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Be e'\"% & >> % Wm AT by ; 5, mits MY SC alac.* = © F . ae - e Mi te " y 1 oe Ae 2s iv = P a A gh ee rey 6 a% aes *. * as “ re Me ae : v4 > * . ae +t k 3) =" Ww & 7% r<- s * a tea) « : ? ig 8 jn roo? a eS J ; 2 at as - 24 an a 4 2 ¢ ” J a & ‘ : a, ’ hy PRA Soy é 4 4 F « 1 4 ye ag . ¥, ,: : » * ™ & . ’ . 2 % * ‘ . a et & te a - ? § : hal * * , ‘ : ’ . ’ é es 4 é P i S Bare & The Prehension of Food........:..-s52....2-2 ee Pee ae 2, ‘Fhe Mouths of Animals... ..........5...3...5. 2422 5D o. he Teeth of Animals. ...éc0..... 2.055. 05000s oe ee 63 4, Deglutition, or How Animals Swallow............... Re. 72 CHAPTER IX. THE ALIMENTARY CANAL... 0.02 cc hoe ccs oc en bebe ds sank 74 CHAPTER X. How: ANIMALS DIGEST.66 ni Oe i ee eee 91 CHAPTER XI. ‘Trem ABSORBENT SYSTEM: . 5 oo sce ss ceeds wou cee be eee eee 94 CHAPTER XII. ‘Tums BLOOD OF ANIMALS i.dee 06) fhe os oh ee ee ee ee 97 CHAPTER XIII. Vee CIRCULATION. OF THE “BpOOD lc 05 4 bt Oe os ws el ee 103 CHAPTER XIV. Tow ANIMALS BREATHE... 2) Srila eee ye oe id CHAPTER XV. SECRETION AND HXCRETION: 22. 2.04.4. 5 ea ee ect fe eke ek ee 121 CHAPTER XVI. ee SKIN AND SKELETON... ios pecan bn oo che ee eee 127 CHAPTER XVII. HOw ANIMALS MOVE: .. 6oceeks Ree ae oe 4 iy dee 1S PART SONG: osc. Fe. ni go Sia ee Die ee eR ee ok koe ae 154 DA OCOMOCION .'s oe)s's vhs he Pu eta toa AC, bb cat ee foe ae> isle) Bateson 157 CHAPTER XVIII THe NERVOUS. SYSTEM 62.0 ove eal tke has bc) ee 166 a: The Senses: 3b eee a ee oe 176 2. Instinct and Intelligence... 0.7. cs ssecse oss. oases se 184 8. The Voices. of. Animales. 34s. ws > <'c5 6 vole dat b pane’ soso 188 CONTENTS. 1X CHAPTER XIX. : 3 PAGE REPRODUCTION............. SPO OS USERS eal i Pied Ge viaie awed. cosine ay ae 191 DEVELOPMENT...........-. SSO’ at Aa A Sere a ala Rn eM gn 197 ne ANTIOTEMGSES cc) Se os chia Sala aps aloe dec eke bang eip sss nae vos 207 oe meltermate Generation. >. 0.0.6 202. h ees too Pa kpc ceuva ety ain See ants 211 BrmerONene ANG OMA see ce a dec one ee es os a's oe te a ... 214 Popbameness arg Variation... 02. acess lke sae eee ae ee wes poten pate 5. Homology, Analogy, and Correlation..................... attacked UPTO Si) iwc ses ahve gs Sb Pane oe Heh ae vidi a doy ay as 220 1 Relations of Number, Size, Form, and Rank...:......2....... 221 evane: Sirugele for Life..........0.-:.. aia a alae Oat 2 ste e 226 PART IL—SYSTEMATIC ZOOLOGY. CHAPTER XXI. Mie MASSIPICATION OF ANIMALS... 0... ..000% cs be cdes custandedesci 231 MRM a a a ashe eka ce pskd inno da vache OG a aw ou ed Oi 238 ee ee eA Dol secs ee eee ood tomas EMG roy acnd 244 eT eee Nae I UW ob a do ole octow ad dae ey eee ee Ralea s 246 INNER Yo ag ipl nar via’ eee 4 60 p a's a ncaa ai ene Ban Vi 257 RCS RES iS Oe ee aie sew na ons DO AAS Cee GME oe 263 POU SEA oe vie vie s/o v0 Nea dee rent a L seahsaperd sol Eero oe een antes 269 RNR eG adel Fs Bake spies «ons s npslebel acu rumen Tum a tien nereeae, « 281 NRE re ee is ies 90, yin wR EE ih oils Se sds 305 RM ME Sa a eho inc Blo ail whee ene yada Re RE eee Bela ss B abel 306 CHAPTER XXII. SYSTEMATIC ARRANGEMENT OF REPRESENTATIVE FORMS............ 362 CHAPTER XXIII. Trim PISTRIBUTION. OF ANIMALS...--02.2-< cece cvcs sccecccee Nae Coaetes 371 NG ees NU ic ag ar eld dl Aa alata ossictatiioe wishin dl sb Oh 0 whe cde eale 381 peer et ee LIDICA RY. 6. ec ese anne chen gecusanancn’ 397 tees acini ley pha Wiss: Aoin'ns <'aiee Ge Uh Ge did viel wo st/casdueees es 399 a oie) Sire & i, Sr nce ha eet INTRODUCTION, 1. Definition of Zoology, and its Place among the Sciences.—The province of Natural History is to describe, compare, and classify natural objects. These objects have been divided into the “organic” and the “inorganic,” or those which are, and those which are not, the products of life. Biology is the science of the former, and Mineralogy the sci- ence of the latter. Biology again separates into Botany, or the Natural History of Plants, and Zoology, or the Natural His- tory of Animals ; while Mineralogy divides into Mineralogy proper, the science of mineral species, and Lithology, the science of mineral aggregates or rocks. Geology is that com- prehensive knowledge of the earth’s structure and develop- ment which rests on the whole doctrine of Natural History. If we examine a piece of chalk, and determine its physical and chemical characters, its mode of occurrence and its uses, so as to distinguish it from all other forms of matter, we have its Mineralogy. But chalk occurs in vast natural beds : the examination of these masses—their origin, structure, po- sition, and relation to other rocks—is the work of the Li- thologist. Further, we observe that while chalk and marble are chemically alike, they widely differ in another respect. Grinding a piece of chalk so thin that we can see through it, and putting it under a microscope, we find imbedded in it innumerable bodies, about the hundredth of an inch in diame- ter, having a well-defined, symmetrical shape, and chambered like a Nautilus. We cannot say these are accidental aggre- gations, nor are they crystals: if the oyster-shell is formed by an oyster, these also must be the products of life. In- deed, the dredge brings up similar microscopic skeletons from the bottom of the Atlantic. So we conclude that chalk is but the dried mud of an ancient sea, the cemetery of count- 19 INTRODUCTION. less animals that lived and died long ago. The considera- tion of their fossil remains belongs to Paleontology, or that part of Biology which describes the relics of extinct forms of life. To study the stratigraphical position of the chalk- bed, and by the aid of its Paleontology to determine its age and part in the world’s history, is the business of Geology. Of all the sciences, Zoology is the most extensive. Its field is a world of varied forms—hundreds of thousands in number. ‘To determine their origin and development, their structure, habits, distribution, and mutual relations, is the work of the Zoologist. But so many and far-reaching are the aspects under which the animal creation may be contem- plated, that the general science is beyond the grasp of any single person. Special departments have, therefore, arisen ; and Zoology, in its comprehensive sense, is the combined re- sult of the labors of many workers, each in his own line of research. | Structural Zoology treats of the organization of animals. There are two main branches: Anatomy, which considers the constitution and construction of the animal frame; and Physiology, which is the study of the apparatus in action. The former is separated into Himbryology, or an account of the successive modifications through which an animal passes in its development from the ege to the adult state; and Morphology, which includes all inquiries concerning the form of mature animals, or the form and arrangement of their or- gans. ‘The microscopical examination of any part, especial- ly the tissues, belongs to Histology. Comparative Zoology is the comparison of the anatomy and physiology of all ani- mals, existing and extinct, to discover the fundamental like- ness underneath the superficial differences, and to trace the adaptation of organs to the habits and spheres of life. It is this comparative science which has led to such grand gen- eralizations as the unity of structure amidst the diversity of form in the animal creation, and by revealing the degrees of affinity between species has enabled us to classify them in - natural groups, and thus laid the foundation of Systematic Zoology. When the study of structure is limited to a par- ticular class or species of animals, or to a particular organ or part, monographic sciences are created, as Ornithotomy, INTRODUCTION. | 13 or anatomy of birds; Osteology, or the science of bones ; -and Odontography, or the natural history of teeth. - Systematic Zoology is the classification or grouping of anl- mals according to their structural and developmental rela- ‘tions. The systematic knowledge of the several classes, as Insects, Reptiles, and Birds, has given rise to subordinate sciences, like Antomology, Herpetology, or Ornithology.'* Distributive Zoology is the knowledge of the successive ap- pearance of animals in the order of time (Paleontology in part), and of the geographical and physical distribution of animals, living or extinct, over the surface of the earth. Theoretical Zoology includes those provisional modes of grouping facts, and interpreting them, which still stand waiting at the gate of science. They may be true, but we cannot say that they are true. ‘The evidence is incomplete. Such are the theories which attempt to explain the origin of life and the origin of species. Suppose we wish to understand all about the Horse. Our first object is to study its structure. The whole body is en- closed within a hide, a skin covered with hair; and if this hide be taken off, we find a great mass of flesh or muscle, the substance which, by its power of contraction, enables the animal to move. On removing this, we have a series of bones, bound together with ligaments, and forming the skel- eton. Pursuing our researches, we find within this frame- work two main cavities: one, beginning in the skull and running through the spine, containing the brain and spinal marrow ; the other, commencing with the mouth, contains the gullet, stomach, intestines, and the rest of the apparatus — for digestion, and also the heart and lungs. Examinations of this character would give us the Anatomy of the Horse, or, more precisely, Hippotomy. The study of the bones alone would be its Osteology ; the knowledge of the nerves would belong to Neurotomy. If we examined, under the microscope, the minute structure of the hair, skin, flesh, blood, and bone, we would learn its Histology. ‘The consid- eration of the manifold changes undergone in developing from the egg to the full-grown animal, would be the Emoéry- * Numbers like this refer to the Notes at the end of the volume. 14 INTRODUCTION. ology of the Horse; and its Morphology, the special study of the form of the adult animal and of its internal organs. Thus far we have been looking, as it were, at a steam- engine, with the fires out, and nothing in the boiler ; but the body of the living Horse is a beautifully formed, active ma- chine, and every part has its different work to do in the working of that machine, which is what we call its life. The science of such operations as the grinding of the food in the complex mill of the mouth ;.its digestion in the labo- © ratory of the stomach ; the pumping of the blood through a vast system of pipes over the whole body ; its purification in the lungs ; the process of growth, waste, and repair ; and that wondrous telegraph, the brain, receiving impressions, sending messages to the muscles, by which the animai is en- dowed with voluntary locomotion—this is Physiology. But Horses are not the only living creatures in the world ; and if we compare the structures of various animals, as the Horse, Zebra, Dog, Monkey, Hagle, and Codfish, we shall find more or less resemblances and differences, enough to enable us to- classify them, and give to each a description which will dis- tinguish it from all others. This is the work of Systematic Zoology. Moreover, the Horses now living are not the only kinds that have ever lived; for the examination of the earth’s crust—the great burial-ground of past ages—reveals the bones of numerous horse-like animals: the study of this pre-adamite race belongs to Paleontology. ‘The chronologi- cal and geographical distribution of species is the depart- ment of Distributive Zoology. Speculations about the ori- gin of the modern Horse, whether by special creation, or by development from some allied form now extinct, are kept aloof from demonstrative science, under the head of Theo- retical Zoology. 2. History.—The Greek philosopher Aristotle (B.c. 384— 322) is called the “‘ Father of Zoology.” Certainly, he is the only great. representative in ancient times, though his fre- quent allusions to familiar works on anatomy show that something had been done before him. His “ History of Animals,” in nine books, displays a wonderful knowledge of external and internal structure, habits, instincts, and uses. His descriptions are incomplete, but generally exact, so far INTRODUCTION. 15 as they go. Alexander, it is said, gave him nine hundred talents to collect materials, and put at his disposal several thousand men, for hunting specimens and procuring infor- mation. ‘The Romans accomplished little in natural science, though their military expeditions furnished unrivalled opportuni- ties. Nearly three centuries and a half after Aristotle, Pliny (A.D. 23-79) wrote his “‘ Natural History.” He was a volu- minous compiler, not an observer : he added hardly one new fact. He states that his work was extracted from over two thousand volumes, most of which are now lost. _ During the Middle Ages, Natural History was studied in the books of the ancients; and at the close of the fifteenth century it was found where Pliny had left it, with the addi- - tion of many vague hypotheses and silly fancies. Albertus Magnus, of the thirteenth century, and Conrad Gesner and Aldrovandus, of the sixteenth, were voluminous writers, not naturalists. In the latter half of the sixteenth century, men began to observe nature for themselves. _ The earliest note- worthy researches were made on Fishes, by Rondelet (1507- 1556) and Belon (1517-1564), of France, and Salviani (1514- 1572), of Italy. They were followed by valuable observa- tions upon Insects, by Redi (1626-1698), of Italy, and Swam- merdam (1637-1680), of Holland ; and towards the end of the same century, the Dutch naturalist, Leeuwenhoeck (1632-1723), opened a new world of life by the use of the microscope. But there was no real advance of Systematic Zoology till the advent of the illustrious John Ray (1628-1705), of Eng- land. His “Synopsis,” published in 1693, contained the first attempt to classify animals according to structure. Ray was the forerunner of “the immortal Swede,” Linneus (1707- 1778), “the great framer of precise and definite ideas of natural objects, and terse teacher of the briefest and clearest expressions of their differences.”” His chief merit was in de- fining generic groups, and inventing specific names.” Scarce- ly less important, however, was the impulse which he gave to the pursuit of Natural History. The spirit of inquiry, which his genius infused among the great, produced voyages of research, which led to the formation of national museums. 16 INTRODUCTION. The first expedition was sent forth by George III. of Eng- land, in 1765. Réaumur (1683-1757) made the earliest zoological collection in France; and the West Indian col- lections of Sir Hans Sloane (1660-1752) were the nucleus of the British Museum. The accumulation of specimens sug- gested comparisons, which eventually resulted in the high- est advance of the science. | : The brilliant style of Buffon (1707-1788) made Zoology popular not only in France, but throughout Europe. While the genius of Linneus led to classification, that of Buffon lay in description. He was the first to call attention to the subject of Distribution. Lamarck (1745-1829), of Paris, was the next great light. The publication of his ‘“ Animaux sans Vertébres,” in 1801, was an epoch in the history of the lower animals. He was also the first prominent advocate of the transmutation of species. But the brightest luminary in Zoology was George Cuvier (1769-1832), a German, born on French soil. Before his time, “there was no great principle of classification. Facts were accumulated, and more or less systematized, but they were not yet arranged according to law ; the principle was still wanting by which to generalize them and give meaning and vitality to the whole.” It was Cuvier who found the key. He was the first so to interpret structure as to be able from the inspection of one bone to reconstruct the entire animal, and assign its position. His anatomical investiga- tions revealed the natural affinities of animals, and led to the grand generalization, that the most comprehensive groups in the kingdom were based, not on special characters, but on different plans of structure. Palissy had long ago (1580) asserted that petrified shells were of animal origin ; but the publication of Cuvier’s “ Memoir on Fossil Elephants,” in 1800, was the beginning of those profound researches on the remains of ancient life which created Paleontology. The discovery of the true relation between all animals, living and extinct, opened a boundless field of inquiry ; and from that day the advance of Zoology has been unparalleled. Special studies of particular parts or classes of animals have so rapidly developed, that the history of Zoology during the last fifty years is the history of many sciences.’ ake a EL. STRUCTURAL ZOOLOGY. The first thing to be determined about a new specimen is not its name, but its most prominent character. Until you know an animal, care not for its name.—AGASSIZ. The great benefit which a scientific education bestows, whether as train- ing or as knowledge, is dependent upon the extent to which the mind of the student is brought into immediate contact with facts—upon the degree to which he learns the habit of appealing directly to N ature.—HUXLEY. COMPARATIVE ZOOLOGY. CHAPTER I. MINERALS AND ORGANIZED BODIES DISTINGUISHED. Nature may be separated into two great kingdoms— that of mere dead matter, and that of matter under the influence of life.‘ These differ in the following points: (1) Composition — While most of the chemical elements are found in different living beings, by far the greater part of their substance is composed of three or four—car- bon, oxygen, and hydrogen; or these three with the addi- tion of nitrogen. Next to these elements, sulphur and phosphorus are most widely distributed, though always found in very small quantities. The organic compounds belong to the carbon series, and contain three, four, or five elements. The former class, comprising starch, sugar, fat, etc., are relatively stable. The latter, possessing the three elements named, with nitrogen and sulphur or phos- phorus, are very complex, containing a very large number of atoms to the molecule, and are usually unstable. Here belong albumen, myosin, chondrin, ete., the constituents of the living tissues. The formula for albumen is said to be O,,H,,.N,,.90,,, or some multiple of this formula. These compounds also contain more or less water, and usually exist in a jelly-like condition, neither solid nor fluid. With these colloid substances alone is life associ- ated. Only these can undergo the rapid decomposition he COMPARATIVE ZOOLOGY. and recomposition necessary to the manifestation of the vital phenomena. (2) Structure— Minerals are homogeneous, while’ organ- ized bodies are usually heterogeneous; 2. ¢., composed of different parts, called tissues and organs, having peculiar uses and definite relations to one another. ‘The tissues and organs, again, are heterogeneous, consisting mainly of microscopic cells, structures developed only by vital ac- tion. All the parts of an organism are mutually depend- - ent, and reciprocally means and ends, while each part of a mineral exists for itself. The smallest fragment of mar- ble is as much marble as a mountain-mass; but the frag- ment of a plant or animal is not an individual. (3) Size and Shape-—Living bodies gradually acquire de- terminate dimensions; so do minerals in their perfect or crystal condition. But uncrystallized, inorganic bodies have an indefinite bulk. Most minerals are amorphous; crystals have regular forms, bounded, as a rule, by plane surfaces and straight lines; plants and animals are cir- cumscribed by curved surfaces, and rarely assume accurate geometrical forms.” (4) Phenomena.— Minerals remain internally at rest, and increase by external additions, if they grow at all. Liv- ing beings are constantly changing the matter of which they are composed, and grow by taking new matter into themselves and placing it among the particles already present. Organized bodies, moreover, pass through a cy- cle of changes—growth, development, reproduction, and death. These phenomena are characteristic of living as opposed to inorganic bodies. All living bodies grow from within, constantly give up old matter and replace it by new, reproduce their kind, and die; and no inorganic body shows any of these phenomena. PLANTS AND ANIMALS DISTINGUISHED. 21 CHAPTER II. PLANTS AND ANIMALS DISTINGUISHED. Ir may seem an easy matter to draw a line between plants and animals. Who cannot tell a Cow from a Cab- bage? Who would confound a Coral with a Mushroom ? Yet it is impossible to assign any absolute, distinctive character which will divide the one mode of life from the other. The difficulty of defining an animal increases with our knowledge of its nature. Linneeus defined it in three words; a century later, Owen declared that a defi- nition of plants which would exclude all animals, or of animals which would not let in a single plant, was impos- sible. Each different character used in drawing the boun- dary will bisect the debatable ground in a different lati- tude of the organic world. Between the higher animals and higher plants the difference is apparent; but when we reflect how many characters the two have in common, and especially when we descend to the lower and minuter forms, we discover that the two “kingdoms” touch, and even dissolve into, each other. This border-land has been as hotly contested among naturalists as many a disputed frontier between adjacent nations. Its inhabitants have been taken and retaken several times by botanists and zoologists; for they have characters that lead on the one side to plants, and on the other to animals. To solve the difficulty, some eminent naturalists, as Hackel and Owen, propose a fourth “kingdom,” to receive those living be- ings which are organic, but not distinctly vegetable or animal. Buta greater difficulty arises in attempting to fix its precise limits. 29, COMPARATIVE ZOOLOGY. The drift of modern research points to this: that there » are but two kingdoms of nature, the mineral and the or- ganized, and these closely linked together; that the lat- _ter must be taken as one whole, from which two great branches rise and diverge. ‘There is at bottom but one life, which is the whole life of some creatures, and the common basis of the life of all; a life of simplest moving and feeling, of feeding and breathing, of producing its kind and lasting its day: a life which, so far as we at present know, has no need of such parts as we call organs. Upon this general foundation are built up the manifold special characters of animal and vegetable existence ; but the tendency, the endeavor, so to speak, of the plant is one, of the animal is another, and the unlikeness between them widens the higher the building is carried up. As we pass along the series of either [branch] from low to high, the plant becomes more vegetative, the animal more animal.” ° ) | Defining animals and plants by their prominent char- acteristics, we may say that a living being which has cell- walls of cellulose, and by deoxidation and synthesis of its simple food-stuffs produces the complicated organic sub- stances, is a plant; while a living being which has albu- -minous tissues, and by oxidation and analysis reduces its complicated food-stuffs to a simpler form, is an animal. But both definitions are defective, including too many forms, and excluding forms that properly belong to the respective kingdoms. No definition is possible which shall include all animals and exclude all plants, or vice versa. (1) Origin both branches of the tree of life start alike: the lowest of plants and animals, as Protococcus and Gre- garina, consist of a single cell. In fact, the cycle of life in all living beings, high or low, begins in a small, round particle of matter—in plants called an ovule, in animals PLANTS AND ANIMALS DISTINGUISHED. 23 an ovum. This cell contains a semi-fluid, called proto- plasm, similar in composition and in function. In the very simplest forms the protoplasm is not enclosed by a membrane, but generally there is a cell-wall. In plants, with few exceptions, this wall is of cellulose, a substance akin to starch; in animals, with few exceptions, the wall is a pellicle of firmer protoplasm, 7. é., albuminous. (2) Composition — Modern research has broken down the partition between plants and animals, so far as chemical nature is concerned. The vegetable fabric and secretions may be ternary or binary compounds; but the essential living parts of plants, as of animals, are quaternary, con- sisting of four elements—carbon, hydrogen, oxygen, and nitrogen. Oellulose (woody fibre), starch, and chlorophyl (green coloring matter) are eminently vegetable products, but not distinctive; for cellulose is wanting in some plants, as some Fungi, and present in some animals, as Tunicates; starch, under the name of glycogen, is found in the liver and brains of Mammals, and chlorophyl gives color to the fresh - water Polyp. Still, it holds good, generally, that plants consist mainly of cellulose, dextrine, and starch; while animals are mainly made up of albumen, fibrine, and gelatine; that nitrogen is more abundant in animal tissues, while in plants carbon is predominant. (3) Form.—No outline can be drawn which shall be com- mon to all animals or all plants. The lowest members of both have no fixed shape. The spores of Confervee can hardly be distinguished from animalcules; the compound and fixed animals, Sea-mat and Sea-moss (Polyzoa), and Corals, often resemble vegetable forms, although in struct- ure widely removed from plants. Similar conditions of life are here accompanied by an external likeness. In free-living animals this resemblance is not found. (4) Structure—A plant is the multiplication of the unit —a cell with a cellulose wall. Some simple animals have 94 COMPARATIVE ZOOLOGY. a similar simple cellular structure; and all animal tissues, while forming, are cellular. But this character, which is permanent in plants, is generally transitory in animals. In the more highly organized tissues the cells are so united as partly or wholly to lose their individuality, and the characteristic part of the tissue is the intercellular sub- stance, while the cells themselves are small and unimpor- tant, or else the cells are melted together and lose their dividing walls, as in striped mnscles and in nerves. Ex- cepting the lowest forms, animals are more composite than plants, 2. ¢., their organs are more complex and numerous, | and more specially devoted to particular purposes. Rep- etition of similar parts is a characteristic of plants; and when found in animals, as the Angle-worm, is called vege- tative repetition. Differentiation and specialization are characteristic of animals. Most animals, moreover, have fore-and-aft polarity; in contrast, plants are up-and-down structures, though in this respect they are imitated by radiated animals, like the Star-fish. Plants are continually receiving additional members; most animals soon become perfect. (5) Physiology—tIn their modes of nutrition, plants and animals stand widest apart. A plant in the seed and an animal in the egg exist in similar conditions: in both cases a mass of organic matter accompanies the germ. When this supply of food is exhausted, both seek nourish- ment from without. But here analogy ends: the plant feeds on mineral matter, the animal on organic. Plants © have the power to form chlorophyl, the green coloring matter of leaves, which uses the force of the sunlight to form starch out of the inorganic substances—carbon-di- oxide and water. They are able also to form albuminoid matter out of inorganic substances. A very few animals which have a substance identical with or allied to chloro- phyl have the same power,’ but in general animals are de- PLANTS AND ANIMALS DISTINGUISHED. 95 pendent for their food on the compounds put together in plants. Colorless plants, possessing no chlorophyl, feed, like animals, on organic compounds. No living being is able to combine the simple elements—carbon, oxygen, hy- drogen, and nitrogen—into organic compounds. The food of plants is gaseous (carbon dioxide and am- monia) or liquid (water), that of animals usually more or less solid. The plant, then, absorbs these foods through its outer surface, while the animal takes its nourishment in larger or smaller masses, and digests it in a special cav- ity. A few exceptions, however, occur on both sides. Certain moulds seem to swallow their food, and certain animals, as the tape-worm, have no digestive tract. Plants are ordinarily fixed, their food is brought to them, and a large share of their work, the formation of organic compounds, is done by the force of the sunlight; while animals are usually locomotive, must seek their food, and are unable to utilize the general forces of nature as the plant does. The plant is thus able to grow much more than the animal, as very little of the nourishment received is used to repair waste, while in most animals the time soon comes when waste and repair are approximately equal. But in both all work done is paid for by waste of substance already formed. In combining carbon dioxide and water to form starch the plant sets oxygen free (6(CO,) +5(H,O)=C,H,,O,;+ 6(O,)): in oxidizing starch or other food the animal uses oxygen and sets carbon dioxide free. The green plant in the sunlight, then, gives off oxygen and uses carbon diox- ide, while plants which have no chlorophyl, at all times, and all plants in the darkness, use oxygen and give off carbon dioxide, like an animal. Every plant begins life like an animal—a consumer, not a producer: not till the young shoot rises above the soil, and unfolds itself to the light of the sun, at the touch of whose mystic rays chlo- 26 COMPARATIVE ZOOLOGY. rophyl is created, does real, constructive vegetation begin ; then its mode of life is reversed—carbon is retained and oxygen set free. Most plants, and many animals, saralepde by budding and division; on both we practise grafting; in both the cycle of life comes round again to the ovule or ovum. Do annuals flower but to die? Insects lay their eggs in their old age. : Both aa ale and plants have sensibility. This is one of the fundamental physiological properties of proto- plasm. But in plants the protoplasm is scattered and buried in rigid structures: feeling is, therefore, dull. In animals, the protoplasm is concentrated into special or- gans, and so feeling, like electricity rammed into Leyden jars, goes off with a flash.” Plants never possess conscious- ness or volition, as the higher animals do. The self-motion of animals and the rooted state of plants is a very general distinction; but it fails where we need it most. It is a characteristic of living things to move. The protoplasm of all organisms is unceasingly active.? Be- sides this internal movement, myriads of plants, as well as animals, are locomotive. Rambling Diatoms, writhing Oscillaria, and the agile spores of Cryptogams crowd our waters, their instruments of motion (cilia) being of the very same character as in microscopic animals; while Sponges, Corals, Oysters, and Barnacles are stationary. A contractile vesicle is not exclusively an animal prop- erty, for the fresh-water Volvox and Gonium have it. The act of muscular contraction in the highest animal is due to the same kind of change in the form of the cells of the ultimate fibrille as that which produces the sensible motions of plants. The ciliary movements of animals and of microscopic plants are precisely similar, and in neither case indicate consciousness or self - determining power. RELATION BETWEEN MINERALS, PLANTS, ETC. 97 Plants, as well as animals, need a season of repose. Both have their epidemics. On both, narcotic and acrid poisons produce analogous results. Are some animals warm-blooded? In germination and flowering, plants evolve heat—the stamens of the Arum, @. g., showing a rise of 20°. In a sense, an Oak has just as much heat as an Elephant, only the miserly tree locks up the sunlight in solid carbon. At present, any boundary of the Animal Kingdom is arbitrary. ‘‘ Probably life is essentially the same in the two kingdoms; and to vegetable life, faculties are super- added in the lower animals, some of which are, here and there, not indistinctly foreshadowed in plants.” ‘It must be said that there are organisms which at one period of their life exhibit an aggregate of phenomena such as to justify us in speaking of them as animals, while at another they appear to be as distinctly vegetable.” CHAPTER Ll. RELATION BETWEEN MINERALS, PLANTS, AND ANIMALS. THERE are no independent members of creation: all things touch upon one another. The matter of the living world is identical with that of the inorganic. The plant, feeding on the minerals, carbon dioxide, water, and am- monia, builds them up into complex organic compounds, as starch, sugar, gum, cellulose, albumen, fibrine, caseine, and gluten. When the plant is eaten by the animal, these substances are used for building up tissues, repairing waste, laid up in reserve as glycogen and fat, or oxi- dized in the blood to produce heat. The albuminoids are essential for the formation of tissues, like muscle, nerve, 28 COMPARATIVE ZOOLOGY. cartilage; but the ternary compounds help in repairing waste, while both produce heat. When oxidized, whether for work or warmth, these complex compounds break up into the simple compounds — water, carbon dioxide, and (ultimately) ammonia, and as such are returned to earth and air from the animal. Both plant and animal end their life by going back to the mineral world: and thus the circle is complete—from dust to dust. Carbonate of ammonia and water, a blade of grass and a horse, are but the same elements differently combined and arranged. Plants compress the forces of inorganic nature into chem- ical compounds; animals liberate them. Plants produce ; animals consume. The work of plants is synthesis, a building-up; the work of animals is analysis, or destruc- tion. The tendency in plants is deoxidation; the tenden- cy in animals is oxidation. Without plants, animals would perish; without animals, plants had no need to be. There is no plant which may not serve as food to some animal. CHAPTER. fY. LIFE. Aut forces are known by the phenomena which they cause. So long as the animal and plant were supposed to exist in opposition to ordinary physical forces or indepen- dently of them, a wtal force or principle was postulated by which the work of the body was performed. It is now known that most, if not all, of the phenomena manifested by a living body are due to one or more of the ordinary physical forces — heat, chemical affinity, electricity, ete. There is no work done which demands a vital force. The common modern view is that vitality is simply a LIFE. 29 collective name for the sum of the phenomena displayed by living beings. It is neither a force nor a thing at all, but is an abstraction, like goodness or sweetness; or, to use Huxley’s expression, to speak of vitality is as if one should speak of the horologity of a clock, meaning its time-keeping properties. A third theory is still possible. The combination of elements into organic cells, the arrangement of these cells into tissues, the grouping of these tissues into organs, and the marshalling of these organs into plans of structure, call for some further shaping, controlling power to effect such wonderful co-ordination. Moreover, the manifesta- tion of feeling and consciousness is a mystery which no physical hypothesis has cleared up. The simplest vital phenomenon has in it something over and above the known forces of the laboratory.” If the vital machine is given, it works by physical forces; but to produce it and keep it in order needs, so far as we now know, more than mere physical force. ‘To this controlling power we may apply the name wetalety. Life is exhibited only under certain conditions. One condition is the presence of a physical basis called proto- plasm. This substance is found in all living bodies, and, so far as we know, is similar in all—a viscid, transpar- ent, homogeneous, or minutely granular, albuminoid mat- ter. Life is inseparable from this protoplasm; but it is dormant unless excited by some external stimulants, such as heat, light, electricity, food, water, and oxygen. Thus, a certain temperature is essential to growth and motion ; taste is induced by chemical action, and sight by luminous ' vibrations. The essential manifestations of animal life may be re- duced to three: contractility ; sensibility, or the peculiar power of receiving and transmitting impressions; and the power of assuemilating food. All these powers are pos- 30 COMPARATIVE ZOOLOGY. sessed by protoplasm, and so by all animals: all move, feel,and grow. But some of the lowest forms are with- out the slightest trace of organs; they seem to be as per- fectly homogeneous and structureless as a drop of jelly. They could not be more simple. They are devoid of muscles, nerves, and stomach; yet they have all the fun- damental attributes of lite—moving, feeling, and eating. It has been supposed that the muscular and nervous mat- ter is diffused in a molecular form; but all we can say is, that the highest power of the microscope reveals no organ- ized structure whatever—4. e., there are no parts set apart for a particular purpose, but a fragment is as good as the whole to perform all the functions of life. The animal series, therefore, begins with forms that feel without nerves, move without muscles, and digest without a stom- ach: in other words, life zs the cause of organization, not the result of it. Animals do not live because they are or- ganized, but are organized because they are alive. CHAPTER V. ORGANIZATION. We have seen that the simplest life is a formless speck of protoplasm, without distinctions of structure, and there- fore without distinctions of function, all parts serving all purposes — mouth, stomach, limb, and lung — indiscrimi- nately. There is no separate digestive cavity, no separate respiratory, muscular, or nervous systems. Every part will successively feed, feel, move, and breathe. Just as in the earliest state of society all do everything, each does all. Every man is his own tailor, architect, and lawyer. But in the progress of social development the principle of ORGANIZATION. 21 the division of labor emerges. First comes a distinction between the governing and governed classes; then follow and multiply the various civil, military, ecclesiastical, and industrial occupations. In like manner, as we advance in the animal series, we find the body more and more heterogeneous and complex by a process of defferentiation, 2. é., setting apart certain portions of the body for special duty. In the lowest forms, the work of life is carried on by very simple appara- tus.” But in the higher organisms every function is per- formed by a special organ. For example, contractility, at first the property of the entire animal, becomes centred in muscular tissue; respiration, which in simple beings is effected by the whole surface, is specialized in lungs or gills; sensibility, from being common to the whole or- ganism, is handed over to the nerves. An animal, then, whose body, instead of being uniform throughout, is made up of different parts for the performance of particular functions, is said to be organized. And the term is as ap- plicable to the slightly differentiated cell as to complex Man. Organization is expressed by single cells, or by their combination into tissues and organs. 1. Cells.—A cell is the simplest form of organized life. In general, it is a microscopic globule, consisting of a del- icate membrane enclosing a minute por- tion of protoplasm. ‘The very simplest _kinds are without granules or signs of circulation; but usually the protoplasm is vranular, and contains a defined sep- arate mass called the nwuclews, within which are sometimes seen one or two, Fig. 1.—Parts of a Cell: rarely more, dark, round specks, named — a,v,y, cell-wall; p, nu- nucleolt. The enveloping membrane is ‘“?"S* % ?Ecleols: extremely thin and transparent, and structureless: it is only an excretion of dead matter acting as a boundary to 39 COMPARATIVE ZOOLOGY. the cell-contents."* The nucleus is generally attached to the inside of the membrane, and is the centre of activity. Cells vary greatly in size, but are generally invisible to the naked eye, ranging from 54,5 to yoda of an inch in diameter. About 4000 of the smallest would be necessary to cover the dot of this letter 2. The natural form of iso- lated cells is spherical; but when they crowd each other, as seen in bone, cartilage, and muscle, their outlines be- come angular, either hexagonal or irregular. Within the narrow boundary of a simple sphere, the cell-membrane, are exhibited all the essential phenomena of life — growth, development, and reproduction. The physiology of these minute organisms is of peculiar inter- est, since all animal structure is but the multiplication of the cell as a unit, and the whole life of an animal is that of the cells which compose it: in them and by them all its vital processes are carried on.” The structure of a cell can be seen in blood-corpuscles, by diluting with a weak (¢ per cent.) solution of salt a drop of blood from a Frog, and placing it under the mi- croscope. (See Fig. 63.) | 2. Tissues.—There are organisms of the lowest grade (as Gregarwma) which consist of a single cell, living for and by itself. In this case, the animal and cell are identical: the Gregarina has as much individuality as the Elephant. But all animals, save these unicellular beings, are mainly aggregations of cells: for the various parts of a body are not only separable by the knife into bones, muscles, nerves, etc., but these are susceptible of a finer analysis by the microscope, which shows that they arise from the devel- opment and union of cells. These cellular fabrics, called tissues, differ from one another both chemically and struct-_ urally, but agree in being permeable to liquids---a prop- erty which secures the flexibility of the organs so essential to animal life. Every part of the human body, for exam- ORGANIZATION. : 33 ple, is moist: even the hairs, nails, and cuticle contain water. The contents as well as the shape of the cells are usually modified according to the tissue which they form: thus, we find cells containing earthy matter, iron, fat, mu- cus, etc. In plants, the cell always retains the characters of the cell; but in animals (after the embryonic period) the cell usually undergoes such modifications that the cellular form disappears. The cells are connected together or enveloped by an intercellular substance (blastema), which may be watery, soft, and gelatinous, firmer and tenacious, still more solid and hyaline, or hard and opaque. In the fluids of the body, as the blood, the cells are separate; 2. e., the blastema is fluid. But in the solid tissues the cells coa- lesce, being simply connected, as in the epidermis, or united into fibres and tubes. In the lowest forms of life, and in all the higher ani- mals in their embryonic state, the cells of which they are composed are not transformed into differentiated tissues: definite tissues make their first appearance in the Sponges, and they differ from one another more and more widely as we ascend the scale of being. In other words, the bod- ies of the lower and the immature animals are more uni- form in composition than the higher or adult forms. In the Vertebrates only are all the following tissues found represented : | (1) Epithelial Tissue—This is the simplest form of cellu- lar structure. It covers all the free surfaces of the body, internal and external, so that an animal may be said to be contained between the walls of a double bag. That which is internal, lining the mouth, windpipe, lungs, blood-ves- sels, gullet, stomach, intestines—in fact, every cavity and canal —is called epetheliwm. It is a very delicate skin, formed of flat or cylindrical cells, and in some parts (as in the wind-pipe of air-breathing animals, and along the gills 3 | 34 COMPARATIVE ZOOLOGY. of the Oyster) is covered with cilia, or minute hairs, about seoey of an inch long, which are incessantly moving. . Con- 3 tinuous with this in- ner lining of the body (as seen on the lip), and covering the outside, is the epidermis, or cuti- cle. It is the outer layer of the “skin,” which we can re- Fig. 2.—Various kinds of Epithelium Cells: a, colum- move by a blister, be from email intone: ho egal hor! and ia A tubes; d, the same, from the windpipe, with single thickness from —l-~ cell magnified about 200 times; c, squamous, from oieig eyelid of a calf, showing changes of form, from the of an inch on the deep to superficial cells, 1 being the scurf. shea as ie din aE sole of the foot. It is constantly wearing off at the sur- face, and as constantly growing in the deeper portion; and in the process of growth and passage outward, the cells change from the spherical form to dead horny scales (seen in scurf and dandruff). In the lower layer of the cuticle we find the pigment cells, characteristic of colored races. Neither the epidermis nor the corresponding tissue within (epithelium) has any blood-vessels or nerves. The epithe- lial tissue, then, is simply a superficial covering, bloodless and insensible, protecting the more delicate parts under- neath. Hairs, horns, hoofs, nails, claws, corns, beaks, scales, tortoise-shell, the wings of Insects, ete., are modifications of the epidermis. The next three sorts of tissue are characterized by a great development of the intercellular substance, while the cells themselves are very slightly modified. (2) Connective Tissue-——This is the most extensive tissue in animals, as it is the great connecting medium by which the different parts are held together. Could it be taken ORGANIZATION. 35 out entire, it would be a complete mould of all the organs. It surrounds the bones, muscles, blood-vessels, nerves, and glands, and is the substance of the ligaments, tendons, ‘‘trne skin,” mucous mem- brane, etc. It varies in character, being soft, ten- der, and elastic, or dense, tough, and generally un- yielding. In the former state, it consists of innu- merable fine white and yel- low fibres, which interlace in all directions, leaving Fre. 3.—Connective Tissue, showing areolar irregular spaces, and form- | Dee ing a loose, spongy, moist web. In the latter, the fibres Fig. 4.—Connective Tissue from human peritoneum; highly magnified; a, blood- vessel. 36 | COMPARATIVE ZOOLOGY. are condensed into sheets or parallel cords, having a wavy, glistening appearance. Such structures are the fascize and tendons. Connective tissue is not very sensitive. It con- tains gelatene—the matter which tans when hide is made into leather. In this tissue the intercellular substances take the form of fibres. The whzte fibres are inelas- tic, and from gode0 tO ga000 of an inch in diameter. They are best seen in the tendons. The yellow fibres are elastic, curled at the ends, very, long, and from ,,+,5 10 =py¢_0! en nee diameter. They are shown in the hinge-ligament of an Oyster. Connec- tive tissue appears areolar, 2. ¢., shows Fig.5.HyalineCantilage, LAterspaces, only under the microscope. Diagram: a, cartilage (3) Cartilaginous Tissue—Lhis tissue, cell; b, cell about to di- : che vide ; ¢, cell divided into known also as “ gristle,” is composed two; d, into four parts. ° , of cells imbedded in a granular or hy- The space between the cells is filled with trans- : ° ° : ee ee suievcoliaiar ee: aline substance, which is dense, elastic, stance; highly magni- bluish white, and translucent. It is eo found where strength, elasticity, and EU insensibility are wanted, as at the Uh joints. It also takes the place of the ek 2 long bones in the embryo. When ae —=) 3, cartilage is mixed with connective tis- a) ae . sue, as in the ear, it is called jibro- car- =e iy Ws > tlage. “ (4) Osséous Tissue.— This hard, opaque : tt tissue, called ‘ bone,” differs from the ; a “| He y former two in having the intercellular Ai ui Ny ‘ ‘i ye spaces or meshes filled with phosphate ai Ag he of lime and other earths, instead of a WYy, © 4 hyaline or fibrous substance. It may Rae Orsiying Cart be called petrified tissue—the quantity cells, passing into com- of earthy matter, and therefore the brit- pact bone, c, and then k 4 : spongy bone, ¢. tleness of the bone, increasing with the Saws Al Hinge i uit Wy ijt ‘ yet { aD ni i i \ d al i ly} i : we i ORGANIZATION. an age of the animal. If a chicken-bone be left in dilute muriatic acid several days, it may be tied into a knot, since the acid has dissolved Be the lime, leaving noth- ing but cartilage and connective tissue. Ifa bone be burned, it be- comes light, porous, and brittle, the lime alone remaining.” Bone is a very vas- cular tissue; that is, it is traversed by minute oe blood-vessels and nerves, Fie. 7.—Transverse aia a Bone (Human which pass through a _—s Femur), x 50, showing Haversian canals. net-work of tubes, called Haversian canals. The canals average y>/55 of an inch, being finest near the surface of the bone, and larger further in, where they form a cancel- lated or spongy structure, and finally merge (in the long bones) into the central vam TEM cavity, containing the SOY AR ' marrow, Under the eae microscope, each canal oN. Leste appears to be the cen- =) © : ° ? | ce tre of a multitude of = AV ‘ | nf lamine, or plates, ar- pm ranged around it. Ly- ing between these plates are little cavities, called lacune, from which ra- diate exceedingly fine Fig. 8,—Frontal Bone of Human Skull under the POTES, OF canalicult. microscope, showing lacuni and canaliculi. These represent the original cells of the bone, and differ in shape and size in different animals. ; . 38 COMPARATIVE ZOOLOGY. True bone is found only in Vertebrates, or back-boned animals. | (5) Dental Tissue—Like bone, a tooth is a combination of earthy and animal matter. It may be called petrified skin. In the higher animals, it consists of three parts: dentene, forming the body of the tooth, and always pres- ent; enamel, capping the crown; and cement, covering the fangs (Fig. 31). The last is true bone, or osseous tissue. Fig. 9.—Highly magnified section of Dentine and Cement, from the fang of a Human Molar: a, b, marks of the original dentinal pulp; d, dentinal tubes, terminating in the very sensitive, modified layer, g; h, cement. ‘Dentine resembles bone, but differs in having neither la- cunse nor (save in Shark’s teeth) canaliculi. It shows, in place of the former, innumerable parallel tubes, reaching from the outside to the pulp-cavity within. The “ivory” of Elephants consists of dentine. Enamel is the hardest substance in the body, and is composed of minute six-sided fibres, set closely together. It is want- ing in the teeth of most Fishes, Snakes, Sloths, Armadillos, Sperm-whales, ete. True dental tissue is confined to Vertebrates. (6) Adipose Tissue.—Certain cells be- come greatly enlarged and filled with fat, so that the original protoplasm oe- cupies a very small part of the space ees 4 within the cell-membrane. These cells Fig. 10.—Adipose lissue,4; are united into masses by connective with fibres of connective , f : : tissue,b. tissue, in the skin (as in the “blub- S, (ge So \\ N \ i \ ee | VN LY Cii\\ MY | + SB WK = SVEN WAN = 4. (Zl egN \ es SE a \ as \ i NAN ADA & a rad NS £ Ne ) ‘ AN ¥\- SBI, | WB 7 FHT SIGE 2a) a) ba 9 \evel= h Wet y . i iy) \ H\ lal ORGANIZATION. | 39 ber” of whales), between the muscles (as in “streaky” meat), or in the abdominal cavity, in the omentum, mes- entery, or about the kidneys. The marrow of bones is an example. Globules of fat occur in many Molluscs and Insects; but true adipose tissue is found only in back- boned animals, particularly the herbivorous. In the aver- age Man, it constitutes about => part of his weight, and a single Whale has yielded 120 tons of oil. The fat of animals has the different names of oil, lard, tallow, suet, spermaceti, etc. It is a reserve of nutriment in excess of consumption, serving also as a packing material, and as a protection against cold. (7) Muscular Tissue.—If we examine a piece of lean meat, we find it is made up of a number of fasciculz, or bundles of fibres, placed side by side, and bound together by connective tissue. The microscope informs us that each fibre is itself a bundle of smaller fibres; and when one of these is more closely examined, it is found to be enclosed in a delicate, glossy tube, called the sarcolemma. This tube is filled with ee r Fig. 11.—Striated Muscular Fibre (of the Pig) very min ute, parallel x 200. The constituent fibres are seen at re fibrils, averaging pate c is a fasciculus, or bundle. of an inch in diameter, and having a striated aspect. Tissue of this description constitutes all ordinary muscle, or “lean meat,” and is marked by regular cross-lines, or Siri. Besides this striated muscular tissue, there exist, in the coats of the stomach, intestines, blood-vessels, and some oth- er parts of Vertebrates, smooth muscular fibres, or mem- 40 COMPARATIVE ZOOLOGY. branes, which show a nucleus under the microscope, and do not break up into fibrils (Fig. 122). The gizzards of fowls exhibit this form. All muscle has the property of. shorten- ing itself when excited; but the contraction of the striated kind is under the control of the will, while the movement of the smooth fibres is involuntary.’” Muscles are well sup- plied with arteries, veins, and nerves; but the color is due to a peculiar pigment, not to the blood. = i Sac is Bit EY A “us! | i 8 Ts ime | #55, an38 i) PRE wigs sem i i: w= PAT pti ny Ta, UY LXEEN EVOXEANCXXTUFUOLEE Hes OTM rrr iy from the Coral to Man. 1 | San Fig. 12. — Striated Muscular tissue is found in all animals (8) Nervous Tissue.—Nervous matter exists under three forms: First—the cellular, con- sisting of nucleated cells, varying from gyn Muscular Fibres, to 45 of an inch in diameter, and found in from the heart of Man, divided by the nerve-centres (Fig. 182), the gray por- transverse septa PC eiiiate nn: tion of the brain, spinal cord, and other gan- cleated portions. olia, Second—the fibrous, consisting of pale, flat, extremely fine filaments. They abound in the sympa- thetic nerves, and are the only nerves found in the Inverte- brates. Third—the tubular. These are much larger than the fibrous, the coarsest being — of an inch in diameter. They consist of tubes enclosing a transparent fibre and a fatty substance called the nerve- marrow.” The delicate tube itself is called neurelem- ma, analogous to the sarcolemma of mus- cular tissue. Nerve-tubes are found only in back-boned animals, in the white sub- stance of the brain, spinal cord, and in the nerves. Fig. 13.—Structure of a Nerve: 1, sheath, or neuri- lemma; .2, med- ullary substance of Schwann; 3, axis cylinder, or ' primitive band. A bundle of fibrous or tubular nervous matter, sur- rounded by connective tissue, constitutes a nerve. ——4 ORGANIZATION. : 41 YAN | 1M > ( Pao lis! N i Wii Ney! SR Se i} st N IW i INE | | tt / V4: A\a) VE SS 7 a \ y ss LN. 5 SSS Ei TT) es, Bi x - Fig. 14.—A Ganglion of the Sympathetic Nerve of a Mouse. 3. Organs,and their Functions.— Animals, like Plants, grow, feel, and move; these three are the capital facts of every organism. Besides these there may be some pecul- jar phenomena, as motion and will. Life is manifested in certain special operations, called Junctions, performed by certain special parts, called or- gans. Thus, the stomach is an organ, whose function is - digestion. A single organ may manifest vitality, but it does not (save in the very lowest forms) show forth the whole life of the animal. For, in being set apart for a special purpose, an organ takes upon itself, so to speak, to do something for the benefit of the whole animal, in return for which it is absolved from doing many things. The stomach is not called upon to circulate or purify the blood. There may be functions without special organs, as the Amoeba digests, respires, moves, and reproduces. by its general mass. But, as we ascend the scale of animal life, we pass from the simple to the complex: groups of cells or tissues, instead of being repetitions of each other, take on a difference, and become distinguished as special parts with specific duties. The higher the rank of the animal, the more complicated the organs. The more complicated the structure, the more complicated the functions. But in 49 | COMPARATIVE ZOOLOGY. all animals, the functions are performed under conditions essentially the same. Thus, respiration in the Sponge, the Fish, and in Man has one object and one means, though the methods differ. A function, therefore, is a group of similar phenomena effected by analogous structures. The life of an animal consists in the accumulation and expenditure of force. The tissues are storehouses of power, which, as they waste, is given off in various forms. Thus, the nervous tissue generates nerve-force; the mus- cles, motion. If we contemplate the phenomena presented by a Dog, the most obvious fact is his power of moving from place to place, a power produced by the interplay of muscles and bones. We observe, also, that his motions are neither mechanical nor irregular; there is method in his movement. He has the power of willing, seeing, hear- ing, feeling, etc.; and these functions are accomplished by a delicate apparatus of nerves. But the Dog does not exhibit perpetual motion. Sooner or later he becomes exhausted, and rest is necessary. Sleep gives only temporary relief. In every exercise of the muscles and nerves there is a consumption or waste of their substance. The blood restores the organs, but in time the blood itself needs renewal. If not renewed, the animal becomes emaciated, for the whole body is laid un- der contribution to furnish a supply. Hence the feelings of hunger and thirst, impelling the creature to seek food. Only this will maintain the balance between waste and repair. We notice, therefore, an entirely different set of — functions, involving, however, the use of motion and will. The Dog seizes a piece of meat, grinds it between its teeth, sends it into the stomach, where it is digested, and then into the intestine, where it is further changed; there the nourishing part is absorbed, and carried to the heart, which propels it through tubes, called blood-vessels, all over the body. In this process of digestion, certain fluids ORGANIZATION. 