, 7 a Asrrirrecesedi apres capa || seoenwans asasteaedie dich Tae tees @vENTIETH CENTURY TEXT-BOOKS EDITED BY ASB. NIGHTINGALE, Pu. 'D.,: LL.D. SUPERINTENDENT OF SCHOOLS, COOK COUNTY, ILLINOIS [ TWENTIETH CENTURY TEXT-BOOKS. ZOOLOGY. ANIMAL STUDIES. A one-book course in Zoology for secondary schools. By DAvID STARR JORDAN, President of Leland Stanford Jr. University; VERNON L. KELLocG, M.S., Professor of Entomology, Leland Stanford Jr. University; and HAROLD HEATH, Professor of Zoclogy, Leland Stanford Jr. University. Cloth, $1.25 net. ANIMAL LIFE. A First Book of Zoology. By DAVID STARR JORDAN and VERNON L., KELLOGG. Cloth, $1.20 net. ANIMAL FORMS. An Elementary Text-Book of Zoology. By DAviID STARR JORDAN and HAROLD HEATH. Cloth, $1.r0 net. ANIMALS. A Text-Book of Zoology. By JORDAN, KELLOGG, and HEATH. (The two foregoing in one volume.) Cloth, $1.80 net. i TEACHER’S MANUALS, ANIMAL STRUCTURES. A Laboratory Manual of Zoology. By D. S. JORDAN and GEORGE C. PRICE, Associate Professor of Zo- ology, Leland Stanford Jr. University. Limp cloth, 50 cents net. D. APPLETON AND COMPANY, NEW YORK. TWENTIETH CENTURY TEXT-BOOKS BNIMAL STUDIES AidieX I-BOOK OF ELEMENTARY ZOOLOGY FOR OSE IN HIGH SCHOOLS AND COLLEGES BY DAVID STARR JORDAN PRESIDENT OF LELAND STANFORD JR. UNIVERSITY VERNON LYMAN KELLOGG PROFESSOR OCF ENTOMOLOGY AND : HAROLD HEATH ASSOCIATE PROFESSOR OF INVERTEBRATE ZOOLOGY IN LELAND STANFORD JR. UNIVERSITY NEW YORK Dey APPEELON* AND COMPANY UOPYRIGHT, 1903 By D. APPLETON AND COMPANY Animal Life A =< Copyright 1900 by D. Appleton and Company Animal Forms j Copyright 1902 by D. Appleton and Company EDITOR’S PREFACE THE publishers are assured from the most expert testi- mony that they are presenting to the educational public, in this volume, a compact but complete treatment of elemen- tary zoology, especially for those institutions of learning which prefer to find in a single book an ecological as well as a morphological survey of the animal world. Animal Life, in the series, treats largely of ecology, Animal Forms of morphology. in this volume the same authors present the salient features of each of the above-named books, with entirely new and additional chapters on Classification, the Economic Value, and the Ancient History of Animals. In Animal Studies an important advance step is taken toward meeting the demand for an elementary zoology that shall treat of the natural history rather than merely of the mor- phology of animals. Several new plates not found in the other volumes have been added. The structure, life habits, environments, economics, and history of fossil animals are each treated with that clearness, conciseness, and complete- ness for which President Jordan is particularly distin- guished. While the book contains adequate material for a year’s work, it is also admirably adapted for those schools that find it necessary to give a shorter time to this subject. The following ideas expressed by Dr. Coulter concerning vi ANIMAL STUDIES the purpose of Plant Studies are entirely applicable to Ani- mal Studies as well: “The book is intended to serve as a supplement te three important factors: “(1) The teacher, who must amplify and suggest at every point; (2) the laboratory, which must bring the pupil face to face with plants and their structures; (3) field-work, which must relate the facts observed in the laboratory to their actual place in Nature, and must bring new facts to notice which can be observed nowhere else.” Jordan and Price’s Animal Structures, a Laboratory Manual of Zoology, will be found eminently useful in con- nection with the reading and study of this text. CONTENTS CHAPTER I.—ConDITIONS OF ANIMAL LIFE . : “II. — PRINCIPLES OF CLASSIFICATION 4TIT.—Tue sIMPLEST ANIMALS OR PROTOZOA . ‘ /IV.—THE SLIGHTLY COMPLEX ANIMALS OR SPONGES XV.—THE C@LENTERATES ‘ - VI.—TuHE worms. ; VITI.— ANIMALS OF UNCERTAIN RELATIONSHIPS ‘VIII.—Mottusxs JIX.—Tue ARTHROPODS . \ X.—ARTHROPODS (continued) CLASS INSECTS XI.—ArtHropons (continued) CLASS ARACHNIDA XII.—EcuHInopERMS 3 : 4 A 4 : XIII.—TuHEeE cuorpDatTeEs XIV.—THE FISHES . 5 XV.—THE AMPHIBIANS . XVI.—THE REPTILES XVII.—THE BIRDs , 5 : 5 ;. : XVIII.—TuE mamMats AXIX.—TuHe Lire cycie a e e e e e > e e 6 XX.—THE CROWDS OF ANIMALS AND THE STRUGGLE FOR EXISTENCE VY XxT.— ADAPTATIONS /XXII.— Anima COMMUNITIES AND SOCIAL LIFE , ITI. —ComMENSALISM AND PARASITISM “XXIV.—PRoTECTIVE RESEMBLANCES AND MIMICRY 109 130 143 150 161 164 182 192 209 232 254 281 290 514 335 350 Vill ANIMAL STUDIES CHAPTER XXXV.—-THE SPECIAL SENSES , \ XXVI.— Instinct anD REASON XXVII.— Economic zooLocy XX VIII.—THE ANIMALS OF THE PAST. XXIX.—GEOGRAPHICAL DISTRIBUTION OF ANIMALS . PAGE . 371 - 387 404 417 . 435 ANIMAL STUDIES CHAPTER I CONDITIONS OF ANIMAL LIFE 1. Divisions of the subject.— Biology is the science which treats of living things in all their relations. It is sub- divided into Zoology, the science which deals with animals, and Botany, which is concerned with plants. The field covered by each of these branches is very extensive. Within the scope of zoology are included all subjects bear- ing on the form and structure of animals, on their develop- ment, and on their activities, including the consideration _of their habits and the wider problems of their distribution and their relations to one another. These various subjects are often conveniently grouped under three heads: Morphology, which treats of the form and structure or the anatomy of organisms; Physiology, which considers their activities; and Ecology, which in- cludes their relations one to another and to their surround- ings. All the phases of plant or animal existence may be considered under one or another of these three divisions. 2. Difference between animals and plants.—lIt is easy to distinguish between the animal and plant when a butterfly is fluttering about a blossoming cherry tree or a cow feed- ing in a field of clover. It is not so easy, if it is, indeed, possible, to say which is plant and which is animal when the simplest plants are compared with the simplest ani- mals. It is almost impossible to so define animals as to 1 2 ANIMAL STUDIES distinguish all of them from all plants, or so to define plants as to distinguish all of them from all animals. While most animals have the power of locomotion, some, like the sponges and polyps and barnacles and numerous parasites, are fixed. While most plants are fixed, some of the low aquatic forms have the power of spontaneous loco- motion, and all plants have some power of motion, as espe- cially exemplified in the revolution of the apex of the growing stem and root, and the spiral twisting of tendrils, and in the sudden closing of the leaves of the sensitive plant when touched. Among the green or chlorophyll- bearing plants the food consists chiefly of inorganic sub- stances, especially of carbon which is taken from the car- bonic-acid gas in the atmosphere, and of water. But some green-leaved plants feed also in part on organic food. Such are the pitcher-plants and sun-dews, and Venus-fly- traps, which catch insects and use them for food nutrition. But there are many plants, the fungi, which are not green —that is, which do not possess chlorophyll, the substance on which seems to depend the power to make organic matter out of inorganic substances. These plants feed on organic matter as animals do. The cells of plants (in their young stages, at least) have a wall composed of a peculiar carbohydrate substance called cellulose, and this cellulose was for a long time believed not to occur in the body of animals. But now it is known that certain sea-squirts (Tunicata) possess cellulose. It is impossible to find any set of characteristics, or even any one characteristic, which is possessed only by plants or only by animals. But nearly all of the many-celled plants and animals may be easily — distinguished by their general characteristics. The power of breaking up carbonic-acid gas into carbon and oxygen and assimilating the carbon thus obtained, the presence of chlorophyll, and the cell walls formed of cellulose, are char- acteristics constant in all typical plants. In addition, the fixed life of plants, and their general use of inorganic sub- CONDITIONS OF ANIMAL LIFE 3 stances for food instead of organic, are characteristics readily observed and practically characteristic of many- celled plants. When the thousands of kinds of one-celled organisms are compared, however, it is often a matter of great difficulty or of real impossibility to say whether a given organism should be assigned to the plant kingdom or to the animal kingdom. In general the distinctive characters of plants are grouped around the loss of the power of locomotion and related to or dependent upon it. 3. Living organic matter and inorganic matter.—It would seem to be an easy matter to distinguish an organism—that is, a living animal or plant—from an inorganic substance. It is easy to distinguish a dove or a sunflower from stone, and practically there never is any difficulty in making suck distinctions. But when we try to define living organic mat- ter, and to describe those characteristics which are peculiar to it, which absolutely distinguish it from inorganic matter, we meet with some difficulties. At least many of the char- acteristics commonly ascribed to organisms, as peculiar to them,arenotso. The possession of organs, cr the composi- tion of the body of distinct parts, each with a distinct func- tion, but all working together, and depending on each other, is as true of a steam-engine as of a horse. That the work . done by the steam-engine depends upon fuel is true; but so it is that the work done by the horse depends upon fuel, or food as we call it in the case of the animal. The oxida- tion or burning of this fuel in the engine is wholly compar- able with the oxidation of the food, or the muscle and fat it is turned into, in the horse’s body. The composition of the bodies of animals and plants of tiny structural units, the cells, is in many ways comparable with the composition of some rocks of tiny structural units, the crystals. But not to carry such rather quibbling comparisons too far, it may be said that organisms are distinguished from inorganic substances by the following characteristics: Organization ; the power to make over inorganic substances into organic 4. ANIMAL STUDIES matter, or the changing of organic matter of one kind, as plant matter, into another kind, as animal matter; motion, the power of spontaneous movement in response to stimuli; sensation, the power of being sensible of external stimuli; reproduction, the power of producing new beings like them- selves; and adaptation, the power of responding to external conditions in a way useful to the organism. Through adap- tation organisms continue to exist despite the changing of conditions. If the conditions surrounding an inorganic body change, even gradually, the inorganic body does not change to adapt itself to these conditions, but resists them unt,! no longer able to do so, when it loses its identity. 4, Primary conditions of animal life.—Certain primary conditions are necessary for the existence of all animals. We know that fishes can not live very long out of water, and that birds can not live in water. These, however, are special conditions which depend on the special structure and habits of these two particular kinds of backboned ani- mals. But the necessity of a constant and sufficient sup- ply of air is a necessity common to both; it is one of the primary conditions of their life. All animals must have air. Similarly both fishes and birds, and all other animals as well, must have food. This is another one of the pri- mary conditions of animal life. That backboned animals must find somehow a supply of salts or compounds of lime to form into bones is a special condition peculiar to these animals. 5. Food.—All the higher plants, those that are green (chlorophyll-bearing), can make their living substance out of inorganic matter alone—that is, use inorganic substances as food. But animals can not do this. They must have already formed organic matter for food. This organic mat- ter may be the living or dead tissues of plants, or the living or dead tissues of animals. For the life of animals it is necessary that other organisms live, or have lived. It is this need which primarily distinguishes an animal from a CONDITIONS OF ANIMAL LIFE 5 plant. Animals can not exist without plants. The plants furnish all animals with food, either directly or indirectly. The amount of food and the kinds of food required by various kinds of animals are special conditions depending on the size, the degree of activity, the structural character of the body, etc., of the animal in question. Those which do the most need most. Those with warmest blood, great- est activity, and most rapid change of tissues are most dependent on abundance, regularity, and fitness of their food. As we well know, an animal can live for a longer or shorter time without food. Men have fasted for a month, or even twomonths. Among cold-blooded animals, like the reptiles, the general habit of food taking is that of an occa- sional gorging, succeeded by a long period of abstinence. Many of the lower animals can go without food for surpris- ingly long periods without loss of life. But the continued lack of food results inevitably in death. Any animal may be starved in time. If water be held not to be included in the general con- ception of food, then special mention must be made of the necessity of water as one of the primary conditions of ani- mal life. Protoplasm, the basis of life, is a fluid, although thick and viscous. To be fluid its components must be dissolved or suspended in water. In fact, all the truly living substance in an animal’s body contains water. The water necessary for the animal may be derived from the other food, all of which contains water in greater or less quantity, or may be taken apart from the other food, by drinking or by absorption through the skin. Sheep are seldom seen to drink, for they find almost enough water in their green food. Fur seals never drink, for they absorb the water needed through pores in the skin. 6. Oxygen.—Animals must have air in order to live, but the essential element of the air which they need is its oxygen. For the metabolism of the body, for the chemical 6 ANIMAL STUDIES changes which take place in the body of every living ani- mal, a supply of oxygen is required. This oxygen is de- rived directly or indirectly from the air. The atmosphere of the earth is composed of 79.02 parts of nitrogen (includ- ing argon), .03 parts of carbonic acid, and 20.95 parts of oxygen. Thus all the animals which live on land are en- veloped by a substance containing nearly 21 per cent of oxygen. But animals can live in an atmosphere containing much less oxygen. Certain mammals, experimented on, lived without difficulty in an atmosphere containing only 14 per cent of oxygen; when the oxygen was reduced to 7 per cent serious disturbances were caused in the animal’s condition, and death by suffocation ensued when 3 per cent of oxygen was left in the atmosphere. Animals which live in water get their oxygen, not from the water itself (water being composed of hydrogen and oxygen), but from air which is mechanically mixed with the water. Fishes breathe the air which is mixed with or dissolved in the water. This scanty supply therefore constitutes their at- mosphere, for in water from which all air is excluded ng animal can breathe. Whatever the habits of life of the animal, whether it lives on the land, in the ground, or in the water, it must have oxygen or die. . Temperature, pressure, and other conditions—Some physiologists include among the primary or essential gen- eral conditions of animal life such conditions as favorable temperature and favorable pressure. It is known from ob- servation and experiment that animals die when a too low or a too high temperature prevails. The minimum or maximum of temperature between which limits an animal can live varies much among different kinds of animals. It is familiar knowledge that many kinds of animals can be frozen and yet not be killed. Insects and other small ani- mals may lie frozen through a winter and resume active life again in the spring. An experimenter kept certain fish frozen in blocks of ice at a temperature of —15° C. CONDITIONS OF ANIMAL LIFE < for some time and then gradually thawed them out un- hurt. Only very hardy kinds adapted to the cold would, however, survive such treatment. There is no doubt that every part of the body, all of the living substance, of these fish was frozen, for specimens at this temperature could be broken and pounded up into fine ice powder. But a tem- perature of —20° C. killed the fish. Frogs lived after being kept at a temperature of —28° C., centipedes at —50° C., and certain snails endured a temperature of —120° C. without dying. At the other extreme, instances are known of ani- mals living in water (hot springs or water gradually heated with the organisms in it) of a temperature as high as 50° C. Experiments with Amebe show that these simplest animals contract and cease active motion at 35° C., but are not killed until a temperature of 40° to 45° C. is reached. The pressure or weight of the atmosphere on the sur- face of the earth is nearly fifteen pounds on each square inch. This pressure is exerted equally in all directions, so that an object on the earth’s surface sustains a pressure on each square inch of its surface exposed to the air of fifteen ~ pounds. Thus all animals living on the earth’s surface or near it, live under this pressure, and know no other condi- tion. For this reason they do not notice it. The animals that live in water, however, sustain a much greater pres- sure, this pressure increasing with the depth. Certain ocean fishes live habitually at great depths, as two to five miles, where the pressure is equivalent to that of many hundred atmospheres. If these fishes are brought to the surface their eyes bulge out fearfully, being pushed out _ through reduced expansion; their scales fall off because of the great expansion of thc skin, and the stomach is pushed out from the mouth till it is wrong side out. Indeed, the bodies sometimes burst. Their bodies are accustomed to this great pressure, and when this outside pressure is sud- denly removed the body may be bursted. Sometimes such a fish is raised from its proper level by a struggle with its 8 ANIMAL STUDIES prey, when both captor and victim may be destroyed by the expansion of the body. Some fishes die on being taken out of water through the swelling of the air bladder and the bursting of its blood-vessels. If an animal which lives normally on the surface of the earth is taken up a very high mountain or is carried up in a balloon to a great altitude where the pressure of the atmosphere is much less than it is at the earth’s surface, serious consequences may ensue, and if too high an altitude is reached death occurs. This death may be in part due to the difficulty in breathing in sufficient oxygen to maintain life, but it is probably chiefly due to the disturbances caused by the removal of the pres- sure to which the body is accustomed and is structurally adapted to withstand. All living animals are accustomed to live under a certain pressure, and there are evidently limits of maximum or minimum pressure beyond which no animal at present existing can go and remain alive. But in the case both of temperature and pressure con- ditions it is easy to conceive that animals might exist which could live under temperature and pressure conditions not included between the minimum and maximum limits of each as determined by animals so existing. But it is impossible to conceive of animals which could live without oxygen or without organic food. The necessities of oxygenand organic food (and water) are the primary or essential conditions for the existence of any animals. Of course, we might include such conditions, among the primary conditions, as the light and heat of the sun, the action of gravitation, and other physical conditions, without which existence or life of any kind would be im- possible on this earth. But we here consider by “ primary conditions of animal life” rather those necessities of living animals as opposed to the necessities of living plants. Neither animals nor plants could exist without the sun, whence they derive directly or indirectly all their energy. CONDITIONS OF ANIMAL LIFE 9 8. Cells.—If we examine very carefully the different parts of some highly developed animal under the high powers of the microscope we find that they are composed of a multi- tude of small structures which bear the same relations to the various organs that bricks or stones do to a wall; and if the investigation were continued it would be found that every organism is composed of one or more of these lesser elements which bear the name of cells. In size they vary exceedingly, and their shapes are most diverse, but, despite these differences, it will be seen that all exhibit a certain general resemblance one to the other. 9. Shape of cells.—In many of the simpler organisms the component cells are jelly-like masses of a more or less spherical form, but as we ascend the scale of life the condi- tion of affairs becomes much more complex. In the mus- cles the cells are long and slender (Fig. 1, D); those form- ing the nerves and conveying sensations to and from all parts of the body, like an extensive telegraph system, are excessively delicate and thread-like; in the skin, ana lining many cavities of the body, where the cells are united into extensive sheets, they range in shape from high and colum- nar to flat and scale-like forms (Fig. 1, E, F,G). The cells of the blood present another type (Fig. 1, B); and so we might pass in review other parts of the body, and con- tinue our studies with other groups of animals, always find- ing new forms dependent upon the part they play in the organism. 10. Size of cells.— Also in the matter of size the greatest variations exist. Some of the smallest cells measure less than one micromillimeter (3345, of an inch) in diameter. Over five hundred million such bodies could be readily stowed away into a hollow sphere the size of the letter be- ginning this sentence. In a drop of human blood of the same size, between four and five million blood-cells or cor- puscles float. And from this extreme all sizes exist up to those with a diameter of 2.5 or 5 c.m. (one or two inches), 2 10 ANIMAL STUDIES as in the case of the hen’s or ostrich’s egg. On the average a cell will measure between .025 to .031 mm. (;;4, and soo Of an inch) in diameter, a speck probably invisible to the unaided eye. While the size and external appearance of a cell are seen to be most variable, the internal structures are found to show a striking resemblance throughout. All are constructed upon essentially the same plan. Differ- ences in form and size are superficial, and in passing to a more careful study of one cell we gain a knowledge of the important features of all. 11. A typical cell.— An egg-cell (Fig. 1, A) or some sim- ple one from the liver or skin may be chosen as a good rep- resentative of a typical cell. To the naked eye it is barely visible as a minute speck; but under the microscope the appearance is that of so much white of egg, an almost trans- parent jelly-like mass bearing upon its outer surface a thin structureless membrane that serves to preserve its general shape and also to protect the delicate cell material within. The comparison of the latter substance to egg albumen can be carried no further than the simple physical appearance, for albumen belongs to that great class of substances which are said to be non-living or dead, while the cell material or protoplasm, as it is termed, is a living substance. We know of no case where life exists apart from protoplasm, and for this reason the latter is frequently termed the physical basis of life. In addition to the features already described, the proto- plasm of every perfect cell is modified upon the interior to form a well-defined spherical mass known as the nucleus. Other structures are known to occur in the typical cell. Experiment shows that the nucleus and cell protoplasm are absolutely indispensable, whatever their size and shape, and therefore we are at present justified in defining the cell as a small mass of protoplasm enclosing a nucleus. 12. Structure of protoplasm.—When seen under a glass of moderate power protoplasm gives no indication of any CONDITIONS OF ANIMAL LIFE aL definite structure, and even with the highest magnification it presents appearances which are not clearly understood. According to the commonly accepted view, it consists of two portions, one, the firmer, forming an excessively delicate Fie. 1.—Different types of cells composing the body of a highly developed animal. A, cell; 7, food materials ; m, nucleus, B, blood-cell. C, nerve-cell with small part of its fiber. D, muscle fiber. E, cells lining the body cavity. F, lining of the windpipe. G, section through the skin. Highly magnified. meshwork (Fig. 1, A) enclosing in its cavities the second more fluid part. Therefore, when highly magnified, the appearance would be essentially like a sponge fully satu- rated with water; but it should be remembered that in the protoplasm the sponge work, and possibly the fluid part, is living, and that both are transparent. There are reasons for thinking that the structure and 12 ANIMAL STUDIES the composition of protoplasm may change somewhat under certain circumstances. It certainly is not everywhere alike, - for that of one animal must differ from that of another, and different parts, such as the liver and brain, of the same form must be unlike. These differences, however, are minor when compared to the resemblances, for, as we shall see, this living substance, wherever it exists, carries on the pro- cesses of waste, repair, growth, sensation, contraction, and the reproduction of its kind. 13. Animal functions—Animals in general lead active, busy lives, collecting food, avoiding enemies, and producing and caring for their young. While the activities of all animals are directed to their own preservation and to the multiplication of their kind, these processes are carried on in the most diverse ways. The manner in which an organ or an organism is made, and the method by which it does its work, are mutually dependent one on the other. As there is an enormous number of species of animals, each differently constructed, there is, accordingly, a very great variety of habits. As we shall see, the lower forms are remarkably simple in their construction, and their mode of existence is correspondingly simple. In the higher types a much greater complexity exists, and their activities are more varied and are characterized by a high degree of elabo- ration. In every case, the animal, whether high or low, is fitted for some particular haunt, where it may perform its work in its own special way and may lead a successful life of its own characteristic type. CHAPTER II PRINCIPLES OF CLASSIFICATION 14. Classification.—It is plain that natural relations of gome sort exist among living organisms. A dog is more like a cat than it is like a sheep. A dog is more like a sheep than either is like a butterfly. The very existence of such terms as animals and plants, insects and fishes, implies various grades of relationship. Classification is the process of reducing our knowledge of these grades of like- ness and unlikeness to a system. By bringing together those which are alike, and separating those which are unlike, we find that these rest on fixed and inevitable laws. Classification is thus defined as “the rational, lawful dis- position of observed facts.” 15. Homology.—All rational classification of plants or animals concerns itself with homologies. Homology means fundamental identity of structure, as distinguished from analogy, which means incidental resemblance in form or function. Thus the arm of a man is homologous with the fore leg of a dog, because in either we can trace throughout deep-seated resemblances or homologies with the other. In every bone, muscle, vein, or nerve the one corresponds closely with the other. The “limb” of a tree, the “arm” of a starfish, or the fore leg of a grasshopper shows no such correspondence. In a natural classification, or one founded on fact, those organisms showing closest homologies are placed together. An artificial classification is one based on analogies. Such a classification would place together a 13 14 ANIMAL STUDIES cricket, a frog, and a kangaroo, because they all jump; or a bird, a bat, and a butterfly, because they all have wings and can fly, although the different kinds of wings are made in very unlike fashion. 16. Natural classification based on homology.—The closest homologies are shown by those animals which have sprung from a common stock. The basis of natural classification, which is an expression of the ancestry of blood relationship of animals, is therefore homology. So far as we know, the actual presence of homologies among animals implies their common descent from some stock possessing the same characters. The close resemblance or homology among the different races of men indicates that all men originally came from one stock. As homology implies blood-relationship, so, on the other hand, common descent im- plies homology, the similar parts being de- rived from a common ancestral stock. It is sometimes said that the inside of an animal tells what it is, the out- side where it has been. In the internal struc- ture, ancestral traits are perpetuated with little change through long periods. The ex- ternal characters, having more to do with surroundings, are much more rapidly altered in response to demands of the environment. A perfect classification would indicate the line of de- scent of each member of the series, those now living ‘ Fie. 2.—Wings showing homology and analogy. Gz lly: 6; .pirG! ie Dab- PRINCIPLES OF CLASSIFICATION 15 haying sprung in natural sequence, by slow processes of change, from creatures of earlier geological periods. It is said that in classification we have “three ancestral docu- ments”: Morphology, Embryology, and Paleontology. In Morphology we compare one form with another, thus a. Elephant, : - c. Rhinoceros. Fie. 3.—Homology of digits of four odd-toed mammals, showing gradual reduction in number and consolidation of bones above.—After RoMANEs. tracing resemblances and differences. In Embryology we trace the development of individuals from the egg, thus finding clues in heredity that will enable us to trace the development of the race. In Paleontology we study the extinct forms directly, thus often finding evidence as to the origin of forms now existing. 17%. Scientific names.—Each of the different kinds of animal or plant is called a species. There is no better definition of species. Thus the red squirrel is a kind or species of squirrel, the gray squirrel is another, the fox squirrel a third. The black squirrel of the East is not a species, because black squirrels and gray squirrels are some- times found in the same nest, born from the same parents. A genus is a group of closely related species—one or more—separated from other genera by tangible structural characters. Thus all the squirrels named above constitute (‘sa1seds 104}O OMY VY} UWaMJaq puqsy @ Aquqoid st vrpamdaqur satsads ayt) *(pUurjsy ajqestyvjapuy) ssvaspoug pyo~monuwt pavouvjau *S Sf S(spurysy ajrvwoeqiy) ssvaspoug DIVIUI DAIIOUDIIUL “GS ‘9 S (PURIST WeYIYD) J9yx[VA Vsosajyy “Gg ‘p {(pur[sy UvoUNC]) ssv4spous DIPIMAIJUL “SY “I {(SpURISyT VO[pulg puR UuOpZuIqy) SSVISPOUS S7j7pa40q Vipauaaqur *S ‘Q {(purIsT SIIVY)) [OIG PAaIoUDJaUL DIAQIOISIVIS ‘“D “SSULYIVUL pUv azZIS UT JIAO pata}}Vos MOU jNq “1O}SIUe UOUTWIOD B WOIy papuadsap [ev :UvIDQ Iy!Ovg ‘spurys~ sosvdyyer) oy} uo UdYHVY (DIaIOjSIG) SSNIO"] —*v “OLY SuiAIvA puv ‘spuryst snowea ay} PRINCIPLES OF CLASSIFICATION LE a single genus. Other squirrel-like animals, as the chip- munk, the flying squirrel, the prairie gopher, or the prairie dog, belong to as many different genera. In the binomial system, invented by Linnzus and ap- plied by him to animals in 1758, the scientific name of an animal consists of two words—the name of its genus and species taken together. The name of the genus comes first. It is a noun, in Latin form, though usually of Greek derivation—ithus Sciurus, the squirrel, in Greek meaning shadow-tail. The name of the species is an adjective in meaning, placed after the noun and agreeing with it. Thus Sciurus hudsonicus is the name of the red squirrel, Sciurus carolinensis of the Eastern gray squirrel, and Sciurus ludovicianus of the fox squirrel; Sciuropterus volans is the flying squirrel, Zamias striatus the Eastern chipmunk, and Spermophilus franklini one of the prairie gophers. The specific name is usually a descriptive adjec- tive—often the name of a locality, sometimes the name of aman. The authority usually written after the name of an animal is that of the one who gave it its, specific name —thus Sciurus hudsonicus Erxleben, which means that Erxleben first called it hudsonicus. Usually the name of the authority is that of the discoverer of the species. When several names are given to the same animal they are called synonyms. The earliest of these names is the right name. All the rest are wrong. | 18. Families of animals.—A group of related genera is ealled a family. The name of a family is derived from that of its principal genus, with the termination ide. Thus all the squirrel-like animals belong to the family of Sciuride. All the sorts of mice to the Muride, from the principal genus, Mus, the mouse. The rabbits are Leporide, from Lepus, the rabbit, and the beavers Castoride, from Castor, the beaver. 19. Higher groups of animals.—In the higher groups we first trace out the different plans of structure. There is Fie. 5.—Three species of jack-rabbits, differing in size, color, and markings, but believed to be derived from a common stock. The differences have arisen through isolation and adaptation, The upper figure shows the head and fore legs of the black jack-rabbit (Lepus insularis), of Espiritu Santo Island, Gulf of California ; the lower right-hand figure, the Arizona jack-rabbit (Lepus aileni), specimen from Fort Lowell, Arizona ; and the lower left-hand figure is the San Pedro Martir jack-rabbit (Lepus martirensis), from San Pedro Martir, Baja California. PRINCIPLES OF CLASSIFICATION ity) some question as to the number of these different types, but we are not far out of the way in recognizing seven principal ones. These give rise to the seven principal branches of the animal kingdom: Protozoa, Celenterata, Mollusca, Vermes, Arthropoda, Echinodermata, and Chor- data (which includes vertebrates). The followers of Cuvier and Agassiz reduced these to four or five: Protozoa, Radi- ata, Mollusca, Articulata, and Vertebrata; but a more thor- ough knowledge of the different groups makes the larger number preferable, the radiates and the articulates being each divided into two. Many zoologists break up the Vermes into several distinct branches. The branches are again divided into classes. Thus the mammals, birds, reptiles, amphibians, fishes, lampreys, and lancelets are classes of vertebrates. The insects form a class of Arthropods. Each class is again divided into orders. The Glires or rodents, the gnawing animals, of which squirrels, mice, and rabbits are examples, form an order of mammals. The hoofed animals, Ungulata, form another, and each of these again contains many families. Intermediate divisions are sometimes recognized, with the prefixes super and sub. A subfamily is a division of a family including certain genera. A superfamily is a group of related families within the limits of an order. The red squirrel belongs to the branch Chordata, class Mammalia, order Glires, family Sciuride, genus Sciwrus, species Hudsonicus. 20. Trinomial names.—Trinomial names are those in which the binomial name of a species is followed by a sec- ond adjective. These indicate subspecies or varieties con- nected with geographical distribution. Thus many forms have a northern variety, a southern variety, one in the mountains, one on the plains, in the forests, or in other peculiar situations. Thus the gray squirrel, typically southern, has a sub- Fie. 6.—Some chipmunks of California, showing distinct species produced through isolation.—From nature, by WILLJAM SACKSTON ATKINSON. PRINCIPLES OF CLASSIFICATION 21 species, Sciurus carolinensis leucotis (white-eared), in the Northern States, larger than the true Sciwrus carolinensis, with the dark band on the back narrower. In Minnesota is another subspecies, Sciurus carolinensis hypopheus, with only a narrow streak of white on the belly. As animals come to be better known we can recognize by name more and more of these subspecies or geographical variations. Even in the same locality the members of a species vary more or less, no two being exactly alike. The name variety is applied to any sort of variation which can be recognized. Usually varieties not having definite geographical range re- ceive no scientific name. When forms in different geograph- ‘ical areas are found to intergrade or mix with one another they are known as subspecies, the one first named being re- garded as the original species. When they do not intergrade they are called distinct species. The subspecies differ from the species in degree only. When the range of a species is crossed by an impassable barrier, the subspecies on either side of the barrier usually becomes in time a distinct spe- cies. Thus distinct species are said to be produced through isolation. ‘The plates which follow may serve as illustra- tions of species and subspecies thus formed. CHAPTER III THE SIMPLEST ANIMALS OR PROTOZOA 21. Single-celled and many-celled animals—In almost every portion of the globe there are multitudes of animals whose body consists of but a single cell; while those forms more familiar to us, and usually of comparatively large size and higher development, such as sponges, insects, fishes, birds, and man himself, are composed of a multitude of cells. For this reason the animal kingdom has been divided into two great subdivisions, the Protozoa including all unicellular forms and the Metazoa embracing those of many cells. 22. Single-celled animals.—The division of the Protozoa comprises a host of animals, usually of microscopic size, inhabiting fresh or salt water or damp localities on land in nearly every portion of the globe. The greater number wage their little, though fierce, wars on one another with- out attracting much attention; others, in the sharp struggle, have been compelled to live upon or within the bodies of other animals, and many have become notorious because of the diseases they produce under such circumstances. A few are in large measure responsible for the phosphores- cence of the sea; and still others have long been favorite objects of study because of their marvelous beauty. Adapted for living under diverse conditions, the bodily form differs greatly, and yet all conform to three or four principal types, of which we may gain a good idea from the study of a few representative forms. 22 THE SIMPLEST ANIMALS OR PROTOZOA 23 23. The Amoeba.—Among the simplest one-celled ani- mals living in the ooze at the bottom of nearly every fresh- water stream or pond is the Ame@ba (Fig. 7, A), whose body is barely visible to the unaided eye. Under the microscope Ngee a’ Iie. 7.—A, the Ameba, highly magnified, showing ¢. v., pulsating vacuole; f, food particle; m, nucleus, The arrows show the direction of movement. B, shape of same individual 30 seconds later. C, an amceba-like animal (Diffiugia) partially enclosed ina shell. D,an Ameda in the process of division, E, Gromia, another shelled protozoan,—After SCHULZE. it is seen to consist of an irregular, jelly-like mass of proto- plasm totally destitute of acell wall. Unlike those animals with which we are familiar, the body constantly changes its shape. A rounded bud-like projection will be seen to appear on one side of the body and the protoplasm of adjacent regions flows into it, thereby increasing its extent. Similar projections at the opposite end of the cell are withdrawn, and their substance may flow into the newly formed lobe, which gradually swells in size and pushes forward. Thus, by constantly advancing the front part of the body and 24 ANIMAL STUDIES retracting the hinder portion, the cell glides or flows along from place to place. Upon meeting with any of the smaller organisms upon which it lives, projections from the body are put out which gradually flow around the prey and it becomes pressed into _ the interior of the cell. The process is not unlike pushing a grain of sand into a bit of jelly. There is no mouth. Any point on the surface serves for the reception of food. Oxygen gas also is taken into the body all over the surface, and wastes and indigestible material are cast out at any point. Nothing exists in these simple forms comparable to the complex systems of organs that carry on these processes in the squirrel. The bodily size of animals is limited, and to this general rule the Ameba is no exception, for upon gaining a certain size, the nucleus divides into two exactly similar portions, and very soon afterward the rest of the body separates into two independent masses of equal size (Fig. 7, D), each of which, when entirely free, contains a nucleus. In this way two daughter amcebe are formed possessing exactly the characters of the parent save that they are of smaller size ; but it is usually not long before they reach their limit of growth, when division occurs again, and so on, generation after generation. It not infrequently happens, however, that the pond or stream; in which the Ameda and other Protozoa live, dries up for a portion of the year. In such an event the body assumes a spherical shape, develops a firm, horn-like mem- brane about itself, and thus encysted it withstands the sum- mer’s heat and dryness and may be transported by the wind, or otherwise, over great distances. When the conditions again become favorable the wall ruptures and the Ameba emerges to repeat its life processes. 24. Some relatives of the Ameba.—AIl amceba-like forms, to the number of perhaps a thousand species, possess this same method of locomotion, but many present some inter- THE SIMPLEST ANIMALS OR PROTOZOA 25 esting additional characters. For example, the form repre- sented in Fig. 7, C, constructs a sac-like skeleton of tiny - pebbles cemented together, into which it may withdraw for protection. Others construct similar envelopes of lime or flint, and still others, as they continue to grow, build on additional chambers, giving rise to a great variety of forms often of wonderful beauty. In the tropics, particularly, some of the shelled Protozoa are so abundant that they may impart a whitish tinge to the water, and in some places their empty shells on falling to the bottom form immense deposits. The chalk cliffs of England are in large measure made up of such shells. 25. The Infusoria.—A little over two hundred years ago it was discovered that wherever water remained stagnant it became favorable for the rapid multiplication of a large number of species of Protozoa which live in such situations. These are known as Infusoria, and, like the preceding spe- cies, are usually of microscopic size and of the most varied shapes. The first striking feature of their organization is the presence of a delicate though relatively firm external cell membrane known as the cuticle, which preserves a defi- nite shape to the body. Such a method of locomotion as exists in the preceding group is consequently an impossi- bility, but other and more highly developed structures per- form the office. These latter organs are of two types, and their general characteristics may be readily understood from an examination of a few species living in the same localities as the Ameba. 26. The Euglena.—The first type exists in the common fresh-water organism known as LHuglena, represented in Fig. 8, A. Here the spindle-shaped body is surrounded by a delicate cuticle perforated at one point, where a funnel- shaped depression, the gullet, leads into the soft proto- plasmic interior. From the base of this depression the protoplasm is drawn out in the form of a delicate whip-like process known as the flagellum. This structure, always 3 26 ANIMAL STUDIES permanent in form, constantly beats backward and forward with great rapidity in a general direction represented in the diagram (Fig. 8,c). The movement from a to b is much more rapid than the reverse, from J to a, which results, like the action of the human arm in swimming, in driving the organism forward. Not only does the flagel- lum serve the purpose of locomotion, but it also produces currents in the water which may serve to bear minute Wake organisms down into the oe gullet, whence they read- ily pass into the soft pro- CY----&& = = / =F f n-2ge a 29 ' Zoi 2 = CV Geax Sf Fig. 8. — Flagellate Infusoria, A, Euglena viridis; c, pulsating vacuole ; ¢, eye-spot; g, gullet ; n, nucleus ; ¢, flagellum. B, Co- Fie. 9.