264 Gill-filaments, 24 Hawks, 360 Gill-opening, 24 Hazelnut-weevil, 250 Gill-slits, 16, 19, 286 Head of arthropods, 46 Gills of lobster, 69 Head kidneys, 26 Gills of molluses, 194 Heart of clam, 99 Gills of vertebrates, 307 Heart of fish, 26 Girdle, pectoral, 18 Heart of grasshopper, 80 Girdles, 296 Heart of lobster, 71 Gizzard, 50, 306, 351 Heart of molluses, 95 Glass-snake, 345 Heart of rat, 58, 59 Glenoid fossa, 37 Heart of shark, 18 Globigerina, 148 Heart-urchins, 282 Glossopharyngeal nerve, 62, 300 | Hellgrammites, 248 Glottis, 309 Hemimetabola, 241 Glottis of frog, 33 Hemiptera, 257 Glottis of rat, 60 Hepatic artery, 55 Glyptodon, 372 Hepatic ceca, 111, 277 Gnathostomata, 317 Hepatic duct, 112 Goats, 387 Hepatic veins, 57 Goldfish, 328 Heredity, 417 Gonads, 18 Hermit-crabs, 227 Gonionemus, 127 Herons, 359 Goose-barnacle, 224 Herring, 329 Gophers, 376 : Hesperornis, 355, 356 Gorilla, 392 Heterocercal fins, 16, 23, 318 Grallatores, 359 Heteropoda, 200 Grantia, 130 Heteroptera, 258 Grasshopper, dissection of, 76 Hexacoralla, 173 Grasshoppers, 243, 246 Hexapoda, 236 Green gland, 71, 218, 220 Hippocampus, 335 428 INDEX. Hippopotamus, 385 Hirudinei, 187 Holocephahi, 325 Holometabola, 241 Holothuridea, 282 Homocercal fins, 16, 23, 318 Homology, 144 Homoptera, 258 Hornbills, 361 Horned pout, 327 Horned toads, 346 Hornets, 255 Horse-mackerel, 331 Horses, 384 Horseshoe-crab, 231 Imago, 262 Incisors, 367 Individual, 406 Ineducabilia, 378 Infusoria, 149 Injecting, 6 Injection mass, 7 Ink-sae, 104 Insecta, 235 Insectivora, 376 Insects, classification, 242 Instruments, 3 Interambulacral arees, 275 Interambulacrals, 113, 115 Intercostal muscles, 309 House-fly, 268 Howlers, 391 Humerus, 38 Humming-birds, 362 Hyenas, 388 Hydra, 167 Hydranth, 123, 164 Hydride, 167 Hydrocaulus, 123 Hydroid, study of, 123, 125 Hydroid medusa, study of, 127 Hydromeduse, 167 Hydrorhiza, 125 Hydrozoa, 165 Hylide, 341 Hymenoptera, 253 Hyoid arch, 19 Hyoid bone, 60, 294 Hyomandibular, 294 Hypertrophy, 70, 77, 215 Hypoglossal nerve, 300 Hypophysis, 62 Hyracoidea, 382 Hyrax, 382 Ibis, 359 Tchneumon-flies, 254 Ichthyopsida, 317 Ichthyosaurs, 349 Idotea, 230 Iliac artery, 56 Jliae vein, 56' Tlio-lumbar vein, 56 Tlium, 296 . Interradial, 110 Io-moth, 265 Tris, 107, 304 Ischium, 296 Isinglass, 326 Isopoda, 230 Isthmus, 24 Jackals, 388 Jellyfish, 164, 173 Jugular veins, 50, 58 Jumping mice, 376 June-bug, study of, 85 June-bugs, 252 Jurassic period, 414 Kangaroos, 372 Kidneys, 314 Kidneys of dogfish, 18 Kidneys of fish, 26 Kidneys of rat, 56, 57 Kiwi, 356, Kogia, 378 Labrum, 79 Lac, 261 Lacertilia, 345 Lacune, 220 Ladybugs, 251 Lamellibranchs, 202 Lampreys, 315 Lamp-shells, 190 Lancelet, 289 | Larva, 241, 250, 408 Larynx, 60 Lateral line, 20, 23 Lateral-line organs, 300 Layer, supporting, 162 Layers of body, 154 Leaf-hoppers, 260 Leeches, 187 Lemmings, 