43 are required, as saliva, gastric juice, and bile: these are secreted by special organs, called glands. Moreover, since not all the food eaten is fitted to make blood, and as the blood itself, in going around the body, acts like a scaven- ger, picking up worn-out particles, we have another func- tion, that of excretion, or removal of useless matter from the system. The kidneys and lungs do much of this; but the lungs do something else. They expose the blood to the air, and introduce oxygen, which, we shall find, is essential to the life of every animal. _ These centripetal and centrifugal movements in the body—throwing in and throwing out—are so related and involved, especially in the lower forms, that they cannot be sharply defined and classified. It has been said that every Dog has two lives—a vegetative and an animal. The former includes the processes of digestion, circulation, respiration, secretion, etc., which are common to all life; the functions of the other, as motion, sensation, and will, are peculiar to animals. The heart is the centre of the vegetative life, and the brain is the centre of the animal life. The aim of the vegetative organs is to nourish the individual, and reproduce its kind; the organs of locomo- tion and sense establish relations between the individual and the world without. The former maintain life; the others express it. The former develop, and afterwards sustain, the latter. The vegetative organs, however, are not independent of the animal; for without muscles and nerves we could not procure, masticate, and digest food. The closer the connection and dependence between these two sets of organs, the higher the rank.” All the apparatus and phenomena of life may be in- cluded under the heads of Nutrition, Motion, SENSATION. —~«A4 COMPARATIVE ZOOLOGY. These three are possessed by all animals, but in a vari- ety of ways. No two species have exactly the same mech- anism and method of life. We must learn to distinguish between what is vital and what is only accessory. That only is essential to life which is common to all forms of life. Our brains, stomachs, livers, hands, and feet are luxuries. They are necessary to make us human, but not living, beings. Half of our body is taken up with a com- plicated system of digestion; but the Amceba has neither mouth nor stomach.. We have an elaborate apparatus of motion; the Oyster cannot stir an inch. Nutrition, Motion, and Sensation indicate three steps up the grade of life. Thus, the first is the prominent function in the Coral, which simply “ vegetates,” the pow- ers of moving and feeling being very feeble. In the higher Insect, as the Bee, there is great activity with sim- ple organs of nutrition. In the still higher Mammal, as Man, there is less power of locomotion, though the most perfect nutritive system; but both functions are subordi- nate to sensation, which is the crowning development. In studying the comparative anatomy and physiology of the animal kingdom, our plan will be to trace the vari- ous organs and functions, from their simplest expression upward to the highest complexity. Thus Vutreteon will begin with absorption, which is the simplest method of taking food; going higher, we find digestion, but in no particular spot in the body; next, we see it confined to a tube; then to a tube with a sac, or stomach; and, finally, we reach the complex arrangement of the higher animals. NUTRITION. AB CHAPTER VI. NUTRITION. ' Nutrition is the earliest and most constant of vital op- erations. So prominent is the nutritive apparatus, that an animal has been likened to a moving sac, organized to convert foreign matter into its own likeness, to which the complex organs of animal life are but auxiliaries. Thus, the bones and muscles are levers and cords to carry the body about, while the nervous system directs its motions in quest of food. The objects of nutrition are growth, repair, and propa- gation. The first object of life is to grow, for no animal is born finished. Some animals, like plants, grow as long as they live; but the majority. soon attain a fixed size. In all animals, however, without exception, food is wanted for another purpose than growth, namely, to repair the waste which is constantly going on. For every exercise of the muscles and nerves involves the death and decay of those tissues, as shown by the excretions. The amount of matter expelled from the body, and the amount of nour- ishment needed to make good the loss, increase with the activity of the animal. The supply must equal the de- mand, in order to maintain the life of the individual; and as an organism can make nothing, it must seek it from without. Not only the muscles and nerves are wasted by use, but every organ in the body; so that the whole struct- ure needs constant renewal. An animal begins to die the moment it begins to live. The function of nutrition, therefore, is constructive, while motion and sensation are destructwe. | 46 COMPARATIVE ZOOLOGY. Another source of demand for food is the production of germs, to propagate the race, and the nourishment of such offspring in the egg and infantile state. This reproduc- tion and development of parts which can maintain an in- dependent existence is a vegetatwe phenomenon (for plants have it), and is a part of the general process of Nutrition. But it will be more convenient to consider it hereafter (chapters xix., xx.). Still another necessity for aliment among the higher animals is the maintenance of bodily heat. This will be treated under the head of Respiration. For the present, we will study Nutrition, as manifested in maintaining the life of an adult individual. In all animals, this process essentially consists in the an- troduction of food, its conversion into tissue, its oardation, and the removal of worn-out material. 1. The food must be procured, and swallowed. (Inges- tion.) 2. The food must be dissolved, and the nutritious parts separated into a fluid. (Digestion.) 3. The nutritive fluid must be carefully taken | up, and then distributed all over the body. (Absorption and Cir- culation.) | 4, The tissues must repair their parts wasted by use, by transforming particles of blood into living matter like themselves. (Assimilation.) 5. Certain matters must be strained from the blood, some to serve a purpose, others to be cast out of the sys- tem. (Secretion and Excretion.) 6. In order to produce work and heat, the food must:be oxidized, either in the blood or in the tissues, after assimi- lation. The necessary oxygen is obtained through expos- ure of the blood to the air in the lungs. (Respiration in part.) 7. The waste products of this oxidation taken up by the blood must be got rid of ; some from the lungs (ear- THE FOOD OF ANIMALS. | AY bon dioxide, water), some from the kidneys (water, urea, mainly), some from the skin (water, salines). (Respira- tion in part, Excretion.) The mechanism to accomplish all this in the lowest forms of life is exceedingly simple, a single cavity and surface performing all the functions. But in the major- ity of animals the apparatus is very complicated: there is a set of organs for the prehension of food; another, for digestion ; a third, for absorption; a fourth, for distribu- tion; and a fifth, for purification. CHAPTER VII. THE FOOD OF ANIMALS. Tue term food includes all substances which contribute to nutrition, whether they simply assist in the process, or are actually appropriated, and become tissue. With the food is usually combined more or less indigestible matter, which is separated in digestion. Food is derived from the mineral, vegetable, and animal kingdoms. Water and salt, for example, are inorganic. The former is the most abundant, and a very essential article of food. Most of the lower forms of aquatic life seem to live by drinking: their real nourishment, how- ever, is present in the water in the state of solution. The Karthworm, some Beetles, and certain savage tribes of Men swallow earth; but this, likewise, is for the organic matter which the. earth contains. As no animal is pro- duced immediately from inorganic matter, so no animal can be sustained by it. Nutritious or tissue-forming food comes from the or- ganic world, and is albuminous, as the lean meat of ani- 48 COMPARATIVE ZOOLOGY. mals and the gluten of wheat; oleagunous, as animal fat and vegetable oil; or saccharine, as starch and sugar. The first is the essential food-stuff; no substance can serve permanently for food—that is, can permanently prevent loss of weight in the body—unless it contains albuminous matter. As stated before, all the living tissues are albu- minous, and therefore albuminous food is required to sup- ply their waste. Albumen contains nitrogen, which is necessary to the formation of tissue; fats and sugars are rich in carbon, and therefore serve to maintain the heat of the body, and to repair part of the waste of tissues. Warm-blooded animals feed largely on farinaceous. or starchy substances, which in digestion are converted into sugar. But any animal, of the higher orders certainly, whether herbivorous or carnivorous, would starve, if fed on pure albumen, oil, or sugar. Nature insists upon a mixed diet; and so we find in all the staple articles of food, as milk, meat, and bread, at least two of these prin- ciples present. As a rule, the nutritive principles in veg- etables are less abundant than in animal food, and the indigestible residue is consequently greater. The nutri- ment in flesh increases as we ascend the animal scale; thus, Oysters are less nourishing than Fish; Fish, less than Fowl; and Fow], less than the flesh of Quadrupeds. Many animals, as most Insects and Mammals, live solely on vegetable food, and some species are restricted to par- ticular plants, as the Silk-worm to the white mulberry. But the majority of animals feed on one another; such are hosts of the microscopic forms, and nearly all the ra- diated species, marine Mollusks, Crustaceans, Beetles, Flies, Spiders, Fishes, Amphibians, Reptiles, Birds, and clawed (Quadrupeds. 3 A few, as Man himself, are omnivorous, 2. é., are main- tained on a mixture of animal and vegetable food. The use of fire in the preparation of food is peculiar to Man, HOW ANIMALS EAT. AQ who has been called “the cooking animal.” e labinm when no i oe i Fia. 23.—Proboscis of a Butterfly. in use. 60 vA ‘Fig. 24.—Mouth of the Horse-fly (Vabanus lin- - COMPARATIVE ZOOLOGY. As most of the Arachnids live by sue- tion, the jaws are seldom used for masti- cation. In the Scorpion, the apparent representatives of the mandibles of an Insect are transformed into a pair of small forceps, and the palpi, so small in Insects, are developed into formidable claws: both of these organs are prehen- cola): antenne; ™, sile, In Spiders, the so-called mandi- mandibles; ma, max- ile; mp, maxillary bles, which move more or less vertically, palpi; lb, labrum; J, labium, or tongue. end in a fang; and the club-like palpi, often resembling legs, have nothing to do with inges- tion or locomotion. Both Scorpions and Spiders have a soft upper lip, and a groove within the mouth, which serves as a canal while sucking their prey. The tongue is external, and situated between a pair of diminutive maxille. In the Ascidians the first part of the alimentary canal is enormously enlarged and modified to serve as a gill- sac. At the bottom of this sac, and far removed from its external opening, lies the entrance to the diges- tive tract proper. Into it the particles of food enter- ing with the water are con- veyed (Fig. 279). The mouth of Verte- X RX ——<——— La, AA = == CE | £Z87ZE PSA Sz l EZ ~~ = Se SS F ( SwSS.8 SS ak Li- S233: La SN == _(—] — NS eS $ SSS SS Fig. 25.—Under Surface of Male Spider: a, c, poison-fang; b, teeth on interior mar- gin of mandible, e; 7, labium; g, thorax; h, limbs; 7, abdomen; 1, spinnerets; m, maxillary palpus; d, dilated terminal joint. HOW ANIMALS EAT. 61 brates is a cavity with a fixed roof (the hard palate) and a movable floor (the tongue and lower jaw), having a trans- verse opening in front,” and a narrow outlet behind, lead- ing to the gullet. Save in Birds and some others, the cavity is closed in front with lips, and the margins of the jaws are set with teeth. In Fishes the mouth is the common entry to both the digestive and respiratory organs; it is, therefore, large, and complicated by a mechanism for regulating the tran- sit of the food to the stomach and the aérated water to the gills. The shts leading to the gills are provided with rows of processes which, like a sieve, prevent the entrance of food, and with valves to keep the water, after it has en- tered the gills, from returning to the mouth. So that the mouths of Fishes may be said to be armed at both ends with teeth-bearing jaws. 4 o i 4 Joy ate i | WO AY! Roars 6 90 COMPARATIVE ZOOLOGY.» hold about five pints; that of the Kangaroo is as long as its body. The intestinal canal in Mammals begins at the pyloric end of the stomach, where there is a kind of valve or cir- cular muscle. Like the stomach, it varies greatly, accord- ing to the nature of the food. It is generally longest in the Vegetable-feeders, and shortest in the Flesh-feeders. The greater length in the former is due to the fact that vegetable food requires a longer time for digestion, and that a great- er bulk of such food is required to obtain a given quantity of nutri- ment. The intestines measure 150 feet in a full-grown Ox, while they are but three times the length of the body in the Lion, and six times in Man. Save in some lower forms, as the Whales, there are two main divisions, the “small” and “large” intestines, at the junction of which is a valve. The former is the longer of the two, UES sree Vere in it digestion is comple co FS 3, an 3 Ta Ry ee cae and ge O co p eted, aS ey at < ee Pane : ‘ Ce hic eS ee), and from it absorption takes place. Fie. 58.—Section of the Wall of The large intestine is a temporary the Human Intestine (ileum), x 50: a, villi; bandd, glands; lodging-place for the useless part c and e, mucous membrane; J, ba. hee circular muscles; g, hy longi. Of the food, until it is expellem peaiaat rauselee: from the body. The beginning of the small intestine is called the duodenum, into which the ducts from the liver and pancreas open. The intes- tinal canal has the same structure as the stomach, and by a peristaltic motion its contents are propelled downward. The inside surface of the small intestine is covered with a host of thread-like processes (vzddz), resembling: the pile of velvet. HOW ANIMALS DIGEST. 9] In taking this general survey of the succession of forms which the digestive apparatus presents among the princi- pal groups of animals, we cannot fail to trace a gradual specialization. First, a simple sac, one orifice serving as inlet for food and outlet for indigestible matter; next, a short tube, with walls of its own suspended in the body- cavity; then a canal passing through the body, and, there- fore, having both mouth and vent; next, an apparatus for mastication, and a swelling of the central part of the canal into a stomach, having the special endowment of secreting gastric juice; then a distinction between the small and large intestine, the former thickly set with villi, and re- ceiving the secretions of large glands. We also notice that food, the means of obtaining it, the instruments for mastication, and the size and complexity of the aliment- ary canal, are closely related. CHAPTER xX. HOW ANIMALS DIGEST. The object of the digestive process is the reduction of food into such a state that it can be absorbed into the system. Jor this purpose, if solid, it is dissolved; for fluidity is a primary condition, but not the only one. Many soluble substances have to undergo a chemical change before they can form parts of the living body. If albumen or sugar be injected into the veins, it will not be assimilated, but be cast out unaltered. To produce these two essential changes, solution and transmutation, two agencies are used —one mechanical, the other chemical. The former is not always needed, for many animals find their food already dissolved, as the 99, COMPARATIVE ZOOLOGY. Butterfly; but solid substances, to facilitate their solu- tion, are ground or torn into pieces by teeth, as in Man; by jaws, as in the Lobster; or by a gizzard, as in the Turkey. : The chemical preparation of food is indispensable.” It is accomplished by one or more solvent fluids secreted in the alimentary canal. The most important, and one al- ways present, is the gastric juice, the secretion of which is restricted to the stomach, when that cavity exists. In the higher animals, numerous glands pour additional flu- ids into the digestive tube, as saliva into the upper part or mouth, and bile and pancreatic juice into the upper part of the intestine. In fact, the mucous membrane, which lines the alimentary canal throughout, abounds with secreting glands or cells. | The Digestive Process is substantially the same in all animals, but it is carried further in the more highly de- veloped forms. In the Infusoria, the food is acted upon by some secretion from the walls of the body-cavity, the exact nature of which is unknown. In the Star-fish and Sea-urchin, we find two solvents—a gastric juice, and another resembling bile; but the two appear to mingle in the stomach. Mollusks and Arthropods show a clear distinction between the stomach and intestine, and the contents of the liver are poured into the latter. There are, therefore, two stages in the digestive act: first, the food is dissolved by the gastric juice in the stomach, form- ing chyme ; secondly, the chyme, upon entering the intes- tine, is changed into chyle by the action of the bile, and is then ready to be absorbed into the system. In Vertebrates, a third solvent is added, the pancreatic juice, which aids the bile in completing digestion. But Mammals and Insects have a still more perfect and elab- orate process; for in them the saliva of the mouth acts chemically upon the food; while the saliva in many other HOW ANIMALS DIGEST. 93 animals has no other office, so far as we know, than to moisten the food for swallowing. Taking Man as an example, let us note the main facts in the process. During mastication, by which the relative surface is increased, the food is mixed with saliva, which moistens the food, and turns part of the starch into grape-sugar. Passed into the stomach, the food meets the gastric juice. This is acid, and, first, stops the action of the saliva; secondly, by means of the pepsin which it con- tains, and the acid, it dissolves the albumen, fibrine, and such constituents of the food. This solution of albumi- noids is called a peptone, and is especially distinguished from other such solutions by its diffusibility—z. e., the ease with which it passes through a membrane. These pep- tones, with the sugars of the food, whether original or the product of the action of the saliva, are absorbed from the stomach. ‘The food, while in the stomach, is kept in con- tinual motion, and, after a time, is discharged in gushes into the intestine. The name chyme is given to the pulpy mass of food in the stomach. In the intestine the chyme meets three flnids—bile, pancreatic juice, and intestinal juice. All of these are alkaline, and at once give the acid chyme an alkaline reaction. This change permits the action of the saliva to recom- oy mence, which is aided by the pancreatic and intestinal juices. The pancreatic juice has much more important functions. It changes albuminoid food into peptones, and probably breaks up the fats into very small par- ticles, which are suspended in a the fluid chyle. This forms an Fre.59.—Chyle Corpuscles, x 500. emulsion, like milk, and causes the chyle to appear whit- ish. The bile has important functions, but little under- 94 COMPARATIVE ZOOLOGY. stood. It saponifies part of the fats, so that they are dis- solved, and prevents the food from decomposing during the process of digestion and absorption. The chyle is slowly driven through the small intestine by the creep- ing, peristaltic motion of its walls,” the nutritious portion being taken up by the absorbents, as described in the next chapter, while the undigested part remaining is discharged from the large intestine.” CHAPTER XI. THE ABSORBENT SYSTEM. Tue nutritive matter (chyle), prepared by the digestive process, is still outside of the organism. How shall it enter the living tissue ? | In animals, like the Infusoria and Polyps, whose digest- ive department is not separated from the body-eavity, the food, as soon as dissolved, mingles freely with the tissues and organs it has to nourish. In the higher Invertebrates having an alimentary canal, the chyle passes, by simple transudation, through the walls of the canal directly into the soft tissues, as in Insects, or is absorbed from the canal by veins in contact with it, as in Sea-urchins, Mollusks, Worms, and Crustaceans, and then distributed through the body. | In Vertebrates only do we find a special absorbent sys- - tem. Three sets of vessels are concerned in the general process by which fresh material is taken up and added to the blood: Capillaries, Lacteals, and Lymphatics. Only the two former draw material from the alimentary canal. ) It is a general law that the food is absorbed as fast as THE ABSORBENT SYSTEM. 86 it is dissolved, and, therefore, there is a constant loss in the passage down the canal. In the mouth and cesoph- agus, the absorption is slight; but much of that which has yielded to the gastric juice, with most of the water, is greedily absorbed by the capillaries of the stomach, and made to join the current of blood which is rushing to the liver. Absorption by the capillaries also takes place from the skin and lungs. Medicinal or poisonous gases and liquids are readily introduced into the system by these channels. We have seen that the oily part of the food passes un- changed from the stomach into the small intestine, where, acted upon by the pancreatic juice, it is cut up into ex- tremely minute particles, and that the undigested albumi- noids and starches are digest- be ed in the intestine. Two .)’ kinds of absorbents are pres- ent in the intestine, lacteals and blood -capillaries. Both , %, the lymphatic and blood sys- y\ tems send vessels into the velvety ville” with which the intestine is lined. The blood- 7 keine Ii Fig. 60.—Lacteal System of Mammal: a. Caplliarles 11e towards the out- descending aorta, or principal artery ; : : b, thoracic duct; c¢, origin of lacteal side of the villus and the vessels, g, in the walls of the intestine, lacteal in the centre. The d; e, mesentery, or membrane attach- ing the intestine to walls of the body; albuminoids and sugars are J, lacteal, or mesenteric, glands. chiefly absorbed by the blood-vessels and go to the liver. The fats pass on into the lacteals, which receive their name from the milky appearance of the chyle. These lacteals unite into larger trunks, which lie in the mesen- tery (or membrane which suspends the intestine from the back wall of the abdomen), and these pour their contents into one large vessel, the thoracic duct, lying along the backbone, and joining the jugular vein in the neck. eS 96 COMPARATIVE ZOOLOGY. The lacteals are only a special part of the great lym- abe system, which absorbs and carries to the thoracic Sey Te aes) ee duct matter from all parts aes 3 | | of the body.” The lymph is a transparent fluid having ““many white blood corpus- cles. It is, in fact, blood, WN minus the red corpuscles, o a while chyle is the same fluid oe rendered milky by numer- Oa. } ous fat- globules. During A Gpepremems? the intervals of digestion, WV (es the lacteals carry ordinary lymph. ‘This fluid is the overflow of the blood —the plasma and white corpus- cles which escape from the blood capillaries, and are not needed by the tissues in which they are. This sur- plus overflow is returned to the blood by the lymphatics. The current is kept up by ge (em the movements of the body, = Se iw and in many Vertebrates, as subclavian veins; 0b, thoracic duct; c, Frogs and Fishes, by lyinph receptaculum chyli. The oval bodies are glands. hearts. Like the roots of Plants, the absorbent vessels do not commence with open mouths; but the fluid which enters them must traverse the membrane which covers their mi- nute extremities. This membrane is, however, porous, and the fluids pass through it by the forces of filtration and diffusion. How the fat gets into the lacteals is not yet well understood, but the lacteals are themselves rhyth- mically contractile,” and force the absorbed chyle tow- THE BLOOD OF ANIMALS. O7 ards the heart. The valves of the lymphatics prevent its return. CHAPTER XIL. THE BLOOD OF ANIMALS. The Blood is that fluid which carries to the living tis- sues the materials necessary to their growth and repair, and removes their waste and worn-out material. The great bulk of the body is occupied with apparatus for the preparation and circulation of this vital fluid. The blood of the lower animals (Invertebrates) differs so widely from that of Man and other Vertebrates, that the former were long supposed to be without blood. In them the blood is commonly colorless; but it has a bluish east in Crustaceans; reddish, yellowish, or greenish, in Worms; and reddish, greenish, or brownish, in Jelly- fishes. The red liquid which appears when the head of a Fly is crushed is not blood, but comes from the eyes. In Vertebrates, the blood is red, excepting the white- blooded fish, Amphoxus.™ As a rule, the more simple the fabric of the body, the more simple the nutritive fluid. In unicellular animals (as Protozoa), in those whose cells are comparatively inde- pendent (as Sponges), and in small and lowly organized animals (like Hydra), there is no special circulating fluid. Each cell feeds itself either directly from particles of food, or from the products of digestion. In Polyps and Jelly-fishes, the blood is scarcely different from the prod- ucts of digestion, although a few blood-corpuscles are pres- ent. But in the more highly organized Invertebrates the blood is a distinct tissue, coagulating, and containing white corpuscles. The blood of the Vertebrates, appar- . 98 COMPARATIVE ZOOLOGY. ently a clear, homogeneous fluid, really consists of minute grains, or globules, of organic matter floating in water. If the blood of a Frog be poured on a filter of blotting - paper, a trans- parent fluid (called plas- ma) will pass through, s\ leaving red particles, re- Jo sembling sand, on the upper surface. Under the microscope, these particles prove to be cells, or flattened disks Fia. 62.—Red Blood-corpuscles of Man: a, shows (called ied uscles), api: circular contour ; b, a biconcave section; c,a taining a nucleus ; some cath Sa are colorless, and others red. The red disks have a tendency to run together into piles; the colorless ones remain single. Meanwhile, the plasma separates into two parts by coagulating; that is, minute fibres form, consisting of jibrene, leaving a pale yellowish fluid, called serum. Had the blood not been filtered, the corpuscles and fibrine would have mingled, forming a jelly-like mass, known as clot. Further, the | serum will coagulate if heated, dividing into hardened albumen and a watery fluid, called serosety, which contains the soluble salts of the blood. These several parts may be expressed thus: Corpuscles {colored ‘ P Ucolorless lot. Blood fibrine i Plasma albumen. serum serosity=water and salts. If now we examine the nutritive fluid of the simplest animals, we find only a watery fluid containing granules. In Radiates and the Worms and Mollusks, there is a sim- ilar fluid, with the addition of a few white corpuscles. But THE BLOOD OF ANIMALS. 99 there is little fibrine, and, therefore, it coagulates feebly or not at all. In the Arthropods and vee Mollusks, the circulating fluid contains colorless nucleated cells, and coagulates.” InVer- tebrates, there are, in ad- dition to the plasma and white corpuscles of In- vertebrates, red corpus- cles, to which their blood owes its peculiar hue. In Fishes, Amphibians, Reptiles, and Birds, 2. e., all oviparous Vertebrates, these red corpuscles are nucleated; but in those of Mammals, no nucleus has been discovered.” | All blood-corpuscles are microscopic. The white are more uniform in size than the red; and generally smaller (except in Mammals), being about seup Of an inch in diameter. The red corpuscles are largest in Amphib- ians (those of Proteus being the ex- treme, or zy Of an inch), next in Fishes, then Birds and Mammals. The u 7 smallest known are those of the Musk- Fic. 64. — Elliptical Corpus- deer. In Mammals, the size agrees cle of the Frog, showing 3 F “a white prominence atthe With the size of the animal only with- ca in a natural order; but in Birds the correspondence holds good throughout the class, the larg- est being found in the Ostrich, and the smallest in the Humming-bird. In Man, they measure 5,45 of an inch, so that it would take 40,000 to cover the head of a pin. As to shape, the colorless corpuscles are ordinarily glob- Fie. 63.—Nucleated Blood-cells of a Frog, x 250. 100 COMPARATIVE ZOOLOGY. ular, or sac-like, in all animals; but they are constantly changing. The form of the red disks is more permanent, epagh they are soft and eee so that they squeeze ~ MANes oso ELEPHANT: MOUSE : MUSK DEER- e1@e-: i. 3200 Ls 2748 | 1.12325 .. HUMMING BIRD PIGEON ; “S{BUIUIB IA “spulgq PROTEUS ‘satdey puv viqrydary “Usd Fig. 65. ape eauee Size and Stape of the red Corpuscies owas through very narrow passages. ‘They are oval, circular, or angular, in Fishes; oval in Reptiles, Birds, and the Camel tribe; and circular in the rest of Mammals. They are double-convex when nucleated, and double-concave when circular and not nucleated. Blood is always heavier than water; but is thinner in cold-blooded than in warm-blooded animals, in herbivores than in carnivores. The blood of Birds, which is the hot- test known, being 10° higher than Man’s, is richest in red corpuscles. In Man, they constitute about one half the mass of blood. The white globules are far less numerous than the red; they are relatively more abundant in venous than arterial blood, in the sickly and ill-fed than in the healthy and vigorous, in the lower Vertebrates than in Birds and Mammals. Their number is subject to great THE BLOOD OF ANIMALS, 101 variations, increasing rapidly after a meal, and falling as rapidly. There is less blood in cold-blooded than in warm-blood- ed animals; and the larger the animal, the greater is the Y » was YI = ~— A Sf oS — <4 SNS reer Sh ZA y Cyt = ae S4, — 4 hy ) RS Zw 4 — SSS iss ‘oj — —~ S Vig & = ‘ RGA y . ir Yr, yA A PSSA Se f Z Maip x OVA d Fie. 66.—Capillary Circulation in the Web of a Frog’s Foot, X 100: a, b, small veins ; d, capillaries in which the oval corpuscles are seen to follow one another in sin- ule series ; c, pigment-cells in the skin. proportion of blood to the body. Man has about a gallon and a half, equal to one thirteenth of his weight. The heart of the Greenland Whale is a yard in diameter. The main Office of the Blood is to supply nourish- ment to, and take away waste matters from, all parts of the body. It is at once purveyor and scavenger. In its circulation, it passes, while in the arterial half of the cap- illaries, within an infinitesimal distance of the various tis- sues. The plasma, carrying the nutritive matter needed, exudes through the walls of the capillary tubes; the tissue assimilates or makes like to itself whatever is suitable for its growth and repair; and the lymphatics (the escape- 102 COMPARATIVE ZOOLOGY. pipes) take up any surplus, and return it to the blood. At the same time, the venous part of the capillary net- work absorbs the waste products of the tissues, expelling the gases by the lungs, and the solid matters by the skin and kidneys. The special function of the several constit- nents of the blood is not wholly known. The colorless corpuscles in Vertebrates are supposed to be the source of the red disks. The latter are the carriers of oxygen, which is taken up by their red matter (hemoglobin) in the lungs, and given up to the tissues. The same office is performed by the blue coloring - matter (heemocyanin) in the blood of certain Invertebrates, as the Squid and Lob- ster. The carbon dioxide is taken up by the plasma. Like the solid tissues, the blood, which is in reality a liquid tissue, is subject to waste and renewal, to growth and decay. The loss is repaired from the products of digestion, carried to the blood by the lacteals, or absorbed directly by the capillaries of the digestive tract. The white corpuscles are probably prepared in many parts of the body, especially the liver, spleen, and lymphatic glands. In the lower organisms, the nutritive food is prepared by contact with the tissues, without passing through special organs. Lymph differs from blood chiefly in containing less albumen and fibrine, and no red disks. Chyle is lymph loaded with fat globules, and is found in the lac- teals and vessels connected with them during the absorp- tion of food containing fat. THE CIRCULATION OF THE BLOOD. 103 CHAPTER XIII. THE CIRCULATION OF THE BLOOD. The Blood is kept in continual motion in order to nourish and purify the body and itself. For as life means work, and work brings waste, there is constant need of fresh material to make good the loss in every part of the system, and of the removal of matter which is no longer fit for use. In the very lowest animals, where every part of the structure is equally capable of absorbing the digested food and is in contact with it, there is no occasion for any circulation, although in them even the blood is not allowed to stagnate. But in proportion as the power of absorption is con- fined to certain parts, the more is the need and the greater the complexity of an apparatus for convey- ing the nutritive fluid to the various tissues. In nearly all animals, the nutritive fluid is con- veyed to the various parts of the body by a system of tubes, called blood-ves- séls. The higher forms Fig. 67. —Venous Valves. They usually oc- cur in pairs, as represented. 104 COMPARATIVE ZOOLOGY. have two sets—arterzes and veins, in which the blood moves in opposite directions, the former carrying blood Ul KC Jrom a central reservoir or heart, A} y the latter taking it ¢o the heart. Oy by In the Vertebrates, the walls of these tubes are made of three coats, or layers, of tissue, the arte- ries being elastic, like rubber, and many of the veins being furnished with valves.° The great artery coming out of the heart is called aorta, and the grand venous trunk, entering the heart on the opposite side, is called vena cava. Both sets divide and subdivide until their branches are finer than hairs; and joining these finest arteries and finest veins are intermediate microscopic tubes, called capzlla- | ries (in Man about sg9 of an inch re nb, tad conilleros 4, in diameter). In‘ theve mae seen in the muscles ofa Dog. thin and delicate are them (mane _ does the blood come in contact with the tissues or the air. In those Vertebrates which have lungs there are two sets of capillaries, since there are two circulations—the systemic, from the heart around the system to the heart again, and the pulmonary, from the heart through the respiratory organ back to the heart. This double course may be illustrated by the figure 8. In gill-bearing animals there are capillaries in the gills, but not a double circu lation. | There is no true system of blood- vessels below the Star-fish. The simplest provision for the distribution of the products of digestion is shown by the Jelly-fish, whose stomach sends off radiating tubes (Fig. 197). Wh i Ail! i ii THE CIRCULATION OF THE BLOOD. 105 The first Approach to a Circulatory System is made by the Star-fish and the Sea-urchin. A vein runs along the whole length of the alimentary tube, to absorb the chyle, and forms a circle around each end of the tube. These circular vessels send off branches to various parts of the body; but as they are not connected by a net-work of capillaries, there can be no circuit (Fig. 39). A higher type is exhibited by the Insects. If we ex- amine the back of any thin-skinned Caterpillar, a long pulsating tube is seen running beneath fj the skin from one end of the body to the other. This dorsal vessel, or heart, as it is called, is open at both ends, and divided by valves into compartments, permitting the blood to go forward, but not backward. Each compartment communicates by a pair of slits, guard- ed by valves, with the body - cavity, so that fluids may enter, but cannot es- cape. “Circulation” is very simple. We have seen that the chyle exudes through the walls of the alimentary ca- nal directly into the cavity of the abdo- men, where it mingles with the blood already there. This mixed fluid is S drawn into the dorsal tube through the Mis. Part of the ae valvular openings as it expands; and a Cockehater bisected: upon its contraction, all the side-valves Z ge iB anlar are closed, and the fluid is forced tow- Compartments; ¢, valve - defending one of the ards the head. Passing out at the front °vifices communicating with the general cavity opening, it is again diffused among and __ of the abdomen. between the tissues of the body. The blood, therefore, does not describe a circle in definite channels so as to re- turn constantly to its point of departure. Many worms (as the Earthworm) have a pulsating tube Ml oe Ty antag 106 COMPARATIVE ZOOLOGY. extending from tail to head above the alimentary canal, a similar tube on the ventral side through which the blood returns, and cross-tubes in every segment. In the Lob- ster and Crab, Spider and Scorpion, the dorsal tube sends Fig. 70.—Circulation in a Lobster: a, heart; b, artery for the eyes; ce, artery for an- tenne; d, hepatic artery; e, superior abdominal artery; jf, sternal artery; g, ve- nous sinuses transmitting blood from the body to the branchie, h, whence it returns to the heart by the branchio-cardiac vessels, 7. off a system of arteries (not found in Insects); but the blood, as it leaves these tubes, escapes into the general cavity, as in other Arthropoda. The Lobster and Crab, however, show a great advance in the concentration of the propelling power into a short muscular sae. be A third development of the circulatory system is fur- nished by the Mollusks. Comparatively sluggish, they need a powerful force-pump in the form of a compact heart. In the Oyster and Snail (Figs. 44, 45), we find such an organ having two cavities—an auricle and a ventricle, one for receiving, and the other for distributing, the blood. The auricle injects the blood into the ventricle, which propels it by the arteries to the various organs. Thence it passes, not immediately to the veins, as in higher ani- mals, but into the spaces around the alimentary canal. A part of this is carried by vessels to the gills or lung, and then returned with the unpurified portion to the auricle. The whole of the blood, therefore, does not make a com- plete circuit. The Clam has a similar heart, but with two auricles. THE CIRCULATION OF THE BLOOD. 107 A still higher form is seen in the Cuttle-fish, the high- est of the Invertebrates, This animal has a central heart, with a ventricle and two auricles, and, in addition, the veins which collect the blood from the system to send it back to the heart by the way of the gills are furnished with two branchial hearts, which accelerate the circulation through those organs. Many of the arte- ries and veins are joined by cap- illaries, but not all; so that in no invertebrate animal is the blood returned to the heart by a continuous closed system of blood- vessels. As a rule, in all animals hav- ing any circulation at all, the cur- rent always takes one direction. This is generally necessitated by valves. But a curious exception is presented by the Ascidians, whose tubular heart is valveless, and the contractions occur alter- nately at one end and then the - other; so that the blood oscil- lates to and fro, and a given ves- sel is at one time a vein and at another an artery. In this re- spect it resembles the foetal heart of higher animals (Fig. 279). In Vertebrates only is the cir- culating current strictly confined to the blood-vessels; in no case general cavity of the body. In aN, '‘& kee ge" Fre. 71.—Circulating Apparatus in the Fish: a, branchial artery ; }, arterial bulb; c, ventricle; d, au- ricle; e, venous sinus; ,f, portal vein; g, intestine; h, vena cava; 1, branchial vessels ; k, dorsal ar- tery, or aorta; 1, kidneys; ™, dorsal artery. does it escape into the other respects, there is 108 COMPARATIVE ZOOLOGY. no great advance in the apparatus of the lowest Verte- brates over that of the highest Mollusks. The heart of = Fishes, as in the Oyster, has two cavities, but its position is reversed. Instead of driv- ing arterial blood over the body, it receives the return- | 2\ ing, or venous, blood, and 77, 4 sends it to the gills. Re- collected from the gills, the blood is passed into a large artery, or aorta, along the back, which distributes it by a complex system of capil- auricle; e, ventricle; c, veins leading to laries among the tissues. i ee These capillaries unite with the ends of the veins which pass the blood into the auri- cle™ (Fig. 48). | In Amphibians and in Reptiles generally (as Frogs, Snakes, Lizards, and Turtles), the heart has three cavities —two auricles and one ventricle. The venous blood from the body is received into the right auricle, and the puri- fied blood from the lungs into the left. Both throw their contents into the ventricle, which pumps the mixed blood in two directions—partly to the lungs, and partly around the system. Circulation is, therefore, incomplete, since the whole current does not pass through the lungs, and three kinds of blood are found in the body—arterial, ve- nous, and mixed. In many animals, however, arrange- ments exist which nearly separate the venous from the arterial blood. The ventricle of Reptiles is partially divided by a par- tition. In the Crocodile, the division is complete, so that there are really four cavities—two auricles, and two ven- tricles. But both ventricles send off aortas which cross THE CIRCULATION OF THE BLOOD. 109 one another, and at that point a small aperture brings the two into communication. The venous and arterial cur- rents are, therefore, mixed, but not within the heart, as in the other Reptiles, nor so extensively. In the structure of the heart, as well as in that of the gizzard, Crocodiles ap- proach the Birds. The Highest Form of the Circulating System is pos- sessed by the warm -blooded Vertebrates, Birds and Mam- Fre. 73.—Heart of the bDugong, a four- chambered heart, the parts being more mals. Not a drop of blood separated than in higher animals: E, ean make the cireuit of the right ventricle; L, left ventricle; D, right auricle; F, pulmonary artery ; body without passing through &: left auricle; A, aorta. the lungs, the circulation to and from those organs being as perfect as the distribution of arterial blood. The heart "ee h g n h Fig. 74. — Theoretical Section of the Human Heart: a, right ventricle: b, inferior vena cava; ec, tricuspid valve; d, right auricle; e, pulmona- ry veins; f, superior vena cava; g, pulmonary arteries; h, aorta; k, left auricle ; 2, mitral valve; m, left ven- tricle; n, septum. consists of four cavities —a right auricle and ventricle, and a left auricle and ventricle. In other words, it is a hollow mus- cle divided internally by a ver- tical partition into two distinct chambers, each of which is again divided by a valve into an auricle and a ventricle. The work of the right auricle and ventricle is to receive the blood from the veins, and send it to the lungs; while the other two receive the blood from the lungs, and propel it over the body. The left ventricle has more to do than any other eavity. The two auricles contract at the same instant; 110 : COMPARATIVE ZOOLOGY. forces it past a valve‘ so also do the ventricles. The course of the current in Birds and Mammals is as follows: the venous blood brought from the system is discharged by two or three large trunks” into- the right auricle, which immediately * into the right ventricle. The ventricle then con- tracts, and the blood rushes through the pulmonary artery past its semi- lunar valves into the lungs, where it is changed from venous to arterial, returning by the pulmonary veins to tion in Fishes: a, auri- h cle: b, ventricle; c, bran- the chial artery; e, branchial veins, bringing blood left auricle. This sends it past the mitral valves into the left ventri- from the gills, d, and ele, which drives it past the semilunar uniting in the aorta, f; g, vena cava. valves into the aorta, and thence, by its ramifying arteries and capillaries, into all parts of the body except the lungs. From the capillaries, the blood, now changed from arterial to venous, is gathered by the veins, and conveyed back to the heart. The Rate of the - Blood -current gener- ally increases with the activity of the animal, being most rapid in Birds.“ In Inseets, however, it is compara- tively slow; but this is because the air is taken to the blood—the whole = s \— ¢ | - = fp ANT LN hy ’ Wily) Fie. 76.—A, Plan of Circulation in Amphibia and Reptiles; B, Plan of Circulation in Birds and Mammals: a, right auricle receiving venous blood from the system; 5}, left auricle receiving arterial blood from the lungs; e, ec’, ventricles; d, e,,f, systemic artery, vein, and capillaries; 9, pulmonary artery; A, &, vein and capillaries. HOW ANIMALS BREATHE. 111 body being bathed in air, so that the blood has no need to hasten to a special organ. However, activity nearly doubles the rate of pulsation in a Bee. The motion in the arteries is several times faster than in the veins, but diminishes as the distance from the heart increases. In the carotid of the Horse, the blood moves 123 inches per second; in that of Man, 16; in the capillaries of Man, 1 to 2 inches per minute; in those of a Frog, 1. - The Cause of the Blood-current may be cilia, or the contractions of the body, or pulsating tubes or hearts. In the higher animals, the impulse of the heart is not the sole means: it is aided by the contractions of the arteries themselves, the movements of the chest in respiration, and the attraction of the tissues for the arterial blood in the capillaries. In the Chick, the blood moves before the heart begins to beat; and if the heart of an animal be suddenly taken out, the motion in the capillaries will continue as before. It has been estimated that the force which the human heart expends in twenty-four hours is about equivalent to lifting 217 tons one foot. CHAPTER XIV. HOW ANIMALS BREATHE. Arterial Blood, in passing through the system, both loses and gains certain substances. It loses constructive material and oxygen to the tissues. These losses are made good from the digestive tract and breathing organ. It gains also certain waste materials from the tissues, which must be got rid of. Of these waste products, one, carbon dioxide, is gaseous, and is passed off from the same organ as that where the oxygen is taken in. This exchange of — 112 COMPARATIVE ZOOLOGY. gases between the animal and its surroundings is called Respiration. The First Object of Respiration is to convert venous into arterial blood. It is done by bringing it to the sur- face, so that carbon dioxide may be exhaled and oxygen absorbed. The apparatus for this purpose is analogous to the one used for circulation. In the lowest animals, the two are combined. But in the highest, each is essentially a pump, distributing a fluid (in one case air, in the other blood) through a series of tubes to a system of cells or capillaries. They are also closely related to each other: the more perfect the circulation, the more careful the pro- vision made for respiration. Respiration is performed either in air or in water. So that all animals may be classed as azr- breathers or water - breathers. The latter are, of course, aquatic, and seek the air which is dissolved in the water. Land-snails, Myriapods, Spiders, Insects, Reptiles, Birds, and Mam- mals breathe air directly; the rest, with few exceptions, receive it through the medium of water. In the former case, the organ is internal; in the latter, it is more or less on the outside. But however varied the organs— tubes, gills, or lungs—they are all constructed on the same prin- ciple —a thin membrane separating the blood from the atmosphere. (1) Sponges, Infusoria, and Polyps have no separate respir- atory apparatus, but absorb air, as well as food, from the currents of water passing through them. In the Star-fish, Sea-urchin, and the like, we find the first distinct respiratory organs, although none are exclu- sively devoted to respiration. There are two sets of ca- nals—one carrying the nutrient fluid, and the other, radi- ating from a ring around the mouth, distributing aerated water, used for locomotion as well as respiration. This may be called the “ water-pipe system.” Besides this, — HOW ANIMALS BREATHE. there are numerous gill-like fringes, which probably aid in respiration (Fig. 39). Fresh-water Worms, like the Leech and Earth-worm, breathe by the skin. The body is always covered by a viscid fluid, which has the property of absorbing air. The air is, therefore, brought into immedi- ate contact with the soft skin, underneath which lies a dense net-work of blood - ves- sels. But most water-breathing animals have gills. The simplest form is seen in Marine Worms: delicate veins projecting through the skin make a series of arborescent tufts along the side of the body; as these float in the water, the blood is purified.“ Bi- valve Mollusks have four flat gills, consist- ing of delicate membranes filled with blood- vessels and covered with cilia. In the Oys- ter, these ribbon-like folds are exposed to ie am the water when eB. the shell opens; y but in the Clam, the mantle en- 113 Fig. 77.—Lob-worm (A renicola piscato- rum), a dorsibran- chiate, showing the tufts of capil- laries, or external gills. The large head is without eyes or jaws. Fig. 78.—Diagrammatic Section of a Lamellibranch (Anodon): a, lobes of mantle; 6, gills, showing transverse partitions; c, ventricle of heart; d, auricles; e, pericardium; f, g, kid- neys; h, venous sinus; &, foot; A, branchial, or pallial, chamber; B, epibranchial chamber. closes them, forming a tube, called sephon, through which the water is driven by the cilia. The aquatic Gastero- pods (Univalves) have either tufts, like the Worms, or comb- like ciliated gills in a cavity behind the head, to which the water is admitted by a siphon. The Cuttle-fish has flat gills covered by the mantle; but the 8 114 COMPARATIVE ZOOLOGY. water is drawn in by muscular contractions instead of by cilia. The end of the siphon through which it is ejected is called the funnel. The gills of Lobsters and Crabs are placed in cavities covered by the sides of the shell (cara- pace); and the water is brought in from behind by the auction of a scoop-shaped process attached to one of the jaws, which constantly bales the water out at the front. The perfection of apparatus for aquatic respiration is_ seen in Fishes. The gills are comb-like fringes supported on four or five bony or cartilaginous arches, and contain myriads of microscopic capillaries, the object being to ex- pose the venous blood in a state of minute subdivision to streams of water. The gills are always covered. In bony fishes they are attached to the hinder side of bony arches, all covered by a flap of the skin, supported by bones (the gill-cover, or operculum), and the water escapes from the opening left at its hinder edge. In Sharks, the gills are placed in pouches which open separately (Iigs. 164 and 287). The act of “breathing water” resembles swallowing, only the water passes the gills instead of en- tering the gullet. (2) Air-breathers have trachec, or lungs. The former consist of two principal tubes, which pass from one end of the body to the other, opening on the surface by apertures, called spor- acles, resembling a row of button-holes along 20 3 the sides of the thorax Se and abdomen, and rami- Fig. 79.—Spiracle of an Insect, x 75. fying through the small- est and most delicate organs, so that the air may follow HOW ANIMALS BREATIIE, 115 the blood wherever it circulates. To keep the pipes ever open, and at the same time leave them flexible, they are provided with an elastic spiral thread, like the rubber tube of a drop-light. Respira- tion is performed by the movements of the abdomen, as may be seen in the Bee when at rest. This “air-pipe system,” as it may be termed, is best developed in In- sects. The “nerves” of an Insect’s wing con- sist of a tube within a tube: the inner one is a trachea carrying air, and the outer one, sheathing it, is a blood-vessel. So perfect Fie. 80. — Tracheal Tube of an Insect, highly magnified, showing _ elastic spiral thread. is the aeration of the whole body, from brain to feet, the blood is oxygenated at the moment when, and on the spot where, it is carbonized; only one kind of fluid is, Ss 2 ‘ ti (C ) ~~ p Ss) i = 4 ST S TP iy yy ~ ) Fig. 81.—Ideal Section of a Bee: a, alimentary canal; h, dorsal vessel; t, trachea ; n, hervous cord. therefore, circulating — arterial. It is difficult to drown an Insect, as the water cannot enter the pores; but if a drop of oil be applied to the abdomen, it falls dead at once, being suffocated. The largest spiracle is usually 116 , COMPARATIVE ZOOLOGY. found on the thorax, as un- der the wing of a Moth: such may be strangled by pinching the thorax. In Millipedes and Centi- pedes, the spiracles open into little sacs connected together by tubes; in Spi- ders and Scorpions, the spiracles, usually four in Fig. 82.—Section through a bronchial tube, number, are the mouths of Lung of a Bird, magnified: a, the cavity; sacs without the tubes, and b, its lining membrane supporting blood- i ¥ vessels; c, perforations at the orifices of the interior of the sac is the lobular passages, d; e, interlobular ‘ ae spaces, containing the terminal branches gather ed into folds. Land-: of the pulmonary vessels supplying the mee Uae ee Pa capillary plexus, f, to the meshes of which snails have One spiracle, ta the air gets access by the lobular passages. aperture, on the left side of the neck, leading to a large cavity, or sac, lined with fine blood-vessels. These sacs represent the primitive idea of a lung, which is but an infolding of the skin, divided up into cells, and covered with capillary veins.” ONY |) ot saz iN Wu as NY 7 / 200000003477] || ep LPS ee or 22807) J 63 Steo; ing OSM) Ny 5 =Og> ~~ J Ms 4 — Ne ~ = 5 Va, aS 1 he dA 4 Le Li) WAY Avie Pe =~ ~ ie \\ ‘ 1 dl i I \ ‘ AW ye Fic. 85.—Lungs of a Frog: a, hyoid apparatus; 6, cartilaginous ring at root of the lungs; c, pulmonary vessels; d, pulmonary sacs, having this peculiarity common to all cold- blooded air-breathers, that the tra- Fie. 86. — Distribution of Air-tubes in Mam- chea does not divide into bronchial branches, but terminates abruptly by orifices which open at once. into the general cavity. A cartilaginous net-work divides the space into lit- tle sacs, on the walls of which the capillaries are spread. malian Lungs: a, larynx; b, trachea; c, d, left and right bronchial tubes; e, Jf, g, the ramifications. In Man the subdivision con- tinues until the ultimate tubes are one twen- ty-fifth of an inch in diameter. Each lobule represents in miniature the structure of the entire lung of a Frog. HOW ANIMALS BREATHE. 119 pipe be tied, and an opening be made in the wing-bone, the bird will continue to respire. The right lung is usn- ally the larger; in some Snakes, the left is wanting en- tirely. In most Vertebrates, lungs are freely suspended ; in Birds, they are fastened to the back. The lungs communicate with the atmosphere by means of the trachea, or windpipe, formed of a series of cartilag- inous rings, which keep it constantly open. It begins in the back part of the mouth, opening into the pharynx by a slit, called the glottes, which, in Mammals, is protected by the valve-like epzglottes. The trachea passes along the neck in front of — the cesophagus, and divides into two branches, or bronchi, \ one for each lung. In Birds and Mam- mals, the bronchial tubes, after entering the lungs, subdivide again into minute’ ramifications. Vertebrates are the only animals that breathe through the mouth or nos trils. Frogs, having no ribs, and Turtles, whose ribs are soldered together into a shield, are compelled to swallow the air. Snakes, Lizards, and Crocodiles draw it into the lungs by the play of the ribs.” Birds, unlike other ani- mals, do not inhale the air by an active effort ; for that is done by the springing-back of the breast-bone and ribs to their natural position. ‘To expel the air, the breast-bone is drawn down towards the back-bone by muscles, which compresses the lungs. | 3 Mammals alone have a perfect thorax—z. ¢., a closed cavity for the heart and lungs, with movable walls (breast- Fig. 87.—Skeleton of a Frog. 190 COMPARATIVE ZOOLOGY. bone and ribs) and a diaphragm, or muscular partition, separating it from the abdomen.” Inspiration (or filling the lungs) and expiration (or emptying the lungs) are both accomplished by muscular exertion; the former, by raising the ribs and lowering the diaphragm, which en- | | large the capacity of the chest, and the air rushes in to prevent a vacuum; _e the latter, by the ascent of the diaphragm and the de- scent of the ribs. | As a rule, the more ac- tive and more muscular an animal, the greater the de- «f° mand for oxygen. Thus, Ji» warm-blooded animals live fast, and their rapidly de- a caying tissues call for rapid » respiration; while in the / “ii ae Oran », cold-blooded creatures the \ waste is comparatively i 1 v al AD i \ Fie. 88.—Human Thorax: a, vertebral col- slow. Respiration 1s most umn; 0, b’, ribs, the lower ones false ; ¢, clavicle; e, intercostal muscles, removed on the left side to show the diaphragm, d; active in Birds, and least in water-breathing animals. Ff, pillars of the diaphragm attached to the lumbar vertebre ; g, muscles for elevating The sluggish Toad respires the ribs; h, sternum. mg more slowly than the busy Bee, the Mollusk more slowly than the Fish. But respi- rations, like beats of the heart, are fewer in large Main- mals than in small ones. An average Man inhales about - 300-400 cubic feet of air per day of rest, and much more when at work. Another result of respiration, besides the purification of the blood, is the production of heat. The chemical combination of the oxygen in the air with the carbon in the tissues is a true combustion; and, therefore, the more SECRETION AND EXCRETION. 