— Paramecium aurelia, a dosiga, with collar surrounding ciliate infusorian. c, Cilia; c.v., the flagellum. C, diagram illus- pulsating vacuoles; f, food trating the action of the fiagel- particles ; g, gullet ; m, buccal lum, All figures greatly enlarged. groove ; 7, nucleus. toplasm of the body, there to undergo the processes of di- gestion and assimilation. In some forms the protoplasm in the region of the flagellum is drawn out in the form of a collar (Fig. 8, B), whose vibratory motion also aids in con- veying and guiding food into the body. 27. The Slipper Animaleule.—The second type of loco- motor organ may be understood from a study of the THE SIMPLEST ANIMALS OR PROTOZOA 24 Slipper Animalcule (Paramecium, Fig. 9), abundant in stagnant water. In this form the cuticle surrounding the somewhat cylindrical body is perforated by a great number lil | / Fic. 10.--Vorticelia, an at- tached ciliate infusori- an, highly magnified. a, fully extended individ- ual; ¢.v., pulsating va- cuole; g, gullet; n, nu- cleus. b, contracted specimen. c, small free- swimming individual, which unites with a sta- tionary individual (one partly united is shown in specimen b). of minute openings through which the internal protoplasm projects in the form of delicate threads. Each process, termed a ciliwm, works on the same principle as the flagellum, but it beats with an almost perfect rhythm and in unison with its fellows, drives the an- imal hither and thither with considera- ble rapidity. On one side of the body is a furrow which deepens as it runs backward and finally passes into the gullet (g), which leads into the interior of the body. Throughout the entire extent it is lined with cilia which create strong currents in the surrounding water and in this way conduct food down the gul.et into the body. Embedded in the outer sur- face of the body, in among the cilia, are also a number of very minute sacks, each containing a coiled thread which may be discharged against the body of any intruder, so that this form is sup- plied with actual organs of defense. Two pulsating vacuoles (c.v.) or simple kidneys are also present, consisting of a central reservoir into which a number of radiating canals extend. 28. The Bell Animalcule and other species—The Bell Animalcule ( Vorti- cella, Fig. 10) is often found in the same situations as the Slipper Animalcule, which in certain respects it resembles, It is generally attached by a slender stalk, and where many 28 ANIMAL STUDIES are growing together they appear like a delicate growth of mold upon the water weed. ‘The stalk is peculiar in being traversed by a muscle fiber arranged in a loose spiral, which, upon any unusual disturbance, contracts together with the body into the form shown in Fig. 10, 8. These few examples serve to show the general plan of organization and the method of locomotion of the Infuso- ria; but, as upward of a thousand species exist, with widely differing habits, many interesting modifications are present. Some have been driven in past time to adopt a parasitic mode of life within the bodies of other animals. At pres- ent they are devoid of locomotor organs, and as they absorb nutritive fluids through the surface of the body all traces of a mouth are also absent. The reproductive processes also are peculiar, but they do not concern us now. 29. Gregarina.— Another type of protozoan worthy of special attention is that of the Gregarina (Fig. 11), various species of which live in the alimentary canal * of crayfishes and centipeds and certain insects. Gregarinais a parasite, living at the expense of the host in whose body it les. It has no need to swim about quickly, and hence has no swim- ming cilia like Paramecium and the young Vorticella. It does need to cling to the inner wall of the alimentary canal of its host, and the body of some species is provided with hooks for that purpose. The food of Gregarina is the liquid food of the host as it exists in the intestine, and which is simply absorbed anywhere through the surface of the body of the parasite. There is no mouth opening nor * Specimens of Gregarina can be abundantly found in the alimen- tary canal of meal worms, the larve of the black beetle (Tenebrio moli- tor), common in granaries, mills, and brans. “Snip off with small scissors both ends of a larva, seize the protruding (white) intestine with forceps, draw it out, and tease a portion in normal salt solution (water will do) on a slide. Cover, find with the low power (minute, oblong, transparent bodies), and study with any higher objective to suit.”— MURBACH. THE SIMPLEST ANIMALS OR PROTOZOA 29 fixed point of ejection of waste material, nor is there any contractile vacuole in the body. In the method of multiplication or reproduction G're- garina shows an interesting difference from Ameba and Paramecium and Vorticella. When the Gregarina is Fie. 11.—Gregarinide. A,a Gregarinid (Actinocephalus oligacanthus) from the in- testine of an insect (after Stern); B and C, spore forming by a Gregarinid (Coc- cidium oviforme) from the liver of a guinea-pig (after LEUcKaART) ; D, E, and F, successive stages in the conjugation and spore forming of Gregarina polymorphe (after KOELLIKER). ready to multiply, its body, which in most species is rather elongate and flattened, contracts into a ball-shaped mass and becomes encysted—that is, becomes inclosed in a tough, membranous coat. This may in turn be covered externally by a jelly-like substance. The nucleus and the protoplasm of the body inside of the coat now divide into many small parts called spores, each spore consisting of a bit of the cytoplasm inclosing a small part of the original nucleus. Later, the tough outer wall of the cyst breaks, and the spores fall out, each to grow and develop into a new Gre- 30 ANIMAL STUDIES garina. In some species there are fine ducts or canals leading from the center of the cyst through the wall to the outside, and through these canals the spores issue. Some- times two Gregarine come together before encystation and become inclosed in a common wall, the two thus forming a single cyst. This isa kind of conjugation. In some spe- cies each of the young or new Gregarine coming from the spores immediately divides by fission to form two indi- viduals. Related to the Gregarine are those minute protozoan parasites which live in the blood-corpuscles of man and some of the lower animals, and are called Hematozoa. Three species of these, living in the blood of man, cause the three kinds of malarial fever, known as tertian, quartan, and remittent. These malarial Hematozoa, known generally as Hemameba, can multiply by asexual sporulation in the blood, but produce also certain sexual individuals, which, when taken into the stomach of a mosquito which has sucked blood from a malarial patient, give rise to a zygote which encysts in the outer walls of the stomach, and breaks up into numerous blasts or embryos, which escape into the blood of the mosquito, and thence to all parts of its body, and especially to the salivary or poison glands. When now this infected mosquito pierces the skin of another man, and pours into the wound, as it regularly does, a quantity of saliva, numbers of larval Hemamebe also enter the blood, and, multiplying here, soon set up the disease malaria in the bitten person. It has been definitely proved that malaria is thus disseminated by mosquitoes, and it is highly probable that it is contracted in no other way. 30. Characteristics common to the Protozoa.—We have now studied the principal structures which serve in loco- motion among these simple one-celled forms, also the means by which they catch their food, and we shall now glance at the internal processes, which are much the same in all. After the food has been taken into the cell, it is proba- THE SIMPLEST ANIMALS OR PROTOZOA 3d bly acted upon by some digestive fluid, for it soon assumes a granular appearance, and finally undergoes complete solu- tion. In every case the oxygen is absorbed through the general surface of the body, and uniting with the living substance, as in the squirrel, liberates the energy necessary for the performance of the animal’s life-work. The wastes thus produced in a large number of forms simply filter out from the body without the agency of anything comparable to a kidney, but in several species they are borne to a definite spot, the pulsating vacuole (Figs. 7, 9, 10, ¢.v.), where they gradually accumulate into a drop about the size of the nucleus. The wall between it and the exterior now gives way, and the excretions are passed out. In active indi- viduals this process may be repeated two or three times a minute, but it is usually of less frequent occurrence. The loss in bodily waste is continually made good by ’ the manufacture of the food into protoplasm, and if the in- come be greater than the outgo, growth ensues. But, as in all other forms, growth is limited, and ultimately the cell is destined to divide, resulting in two new individuals. This process may be repeated many times, but not indefinitely, for sooner or later various members of the same species unite in pairs temporarily or permanently, exchange nu- clear material, and separate again with apparently renewed energy and the ability to divide for many generations. 31. Simple and complex animals.—It is important to note that these same processes of waste, repair, growth, feeling, motion, and multiplication are the same as those of the squirrel, and, furthermore, are common to all living crea- tures, so that the difference between animals is not in their activities, but in their bodily mechanisms; and according to the perfection of this, the animal is high or low in the scale. Comparing, for example, the Ameba and Slipper Animalcule, which are relatively low and high Protozoa, we find in the former that any part of the body serves in loco- motion and in the capture of food, while in the latter these 32 ANIMAL STUDIES same functions are performed by definite structures, the cilia and gullet. Now, it is well known that a workman is able to make better watch-springs, when this is his sole duty, than another who must make all parts of the watch; and likewise, where a definite task is performed by a defi- nite structure, it is more efficiently done than where any and every part of the body must carry it on. So the Ameba, in which definite tasks are performed by any part of the body indifferently, is less perfect and thus lower than the Paramecium, where these functions are performed by special organs. As we ascend the scale of life we find this division of labor among special parts of the body more complete, the organs, and therefore the animal, more com- plex, and better fitted to carry on the work of its life. a. CHAPTER IV THE SLIGHTLY COMPLEX ANIMALS OR SPONGES 82. Their relation to the Protozoa.— While the greater number of one-celled forms are not united with their fel- lows, there are several species where the reverse is true. In Fig. 12, for example, a fresh-water form known as Pandorina is represented, consisting of sixteen cells embedded in a spherical, jelly-like substance, each one of which is precisely like its companions in form and activity. The aggregation may be looked upon as a colo- ny of sixteen Protozoa united together to derive the benefit of increased locomotion and a larger amount of food in consequence. As a result of such a union they have not lost their independence, for if one be separated from the main Fie. 12.—Pandorina (from Nature). company it continues to exist. Highly magnified. From such a simple colonial type we may pass through a series of several more complex forms which reach their highest development in the beau- tiful organism, Volvoz (Fig. 13). In this form the indi- vidual members, to the number of many thousand, are ar- ranged in the shape of a hollow sphere. The united efforts of the greater number, which bear on their outer surfaces two flagella, drive the colony with the rolling movement do 34 ANIMAL STUDIES from place to place. As just indicated, some individuals lack the flagella, and their subsequent careers show them to be of a peculiar type. Sooner or later each undergoes Fie. 13.—A, Volvox minor, entire colony (from Nature). B, C, and D, reproduc- tive cells of Volvoa globaior. “ a Ndi A, ss garg Sy. - : ¢ Fic. 27.—Sea anemones (the two upper figures) and solitary coral polyps. in position. Below the esophagus each partition projects into the great cavity of the body and bears upon its inner free edge several important structures. The first of these, known as the mesenteric filaments (Fig. 28), appearing like delicate frills, plays an active part in the digestion of the food. Associated with these are long, slender threads, THE CAQZLENTERATES 55 closely packed with innumerable lasso-cells, which may be thrown out through openings in the body wall when the animal is attacked. Lasso-cells are also very numerous on the tentacles, which are thus to some extent defensive, but are chiefly active in capturing the crabs and small fish which serve as food. The partitions also carry eggs which may undergo the first stages of their growth within the body, and when finally able to swim are sent out through the mouth opening by hundreds to seek out favorable situa- tions, there to set- tle down and re- main. In some spe-. cies the young may sometimes arise as buds, as in Hydra (Fig. 27), and in others the animals have been described as splitting longi- tudinally into two Fig. 28.—Longitudinal section through the body of a equal-sized 4) Ie sea-anemone. o0é, esophagus; m. f., mesenterial 51. Corals.— The filaments ; 7., reproductive organs. coral polyps also belong to this group, showing a very close resemblance to the sea-anemones. In most cases they develop a firm skel- eton of lime, commonly known as “coral,” which serves to protect and support the body. Ina few species the polyps throughout life are solitary, and with skeleton comparative- ly simple (Fig. 27); but the larger number of species be- come more complex by developing kuds, which retain their connection with the parent, and in turn produce other out- growths with the ultimate result that highly branched 56 ANIMAL STUDIES colonies are produced (Fig. 29). At the same time the outer layer of the body is continually forming a skeleton which encloses the colony as a sheath, except at the ter- mination of each branch, where the mouth and tentacles are located. In certain species—for example, the sea pens (Pennatula) and sea fans (Gorgonia)—a skeleton may be Fig. 29.—Small portions of coral colonies, with some of the polyps expanded. formed of myriads of lime spicules, somewhat like those of the sponge, which are bound together by the fleshy substance of the body; but the skeleton of most of the common forms in the ocean, and the coral found in general collections, is stony. According to their method of branching, such specimens have received various popu- lar names, such as brain, stag-horn, organ-pipe, and fun- gous corals. —_—-s ee ow sie ot Fane Fie. 30.—Coral island (Nanuku Levu, of the Fiji group). (After a photograph by Max AGassiz.) : if eZ Gj y pea AA WR ff ue I. \ Wes A kG , o Sa } NAS ve pAb Se AF WHE § BCA Me Fie. 31.—Shore of a coral island, with cocoanut palms. (After a photograph.) 5 58 ANIMAL STUDIES Nearly all species, like the sea-anemones, are brilliantly colored during life, and several are highly phosphorescent. All are marine, and while they are found everywhere, from the shoreline to great depths, the more abundant and larger species inhabit the clear, warm waters of the tropics down to a depth of one hundred and sixty feet. In such regions the stag-horn corals especially grow in the wildest profusion, and become tall and greatly branched. Except in quiet water they are continually being broken by the waves, beaten into fragments, and the resulting sand is deposited about their bases. As a result of this continu- ous growth and erosion, there have been formed from coral sand mixed with the shells of mollusks and the skeletons of various Protozoa several of the islands along the Florida coast and many of those of the Pacific, some of them hundreds of miles in extent. CHAPTER VI THE WORMS 52. General Characteristics—The bodies of the animals comprising the two preceding groups are exposed on all sides equally to the water in which they live and are radi- ally symmetrical; but in the worms, one side of the body is fitted for creeping, and for the first time we note a well- marked dorsal (back) and ventral (under) surface. In the former, the body, like a cylinder, may be divided into simi- lar halves by any number of planes passing lengthwise through the middle; but in the worms, the right and left halves only are exposed equally to their surroundings, and there is, accordingly, only one plane which divides the body into corresponding halves, so that these animals, like all higher forms, are bilaterally symmetrical. In creeping, also, one end of the body is directed forward and it thus be- comes correspondingly modified. It usually bears the mouth, and may be provided with eyes, feelers, or organs of touch, and various other structures which enable the worm to recognize the nature of its ‘surroundings. The nervous and muscular systems are better developed than in the foregoing groups, and we note a greater vigor and defi- niteness in the animal’s movements, and in various ways the worms appear better able to avoid or ward off their enemies, recognize and select their food, and in general adapt them- selves to the conditions of life. The division of the worms is a very large one, and in some respects difficult to define, owing to the close resem- 59 60 ANIMAL STUDIES blance which many of them show to animals in other groups. All the invertebrates, therefore, except the crabs and insects, were placed in one group until subsequent study made it possible to classify them more exactly. Ac- cording to the general shape of the body, and the arrange- ment of internal organs, worms are divided into a number of groups, chief among which are the flatworms, the thread or roundworms, and the ringed worms or annelids. THE FLATWORMS 53. Form and habitat.—The flatworms, as their name indicates, are much flattened, leaf-like forms, some species living in damp places on land, in fresh-water streams or ponds, or along the seacoast, while a variety of other spe- cies are parasitic. The free forms (Fig. 32) are usually small, barely reaching a length greater than five or seven cen- timeters (2 to 3 inches), but some of the parasitic species (Fig. 36) attain the great length of six to thirteen me- ters (20 to 40 feet). The free-living forms usu- ally occur on the under side of stones, and frequently are so delicate that a touch is sufficient to destroy them. A few species are almost trans- Fie. 32.—A, fresh-water flatworm (Pla- : naria); B, marine flatworm (Lepto- parent, while many are col- plana). Enlarged, from Nature. ored to harmonize completely with their surroundings, so that, even though fragile and defenseless, they escape the attacks of enemies by being overlooked. The night-time or dark days are their hunting THE WORMS 61 season, and at such periods they may be found moving about with a steady gliding motion (due to cilia covering the en- tire body), varied occasionally by a looping, caterpillar move- ment, or by swimming with a flapping of the sides of the body. When watched at such times they may sometimes be seen to snatch up small worms, snails, small crabs and insects, which serve as food. More closely examining one of these forms, for example, the species usually found on the under side of sticks and stones in our shallow fresh-water streams (Fig.32, A), we note that the forward end is not developed into a well-defined head as in the higher worms, but is readily determined by the presence of very simple eyes and tentacles, while the lower creeping surface is dis- tinguished by a lighter color and the presence of the mouth. Through this small opening a slender proboscis (in reality the pharynx) may be extended some distance, and may be seen to hold the small organisms upon which it lives until they are suffi- ciently digested to be taken into the body. 54. Digestive system.—In the smaller flatworms, some Fig. 33.—Anatomy of fresh-water fiat- of which are scarcely larger worm (Planaria). exs, excretory sys- than many of the Protozoa, ee flame-cell (7). The all- the alimentary canal is a sim- ntary canal is stippled. B, nery- ous system. ple unbranched tube; but in the larger forms such an ap- paratus is replaced by a greatly branched digestive tract which furnishes an extensive surface for the rapid absorp- 62 ANIMAL STUDIES tion of food, and extending deep into the tissues of the body, carries nutriment to otherwise isolated regions. In the fresh-water forms and their allies there are three main branches of the intestine (Fig. 33), while in many of those from the sea there are several, and their arrangement affords a basis for their general classification. 55. Exeretory system.—In the sponges and celenterates the wastes are cast out by the various cells into the gastric cavity or at once to the exterior with- out the aid of any pronounced system of vessels; but in the flatworms sev- eral of the organs are deeply buried within the tissues of the body and a drainage system becomes a necessity. This consists of a paired system of ves- sels extending the length of the ani- mal (Fig.33) and provided with numer- ous branches, some of which open at various points on the surface of the body, while the others terminate in "<%= worm (after Lane). f, spaces (Fig. 34, s) among the organs in flagellum ; n, nucleus; what are known as flame-cells. The 8, spaces among the or- - x - gans of the body; 2, substances which accumulate in these waste Sane spaces are gathered up by the flame- cell, poured into the space it contains, and by means of the vibratory motion of its flagellum (f/f), a movement bearing a fancied resemblance to the flickering of a flame in the wind, are borne through the tubes to the exterior. 56. Nervous system and sense-organs.—In the sponges no definite nervous system is known to exist, the slight move- ments which the cells are able to undergo being regulated somewhat as they are in the Protozoa. Among the celen- terates certain of the cells scattered over the surface of the body are set aside as nerve-cells, and, more or less united by means of fibers extending from them, convey impulses over the body. Inthe flatworms the larger number of nerve-cells THE WORMS 63 are collected into two definite masses (Fig. 33, B), which constitute a simple brain on which the eyes are situated and from which bundles of nerve fibers pass to all parts of the body, the two extending backward being especially noticeable. As in the squirrel, these are distributed to the muscles and other organs to regulate their activity, while those distributed to the skin, especially in the forward part of the body, convey stimuli produced by touch. The branches connecting with the eyes enable the animal to distinguish light from darkness, but are probably too sim- ple to allow it to clearly distinguish objects of the outside world. The sense of smell and possibly that of taste are also present, but are relatively feeble. Some other characters of this class will be noted in the consideration of the two following classes. 57. Parasitic flatworms (trematodes)—parasitism.—Men- tion has already been made of the associations of two ani- mals as “messmates” for mutual benefit, such as the Hy- dractinia growing on the surface of the shell inhabited by the hermit crab, to which it gives protection by means of its nettle-cells, while in turn being borne continually into regions abounding with food. More frequently, however, one animal derives benefit from another without making any compensation. For example, many species of flatworms live within the shells of certain snails and upon the bodies of sea-urchins and starfishes, where they gather in their food supply safe from the attacks of enemies. Such asso- clations are probably without much if any inconvenience to the animal thus inhabited, and it also appears probable that the tenants are transients, using the mollusk or star- fish only as a temporary home. But from this condition of affairs it is only a short step to the parasitic habit, where the association becomes permanent and the occupant is provided with various structures which prevent its sepa- ration from its host. This latter kind of union occurs , throughout the group of trematodes; all are parasitic, and 64 ANIMAL STUDIES their internal organization, so closely resembling that of the free-living forms as to need no further description, in- dicates that they are descendants of the lat- ter. In the greater number the body is flat, and a few species still retain their outer coat of cilia ; but since these are no longer of service as locomotor organs they have gen- erally disappeared, and in their place numer- ous adhesive organs, such as spines, hooks, and suckers (Fig. 35), have arisen, which en- able the animals to hold on with great te- nacity. Thus attached to its host, and using it as a convenient and comparatively safe means of locomotion, the parasite may still Fie. 35. — A parasitic flatworm (Epidella). m mouth ; 0, opening of reproductive system ; s, sucker and spines for attachment. The di- gestive system is stippled; nervous system black. Enlarged 8 times, from Nature. continue to capture, small animals for food or may derive its nourishment from the tissues of the host. In addition there are numbers of internal parasites, living almost ex- clusively in the bodies of vertebrate animals, scarcely a sin- gle one escaping their ravages. 58. Life history.—In the external parasites the young hatch out and with comparative ease make their way to another host; but the young of an internal parasite, inhab- iting the alimentary canal, have a very slight chance in- deed of ever reaching a similar location in another host. THE WORMS 65 For this reason an almost incredible number of eggs is laid, and some extraordinary measures are employed in effecting the desired result. Probably the best-known example is that of the liver fluke inhabiting the bile-ducts in the sheep. Each worm lays several hundred thousand eggs, which make their way from the host, and if they chance to fall in pools of water or damp situations may proceed to develop, other- wise not. If the surroundings be favorable, the young, like little ciliated Infusoria, escape from their shells and rest- lessly swim or move about for a short time, and if during this time they come in contact with certain species of snails living in these situations they at once bore into their bodies. Here they produce other young somewhat resem- bling a tadpole, that now make their escape from the snail. In a short time each one crawls upon a blade of grass, and surrounds itself with a tough shell, where it may remain for several weeks. If the grass on which they rest be eaten by a sheep, they finally make their way to the bile-ducts and there become adult. The life cycle is now complete; the young form has found a new host; and the process shows how wonderfully animals are adapted to the conditions which surround them, and how closely they must conform to these conditions in order to exist. 59. The tapeworms (cestodes).—The cestodes, or tape- worms, are also parasitic flatworms in which the effects of such a mode of life are strongly marked. They occur almost exclusively in the bodies of vertebrate hosts and exhibit a great variety of bodily forms, in some cases resem- bling rather closely the trematodes, but in others strikingly different. In the latter type the body is usually of great length (from a few centimeters to upwards of sixteen meters (50 feet) ), and terminates in a “head ” (Fig. 36) provided, in the different species, with a great variety of hooks and spines and numbers of suckers for its attachment to the body of the host. From the head the body extends back- ward in the gradually enlarging ribbon-like body, slender at 66 ANIMAL STUDIES first and scarcely showing the segments which finally be- come so prominent a feature. When carefully examined, a two-lobed brain is found in the “ head,” and from it nerves extend the entire length of the body, followed throughout their course by the tubes of the excretory system; also each segment contains a perfect reproductive system, so that even if it be separated from the others it may continue to exist for a consid- erable length of time. Furthermore, the tapeworms are surrounded by the predigested fluids of their host; a special alimentary canal is therefore superfluous, and all traces of it have disappeared. . 60. Development.—As the animal [LS clings in this passive way to the body ; “2 of its host the segments, loaded with Fre. 36.—Tapeworm (Tenia . solium). In upper left- eggs ready for development, separate hana commer of figure is one after another from the free end the much enlarged head. of the body, pass to the exterior, and — AE ee slowly crawling about like independent organisms, lay great numbers of eggs, which may find an intermediate host as in the life cycle of the liver fluke, and so in time find their permanent resting-place. Fortunately in all these parasitic forms, though an inconceivably great number of eggs are laid, only a comparatively few reach maturity. Even these, however, may cause at times great destruction among the higher, and especially our domestic, animals, often doing damage amounting to many millions of dollars per year. 61. The tapeworm in relation to regeneration.—It has been known for more than one hundred and fifty years that some of the lower animals possess to a surprising degree the ability to regenerate parts of the body lost through injury. The Hydra, hydroids, and some of the jelly-fishes 3 (wingers @® wpe THE WORMS 67 may be cut into a number of pieces, each of which will develop into a complete individual; and this power of recoy- ery from the injuries produced by enemies is of the great- est service in the perpetuation of the species. This ability is also present in certain flatworms, and some species are known which voluntarily separate the body into two por- tions, each of which becomes an adult. In other species a similar process results in the formation of a chain of six individuals, placed end to end, the chain finally breaking up into as many complete worms. It is possible that the tapeworm may also be looked upon as a great chain of united individuals produced by the division of a single original parent, which becomes adapted for attaching the others until they separate. These latter are capable only of a very sluggish movement, and, devoid of mouth and ali- mentary canal, are not able to digest their food, but their life work is to so lay their eggs that they may develop into other individuals, and for this they are well adapted. NEMATODES (THREADWORMS) 62. General characters.—This class of worms is com- posed of an enormous number of different species, some para- sitic, others free all or a portion of their lives, and in view of the fact that they inhabit the most diverse situations it is remarkable that they are so uniform in their structure. In all the body is slender, and the general features of its organ- ization may be readily understood from an examination of the “vinegar eel” (Fig. 37, A). This small worm (not an eel), a millimeter or two in length, lives on the various forms of mold that grow in fermenting fruit juices, especially after a little sugar or paste has been added. A tough cuti- cle surrounds the body, preserving its shape and at the same time protecting the delicate organs against the action of the acids in which it lives. Through this may be seen great bands of muscles extending the entire length of the body and producing the wriggling movements of swimming 68 ANIMAL STUDIES or crawling. They also give support to a brain, which is in the form of a collar encircling the pharynx near the head, and to the great nerves which extend from it. Still further within the transparent body the alimentary canal may be distinguished as a straight tube passing directly through the animal. ‘The alimentary canal les freely in a great space, the body cavity, traces of which may exist in the flatworms in the form of hollow spaces into which the kid- neys open. It is possible that in this form also the kidneys open into this space, and it is roomy enough besides to afford lodgment for the reproductive organs in addition to a large amount of fluid which is probably somewhat of the nature of blood. A space in some respects similar to this occurs in all the animals above this group, and as we shall see, it is often cu- riously modified and serves for a Fig. 37. — Thread- or round- number of different and highly im- worms. A, vinegar eel (An- portant purposes.. In the round- i); cso . pharynx ; 7, intestine; 0v., worms the fluid it contains proba- developing young. B, Tri: bly acts in the nature of a blood = ##”a. From Nature, greatly enlarged. system, distributing the food and oxygen to various parts of the body and carrying the wastes to the kidneys for removal. 63. Multiplication.—In the matter of the production of new individuals the greatest differences exist. In some threadworms, for example the “vinegar eel,” eggs develop within the body and the young are born with the form of the parent. In other cases the eggs are laid in the water, where they, too, may directly grow to the adult condition; but in THE WORMS 69 the greater number of species the development is round- about, and one or more hosts are inhabited before the young assume the adult condition. Such is the case with the dreaded Trichina (Fig. 37, B), which infests the bodies of several animals, particularly the rat. When these forms are introduced into the alimentary canal of the rat, for example, they soon lay a vast quantity of eggs, sometimes many millions, which develop into young that bore their way into the muscles of the body, where they may remain coiled up for years. If the body of the rat be eaten by some . carnivorous animal, these excessively small young are lib- erated during the process of digestion and rapidly assume the adult condition in the alimentary canal, likewise giving rise to young which pursue again the same course of de- velopment. Another example of a complicated life history is in the Gordius or “horsehair snake” (a true worm and not a snake) frequently seen in the spring in pools where it lays its eggs. These eggs develop into young which bore their way into different insect larve, which are in turn eaten by some spider or beetle, and the worm thus transferred to a new host. In this they grow to a considerable size, and then make their exit from the body of the host and finally become adult. 64. Spontaneous generation. —The ancients believed that many animals were spontaneously generated. The early naturalists thought that flies arose by spontaneous genera- tion from the decaying matter of dead animals; from a dead horse come myriads of maggots which change into flesh flies. Frogs and many insects were thought to be generated spontaneously from mud. Eels were thought to arise from the slime rubbed from the skin of fishes. Aris- totle, the Greek philosopher, who was the greatest of the ancient naturalists, expresses these beliefs in his books. It ‘was not until the middle of the seventeenth century— Aristotle lived three hundred and fifty years before the 70 ANIMAL STUDIES birth of Christ—that these beliefs were attacked and be- gan to be given up. William Harvey, an English natural- ist, declared that every animal comes from an egg, but that the egg might “proceed from parents or arise spontane- ously or out of putrefaction.” In the middle of the same century Redi proved that the maggots in decaying meat which produce the flesh flies develop from eggs laid on the meat by flies of the same kind. Other zoologists of this time were active in investigating the origin of new indi- viduals. And all their discoveries tended to weaken the belief in the theory of spontaneous generation. Finally the adherents of this theory were forced to restrict their belief in spontaneous generation to the case of parasites and the animalcules of stagnant water. It was maintained that parasites arose spontaneously from the matter of the living animal in which they lay. Many para- sites have so complicated and extraordinary a life history that it was only after long and careful study that the truth regarding their origin was discovered. No case of spon- taneous generation among parasites is known. If some water in which there are apparently no living organisms, however minute, be allowed to stand for a few days, it will come to be swarming with microscopic plants and animals. Any organic liquid, exposed for a short time, becomes foul through the presence of innumerable bacteria, etc. But it has been certainly proved that these organisms are not spontaneously produced by the water or organic liquid. A few of them enter the water from the air, in which there are always greater or less numbers of spores of microscopic organisms. These spores germinate quickly and the rapid succession of generations soon gives rise to the hosts of bacteria and Protozoa which infest all standing water. If all the active organisms and inactive spores in a glass of water are killed by boiling the water, “sterilizing ” it, as it is called, and this sterilized water be put into a sterilized glass, and this glass be so well closed that germs THE WORMS f(a) or spores can not pass from the air without into the steril- ized liquid, no living animals will ever appear init. It is now known that flesh will not decay or liquids ferment except through the presence of living animals or plants. Fic. 38.—The multiplication of Amebdba by simple fission. To sum up, we may say that we know of no instance of the spontaneous generation of organisms, and that all the ani- mals whose life history we know are produced from other animals of the same kind. “ Omne vivum ex vivo,” All life from life. 72 ANIMAL STUDIES ANNELIDS OR SEGMENTED WORMS 65. The earthworms and their relatives—Leaving the groups of the parasitic animals, which have been driven from the field of active existence and in many ways are degraded by such a mode of life, we pass on to the higher free-living worms, where brilliant colors, peculiar habits, or remarkable adaptations render them peculiarly interesting. In consid- ering first their general organization, we may use the earth- Fig. 39.—Earthworm (Lumbricus terrestris). m, mouth ; ¢, girdle or clitellum. worm (Fig. 39) (sometimes called angle-worm or fish-worm) as a type because of its almost universal distribution. The body is cylindrical, shows well-marked dorsal and ventral surfaces, and, as in all of the annelids, is jointed, each joint being known as a segment. Anteriorly it tapers to a point, and the head region bearing the mouth is ill- defined, unlike many sea forms, yet serves admirably for tunneling the soil in which all earthworms live. In this process the animal is also aided by bristles or sete which project from the body wall of almost every segment and may be stuck into the earth to afford a foothold. 66. Food and digestive system.—The earthworms are nocturnal animals, seldom coming to the surface during the day except when forced to do so by the filling of their tun- nels with water or when pursued by enemies. At night they usually emerge partially, keeping the posterior end of the body within the burrow, and thus they scour the sur- rounding areas for food, which they appear, in some cases at least, to locate by a feeble sense of smell. They also frequently extend their habitations, and in so doing swallow enormous quantities of earth from which they digest out any nutritive substances, leaving the indigestible matter in — THE WORMS 73 coiled “ castings ” at the entrance of the burrows. In thus mixing the soil and rendering it porous they are of great service to the agriculturist. Although earthworms are omnivorous they also manifest a preference for certain kinds of food, notably cabbage, celery, and meat, which leads us to think that they have a sense of taste. All these substances are carried into their retreats and devoured, or are used to block the entrance during the day. The food thus carried into the body is digested by a system (Fig. 40) composed of several portions, ; Af ia a Se ett Fie. 40.—Earthworm (Lumbricus) disvected from left eh 6, brain; c, crop; d, outer opening of male reproductive system ; dv, dorsal blood-vessel ; g, gizzard ; h, pulsating vessels or ‘‘ hearts’; z, intestine; k, kidney ; m, mouth; 7. c., nerve- cord ; oe, esophagus ; 0, ovary ; od, oviduct; ph, pharynx; 7, testes; s.7., sem- inal receptacles ; v.v., ventral vessel. each of which is modified for a particular part in the pro- cess. The mouth (m) leads into a muscular pharynx (ph) whose action enables the worm to retain its hold on various objects until swallowed, and this in turn is continuous with the esophagus. From here the food is passed into the thin- walled crop (¢),and from this storehouse is gradually borne into the gizzard (g), whose muscular walls reduce it to a fine pulp now readily acted upon by the digestive fluids. These, resembling in their action the pancreatic juice of higher animals, are poured out from the walls of the intestine into which the food now makes its way; and as it courses down this relatively simple tube the nutritive substances are ab- sorbed while the indigestible matters are cast away. 67. Circulatory system.—In all the groups of animals up to this point the digested food is carried through the body by a simple process of absorption, or in the threadworms by 6 74 ANIMAL STUDIES means of the fluid in the body cavity; but in the earthworm the division of labor between different parts of the body is more perfect, and a definite blood system now acts as a distributing apparatus. This consists primarily of a dorsal vessel lying along the dorsal surface of the alimentary canal (Fig. 40), from which numerous branches are given off to the body wall, and to the digestive system through which they ramify in every direction before again being collected into a ventral vessel lying below the digestive tract. In some of the anterior segments a few of the connecting vessels are muscular and unbranched, and during life pul- sate like so many hearts to force the blood over the body, forward in the dorsal vessel, through the “ hearts” into the ventral vessel, thence into the dorsal by means of the small connecting branches. Some of the duties of this vascular system are also shared by the fluid of the body cavity, which is made to cir- culate through openings in the parti- tions by the contractions of the body wall of the animal in the act of crawl- ing. In this rough fashion a consider- able amount of nutritive material and oxygen are distributed to various or- gans, and wastes are carried to the kid- yy¢ 41. _piagram of earth- neys to be removed. worm kidney. 6, blood- 68. Exeretion—In nearly all of the cae ‘eae pat ea segmented worms there is a pair of 0, outer opening; 8, kidneys to every segment (Figs.40, 41), ““P'ums % body wallh Each consists of a coiled tube wrapped in a mass of smail blood-vessels, and at its inner end communicating with the body cavity by means of a funnel-shaped opening. In some unknown way the walls of the kidney extract the waste materials from the blood-vessels coursing over it and pass them into its tubular cavity. At the same time the cilia about the mouth of the funnel-shaped extremity are THE WORMS 16) driving a current from the body-cavity fluids, which wash the wastes to the exterior. 69. Nervous system.—The nervous system of the earth- worm consists first of a brain composed of two pear-shaped masses united together above the pharynx (one shown in Fig. 34), from which nerves pass out to the upper lip and the head, which are thus rendered highly sensitive. Two other nerves also pass out from the brain, and, coursing down on each side of the pharynx lke a collar, unite below it and extend side by side along the under surface of the digestive system throughout its entire extent. In each segment the two halves of this ventral nerve-cord are united by a nerve, and others are distributed to various organs, which are thus made to act and in proper amount for the good of the body as a whole. In its relation to the outside world the chief source of information comes to the earthworm through the sense of touch, for definite organs of sight, taste, and smell are but feebly developed, while ears appear to be entirely absent. Nevertheless these are sufficient to enable it to lead a suc- cessful life, as is evidenced by the great number cf such worms found on every hand. 70. Egg-laying.