375 Lemurs, 390 Lens, 107 Lepas, 224 Lepidoptera, 261 Lepidosteus, 326 Lepisma, 243 Leptocardii, 289 Leucania, 262, 263 Leucocytes, 314 Lice, 261 Lice, fish, 222 Limax, 201 Limpets, 199 Limulus, 231 Lines of growth, 98, 194 Lingual ribbon, 106, 195 Lion, 388 Liver-fluke, 180 Lizards, 345 Llama, 385 Lobosa, 148 Lobster, dissection of, 67 Lobsters, 226 Locomotion, 402 Locusts, 243, 246 Long-horn beetles, 252 Loons, 358 Lophobranchii, 333 Luna-moth, 265 Lung-fishes, 334 Lung of molluses, 195 Lymph hearts, 32 Lymphaties, 55 Macaque, 392 Mackerel, 331 Macrura, 226 Madreporite, 110, 274 Maggots, 267 Malacostraca, 225 Malagassy region, 411 INDEX. Malaria, 152 429 Malpighian tubes, 80, 218, 238 Mammalia, 363 Mammals, age of, 414 Mammoth, 382 Man, 392 Manatee, 380 Mandible of bird, 48 Mandibles of Crustacea, 219 Mandible of frog, 38 Mandibles of insects, 79 Mandibles of lobster, 69 Mandibulate, 240 Mangabey, 392 Manis, 373 Mantle, 99, 193 Mantle artery, 104 Mantle-chamber, 194 Manubrium, 127 Marabou, 359 Marmosets, 391 Marsipobranchs, 316 Marsupial bones, 370 Marsupialia, 370 Marten, 388 Mastodon, 382 Material, dealers in, 5 Maxilla of lobster, 69 Maxille of Crustacea, 217 Maxillary bone, 39 Maxillipeds, 68, 219 May-flies, 247 Meckel’s cartilage, 40 Mediastinum, 57 Medusa, 164, 173 Medusa-buds, 124 Megatherium, 373 Melicertum, 164 Menhaden, 329 Mentomeckelian bone, 39 Merostomata, 231 Mesencephalon, 299 Mesenterial artery, 18, 55 Mesenterial vein, 55 Medulla oblongata, 20, 29, 299 Mesenterial filaments, 122, 169 Mesentery, 17, 26, Ot 12) 4382: 307 Mesoderm, 155 430 INDEX. Mesogloea, 126, 162 Mesonephros, 18 Mesothorax, 77, 237 Mesozoic age, 414 Metacarpals, 297 Metacarpus, 38 Metameres, 67, 183, 215 Metamorphosis, 24, 408 Metatarsals, 297 Metathorax, 77, 237 Metazoa, 154 Metencephalon, 299 Metridium, 120, 173 Mice, 375 Microstomum, 179 Midbrain, 299 Milk dentition; 367 Milkweed-butterfly, 266 Mink, 388 Minnows, 328 Miocene period, 414 Mites, 234 Moccasin, 347 Mola, 334 Molars, 367 Moles, 376 Molgula, 289 Mollusca, 193 Molluscoidea, 189 Monkeys, 390 Monotocardia, 200 Monotremata, 369 Morphology, 403 Mosquitos, 269 Mother of pearl, 206 Moths, 261 Motor nerves, 298 Mourning-cloak, 266 Mouth-parts of Crustacea, 219 Mouth-parts of insects, 79 Mouth-parts of lobster, 68 Miuller’s fluid, 8 Musca, 269 Muscle-plates, 17, 25 Muscle-plates of frogs 33 Muskalonge, 328 Muskrat, 376 Musk-ox, 387 Mussels, 206 Mya, 207 Myelencephalon, 299 Mylodon, 373 Myotomes, 17, 25, 33 Myriapoda, 236 Myrmeleon, 249 Mytilus, 206 Naked molluscs, 200 Nanda, 356 Narwal, 379 Nasal bones, 38 Natatores, 358 Nauplius, 221 Nautilus, 209, 210 Nearctic region, 409, 411 Nebalia, 225 Nemathelminthes, 182 Neotropical region, 409, 410 Nephridium, 95, 184, 220, 314 ephrostome, 185 eptunus, 228 ereis, 185 Vettle-cells, 124, 162 eural arch, 20, 291 Neural process, 27 