121 active the animal and its breathing, the higher its temper- . ature. Birds and Mammals have a constant temperature, which is usually higher than that of the atmosphere (108° and 100° F. respectively). They are therefore called con- stant-temperatured or warm-blooded. Other animals do not vary greatly in temperature from that of their sur- roundings, and are called changeable-temperatured or cold- blooded. Still, their temperature does not agree exactly with that of the air or water. The Bee is from 3° to 10°, and the Earth-worm and Snail from 1$° to 2°, higher than the air. ‘The mean temperature of the Carp and Toad is pit; of Man; 98°; Dog, 99°; Cat, 101°; Squirrel, 105°; Swallow, 111°. CHAPTER XV. SECRETION AND EXCRETION. In the circulation of the blood, not only are the nutrient materials deposited within the body in the form of tissue, but certain special fluids are separated and conveyed to the external or internal surfaces of the body. These flu- ids are of two kinds: some, like saliva, gastric juice, bile, milk, etc., are for useful purposes; others, like sweat and. urine, are expelled from the system as useless or injurious. The separation of the former is called secreteon,; the re- moval of the latter is excretzon. Both processes are sub- stantially alike. | In the lower forms, there are no special organs, but se- cretion and excretion take place from the general surface. The simplest form of a secreting organ closely resembles that of a respiratory organ, a thin membrane separating the blood from the cavity into which the secretion is to 122 COMPARATIVE ZOOLOGY. be poured. Usually, however, the cells of the membrane manufacture the secretion from materials furnished by the blood. Even in the higher animals, there are such secret- ing membranes. The membranes lining the nose and ali- mentary canal and enclosing the lungs, heart, and joints, secrete lubricating fluids. membrane into little saes or short tubes (follicles), each having its own outlet, is the type of all secreting and ex- creting organs. The lower tribes have nothing higher, and the apparatus for pre- paring the gastric fluid at- tains no further develop- ment even in Man. When Fie. 89.—Three plans of secreting Mem- g elyster of these follicles, or branes. The heavy line represents the areolar-vascular layer; the next line is sacs, discharge their contents the basement, or limiting membrane; ; and the dotted line the epithelial layer: by one common duct, we a shows increase of surface by simple i plaited or fringed projections; 6, five have a gland. But whether modes of increase by recesses, forming membrane follicle or olan d simple glands, or follicles; c, two forms 4 —) ? of compound glands. the organ 18 covered with a net-work of blood-vessels, and lined with epithelial cells, which are the real agents in the process. The chief Secreting Organs are the salwary glands, gastric follocles, pancreas, and liver, all situated along the digestive tract. | 1. The salivary glands, which open into the mouth, se- crete saliva. They exist in nearly all Vertebrates, higher -Mollusks, and Insects, and are most largely developed in such as live on vegetable food. The saliva serves to In- bricate or dissolve the food for swallowing, and, in some Mammals, aids also in digestion of starch.” The infolding of such a SECRETION AND EXCRETION. BOR 2. The gastric follicles are minute tubes in the walls of the stomach secreting gastric juice. They are found in all Vertebrates, and in the higher Mol- lusks and Arthropods. In the lower forms, a simple membrane lined with cells serves the same purpose. Under the microscope, the soft mucous mem- brane of the human stomach presents a honey-comb appearance, caused by nu- merous depressions or cells. At the bot- tom of these depressions are clusters of spots, which are the orifices of the tubu- lar follicles. The follicles are about 54, of an inch in diameter, and number mmill- ions. 3. The pancreas, or “‘sweetbread,” so ore important in the process of digestion, stomen of 4 Eee when present, exists only in the Verte- fies is J Rae ss brates, and perhaps in the higher Mol- !mmar epithelium, lusks. In its structure and its secretion it closely resem- bles the salivary glands. In the Outtle-fish, it is repre- sented by a sac; in Fish- es, by a group of follicles. It is proportionally larg- est in birds whose sali- vary glands are deficient. The pancreatic juice en- Aaa ters the duodenum. Foss Nea Rig > _ 4. A liver in some form \. ys, Nears is found in all animals having a distinct diges- ; tive cavity. In Mollusks Fie OL Paneens of Mano; g.zutbindder: and Vertebrates, it is the loric valve ; e, 7, duodenum. largest gland in the body. The higher the animal, the more compact the organ. 194 COMPARATIVE ZOOLOGY. Thns, in Polyps it is represented by yellowish cells lining the stomach ; in Insects, by cells in the wall of the stom- ach; in Mollusks, by a cluster of sacs, or follicles, forming a loose compound gland. In Vertebrates, the liver is well defined, and composed of a multitude of lobules (which give it a grahular appearance) arranged on the capillary veins, like grapes on a stem, and containing nucleated secreting cells. It is of variable shape, but usually two, three, or five lobed, and is centrally situated—in Mam- mals, just below the diaphragm. In most Vertebrates, there is an appendage to the liver, called the gall-bladder, which is simply a reservoir for the bile when not wanted. ‘The so-called liver of Invertebrates is probably more A on \ C Y ‘Soe 7 ed Vi a TE ' 4 e e/g oy ‘SS K yyy yy} | )) 4 Sy AWAY \\ / DHE | W\\\yy ed IGG yy q \\ Vi Oe gh 0 ANS = SF Z ==; | WHEL: 7 a SS SS A SMI) 5 S S \ \\ \\ Fria. 92.—Liver of the Dog, F, F; D, duodenum and intestines; P, pancreas; 1, spleen; e, stomach, f, rectum; R, right kidney; B, gall-bladder; ch, cystic duct; F, lobe of liver dissected to show distribution of portal vein, VP, and hepatic vein, vk; d, diaphragm; VC, vena cava; C, heart. SECRETION AND EXCRETION. ee like the pancreas of Vertebrates in function, as its secre- tion digests starches and albuminoids. The liver of Ver- tebrates is both a secretory and an excretory organ. The bile perfornmis an important, although ill-understood, funce- tion in digestion, and also contains some waste products. The gland also serves to form sugar from ‘part of the digested food, and may well be called a chemical work- shop for the body. In animals of slow respiration, as Crustaceans, Mollusks, Fishes, and Reptiles, fat accumu- lates in the liver. ‘“ Cod-liver oil” is an example. - The great Excreting Organs are the lungs, the kid- neys, and the skin; and the substances which they re- _move from the system—carbonie acid, water, and urea— are the products of decomposition, or organic matter on its way back to the mineral kingdom.” Different as these urgans appear, they are constructed upon the same prin- ciple: each consisting of a very thin sheet of tissue sepa- rating the blood to be purified from the atmosphere, and straining out, as it were, the noxious matters. All, more- over, excrete the same substances, but in very different proportions: the lungs exhale carbon dioxide and water, with a trace of urea; the kidneys expel water, urea, and a little carbon dioxide; while the skin partakes of the nat- ure of both, for it is not only respiratory, especially among _ the lower animals, but it performs part of the work of the kidneys when they are diseased. 1. The lungs (and likewise gills) are mainly excretory organs. The oxygen they impart sweeps with the blood through every part of the body, and unites with the tis- sues and with some elements of the blood. Thus are pro- duced heat and work, whether muscular, nervous, secre- tory, etc. Asa result of this oxidation, carbon dioxide, water, and urea or a similar substance, are poured into the blood. The carbon dioxide and part of the water are passed off from the respiratory organs. This process is 126 COMPARATIVE ZOOLOGY. more immediately necessary to life than any other: the arrest of respiration is fatal. 2. While the lungs (and skin also, : Kay to a slight degree) are sources of GEESE, gain as well as loss to the blood, the Zs( kidneys are purely excretory organs. Their main function is to eliminate - the solid products of decay which ‘cannot pass out by the lungs. In Mammals, they are discharged in solution; but from other animals which drink little the excretion is more or less solid. In Insects, the kidneys are groups of tubes; in the Hie. 98 Section of Human Uigber Mollusks, they are represent Kidney, showing the tubu- ed by spongy masses of follicles; in lar portion, 3, grouped into cones; 7, the ureter, or out- Vertebrates, they are well-developed Rae glands, two in number, and consist- ing of closely packed tubes. | 3. The skin of the soft-skinned animals, particularly of Amphibians and Mammals, is covered with minute pores, which are the ends of as many delicate tubes that le coiled up into a knot within the true skin. These are the sweat-glands, which excrete water, and with it certain salts and gases. Besides these secretions and excretions, there are others, confined to particular animals, and designed for special purposes: such are the oily matters secreted from the skin of quadrupeds for lubricating the hair and keeping the skin flexible; the tears of Reptiles, Birds, and Mam- mals; the milk of Mammals; the ink of the Cuttle-fish ; the poison of Jelly-fishes, Insects, and Snakes; and the silk of Spiders and Caterpillars. ~y - we > R BS S SS NE < & S Ye apis 7 THE SKIN AND SKELETON. Toy CHAPTER XVI. THE SKIN AND SKELETON. The Skin, or Integument, is that layer of tissue which covers the outer surface of the body. The term Skeleton is applied to the hard parts of the body, whether external or internal, which serve as a framework or protection to the softer organs, and afford points of attachment to mus- eles. If external, as the crust of the Lobster, it is called Exoskeleton ; if internal, as the bones of Man, it is called Endoskeleton. The former is a modification of the skin; the latter, a hardening of the deeper tissues. 1. The Skin.—In the lowest forms of life, as Ameeba, there is no skin. The jelly of which they are composed is firmer outside than inside, but no membrane is present. In Infusoria, there is a very thin cuticle covering the ani- mal. They have thus a definite form, while the Ameebee continually change. Sponges and Hydras also have no true skin. But in Polyps, the outside layer of the animal is separated into two portions—ecderon and enderon”™— which may be regarded as partly equivalent to epiderinis and dermis in the higher animals. These two layers are, then, generally present. The outer is cellular, the latter fibrous, and may contain muscular fibres, blood-vessels, nerves, touch-organs, and glands. It thus becomes very complicated in some animals. In Worms and Arthropods, the cellular layer, here called hypodermis, excretes a structureless cuticle, which - may become very thick, as in the tail of the Horseshoe Crab, or may be hardened by deposition of lime-salts, as in many Crustacea. The loose skin, called the mantle, 128 ._COMPARATIVE ZOOLOGY. which envelopes the body of the Mollusk corresponds to the true skin of higher animals. The border of the man- tle is surrounded with a delicate fringe, and, moreover, contains minute glands, which secrete the shell and the coloring matter by which it is adorned. The Tunicates have a leathery epidermis, remarkable for containing, in- stead of lime, a substance resembling vegetable oelaleae | In Mammals, whose skin is most fully developed, the dermis is a sheet of tough elastic tissue, consisting of in- terlacing fibres, and containing blood-vessels, lymphatics, sweat-glands, and: nerves. It is the part converted into leather when hides are tanned, and attains the extreme thickness of three inches in the Rhinoceros. The upper surface in parts of the body is covered with a vast num- ber of minute projections, called papilla, each containing the termination of a nerve; these are the essential agents in the sense of touch.” ‘They are best seen on the tongue of an Ox or Cat, and on the human fingers, where they are arranged in rows. Covering this sensitive layer, and accurately moulded to all its furrows and ridges, lies the bloodless and nerve- less epidermis. It is that part of the skin which is raised in a blister. It is thickest where there is most. pressure or hard usage: on the back of the Camel it attains un- usual thickness. The lower portion of the epidermis (called rete mucosum) is comparatively soft, and consists of nucleated cells containing pigment-granules, on which the color of the animal depends. ‘Towards the surface the cells become flattened, and finally, on the outside, are changed to horny scales (Fig. 2, ¢). : These scales, in the higher animals, are constantly wear- ‘jing off in the form of scurf, and as constantly being renewed from below. In Lizards and Serpents, the old epidermis is cast entire, being stripped off from the head to the tail; in the Toad, it comes off in two pieces; in the THE SKIN AND SKELETON. 129 Fie. 94.—Section of Skin from Horse’s Nostril: E, epidermis; D, deimis; 1, horny layer of epidermis; 2, rete mucosum; 3, papillary layer of dermis; 4, excretory duct of a sudoriparous, or sweat, gland; 5, glomerule, or convoluted tube of the same; 6, hair follicle; 7, sebaceous gland; 8, internal sheath of the hair follicle ; 9, bulb of the hair; 10, mass of adipose tissue. Frog, in shreds; in Fishes and some Mollusks, in the form of slime. However modified the epidermis, or whatever its appendages, the like process of removal goes on. Mam- mals shed their hair; Birds, their feathers; and Crabs, their shells. When the loss is periodical, it is termed moulting. 2. The Skeletons. —(1) The Exoskeleton is developed by the hardening of the skin, and, with very few excep- tions, is the only kind of skeleton possessed by inverte- brate animals. The usual forms are coral, shells, crusts, scales, plates, hairs, and feathers. It is horny or calca- reous; while the endoskeleton is generally a deposit of earthy material within the body, and is nearly confined to the Vertebrates. The exoskeleton may be of two kinds —dermal and epidermal. The microscopic particles of living jelly, called Polycis- tina and Foraminifera, possess siliceous and calcareous shells of the most beautiful patterns. The Sponge has a 9 7 130 COMPARATIVE ZOOLOGY. skeleton of horny fibres, which is the sponge of commerce. Coral is the solid framework of certain Polyps. There are two kinds: one represented by the common white coral, which is a calcareous secretion within the body of Fie. 95.—1, Vertical Section, and, 2, Transverse Section, of a sclerodermic Corallite: a, mouth; 0b, tentacles; c, stomach; d, intermesenteric chamber; e, mesentery; J, septum: g, endoderm; h, epitheca; k, theca, or outer wall; m, columella; 1, short partitions; p, tabula, or transverse partition; rv, sclerobase; s, ceenenchy- ma, or common substance connecting neighboring corallites; ¢, ectoderm; 2, pali, or imperfect partitions. the Polyp, in the form of a cylinder, with partitions ra- diating towards a centre (scleroderm); the other, repre- sented by the solid red coral of jewelry, 1s a central axis deposited by a group of Polyps on the outside (sclero- Fie. 96.—Shell of Sea-urchin (Cidavis) without its spines. and beautiful construction. The shell base). The first sortisa dermal,the latter an epider- mal, exoskeleton. The skeleton of the Star-fish is a leathery skin stud- ded with caleare- ous particles and plates. The Sea- urchin is covered with an inflexible shell of elaborate is really a ealcified THE SKIN AND SKELETON. 131 skin, being a net-work of fibrous tissue and earthy matter. It varies in shape from a sphere to a disk, and consists of hundreds of angular pieces accurately fitted together, like mosaic-work. ‘These form ten zones, like the ribs of a melon, five broad ones alternating with five narrower qt ettat fi ® ©.o% 44 CATT s 2 STN ROY Ce’. e @e6 ry) e@ ) { F) e® Ltt he Fie. 97.—Structure of Sea-urchins’ Spines: 1, a, spine of Cidaris cut longitudinally ; t, 8, ball-and-socket joint ; p, pedicellariz ; 2, 3, transverse sections of spines of Cidaris and Echinus. ones. The former (called interambulacra) are covered with tubercles bearing movable spines. The narrow zones (called ambulacra, as they are likened to walks through a forest) are pierced with small holes, throngh which the animal sends out fleshy sucker-feet. The skin of the Crab and Lobster is hardened by cal- careous deposit into a “crust,” or shell; but, instead of forming one piece, it is divided into a series of segments, which move on each other. The number of these seg- ments, or rings, is usually twenty-one—to the head, tho- rax, and abdomen, seven each. In the adult, however, the rings of the head and thorax are often soldered to- gether into one shield, called cephalo-thorax ; and in the Horseshoe Crab the abdominal rings are also united. The shell of Crustaceans is periodically cast off, for the ani- mals continue to grow even after they have reached their 132 COMPARATIVE ZOOLOGY. | mature form. This moulting is a very remarkable opera- tion. How the Lobster can draw its legs from their cases : without unjointing or sphtting them was long a puz zle. The flesh be- drawn through the joints, the wounds thus caused quickly healing. The east- off skeleton is a per- fect copy of the an- imal, retaining in their places the del- icate coverings of the eyes and anten- Fie. 98.—Diagram of an Insect: A, head bearing the lining membrane of eyes and antenne; B, prothorax, carrying the first pair of legs; C, mesothorax, carrying the second the stomach with its pair of legs and first pair of wings; D, carrying the third pair of legs and second pair of wings; E, ab- teeth. domen, with ovipositor, F; 1, coxa, or hip; 2, tro- chanter; 3, femur, or thigh; 4, tibia, or shank; 5, tar- The horny crust sus, or foot; 6, claw. of Insects ditters from that of Crustaceans in consisting mainly of a horny substance called chitine and in containing no lime. The head, thorax, and abdomen are distinct, and usually con- sist of fourteen visible segments—one for the head, three for the thorax (called prothorax, mesothorax, and metatho- rac),and ten for the abdomen. The antenne, or feelers, legs, and wings, as well as hairs, spines, and scales, are ap- pendages of the skeleton. As Insects grow only during the larval, or caterpillar, state, moulting is confined to that period. These skeletons are epidermal, deposited in suc- cessive layers, from the inside, and are, therefore, capable of but slight enlargement when once formed. comes soft, and is. ne, and even the - THE SKIN AND SKELETON. 133 The shells of Mollusks are well-known examples of exo- skeletons. ‘The mantle, or loose skin, of these animals se- eretes calcareous earth in successive layers, converting the epidermis into a “shell.” So various and characteristic is the microscopic character of shells, that a fragment is sometimes sufficient to determine the group to which it belongs. Many shells resemble that of the Fresh-water Mussel (Unio), which is composed of three parts: the ex- ternal brown epidermis, of horny texture; then the pris- matic portion, consisting of minute columns set perpen- dicularly to the surface; and the internal nacreons layer, or “ mother-of-pearl,” made up of exceedingly thin plates. The pearly lustre of the last is due to light falling upon the outcropping edges of wavy lamine.” In many eases, the prismatic and nacreous layers are traversed by minute tubes. Another typical shell-structure is seen in the com- mon Cone, a section of which shows three layers, besides the epidermis, consisting of minute plates set at different angles. The Nautilus is composed of two distinct layers: the outer one having the fracture of broken china; the ° inner one, nacreous. Most living shells are made of one piece, as the Snail; _ these are called “univalves.” Others, as the Clam, con- sist of two parts, and are called “ bivalves.” In either case, a valve may be regarded as a hollow cone, growing in a spiral form. The ribs, ridges, or spines on the ont- side of a shell mark the successive periods of growth, and, therefore, correspond to the age of the animal. The figures on the following page show the principal parts of the ordinary bivalves and univalves. The valves of a bivalve are generally equal, and the umbones, or beaks, a little in front of the centre. The valves are bound to- gether by a ligature near the umbones, and often, also, by means of a “hinge” formed by the “teeth” of one valve interlocking into cavities in the other. The aperture of 134 COMPARATIVE ZOOLOGY. a univalve is frequently closed by a horny or calcareous plate, called “ operculum,” which the animal carries on its back, and which is a part of the exo- skeleton. The shells of Mollusks are epidermal, and are, therefore, dead and incapable of true repair. When broken, they can be mended h ————\\ X ) Kod ay Fie. 99.—Left Vaive of a Bivalve Mollusk (Cytherea Fie. 100. —Section of a Spiral chione): h, hinge ligament; uw, umbo; J, lunule; Univalve (Triton corrugatus) : c, cardinal, and ¢,?¢’, lateral teeth; a,a’, impres- a, apex; b, spire; c, suture; sions of the anterior and posterior adductor mus- d, posterior canal; e, outer cles; y, pallial impression ; s, sinus, occupied by lip of the aperture; jf, ante- the retractor of the siphons. rior canal. only by the animal pouring out lime to cement the parts together. They cannot grow together, like a broken bone. Imbedded in the back of the Cuttle-fish is a very light spongy ‘‘ bone,” which, as already observed, is a secretion from the skin, and therefore belongs to the exoskeleton. It has no resemblance to true bone, but is formed, like shells, of a number of calcareous plates. Nevertheless, the Cuttle-fish does exhibit traces of an endoskeleton: these are plates of cartilage, one of which surrounds the brain, and hence may be called a skull. To this cartilage, not to the “ cuttle-bone,”’ the muscles are attached. In Vertebrates, the exoskeleton is subordinate to the endoskeleton, and is feebly developed in comparison. It THE SKIN AND SKELETON. 135 is represented by a great variety of appendages to the skin, which are mainly organs for protection, not for sup- port. Some are horny developments of the ep- idermis, such as_ hairs, feathers, nails, claws, hoofs, horns, and the scales of Reptiles; oth- ers arise from the hard- ening of the dermis by calcareous matter, as the WW \\; NOS SS Fie. 101.—Skeletal Architecture aS the Armadil- scales of Fishes, the bony lo, showing the relation of the carapax to the plates of Crocodiles and vertebral column. Turtles, and the shield of the Armadillo. The scales of Fishes (and likewise the spines of their vertical fins) lie imbedded in the overlapping folds of the skin, and are covered with a thin, slimy epidermis. The scales of the bony Fishes (Perch, Salmon, etc.) consist of Fia. 102.—Diagrammatic Section of the Skin of a Fish (Carp): a, derm, showing lam- inated structure with vertical fibres, b; c, gristly layer; e, laminated layer, with calcareous granules; d, superficial portion developing into scales ; J, scale-pit. two layers, slightly calcareous, and marked by concentric and radiating lines. Those of the Shark have the structure of teeth, while the scutes, or plates, of the Crocodiles, Turtles, and Armadillos are of true bone. The scales of Snakes and Lizards are horny epidermal plates covering the overlapping folds of the true skin. In some Turtles these plates are of great size, and are called “ tortoise-shell;” they cover the scutes. The scales on the legs of Birds, and on the tail of the Beaver and Rat, have the same structure. Nails are flattened horny plates developed from the upper surface of the fingers 136 COMPARATIVE ZOOLOGY. Wi aA AEE iis yy WEA and toes. Claws are sharp conical nails, being devel- oped from the sides as well as upper surface; and hoofs are blunt cylin-- drical claws. Hol- low horns, as of the Ox, may be likened to claws sheathing a bony core. The Fie. ae Seas oe ee x the Forefoot of the Horse horn of the Rhinoe- (middle digit): 1,2, 4, proximal, middle, and distal, or ungual, phalanges; 3, sesamoid, or nut-bone ; . e©os is a solid mass 6, 7, tendons; 9, elastic tissue; 8, 10, internal and of e idermal fi external floor of the hoof; 11, 12, internal and exter- P bres. nal walls. rattles of the Rattlesnake, and the beaks of Turtles and Birds, are hke- wise epidermal. Hairs, the characteristic clothing of Mammals, are elongated horny cones, composed of “pith” and “crust.” The latter is an outer layer of minute overlapping scales, which are directed towards the point, so that rubbing a human hair or fibre of wool between the thumb and finger pushes the root- end away. The root is bulbous, and is contained in a minute de- pression, or sac, formed by an in- folding of the skin. Hairs are usn- ally set obliquely into the skin. Poreupine’s quills and Hedgehog’s spines make an easy transition to ‘“‘'Whalebone,” the Fie.104. aan of the Rootand part of the Shaft of a Human Hair; it is covered with epi- dermic scales, the inner layer, c, forming the outer covering of the shaft, being imbricated ; the root consists of angular cells loaded with pigment. THE SKIN AND SKELETON. 137 feathers, which differ from hairs only in splitting up into numerous lamine. They are the most complicated of all the modifications of the epidermis. They consist of a “quill” (answer- ing to the bulb of a hair), and a “shaft,’ supporting the “vane,” which is made up of “ barbs,” * bar- bules,”’ and interlocking “ process- es.” The quill alone is hollow, and has an orifice at each end. Thus feather is moulded on a papilla, the shaft lying in a groove on one side of it, and the vane wrapped around it. When the feather emerges from the skin, it unfolds itself. Thus shaft and vanes together resemble the quill split down one side and spread out. The teeth of Mollusks, Worms, and Arthropods are also epidermal structures. Those of Vertebratesare mixed in their origin, the dentine be- ing derived from the dermis and the enamel from the epidermis. In all cases teeth belong to the exoskeleton. (2) The Endoskeleton, as we have seen, 1s represented in the Cuttle- fish. With this and some other exceptions, it 1s peculiar to Verte- MOLLE AE =f — x os Vege LIED LZ, & ape} i i | \ \\W () Fie. 105.—Parts of a Feather: a, quill, or barrel; 0, shaft; c, vane, or beard; d, accessory plume, or down; @, f, lower and upper umbilicus, or ori- fice, leading to the interior of the quill. =€ brates. In the Cuttle-fish, and some Fishes, as the Stur- geon and Shark, it consists of cartilage; but in all others (when adult) it is bone or osseous tissue. Yet there is a diversity in the composition of bony skeletons; that of fresh-water Fishes contains the least earthy matter, and that of Birds the most. Hence the density and ivory- 138 COMPARATIVE ZOOLOGY. whiteness of the bones of the latter. Unlike the shells of Mollusks and the crust of the Lobster, which grow by the addition of layers to their borders, bones are moist, living parts, penetrated by blood-vessels and nerves, and covered with a tough membrane, called perzosteum, for the attach- ment of muscles. The surface of bones is compact; but the interior may — be solid or spongy (as the bones of Fishes, Turtles, Sloths, and Whales), or hollow (as the long bones of Birds and the active quadrupeds). There are also cavities (called ‘sinuses ’’) between the inner and outer walls of the skull, as is remarkably shown by the Elephant. The cavities in the long bones of quadrupeds are filled with marrow; those in the long bones of Birds and in skulls contain air. The number of bones not only differs in different ani- mals, but varies with the age of an individual. In very early life there are no bones at all; and ossification, or the conversion of cartilage into bone, is not completed until maturity. This process begins at a multitude of points, and theoretically there are as many bones in a skeleton as centres of ossification. But the actual number is usually much less—a result of the tendency of these centres to coalesce. Thus, the thigh-bone in youth is composed of five distinct portions, which gradually unite. So in the lower Vertebrates many parts remain distinct which in the higher are joined into one. The occiput or back-bone of Man’s skull is the union of four bones, which are seen separate in the skull of the Fish, or of a baby. A complete skeleton, nade up of all the pieces which might enter into its composition, does not exist. Every Vertebrate has some deficiency. All, except Amphioxus, have a skull and back-bone; but in the development of the various parts, and especially of the appendages, there is endless variety. Fishes possess a great number of skull- bones, but have no fingers and toes. The Snake has plenty THE SKIN AND SKELETON. 139 of ribs and tail, but no breast-bone; the Frog has a breast- bone, but neither tail nor ribs. As the skeleton of a Fish is too complicated for the primary student, we will select *slsi1v} ‘g9 * Wnou -Bd[Bd 10 ‘aay {gg + vinqy ‘29 * BIqT} ‘99 ‘ v[[e}ud “99 +.amutey ‘gg yore oIqnd ‘pg + WNnIYOsS! “gg + WNIT ‘49 ‘sndivovjau “e@ tsndavo ‘9g ‘vuln ‘gg ‘snipes ‘pq Ssnistuny ‘gg :vindvos ‘Tg *(s[epnBo 910 OL 0} g Wor Sutavy ul A[Go Bog oy} Jo Vy} WOT siayiIp UoVry oy} Jo UWUIN[OD [V1Qe}10A oY) [VpNvd Ss Je Se ~ 1) Hf ) Ail\) LOSE Al Sry és A je 4 & on a Tem la” Waa Wee ‘L ‘ [vives ‘g favquiny “JT + [essop ‘q *BiqayladA [BOTAIO. ‘OD 2 (0a) $2747) WOT 94} JO UOJO[OYS—‘9OL “ST rupeds. It should be remembered, however, that all Ver- tebrates are formed on one plan. In the lowest Vertebrate, Amphioxus, the only skeleton is a cartilaginous rod running from head to tail. There is no skull, nor ribs, nor limbs. In the cartilaginous Fishes, 140 COMPARATIVE ZOOLOGY. the backbone is only partially ossified. But usually it consists of a number of separate bones, called vertebra, ar- ranged along the axis of the body. They range in number from 10 in the Frog to 305 in the Boa-constrictor. The skull, with its appendages, and the vertebre, with the ribs and sternum, make up the aaal skeleton. The shoulder and pelvic girdles and the skeleton of the limbs constitute - the appendicular skeleton. A. typical vertebra consists of a number of bony pieces so arranged as to form two arches, or hoops, connected by Vea ~\ 4 NOMA? = Dp Fie. 107.—Vertebree—A, cervical; B, dorsal; 2, centrum; 4, transverse process, con- taining foramen, a, for artery; 5, articular process; 8, spinous process, or neural spine; 1, neural canal; 6, facets for head of rib, the tubercle of the rib fitting in a facet on the process, 4; 6, laming, or neurapophyses. a central bone, or centrum.” The upper hoop is called the neural arch, because it encircles the spinal marrow ; the lower hoop is called the hemal arch, because it en- closes the heart and the great central blood-vessels. An actual vertebra, however, is subject to so many modifica- tions, that it deviates more or less from this ideal type. Selecting one from the middle of the back for an exam- ple, we see that the centrum sends off from its dorsal side two branches, or processes, called newrapophyses. These meet to form the neural arch, under which is the neural canal, and above which is a process called the neural spine. On the anterior and posterior edges of the arch are smooth surfaces, or zygapophyses, which in the natural state are covered with cartilage, and come in contact with THE SKIN AND SKELETON. 141 the corresponding surfaces of the preceding and succeed- ing vertebree. The bases of the arch are notched in front and behind, so that when two vertebree are put together a round opening (¢ntervertebral foramen) appears between the pair, giving passage to the nerves issuing from the spinal cord. From the sides of the arch, blunt transverse processes project outward and backward, called diapophy- ses. Such are the main elements in a representative ver- tebra. The hemal arch is not formed by any part of the vertebra, but by the ribs and breast-bone. Theoretically, however, the ribs are considered as elongated processes from the centrum ( pleurapophyses), and in a few cases a hemal spine is developed corresponding to the neural spine. | The vertebre are united together by ligaments, but chiefly by a very tough, dense, and elastic substance be- tween the centra. The neural arches form a continuous canal which contains and protects the spinal cord; hence the vertebral column is called the neuroskeleton. The column is always more or less curved; but the beautiful sigmoid curvature is peculiar to Man. The vertebree gradually increase in size from the head towards the end of the trunk, and then diminish to the end of the tail. The neural arch and centrum are seldom wanting; the first vertebra in the neck has no centrum. and the last in the tail is all centrum. ‘The vertebre of the extremities (head and tail) depart most widely from the typical form. The vertebral column in Fishes and Snakes is divisible into three regions — head, trunk, and tail. But in the higher animals there are six kinds of vertebre: cranial, cervical, dorsal, lumbar, sacral, and caudal. Lhe cranial vertebre form the skull.” They are greatly modified, as the neural arches are expanded to enclose the brain. The number of distinct bones composing the skull is greatest in Fishes, and least in Birds: this arises partly COMPARATIVE ZOOLOGY. 142 Wk LY ti @ rm rt r & Lon | Gy THE SKIN AND SKELETON. 143 € BONES OF THE MAMMALIAN SKULL.* BRAIN-CASE. NASAL. FRONTAL. PARIETAL. SUPRAOCCIPITAL. LAC|HRYMAL. SQUAMOSAL. N OSE. ORBITOSPHENOID. EYE. ALISPHENOID. PERI- EAR, OTIC. EXOCCIPITAL. MALAR. TYMPANIC, ETHMOID. PRESPHENOID. BASISPHENOID, BASIOCCIPITAL. VOMER. HYOID ARCH. PREMAXILLA. MAXILLA. PALATINE. PTERYGOID. LOWER JAW, OR MANDIBLE, THE SKULL OF THE DOG. Fig. 108.—Under surface. Fie. 109.—Upper surface. Fie. 110.—Longitudinal ver- tical section; one-half natural size: SO, supraoccipital; HxO, exoccipital; BO, basioccipital; P, interparietal; Pa, parietal; Fr, frontal; Sq, squamosal; Ma, malar; ZL, lachrymal; Mz, maxilla; PMz, premaxilla; Na, nasal; MT, maxillo- turbinal; #7, ethmoturbinal; ME, ossitied portion of the mesethmoid; CE, cri- briform, or sieve-like, plate of the ethmoturbinal; VO, vomer; PS, presphenoid; OS, orbitosphenoid; AS, alisphenoid; BS, basisphenoid; Pl, palatine; Pt, pterygoid; Per, periotic; 7'y, tympanic bulla; an, anterior narial aperture; ap, or apf, anterior palatine foramen; ppf, posterior palatine foramen ; 70, infra- orbital foramen; pos, postorbital process of frontal bone; op, optic foramen; sf, sphenoidal fissure; fr, foramen rotundum, and anterior opening of alisphenoid canal; as, posterior opening of alisphenoid canal; fo, foramen ovale; jim, fora- men lacerum medium; gf, glenoid fossa; gp, postglenoid process; pg/f, post- glenoid foramen; eam, external auditory meatus; sm, stylomastoid foramen ; Jip, foramen lacerum posterius ; ¢f, condylar foramen; pp, paroccipital process ; oc, Occipital condyle; fm, foramen magnum; a, angular process; s, symphysis of the mandible where it unites with the left ramus; 7d, inferior dental canal; cd, condyle; cp, coronoid process; the * indicates the part of the cranium to which the condyle is articulated when the mandible is in place; the upper border in which the teeth are implanted is called alveolar; sh, eh, ch, bh, th, hyoidean ap- paratus, or os lingue, supporting the tongue. In the skulls of old animals, _ there are three ridges: occipital, behind; sagittal, median, on the upper surface ; and superorbital, across the frontal, in the region of the eyebrows. The last is highly developed in the Gorilla and other Apes. * In this diagram, modified from Huxley's, the italicized bones are single; the rest are double. Those in the line of the Ethmoid form the Cranio-facial Azis: these, with the other sphenoids and occipitals, are developed in cartilage; the rest are membrane bones. In the Human skull, the four occipitals coalesce into one. 144 COMPARATIVE ZOOLOGY. from the fact that the bones remain separate in the for- mer case, while those of the chick become united together (anchylosed ) in the full-grown Bird; but many bones are present in the Fish which have no representatives in the Bird. The skull consists of the brain-case and the face. The principal parts of the skull, as shown in the Dog’s, are: 1. The occzpital bones behind, enclosing a large hole, or foramen magnum, on each side of which are rounded prominences, called condyles, by which the skull articulates with the first cervical vertebra. 2. The parietal. 3. The Frontal. These three form the main walls of the brain. 4, The sphenovd, on the floor of the skull in front of the occipital, and consisting of six pieces. 5. The temporal, in which is situated the ear. In Man this is one bone; but in most animals there are three or more—the periotic, tympanic, and sguamosal. 6. The malar, or “cheek-bone,” which sends back a process to meet one from the squamo- sal, forming the zygomatic arch. . The nasal, or roof of Fig. 111. —Skull of the Horse: 1, premaxillary bone; 2, upper incisors; 3, upper canines; 4, superior maxillary; 5, infraorbital foramen; 6, superior maxillary spine; 7, nasal bones; 8, lachrymal; 9, orbital cavity; 10, lachrymal fossa; 11, malar; 12, upper molars; 13, frontal; 15, zygomatic arch; 16, parietal; 17, oc- cipital protuberance; 18, occipital crest; 19, occipital condyles; 20, styloid proc- esses; 21, petrous bone; 22, basilar process; 23, condyle of inferior maxillary ; 94, parietal crest; 25, inferior maxillary; 26, lower molars; 27, anterior maxillary foramen; 28, lower canines; 29, lower incisors. THE SKIN AND SKELETON. 145 the nose. 8. The maailla; that part of the upper jaw in which the canines, premolars, and molars are lodged. 9. The premaxilla, in which the upper incisors are situated. 10. The palatine, which, with the maxillary bones, forms the roof of the mouth. ‘There are two appendages to the skull: the mandzble, or lower jaw, whose condyles, or rounded extremities, fit into a cavity (the glenoid) in the temporal bone; and the hyozd, situated at the root of the tongue. ; The simplest form of the skull is a cartilaginous box, as in Sharks, enclosing the brain and supporting the car- tilaginous jaws and gill arches. In higher Fishes this box is overlaid with bony plates and partly ossified. In Frogs the skull is mainly bony, although a good deal of the car- tilage remains inside the bones. In higher Vertebrates the cartilage never makes an entire box, and early disappears. The cervical vertebre, or bones of the neck, are peculiar in having an orifice on each side of the centrum for the passage of an artery. The first, called atlas, because it supports the head, has no centrum, and turns on the sec- ond, called axzs, around a blunt process, called the odon- tod. The centra are usually wider than deep, and the neural spines very short, except in the last one. The number of cervical vertebrae ranges from 1 in the Frog to 25 in the Swan. The dorsal vertebre are such as bear ribs, which, uniting with the breast-bone, or sternwm, form a bony arch over the heart and lungs, called the thorax. The sternum may be wanting, as in Fishes and Snakes, or greatly developed, as in Birds. When present, the first vertebra whose ribs are connected with it is the first dorsal. The neural spines of the dorsal series are generally long, pointing backward. The lumbar vertebre are the massive vertebree lying in the loins between the dorsals and the hip-bones. Lhe sacral vertebre lie between the hip-bones, and are 10 146 COMPARATIVE ZOOLOGY. generally consolidated into one complex bone, called sa- — crum. The caudal vertebre are placed behind the sacrum, and form the tail. They diminish in size, losing processes and neural arch, till finally nothing is left but the centrum. | They number from 3 or 4 in Man to 270 in the Shark. Besides the lower jaw, hyoid, and ribs, Vertebrates have other appendages to the spinal column—two pairs of lambs.” The fore limb is divided into the pectoral arch (or shoulder girdle), the arm, and the hand. The arch is fastened to the ribs and vertebree by powerful muscles, and consists of three bones, the scapula, or shoul- der- blade, the coracozd, and the clavicle, or collar-bone. The scapula and coracoid are generally united in Mam- mals, the latter forming a process of the former; and the clavicles are frequently wanting, as in the hoofed animals. The humerus, radius, and ulna are the bones of the arm, the first articulating by ball-and-socket joint with the scapula, and by a hinge-joint with the radius and ulna. The humerus and radius are always present, but the ulna may be absent. The bones of the hand are divided into those of the carpus, or wrist; the metacarpus, or palm ; and the phalanges, or fingers. The fingers, or “ digits,” range in number from 1 to 5. ! The hind limb is composed of the pelvze arch (or hip- bones), the deg, and the foot. These parts correspond ~ closely with the skeleton of the fore limb. Like the shoulder, the pelvic arch, or 0s tn~nominatum, consists of three bones—zlium, ischium, and pubis. The three are distinct in Amphibians, Reptiles, and in the young of higher animals; but in adult Birds and Mammals they become united together, and are also (except in Whales) solidly attached to the sacrum. The two pelvic arches and the sacrum thus soldered into one make the pelvis. The leg-bones consist of the femur, or thigh; the écbza, or THE SKIN AND SKELETON. 147. shin-bone; and the jebwla, or splint-bone. The rounded head of the femur fits into a cavity (acetabulum) in the pelvic arch, while the lower end articulates with the tibia, and sometimes (as in Birds) with the fibula also. An ex- tra bone, the patella, or knee-pan, is hung in a tendon in front of the joint between the femur and tibia of the high- er animals. The foot is made up of the tarsus, or ankle; the metatarsus, or lower instep; and the phalanges, or toes. The toes number from 1 in the Horse to 5 in Man. Certain parts of the skeleton, as of the skull, are firmly joined together by zigzag edges or by overlapping; in either case the joint is called a sutwre. But the great majority of the bones are intended to move one upon an- other. The vertebra are locked together by their proc- esses, and also by a tough fibrous substance between the centra, so that a slight motion only is allowed. The limbs furnish the best examples of movable articulations, as the ball-and-socket joint at the shoulder, and the hinge-joint at the elbow. The bones are held together by ligaments, and, to prevent friction, the extremities are covered with cartilage, which is constantly lubricated with an unctuous fluid called synovia. CHEMICAL COMPOSITION OF BONES. Cop. Tortoisz.| Hawk. Man. | Phosphate of Lime, with trace of | Wingate of Toime......65..5....0000 57.29 52.66 64.39 59.63 Carbonate of Lime................... 4.90 12.53 7.03 7.33 | Phosphate of Magnesia............. 2.40 0.82 0.94 1.32 | Sulphate, Carbonate, and Chlorate Cait ee Me 1.10 0.90 0.92 0.69 Glutine and Chondrine............. 32.31 31.75 25.73 29.70 PEE RS, Co 2.00 1.34 0.99 1.33 100.00 | 100.00 | 100.00 | 100.00 E ZOOLOGY. COMPARATIV 148 ; “Ty [vue ‘9g t seshydodeied ‘n ‘eg : soutds [PUY ‘q ‘eg uy [vides ‘Tg !auoqg orajed ‘og ‘sug [esiop “Gy +sat0q snouldsieyal ‘6y ‘py, !sesseooid UIOJI[AIS ‘G) *8QlI ‘ZL * Ty ‘UY [VpNVd ogy Jo JuoMYOV}}e ‘od *Tepneo ‘69 + a1q -a}10A [VUIWOpE ‘9 ‘19 *sasB[yaIVvd leseq ‘eg ‘ upndvos ‘zg + ploov100 *1¢ ‘uy peojoed Jo skvi [eyLoIp ‘0g ! epoTAvyo ‘gp Sagpravpeidnus ‘yp * e1odwa}-ysod ‘op tsaprofy sO oY} JO sayouBI VY} TeeMjoq Sutf[ ‘teXyoun ‘gp | 1epnSue ‘gg * avpnorqae ‘eg $yj90} OU} SuLULe}UOD MU Jamo] 9y1 Jo Jed qvyqy—Aivjuep Se $un[nodadosezul ‘gg ¢ uNUdIedoqns ‘ze Saqeapenb ‘Tg : wn[nosedoaid ‘og ‘ sSuruado-[]19 oy} Sutsoyo ‘deg azo ‘unjuo1edo ‘gz ‘ proSAraydeyjour ‘yz * plos -k191d0390 ‘7% {| [elodwajojsvul “EZ * (SeyslA 0} reyjnoed) peroduieieadns ‘1% ¢gaiuid [BIIqioqus ‘0g *[esvuoid ‘ET + Alv[[Ixeul ‘gy ¢ Arvyixvmaid ‘y7 S[esea ‘oT toqosagd ‘gt Sorjgord ‘Tr $pesdroooxe “6 * eyidyooowsdus ‘g *yejozred *y ‘ ;eyuoayysod “p $yeiuody ‘Ts (segwranyf vosag) Ydlad oY} JO UO[IAS— BIT “OT 8 EEE TST ete SZEETESIV ss 93 DEAE 2S 9 Wr : Is \N Sp | LSSss4 RT eg 149 THE SKIN AND SKELETON. _ st NC SS \ ) q SS \ \ e i LY Quen Fie. 113.—Skeleton of the Crocodile. Nes IS = URALA xi pee] eRe ey Wy we G 150 COMPARATIVE ZOOLOGY. = SS 23> S| 3 a ca 7 Ss = 8 Fig. 115.—Skeleton of the Tortoise (plastron removed): a, cervical vertebre; c, dor- sal vertebre; d, ribs; e, marginal bones of the carapace; Jl, scapula; &, precora- coid ; b, coracoid; J, pelvis; 7, femur; g, tibia ; h, fibula. Z 4%% j Fie. 116.—Skeleton of a Vulture: 1, cranium—the parts of which are separable only in the chick; 2, cervical vertebre; 3, dorsal; 4, coccygeal, or caudal; the lumbar and sacral are consolidated ; 5, ribs; 6, sternum, or breast-bone, extraordinarily developed; 7, furculum, clavicle, or ‘‘wish-bone;’’ 8, coracoid; 9, scapula; 10, humerus; 11, ulna, with rudimentary radius; 12, metacarpals; 13, phalanges of the great digit of the wing; 19, thumb; 14, pelvis; 15, femur; 16, tibia-tarsus and fibula, or crus; 17, tarso-metatarsus; 18, internal digit, or toe, formed of three phalanges; the middle toe has four phalanges ; the outer, five; and the back toe, or thumb, two. THE SKIN AND SKELETON. 151 Fig. 117.—Skeleton of the Horse (Equus caballus): 22, premaxillary; 12, foramen in the maxillary; 15, nasal; 9, orbit; 19, coronoid process of lower jaw; 17, surface of implantation for the masseter muscle; there are seven cervical vertebre, nine- teen dorsal, D-D; five lumbar, a-e; five sacral, /-7; and seventeen caudal, p-r; 51, scapula, or shoulder-blade; 7, spine, or crest; h, coracoid process (acromion - wanting); 1, first pair of ribs (clavicle wanting, as in all Ungulates) ; e, sternum; a, shaft of humerus; 8, deltoid ridge; g, head fitting in the glenoid cavity of the scapula—near it is a great tuberosity for the attachment of a powerful muscle; k, condyles ; 54, radius, to which is firmly anchylosed a rudimentary ulna, 55, the olecranon; 56, the seven bones of the carpus, or wrist; 57, larze metacarpal, or **cannon-bone,” with two “ splint-bones ;” 58, fetlock-joint ; 59, phalanges of the developed digit, corresponding to the third finger in Man; 62, pelvis; 63, the great trochanter, or prominence on the femur, 65; 66, tibia; 67, rudimentary fibula; 68, hock, or heel, falsely called knee; 69, metatarsals. —— ~e-enwe-— -——._- COMPARATIVE ZOOLOGY. -—-— ~~ ~. — ie yp); 8 Stee oe Fig. 119.—Skeleton of an Elephant (£ lephas Indicus). Po 153 THE SKIN AND SKELETON. Fic. 120.—Skeleton of the Chimpanzee (T7roglodytes Niger). Pe ~ ih i: bi 154: COMPARATIVE ZOOLOGY. CHAPTER XVII. HOW ANIMALS MOVE. 1. THE power of animal motion is vested in protoplasm, cilia, and muscles. The power of contractility is one of the ultimate physiological properties of protoplasm, like sensibility and the power of assimilation. Protoplasma- animals, like the Amceba and Rhizopoda, move by the contractility of their protoplasm, as also may the germs of higher animals upon the yolk of the egg. The proto- plasm may be extended into projections called pseudopodia, by whose contraction the animal may move (Fig. 186). Infusoria, and nearly all higher animals, possess caza (Fig. 188). These are microscopic hairs (Fig. 2, 6) which have the power of bending into a sickle-shape and straight- ening out. As they bend much faster than they straight- en, and as they all work together, they can cause motion of the animal, or may serve to produce currents in the water, the animal remaining at rest. They are seen on the outside of Infusoria, and of very many embryos of higher animals, serving as paddles for locomotion; they fringe the gills of the Oyster, creating currents for respi- ration; and they line the passage to our lungs to expel the mucus. lagella (Fig. 189) are a sort of long cilia, which are thrown into several curves when active, resem- bling a whip-lash, whence their name. Both cilia and fila- gella seem to be wanting in Arthropods. The cause of ciliary motion is unknown. Their one- sided contraction is their property, as the straight con- traction of the muscle-fibre belongs to it. No structure can, however, be seen in them with the microscope. No HOW ANIMALS MOVE. 155 nerves go to them, yet they work in concert, waves of motion passing over a surface covered with cilia, as over a field of grain moved by the wind. But muscular tissue is the great motor agent, and exists in all animals from the Coral to Man.” The power of contractility, which in the Ameeba is diffused throughout the body, is here confined to bundles of highly elastic fibres, called muscles. When a muscle contracts, it tends Fig. 121.—A Contracting Muscle. to bring its two ends together, thus shortening itself, at the same time increasing in thickness. This shrinking property is excited by external stimulants, such as elec- tricity, acids, alkalies, sudden heat or cold, and even a sharp blow; but the ordinary cause of contraction is an influence from the brain conveyed by a nerve. The prop- erty, however, is independent of the nervous system, for the muscle may be directly stim- ulated. The amount of force with which a muscle contracts depends on the number of its fibres; and the amount of shortening, on their length. As arule, muscles are white in cold-blooded animals, and red in the warm-blooded. They are white in all the Invertebrates, Fishes, Batrachians, and Reptiles, except Salmon, Sturgeon, and Shark; and red in Birds and Mammals, except in the breast of the com- F', 122 — Un- striped Muscu- mon fowl, and the like.” eee : , : enlarged; n, It is also a rule, with some exceptions, that nucleus. b] 9 the voluntary muscles of Vertebrates, and all the muscles 156 COMPARATIVE ZOOLOGY. of the Lobster, Spider, and Insect tribes, are striated ; while the involuntary muscles of Vertebrates, and all the muscles of Radiates, Worms, and Mollusks, are smooth. All mus- cles attached to internal bones, or to a jointed external skeleton, are striated. ‘The voluntary muscles of Verte- brates are generally solid, and the involuntary hollow.” This leads to another classification of muscles: into — those which are attached to solid parts within the body; those which are attached to the skin or its modifications ; and those having no attachments, being complete in them- selves. The last are hollow or circular muscles, enclosing a cavity or space, which they reduce by contraction. Ex- amples of such are seen in the heart, blood-vessels, stom- ach, iris of the eye, and around the mouth. In the lower Invertebrates, the muscular system is a net-work of longi- tudinal, transverse, and oblique fibres intimately blended with the skin, and not divisible into separate muscles. As in the walls of the human stomach, the fibres are usually in three distinct layers. This arrangement is exhibited by soft-bodied animals, like the Sea-anemone, the Snail, and the Earth-worm. Four thousand muscles have been count- ed in a Caterpillar. There are also “skin-muscles” in the higher animals, as those by which the Horse produces a twitching of the skin to shake off insects, and those by which the hairs of the head and the feathers of Birds are made to stand on end. Invertebrates whose skin is hard- ened into a shell or crust have muscles attached to the inside of such a skeleton. Thus, the Oyster has a mass of parallel fibres connecting its two valves; while in the Lobster and Bee fibres go from ring to ring, both longi- tudinally and spirally. The muscles of all Invertebrates are straight parallel fibres, not in bundles, but distinct, and usually flat, thin, and soft. The great majority of the muscles of Vertebrates are attached to the bones, and such are voluntary. The fibres, HOW ANIMALS MOVE. TST which are coarsest in Fishes (most of all in the Rays), and finest in Birds, are bound into bundles by connective tis- sue; and the muscles thus made up are arranged in layers around the skeleton. Sometimes their extremities are at- tached to the bones (or rather to the periosteum) directly ; but generally by means of white inelastic cords, called tendons. In Fishes, the chief masses of muscle are dis- posed along the sides of the body, apparently in longitu- dinal bands, reaching from head to tail, but really in a series of vertical flakes, one for each vertebra. In propor- tion as limbs are developed, we find the muscles concen- trated about the shoulders and hips, as in quadrupeds. The bones of the limbs are used as levers in locomotion, the fulcrum being the end of a bone with which the mov- ing one is articulated. Thus, in raising the arm, the hu- merus is a lever working upon the scapula as a fulcrum. The most important muscles are called extensors and flex- ors. ‘The latter are such as bring a bone into an angle with its fulerum—as in bending the arm—while the for- mer straighten the limb. Adbductors draw a limb away from the middle line of the body, or a finger or toe away from the axis of the limb, while adductors bring them back. 2. Locomotion.—AH animals have the power of vol- untary motion, and all, at one time or another, have the means of moving themselves from place to place. Some are free in the embryo-life, and fixed when adult, as the Sponge, Coral, Orinoid, and Oyster. There may be no regular well-defined means of progression, as in the Ame- ba, which extemporizes arms to creep over the surface; or movement may be accomplished by the contraction of the whole body, as in the Jelly-fish, which, pulsating about fifteen times in a minute, propels itself through the water. So the Worms and Snakes swim by the undulations of the body. | But, as a rule, animals are provided with special organs 158 COMPARATIVE ZOOLOGY. for locomotion. These become reduced in number, and progressively perfected, as we advance in the scale of rank. Thus, the Infusorian is covered with thousands of hair-like cilia; the Star-fish has hundreds of soft, unjoint- ed, tubular suckers; the Centipede has from 30 to 40 jointed hollow legs; the Lobster, 10; the Spider, 8; and the Insect, 6; the Quadruped has 4 solid limbs for loco- motion; and Man, only 2. (1) Locomotion in Water—As only the lower forms of life are aquatic, and as the weight of the body is partly sustained by the element, we must expect to find the or- gans of progression simple and feeble. The Infusoria swim with great rapidity by the incessant vibrations of the delicate filaments, or cilia, on their bodies. The com- mon Squid on our coast admits water into the interior of the body, and then suddenly forces it out through a fun- nel, and thus moves backward, or forward, or around, ac- cording as the funnel is turned—towards the head, or tail, or to one side. The Lobster has a fin at the end of its tail, and propels itself backward by a quick down-stroke of the abdomen. But Fishes, whose bodies offer the least resistance to progression through water, are the most perfect swimmers. Thus, the Salmon can go twenty miles an hour, and even tN Ae NA OM Sees Ca — ania. \ Ns Fig. 123.—The Fins of a Fish [Pte merch). ascend cataracts. They have fins of two kinds: those set obliquely to the body, and in pairs; and those which are HOW ANIMALS MOVE. 159 vertical, and single. The former, called pectoral and ven- tral fins, represent the fore and hind limbs of (Juadrupeds. The vertical fins, which are only expansions of the skin, vary in number; but in most Fishes there are at least three: the caudad, or tail-fin; the dorsal, or back-fin; and the anal, situated on the abdomen, near the tail. The chief locomotive agent is the tail, which sculls like a stern-oar; the other fins are mainly used to balance and raise the body. When the two lobes of the tail are equal, and the vertebral column stops near its base, as in the Trout, it is said to be homocercal. If the vertebree extend into the upper lobe, making it longer than the lower one, as in the Shark, the tail is called hetero- cercal. The latter is the more effec- “Sve the incu et Mrertorewarying the: course; the . ie. rin ale me Shark, e. g., will accompany and __ resultant of the two im- eons pulses is the straight line gambol around a ship in full sail in front. across the Atlantic. The Whale swims by striking the water up and down, instead of laterally, with a fin-like horizontal tail. Many air-breathing animals swim with facility on the surface, as the Water-birds, having webbed toes, and most of the Reptiles and Quadrupeds. (2) Locomotion in Air—The power of flight requires a special modification of structure and an extraordinary muscular effort, for air is 800 times lighter than water. Nevertheless, the velocity attainable by certain Birds is greater than that of any Fish or Quadruped; the Hawk being able to go at the rate of 150 miles an hour. The bodies of Insects and Birds are made as light as possible by the distribution of air-sacs or air-cavities.” The wings of Insects are generally four in number; 160 COMPARATIVE ZOOLOGY. sometimes only two, as in the Fly. They are moved by muscles lying inside the thorax. They are simple expan- sions of the skin, or crust, being composed of two delicate films of the epidermis stretched upon a net-work of tubes. There are three main varieties: thin and transparent, as in the Dragon-fly ; opaque, and covered with minute col- ored scales, which are in reality flattened hairs, as in the Butterfly ; and hard and opaque, as the first pair (called elytra) of the Beetle. | The wings of Birds, on the other hand, are modified fore-limbs, consisting of three sets of feathers (called pre- mary, secondary, and tertiary), inserted on the hand, fore- arm, and arm. The muscles which give the downward stroke of the wing are fastened to the breast-bone; and their power, in proportion to the weight of the Bird, is very great. Yet the Insect is even superior in vigor and velocity of flight.“ In ascending, the Bird slightly rotates the wing, striking downward and a little backward; while the tail acts as a rudder. A short, rounded, concave wing, as in the common Fowl, is not so well fitted for high and Fa. 195, Wlameueaen taking Wing. of the Eagle. The wing is folded by means of an elastic skin and muscle connecting the shoulder and wrist. Be- sides Insects and Birds, a few other animals have the power HOW ANIMALS MOVE. 161 of flight, as Bats, by means of long-webbed fingers; Fly- ing Fishes, by large pectoral fins. Flying Reptiles, Flying Squirrels, and the like, have a membrane stretched on the long ribs, or connecting the fore and hind limbs, which they use as a parachute, enabling them to take very long leaps. (3) Locomotion on Solids. — This requires less muscular effort than swimming or flying. The more unyielding the basis of support, the greater the amount of force left to move the animal along. The simplest method is the suctorial, the animal attaching itself to some fixed object, and then, by contraction, dragging the body onward. But the higher and more common method is by the use of bones, or other hard parts, as levers. The Star-fish creeps by the working of hundreds of tubular suckers, which are extended by being filled with WSF eo A TLL EnU TOU mH TV aie > (=| ee atest Fie. 126.