—In digging up the soil ee earth- worms abound one frequently finds small yellowish or brownish bodies looking something like a grain of wheat. These are the cocoons in which the earthworms lay their eggs, and the method by which this is performed is unique. We have already noted the presence of a swollen girdle (the clitellum) about the body of the worm. At the breed- ing season this throws out a fluid which soon hardens into an encircling band. By vigorous contractions of the body this horn-like collar is now slipped forward, and as it passes the openings of the reproductive organs the eggs and sperms are pushed within it. They thus occupy the space between the worm and the collar, and when the latter is shoved off over the head its ends close as though drawn to- 76 ANIMAL STUDIES gether by elastic bands. A sac, the cocoon, is thus pro- duced, containing the eggs and a milky, nutritive substance. In a few weeks the worm develops and, bursting the wall of its prison, makes its PC escape. axe Y1. Distribution. — The earthworms and their allies are found widely distributed throughout the world, and all exhibit many of the 2S Gos characters just described. ax The greatest differences GE ZS arise in their mode of life: As some are truly earthworms, aS but others are fitted for a Zan purely aquatic existence in ATS fresh water or along the Ae seacoast ; a few have taken ae up abodes in various ani- eee mals and plants, and in ae some of these situations they es extend far up the sides of pas the higher mountains. In a all, the head is relatively ZS indistinct, the number of bristles on each segment Fie. 42.—A marine worm (Nereis). A, ap- few, and for this and other © ‘cmc. acu/ 4ceenn a reasons all are included in the subclass Oligochexta, or ‘“‘ few-bristle ” worms. 72. Nereis and its allies—In many of the above-men- tioned situations members of a more extensive group of worms are found, with highly developed heads and many bristles arranged along the sides of the body. These are the Polychetes or “ many-bristle ” worms, and as a repre- sentative we may take Nereis (Fig. 42), a very common THE WORMS 77 form along almost any seashore. The body presents the Same segmented appearance as the earthworm, but the head (Fig. 43, A) is provided with numerots sense organs, chief among which are four eyes and several tentacles or “ feelers.” The segments behind the head Fie. 48.—A, head and one of the lateral appendages (B) of a marine worm (Nereis branatii); al, intestine; f, “‘ gill” ; %, kidney ; 7, nerve cord ; s, bristles for locos motion. differ very little from one another, and, unlike those of the earthworm, each bears a pair of lateral plates (Figs. 41, 42, B) or paddles with many lobes, some of which bear numerous bristles. By a to-and-fro movement these organs aid in pushing the animal about, or may enable certain spe- cies to swim with considerable rapidity. As in all other worms, respiration takes place through the surface of the body, the area of which is increased by the development, on certain portions of the paddles (para- podia), of plates penetrated with numerous blood-vessels, which thus become special respiratory organs or gills (Fig. 42, B). In their internal organization the Polychetes are con- structed practically on the same plan as the earthworms, the principal difference being in the reproductive system. In the earthworm this is restricted to some of the forward segments, while in the present group the eggs and sperms 78 ANIMAL STUDIES are developed in almost every segment, whence they are finally swept to the exterior through the tubes of the kid- neys (Fig. 43, B). The Nereis and its immediate relatives are all active forms, and by means of powerful jaws, which may be quickly extended from the lower part of the mouth cavity, they capture large numbers of small crustaceans, mollusks, and worms which happen in their path. Others more distantly related make their diet of seaweed, and many living on the sea bottom swallow great quantities of sand, from which they absorb the nutritious substances. 73. Sedentary forms.—Preyed upon by many enemies, a large number of species have been forced to abandon an active ex- istence save in their early youth, and to construct many interesting devices for their protection. Numerous species, shortly after they commence to shift for themselves, build about their bodies tubes of lime (Fig. 45), from which they may emerge to gather food and into which they may dash in times of danger. As the worm grows the tube is correspondingly enlarged, and these tubes, in all stages of construction and variously 14 coiled, may be found on almost every avail- py¢. 44.—A common able spot at the seashore, and may often marine worm (Po- be seen on the shells of oysters in the Jit ectenaed pre markets. boscis and over- In other species the tube is like thin cia horn, and may be further strengthened or concealed by numerous pebbles, bits of carefully selected seaweeds, or highly tinted shells, which give them a very attractive appearance. Such species usually develop out of immediate contact with other forms, but a few live so closely associated together that their twisted tubes THE WORMS 19 form great stony masses, sometimes several feet in diam- eter. 74. Effects of an inactive life—In many species such a sedentary life has resulted in the almost complete disap- pearance of the lateral appendages, which therefore no longer serve as organs of respiration, and this function hag been shifted accordingly on to other structures. These new organs are situated principally on the exposed head, Fie. 45.—Sedentary tube-dwelling marine worms, upper left hand Sadel/a (one-half natural size), the remainder Serpula (enlarged twice). From lite. and Fig. 39 shows the general appearance of some com- mon species. The corners of the mouth have expanded into great plumes, sometimes wondrously colored like a full-blown flower, and these, bounteously supplied with blood-vessels, act as gills) When disturbed, the plumes are hastily withdrawn into the tube, and some of the so-called serpulids (Fig. 45, bottom of figure) close the entrance with a funnel-shaped stopper. While the plumes are primarily respiratory organs, they also act as delicate feelers, and may even bear a score or more of eyes; and in addition, being 80 ANIMAL STUDIES covered with cilia, create the currents of water which bring minute organisms serving as food within reach of the mouth. 75. Development.—Unlike the earthworms, the Poly- chetes lay their eggs in the sea water, where they are left alone to develop as best they may. Both the male and female Nereis, as the egg-laying time approaches, undergo remarkable changes in their external appearance, resulting in the form shown in Fig. 42, A. They are now active swimmers, and thus are able to scatter the fertilized eggs over wide and more or less favor- able areas. The young also for a time are free-swimming, but finally end their migrations by settling to the sea bottom, where they gradually attain the adult condition. As in some of the flatworms, re- production may also occur asexually by the division of the animal into two or more parts, each of which subse- quently becomes a complete indi- vidual. In other species growth of various parts may result in two com- ‘plete worms at the time of separation ; and from such forms we may trace a fairly complete series up to those in 2s We co bat ES PR Me BS oe ng 2 “ aio ee Nan g ; * Ph ee “4 | Py » ; ae ak oe Pm TP AR AT re : Sh aed Bio 2 r J « which the original parent breaks up Fic. 46.—A leech (Macrobdet- : : Za). Right-hand figure il- into twenty to thirty young. lustrates alimentary canal. “6. The leeches.— At first sight >’, pharynx; ¢, crop; p, the leeches (Fig. 46), or at least the a smaller, more leaf-like forms, might be mistaken for flatworms, especially for some of the para- sitic species. As in the latter, the mouth is surrounded by a sucker, and another is located at the hinder end of the body, but beyond this point the resemblance ceases. The THE WORMS 81 outer surface is delicately marked off into eighty or a hun- dred rings, of which from three to five are included in one of the deeper true segments corresponding to those of other annelids. From two to ten pairs of simple eyes are borne on the head, and owing to the fact that they are active swimmers, or move by caterpillar-like looping, loco- motor spines are unnecessary and absent. In their internal organization, however, there are many features which in- dicate a close relationship with the Oligochetes or few- bristle worms. The nervous, circulatory, and certain char- acteristics of the excretory systems are decidedly similar, but, on the other hand, there are some facts difficult to explain, which have led some zoologists to believe that the relationship of these animals can not at present be determined. 77. Haunts and habits—The leeches usually dwell in among the plants in slowly running streams, but some occur in moist haunts on land, and a considerable number live in the sea. All are “bloodsuckers ’—fierce carnivo- rous worms, whose bite is so insidiously made that the vic- tim frequently is ignorant of their presence. Fishes, frogs, and turtles are the most frequently attacked, but cattle and other animals which come down to drink also become their prey. In some of the tropical countries the land-leeches are present in large numbers secreted among the leaves, and so severe are their attacks that various animals, even man, succumb to their united efforts. Adhering by their suck- ers, they puncture the skin, some using triple jaws, and fill themselves until they become greatly distended, when they usually drop off and digest the meal at leisure. In certain species the intestine is provided with lateral pouches (Fig. 45), which serve to store up the food until the time for digestion arrives. A full meal is sufficient with some species to last for two or three months, and the medicinal or horse-leech when gorged with food may con- sume a year in digesting it. 82 ANIMAL STUDIES 78. Egg-laying.—The eggs of some leeches are stored up in a cocoon like that of the earthworm, which is attached to submerged plants or placed under stones. When the young are able to lead independent lives they emerge with the form of the parent. A leaf-like form, Clepsine, some- times found adhering to turtles, fastens the eggs to the under side of its body, and the young when hatched remain there for several days, adhering by their posterior suckers. CHAPTER VII ANIMALS OF UNCERTAIN RELATIONSHIPS In this chapter we shall consider in a brief way a number of different groups of animals whose relationships are un- certain. Up to the present time the study of their habits, structure, and development has been of too fragmentary or unrelated a character to enable the majority of zoologists to agree upon their classification. Nevertheless, many of Fie. 47.—A wheel- animalcule (Roti fer). them are highly interesting and attractive, often very common, and in some respects they hold important positions in the animal kingdom. 79. The rotifers or wheel-animalcules.— The rotifers or wheel-animalcules are rela- tively small and beautiful organisms, rarely ever longer than a third of an inch, but at times so abundant that they may impart a reddish tinge to the water of the streams and ponds in which they live. At first _ sight they might be mistaken for one-celled animals, but the presence of a digestive tract and of reproductive elements soon dis- pels such a belief. Examined under the microscope, the more common forms are seen to possess an elongated body terminat- ing at the forward end in two disk-like expansions beset along the edges with powerful cilia. These serve to drive the animal about, or, when it remains temporarily attached 83 84 ANIMAL STUDIES by the sticky secretion of the foot, to sweep the food-par- ticles down into the mouth. Through the walls of the . transparent body such substances are seen to pass into the stomach, where they are rapidly hammered or rasped into a pulp by the action of several teeth located there. In the absence of a circulatory system the absorbed food is conveyed by the fluid of the body-cavity, which also con- veys the wastes to the delicate kidneys. Several other features of their organization are of much interest, espe- clally to the zoologist, who believes that he gains from their simple structure some ideas of the ancestors of the modern worms, mollusks, and their allies. During the summer the rotifers lay two sizes of “summer eggs,” which are remarkable for developing without fertilization. The large size give rise to females, the smaller to males, the latter appearing when the conditions commence to be un- favorable. The “ winter eggs,” fertilized by the males and covered with a firm shell, are able for prolonged periods to withstand freezing, drought, or transportation by the wind. The adults also are able under the same adverse conditions to surround themselves with a firm protective membrane and to exist for at least a year. Once again in the presence of moisture the shell dissolves, and in a surprisingly short space of time they emerge, apparently none the worse for the prolonged period of quiescence. 80. Gephyrea.—There is a comparatively large group of worm-like organisms, over one hundred species in all, which at present hold a rather unsettled position in the animal kingdom. Some of the more common forms (Fig. 48) living in the cracks of rocks or buried in the sand, usually in shallow tide pools along the seashore, have a spindle- shaped body terminated at one end by a circlet of tentacles which surround the mouth. On account of their external resemblance to many of the sea-cucumbers (Fig. 95), they were earlier associated in the same group; but an examina- tion of their internal organization inclines many zoologists ANIMALS OF UNCERTAIN RELATIONSHIPS 85 to the belief that the ancestors of some of these animals were segmented worms whose present condition has arisen possibly in accordance with their sluggish habits. This view is strengthened by the fact that in a very few species the larve are dis- tinctly segmented, but lose this char- acter in becoming adult. As before mentioned, the greater number of species live in bur- rows in the sand or crevices in the rocks, from which they reach out and gather in large quantities of sand. As these substances Fie. 48.—A gephyrean worm (Dendrostoma). Specimen pass down the in- on left opened to show &, kidney, m, muscle bands, ° : and 7.¢., nerve-cord. testine the nutri- tive matters are di- gested and absorbed, while the indigestible matters are voided to the exterior. When large numbers are associated together they are doubtless important agents in modifying the character of the sea bottom, thus acting like the earth- worms and their relatives. 81. The sea-mats (Polyzoa).—The sea-mats or Polyzoa constitute a very extensive group of animals common on the rocks and plants along the seashore, and frequently seen in similar situations in fresh-water streams. A few lead lives as solitary individuals, but in the greater number of species the original single animal branches many times, giving rise to extensive colonies. In some species these extend as low encrusting sheets over the objects on which they rest; while in others the branches extend into the 86 ANIMAL STUDIES surrounding medium and assume feathery shapes (Fig. 49), which often bear so close a resemblance to certain plants Fie. 49.—Lamp-shells or Brachiopods (on left of figure), fossil and living, and (on right) plant-like colonies of sea-mats. that they are frequently preserved as such. What their exact position is in the animal scale it is somewhat difficult to say; but judging especially from their development, it appears probable that they are distant relatives of the seg- mented worms. ANIMALS OF UNCERTAIN RELATIONSHIPS 87 82. Lamp-shells or Brachiopods.—Occasionally one may find cast on the beach or entangled in the fishermen’s lines or nets a curious bivalve animal similar to the form shown in Fig. 49. These are the Brachiopods, or lamp- shells. The remains of closely related forms are often abundant as fossils in the rocks (Fig. 49). Over a thousand species have been preserved in this way, and we know that in ages past they flourished in almost incredible numbers and were scattered widely over the earth. Unable to adapt themselves to changing conditions or unable to cope with their enemies, they have gradually become extinct, until to-day scarcely more than one hundred species are known. These are often of local distribution, and many are com- paratively rare. For a long period the Brachiopods, owing to their pecul- iar shells, were classed together with the clams and other bivalve mollusks. The presence of a mantle also strength- ened the belief; but closer examination during more recent years has shown that the shells are dorsal and ventral, and not arranged against the sides of the animal as in the clams. Another peculiar structure consists of two great spirally coiled “arms,” which are comparable in a general way to greatly expanded lips. The cilia on these create, in the water currents which sweep into the mouth, the small animals and plants that serve as food. The internal organ- ization resembles in a broad way that of the animals con- sidered in the previous section, and it now appears that both trace their ancestry back to the early segmented worms. 83. Band or nemertean worms.—In a few cases band or nemertean worms have been discovered in damp soil or in fresh-water streams. These are commonly small and incon- spicuous, and are pigmies when compared with their marine relatives, which sometimes reach 2 length of from fifty to eighty feet. Many of the marine species (Fig. 50) are often found on the seashore under rocks that have been exposed 88 ANIMAL STUDIES . by the retreating tide. They are usually highly colored with yellow, green, violet, or various shades of red, and are so twisted into tangled masses that the differ- ent parts of the body are indistinguishable. As the animal crawls about, a long thread- like appendage, the pro- boscis, is frequently shot out from its sheath at the forward end of the body and appears to be used as a blind man uses his stick. At other times, when small worms and other animals are Fig. 50.—A band or nemertean worm. A, entire worm; B, head, bearing numerous eyes and spine-tipped proboscis. encountered, the proboscis is shot out farther and with greater force, impaling the victim on a sharp terminal spine (Fig. 50). The food is now borne to the mouth, located near the base of the proboscis, is passed into the digestive tract, traversing the entire length of the body, and is far- ther operated on by systems of organs too one to be considered here. CHAPTER VIII MOLLUSKS 84. General characters.—For very many years the mol- lusks—that is, the clams, snails, cuttlefishes, and their allies —have been favorite objects of study largely because of the durability, grace, and coloration of the shell. The latter may be univalve, consisting of one piece, as in the snails, or bivalve, as in the clams and mussels, and may possess almost every conceivable shape, and vary in size from a grain of rice to those of the giant clam (Tridacna) of the East Indian seas, which sometimes weighs five hundred pounds. These external differences are but the expression of many internal modifications, which, while adapting these animals for dif- ferent modes of life, are yet not sufficient to disguise a more fundamental resemblance which exists throughout the group. In some respects the mollusks show a close resemblance to the annelid worms, but, on the other hand, the body is usually more thick-set and totally devoid of any signs of segmentation. In every case the skin is soft and slimy, demanding moist haunts and usually the protection of a shell, and the body is modified along one surface to form a foot or creeping disk which serves in Jocomotion. The internal organization is somewhat uniform, and will admit of a general description later on. Mollusks are divided into three classes, viz.: The Lamellibranchs, em- bracing the clams; the Gasteropods, or snails; and the Cephalopods, or cuttlefishes, squids, and related forms. 85. Lamellibranchs (clams and mussels)—Numerous rep- resentatives of this class, such as the clams and mussels, 7 89 90 ANIMAL STUDIES occur along our seacoasts or are plentifully distributed in the fresh-water streams and lakes. They are distinguished from other mollusks by a greatly compressed body, which is enclosed in a shell consisting of two pieces or valves locked together by a hinge along the dorsal surface. Rais- ing one of these valves, the main part of the body may be seen to occupy almost completely the upper (dorsal) part of the shell (Fig. 51), and to be continued below into the muscular hatchet-shaped foot (/t.), which aids the clam in plowing its way through the sand or mud in which it lives. Arising on each side of the back of the animal and extend- ing its entire length is a great fold of skin, which com- pletely lines the inner surface of the corresponding valve ‘of the shell. These are the two mantle Jobes (m) instru- mental in the formation of the shell, and enclosing between them a space containing the foot and a number of other important structures, the most conspicuous of which are the gills (g), consisting of two broad, thin plates attached along the sides of the animal and hanging freely into the space (mantle cavity) between the mantle and the foot. Owing to this lamella-like character of the branchia or gills the class derives its.name, lamellibranch. To illustrate the relations of these various organs to one another the clam has been compared to a book, in which the shells are repre- sented by the cover, the fly-leaves by the mantle lobes, the first two and last two pages by the gills, and the remaining leaves by the foot. In the clams, however, the halves of the mantle, like the halves of the shell, are curved, and thus enclose a space, the mantle cavity, which -is partly filled by the gills and foot. Unlike the other mollusks which usually lead active and more aggressive lives, the clams show scarcely a sign of a head and tentacles, and other sense organs are likewise absent from this region. The mouth also lacks definite organs of mastication, and as devices for catching and holding food are not developed, the food is brought to the MOLLUSKS 91 mouth by means of the cilia on the gréat triangular lips or palps which bound it on each side (Fig. 51, A, 7). Fie. 51.—Anatomy of fresh-water clam. A, right valve of shell removed ; B, dissec- tion to show internal organs. a, external opening of kidney ; @.a., the anterior muscle for closing the shell; 6, opening of reproductive kidney ; c, brain; /t., foot; g, gill; h, heart; i, intestine ; k, kidney; 2, liver; m, mantle (upper fig.), mouth (lower fig.); p, palp (upper fig.), foot nerves (lower fig.) ; p.a., hinder ’ muscle for closing the shell; s, space through which the water passes on leaving the body ; st, stomach ; v, nerves supplying viscera. - Between the halves of the shell in the hinge region is 4 horny pad that acts like a spring, and without any muscu- lar effort on the part of the clam keeps the shells open. 92 ANIMAL STUDIES These are also united by two great adductor muscles, located at opposite ends of the animal (Fig. 51, A, a.a., p.a.), which in times of disturbance contract and firmly close the shell. Upon their relaxation the shell opens, the clam extends its foot, and plows its way leisurely through the mud, or re- mains buried, leaving only the hinder portion of its gaping shell exposed. Through this opening a current of water is continually passing in and out, owing to the action of the cilia covering the gills, and by placing a little car- mine or coloring matter in the ingoing stream we may trace its course through the body. Passing in between the mantle and the foot it travels on toward the head, giving off small side streams which are continually made to enter minute openings in the gills, whence they are conducted through tubes in each gill up to a large canal at its base, where it is carried backward to the exterior. In this pro- cess oxygen gas is supplied to the number of blood-ves- sels traversing the gills,and at the same time considerable quantities of minute organisms and organic débris are hurried forward toward the head, where they encounter the whirlpools made by the cilia on the lips and are rapidly whisked down into the mouth and swallowed. 86. Rock- and wood-boring clams.—Other similar forms are rendered even more secure through their ability to bore in solid rock. In the common Piddock, for example (Fig. 52), the shell is beset with teeth like a rasp, which gradually enlarge the cavity as the animal grows, until it becomes a prisoner with no means of communication with the exterior save the small opening through which the siphons project. This is also the case with the TZeredo, frequently called the shipworm, which swims about for some time during early life and then, about the size of a small pinhead, settles down upon the timbers of wharves or unsheathed ships, into which it rapidly tunnels. Throughout life its excavation is extended sometimes to a distance of two to three feet, and imprisoned yet safe at MOLLUSKS 93 the bottom of its burrow, it extends its slender siphons up the tube and out of the entrance for its food supply. Often hundreds of individuals enter the same piece of wood, which becomes thoroughly riddled within a short Fie. 52.—The piddock (Zirphea crispata), a rock-boring mollusk. Natural size, from life. time, and though giving no outward sign of weakness may collapse with its own weight. Incalculable damage is thus rendered to the shipping interests, and in consequence much has been done to check their ravages, but they are far from being completely overcome. 87. Other stationary species—A large number of other species, while small and inconspicuous, are also free to 94 ANIMAL STUDIES move about, but as they become larger they lose this ability either wholly or periodically. In the edible mussels (Myti- lus, Fig. 53), for example, which are associated in great numbers on the rocks along our coasts, the foot early be- comes long and slender and capable of reaching out a con- siderable distance from the shell to attach threads (byssus), which it spins, to foreign objects. These are remarkably strong, and when several have been spun it becomes a mat- ter of much difficulty to dislodge them. After remaining anchored in one situation for a while the mussel may vol- Fic. 53.—The edible mussel (Mytilus edulis), showing the threads by which it is attached. Natural size, from life. untarily free itself, and in a labored fashion move to some other more favorable spot where it again becomes attached, but there are numerous species, such as “fan shells” (Pinna), scallops, Anomia, and a few fresh-water forms, where the union is permanent. Finally, in the oysters, some of the scallops, and a num- ber of less familiar forms, the young in very early life drop down upon some foreign object to which the shell soon becomes firmly attached, and in this same spot they pass the remainder of their lives. The oyster usually falls upon the left half of its shell, which becomes deep. and capacious enough to contain the body, while the smaller right valve MOLLUSKS 95 acts asa lid. As locomotion is out of the question, the foot never develops, and the shell is held by only one adductor muscle, whose point of attachment in the oyster is indicated by a brown scar in the interior of the shell. 88. Internal organization.—It is thus seen that the ex- ternal features of the clam are variously modified, according to the life of the animal, but the internal organization is much more uniform. In nearly every species the food con- sists of floating organisms, which are driven by the palps into the mouth and on to the simple stomach, where it is subjected to the solvent action of the fluids from the liver (Fig. 51, B, 7) before entering the intestine. This latter structure is usually of considerable length, and in the active species extends down into the foot, and it is also peculiar in passing through the ventricle of the heart. Traversing the intestine the nutritive portion of the food is absorbed, and is conveyed over the body by a circulatory system more highly developed than in the higher worms. On the dorsal side of the clam, in a spacious pericardial chamber, the large heart is situated (Fig. 51, 2), consisting of a median highly muscular ventricle surrounding the intestine and of two thin auricles, one on either side. From the former, two arteries with their numerous branches convey the blood to all parts of the body, where it accumulates, not in capilla- ries and veins, but in spaces or sinuses among the muscles and various organs, constituting a somewhat indefinite sys- tem of channels which lead to the gills and kidneys. In these organs the blood delivers up the waste which it has accumulated on its journey, and absorbing a supply of oxygen, it flows into the great auricles, which in turn pass it into the ventricle to circulate once more throughout the body. The excretory apparatus, consisting usually of two kid- neys, of which one may degenerate in many snails, bears a close resemblance to that of the annelids. In the clam, for instance, each consists of a bent tube symmetrically ar- 96 ANIMAL STUDIES ranged on each side of the body (Fig. 51, B, £), and the inner ends (a), corresponding to the ciliated funnel of the anne- lid kidney, open into the pericardial cayity. The walls are continually active in extracting wastes from the blood supplied to them, and these, together with the substances swept out from the pericardial cavity, traverse the tube and are carried to the exterior. In other mollusks the kidney may be more compact, or greatly elongated, or otherwise peculiar, but in reality they bear a close resemblance to those of the clam. 89. Nervous system.—The nervous system, like the ex- cretory, differs considerably in different mollusks, yet the resemblances are fairly close throughout. In the clam the cerebral ganglia corresponding to the “brain” in annelids is located at either side, or above the mouth, and from it several nerves arise, the larger passing downward to two pedal ganglia (~) embedded in the foot and to the visceral ganglia (v) far back in the body (Fig. 51, B). These nerve centers continually send out impulses which regulate the various activities of the body and also receive impressions from without. These come chiefly through the sense of touch, for in the clams the other senses are usually either feebly developed or altogether absent. 90. Development.—In the mollusca new individuals al- ways arise from eggs, which are commonly deposited in the water and there undergo development. In the fresh-water clams the reproductive organ is usually situated in the foot (Fig. 51), while in the oyster and similar inactive species it is attached to the large adductor muscle. In these latter, and in many other marine forms, the eggs are shed directly into the sea, where they are left to undergo their development buffeted by winds and waves and subject to the attack of numerous enemies. Under such circumstances the chances of survival are slight, and for this reason eggs are laid in vast numbers, which have been variously estimated for the oyster, for example, from two to forty million. Develop- MOLLUSKS 97 ment proceeds at first much as in the sponge, but soon the shell, foot, gills, and various other molluscan structures put in an appearance, and the few surviving young which have been free-swimming now settle down in some fayor- able spot, and attach themselves or burrow according to their habit. Y 91. Life history of fresh-water clams.—The life history of our common fresh-water clams is perhaps one of the most remarkable known among mollusks. The parent stores the eggs, aS soon as they are laid, in the outer gill plate, and there, well protected, they undergo the first stages of their development, which results in the formation of minute young enclosed in a bivalve shell beset with teeth. These are often readily obtained, sometimes as they are escaping from the parent, and when examined under the microscope are seen to rapidly open and close their shells in a snapping fashion when in the least disturbed. In a state of nature this latter movement may result in attaching the young to the fins or gills of some passing fish, which is necessary to its further development. Within a short time it becomes completely embedded in the flesh of its host, from which, as a parasite, it draws its nourishment, and during the next few weeks undergoes a wonderful series of transforma- tions resulting in a small mussel, which breaks its way through the thin skin of the fish and drops to the bottom. _ 92. The gasteropods.—The gasteropods, including snails, slugs, limpets, and a host of related forms, fully twenty thousand different species in all, are found in most of our fresh-water streams and lakes and in moist situations on land, while great numbers live along the seashore and at various depths in the ocean, even down as far as three _ miles. Examining any of them carefully we find many of the same organs as in the clams, but curiously changed and adapted for a very different and usually active life. In our common land snails (Fig. 54), which we may well examine before passing on to a general survey of the group, the first 98 ANIMAL STUDIES striking peculiarity is in the univalve shell, with numerous whorls, into which the animal may at any time withdraw completely. Ordinarily this is carried on the back of the spindle-shaped body, which is fashioned beneath into a great Fic. 54.—The slug (Ariolimax) and common snail (Helix). From life. flat sole or creeping surface that bears on its forward bor- der a wide opening through which mucus is continually issuing to enable the snail to slip along more readily. Slime also exudes on other points on the surface of the body and affords a valuable protection against excessive heat and drought. Unlike the clams, the forward end of the body is devel- oped into a well-marked head bearing the mouth and a complicated mechanism for gathering and masticating food, together with two pairs of tentacles, one of which carries the eyes. On the right side of the animal, some distance behind the head, is the opening of the little sac-like mantle cavity (Fig. 54) which contains the respiratory organs, and into which the alimentary canal and the kidneys pour their wastes. The relation of these organs to the mantle cavity is the same as in the clams, though the cavities differ much in size and position. 93. Other snails. The shell—Extending our acquaint- ance to other species of snails, we find the same general plan of body, although somewhat obscured at times by MOLLUSKS ey many modifications. A foot is generally present, also a more or less well-developed head, and the body is usually surrounded by a shell which varies widely in shape and size in different species. In the common limpets the early coiled shell is transformed into an uncoiled cap-like one, and in the keyhole limpets is perforated at its summit. The chitons or armadillo- snails (Fig. 55), often found associated with the limpets, carry a most peculiar shell con- sisting of eight plates, which enables the ani- mal to roll up like an armadillo when dis- Fie. 55.—The chiton, armadillo-snail or sea-cra- t+tyrbed. A shell is by dle. The left-hand figure shows mouth in center of proboscis, the broad foot on each no means a necessity ’ side of which are numerous small gills. The however, for in many right-hand figure shows the mantle and shell, : composed of eight plates. From life, one- species, such as the half natural size. beautiful naked snails or Nudibranchs (Fig. 56) common along our coasts, it may be entirely absent, or, as in the ordinary slugs, reduced to a small scale em- beddea in the skin. 94. Respiration.—A considerable quantity of oxygen is absorbed through the skin, as in all mollusks, but the chief part of the process is usually taken by the plume-like gills, one or two in number, which are located in the mantle cavity. In the chitons (Fig. 55) the number of gills is greater, amounting in some species to over a hundred, while in the Nudibranchs (Fig. 56) gills are absent, their places being taken by more or less feathery expansions of the skin on the dorsal surface. Many of the gasteropods left exposed on the rocks by a retreating tide retain water in the mantle cavity, from which they extract the oxygen until submerged again. 100 ANIMAL STUDIES Others breathe by means of gills while under water, and by the surface of the body and the moist walls of the mantle Fie. 56.—Three different species of naked marine snails or Nudibranchs. Natural size, from life. cavity when exposed. In some of the small Littorinas attached so far from the sea as to be only occasionally washed by the surf this latter method may prevail for days together—in fact they live better out of water than in it. It is not difficult to imagine that such forms, keeping in moist places, might wander far from the sea, and, losing their gills, become adapted to a terrestrial life. It is believed that in past times this has actually occurred, and that our land forms trace their descent from aquatic ances- tors. To-day they breathe by a lung—that is, they take oxygen through the walls of the mantle cavity, as the slug may be seen to do, though in some species traces of the old gill yet remain. 95. Food and digestive system.— Many mollusks live upon seaweeds, and the greater number of terrestrial forms are fond of garden vegetables or certain kinds of lichens, but, on the other hand, the latter, together with a large number of marine snails, are carnivorous. In all cases the food requires to be masticated, and, unlike the clams, the mouth is usually provided with horny jaws, and an additional) MOLLUSKS 101 masticatory apparatus which consists of a kind of tongue with eight to forty thousand minute teeth in our land forms (Fig. 57), while in certain marine snails they are beyond computation. With the licking motion of the tongue this rasp tears the food into shreds before it is swallowed, and in the whelks or borers it serves to wear a circular hole through the shells of other mollusks, which are thus killed and devoured. This latter process is facili- tated by the secretion of the salivary glands, which has a softening effect upon the shell. Ordinarily the saliva of snails exercises some di- ) gestive action. Fie. 57.—A small portion of the radula or In the stomach of some tongue-rasp of a snail (Sycotypus). snails are teeth or h orny ridges which also are instrumental in crushing the food, and in numerous minor respects peculiarities exist in differ- ent species according to the nature of the food; but in its general features the digestive tract is similar to that of the clams. The processes of circulation and excretion are also car- ried on by means of systems which show a certain resem- blance to those of the clams. As might be expected, certain differences exist, sometimes very great, but they are of too technical a nature to concern us further. 96. Sense-organs of lamellibranchs and gasteropods,— The eyes of mollusks differ widely in their structure and the position they occupy in the body. In our common land snails two pairs of tentacles are borne on the head, the lower acting as feelers, while each of the upper ones bears on its extremity the eye, appearing as a minute black dot (Fig. 54). In this same position the eyes of many marine snails occur, but there are numerous species in which there are other accessory eyes. In many of the 102 ANIMAL STUDIES . limpets, for instance, there are numbers of additional eyes carried on the mantle edge just under the eaves of the shell, and forming a row completely encircling the body. (In the scallops there are two rows of brilliantly colored eyes, set like jewels on the edges of the mantle just within the halves of the shell.) In the chitons the eyes of the head disappear by the time the animal attains maturity, and in some species at least their place appears to be taken by great numbers of eyes, sometimes thousands, which are embedded in the shells. On the other hand, eyes are com- pletely absent in certain species of burrowing snails and in several living in the gloomy depths of the sea far from the surface; they appear to be absent also from fresh-water clams; but the fact that certain species close their shell when a shadow falls upon theni, leads to the belief that while actual eyes are not present the skin is extremely sensitive to light. This is also the case with many snails. 97. Smell.—Since the sense of sight is generally unde- veloped in the mollusks, they rely chiefly upon touch and smell for recognizing the presence of enemies and food. Tentacles upon the head and other parts of the body, and a skin abundantly supplied with nerves, show them to pos- sess a high degree of sensibility; but in the greater num- ber of species the sense of smell is of chief importance. _ Many experiments show that tainted meat and strongly scented vegetables concealed from sight and several feet distant from many of our land and sea mollusks will attract them at once. In these forms the sense of smell appears to _be located on the tentacles, but additional organs, possibly of smell, are located on various portions of the body, usu-. ally in the neighborhood of the gills. 98. Taste and hearing.—Several mollusks appear to be almost omnivorous, but others are decidedly particular in their choice of food, which leads us to suspect that they possess to some extent the sense of taste. Nerves supply- ing the base of the mouth have also been detected, which MOLLUSKS 103 may be those of taste; but experiments along the line are difficult to perform, and our knowledge of this subject is far from complete. The same is true of hearing. Certain organs, interpreted as ears and located in the foot, have the form of two hollow sacs, containing one or more solid particles of sand or lime, whose jarrings, when effected by sonorous bodies, may result in hearing. On the other hand, it is held by some that they, like the semicircular canals of higher animals, may regulate the muscular movements which enable the animal to keep its balance. 99. Egg-laying habits and development.—The egg-laying habits of the gasteropods differ almost as widely as their haunts. The terrestrial forms lay comparatively few eggs, ranging in size from small shot to a pigeon’s egg in some of the tropical species. These are buried in hollows in the ground or under sticks and stones, and after a few weeks hatch out young snails having the form of the adult. The same is also true of most of the fresh-water snails, which lay relatively smaller eggs embedded in a gelatinous mass frequently found attached to sticks and leaves, or on the walls of aquaria in which they are confined. Many marine species construct capsules of the most varied patterns which they attach to different objects, and in these the young are protected until they hatch. In the limpets and many of the chitons the eggs are laid by thousands directly in the water, and after a short time develop into free-swim- ming young, differing considerably from the parent in ap- pearance. Those escaping the ravages of numerous enemies finally settle down in a favorable situation and gradually assume the form of the adult. 100. Age, enemies, and means of defense of lamellibranchs and gasteropods.— How much time is consumed by the young in growing up, and the length of time they live, are ques- tions generally unsettled. It is said that the oyster requires five years to attain maturity, and lives ten years; the fresh- water clam develops in five years, and some species live from 104 ANIMAL STUDIES twelve to thirty years; and the average length of life of the snail appears to be from two to five years. Certain it is that mollusks have numerous enemies besides man which prevent multitudes from living lives of normal length. Birds, fishes, frogs, and starfishes beset them continually, and many fall a prey to the ravages of internal parasites or to other mollusks. Under ordinary circumstances the shell is sufficient protection, and the spines disposed on the sur- face in many species render the occupant still less liable to attack. Many snails carry on the foot a horny or calcare- ous plate known as the operculum, which closes the en- trance of the shell like a door against intruders. Certain noxious secretions poured out from the skin also serve as a means of defense, and many Nudibranchs (Fig. 56) bear nettle-cells on the processes of the body, which probably render them distasteful to many animals. Finally, there are numerous clams, mussels, snails, and slugs whose colors harmonize so closely with their surroundings that they al- most completely baffle detection, and enable them to lead as successful a life as those provided with special organs of defense. 