Neural spine, 27 Neuroptera, 248 Newts, 340 Nictitating membrane, 44, 48, 303 Nidamental gland, 104 Notochord, 19, 42, 286, 290 Notochordal sheath, 19° Nototrema, 341 Nudibranchs, 200 Nucleolus, 126 Nucleus, 126, 133, 140 Nutria, 375 ZAAZAzZA Occipital condyle, 38 Ocelli, 79, 217 Octocoralla, 172 Octopoda, 211 Octopus, 212 Ocular plates, 116 Oculomotor nerve, 300 Odonata, 247 Odontophore, 196, 195 Odontornithes, 356 (Kneis, 267 (Esophageal commissure, 184 (Esophagus, 305 Oil-bottle beetle, 253 Oil-glands, 350 Olfactory lobes, 28 Olfactory membrane, 21 Olfactory nerve, 20, 299 Olfactory organs, 301 Olfactory tract, 20 Oligochetz, 187 Olive-shells, 200 Olynthus, 158 Omenta, 17 Omosternum, 37 Opercular bones, 29 Operculum, 24, 198, 308 Ophidia, 347 Ophiopholis, 278 Ophiuroidea, 278 Opisthobranchia, 200 Opisthoccelous, 292 Opossum, 371 Optic ganglion, 107 Optic lobes, 20, 28, 299 Optic nerve, 20, 300 Optic thalamus, 20 Oral, 276 Oral surface, 110 Orang-utan, 392 Orbit, 46 Order, 1438 Organ of Bojanus, 100 Organ of Corti, 366 Organs, 154, 156 Origin of species, 414 Orioles, 363 Ornithorhynchus, 369 Ornithure, 356 Orthoceratites, 211 Orthoptera, 243 Oscines, 361 Osculum, 158 Ossification, 293 Ostia of heart, 70 Ostium, 130 Ostracoda, 224 Ostriches, 356 INDEX. 43] Otoliths, 302 Otter, 388 Ovary, 315 Oviduct, 34 Ovipositor, 76, 238, 253 Ox-bot, 268 Ox-warble, 268 Oyster, dissection of, 102 Oysters, 204 Pachydermata, 384 Pacific region, 411 Palearctic region, 409, 411 Palate, 60 Palatine bone, 39 Paleozoic age, 413 Pallial line, 101 Pallial sinus, 101 Palpi of clam, 99 Palpus, 79 Pancreas, 17, 34, 55 Pangolin, 373, 374 Panther, 388 Paper nautilus, 209, 212 Paramecium, 134, 151 Parapodia, 185 Parasita, 261 Parasphenoid bone, 39 Parencephalon, 299 Parieto-splanchnic ganglion, 100 Parotid gland, €0 Parrots, 361 Parthenogenesis, 142 Passeres, 361 Pearl-oyster, 205 Pearls, 206 Pearly Nautilus, 209 Pea-weevil, 253 Pecten, 205 Pectoral fins, 16, 23 Pectoral girdle, 18, 296 Pedal ganglion, 100 Pedata, 284 Pelagic fauna, 412 Pelvic girdle, 38, 296 Pen, 107 Pencil, 3 Penguin, 358 Pennaria, 123, 165 432 Pentacrinus, 280 Perch, 332 Pericardial cavity, 18, 26 Pericardium, 195, 310 Perisare, 123, 165 Perissodactyla, 383 Peristome, 115 Peritoneal cavity, 54, 368 Peritoneum, 17, 25, 307 Permanent dentition, 367 Permian period, 413 Petromyzon, 316 Phalangers, 371 Phalanges, 297 Phalangida, 234 Phalangium, 234 Pharyngognathi, 332 Pharynx, 24, 305 Pheasants, 357 Phyllopoda, 222 Phylloxera, 260 Physalia, 168 Physiology, 395 Physostomi, 327 Pickerel, 328 Picrosulphurice acid, 9 Pigeons, 360 Pigs, 385 Pike, 328 Pill-bug, 229 Pinnipedia, 388, 389 Pinworms, 182 Pipa, 341 Pipe-fish, 334 Pisces, 317 Pituitary body, 37 Placenta, 372 Placentalia, 372 Placoid scale, 17, 318 Planaria, 179 Plantigrade, 388 Plant-lice, 260 Plants and animals, 137 