—Diagrammatic section of Star-fish: a, mouth; b, stomach; c, hepatic cx- cum; d, dorsal or aboral surface; e, ambulacral plates; 7, ovary; g, tubular feet ; h, internal sacs for extending the feet. fluid forced into them by little sacs. The Clam moves by fixing and contracting a muscular appendage, called a “foot.” The Snail has innumerable short muscles on the under side of its body, which, by successive contrac- tions, resembling minute undulations, enable the animal to glide forward apparently without effort. The Leech has a sucker at each end: fixing itself by the one on its tail, and then stretching the body, by contracting the mus- cular fibres which run around it, the creature fastens its mouth by suction, and draws forward the hinder parts by 11 162 COMPARATIVE ZOOLOGY. the contraction of longitudinal muscles. The Earth-worm lengthens and shortens itself in the same way as the Leech, but instead of suckers for holding its position, it has nu- merous minute spines pointing backward; while the Cat- erpillar has short Jegs for the same purpose. ‘The legless Serpent moves by means of the scutes, or large scales, on the under side of the body, acted upon by the ribs. In a straight line, locomotion is slow; but by curving the body, laterally or vertically, it can glide or leap with great rapidity. | Most animals have movable jointed limbs, acted upon as levers by numerous muscles. The Centipede has forty- two legs, each with five joints and a claw. The Crab has five pairs of six - jointed legs; but the front pair is modified into pincers for prehen- sion. With the rest, which end in a sharp claw, the Crab moves backward, forward, or sideways. The Spider has eight legs, usually seven -joint- ed, and terminating Fie. 127.—Feet of Insects: A, Bibio febrilis; B, 11) two claws toothed House - fly (Musca domestica); C, Water-beetle _. (Dytiscus). like a comb, and a third which acts like a thumb. In running, it moves the first right leg, then the fourth left; next, the first left, and then the fourth right; then the third right and sec- ond left together; and lastly, the third left and second right together. The front and hind pairs are, therefore, moved like those of a quadruped. The ‘Insect has six Fx = = = = : — = S . ~S S st fi S= \ z yi Oiler \s ), a had) ONS, be 4 Resaren a oar F eeu HOW ANIMALS MOVE. 163 legs, each of five parts: the coxa; trochanter; femur ; tibia, or shank; and tarsus. The last is subdivided usu- ally into five joints and a pair of claws. Such as can walk upside down, as the Fly, have, in addition, two or three pads between the claws.“ These pads bear hairs which secrete a sticky fluid, by means of which the Fly adheres to the surface. While the leg-bones of Verte- brates are covered by the muscles which move them, the limbs of Insects are hollow, and the muscles inside. The fore legs are directed forward, and the two hinder pairs backward. In motion, the fore and hind feet on one side, and the middle one on the other, are moved simultane- ously, and then the remaining three. The four-legged animals have essentially the same appa- ratus and method of motion. The Crocodile has an awk- ward gait, owing to the fact that the limbs are short, and placed far apart, so that the muscles act at a mechanical dis- advantage. The Tortoise is proverbially slow, for a similar reason. Dothswim betterthan they walk. Lizards arelight and agile, but progression is aided bya wriggling of the body. | The locomotive organs of the mammalian quadrupeds are much more highly organized. The bones are more compact; the vertebral column is arched, and yet elastic, between the shoulder and hip, and the limbs are placed vertically underneath the body. The bones of the fore limb are nearly in a line; but those of the hind limb, which is mainly used to project the body forward, are more or less inclined to one another, the angle being most marked in animals of great speed, as the Horse. Some walk on hoofs, as the Ox (Ungulate); some on the toes, as the Cat (Digitigrade); others on the sole, touching the ground with the heel, as the Bear (Plantigrade). In the Pinnigrade Seal, half of the fore limb is buried under the skin, and the hind limbs are turned backward to form a fin with the tail. The normal number of toes is five; but 164 COMPARATIVE ZOOLOGY. Fig. 128. — Feet of Carnivores: A, Plantigrade (Bear); B, Pinnigrade (Seal): C, — Digitigrade (Lion). some may be wanting, so that we have one-toed animals (as Horse), two-toed (as Ox), three-toed (as Rhinoceros), four-toed (as Hippopotamus), and five-toed (as the Ele- phant). The Horse steps on what corresponds to the nail of the middle finger; and its swiftness is conditioned on the solidity of the extremities of the limbs. Horses of the greatest speed have the shoulder-joints directed at a considerable angle with the arm. Sy Spe aan ae = Sees Socapiy mers cent, Fia. 129. —Feet of Hoofed Mammals: A, Elephant; B, Hippopotamus; C, Rhinoc- eros; D, Ox; H, Horse. a, astragalus; cl, calcaneum, or heel; s, naviculare; 8, cuboides ; ce, ci, cm, cuneiform bones; the numbers indicate the digits in use. HOW ANIMALS MOVE. 168 The order in which the legs of Quadrupeds succeed each other determines the various modes of progression, called the walk, trot, gallop, and leap. Many, as the Horse, have all these movements; while some only leap, as the Frog and Kangaroo. In leaping animals, the hind limbs are extraordinarily developed. In many Mammals, like the Squirrel, Cat, and Dog, the fore legs are used for prehension as well as locomotion. Monkeys use all four, a | Fie. 130.—Muscles of the Human Leg: sartorius, or ‘‘tailor’s muscle,” the Fig. 131. — Muscles of an Insect’s Leg (Melolontha vulgaris): a, flexor, and - Jongest muscle in the body, flexes the leg upon the thigh; rectus femoris and vastus externus and internus ex- tend the leg, maintaining an erect posture; gastrocnemius, or ‘ calf,” used chiefly in walking, for raising the heel. Another layer underlies these superficial muscles. b, extensor, of tibia; c, flexor of foot; d, accessory muscle; e, extensor of claw; jf, extensor of tarsus. The joints are restricted to movements in one plane; and therefore the mus- cles are simply flexors and extensors. All the muscles are within the skele- ton. 166 COMPARATIVE ZOOLOGY. and also the tail, for locomotion and prehension, keeping a horizontal attitude; while the Apes, half erect, as if they were half-quadruped, half-biped, go shambling along, touching the ground with the knuckles of one hand and then of the other. In descending the scale, from the most anthropoid Ape to the true Quadruped, we find the ~ centre of gravity placed increasingly higher up—that is, farther forward. Birds and Men are the only true bipeds ; the former standing on their toes, the latter on the soles of the feet. ‘Terrestrial Birds walk and run; while Birds of flight usually hop. The Ostrich can for a time outrun the Arabian Horse; and the speed of the Cassowary ex- ceeds that of the swiftest Greyhound. CHAPTER XVIII. THE NERVOUS SYSTEM. Nervous Matter exists in the form of cells, fibres, or tubes. In the cellular state it is grayish, and accumulated in masses, called ganglia, or centres, which alone origi- nate nervous force; the fibrous and tu- erally white, and arranged in bun- dles, called nerves, _ which serve only as ‘conductors. Most nerves contain two Fra. 132. — Nerve-cells from Human Brain: A, associ- kinds of fibres, like ated with nerve-tubes and blood-vessels; B, multi- , polar nucleated cells. In structure, but bularkindsare gen- | THE NERVOUS SYSTEM. 167 each having its distinct office: one carries impressions re- ceived from the external world to the gray centres, and hence is called an afferent, or sen- sory, nerve; the other conducts an influence generated in the centre to the muscles, in obedi- ence to which they contract, and hence it is called an efferent, or motor, nerve. Thus, when the finger is pricked with a pin, af- ferent nerve - fibres convey the Fig. 133.—Nervous System of Star- impression to the centre — the fish: Diagram —v7, nervous ring around mouth; %, radial nerves to spinal cord, which immediately each arm, ending in the eye. transmits an order by efferent fibres to the muscles of the hand to contract. If the former are cut, sensation is lost, but voluntary motion remains; if the latter are cut, the animal loses all control over the muscles, although sensi- bility is perfect; if both are cut, the animal is said to be Fie. 134. — Nervons System of a Mollusk (the Gasteropod Aplys- ia): a, anterior ganglion; c, ce- phalic; U, lateral; g, abdominal. paralyzed. The nerve-fibres are connected with nerve-cells in the central organs, and at the outer ends are connected with the mus- cular fibres, or with various sen- sory end-organs in the skin or other parts of the body. The nature of nerve-force is not known. As to the velocity ofa nervous impulse, we know it is far less than that of electricity or light, and that it is more rapid in warm-blooded than in cold-blood- ed animals, being faster in Man than in the Frog. In the latter it averages about 85 feet per second, in the former over 100 feet. 168 COMPARATIVE ZOOLOGY. The very lowest animals, like the Amceba and Infuso- ria, have no nerves, although their protoplasm has a gen- eral sensibility. The Hydra has certain cells which are, perhaps, partly nervous and partly muscular in function. The Jelly-fish has a nervous system, consist- ing of a net-work of threads and ganglia scattered all over its disk. We should look for a definite system of ganglia and nerves only in those animals which pos- sess a definite muscular structure, and show definitely co-ordinat- Yt a ty > YO ed muscular movements. ays In the Star-fish we detect NZ” . . A oe the first clear specimen ot a a ° x = sucha system. It consists AON e an == a Fra. 135.—Nervous Sys- of aringaroundthe mouth, =XBees: tem of Clam: c¢, cere- Sie : : 709 5 bral ganglion ; p, ped- made of five ganglia. of y al ganglia; ps, parie- : : ere } tosplanchnicganglia; equal size, with radiating HS ce’, cerebral commis- ‘ ; il sure: p’, commissure Herves. The Mollusks are Sa from cerebralto pedal. distinguished by an irregu- Ik , ganglia; ps’, commis- AY] x sure from cerebral to larly scattered nervous Sys- —2jpe parietosplanchnic ganglia; oe, cesopha- tem. The Clam has three ! SX A te - main pairs of connected — ie 9 ganglia—one near the mouth, one in the’ - NS foot, and the third in the posterior region, ALY @ ® - x i near the siphons. In the Snail, these are iS P ) 9g A\ 77 united into a ring around the gullet, and HIN there are other ganglia scattered through | the body. The same is true of the Cuttle- Fre. 136. — Nervous hoe 4 System of a Cater- fish, where the brain is partly enclosed in a __ pinar (Spnine Ut- 42 , Y . gustri): the first cartilaginous box (Fig. 151). anes cephalic, or In the simpler worms there is but a sin- e#4, ganglion. gle ganglion orasingle pair. The Earth-worm has a pair of brain-ganglia lying above the gullet, and connected by THE NERVOUS SYSTEM. 169 two cords with a ventral chain of ganglia—one pair, ap- parently a single one, for each segment. In the lower Arthropods, such as Crustacea, Centipedes, and Larval In- sects, the arrangement is substan- tially thesame. In higher Insects and Crustacea, many of the gan- glia are fused together in the head and thorax, indicating a concen- tration of organs for sensation and locomotion. In Vertebrates, the nervous system is more highly developed, more complex, and more concen- trated than in the lower forms. In fact, there are some parts, as the brain, to which we find nothing homologous in the Invertebrates ; and while the actions of the lat- ter are mainly, if not wholly, au- tomatic, those of backboned ani- mals are voluntary. Its position, moreover, is peculiar, the great mass of the nervous matter being accumulated on the dorsal side, and enclosed by the neural arches of the skeleton. The brain and spinal cord lie in the cavity of the skull and spinal column, wrapped in three membranes. Both consist of gray and white nervous matter; but in the brain the gray is on the out- side, and the white within; while Fta4. 187.—Human Brain and Spina! Cord, one fifth natural size: a, great longitudinal fissure; 0, an- terior lobe; c, middle lobe; ad, medulla oblongata; e, cerebel- lum; /f, first spinal nerve; g, brachial plexus of nerves supply- ing the arms; h, dorsal nerves; 7, lumbar nerves; &, sacral plexus of nerves for the limbs; lJ, cauda equina: the figures indicate the twelve pairs of cranial nerves, of which 1 is olfactory, 2 optic, and 8 auditory. the white of the spinal cord is external, and the gray in- ternal. Both are double, a deep fissure running from the 170 COMPARATIVE ZOOLOGY. forehead backward, dividing the brain into two hemi- spheres, and the spinal cord resembling two columns welded together; even the nerves come forth in pairs to the right and left. The brain is the organ of sensation and voluntary motion; the spinal cord is the organ of in- voluntary life and motion. The brain, above the medulla oblongata, may be removed, and yet the animal, though it cannot feel, will live for a time, showing that it is not ab- solutely essential to life; in fact, the brain does nothing in apoplexy and deep sleep. All of the cord, except that part containing the centres for respiration and circulation, may also be destroyed, without causing immediate death. The Brain is that part of the nervous system contained in the skull. It increases in size and complexity as we pass from the Fishes, by the Amphibians, Reptiles, and Birds, to Mammals. Thus, the body of the Cod is 5000 times heavier than its brain—in fact, the brain weighs less than the spinal cord; while in Man, the brain, compared with the body, is as 1 to 36, and is 40 times heavier than the spinal cord. The brains of the Cat weigh only 1 oz. ; of the Dog, 6 oz. 54 dr.; and of the Horse, 22 oz. 15 dr. The only animals whose brains outweigh Man’s are the Elephant and Whale—the maximum weight of the Ele- phant’s being 10 lbs., and of the Whale’s 5 lbs.; while the human does not exceed 4 lbs. Yet the human brain is heavier in proportion to the body. But quality must be considered as well as quantity, else the Donkey will outrank the Horse, and the Canary-bird, Man; for their brains are relatively heavier. The main parts of the brain are the cerebrum, cerebel- lum, and medulla oblongata. The cerebrum is a mass of white fibrous matter covered by a layer of gray cellular matter. In the lower Verte-_ brates, the exterior is smooth; but in most of the Mam- mals it is convoluted, or folded, to increase the amount of, THE NERVOUS SYSTEM. 171 the gray surface. The convolutions multiply and deepen as we ascend the scale of size and intelligence, being very complex in the Elephant and Whale, Monkey and Man. As arule, they are proportioned to the intelligence of the animal; yet the brains ) of the Dog and Horse i are smoother than those aiv a oe of the Sheep and Don- y i A key. Evidently the (li 7 quality of the gray mat- ter must be taken into ff LY; account. Save in the | it =. V a bony Fishes, the cere- Las brum is the largest por- tion of the brain; in yo = N ax N eet ie ° A 7 @ Man it is over eight ST ays SS times heavier than the WAS) Ki" Wi WNC cerebellum. SS (eee The cerebellum, or | “little brain,” les be- wap : ii hind the cerebrum, and, er ! like it, presents an ex- Sa ternal gray layer, with a white interior. In Mammals, it is likewise finely convoluted, con- Fig. 138. -—- Brain of the Horse—upper view, one sist ng of gray an d half natural size: a, medulla oblongata; }, !at- white laminge. and is ©"! and middle lobes of cerebellum; ¢, inter- Here ; lobular fissure; d, cerebral hemispheres; e, ol- divided into two lobes, _ factory lobes. or hemispheres. In the rest of the Vertebrates, the cere- bellum is nearly or quite smooth; and in the lowest Fish- es it is merely a thin plate of nervous matter. In many Vertebrates, however, it is larger, compared with the cere- brum, than in Man, since in Man the cerebrum is extraor- dinarily developed. 172. COMPARATIVE ZOOLOGY. The medulla oblongata is the connecting link between — the cerebrum and cerebellum and the spinal cord. In structure, it resembles the spinal cord—the white matter being external and the gray internal. The former lies beneath or behind the brain, passing through the foramen magnum of the skull, and merging imperceptibly into the cord. The latter is a continuous tract of gray matter en- closed within strands of white fibres. It usually ends in the lumbar region of the vertebral column, but in Fishes it reaches to the end of the tail. In Fishes, Amphibians, and Reptiles, the cord outweighs the brain: in Birds and Mammals, the brain is heavier than the cord. In Man, it weighs about an ounce and a half. Besides these parts, there are also the olfactory and the optic lobes, which give rise respectively to the nerves of smell and sight. The parts of the brain are always in pairs; but in rela- tive development and po- sition they differ widely in the several classes of Ver- tebrates. In Fishes and Reptiles, they are arranged in a horizontal line; in Birds and Mammals, the axis of the spinal cord | bends to nearly a right an- Fig. 139.—Brain of ole in passing through the the Perch, upper view: a, cerebel- brain, so that the lobes no lum; b, optic e e e e lobes; c, cere- longer lie in a straight line. b ; 7, olfacto- hae ; seas g, me. LX Man, the fore-brain is is 140.—Brain of the rete : rog, upper view, X 4: dulla oblongata. so developed that it cov. ‘Xolttetoryndseeia Ifactory lobes; He, cer- ers all the other lobes. In looking down Syraineniepheree, Pu 7 ‘ ; pineal gland; Fho and upon the brain of a Perch, we see In Evy, third and fourth front a pair of olfactory lobes (which _ ventricles; Lop, optic hes i lobes; C, cerebellum ; send forth the nerves of smell), behind mo, medulla oblongata. THE NERVOUS SYSTEM. 13 them the small cerebral hemispheres, then the large optic lobes (in which originate the nerves of sight), and, last of all, the cerebellum. Not till we reach Man and the Apes do we find the cerebrum so highly developed as to overlap both the olfactory lobes in front and the cerebellum behind. Functions of the Brain—The cerebrum is the seat of in- telligence and will. It has no direct communication with the outside world, receiving its consciousness of external objects and events through the spinal cord and the nerves of special sense.” The cerebellum seems to preside over the co-ordination of the muscular movements. When removed, the animal A. CO Pm emf wt ce ox Wii gi \ . Gillin. FAD AC \\ \ (isi i FF il UN y f —_ A Oe Crp EEA ae Pr) SO Ww Py V/; ALO, Fra, 141.—A, C, upper and side views of the Brain of a Lizard; B, D, upper and side views of the Brain ofa Turkey: O1f, olfactory lobes; Hmp, cerebral hemispheres; Pn, pineal gland; Mb, optic lobes of the middle brain; Cb, cerebellum; MO, me- dulla oblongata; i, optic nerves; iv and vi, nerves for the muscles of the eye; Py, pituitary body. desires to execute the mandates of the will, but cannot; its motions are irregular, and it acts as if intoxicated. It is usually largest in animals capable of the most compli- cated movements; being larger in the Ape than in the Lion, in the Lion than in the Ox, in Birds than in Rep- tiles. The cerebellum of the Frog is, however, smaller than that of Fishes (Figs. 139,140). The olfactory and op- tic lobes receive the messages from their respective nerves. 174 COMPARATIVE ZOOLOGY. The medulla oblongata is not only the medium of com- munication between the brain and the spinal cord, but it i NK MGM \ { Mi si ti ii wi HN Me hs | t NA i Nit ly Fig. 142.—Brain of the Cat (Felis do- Fig. 148. —Brain of the Orang-utan, mestica): a, medulla oblongata; 6, upper surface; one third natural cerebellum; c, cerebrum. size. is itself a nervous centre: the brain above and the cord below may be removed without death to the animal, but the destruction of the medulla is fatal. Of the twelve pairs of nerves issuing from the contents of the skull (en- cephaton), ten come from the medulla oblongata. Among these are the nerves of hearing | \ \ i Fig. 144.—Human Brain, side view: 1, Fig. 145.— Human Brain, upper v.ew, medulla oblongata; 3, cerebellum; 5, one third natural size: 1, anterior frontal convolutious of cerebrum. lobes ; 2, posterior; 3, great median fissure. and taste, and those that control the lungs and heart. Res- piration ceases immediately when the medulla is injured. THE NERVOUS SYSTEM. 175 The spinal cord is a centre for originating involuntary actions, and is also a conductor—propagating through its central gray matter the impressions received by the nerves to the brain, and taking back through its fibrous part the impulses of the brain. In Man, thirty-one pairs of nerves arise from the cord tosupply the whole body, except the head. Each nerve has an ante- rior and a posterior root. The fibres of the former go to the muscles, and hence carry the impulses which cause muscular contraction (hence call- ed motor jibres); those of the posterior root con- vey sensations from the exterior to the central organs (sensory). The fibres leading from the brain to the cord cross one another in the me- Fig. 146.—Relation of the Sympathetic and Spinal Nerves: c, fissure of spinal cord; a, anterior of dulla oblon gata, sO th at dorsal ny nee | P; posterior Ue NT ue : : ganglion; a’, anterior branch; p’, posterior if the nr eht cerebral branch; s, sympathetic; e, its double junction : F by white and gray filaments. hemisphere be diseased, the left side of the body loses the power of voluntary motion. The sympathetic nervous system 1s a double chain of ganglia, lying along the sides of the vertebral column in the ventral cavity. From these ganglia nerves are given off, which, instead of going to the skin and muscles, like the spinal nerves, form net-works about those internal organs | over which the will has no control, as the heart, stomach, 176 COMPARATIVE ZOOLOGY. and intestines. Their apparent office is to stimulate these organs to constant activity, but is little understood. 1. The Senses. Sensation is the consciousness of impressions on the sensory nerves. ‘These impressions produce some change | in the brain; but what that change is, is a darkness on which no hypothesis throws light. Obviously, we feel only the condition of our nervous system, not the a which excite that condition.” All animals possess a general sensibility diffused over the greater part of the body.” This sensibility, like as-- similation and contractility, is one of the primary physio- logical properties of protoplasm. But, besides this (save in the very lowest forms), they are endowed with special nerves for receiving the impressions of light, sound, ete. These nerves of sense, as they are called, although struct- urally alike, transmit different sensations: thus, the Ear can- not recognize light, and the Eye cannot distinguish sounds. In the venee the organs of sight, hearing, and smell are situated in pairs on each side of the head; that of taste, in the mucous membrane covering the tongue; while the sense of touch is diffused over the skin. Sight and hearing are stimulated, each by one agent only; while touch, taste, and smell may be excited by various substances. The agents awakening sight, hearing, and touch are physical; those causing taste and smell are chemical. Animals differ widely in the numbers and keenness of their senses. But there is no sense in any one which does not exist in some other. Touch is the simplest and the most general sense; no an- imal is without it, at least in the form of general sensibility. It is likewise the most positive and certain of the senses. . In the Sea-anemone, Snail, and Insect, it is most acute in the ‘ feelers” (tentacles, horns, and antenne),” in the Oys- THE NERVOUS SYSTEM. gy ae: ter, the edge of the mantle is most sensitive; in Fishes, the lips; in Snakes, the tongue; in Birds, the beak and under side of the toes; in Quadrupeds, the lips and tongue; and in Monkeys and Man, the lips and the tips of the tongue and fin- gers. In the most sensitive parts of Birds and Mam- mals, the true skin is raised up into multitudes of mi- nute elevations, called pa- pille, containing loops of capillaries and nerve-filaments. There is a correspondence between the delicacy of touch and the development of in- telligence. The Cat and Dog are more sagacious than hoofed animals. The Elephant and Parrot are remark- ably intelligent, and are as celebrated for their tactual power. 3 Taste is more refined than touch, since it gives a knowledge of properties which cannot be felt. It is al- ways placed at the entrance to the digestive canal, as its chief purpose is to guide animals in their choice of food. | No special organ of taste can be de- @\ tected in the Invertebrates, although OW Valo \ @ | all seem to exercise a faculty in se- Kea we ee lecting their food. Even in Fishes, sig eee ee ae Amphibians, Reptiles, and Birds this Palm, x 35, the cuticle bee Sense 1S very obtuse, for they bolt aaa ies their food. But the higher Verte- brates have it well developed. It is confined to the tongue, and is most delicate at the root.” Qa ~“ Fig. 158.—Section of the Human Retina, x 400: 1, internal limiting membrane; 2, optic-nervefibres; 3, ganglion cells; 4, internal molecular layer; 5, internal granules ; 6, external molecular layer; 7, externalgranules; 8,externallimiting membrane; 9, layer of rods and cones; 10, pigment layer. through the sclerotic and choroid coats, expands into the transparent retina, which consists of several layers — 184 COMPARATIVE ZOOLOGY. fibrous, cellular, and granular. The most sensitive part is the surface lying next to the black pigment. And here is a peculiarity of the vertebrate eye: the nerve-fibres, en- tering from behind, turn back and look towards the bot- tom of the eye, so that vision is directed backward; while invertebrate vision is directly forward. In Vertebrates only, the optic nerves cross each other (decussate) in pass- ing from the brain to the eyes; so that the right side of the brain, e. g., receives the impressions of objects on the left side of the body.” : Generally, the eyes of Vertebrates are on opposite sides of the head; but in the Flat-fishes both are on the same side. Usually, both eyes see the same object at once; but in most Fishes the eyes are set so far back, the fields of vision are distinct. The cornea may be flat, and the lens globular, as in Fishes; or the cornea very convex, and the lens flattened, as in Owls. Purely aquatic animals have neither eyelids nor tears, but nearly all others (especially Birds) have three lids.** The pupil is usually round; but it may be rhomb-shaped, as in Frogs; vertically oval, as in Crocodiles and Cats: or transversely oval, as in Geese, Doves, Horses, and Ruminants. Many Quadrupeds, as the Cat, have a membrane (¢apetwm) lining the bottom of the eyeball, with a brilliant metallic lustre, usually green or pearly: it is this which makes the eyes of such animals luminous in the dark. 2. Instinct and Intelligence. _ The simplest form of nervous excitement is mere sensa- tion. Above this we have sensation awakening conscious- ness, out of which come those voluntary activities grouped together under the name of Instinct; and, finally, Intelli- gence. The lowest forms of life are completely under law, for their movements seem to be due solely to their organiza- THE NERVOUS SYSTEM. 185. tion. ‘They are automatons, or creatures of necessity. Such, also, are some actions in the higher animals, as breathing, the beating of the heart, the contractions of the iris, and all the first movements of an infant.” But, generally, the actions of animals are not the result of mere bodily organization. The inferior orders are under the control of Instinct, 2. é@., an apparently untaught ability to perform actions which are useful to the animal.’” They seem to be born with a measure of knowledge and skill (as Man is said to have innate ideas), acquired neither by reason nor experi- ment. For what could have led Bees to imagine that by feeding a worker-larva with royal jelly, instead of bee- bread, it would turn out a queen, instead of a neuter? In this case, neither the habit nor the experience could be inherited, for the worker- bees are sterile. We can only guess that the discovery has been communicated by the survivors of an older swarm. Uniformity is another char- acteristic feature of instinct. Different individuals of the same species execute precisely the same movements under like circumstances. The career of one Bee is the career of any other. We do not find one clever and another stupid. Honey-combs are built now as they were before the Christian era. The creatures of pure instinct appear to be tied down, by the constitution of their nervous sys- tem, to one line of action, from which they cannot spon- taneously depart. The actions vary only as the structure changes." There is a wonderful fitness in what they do, but there is no intentional adaptation of means to ends. All animals, from the Star-fish to Man, are guided more or less by instinct; but the best examples are furnished by the insect-world, especially by the social Hymenopters (Ants, Bees, and Wasps). The Butterfly carefully pro- vides for its young, which it is destined never to see; many Insects feed on particular species of plants, which 186 COMPARATIVE ZOOLOGY. they select with wonderful sagacity; and Monkeys avoid poisonous berries; Bees and Squirrels store up food for the future; Bees, Wasps, and Spiders construct with mar- vellous precision; and the subterranean chambers of Ants and the dikes of the Beaver show engineering skill; while Salmon go from the ocean up the rivers to spawn; and Birds of the temperate zones migrate with great regu- larity. 3 But in the midst of this automatism there are the glim- merings of intelligence and free-will. We see some evi- dence of choice and of designed adaptation. Pure in- stinct should be infallible. Yet we notice mistakes that remind us of mental aberrations. Bees are not so eco- nomical as has been generally supposed. A mathemati- cian can make five cells with less wax than the Bee uses" for four; while the Humble-bee uses three times as much material as the Hive bee. An exact hexagonal cell does not exist in nature. Flies lay eggs on the earrion-plant because it happens to have the odor of putrid meat. The domesticated Beaver will build a dam across its apartment. Birds frequently make mistakes in the construction and location of their nests. In fact, the process of cheating animals relies on the imperfection. of instinct. Nor are the actions of the brute creation always perfectly uni- form; and, so far as animals conform to circumstances, they act from intelligence, not instinct. There is proof that some animals profit by experience. Birds do learn to make their nests; and the older ones build the best. Trappers know well that young animals are more easily caught than old ones. Birds brought up from the egg, in cages, do not make the characteristic nests of their species; nor do they have the same song peculiar to their species, if they have not heard it. Chimney-swallows cer- tainly built their nests differently in America three hun- dred years ago. A Bee can make cells of another shape, THE NERVOUS SYSTEM. | 187 for it sometimes does; its actions, therefore, being elec- tive and conditional, are in a measure the result of calcu- lation. The mistakes and variations of instinct are indications that animals have something more —a limited range of that principle of Intelligence so luminous in Man. No precise line can be drawn between instinctive and intel- ligent acts; all we can say is, there is more freedom of choice in the latter than the former; and that some ani- mals are most instinctive, others most intelligent. Thus, we speak of the instinct of the Ant, Bee, and Beaver, and the intelligence of the Elephant, Dog, and Monkey. Instinct loses its peculiar character as intelligence becomes developed. Ascending from the Worm and Oyster to the Bee, we see the movements become more complex in character and more special in their objects; but instinct is supreme. Still ascending, we observe a gradual fading- away of the instincts, till they become subordinate to higher faculties—will and reason. We can predict with considerable certainty the actions of animals guided by pure instinct; but in proportion as they possess the power of adapting means to ends, the more variable their actions. Thus, the architecture of Birds is not so uniform as that of Insects.” We must credit brutes with a certain amount of obser- vation and imitation, curiosity and cunning, memory and reason. Animals have been seen to pause, deliberate, or experiment, and resolve. The Elephant and Horse, Dog and Monkey, particularly, participate in the rational nat- ure of Man, up to a certain point. Thinking begins wher- ever there is an intentional adaptation of means to ends; for that involves the comparison and combination of ideas. Animals interchange ideas: the whine of a Dog at the door on a cold night certainly implies that he wants to be let in. Bees and Ants, it is well known, confer by 188 COMPARATIVE ZOOLOGY. passing their antennee. All the higher animals, too, have similar emotions—as joy, fear, love, and anger. While instinct culminates in Insects, the highest. devel- opment of intelligence is presented in Man.’* In Man only does instinct cease to be the controlling power. He stands alone in having the whole of his organization con- formed to the demands of his brain; and his intelligent acts are characterized by the capacity for unlimited prog- ress. The brutes can be improved by domestication ; but, left to themselves, they soon relapse into their origi- nal wildness. Civilized Man also goes back to savagery; yet Man (though not all Men) has the ambition to exalt his mental and moral nature. He has a soul, or conscious relation to the Infinite, which leads him to aspire after a_ lofty ideal. Only he can form abstract ideas. And, finally, he is a completely self-determining agent, with a prominent will and conscience—the highest attribute of the animal creation. In all this, Man differs profoundly from the lower forms of life. 3. The Voices of Animals. Most aquatic animals are mute. Some Crabs make noises by rubbing their fore-legs against their carapace ; and many Fishes produce noises in various ways, mostly by means of the swim-bladder. Insects are the Inverte- brates which make the most noise. Their organs are usu- ally external, while those of Vertebrates are internal. In- sects of rapid flight generally make the most noise. In some the noise is produced by friction (stridulation) ; in oth- ers, by the passage of air through the spiracles (humming). The shrill notes of Crickets and Grasshoppers are pro- duced by rubbing the wings against each other, or against the thighs; but the Cicada, or Harvest-fly, has a special apparatus—a tense membrane on the abdomen, acted upon by muscles. The buzzing of Flies and humming of Bees THE NERVOUS SYSTEM. 189 are caused, in part, by the vibrations of the wings; but the true voice of these Insects comes from the spiracles of the thorax. Snakes and Lizards have no vocal cords, and can only hiss. Frogs croak’ and Crocodiles roar, and the huge Tortoise of the Galapagos Islands utters a hoarse, bellow- ing noise. The vocal apparatus in Birds is situated at the lower end of the trachea, where it divides into the two bron- chi.” It consists mainly of a bony drum, with a cross- bone, having a vertical membrane attached to its upper edge. The membrane is put in motion by currents of air passing on either side of it. Five pairs of muscles (in the Songsters) adjust the length of the windpipe to the pitch of the glottis. The various notes are produced by differ- ences in the blast of air, as well as by changes in the ten- sion of the membrane. The range of notes is commonly within an octave. Birds of the same family have a simi- lar voice. All the Parrots have a harsh utterance; Geese and Ducks quack; Crows, Magpies, and Jays caw; while the Warblers differ in the quality, rather than the kind, of note."* The Parrot and Mocking-bird use the tongue in imitating human sounds. Some species possess great com- pass of voice. The Bell-bird can be heard nearly three miles; and Livingstone said he could distinguish the voices of the Ostrich and the Lion only by knowing that the for- mer roars by day, and the latter by night. — The vocal organ of Mammals, unlike that of Birds, is in the upper part of the larynx. It consists of four car- tilages, of which the largest (the thyroid) produces the prominence in the human throat known as “ Adam’s ap- ple,” and two elastic bands, called ‘‘ vocal cords,” just be- low the glottis, or upper opening of the windpipe. The various tones are determined by the tension of these cords, which is effected by the raising or lowering of the thyroid 190 COMPARATIVE ZOOLOGY. cartilage, to which one end of the cords is attached. The will cannot influence the contraction of the vocalizing muscles, except in the very act of vocalization. The vo- cal sounds produced by Mammals may be distinguished into the ordinary voice, the cry,and the song. The second is the sound — made by brutes. The Whale, Porpoise, Ar- madillo, Ant-eater, Porcupine, and Giraffe are generally silent. The Bat’s voice is probably the shrillest sound audible to hu- torneo a eat: There is little modulation in profile; a, half brute utterance. The Opossum purrs, tlie of the _ hyoid bone; e, trae Sloth and Kangaroo moan, the Hog grunts aus yerisit. OF Squeals, the Tapir whistles, the Stag bel- » lows, and the Elephant gives a hoarse trump- et sound from its trunk and a deep groan from its throat. All Sheep have a guttural voice; all the Cows low, from the Bison to the Musk-ox; all the Horses and Donkeys neigh; all the Cats mzau, from the domestic animal to the Lion; all the Bears growl; and all the Canine family— Fox, Wolf, and Dog — bark and howl. The Howling- monkeys and Gorillas have a large cavity, or sac, in the throat for resonance, enabling them to utter a powerful voice; and one of the Gibbon-apes has the remarkable power of emitting a complete octave of musical notes. The human voice, taking the male and female together, has a range of nearly four octaves. Man’s power of speech, or the utterance of articulate sounds, is due to his intel- lectual development rather than to any structural differ- ence between him and the Apes. Song is produced by the vocal cords, speech by the mouth. REPRODUCTION. 191 CHAPTER XIX. REPRODUCTION. Ir is a fundamental truth that every living organism has had its origin in some pre-existing organism. The doctrine of “spontaneous generation,’ or the supposed origination of organized structures out of inorganic parti- cles, or out of dead organic matter, has not yet been sus- tained by facts. Reproduction is of two kinds— sexual and asexual. All animals, probably, have the first method, while a very great number of the lower forms of life have the latter also. Of asexual reproduc- tion there are two kinds — Self - division and Budding. Self-division, the simplest mode possible, is a natural breaking-up of the body into distinct surviving parts. This process is sometimes ex- traordinarily rapid, the increase of one animal- cule (Paramcecium ) be- ing computed at 268 Fic. 160.—Reproduction of Infusoria (Vorticel- le and others) by fission or Lee millions in a month. It may be either transverse or longitudinal. Of the first sort, Figs.1,2, and 3 (Fig.160) are exainples; of the latter, 192 COMPARATIVE ZOOLOGY. Figs. 4,6,9-18. This form of reproduction is, naturally, confined to animals whose tissues and organs are simple, and so can easily bear division, or whose parts are so ar- ranged as to be easily separable without serious injury. The process is most common in Protozoa, Worms, and Polyps. Budding is separated by no sharp line from Self-divi- | sion. While in the latter a part of the organs of the par- ent go to the offspring, in the former one or more cells of the original animal begin to develop and multiply so as to grow into a new animal like the parent. The proc- ess in animals is quite akin to the same operation in plants. The buds may remain permanently attached to the parent-stock, thus making a colony, as in Corals and Bryozoa (continuous budding), or they may be detached at some stage of growth (discontinuous budding). This separation may occur when the bud is grown up, as in Hydra (Fig. 191), or as in Plant-lice, Daphnias (Fig. 255), and among other animals the buds may be internal, and detached when entirely undeveloped and externally re- sembling an egg. They differ, however, entirely from a true egg in developing directly, without fertilization. Sexual Reproduction requires cells of two kinds, usu- ally from different animals. These are the germ-cell or egg, and the sperm-cell. The embryo is developed from the union of the two cells.’ The egg consists essentially of three parts, the germinal ‘vesicle, fhe yolk, and the witelline membrane, which sur- rounds both the first. It is ordinarily globular in shape. Of the three parts, the primary one is the germinal vesi- cle—a particle of protoplasm. The yolk serves as food for this, and the membrane protects both. When a great mass of yolk is present, it is divisible into two parts—for- mative and food yolk. The latter is of a more oily nature than the former, and is usually not segmented with the eS Ste ae em ae aad REPRODUCTION. 193 egg. The structure of the hen’s egg is more complicated. The outside shell consists of earthy matter (lime) depos- ited in a net-work of animal matter. . It is minutely porous, to allow the Ch) passage of vapor and air to and fro. f Lining the shell is a double mem- y brane (membrana putaminis) resem- bling delicate tissue-paper. At the Nig larger end, it separates to enclose 4 »,, 16) Theoretical Eve, bubble of air for the use of the chick. 0° Cell: », vitelline mem- : brane; y, oleaginous pole ; Next comes the albumen, or “ white,” a, albuminous pole; p, . aan Purkinjean, or germinal, in spirally arranged layers, within vesicle; w, Wagnerian, or which floats the yolk. The yolk is semah%* prevented from moving towards either end of the egg by two twisted cords of albumen, called chalaze; yet is al- lowed to rise towards one side, the yolk being lighter than the albumen. The yolk is composed of oily granules (about 34, of an inch in diameter), enclosed in a sac, called the vitelline membrane, and disposed in concentric layers, like a set of vases placed one within the other. That part of the yolk which extends from the centre to a white JON SA ri / Fig. 162. — Longitudinal Section of Hen’s Egg before incubation: a, yolk, showing concentric layers; a’, its semi-fluid centre, consisting of a white granular sub- stance — the whole yolk is enclosed in the vitelline membrane; b, inner dense part of the albumen ; 0’, outer, thinner part; c, the chalaze, or albumen, twisted by the revolutions of the yolk; d, double shell-membrane, split at the large end to form the chamber, f; e, the shell; h, the white spot, or cicatricula. 13 194 COMPARATIVE ZOOLOGY. spot (cicatricula) on the outside cannot be hardened, even with the most prolonged boiling. The cicatricula, or em- -bryo-spot—the part for which all the rest was made—is a thin disk of cellular structure, in which the new life first appears. This was originally a simple cell, but de- velopment has gone some way before the egg is laid. It is always on that side which naturally turns uppermost, for the yolk can turn upon its axis; it is, therefore, al- ways nearest to the external air and to the Hen’s body— two conditions necessary for its development. There is another reason for this polarity of the egg: the lighter and most delicate part of the yolk is collected in its upper part, while the heavy, oily portion remains be- neath. | In most eggs the shell and albumen are wanting. When the albumen is present, it is commonly covered by a mem- brane only. In Sharks, the envelope is hore and in Crocodiles it is calcareous, as in Birds. The egg of the Sponge has no true vitelline membrane, and is not unlike an ordinary ameeboid cell. An egg is, in fact, little more than a very large cell, of which the germinal vesicle is the nucleus. The size of an egg depends mainly upon the quantity of yolk it contains; and to this is proportioned the grade of development which the embryo attains when it leaves the egg." In the eggs Fre. 163.—Egg of Sponge: Of the Star-fishes, Worms, Insects, Mol- oe lusks (except the Cuttle- fishes), many Amphibians, and Mammals, the yolk is very minute and formative, 2. ¢., it is converted into the parts of the future embryo. In the eggs of Lobsters, Crabs, Spiders, Cepha- lopods, Fishes, Reptiles, and Birds, the yolk is large and colored, and consists of two parts—the formative, or REPRODUCTION. 195 germ-yolk, immediately surrounding the germinal vesicle ; and the nutritive, or food-yolk, constituting the greater part of the mass, by which the young animal in the egg- life is nourished. In the latter case, the young come forth more mature than where the food-yolk is wanting. As to form, eggs are oval or elliptical, as in Birds and Crocodiles; spherical, as in Turtles and Wasps; cylindri- eal, as in Bees and Flies; or shaped like a hand-barrow, with tendrils on the corners, as in the Shark. The eggs Fia. 164.—Ege of a Shark (the external gills of the embryo are not represented). of some very low forms are sculptured or covered with hairs or prickles. The number of eggs varies greatly in different animals, as it is in proportion to the risks during development. Thus, the eggs of aquatic tribes, being unprotected by the parent, and being largely consumed by many animals, are multiplied to prevent extinction. The spawn of a single Cod contains millions of eggs; that of the Oyster, 6,000,- 000. A Queen-bee, during the five years of her existence, lays about a million eggs. Eggs are laid one by one, as by Birds; or in clusters, as by Frogs, Fishes, and most Invertebrates. The spawn of the Sea-snails consists of vast numbers of eggs adhering together in masses, or in sacs, forming long strings. As a rule, the higher the rank, the more care animals 196 COMPARATIVE ZOOLOGY. | take of their eggs and their young, and the higher the temperature needed for egg-development. In the major- ity of cases, egos are left to themselves. ‘The fresh-water Mussel (Unio) carries them within its gills, and the Lob- ster under its tail. The eggs of many Spiders are envel- oped in a silken cocoon, which the mother guards with jealous care. Insects, as Flies and Moths, deposit their egos where the larva, as soon as born, can procure its own food. Most Fishes allow their spawn, or roe, to float in the water; but a few build a kind of flat nest in the sand or mud, hovering over the eggs until they are hatched; while the Acara of the Amazons carries them in its mouth. The Amphibians, generally, envelop their eggs in a gelatinous mass, which they leave to the elements; but the female of the Surinain Toad carries hers on her back, where they are placed by the male. The great Am- azon Turtles lay their eggs in holes two feet deep, in the sand; while the Alligators simply cover theirs with a few leaves and sticks. Nearly all Birds build nests, those of the Perchers being most elaborate, as their chicks are de- pendent for a time on the parent.” The young of Mar- supials, as the Kangaroo, which are born in an extremely immature state, are nourished in a pouch outside of the body. But the embryo of all other Mammals is devel- oped within the parent to a more perfect condition, by means of a special organ, the placenta. It is a general law, that animals receiving in the embryo state the longest and most constant parental care ultimately attain the high- est grade of development. The Protozoa, which have no true eggs, have a sort of reproduction called conjugation. In this process two Amcebeze unite into one mass, surround theinselves with a case, in which they divide into several parts, each portion becoming a new Ameeba. | The sperm-cells differ from the egg in being very small, DEVELOPMENT. 197 usually motile, and in that a large number are usually produced from a single cell of the animal, while the egg represents an entire cell. The union of the sperm-cell with the germinal vesicle (fertizzation) is the first step in development, and without it the egg will not develop. But the nature of the process is unknown. CHAPTER XX. DEVELOPMENT. Development is the evolution of a germ into a com- plete organism. The study of the changes within the egg constitutes the science of Embryology; the transforma- tions after the egg-life are called metamorphoses, and in- clude growth and repair. The process of development is a passage from the gen- eral to the special, from the simple to the complex, from the homogeneous to the heterogeneous, by a series of dif- ferentiations. _It brings out first the profounder distine- tions, and afterwards those more external. That is, the most essential parts appear first. And not only does de- velopment tend to make the several organs of an individ- ual more distinct from one another, but also the individual itself more distinguished from other individuals and from the medium in which it lives. With advancing develop- ment, the animal, as a rule, acquires a more specific, defi- nite form, and increases in weight and locomotive power. Life is a tendency to individuality. | The first step in development, after fertilization, is the segmentation of the egg, by a process of self-division. In the simplest form, the whole yolk divides into two parts; these again divide, making four, eight, sixteen, etc., parts, — 198 COMPARATIVE ZOOLOGY. until the whole yolk is subdivided into very small por- tions (cells) surrounding a central cavity. This stage is known as the “ mulberry-mass,” or blastula (Fig. 165, ¢). ° Ofc: rae) 05 [6 o; Ske S 0 . AO ; go ie) {e) edo Fig. 165.—First Stages in Segmentation of a Mammalian Egg: A, first division into halves, with spermatozoa around it; Band C, progressive subdivision, ultimato- ly transforming the vitellus, or yolk, into a ‘‘ mulberry mass” of globules, or em- bryo-cells. If the yolk is larger, relatively to the germinal vesicle, the process of division may go on more slowly in one of the two parts of the egg, first formed; or in very large eggs, like those of Birds and Cuttle-fishes, only a small part of the yolk subdivides. In some form, the process of segmentation is found in the eggs of all animals, as is also the following stage. This step is the differentiation of the single layer of cells into two parts, one for the body-wall, the other for the wall of the digestive tract. In the typical examples, this is accom- plished by one part of the wall of Fia. 166.—Diagram of Gastra- the blastula turning in, so far as to la of a Worm (Sagitta): a, ° primitive mouth: b, primi. convert the blastula into a sort of TOPs Aenametine ‘on, double-walled cup, the gastrula (Fig. endoderm; ec, ectoderm. 166). One half of the wall of the blastula is now the outer wall of the germ, the other half that of the digestive cavity; the original blastula-cavity is now the body-cavity, and the new cavity formed by the infolding is the stomach, and its opening is both mouth DEVELOPMENT. 199 and vent (Figs. 165, 166). Some adult animals are little more than such a sac. Hydra (Fig. 191), for instance, is little different from a gastrula with tentacles, and one of its relatives wants even these additions. Ordinarily, however, development goes much further. From the two original layers arises, in various ways, a third between them, making the three primitive germ-layers— epiblast, mesoblast, and hypoblast. This new layer is nec- essarily in the primitive body-cavity, which it may fill up; or usually a new body-cavity is formed, in different ways in different groups. In by far the great majority of animals the digestive tract gets a new opening, which usually becomes the mouth; and the old mouth may close, or serve only the functions of the vent. From this point the development of each group must be traced in detail. Development of a Hen’s Egg.— After the segmentation the germinal disk divides into two layers, between which a third is soon formed. The upper layer (epzblast) gives Fig. 167.—Vertical Sections of au Egg, showing progressive stages of development: a, notochord; 0, medullary furrow, becoming a closed canal in the last. rise to the cuticle, brain, spinal cord, retina, crystalline lens, and internal ear. From the lower layer (Aypoblast) is formed the epithelium of the digestive canal. From the middle layer (mesoblast) come all the other organs— muscles, nerves, bones, etc. The mesoblast thickens so as to form two parallel ridges running lengthwise of the germ, and leaving a groove between them (medul- lary furrow and ridges). The ridges gradually rise, carrying with them the epiblast, incline towards each oth- er, and at last unite along the back. So that we have a 200 COMPARATIVE ZOOLOGY. tube of epiblast surrounded by mesoblast, which is itself covered by epiblast. This tube becomes the brain and spinal cord, whose central canal, enlarging into the ven- tricles of the brain, tells the story of its original forma- tion. Beneath the furrow, a delicate cartilaginous thread appears (called notochord)--the predecessor of the back- bone. Meanwhile the mesoblast has divided into two layers, except in the middle of the animal, beneath the spinal cord, and in the head. One of these layers remains attached to the epiblast, and with it forms the body-wall ; the other bends rapidly downward, carrying the hypoblast with it, and forms the wall of the intestine. The space thus left between the layers of the mesoblast 1s the body- cavity. At the same time, the margin of the germ ex- tends farther and farther over the yolk, till it completely encloses it. So that now we see two cavities—a small one, containing the nervous system; and a larger one be- low, for the digestive organs. Presently, numerous rows of corpuscles are seen s= on the middle layer, which are subsequent- ly enclosed, forming a net-work of eapillari Fig. 168.—Rudimentary Hearts, human: 1, venous ap oe, trunks; 2, auricle; 3, ventricle; 4, bulbus arte- called the vascular area. riosus. A dark spot indicates the situation of the heart, which is the first distinctly bounded cavity of the circulatory system. It is a short tube lying lengthwise just behind the head, with a feeble pulsation, causing the blood to flow backward and for- ward. ‘The tube is gradually bent together, until it forms a double cavity, resembling the heart of a Fish. On the fourth day of incubation, partitions begin to grow, divid- ing the cavities into the right and left auricles and ven- tricles. The septum between the auricles is the last to be finished, being closed the moment respiration begins. DEVELOPMENT. 901 The blood-vessels ramify in all directions through the yolk, making it a spongy mass, and all perform the same office; it is not till the fourth or fifth day that arteries can be distinguished from veins, by being thicker, and by carrying blood only from the heart.” Fig. 169.—Embryo in a Hen’s Egg during the first five days: A, hypoblast; B, lower layer of mesoblast; C, upper layer of mesoblast and epiblast united, in the last figures forming the amniotic sac; D, vitelline membrane; e, thickened blasto- derm, the first rudiment of the dorsal part (in the last figure it marks the place of the lungs); hk, heart; a, b, its two chambers; c, aortic arches; m, aorta; 2, liver ; p, allantois. 202 COMPARATIVE ZOOLOGY. The embryo lies with its face, or ventral surface, tow- ards the yolk, the head and tail curving towards each Fi. 170.—Hen's Eve, more highly developed. The embryo is enveloped by the am- nion, and has the umbilical vessel, or remnant of the yolk, hanging from its un- der surface; while the allantois turns upward, and spreads out over the internal surface of the shell-membrane. (From Dalton’s ‘‘ Physiology.’’) other. Around the embryo on all sides the epiblast and upper layer of the mesoblast rise like a hood over the Fig. 171. — Mammalian Embryo, with al- lantois fully formed: 1, umbilical vesi- cle, containing the last of the yolk; 2, amnion; 3, allantois, on which the fringes of the placenta are developing. (From Dalton’s ** Physiology.”’) back of the embryo till they form a closed sac, called the amnion. It is filled with a thin liquid, which serves to protect the embryo. Mean- while, another important or- gan is forming on the other side. From the hinder por- tion of the alimentary canal an outgrowth is formed which extends beyond the wall of the embryo proper into the cavity of the amni- on and spreads out over the whole inner surface of the shell, so that it partly surrounds both embryo and inner layer of the amnion (amnion prop- DEVELOPMENT. _ 203 er). This is the allantois. It is full of blood-vessels, and it serves as the respiratory organ until the chick picks the shell and breathes by its lungs.” The chorion is the out- ermost part of the allantois, and the placenta of Mammals is the shaggy, vascular edge of the chorion. _ The alimentary canal is at first a straight tube closed at both ends, the middle being connected with the yolk-bag. As it grows faster than the body, it 1s thrown into a spi- ral coil; and at several points it dilates, to form the crop, stomach, gizzard, ete. The mouth is developed from an infolding of the skin. The liver is an outgrowth from the digestive tube, at first a cluster of cells, then of folli- cles, and finally a true gland. The lungs are developed on the third day as a minute bud from the upper part of the alimentary canal, or pharynx. As they grow in size, they pass from a smooth to a cellular condition. The skeleton at the beginning consists, like the noto- chord, of a cellular material, which gradually turns to ear- tilage. Then minute canals containing blood-vessels arise, and earthy matter (chiefly phosphate of lime) is deposited between the cells. The primary bone thus formed is compact: true osseous tissue, with canaliculi, laminee, and Haversian canals, is the result of subsequent absorption." Certain bones, as those of the face and cranium, are not preceded by cartilage, but by connective tissue: these are called membrane bones. Ossification, or bone-making, be- gins at numerous distinct points, called centres ; and, the- — oretically, every centre stands for a bone, so that there are as many bones in a skeleton as centres of ossification. But the actual number in the adult animal is much small- er, as many of the centres coalesce." The development of the backbone is not from the head or from the tail, but from a central point midway between: there the first ver- tebree appear, and from thence they multiply forward and backward. a 204 COMPARATIVE ZOOLOGY. The limbs appear as buds on the sides of the body; these lengthen and expand so as to resemble paddles— the wings and legs looking precisely alike; and, finally, they are divided each into three segments, the last one subdividing into digits. The feathers are developed from the outside cells of the epidermis: first, a horny cone is formed, which elongates and spreads out into a vane, and this splits up into barbs and barbules. The muscle-fibres are formed either by the growth in length of a single cell, or by the coalescence of a row of cells: the cell-wall thus produces a long tube—the sarco- lemma of a fibre—and the granular contents arrange them- selves into linear series, to make fibrillee. Nervous tissue is derived from the multiplication and union of embryo-cells. The white fibres at first resemble the gray. The brain and spinal marrow are developed from the epiblastic lining of the medullary furrow. Soon the brain, by two constrictions, divides into fore- brain, mid-brain, and hind-brain. The fore-brain throws out two lateral hemispheres (cerebrum), and from these pro- trude forward the two olfactory lobes. From the mid- dle- brain grow the optic lobes; and the hind- brain is separated into cerebellum and medulla oblongata. The essential parts of the eye, retina and crystalline lens, are developed, the former as a cup-like outgrowth from the fore-brain, the latter as an ingrowth of the epidermis. An infolding of the epidermis gives rise to the essential parts of the inner ear, and from the same layer come the olfactory rods of the nose and the taste-buds of the tongue. So that the central nervous system and the essential parts of most of the sense-organs have a common origin. Modes of Development.