101. Cephalopods.—The animals belonging to this class, such as the squids and cuttlefishes (Fig. 58), are by far the most highly developed mollusks. They are of great strength, capable of very rapid movements, and several spe- cies are many times the largest invertebrates. In almost every case there is a well-defined head bearing remarkably perfect eyes, and also a circle of powerful arms provided with numerous suckers which aid in the capture of food (Fig. 58). Posteriorly the body is developed into a pointed or rounded visceral mass which to a certain extent is free from the head, giving rise to a well-marked neck. Some forms, such as the squids (Fig. 58, upper figure), are pro- vided with fins which drive the animal forward, but in com- mon with other cephalopods they are capable of a very rapid backward motion. By muscular movements water is taken MOLLUSKS 105 into the large mantle cavity within the body, a set of valves prevents its exit through the same channels, and upon a vigorous contraction of the body walls the water is forced out rapidly through the small opening of the funnel, which Fic. 58.—Cephalopods. Lower figure, the devil-fish or octopus (Octopus punctatus). The upper figure represents the squid (Loligo pealii) swimming backward by driving a stream of water through the small tube slightly beneath the eyes. From life, one-third natural size. drives the animal backward after the fashion of an explod- ing sky-rocket. In this way they usually escape the fishes and whales that prey upon them, but an additional device has been provided in the form of a sac within the body, whose inky contents may be liberated in such quantity as to cloud the water for a considerable distance, and thus enable them to slip away unseen into some place of safety. Most of the cephalopods are further protected by their ability to assume, like the chameleon, the color of the object 8 106 ANIMAL STUDIES @# upon which they rest. In the skin are embedded multi- tudes of small spherical sacs filled with pigments of various colors, chiefly shades of red, brown, and blue, each sac be- ing connected with a nerve and a series of delicate muscles. If the animal settles upon a red surface, for example, a nerve impulse is sent to each of the hundreds of color sacs of corresponding shade, causing the muscles to contract and flatten the bag like a coin, and thus exposing a far greater surface than before, they give the animal a reddish hue. In the twinkling of an eye they may completely change to another tint, or present a mottled look, and some may even throw the surface of the skin into numerous small projections that make the animal appear part of the rock upon which it rests. These devices not only serve for protection, but they also aid in enabling these mollusks to steal upon their prey, chiefly fishes, which they destroy in great numbers with lionlike ferocity. The devil-fishes and a number of other species are usu- ally found creeping along the sea bottom, generally near shore, and are solitary in their habits, while the squids re- main near the surface and frequently travel in great com- panies, sometimes numbering hundreds of thousands. In size they usually range from a few inches to a foot or two in length, but a few devil-fishes and squids attain a greater size, some of the latter reaching the enormous length of from forty to sixty feet. There are many stories of their great strength and of their voluntarily attacking people and even overturning boats, but the latter are in almost every case sailors’ yarns. In their external organization the cephalopods have little to remind one of any of the preceding mollusks, and their internal structure shows only a distant resemblance. In the Octopi (Fig. 58) the shell is lacking ; in the squid it is called the pen, and consists of a horn-like substance with- out any lime deposit; in the cuttlefishes it is spongy and plate-like, and is a familiar object in the shops ; and, finally, MOLLUSKS 107 in the nautilus it is coiled and of considerable size, and, un- like that of any other cephalopod, it is carried on the out- side of the animal. Interiorly it is divided by a number of partitions into chambers, the last one of which is occupied by the animal. | The alimentary canal shows some resemblance to that of other mollusks, but, as in the case of the other systems of the body, it possesses a far higher state of development. The mouth is situated in the center of a circle of arms, which in reality are modified portions of the foot, and is furnished with two parrot-like jaws. From this point the esophagus leads back into the body mass to the stomach, which with the liver and intestine are sufficiently like those of the clam and snail to require no further comment. Respiration is effected by the skin to a certain extent, but chiefly by two gills (four in the nautilus), and the cir- © culatory system, which conveys the blood to and from these organs and over the body with its complex heart, arteries, capillaries, and veins, is more highly developed than in any other invertebrate. As might be expected in animals with so great sagacity and cunning, the nervous system and the sense-organs reach a degree of development but little short of what we find in some of the vertebrates. The chief part of the nervous system is located in the head, protected by a cartilaginous skull, a very rare structure among invertebrates; and while the different ganglia may be recognized in a general way and be found to correspond to a certain extent to those of foregoing mollusks, they are so largely developed and massed together that it is impossible at present to under- stand them fully. From this point nerves pass to all regions of the body, to the powerful muscles, the viscera, and the organs of special sense, controlling the complex mechanism in all its workings. There is no doubt that the cephalopods see distinctly for considerable distances, and a careful examination of 108 ANIMAL STUDIES . the eye of the squids and cuttlefishes has shown them to be remarkably complex and in many respects to be constructed upon much the same plan as those of the vertebrates. As to the other senses not so much is known, but undoubtedly many species of cephalopods are possessed of a shrewdness and cunning not shared by any other invertebrates, save some of the insects and spiders, and are vastly more highly organized than their molluscan rela- tives. CHAPTER IX THE ARTHROPODS 102. General characters.—In the Arthropods, that is, the crabs, lobsters, shrimps, insects, spiders, and a vast host of related forms, the body is bilaterally symmetrical, and is composed of a number of segments arranged in a series, as in the earthworm and other annelids. A hornlike cu- ticle, sometimes called the shell, bounds the external sur- face—in early life thin and delicate, but later relatively thick, and often further strengthened by lime salts. Along the line between the segments this coat of mail remains thin and forms a flexible joint. Appendages also are borne on each segment, not comparatively short and fleshy out- growths like the lateral appendages of many of the worms, but usually long and jointed (hence the name Arthropod, meaning jointed foot), and variously modified for many different uses. 103. Classification.—The species belonging to this group éutnumber the remainder of the animal kingdom. Their haunts also are most diverse. Some are adapted for lives zn the sea and fresh water, others for widely different sit- uations 6n land, and a great number are constructed for a life on the wing. A certain resemblance exists among them all, but the modifications which fit them for their different habitats are also profound, and have resulted in the division of the Arthropods into five classes. The first class (Crus- tacea) contains the crayfish, crabs, etc. ; the second (Ony- chophora) includes the curious worm-like peripatus (Fig. 109 110 ANIMAL STUDIES 72); the third (Myriapoda, meaning myriad-footed) em- braces the centipeds and “thousand-legs”; the fourth (Insecta) contains the insects; and the fifth (Arachnida) includes the scorpions, spiders, and mites. 104. The Crustacea.—The number of species of crusta- - ceans is estimated to be about ten thousand, and while the greater number of these are marine, many are found in fresh water and a few occur on land. in size they range from almost microscopic forms to the giant crabs and lobsters. They differ also in shape to a remarkable degree, but at the same time there is a decided resemblance through- out the group, except in those species which have become modified by a parasitic habit. The characteristic external skeleton is invariably present, and gives evidence of the deep internal segmentation of the body. In the simple Crustacea this is very apparent, but in the higher forms it is usually more or less obscured, owing to the fusion of some of the different segments, especially those of the head, as in the crayfish (Fig. 65). The class of the Crustacea is subdivided into two sub- classes (Hntomostracaand Malacostraca), the first containing the fairy-shrimps (Branchipus, Fig. 59) and their allies, the copepods (such as Fig. 60), the barnacles (Fig. 61), and a number of other species. In their organization all are com- paratively simple, usually small, and the appendages show relatively little specialization. The other subclass contains the more highly developed and usually large-sized Crustacea, among which are the shrimps, crayfishes, lobsters, crabs, and a number of other forms. 105. Some simple Crustacea.— While the members of the first subclass are minute and inconspicuous, several species are often remarkably abundant in our small fresh-water pools. Among these is the beautifully colored fairy-shrimp (Branchipus, Fig. 59), with greatly elongated body and leaf-like appendages, whose relatively simple character leads the zoologist to think that they are among the simplest THE ARTHROPODS 111 Crustacea, and in several poimts resemble the ancestral form from which all the modern species have descended. Some nearly related forms are provided with a great fold of the body-wall, which may almost completely conceal the animal from above, or it may be formed like a bivalve clam-shell, within which the entire body may be withdrawn. This Fic. 59.—Fairy-shrimp (Branchipus). 6, brood-pouch; e, é, compound and simple eyes; /, paddle-shaped feet ; h, tu- bular heart ; 2, intestine. latter character is also found in the water-fleas (Daphnia), very much smaller forms, and sometimes occurring in mil- lions on the bottoms of our ponds and marshes. They are readily distinguished from the fairy-shrimp by the short- ness of the body, the small number of appendages, and by their habit of using their antenne as swimming organs, which gives to their locomotion a jerky, awkward character. 106. Cyclops and relatives.— Cyclops (Fig. 60), the repre- sentative of a number of lowly forms belonging to the order of Copepods, is one of the commonest fresh-water Crustacea. The forward segments of the spindle-shaped body are cov- ered by a large shield or carapace, the feet are few in num- ber, and, like its fabled namesake, it bears an eye in the center of the forehead. Nearly related species are also re- markably abundant at the surface of the sea, at times occur- 112 ANIMAL SILUDIES ring in such vast numbers that they impart a reddish tinge to the water over wide areas, and at night are largely re- Fie. 60.—Cyclops. ¢.s., eggs; 2, intestine; ov, reproductive organ. sponsible for its phos- phorescence. Many oth- ers are parasitic in their habits, and scarcely a salt-water fish exists but that at one time or an- other suffers from their attacks. On the other hand, many fresh- and salt-water fishes depend upon the free-swimming forms for food, and hence, from an economic point of view, they are highly important organ- isms. . 107. Barnacles,—The parasitic habit and the lack of locomotion has also produced marvelous changes among the bar- nacles, so great that originally they were placed among the mol- lusks; and as with the parasitic copepods, their true posi- tion was only known after their life-history had been de- termined. In the goose-barnacles* the body, attached by a fleshy stalk to foreign objects, is enclosed by a tough membrane, corresponding to the carapace of other Crus- tacea, In which are embedded five calcareous plates. This * So called because of the belief, which existed for three hundred years prior to the present century, that when mature these animals give birth to geese. THE ARTHROPODS 113 is open along one side, and allows the feather-like feet to project and produce currents in the surrounding water which -brings food within reach. In the acorn-barnacles (Fig. 61) the stalk is absent, and the body, though possess- above. Natural size. ing the same general character as the goose-barnacles, is shorter, and enclosed in a strong palisade consisting of six calcareous plates. The larger number of barnacles attach themselves to the supports of wharves, the hulls of ships, floating tim- bers, the rocks from the shore-line down to considerable depth, and a few species occur on the skin of sharks and whales. On the other hand, there are several species which are parasitic, and in accordance with this mode of life ex- hibit various degrees of degeneration. In the most extreme 114 ANIMAL STUDIES cases (Sacculina) the sac-like body, attached to the abdo- men of crabs, is entirely devoid of appendages and any signs of segmentation. A root-like system of delicate fila- ments extends from the exposed part of the animal into the host and absorbs the necessary nutriment. The mouth and alimentary canal are accordingly absent—in fact, the body contains little but the reproductive organs and a very simple nervous system. 108. Structure.—In the internal organization of these smaller crustaceans many differences may be noted, though they are usually less profound than the external. Ordi- narily the alimentary canal is a straight tube passing through the body, and is provided with a pouch-like stomach, and a more or less clearly defined liver. In all, except the parasitic species, the external mouth-ap- pendages masticate the food, and in a very few of the above-described groups it may be further ground between the horny ridges on the stomach-walls. After this pre- liminary treatment it is subjected to the action of the digestive juices, and when liquefied is absorbed into the body. Here it is circulated by a blood-system of widely different character. In many cases definite arteries and veins are absent. The blood courses through the body in the spaces between the different organs propelled by the beating of the heart, which it is made to traverse. In Cyclops (Fig. 60) even the heart is absent, and the blood is made to circulate by contractions of the intestine. In most of these smaller Crustacea considerable oxygen is ab- sorbed through the body-wall; but in several species, for example, the fairy-shrimp (Fig. 59), special gills are devel- oped on the appendages of the body. 109. Multiplication.— Among the Crustacea thus far con- sidered the males are usually readily recognized owing to their small size. The females also are usually provided with brood-pouches in which the developing eggs are pro- tected. In almost every case the young are born in the THE ARTHROPODS 115 form of minute larve, provided with three pairs of append- ages, a median eye (Fig. 62), and a firm external skeleton or cuticle. This latter prevents the continuous growth of the larve or nauplius, and every few days it is thrown off, and while the new one is forming the body enlarges. Dur- ing this time new appendages are eeraped, so that after each moult the young crusta- cean emerges less like its = former self and more and more ° like its parents. In the bar- nacles, after several moults have taken place, the young become permanently attached by means of their first anten- ne, their thoracic feet change into feathery appendages, and several other changes occur. In some of the parasitic bar- nacles (Sacculina) the larva attaches itself to a crab, throws off its various appendages, and, after other great degenerative changes, enters its host. For a time, therefore, their development is toward greater com- plexity, but the later stages constitute a retrograde meta- morphosis. 110. More complex types.—The larger, more useful, and usually more familiar Crustacea belong to the second divi- sion (subclass Malacostraca). It comprises such animals as the shrimps, crayfish, lobsters, crabs, and a number of other forms which are at once distinguished from the preceding by the constant number of segments composing the body. Of these, five constitute the head, eight the thorax, and seven the abdomen. The head segments are always fused together, and with them one or more thoracic segments unite to form a more or less complete cephalothorax. Also, AKI \ Ne ol (la HHT \ Fic. 62.—Development of a barnacle (Lepas). a, larva; 6, adult. 116 ANIMAL STUDIES some of the head segments give rise to a great fold of the body-wall, the carapace, which extends backward and covers all or a part of the thorax, with which it may firmly unite, as in the crayfish. The appendages are usually highly spe- cialized, and are made to perform a variety of functions. 111. The shrimps——Among the simplest of these are the opossum-shrimps (lig. 63) and their relatives, small trans- Fic. 63.—The opossum-shrimp (Mysis americana). parent creatures often seen swimming in great numbers at the surface of the sea or hiding among the seaweeds along the shore. In general appearance they resemble crayfishes or prawns, but are readily distinguished by the two-branched thoracic feet. This “split-foot” character also occurs among many of the preceding Crustacea, and is generally a badge of low organization, tending to disappear in the more highly organized forms. In this and other respects the shrimps are especially interesting in their relation to the preceding Crustacea, and in the fact that they may closely resemble the ancestors of the modern prawns (Fig. 64), lobsters, crayfishes, and crabs. 112. Crayfishes and lobsters.—The last-mentioned spe- cies and their allies, usually large and familiar forms, con- stitute a group known as the decapods (meaning ten feet), referring to the number of thoracic feet. Among the mem-, bers of this division probably none are more familiar than the crayfishes, which occur in most of the larger rivers and their tributaries throughout the United States and Europe. It is their habit to remain concealed in crevices of rocks THE ARTHROPODS a ker or in the mouths of the burrows which they excavate, and from which they rush upon the small fish, the larve of many animals, and other equally defenseless creatures which constitute their bill of fare. In turn they are eagerly sought by certain birds and four-footed animals, and, especially in France, are extensively used for food by man. Closely related to the crayfishes and dif- fering but little from them structurally are s the lobsters. In this N ‘ country they are con- ) fined to the rocky coasts 3 SS X from New Jersey to , ™Q& Labrador, living upon “= fish, fresh or otherwise, iy various invertebrates, and occasionally sea- weeds. Far more than the crayfish, the lobster is in demand as an arti- cle of food. By the aid Se of nets or various traps Fia. 65.—The crayfish (Astacus). 4 118 ANIMAL STUDIES . millions are caught each year, and to such an extent has their destruction proceeded that in many places they are well-nigh exterminated. At the present time, however, leg- islation, numerous hatcheries, and a careful study of their life habits is doing much to better matters and inciden- tally to put us in possession of many interesting zoological facts along this line, some of which will be mentioned later. Frequently the prawns, especially the larger ones, and a spiny lobster (Palinurus), are mistaken for crayfishes or lobsters, but they differ from them in the absence of the large grasping claws. Along almost.any coast some of these animals are to be found, often beautifully colored and harmonizing with the seaweeds among which they live, or so transparent that their internal organization may be distinctly seen. Farther out at sea other species swim in incredible numbers, feed- ing upon minute organisms, aud in turn fed upon by numer- ous fishes and whales; and, especially on the Pacific coast, shrimp-fishing is an important industry. 113. The hermit-crabs—The last of these long-tailed decapods is the interesting group of the hermit-crabs, which occur in various situations in the sea. In early life they take possession of the empty shell of some snail, and the protected abdomen becomes soft and flabby, while the appendages in this region almost completely disappear. The front part of the body, on the other hand, continually grows in firmness and strength, and is admirably adapted for the continual warfare which these forms wage among themselves. As growth proceeds the necessity arises for a larger shell, and the crab goes “ house-hunting” among the . empty shells along the shore, or it may forcibly extract the snail or other hermit from the home which strikes its fancy. Many of the hermit-crabs enjoy immunity from the attacks of their belligerent relatives by allowing various hydroids to grow upon their homes. Others attach sea- anemones to their shells or to one of their large claws, THE ARTHROPODS 119 which they poke into the face of any intruder. While. the anemones or hydroids are made to do valiant service Fig. 66.—Hermit-crab (Pagurus bernhardus) in snail shell covered with Hydractinia. with their nettle-cells, they also enjoy the advantages of a large food-supply which is attendant upon the free ride. 114. The crabs.—The most highly developed Crustacea are the crabs or short-tailed decapods which abound between tide-marks alongshore, and in diminishing numbers extend to great depths. The cephalothorax is usually relatively wide, often wider than long, and the greatly reduced abdo- men is folded against the under side of the thorax. Corre- lated with the small size of the abdomen, the appendages of that region disappear more or less, but the remaining appendages are similar to those of the crayfish or lobsters. All these different parts, however, are variously modified in each species to fit it for its own peculiar mode of life. In some forms, such as the common cancer-crab (Fig. 67), the legs are comparatively thick-set and possessed of great strength, enabling them to defend themselves against most enemies. On the other hand, there are the spider-crabs with small bodies and relatively long legs, withal weak, and 120 ANIMAL STUDIES . yet so harmonizing with their surroundings that they are as likely to survive as their stronger relatives. In this Fic. 67.—Kelp-crab (Hpialtus productus) in upper part of figure; to the right the edible crab (Cancer productus), and the shore-crab (Pugettia richii). connection it is interesting to note that the giant crab of Japan, the largest crustacean, being upward of twenty feet from tip to tip of the legs, is a spider-crab, constructed on Fic. 68.—The fiddler-crab (Gelasimus). Photograph by Miss Many RATHBUN the same general pattern as our common coast forms. Between these two extremes numberless variations exist, THE ARTHROPODS 121 some for known reasons, but more often not readily under- stood. And not only does the form vary, but the external surface may be sculptured or beset with spines or tubercles which frequently render the animal inconspicuous amid its natural surroundings. Such an effect is heightened by the presence of sponges, hydroids, and various seaweeds which the crab often permits to gather upon its body. 115. Pill-bugs and sandhoppers.—Tinally there remain the groups of the pill- or sow-bugs (Isopods) and the sand-fleas or sandhoppers (Amphipods). In the first of these the body is usually small and compressed, the thorax more or less plainly segmented, and the seven walking (thoracic) legs are similar. In the female each leg bears at its base a thin membranous plate which extends inward and hori- Fic. 69.—Isopod or pill-bug (Porcellio laevis). zontally, thus forming on the under side of the body a brood-pouch (Fig. 69) in which the young develop. As one may readily discover in any of the common species, the abdominal segments are more or less fused, and bear appendages adapted for respiration and, in the aquatic forms, for swimming. 9 122 ANIMAL STUDIES The marine isopods occur in the sand, under rocks, and in the seaweeds; many are parasitic upon fishes; and the ter- restrial forms (Fig. 69) are very common objects under old Fic. 70.—Amphipods or sand-fleas (Gammarus, upper species, and Capreila). logs and in cellars, where they live chiefly on vegetable mat- ter. In the sand-fleas the body is compressed from side to side, and while the thorax shows distinct segments, the legs are frequently dissimilar, and some may bear pincers. One of their most distinctive marks concerns the last three ab- dominal appendages, which are usually modified for leaping. The sand-fleas (Fig. 70) are familiar objects to any one who has collected along the beach and has turned over the: cast-up seaweeds, while numbers of small species ofSen oc- cur among the plants in our fresh-water ponds. Some most curious and highly modified forms, whose general appear- ance is shown in the lower part of Fig. 70, occur among THE ARTHROPODS 123 hydroid colonies, with which their bodies harmonize in form and color. And, lastly, most bizarre creatures, known as “ whale-lice,” attach themselves to the skin of whales, of which each species acts as host for one or more kinds. 116. Internal organization.— Most Crustacea are carnivo- rous, preying upon almost any of the smaller animals within convenient reach; a much smaller number live on vege- table food; and there are many, such as the crayfishes, lob- sters, and numerous crabs, which are also notorious scayen- gers. In these latter forms the food is held in one of the large pincers, torn into shreds by the other, and transferred to the mouth-parts, where, as in all Crustacea, it is soon reduced to a pulp by their rapid movemients. In many species the food is now ready for the digestive process, but not so in the higher forms. If the stomach of any of these, for example, the crabs or crayfishes, be opened, three (Fig. 71, s) large teeth operated by powerful muscles will be noted, and beyond these a strainer consisting of many closely set hairs. In operation this “gastric mill” takes the food passed on from the mouth-parts, and crushes and tears it. until fine enough to pass through the strainer, whereupon it is dissolved by the juices from the liver and is absorbed as it passes down the intestine. The circulatory system is usually highly developed, and consists of a heart, in some species almost as long as the body, though usually shorter (Fig. 71), from which two or more arteries branch to all parts of the body. Here the blood, instead of emptying into definite veins, pours into a series of spaces or sinuses in among the muscles and other organs of the body, through which it makes its way back to the heart. During this return journey it is usually made to traverse definite respiratory organs, either situated upon the legs or, as feathery outgrowths, upon the sides of the body, and generally concealed under the carapace. A por- tion of the blood is also continually sent to the kidneys, which are located either at the base of the second antenne 124 ANIMAL STUDIES . (and known as green glands), as in the crayfishes or crabs, or on the second maxille (shell-glands) in many of the Fic. 71.—Dissection of crayfish. 0, brain; h, heart; i, intestine ; %, kidney ; 2, liver; m, herve-cord ; 7, reproductive organ ; s, stomach, showing two teeth in position, simpler crustaceans. Their method of operation is much like that of the kidneys in the earthworm. 117. Nervous system and special senses.—The nervous sys- tem also shows a decided resemblance to that of the anne- lids. The cerebral ganglia or brain is situated above the alimentary canal in the head, and connects with the ven- trally lying cord by a collar. As in the earthworm, this ventral cord is double, and bears a pair of swellings or gan- glia in each segment. In the crayfish, crabs, and other highly modified forms, where the segments tend to fuse, several of these ganglia may also unite, and except in early life their number cannot be determined. Among the less specialized Crustacea the order of intel- ligence is low, though perhaps it may prove to be higher than is usually supposed when such forms have been more thoroughly studied. The following quotation relating to the lobster applies even more to the higher forms, the crabs : “ Sluggish as it often appears when out of water and when partially exhausted, it is quite a different animal when free to move at will in its natural environment on the sea- THE ARTHROPODS 125 bottom. It is very cautious and cunning, capturing its prey by stealth, and with weapons which it knows how to conceal. Lying hidden in a bunch of seaweed, in a crevice among the rocks, or in its burrow in the mud, it waits until its victim is within reach of its claws, before striking the fatal blow. The senses of sight and hearing are probably far from acute, but it possesses a keen sense of touch and of smell, and probably also a sense of taste.” Although enclosed in a horny and often very thick and strong armor, the sense of touch is very keen in the Crustacea and in arthropods generally. On many of the more exposed portions delicate hairs or pits connected with the nervous system occur in great abundance. Some of these, usually on the antenne, undoubtedly serve in detecting odors, but the remainder are considered to be tactile. In the higher Crustacea, such as the crayfish, lobsters, and crabs, ears are usually found, consisting of sacs lined with similar delicate hairs, and containing sey- eral minute grains of sand, which in many cases make their way through the small external opening. Vibrations com- ing through the water gently shake the grains of sand, causing them to strike against the hairs which communi- cate with the nervous system—a very simple ear, yet suffi- cient for the needs of the animals. The eyes of the Crustacea and arthropods in general are either simple or compound. ‘The simple and frequently single eyes usually consist of a relatively few cells embedded in a quantity of pigment and connected with the nervous system. It is doubtful whether they perceive objects as anything more than highly blurred images, and perhaps they merely recognize the difference between light and darkness. The compound eyes, on the other hand, are remarkably complex structures, often borne on the tops of movable stalks, as in the common crabs and crayfishes. Each consists of an external transparent cornea, divided into numerous minute hexagonal areas corresponding to as 126 ANIMAL STUDIES many internal rods of cells, provided with an abundant nerve-supply. These latter elements may perhaps repre- sent simple eyes grouped together to form the compound one; and it appears possible that each element may form a complete image of an object, as each of our eyes is known todo. On the other hand, many hold that the complete eye forms only one image, a mosaic, each element con- tributing its share. 118. Growth and development.—As we have seen, the simpler Crustacea hatch as minute larve (Fig. 62), and dur- ing their growth to the adult condition are especially sub- ject to the attacks of multitudes of hungry enemies. In the higher forms, such as the crabs, some of these early transformations take place while the young are still within the egg and attached to the parent. Accordingly, the little ones are fairly similar to their parents, and their later his- tory is very well exemplified by the lobster. The eggs of the lobster are most frequently hatched in the summer months, usually July, after they have been carried by the parent for upward of a year. The young, about a third of an inch in length, at once disperse, undergo four or five moults during the next month, then, ceasing their swimming habits, settle to the bottom among the rocks. At this time, twice their original size, they closely resemble their parents, and their further development is largely an increase in size. “The growth of the lobster, and of every arthropod, apparently takes place, from in- fancy to old age, by a series of stages characterized by the growth of a new shell under the old, by the shedding of the outgrown old shell, a sudden increase in size, and the gradual hardening of the shell newly formed. Not only is the external skeleton cast off in the moult and the linings of the masticatory stomach, the esophagus, and intestine, but also the internal skeleton, which consists for the most part of a complicated linkwork of hard tendons to which muscles are attached.” THE ARTHROPODS 127 119. Peripatus (class Onychophora).—It is generally be- lieved that the Crustacea, insects, and spiders, together with their numerous relatives, trace their ancestry back to animals that bore a certain resemblance to the segmented worms. Most of these ancient types have long been extinct, but here and there throughout the earth we occasionally meet with them. Among the most interesting of these are a few widely distributed species belong- ing to the genus Peripatus (Fig. 72), but as they are comparatively rare we shall dis- miss them with a very brief description. They usually dwell in warm countries, un- der rocks and decaying wood, emerging at night to feed on insects, which they ensnare in the slime thrown out from the under surface of the head. Their external form, their excretory system, and. various other organs are worm-like. On the other hand, the appendages are jointed, and one pair has been modified into jaws. The peculiar breathing organs characteristic of the in- sects are also present. Peripatus therefore gives us an interesting link between the worms and insects, and also affords an idea © of the primitive insects from which the modern forms have descended. 120. The centipeds and millipeds (class Myriapoda).— Many of the myriapods—that is, the centipeds and thousand-legged worms —are familiar objects under logs and stones Fig. 72.—Peripatus (Peripatus eiseni). Twice the natural size. throughout the United States. The first of these (Fig. 73) are active, savage creatures, devouring numbers of small animals, which they sting by means of poison-spines on the tips of the first pair of legs. The bite of the larger tropical 128 ANIMAL STUDIES ° species especially causes painful but not fatal wounds in man. On the other hand, the millipeds (Fig. 74) or thousand- legs are cylindrical, slow-going animals, feeding on vegetable Fie. 73.—Centiped. Fie. 74.—Thousand-legs or milliped (/udus). One-half natural size. Natural size. substances without causing any particular damage, except in the case of certain species, which work injury to crops. When disturbed they make little effort to escape, but roll into a coil and emit an offensive-smelling fluid, which ren- ders them unpalatable to their enemies. All present a great resemblance to the segmented worms, as their popular names often testify; but, on the other hand, many points in their organization indicate a closer relationship to the insects. As in the latter, the head is distinct, and bears a pair of antenne, the eyes, and two or three pairs of mouth-parts. The trunk is more worm-like, and consists of a number of similar segments, each bearing THE ARTHROPODS 129 one or two pairs of jointed legs. In their internal organ- ization the character of the various systems closely resem- bles that of the insects, and will be more conveniently described in that connection. Among the myriapods the females are usually larger than the males. Some of the centipeds deposit a little mass of eggs in cavities in the earth and then abandon them, while others wrap their bodies about them and pro- tect them until the young are hatched. The millipeds lay in the same situations, but usually plaster each egg over with a protective layer of mud. After several weeks the young appear, often like their parents in miniature, but in other species quite unlike, and requiring several molts to complete the resemblance. CHAPTER X ARTHROPODS (Continued). CLASS INSECTS 121. Their numbers.—It has been estimated that upward of three hundred thousand named species of insects are known to the zoologist, and that these represent a fifth, or possibly a tenth, of those living throughout the world. Many of these species, as the may-flies and locusts, are represented by millions of individuals, which sometimes travel in such great swarms that they darken the sky. With nearly all of these the struggle for existence is fierce and unrelenting, and it is little wonder that such plastic animals have changed in past times and are now becoming modified in order to adapt themselves to new situations where food is more abundant and the conditions less severe. Owing to such modifications we find some species fitted for flying, others for running and leaping, or for a life underground, and many for a part or all of their lives are aquatic in their habits. 122. External features—The body of an insect—the grasshopper, for example—consists of a number of rings arranged end to end,as we have seen them in the Crustacea and the segmented worms. In the abdomen these are clearly distinct, but in the thorax, and especially the head, they have become so intimately united that their number is a matter of uncertainty. These three regions—head, thorax, and abdomen—are usually clearly defined in most insects, but they are modified in innumerable ways in ac- cordance with the animal’s mode of life. 180 ARTHROPODS. CLASS INSECTS 131 The head usually carries the eyes, a pair of feelers (an- tenne), and three pairs of mouth-parts which may be fash- ioned into a long, slender tube to be used in sucking, and frequently as a piercing organ ; or they may be constructed for cutting and biting. The thorax bears three pairs of legs and usually two pairs of wings; sometimes one pair or none. The appendages of the abdomen are usually small and few in number, or even absent. 123. Internal anatomy.—The restless activity of insects _ is proverbial. Some appear to be incessantly moving about. either on the wing or afoot, and are endowed with com- paratively great strength. Ants and beetles lift many times their own weight. Numerous insects are able to leap many times their own length, and others perform different kinds of work with a vigor and rapidity unsurpassed by any other class of animals. As is to be expected, the muscular sys- tem is well developed, and exhibits a surprising degree of complexity. Over five hundred muscles are required for the various movements of our own bodies, but in some of the insects more than seven times this number exist. The amount of food necessary to supply this relatively immense system with the required nourishment is correspondingly large. Many insects, especially in an immature or larval condition, devour several times their own weight each day. Their food may consist of the juices of animals or plants, which they suck out, or of the firmer tissues, which are bitten or gnawed off. Not only do the mouth-parts stand in direct relation to the habits of the animal and to its food, but, as we have often noticed before, the internal organization is also adapted for the digestion and distribution of the nutritive substances in the most economical way. For this reason we find the alimentary canal differing widely in the various forms of insects. In each case it extends from the mouth to the opposite end of the animal, and ordinarily consists of a number of different parts. In the insect shown in 132 ' ANIMAL STUDIES Fig. 75 the mouth soon leads into the esophagus, which in turn leads into the crop that serves to store up the food until ready for its entry into the stomach; or in some of the ants, bees, and wasps it may contain material which may be disgorged and fed to the young. In many cases the stomach is small and ill-defined as in Fig. 75, and again it may reach enormous dimensions, near- ly filling the body. It may also bear numerous lobes or delicate hair-like processes, which afford a greater sur- face for the absorption of food. Behind the stomach are a number of slender outgrowths that are believed to act as kidneys. Beyond their insertion lies the in- testine, which, like the Z stomach, is the subject of Fie. ,75.—Cockroach, dissected to show ali- many modifications in the ie al. c.—After HatscHEK different kinds of insects. The digested food is rap- idly absorbed through the coats of the stomach and intes- tine and enters a circulatory system which reminds us of what exists in many of the Crustacea. The heart is situ- ated above the digestive tract, and from it arteries pass out to different parts of the body. Here the blood leaves the vessels and is poured directly into the spaces among the viscera, whence it is finally conducted through irregular channels to the heart by its pulsations. In the Crustacea the blood is made to pass through a respiratory system usually in the form of definite gills, and the oxygen with which it is charged is distributed to all ARTHROPODS. CLASS INSECTS 133 parts of the body. In the insects the blood serves almost entirely to carry the food, and the oxygen is conveyed through the animal by a remarkable contrivance found only in the insects, the spiders, and a few related forms. 124. Respiratory system.—If we examine an insect, the grasshopper for example, we find a number of small brown spots on each side of the abdomen, each of which under a magnifying-glass is seen to be perforated by a narrow slit. Carefully opening the body, we find that each slit is in communication with a white, glistening tube that rapidly branches and penetrates to all parts of the animal. When the body is expanded the air rushes into the outer openings, on through the open tubes, and is distributed with great rapidity to all the tissues of the body. In many insects some of these tubes connect with air-sacs which probably serve to buoy up the insect during its. flights through the air. 125. Wingless insects (Aptera).—The simplest of all in- sects are the fishmoths and springtails, relatively small organisms covered with shining scales or hairs. The first of these is occasionally seen running about in houses feed- ing upon cloth and other substances, while the latter live in damp places under stones and logs. They are without wings, but are able to run rapidly and to leap considerable distances. In addition to the ordinary appendages, the abdomen bears what are perhaps rudimentary legs, a fact which, together with their relatively simple structure, strengthens the belief that the insects have descended from centiped-like ancestors. 126. Grasshoppers, crickets, katydids, etc. (Orthoptera).— Rising higher in the scale of insect life, we arrive at the group of the cockroaches, crickets, grasshoppers, locusts, and other related insects. Four wings are present, the first pair thickened and overlapping the second thinner pair. The latter are folded lengthwise like a fan, which is said to have given the name Orthoptera (meaning straight-winged) to 134 ANIMAL STUDIES . this group of insects. These extend all over the world, being particularly abundant in the warmer countries, and their strong biting mouth-parts and voracious appetites render many of them dreaded pests to the farmer. The cockroaches are nocturnal in their habits, racing about at night, devouring victuals in the pantry and gnawing the bindings of books. During the day their flat bodies enable them to secrete themselves in crevices wherever there is sufficient moisture. In the grasshoppers, locusts, katydids, and crickets the body is more cylindrical, and the hind pair of legs are often greatly lengthened for leaping. The crickets and katydids are nocturnal, the former re- maining by day in burrows which they construct in the earth, the latter resting qui- c : : etly in the trees. At night Fie. 76.—The Rocky Mountain locust.— After RitEy, from The Insect World. they feast upon vegetable matter principally, though some species are known to prey on small animals. Those insects we usually term grasshoppers (properly called lo- custs) are specially destructive to vegetation. Some spe- cies are strong fliers, and this, connected with their abil- ity to multiply rapidly, renders them greatly dreaded pests. They have been described as flying in great swarms, form- ing black clouds, even hiding the sun as far as the eye could reach. The noise made by their wings resembled the roar of a torrent, and when they settled upon the earth every vestige of leaf and delicate twig soon disappeared. The eggs of the majority of Orthoptera are laid in the ground, where they frequently remain through the winter. When hatched the young quite closely resemble the parents, and, after a relatively slight metamorphosis, assume the adult form. 127. Dragon-flies, may-flies, white ants, ete.