Plasma, 314 Plasmodium, 151 Plastron, 44, 348 Plathelminthes, 178 Plectognathi, 333 Pleistocene period, 414 INDEX, Plesiosaurs, 349 Plethodon, 340 Pleural cavity, 57, 368 Pleurobranchiz, C9 Plexus of nerves, 36 Pliocene period, 414 Ploughshare-bone, 353 Pneumogastric nerve, 59, 300 Pocket-rats, 376 Podobranchiz, €9 Poison-fangs, 347 Polian vesicles, 113 Polychetz, 185 Polymorphism, 407 Polyphemus-moth, 265 Polyps, 171 Polyzoa, 189 Pompano, 331 Porcupines, 375 Porgy, 332 Porifera, 158 Porpoise, 379 Portal vein, 55 Portuguese man-of-war, 168 Postcava, 56 Potato-beetle, 241 Poulpes, 212 Precoces, 353 | Prairie-dogs, 376 Prawns, 227 Precava, 58 Premaxillary bone, 24, 39 Premolars, 367 Preoral lobe, 92 Primary feathers, 48 Primates, 390 Pristis, 323 Proboscidia, 381 Proboscis, 123, 127 Process, hemal, 27 Process, neural, 27 Process, transverse, 37 Proccelous, 292 Proglottid, 181 Prometheus-moth, 265 Prootic bone, 39 Prosencephalon, 299 Prothorax, 77, 237 Protoplasm, 126, 139 Protopterus, 335, Protozoa, 144 Proventriculus, 50, 351 Pseudoneuroptera, 246 Pseudopodia, 132, 147 Pseudopleuronectes, 330 Pterodactyls, 350 Pteropods, 201 Pterygoid bone, 39, 294 Pterygoquadrate, 294 Pubis, 296 INDEX. Pulmonary artery, 35, 59, 313 Pulmonary vein, 59 Pulmonata, 201 Pupa, 241, 262 Pupa of beetles, 250 Pupil, 304 Pygostyle, 353 Pyloric ceca, 25, 307 Pyloric part of stomach of star- | fish, 276 _ Pythons, 347 Quadrate, 39, 51, 294 Quadratojugal bone, 39 Quahog, 203 Quaternary, 414 Rabbits, 375 Raccoon, 388 Racemose vesicles, 113 Radial, 110, 113, 127, 174 Radial nerve, 114 Radial symmetry, 404 Radiata, 162, 273 Radii, 275 Radiolaria, 149 Radio-ulna, 38 Radius, 45, 297 Radula, 106, 195 Raia, 323 Raiz, 324 Ranide, 341 Raptores, 359 Rasores, 357 Rat, dissection of, 53 Rats, 375 Rattlesnake, 347 Rays of fins, 23 Recent period, 414 Rectal gland, 17 Rectum, 34, 54 Red coral, 172 Reference-books, 10 Regularia, 281 Remora, 331 Renal artery, 56 Renal vein, 56 Reproduction, 403 433 Reproductive organ of dogfish, 18 Reproductive organs of fish, 26 Reproductive organs of frog, 34 Reptilia, 342 Reptiles, age of, 414 Respiration, 398 Retina, 107, 304 Retractors, 112 Rhea, 357 Rhinoceros, 383 Rhizopoda, 147 Rhynchophora, 250 Ribs, 291 Ring-canal, 127, 166, 274 Ring-nerve, 113 Rodentia, 374 Roots of nerve, 36 | Rose-beetle, 251 | Round worms, 182 Ruminants, 385 Rytina, 380 Sable, 388 Sacral region, 292 Salamanders, 340 Salivary gland, 60 Salmo, 328 Salmon, 328 Sand-cakes, 281 Sand-dollars, 281 Sand-wasp, 256 Sapajous, 391 Sauropsida, 342 Saurure, 355 Savigny’s law, ¢8, 78 Sawfish, 323, 324 Sawflies, 254 Scale-bugs, 261 434 Scales of fishes, 23, 317 Scallops, 205 Scansores, 360 Scaphognathite, 69 Scaphopoda, 201 Scapula, 37, 296 Scarabeans, 252 Sciatic nerve, 36, 63 Sciatic plexus, 63 Sclerotic, 304 Scolex, 181 Scomber, 332 Scorpionida, 232 Scorpions, 