—The structure and embryology of a Hen’s egg exhibit many facts which are common to all animals. But every grand division of the Animal Kingdom has its characteristic method of developing. oe DEVELOPMENT. | 205 - Protozoans differ from all higher forms in having no true eggs. The egg of the Hydroid, after segmentation, becomes a hollow, pear-shaped body, covered with cilia. Soon one end is indented; then the indentation deepens until it reaches the interior and forms the mouth. The animal fastens itself by the other end, and the tentacles appear as buds. In the Sea-anemone, the stomach is turned in, and the partitions appear in pairs. In the Oyster, the egg segments into two dneaual parts, one of which gives rise to the digestive tract and its de- rivatives, while from the smaller part originate the skin, gills, and shell. It is soon covered with cilia, by whose help it swims about. The embryo of an Insect shows from the first a right and left side; but the first indication that it is an Articu- late is the development of a series of indentations divid- ing the body into successive rings, or joints. Next, we observe that the back lies near the centre of the egg, the ventral side looking outward; 7. e., the embryo is doubled upon itself backward. And, finally, the appearance of three pairs of legs proves that it will be an Insect, rather than a Worm, Crustacean, or Spider. The Vertebrate embryo hes with its stomach towards the yolk, reversing the position of the Articulate; but the grand characteristic is the medullary groove, which does not exist in the egg of any Invertebrate. This feature is connected with another, the setting apart of two distinct regions —the nervous and nutritive. There are three modifications of Vertebrate development: that of Fishes and Amphibians, that of True Reptiles and Birds, and that of Mammals. The amnion and allantois are wanting in the first group; while the placenta (which is the allan- tois vitally connected with the parent) is peculiar to Mam- mals. In Mammals, the whole yolk is segmented; in 206 COMPARATIVE ZOOLOGY. Birds, segmentation is confined to the small white speck seen in opening the shell. At the outset, all animals, from the Sporise to Man, appear essentially alike. All, moreover, undergo seg- mentation, and most have one form or other of the gastrula stage. But while Vertebrates and Invertebrates can travel together on the same road up to this point, here they diverge—never to meet again. For every grand group early shows that it has a peculiar type of construc- tion. Every egg is from the first impressed with the power of developing in one direction only, and never does it lose its fundamental characters. The germ of the Bee is divided into segments, showing that it belongs to the Articulates; the germ of the Lion has the medullary stripe—the mark of the coming Vertebrate. The blasto- dermic layer of the Vertebrate egg rolls up into two tubes —one to hold the viscera, the other to contain the nervous cord; while that of the Invertebrate egg forms only one such tubular division. The features which determine the subkingdom to which an animal belongs are first devel- oped, then the characters revealing its class. There are differences also in grade of development as well as type. For a time there is no essential difference between a Fish and a Mammal: they have the same ner- vous, circulatory, and digestive systems. There are many such cases, in which the embryo of an animal represents the permanent adult condition of some lower form. In other words, the higher species, in the course of their de- velopment, offer likenesses, or analogies, to finished lower species. —The human germ, at first, cannot be distinguished from that of any other animal: for aught we can see, it may turn out a Frog or a Philosopher. The appearance of a medullary stripe excludes it at once from all Inverte- brates. It afterwards has, for a time, structures found in the lower classes and orders of Vertebrates as permanent DEVELOPMENT. 907 organs. Tor a time, indeed, the human embryo so closely resembles that of the lower forms as to be indistinguisha- ble from them; but certain structures belonging to those forms are kept long after the embryo is clearly human.’”* All the members of a group do not reach the same degree of perfection, some remaining in what corresponds to the immature stages of the higher animals. Such may be called permanently embryonic forms. Sometimes an etnbryo develops an organ in a rudimen- tary condition, which is lost or useless in the adult. Thus, the Greenland Whale, when grown up, has not a tooth in its head, while in the embryo life it has teeth in both jaws; unborn Calves have canines and upper incisors; and the female Dugong has tusks which never cut the gum. The “splint-bones” in the Horse’s foot are unfin- ished metatarsals. Animals differ widely in the degree of development reached at ovulation and at birth. The eggs of Frogs are laid when they can hardly be said to have become fully formed as eggs. The eggs of Birds are laid when segmentation is complete, while the eggs of Mammals are retained by the parent till after the egg-stage is passed.'” Ruminants and terrestrial Birds are born with the power of sight and locomotion. Most Carnivores, Rodents, and perching Birds come into the world blind and helpless ; while the human infant is dependent for a much longer tne: 1. Metamorphosis. Few animals come forth from the egg in perfect condi- tion. The vast majority pass through a great variety of forms before reaching maturity. These metamorphoses (which are merely periods of growth) are not peculiar to Insects, though more apparent in them. Man himself is developed on the same general principles as the Butterfly, but the transformations are concealed from view. The 208 COMPARATIVE ZOOLOGY. Coral, when hatched, has six pairs of partitions; after- wards, the spaces are divided by six more pairs; then twelve intermediate pairs are introduced; next, twenty- four, and so on. The embryonic Star-fish has a long body, with six arms on a side, in one end of which the young Star-fish is developed. Soon the twelve-armed body is absorbed, and the young animal is of age. Worms are continually growing by the addition of new segments. Nearly all Insects undergo complete metamor- phosis, 2. ¢., exhibit four distinct stages of existence—egg, larva, pupa, and imago. The worm-like larva’’ may be called a locomotive-egg. It has little resemblance to the parent in structure or habits, eating and growing rapidly. Then it enters the pupa state, wrapping itself in a cocoon, or case, and remaining apparently dead till new organs are developed; when it escapes a perfect winged Insect, Fia. 172.—Butterfly in the Imago, Pupa, and Larva States. or imago.”* Wings never exist externally in the larva; and some Insects which undergo no apparent metamor- phosis, as Lice, are wingless. ‘The Grasshopper develops from the young larva to the winged adult without chang- DEVELOPMENT. 999 ing its mode of life. In the development of the common Crab, so different is the outward form of the newly es Fig. 173.—Metamorphosis of the Mosquito (Culex pipiens): A, boat of eggs; B, some of the eggs highly magnified ; d, with lid open for the escape of the larva, C; D, pupa; E, larva magnified, showing respiratory tube, e, anal fins, 7, antenne, g; F, imago; a, antenne; b, beak. , hatched embryo from that of the adult, that the former has been described as a distinct species. _ The most remarkable example of metamorphosis among Vertebrates is furnished by the Amphibians. A Tadpole —the larva of the Frog—has a tail, but no legs; gills, in- stead of lungs; a heart precisely like that of the Fish; a horny beak for eating vegetable food, and a spiral intes- tine to digest it. As it matures, the hinder legs show themselves, then the front pair; the beak falls off; the tail and gills waste away; lungs are created; the diges- tive apparatus is changed to suit an animal diet; the heart is altered to the Reptilian type by the addition of another auricle; in fact, skin, muscles, nerves, bones, and blood- vessels vanish, being absorbed. atom by atom, and a new set is substituted. Mowlting, or the periodical renewal of epidermal parts, as the shell of the Lobster, the skin of 14 210 COMPARATIVE ZOOLOGY. the Toad, the scales of Snakes, the feathers of Birds, and the hair of Mammals, may be termed a metamorphosis. Fia. 174. atretesaon phostée of the Newt. The change from milk-teeth to a permanent set is another example. An animal rises in organization as development ad- vances. Thus, a Caterpillar’s life has nothing nobler about it than the ability to eat, while the Butterfly ex- pends the power garnered up by the larva in a gay and busy life. But there are seeming reversals of this law. Some mature animals appear lower in the scale than their young. The larval Cirripede has a pair of magnificent compound eyes and complex antennze; when. adult, the antennee are gone, and the eyes are reduced to a single, simple, minute eye-spot. So the germs of the sedentary Sponge and Oyster are free and active. The adult ani- mal, however, is always superior in alone possessing the power of reproduction. Such a process is known as retro- grade metamorphosis. There are certain larval forms so characteristic of the DEVELOPMENT. | yA great groups of the animal kingdom as to demand notice. Most Worms leave the egg as a larva, called the YMC ae: sphere (Fig. 175), an oval larva, having mouth and anus, and a circle of cilia anterior to the mouth. This larval stage is common to Worms with the most diverse adult forms and habits. It is also found in all the great groups of Mol- eae iN lusks. Clams, Snails, and Cuttle-fish all have Wore the stage represented in their history. The Mol- circle ofcitia. lusks usnally pass through a later stage called the veliger (Fig. 176), in which a circle of cilia ho- mologous to that of xe, the trochosphere is | -s borne by a lobed expansion on the 2/* head, called the ve- Fig. 176.--Larval Gasteropoda: A, B, Trochus; C, Ter- lum, or sail. The gipes; a, trochosphere; 1, velum : B, veliger ; d, = mouth; f, foot; s, shell; C, veliger ; d, foot ; c, tenta- Getacen which cle; 0, ear exhibit so great a range of form in the adult state, all pass through a stage in which they are substantially alike. Forms as different in appearance as Barnacles, Entomostracans, and Prawns hatch out as Vauplw, little oval animals, with a straight intestine, three pairs of legs, and a simple eye (Fig. 177). See Figs. 253, 254, 255, 256. Fig. 256 represents the ‘Lobster, which does not hatch as a Nauplius, but is not very unlike the Prawn. These larval forms are of great interest, because they disclose the relationships of the adult forms, as the gastrula stage hints at the common relationships of all animals above Protozoa. 2. Alternate Generation. Sometimes a metamorphosis extending over several generations is required to evolve the perfect animal; “in 212 COMPARATIVE ZOOLOGY. Fig. 177.—Nauplius of Entomostracan (Canthocamptus). See Fig. 255. A, first an- tenna; An, second antenna; a, anus; ZL, labrum; O, ocellus; S, stomach. (From Brooks, after Hoek.) other words, the parent may find no resemblance to him- self in any of his progeny, until he comes down to the great-grandson.” Thus, the Jelly-fish, or Medusa, lays egos which are hatched into larvee resembling Infusoria— little transparent oval bodies covered with cilia, by which they swim about for a time till they find a resting-place. One of them, for example, becoming fixed, develops rap- idly ; it elongates and spreads at the upper end; a mouth is formed, opening into a digestive cavity; and tentacles multiply till the mouth is surrounded by them. At this stage it resembles a Hydra. Then slight wrinkles appear along the body, which grow deeper and deeper, till the animal looks like ‘a pine-cone surmounted by a tuft of tentacles ;” and then like a pile of saucers (about a dozen DEVELOPMENT. 213 in number) with scalloped edges. Next, the pile breaks up into separate segments, which are, in fact, so many dis- tinct animals; and each turning over as it is set free, so as to bring the mouth below, develops into an adult Me- dusa, becoming more and more convex, and furnished with tentacles, circular’ canals, and other organs exactly like those of the progenitor that laid the original egg Here we see a Medusa producing eggs which develop into stationary forms resembling Hydras. The Hydras a@g “(= ; CL @ aE 2 Fig. 178.—Alternate Generation: a, b,c, ova of an Acaleph (Chrysaora) ; d, e, f, Hy- dras; g, hk, Hydras with constrictions; 7, Hydra undergoing fission; k, one of the separated segments, a free Medusa. then produce not only Meduse by budding in the manner described, but also other Hydras like themselves by bud- ding. All these intermediate forms are transient states of the Jelly-fish, but the metamorphoses cannot be said to occur in the same individual. While a Caterpillar becomes a Butterfly, this Hydra-like individual produces a number of Medusee. Alternate generation is, then, an alternation of asexnal and sexual methods of reproduction, one or more generations produced from buds being followed by a single generation produced from eggs. Often, as in the fresh-water Hydra, the two kinds of generations are alike in appearance. The process is as wide-spread as asexual reproduction, being found mostly in Sponges, Coelenterates, and Worms. It is also found in certain 214 COMPARATIVE ZOOLOGY. Crustacea and Insects. The name is sometimes limited to cases where the two kinds of generations differ in form. 8. Growth and Repair. Growth is increase of bulk, as Development is increase of structure. It occurs whenever the process of repair exceeds that of waste, or when new material is added | faster than the tissues are destroyed. ‘There is a specific limit of growth for all animals, although many of the low cold-blooded forms, as the Trout and Anaconda, seem to grow as long as they live. After the body has attained its maturity, 2. e., has fully developed, the tissues cease to grow ; and nutrition is concerned solely in supplying the constant waste, in order to preserve the size and shape of the organs. A child eats to grow and repair; the adult eats only to repair.” Birds develop rapidly, and so spend most of their life full-fledged; while Insects generally, Fishes, Amphibians, Reptiles, and Mammals mature at a comparatively greater age. The perfect Insect rarely changes its size, and takes but little food; eating and growing are almost confined to larval life. The crust of the Sea-urchin, which is never shed, grows by the addition of matter to the margins of the plates. The shell of the Oyster is enlarged by the deposition of new laminze, each extending beyond the other. At every enlargement, the interior is lined with a new nacreous layer; so that the number of such layers in the oldest part of the shell indi- cates the number of enlargements. When the shell has ‘reached its full size, new layers are added to the inner surface only, which increases the thickness. It is the margin of the mantle which provides for the increase in length and breadth, while the thickness is derived from the whole surface. The edges of the concentric laminee are the “lines of growth.” The Oyster is full-grown in about five years. The bones of Fishes and Reptiles are DEVELOPMENT. 215 continually growing; the long bones of higher animals increase in length so long as the ends (epiphyses) are sep- arate from the shaft. The limbs of Man, after birth, grow more rapidly than the trunk. The power of regenerating lost parts is greatest where the organization is lowest, and while the animal is in the young or larval state. It is really a process of budding. The upper part of the Hydra, if separated, will reproduce the rest of the body; if the lower part is cut off, it will add the rest. Certain Worms may be cut into several pieces, and each part will regain what is needed to com- plete the mangled organism. The Star-fish can reproduce its arms; the Holothurian, its stomach; the Snail, its ten- tacles; the Lobster, its claws; the Spider, its legs; the Fish, its fins; and the Lizard, its tail. Nature makes no mistake by putting on a leg where a tail belongs, or join- ing an immature limb to an adult animal. In Birds and Mammals, the power is limited to the reproduction of cer- tain tissues,‘as shown in the healing of wounds. Very rarely an entire human bone, removed by disease or sur- gery, has been restored. The nails and hair continue to grow in extreme old age. 4, Likeness and Variation. It is a great law of reproduction that all animals tend to resemble their parents. A member of one class never produces a member of another class. The likeness is very accurate as to general structure and form. But it does not descend to every individual feature and trait. In other words, the tendency to repetition is qualified by a tendency to variation. Like produces like, but not ex- actly. The similarity never amounts to identity. So that we have two opposing tendencies —the hereditary ten- dency to copy the original stock, and a distinct tendency to deviate from it. 216 COMPARATIVE ZOOLOGY. ¢ This is one of the most universal facts in nature. Ev- ery development ends in diversity. All know that no two individuals of a family, human or brute, are abso- lutely alike. There are always individual differences by which they can be distinguished. Evidently a parent does not project precisely the same line of influences upon each of its offspring. This variability makes possible an indefinite modifica- tion of the forms of life. For the variation extends to the whole being, even to every organ and mental char- acteristic as well as to form and color. It is very slight from generation to generation; but it can be accumulated oy choosing from a large number of individuals those which possess any given variation in a marked degree, and breeding from these. Nature does this by the very gradual process of “ natural selection ;’ Man hastens it, so to speak, by selecting extreme varieties. Hence we have in our day remarkable specimens of Poultry, Cattle, and Dogs, differing widely from the wild races. | Sometimes we notice that children resemble, not their parents, but their grandparents or remoter ancestors. This tendency to revert to an ancestral type is called atavism. Occasionally, stripes appear on the legs and shoulders of the Horse, in imitation of the aboriginal Horse, which was striped like the Zebra. Sheep have a tendency to revert to dark colors. The laws governing inheritance are unknown. No one can say why one peculiarity is transmitted from father to son, and not another; or why it appears in one member of the family, and not in all. Among the many causes which tend to modify animals after birth are the quality and quantity of food, amount of temperature and light, pressure of the atmosphere, nature of the soil or water, habits of fellow-animals, ete. ; Occasionally animals occur, widely different in struct- : | ~ DEVELOPMENT. 917 ure, having a very close external resemblance. SBarnacles were long mistaken for Mollusks, Polyzoans for Polyps, and Lamprey-eels for Worms. Such forms are termed homomorphie. Members of one group often put on the outward ap- pearance of allied species in the same locality: this is called memicry. ‘“ They appear like actors or masquerad- ers dressed up and painted for amusement, or like swin- dlers endeavoring to pass themselves off for well-known and respectable members of society.” Thus, certain But- terflies on the Amazons have such a strong odor that the Birds let them alone; and Butterflies of another family in the same region have assumed for protection the same form and color of wing. So we have bee-like Moths, beetle-like Crickets, wasp-like Flies, and ant-like Spiders ; harmless and venomous Snakes copying each other, and Orioles departing from their usual gay coloring to imi- tate the plumage, flight, and voice of quite another style of Birds. The species which are imitated are much more abundant than those which mimic them. There is also a general harmony between the colors of an animal and those of its habitation. We have the white Polar Bear, the sand-colored Camel, and the dusky Twilight-moths. There are Birds and Reptiles so tinted and mottled as ex- actly to match the rock, or ground, or bark of a tree they frequent; and there are Insects rightly named “ Walking- sticks” and “ Walking-leaves.” These coincidences are not always accidental, but often intentional on the part of nature, for the benefit of the imitating species. Gener- ally, they wear the livery of those they live on, or ape the forms more favored than themselves. 5. Homology, Analogy, and Correlation. The tendency to repetition in the development of ani- mals leads to some remarkable affinities. Parts or organs, 218 COMPARATIVE ZOOLOGY. having a like origin and development, and therefore the same essential structure, whatever their form or function, are said to be homologous; while parts or organs corre- sponding in use are called analogous. By serial homol- ogy 1s meant the homology existing between successive parts of one animal. The following are examples of homology: the arms of Man, the fore-legs of a Horse, the paddles of a Whale, the wings of a bird, the front flippers of a Turtle, and the _ pectoral fins of a Fish; the proboscis of a Moth, and the jaws of a Beetle; the shell of a Snail, and both valves of a Clam. The wings of the Bird, Flying Squirrel, and Bat are hardly homologous, since the wing of the first is de- veloped from the fore-limb only; that of the Squirrel is an extension of the skin between the fore and hind limbs; while in the Bat the skin stretches between the fingers, aad®then down the side to the tail. Examples of serial homology: the arms and legs of Man; the upper and lower set of teeth; the parts of the vertebral column, however modified; the scapular and pelvic arches; the humerus and femur; carpus and tarsus; the right and left sides of most Animals; the dorsal and anal fins of Fishes. The legs of a Lobster and Lizard, the wings of a Butter- fly and Bird, the gills of a Fish, and the lungs of other Vertebrates, are analogous. The air-bladder of a Fish is homologous with a lung, and analogous to the air-cham- bers of the Nautilus. | In the midst of the great variety of form and structure in the animal world, a certain harmony reigns. Not only are different species so related as to suggest a descent from the same ancestor, but the parts of any one organ- ism are so closely connected and mutually dependent that the character of one must receive its stamp from the char- acter of all the rest. Thus, from a single tooth it may be inferred that the animal had a skeleton and spinal cord, DEVELOPMENT. 919 and that it was a carnivorous, hot-blooded Mammal. Cer- tain structures always co-exist. Animals with two occipi- tal condyles, and non - nucleated blood - corpuscles, suckle Fig. 179. Fie. 181. Fig. 182. HOMOLOGIES OF LIMBS. Fig. 179.—Arm and Leg of Man, as they are when he gets down on all-fours. Fie. 180.—Fore and Hind Legs of Tapir. Fie. 181.—Fore Leg of Seal and Hind Leg of Alligator. Fie. 182.—Wing of the Bat. S, scapula; I, ilium, or shin-bone of pelvis; H, humerus; F, femur; O, olecranon, or tip of the elbow; P, patella; U, ulna; T, tibia; R, radius; Fi, Fibula; Po, pollex, or thumb; Ha, hallex, or great toe. Compare the fore and hind limbs of the same animal, and the fore or hind limbs of different animals. Note the directions of the homologous seg- ments. 990 COMPARATIVE ZOOLOGY. their young, 7. ¢, they are Mammals. All Ruminant hoofed beasts have horns and cloven- feet. If the hoofs are even, the horns are even, as in the Ox; if odd, as in the Rhinoceros, the horns are odd, z. ¢., single, or two placed one behind the other. Recent creatures with feath- ers always have beaks. Pigeons with short beaks have | small feet; and those with long beaks, large feet. The Jong limbs of the Hound are associated with a long head. A white spot in the forehead of a Horse generally goes with white feet. Hairless Dogs are deficient in teeth. Long wings usually accompany long tail-feathers. White Cats with blue eyes are usually deaf. A Sheep with nu- merous horns is likely to have long, coarse wool. Homol- ogous parts tend to vary in the same manner; if one is diseased, another is more likely to sympathize with it than | one not homologous. This association of parts is called correlation of growth. 6. Individuality. It seems at first sight very easy to define an individual animal. Es Fig. 204.—Diploria cerebriformis, or ‘* Brain-coral ;” one half natu CCQELENTERATA. 255 efi Wes : SS —— > S ) Me ~ --- SSoaer Wi eS" Mh Ui, ZAI . ROSA CRO Fic. 205.—Astreea votulosa. West Indies. PR M yy The main kinds of reefs are fringeng, where the reef is close to the shore; barrier, where there is a channel be- ! i 1 } (ih " an Fia. 206.—Cell of Madrepore Coral, . magnified. The cup-like depres- Fia. 207.—Fragment of Red Coral (Coral- sion at the top of a coral skeleton lium rubrum), showing living cortex is called calicle. and expanded Polyps. Mediterranean. 256 COMPARATIVE ZOOLOGY. tween reef and shore; encorcling, where there is a small island inside of a large reef; and coral islands, or atolls, where there is simply a reef with no land inside of it. All reefs begin as fringing-reefs, and are gradually changed into the other forms by the slow sinking of the bottom of the ocean. This sinking must be slower than the upward growth of the reef, else it will be drowned out. Probably the reef does not grow more than five feet in a thousand years; and, as reefs are often more than two thousand. feet thick, they must be very old. | (2) Sclerobasic Corals—Corallium rubrum, the precious coral of commerce, is shrub-like, about a foot high, solid throughout, taking a high polish, finely grooved on the surface, and of a crimson or rose-red color. In the living Fig. 208.—Sea-fan (Gorgonia) and Sea-pen (Lennatula). state the branches are covered with a red ccenosare stud- ded with Polyps. Gorgonia, or “Sea-fan,” differs from all the other representative forms in having a horny axis covered with calcareous spicules. ‘The branches arise in the same vertical plane, and unite into a beautiful net- work. . brachia, Cestum, and Beroé) secrete ECHINODERMATA. O51 CLASS III.—Ctenophora. The Ctenophora (as the Pleuro- re va no hard deposit. They are trans- parent and gelatinous, swimming on the ocean by means of eight comb- like, ciliated bands, which work like paddles. The body is not contrac- tile, as in the Jelly-fishes. They are considered the highest of Ccelente- rates, having a complex nutritive ap- Fie. 209.—A Ctenophore (Pleu- F robrachia pileus); natural paratus and a definite nervous sys- size. tem. eee _— Ce ee ie Subkingdom III.—EcuimopERMATA. The Echinoderms, as Star-fishes and Sea- urchins, are distinguished by the possession of a distinct nervous sys- tem (a ring around the mouth); an alimentary canal, com- Fig. 210.—Forms of Echinoderms, from radiate to annulose type: a, Crinoids; 3, Ophiurans; c, Star-fish; d, Echini; e, Holothurians. pletely shut off from the body-cavity, and having both oral and anal apertures; a water-vascular system of circnu- 17 958 COMPARATIVE ZOOLOGY. lar and radiating canals, connected with the outside water by means of the madreporic tubercle, and a symmetrical arrangement of all the parts of the body around a central axis in multiples of five." There are four principal class- es, all exclusively marine and solitary, and all having the power of secreting more or less calcareous matter. Criass [.—Crinoidea. The Crinoids, or “ Sea-lilies,” are fixed to the sea-bottom by means of a hollow, jointed, flexible stem. On the top of the stem is the body proper, resembling a bud or ex- panded flower, containing the digestive apparatus, with the surrounding arms, or tentacles. The mouth looks up- ward. There is a complete skeleton for strength and sup- port, the entire animal—body, arms, and stem—consisting of thousands of stellate pieces connected together by liv- ing matter. Crinoids were very abundant in the old geo- ologic seas, and many limestone strata were formed out of their remains. They are now nearly extinct: dredging in the deep parts of the oceans has brought to light a few living representatives. Cuass Il.— Ay WY xe. io : aM wks Fia. 216.—Tape-worm (Tenia solium): a, head; 0, ¢, Fig. 217.—Planarian d, segments of the body. worm. VERMES. 265 which are really reproductive joints. It develops from the egg in the digestive canal of the Pig, burrows into the cellular tissue of the animal, and there becomes en- cased. It thus causes the disease “ measles.” If the pork be eaten by man, in an uncooked condition, this case is dissolved by the gastric juice, and the embryo develops into the Tape-worm, attaching itself to the intestine by its “head,” and budding off the reproductive segments. As these become ripe and filled with fertilized eggs, they are detached, and pass off with the excrement. The disease called “rot,” in Sheep, is produced by the Fluke (Distoma), a member of this class. Crass I].—Nematelminthes. The Round, or Thread, Worms include free forms, as the Vinegar-eel; parasitic forms, as the Pin-worm and Trichina; and forms free when adult, and parasitic when young, as the Hair-worm ((Gor- dius). The Trichina is usu- ally derived by Man from the flesh of the Pig. It exists in the muscles, enclosed in mi- croscopic cases. If the meat be eaten uncooked or partially cooked, the cases are dissolved, and the Trichine become sexually mature in the intestines. The young are produced and bur- Fig. 218. — Trichina spiralis: I, male; a, mouth: } i c, intestine; II, capsules, with Trichine in mus- row their way into the cle, much enlarged. 266 COMPARATIVE ZOOLOGY. muscles, where they become encysted. In burrowing, they cause great pain and fever, and sometimes death. The adult Worm is about +4, inch long. Crass II].—Rotifera. ‘The Wheel-animalcules, mostly found in fresh water, are minute Worms of few segments, having on the ante- my rior end a disk ciliated on the edge, oN whence their name. They are from \ soo to zz of an inch long. They can bear drying and revivifying, like seeds. Ny Aa My Crass 1V.—Polyzoa. These minute Worms resemble the Polyps in appearance, living in clusters, each individual inhabiting a delicate cell, or tube, and having a simple mouth surrounded with ciliated tentacles. The colony often takes a plant-like form; sometimes spreads, like fairy-chains or lace-work, over other bodies; or covers rocks and sea-weeds in patches with a i delicate film. The majority secrete car- Fia. 219. — Rotifer, or bonate of lime. A Polyzoan shows its su- ‘* Wheel-animalcule ”’ pines ‘ ea aaa (Hydatina ), highly periority to the Coral, which it imitates, elt iam in possessing a distinct alimentary canal and a well-defined nervous system. The cells of a group never have connection with a common tube, as in Celen- terates. There are both marine and fresh-water species. This group and the next following are related to the Mollusca. Crass V.—Brachiopoda. These Worms have a bivalve shell, the valves being applied to the dorsal and ventral sides of the body. The valves are unegual, the ventral being usually larger, and VERMES. 267 Fig. 220.—Polyzoans: 1. Hornera lichenoides, natural size. 2. Branch of the same, magnified. 3. Discopora Skenei, greatly enlarged. more convex; but they are symmetrical, 2. ¢., a vertical line let fall from the hinge divides the shell into two equal parts. The ventral valve has, in the great major- ity, a prominent beak, perforated by a foramen, or hole, through which a fleshy foot protrudes to attach the ani- mal to submarine rocks. The valves are opened and shut by means of muscles, and in most cases they are hinged, having teeth and _ sockets * ( %, ae LS i) i | —= — SN ~ i} =— -a—_- ————> —————$—$ — —, i (] | iil Wi wl yp Fig. 221.— A Brachiopod (Terebratulina septentrionalis). Atlantic coast. near the beak. The mouth faces the middle of the mar- Fia. 222.—Dorsal Valve of a Brachiopod (Terebratula), showing, in descending gin opposite the beak : and ___ order, cardinal process, dental sockets, Drips 7 ie hinge-plate, septum, and loop support- on either side of itisalong, ing the ciliated arms. LL — 268 COMPARATIVE ZOOLOGY. fringed “arm,” generally coiled up, and supported by a calcareous framework. The animal, having no gills, re- spires by the arms and the mantle. Brachiopods were once very abundant, over two thousand extinct species having been described; but less than a hundred species are now living.’ They are all marine, and fixed; but of all Worms, they enjoy the greatest range of climate and depth. Crass VI.—Annelides. The Annelides include the highest and most specialized Worms. They have many segments, spines or suckers for locomotion, a supercesophageal brain, a ventral chain z \V ta ANN NY) NN SS Zs; ZA \ gee \ } eA 5, Ora Ki C ( Gi; EIEN (OM “\ smi is Fig. 223.—Marine Worm (Cirratulus grandis), with extended cirri. Atlantic. of ganglia, and a closed blood-system. There are three main divisions: the flattened Leeches, without definite segments or bristles, and with suckers for locomotion; the MOLLUSCA. 269 _ Earth-worms and their allies, which have few bristles on each segment (Oligochete); and the Sea-worms, with nu- merous bristles, arranged in two clusters on each side of each segment (Polychete). These last are the largest of the Worms, and may have a distinct head, bearing tentacles and eyes. The cesopha- gus is often turned in, so as to form a proboscis, which bears horny jaws, and can be protruded at the will of the animal (Fig. 17). Subkingdom V.—Mo .uvsca. A Mollusk is a soft- bodied animal, without internal skeleton, and without joints, covered with a moist, sensi- tive, contractile skin, which, like a mantle, loosely envel- ops the creature. In some cases the skin is naked, but generally it is protected by a calcareous covering (shell). The length of the body is less in proportion to its bulk than in other animals. The lower class has no distinct head. The nervous system consists of three well-devel- oped pairs of ganglia, which are principally concentrated around the entrance to the alimentary canal, forming a ring around the throat. The other ganglia are, in most cases, scattered irregularly through the body, and in such the body is unsymmetrical. The digestive system is greatly developed, especially the liver, as in most aquatic animals. Except in the Cephalopods, the muscles are at- tached to the skin, or shell. ‘There is a heart of two chambers (auricle and ventricle) or three (two auricles and ventricle). As in all Invertebrates, the heart is arte- rial. In Mollusks, with rare exceptions, we find no repe- tition of parts along the antero-posterior axis. They are _ best regarded as Worms of few segments, which are fused together and much developed. The total number of living species probably exceeds twenty thousand. The great majority are water-breathers, and marine; some are 270 COMPARATIVE ZOOLOGY. fluviatile or lacustrine, and a few are terrestrial air-breath- ers. All bivalves, and nearly all univalves, are aquatic. Each zone of depth in the sea has its particular species. Cxiass [.—Lamellibranchiata. Lamellibranchs are all ordinary bivalves, as the Oyster and Clam. The shells differ from those of Brachiopods in being placed on the right and left sides of the body, so that the hinge is on the back of the animal, and in being unequilateral and equivalved.’* The umbo, or beak, is the point from which the growth of the valve commences. Fia. 224,—Pearl Oyster Both Brachiopods and Lamellibranchs (Meleagrina margariti- 3 fera); one fourth nat- are headless; but in the latter the mouth bral size. Ceylon. points the same way as the umbo, é. e., towards the anterior part. The length of the shell is measured from its anterior to its posterior margin, and its breadth from the dorsal side, where the hinge is, to the opposite, or ventral, edge. The valves are united to the animal by one muscle (as in the Oyster), or two (as in the Clam), and to each other by a hinge. In some species, as some fresh- water Mussels, the hinge is simply an elastic ligament, passing on the outside from one valve to the other just behind the beak, so that it is on the stretch when = Za the valves are closed, and another placed Fis. 225. — Salt - water between the edges of the valves, so that perenne it is squeezed as they shut, like the spring “*** in a watch-case. Such bivalves are said to be edentulous. But in the majority, as the Clam, the valves also articulate by interlocking parts called teeth. The valves are, there- fore, opened by the ligaments, and closed by the muscles. MOLLUSCA. rie | The margin of the shell on which the ligament and teeth are situated is termed the hinge-line. Lamellibranchs breathe by four plate-like gills (whence the name), two on each side underneath the mantle (Fig. 78). In the higher forms, the mantle is rolled up into two tubes, or siphons, for the inhalation and exhalation of water. They feed on infusorial particles filtered from the water. A few are fixed; the Oyster, e. g., habitually lying ~\ WY ») > \Y < XY Y) bh vapsias \ \ S yA : Mie Wy SN s LY 1 \ 1) - aS i i ANN Fig. 226.—Lamellibranch (Mactra): a, foot; 6, c, siphons. on its left valve, and the Salt-water Mussel hanging to the rocks by a cord of threads called “ byssus ;” but most have a “foot,” by which they creep about. Unlike the Oyster, also, the majority live in an erect position, rest- ing on the edges of their shells. Over four thousand living species are known. These are fresh-water and marine, and range from the shore to a depth of a thou- sand feet. - The chief characters for distinguishing Lamellibranchs are the muscular impressions,” whether one or two; the presence of a pallial sinus, which indicates the possession of siphons; the structure of the hinge, and the symmetry of the valves. | The following are the leading types of structure, as shown by the shells: 1. Monomya: with one adductor muscle; no siphons; foot wanting, or very small; shell unequivalve and eden- 2T2 : COMPARATIVE ZOOLOGY. tulous—as the Oyster (Ostrea), Scallop (Pecten), and Pearl Oyster (Avicula). | 2. Heteromya: with two unequal adductor muscles and no siphons—as the Sea-mussel (J/y- telus). 3. Lsomya: with two equal ad- ductor muscles. There are two sec- tions of this order: a. Those with no siphons, and hence no pallial sinus —as the Fresh - water Mussel (Unio), Cockle (Cardiwm), and “the eee one third natural giaut of the bivalve race” (Trédac- size. China seas. ne). 6. Those with siphons and pal- lial sinus—as the common Clam (J/ya), Quohog ( Venus), and Razor-shell (Soden). Cuass I1.—Gasteropoda. The Snails are, with rare exceptions, all univalves.™ The body is coiled up in a conical shell, which is usually Fig. 228.—Whelk (Buccinum), showing operculum, o, and siphon, 8. spiral, the whorls passing obliquely (and generally from right to left)’ around a central axis, or “columella.” MOLLUSCA. 273 When the columella is hollow (perforated), the end is called the “umbilicus”? When the whorls are coiled around the axis in the same plane, we have a discoidal shell, as the Planorbis. The mouth, or “aperture,” of the shell is “entire” in most vegetable-feeding Snails, and notched or produced into a canal for the siphons in the carnivorous species. The former are generally land and fresh-water forms, and the latter all marine. In some Gasteropods, as the River-snails and most Sea- snails, a horny or calcareous plate (operculum) is secreted on the foot, which closes the aperture when the animal with- draws into its shell. In locomotion, the shell is carried with the apex directed backward. The body of most Gasteropods is unsymmetrical, the organs not being in pairs, but single, and on one side, instead of central. The mantle is continuous around the body, not bilobed, as in Lamellibranchs. A few, as the common Garden-snail, have a lung; but the vast majority breathe by gills. The head is more or less distinct, and provided with two tentacles, with auditory sacs at their bases; two eyes, which are often on stalks; and a strap- like tongue covered with minute teeth. The heart is sit- uated, in the majority, on the right side of the back, and has two cavities. The nervous ganglia are united into an cesophageal ring or collar. All, except the Pteropods, move by means of a ventral disk or foot. Gasteropods are now the reigning Mollusks, comprising three fourths of all the living species, and are the types of the subkingdom. They have an extraordinary range in latitude, altitude, and depth. Omitting a few rare and aberrant forms, we may sepa- rate the class into the following orders: 1. Pteropods.—These are small, marine, floating Mol- lusks, whose main organs of motion resemble a pair of wings or fins coming out of the neck, whence the com- 18 2974 COMPARATIVE ZOOLOGY. mon name, “Sea- butterflies.” Many have a delicate, transparent shell. The head has six appendages, armed with several hundred thousand micro- scopic suckers—a prehensile apparatus unequalled in complication. Pteropods occur in every latitude, but generally in mid-ocean, and in the arctic regions © | are the food of Whales and Sea-birds. Fie. 299.—A Pteropod(Hy. 2 Opesthobranchs.—These low Gas- alea tridentata). Atlantic. teropods are, for the most part, naked Sea-slugs, a few only having a small shell. The feathery gills are behind the heart (whence the name). They are found in all seas, from the arctic to the torrid, generally on rocky coasts. When disturbed, most of them draw themselves up into a lump of jelly or tough skin. Fia. 231.—Bulla ampul- la, or ‘* Bubble-shell ;”’ Fig. 230.—A Tritonian (Dendronotus arborescens). three fourths natural _British seas. size. Indian Ocean. Examples: Sea-lemon (Dorvs), the beautiful Z72¢onea, the painted olzs, the Sea-hare (Aplysia), which a a purple fluid, and the Bubble-shell (Luda). 3. Pudmondies —These air-breathing Gasteropods, rep- resented by the familiar Snail, have the simplest form of lung—a cavity lined with a delicate net-work of blood- vessels, which opens externally on the right side of the neck. This is the mantle-cavity. The entrance is closed by a valve, to shut out the water in the aquatic tribes, and the hot, dry air of summer days in the land species. They are all fond of. moisture, and are more or less slimy. Their shells are lighter (being thinner, and containing less MOELUSCA/() O75 earthy matter) than those of marine Mollusks, having to be carried on the back without the support of the water. Fig. 232.—A, Land-snail. (Helix) ; B,C D, Sirs (Limax); E, F, G, Pond-snails . (Limnea, Paludina, and Planorbis). Their eggs are laid singly, while the eggs of other orders are laid in chains. | They are found in all zones, but are most numerous where lime and moisture abound. All feed on vegetable matter. A. few are naked, as the Slug; some are terrestrial; others live in fresh water. The Land - snails, represented by the common //eliz, the gigantic Bulimus, and the Slug (Zzmaz), are distinguished by their four “horns,” the short front pair being the true tentacles, and the , long hinder pair being the eye-stumps. Te oro hair natural They have a saw-like upper jaw for ** Guiana. biting leaves, and a short tongue covered with minute teeth. The Pond-snails, as Zemnwa and Planorbis, differ 276 | COMPARATIVE ZOOLOGY. Fig. 234.—Cowry (Cypreea capensis): two Fig. 235.—Haliotis, or **‘ Pearly Ear- thirds natural size. South Africa. shell.” \i f YY Fig. 236. — Spindle- Fig. 237. — Cassis rufa, or shell (Fusus colus) ; ‘*Helmet-shell;” one fourth one half natural natural size. Indian Ocean. size. Ceylon. Pa Wiss Ng hire, pee mall Woe Fig. 239.—Cone-shell (Conus Fria. 240.—Chiton squa- marmoreus); two thirds mosus; one half natu- natural size. China seas. ral size. West Indies. Pacific coasts. sl it Ao Hoe VAN A \ ay AWN ae Si N \ SA ) SRN Dy CER \ \\W WW SS I eet AN NS \ A ITN G S : EY. | GY SZ hw} Uf SZ SA ~ aS: / =r > —_— Fig. 238.—Auger-shell (Terebra maculata) ; one half natural size. China seas. \ \. OO FEAST ANSS ATTN WS AVANY i Mageadt Aine WT unas’ il A \\ wate Be nm Wy il il Fia. 241.—Volute (Voluta musica); one half nat- ural size. West Indies. MOLLUSCA. Fig. 243.—Strombus gigas, or ‘* Winged- West shell;” one fifth natural size. Indies. Fig. 242. —Top-shell (Turbo marmo- one fourth natural size. TAatus ) 5 China seas. Fig. 245.—Key-hole Limpet (Fissurella West Indies. Fig. 244. — Paludina, a Fresh-water Snail. listeri). helk (Nassa reticulata). England. lata), and Dog-w Fig. 246.—Ear-shell (H. tubercu 978 COMPARATIVE ZOOLOGY. in having no eye-stalks, the eyes being at the base of the tentacles. They are obliged to come frequently to the surface of the water to breathe. 4. Prosobranchs. — These are aquatic Gasteropods, breathing by gills situated in front of the heart. They are the most highly organized and the most abundant of the crawling Mollusks. Nearly all are marine, and all have a shell. Among the lower forms are the singular Cheton, cov- ered with eight shelly plates; Limpet (Patella), well known to every sea-side visitor; and the beautiful Ear- shell (//alzotis), frequently used for ornaments and inlaid- work. fie | In the higher Prosobranchs, the gills are comb-shaped and the sexes are distinct. The group includes all the spiral univalve sea-shells, and a few fresh-water shells. Many have the aperture entire, which is closed with an operculum: as the dull-colored Paludina and Melania from fresh water, and the pyramidal Z7vochus, pearly Tur- bo, screw-like Turritella, common Periwinkle (Littoria), and globular Vatzca from the sea. Others, the highest of the race, have the margin of the aperture notched or produced into a canal, and are carnivorous and marine: such are nearly all the sea-shells remarkable for their beautiful forms, enamelled surfaces, and brilliant tints, as the Cowry (Cyprea), Volute, Olive, Cone, Harp, Whelk (Buccinum), Cameo -shell (Cassis), Rock - shell (dlurea), Trumpet-shell (Zrzton), Spindle-shell (’usus), and Wing- shell (Strombus). Crass I[].—Cephalopoda. The Cephalopods stand at the head of the subkingdom. The head is set off from the body by a slight constriction, and furnished with a pair of large, staring eyes, a mouth armed with a rasping tongue and a parrot-like beak, and MOLLUSCA. oma eight or more tentacles or arms. The body is symmetri- cal, and wrapped in a muscular mantle. The nervous system is more concentrated than in other Invertebrates; the cerebral ganglia are partly enclosed in a cartilaginous cranium. All the five senses are present. The class is entirely marine (breathing by plume-like gills on the sides of the body), and carnivorous. The naked species are found in every sea. Those with chambered shells (as Vautelus, Ammonites, and Orthoceras) were once. very abundant: more than two thousand fossil species are known, but only one living representative — the Pearly Nautilus. 1. Letrabranchs. — This order is characterized by the possession of four gills, forty or more short tentacles, and an external, chambered shell. The partitions, or septa, of the shell are united by a tube called “siphuncle,” and the ee ae Fig. 247.—Pearly Nautilus, witn shell bisected ; one half natural size. Indian Ocean. animal lives in the last and largest chamber."* The liv- ing Nautilus has a smooth, pearly shell, a head retractile within the mantle or “hood,” and calcareous mandibles, well fitted for masticating Crabs, on which it feeds. This 280 COMPARATIVE ZOOLOGY. straggler of a mighty race dwells in the deep parts of the Indian Ocean, crawling on the bottom; and, while the shell is well known, only a few specimens of the animal have ever been obtained. 2. Dibranchs.—These are the most active of Mollusks, and the tyrants of the lower tribes. Among them are the largest of invertebrate animals. They are naked, hav- ing no external shell covering the body, but usually a horny or caleareous part within. They have a distinct head, prominent eyes, horny mandibles, eight or ten arms furnished with suckers, two gills, a complete tubular fun- nel, and an ink-bag contain- ing a peculiar fluid (sepza), of intense blackness, with which the water is darkened to fa- cilitate escape. They. have the power of changing color, like the Chameleon. They crawl with their arms on the bottom of the sea, head downward, and also swim backward or forward, usual- ly with the back downward, by means of fins, or squirt themselves backward by fore- : ing water forward through Lo AR ag gy The Paper Nautilus (A7- . gonauta) and the Poulpe (Octopus) have eight arms. The female Argonaut secretes a thin, unchambered shell for carrying its eggs. The Squid (Lolzgo) and Cuttle- fish (Sepia) have ten arms, the additional pair being much longer than the others. Their eyes are movable, while ARTHROPODA. 981 those of the Argonaut and Poulpe are fixed. The Squid, so much used for bait by cod-fishermen, has an internal horny “pen,” and the Cuttle has a spongy, calcareous “bone.” The extinct Belemnite had a similar structure. Fig. 249.—Paper Nautilus (Argonauta argo): 1, swimming towards a by ejecting wa- ter from funnel, 0; 2, crawling on the bottom; 3, coiled within its shell, which is one fourth natural size. Mediterranean. Squid have been found with a body seven feet and arms twenty-four feet long, and parts of others still larger—as much as fifty feet in total length. Subkingdom VI.—ARTHROPODA. This is larger than all the other subkingdoms put to- gether, as it includes the animals with jointed legs, such as Crabs and Insects. These differ widely from the Mol- luscan type in having numerous segments, and in show- ing a repetition of similar parts; and from the Worms in having a definite number of segments and jointed legs. | _ The skeleton is outside, and consists of articulated seg- ments or rings. The limbs, when present, are likewise jointed and hollow. The jaws move from side to side. The nervous system consists mainly of a double chain of 982 , COMPARATIVE ZOOLOGY. ganglia running along the ventral surface of the body under the alimentary canal. The brain is in the form of a ring encircling the gullet. The alimentary canal and the circulatory apparatus are nearly straight tubes lying lengthwise —the one through the centre, and the other along the back. The skeleton is composed of a horny substance (chitine), or of this substance with carbonate of lime. All the muscles are striated. | There are four classes, of which the first is water-breath- ing, and the others air-breathing. ©Oxiass 1.—Crustacea. The Crustacea™ are water-breathing Arthropoda, usu- ally with two pairs of antennee.’® Among them are the largest, strongest, and most voracious of the subkingdom, armed with powerful claws and a hard cuirass bristling with spines. Although constructed on a common type, Crustaceans exhibit a wonderful diversity of external form: contrast, for example, a Barnacle and a Crab. We will select the Lobster as illustrative of the entire group. A typical Crustacean consists of twenty-one segments, of which seven belong to the head, seven to the thorax, and seven to the abdomen.” In the Lobster, however, as in all the higher forms, the joints of the head and tho- rax are welded together into a single crust, called the cephalo-thorax. On the front of this shield is a pointed process, or rostrum, and attached to the last joint of the abdomen (the so-called “tail”) is the sole representative of a tail—the ¢elson. This skeleton is a mixture of chitine and calcareous matter.” | | On the under-side of the body we find numerous ap- pendages, feelers, jaws, claws, and legs beneath the ceph- alo-thorax, and flat swimmerets under the abdomen. In fact, as a rule, every segment carries a pair of movable appendages. The seven segments of the head are com- ARTHROPODA. 283 pressed into a very small space, yet have the following members: the eye-stalks; the short and the long anten- ne; the mandibles, or jaws, between which the mouth opens; the two pairs of maxillee; and a pair of modified limbs, called “ foot-jaws.” The thorax carries two more pairs of foot-jaws and five pairs of legs. The foremost legs, “the great claws,” are extraordinarily de- veloped, and terminat- ed by strong pincers (chele). Of the four slender pairs succeed- ing, two are furnished with claws, and two are pointed. The last pair of swimmerets, to- gether with the telson, form the caudal fin— the main instrument of locomotion ; the others (called “false feet”) are used by the female for carrying her eggs. The eyes are raised on stalks so as to be mov- : : Fre. 250.—Under-side of the Cray-fish, or Fresh- able (since the head is water Lobster (Astacus fluviatilis): a, first pair fixed to the thorax), of antennz; b, second pair, c, eyes; d, open- ing of kidney; e, foot-jaws; J, g, first and fifth and are compound, _ pair of thoracic legs; 4, abdominal feet; i, anus; k, caudal fin. made up of about two thousand five hundred square facets. At the base of each small antenna is a minute sac, whose month is guarded by hairs: this is the organ of hearing. The gills, twenty on a side, are situated at the bases of the legs and enclosed in two chambers, into which water is freely admitted, in fact, drawn, by means of a curious attachment to one of the Te a ma 284 COMPARATIVE ZOOLOGY. maxille, which works like the “screw” of a propeller. The heart is a single oval cavity, and drives arterial blood —a dusky fluid full of corpuscles. The alimentary canal consists of a short gullet, a gizzard-like stomach, and a straight intestine. Crustaceans pass through a series of strange metamor- phoses before reaching their adult form. They also peri- odically cast the shell, or moult, every part of the integu- ment being renewed; and another remarkable endowment is the spontaneous rejection of limbs and their complete restoration. Many species are found in fresh water, but the class is essentially marine and carnivo- rous. Of the numerous orders of this great class we will mention only four: 1. Corripeds, distinguished by being fixed, by having a shelly covering, and by their feathery arms (cir7z). Such are Barnacles (Lepas)and Acorn-shells( Lalanus), so common on rocks and timbers Fig. 251.—Idotea robusta: a Te- by the sea-shore. tradecapod. “U..8. coast. 2. Hntomostracans, which agree in having a horny shell and no abdominal limbs; repre- sented by the little Water-fleas (Cyclops) of our ponds, and Fig. 252.—Amphithoé maculata: a Sand-flea. the Brine-shrimps (Artemia), and many others. The King- crabs (Limulus) and the extinct Trilobites were formerly ARTHROPODA. 985 A aR CATR ANS y IM SWAIE SI SN NMOONUOL Ne Yy yaa y Yj Yi ys, Fig. 253.—Barnacles, or Pedunculate Cirripedes (Lepas anatifera). united to this class, but now are known to be widely re- moved from it. ‘The former is by some authors removed from the Crustacea. 3. Tetradecapods, small, fourteen-footed species; as the Fr@. 254,—Acorn-shells (Balanus) on Fig. 255.—Water-fleas: 1, Cyclops communis ; the Shell ofa Whelk (Buccinum). __ 2, Cypris unifasciata; 3, Daphnia pulex. 286 COMPARATIVE ZOOLOGY. Wood-louse, or Sow-bug (Oniscus), so common in damp places, the Slaters (/dotea), and the Sand-fleas (Gammarus), seen by the sea-side. 4. Decapods, having ten legs, as the Shrimp (Crangon), 2 Aig i ~ % | hm Papen < K Wy Nias cack ivy _- — ' / —o ~~~ a, ee ee = aoe NN ee a. = we A oe y Fig. 257.—Swimming Crab (Platyonychus). ARTHROPODA. 987 Oray-fish (Astacus), Lobster (Homarus), and Crab (Can- cer). Crabs differ from Lobsters chiefly in being formed for creeping at the bottom of the sea instead of swim- ming, and in the reduction of the abdomen or “tail” to a rudiment, which folds into a groove under the enormous thorax. They are the highest and largest of living Crus- tacea: they have been found at Japan measuring fifteen feet between the tips of the claws. | ©Cxiass [].—Arachnida. The Arachnids are closely related to the Crustaceans, having the body divided into a cephalo-thorax and abdo- men.”* To the former are attached eight legs of seven joints each; the latter has no locomotive appendages. The head carries two, six, or eight eyes, smooth and ses- sile (2. é., not faceted and stalked, as in the Lobster), and approaching the eye of the Vertebrates in the complete- ness and perfection of their apparatus. The antenne, if’ present, are only two, and these are not “feelers,” but modified to serve for the prehension of food.” They are all air-breathers, having spiracles which open either into air-sacs or traches. ‘The young of the higher forms un- dergo no metamorphosis after leaving the egg. Arachnids number nearly five thousand species. The typical forms are divided into three groups: 1. Acarena, represented by the Mites and Ticks. They have an oval or rounded body, without any marked artic- ulations, the head, thorax, and ea being apparently Ue merged into one. They have = ind brain ; only s single sh Fia. 258. —A Mite (Demodex ‘jollicuto- glion lodged in the abdomen. wm), one of the lowest Arachnids; a parasite in human hair-sacs; X 120. They breathe by tracheee. The mouth is formed for suction, and they are generally para- -sitic. The Mites (Acarus) are among the lowest of Ar- 288 COMPARATIVE: ZOOLOGY. ticulates. The body is soft and minute. The Ticks (Lxodes) have a leathery skin, and are sometimes half an inch long. The mouth is furnished with a beak for piere- ing the animal it infests. 