—The dragon-, caddis-, may-flies, ant lions, and the white ants possess four ARTHROPODS. CLASS INSECTS 135 thin and membranous wings incapable of being folded. These possess a network of delicate nervures, giving the general name nerve-winged insects to these various small orders. Of the forms mentioned above, all but the white ants lay their eggs in the water, and the developing larve Fia. 77.—Dragon-fiy (Libellula pulchella). spend their lives in this medium until the time comes for their complete metamorphosis into the adult. The larve of the caddis-flies protect themselves within a tube of stones or sticks bound together with silken threads, which they usually attach to the under side of stones in running water. On the other hand, the young of the dragon- and may-flies, pro- vided with strong jaws, are active in the search of food and very voracious. In time they emerge from their larval skin and the water in which they live, and after a life spent on the wing they deposit their eggs and perish. The adult ant-lion, a type of the related order (Neuroptera), which has somewhat the appearance of a small dragon-fly, lays its eggs in light sandy soil. In this the resulting larve exca- vate funnel-shaped pits, at the bottom of which they lie con- 136 ANIMAL STUDIES cealed. Insects stumbling into their pitfalls are pelted with sand, which the ant-lion throws at them with a jerky motion of the head, and are speedily tumbled down the shifting sides of the funnel to be seized and devoured. While the white ants are not in any way related to the true ants, they possess many similar habits. Associated in great companies, they excavate winding galleries in old logs and stumps, and, further, are most interesting because of the division of labor among the various members. The wingless forms are divided into the workers, which exca- vate, care for the young, and otherwise labor for the good of the others; and into the soldiers, huge-headed forms, Fie. 78.—Ant-lion larva plowing its way through the sand (upper figure) while an- other is commencing the excavation of a funnel-shaped pit similar to one on right. Photograph by A. L. MELANDER and C. T. BRUES. whose strong jaws serve to protect the colony. The re- maining winged forms are the kings and queens. In the spring many of the royalty fly away from home, shed their wings, unite in pairs, and set about to organize a colony. The queen rapidly commences to develop eggs, and in some ARTHROPODS. CLASS INSECTS 137 species her body becomes so enormously distended with these that she loses the power of locomotion and requires to be fed. A single queen has been known to lay eggs at the rate of sixty per minute (eighty thousand a day), and i] Fie. 79.—Termites or white ants. a, queen; 6, winged male; c, worker; d, soldier. those destined to royal rank are so nursed that they advance farther in their development than the remaining sterile and wingless forms. 128. The bugs (Hemiptera).—The large and varied group of the bugs (Hemiptera) includes a number of semi-aquatic species, such as the water-boatmen, often seen rowing themselves along in the ponds by means of a pair of oar- shaped legs, in search of other insects. Somewhat similar at first sight are the back-swimmers, with like rowing habits, but unique in swimming back downward. Both of these bugs frequently float at the surface, and when about to undertake a subaquatic journey they may be seen to imprison a bubble of air to take along. Closely related are the giant water-bugs (Fig. 80), which often fly from pond to pond at night. In such flights they are frequently 10 138 ANIMAL STUDIES . attracted by lights, and have come to be called “electric light bugs.” Among our most dreaded insect pests are the chinch- bugs—small black-and-white insects, but traveling in com- panies aggregating many millions. As they go they feed upon the stems and leaves of grain, which they devour with extraordinary ra- pidity. The squash-bug family is also extensive, and destructive to the young squash and pumpkin plants in the early spring. The lice are small, curiously shaped bugs, which suck the blood of other animals. The plant-lice, also small, suck the juices of plants, and are often exceedingly destructive. This is especially true of the phylloxera, a plant-louse Fic. €0.—Giant water-bug (Se~ which causes annually the loss of phus dilatatus), with eggs at- tached. millions of dollars among the vine- yards of this and other countries. Even more destructive are the scale-insects, curiously mod- ified forms, of which the wingless females may be found on almost any fruit-tree and on the plants in conservatories, their bodies covered with a downy, waxy, or other kind of covering, beneath which they remain and lay their eggs. 129. The flies (Diptera)—The group of the Diptera (meaning two-winged) includes the gnats, mosquitoes, fleas, house-flies, horse-flies (Fig. 81), and a vast company of related forms. Only a single pair of wings is present, the second pair being rudimentary or fashioned into short, thread-like appendages known as balancers, though they probably act as sensory organs and are not directly con- cerned with flight. The mouth-parts are adapted for pier- cing and sucking. The eyes, constructed on the same plan ARTHROPODS. CLASS INSECTS 139 as those of the Crustacea, are comparatively large, and are frequently composed of a great number of simple eyes united together, upward of four thousand forming the eye of the common house-fly. These insects are widely distrib- — uted throughout the world, where they inhabit woods, fields, or houses as best suits their needs. Their food is varied. Some suck the juices of plants, others attack ani- mals, and, while many are trouble- some pests, others, especially in the early stages of their existence, are of great benefit. , & 130. Typical forms.—Owing to Fie. ¢1.—Horse-fly (Therio- the widely different habits and eS structure of the members of this group, we shall briefly consider two examples, the mosquito and the house-fly, which will give us a fairly good idea of the characteristics of all. The eggs of the mosquito are laid in sooty-look- ing masses on the surface of stagnant pools. Within a very short time the young hatch, and, owing to their pecul- lar swimming movements, are known as “wrigglers.” They are then active scavengers, devouring vast quantities of noxious substances and performing a valued service. They frequently rise to the surface, take air into the tracheal system, which opens at the posterior end of the body, and descend again. After an increase in growth and many in- ternal changes resulting in a chrysalis-like stage, they rise to the surface, split the shell, and, using the latter as a float, carefully balance themselves and soon fly away. The house-fly usually lays its eggs in decaying vegetable matter, and the young, maggot-like in form, are active scavengers. They too undergo deep-seated changes during the next few days, finally transforming into the adult. 140 ANIMAL STUDIES Many of this great group of the flies spend their early life in the water or other medium acting as scavengers; but, on vhe other hand, numbers attack domestic and other animals, and throughout their entire lives are an intolerable plague. 131. The beetles (Coleoptera).— Owing to the ease of pres- ervation and their bright colors, the beetles have probably been more widely collected than other insects. Fully ten yo ‘ le 4 ly, % j Fie. 82.—Long-horned borer (Zrgates). Larva (left-hand figure), pupa, and adult insect. thousand distinct species are known in North America alone. They are all readily recognized by the two firm, horny sheaths enclosing the two membranous wings, which alone are organs of flight. The mouth is provided with jaws, which are used in gnawing. Some prey on noxious insects or upon decaying vegetable or animal matter, and are often highly beneficial; but others attack our trees and domestic animals, and work incalculable damage. ARTHROPODS. CLASS INSECTS 141 In some of the stag- or wood-beetles (Fig. 82), which we may select as types, the adults are often found crawling about on or beneath the bark of trees, living on sap or small animals. The eggs laid in these situations develop into grub-like larve, which bore their way through living or dead wood, and in this condition sometimes live four or five years. They then transform into quiescent pupe (Fig. 82), which finally burst their shells and emerge in the adult form. Others, like water-beetles and the whirligig- beetles, whose mazy motions are often seen on the surface of quiet streams, pass the larval period in the water. Under somewhat different conditions we find the potato- bugs, lady-bugs, fire-flies, and their innumerable relatives, but the changes they undergo in becoming adult are essen- tially the same as those described for the other members of the order. 132. The moths and butterflies (Lepidoptera).—The moths and butterflies occur all over the world. In their mature Fie. 83.—Monarch-butterfly (Anosia plexippus). From photograph by A. L. MELAN- DER and C. T. BRUEs. state they are possessed of a grace of form and movement and a brilliancy of coloration that elicit our highest admi- ration. The mouth-parts are developed into a long pro- boscis, which may be unrolled and used to suck the nectar out of flowers, though in many of the adult moths, which never feed, it may remain unused. The wings, four in number, are covered with beautiful overlapping scales that 142 - ANIMAL STUDIES adhere to our fingers when handled. This feature, and the general plan of the body, which is much the same through- out the group, enables us to recognize most of them at once. Fie. 84.—The silver-spot (Argynnis cybele). Photograph by A. L. MELANDER and C. T. BRUES. 133. The ants, bees, wasps, etc. (Hymenoptera).—The ants, bees, and wasps are the best-known insects belonging to this order. They are characterized by four membranous wings, by biting and sucking mouth-parts, and the female is often provided with a sting. All undergo a complete metamorphosis. The eggs may be laid in the bodies of other insects, or they may be placed in marvelously con- structed homes, and be the objects of the greatest atten- tion, the parents or attendants often risking or losing their lives in their defense. The members of this order have long attracted attention, largely on account of their re- markable instinctive powers. They live in highly organized communities, and certain of their characteristics may be illustrated by a study of some of the more familiar forms. CHAPTER XI ARTHROPODS (Continued). CLASS ARACHNIDA 154. General characters.—In this group, comprising the spiders, mites, and a large assemblage of related species, we again meet with great differences in form and structure which fit them for lives under widely different conditions. The three regions of the body, head, thorax, and abdomen, so clearly marked in the insects, are here less plainly de- fined. The head and thorax are usually closely united, and in the mites the boundaries of the abdomen are also indis- tinct. The appendages of the head are two in number, and probably correspond to the antenne and mandibles of other Arthropods. In the scorpions and some species of mites these are furnished with pincers for holding the prey, and in other forms they act as piercing organs. Usually the thorax bears four pairs of legs, a characteristic which readily separates such animals from the insects. The internal organization differs almost as much as does the external. In many species it shows a considerable re- semblance to that of some insects, but in others, especially those of parasitic habits, it departs widely from such a type. Respiration is affected by means of trachex, or lung-books, which consist of sacs containing many blood-filled, leaf-like plates placed together like the leaves of a book. Usually, as in the insects, the young hatch from eggs which are laid, but in the scorpions and some of the mites the young develop within the body and at birth resemble the parent. Almost all of these organisms live either as 143 144 ANIMAL STUDIES parasites or as active predaceous animals upon other animals. For this purpose many are provided with keen senses for detecting their prey and poisonous spines for despatching it. 135. The scorpions,—Owing to the stout investing armor, the strong pincers, and the general form of the body, the scorpions might at first sight be mistaken for near relatives of the crayfish or lobster. A more careful examina- tion will show that the two pairs of pincers prob- ably correspond to the antenne and mandibles of the Crustacea that have become modified for seiz- ing the food. The swol- len part of the animal lying behind the four pairs of legs is a part of the abdomen, of which the slender “tail” consti- tutes the remainder. On the tip of the tail is a curved spine supplied ? with poison glands. Sev- Peaensy baal: | eral pairs of eyes are borne Fig. ramones showing pincer-like mouth- on the dorsal surface of parts and spine-tipped tail. the head and thorax, while on the under side of the animal several slit-like openings lead into as many small cavities containing the lung-books. The scorpions are the inhabitants of warm countries, where they may be found under sticks and stones through- out the day. At night they leave their homes in search of food, which consists chiefly of insects and spiders. These are seized by means of the pincers, and the sting is driven into them with speedily fatal results. It is doubtful if the poison causes death in man, but the sting of some of the 7 . iy cee Le Saad citaiallleaee 3 ‘ Witle XE ate 4 oy { t ARTHROPODS. OGLASS ARACHNIDA 145 larger species, which measure five or six inches in length, may produce certain disorders chiefly affecting the circula- tion. In this country there are upward of thirty species, mest of which are comparatively small. 136. The harvestmen.—The harvestmen or daddy-long- legs are small-bodied, long-legged creatures which resemble in general appearance several of the spiders. They differ from them, however, in the possession of claws correspond- ing to the smaller ones of the scorpion, and in their method of respiration, which is similar to that of insects. During the day they conceal themselves in dark crevices or stride slowly about in shaded places; but at night they emerge into more open districts and capture small insects, from which they suck the juices. 137. The spiders.—The spiders are world-wide in their distribution, and are a highly interesting group, owing chiefly to their peculiar habits. Examining any of our familiar species, it will be seen that the united head and thorax are separated by a narrow stalk from the usually distended abdomen. ‘To the under side of the former are attached four pairs of long legs, a pair of feelers, and the powerful jaws supplied with poison-sacs, while eight shin- ing eyes are borne on the top of the head. On the abdo- men, behind the last pair of legs, are small openings into the lung cavities which contain a number of vascular, leaf- like projections known as lung-books. In some species a well-marked system of trachezx are also present. At the hinder end of the body are four or six little projections, the spinnerets, each of which is perforated with many holes. Through these the secretion. from the glands be- neath is squeezed out in the form of excessively delicate threads, often several hundred in number, which harden on exposure to the air. According to the use for which these are intended, they may remain a tangled mass or become united into one firm thread ; and according to the habits of the animal, they may be used for enclosing their eggs, 146 ANIMAL STUDIES for lining their burrows, or for the construction of webs of the most diverse patterns. | 138. The habits of spiders.— Many species of spiders, some of which are familiar objects in fields and houses, construct sheets of cobweb with a tube at one side in which they may > - — . SS Paat =. < fi etogs “Se = a z 3 wees HS oe os Pe See a te F * het a Fe ~~ 3 ¥ py eae be t . 2, ae eS ae eee te ical de Fie. 86.—A tarantula-spider (Hurypelma lentzii). Natural size. Photograph by A, L. MELANDER and C. T. BRUEs. lie in wait for their prey or through which they may escape in times of danger. In the webs of the common orb- or wheel-weavers several radial lines are first constructed, and upon these the female spider spins a spiral web. Resting in the center of this or at the margin, with her foot on some of the radial threads, she is able to detect the slight- est tremor and at once to rush upon the entangled captive. Some of the bird-spiders and their allies, living in trop- ical America, and attaining a length of two inches, con- struct web-lined burrows in the ground. From these they stalk their prey, which consists of various insects and even ARTHROPODS. CLASS ARACHNIDA 147 small birds. These are almost instantly killed by the poison- fangs, and are then carried to the burrow, where the juices of the body are extracted. The trap-door spiders of the southwestern section of the United States also dig tunnels, which they cover with a closely fitting lid com- posed of earth. Raising this they come out in search of insects, but if sought in turn, they dash into the burrow, closing the door after them, and holding it with such firm- ness that it is rarely forced open. If this should hap- pen, there are sometimes blind passage-ways, also closed with trap-doors, which usually baffle the ae ge Fia. 87.—Trap-door spider and burrow Finally, there are ( Cteniza). among the thousand spe- cies of spiders in the United States a considerable propor- tion which construct no definite web. Many of these may be seen darting about in the sunshine on old logs and fences, often trailing after them a thread which may sup- port them if they fall in their active leaping after in- sects. 139. Breeding habits.—The male spiders are usually much smaller than the females, and some species are only one- fifteenth as long as the female and one one-hundredth of its weight. They are usually more brilliantly colored, more active in their movements, yet rarely spinning their own webs and capturing their own food, preferring to live at the expense of the female. At the breeding season the males of several species make a most interesting display 148 ANIMAL STUDIES of their colors, activity, and gracefulness before the females; and the latter, after watching these exhibitions, are said to select the one who has “shown off” in the most pleasing fashion. The life after this may be stormy, resulting in the death of the male; but ordinarily the results are not so disastrous, and in a little while the female deposits her eggs in cases which she spins. In these the young develop, sometimes wintering here, and emerging in the spring to scamper about in search of food, or to drift through the air to more favorable spots on fluffy masses of cobweb. Few groups of animals are more interesting objects of study and more accessible. Their bites are rarely more serious than those of the mosquito—never fatal; and a careful study of any species, however common, will undoubtedly bring to light many interesting and unknown facts. 140. The mites and ticks.——The mites and ticks are the simplest and among the smallest of the animals belonging to this group. To the at- tentive observer they are rather com- mon objects, with homes in very dif- ferent situations. Some occur on liv- ing and decaying vegetation, in old flour and unrefined sugar, while oth- ers live in fresh water and a few in the sea. Almost all tend toward parasitism. Some of the insects which they pierce and destroy are a pest to man, but on the other hand some are intolerable owing to the diseases they produce. As to other parasitic organisms, degradation of structure is manifest. The respiratory system, so important to the active life of the insects, may be absent, the animal breath- ing through its skin. The circulatory system may be want- ing, the blood occupying spaces among the various organs being swept about by the animal’s movements. And many Fie. 88.—The itch-mite (Sar- coptes scabéi). ARTHROPODS. CLASS ARACHNIDA 149 other peculiarities have arisen which fit them for their different modes of life. 141. The king crab (Limulus).—The king crab may be found crawling over the bottom or plowing its way through the sand and mud in many of the quiet bays from Maine to Florida. The large head and thorax of these animals are united into a horse- shoe-shaped piece, be- hind which lies the triangular abdomen. On the curved front surface of the former are a pair of small me- dian eyes, and farther outward are two larger compound ones. On the ventral side are six pairs of append- ages, instrumental in capturing and tearing the small animals that serve as food, and functioning in con- nection with the ter- minal spine as locomo- Fig. 89.—The king or horseshoe crab (Limulus polyphemus). tor organs. On the ventral surface of the abdomen are numerous plate-like flaps which serve in respiration, and in the imperfect swimming movements in which these animals occasionally indulge. These relatively large and clumsy creatures are the rem- nant of a great number of strange, uncouth animals that in- habited the earth in past ages. Many of them show a close resemblance to the scorpions. The anatomy and develop- ment also show certain points of resemblance, and by some are thought to give us an idea of the ancient type of spider- like animal from which the modern forms have descended. CHAPTER XII ECHINODERMS 142. General characters.—The division of the echino- derms includes the starfishes, sea-urchins, serpent- or brittle- stars, sea-cucumbers, and crinoids or sea-lilies. All are ma- rine forms, and constitute a conspicuous portion of the animals along almost any coast the world over. From these shallow-water situations they extend to the greatest depths of the ocean, and the bodily form possesses a great number of variations, adapting them to lives under such diverse conditions; and yet there is perhaps no group of organisms so clearly defined or exhibiting so close a resem- blance throughout. At one time it was thonght that their radial symmetry was an indication of a close relationship to the celenterates, but more careful study has shown them to be much more highly developed than this latter group, and widely separated from it. A skeleton is almost always present, consisting of a number of calcareous plates embed- ded in the body-wall, and often supporting numbers of pro- tective spines, which fact has given to the group the name Echinoderm, meaning hedgehog skin. 143. External features.—The body of a starfish (Fig. 90) consists of a more or less clearly defined disk, from which the arms, usually five in number, radiate like the spokes of a wheel. At the center of the under side the mouth is located, and from it a deep groove, filied with a mass of tubular feet, extends to the tip of each arm. Innumerable calcareous plates firmly embedded in the body-wall serve 150 ECHINODERMS Pot for the protection of the internal organs, and at the same time admit of considerable movement. In the brittle-stars (Fig. 91) the central disk is much more sharply defined than in the preceding forms, and the long snake-like arms are capable of a very great freedom of movement, enabling the animal to glide over the sea-bottom, or through the crevices of the rocks, at a surprising rate. Tn several species, otherwise closely resembling those Fic. 90.—Starfish (Asterias ocracea), ventral view. One-half natura! size, in Fig. 91, the arms divide repeatedly. These are the so- called basket-stars, living in the deeper waters of the sea, where they, like other brittle-stars, act as scavengers and devour large quantities of decomposing plant or animal remains. At first sight the globular spiny sea-urchins (Fig. 93) would scarcely be recognized as close relatives of the star- fishes. A closer examination, however, shows the mouth to be located on the under side of the body; from it five rows of feet radiate and terminate close to the center of the dorsal side, and the arrangement of the plates forming the 152 ANIMAL STUDIES skeleton indicate that the sea-urchin is comparable to a starfish, with its dorsal surface reduced to insignificant proportions. In the sea-urchins the calcareous plates possess a great regularity, and are so closely interlocked that they prevent .— a 4 1 a a IS ee eee es ee Fig. 91.—Brittle- or serpent-stars (species undetermined). Natural size. a — at any motion of the body-wall. Also, each plate is usually provided with highly developed spines, movable upon a ball- and-socket joint. These spines serve for locomotion, and, in some instances, for conveying food to the mouth. A considerable number of sea-urchins show an irregularity in form which destroys to a corresponding degree the radial symmetry. This is due to various causes, but especially to a compression of the body, which, in the “sand-dollars,” ECHINODERMS 153 has resulted in the production of a thin, cake-like form (Fig. 94). If the spherical body of a sea-urchin were to be stretched in the direction of a line joining the mouth and the center Fie. 92.—Basket-star (Astrophyton). One-half natural size. of the dorsal surface, a form resembling a sea-cucumber (Fig. 95) would be the result. These latter organisms live among crevices of the rocks, embedded in the mud or bur- rowing in the sand at the bottom of the sea. In such situa- tions they are well protected, and a highly developed skele- ton, such as that of the sea-urchin, would not only be of little value, but a positive hindrance to locomotion. The skeleton, therefore, is much reduced, consisting of a few scattered calcareous plates embedded in the fleshy body- wall. Another peculiar feature is almost universally pres- ent, in the form of a circlet of tentacles surrounding the mouth, which serve either for the purpose of respiration, for locomotion, or to convey food to the mouth. A very good imitation of the general plan of a sea-lily © -or crinoid (Fig. 96) could be made by attaching a serpent- ice : 154 ANIMAL STUDIES , star, especially one of the basket-stars, by its dorsal side to astalk. In the crinoids the numerous branches of the arms are compara- tively short, and in the arrangement of the internal organs there are numer- ous differences, but for all that the re- semblance of these ~y organisms tc the other echinoderms is undoubted. 144. Haunts. — The greater num- ber of starfishes occur alongshore, slowly crawling Fie. 93.—Sea-urchin (Strongylocentrotus purpuratus) about sea a: Wii: ’ food, or concealed in dark crevices of the rocks, where they may often be found as the tide goes out, and we know that in gradually lessening nnmbers other species lead similar lives at different levels far down in the dark and gloomy depths. In these same locations the sea- urchins occur, sometimes singly, but more usually associa- ted in great numbers, several species excavating hollows in the rocks, within which they obtain protection. The brit- tle-stars and sea-cucumbers may also be found occasionally in open view, but more often they make their way about in search of food buried in the sand. The crinoids are usual- ly inhabitants of deeper water, where they are found asso- ciated often in great numbers. A few species upon attain- ing the adult condition separate from the stalk, and are able to move about (Fig. 97), but the remaining species never shift their position. ECHINODERMS 155 145. The organs of defense and repair of injury.—As we have seen, the body-wall of the echinoderms is provided with a series of plates, often bearing spines which serve as organs of defense, and to protect the internal organs. The starfishes and sea-urchins also possess numerous modified spines ( pedicellaria) scattered over the surface of the body, which have the form of miniature birds’ beaks, fastened to slender muscular threads. During life these jaws continu- ally open and close, and it is said they clean the body of débris that settles on it; but on the other hand there are several reasons for the belief that they also act as organs of defense. Thus protected, the natural enemies of echino- derms appear to be relatively few, and are confined chiefly to some of the fishes whose teeth are especially modified for crushing them. In this way, and owing to the action of the breakers, they suffer frequent injury, but many species exhibit to a remark- able degree the ability to re- generate lost parts. Experi- ments show that if all the arms of a starfish be separa- ted from the disk the latter will within two or three months renew the arms : and Fie. 94.—Sand-dollar, a flat sea-urchin. : 4 Natural size. a single arm with a part of the disk is able to renew the missing portions in about the same length of time. The brittle-stars, as their name indicates, are usually ex- cessively delicate, often dropping all of their arms upon the slightest provocation; but here again the ability is present to develop the lost portions. Sea-cucumbers resent rough treatment by vigorously contracting their muscular walls and removing from the body almost the entire digestive tract, the respiratory tree, 156 ANIMAL STUDIES ° and a portion of the locomotor system; but some species, at least, renew them again. In some of the starfishes and brittle-stars portions of the body appear to be voluntarily de- tached and to develop into new ‘individuals, and it is thought that such self-mutilation is a normal method of reproduction. 146. Locomotor system.—One of the most characteristic and remarkable features of the echi- noderms is the water-vascular system, a series of vessels con- taining water which serve in the process of locomotion. ‘Their arrangement and mode of opera- tion are, with slight modifica- tions, the same throughout the group, and may be readily un- derstood from their study in Fie. 95.—Sea-cucumber (Cucu- the starfish. maria sp.). Natural size. On the dorsal surface of a starfish, in the angle between two of: the arms, is a round, slightly elevated, calcareous plate, the madreporic body (Fig. 98, m.p.), which under the microscope appears full of holes, like the “rose” of a watering-pot. This connects with a tube that passes to the opposite side of the body, where it enters a canal completely encircling the mouth. On this ring-canal a number of sac-like reservoirs with muscular walls are at- tached, and from it a vessel extends along the under sur- face of each arm from base to tip. Each of these radial water-mains gives off numerous lateral branches that open out into small reservoirs similar to those located on the ring-canal, and a short distance beyond communicate through the wall of the body with one of the numerous- P38 fay" eo ee lesb hes Vad Lo Ue ga°% aes) t Akey Date Raines ECHINODERMS 157 tube-feet, which, as we have seen, are slender tubular or- gans, many in number, filling the grooves on the ventral surface of each arm. ‘This entire system of tubes and reservoirs is full of water, taken in, it is said, through the perforated plate, and, when the starfish wishes to advance, many of the little reservoirs con- tract, forcing water into the cav- ity of the feet, with which they are in communication, thus ex- tending the extremity of the tubes a considerable distance. The terminal sucker of each foot, act- ing upon the same principle as those on the cuttlefish, attaches firmly to some foreign object, whereupon the muscles of the foot contract, drawing the body toward the point of attachment. This latter movement is similar to that of a boatman pulling him- self to land by means of a rope fastened to the shore. When the shortening of the tube-feet has ceased, the sucking disks release their attachment, project them- selves again, and this process is‘ repeated over and over. At all ‘. times some of the feet are con- tracting, and a steady advance of the body is the result. Fig. 96.—Sea-1ily or crinoid. This method of locomotion also obtains in the sea-urchins and cucumbers, but in the serpent-stars the tube-feet have become modified into feel- ers, and the animal moves, often rapidly, by means of twist- ing movements of the arms. The feet have this character also in the crinoids, where the animal is generally without 158 ANIMAL STUDIES the power of locomotion. In some of the sea-cucumbers five equidistant rows of tube-feet extend from one end of the body to the other, and the animal crawls worm-like upon any side that happens to be down; but certain spe- cies living in the sand, where tube - feet will not work satisfactorily, have lost all traces of them, and creep like an earthworm from place to place. In all the sea-cucumbers the feet, situated nearthe mouth, have been curiously re 97.—An anaunbhind eaeend (Antedon). One- modified to form a cr: half natural size. clet of tentacles, which range in form from highly branched to short and thick structures, and in func- tion from respiratory organs and those of touch to con- trivances for scooping up sand and conveying it to the mouth. 147. Food and digestive system.—In the echinoderms the body-wall is comparatively thin (Fig. 98), and encloses a great space, the body-cavity, in which the digestive and re- productive organs are contained. As the former in yarious species is adapted for acting upon very different kinds of food, it shows many modifications; but there area few prin- cipal types which may be briefly considered. In the starfishes the mouth enters almost directly into the cardiac division of the stomach, a capacious, thin-walled sac, much folded and packed away in the disk and bases of the arms (Fig. 98, 0). This in turn leads into the second pyloric portion (a), with thicker walls and dorsal, to the first, from which a short intestine leads to the exterior, near the center of the disk. Another conspicuous and im- portant feature is the so-called liver, consisting of a pair peel ECHINODERMS 159 of closely branched, fluffy glands (7), extending the entire length of each arm and opening into the pyloric stomach. The starfishes are carnivorous and highly voracious, de- vouring large numbers of barnacles and mollusks which hap- pen in their path. If these are small and free they are taken directly into the stomach, but when one of relatively large size is encountered the starfish settles down upon it, and, slowly pushing the cardiac stomach through the mouth, envelops it in the folds. Digestive fluids are now poured over it, and the victim is speedily despatched and in a partly digested condition is gradually absorbed into the body, leay- a 7 Reser IBN 77? Ney essen aw Tied ede? Y r H 2 In 4 e = H J ks LS 7h i= aaa Fie. 98.—Dissection of starfish to show: a, pyloric stomach ; 3, bile-ducts (above), cardiac stomach (below); 0.c., body-cavity; jf, feet; g, spines; z, intestine; 1, liver; m, mouth; m.p., madreporic plate; 7, reservoir; 7.c., ring canal; 7.m., Stomach retractor muscle; 7.v., radial vessel; s, stone canal; ¢, respira- tory tree. ing the shell and other indigestible matters upon the exte- rior. Oysters and clams close their shells when thus attacked, but a steady, continuous pull on the part of the starfish finally opens them, and the stomach is spread over the fleshy portions with speedily fatal results. In the interior of the body the food is transferred to the pyloric stomach, sub- jected to the action of the liver, and when completely dis- solved is borne to all parts of the body. 160 ANIMAL STUDIES The digestive system of the starfishes, with its various subdivisions and appendages, is in some respects more com- plicated than in the other classes. This is most strikingly the case with the serpent-stars, where the entire system for disposing of the minute animals and plants on which it feeds consists c! a simple sac communicating with the exterior by a single opening—the mouth. In the sea-cucumbers large quantities of sand are taken into the body, and the minute organisms and organic mat- ter are digested from it. In the sea-urchins the mouth is provided with five teeth, and the food consists of minute bits of seaweeds, which these snip off. Such diets evidently require a comparatively simple digestive apparatus, for in both it consists throughout its whole extent of a tube of equal caliber, in which the various divisions of esophagus, stomach, and intestine are little, if at all, defined. This is usually somewhat longer than the body, and therefore thrown into several loops; and in the sea-cucumbers its last division is expanded and furnished with more highly mus- cular walls, which aid in respiration. 148. Development.— With but a few exceptions, the eggs of the echinoderms are laid directly in the surrounding water, and for many days the exceedingly minute young are borne great distances in the tidal currents. During this period they show no resemblance to their parents, and only after undergoing remarkable transformations do they assume their permanent features. In every case they have a five-rayed form in early youth, but in several species of starfishes additional arms develop until there may be as many as twenty or thirty. CHAPTER XIII THE CHORDATES 149. General characters.— U p to the present time we have been studying the representatives of a vast assemblage of animals whose skeletons, if they have any at all, are located on the outside of the body. In the corals, the mighty com- pany of arthropods, and the echinoderms, it is external. On the other hand, we shall find that the animals we are now ‘about to consider, the fishes, frogs, lizards, birds, and mam- mals, are in possession of an internal skeleton. In some of the simpler fishes and in a number of more lowly forms (Fig. 99) it is exceedingly simple, and consists merely of a gristle- like rod, the notochord (Fig. 101, nc), extending the length of the body and serving to support the nervous system, which is always dorsal. This is also the type of skeleton found in the young of the remaining higher animals, but as they grow older the notochord gives way to a more highly developed cartilaginous or bony, jointed skeleton, the vertebral column. In the young of all these back-boned or chordate ani- mals, the sides of the throat are invariably perforated to form a number of gill-slits. In the lower forms these per- sist and serve as respiratory organs, but in the higher ani- mals they disappear in the adult. The chordates are thus seen to be distinguished by the possession of a dorsal nery- ous cord supported by an internal skeleton and by the presence of gill-slits, characters which separate them widely from all invertebrates. The chordates may be divided into ten classes, seven of 161 162 ANIMAL STUDIES which (the lancelets, lampreys, fishes, amphibians, reptiles, birds, and mammals) are true vertebrates, while the others embrace several peculiar animals of much simpler organiza- tion. 150. The ascidians——Among the latter are a number of remarkable species belonging to the class of ascidians or sea-squirts (Fig. 99). These are abundantly represented along our coasts, and are readily distinguished by their sac-like bodies, which are often attached at one end to shells or rocks. On the opposite extremity two openings exist, through which a constantstream of water passes, bearing minute organisms serving as food. When disturbed they frequently expel the water from these pores with considerable : force, whence the name Fig. 99.—Ascidian or sea-squirt. se sea-squirt.” While many lead solitary lives, numerous individuals of other species are often closely packed together in a jelly-like pad attached to the rocks, and others not distantly related are fitted to float on the surface of the sea. The young when hatched resemble small tadpoles both in their shape and in the arrangement of some of the more important systems of organs. For a few hours each swims about, then selecting a suitable spot settles down and ad- heres for life. From this point on degeneration ensues. THE CHORDATES 163 The tail disappears, and with it the notochord and the greater part of the nervous system. The sense-organs van- ish, the pharynx becomes remodeled, and numerous other changes occur, leaving the animal in its adult condition, with little in its motionless, sac-like pony: to remind one of a vertebrate. 151. The vertebrates.—Sinee the remainder of this vol- ume is concerned with the vertebrates it will be well at the outset to gain some knowledge of their more important characteristics. One of the most apparent is the presence of a jointed vertebral column, composed of cartilage or bone, which supports the nervous system. ‘To it are also usually attached several pairs of ribs, two pairs of limbs, either fins, legs, or wings, and in front it terminates in a more or less highly developed skull. In the space par- tially enclosed by the ribs, the body-cavity, a digestive sys- tem is located, which consists of the stomach and intestine, together with the attached liver and pancreas. The cir- culatory system is also highly organized, and consists of a muscular heart, arteries, and veins which ramify through- out the body. Breathing, in the aquatic animals, is car- ried on by means of gills, and in the air-breathing forms by means of lungs, which, like the gills, effect the removal of carbonic-acic gas and the absorption of oxygen. The nervous system, consisting of the brain situated in the head and the spinal cord extending through the body above the back-bone, even in the lower vertebrates, is far more cormplex than in the invertebrates. ‘The sense-organs also attain to a high degree of acuteness, and in connec- tion with the highly organized nervous system enable these _ forms to lead far more varied and complex lives than in any of the animals heretofore considered. CHAPTER XIV THE FISHES i 152. General characters.——In a general way the name fish is applied to all vertebrates which spend the whole of their life in the water, which undergo no retrograde metamorphosis, and which do not develop fingers or toes. Of other aquatic chordates or vertebrates the ascidians un- dergo a retrograde metamorphosis, losing the notochord, and with it all semblance of fish-like form. The amphibians, on the other hand, develop jointed limbs with fingers and toes, instead of paired fins with fin rays. A further com- parison of the animals called fishes reveals very great dif- ferences among them—differences of such extent that they cannot be placed in a single class. At least three great groups or classes must be recognized: the Lancelets, the Lampreys, and the True Fishes. The general characters of all these groups will be better understood after the study of some typical fish, that is one possessing as many fish-like features as possible, unmodified by peculiar habits. Such an example is found in the bass, trout, or perch. In either fish the pointed head is united, without any external sign of a neck, to the smooth, spindle-shaped body, which is thus fitted for easy and rapid cleaving of the water when propelled by the waving of the powerful tail (Fig. 100). A keel also has been provided, enabling the fish to steer true to its course. This consists of folds of skin arising along the middle line of the body, supported by numerous bony spines or cartilaginous 164 THE FISHES 165 rays. These are the unpaired fins, as distinguished from the paired ones, which correspond to the limbs of the higher vertebrates. In the bass or perch the latter are of much service in swimming, and are also most important organs in directing the course of the fish upward or downward, or for Fie. 100.—Yellow perch (Perca fiavescens). df, dorsal fins ; pe, pectoral fin ; v, ven- tral fin; @, anal fin; c, caudal fin. aiding the tail in changing the course from side to side; or they may be used to support the animal as it rests upon the bottom in wait for food; and, finally, they may serve to keep the body suspended at a definite point. In addition to an internal skeleton the bass or perch, like the greater number of fishes, is more or less enclosed and protected by an external one, consisting ofa beautifully arranged series of overlapping scales, which afford protec- tion to the underlying organs, and at the same time admit of great freedom of movement. These usually consist of a horny substance, to which lime is sometimes added, and are peculiar modifications of the skin, something like the feathers, nails, and hoofs of higher forms. | 153. The air-bladder.