232 Scutelle, 347 Scyphomeduse, 173 Scyphozoa, 169 Sea-anemone, dissection of, 120 Sea-anemones, 169, 171 Sea-bass, 332 Sea-cows, 380 Sea-cucumbers, 282 Sea-horse, 334 Sea-lilies, 279 Sea-lions, 390 Sea-peach, 289 Sea-pear, 289 Sea-snake, 348 Sea-squirt, 289 Sea-urchin, 115, 280 Seals, 388 Secondary feathers, 48 Sedentaria, 185 Segmented animals, 404 Segments, 67 Semicircular canals, 302 Semilunar fold, 303 Sensation, 401 Sensory nerves, 298 Sepia, 209, 212 Septa, 93, 121, 169, 183 Serpent stars, 278 Sete, 92, 185 Seventeen-year locust, 259 Sexual dimorphism, 407 Sexual reproduction, 405 Shad, 329 Sharks, 323 Sheep, 387 INDEX. Sheep-bot, 269 Sheepshead, 332 Shell of molluses, 194 Shellac, 261 Shell-gland, 218, 220 Ship-worm, 207 Shore-crab, 229 Shoulder-girdle, 37, 296 Shrews, 376 Shrimp, 227 Silicea, 160 Silkworms, 265 Silurian period, 413 Silver-fish, 243 Sinus venosus, 18 Siphon of Acephala, 202 Siphon of squid, 103, 208 Siphonal cartilages, 104 Siphonata, 207 Siphonoglyphe, 120 Siphonophore, 164 Siphons of clam, 99 Sirenia, 380 Skate, 323, 324 Skeleton of frog, 37 Skeleton of turtle, 45 Skeletons, making of, 32 Skippers, 265 Skull of bird, 51 Skull of frog, 38 Skunks, 388 Sloths, 373 Slugs, 201 Smallpox, 152 Snails, 201 Snake, study of, 47 Snakes, 347 Snipe, 359 Snout-beetle, 250 Soft-shell crab, 228 Somites, 67, 183, 215 Sonoran region, 411 Sow-bug, 229 Sow-bug, study of, 73 Spanish flies, 253 Spatangoids, 282 Specialization, 145 Species, 143 Spermaceti, 379 Spermatozoa, 126, 141 Sphenethmoid bone, 38 Sphex, 256 Sphinx moths, 264 Spicules, 130, 159 Spiders, 233 Spinal accessory nerve, 62 Spinal cord, 19, 298 Spinal nerves, 36, 298 Spine, hemal, 27 Spine, neural, 27 Spinnerets, 233 Spiny ant-eaters, 369 Spiracles, 16, 76 Spiracles of insects, 239 Spiracular cleft, 308 Spiral valve, 17, Spirostrephon, 236 Spittle-insects, 260 Splenic artery, 55 Splenic vein, 55 Splint-bones, 384 Sponge, study of, 130 Sponges, 158 Spongia, 130 Spongida, 158 Sporozoa, 151 Spring-beetle, 251 Spring-tails, 243 Squali, 323 Squamosal bone, 39 Squash-bug, 258 Squash-bug, study of, 89 Squid, 212 Squid, dissection of, 103 Squirrels, 376 Stapes, 366 Starfish, dissection of, 110 Starfish larva, 273 ~ Starfishes, 276 Starling, 363 Stegocephali, 341 Stellate ganglia, 210 Stentor, 151 Sternum, 37, 293 Sting of insects, 238, 254 Stink-bug, 259 Stolon, 165 Stomach of vertebrates, 306 INDEX. Stomach-worms, 182 Stone-canal, 112, 274 Storks, 359 Streptoneura, 198, 199 Strombus, 200 Strongylocentrotus, 115 Struggle for existence, 415 Struthii, 356 Sturgeon, 326 Stylonichia, 150 Subclavian artery, 59 Subelavian vein, 58 Subumbrella, 127 Suckfish, 331 Sunfish, 332, 333 Supporting layer, 126, 162 Supra-anal plate, 77 Supra-renal capsule, 56 Supra-scapula, 37 Surf-fish, 332 Surinam toad, 341 Survival of fittest, 415 Suspensory apparatus, 322 