2. Pedipalpi, or Scorpions, characterized by very large maxillary palpi ending in forceps, and a prolonged, joint- ed abdomen. ‘The nervous and circulatory systems are more highly organized than those of Spiders; but the long, tail-like abdomen and the abnormal jaws place them Fig. 259.—Scorpion (under surface) and Centipede. in a lower rank. The abdomen consists of twelve seg- ments: the anterior half is as large as the thorax, with no well-marked division between; the other part is compara- tively slender, and ends in a hooked sting, which is perfo- rated by a tube leading to a poison-sac. The mandibles are transformed into small, nipping claws, and the eyes generally number six. Respiration is carried on by four pairs of pulmonary sacs which open on the under surface ARTHROPODA. 289 of the abdomen. The heart is a strong artery, extending along the middle of the back, and divided into eight separate chambers. Scorpions are confined to the warm-temperate and tropical regions, usually lurking in dark, damp places. The Harvest-men (Phalangium), frequently seen about our houses, belong to this order. They have a short, thick body and extremely long legs, and breathe by trachee. 3. Araneina, or Spiders. They are distinguished by their soft, unjointed abdomen, separated from the thorax by a narrow constriction, and provided at the posterior end with two or three pairs of appendages, called “ spin- Fra. 260.—A, female Spider; B, male of same species; C, arrangement of the eyes. nerets,” which are homologous with legs. The office of the spinnerets is to reel out the silk from the silk-glands, the tip being perforated by a myriad of little tubes, through which the silk escapes in excessively fine threads. An ordinary thread, just visible to the naked eye, is the 19 290 COMPARATIVE ZOOLOGY. union of a thousand or more of these delicate streams of silk.’ These primary threads are drawn out and united by the hind legs. The mandibles are vertical, and end in a powerful hook, in the end of which opens a duct from a poison-gland in ~ the head. The maxille, or “palpi,” which in Scorpions are changed to formidable claws, - in Spiders resemble the thoracic feet, and are often mistaken for a fifth pair. The brain is NS of larger size, and the whole nervous system Fig. 261.—Spin- more concentrated than in the preceding or- neretsoftheSpi- ° ; der, b,c; a,pal- der. There are generally eight simple eyes, puiorm organs: yarely six. They breathe both by trachee and Iung-like sacs, from two to four in number, situated under the abdomen. All the species are carnivorous. The instincts of Spiders are of a high order. They are, perhaps, the most wily of Articulates. They display re- markable skill and industry in the construction of their webs; and some species (called “ Mason Spiders”) even . excavate a subterranean pit, line it with their silken tapes- try, and close the entrance with a lid which moves upon a hinge.” Crass II].—Myriapoda. Myriapods differ from Crustaceans and Spiders in hay- ing the thorax merged in the abdomen, while the head is free. In other words, the body is divided into similar segments, so that thorax and abdomen are scarcely distin- guishable. They resemble Worms in form and in the simplicity of their nervous and circulatory systems; but the skin is stiffened with chitine, and the legs (indefinite in number) are articulated. The legs resemble those of Insects, and the head appendages follow each other in the same order as in Insects—eyes, antenne, mandibles, max- illee, and labium. They breathe by traches, and have two antennee and a variable number of eyes. ARTHROPODA. 991 There are two orders: 1. Chilognatha, having a cylindrical body, each segment furnished with two pairs of legs. They are of slow loco- motion, harmless, and vegetarian. The Thousand-legged Worm (/ulus) is a common representative. 2. Chilopoda, characterized by having a flattened body composed of about twenty segments, each carrying one pair of legs, of which the hindermost is converted into spines. They have longer antenne than the preceding, and the mouth is armed with two formidable fangs con- nected with poisonous glands. They are carnivorous and active. Such is the Centipede (Scolopendra, Fig. 259). Crass IV.—Insecta. Insects are distinguished by having head, thorax, and abdomen distinct, three pairs of jointed legs, one pair of antenne, and generally two pairs of wings. The number of segments in the body never exceeds twenty. The head, apparently one, is formed by the union of four segments. The thorax consists of three —the prothorax, mesothoram, and metathorax—each bearing a pair of legs; the wings, if present, are carried by the last two segments. The ab- domen is normally composed of ten segments, more or less movable upon one another. The skin is hardened with chitine, and to it, as in all Arthropods, the muscles are at- tached. The organs of sense are confined to the cephalic division of the body, the motor organs to the thoracic, and the vegetative to the abdominal. All the appendages are hollow. The antenne are inserted between or in front of the eyes. ‘There is a great variety of forms, but all are tubu- lar and jointed. They are supposed to be organs of touch, and also seem to be sensitive to sound. ‘The eyes are usually compound, composed of a large number of hexago- nal cornes, or facets (from fifty in the Ant to many thou- 292 COMPARATIVE ZOOLOGY. sands in the winged Insects). They are never placed on Fig. 262.—Under surface of a Beetle (Harpatus cali- ginosus): a, ligula; b, paraglosse; c, supports of labial palpi; d, labial palpus; e, mentum; J, in- ner lobe of maxilla; g, outer lobe; h, maxillary palpus; 7, mandible; k, buccal opening; 2, gula, or throat: m, buccal sutures; n, gular suture; 0, prosternum ; p, episternum of prothorax ; p’, epi- meron; q, q’, q’’, coxe;: r, r, r, trochanters; 38, s', 8’, femora, or thighs; ¢, v’, t’, tibe; v, ventral abdominal segments ; w, episterna of mesothorax ; x, mesosternum; y, episterna of metathorax; y’, epimeron; z, metasternum. and foot.’” Some larvee have also ocellt. movable stalks, as the Lobster’s. Besides these, there are three simple eyes, called The mouth may be fitted for bit- ing (masticatory), as in Beetles, or for suck- ing (suctorzal), as in Butterflies. The mas- ticatory type, which is the more complete, and ofwhich the other is but a modification, consists of four horny jaws (mandibles and macille) and an up- per and an under lip (labrum and labium). Sensitive palpi (maa- allary and labial) are developed from the lower jaw and lower lip. The labium is also prolonged into a ligula, or tongue. The legs are invari- ably six in the adult, the fore-legs direct- ed forward and the hinder pairs back- ward. Hach consists of a hip, thigh, shank, “false legs,” without ARTHROPODA. 293 joints, on the abdomen, upon which they chiefly rely in locomotion. The wings are expansions of the crust, stretched over a net-work of horny tubes. The venation, or arrangement of these tubes (called veens and veinlets), _particularly in the fore-wings, is peculiar in each genus. In many Insects, the abdomen of the female ends in a tube which is the sheath of a sting, as in the Bee, or of an ovepositor, or “borer,” as in the Ichneumon, by means of which the eggs are deposited in suitable places. Cephalization is carried to its maximum in this class, and we have animals of the highest instincts under the articulate type. The “brain” is formed of several gan- glia massed together, and lies across the upper side of the throat, just behind the mouth. The main cord lies along the ventral side of the body, with a swelling for each seg- | ment; besides this, there is a visceral nerve representing, in function, the sympathetic system of Vertebrates. The digestive apparatus consists of a pharynx, gullet (to which a crop is added in the Fly, Butterfly, and Bee tribes), giz- _zard, stomach, and intestine. There are no absorbent ves- sels, the chyme simply transuding through the walls of the canal. The blood, usually a colorless liquid, is driven by a chain of hearts along the back, 7. ¢., by a pulsating tube divided into valvular sacs, ordinarily eight, which allow the current to flow only towards the head. As it leaves this main pipe, it escapes into the cavities of the body, and thus bathes all the organs. Although the blood does not circulate in a closed system of blood-vessels, as in Vertebrates, yet it always takes one set of channels in go- ing from the heart, and another in returning. Respira- tion is carried on by trachez, a system of tubes opening at the surface by a row of apertures (spzracles), generally nine on each side of the body. — The sexes are distinct, and the larve are hatched from egos. As a rule, an Insect, after reaching the adult, or 294 COMPARATIVE ZOOLOGY. imago, state, lives from a few hours to several years, and dies after the process of reproduction. Growth takes place only during larval life, and all metamorphoses occur then. Among the social tribes, as Bees and Ants, the majority (called “ workers”) do not develop either sex. Insects (the six-footed Arthropods) comprise nearly one half of the whole Animal Kingdom, or from one hundred and seventy thousand to two hundred thousand species. They are grouped into seven orders: Lower series: body usually flattened; prothorax large and) Neuroptera, squarish; mouth-parts usually adapted for biting; met- | Orthoptera, amorphosis often incomplete; pupa often active; larva | Hemiptera, flattened, often resembling the adult. Higher series: body usually cylindrical; prothorax small; } mouth-parts more generally formed for sucking; meta- morphosis complete; pupa inactive; larva usually cylin- Coleoptera. Diptera, Lepidoptera, H tera. drical, very unlike the adult. {Peers 1. Neuroptera have a comparatively long,.slender body, ARR 4) SNS : TL RY n aaa INE> Fie. 263.—Dragon-fly (Libellula). and four large, transparent wings, nearly equal in size, membranous and lace-like. Such are the brilliant Dragon- .ARTHROPODA. | 295 flies, or Devil’s Darning-needles (Lebel/ula), well known by the enormous head and thorax, large, prominent eyes (each furnished with twenty-eight thousand polished lenses), and Scorpion-like abdomen; the delicate and short-lived May-flies (Hphemera); Caddis-flies (Phryga- nea), whose larvee live in a tubular case made of minute stones, shells, or bits of wood; the Horned Corydalis (Corydalus), of which the male has formidable mandibles twice as long as the head; and the White Ants (Zermes) of the tropics. 2. Orthoptera have four wings: the front pair some- what thickened, narrow, and overlapping along the back ; the hind pair broad, net-veined, and folding up like a fan Fic. 264,—Metamorphosis of a Cricket (Gryllus). upon the abdomen. The hind legs are usually large, and fitted for leaping, all the species being terrestrial, although some fly as well as leap. The eyes are small, the mouth remarkably developed for cutting and grinding. The lar- 296 COMPARATIVE ZOOLOGY. CSN Fig. 265.—Metamorphosis of an Hemipter, Water-boatman (Notonecta). vee and pupe are active, and resemble the imago. They are nearly all vegetarian. Hach family produces charac- teristic sounds (stridulation). The representative forms Wy C is il) Fig. 266.—Seventeen-year Cicada (Cicada septendecim): a, pupa; b, the same, after the imago, c, has escaped through a rent in the back; d, holes in a twig, where the eggs, e, are inserted. ARTHROPODA. 997 are Crickets (Gryllus), Locusts (Locusta), Grasshoppers (Acrydium), Walking -sticks (Phasma), and Cockroaches (Llatta). 3. Hemiptera, or “ Bugs,” are chiefly characterized by a suctorial mouth, which is produced into a long, hard, beak, in which mandibles and maxille are modified into bristles and enclosed by the labium. The four wings are 19 irregularly and sparsely veined, sometimes wanting. The body is flat above, and the legs slender. The larva differs from the imago in wanting wings. In some species the fore-wings are opaque at the base and transparent at the apex, whence the name of the order. Some feed on the juices of animals, others on plants. Here belong the wingless Bed-bug (Cumex) and Louse (Pediculus), the Squash-bug (Coreus), Water-boatman (Votonecta), Seven- teen-year Locust (Czcada), Cochineal (Co¢cus), and Plant- louse (Aphis). | 4. Coleoptera, or “ Beetles.” This is the largest of the orders, the species numbering about ninety thousand. They are easily recognized by the elytra, or thickened, Fig. 267.—a, imago, and Bb, larva, of the Goldsmith Beetle (Cotalpa lanigera); c, pupa of June-bug (Lachnosterna fusca). horny fore-wings, which are not used for flight, but serve to cover the hind pair. When in repose, these elytra are always united by a straight edge along the whole length. The hind wings, when not in use, are folded transversely. 298 COMPARATIVE ZOOLOGY. The mandibles are well developed, and the integument generally is hard. The legs are strong, for the Beetles are among the most powerful running Insects. The lar- vee are worm-like, and the pupa is motionless. The high- est tribes are carnivorous. ‘The most prominent forms S Pe iG Fig. 268.—Sexton Beetles (Necrophorus vespillo), with larva and aye They ne burying a mouse, preparatory to laying their eggs in it. , are the savage but beautiful Tiger Beetles (Cicindela) ; the common Ground Beetles (Carabus), whose hind wings are often absent; the Diving Beetles (Dytescus), with boat-shaped body, and hind legs changed into oars; the Carrion Beetles (Sipha), distinguished by their black, flat ARTHROPODA. 299 bodies and club-shaped antenne; the Goliath Beetles (Scarabeus), the giants of the order; the Snapping-bugs (Hater); the Lightning-bugs (Pyrophorus); the spotted Lady-birds (Coccinella); the showy, Long-horned Beetles Fig. 269.—Metamorphosis of the Mosquito (Culex pipiens). 300 COMPARATIVE ZOOLOGY. (Cerambycide); and the destructive Weevils (Curculio- nide), with pointed snouts. 5. Diptera, or “ Flies,’ are characterized by the sagt mentary state of the hinder pair of wings. Although” having, therefore, but one available pair, they are gifted with the power of very rapid flight. While a Bee moves its wings one hundred and ninety times a second, and a Butterfly nine times, the House-fly makes three hundred and thirty strokes. A few species are wingless. The eyes are large, with numerous facets. In some forms, as the House- fly, all the mouth-parts, except the labium, are rudimen- tary; and the labinm has an expanded tip, by means of Fig. 270. —Metamorphosis of the Flesh- -fly (Sarcophaga carnaria) : a, eggs; b, young maggots just hatched; ¢, d, full-grown maggots; e, pupa; J, imago. which the fly licks up its food. In other forms, as the Mosquito, the other mouth-parts are present as bristles or lancets, fitted for piercing; the thorax is globular, and the legs slender. The larvee are footless grubs. The Diptera number about twenty-four thousand. Among them are the Mosquitoes (Culex); Hessian-fly (Cecedomyia), so de- structive to wheat; Daddy-long-legs (Z7pula), resembling a gigantic Mosquito; the wingless Flea (Pudesx); besides the immense families represented by the House-fly (A/us- ca) and Bot-fly (Zstrus). 2 \ ()) \U) / () 6. Lepidoptera, or “ But- terflies” and ‘ Moths,” are nes known chiefly by their four large wings, which are thick- ly covered on both sides by minute, overlapping scales, Fig. 271.—Scales from the Wings of vari- ; ous Lepidoptera. The scales are of different ARTHROPODA. | 301 colors, and are often arranged in patterns of exquisite “beauty. They are in reality modified hairs, and every family has its partic- ular form of scale. (Qgieeeies': The head is small, Sam ae and the body cylin. @=Ree drical. The legs are not used for locomo- tion. All the mouth parts are nearly obso- lete except the maxil- le, which are fash- ioned into a “ probos- tq?) 1 Fig. 272.—Part of the Wing of 7 Moth (Saturnia) umping u & ’ cis” for P pee Te magnified to show the arrangement of scales. the nectar of flowers. The larve, called ’‘ caterpillars,” have a worm-like form, and from one to five pairs of abdominal legs, in addition to the three on the thorax. The mouth is formed for mas- tication, and (ex- cept in the larvee of Butterflies) the lip has a spinneret connected with silk- glands. There are three groups: the gay Butterflies, having knobbed or hooked antennee, and flying in the day only; the dull-colored Sphinges, with antenne thickened in the middle, and flying at twilight ; and the nocturnal Moths, which generally prefer the night, and whose antenne are thread-like and often feathery. Generally, when at rest, the Butterflies keep their wings raised vertically, while | Fie. 273.— Vanessa polychloros, or ‘* Tortoise-shell But- terfly.”’ COMPARATIVE ZOOLOGY. _ Fie. 274.—Moth and Larva of Attacus pavonia-major. The pupa of the former is unprotected, and is usually suspended by a bit of silk:’®* the pupa of the Moths is enclosed in a cocoon. the others hold theirs horizontally. Y aS : / “J ey —— Fig. 275.—Fruit-moth (Carpocapsa pomonella): 6, larva ; a, chrysalis; c, imago. ARTHROPODA. 303 From twenty-two thousand to twenty-four thousand Lepidopterous species have been identified. Some of the most common Butterflies are the swallow-tail Papilio, the white Pieris, the sulphur- yellow Colzas, the Argynnis, with silver spots on the under a side of the hind wings; the Vanessa, with notched wings. The Sphinges exhibit little variety. They have narrow, powerful wings, and are some- times mistaken for Humming- birds. The “ potato-worm ” is the caterpillar of a Sphinx. The most conspicuous Moths are the large and beautiful Attacus, distinguished Lay ¢ Fie. 276. — Head of a Caterpillar, from triangular, transparent spot beneath: a, antenne; b, horny jaws: i ; c, thread of silk from the conical fusu- im tae entre of thé wing; tus, on either side of which are rudi- the white Bombyx, or “silk- ony Palpt worm ;” the reddish-brown Clistocampa, whose larva, “ the American Tent-caterpillar,” spreads its web in many an apple and cherry tree; the pale, delicate Geometrids ; and the small but destructive Zenezds, represented by the Clothes-moth. 7. Hymenoptera, comprising at least twenty-five thou- sand species, include the highest, most social, and, we may add (Gif we except the Silk-worm), the most useful, of In- sects. They have a large head, with compound eyes and three ocelli, mouth fitted both for biting and lapping, legs formed for locomotion as well as support, and four wings equally transparent, and interlocking by small hooks during flight. The females are usually provided with a sting, or borer. The larve are footless, helpless grubs, and generally nurtured in cells, or nests. Such are 304 COMPARATIVE ZOOLOGY. the Honey-bees (Apes), Humble-bees (Lombus), Wasps (Vespa), Ants (Formica), Ichneumon-flies, and Gall-flies. Those living in societies exhibit three castes: females, or “queens ;”’ “workers.” There is but one queen in a hive, and she is treated with the greatest distinction, even when dead. She dwells in a large, pear-shaped cell, opening down- ward. She lays three kinds of eggs: from the first come forth workers, the second produces males, and the last females. The drones, of which there are about eight — hundred in an ordinary hive, are marked by their great size, their large eyes meeting on the top of the head, and a b c Fig. 277.—Honey-bee (Apis mellifica): a, female; b, worker ; c, male. by being stingless. The workers, which number twenty to one drone, are small and active, and provided with stings, and hollow pits in the thighs, called “ baskets,” in which they carry pollen. Their honey is nectar elabo- rated in the crop by an unknown process; while the wax is secreted from the sides of the abdomen and mixed with saliva. There is a subdivision of extra labor: thus there are wax-workers, masons, and nurses. Ants (except the Saiiba) have but two classes of workers. While Ants live in hollow trees or subterranean chambers (called formz- carwum), Honey-bees and Wasps construct hexagonal cells. The comb of the Bee is hung vertically, that of the Wasp is horizontal. males, or “drones; and neuters, or sexless | eet TUNICATA. 305 Subkingdom VII.—Tunicata. This small and singular group of animals has relations with the worms on the one hand and with the Vertebrates on the other. The most common forms (the solitary As- cidians) are enclosed in a leathery, elastic bag, one end of which is fastened to the rocks, while the other has two orifices, for the inlet and exit of a current of water for nutrition and res- piration. They are without head, feet, arms, or shell. In- deed, few animals seem more Fria. 278.—An Ascidian. helpless and apathetic than these apparently shapeless be- ings. The tubular heart exhibits the curious phenomenon of reversing its action at brief intervals, so that the blood Fi4¢.279.—Diagram ofSim- ple Ascidian: B,S, bran- chial sac; mn, nervous ganglion ; 8, stomach; 7, intestine; 0, reproduc- tive organ; A, heart. oscillates backward and forward in the same vessels. Another peculiarity is the presence of cellulose in the skin. The water is drawn by cilia into a branchial sac, an enlargement of the first part of the intestine, whence it escapes through openings in the sides, to the excurrent ori- fice, while the particles of food drawn in with the water are retained and passed into the intestine. The larva is active, swimming by means of a long tail. It looks like a tadpole, and has a notochord and a nervous system closely resembling those of a Vertebrate. Afterwards it at- taches itself by the head, the tail is ab- sorbed, and the nervous system is re- duced to a single small ganglion. 20 306 COMPARATIVE ZOOLOGY. Subkingdom VIII.—VeErresrata. This grand division includes the most perfect animals, or such as have the most varied functions and the most numerous and complex organs. Besides the unnumbered host of extinct forms, there are about twenty-five thousand living species, widely differing among themselves in shape and habits, yet closely allied in the grand features of their organization, the general type being endlessly modified. The fundamental distinctive character of Vertebrates is the separation of the main mass of the nervous system eS from the general cav- ity of the body, A transverse section of the body exhibits two cavities, or tubes—the = dorsal, containing the @)\ cerebro-spinal nervous ey \ system; the ventral, in- closing the alimentary canal, heart, lungs, and a double chain of gan- glia, or sympathetic system. This ven- tral, or heemal, cavity corresponds to the Cc fe) @ a Fig. 280.—Ideal Plans of the Subkingdoms. JV, transverse section of vertebrate type; v, the whole body of an In- same, inverted. M, transverse section of mol- ‘ : a: luscous type; and Md, of molluscoid. A and vertebrate y) while the Ad, transverse sections of articulate type, high : and low. C, longitudinal section of cclente- dorsal, oe neural, 18 rate type; a, alimentary canal; c, body-cavity. added. In the other figures, the alimentary canal is shaded, the heart is black, and the nervous Vertebrates are also ‘Waa a distinguished by an in- ternal, jointed skeleton, endowed with vitality, and capa- ble of growth and repair. During embryo-life it is rep- resented by the notochord ; but this is afterwards replaced VERTEBRATA. 307 by a more highly developed vertebral column of cartilage or bone. The column and craninm are never absent in the craniota; other parts may be wanting, as the ribs in Frogs, limbs in Snakes, etc.” The limbs are never more than four, and are always articu- lated to the heemal side of the body, while the legs of Inver- tebrates are developed from the neural side. The muscles moving the limbs are attached to the endoskeleton. The circulation of the blood is complete, the arteries being joined to the veins by eapil- laries, so that the blood never escapes into the visceral cav- ity as in the Invertebrates. All have a portal vein, carry- ing blood through the liver; all have lacteals and lym- phatics. The blood is red, and contains both kinds of corpuscles.” The teeth are developed from the dermis, never from the cuticle, as in Mollusks and Articulates; the jaws move vertically, and are never modified limbs. The ,,. liver and kidneys are always present. The respiratory or- gans are either gills or lungs, \\ —S ~~ SSS 281.— Diagram. of Circulation in the higher Vertebrates: 1, heart; 2, lungs; 3, head and upper extremities ; 4, spleen; 5, intestine; 6, kidney; 7, lower extremities; 8, liver. (From Dalton’s * Physiology.”’) 308 COMPARATIVE ZOOLOGY. or both. Vertebrates are the only animals which breathe through the mouth. The nervous system has two marked divisions: the cerebro-spinal, presiding over the functions of animal life (sensation and locomotion); and the sympathetic, which partially controls the organic functions (digestion, respi- ration, and circulation). In no case does the gullet pass through the nervous system, as in Invertebrates, and the mouth opens on the side opposite to the brain. Probably none of the five senses are ever altogether absent. The form of the brain 1s modified by the relative development of the various lobes. In the lower Vertebrates, the cere- bral hemispheres are small—in certain Fishes they are actually smaller than the optic lobes—in the higher, they nearly or quite overlap both olfactories and cerebellum. The brain may be smooth, as in most of the cold-blooded animals, or richly convoluted, as in Man. | There is no skull in Amphioxus. In the Marsipo- branchii and Elasmobranchii it is cartilaginous. In other fishes it is cartilage overlaid with bone. In Amphibians and Reptiles, it is mingled bone and cartilage. In Birds and Mammals, mainly or wholly bony. The human skull contains fewer bones than the skull of most animals, ex- cepting Birds. The skull of all Vertebrates is divisible into two regions: the cranium, or brain-case, and the face. The size of the cranial capacity, compared with the area of the face, is generally the ratio of intelligence. In the lower orders, the facial part is enormously predominant, the eye-orbits are directed outward, and the occipital con- dyles are nearly on a line with the axis of the body. In the higher orders, the face becomes subordinate to the cranium, the sensual to the mental, the eyes look forward, and the condyles approach the base of the cranium. Oom- pare the “snouty ” skull of the Crocodile and the almost vertical profile of civilized Man. A straight line drawn gah d VERTEBRATA. 309 from the middle of the ear to the base of the nose, and another from the forehead to the most prominent part of the upper jaw, will include what is called the faczal an- gle, which roughly gives the relation between the two re- gions, and therefore the rank of the animal.’ In the cold-blooded Vertebrates the brains do not fill the craninin; while in Birds and Mammals a cast of the cranial cavity well exhibits the general features of the cerebral surface.” All Vertebrates are single and free. Mammals bring forth their young alive, having directly nourished them from the mother before birth (wewzparous). In almost all the others the nourishment is laid up in the egg, which is laid before hatching (ovzparous), or is retained in the mother until hatched (ovoveveparous), as in some Reptiles and Fishes. There are two great divisions of the subkingdom, Acrania and Craniota, or Vertebrates without skulls and those with skulls. The Craniota are divided into five great classes: Fishes, Amphibians, Reptiles, Birds, and Mammals. The first three are “cold-blooded,” the other two are ‘ warm- blooded.” Fishes and Amphibians have gills during the whole ora part of their lives, while the rest never have gills. Fishes and Amphibians in embryo have neither amnion nor allantois, while the other three are provided with both. There are three provinces of skull-bearing Vertebrates. Fishes and Amphibians agree in having gills, in want- ing amnion and allantois, and in possessing nucleated red blood-corpuscles (chthyopsida). Birds and Reptiles agree in having no gills, but both amnion and allantois, in the articulation of the skull with the spine by a single condyle, in the development of the skin into feathers or scales,.and in circulating oval, nucle- ated, red corpuscles (Sauropsida). Mammals differ from Birds and Reptiles in having two 310 COMPARATIVE ZOOLOGY. occipital condyles, and their blood-corpuscles are not nu- cleated '* (ALammalia). ; €& commencement of alimentary canal; c, ; m, bulbs of branchial arteries; %, ductus. ar- a, mouth; d, branchial chamber abdominal pore; f, cecal appendage; J, arterial heart; n, vena cava teriosus; 0, heart of vena porte; g, intestine; b, anus. Fie. 282.—Lancelet (Amphioxus lanceolatus) : Driviston I.—Acrania. Vertebrates without a skull. Mediterranean. CiAss.—Pharyngobranchii. The Acrania are represented by the singular animal Amphioxus or Lancelet. It is about two inches long, semi-transparent, without skull, limbs, brain, heart, or red blood-corpuscles. It has for a skeleton a notochord only. It breathes by very numerous gill arches, without fringes, and the water is drawn in by cilia, which line the gill slits. The embryo develops into a gastrula closely resembling that of the Invertebrates. The animal lives in the sandy bottom of shallow parts of the ocean, and has been found in the Mediterranean Sea, in the Indian Ocean, and on the east coast of North and South America. Division [[.—Craniota. Vertebrates with a distinct skull. Crass |].—Pisces. Fishes are the lowest of Verte- brates. They fall far behind the rest in strength, intelligence, and _sensi- bility. The eyes, though large, are almost immovable, bathed by no tears, and protected by no lids. Dwelling in the realm of silence, ears are little ~*~ VERTEBRATA. S11 needed, and such as they have are without external parts, the sound being obliged to pass through the cranium. Taste and smell are blunted, and tonch is nearly confined to the lips. The class yields to no other in the number and variety of its forms. It includes nearly one half of all the ver- tebrated species. So great is the range of variation, it is difficult to frame a definition which will characterize all the finny tribes. It may be said, however, that Fishes are the only backboned animals having median fins (as dorsal and anal) supported by fin-rays, and whose limbs (pectoral and ventral fins) do not exhibit that threefold division (as thigh, leg, and foot) found in all other Vertebrates.™ The form of Fishes is admirably adapted to the element in which they live and move. Indeed, Nature nowhere presents in one class such elegance of proportions with such variety of form and beauty of color. The head is Fig. 283.—Scales of Fishes: A, cycloid scale (Salmon); B, ctenoid scale (Perch); C, placoid scale (Ray); D, ganoid scales (Amblypterus)—a, upper surface; b, under surface, showing articulating processes. disproportionately large, but pointed to meet the resist- ance of the water. The neck is wanting, the head be- ing a prolongation of the trunk. The viscera are closely packed near the head, and the long, tapering trunk is left free for the development of muscles which are to move the tail—the instrument of locomotion. The biconcave vertebrae, with intervening cavities filled with elastic gel- atine, are designed for rapid and versatile movements. The body is either naked, as in the Lamprey, or covered with 312 COMPARATIVE ZOOLOGY. polished, overlapping scales, as in the Perch.. Rarely, as in the Sturgeon, it is defended by bony plates, or by minute, hard spines, as in the Shark. Scales with smooth, circular outline are called cyclowd ; those with notched or spiny margins are ctenoid. Enameled scales are ganozd, and those with a sharp spine, like those of the Shark, are placord. The vertical fins (dorsal, anal, and caudal) are peculiar to Fishes. The dorsal vary in number, from one, as in the Herring, to three, as in the Cod; and the first dorsal may be soft, as in the Trout, or spiny, as in the Perch. Fig. 284.—Blue-fish (Temnodon saltator). All seas. If the dorsals are cut off, the Fish reels to and fro. The caudal may be homocereal, as in ordinary species; or het- erocercal, as in Sharks. In ancient heterocercal Fishes, the tail was frequently vertebrated. The pectoral and ventral fins stand for the fore and hind limbs of other Vertebrates. As the specific gravity of the body is greater than that of the water, most Fishes are provided with an air- bladder, which is an outgrowth from the cesopha- gus. This is absent in such as grovel at the bottom, as the Rays, and in those, like the prone endowed with compensating muscular power. Fishes have no prehensile organ besides the mouth. Both jaws are movable. The teeth are numerous, and a VERTEBRATA. 313 may be recurved spines, as in the Pike; flat and triangu- lar, with serrated edges, in the Shark; or flat and tessel- lated in the Ray. They feed principally on animal mat- ter. The digestive tract is relatively shorter than in other Vertebrates.'° The blood is red, and the heart has rarely more than two cavities, an auricle and a ventricle, both on the venous side. Ordinary Fishes have four gills, which are covered by the operculum, and the water escapes from an opening behind this. In Sharks there is no operculum, Fic, 285.—Salmon (Salmo salar). Both hemispheres. and each gill opens separately. The brain consists of sev- eral ganglia placed one behind the other, and occupies but a small part of the cranial cavity. Its average weight to the rest of the body may be as low as 1 to 3000. The eggs of bony Fishes are naked and multitudinous, some- times numbering millions in a single spawn; those of the Sharks are few, and protected by a horny shell. There are about thirteen thousand species of Fishes, of which over two thirds are Teleostei. There are two sub- classes of Pisces. 314 COMPARATIVE ZOOLOGY. Susc.tass [.—Marsipobranchii. The Lampreys and Hag-fish have a persistent noto- chord, a cartilaginous skull, no lower jaw, a round, suctorial — mouth, horny teeth, one nasal-organ, no scales, limbs, or gill- ie. 286.—Lamprey (Petromyzon Americanus). At- arches. ‘I'he gills are a ~ pouch-like (whence the name of the class), and open separately. They are found both in salt and fresh water. Supciass I].—Pisces Proper. The true Fishes have two nasal organs, and well-devel- oped jaws and gill-arches. There are four orders: | 1. HLlasmobranchii, having a cartilaginous skeleton, and a skin naked or with placoid scales. The gill-openings are uncovered; and the mouth is generally under the head. The ventral fins are placed far back; the pectorals are large, in the Rays enormously developed; and the tail is heterocercal. Such are the Sharks, Rays, and Chimeera. Fic. 287.—Shark (Carcharias vulgaris). Atlantic. VERTEBRATA. 315 They are all marine. The largest Shark found, and there- fore the largest Fish, measured forty feet in length. Fie. 288.—Thornback (Raia clavata). European seas. 2. Ganorder, distinguished by their enameled scales or bony plates. The endoskeleton is usually not completely ossified; the ventral fins are placed far back; and the tail is generally heterocereal. The gills are like those of the bony Fishes, and the air-bladder has a duct, and may aid in respiration. This was one of the largest orders in old geological history. The few modern representatives, as the Sturgeon, Gar-pike, Mud (or Dog) Fish, and Polyp- terus, are essentially fresh-water. 3. TLeleostei, in- cluding all the com- mon Fishes having a bony endoskeleton Fig. 289.— Gar-pike (Lepidos‘eus osseus). Lake Ontario 316 COMPARATIVE ZOOLOGY. Fig. 290.—Sturgeon (Acipenser sturiv). Atlantic coast. and a scaly exoskeleton. The skull is extremely com- plicated ; the upper and lower jaws are complete, and the gills are comb-like or tufted. The tail is homocercal; the other fins are varia- Z Ey « ble in number and Fig. 291.—Cat-tioh, or laorued Pout (Pimelodus catus). position. In the American rivers. : soft - finned Fishes, the ventrals are ab- sent, as in the Eels; or attached to the abdomen, as in the Salmons, Herrings, 3 Pikes, and Carps; or placed under the throat, as in the Cod, Haddock, and Flounder. In the spiny-finned Fishes, the ventrals are generally under or in front of the pectorals, and the scales ctenoid, as in the Perches, Mullets, and Mackerels. 4. Dipnor. These Fishes connect the class with the Amphibia. They have an eel-like body, covered with cycloid scales; an embryonic notochord for a back-bone; Fig. 292.—Cod (Morrhua Americana). Atlantic coast. Fig. 293.—Protopterus annectens; one fourth natural size. African rivers. VERTEBRATA.. 317 long, ribbon-like pectoral and ventral fins, set far apart; two auricles, and one ventricle; and, besides gills, a cellu- lar air-bladder, which is used as a lung. The representatives are Ceratodus from Australia, Pro- topterus trom Africa, and Lepidoseren from Brazil. Crass [I].—Amphibia. These cold-blooded Vertebrates are distinguished by having gills when young, and true lungs when adult. They have no fin-rays, and the limbs, when present, have the same divisions as those of higher animals. The skin is soft, and generally naked, and the skeleton is ossified. The skull is flat, and articulates with the spinal column by two condyles. There is no distinct neck; and the ribs are usually small or wanting. The heart consists of two auricles and one ventricle. All undergo metamorphosis upon leaving the egg, passing through the “ tadpole” state. They commence as water-breathing larvee, when they re- semble Fishes in their respiration, circulation, and locomo- tion. In the lowest forms, the gills are retained through life; but all others have, when mature, lungs only, the gills disappearing. The cuticle is frequently shed, the mode varying with the habits of the species." The com- mon Frog, the type of this class, stands intermediate be- tween the two extremes of the vertebrate series; no fun- damental part is excessively developed. There are about four hundred and fifty liv- ing species, grouped in four orders: 1. Urodela have a naked skin, a tail, and two or four limbs. Some retain their gills through life, as the Frag. 294.—Head and Gills of Menobranchus. Cayuga Lake. 318 COMPARATIVE ZOOLOGY. Proteus of Austria, Menobranchus of the eastern United States, and the two-legged Mud-eel (Sizer) of South Car- olina. Others drop their gills, and always have four limbs, as the aquatic Newts and land Salamanders.’” Tlie fore limbs first make their appearance in the tadpole. 2. Labyrinthodontia, now extinct, resembled gigantic Salamanders, except in their complex teeth and exoskele- | ton of bony plates. : 3. Cecilia have neither tail nor limbs, a snake-like form, Wf iy Y) Aa Fig. 295.—Proteus anguinus. Europe. minute scales in the skin, and well-developed ribs. They are confined to the tropics. 4. Batrachia include all the well-known tailless Am- phibians, as Frogs ~ and Toads. They Sees have a moist, naked skin, ten vertebra, andnoribs. As they Fig. 296.—Red Salamander (Pseudotriton ruber). breathe by swallow- United States. ing the air, they can be suffocated by holding the mouth open. They have , 4a) ae A meet ea i VERTEBRATA. 319 four limbs—the hinder the longer, and the first developed. They have four fingers and five toes. The tongue is long, and, fixed by its an- terior end, it can be rapidly thrown out as an organ of prehen- fon -,lhe eggs are laid in the water en- veloped in a gilairy mass; and the tadpoles , resemble the Urodelans, till both gills and tail are absorbed. Frogs (ana) have teeth in the upper jaw, and webbed feet; Toads (ufo) are higher in rank, and have neither teeth nor fully webbed feet. The former have been known to live sixteen years, and the latter thirty-six. Fig. 297.—Frog (Rana). Crass I[I].—Reptilia. These air-breathing, cold-blooded Vertebrates are dis- tinguished from all Fishes and Amphibians by never hav- ing gills, and from birds by being covered with horny scales or bony plates. The skeleton is never cartilaginous; and the skull has one occipital condyle. The vertebree are ordinarily concave in front; and the ribs are well devel- oped. With few exceptions, all are carnivorous; and teeth are always present, except in the Turtles, where a horny sheath covers the jaws. The teeth are never fastened in sockets, except in Crocodiles. The jaws are usually very wide. The heart has three chambers, save in Crocodiles, where the ventricle is partitioned. but in all cases a mixture of arterial and venous blood is circulated. The lungs are large, and coarsely cellular. The limbs, when present, are provided with three or more fingers as well as toes. There are about fifteen hundred species and four orders of living Reptiles: the first two have horny 320 COMPARATIVE ZOOLOGY. scales, the others have ‘bony plates combined with scales. 1. Ophidia, or Snakes, are characterized by the absence of visible limbs; by the great number of vertebrae, amounting to over four hundred in the great Serpents; by a corresponding number of ribs, but no sternum; and no true eyelids, the eyes being covered with a transparent LE. i ar | Salt! LS Wi Ly \ WW a . SNe | WA V7 Fie. 298.—Adder, or Viper (Pelias berus). England. skin. The tongue differs from that of nearly all other Reptiles in being bifid and extensile. The mouth is very dilatable. The skin is frequently shed, and always by re- versing it. Snakes make their way on land or in water with equal facility. As a rule, the venomous Snakes, as Vipers and Rattle- snakes, are distinguished by a triangular head covered with small scales; a constriction behind the head; two or more fangs, and few teeth; small eyes, with vertical pupil; and short, thick tail. Inthe harmless Snakes, the head gradu- ally blends with the neck, and is covered with plates; the teeth are comparatively numerous in both jaws; the pu- na ae VERTEBRATA. 391 Fig. 299.—a, Head of a Harmless Snake (upper view); b, heads of various Venomous Snakes. pil is round, and the tail tapering. This rule, however, has many exceptions. 2. Lacertilia, or Lizards, may be likened to Snakes pro- vided with four limbs, each having five digits."* The body is covered with horny scales. All have teeth, which are simple in structure; and the halves of the lower jaw are firmly united in front, while those of Snakes are KS {ep Han ND \\ N Cy WAS ron SAN =t Py —~ af A \ VT. aA JWG My) my Niase Birds have four toes (the external or “ lit- Fig. 304.—Principal Parts of a Bird: a, primaries ; 99 A b, secondaries ; c, spurious wing ; d,wing-coverts ; tle toe is al ways é, tertiaries; f, throat, or jugulum; g, chin; h, . E bill; the meeting-line between the two mandi- wanting) » Many have bles is the commissure; the ridge on the upper ] mandible is called culmen; that of the lower, three, the hallua, a gonys; the space between the base of the upper ¢ big ? toe being ab- : : A ’ mandible and the eye is the lore; 7, forehead; k, : crown; J/, scapular feathers; m, back; n, meta- sent 5 while the Os- tarsus, often called tarsus or tarso-metatarsus ; t x +h h b tt 0, abdomen; p, rump; q, upper tail-coverts; 7, 1c as DUL TWO, an- ee ee swering to the third and fourth. The normal number of phalanges, reckoning from the hallux, is 2, 3,4,5. The toes always end in claws. ; oti Birds have neither lips nor teeth, epiglottis nor dia- phragm. The teeth are wanting, because a heavy masti- cating apparatus in the head would be unsuitable for flight. The beak, crop, and gizzard vary with the food. It is a peculiarity of all Birds, though not confined to VERTEBRATA. 397 them, that the generative products and the refuse of di- gestion are all discharged through one common outlet. The sole organs of prehension are the beak and feet. The circulation is double, as in Mammals, starting from a four-chambered heart. Respiration is more complete than in other Vertebrates. The lungs are fixed, and com- municate with air-sacs in various parts of the body, as along the vertebral column, and also with the interior of many bones, as the humerus and femur, which are usu- ally hollow and marrowless."* Both brain and cord are much larger relatively than in Reptiles; the cranium is larger in proportion to the face ; and the parts of the brain are not situated in one plane, one behind the other. The cerebrum is round and smooth, and the cerebellum single- lobed. The ears resemble those of Crocodiles; but the eyes are well developed, and protected by three lids. They are placed on the sides of the head, and the pupil is al- ways round. The sexes generally differ greatly in plu- mage, in some cases more widely than two distinct species, but the coloration of either sex of any one species is very constant. There are two subclasses.” Supciass I.—Ratite (Cursores). This small and singular group is characterized by hav- ing no keel on the breastbone, rudimentary wings, feath- ers with disconnected barbs, and stout legs. The African Ostrich has two toes, the Cassowary three, and the Apte- ryx four. Its representatives are the Ostrich (Séruthzo) of Africa and Arabia, South American Ostrich (/?hea), Cassowary (Casuarvus) of the East Indian Archipelago and Austra- lia, Emu (Dromeus) of Australia, and Apteryx, or Kiwi- kiwi, of New Zealand. Besides these, there are extinct gigantic forms from Madagascar (4 pyornis) and from 328 COMPARATIVE ZOOLOGY. 8 New Zealand (Di- nornis, or Moa). This singular ge- ographical distri- bution, like that of the Dipnoi and that the group was once widely spread over the earth, but is now greatly re- stricted in area. Supciass II. Carinatee. Birds with a ‘ keeled sternum, Fia. 305.—African Ostrich (Struthio camelus). and with devel- oped functional wings. _ A. Aquatic Brrps.—Specially organized for swimming ; the body flattened, and cov- ered with water-proof cloth- ing—feathers and down; the legs short (the knees being wholly withdrawn within the skin of the body), and set far apart and far back; the feet webbed, and hind-toe elevated or absent. The legs are al- ways feathered to the heel at least. They are the only birds whose neck is sometimes longer than the legs. _ BE OER ‘ ee og We ty 1. Pygopodes, or Divers.— as Fig. 306.—Penguin (Aptenodytes Pennan- These lowest of the feathered tii). Falkland Islands. Marsupials, shows VERTEBRATA. 329 3. fs Yu, el ee 4! ey 2 ( sh Ne i SF > WSS cad” fy SSS Fie. 307.—Loon (Colymbus torquatus). North America. tribe have very short wings and tail, and the legs are placed so far back that they are obliged, when on land, to stand nearly bolt upright. ‘They are better fitted for div- ing than for flight, or even swimming. They belong to the high latitudes, living on Fishes mainly, and are repre- sented by the Penguins, Auks, Loons, and Grebes. 9. Longypennes, or Gulls.—Distinguished by their long, Fig. 308.—Tern (Sterna). 330 COMPARATIVE ZOOLOGY. Fig. 309. —Cormorant (Graculus). pointed wings, usually long tail, and by great powers of flight. They are all carnivorous. Such are the Gulls and Terns, which frequent the sea-coast, lakes, and rivers; and the Albatrosses and Pe- trels (the largest and smallest of web-footed Birds), which are oce- 7 auie. | wn oe 3. Totipalmates, or (/’ Cormorants. —Charace- CY terized by a long bill, WU generally hooked; / wings rather long; and toes long, and all four “2? (/ aN Slt tttts {A ‘A a Us ci \ a \ e e Is) Mi {hh joined together by a broad webs. Throat Fig. 310.—Wild Goose (Bernicla Canadiensis). United States. generally naked, and furnished with a sac. The majority are large sea- birds, VERTEBRATA. 2oT and feed on Fishes, Mollusks, and Insects. Examples are the Cormorants, Pelicans, and Gannets. 4. Lamellirostres, or Ducks, have a heavy body, moder- ate wings, short tail, flattened bill, covered by a soft skin, ~ en ——— . S i = = Le SSS SSS > SF) SSS Fia. 311. —Wild Duck (Anas boschas). North America. with ridges along the edges. Diet more commonly vege- tarian than animal. The majority inhabit fresh water— as the Ducks, Geese, Swans, and Flamingoes. B. TERRESTRIAL Birps.—This group exhibits great diver- sity of structure ; but all agree in being es- ~ pecially terrestrial in Wit \ es habit, spending most NSH WN Hilly Ml Aas my UNE } i Ne | ih uf i Mil | of the time on the SaaS FV ground, not on trees or the water, al- though manyofthem -~ heey ——— SS — — SSS fly and swim well. fie. 312.—Sandpiper (Tringa hypolewea). England. 332 COMPARATIVE ZOOLOGY. The legs are long or strong, and the knee is free from the body. The hind toe, when present, is small and ele- vated. 5. Grallatores, or ~W aders.—These are readily distin- guished by their long and bare legs. Generally, also, the toes, neck, and bill are of proportion- ate length, and the tail short. They feed on small ani- mals, and, with a few exceptions, fre- quent the banks of rivers. In flying, their legs are stretched out behind, while in most other Birds they are folded under the body. Such are the Rails, »~s Cranes, Herons, Storks, Ibises, Stilts, Snipes, Sandpipers, and Ploy- ers. 6. Leasores, or Scratch- ers.— As a rule, this order, so valuable to Man, is characterized by a short, arched bill; Fig. 313.—Heron (Ardea). short and concave i Sa Shae W1Ngs, unfitted for PrO- Fre, 314.—Rail, or Marsh Hen (Rallus elegans). tracted flight; stout Poles ae, legs, of medium length; and four toes, the three in front VERTEBRATA. 333 being united by a short web, and terminating in blunt claws. ‘The legs are usually feathered to the heel, some- times (as in Grouse) to the toes. The feathers of the body are large and coarse. The males generally have gay plumage, and some appendage to the head. The nostrils are covered by a scale or valve. Their main food is Fig. 315.—Prairie-chicken (Cupidonia cupido). oat Western prairies. grain. Such are the Grouse, Partridges, Turkeys, Pheasants, Poultry, and Cu- rassows. ‘To these may be added, 7. Columba, or Pigeons and Doves, although they stand gee, intermediate between the terrestrial and perching Birds, as the Flamingoes link the aquatic and terres- trial. They differ from the typical Rasores in having wings for prolonged flight, and slender legs, fitted rath- er for an arboreal life, with. toes not united, and the hind toe on a level with the rest. | C. Ariat Birps.—This Fig. 316.—Ring-dove (Cotanta palumbus). highest and largest group Engle includes all those Birds whose toes are fitted for grasping or perching, the hind . toe being on a level with the rest. The knee is free from the body, and the leg is generally feathered to the heel. SS 5 +s SSS = > 304 COMPARATIVE ZOOLOGY. The wings are adapted for rapid or long flight ; and they hop, rather than walk, on the ground.” They always live in pairs; and the young are hatched helpless. 8. Laptores, or Birds of Prey, differ from all other - Birds, except Parrots, in having a strongly hooked bill and a waxy membrane (cere) at the base of the upper mandible; and from Parrots, Fig. 317.—Barn-owl (Strix flam- Fig. 318. — Fish-hawk (Pandion Carolinensis). mea). Both hemispheres. United States. in having three toes in front and one behind. The toes are armed with long, strong, crooked talons; the legs are robust; and the wings are of considerable size, adapted SALLEWUDLOLOT. Fig. 319.—Golden Eagle (Aquila chrysaetos). North America and Europe. VERTEBRATA. 295 for rapid and powerful flight. The bill is stout and sharp, and usually toothed. All are carnivorous. The female is Jarger than the male, except the Condor. There are two sections: the Diwrnal, whose eyes are on the sides of the head, wings pointed, and metatarsus and toes covered over with scales, as the Vultures, Kites, Hawks, Falcons, and Eagles; the Vocturnal, whose large eyes are directed for- ward, and surrounded by radiating feathers, metatarsus feathered, and plumage soft, as the Owls. 9. Picarie.—This polymorphic group has hardly any peculiarities in common.’ The toes are usually paired, two in front and two behind. There are three divisions of the order: Cypselz, or Swifts, Goat-suckers, and Humming-birds; Cuculi, or Cuckoos, Kingfishers, Trogons, Toucans, Hornbills, and Hoopoes ; and P2cz, or Woodpeckers. These Birds are not musical, and only ordinary fliers. They feed on Insects or fruit. The majority make nests in the hollows of old trees; but the Cuckoos lay in the nests of other Birds. In climbing, the Woodpeckers are assisted by their stiff tail. Af Wy, fy Me = ~ . S SS Ul Tih Za IM WSS Central America. COMPARATIVE ZOOLOGY. 336 Fira. 321.—Trogon elegans. VERTEBRATA. _ 337 10. Psittaci, or Parrots.—These birds have a strong, arched upper bill, with a cere at the base, a fleshy, thick, and movable tongue, and paired toes. They have, usual- ly, brilliant plumage. They live in trees and feed on fruits. Such are the Parrots, Paroquets, and Cockatoos. 11. /nsessores, or Perchers.—This order is the most nu- ~ Fig. 323.—Goat-sucker (Caprimulgus). 22 338 COMPARATIVE ZOOLOGY. merous and varied in the whole class. It comprehends all those tribes which live habitually among trees, excepting Fig. 324.—White-throated Sparrow (Zonotrichia albicollis), United States. Fig. 325.—Redstart (Setophaga ruticilla). States. United States. the Rapacious and Climbing Birds, and whose toes — three in front, and one be- hind—are eminently fitted for perching only. The legs are slender, and seldom used for locomo- tion. They are divisible into two sections: a. Clamatores, with nothing in common but a harsh voice. In most, the tarsus is enveloped in a row of plates, which meet behind in a groove, and the bill broad, and bent down ab- ruptly at the tip. The typical repre- sentatives are the Tyrant Fly-catchers. b. Oscines, or Song- sters, all of whom have a vocal appara- tus, though all do not sing. The an- terior face of the tarsus is one continuous plate, or divided transversely into large scales; and the plates on the sides meet be- VERTEBRATA. 339 hind in a ridge. The toes, always three in front and one behind, are on the same level. The eggs are usu- ally colored. Here belong the Ravens, Crows, Jays, Birds- of - Paradise, Blackbirds, Orioles, Larks, Sparrows, Tan- Fig. 323.—Swallow (Hirundo),. | 340 COMPARATIVE ZOOLOGY. agers, Wax-wings, Swallows, Wrens, Warblers, Thrushes, etc. Crass V.—Mammalia. Mammals are distinguished from all other Vertebrates by any one of the following characters: they suckle their young; the thorax and abdomen are separated by a per- fect diaphragm; the red corpuscles of the blood have no nucleus, and are therefore double-concave; and either a part or the whole of the body is hairy at some time in the life of the animal.” They are all warm-blooded Vertebrates, breathing only by lungs, which are suspended freely in the thoracic cav- ity; the heart is four-chambered, and the circulation is double, as in Birds; the aorta is single, and bends over the left bronchial tube; the large veins are furnished with valves; the red corpuscles differ from those of all other Vertebrates in having no nucleus and in being circular (except in the Camel); the entrance to the windpipe is always guarded by an epiglottis; the cerebrum is more highly developed than in any other class, containing a greater amount of gray matter and (in the higher orders) more convolutions; the cerebellum has lateral lobes, a mammalian peculiarity, and there is a corpus callosum and a pons varoli; the cranial bones are united by sutures, and they are fewer than in cold-blooded Verte- brates; the skull has two occipital condyles, a feature shared by the Amphibians; the lower jaw consists of two pieces only (often united), and articulates directly with the cranium; with four exceptions there are always seven cervical vertebree ;’” the dorsal vertebree, and there- fore the ribs, vary from ten to twenty-four; the lumbar vertebrze number from two to nine; the sacral from three to nine, and the caudal from two to forty-six ; the articu- lating surfaces of the vertebrae are generally flat; the fore-limbs are never wanting, and the hind-limbs only in VERTEBRATA. 24] a few aquatic forms; excepting the Whales, each digit car- ries a nail, claw, or hoof; the teeth (always present, save in certain low tribes) are planted“in sockets ; the mouth is closed by flexi- ble lips; an external ear is rarely ab- sent; the eyes are always present, though rudimentary in some burrow- ing animals; they are viviparous ; and, finally, and perhaps above all, while in all other animals the embryo is developed from the nourishment laid up in the egg itself, in Mammals it draws its support, almost from the beginning, directly from the parent, and, after birth, it is sus- tained for a time by the milk se- creted by the mammary glands. From the first, therefore, till it can care for itself, the young Mam- mal is in vital connection with the parent. Fig. 329.—Longitudinal Section of Human Body (theoretical) : a, cerebro-spinal nervous sys- _ tem; b, cavity of nose; c,cav- Fie. 330.— Transverse Section of Human Body ity of mouth; d, alimentary (theoretical): a, cerebro-spinal nervous axis canal; e, chain of sympathet- contained in neural tube; e, chain of sympa- ic ganglia; jf, heart; g, dia- thetic ganglia; d, alimentary canal; /, heart; phragm. h, heemal tube. SUBCLASS I.—Ornithodelphia. These Mammals have but one outlet for the intestine,. urinary and reproductive organs, as in Birds. They are implacental. There is but one order. 342 COMPARATIVE ZOOLOGY. 1. Monotremata.—This order includes two singular forms, the Duck-mole (Ornithorhynchus) and Spiny Ant- eater (Lchidna), both confined to the Australian conti- nent and New Guinea. The former has a covering of fur, a bill like that of a Duck, and webbed feet. The lat- ter is covered with spines, has a long, toothless snout, like the Ant-eater’s, and the feet are not webbed. Both bur- row, and feed upon Insects. The brain is smooth in the Ornithorhynchus, and folded in the Echidna. In both, the cerebral hemispheres are loosely united by transverse fibres, and do not cover the cerebellum and olfactory lobes.’” : Susctass II.—Didelphia. In these implacental Mammals the uterus is divided . into two parts. 2. Marsupialia are distinguished by the fact that the young, always born premature, are transferred by the mother to a pouch on the abdomen, where they are at- tached to the nipples, and the milk is forced into their mouths by special muscles.” They have “ marsupial VERTEBRATA. 349 bones” projecting from the pelvis, which may serve to support the pouch; but as the Monotremes have the same bones, but no pouch, they doubtless have some other fune- tion. These bones are peculiar to animals. having no. pla- centa, namely, to Monotremes and Marsupials. The brains of Marsupials resemble those of the Monotremes, except that the cerebrum of the Kangaroo covers the olfactory lobes. All have the four kinds of teeth, and all are cov- ered with fur, never with spines or scales. Except the Opossums of America, all are restricted to Australia and Fig. 332.