—Naturally a fish’s body is heavier than the water in which it lives, and there are reasons for thinking that the air-bladder (Fig. 106, a.d/.) acts in the 166 ANIMAL STUDIES bass and perch and many other fishes as a float to enable them, without much effort, to remain suspended at a defi- nite level. By compressing this sac, partly by its own mus- cles and partly by those of the body-wall, the bulk of the fish is made less, and it sinks; upon the relaxation of these same muscles the body expands and rises again. Deep-sea fishes, when brought to the surface, where the pressure is relatively slight, are found with their air-bladders so dis- tended that they can not sink again, and the float of surface fishes would be as useless if they were to be carried into the depths below, so that such fishes are compelled to keep within tolerably definite limits of depth. Morphologically considered, the air-bladder is a modified or degenerate lung, and in many fishes it is lost altogether. 154. Respiration —Looking down the throat of the perch, or any other fish, a series of slits (the gill-openings), usually four or five in number, may be seen on each side communi- cating with the exterior. In the sharks these outer open- ings are readily seen, but in the bony fishes they open into a chamber on each side of the head, covered by a bony plate or gill-cover that is open behind. On raising these flaps the gills may be seen composed of great numbers of bright- red filaments attached to the bars between each slit. Dur- ing life the fish may be seen to open its mouth at regular intervals, and, after gulping in a quantity of water, to close it again, contracting the sides of the throat to force it out of the gill-openings and over the gill-filaments to the exte- rior. During this process the blood traversing the excess- ively thin filaments extracts the oxygen from the water and carries it to other parts of the body. With this information, let us return to the study of the three classes of fishes. 155. The lancelet (Branchiostoma).—The lancelet, some- times called amphioxus (Fig. 101), the type of the class Lepfo- cardi, is a little creature, half an inch to four inches long, in the different species, transparent and colorless, living chiefly THE FISHES 167 in sand in warm seas, the ten species being found in as many different regions. A lancelet may be regarded as a vertebrate reduced to its lowest terms. Instead of a jointed back-bone, it has a cartilaginous notochord, running from the head to the tail. A nervous cord lies above it, enclosed in amembranous sheath. No skull is present, and the nerve-cord does not swell intoa brain. There are no eyes and no scales. The mouth is a vertical slit, without jaws. ‘There is no trace of the shoulder-girdle (shoulder- blade and ccliar-bone) or pelvis (hip-bone) from which FF = ne een MM Mihi EE GE AAW WNGS SS Zicss Se a EA 0 EN ee Ow ae a = SSS Fie. 101.—The California lancelet (Branchiostoma californiense). Twice the natural size. g, gills; /, liver; m, mouth; 7, nerve-cord ; mc, notochord. spring the paired fins, which, in true fishes, correspond to arms andlegs. The circulatory system is fish-like, but there is no heart, the blood being driven about by the contraction of the walls of the vessels. Along the edge of the back and tail is a rudimentary fin, made of fin-rays connected by mem- brane. In the character and arrangement of its organs the lancelet is certainly like a fish, but in degree of develop- ment it differs more from the lowest fish than the fish does from a mammal. 156. Lampreys (or Cyclostomes).—The class of lampreys stands next in development (Fig. 102). The notochord gives way anteriorly to a cartilaginous skull, in which is con- tained the brain, of the ordinary fish type. There are eyes, and the heart is developed, and consists of an auricle and a ventricle. As distinguished from the true fish, the lam- preys show no trace whatever of limbs or of the bones which would support them. The lower jaw is wholly want- ing, the mouth being a roundish sucking disk. The fins 168 ANIMAL STUDIES are better developed, but of the same structure as in the lancelet. There is no bony matter in the skeleton, and there are no scales. The nasal opening is single on the top of the front of the head. There are about twenty-five species in this class. Some of them, called lampreys, ascend the streams from the sea Fie. 102.—Lampreys. in the spring for the purpose of spawning. The young undergo a metamorphosis, at first being blind and tooth- less. The adults feed mostly on the blood of fishes, which they suck after scraping a hole in the flesh with their rasp- like teeth. The others, called hag-fishes, live in the sea and bore into the bodies of other fishes, whose muscles they devour. All are slender, smooth, and eel-shaped. From their structure and development we suppose that these eel-like forms existed long ago, probably before the more highly developed sharks and bony fishes made their appearance, but it is difficult to determine whether their simple organization is of such long standing or is not in part the result of semiparasitic habits, or a life spent THE FISHES 169 largely in burrowing. Like the lancelet and other simple chordates, they are of the greatest interest to the zoologist who gains from them some idea of the lowly vertebrate forms that peopled the earth long ago. 157. True fishes.—The third class, Pisces or true fishes, to which the shark as well as the bass and perch belong, has a well-developed skeleton, skull, and brain. The lower jaw is developed, forming a distinct mouth, and there is at least a shoulder-girdle and pelvis; although the fins these should bear are not always developed, the general traits are those we associate with the fish. Of the true fishes, there are again sey- eral strongly marked groups, usually called sub-classes, two of them wholly extinct. Of these, three chiefly interest us. 158. The sharks and skates.—Very early in the life of the sharks (Fig. 103) and skates (Selachii or Hlasmobranchii) Fie. 103.—Soup-fin shark (Galeus zyopterus) from Monterey, Cal. a notochord appears, similar to that in the lancelet and the lampreys. As growth proceeds its sheath becomes broken up into a series of cartilaginous rings, which thus appear like spools strung on a cord. As the fish grows older these “spools” or vertebre grow solid, cutting the notochord into little disks, and great flexibility is thus secured. Cartilagi- nous appendages also grow up and cover the spinal nerve- cord lying above, and give strength to the unpaired fins; the paired fins also have their supports. The shoulder- 12 170 ANIMAL STUDIES girdle is placed behind the skull, leaving room for a distinct neck ; strong bars of cartilage bear the gills; others form jaws to carry the teeth; and a complex skull protects the brain and sense-organs, which are of a relatively high state of devel- opment. Throughout life the skeleton is of cartilage, with perhaps here and there a little bone where greater strength is required. Besides these, there are numerous minor characters which the student will readily find for himself. The sharks and skates or rays live chiefly in the sea, and some reach an enormous size, the largest of all fishes. Some are very ferocious and voracious; others are very mild and weak, and the development of teeth is in direct pro- portion to their voracity of habit. In earlier geologic times there were many more species of them than now exist. 159. The lung-fishes.—The lung-fishes (Dipnoi) are pe- culiar forms living in some of the rivers of Australia and the tropical regions of Africa and South America. In these the air-bladder is developed as a perfect lung. During the wet season they breathe like other fishes by means of gills, but as the rivers dry up they burrow into the wet mud and breathe by means of lungs which are spongy sacs of which the air-bladder of other fishes is a degenerate representative. As we shall see, they resemble in this respect the tadpoles and some adult Amphibia (frogs and salamanders). The paired fins are also peculiar in structure, having an elongate jointed axis, with a fringe of rays along its length, a struc- ture almost as much like that of the limbs of a frog as that of a fish’s fin. In fact the Dipnoi must be regarded as an ancestral type, an ally of the generalized form from which Amphibia and bony fishes have descended. Only four liv- ing species of dipnoans are known, but great numbers of fossil species are found in the rocks. 160. The bony fishes (Teleostei)—The bony fishes, or Teleosts, are distinguished by the bony skeleton, the sym- metrical tail, and by the development of the air-bladder as a more or less completely closed sac, useless in respiration. THE FISHES 7a Often this organ is altogether wanting, as in the common mackerel. About twelve thousand kinds of bony fishes are known. ‘The species swarm in every sea, lake, or river throughout the earth, and some form. or another among them is familiar to every boy inthe land. These fishes are divided into about two hundred families, and these may be arranged in fifteen to twenty orders. As these are mostly distinguished by features of the skeleton, we need not name them here. In Jordan and Evermann’s Fishes of North and Middle America, as well as in various other books, the student of fishes can find the characters by which orders may be distinguished. 161. Sturgeons and garpikes (Ganoidei).— While the great majority of the typical fishes possess a bony skeleton, there are a few quaint types—the ganoid fishes showing ancient traits. In some of these, as the sturgeon, the skeleton is cartilaginous. In the garpike and bowfin it is long, as in the teleosts. Most of this group are now extinct. At present in this country the ganoids are represented by sey- eral species, the best known being the sturgeons. These in- habit the Great Lakes, the Mississippi, and its tributaries; while other species ascend the rivers to spawn. These are the largest fishes found in fresh water, attaining a length of ten or twelve feet, and a weight of five hundred pounds. Their food consists of small plants and animals, which they suck in through their tube-ike mouth. The garpikes live in the larger lakes and rivers throughout the East and Mississippi Valley. Their bodies, from three to ten feet in length, according to the species, are covered with compara- tively large regularly arranged square scales, and the upper jaw is elongated to form a kind of beak, abundantly sup- plied with teeth. They are carnivorous, voracious fishes, working great havoc among the more defenseless food- fishes. Equally destructive is the voracious bowfin (Ama), a fish useless as food, but of very go 8 interest from its relation to extinct forms. 172 ANIMAL STUDIES 162. The catfishes—Among the lowest bony fishes we may place the great group to which almost all fresh-water fishes belong. In this group the four vertebre situated next the head are firmly united, and by means of certain small lever-like bones a connection is formed between the air-blad- der and the ear of the fish, which is sunk deep in the skull. The air-bladder thus becomes a sounding organ in the function of hearing. The family of catfishes possesses this structure, and the student should look for it in the first one he catches. The catfishes are remarkable for the long feel- ers about the mouth, with which they pick their way on the bottom of a pond. There are many kinds the world over. The small ones are known as horned pout or bullhead. In these the dorsal and pectoral fins are armed each with a strong, sharp spine, which is set stiff when the fish is dis- turbed, and makes them very troublesome to handle. The catfishes have no scales. 163. The carp-like fishes.—The still greater carp family includes all the carp, dace, minnows, and chubs. They have the air-bladder joined to the ear, just like the catfish, but they lack the long feelers and the fin spines, while the soft body is covered with scales, and there are no teeth in the mouth. In the throat are a few very large teeth, which the ingenious boy should find. In the sucker family these throat teeth are like the teeth of a comb, and the mouth is fitted for sucking small objects on the river bottom. 164. The eels—In the great order of eels the body is long and slim, scaleless, or nearly so, with no ventral fins. The shoulder-girdle has slipped back from the head. so as to leave a distinct neck, while ordinary fishes have none. Of eels there are very many kinds—some large and fierce, some small as an earthworm; and on2 kind comes into fresh water. 165. Herring and salmon.—In the great order which in- cludes the herring and salmon the vertebre are all alike, the ventral fins far from the head, and the scales smooth to THE FISHES 173 the touch. The herring and shad are examples, as also the - salmon and trout. Some live in the great depths of the sea, even five miles below the surface. These are very soft in body, being under tremendous pressure. They are inky black—for the sea at that depth seems black as ink—and most of them have luminous spots which give them light in the darkness. Some species have the forehead luminous, like the headlight of an engine. Most of these deep-sea fishes are very voracious, for there is nothing for them to feed on save their neighbors. 166. The pike, sticklebacks, etc.—Several small orders stand between these soft-rayed, smooth-scaled fishes and Fie. 104.—The blindfish and its parentage. A, Dismal Swamp fish (Chologaster avitus), the ancestor of (B) Agassiz’s cave fish (Chologaster agassizi) and (C) cave blindfish (Typhlichthys subterraneus). the form, like the perch and bass, which has many spines in the dorsal fin. Among these transitional forms is the pike (Fig. 105) —long, slender, circumspect, and voracious, lying in wait under a lily-pad; the blindfish, which lost its eyes through long living in the streams of the great caves; the stickleback, small, wiry, malicious, and destructive, steal- ing the eggs and nibbling the fins of any larger fish; the sea-horse, often clinging with its tail to floating “LOATHING “AA “IT Aq YdvaSojoyd wo = *(wos7z) oxd oT— SOL “PLT THE FISHES 175 seaweed, the male carrying the eggs about in his pocket until they hatch; the mullet, stupid, blundering, feeding on minute plants, crushing them in a gizzard like that of a hen, but withal having soft flesh, good for the table; the flying-fishes, which sail through the air with great swiftness to escape their enemies. 167. The spiny-rayed fishes—In the group of spiny- rayed fishes the ventral fins are brought forward and joined to the shoulder-girdle. The scales are generally rough to the touch, and the head is usually roughened also. There are many in every sea, ranging in size from the Everglade perch of Florida, an inch long, to the swordfish, which is thirty. These are the most specialized, the most fish-like of all the fishes. Leading families are the perch, in the fresh waters, the common yellow perch, familiar to all boys in the Northeastern States; the darters, which are dwarf perches, beautifully colored and gracefully formed, living on the bottoms of swift rivers; the sunfishes, with broad bodies and shining scales, thriving and nest-building in the quiet eddies; the sea-bass of many kinds, all valued for the table; the mackerel tribe, mostly swimming in great schools from shore to shore. After these come the multi- tude of snappers, grunts, weakfishes, bluefishes, rose-fishes, valued as food. Then follow the gurnards, with bony heads; the sculpins, with heads armed with thorns, the small ones in the rivers most destructive to the eggs of trout; and at the end of the long series a few families in which the spines once developed are lost again, and the fins have only soft and jointed rays. It is a curious law of development that when a structure is once highly special- ized it may lose its usefulness, at which point degeneration at once sets in. Among fishes of this type are the cod- fishes, with spindle-shaped bodies, and the flounders, with flat bodies. The flounders lie on the sand with one side down, and the head is so twisted that the eyes come out to- gether on the side that lies uppermost. This side is col- “LOTHHOAS “MY Aq Ydeisojoyd wo1q—(s70pphow seuodeT) ysyuns poxree-Su0']—"90] ea) A: § vile ‘ . * . winbee NAW Any WAG 5 AY ht Wat ay AN Hay ete _ THE FISHES UTE ored like the bottom—sand colored or brown or black—and the under side is white. When the flounder is first hatched, the eyes are on each side of the head, and the animal swims upright in the water like other fishes. But it soon rests on the bottom ; it turns to one side, and as the body is turned over the lower eye begins to move over to the other side. Finally, we may close the series with the anglers, in which the first dorsal spine is transformed into a sort of fishing- — pole with a bait at the end, which may sometimes serve to lure the little fishes, which are soon swallowed when once in reach of the capacious mouth. 168. Internal anatomy.—A few fishes are vegetarians, but the greater number are carnivorous. Some swallow large quantities of sand of the sea-bottom and absorb from it the small organisms living there. Others are provided with beaks for nipping off corals and tube-dwelling worms. Huge plate-like teeth enable others to crush mollusks, sea-urchins, and crabs, and many are adapted for preying upon other fishes. The latter are often able to escape, owing to the presence of numerous spines, sometimes supplied with poison-glands; or their colors are protective, and a vast number of devices are present which enable them with some degree of surety to escape their enemies and capture food. Usually, without mastication, the food passes into the digestive tract (Fig. 107), which in the main resembles that of the squirrel, but varies considerably according to the nature of the food it is required to absorb. As in other animals, it is usually longer in the vegetable feeders. In most fishes the walls of the canal are pushed out at the junction of the stomach and intestine, to form numerous processes like so many glove-fingers (the pyloric ceca, Fig. 107, py.c.), which probably serve to increase the absorptive surface. The same result is obtained in other ways, chiefly by numerous folds of the lining of the canal. The blood-system is much more complex in the fishes 178 ANIMAL STUDIES than in any of the invertebrates. It also differs in its gen- eral plan from that of most adult vertebrates, owing to the peculiar method of respiration. In almost every case the vessels returning from all parts of the body unite into one vein leading into the heart, which consists of only one auricle and ventricle (Fig. 107). From the heart the blood WU SOMETERTE obi a rn aTTES RTT Wy ‘ ae WS a ait at Ez a nde Fic. 107.—Dissection of a bony fish, the trout (Salmo). a.bl., air-bladder ; an., anal opening ; au., auricle ; gi.st., gills; gul., esophagus ; int., intestine; kd., kidney; Ir., liver ; l.ov., ovary ; opt./., brain ; py.c., pyloric cceca ; sp.c., spinal cord ; spi., spleen ; ey stomach ; 2, ventricle. is forced through the gills, with all their delicate filaments, and now, laden with oxygen and nutritious substances, al- ready absorbed from the coats of the digestive tract, it travels on to all parts of the body, continually unloading its cargo in needy districts and waste matters in the kid- neys before returning once more to the heart. 169. The senses of fishes——The habits of fishes indicate that they know considerable of what is going on in the out- side world, and their well-developed sense-organs show the degree of their sensitiveness. A share of this information comes through the sense of touch, which is distributed all over the surface of the body, chiefly in the more exposed regions sometimes especially provided with fleshy feelers, like those on the chin of the catfish. THE FISHES Gs, The sense of smell appears to be fairly developed, as is that of hearing ; but there is no evidence of a sense of taste. A few fishes chew their food, and may possibly taste it, but there are others that swallow it whole, and in all there are relatively a few nerves going to the tongue or floor of the mouth. The eyes of most fishes are highly developed, and are of the greatest use at all times. Exceptions to the rule are found in certain species which live in caves or in the dark abysses of the ocean. In some of these the eyes have dis- appeared amost completely, and the sense of touch be- comes correspondingly more acute; in other deep-sea forms they have grown to a large size, enabling them to distin- guish objects in the gloom, like the owls and other noc- turnal animals. Embedded in the skin of some of these deep-sea fishes, and certain nocturnal ones, are peculiar spots, composed of a glandular substance, which produces a bright glow like that of the fireflies. These may be located on the head or arranged in patterns over various parts of the body, and may serve to light the fish on its way and enable it to see its food to better advantage, or it may act as a lure to many fishes that become victims to their own curiosity. In those fishes which are active most of the time the eyes are located on the sides of the head, and in those which remain at or near the bottom they are turned toward the top; in every case where they can be used to the best advantage. 170. Breeding habits Among fishes the egg-laying time usually comes with the spring, when the males of several species become more resplendent, and sometimes engage in struggles for their respective mates. In others this cere- mony is performed without show of hostility. Some make nests, while others lay their eggs loosely in the water. In the salmon family, the eggs are laid in cooling waters, ~ as in rivers or brooks. The young make their way down- ward, often entering the sea. When the young in the sea 180 - ANIMAL STUDIES become mature they emigrate in great companies, and make their way hundreds, perhaps thousands, of miles to the rivers in which they spent their youth. Up these streams they rush in crowds, leaping over waterfalls and rapids, and, dashed and battered on the rocks, many, and in some species all, die from injuries or exhaustion after the breed- ing season is passed. The eggs, like those of the chubs, suckers, sunfishes, and catfishes, are usually buried in shal- low holes in the sand, and the males of most fishes keep a faithful watch over the young until they are able to live in safety. In some of the sticklebacks and in several marine species elaborate nests are composed of grass or seaweeds; some of the catfishes carry the eggs until they hatch in their mouths or else in folds of spongy skin on the under side of the body; in the pipefishes and sea-horses a slender sac along the lower surface of the male acts as a brood- pouch, in which the female places the eggs to remain until developed; and some fishes, such as the surf-fishes and a number of the sharks, bring forth their young alive. On the other hand, the young of many of the herrings, salmon, cod, perch, and numerous other fishes are abandoned at their birth, and fall a prey to many animals, even the par- ents often devouring their own eggs. In the former cases, where the young are protected, only a relatively few eggs are produced: where they are aban- doned the female often lays many millions. In every case the number of eggs is in direct relation to the chances the young have of reaching maturity, a few out of each brood surviving to perpetuate the race. 171. Development and past history.—The eggs of the higher bony fishes are usually small (one-tenth to one-third of an inch in diameter), and the young when they hatch are accordingly little; in the sharks the eggs are larger, the size of a hen’s egg or even larger, and the young when born are relatively large and powerful. These differences, however, do not greatly affect the early development, for THE FISHES | 181 in every case the head and then the trunk soon become formed, gills arise, the nervous system appears, which is invariably supported by a skeleton in the form of a gristly rod—the notochord. In the lower forms of fishes this per- sists throughout life; but in the sharks and skates it be- comes replaced in the adult by another and higher type of skeleton, which is much more specialized with the bony fishes. Those who study the fossils on the rocks tell us that the first fishes were very simple, and many believe that their skeleton, like that of the little growing fish, consisted only of a notochord. Many of these old forms died out long ago, while others gradually changed in one way and another to adapt themselves to their surroundings, the con- stant need of adaptation having resulted in the multitude of present-day types. Some of the sharks have probably changed relatively only to a slight extent; others, like the garpike, are much more altered; and the bony fishes are far from their original estate, though their development has been rather toward a greater specialization for aquatic life than an advance upward. ‘The little fish in its growth from the egg thus repeats the history of its ancestral development; but as though in haste to reach the adult condition, it omits many important details. Moreover, the record in the rocks is not complete, and we have many things yet to learn of the ancient fishes and their develop- ment from age to age to the present day. CHAPTER AV THE AMPHIBIANS IN many respects the amphibians—toads, frogs, and sala- manders—resemble the fishes, especially the lung-fishes (Dipnoi). The modern amphibians are essentially fishes in their early life, but in developing legs and otherwise changing their bodily form they become adapted for a life on land under conditions differing from those of the fishes. Judging from this class of facts, we may assume that fish- like ancestors, by the development of the lungs, became fitted for a life on land, and that from these the amphib- ians of our times have been derived. 172. Development.—The eggs of the Amphibia are laid during the spring months in fresh-water streams and ponds. They are globular, about as large as shot, and are embedded in a gelatinous envelope (Fig. 108). They are either de- posited singly or in clumps, or festooned in long strings over the water-weeds. During the next few days development proceeds rapidly under favorable conditions, resulting in an elongated body with simple head and tail. In this condition they are hatched as tadpoles. As yet they are blind and mouthless, but lips and horny jaws soon appear, along with highly developed eyes, ears, and nose. External fluffy gills arise on the sides of the head, and slits form in the walls of the throat, between which gills are attached, and over which folds of skin develop, as in the fishes. A fin-fold like that of the lancelet or lamprey appears on the tail. The brain and spinal cord, extending along the line of the back, are supported by a gristly notochord, and complete and com- 182 THE AMPHIBIANS 183 plex internal organs adapt the animal to a free-swimming existence for days to come. The tadpole is now, to all intents and purposes, a fish— a fact most clearly recognized in its form, method of loco- Fie. 108.—Metamorphosis of the toad.—Partly after GAGE. motion, the arrangement of the gills, and the general plan of the circulatory system. 173. Further growth—In the course of the next few weeks hind limbs develop beneath the skin, through which they finally protrude. In the same manner, fore limbs arise at a later date. In position these organs are like the paired fins of fishes, but they are intended for crawling or leaping on land, and are modified in accordance with this need. As in the higher vertebrates, the hmbs develop as arms and legs, with long fingers and toes, between which are stretched webs of skin, which serve in swimming. 184 ANIMAL STUDIES In the meantime large internal changes are also taking place. The wall of the esophagus has gradually pouched out to form the lungs. They are richly suppled with blood- vessels, closely resembling in their general features the lungs of the lung-fishes. The animal now rises to the sur- face occasionally to gulp in air, and it also continues to breathe by means of gills. At this stage of its existence, therefore, the larva is amphibious (two-living), and we have the interesting example of an animal extracting oxygen from both the water and the air. The diet of the tadpole at this time changes from vegetable to animal substances, and horny teeth give way to the small teeth of the frog, and the digestive system undergoes an entire remodeling to adapt it to its new duties. The young amphibian— whether frog, toad, or salamander—is now a four-legged creature, with well-developed head and tail, with lungs and gills, though the latter are usually fast disappearing, and is rapidly assuming those characters which will fit it for a terrestrial or semiaquatic existence. 174. The salamanders.—The changes which now ensue in such a larva in reaching the adult condition are relatively slight in the lower salamanders. The external gills often persist (Fig. 111), the lungs are also functional, and the changes are largely those of increase of size. In the larger number of species the gills disappear more or less com- pletely (Fig. 109), such species often abandoning the water for homes in damp soil or under stones and logs, returning to it only when the time comes for their eggs to be laid. The limbs are always relatively weak, never supporting the body from the ground, but serving in a clumsy way to push it from place to place. In the aquatic forms the tail con- tinues to serve as a swimming organ. In some species the hind legs become rudimentary, or even entirely lacking. A still further modification occurs in a few burrowing spe- cies, which move by wrigglings of the body, and are with- out either pairs of legs. THE AMPHIBIANS 185 In geological times many of the salamanders were of great size, several feet in length, and some were enclosed in an armor consisting of bony plates. All now living have the skin naked, and with the exception of the giant species of Japan, three feet in length, and a few similar forms in America, the modern representatives are comparatively Fie. 109.—Blunt-nosed salamander (Amblystoma opacum). Photograph by W. H. FISHER. feeble and measure their length by inches. Only a few, on account of their bright colors, are particularly attractive, while the others are usually shunned and considered re- pulsive, chiefly because of their supposed poisonous char- acter, though in reality few animals are more harmless. 175. Tailless forms.—In the frogs and toads the meta- morphosis which the young undergo is almost as profound as that which takes place with the insects. The gills, to- gether with their blood-vessels, disappear completely. The tail, with its muscles, nerve-supply, and skeleton, is ab- sorbed. The cartilaginous notochord gives way to a jointed back-bone. A skull is developed; numerous bones form in the limbs, affording an attachment for the powerful muscles which make the toad, and especially the frog, expert swim- 13 186 ANIMAL STUDIES mers and leavers, and thus equipped they hereafter lead a wholly terrestrial or semiaquatic life. 176. Distribution and common forms.—All the Amphibia are dependent upon moisture. Almost all are hatched and developed in fresh water, and those which leave the water return to it during the breeding season. So we find repre- sentatives of the group all over the world having much the same range as the fresh-water fishes. The great majority of the salamanders are confined to the northern hemisphere, but the toads and frogs are almost universally distributed. Among the salamanders in this country only a relatively few species completely retain their external gills. This is the case with sirens and mud-puppies or water-dogs (Fig. 111), which may occasionally be seen in the clear waters of our lakes and rivers crawling slowly about in search of food, and every now and then rising to the surface to gulp in air. The remainder lose their gills more or less com- pletely, and usually leave the water for damp haunts on land. One of the blunt-nosed salamanders, known as the tiger salamander (Amdlystoma tigrinum), is found in moist localities in most parts of the United States. Besides these are numerous small species, among them the newts (Die- myctylus), ranging widely over the United States, living under logs and stones and feeding upon the small insects and worms inhabiting such situations. In several species of salamanders the lungs disappear with age, and respira- tion is performed solely through the surface of the skin. The tailless amphibians are much more abundant and familiar objects than the salamanders, and from the open- ing of spring until late in the fall they are met with on every hand. With few exceptions the frogs live in or about ponds and marshes, in which they obtain protection in troublous times and from which they derive the store of worms and insects that serve as food. On the other hand, the tree-frogs, as their name indicates, usually abandon the ‘water and repair to moist situations in trees and other vege- THE AMPHIBIANS 187 tation. Their shrill, cricket-like calls are often heard in the summer. The fingers and toes are more or less dilated into disks at their tips, enabling them to climb with con- siderable facility; and they are further adapted to their surroundings on account of their protective colors. The toads undergo their metamorphosis while very small, and approach the water only at the breeding season. During the day they remain concealed in holes and crevices, but at the approach of evening come out in search of food. 177. Means of defense.—The food of the members of this group consists chiefly of small fishes, insect larve, snails, and little crustaceans, which are swallowed whole. On the other hand, many Amphibia prey on each other, while most of them are eagerly sought by birds and fishes. Some, as the toads, stalk their food only during the night-time or depend upon their agility to escape their enemies. Others are colored protectively, the markings. of the skin resem- bling the foliage of the earth upon which they rest, and in some species, as the tree-toads, this color-pattern changes as the animal shifts its position. A few species are most brilliantly colored with red, green, yellow, or combinations of these, in striking contrast to their surroundings. They have apparently few enemies, possibly because of an un- pleasant odor or taste, and it has been suggested that their gorgeous tints are danger-signals, warning their would-be captors from attempting a second time to devour them. At the same time it is well known that the somber-hued toads emit a milky secretion from the warty protuberance of their skin which is intensely bitter, irritating to delicate skin, and poisonous to several animals. 178. Skeleton.— As in all vertebrates, the skeleton of the amphibian first arises as a cartilaginous rod, the notochord, which is afterward replaced by a jointed back-bone, to which the limbs are attached. The back-bone is anteriorly modified into a flat, usually complex, skull. In the sala- manders the number of vertebre is sometimes very large, 188 ANIMAL STUDIES and the body correspondingly long and snake-like; but in other cases parts of the vertebre are reduced in number, and the body is rather short and thick. In the frogs and toads this reduction reaches its culmination, for only nine distinct vertebra are present, the tail vertebra, correspond- ing to those of the salamanders, being represented by a rod-like bone, the urostyle, made of segments grown to- gether. 179. Digestive and other systems.—In its main characters the digestive tract of the amphibian (F ig. 110) resembles (tb "ae, apovd dls “lo kd ovd : ~ US apord. Te oe ; eg ae EEA s LN. 7 or 9 : oa 4 : ii 4 j; : z Pe lr SS duo. Fic. 110.—Dissection of toad (Bufo). an., anal opening; au., auricle ; 5/., bladder; duo., duodenum ; Jng., lung ; dr., liver; pn., pancreas ; ret., rectum ; spi., spleen; st., stomach ; v., ventricle. that of the fishes and the squirrel. The mouth is usually large, and the teeth are very small, as in the frog or sala- mander, or are lacking completely, as in the common toad. In many salamanders the tongue, like that of a fish, is fixed and incapable of movement. In most of the frogs and toads it is attached to the front of the mouth, leaving its hinder portion free, and capable of being thrown over and outward for a considerable distance. In the throat region gill-clefts may persist, but they usually close as the lungs reach their development. The succeeding portions of the canal are comparatively straight in the elongated forms, or THE AMPHIBIANS 189 more or less coiled in the shorter species. In some cases no well-marked stomach exists, but ordinarily the different portions, as they are shown in Fig. 110, are well defined. As noted above, the circulation in the tadpole is the same as in fishes, then lungs arise, and for a time respi- ration is effected both by gills and lungs, and the cir- culation resembles in its essential points that of the lung-fishes. This may continue throughout life, but more frequently the gills and their vessels disappear, and the circulation approaches that of the reptiles. In such forms the heart consists of two auricles and one ventricle. Into the left auricle pours the pure blood from the lungs; into the right the impure blood from the body. To some extent these mix as they are forced into the general cir- culation by the single ventricle. The amount of oxygen carried is therefore smaller than in the higher air-breathers, the amount of energy is proportionately less, and hence it is that all are cold-blooded and of comparatively sluggish habits. In some species of salamanders the lungs may also dis- appear, and breathing is carried on by the skin, as it is to a certain extent in all amphibians. In the frogs and toads lungs are invariably present, and vocal organs are situated at the opening of the windpipe in the throat. These pro- duce the characteristic croaking and shrilling, which in many species are intensified through the agency of one or two large sacs communicating with the mouth-cavity. Although the brain is small in the amphibians, it is more complex in several respects than it is in fishes. The eyes are also usually well developed, but in some of the cave and burrowing salamanders they are concealed beneath the skin, and are rudimentary. The ear varies considerably in complexity in the different species, but in the possession of semicircular canals and labyrinth resem- bles that of the fishes. In the frogs and toads, as one may readily discover, the drum or tympanum is external, ap- 190 ANIMAL STUDIES pearing as a smooth circular area behind the eye. Organs of touch, smell, and taste are likewise developed in varying degree of perfection. 180. Breeding-habits.—While the great majority of am- phibians mate in the spring and deposit their eggs in the water, often to the accompaniments of croakings and pip- ings almost deafening in intensity, several species, for various reasons, have adopted different methods. Some of the salamanders bring forth young alive, and several species of toads and frogs are known in which the young are cared for by the parent until their metamorphosis is complete. In one of the European toads (Alytes) the male winds the strings of eggs about his body until the tadpoles are Fie. 111.—Salamanders. The axolotl (the larva of Am- blystoma tigrinum) and the newt (Diemyctylus to- «© TOsUs). ready to hatch ; and in a few species of tree-toads the eggs are stored in a great pouch on the back of the parent until the early stages of growth are over. In the Surinam toad of South America the eggs are placed by the male on the back of the female, and each sinks into a cavity in the spongy skin. Here they pass through the tadpole stage without the usual attendant dangers, and emerge with the form of the adult. THE AMPHIBIANS bball Sunlight and warmth are apparent necessities for speedy development. Tadpoles kept in captivity where the con- ditions are generally unfavorable may require years to as- sume the adult form. As mentioned above, the tiger sala- mander (Amblystoma tigrinum) occurs in most parts of the United Statesand Mexico. In the East this species dropsits gills in early life as other saiamanders do, and assumes the adult form, but in the cold water of high mountain lakes, in Colorado and neighboring States, it may never become adult, always remaining as in Fig. 111. This peculiar form is locally known as axolotl. In this condition it breeds. It is thus one of the very few examples of animals whose un- developed larve are able to produce their kind. Owing to this trait it was at first considered a distinct species, and many years elapsed before its relationship to the true adult form was discovered. CHAPTER XVI THE REPTILES 181. General characteristics.—In all the reptiles the gen- eral shape of the body, and to some extent the internal plan, is not materially different from that seen among the amphibians. In spite of external resemblance the actual relationship is not very close. It appears to be true that ages ago the ancestors of the modern reptiles were aquatic animals, possibly somewhat similar to some of the sala- manders; but they have become greatly changed, and are now, strictly speaking, land animals. At no time in their development after leaving the egg do we find them living in the water and breathing by gills. Some species, such as the turtles, lead aquatic or semiaquatic lives, but the modifications which fit them for such an existence render them only slightly different from their land-inhabit- ing relatives. The skin bears overlapping scales or horny plates, united edge to edge, as in the turtles, enabling them to withstand the attacks of enemies and the effects of heat and dryness. Indeed, it is when heat is greatest that rep- tiles are most active. In no other class of vertebrates, and very few invertebrates, do normal activities of the body appear to be so directly dependent upon external warmth. In the presence of cold they rapidly grow sluggish, and sink into a dormant state. As in the case of all animals, habits depend upon structure, and accordingly among the reptiles we find many remarkable modifications. enabling them to lead 192 THE REPTILES 193 widely different lives. Nevertheless all are constructed upon much the same plan. 182. The lizards (Sauria)—As in the amphibians, es- pecially the salamanders, the body (Fig. 112) consists of a relatively small head united by a neck to the trunk, Pi nd nt ee ih i Fig. 112.—Common lizard or swift (Sceloporus undulatus). Photograph by W. H. FISHER. which, in turn, passes insensibly into a tail, usually of con- siderable length. Two pairs of limbs are almost always present, and these exhibit the same skeletal. structure as in the amphibians; but in their construction, as in the other divisions of the body, we note a grace of propor- tion and muscular development which enable the lizards to execute their movements with an almost lightning-like rapidity. The mouth is large and slit-like, well armed with ‘teeth, and the eyes and ears are keen. Scales of various 194 ANIMAL STUDIES . forms and sizes, always of definite arrangement, cover the body. The scales are always colored, in some species as brilliantly as the feathers of birds, and usually harmonize with the surroundings of the animal, enabling it to escape the attacks of its many enemies. Altogether the lizards are a very attractive group of animals. As in the salaman- ders, the vertebral column is usually of considerable length, but it too presents a lighter appearance and a greater flexi- bility. Slender ribs are present, and a breast-bone and the girdles which support the limbs. Although more ossified than in the amphibians, the skull still continues to be com- posed here and there of cartilage. The roof also is yet incomplete, but with the firm plates on the surface of the head ample protection is afforded the small brain under- neath. As above mentioned, the limbs are slender and insufficient to support the body, which accordingly rests upon the ground, and by its wrigglings and the pushing of the limbs is borne from place to place. It will be recalled that some of the salamanders living in subterranean haunts and burrowing in the soil have no need of limbs, and the latter have accordingly disappeared. This condition is paralleled by certain species of lizards. The blindworms (which are neither blind nor worms, but true lizards, though snake-like in appearance) are devoid of limbs, as are also the “ glass-snakes.” In some species the hinder pair arise in early life, but they remain smali, and ultimately disap- pear. In almost all lizards the tail is very brittle, breaking at aslight touch. In such case the lost member will grow again after a time. 183. The snakes (Serpentes).—The snakes are character- ized by a cylindrical, generally greatly elongated body, in which the divisions into head, neck, trunk, and tail are not sharply defined. As we have seen, this is also true of cer- tain lizards, but the naturalist finds no difficulty in detecting the differences between them. Another peculiarity of the snakes is in the great freedom of movement of the bones THE REPTILES 195 not concerned with the protection of the brain. In the reptiles the lower jaw does not unite directly with the skull, as in the higher animals, but to an intermediate bone, the quadrate, which is attached to the skull. In the snakes these unions are made by means of elastic liga- ments. ‘The two halves of the lower jaw are also held ae Fie. 113.