Swallowtail-butterflies, 266 Swans, 358 Sweetbread, 310 Swellfish, 333 Swim-bladder, 310, 320 Swimmerets, 67 Swine, 385 Sword-fish, 331 Sycon, 159 Symmetry, 404 Systemic circulation, 59 Systemic heart, 104, 195 Systole, 134 Tactile, organs, 300 Tadpole, dissection of, 41 Tenia, 181 Tailed birds, 355 Tapeworms, 181 Tapirs, 383 Tarsals, 297 Tarso-metatarsus, 49 Tarsus, 38 Tarsus of insects, 78 Taste-organs, 301 Tautog, 332 435 436 Teeth of mammals, 367 Teleost, dissection of, 22 Teleostei, 326 Telson, 68 Terebratulina, 190 Teredo, 207 Termites, 247 Tertiary, 414 Tertiary feathers, 49 Test, 115 Testis, 315 Testudinata, 348 « Tetrabranchiata, 211 Tetradecapoda, 229 Thalamencephalon, 299 Theca, 167. Thoracic duct, 55 Thorax of arthropods, 216, 237 Thrushes, 363 Thylacine, 371 Thylacoleo, 372 Thymus gland, 58, 310, Thyroid gland, 310 Thysanura, 243 Tibia, 45, 78, 297 Tibio-fibula, 38 Ticks, 2384 Tiger, 388 Tiger-beetles, 251 Tissues, 156 Toads, 341 Tongue of butterflies, 263 Tongue of vertebrates, 305 Toothed birds, 356 Tooth, dermal, 17 Tooth shells, 201 Torpedo, 324 Tortoises, 348 Toucans, 360 Trachea, 60, 309 Trachea of arthropods, 80, 217, 239 Transverse process, 37, 291 Tree-hoppers, 260 Tree-toads, 341 Trematodes, 180 Triassic period, 414 Trichechus, 381 Trichina, 182 INDEX. Trichinosis, 183 Trigeminal nerve, 20, 300 Trilobites, 225 Trochanter, 77 Trochlearis nerve, 300 Trochophore, 186, 197 Tropic bird, 358 Trout, 328 Truncus arteriosus, 18 Trunk-fish, 333 Trunk-region, 292 Tube-feet, 110 Tubicola, 185 Tunicata, 287 Tunny, 331 Turbellaria, 180 Turbot, 330 Turkeys, 357 Turtle, dissection of, 44 Turtles, 348 *Twixt-brain, 20, 24, 299 Tympanic membrane, 33, 303 Tympanic membrane of grass- hopper, 76 | Ulna, 45, 297 Umbo, 98 Uncinate process, 353 ngulata, 383 nio, 98, 206 reter, 34, 56 Jrinary bladder, 34, 54 Jrodela, 310 rostyle, 37 aqqqe¢o Vagus nerve, 21, 59, 300 Valves of shell, 98, 194 Vampyre, 378 Variation, 416 Velum, 127, 166 Venous sinus, 26 Ventral aorta, 18, 26, 310 Ventral fins, 16, 23 Ventricle, 18, 26, 59, 310 Ventricles of brain, 29, 62, 298 Venus, 203 Vermes, 178 Vertebra, 27, 37, 290 Vertebral column, 27 Vertebrata, 290 Villi, 307 Vinegar-eels, 182 Visceral ganglion, 196 Visceral skeleton, 290, 293 Vital force, 139 Vitreous humor, 304 Vocal chords, 61 Vomer, 39 Vorticella, 151 Vultures, 360 Walking-stick, 245 Walrus, 390 Wasp, study of, 87 Wasps, 255 Water-beetles, 251 Water-skaters, 258 Water-snakes, 348 Water vascular system, 117 Weasels, 388 INDEX. 437 Weevils, 250 Whalebone, 380 Whales, 378 White ants, 247 Whitefish, 328 White Mountain butterfly, 267 Wickersheimer’s fluid, 6 Windpipe, 309 Wing coverts, 49 Wireworms, 252 Wishbone, 51, 297, 354 Wolffian bodies, 18 Wolves, 388 Wombat, 371 Woodchuck, 376 Woodpeckers, 361 Worms, 178 Wrens, 363 Xiphisternum, 37 Zooid, 123, 164 a * Banos a tag a ~ Re Nas