—Virginian Opossum (Didelphys Virginiana). adjacent islands. The Marsupials are almost the only Mammals of Australia, a few species of Rodents and Bats being the only placental Mammals. The Marsupials have here developed into forms corresponding in their habits to the orders of placental Mammals in the rest of the world. The Kangaroos take the place of the large her- bivores—the Ungulates. The Thylacinus and Dasyurus are the marsupial carnivora. Other forms are squirrel- like in shape and habits, and still others are insectivorous. 344 COMPARATIVE ZOOLOGY. SuscLtass II[].—Monodelphia or Placental Mammals. In these Mammals the young are connected with the mother by means of a vascular structure, the placenta, by which they are nourished. They are born in a relatively perfect condition. 3. Hdentata.—This strange order contains very diverse forms, as the leaf-eating Sloths and the insectivorous Ant- eaters and Armadillos of South America, and the Pango- lin and Orycteropus of the Old World. The gigantic fos- le 3 Ssils, Megatherium and as Cc ia, Glyptodon, belong to aay 7 ts this group. The Sloths Fig. 333.—Skull of the Great Ant-eater (Myrme- and Ant-eaters are cov- cophaga jubata): 15, nasal; 11, frontal; 7, pa- ered with coarse hair: rietal; 3, superoccipital ; 2, occipital condyles; ‘ 28, tympanic; 73, lachrymal; 32, lower mandi- the Armadillos and - an- ceases golins, with an armor of plates or scales. The Ant-eaters and Pangolins are strict- ly edentate, or toothless; the rest have molars, wanting, however, enamel and roots. In general, it may be said that the order. includes all quadrupeds having separate, clawed toes and no incisors. The Sloths are arboreal; the ay, i : i ~ = ——————————————————— 3 3 = “s — ei ie seen ae =a © ps," aT ye SS Sip = Oe, U, f = is — > a ~ x 2 = (Ve x ans KS ee vase SS r SE .\ Ness a . oe - ~ Fay Caen oernes = \ lle a: Fia. 3384.—Armadillo (Dasypus). VERTEBRATA. 345 others burrow. The brain is generally smooth; but that of the Ant-eater is convoluted, and has a large corpus cal- losum; but in all the cerebellum and part of the olfac- tory lobes are exposed. 4, Lodentia, or Gnawers, are characterized by two long, curved incisors in each jaw, enameled in front, and per- petually growing; they are specially formed for nibbling. cg 7\YS\. ‘i ; N ss \ , Fe HW SSSR : _ y 22 LOK SSS eR 7 ‘ ‘) A ee ; AAW 27 WANS a SS Fie. 3385.—Skull of a Rodent (Capybara): 22, premaxillary ; 21, maxillary ; 26, mo- lar ; 27, squamosal; 73, lachrymal; 15, nasal; 11, frontal; 4, occipital processes, unusually developed; 7, incisors; a, angle of lower jaw. Separated from them by a wide space (for canines are wanting), are the flat molars, admirably fitted for grind- ing. The lower jaw has longitudinal condyles, which work freely backward and forward in longitudinal fur- rows. Nearly all have clavicles; and the toes'are clawed. The cerebrum is nearly or quite smooth, and covers but a small part of the cerebellum. All are vegetarian. sass Pci AY uh aa Y WN S af a fe Gigi ty oH } OSI snet eke “e | GN), SA. SO iia \ Ay HU) BAN ANS N Yt Fia. 336.—Incisor Teeth of the Hare. 346 COMPARATIVE ZOOLOGY. More than one half of all known Mammals are Rodents. They range from the equator to the poles, over every con- tinent, over mountains and plains, deserts and woods. The Fia. 337.—Beaver (Castor Canadensis). North America. more important representatives are the Porcupines, Capy- baras, Guinea-pigs, Hares, Mice, Rats, Squirrels, and Bea- vers. The Capybara and Beaver are the giants of the race. 5. /nsectwwora are diminutive, insect-eating animals, some, as the Shrew, being the smallest of Mammals. They have small, smooth brains, which, as in the preceding orders, leave uncovered the cerebellum and olfactory lobes. The molar teeth bristle with sharp, pointed cusps, and are associated with ca- long muzzle, short legs, and clavicles. The feet are formed for walking or grasping, and are plantigrade, five-toed, and clawed, The Shrew, Hedgehog, and Mole are examples. 6. Cheiroptera, or Bats, repeat the chief characters of the Insectivores; but some (as the Flying-fox) are fruit- eaters, and have corresponding modifications of the teeth. They are distinguished by their very long fore-limbs, nines and incisors. They have a ys VERTEBRATA. 347 which are adapted for flight, the fingers being immense- ly lengthened, and united by a membranous web. The toes, and one or two of the fingers, are armed with hooked ===>. Fia. 339.—Bat (Vespertilio). nails. The clavicles are remarkably long, and the ster- num is of great strength; but the whole skeleton is ex- tremely light, though not filled with air, as in birds. The eyes are small, the ears large, and the sense of touch is very acute. The favorite attitude of a Bat when at rest is that of suspension by the claws, with head downward. They are all nocturnal. Fig. 340,—Skeleton of a Bat.. 348 COMPARATIVE ZOOLOGY. 7. Cetacea, or Whales, have the form and life of Fishes, yet they possess a higher organization than the preceding orders. They have a broad brain, with many and deep foldings; the foramen magnum of the skull is entirely posterior; the whole head is disproportionately large, and the jaws greatly prolonged. The body is covered with a thick, smooth skin, with a layer of fat (“‘ blubber”’) under-. . Ftq. 341.—Ontline of the Sperm-whale (Physeter): a, blow-hole ; b, the case contain- ing spermaceti; c, junk; d, bunch of the neck—between it and the corner of the mouth is the eye; h, hump; 7, ridge; k, the small; /, tail, or flukes. Between the dotted lines are the spiral strips of blubber. Maximum length, sixty feet. South Atlantic. neath; there are no clavicles; the hind-limbs are want- ing, and the front pair changed to paddles; the tail ex- pands into a powerful, horizontal fin; neck and external ears are wanting; the eyes small, with only two lids; the nostrils (“ blow-holes”)—double in the Whale, single in the Porpoise—are on the top of the head. All are carniv- orous, and essentially marine, a few Dolphins only be- ing found in the great rivers. In the Whalebone Whales, . the teeth are absorbed, and disappear before birth, and their place is supplied by horny “ baleen” plates. “ The Whale feeds by putting this gigantic strainer into opera- tion, as it swims through the shoals of minute Mollusks, Crustaceans, and Fishes, which are constantly found at the surface of the sea. Opening its capacious mouth, and al- lowing the sea-water, with its multitudinous tenants, to fill the oral cavity, the Whale shuts the lower jaw upon the baleen plates, and, straining out the water through them, swallows the prey stranded upon its vast tongue.” In the VERTEBRATA. 349 — ———S—— —— —— Zr — i ——_— —— SSS i \ \ \ \, | \ \ ) aA \ \ Ny hie t Wh " Fie. 342.—Greenland Whale (Balena mysticetus). North Atlantic. other Cetaceans teeth are developed, especially in Dol- phins and Porpoises; but the Sperm Whale has them only in the lower jaw, and the Narwhal can show but a single tusk. The Dolphins are the only Mammals having no organ of smell. 8. Svrenia resemble the Cetaceans in shape, but are close- ly allied to the hoofed animals in organization. They have the limbs of the Whales, and are aquatic; but they are herbivorous, and frequent great rivers and estuaries. They have two sets of teeth, the Cetaceans having but 350 COMPARATIVE ZOOLOGY. Fia. 343.—Troop of Dolphins, with Manatee in the distance. one. They have a narrow brain; bristles scantily cover- ing the body; and nostrils placed on the snout, which is large and fleshy. The living representatives are the Ma- natee, of both sides of the tropical Atlantic Ocean, and the Dugong, of the East Indies. 9. Proboscidia.— This race of giants, now nearly ex- tinct, is characterized by two upper incisors in the form of tusks, mainly composed of dentine (ivory). In the extinct Dinotherium the tusks projected from the lower jaw; and in the Mastodon, from both jaws. Canines are wanting. The molars are few and large, with transverse ridges (Ele- phant) or tubercles (Mastodon). The cerebrum is large and convoluted, but does not cover the cerebellum. The skull is enormous, the size arising in great measure from the development of air-cavities between the inner and outer plates. The nose is prolonged into a flexible trunk, which is a strong and delicate organ of prehension. There are four massive limbs, each with five toes incased in VERTEBRATA. ool broad, shallow hoofs, and also with a thick, tegumentary pad. The knee is below and free from the body, as in Monkeys and Men. Clavicles are wanting. The body of the Elephant is nearly naked; but the Mammoth, an ex- tinet species, had a covering of long woolly hair. Ele- phants live in large herds, and subsist on foliage and grass. There are but two living species: the Asiatic, with long head, concave forehead, small ears, and short tusks; and the African, with round head, convex forehead, large ears, and long tusks.'” 10. Ungulata, or Hoofed Quadrupeds.—This large or- der, comprehending many animals most useful to Man, is distinguished by four well-developed limbs, each furnished with not more than four complete toes, and each toe in- cased in a hoof. The leg, therefore, has no prehensile power; it is only for support and locomotion. Clavicles are wanting; and the radius and ulna are so united as to prevent rotation. ‘There are always two sets of teeth, 7. ¢., milk-teeth are succeeded by a permanent set. The grind- ers have broad crowns. As a rule, all are herbivorous. The brain is always convoluted, but the cerebellum is largely uncovered. Ungulates are divided into the odd and even toed. a. The Odd-toed, as the three-toed Rhinoceros and Tapir,’” and the one-toed Horse.’ The first is distinguished by its very thick skin, the absence of canines, and one or two horns on the nose. The Tapir has the four kinds of teeth, and a short proboscis. The dental formula of the Horse is— i=, ci, » pm =—, m—% — 40, The canines are often wanting in the mare. The Horse walks on the third finger and toe. The metacarpals and metatarsals are greatly elongated, so that the wrist and heel are raised to the middle of the leg. 6. The Hven-toed 352 COMPARATIVE ZOOLOGY. Ungulates— Hog, Hippopotamus, and Ruminants— have two or four toes. The Hog and Hippopotamus have the Fig. 344.—Indian Rhinoceros (R. unicornis). four kinds of teeth, and, in the wild state, are vegetarian. The Ruminants have two toes on each foot, enveloped in hoofs which face each other by a flat side, so that they ap- pear to be a single hoof split or “cloven.” Usually there are also two supplementary hoofs behind, but they do not ordinarily touch the ground. All chew the cud, and have a complicated stomach. They have incisors in the lower jaw only, and these are apparently eight; but the two outer ones are canines.’ The molars are flat, typical grinders. The dental formula of the Ox is— With few exceptions, as the Camel, all Ruminants have horns, which are always in pairs. Those of the Deer are solid, bony, and deciduous; those of the Giraffe and An- VERTEBRATA. 353 Fig. 345.—Stag, or Red Deer (Cervus eclaphus). Europe. telope are solid, horny, and permanent; in the Goat, Sheep, and Ox they are hollow, horny, and permanent. 11. Carnwora, or Beasts of Prey, may be recognized by their four long, curved, acute, canine teeth, the gap be- tween the incisors and canines in the upper jaw for the reception of the low- | er canine, and molars graduating from a tu- berculate to a trench- ant form, in propor- tion as the diet de- viates from a miscel- laneous kind to one strictly of flesh. The incisors, except in the P innigrades, number Fia. 346.—Raccoon (Procyon lotor). United States. 23 AY REN RY AS WW ARS ON NS a VL LOS Yy "ess UN Via Y 6 45 , sheen J if or ONT a BCR 354 COMPARATIVE ZOOLOGY. six in each jaw. ‘There are always two sets. The skull is comparatively small, the jaws are shorter and \ v ~ ors AN iis igit Oe Oe ee a SE I Se ee eee =e ee SSeS eS Fig. 348.—Ermine-weasel (Putorius Noveboracensis). United States. ~\ . oN Wh Ma Fig. 349.—Red Fox (Vulpes fulvus). United States. ig covered with abundant hair. deeper than in Un- gulates, and there are numerous bony ridges on the in- side and outside of the cranium— the high occipital crest being special- ly characteristic. The cerebral hem- ispheres are joined by a large corpus callosum, but the cerebellum is nev- er completely cov- ered. Both pairs of limbs are well developed, the front being pre- hensile; but the clavicles are rudi- mentary. The hu- merus and femur are mainly en- closed in the body. The digits, never less than four, al- ways have sharp and pointed claws.’ ‘The body Qarnivores are divided according to the modifications of the limbs: a. Pinnigrades, having short feet expanded VERTEBRATA. QhR into webbed paddles for swimming, the hinder ones being bound in with the skin of the tail. Such are the Seals, Walrus, and Eared Seals, or Sea-lions. 6. Plantigrades, in which the whole, or nearly the whole, of the hind-foot forms a sole, and rests on the ground. The claws are not retractile; the ears are small, and tail short. Bears, Bad- gers, and Raccoons are well-known examples. c. Dagzte- grades keep the heel raised above the ground, walking on the toes. The majority have long tails. Such are the Weasels, Otters, Civets, Hyenas, Foxes, Jackals, Wolves, Dogs, Cats, Panthers, Leopards, Tigers, and Lions. The Fig. 350.—Southern Sea-lion (Otaria jubata). Antarctic Ocean. last five differ from all others in having retractile claws, and the radius rotating freely on the ulna. The Cats have thirty teeth; the Dogs, forty-two, or twelve more molars. In the former, the tongue is prickly; in the latter, smooth. 12. Prosimti or Lemurs. These singular mammals, sometimes included in the next order, have affinities with Rodents, Insectivora, and Primates. They are covered with soft fur, have usually a long tail, pointed ears, fox- like muzzle, and curved nostrils. They walk on all fours, and the thumb and great toe are generally opposable to the digits. The second toe has a long, pointed claw in- 356 COMPARATIVE ZOOLOGY. stead of a nail. The cerebrum is relatively small, and flattened, and does not cover the cerebellum and olfactory lobes."” They are found mainly in Madagascar. 13. Primates, the head of the kingdom, are char- acterized by the posses- sion of two hands and two feet. The thigh is free from the body, and all the digits are fur- nished with nails, the first Fie. 351.—Lemur (L. ruber), Madagascar. on the foot enlarged to a “oreat toe.” Throughout the order, the hand is eminently or wholly prehensile, and the foot, however prehensile it may be, is always locomotive.’* ‘The clavicles are perfect. The eyes are situated in a complete bony cavity, and look forward. There are two sets of teeth, all enamelled ; and the incisors number four in each jaw. They are divided into Monkeys and Apes, and Man. The Monkeys of tropical America have, generally, a long, prehensile tail; the nostrils are placed far apart, so that the nose is wide and flat: the thumbs and great toes are fitted for grasping, but are not opposable to the other digits; and they have four molars more than the Apes or Man—that is, thirty-six teeth in all. In the Apes of the Old World the tail is never prehensile, and is sometimes wanting; the nostrils are close together; both thumbs and great toes are opposable; and the teeth, though numbering the same as Man’s, are uneven (the incisors being prominent, and the canines large), and the series is interrupted by a gap on one side or other of the canines. Their average size is much greater than that of the Monkeys, and they are not so strictly arboreal. In both Monkeys and Apes, the cerebrum covers the cere- VERTEBRATA. 357 ST ET OL CT a age Ue atin = oa ue 4 Asis j= Le \e D ri Z @ vod PAL Fig. 352.—White-throated Sapajou (Cebus hypolencus). Central America. bellum.“ While in the Monkeys the skull is rounded and smooth, that of the Apes, especially those coming nearest to Man—the anthropoid, or long-armed, Apes, as Gorilla, Chimpanzee, Orang, and Gibbon—is characterized by strong crests. Monkeys take a horizontal position; but the Apes assume a sem1- erect attitude, the legs being shorter than the arms. In ZO, cA fj ( he | sess \ \ I Bas be —Skull of Orang-utan (Simia Fig. 354.—Skull of Chimpanzee (7'roglo- satyrus). dytes Niger). ee Fira, 353. 358 COMPARATIVE ZOOLOGY. all the Primates but Man, the body is clothed with hair, which is generally longest on the back. Several Mon- keys and Apes have a beard, as the Howler and Orang. Fig. 355.—Female Orang-utan (from photograph). Borneo. The Orang is the least human of all the anthropoid } Y J 4 ) y! BrP Fig. 356.—Skeletons of Man, Chimpanzee, and Orang. * VERTEBRATA. 359 Apes as regards the skeleton, but comes nearest to Man in the form of the brain. The Chimpanzee approaches Man more closely in the character of its cranium and teeth,and the proportional size of the arms. The Gorilla is most Man-like in bulk (sometimes reaching the height of five feet six inches), in the proportions of the leg to the body and of the foot to the hand, in the size of the heel, the form of the pelvis and shoulder-blade, and vol- ume of brain.” Man differs from the Apes in being an erect biped. In him, the vertebrate type, which began in the horizon- tal Fish, finally became vertical. No other animal habit- ually stands erect; in no other are the fore-limbs used exclusively for head- purposes, and the hind pair solely for locomotion. His limbs are naturally parallel to the axis of his body, not perpendicular. They have a near equality of length, but the arms are always somewhat shorter than the legs. In all the great Apes the arms reach below the knee, and the legs of the Chimpanzee and Gorilla are relatively shorter than Man’s. Man only has a finished hand, most perfect as an organ of touch, and most versatile. Both hand and foot are relatively shorter than in the Apes. ‘The foot is planti- a b Fia. 357.—Foot (a) and Hand (8) of the Gorilla. 360 COMPARATIVE ZOOLOGY. grade; the leg bears vertically upon it; the heel and ereat toe are longer than in other Primates; and the great toe is not opposable, but is used only as a fulcrum in locomotion. The Gorilla has both an inferior hand and inferior foot. The hand is clumsier, and with a shorter thumb than Man’s; and the foot is prehensile, _ and is not applied flat to the ground.” The scapular and pelvic bones are extremely broad, and the neck of the femur remarkably long. Man is also singular in the double curve of the spine: the Ba- boon comes nearest to Man in this respect. The human skull has a smooth, rounded outline, ele- | vated in front, and devoid of crests. ‘The cranium great- ly predominates over the face, being four to one;’” and no other animal (except the Siamang Gibbon) has a chin. Man stands alone in the peculiarity of his dentition: his teeth are vertical, of nearly uniform height, and close ‘together. In every other animal the incisors and canines are more or less inclined, the canines project, and there are vacant spaces.” Man has a longer lobule to his ear than any Ape, and no muzzle. The bridge of his nose is decidedly convex ; in the Apes generally it is flat. Man has been called the only naked terrestrial Mam- mal. His hair is most abundant on the scalp ; never ou the back, as in the Apes. Man has a more pliable constitution than the Apes, as shown by his world-wide distribution. The animals near- est him soon perish when removed from their native places. Thongh Man is excelled by some animals in the acute- ness of some senses, there is no other animal in which all the senses are capable of equal development. He only has the power of expressing his thoughts by articulate speech, and the power of forming abstract ideas. Man differs from the Apes in the absolute size of —— eh ee eee oe VERTEBRATA. 261 Fig. 358.—Australian Savage. brain, and in the greater complexity and less symmetrical] disposition of its convolutions. The cerebrum is larger in proportion to the cerebellum (being as 8% to 1), and the former not only covers the latter, but projects beyond it. The brain of the Gorilla scarcely amounts to one third in volume or one half in weight of that of Man. ae 359.—Skull of European. | 3 Fie. 360.—Skull of Negro. Yet, so far as cerebral structure goes, Man differs less from the Apes than they do from the Monkeys and Le- murs. 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Sao, yoou PpUv S99T—'SaMOLVIIVAN ‘G wapiC *[OUMSANAOT, xe x ARRANGEMENT OF REPRESENTATIVE FORMS. 24- COMPARATIVE ZOOLOGY. 370 “OUWOFT 330010 + U9AD 44994 MIWA 2980] S[LIjsou ‘snqag ?4Aede s[i1jsou ‘nwmaT :081e, sive pue sofa ‘s[l4jsou podeys-Aoupry + pomeyo ‘yjems ‘[vatoqiy—'lINIsodd “BI 4ap/O "SUaq + OPBISIILSIp . ‘SNSLQ repBistyueld ‘proud :opvadtuuid ‘snnby :pa01-ppo "s0g :pa0}-U0Ad $ [leu yep Uyak tt woaoun yjoo} ( 90} Jwors SMef ovo UL SLospoul INO{—‘SHLYNIA “ET ap4O Squvyouaty savour ‘ pedojoa -op [[OM SOUIUBD ‘SLID ‘ 8.10}8d-YSe]{—"VAOAINAVD ‘LL 4ap40 | ssyoou ¢gIBjOUl Jey ‘adiel ‘ UBLIVJOSaA—"VLVINON() “OL LaplO ‘panurquoj—ellemuUleyAL “A S8VTO “panurjuUoy —el[ewuuUleyAl ‘T]] HONIAOUT “PanuyuUoy —VLVAdALAd A WOpsUIyquys THE DISTRIBUTION OF ANIMALS. 3701 CHAPTER XXIII. THE DISTRIBUTION OF ANIMALS. Lirz is everywhere. In the air above, the earth be- neath, and the waters under the earth, we are surrounded with life. Nature lives: every pore is bursting with life; every death is only a new birth, every grave a cradle. The air swarms with birds, Insects, and invisible animal- cules. The waters are peopled with innumerable forms, from the Protozoan, millions of which would not weigh a grain, to the Whale, so large that it seems an island as it sleeps upon the waves. The bed of the sea is alive with Crabs, Shells, Polyps, Star-fishes, and Foraminifera. Life everywhere—on the earth, in the earth, crawling, creep- ing, burrowing, boring, leaping, running. Nor does the vast procession end here. The earth we tread is largely formed of the débris of life. The quarry of limestone, the flints which struck the fire of the old Revolutionary muskets, are the remains of countless skele- ‘tons. The major part of the Alps, the Rocky Mountains, and the chalk cliffs of England are the monumental rel- ics of by-gone generations. Irom the ruins of this living architecture we build our Parthenons and Pyramids, our St. Peters and Louvres. So generation follows generation. But we have not yet exhausted the survey. Life cradles within life. The bodies of animals are little worlds hav- ing their own fauna and flora. In the fluids and tissues, in the eye, liver, stomach, brain, and muscles, parasites are found; and these parasites often have their parasites liv- ing on them. ST? COMPARATIVE ZOOLOGY. ‘*Great fleas have little fleas and smaller fleas to bite "em; And these again have other fleas, and so ad infinitum.” Thus the ocean of life is inexhaustible. It spreads in every direction, into time past and present, flowing every- where, eagerly surging into every nook and corner of cre- ation. On the mountain-top, in the abysses of the Atlan- | tic, in the deepest crevice of the earth’s crust, we find traces of animal life. Nature is prodigal of space, but - economical in filling it.” Animals are distributed’ over the globe according to definite laws, and with remarkable regularity. Each of the three great provinces, Earth, Air, and Wa- ter, as also every continent, contains representatives of all the classes; but the various classes are unequally repre- sented. Every great climatal region contains some species not found elsewhere, to the exclusion of some other forms. Every grand division of the globe, whether of land or sea, each zone of climate and altitude, has its own fauna. And, in spite of the many causes tending to disperse ani- mals beyond their natural limits, each country Ly its peculiar zoological physiognomy. The space occupied by the different groups of animals is often inversely as the size of the individuals. Compare the Coral and Elephant. The fauna now occupying a separ ate area is closely al- lied to the fauna which existed in former geologic times. Thus, Australia has always been the home of Marsupials, and South America of Edentates. It is a general rule that groups of distinct species are circumscribed within definite, and often narrow, limits. Man is the only cosmopolitan; yet even he comprises sev- eral marked races, whose distribution corresponds with the great zoological regions. The natives of Australia are as grotesque as the animals. Certain brutes likewise have a great range: thus, the Puma ranges from Canada to Pata- THE DISTRIBUTION OF ANIMALS. Sie gonia; the Musk-rat, from the Arctic Ocean to Florida; the Ermine, from Behring’s Straits to the Himalayas; and the Hippopotamus, from the Nile and Niger to the Orange River.” Frequently, species of the same genus, living side by side, are widely different, while there is a close resem- _blanee between forms which are antipodes. The Mud-eel of South Carolina and Menobranchus of the Northern States have their relatives in Japan and Austria. The American Tapir has its mate in Sumatra; the Llama is related to the Camel, and the Opossum to the Kangaroo. _ The chief causes modifying distribution are tempera- ture, topography, ocean and wind currents, humidity and light. To these may be added the fact that animals are ever intruding on each other’s spheres of existence. High mountain -ranges, wide deserts, and cold currents in the ocean are impassable barriers to the migration of most species. Thus, river-fish on opposite sides of the Andes differ widely, and the cold Peruvian current prevents the growth of coral at the Galapagos Islands. So a broad river, like the Amazons, or a deep, narrow channel in the sea, is an effectual barrier to some tribes. Thus, Borneo belongs to the Indian region, while Celebes, though but a few miles distant, is Australian in its life. The faunze of North America, on the east coast, west coast, and the open plains between, are very different. Animals dwelling at high elevations resemble those of colder latitudes. The same species of Insects are found on Mount Washington, and in Labrador and Greenland. The range does not depend upon the powers of loco- motion. The Oyster extends from Halifax to Charles- ton, and the Snapping-turtle from Canada to the equa- tor; while many Quadrupeds and Birds have narrow hab- itats. ate The distribution of any group is qualified by the nature ol4 COMPARATIVE ZOOLOGY. of the food. Carnivores have a wider range than herbi- vores. Life diminishes as we depart from the equator north or south, and likewise as we descend or ascend from the level of the sea. The zones of geography have been divided by zoolo- gists into narrower provinces. Five vertical regions in the sea have been recognized: the Littoral, extending be- tween tide-marks; the Laminarian, from low water to fifteen fathoms; the Coralline, from fifteen to twenty fathoms; the deep-sea Coral, from fifty to one hundred fathoms; and the Bathybian, from one hundred fathoms down; but since life has been found to extend to great depths in the ocean—as great as three thousand fathoms —these divisions are of little importance. Every marine species has its own limits of depth. It would be quite as difficult, said Agassiz, for a Fish or a Mollusk to cross from the coast of Europe to the coast of America.as for a Reindeer to pass from the arctic to the antarctic regions across the torrid zone. Marine animals congregate mainly © along the coasts of continents and on soundings. The meeting - place of two maritime currents of different tem- peratures, as on the Banks of Newfoundland, favors the development of a great diversity of Fishes. Every great province of the ocean contains some repre- sentatives of all the subkingdoms. Deep-sea life is diver- | sified, though comparatively sparse. Examples of all the five invertebrate divisions were found in the Bay of Bis- cay, at the depth of two thousand four hundred and thir- ty-five fathoms.” Distribution in the sea is influenced by the temperature and composition of the water and the character of the bottom. The depth acts indirectly by modifying the temperature. Northern animals approach nearer to the equator in the sea than on the land, on account of cold THE DISTRIBUTION OF ANIMALS. 375 currents. The heavy aquatic Mammals, as Whales, Wal- ruses, Seals, and Porpoises, are mainly polar. The land consists of the following somewhat distinct areas : the Neotropic, comprising South America, the West Indies, and most of Mexico; the Nearctic, including the rest of America; the Palearctic, composed of the eastern continent north of the Tropic of Cancer, and the Hima- layas; the Ethiopian, or Africa south of the Tropic of Cancer; the Oriental, or India, the southern part of Chi- na, the Malay Peninsula, and the islands as far east as Java, Borneo, and the Philippine Islands; and the Aus- tralian, or the eastern half of the Malay Islands and Aus- tralia. These are Mr. Wallace’s regions. Other writers unite the northern parts of both hemispheres into one region, and the Oriental with the Ethiopian regions. Life in the polar regions is characterized by great uni- formity, the species being few in number, though the number of individuals is immense. The same animals in- habit the arctic portions of the three continents; while the antarctic ends of the continents, Australia, Cape of Good Hope, and Cape Horn, exhibit strong contrasts. Those three continental peninsulas are, zoologically, separate worlds. In fact, the whole southern hemisphere is pecul- ilar. Its fauna is antique. Australia possesses a strange mixture of the old and new. South America, with newer Mammals, has older Reptiles; while Africa has a rich vertebrate life, with a striking uniformity in its distribu- _ tion. Groups, old geologically and now nearly extinct, are apt to have a peculiar distribution ; as the Edentata in South America, Africa, and India; the Marsupials in Aus- tralia and America; the Ratite in South America, Africa, Australia, and New Zealand. | In the tropics, diversity is the law. Life is more varied and crowded than elsewhere, and attains its highest devel- opment. | 376 COMPARATIVE ZOOLOGY. The New-world fauna is old-fashioned, and inferior in rank and size, compared with that of the eastern con- tinents. As a rule, the more isolated a region the greater the variety. Oceanic islands have comparatively few species, but a large proportion of endemic or peculiar forms. Ba- trachians are absent, and there are no indigenous terrestrial Mammals. The productions are related to those of the nearest continent. When an island, as Britain, is sepa- rated from the mainland by a shallow channel, the mam- malian life is the same on both sides. . Protozoans, Ceelenterates, and Echinoderms are limited to the waters, and nearly all are marine. Sponges are mostly obtained from the Grecian Archipelago and Baha-— mas, but species not commercially valuable abound in all seas. Coral-reefs abound throughout the Indian Ocean and Polynesia, east coast of Africa, Red Sea, and Persian Gulf, West Indies, and around Florida; and Corals which do not form reefs are much more widely distributed, be- ing found as far north as Long Island Sound and Eng- land. Crinoids have been found, usually in deep sea, in very widely separated parts of the world—off the coast of Norway, Scotland, and Portugal, and near the East and West Indies. The other Echinoderms abound in almost every sea: the Star-fishes chiefly along the shore, the Sea- urchins in the Laminarian zone, and the Sea-slugs around coral-reefs. Worms are found in all parts of the world, in sea, fresh water, and earth. They are most plentiful in the muddy or sandy bottoms of shallow seas. Living Brachiopods, though few in number, occur in tropical, temperate, and arctic seas, and from the shore to great depths. Polyzoa have both salt and fresh water forms, and Annelids include land forms, as the Earth-worm and some Leeches. Mollusks have a world-wide distribution over land and * ie —s S THE DISTRIBUTION OF ANIMALS. OEE sea. The land forms are restricted by climate and food, the marine by shallows or depths, by cold currents, by a sandy, gravelly, or mud bottom. The Bivalves are also found on every coast and in every climate, as well as in rivers and lakes, but do not flourish at the depth of much more than two hundred fathoms. The fresh-water Mus- sels are more numerous in the United States than in Europe, and west of the Alleghanies than east. The sea- shells along the Pacific coast of America are unlike those of the Atlantic, and are arranged in five distinct groups: Aleutian, Californian, Panamic, Peruvian, and Magel- lanic. On the Atlantic coast, Cape Cod and Cape Hatte- _ ras separate distinct provinces. Of land Snails, Heliw has an alinost universal range, but is characteristic of North — America, as Bulimus is of South America, and Achatuna of Africa. The Old World and America have no species in common, except a few in the extreme north. The limits of Insects are determined by temperature and vegetation, by oceans and mountains. There is an insect-fauna for each continent, and zone, and altitude. The Insects near the snow-line on the sides of mountains in the temperate region are similar to those in polar lands. The Insects on our Pacific slope resemble those of Europe, while those near the Atlantic coast are more like those of Asia. Not half a dozen Insects live in the sea. The distribution of Fishes is bounded by narrower lim- its than that of other animals. A few tribes may be called cosmopolitan, as the Sharks and Herrings; but the species are local. Size does not appear to bear any relation to latitude. The marine forms are three times as numerous as the fresh-water. The migratory Fishes of the northern hemisphere pass to a more southern region in the spring, while Birds migrate in the autumn. Living Reptiles form but a fragment of the immense number which prevailed in the Middle Ages of Geology. 378 | COMPARATIVE ZOOLOGY. Being less under the influence of Man, they have not been forced from their original habitats. None are arctic. America is the most favored spot for Frogs and Salaman- ders, and India for Snakes. Australia has no Batrachians, and two thirds of its Snakes are venomous. In the United AN VGN Nipn. Ni vy Na SH] |. yy Ds 7 f\ } QV 6 Wi SARS YN SRE M WAY}\) WH ba OD a Sy goth ! ’ 4 A Dey | CN, Zs Was Sk Fie. 361.—Zones of Animal Life. States, only twenty-two out of one hundred and seventy- six are venomous. Frogs, Snakes, and Lizards occur at elevations of over fifteen thousand feet. Crocodiles, and most Lizards and Turtles, are tropical. Swimming Birds, which constitute about one fourteenth of the entire class, form one half of the whole number in THE DISTRIBUTION OF ANIMALS. 379 Greenland. As we approach the tropics, the variety and number of land Birds increase. Those of the torrid zone are noted for their brilliant plumage, and the temperate forms for their more sober hues, but.sweeter voices. In- dia and South America are the richest regions. Hum- mers, Tanagers, Orioles, and Toucans are restricted to the New World. Parrots are found in every continent ex- cept Europe; and Woodpeckers occur everywhere, save in Australia. The vast majority of Mammals are terrestrial; but Ce- taceans and Seals belong to the sea, Otters and Beavers de- light in lakes and rivers, and Moles are subterranean. As of Birds, the aquatic species abound in the polar regions. Marsupials inhabit two widely separated areas — America and Australia. In the latter continent they constitute two thirds of the fauna, while all placental Mammals, ex- cept Bats and a few Rats and Squirrels, are wanting. Excepting a few species in South Africa and South Asia, Edentates are confined to tropical South America. The equine family is indigenous to South and East Africa and Southern Asia. In North America, Rodents form about one half the number of Mammals; there are but three species in Madagascar. Ruminanfs are sparingly repre- sented in America. Carnivores flourish in every zone and continent. The prehensile-tailed Monkeys are strict- ly South American; while the anthropoid Apes belong to the west coast of Africa, and to Borneo and Sumatra. Both Monkeys and Apes are most abundant near the equa- tor; in fact, their range is limited by the distribution of palms. | NOTES. ’ The complete and elaborate natural history of a single species or limited group is called a Monograph, as Darwin’s ‘*‘ Monograph of the Cirripedia.”’ A Memoir is not so formal or exhaustive, giving mainly original investiga- tions of a special subject, as Owen’s ‘‘ Memoir on the Gorilla.” * Before the time of Linnzus, the Lady-bug, e. g., was called ‘‘ the Cocci- nella with red coleopters having seven black spots.” He called it Coccinella septem-punctata. $ Mandino (1315) and Berenger (1518), of Bologna, and Vesalius, of Brus- sels (1550), were the first anatomists. Circulation of the blood discovered by Harvey, 1616. The lacteals discovered by Asellius, 1622, and the lym- phatics by Rudbek, 1650. Willis made the first minute anatomy of the brain and nerves, 1664. The red blood-corpuscles were discovered by Leeuwen- hoek and Malpighi, 1675. Infusoria first observed by Leeuwenhoek, 1675 ; the name given by Muller, 1786. Swammerdam was the founder of Ento- mology, 1675. Comparative anatomy was first cultivated by Perrault, Pec- quet, Duverney, and Méry, of the Academy of Paris, the latter part of the seventeenth century. Malpighi, the founder of structural anatomy, was the first to demonstrate the structure of the lungs and skin, 1690. About the same time, Ray and Willoughby first classified Fishes on structural grounds. Foraminifers were seen by Beccarius one hundred and fifty years ago; but their true structure was not demonstrated till 1835, by Dujardin. Peyssonel published the first elaborate treatise on Corals, 1727. Haller was the first to distinguish between contractility and sensibility, 1757. White blood-corpus- cles discovered by Hewsonin 1775. Spallanzani was the first to demonstrate the true nature of the digestive process, 1780. Cuvier and Geoffroy, in 1797, proposed the first natural classification of animals. Before that, all Inverte- brates were divided into Insects and Worms. Lamarck was the first to study -Mollusks, 1800; before him, attention was confined to the shell. He sepa- - rated Spiders from Insects in 1812. The law of correlation enunciated by Cuvier, 1826. Von Baer was the founder of Embryology, establishing the doctrine omnia ex ovo, 1827; but the first researches in Reproduction were made by Fabricius about 1600, and by Harvey in 1651. Wolff, in the last century, was the pioneer in observing the phenomena of Development. Sars first observed alternate generation, 1833. Duméril is considered the father ef Herpetology, and Owen of Odontology. Schleiden and Schwann pub- lished their celebrated researches in cell-structure, 1841; but Bichat, who died 1802, was the founder of Histology. Protoplasm was discovered by Dujardin in 1835, and called Sarcode, 382 NOTES. * This twofold division is arbitrary. No essential distinction, founded on the nature of the elements concerned, or the laws of their combination, can be made; and so many so-called organic substances, as urea, ammonia, alco- hol, tartaric and oxalic acids, alizarine, and glucose, have been prepared by inorganic. methods, that the boundary-line is daily becoming fainter, and may in time vanish altogether. We would here utter our protest against the in- troduction of any more terms like znorganic, invertebrate, acephalous, etc., which express no qualities. | 5 Even the works of nearly all animals proceed in curves. . : 6 London Quarterly Review, January, 1869, p. 142. It is true of any great primary group of animals, as of a tree, that it is much more easy to define the summit than the base. 7 De Bary on ‘‘ Myxomycete ;” Darwin on ‘‘ Carnivorous Plants.” 8 “* There are certain phenomena, even among the higher plants, connected with the habits of climbing plants and with the functions of fertilization, which it is very difficult to explain without admitting some low form of a general harmonizing and regulating function, comparable to such an obscure manifestation of reflex nervous action as we have in Sponges and in other animals in which a distinct nervous system is absent.”—Prof. WYVILLE Tuomson’s Introductory Lecture at Edinburgh. ° <¢Tf nature had endowed us with microscopic powers of vision, and the integuments of plants had been rendered perfectly transparent to our eyes, the vegetable world would present a very different aspect from the apparent immobility and repose in which it is now manifested to our senses.” —Hum- BOLDT’S Cosmos, i., 341. 10 See Gray’s ‘‘ Structural Botany,” p. 350; Rolleston’s ‘* Forms of Ani- mal Life,” p. 143. 11 *¢Tife has been called the vital force, and it has been suggested that it may be found to belong to the same category as the convertible forces, heat and light. Life seems, however, to be more a property of matter in a certain state of combination than a force. It does no work, in the ordinary sense.” -—Prof. WyviLLe THomson. | 12 There was a time in our history when a single membrane discharged all the functions of life — digesting, respiring, secreting. The separation of a heart, lung, stomach, liver, etc., for special duty was an after-considera- © tion. 13 The vegetable cell has usually two concentric coverings: cell-wall and primordial utricle. In animal cells the former is wanting, the membrane representing the utricle. As a general fact, animal cells are smaller than vegetable cells. 14 Cells are not the sources of life, as once thought, but are the products of protoplasm. ‘‘ They are no more the producers of vital phenomena than the shells scattered in orderly lines along the sea-beach are the instruments by which the gravitation- force of the moon acts upon the ocean. Like these, the cells mark only where the vital tides have been and how they have acted.” —Prof. HuxLey. 15 Many of the bones of the skull are preceded by membrane—hence called membrane-bones. NOTES. 333 © In the heart, the muscular fibres are striated, yet involuntary; but the sarcolemma is wanting. *7 Other names are medullary sheath and white substance of Schwann. *® We may, however, infer that the animal functions are not absolutely essential to the vegetative, from the facts that plants digest without mus- cles or nerves, and that nutrition takes place in the embr VO long before the nerves have been developed. 19 This is not strictly true, for the Elm and Oak, the Trout and Alligator, do reach a maximum size. 20 Scorpions and Spiders properly feed upon the juices ot their victims after lacerating them with their jaws, but fragments of Insects have been found in their stomachs. "1 The real tongue forms the floor of the mouth, and is found as a distinct part in a few Insects, as the Crickets. 22 In the Marsipobranchii, it is circular or oval. 73 The mouth of the Whale is exceptional, the walls not being dilatable. The act of sucking is characteristic of all young Mammals, hence the need of lips. 24 The Ant-eater has two callous ridges in the mouth, against which the insects are crushed by the action of the tongue. 2° The baleen plates do not represent teeth; for in the embryo of the Whale we find minute calcareous teeth in both jaws, which never cut the gum. The whalebone is a peculiar development of hair in the palate, and under the microscope it is seen to be made up of fibres which are hollow tubes. . 26 The ‘‘ tusks” of the Elephant are prolonged incisors; those of the Wal- rus, Wild Boar, and Narwhal are canines. 27 ¢T was one day talking with Prof. Owen in the Hunterian Museum; when a gentleman approached, with a request to be informed respecting the nature of a curious fossil which had been dug up by one of his workmen. As he drew the fossil from a small bag, and was about to hand it for exam- ination, Owen quietly remarked, ‘That is the third molar of the under- jaw of an extinct species of rhinoceros.’’’— Lewes’s Studies in Animal Life. 28 This gap or interspace, so characteristic of the inferior Mammals, is called diastema. It is wanting in the extinct Anoplotherium, is hardly per- ceptible in one of the Lemurs, and is not found in Man. 22 In the Spermaceti-whale, the teeth are fixed to the gum. “© The Iguana among Reptiles, and Fishes with pavement-teeth, approach the Mammals in this respect. 31 This movement is called peristaltic or vermicular, and characterizes all the successive movements of the alimentary canal. 82 Fishes and Amphibians have no saliva, but a short gullet. Birds are aided by a sudden upward jerk of the head. 33 Fishes and Reptiles have no pharynx proper, the nostrils and glottis opening into the mouth. 4 This movement of the pharynx and cesophagus is wholly involuntary. Liquids are swallowed in exactly the same way as solids. oo4 NOTES. *° The few animals in which the digestive cavity is wanting are called agastric, and agree in having a very simple structure. Such are some Ento- zoa (as 'Tape-worm) and unicellular Protozoa (as Gregarina). They absorb the juices, already prepared, by the physical process of endosmose. ‘There are Other minute Organisms which seem to be able to extract the necessary elements, C H ON, from the medium in which they live. ® The cavity of a Sponge is perhaps homologous with the digestive cavity, but is not functionally such. Each cell lining it does its own digestion, tak- ing the food from the water circulating in the cavity. °7 “Nothing is more curious and entertaining than to watch the neatness and accuracy with which this process is performed. One may see the rejected bits of food passing rapidly along the lines upon which these pedicellariz occur in greatest number, as if they were so many little roads for the con- veying away of the refuse matters; nor do the forks cease from their labor till the surface of the animal is completely clean and free from any foreign substance.”—AcGassiz’s Sea-side Studies. *8 In the larva of the Bee, the anal orifice is wanting. | 39 The length of the canal in Insects is not so indicative of the habits as in Mammals. Thus, it is nearly as long and more complicated in the carnivo- rous Beetles than in the honey-sipping Butterflies. 40 The object of this is unknown. It does not occur in the Oyster. *1 In the Nautilus, this is preceded by a capacious crop. 42 In the Shark, this is impossible, owing to a great number of fringes in the gullet hanging down towards the stomach. *3 At the beginning of the large intestine in the Lizards (and in many Ver- tebrates above them, especially the vegetarian orders), there is a blind sac, called caecum. * 44 The Crocodile is said to swallow stones sometimes, like Birds, to aid the gastric mill. 45 In the crop of the common Fowl, vegetable food is detained sixteen ' hours, or twice as long as animal food. The Dormouse, among Mammals, has an approach to a crop. *6 In Invertebrates, the gizzard, when present, is situated between the crop and the true stomach; in Birds, it comes after the stomach. *7 The Tape-worm has no digestive apparatus, but absorbs the already di- gested food of its host. This is no exception to the rule. The chemical preparation of the food has preceded its absorption. *8 We find the most abundant saliva in those Mammals that feed on herbs and grain, but its action on starch is extremely feeble. 49 It is probable that the digestive part of the alimentary canal in all animals manifests a similar mechanical movement. It is most remark- able in the gizzard of a fowl, which corresponds to the pyloric end of the human stomach. This muscular organ, supplying the want of a mas- ticatory apparatus in the head, is powerful enough to pulverize not only grain, but even pieces of glass and metal. This is done by two hard muscles moving obliquely upon each other, aided by gravel purposely swal- lowed by the bird. The grinding may be heard by means of the stetho- scope. NOTES. 396 °° Chyle is opaque in carnivores; more or less transparent in all other Ver- tebrates, as in Birds, since the food does not contain fatty matter. 51 In Fishes, the villi are few or wanting. In Man, they number about 10,000 to the square inch. 52 Except, perhaps, the tendons, ligaments, epidermis, etc. 53 The phenomenon produced by these properties conjointly, capillary at- traction and diffusion, is called endosmosis. 64 The blood is colorless also in the muscular part of Fishes. That of Birds is of the deepest red. The coloring matter of the red blood in worms is not in the corpuscles, but in the plasma. °° Coagulation may be artificially arrested by common salt. Arterial blood coagulates more rapidly than venous. ‘The disposition of the red corpuscles in chains, or rouleaux, does not occur within the blood-vessels. The cause has not been discovered. °°'The corpuscles of Invertebrates are usually colorless, even when the blood is tinged. 57 Except during the foetal life. The corpuscles of the Camel are non- nucleated, as in other Mammals. If the transparent fluid from a boil be examined with a microscope, it will be seen to be almost composed of col- orless corpuscles, showing their use in repairing injuries. °8 There are no valves in the veins of Fishes, Reptiles, and Whales, and few in Birds. 5? Capillaries are wanting in the epidermis, nails, hair, teeth, and cartilages. Hence, the epidermis, for example, when worn out by use, is not removed by the blood, like other tissues, but is shed. 60 A part of the blood, however, in going from the capillaries to the heart, is turned aside and made to pass through the liver and kidneys for purifica- tion. This is called the portal circulation, and exists in all Vertebrates, ex- cept that in Birds and Mammals it is confined to the liver. *! Two in the higher Mammals, three in the lower Mammals, Birds, and Reptiles. They are called vene cave. 62 ‘Tricuspid in Mammals, triangular in Birds. 6° The pulse of a Hen is 140; of a Cat, 110 to 120; of a Dog, 90 to 100; and of an Ox, 25 to 42. 6* The bivalve Brachiopods breathe by delicate arms about the mouth, and by the ‘* mantle.” 6° The air-bladder, found in most Fishes, is another rudiment of a lung, although it is used, not for respiration, but for altering the specific gravity of the Fish. In the Gar-pike of our Northern lakes, it very closely resem- bles a lung, having a cellular structure, a tracheal tube, and a glottis. It is here functional. The gills represent lungs only in function; they are totally distinct parts of the organism. °° In the human lungs they number 600,000,000, each about 52,5 of an inch in diameter, with an aggregate area of 132 square feet. The thickness of the membrane between the blood and the air is 5445 of an inch. The lungs of Carnivores are more highly developed than those of Herbivores. In the Manatee, they are not confined to the thorax, but extend down nearly to the tail, 25 336 NOTES. 67 Crocodiles are the only Reptiles whose nostrils open in the throat behind the palate, instead of directly into the mouth-cavity. This enables the Croc- odile to drown its victim without drowning itself; for, by keeping its snout above water, it can breathe while its mouth is wide open. 68 A rudimentary diaphragm is seen in the Crocodile and Ostrich. 6° The poison-glands of venomous Serpents and the silk-vessels of Cater- pillars are considered to be modified salivary glands. Birds, Snakes, and Cartilaginous Fishes have no urinary bladder. 7° Since the weight of a full-grown animal remains nearly uniform, it must lose as much as it receives; that is, the excretions, iucluding the solid resid- uum ejected from the intestinal canal, equal the food and drink. "1 Other names for derm are, cutis, corium, enderon, and true skin; and for epidermis, cuticle, ecderon, and scarf-skin. The derm is often so inti- mately blended with the muscles that its existence as a distinct layer is not easily made out. Even in Infusoria, we find the tunic double, an outside cuticula lined by a soft cortical layer ; and in Jelly-fishes, naturalists distin- guish an ectoderm, endoderm, and mesoderm. 7 See Fig. 148. Papillz are scarcely visible in the skin of Reptiles and Birds. 73 The animal basis of this structure is chitine, a peculiar horn-like substance found in the hard parts of all the articulated animals. ™ The shell is always an epidermal structure, even when apparently internal. The horny ‘‘ pen”’ of the squid, the ‘* bone”’ of the Cuttle-fish, and the cal- careous spot on the back of the Slug are only concealed under a fold of the mantle. So the shell of the common Unio, or fresh-water clam, is covered with a brownish or greenish membrane, which is the outer layer of the epider- mis. Where the mantle covers the lips ofa shell, as in most of the large sea- snails, or where its folds cover the whole exterior, as in the polished Cowry, the epidermis is wanting, or covered up by an additional layer. 75 The pearls of commerce, found in the mantle of some Mollusks, are simi- Jar in structure to the shell; but what is the innermost layer in the shell is placed on the outside in the pearl, and is much finer and more compact. The pearl is formed around some nucleus, as an organic particle, or grain of sand. 76 When the centrum is concave on both sides, as in Fishes, it is said to be amphicelous ; when concave in front and convex behind, as in Crocodiles, it is called procwlous; when concave behind and convex in front, as in the neck-vertebree of the Ox, it is opisthocelous. In the last two cases, the ver- tebrz unite by ball-and-socket joints. 77 Whether the skull represents any definite number of vertebre is still under discussion. We cannot speak of ‘‘cranial vertebree” in the same sense as ‘‘ cervical vertebre.”” The most that can be said is that in a general way the skull is homologous to part of the vertebral column (B). 78 A few have but one pair, the Whale and Siren wanting the hind pair; while some have none at all, as the Snakes and lowest Fishes. In land ani- mals, the posterior limbs are generally most developed : in aquatic animals, the anterior. Dr. Wyman contends that the limbs are tegumentary organs, and attached to the vertebral column in the same sense that the teeth are attached to the jaws. Other theories are that they originate from gill-arches (Gegenbaur) or that they are remains of a once continuous lateral fin (Thacher). NOTES. 387 ” The first trace of muscular tissue is found in the stem of Vorticella—an Infusorian. In Hydra we find neuro-muscular cells, and the Jelly - fishes have muscular tissue. ®° The muscles of some Invertebrates, as Spiders, are yellow. *! The muscles of the heart and gullet are striped. In the lower animals these distinctions of voluntary and involuntary, striated and smooth, solid and hollow, muscles can seldom be made. 2 The skeleton of the Carrion-crow, for example, weighs, when dry, only twenty-three grains. °° The Dragon-fly can outstrip the Swallow; nay, it can do in the air more than any bird—it can fly backward and sidelong, to right or left, as well as forward, and alter its course on the instant without turning. It makes twen- ty-eight beats per second with its wings; while the Bee makes one hundred and ninety, and the House-fly three hundred and thirty. The swiftest Race- horse can double the rate of the Salmon. So that Insect, Bird, Quadruped, and Fish would be the order according to velocity of movement. 84 The theory that Flies adhere by atmospheric pressure is now abandoned. 8° More precisely, the term brain, or brains, applies only to the cerebrum, while the total contents of the cranium are called encephalon. 8° The exact functions of the cerebrum are not yet clearly understood. If we remove it from Fishes, or even Birds, their voluntary movements are little affected; while the Amphiorus, the lowest of Fishes, has no brain at all, but its life is regulated by the spinal cord. Such mutilated animals, however, make no intelligent efforts. The substance of the cerebrum, as also the cerebellum, is insensible, and may be cut away without pain to the animal; and when both are thus removed, the animal still retains sensation, but not consciousness. 87 It is very difficult to define sensation, or sensibility. The power is pos- sessed by animals which have neither nervous system nor consciousness. These low manifestations of sensibility are called irritability—the power by which an animal is capable of definitely responding to a stimulus from with- out. The response is not called out by the direct action of the stimulus, but is determined mainly by the internal structure and condition of the animal. 88 Parts destitute of blood-vessels, as hair, teeth, nails, cartilage, etc., are not sensitive. The impressibility of the nerves is proportioned to the activ- ity of circulation. According to the recent investigations of Dr. Bowditch, the channels of motor and sensitive impressions lie in the lateral, and not in the anterior and posterior, columns of the spinal cord. 69 **'Tentacles”” and ‘‘horns”’ are more or less retractile, while antennz are not, but all are hollow. Antenne alone are jointed. 9° In Man, the soft palate and tonsils also have the power of tasting. *! No organ of hearing has been discovered with certainty in the Radiates and Spiders. The ‘‘ear” of many lower animals is probably an organ for perceiving the animal’s position rather than sound—an “‘ equilibrium organ.” It is wanting in the aquatic Mammals. Crocodiles have the first repre- sentative of an outside ear in the form of two folds of skin. _ * This, like the definition of smell and hearing, is loose language. There is no such thing as sound till the vibrations strike the tympanum, nor even 388 NOTES. then, for it is the work of the brain, not of the auditory nerve. Sound is the sensation produced by the wave-movement of the air. If thus defined in terms of sensation, light is nothing; without eyes the world would be wrapped in darkness. Some Protozoa have a pigment spot as an eye. °* In Invertebrates and aquatic Vertebrates, the crystalline lens is globu- lar; or, in other words, it is round in short-sighted animals, and flattish in the long-sighted. The lens of the Invertebrate is not exactly the same as the lens of the Vertebrate eye, though it performs the s same function; it is really a part of the cornea. °° The Ant has fifty in each eye, the House-fly four thousand, the Dragon- fly twenty-eight thousand. °° The pigment, therefore, while apparently in front of the retina, is really behind it, as in Vertebrates. The layer beneath the cornea, serving as an ‘iris,’ is wanting in nocturnal Insects, since they need every ray of light. The optic nerve alone is insensible to the strongest light. °7 It should be noticed that this corresponds with another peculiar fact already mentioned, that either hemisphere of the brain controls the muscles on the opposite side of the body. In Invertebrates, the motor apparatus is governed on its own side. 98 Sharks have eyelids, while Snakes have none. ‘The third eyelid (called nictitating membrane) is rudimentary in many Mammals. °° An infant would doubtless learn to walk if brought up by a wild beast, since it was made to walk. Just as an Infusorium moves its cilia, not be- cause it has any object, but because it can move them. New-born puppies, deprived of brains, have suckled; and decapitated Centipedes run rapidly. Such physical instincts exist without mind, and may be termed ‘‘ blind im- pulses.” 