—Blacksnake (Bascanion constrictor). Photograph by W. H. FisHER. together by a similar band, so that the entire palate and lower jaw are loosely hung together. This enables the snake to distend its mouth and throat to an extraordinary degree, and to swallow frogs and toads but slightly smaller than itself. Where the prey is of relatively small size, the halves of the lower jaw alternate with each other in pulling backward, thus drawing the food down the throat. The food is never masticated. The teeth are usually small and recurved, and serve only to hold the food until it may be swallowed. The latter process is facilitated by the copious secretion of the salivary glands, which become very active at this time. A further character of the snakes is the absence exter- 196 ANIMAL STUDIES nally of any trace of limbs. However, in some of the pythons and boas hind limbs are present in the form of small groups of bones embedded beneath the skin and ter- minating in a claw. ‘There thus appears to be no doubt that the ancestors of the modern snakes were four-footed, lizard-like creatures, which have assumed the present form in response to the necessity of adaptation to new conditions. More than any other order of vertebrates do the snakes deserve the name of creeping things, and yet their method of locomotion enables them to crawl and swim with a ra- pidity equal to that of many of the more highly developed animals. This depends chiefly upon certain peculiarities of the skeleton, which consists merely of a skull, vertebral column, and ribs. The vertebre, usually two or three hun- dred in number, are united together by ball-and-socket joints, and each attaches by similar joints a pair of slender ribs. These in turn are attached to the broad outer plates upon which the body rests, and the whole system is operated by a powerful set of muscles. Upon the contraction of the muscles the ventral plates are made to strike backward upon the ground or other rough surface, which drives the body forward. Also, the ribs may be made to move back- ward and forward, and the snake thus progresses like a centiped or “ thousand-legs.” 184, The turtles (Chelonia)—In many respects the tur- tles are the most highly modified of all the reptiles. The body (Fig. 114) is short and wide and enclosed in a shell or heavy armor, consisting of an upper portion, the carapace, and a flat ventral plate, the plastron. The shape of the carapace varies greatly from a low, flat shield to a highly vaulted dome, remaining cartilaginous throughout life, as in the soft-shelled turtles, or becoming bony and of great strength. The two portions of the shell form a box-like armor through whose openings may be extended the head, tail,and limbs. As a means of protection the turtle may retract these organs within the shell. The head is generally THE KEPTILES 197 thick-set and muscular, and provided with horny jaws entirely destitute of teeth, like those of the birds. The limbs also are usually short and thick and variously shaped, and adapted for aquatic or terrestrial locomotion. The number of vertebre in the body and tail are relatively few, and the thick and heavy body is devoid of the elements of grace and agility of movement characteristic of the other reptiles. On the other hand, the former enjoy a freedom from the attacks of enemies not accorded to animals in general. At first sight the appearance of a turtle does not indi- cate a close relationship to the other reptiles, but a more Fig. 114.—Box-turtle (Terrapene carolina). careful examination, and especially of their development, discloses a remarkable resemblance. The head, tail, and limbs are essentially similar to those of the lizards, but in the trunk region peculiar modifications have taken place. The ribs at first separate, as in other animals, flatten greatly, and unite with a number of bones embedded in the skin, thus forming one great plate overlying the back of the animal. About the circumference of the shield other dermal or skin-bones are added, which increase the area of the carapace, and at the same time still others have 198 ANIMAL STUDIES arisen and united on the ventral surface to form the plas- tron. In this process the shoulder- and hip-girdles which attach the limbs come to be withdrawn into the body, and we have the curious example of an animal enclosed within its back-bone and ribs. This is even more the case with. the box-turtles (Fig. 114), common in the eastern United States, whose ventral plate is hinged so that after the limbs, head, and tail have been withdrawn it may be made to act like a lid to completely enclose the fleshy parts of the body. Scales and horny plates are present, as in other reptiles, the former covering all parts of the body except the cara- pace and plastron, which support the plates. In nearly all species the latter are of considerable size, and in the tor- toise-shell turtles are valuable articles of commerce. They also are sculptured in a fashion characteristic of each spe- cies, and may, like the colors of other animals, render them more like their surroundings, and consequently incon- spicuous. 185. Crocodiles and alligators (Crocodilia),—The alligators (Fig. 115) and crocodiles are much more complex in struc- ture than the lizards, though their general form is much the same. The body is covered with an armor of thick bony shields and horny scales. These, along the median line, are keeled, and extending along the length of the laterally com- pressed tail form an efficient swimming organ and rudder. The mouth is of large size, and is bounteously supplied with large conical teeth, which are set in sockets in the jaw, and not fused with it, as in many of the lizards. The nose and ears may be closed by valves to prevent the entrance of water, and a similar structure blocks its passage beyond the throat while the mouth is open. When large animals, such as hogs or calves, are captured as they come to drink, these devices enable the alligator or crocodile to sink with them to the bottom and hold them until drowned. The limbs, short and powerful, are efficient organs of locomo- THE REPTILES 199 tion on land, and together with the general shape of the body, are also well adapted for swimming. Fre. 115.—Alligator (Alligator mississippiensis). 186. Distribution of the lizards——In a general way the number of reptiles is greatest where the temperature is highest. ‘The tropics therefore abound in species, often of large size, and usually of bright coloration. As one travels northward the numbers rapidly diminish, their size is smaller, and the tints less pronounced. In all probability not less than four thousand known reptiles exist, whose haunts are of the most varied description. In North America the lizards are almost exclusively confined to the southern portions, only a very few species extending up to the fortieth parallel.. Among these the skinks (Humeces) are most widely distributed. The blue- tailed skink is probably the most familiar, a small lizard eight or ten inches in length, dark green with yellowish streaks and a bright-blue tail. On sunny days it may sometimes be seen darting about on the bark of trees in search of insects, upon which it feeds. One of the most familiar lizards in this country is the “ olass-snake,” found burrowing in the drier soil of the southern half of the United States east of the Mississippi. 200 ANIMAL STUDIES Both pairs of limbs are absent, but by wriggling movements of the body this lizard is able to force its way through light soil with considerable rapidity. It is a matter of some difficulty to secure entire specimens, for with other than the gentlest handling the tail severs its connection with the body, as the vertebre in this portion are extremely brittle. This peculiarity, together with its shape, has given it the popular name of glass-snake. Many species of liz- ards will thus detach the tail, a habit which is a means of protection, enabling the animal to scamper away into a place of safety while its enemy is concerning itself with the detached member. Later on a new tail develops, though usually of a less symmetrical form. 187. Horned toads.—The horned toads ( Phrynosoma) are lizards peculiar to the hot, sandy deserts and plains of Fie. 116.—Gila monster (Heloderma suspectum). One-third natural size. Mexico and the western United States. The body is com- paratively broad and flat, almost toad-like, and is covered with scales and spines of brownish and dusky tint, so like dried sticks and cactus spines in form and color as to ren- der them difficult of detection. In captivity they readily THE REPTILES 201 adapt themselves to their new surroundings, become tame, and feast on flies, ants, and other insects, which they cap- ture by the aid of their long tongue. The horned toads are perfectly harmless creatures, but when irritated some- times perform the remarkable feat of spurting a stream of blood from the eye toward the intruding object for a dis- tance of several inches. This has been regarded by some as a zoological fable; but there are many who have watched the horned toad in its natural state and in captivity, and they assure us that it is a fact. In the hot deserts of Arizona and Sonora is another peculiar species of lizard known as the Gila monster (Helo- derma) (Fig. 116), having the distinction of being the only poisonous lizard known. Further protection is afforded by bony tubercles on the head and by scales over the remainder of the body, all of which are colored brown or various shades of yellow, giving the animal a peculiar streaked and blotched appearance. 188. Distribution of the snakes—The snakes are much more common than the lizards. All over the United States one meets with them, especially the garter- or water-snakes. Of less wide distribution are the black-, grass-, and milk- snakes, and a number of less known species, all of which are perfectly harmless and often make interesting pets. Some of them when cornered show considerable temper, flatten the head and hiss violently, and imitate poisonous forms, but venomous snakes are comparatively few in num- ber in northern and eastern United States. In the south- ern portions of the country they become more abundant. Along the streams and in the swamps the copperheads, and especially the water-moccasins, often lie in wait for frogs und fish. Both these species are especially dreaded, as they strike without giving any warning sound, but the name aod bad reputation of the moccasin is often, especially in the South, transferred to perfectly harmless water-snakes. On higher ground are the rattlesnakes (Crotalus), once 14 202 ANIMAL STUDIES . abundant but now in many regions well-nigh exterminated. In these species the tail terminates in a series of horny TR ROS OES AR MR MONEE S78 TD Fie. 117.—Diamond-rattlesnake (Crotalus adamanteus), Photograph by W. H. FISIER. rings that produce a buzzing sound like that of the locust when the tail is rapidly vibrated. 189. Distribution of the turtles.—The turtles are perhaps somewhat less dependent upon warmth than other reptiles, yet they too delight to bask in the sunshine, and soon grow sluggish in its absence. In all our fresh-water streams and ponds they are familiar objects, and several species extend up into Canada. Among the turtles the soft shell, the painted and the snapping turtles have the widest distri- bution, scarcely a good-sized stream or pond from the Gulf of Mexico to Canada, and even farther north, being without one or more representatives. All are carnivorous and vora- cious, and the snapping turtles are especially ferocious, and “for their size are the strongest of reptiles.” In the woods and meadows the wood-tortoise and box-turtles are occa- THE REPTILES 203 sionally met with, and at sea several turtles exist, some of them of great size. Among these is the leather-turtle, found in the warmer waters of the Atlantic, lazily floating at the surface or actively engaged in capturingfood. They attain a length of from six to eight feet, and a weight of over a thousand pounds, and are sometimes captured for food when they come ashore to bury their eggs in the sand. By this same method the loggerheads, the hawkbills, and the common green turtles are also captured in consider- able numbers. These are of smaller size, and the second named is of considerable value, as the horny plates cover- Fig. 118.—Hawkbill turtle (Hretmochelys imbricata). ing the shell furnish the tortoise-shell of commerce. These plates are removed after the animal is killed, by soaking in warm water or by the application of heat. 190. Food and digestive system.—Some reptiles, among which are a number of species of lizards and the box- and green turtles, are vegetarians, but the great majority are 204 ANIMAL STUDIES carnivorous, and usually very voracious. The lizards espe- cially devour large quantities of insects and snails, together with small fishes and frogs. The latter figure largely in the turtle’s bill of fare, and in that of the snakes, which also capture birds and mammals. On the other hand, many of the reptiles prey upon one another; and they are the favorite food of hawks and owls and numerous water-birds, of skunks and weasels and many other animals, which look for them continually. Many of the turtles, owing to their protective armor, and the snakes because of their poison- ous bite or great size and strength, are more or less ex- empt, but this is not true of their eggs and young. The smaller species depend upon keenness of sense, agility, and inconspicuous tints. These latter may undergo changes according to the character of the surroundings, but usually only to a slight extent. The chameleons of the tropics and a similarly colored green lizard on the pine-trees in the Southern States are able to change with great rapidity from green, through various shades, to brown. 191. Respiration and circulation While still in the egg the young lizard develops rudimentary gills, and thus bears ath at Lng “ole hd Fie. 119.—Dissection of lizard (Sceloporus). an., anal opening ; aw., auricle; crd.h., brain ; coec., intestine; kd., kidney ; J./ng., left lung; /r., liver; pn., pancreas ; sp.c., Spinal cord ; sp/., spleen ; s¢., stomach ; v., ventricle of heart. evidence to the fact that its distant ancestors were aquatic ; but before hatching they disappear, and lungs arise, which THE REPTILES 205 remain functional throughout life. Corresponding to the shape of the body, these are usually much elongated and ordinarily paired (Fig. 119, /./mg.). The snakes are peculiar in haying the left lung rudimentary or even lacking com- pletely, while the right one becomes greatly elongated and extends far back into the body. In nearly all the reptiles the amount of oxygen brought into the lungs is relatively large and the activity of the animal is proportionately great. The circulation of reptiles shows an advance be- yond that of the Amphibia. As in the latter, there are two distinct auricles; but the chief difference arises from the fact that the ventricle is more or less divided by a par- tition which to a considerable degree prevents the blood returning from the lungs from mixing with the impure blood as it returns from its journey over the body. In the crocodiles and alligators the partition is complete, and the circulation thus approaches close to that of the higher animals. 192. Hibernation.—Attention has already been called to the fact that reptiles are very susceptible to cold, rapidly growing less active as the temperature lowers. When win- ter comes on they seek protected spots, and either alone or grouped together hibernate. The various activities of the body during this period are at very lowebb. The blood barely circulates, breathing is imperceptible, and stiff and insensible to the world about them they remain until the warmth again stirs them to their former activity. Some of our common turtles must also pass a somewhat similar sleep while embedded far down in the mud during the disappearance of the ponds in summer. At such times no food is taken, but owing to their loss in weight it is probable that a slow consumption of the body supplies the small amount of necessary energy. 193. Nervous system and sense-organs,—At first sight one is struck with the small size of the brain of fishes, Am- phibia, and reptiles. Their intelligence likewise is at low 206 ANIMAL STUDIES ebb. Almost all the movements and operations of the body appear to be carried on by the animal with little apparent thought. Their acts, like most of the animals below them, are said to be instinctive; yet they are sufficiently well done to enable the animal to procure its food, avoid its enemies, | and lead a successful life. As is true of other animals, the ability of the reptile to cope with its surroundings depends to a great extent upon the keenness of one or all of its or- gans of special sense. In the reptiles the sense of sight is perhaps sharpest, but there is considerable variation in this respect. Movable eyelids are present in most lizards, to- gether with a third, known as the nictitating membrane, a thin, transparent fold located at the inner angle of the eye, over which it is drawn with great rapidity. Snakes have no movable eyelids, hence the eye has a peculiar stare. Furthermore, their sense of sight, except in a few tree-dwell- ing species, appears to be defective, the majority depending largely upon the sense of touch. In all the vertebrates a very peculiar organ known as the pineal gland or eye is situated on the roof of the brain. In several lizards its position is indicated by a trans- parent area in one of the plates of the head, and by an opening in the bones of the roof of the skull. In young reptiles, and especially in one of the New Zealand lizards (Hatteria, Fig. 120), its resemblance to an eye is decidedly striking. Lens, retina, pigment, cornea, are all present much as they are in some of the snails, but they finally degenerate more or less as the animal reaches maturity. It is a general belief that it represents the remnant of an organ of sight, a third eye, which looked out through the roof of the skull in some of the ancient vertebrates. With the possible exception of the few species of reptiles which produce sounds, probably to attract their mate, the sense of hearing is not particularly well developed. The senses of smell and taste are also comparatively feeble. The latter sense is locatea in the tongue, which is also popularly THE REPTILES 207 supposed to serve for the purpose of defense, and that it is in some way related to the poison-glands. This, however, is an error. The tongue is used primarily as an organ of Fie. 120.—Tuatera (Sphenoadn punciatus). touch, and in snakes especially it is almost continually darted in and out to determine the character of the animal’s surroundings. 194. Egg-laying.— The eggs of the reptiles are relatively large and enclosed in a shell like a bird’s egg, the shell, however, being leathery rather than made of lime. These are deposited in some warm situation, and generally left to themselves to hatch. Under stones, logs, and leaves, or buried lightly in the soil, are the positions most frequently chosen by the lizards and snakes. The turtles almost invariably select the warm sand at the edge of the water, and after scooping a hole lay numerous spherical eggs, usually at night. The alligators lay upward of a hundred eggs about the size of those of a goose, and guard them jealously until and even after they hatch. On the other hand, the young of many lizards and snakes are born alive, the eggs being hatched within the body. Many reptiles are surprisingly slow in attaining maturity, and live to an age attained by few other animals. It isa well-known fact that turtles live fully a hundred years, and 208 ANIMAL STUDIES probably the same is true of the crocodiles and alligators and some of the larger snakes. Their enemies are few, and death usually results when the natural course is run. Throughout life all reptiles periodically shed their skin, as birds do their feathers and mammals their fur. In the snakes and some of the lizards the skin at the lips loosens, and the animal gradually slips out of its old slough, bright and glossy in the new one which previously developed. In the others the old skin hangs on in tatters, gradually com- ing away as they scamper through the grass. Fie. 121.—Head of the lizard, or ‘“‘ horned toad ” (Phrynosoma blanivillei), showing the translucent pearly scale covering the pineal eye—From nature, by W. S. ATKINSON. CHAPTER XV IT THE BIRDS 195. Characteristics—Birds form one of the most sharp- ly defined classes in the animal kingdom, and the variations among the different species are relatively small. “The ostrich or emu and the raven, for example, which may be said to stand at onposite ends of the series, present no such anatomical differences as may be found between a common lizard and a chameleon, or between a turtle and a tortoise,” and these we know to be relatively slight. In many respects the birds resemble the reptiles, and long ago in the world’s history the relationship was much closer than now, as we know from certain fossil remains in this country and in Europe. One of the earliest of these fossil birds, the Archeopteryx, is a most remarkable com- bination of bird and lizard. Unlke any modern bird, the jaws were provided with many conical reptile-like teeth. The wings were rather small, and the fingers, tipped with claws, were distinct, not grown together, as in modern birds. The tail was as long as the body, and many-jointed, like a lizard’s, each vertebra carrying two long feathers. The bird was about the size of a crow, and it probably could not fly far. Other ancient types have been discovered— principally sea-birds—many of which existed when the Pacific extended over the region now occupied by the Rocky Mountains. These were all of the same generalized type, intermediate between reptile and bird. This fact leads us to the belief that birds descended from reptilian 209 210 ANIMAL STUDIES ancestors, and in becoming more perfectly adapted for an aerial life have developed into our modern forms. In the modern birds the most important peculiarities, those which separate them from all other animals, are correlated with the power of flight. The body is spindle- shaped, for readily cleaving the air. The fore limbs serve as wings. The hind limbs, supporting the weight of the body from the ground, are usually well developed. A series of air-chambers usually exists in powerful fliers. This serves a purpose analogous to that of the air-bladder of a fish, giving buoyancy. But the most characteristic mark of a bird, as above stated, is its feathers, universally present and never found outside the class. Like the scales of lizards, and probably derived from similar structures, they are of different forms, and serve a variety of purposes. The larger ones, with powerful shafts, and forming the tail, act as a rudder. Those of the wings give great expanse with but little increase in weight, and are so constructed that upon the down-stroke they offer great resistance to the air, and push the bird forward, while in the reverse direction the air slips through them readily. In flight these movements of the wing may be too rapid for us to follow, as in the humming-birds, though they are usually much slower, two to five hundred a minute in many power- ful fliers, such as the ducks, and frequently long-continued enough to carry them many hundreds of miles at a single flight. The remaining feathers are soft and downy, giving roundness to the body and enabling it to cleave the air with greater ease, and, being poor conductors of heat, they aid in keeping the body at the high temperature characteristic of birds. In most birds the body is not uniformly clothed in feathers. Naked spaces, usually hidden, intervene between the feather tracts, and on the feet and toes scales exist. 196. Molting.—As we all know, the growth of feathers, unlike that of hair and nails, is limited, and after they have become faded and worn out they are shed, and new ones THE BIRDS 211 arise to take their place. This process of molting is usually accomplished gradually, without diminishing the powers of flight; but in the ducks and.some other birds all the wing- and tail-feathers drop out simultaneously, leaving the bird to escape its enemies by swimming and diving. The molting-process usually takes place in the fall, after the nesting and care for the young is over, and often when the need for a heavy winter coat commences to be felt. Many birds also don what are called courting colors, ruffs, erests, and highly colored patches, in the spring, previous to the mating season, doubtless for the purpose of attract- ing or impressing their mates. In other cases the change appears to be related to the bird’s surroundings. A most beautiful example of this is the ptarmigans—grouse-like birds living far to the north. During winter they are per- fectly white and are almost invisible against the snow; but. in the spring, as the snow disappears, the white feathers gradually fall out and new ones arise. The latter so har- monize “with the lichen-colored stones among which it delights to sit, that a person may walk through a flock of them without seeing a single bird.” There are also numerous birds, chiefly those that go in flocks, which possess what are known as color-calls or recog- nition-marks. These may consist of various conspicuous spots or blotches on different parts of the head or trunk, such as we see in the yellowhammer or meadow-lark ; or one or more feathers of the wings or tail may be strikingly colored, as in many sparrows and warblers. During the time the bird remains at rest these usually are concealed under neighboring feathers, but during flight they are strikingly displayed. It may possibly be true, as many have urged, that these color-signals are for the purpose of enabling various members of the flock to readily follow their leader; but this and many other interesting questions regarding the color of birds and other animals have not yet received final answers. | 212 ANIMAL STUDIES | In very many animals, fishes as well as birds, the tints on the under side of the body are usually relatively light colored, shading gradually into a darker tint above. This is in all probability a protective device, as was recently shown by Mr. A. H. Thayer, an American artist. His ex- periments show that the light from above renders the back less dark, and that the shadow beneath is neutralized by the light color. The bird thus appears uniformly lighted, and this effect, together with streaks and blotches, renders them invisible at surprisingly short distances. 197. Skeleton.—Turning now to the internal organization of birds, we find many points in common with other verte- brates, especially the reptiles, but many interesting modifi- cations are also present that adapt them for flying and for collecting their food. According to the nature of the food, the beak may have a great variety of forms. The skull may be thick and heavy, or thin and fragile, but these are mat- ters of proportion of the various parts possessed by all birds. The neck also is of differing length; but it is in the trunk region that the greatest changes have arisen, as we may see in any of our ordinary birds. For example, the vertebre of this part of the body are more or less fused together into rigid framework, to which are attached the ribs that in turn unite with the breast-bone. In the fliers the latter bears a vertical plate or keel, to which the great muscles that move the wings are attached. The tail con- sists, like that of the old-fashioned birds, of several verte- bree, but these are of small size and fused together into a little knob that supports the tail-feathers. The fore limbs are used for flight, but there are the same bones that exist in the fore limbs of other vertebrates—one for the upper arm, two for the lower, a thumb carrying a few feathers, and known as the bastard wing, and indications of several bones that form the hand. In the hind limb the resem- blance is equally apparent, though its different parts are of relatively large size to support the body. It is interest- THE BIRDS 213 ing to note that the knee has been drawn far up into the body, and that the joint above the foot is in reality the ankle. We thus see that the bird’s skeleton presents the same general plan as that of the lizard, for example; but in order to combine the elements of strength, lightness, and com- pactness essential to successful flight, it has been necessary to remodel it to a considerable degree. 198. Other internal structures.—The lungs of birds con- sist of two dark-red organs buried in the spaces between the ribs along the back. Each communicates with extensive thin-walled air-sacs extending into the space between the bl vz lpi SE he" kd? sia hig GE me Ba yf, f= A a Spor Giz. nd3-Ung, pure Gilt coe. ps LGM py vei NS ai Fig. 122.—Anatomy of a bird. aw., auricle ; cbl. and crb.h., cerebellum and cerebral hemispheres (divisions of the brain); duo., intestine (with portion removed) ; giz., gizzard; kd., kidney; 7.dng., lung; ¢t7., trachea or windpipe ; vent., ven- tricle. various organs, and in many birds of flight extending into the bones of the body, decreasing their specific gravity. “The enormous importance of this feature to creatures destined to inhabit the air will be readily understood when _ we learn that a bird with a specific gravity of 1.30 may have this reduced to only 1.05 by pumping itself full of air.” As we know, air is taken into the body in order that the oxygen it contains may combine with the tissues of the body to liberate the energy necessary for the work of its 214 ANIMAL STUDIES life. The life of birds is at high pressure, hence their need of much oxygen. They habitually breathe deeper breaths than other animals. The air passing into the body tray- erses the entire extent of the lung on its way back to the air-sacs, with the result that large quantities of oxygen are taken into the body. This is distributed by a circulatory system of a more highly developed type than in any of the preceding groups of animals. The ventricles of the heart no longer communicate with each other, and the pure and impure blood never mingle. Furthermore, the beating of the heart is comparatively rapid, rushing the oxygen as fast as it enters the blood to all portions of the body. The result is that everywhere heat is being generated, so neces- sary to life and activity. In the lower animals no special means are employed to — husband the energy thus produced, but in the birds the body is jacketed in a non-conducting coat of feathers which prevents its dissipation. For this and other reasons the birds, summer and winter, maintain an even and relatively high temperature (102°-110°). Like the mammals, birds are warm-blooded animals, full of energy, restlessly active to an extent realized in few of the cold-blooded animals. 199. Digestive system.—This life, at high pressure, de- mands a relatively large amount of food to make good the losses due to oxidation. The appetites of some growing birds is only satiated after a daily meal equal to from one to three times their own weight, and after reaching adult size the amount of daily food required is probably not less than one-sixth their weight. The nature of the food is exceedingly varied, and the digestive tract and certain ac- cessory structures are obviously modified in accordance with it. The beak, always devoid of teeth in the living form, varies extremely according to the work it must per- form. The same is true of the tongue, and many correlated modifications exist in the digestive apparatus. In the birds of prey and the larger seed-eating species, such as the THE BIRDS 215 pigeons and the domestic fowls, the esophagus dilates into a crop, in which the food is stored and softened before being acted upon by the gizzard. The latter is the stomach, pro- vided with muscular walls, especially powerful in the seed- eaters, and with an internal corrugated and horny lining which, in the absence of teeth, serves to crush the food. In some species, such as the domestic fowls and the pigeons, this process is aided by the grinding action of pebbles swallowed along with the food. The remaining portions, with pancreas and liver, vary chiefly in length, and are sufficiently shown in Fig. 122 to require no further descrip- tion. 200. Nesting-habits.—A few birds, such as the ostriches and terns, merely scoop a hollow in the earth, and make no further pretense of constructing a nest. On the other hand, some birds, such as the humming-birds and pewees, build wonderful creations of moss, lichens, and spider-webs, lining it with down, and concealing it so skilfully that they are not often found. Every bird has its own particular ideas as to the fitness of its own nest, and the results are remarkably different, and form an interesting feature in studying the habits of birds. Usually the female takes upon herself the choice of the nest and its construction ; but these duties are in some species shared by the male. After the eggs are laid, the male may also aid in their incubation, or may carry food to the female. In other species—for example, the pigeons and many sea-birds—the parents take turns in sitting upon the eggs and in the sub- sequent care of the young. Finally, there are certain birds, such as the cuckoo and cowbirds, which take advantage of the industry of other species and deposit an egg or two in the nests of the latter. All the work of incubation and care of the young is assumed by the foster-parents, which sometimes neglect their own offspring in their desperate attempts to satisfy the appetites of the rapidly growing and unwelcome guests. 216 ANIMAL STUDIES . The eggs of birds are relatively large, and are often delicately colored. In some species the blotches and streaks of different shades are probably protective, as in the plovers and sandpipers, whose eggs blend perfectly with their sur- roundings, but many other cases exist not subject to such an explanation. The young require a high degree of heat for their devel- opment, and this is usually supplied by the parent. Ina very general way the length of sitting, or incubation, is proportional to the size of the egg, being from eleven to fourteen days in the smaller species, to seven or eight weeks in the ostriches. Before hatching, a sharp spine develops on the beak, and with this the young bird breaks its way through the shell. Among the quails, pheasants, plovers, and many other species, the young are born with a covering of feathers, wide-open eyes, and the ability to follow their parents or to make their own way in the world. Such nestlings are said to be precocial, in distinction to the altrical young of the more highly specialized species, such as the sparrows, woodpeckers, doves, birds of prey, and their allies, which are born helpless and depend for a considerable time on the parents for support. Some of the owls, crows, woodpeckers, sparrows, quails, etc., remain in the same localities where they are bred. They are resident birds. Most kinds of birds, at the ap- proach of winter, migrate toward the southern warmer climes, some species traveling in great flocks, by day or night, and often at immense heights. In some cases this movement appears to be directly related to the food-supply ; but there are many apparent exceptions to such a theory, and it is possible that many birds migrate for other reasons. Certain species migrate thousands of miles, along fairly definite routes, the young, sometimes at least, guided by the parents, which in turn appear to remember certain landmarks observed the year before. Sea-birds, in their journeys northward or southward, keep alongshore, occa- THE BIRDS Al sionally veering in to. get their bearings or to rest, espe- cially in the presence of fogs. 201. Classification.—Most zoologists make two primary divisions of the living types of birds—those like the ostrich with flat breast-bones, and the other the ordinary birds, in which the breast-bone has a strong keel for the attachment of the powerful muscles used in flight. This distinction is not of high importance, but we may use it as a convenience in the description of a few typical forms belonging to sev- eral orders into which these two divisions are subdivided. 202. The ostriches, etc. (Ratite).—From specimens in- troduced or from pictures we are doubtless familiar with the ostriches and with some of their relatives. The African ostrich (Struthio camelus, Fig. 123) is the largest of living birds, attaining a height of over seven feet, and is further characterized by a naked head and neck, two toes, and fluffy, plume-like feathers over parts of the body. They are natives of the plains and deserts of Africa, where they travel in companies, several hens accompanying the male. When alarmed, they usually escape by running with a swift- ness greater than that of the horse, but if cornered they defend themselves with great vigor by means of their powerful legs and beaks. Their food consists of insects, leaves, and grass, to which is added sand and stones for grinding the food, as in the domestic fowl. The American ostriches or rheas, are smaller ostrich-like birds, living on the plains of South America. Their habits are essentially the same as those of the African species. 203. The loons, grebes, and auks (Pygopodes).—The birds in this and some of the following orders are aquatic in their habits. All have broad, boat-like bodies, which, with the thick covering of oily feathers, enables them to float without effort. The legs are usually placed far back on the body—a most favorable place for swimming, but it ren- ders such birds extremely awkward on land. The grebes are preeminently water-birds. The pied-billed grebe or dab- 15 wa . = Fie. 123.—African or two-toed ostrich (Sfruthio camelus). Photograph by W1L- LIAM GRAHAM. THE BIRDS 219 chick (Podilymbus podiceps), for example, found abun- dantly on the larger lakes and streams throughout the United States, captures its food, sleeps, and breeds with- out leaving the water. The loons living in the same situa- tions as the dabchick are also remarkable swimmers and divers. Of the three species found in this country, the common loon or diver (Gavia imber) attains a length of three feet, and is otherwise distinguished by its black plumage, mottled and barred with white, which is also the color of the under parts. The auks, murres, and puffins are marine, and, like their inland relatives, are expert swimmers and divers, strong fliers, and spend much of their time on the open sea. During the breeding-season they assemble in vast numbers on rugged cliffs along the shore, and lay their eggs on the bare rock or in rudely constructed nests. 204. The gulls, terns, petrels, and albatrosses (Longi- pennes).—The birds belonging to this group are among tne most abundant along the seacoast, and several species make their way inland, where they often breed. All are char- acterized by long, pointed wings and pigeon or swallow-like bodies, which are carried horizontally as the bird waddles along when. ashore. Many are excellent swimmers and powerful fliers, especially the petrels and albatrosses, which sometimes travel hundreds of miles at a single flight. The gulls are abundantly represented along our coasts, where they frequently associate in companies, usually rest- ing lightly on the surface of the water, or wheeling lazily through the air on the lookout for food. The terns are of lighter build than the gulls and are more coastwise in their habits, and are further distinguished by plunging like a kingfisher for the fishes on which they live. Both the gulls and terns breed in colonies, every available spot over acres of territory being occupied by their nests, which are usually built of grass and weeds placed on the ground. The petrels and albatrosses are at home on the high 220 ANIMAL STUDIES . seas, rarely coming ashore except at the breeding-season. Some species of the former are abundant off our shores; especially the stormy petrel (Procellaria pelagica) or Mother Carey’s chickens ( Oceunttes oceanicus), which are often seen winging their tireless flight in the wake of ocean vessels. Among the dozen or so albatrosses few reach our shores. The wandering albatross (Diomedea exulans), celebrated in story and as the largest sea-bird (fourteen feet between the tips of its outstretched wings), is an inhabitant of the southern hemisphere, and only rarely extends its journeys to more northern regions. 205. Cormorants and pelicans (Steganopodes).—The cor- morants and pelicans are comparatively large water-birds Fie. 124.—White pelicans (P. erythrorhynchus) and whooping-crane (Grus ameri- cana). Photograph by W. K. FIsHER. usually abundant along the seashore and in many sections of the United States. The cormorants or shags are glossy THE BIRDS 221 black in color, with hooked bills, long necks, and short wings, which give them a duck-like flight. The much larger pelicans (Fig. 124) are at once distinguished by long bills, from which is suspended a capacious membranous sac. All these birds are sociable in their habits, breeding, roost- ing, and fishing in great flocks. Their food consists of fishes, which the shags pursue under water and capture in their hooked beaks; while the pelicans, diving from a con- siderable height or swimming rapidly on the surface, use their pouches as dip-nets. The nests, usually built of sea- weed or of sticks, are placed on rocky cliffs or on the ground in less elevated places. 206. Ducks, geese, and swans (Lamellirostres).—The birds of this order, with their broad, flat, serrated beaks, short legs, and webbed feet, are well known, for in a wild or domesticated state they extend all over the earth. All are excellent swimmers, many dive remarkably well, and are strong on the wing. While a considerable number breed within the United States, their nesting-grounds are gener- ally farther north, and in the early spring it is not unusual to see them migrating in flocks from their warmer winter homes. Among the ducks, the mergansers, mallards (from which our domestic species have been derived), the teals, and the beautiful wood-duck remain with us the year round, dwelling on quiet streams and shallow ponds, living on fish, Crustacea, and seeds. In the more open waters of the larger lakes and along the seacoast we find the can- vasback, the scaup-ducks, and the eiders which supply the famous down of commerce. Of the few species of geese which inhabit the United States, the Canada goose (Granta canadensis) is perhaps the most familiar. During their migrations to the nesting sites they fly in V-shaped flocks, their “honks” announcing the opening of spring. The brant (B. dernicia) is also common in the eastern part of the country, where it, like its relations, lives on vegetable substances entirely. ‘The swans are familiar in their semi- 222 ANIMAL STUDIES domesticated state, but the two beautiful wild swans found in this country are rarely seen. 207. The herons and bitterns (Herodiones).—The herons and bitterns are also aquatic in their habits, but, unlike the swimming-birds, they seek their food by wading. Adapting them for such an existence, the legs and neck are usually very long, and the bill, longer than the head, is sharp and slender. Among the relatively few species in the United States, the great blue heron (Ardea herodias) is widely dis- tributed, and may often be seen standing motionless in some shallow stream on the lookout for fish, or it may wander away into the meadows and uplands to vary its diet with frogs and small mammals. Lyven more familiar is the little green heron or poke (Ardea virescens), which also is seen widely over the country. The night-herons, as their name indicates, stalk their prey by night, and during the day roost in companies—a characteristic common to most herons. The bitterns or stake-drivers are at home in reedy swamps, where they live singly or in pairs, and throughout the night, during times of migration, utter a booming noise resembling the driving of a stake into boggy ground. As a rule, the herons breed as they roost—in companies—build- ing bulky platforms, usually in trees. The bitterns, on the other hand, secrete their nests on the ground in the rushes of their marshy home. 208. Cranes, rails, and coots (Paludicole).