100 We say ‘‘apparently,” because it may be a fixed habit, first learned by experience, transmitted from generation to generation. A duckling may go to the water, and a hound may follow game in some sense, as Sir John Her- schel takes to astronomy, inheriting a taste from his father. Breeders take advantage of this power of inheritance. 101 We may divide the apparently voluntary actions of animals into three classes. First, organic, in which consciousness plays no part, and which are due wholly to the animal machine. Second, znstinctive, in which conscious- ness may be present, but which are not controlled by intelligence. Third, associative, in which the animals act under conscious combination of distinct, single ideas, or past impressions. ‘To these we may add rational acts, in which the mental process takes place under the laws of thought. 102 «¢ Thus, while the human organism may be likened to a keyed instru- ment, from which any music it is capable of producing can be called forth at the will of the performer, we may compare a Bee, or any other Insect, to a barrel-organ, which plays with the greatest exactness a certain number of tunes that are set upon it, but can do nothing else.”,—Carrenter’s Mental Physiology, p. 61. This constancy may be largely due to the uniformity of conditions under which Insects live. 103 We may say, as a rule, that the proportion of instinct and intelligence in an animal corresponds to the relative development of the spinal cord and a . a ii NOTES. 389 cerebrum. As a rule, also, the addition of the power to reason comes in with the addition of a cerebrum, and is proportioned to its development. Between the lowest Vertebrate and Man, therefore, we observe successive types of intelligence. Intelligence, however, is not according to the size of the brain (else Whales and Elephants would be wisest), but rather to the amount of gray matter in it. A honey-comb and an Oriole’s nest are con- structed with more care and art than the hut of the savage. It is true, this is no test of the capability of the animal in any other direction; but when they are fashioned to suit circumstances, there is proof of intelligence in one direction. 3 104 An exception to the general rule that the smaller animals have more acute voices. 105 Tt is wanting in a few, as the Storks. #° ‘The Nightingale and Crow have vocal organs similarly constructed, yet one sings and the other croaks. 107 ‘These cells are detached portions of the parental organisms. Gener- ally, these two kinds of cells are produced by separate sexes; but in some cases, as the Snail, they originate in the same individual. Such an animal, in which the two sexes are combined, is called an hermaphrodite. 18 The eggs of Mammals are of nearly uniform size; those of Birds, Insects, and most other animals are proportioned to the size and habits of the adult. Thus, the egg of the AXpyornis, the great extinct bird of Mada- gascar, has the capacity of fifty thousand Humming-birds’ eggs. 109 As a general rule, when both sexes are of gay and conspicuous colors, the nest is such as to conceal the sitting Bird; while, whenever there is a striking contrast of colors, the male being gay and the female dull, the nest is open. Such as form no nest are many of the Waders, pee) Scratch- ers, and Goatsuckers. 11° This lies at first transversely to the long axis of the egg. As the chick develops, it turns upon its side. 111 The blood appears before the true blood-vessels, in intercellular spaces. It is at first colorless, or yellowish. 112 Exactly as the blood in the capillaries of the lungs is aérated by the external air. 113 Thus, the hollow wing-bone was at first solid, then a marrow-bone, and finally a thin-walled pneumatic bone. The solid bones of Penguins are ex- amples of arrested development. _ 114 The thigh-bone ossifies from five centres. ‘The bone eventually unites to one piece. 115 Muscle is mainly fibrine and myosin, while nerve is neurin. 6 For this reason, Mammals are called viviparous ; but, strictly speaking, they are as oviparous as Birds. ‘The process of reproduction is the same, whether the egg is hatched within the parent or without. The eggs of Birds contain whatever is wanted for the development of the embryo, except heat, which must come from without. Mammals, having no food-yolk, obtain their nutrition from the blood of the parent, and after birth from milk. 117 The larve of Butterflies and Moths are called caterpillars; those of Beetles, grubs; those of Flies, maggots; those of Mosquitoes, wigglers. The 390 NOTES. terms larva, pupa, and imago are relative only; for, while the grub and cat- erpillar are quite different from the pupa, the bee-state is reached by a very gradual change of form, so that it is difficult to say where the pupa ends and the imago begins. In fact, a large number of Insects reach maturity through an indefinite number of slight changes. The Humble-bee moults at least ten times before arriving at the winged state. | ' 118 Every tissue of the larva disappears before the development of the new tissues of the imago is commenced. The organs do not change from one into the other, but the new set is developed out of formless matter. The pupa of the Moth is protected by a silken cocoon, the spinning of which was the last act of the larva; that of the Butterfly is simply enclosed in the dried skin of the larva, which is called chrysals because of its golden spots. The pupa of the Honey-bee is called nymph; it is kept in a wax-cell lined with silk, spun by the nursing-bee, not by the larva. The time required to pass from the egg to the imago varies greatly: the Bee consumes less than twenty days, while the Cicada requires seventeen years. | 119 Compare the amount of food required in proportion to the bulk of the body, and also with the amount of work done, in youth, manhood, and old age. 120 Excepting, perhaps, that the new tail of a Lizard is cartilaginous. 121 The patella, or knee-pan, has no representative in the fore-limb, and, strictly, it belongs to the muscular system, rather than to the skeleton. Some anatomists contend that the great toe is homologous with the little finger, in- stead of the thumb. 122 « Movuusca. III. 6. Cephalopoda. Do. S.J VII. MOo.Ltusca. 3. Tunicata. TUNICATA. | 2. Brachiopoda. Do. 4, | L 1. Polyzoa. Do. B | , [ 1. Platyhelminthes. : IV. a 2. Nematelminthes. VERMES. | t Annetida= : 3. Rotifera. | Iv. ee 6. eyed ; J rustacea. O. : 7 3 oa | 3. Arachnida. eter be ve 4, Myriapoda. Do. 3. f ARTHROPODA. _ 5. Insecta. Do. 4. J 392 NOTES. The two subkingdoms of the earlier edition are thus divided into four. The Classes remain the same, except the Annelida. 137 The most important genera are Terebratula, Rhynchonella, Discina, Lingula, Orthis, Spirifer, and Productus. The first four have representa- tives in existing seas. Most naturalists now admit their affinity to the worms, although some still keep them in the subkingdom Mollusca. 138 There are some exceptions: the Oyster is unequivalved, and the Pecten equilateral. 189 ‘The chief i apreesioie left on the shell are those made by the muscles— the dark spots called ‘‘eyes” by oyster-men; the pallial line made by the margin of the mantle; and the bend in the piillin! line, called padlial sinus, which exists in those shells having retractile siphons, as the Clam. 140 The Clam is the highest of Lamellibranchs, and the Oyster one of the lowest. The Mya arenaria, or ‘*‘Soft Clam,” has its shell always open a little; while Venus mercenaria, or ‘‘ Hard Clam,” keeps its shell closed. 141 The Slug has no shell to speak of, and the Chiton is covered with eight pieces. It may be remembered, as a rule, that all univalve shells in and around the United States are Gasteropods, and that all bivalves in our rivers and lakes, and along our sea-coasts (save a few Brachiopods), are Lamelli- branchs. ‘42 Hold the shell with the apex up and the mouth towards the observer. If the mouth is on his right, the shell is right-handed or dextral, if on his left, sinistral. In other words, a right-handed shell is like a right-handed screw. 143 Instead of a strong breathing-tube with a valve, answering for a force- pump and propeller, as in the Cuttle-fish, it has only an open gutter made by a fold in the mantle, like the siphons of the Gasteropods. The back cham- bers are filled with nitrogen gas. ? The common Poulpe has two thousand suckers, each a wonderful little air- pump, under the control of the animal’s will. 144 The order of the classes is one of relation rather than of rank. They cannot be arranged serially. ‘The Myriapods have a worm-like multiplica- tion of parts, degrading them, and their nervous system is simpler than that of Caterpillars; yet their heads show a close relationship to Insects. The Arachnids include some lower forms than Myriapods; on the other hand, for their wonderful instincts, Owen places them above the Insects. They are closely allied to Crustaceans, and stand more nearly between Crustaceans and Insects than between Myriapods and Insects. 145 Certain Crabs live on dry land, but they manage to keep their gills wet. 146 The student should remember that this threefold division is not equiva- lent to the like division of a vertebrate body. 147 Hach ring (called somite) is divisible in two arcs, a cores and ventral, and each arc consists of four pieces. 148 The four pairs of legs in Arachnids answer to the third pair of maxillez and the three pairs of maxillipedes in the Lobster. The great claws of Scorpions are the first maxille of the Lobster, as are the pedipalpi of Spiders. NOTES. 393 149 ‘The antenne are more probably altogether undeveloped, and the jaws of the Spider correspond to the mandibles of the Lobster. °° Compare the single thread of the Silk-worm and other caterpillars. 1 The common Spider, Lpetra, which constructs with almost geometri- cal precision its net of spirals and radiating threads, will finish one in forty minutes, and just as regularly if confined in a perfectly dark place. 452 These parts do not correspond to the parts so named in human anatomy. See also p. 162. 53 The pupa-case is often ornamented with golden spots in Butterflies ; hence the common name chrysalis. 154 Tn aquatic animals the posterior limbs are the ones aborted or reduced, if any; in land animals the fore-limbs are usually sacrificed. _ 155 The smallest corpuscles are found in Ruminants; the largest in Am- phibians with permanent gills. The average size in Birds is double that in Man, and about equal to that in the Elephant. Those of Monkeys are a trifle smaller than the human. In the embryo they are larger than in the adult. Camels only among Mammals have oval disks. 456 The facial angle becomes of less and less importance as we go away from man, and for two reasons. Where the brains do not fill the brain-case the angle is obviously of little value, and if the jaws are largely developed the angle is reduced, although intelligence may not be altered. 187 Oblong human skulls, whose diameter from the frontal to the occipital greatly exceeds the transverse diameter, are called dolichocephalic ; and such are usually prognathous, 2. e., have projecting jaws, as the negro’s. Round skulls, whose extreme length does not exceed the extreme breadth by a greater proportion than 100 to 80, are brachycephalic ; and such are gener- ally orthognathous, or straight-jawed. 88 The classes are variously grouped into the Hematocrya, or Cold- blooded, and the Hematotherma, or Warm-blooded; into the Branchiata and Abranchiata ; into the Allantoidea and Anallantoidea. 459 Tt would be safe to say that any living Vertebrate with side fins sup- ported by fin-rays is a Fish; but the extinct Reptile Lchthyosaurus also had them. 160 «The capacity for growing as long as life lasts, which some Fishes are said to possess, may be explained by the facts that their bodies are, firstly, of very nearly the same specific gravity as the water in which they live, and, secondly, of a temperature which is but a very little higher than that which they are there exposed to. ‘Thus the force which in other animals is ex- pended in the way of opposition to that of gravity and in the way of pro- ducing heat is available for sustaining continuous growth.”-—RoLLESTON. 6! Amphibians with a moist skin are also remarkable for their cutaneous respiration. ‘They will live many days after the lungs are removed. Their vertebrae vary in form: in the lowest they are biconcave, like those of Fishes ; in Salamanders they are opisthoccelous: in the Frogs and Toads they are usually proceelous. 162 Salamanders are often taken for Lizards, but differ in having gills in early life and a naked skin. ‘The Proteus and Siren resemble a tadpole ar- rested in its development, O04 NOTES. +63 The Surinam Toad has no tongue. . ‘* ‘The posterior pair of limbs is sometimes represented by a pair of small bones; and the Boas and Pythons show traces of external hind-limbs. ** There are some notable exceptions. The Slow-worm is legless, and the Chameleon has a soft skin, with minute scales. *°° According to Owen; but Huxley insists that the plastron belongs to the exoskeleton. he 67 Knees always bend forward, and heels always bend backward. 168 We cannot claim that this airy skeleton. is necessary for flight. ‘The bones of the Bat are free from air, yet it is able to keep longer on the wing than the Sparrow. The common Fowl has a hollow humerus; while some Birds of long flight, as the Snipe and Curlew, have airless bones. 69 The fossil Archeopteryzx, a lizard-like Bird, is placed in a separate di- vision, Saurure. Birds have also been divided according to their degree of development at birth into (1) Hesthogenous, as Fowls, Ostriches, Plovers, Snipes, Rails, Divers, and Ducks, whose chick is hatched completely clothed, has perfect senses, runs about, and feeds itself. When full grown, it uses its feet rather than wings, flying with a rapid, labored stroke, and taking the first opportunity to settle on land or water, not on trees; the male is po- lygamous and pugnacious; the female makes little or no nest; and neither sex sings. ‘This group is of the best use to man, and approaches more near- ly to Mammals, the habitual use of the legs and preference for land or water degrading it as a Bird and raising it in the list of animals; (2) Gymnogenous, as Gulls, Pelicans, Birds of Prey, Herons, Sparrows, Woodpeckers, and Pigeons, whose chick comes helpless, blind, and naked; it can neither walk nor feed itself, but gapes for food; the adult is monogamous, and builds elaborate nests in trees and perches; many sing; all are habitual fliers. These are birds par excellence, gifted with higher intelligence than the others, and are never domesticated for food. ‘70 Hopping is characteristic of and confined to the Perchers; but many of them, as the Meadow-lark, Blackbird, and Crow, walk. 11 This order is artificial. But it is better to retain it until ornithologists agree upon some natural arrangement. The classification of birds is taken from Coues’s ‘‘ Key to North American Birds,” as being the work on orni- thology in most general use. 1722 The Whales are hairy during fcetal life only. 13-The Manati has 6; Hoffmann’s Sloth 6; and two species of three-toed Sloth have respectively 8 and 9. 174 As in the Whale, Porpoise, Seal, and Mole. ‘Teeth are wanting in the Whalebone Whales, Ant-eaters, Manis, and Echidna. 1% The Monotremes resemble Marsupials in having marsupial bones, but have no pouch. They differ from all other Mammals in having no distinct nipples. 1 The pouch is wanting in some Opossums and the Dasyurus. 7 For the best account of the Elephant, see Tennant’s ‘‘ Ceylon” or Brehm’s ‘‘ Thierleben.” “8 The fore-feet of the Tapir have four toes, but one does not touch the ground. NOTES. 395 9 The extinct Horse (Hipparion) had three toes, two small hoofs dangling behind. The foot of the Horse is of wonderful structure. ‘The bones are constructed and placed with a view to speed, lightness, and strength, and bound together by ligaments of marvellous tenacity. ‘There are elastic pads and cartilages to prevent jarring; and all the parts are covered by a living membrane which is exquisitely sensitive, and endows the foot with the sense of touch, without which the animal could not be sure-footed. ‘The hoof itself is a world of wonders, being made of parallel fibres, each a tube com- posed of thousands of minute cells, the tubular form giving strength. There are three parts, ‘* wall,” ‘‘ sole,” and ‘‘ frog ””—the triangular, elastic piece in the middle, which acts as a cushion to prevent concussion and also slipping. 180 The Camel and Llama are exceptional, having two upper incisors and canines, are not strictly cloven-footed, having pads rather than hoofs, and are hornless. 81 The Hyena alone of the ‘Carnivores has only four toes on all the limbs, and the Dog has four hind-toes. ‘The Lion is the king of beasts in majesty, but not in strength. Five men can easily hold down a Lion, while it re- quires nine to control a Tiger. 182 The eye-orbits of the Lemurs are open behind. The Flying Lemur ( Galeopithecus) is considered an Insectivore. 183 The old term Quadrumana is rejected because it misleads, for Apes, as well as Men, have two feet and two hands. ‘There is as much anatomical difference between the feet and hands of an Ape as between the feet and hands cf Man. Owen, however, with Cuvier, considers the Apes truly ‘‘ four- handed.” 184 It fails to cover in the Howling Monkey and Siamang Gibbon; but in the Squirrel Monkey it more than covers, overlapping more than in Man. As to the convolutions, there is every grade, from the almost smooth, brain of the Marmoset to that of the Chimpanzee or Orang, which falls but little below Man’s. *5 The tailed Apes of the Old World have longer legs than arms, and generally have ‘* cheek-pouches,” which serve as pockets for the temporary stowage of food. 8° In the human infant, the sole naturally turns inward; and the arms of the embryo are longer than the legs. 87 The Aye-aye, the lowest of the Lemurs, is remarkable for the large proportion of the cranium to the face. 88 This feature was shared by the extinct Anoplotherium, and now to some extent by one of the Lemurs ( TYarszus),. *89 "We have treated Man zoologically only. His place in Nature is a wider question than his position in Zoology; but it involves metaphysical and psychological considerations which do not belong here. 490 See Lewes’s charming ‘‘ Studies in Animal Life.” Doubtless an ex- amination of all the strata of the earth’s crust would disclose forms im- mensely outnumbering all those at present known. And even had we every fossil, we would have but a fraction of the whole, for many deposits have been so altered by heat that all traces have been wiped out. Animal life is 396 NOTES. much more diversified now than it was in the old geologic ages; for several new types have come into existence, and few have dropped out. #91 Among the types characteristic of America are the Gar-pike, Snapping- turtle, Hummers, Sloths, and Musk-rat. Many of our most common animals are importations from the Old World, and therefore are not reckoned with the American fauna; such as the Horse, Ox, Dog and Sheep, Rats and Mice, Honey-bee, House-fly, Weevil, Currant-worm, Meal- worm, Cheese- maggot, Cockroach, Croton-bug, Carpet-moth and Fur-moth. Distribution is complicated by the voluntary migration of some animals, as well as by Man’s intervention. Besides Birds, the Bison and Seals, some Rats, certain Fishes, as Salmon and Herring, and Locusts and Dragon-flies among In- sects, are migratory. +92 ‘When the cable between France and Algiers was taken up from a depth of eighteen hundred fathoms, there came with it an Oyster, Cockle-shells, Annelid tubes, Polyzoa, and Sea-fans. Ooze brought up from the Atlantic plateau (two thousand fathoms) consisted of ninety-seven per cent. of Fora- minifers. : THE NATURALIST’S LIBRARY. Tue following works of reference, are recommended : General Works and Teat-books. Aaassiz, Methods of Study in Natural History. Agassiz and Goutp, Principles of Zook ogy. Ro.urston, Forms of Animal Life. Lewes, Studies of Animal Life. Jones, General Outline of the Organiza- tion of the Animal Kingdom. Huxtey and Martin, Elementary Biol- ogy. Owen, Comparative Anatomy of Inverte- brates and Vertebrates. Van ver Hoeven, Handbook of Zoology. Woop, Illustrated Natural History. Nicnotson, Manual of Zoology. Tenney, Elements of Zoology. Mokrsg, First Book of Zoology. Jones, Animal Creation. Packarp, Zoology. GEGENBAUR, Comparative Anatomy. Invertebrates. Hvxtey, Anatomy of Invertebrated Ani- mals. Maca.uistTeR, Introduction to Animal Morphology. Brooxs, Handbook of Invertebrate Zool- ogy. - Srrsotp, Anatomy of Invertebrates. Vertebrates. Huxuty, Anatomy of Vertebrated Ani- mals. Maca.uisTEr, Morphology of Vertebrates. Huxvry and Hawxtns, Atlas of Compar- ative Osteology. Fiower, Osteology of Mammalia. CHAUVEAU, Comparative Anatomy of Do- mesticated Animals. Mivart, Lessons in Elementary Anatomy. accessible to the American student, Mivart, The Cat. Gray, Anatomy, Descriptive and Surgical. StTRrokER, Handbook of Human and Com- parative Histology. Embryology. Baurour, Comparative Embryology. Foster and Batrour, Elements of Embry- ology. PackarpD, Life Histories of Animals. Physiology. CARPENTER, Comparative Physiology. Houxtry, Lessons in Elementary Physiol- ogy. Foster, Text-book of Physiology. Martin, The Human Body. Fuint, Physiology. Geographical Distribution. WauuLaogz, Geographical Distribution of Animals. | Murray, Geographical Distribution of Mammals. Microscopy. CARPENTER, The Microscope and its Rev- elations. GRIFFITHS and HEenFrey, The Micrograph- ic Dictionary. ae Darwinism. Scumipt, Descent and Darwinism. HakoKkE1, History of Creation. Darwty, Origin of Species. Hux.uety, Lay Sermons, etc. Mrvart, Lessons from Nature. Special Works. Cuark, Mind in Nature. Aeassiz, Sea-side Studies in Natural His- tory. 398 Taytor, Half-hours at the Sea-side. Greene, Manuals of Sponges and Celen- terata. ‘ Dana, Corals and Coral Islands. VERRILL and Sm1tu, Invertebrates of Vine- yard Sound: GouLp and Binney, Invertebrata of Mas- sachusetts. Woopwarp, Manual of Mollusca. PacKaRrD, Guide to the Study of Insects. Dutnoan, Transformations of Insects. Storer, Fishes and Reptiles of Massachu- setts. Of serial publications, the student THE NATURALIST’S LIBRARY. Cours, Key to North American Birds. JORDAN, Popular Key to the Birds, etc., of Northern United States. - Barrp, Brewer, and Ripeway, Birds of North America. Barrp, Mammals of North America. Aizen, Mammalia of Massachusetts. Scammon, Marine Mammals of North Pa- cific. PrscoHEL, The Races of Man. , Marsu, Man and Nature. Tytor, Primitive Culture. NicHoxson, Paleontology. should have access to the American Naturalist, American Journal of Science, Popular Science Monthly, Smith- sonian Contributions and Miscellaneous Collections, Bulletins and Proceed- ings of the various societies, Annals and Magazine of Natural History, and Nature. ‘ The following German works are recommended as having no English equivalents : Cravs, Grundztge der Zoologie. PAYENSTEOHER, Allgemeine Zoologie. Bronn, Classen und Ordnungen des Thier- Also the periodicals— Zoologischer Anzeiger. reichs (unfinished and expensive, but indispensable to the working zoolo- gist). Biologisches Centralodlatt. INDEX. In the Index the numbers in Roman type (21) refer to pages; those in bold-faced type (40) refer to cuts. No attempt is made to analyze the statements made for each group in Part II. Reference is made for each class or prominent order to those cuts in Part I. which illustrate the group. ABsoRPTION, Invertebrates, 94. 66 Alimentary = Vertebrates, 94, 60, 61. és Mammals, 85. ; microscopic anatomy Acalephe, 247. a see Jelly-fish. Acarina, 287, 258. Acarus, 287. Acetabulum, 147. Acipenser, 315, 290. Acorn-shell, 284, 254. a see Barnacle. Acrania, 309, 310, 282. Actinaria, 251, 199, 201-206. Seam Polyp, 251, 199. anatomy of 38, 95, 198. " blood of, 97. - development of, 205, 208. oi liver-cells of, 124. ‘? mouth of, 55, 199. id nettle-cells of, 51. * prehension of, 51. “ reproduction of, 192. respiration of, 112. - skeleton of, 130, 95. hs skin of, 127. Adder, 320, 298. Adipose Tissue, 38, 10. AXolis, 274. Air-bladder, 117. Albatross, 330. Albumen, 19. Alcyonaria, 256, 200, 207, 208. Alcyonium, 256, 208. Alimentary Canal; 74. ae Coelenterata, 75. Crustacea, 76. duodenum, 90. Fishes, 80. Insects, 78. development of, 203. Echinoderms, 76. of, 57, 58. Je Mollusks, 80. ‘6 Protozoa, 74. ‘* ~=6Spiders, 79. ‘* stomach, 87. ‘* structure of, 89. ‘¢ see Intestine, Mouth, Stomach, Teeth. Allantoidea, 393. Allantois, 117, 203, 169-171. Alligator, 324, 308. 66 nest, 196. Alternate generation, 212. Ambulacra, 131. Ammonite, 279. Amnion, 202, 170, 171. Ameba, 241, 185. 66 cé 66 66 Amphibia, 317, 68, 65, 76, 85, 87, conjugation of, 196. ectosarc of, 75. feeding of, 55. locomotion of, 154, 157. 294- 296. blood of, 99, 68-65. brain of, 172, 140. circulation of, 108, 76. lungs of, 118. mouth of, 61. see Frog. Amphicelous, 386. Amphioxus, 310, 282. 66 66 feeding of, 50. skeleton of, 139. Amphithoé, 284, 252. Analogy, 218. Anchylosis, 143. Animal, defined, 22. Animalcule, see Protozoa. 400 Annelides, 268, 17, 228. Anodon, 78; see Clam. Anoura, 318. Ant, 304. Ant-eater, 344, 333. Antenne, 177, 147. Anthozoa, 250, 38, 95, 198, 208. Ape, 357, 120, 333-357. Apis, 304, 277. Aplysia, 274. Apteryx, 327. Arachnida, 287. en see Centipede, Scorpion, Spi- der. Araneina, 289, 18, 25, 260, 261. A see Spider. Ardea, 332, 318. Arenicola, 113, 77. Areolar Tissue, 35, 3. Argonauta, 280, 249. Armadillo, 135, 344, 101, 384. Artery, 104. Arthr DReHS, 281. blood of, 99. development of, 205. si number of, 221. - skin of, 127. ‘6 *_-gee Crab, Insect, Lobster, My- riapoda, Spider. Ascidian, 305, 278, 279. + circulation of, 107. os mouth of, 60. iy skin of, 127. Astacus, 283, 250. Asterias, 260. “ see Starfish. Asteroidea, 258, 126, 188, 212, 213. Astrea, 252, 208. Astrophyton, 260. Atavism, 216. . Attacus, 302, 274. Auger-shell, 276, 288. Auk, 329. Aurelia, 248, 195. re see Jelly-fish. Aves, 325, 50, 65, 76, 105, 116, 125, 162, 170. Bawirvsa, 69, 34. Baboon, 359. Balena, see Whale. Balanus, 284, 254. Barnacle, 284, 258, 254. f metamorphosis of, 210. i mouth of, 57. si see Cirripedia. Basket-fish, 260. Batrachia, 318, 68, 65, 76, 85, 87, 296, 297. . see Frog. Bats, 346, 339, 340. Beaver, 346, 337. INDEX. Bed-bug, 297. pod) 303, 277. alimentary canal of, 42. ** eggs of, 195. ** eye of, 156. ‘* instincts of, 185, ** mode of feeding of, 50. ‘¢ mouth of, 59, 22. ‘¢ section of, 81. temperature of, 121. see Hymenoptera, Insecta. ae 297, 267, 268. alimentary caval of, 41. ‘¢ development of, 297, 267. ‘¢ eye of, 182, 156. ‘* mouth of, 57. ‘¢ skeleton of, 292, 262. *¢ see Coleoptera, Insecta. Belemnite, 281. Bernicla, 310. Beroé, 257. Bile, 98. Bird-of-Paradise, 339. ae 325, 304-328. alimentary canal of, 84, 50. ‘¢ anatomy of, 50, 304. ‘¢ beak of, 54. ‘¢ blood corpuscles of, 99, 68. ‘* brain of, 141. ‘¢ breathing of, 119. ‘circulation of, 107, 76. «¢ distribution of, 378. *¢ drinking of, 50. “ ~ege of, 193, 162. ‘* embryo of, 170. se eye of, 184. ‘© feather of, 137, 204, 105. “flight of, 160, 125. ‘* gizzard of, 84, 384, 50. ‘¢ heart of, 109. ‘© locomotion of, 166. ‘© Jungs of, 118, 50. ‘¢ mouth of, 62. ‘* skeleton of, 143, 116. ‘¢ smell of, 118. ‘¢ temperature of, 121. ‘6 voice of, 189. ‘¢ 6wings of, 160, 304. Bivalve, see Clam, Lamellibranchiata, Oyster. Blackbird, 339. Blastema, 33. Blastula, 198, 165. Je 97. circulation of, 103. ** corpuscles, 98, 99, 62-65. ‘¢ development of, 200. ‘¢ functions of, 97 ‘¢ of Invertebrates, 97. ‘6 rate of motion of, 111. “ temperature of, 100. INDEX. Blood of Vertebrates, 98. ‘6 vessels, 104. Blubber, 348. Bluefish, 312, 284. Boa, skull of, 72, 37. Bone, composition of, 147. ‘¢ development of, 203. ‘* ‘structure of, 36, 7, 8. Bos, see Ox. Brachiopoda, 266, 221, 222. Brachycephalic, 393. Bradypus, 344. Brain, 170. “* case of, see Skull. * development of, 204. ** functions of, 173. ‘* parts of, 170. * 6wweight of, 170. Brain-coral, 232, 204. Bronchus, 119, 86. Bryozoa, see Polyzoa. Bubble-shell, 274, 231. Buccinum, 272, 228. Budding, 192. Bufo, 318. ‘* - see Toad. Bugs, mouth of, 59. ‘* see Hemiptera. Bulimus, 275, 283. Bulla, 272, 231. Butterfly, 273. * anatomy of, 48. metamorphosis of, 208, 172. be mimicry of, 217. me mouth of, 59, 28. 7 scales of, 271, 272. CADDIS-FLY, 295. Cecilia, 318. Cecum, 51. Calcispongia, 246. Camel, 352. Cameo-shell, 278, 237. Canaliculi, 37, 8. Canine teeth, 69, 34, 35. Capillaries, 104, 66, 68. Caprimuilgus, 338, 3238. Capybara, 346. Carapace, 323, 115. Cardium, 227. Carinate, 328. Carnivora, 353, 90, 92, 106, 108-110, 128, 142, 346, 350. ss brain of, 142. — = teeth of, 70. Cartilage, 36, 5. Cassis, 278, 237. . Cassowary, 327. Castor, 346, 387. Cat, 355. ‘¢ brain of, 142. 26 ) Caterpillar, 301. Catfish, 316, 291. 401 Cat, teeth of, 70. anatomy of, 78, 40. circulation in, 105, 69. ee false legs of, 172. es head of, 303, 276. a heart of, 105, 69. ch jaws of, 53, 276. locomotion of, 162. * muscles of, 156. nervous system of, 169, 130. see Butterfly, Insecta, Lepi- doptera. Cebus, 357, 352. Cell, 31, 1. | Cement, 66, 31. Centipede, 291, 259. Cephalization, 225. } Cephalopoda, 278, 16, 47, 151, 247-249. es see Cuttlefish, Squid. | Cephalo-thorax, 282. Cerebellum, 171. Cerebrum, 170. | Ceryle, 338, 327. | Cetacea, 348, 30, 341, 342. e see Whale. | Chalaza, 193, 162. Chameleon, 322. “y tongue of, 81. Cheiroptera, 346, 339, 340. Chelonia, 322, 115, 301, 302. pi see Turtle. | Chelydra, 323. Chilognatha, 291. Chilopoda, 291, 259. Chimera, 314. Chimpanzee, 357, 354, 356. - skeleton of, 120. “ teeth of, 35. Chitine, 132. Chiton, 276, 240. Chlorophy], 23. Choroid, 183. Chrysaora, 213, 178. Chrysalis, 208, 390, 172. Chyle, 93, 59. Chyme, 92. Cicada, 297, 266. Cicatricula, 194. Cidaris, 262, 96, 97. Cilia, 154, 2. Ciliata, 248, 188. Circulation in Arthropoda, 106. & in Ascidians, 107. fe in Birds, 109. ss development of, 200. Us in Echinodermata, 105. Si in Insects, 105. in Mammalia, 109. “s in Mollusca, 106. 402 Circulation in Vermes, 105. a in Vertebrata, 107, 281. 4 see Heart. Cirripedia, 284, 258, 204. a see Barnacle. Cam, 272. adductors of, 46. “alimentary canal of, 80, 44, 46. ‘“* anatomy of, 46. *¢ circulation in, 106. ‘¢ ear of, 178, 150. ‘¢ foot of, 161, 46. ‘© gills of, 113, 78: ‘© heart of, 106, 46. ‘+ hinge of, 270. ‘* locomotion of, 161. ‘* mouth of, 56. ‘* nervous system of, 168, 188. ‘* prehension of, 50. ‘¢ shell of, 133, 99. ‘* siphons of, 46. ‘¢ see Lamellibranchiata, Oyster. Clamatores, 338, 322. Class, 235. Classification, 231. r Table, 239. s synopsis of, 302. Claws, 136, Cloaca, 85. Clypeaster, 262. Coagulation, 98. Cochineal, 297. Cockle, 272, 227. Cockroach, 297. Cod, 316, 292. ‘* eggs of, 195 Celenterata, 246. sf number of, 221. at see Actinoid Polyp, Hydra, Jelly-fish. Coleoptera, 297, 41, 156, 267, 268. fu see Beetle. Columbae, 323, 316. Condor, 335. Cone-shell, 276,. 289. Conjugation, 196. Connective Tissue, 34, 3, 4. Coral, 130, 251, 95, 201-208. *¢ see Actinoid Polyp. Corallium, 256, 207. Coral reef, 254. Cormorant, 330, 309. Cornea, 183. Corpuscles, see Blood. Correlation, 218. Cowry, 276, 234. Corydalus, 295. Crab, 287, 257. ‘* locomotion of, 162. ‘“« vocal organs of, 188. ** see Lobster. INDEX. Crane, 332. Craniota, 309. Cranium, 141. Cray-fish, 282, 250. Cricket, 295, 264. Crinoidea, 258, 211. Croceaina, 323, 303. exoskeleton of, 135. oa heart of, 108. me locomotion of, 163. Ey mouth of, 61, 26. ‘2 skeleton of, 149, 118. ne stomach of, 82, 49. tg see Reptilia. Crow, 339. Crustacea, 282. x nauplius of, 211, 177. ce see Crab, Lobster. Ctenactis, 253, 202. Ctenophora, 257, 209. Cuckoo, 335. Cuculi, 335, 321. Curassow, 333. Cursores, 327, 305. Cuticle, 12S. Cutis, 128. each, 280, 248. anatomy of, 47. ty alimentary canal of, 80, 47. a beak of, 52, 47. es brain of, 168, 151. “4 circulation in, 107. s ear of, 151. = eye of, 181, 151. a heart of, 107. - ink-bag of, 47. Re mouth of, 57. i pancreas of, 123. ae prehension of, 52. . skeleton of, 134. a suckers of, 16. oe see Cephalopoda, Squid. Cyclops, 284, 205. Cypreea, 276, 234. Cypris, 284, 255. Cypseli, 335, 320. Dappy-Lone-Lxas, 289, 300. Daphnia, 284, 255. Dasypus, 344, 384. Dasyurus, 343. Decapoda (Crustacea), 286, 70, 248, 250, 256, 257. su (Dibranchiata), 280. Decussation, 184, Deglutition, 72. Delphinus, 349, 348. Demodex, 287, 258. Dental Formule, 70. ‘© Tissue, 38, 31. Dentine, 38, 66, 31. Sie = INDEX. Dermis, 128. oa ement, 197. by alternate generation, 211. of Bird, 199. of blastula, 198, 165. of embryonic forms, 207. of gastrula, 193, 166. of Invertebrates, 204. by metamorphosis, 207. by metamorphosis, retro- grade, 210. oviparous, 309. ovoviviparous, 309. segmentation of egg, 197. of Vertebrates, 205. viviparous, 309. see Metamorphosis, Repro- duction. Diaphragm, 86, 88. ~ Diastema, 70, 383. Dibranchiata, 280, 16, 47, 151, 248, 249. Differentiation, 31. PIESSHOR, chemical, 92. of Invertebrate, 92. of Man, 93. object a 91. of Vertebrate, 92. Digitigrade, 355, 128. Diploria, 254, 204. Dipnoi, 316, 293. Diptera, 66 300, 24, 127, 173, 269, 270. see Fly, Mosquito. Discophora, 220. Distribution, 371-379. Divers, 328. Dog, 354. => Yrain. of,.171. ** skull of, 143. ** teeth of, 68. Dolichocephalic, 393. Dolphin, 66 349, 348. teeth of, 68. Doris, 274. Dove, 333, 316. Dragon-fly, 294, 263. 66 flight of, 387. Duck, 331, 311. Duck-mole, 342, 381. Dugong, 350. 66 heart of, 78. Duodenum, 90. EaGte, 334, 319. Ear, 179, 387, 152. Ear-shell, 278, 285, 246. Har ees 269. alimentary canal of, 77. circulation in, 105. locomotion of, 162. nervous system of, 168. prehension of, 52. Xcderon, 127. Echidna, 342. Echinodermata, 257. 66 Kchinus, 262, 214. e see Sea-urchin. EHdentata, 344, 101, 333, 334. Egg, fertilization of, 197. ‘* form of, 195. ** number of, 195. ‘* segmentation of, 197, 165. ‘* structure of, 192, 161, 168. Elasmobranchii, 314, 287, 288. * see Ray, Shark. Pepe 350. brain of, 170, ete foot of, 129. a skeleton of, 119. sh teeth of, 69, 36. 5 trunk of, 66. ys tusks of, 71, 66, 119. Ra voice of, 189. Elytra, 297. Embryology, 197. Kmu, 327. Enamel, 66, 31. Encephalon, 170. Enderon, 127. Endoskeleton, 127. Entomostraca, 284, 255. Kpiblast, 199. Epidermis, 34. Epiglottis, 119, 159. Hpithelium, 33, 2. Equus, see Horse. Kuplectella, 246. Excretion, 121, 125. Exoskeleton, 127. Eye, of Invertebrates, 180. ‘* of Vertebrates, 181. ‘¢ development of, 204. FacraL ANGLE, 309. | Falcon, 335. Family, 235. Fat, 38, 10. Feathers, 137, 105. Us development of, 204. Felis, 355. Fertilization of Egg, 197. Fibrine, 98. Bieter 310. air-bladder of, 117, 48. ‘¢ alimentary canal of, 80, 48. ‘© blood of, 99, 100, 68. ‘¢ brain of, 172, 189. “¢ circulation in, 107, 51, 78. se eye of, 184. ‘fins of, 158, 128. ‘gills of, 114, 48. 403 number of species of, 221. Echinoidea, 261, 28, 39, 96, 97, 214. 404 — heart of, 108, 48. locomotion of, 159, 124, ‘¢ mouth of, 61. — **% muscles of, 157, 48. number of species of,,313. ovary of, 48. | _ pancreas of, 123. prehension of, 54. “ scales of, 135, 102, 288. ‘¢ skeleton of, 112. ‘© skull of, 188, 112. ‘¢ teeth of, 61, 67,.32. Fish-hawk, 335, 318. Fission, 191, 160. - Flagella, 154, 187. _ Flagellata, 248, 187. Flamingo, 331. Flea, 300. Flight of Bats, 161. ‘¢ of Birds, 160. ‘© of Insects, 159: Fluke, 265. Flustra, 267, 220. Bly, 300. buzzing of, 188. ** foot of, 127. ‘© metamorphosis of, 270. “ mode of feeding of, 50.. ** mouth of, 59, 24. “¢ see Diptera, Mosquito. Fly-catcher, 338, 322. Flying Fox, 346. Follicle, 123, 90. Food, 47-49. Foramen magnum, 172. Foraminifera, 51, 241, 15, 186. Forms of animals, 222. Fox, 355, 349. BYOB, 318, 297. alimentary eanal of, 82. ‘¢ pblood-corpuscles of, 99, 68, 65. ‘¢ preathing of,.119. “circulation in, 108, 76. ‘6 6 food of, 49. ‘6 heart of, 108. ‘* lungs of, 118, 85. ‘¢ lymph-heart of, 96. *¢ metamorphosis of, 209. ‘* respiration in, 117-119. “¢ skeleton of, 119, 140, 145, 87. ‘¢ tongue of, 61. “« -vertebre of, 140, 87. Fruit-moth, 303, 278. Function, 41. Fungia, 252, 202. GALL-BLADDER, 124, 92. Gall-fly, 303. Ganglion, 166, 14, 146. Gannet, 331. Ganoidei, 315, 289, 290. INDEX. Gar-pike, 315, 289. Gasteropoda, 20, 29, 45,100, 154, 176, 272. uf see Snail. Gastric glands, 123, 90. ‘¢ juice, 93. Gastrula, 198, 166. Gavial, 324. Gecko, 322. Gelatine, 36. Genus, 235. Germinal vesicle, 192. Gibbon, 357. Gills, 114, 125, 48. Giraffe, 353. Gizzard of Invertebrates, 79. ‘* of Vertebrates, 84. Gland, 121, 89. ““' gastric, 123, 90. t. liver, 123, 92. ‘* pancreas, 123, 91. ‘salivary, 122. ‘* sweat, 126, 94. Globigerina, 242. Glottis, 119. Glycogen, 23. Goatsucker, 338, $23. Goniaster, 260, 212. Goose, 331, 310. Gorgonia, 256, 208. Gorilla, 357, 357. Grallatores, 332, 318. Gr asshopper, 297. development of, 208. gizzard of, 79. y mouth-parts of, 58, 21. ie stridulation, 188. Grebe, 329. Gregarinida, 240, 184. Grouse, 333, 315. Growth, 214. | Grubs, 389. Gryllus, 295, 264. Guinea-pig, 345. Gulls, 329. H &]mMatrocorya, 393. Heematotherma, 393. Heemocyanin, 102. Hemoglobin, 102. Hag-fish, 54, 314. Hair, 136, 94, 104. Hair-worm, 262. Haliotis, 278, 235, 246. Hand, 359. Hare, 346, 386. Harvest-man, 289. Haversian Canals, 37, 7@. Hawk, 335, 318. Hearing of Invertebrates, 178. ‘“* . of Vertebrates, 179. Heart, Arthropoda, 105, 69, 70. Biase Heart, development of, 200, 168. ‘* of Mollusks, 106. ‘* of Tunicates, 107, 279. ‘© of Vertebrates, 107-109, 71-74. Heat, 121. Hedgehog, 346. Helix, 275, 282. Hemiptera, 297, 265, 266. af mouth of, 59. Heron, 332, 318. Heterocercal, 159, 128. Heteromya, 272. Hippopotamus, 352. ae foot of, 129. Histology, 12. Hog, 352. ‘* teeth of, 67. Holothuroidea, 262, 215. Homarus, see iobaver. Homo, see Man. -~ Homocerceal, 159, 287. Homology, 217. es serial, 218. Homomorphism, 217. Hoofs, 136, 103. Hornera, 267, 220. Horns, 136. Horse, brain of, 171, 188. hoof of, 136, 164, 108, 129. aa skeleton of, 151, 117. = ‘sieuil of, 144, 111. ‘¢ splint-bones of, 207. ‘* stomach of, 88, 53. Horse-fly, mouth of, 60, 24. Horseshoe-crab, 284. ts 7 jaws of, de. ue ‘* sKeleton of, 181. Hummer, 335. Hyalea, 274, 229. Hydra, 246, 191. “budding of, 192. ‘¢ digestive cavity of, 75. ‘¢ nerve-cells of, 168. = repair of, 215. Hydroid, see Hydrozoa. Hydrozoa, 246, 178, 191-196. aS development of, 205. os metamorphosis of, 212. Uk see Jelly-fish. ‘Hyena, 355. Hymenoptera, 303, 22, 42, 81, 277. gs see Bee. Hypoblast, 199. Ibis, 332. Ichneumon, 304. Ichthyopsida, 309. Ichthyosaurns, 324. Idotia, 286, 251. Iguana, 322. Incisors, 68. INDEX. t Individual, 220. te LL described, 243, 160. digestive cavity of, 75. i fission, 191, 160. bi mode of feeding of, 50. aL: motion of, 154. Ey mouth of, 55. respiration of, 112. iy skin of, 127. Inheritance, 217. Insectivora, 346. Insecta, 291. ee absorption of, 94. 405 Be alimentary canal of, 79, 41-48. = anatomy of, 48, 81. a antenne of, 147. ‘* -chrysalis of, 172. sf circulation in, 105, 292. ake development of, 205. = ear of, 179. Be eye of, 181, 155, 156. ue feet and legs of, 162, 127, 181. &e flight of, 159. “ gpazard-of, (9: a heart of, 105, 69. ie kidney of, 126, 41, 42. . liver of, 124. 4s locomotion of, 159, 162. ee metamorphosis of, 207, 172, 264-267. is mouth of, 57. ee mouth-parts of, 53, 21-24. = muscles of, 156, 131. ‘¢ . nervous system of, 169, 48. re respiration in, 114,291. ze salivary glands of, 122. ‘¢ silk glands of, 40. 178, ‘¢ skeleton of, 132, 292, 98, 262. - smell of, 178. 4 spiracle of, 114, 79. i: touch of, 177, 147. sie trachese of, 114, 40, 80, 81. “« _ wings of, 159. Insessores, 337, 322-828. Inspiration, modes of, 115, 119, 120. Instinct, 184. Intelligence, 187. Intestine of Amphibian, 82. a of Bird, 84. i of Fish, 81. be of Mammal, 85. ef of Reptile, 82. be see Alimentary Canal. Isomya, 272. Ivory, 66. Jaws, 51-71. Jay, 339. Jelly-fish, 247, 193-197. re blood of, 97. Sf development of, 212, 178, 198. 406 po eye of, 180. mode of feeding of, 51. mouth of, 55. sy nerves of, 168. < nettle-cells of, 51. a reproduction of, 212. Joints, 147. dulus, 291. KaneGaroo, 88, 343. Kidney, 126, 41, 93. King-crab, see Horseshoe-crab. Kingfisher, 335, 327. Kite, 335. Lasium and Lasroum, 58, 21. Labyrinthodontia, 318. Lacerta, 321, 300. Lacertilia, 321. Lachnosterna, 297, 267. Lacteals, 94, 60. Lacune, 37, 8. Lamellibranchiata, 270, 44, 46, 78, 99, 135, 150, 224-227. es eye of, 181, 158. us see Clam. Lamellirostres, 331, 311. Lamprey, 286. Lamp-shell, 266, 221. Lancelet, 310, 282. Land-snail, 275, 282. Lark, 340. Larynx, 189, 159. Lasso-cells, 51. Leech, 268. ‘* alimentary canal of, 77. ‘6 jaws of, 64. ‘¢ locomotion of, 161. ‘* mode of feeding of, 50. Lemur, 355, 351. Lepas, 284, 258. Lepidoptera, 300, 48, 172. pisses see Butterfly. Lepidosiren, 317. | Lepidosteus, 315, 289. Libellula, 294, 268. Life, distribution of, 372. INDEX. Lion, 355. ‘¢ foot of, 128. ‘* skeleton of, 106. ‘¢ stomach of, 88, 58. Liver, 123, 92. Lizard, see Lacertilia. Lobster, 106, 70, 256. alimentary canal of, 78. ‘© anatomy of, 282. ‘* circulation in, 106, 70. oe ear of, 179. ig eggs of, 196. * gills of, 114. ‘¢ gizzard of, 64. fe locomotion of, 158. _ moulting of, 132. HS mouth of, 57. ‘¢ prehension of, 53, 57. E respiration in, 114. e skeleton of, 131. Lob-worm, 77. Locomotion of Arthropoda, 162. es of Birds, 160. oe of Fishes, 158. “4 of Insects, 159. ef of Mollusks, 161. nk of Starfish, 161. ee of Vertebrates, 163. 2 of Worms, 161. Locust, 297. Loligo, see Squid. Longipennes, 329, 308. Loon, 328, 307. Louse, 297, 59. Lucernaria, 197. Lumbricus, see Earth-worm. Lungs, function of, 125. ‘¢ of Snail, 116. ‘¢ surface of, 385. ‘“¢ of Vertebrates, 117. Lymph, 102. Lymphatics, 94, 61. Lymph-heart, 96. Maorra, 271, 46, 226. Madrepore, 252, 201, 206. Madreporic plate, 258, 39. Maggots, 389. ‘* duration of, 226. Mammalia, 309. ‘* nature of, 28. ea alimentary canal of, 85. ‘* struggle for, 227. 33 anatomy of, 87, 52. Lightning-bug, 299. id blood-corpuscles of, 99, 65. Ligula, 58, 21. brain of, 171, 188, 142-145. Likeness, 215. 7 circulation in, 109, 76, 281. Limax, 275, 232. : * digestion of, 92, 51. Limbs, development of, 204. Fr drinking of, 50, ‘© skeleton of, 146. his ear of, 179, 152. Limnea, 275, 2382. es ege of, 198, 165. Limpet, 278, 245. is embryo of, 202, 171. Limulus, 284. ts eye of, 183, 157. a see Horseshoe-crab. - ac hair of, 136, 104. yo heart of, 109, 78, 74. locomotion of, 163. ig lungs of, 118, 86. a mouth of, 62. a palate of, 86, 27, 51. ie placenta of, 196, 203, 171. % respiration in, 120, és skeleton of, 139. “ig smell of, 178, 149. rE teeth of, 68. ee touch of, 177. e voice of, 189, 159. Man, 359. ‘* pblood-corpuscles of, 99, 62. ‘brain of, 170, 171, 187, 144, 145. ‘* digestive tract of, 1. =, ear of, 179, 152. “eye of, 198, 157. ‘** mouth of, 86, 27. ‘* muscles of leg of, 165, 180. “* nose of, 178, 149. Manatee, 350, 348. Mandibles, 58, 21. Mantis, 53. Mantle, 127, 46. Marsipobranchii, 314, 286. Marsupialia, 342, 382. Mastodon, 350. May-fly, 295. Meandrina, 252. Medulla oblongata, 172. Medusa, see Jelly-fish. Megatherium, 344. Melania, 278. Menobranchus, 317, 294. Mesentery, 83. Mesoblast, 199. Metamorphosis, 207. of Crab, 209. 4 of Frog, 209. cs of Insect, 208. He of Grasshopper, 208. ae of Starfish, 208. Metazoa, 244. Millepede, see Myriapoda. Millepore, 391. Mimicry, 217. Minerals and Organisms, 19. - Mite, 287, 258. Molar Teeth, 69. Mole, 346. Mollusca, 269. a absorption of, 94. is anatomy of, 48, 46, 47, 78. ra circulation in, 106. af development of, 205. “ digestion of, 92. - distribution of, 377. # growth of, 214. Be kidney of, 126, 78. fs liver of, 124. INDEX. 407 Mollusca, locomotion of, 161. 66 metamorphosis of, 269. mode of feeding of, 52. mouth of, 56. nervous system of, 168, 134, 151, 157. number of species of, 221. respiration in, 113, 46, 47, 78. salivary glands of, 122. shell of, 133, 385, 99, 100. skin of, 127. see Clam, Cuttle- fish, Snail, Squid. Monad, 243, 187. Monera, 240, 188. Monkey, 356, 19, 352. see Primates. Monomya, 271. Monotremata, 342, 331. S mouth of, 62. Mosquito, 300, 173, 269. 66 66 metamorphosis of, 208. mode of feeding of, 50. Moth, 302, 274-276. 66 66 66 anatomy of, 79, 48. metamorphosis of, 274. see Butterfly, Lepidoptera. Motor Nerves, 167. Moulting, 128, 209. Mouse, 346. Mouth, 55. 66 of Arthropoda, 57. of Ascidia, 60. of Birds, 62. of Calenterata, 55. of Echinodermata, 56. of Fishes, 61. of Infusoria, 55. of Mammals, 62. of Mollusks, 56. of Parasites, 55. of Reptilia, 61. of Vermes, 57. of Vertebrata, 60. Mucous Membrane, $9. Mud-fish, 315. Murex, 275. Mug, 346. Musca, see Diptera, Fly. Muscle, 39, 12, 122. 66 66 ce 66 development of, 204. of Invertebrates, 156. kinds of, 155. of Vertebrates, 156. Mushroom-coral, 252, 202. Mussel, 270, 225. Ba Ns 290, 259. alimentary canal of, 77. mouth of, 57. respiration in, 116. see Centipede. 408 | . INDEX Myrmecophaga, 344, 338. Mytilus, 270, 225. NaIx3s, 135. Narwhal, 223, 68. Natatores, 328. Natica, 27S. Natural Selection, 227, Nauplius, 211, 177. Nautilus, 279, 247. Nematelminthes, 265, 218. Nereis, 268, 17. Nerve-cells, 40, 182. ‘¢ fibres, 40, 18. ‘* kinds of, 167. ‘¢ velocity of impulse of, 167. Nervous System, 168. ag of Arthropoda, 169. ee = Brain, 170. a ‘© development of, 199, 67. fe Fe of Mollusks, 168. a re Spinal Cord, 175. ee ty of Starfish, 168. - re pe Sympathetic, 175, 146. ee ve of Vertebrates, 169. s fe of Worms, 16S. Nenroptera, 294, 268. 7 seé Dragon-fly. Neuroskeleton, 141. Newt, 318, 296. Nomenclature, Zoological, 236. Notochord, 200, 167. Nucleolus, 31, 1. Nucleus, 31, 1. Nummulite, 242. Nutrition, 45. Nymph, 377. Ocrrnxt, 181. Octopus, 280. Gsophagus, 86. Olfactory Lobes, 172. Nerves, 178. Olive-shell, 278. Oniscus, 286. Operculum, 114, 134, 228. Ophidia, 320. % see Snake. Ophiura, 260. Opisthobranchs, 274, 352, 280, 231. Opisthocelous, 383. Opossum, 342, 382. Optic Lobes, 172. Orang-utan, 357, 853, 355. Order, 235. Organ, 41. Organization, 30. Organ-pipe Coral, 251, 200. Oriole, 339. Ornithorhynchuis, 342, 331. Orthoceras, 287. Orthoptera, 217, 295, 21, 264. rs see Grasshopper. Orycteropus, 344. Oscines, 338. Osseous Tissue, see Bone. Ossification, 37, 203. Ostrea, 272. ‘¢ see Oyster. Ostrich, 327, 305. Otoliths, 178, 156. Ovipositor, 293. Owls, 335, 317. Ox, alimentary canal of, 90. ‘“* foot of, 352, 129. ‘* teeth of, 352. ‘* see Ungulata. Oyster, anatomy of, 80, 44. ‘“) development of, 205. ‘© eggs of, 195. ‘© heart of, 106, 44. ‘* mouth of, 56. ‘* prehension of, 50. ‘¢ respiration in, 113. ‘6 see Clam, Lamellibranchiata. ~ PALATE, 61. | Pallial Sinus, 271, 99. Palpi, 58, 21. Paludina, 278, 244. Pancreas, 123, 91. Pancreatic Juice, 93. Pangolin, 344. Paper Nautilus, 280, 249. Papilio, 303. Papille, 128, 148. Paramecium, 243, 188. se see Infusoria. Parrot, 337, 320. ‘“* tongue of, 62. | Partridge, 333. Patella, 278. Pavement-teeth, 67, 32. Pearl-oyster, 224. Pectoral Arch, 146. Pedicellaria, 77, 97. Pedipalpi, 288. see Scorpion, Pelias, 320, 298. Pelican, 331. Penguin, 329, 306. Pennatula, 256, 208. Pentacrinus, 258, 211. Pepsin, 93. Peptone, 93. Perch, skeleton of, 112. Perchers, 337. Periosteum, 138. Peristaltic Movement, 89. Periwinkle, 278. Petrel, 330. Petromyzon, 314, 286. INDEX. _ Pharyngobranchii, 310, 282. Pharynx, 85. Pheasant, 333. Phoca, 354. Physalia, 246, 194. Physeter, 348, 341. : see Whale. Picarie, 335. Pici, 335, 320. Pigeon, 333, 316. Pinnigrade, 354, 128. Pisces, 310, 48, 51, 65, 75, 102, 112, 1238, 124, 139, 283-295. ‘6 gee Fish. Placenta, 196, 171. Planaria, 264, 217. Plant, 22. ‘* food of, 25. ‘* functions of, 24. Plantigrade, 355, 128. Plant-louse, 297. Plasma of blood, 98. Plastron, 323. Platyhelminthes, 264, 216, 217. yi see Tape-worm. Platyonychus, 287, 257. Pleurobrachia, 257, 209. Plover, 332. Poison-fangs, 68, 338. Polycistina, 242, 186. Polyp, 250. ‘¢ see Actinia. Polyzoa, 266, 220. Pond-snail, 275, 282. Porcupine, 346. Porites, 252. Porpoise, 88, 349, 54. Portal circulation, 307, 385, 281 Portuguese Man-of-war, 246, 194. Potato-worm, 303. Poulpe, 280. Prairie Chicken, 333, 315. Primates, 356, 35, 120, 148-145, 352-358. he brain of, 143-145. 8s skeleton of Chimpanzee, 120. ex teeth of Chimpanzee, 35. ry see Ape, Man, Monkey. Proboscidea, 350, 36, 119, 129. Proboscis of Butterfly, 59, 23, wi of Elephant, 62, 119. Procelons, 383. Prognathous, 393. Prosobranchs, 278, 2384-246. Proteus, 318, 295. o blood-corpuscle of, 99, 65. Protista, 21. Protoplasm, 31. Protopterus, 316, 298. Protozoa, 238. He number of species of, 221. see Ameeba, Infusoria. ' Reptilia, 319. 66 409 Pseudopodia, 51, 15. Pseudotriton, 318, 296. Psittaci, 337, 820. Pteropoda, 274, 229. a mouth of, 56. Pulmonates, 274, 282, 288. Pulse, 385. Pupil, 183, 158. Pygopodes, 328, 306, 307. QUADRUMANA, 356. Raccoon, 355, 846. Radiates, 233. Radiolaria, 241, 186. Rail, 332, 314. Rana, see Frog. Range of Animals, 373. Rank of Animals, 224. Raptores, 334, 116, 317-319. Rasores, 332, 815. Rat, 346. Ratite, 327, 305. Rattlesnake, 68, 38. Raven, 339. Ray, 314, 288. ‘* teeth of, 67, 32. Razor-shell, 272. Redstart, 338, 325. Repair, 215. Reproduction, 191. i asexual, 191. . by budding, 192. = checks on, 227. = by division, 191. rapidity of, 226. oy sexual, 192. alimentary canal of, 82. ae brain of, 172, 141. ch circulation in, 108, 76. corpuscles of, 99, 68. ef distribution of, 378. as lungs of, 118, 84. * mouth of, 61. ci prehension of, 61. -% scales of, 135. = teeth of, 67. oe voice of, 189. es see Crocodile, Turtle. Respiration, 111. ee in Crustacea, 114. Lizard, Snake, ee in Echinoderms, 112. ee in Fishes, 114. e in Insects, 114. in Mollusks, 113. a rate of, 120. ie in Vertebrates, 117. a in Worms, 113. tete mucosum, 128. 410 INDEX. Retina, 183, 158. Rhea, 327. Rhinoceros, 351, 344. Rhizopoda, 240, 15, 185, 186. a skeleton of, 129. Rodentia, 345, 385, 336, 337. ‘¢ teeth of, 71, 385. Rotifera, 266, 219. Hy jaws of, 64. Rudimentary Organs, 207. Ruminantia, 351. + stomach of, SS, 56. 2 see Ox, Ungulata. SALAMANDER, 318, 296. metamorphosis of, 174. Saliva, function of, 93. Salivary Glands, 122. Salmon, 316, 285. Sand-flea, 284, 252. Sandpiper, 332, 312. Sarcolemma, 39, 204. sauropsida, 309. Saurure, 394. Scales of Butterflies, 301, 272. ‘* of Fishes and Reptiles,135, 102,288. Scallop, eye of, 181, 1538. vs shell of, 272. Scapular Arch, 146. Scarabeeus, 299. Scarf-skin, 128. Sclerobase, 129. Scleroderm, 129. Sclerotic, 183. Scolopendra, 291, 259. Scorpion, 288, 259. c mouth of, 60. ne respiration in, 116. Sea-anemone, see Polyp. Sea-blubber, 247. Sea-butterfly, 273, 229. Sea-fan, 256, 208. Sea-hare, 274. Seal, 355, 128. Sea-lemon, 274. Sea-lily, 258, 211. Sea-lion, 355, 350. Sea-slug, 274. Sea-urchin, 262, 214. i: absorption by, 94. alimentary canal of, 76, 39. 66 # anatomy of, 39. ng circulation in, 105. ef digestion in, 92. sd growth of, 214. ag mode of feeding, 52. ob mouth of, 56. * respiration in, 112. - shell of, 28. ie skeleton of, 130, 96. 4 spines of, 130, 97. Sea-urchin, teeth of, 64, 28. | Sea-worm, 268, 17, 228. Secretion, 121. a see Gland. Segmentation of egg, 197, 165. Self-division, 191, 160. Sensation, 176. Sense of hearing, 178. ‘* of sight, 180. ‘* of smell, 177. ‘¢ of taste, 177. ‘* of touch, 176. Sense-organs, see Sense. ak development of, 204. Sensibility, 176. Sepia, 280, 248. Serpent, see Snake. Sertularia, 247, 192. Serum, 98. Setee, 269. Setophaga, 340, 325. Seventeen-year locust, 297, 266. Shark, 314, 287. ** eggs of, 194, 164. ** gills of, 114, 287 ‘¢ skeleton of, 137, 145. Shells of Crustacea, 131. ‘¢ of Echinoderms, 130. ‘* of Mollusks, 133. Shoulder-girdle, 146. Shrew, 63, 346, 388. Shrimp, 286. Sight, of Arthropods, 181. ‘¢ of Celenterates, 180. ‘* of Mollusks, 181. ‘* of Vertebrates, 182. Silk-gland, 40. Silk-worm, 303. Simia, 358, 358, 355. Sinuses, 138. Siphonophora, 248, 194. Siphuncle, 279, 247. « Siren, 318. Sirenia, 349, 73, 343. ae see Dugong. Size of Animals, 221. Skeleton, of Arthropoda, 131. re of Birds, 116, 144. a of Celenterates, 130. Hs of Echinoderms, 130. oi of Fish, 188, 144, 112. <3 of limbs, 146. ae Lion, 139, 116. i Mammals, 139, 106, 114, 117- 120. 5.0 ks Moliusks, 133. o Reptiles, 112, 115. is of skull, 141, 108, 111. rs of Vertebrates, 134. ne of Whale, 114. i see Exoskeleton. } | ren Sa INDEX. Skin of Invertebrates, 127. ‘¢ of Vertebrates, 128. Skull, 141. Slater, 284, 251. Slug, 274, 282. Smell, 177. Snail, 272. ‘* alimentary canal of, 80, 45. ‘* anatomy of, 45. ‘* circulation in, 106, 45. “* eye of, 181, 154. =p oilig Of, FS: ‘* gizzard of, 64. ‘+ heart of, 48. ‘6 jaw of, 56, 20. ‘* larva of, 176. ** locomotion of, 161. ‘Jung of, 116, 274, 45. ** mode of feeding, 52. ‘* mouth of, 56. ‘* nervous system of, 168, 184, 154. “© operculum of, 114, 134, 228. ‘¢ respiration in, 116, 40, 228. ** shell of, 133, 100, 228, 283-246. ‘* siphon of, 228. ‘© smell of, 178. ‘teeth of, 65, 29. ** tentacles of, 176, 154, 228. ‘© see Gasteropoda. ena, 320, 298, 299. deglutition of, 73. ** locomotion of, 162. ‘© lungs of, 119, 84. ‘¢ poison apparatus of, 68, 33. ** seales of, 135. sical) of, 37. ‘* stomach of, 82. “tongue of, 61. ‘¢ ~—-Vertebree of, 140. «* voice of, 189. *¢ see Boa, Ophidia, Reptilia. Snapping-bug, 299. Snipe, 332. Solaster, 260. Somite, 392. Songsters, 338. Sorex, 346, 338. Sow-bug, 285. Sparrow, 339. ‘Species, defined, 235. » number of, 221. Sperm-whale, see Whale. Sphinx-moth, 303, 48. ae classification of, 289, 260. alimentary canal of, 79. ‘* appendages of, 25. ‘¢ circulation in, 106. ‘¢ fangs of, 53, 18, 25. ** mouth of, 60, 25. ‘* respiration in, 116. ‘* spinnerets of, 289, 25, 261. 411 Spider, web of, 289, 260. Spinal column, 140. te cord, 175. Spinneret of Spider, 289, 261. es of Caterpillar, 301, 276. Spiracle, 114, 79. Spongida, 244, 189, 190. me alimentary canal of, 76. ie anatomy of, 189. egg of, 194, 168. sh feeding of, 50, 189. respiration in, 112. ss skeleton of, 129, 190, Squash-bug, 297. Squid, 280. ‘* locomotion of, 158. ‘* see Cuttletish. Squirrel, 346. Stag, 352, 345. Star-fish, alimentary canal of, 76, 126. ‘i anatomy of, 126. s circulation in, 105, 126. classification of, 258. “a development of, 208. a digestion in, 92. locomotion of, 161, 126. metamorphosis of, 207. ss mode of feeding of, 51. of mouth of, 56. fr nervous system of, 168, 183. s respiration in, 112. i see Echinodermata. Stilt, 332. Stomach, 82-89. - digestion in, 93. Stork, 332. Stridulation, 188. Strombus, 278, 248. Struggle for Life, 226. Struthio, 327, 308. Sturgeon, 315, 290. Subkingdom, 233. Sun-fish, 247. Sun-star, 260. Survival of Fittest, 226. Suture, 147. Swallow, 340, 328. Swan, 331. Swift, 335. Swimmeret, 282. Symmetry, 222. Sympathetic nervous system, 175, 146. Synovia, 147. Tanta, See Tape-worm. Tanager, 339. Tapetum, 184. Tape-worm, 264, 216. 2 feeding of, 49. Tapir, 63, 351. Taste, 177. 412 wa of Amphibia, 67. of Fishes, 61, 66, 67. a OS OE Invertebrates, 63. ‘of Mammals, 68, 70. * of Reptiles, 67. ‘¢ structure of, 38, 66, 9, 31. Teleostei, 315, 284, 290-292. Telson, 282. Temperature of Animals, 121. Tendon, 36. Tentacie, 51. Tent-caterpillar, 303. Termes, 295. Terebra, 278, 238. Terebratula, 267, 222. Terebratulina, 267, 221. Termite, 295. Tern, 329, 308. Testudo, see Turtle. Tetrabranchs, 279, 247. Tetradecapods, 285, 251, 252. Thoracic duct, 95, 61. Thorax, 119, 88. Thornback, 315, 288. Thousand-legged Worm, see Julus. Thrush, 340. Thylacinus, 343. Thyroid Cartilage, 189, 189. Ticks, 288. Tissue, 33. Toad, 318. Tongue, of Batrachians, 61. Hy of Birds, 62. re of Fishes, 61. a of Insects, 50, 58. Ht of Mammals, 63. ie of Mollusks, 52. ts of Spiders, 60. Top-shell, 278, 242. Tortoise, 323, 802. Ay see Turtle. Totipalmates, 330, 309. Toucan, 335. Touch, 176. Trachea, 119. Trachee, 114, 40, 79, 80, 81. Trichina, 265, 218. Tridacne, 272. Trilobite, 284. Trionyx, 322. Triton, 318, 296. Tritonian, 274, 230. Trochosphere, 211, 175. Trochus, 278. 4 embryo of, 211, 176. - Trogon, 335, 321. Tubipora, 252, 200. ‘Tunicata, 305, 278, 279. i see Ascidians. Turbo, 278, 242, Turkey, 333. INDEX. ' Turritella, 278. A = 322 olan , 301, 302. entary canal of, 82. -e breathing of, 119. us mou th of, 61. «¢ shell of, 135.. ‘¢ skeleton of, 115. “¢ see Chelonia. Tusks, 383. Types, 233. ho ee Uneurara, 351, 58,56, 108, 111, 117, 118, - 66 Unio, 272. 129, 188, 344, 345. feet os 129. ‘* eggs of, 196. Univalve, see Snail. Urodela, 317, 294-296. VARIATION, 216. Variety, 235. Veins, 104, 67. Veliger, 211, 176. Vena cava, 104. Venus, 272. Venus’-basket, 246. Vermes, 263, eS see 17, 77,175. Earth-worm, Worms. Vertebre, development of, 203. 66 k 66 n Vertebrata, 66 inds of, 140, 106, 107. umber of, 140. 306. absorption in, 94. alimentary canal of, 80. blood of, 98. brain of, 170 circulation in,107, 281. development of, 205. digestion in, 92. ear of, 179. exoskeleton of, 134. eye of, 183. gastric glands of, 123. heart of, 107. kidney of, 126. liver of, 124. lungs of, 117. mode of feeding of, 54. mouth of, 60. muscles of, 156. nervous system of, 169. number of species of, 221. pancreas of, 123. salivary glands of, 122, skeleton of, 137. skin of, 128. stomach of, 80. - teeth of, 66. tongue of, 60. see Bird, Crocodile, Fish, Frog, Mammal, Reptile. Villi, 90, 58. Vinegar-eel, 265. Vireo, 340, 326. Vitelline Membrate, 193. Viviparous, 309. Vocal Cords, 189. Voice, of Invertebrates, 1S8. *¢ of Vertebrates, 189. Volute, 278, 241. Vorticella, 243, 160. Vulture, 335, 116. WALKING-STICK, 297. Walrus, 355, 383. Warbler, 340. Wasp, 304. Water-boatman, 297, 265. Water-fleas, 284, 255. Wax-wing, 340. Weasel, 355, 348. Weevil, 300. Whale, 348, 341, 342. ‘“* baleen of, 65, 30. ‘¢ brain of, 170. Tab Of, 39: ‘“* mode of feeding of, 50. ‘¢ mouth of, 62. swimming of, 159. ‘¢ teeth of, 383. Whelk, 278, 228. ‘6 see Snail. White Ant, 295. INDEX. 413 Windpipe, 119, 86. Wings, of Bats, 161, 839, 340. ‘sof Birds, 160, 304. ‘6 of Insects, 159, 266. Wolf, 355, 347. Wombat, 343. Woodpecker, 335, 320. Worms, 263. + absorption in, 94. alimentary canai of, 77. Bb blood of, 98. eye of, 17. - head of, 17. jaws of, 17. ne larva of, 175. locomotion of, 161. ee mouth of, 57. number of species of, 221. proboscis of, 17. a0 reproduction in, 192. . respiration of, 113, 77. a skin of, 127. see Earth-worm. Wren, 340. Yok, 192. ZOOLOGICAL analysis, 236. bs barriers, 375. ie history, 18. a provinces, 376. Zoology, 19. THE END. She ee sibleweg Fes 4 4 —