—In their ex- ternal form the cranes and rails resemble the herons, but in their internal orgrnization they differ considerably. They likewise inhabit marshy lands, but usually avoid wading, picking up the frogs, fish, and insects or plants along the shore or from the surface of the water. The cranes are comparatively rare in this country, yet one may occasion- aily meet with the whooping-cranes (Grus americana) and sand-hill cranes (Grus mexicana), especially in the South and West. They are said to mate for life, and annually repair to the same breeding-grounds, where they build their THE BIRDS 223 nests of grass and weeds on the ground in marshy places. The rails are more abundant, though rarely seen on ac- count of their habit of skulking through the swamp grasses. Only rarely do they take to the wing, and then fly but a short distance, with their legs dangling awk- wardly. Closely related to them are the coots or mud-hens (Fulica americana), which may be distinguished, however, by their slaty color, white bills, and lobed webs on the toes, and consequent ability to swim. All over the United States they may be seen resting on the shores of lakes or quiet streams, or swimming on the surface gathering food. The nest consists of a mass of floating reeds, which the young abandon almost as soon as hatched. 209. The snipes, sandpipers, and plovers (Limicole).—The snipes, sandpipers, and plovers are usually small birds, widely scattered throughout the country wherever there are sandy shores and marshes. In most species the legs are long, and in connection with the slender, sensitive bill fit the bird for picking up small animals in shallow water or probing for them deep in the mud. During the greater part of the year they travel in flocks, but at the nesting- season disperse in pairs and build their nests in shal- low depressions in the earth. The eggs are usually streaked and spotted, in harmony with their surroundings, as are the young, which leave the nest almost as soon as hatched. Fully fifty species of these shore-birds live within the confines of the United States. Among these the woodcock (Philohela minor) and snipe (Gallinago delicata) are abun- dant in many places inland, where they probe the moist soil for food, and in turn are eagerly sought by the sportsman. Even more familiar are the sandpipers and plovers, which are especially common along the seacoast, and are also abundantly represented by several species far inshore. Among the latter are the well-known spotted sandpiper or “tip-up ” (Actitis macularia) and the killdeer plover (7g- 224 ANIMAL STUDIES alitis vocifera), which inhabit the shores of lakes and streams throughout the country. 210. Quail, pheasants, grouse, and turkeys (Galline).—The quail, grouse, and our domestic fowls are all essentially : ! | Fig. 125.—California quail (Lophortyx californicus). Two-thirds natural size. ground-birds, and their structure well adapts them to such a life. The body is thick-set, the head small, and the beak heavy for picking open and crushing the seeds and berries THE BIRDS 229 upon which they live. The legs and feet are stout, and fitted for scratching or for running through grass and underbrush. Frotective colors also prevent detection, but if close pressed they rise into the air with a rapid whirring of their stubby wings, and after a short flight settle to the ground again. During the breeding-season the male usu- ally mates with a number of hens, which build rough nests in hollows in the ground, where they lay numerous eggs. The young are precocial. The quail or bob-white (Colinus virginianus) and the ruffed grouse (Donasa umbellus) occur throughout the Eastern States. Over the same area the wild turkey (Meleagris gallopavo) once extended, but is now almost extinct. The prairies of the middle West support the prairie-hen (Tympanuchus americanus), and the valleys and mountains of the far West are the home of several species of quails, some of which are beautifully crested. 211. Pigeons and doves (Columbe).—The pigeons and doves belong to a small yet well-defined order, with upward of a dozen representatives in the United States. They are of medium size, with small head, short neck and legs, and among other distinguishing characters frequently possess a swollen, fleshy pad in which the nostrils are placed. In former years the passenger-pigeon (Hctopistes migratorius), inhabiting eastern North America, was probably the most common species in this country. Their flocks contained thousands, at times millions, of individuals, which often traveled hundreds of miles a day in search of food, to return at night to definite roosts—a trait which enabled the hunter to practically exterminate them. At present the mourning- or turtle-dove (Zenaidura macroura) is the most familiar and wide-spread of the wild forms. The domestic pigeons are all descendants of the common rock-dove (Columba livia) of Europe, the numerous varieties such as the tum- blers, fantails, pouters, etc., being the product of man’s careful selection. In the construction of the nest, usually 226 ANIMAL STUDIES a rude platform of twigs, and in the care of the young both parents have a share. The young at hatching are blind, naked, and perfectly helpless, and are fed masticated food from the crops of the parents until able to subsist on fruits and seeds. 212. Eagles, hawks, owls, etc. (Raptores)—The birds of prey, all of which belong to this order, are carnivorous, often of large size and great strength, and are widely dis- tributed throughout this country. The vultures live on carrion, some of the small hawks and owls on insects, while the majority capture small birds and mammals by the aid of powerful talons. In every case the beak is hooked, and the perfection of the organs of sight and hearing is unequaled by any other animal, man included. They live in pairs, and in many species mate for life. As a rule, the female incubates the eggs, and the male assists in collecting food. Among the vultures, the turkey-buzzard (Cathartes aura) is most abundant throughout the United States, especially in the warmer portions, where it plays an important part as a scavenger. Of the several species of hawks, the white- rumped marsh-hawk (Circus hudsonius), the red-tailed hawk (Luteo borealis), the red-shouldered hawk (Buteo lineatus), and above all the bold though diminutive spar- row-hawk (Falco sparverius) are the most abundant and familiar. In the more unsettled regions live the golden eagle (Aquila chrysaetus) and bald eagle (Haliaetus leuco- cephalus). The owls are nocturnal, and not so often seen as the other birds of prey, yet the handsome and fierce barn or monkey-faced owl (Strix pratincola), and the larger species, such as the great gray owl (Scotiaptex cinereua), and the beautiful snowy owl (Vyctea nyctea), are more or less common, and occasionally seen. Much more abundant is the little screech-owl (Megascops asio), and in the West- ern States the burrowing-owl (Speotyto cunicularta), which lives in the burrows of the ground-squirrels and prairie- 227 THE BIRDS g Zi cp. \ We Fiercest and strongest of the tribe is the great ‘\ a \\ AS \y ae horned owl (Bubo virginianus). dogs. A Fie. 126.—Golden eagle (Aquila chrysaetus). 213. Cuckoos and kingfishers (Coccyges).—Omitting the order of parrots (Psittact), whose sole representative in this country is the almost exterminated Carolina parrakeet 228 ANIMAL STUDIES (Conurus carolinensis), we next arrive at the cuckoos and kingfishers, which differ widely in their habits. The black- or yellow-billed cuckoos or rain-crows are shy, retiring birds, with drab plumage, and though seldom seen are often fairly abundant, and are of much service in destroying insects. Unlike their shiftless European relatives, which lay their eggs in the nests of others birds, they build their own airy homes in some bush or hedgerow, and raise their brood with tender care. The belted kingfisher (Ceryle alcyon) is also of a retiring disposition, and spends much of its time on some branch overlooking the water, occa- sionally varying the monotony by dashing after a fish, or flying with rattling cry to another locality. Their nests are built in holes in banks, and six or eight young are annually reared. 214. The woodpeckers (Pici)—The woodpeckers are widely distributed throughout the world, and are preemi- nently fitted for an arboreal life. The beak is stout for chiseling open the burrows of wood-boring insects, which are extracted by the long and greatly protrusible tongue. The feet, with two toes directed forward and two backward, are adapted for clinging, and the stiff feathers of the tail serve to support the bird when’ resting. Almost all are bright- colored, with red spots on the head, at least in the males, which may further attract their mates by beating a lively tattoo with their beaks on some dry limb. The glossy white eggs are laid in holes in trees, and both parents are said to share the duties of incubation and feeding the young. Among the more abundant and well-known species is the yellowhammer or flicker (Colaptes auratus), which extends throughout the United States. Somewhat less widely distributed is the red-headed woodpecker (Jelaner- pes erythrocephalus), and the small black-and-white downy woodpecker (Dryobates pubescens). This is often called sapsucker, but incorrectly so, as, like all but one of our other woodpeckers it feeds on insects. The yellow-bellied wood- THE BIRDS 229 pecker (Sphyrapicus varius) is a real sapsucker, living on the juices of trees. A close relative of the red-headed woodpecker, the California woodpecker (Melanerpes formi- civorus), is renowned for its habit of boring holes in bark and inserting the acorns of the live oak. Subsequently the bird returns, and breaking open the acorns, devours the grubs which have infested them, and apparently eats the acorns also. 215. Swifts, humming-birds, etc. (Macrochires).—The birds of this order are rapid, skilful fliers, and their wings are very long and pointed. The feet, on the other hand, are Fie. 127.—Night-hawk (Chordeiles virginianus) on nest. Photograph by H. K. Jos. small, relatively feeble, and adapted for perching or cling- ing. Accordingly, the insects upon which they feed are taken during fight by means of their open beaks. The night-hawk (Chordeiles virginianus), roosting lengthwise on a branch by day, at nightfall. takes to the wing, and high in the air pursues its food after the fashion of a swallow. In the same haunts throughout the United States the whip- 230 ANIMAL STUDIES poorwill (Antrostomus vociferus) occurs, sleeping by day, but active at night. Neither of these birds constructs nests, but lays its streaked and mottled eggs directly on the ground. The chimney-swifts (C’etura pelagica), swallow- like in general form and habits, but very unlike the swallows Fig. 128.—Anna hummers (one day old), showing short bill and small size of body, Compare with last joint of little finger. in structure, frequent hollow trees or unused chimneys, to which they attach their shallow nests. The nearly related humming-birds are chiefly natives of tropical America, only a few species extending into the Unitcd States. Of these the little, brilliantly colored, and pugnacious ruby throat (Trochilus colubris) is the most widcly distribuicd. Its nest, like that of other hummers, is composed of moss and lichens bound together with cobweb and lined with down. 216. Perching birds (Passeres)—The remaining birds, over six thousand in all, belong to one order, the Passeres or perchers. They are characterized by great activity, interesting habits, frequently by exquisite powers of song, and in addition to several other structural arrangements have the feet adapted for perching. Their nesting habits THE BIRDS Jai differ widely, but in every case the young are helpless at the time of hatching, and require the care of the parents. The perchers constitute the greater number of the birds living in the meadows and woods, and are more or less Fig. 129.—Anna hummer (Calypte anna) on nest. common, and consequently familiar everywhere. Among the families into which the order is divided that of the fly- catchers (7yrannide), the crows and jays (Corvide), the orioles and blackbirds (Icterid@), the finches and sparrows (Fringillide), the swallows (Hirundinide), the warblers (Mniotiltide), the thrushes, robins, and bluebirds ( Turdide), are the more familiar, though the others are equally inter- esting. CHAPTER XVIII THE MAMMALS 217. General characteristics The mammals, constituting the last and highest class of the vertebrates, comprise such forms as the opossum and kangaroo, the whales and por- poises, hoofed and clawed animals, the monkeys and man. All are warm-blooded, air-breathing animals, haying the skin more or less hairy. The young are born alive, except in the very lowest forms, which lay eggs like reptiles, and for some time after birth are nourished by milk supplied from the mammary glands (hence the word smammals) of the mother. The skeleton is firm, the skull and brain within are relatively large, and, with few exceptions, four limbs are present. Most of the mammals inhabit dry land. A number, however, such as the whales and seals, are aquatic; while others, such as the beavers, muskrats, etc., though not especially adapted for an aquatic life, are, nevertheless, active swimmers, and spend much of their time in the water. Mammals tend to associate in companies, as we may witness among the ground-squirrels, prairie-dogs, rats, mice, and the seals and whales. In many cases they band for mutual protection, and often fight desperately for one another. Claws, hoofs, and nails are efficient weapons, and spiny hairs, as on the porcupines, bony plates, such as encircle the bodies of the armadillos, and thick skin and hair, serve as a protection. The hair is also frequently colored to harmonize the animal with its surroundings. 232 THE MAMMALS 233 Some rabbits and hares in the far north don a white coat in the winter season. 218. Skeleton.—As in other vertebrates, the external form of mammals is dependent in large measure upon the internal skeleton. This consists of relatively compact bones, the cavities of which are filled with marrow. Those forming the skull are firmly united, and, as in other verte- brates, afford lodgment fcr several organs of special sense and for the brain, which, like that of the birds, completely fills the cavity in which it rests. The vertebral column to which the skull is attached differs considerably in length, but it invariably gives attachment to the ribs, and to the basal girdles supporting one or two pairs of limbs. Gener- ally speaking, the number of bones in the head and trunk of all mammals is the same, so the variations we note in the species about us, for example, are simply due to differ- ences of shape and proportion. As we are aware, there is a great dissimilarity between the length of the neck of man and that of the giraffe, yet the number of bones in each is precisely the same. On the other hand, the variations occurring in the limbs are often due to the actual disap- pearance of parts of the skeleton. Five digits in hand and foot is the rule, and yet, as we well know, the horse walks on the tip of its middle finger and toe, the others being represented by small, very rudimentary, splint bones attached far up the leg. The even-hoofed animals walk on two digits, two smaller hoofed toes being often plainly visible a short distance up the leg, as in the pig. In the whales the hind limbs have completely disappeared, and in the seals, where the fore limbs are modified, as in the whales, into flippers, the hind limbs show many signs of degeneration. 219. Digestive system.—Some mammals, such as man, monkeys, and pigs, are omnivorous; others, like the cud- chewers and gnawers, are vegetarians; and still others, like the foxes, weasels, and bears, are carnivorous. In 16 934 ANIMAL STUDIES . every case the food substances are acted on by a digestive system constructed on the same general plan as that in man, yet modified according to the specific work it is required to perform. The teeth especially afford a valuable indication of the animal’s feeding habits, and, as we may notice later, are also of much value in classification. They consist of incisors used in biting, canines for tearing, and premolars and molars for crushing and grinding. The remaining portions of the digestive tract, esopha- gus, stomach, and intestine, with their appended glands, are usually not unlike those possessed by the squirrel. The chief differences are in the size of the various regions. I'he stomach, for example, may be long and slender or of great dimensions, and its surface may further be increased by several lobes, which are especially well developed in the ruminants or cud-chewers. The intestine, relatively longer in the mammals than in any other class of vertebrates, also exhibits great differences in length and size. In the flesh- eating species its length is about three or four times the length of the body, while in the ruminants it is ten or twelve times the length of the animal. 220. Nervous system and sense-organs,— As before noted, the nervous system of mammals is characterized by the large size and great complexity of the brain. Even in the simpler species the cerebral hemispheres (large front lobes of the brain) are well developed, and in the higher forms of the ascending series they form by far the larger part of the brain. The sense-organs also are highly developed, and are constructed and located much as they are in man. The greatest variations occur in the eyes. In some of the burrowing animals they are usually small, and in some of the moles and mice may even be buried beneath the skin and very rudimentary. On the other hand, they are large and highly organized in nocturnal animals; more so, usually, than in those which hunt their prey by day. The ears also have different grades of perfection, which THE MAMMALS 235 appear to be correlated with the habits of the animal. Among the species of subterranean habits the sense of hear- ing is largely deficient; but, on the other hand, it is ex- ceedingly keen in the ruminants, and enables them to detect their enemies at surprisingly great distances. In these creatures the outer ears are of large size and great mobility, and, placed as they are on the top of the head, serve to con- centrate the sound-waves on the delicate apparatus within, In the mammals the sense of smell reaches its highest de- velopment, especially among the carnivores which scent their prey. On the other hand, it is said to be absent in the whales and very deficient in the seals. The sense of taste, closely related to that of smell, is located in taste-buds on the tongue, and is also more acute than in any other class of animals. The sense of touch, located over the surface of the body, is especially delicate on the tips of the fingers, the tongue, and lips, which often bear long tactile hairs, called whiskers or vibdrisse. 221. Mental qualities—Correlated with the high degree of perfection of the brain and sense-organs the mammals show a higher degree of development of the intellectual faculties than any other class of animals. In many cases their acts are instinctive, and not the result of previous training and experience. Just as the duck hatched in an incubator instinctively takes to the water and pecks at its food, or as the bee builds its symmetrical comb, many of the mammals perform their duties day by day. On the other hand many other mammals are also undoubtedly in- telligent. They possess the faculty of memory; they form ideas and draw conclusions; they exhibit anger, hatred, and self-sacrificing devotion for their companions and offspring that is different from that in man only in degree and not in kind. In fact, intelligence differs from instinct primar- ily in its power of choice among lines of action. 222. Classification.—Of the eleven orders into which the mammals have been divided eight are represented in this 1Ze. About one-tenth natural s ypus). us} S ~n isa) ~ a re) 2 DQ —Three-toed 130. Fig. THE MAMMALS 237 country. Of the other three the first (Monotremes) and simplest of the eleven is represented by the duck-mole ETI SST ON RN RN das DC OS ENC IE ER eee Fie. 131.—Australian duck-mole (Ornithorhynchus paradoxus). One-fifth natural size. (Ornithorhynchus) living in the Australian rivers. Its general appearance and mode of life are illustrated in Fie. 132.—The manatee, or sea-cow (7richechus latirostris). A living species of sea- cow related to the now extinct Steller’s sea-cow. THE MAMMALS 239 Fig. 131. The duck-moles are the only mammals which lay eggs. These are deposited in a carefully constructed nest where the young are hatched. Another order (Hden- tata) includes a number of South and Central American forms, among which are the ant-eaters, armadillos, and tree- inhabiting sloths (Fig. 130). Still another order (Sirenia) includes the fish-shaped marine dugong and sea-cows or manatees (Fig. 132), of which one species is found occasion- ally on the Florida coast. The remaining orders are de- scribed in the succeeding sections. 223. The opossums and kangaroos (Marsupialia).—The lowest order of mammals represented in the United States SN La ey al Se Ul So Ne Fic. 133.—Opossum (Didelphys virginiana). One-tenth natural size. Photograph by W. H. FIsHErR., is that of the marsupials. It includes the opossums and kangaroos, together with a number of comparatively small . and unfamiliar animals living chiefly in and about Australia. 240 ANIMAL STUDIES The opossums, fairly abundant throughout the warmer portions of this country, are rat-like creatures, with scaly tails, yellowish-white fur, large head, and pointed snout. Except at the breeding season they lead solitary lives, sleeping in the holes of trees by day and at night feeding on roots, birds, and fruits. The kangaroos, familiar from specimens in menageries or museums, chiefly inhabit the plains of Australia. The giant gray kangaroos (Macropus giganteus), attaining a height of over six feet, go in herds, and owing to the great development of their hind limbs and tails are able, when alarmed, to travel with the swiftness of a horse. Several smaller species, some no larger than rabbits, live among the brush, and like their larger relatives crop the grass and tender herbage with sharp incisor teeth. While the marsupials do not lay eggs as does the duck- mole, they allow them to develop within the body for a very short time only. Hence the young, when born, are scarcely more than an inch in length, and are blind, naked, and perfectly helpless. At once they are placed by the mother in the pouch of skin, or marsupium, on the under side of her body. In this the young are suckled and pro- tected until able to gather their own food and fight their own way. 224. Rodents or gnawers (Glires).—The rodents are a large group of mammals, including such forms as the rats, mice, squirrels, gophers, and rabbits. They are readily dis- tinguished by their clawed feet adapted for climbing or burrowing, and by large curved incisor teeth. Unlike ordinary teeth, they grow continually, and, owing to the restriction of the hard enamel to their front surfaces, wear away behind faster. than in front, thus producing a chisel- like cutting edge. The largest of our native rodents is the porcupine (Erethizon dorsatus), which ranges from Maine to Mexico, and attains a length of nearly three feet. Many of the hairs THE MAMMALS 241 of the body have the form of stiff, barbed spines (Fig. 134), readily dislodged so that the animal requires no other wea. pon of defense. The rabbits and hares are of smaller size, and the cottontails especially are widely distributed. West of the Mississippi the jack-rabbits are familiar, and are Fie. 134, —Porcupine (Hystrix cristata). One-tenth natural size.—After BREHM. famous for their great speed. Like the porcupines, they feed on leaves and grass, and are often very destructive. The mice, especially the field and white-footed mice, are abundant in woodland and meadow throughout the United States. The house-mouse (Mus musculus) is a native of Europe, as is the common rat (JZ. decumanus), which was imported over a century ago. The wood-rat (Veotoma), however, is native, and may be found in many localities from east to west. The muskrat (Fiber zibethicus), beaver (Castor canadensis), and woodchuck (Arctomys monaz) were also more or less plentiful formerly, but in many localities are well-nigh exterminated. The squirrels, on the other hand, continue to exist in large numbers. The prairie- 242 ANIMAL STUDIES dogs, ground-squirrels, and chipmunks of the terrestria species are of frequent occurrence, and of the tree-dwellers the fox, gray and red squirrels are well known in many sections of the United States. 225. Insect-eating mammals (Insectivora)—The shrews and moles belonging to this order are representatives of a large group of small animals, which, unlike the major number of rodents, live on insects. The shrews, of which there are several species in this country, are small, mouse- like creatures, nocturnal in their habits, and hence rarely seen. The moles are of much larger size, and owing to their burrowing proclivities scarcely ever appear above ground, but excavate elaborate burrows with their shovel- like feet, devouring the insects which fall in their way. The common mole (Scalops aquaticus) extends from the eastern seaboard to the Mississippi River, where it is replaced by the prairie-mole (S. argenteus), which extends far to the west, into a country inhabited by other species. 226. The bats (Cheiroptera).—The bats are also insectiy- orous, but their habits are widely different from those of the shrews and moles. The forearm and the fingers of the fore limbs are greatly elongated, and are connected by a thin papery membrane, which also includes the hind limbs and tail, and serves as an efficient organ of flight. During the day they remain. suspended head downward in some dark cranny, awakening at nightfall to capture flying insects. Several species are found in this country, the most common being the little brown bat ( Vespertilio fus- cus), with small, fox-like face, large erect ears, and short olive-brown hair. The red bat (Lasiurus borealis) is also plentiful everywhere throughout the United States, and is distinguished from the preceding by its somewhat larger size and long reddish-brown fur. 227. The whales and porpoises (Cete)—The animals belonging to this order, the whales (Fig. 135), porpoises, and dolphins, are aquatic animals bearing a resemblance to fishes THE MAMMALS 243 only in external form. The cylindrical body has no distinct neck, the comparatively large head uniting directly with Le : ™ : - i e : < ere et | a ; * i - be | = = = = oe SS the cylindrical body, which terminates in the tail with hori- zoutally placed fins. No external signs of hind limbs exist, Attains a length of seventy feet. Fia@. 135.—Humpback whale (Megaptera versabilis). 244 ANIMAL STUDIES while the fore limbs are short and capable of being moved only as a whole. External ears are also absent. The eyes are exceedingly small, those of individuals attaining a length of from fifty to eighty feet, being in some species, at least, but little larger than those ofan ox. These are often placed at the corners of the mouth. The nasal openings, often known as blow-holes, are situated on the forehead, and as the whale comes to the surface for air afford an outlet for the stream of breath and vapor often blown high in the air—a process known as spouting. In some of the whales, such as the dolphin, porpoise, and sperm-whales, the teeth persist throughout life, but in most of the larger species they never “cut ” the gum, but early disappear, and their place is taken by large numbers of whalebone plates with frayed edges which act as strainers. The smaller-toothed forms (porpoises, dolphins, and several species of grampus) are frequently seen close to the shore, where they are usu- ally actively engaged in capturing fish. On the other hand, the larger species, such as the humpback, right whale, and sulfurbottom, not uncommon along our coasts, especially to the northward, live on much smaller organisms. With open mouth these whales swim through the water until they collect a sufficient quantity of jelly-fishes, snails, and crustacea, then closing the mouth strain out the water through the whalebone fringes and swallow the residue. As noted above, the animals of this order are almost wholly devoid of hair, but the heat of the body is retained by a thick layer of fat beneath the skin. This “ blubber” also gives lightness to the body (as do the voluminous lungs), and, furthermore, yields large quantities of oil, which in former times made ‘‘ whale-fishing ” a profitable industry. The whales bear one, rarely two offspring, which are solicit- ously attended by the mother for a long time. The smaller species grow to a length of from five or eight feet (por- poises, dolphins) to twice this size (grampuses); while the larger whales, by far the largest of animals, range from THE MAMMALS 245 thirty to over a hundred feet in length with a weight of many tons. 228. Hoofed mammals (Ungulata).—The order of hoofed animals or ungulates includes a large number of forms like the zebra, elephant, hippopotamus, giraffe, deer, and several other wild species, some of which are domesticated, such as horses, sheep, goats, and cattle. All of these animals walk on the tips of their toes, and the claws have become developed into hoofs. The order is divided into the odd- toed forms (perissodactyls), such as the rhinoceros with three toes and the horse with one, and the even-toed (artio- dactyls), as the pigs with four, and the ox, deer, etc., with two toes. The even-toed forms are again divided into those which chew the cud (ruminants) and those which do not (non-ruminants). No living native odd-toed mammal exists in this country, and of the wild even-toed species all are ruminants. In the members of this latter group the swallowed food passes into a capacious sac (the paunch), is thoroughly moistened, and passed into the second division (the honeycomb), later to be regurgitated and ground by the powerful molars. It is then reswallowed, and under- goes successive treatment in the other two divisions of the stomach (the manyplies and reed) before entering the intestine. Among the North American ruminants, the deer family (Cervide) is the best represented. In the more unsettled regions of the East the red deer is still com- mon, and the same may be said of the white-tailed, black- tailed, and mule-deer of the West. Among the woods > and lakes to the northward live the reindeer and caribou, and the largest of the deer family, the moose, which attains the size of the horse. Of nearly the same size is the wapiti or elk. Im all of the above-mentioned species the horns, if present, are confined to the male (except in the reindeer), and are annually shed after the breeding season. 246 ANIMAL STUDIES The native hollow-horned ruminants (Bovide) are at present confined to the Western plains, and comprise the pronghorn antelope (Antilocapra americana), the wary big- horn or Rocky Mountain sheep ( Ovis canadensis), living in mountain fastnesses, and the buffalo or bison (Bison ameri- canus). SES re Ppl = x EA 7 , " — ttt Ln Fig. 157.—The brown pelican, showing gular sac, which it uses in catching and holding fishes that form its food. adapted for the catching of insects. The ant-eater, for example, has a curious, long sticky tongue which it thrusts forth from its cylindrical snout deep into the recesses of the ant- hill, bringing it out with its sticky surface covered with ants. Animals which feed on nuts are fitted with strong teeth or beaks for crack- ing them. Similar teeth are found in those fishes which feed on crabs, snails, or sea-ur- chins. Those mammals like the horse and cow, that feed on plants, have usually ADAPTATIONS 293 broad chisel-like incisor teeth for cutting off the foliage, and teeth of very similar form are developed in the ditf- ferent groups of plant- eating fishes. Molar teeth are found when it Fig. 159.—Scorpion, showing the special devel- : opment of certain mouth parts (the maxil- _ F'6- 160.—Head of mosquito (fe- lary palpi) as pincer-like organs for grasp- male), showing the APES ing prey. At the posterior tip of the body needle-like mouth parts which is the poisonous sting. compose the ‘* bill.” is necessary that the food should be crushed or chewed, and the sharp canine teeth go with a flesh diet. The long neck of the giraffe en- ables it to browse on the foliage of trees in grassless regions. Insects like the leaf- beetles and the grasshop- pers, that feed on the foliage of plants, have a Fie. 161.—The praying-horse (Mantis) with pair of jaws, broad but fore legs developed as grasping organs. 294 ANIMAL STUDIES sharply edged, for cutting off bits of leaves and stems. Those which take only liquid food, as the butterflies and sucking-bugs, have their mouth parts modified to form a slender, hollow sucking beak or proboscis, which can be Fie. 162.—Acorns put into bark of tree by the Californian woodpecker (Melanerpes formicivorus bairdit). ~ —¥From photograph, Stanford Uni- versity, California. thrust into a flower nectary, or into the green tissue of plants or the flesh of animals, to suck up nectar or plant sap or blood, depending on the special food habits of the in- sect. The honey-bee has a very complicated equipment of mouth parts fitted for tak- ing either solid food like pol- len, or liquid food like the nectar of flowers. The mos- quito has a “bill” (Fig. 160) composed of six sharp, slender needles for piercing and lac- erating the flesh, and a long tubular under lip through which the blood can flow into the mouth. Some predaceous insects, as the praying-horse (Fig. 161), have their fore legs developed into formidable grasping organs for seizing and holding their prey. 256. Adaptation for self-de- fense.—For self-protection, car- nivorous animals use the same weapons to defend themselves which serve to secure their prey; but these as well as other animals may protect themselves in other fashions. Most of the hoofed animals are provided with horns, struc- ADAPTATIONS 295 Fie. 163.—Section of bark of live oak tree with acorns placed in it by the Californian woodpecker (Melanerpes formicivorus bairdii).—From photograph, Stanford University, California. tures useless in procuring food but often of great effective- ness as weapons of defense. To the category of structures useful for self-defense belong the many peculiarities of col- oration known as “recognition marks.” These are marks, 296 ANIMAL STUDIES not otherwise useful, which are supposed to enable mem- bers of any one species to recognize their own kind among the mass of animal life. To this category belongs the black tip of the weasel’s tail, which re- mains the same whatever the changes in the outer fur. Another example is seen in the white outer feathers of the tail of the meadow-lark as well as in certain sparrows and warblers. The white on the skunk’s back and tail serves the same purpose and also asa warning. It is to the skunk’s advan- tage not to be hidden, for to be seen in the crowd of animals is to be avoided by them. The songs of birds and the calls of various creatures serve also as recognition marks. Each spectes knows and heeds its own characteristic song or cry, and it is a source of mutual Fic. 164—Centiped, The Protection. The fur-seal pup knows foremost pair of legsis its mother’s call, even though ten thou- eee aid ee sand other mothers are calling on the gans. An adaptation rookery. creed. as The ways in which animals make themselves disagreeable or dangerous to their captors are almost as varied as the animals them- selves. Besides the teeth, claws, and horns of ordinary attack and defense, we find among the mammals many special structures or contrivances which serve for de- fense through making their possession unpleasant. The scent glands of the skunk and its relatives are noticed above. The porcupine has the bristles in its fur specialized as quills, barbed and detachable. These quills fill the mouth of an attacking fox or wolf, and serve well the pur. pose of defense. The hedgehog of Europe, an animal of different nature, being related rather to the mole than to ADAPTATIONS 297 the squirrel, has a similar armature of quills. The armadillo of the tropics has movable shields, and when it withdraws its srg | “ P ati + ae foi estes a: ai ni ~ ao Fic. 165.—F lying fishes. (The upper one a species of Cypselurus, the lower of Exoce- tus.) These fishes escape from their enemies by leaping into the air and sailing or ‘‘flying”’ long distances. head (which is also defended by a bony shield) it is as well protected as a turtle. Fig. 166.—The horned toad (PArynosoma blainviilei). The spiny covering repels many enemies. Special organs for defense of this nature are rare among birds, but numerous among reptiles. The turtles are all 20 7 298 ANIMAL STUDIES protected by bony shields, and some of them, the box-tur- tles, may close their shields almost hermetically. The snakes broaden their heads, swell their necks, or show their forked tongues to frighten their enemies. Some of them Fig. 167.—Noki or poisonous scorpion-fish (Hmmydrichthys vulcanus) with poison- ous spines, from Tahiti. are further armed with fangs connected with a venom gland, so that to most animals their bite is deadly. Besides its fangs the rattlesnake has a rattle on the tail made up of a Vek " nm Fie. 168.—Mad tom (Schilbeodes furiosus) with poisoned pectoral spine, succession of bony clappers, modified vertebre, and scales, by which intruders are warned of their presence. This sharp and insistent buzz is a warning to animals of other species and a recognition signal to those of its own kind. ADAPTATIONS 299 Even the fishes have many modes of self-defense through giving pain or injury to those who would swallow them. The cat-fishes or horned pouts when attacked set immoy- ably the sharp spine of the pectoral fin, inflicting a jagged wound. Pelicans who have swallowed a cat- fish have been known to die of the wounds inflicted by the fish’s spine. In the group of scorpion- fishes and toad-fishes are certain genera in which these spines are provided with poison glands. These may inflict very severe wounds to other fishes, or ’ even to birds or man. One of this group @& of poison-fishes is the noki (Zmmydrich- thys, Fig. 167). A group of small fresh- water cat-fishes, known as the mad toms (Fig. 168), have also a poison gland attached to the pectoral spine, and its sting is most exasperating, like the sting of a wasp. The sting-rays (Fig. 169) of many species Fie. 169.—A sting-ray have a strong, jagged spine on the tail, (U7vepius gooden, covered with slime, and armed with broad saw-like teeth. This inflicts a dangerous wound, not through the presence of specific venom, but from the dan- ger of blood poisoning arising from the slime, and the ragged or unclean cut. Many fishes are defended by a coat of mail or a coat of sharp thorns. The globe-fishes and porcupine-fishes (Fig. 170) are for the most part defended by spines, but their instinct to swallow air gives them an additional safeguard. When one of these fishes is disturbed it rises to the surface, 300 ANIMAL STUDIES gulps air until its capacious stomach is filled, and then floats belly upward on the surface. It is thus protected from other fishes, though easily taken by man. The torpe- do, electric eel, electric cat-fish, and star-gazer, surprise and stagger their captors by means of electric shocks. In the torpedo or electric ray (Fig. 171), found on the sandy shores of all warm seas, on either side of the head is a large honeycomb-like structure which yields a _ strong electric shock whenever the live fish is touched. This shock is felt severe- ly if the fish be stabbed with a knife or metallic spear. The electric eel of the rivers of Para- guay and southern Bra- zil is said to give severe shocks to herds of wild horses driven through the streams, and similar accounts are given of the electric cat-fish of the Nile. Among the insects, Fie. 170.—Porcupine-fish (Diodon hystrix), the lower ones swimming normally, the upper one floating belly upward, with inflated the possession of stings stomach.—Drawn from specimens from the Florida Keys. is not uncommon. The wasps and bees are fa- miliar examples of stinging insects, but many other kinds, less familiar, are similarly protected. All insects have their bodies covered with a coat of armor, composed of a horny substance called chitin. In some cases this chitin- ADAPTATIONS 301 ous coat is very thick and serves to protect them effectu- ally. This is especially true of the beetles. Some insects are inedible (as mentioned in Chapter XXIV), and are con- spicuously colored so as to be readily recognized by in- sectivorous birds. The birds, knowing by experience that these insects are ill-tasting, avoid them. Others are ef- fectively concealed from their enemies by their close resemblance in color and marking to their surroundings. These protective resem- blances are discussed in Chapter XXIV. 257. Adaptation for rival- ry.—In questions of attack and defense, the need of meet- ing animais of their own kind as well as animals of other races must beconsidered. In struggles of species with those of their own kind, the term rivalry may be applied. Actual warfare is confined mainly to males in the breed- ing season and to polyga- mous animals. Among those in which the male mates with many females, he must struggle with other males for their possession. In all the groups of vertebrates the sexes are about equal innum- Fic. 171.—Torpedo or electric ray (War- here) Where mating ante ts, Heats orth showing electric - either for the season or for life, this condition does not involve serious struggle or destructive rivalry. Among monogamous birds, or those which pair, the male courts the female of his choice by song and by display 302 ANIMAL STUDIES of his bright feathers. The female consents to be chosen by the one which pleases her. It is believed that the hand- somest, most vivacious, and most musical males are the ones most successful in such courtship. With polygamous animals there is intense rivalry among the males in the mating season, which in almost all species is in the spring. The strongest males survive and reproduce their strength. The most notable adaptation is seen in the superior size of teeth, horns, mane, or spurs. Among the polyga- mous fur seals and sea lions the male is about four times Fie. 172.—A wild duck (Ay/hya) family. Male, female, and precocial young. the size of the female. In the polygamous family of deer, buffalo, and the domestic cattle and sheep, the male is larger and more powerfully armed than the female. In the polyg- amous group to which the hen, turkey, and peacock belong the males possess the display of plumage, and the structures adapted for fighting, with the will to use them. 258. Adaptations for the defense of the young.—The pro- tection of the young is the source of many adaptive struc- tures as well as of the instincts by which such structures are ADAPTATIONS B08 utilized. In general, those animals are highest in develop- ment, with best means of holding their own in the struggle ee : ( 2 tet a ox ee 7 . 3 ¥ mR “Se ; = ; | i : : bs tee we * : oper : poke pie ae terfly (Papilio), harmonizing with the stance of variable protective Darivontn hich it reste: resemblance is shown by the chrysalids of certain butterflies. An eminent English nat- uralist collected many caterpillars of a certain species of 354 ANIMAL STUDIES butterfly, and put them, just as they were about to change into pup or chrysalids, into various boxes, lined with paper of different colors. The color of the chrysalid was found 1 oor aneenee autor one georesonED | “ ; | EEE s e Fic. 215.—Chrysalid of butterfly (lower left-hand projection from stem), showing pro- tective resemblance. Photograph from Nature. to harmonize very plainly with the color of the lining of the box in which the chrysalid hung. It is a familiar fact to entomologists that most butterfly chrysalids resemble in PROTECTIVE RESEMBLANCES, AND MIMICRY 355 color and general external appearance the surface of the object on which they rest (Figs. 214 and 215). 282. Special protective resemblance.—Far more striking are those cases of protective resemblance in which the ani- mal resembles in color and shape, sometimes in extraor- dinary detail, some particular object or part of its usual environment. Certain parts of the Atlantic Ocean are covered with great patches of sea-weed called the gulf-weed (Sargassum), and many kinds of animals—fishes and other creatures—live upon and among the alge. No one can fail to note the extraordinary color resemblances which exist between those animals and the weed itself. The gulf-weed is of an olive-yellow color, and the crabs and shrimps, a cer- tain flat-worm, a certain mollusk, and a little fish, all of which live among the Sargassum, are exactly of the same shade of yellow as the weed, and have small white markings on their bodies which are characteristic also of the Sargas- sum. The mouse-fish or Sargassum fish and the little sea- horses, often attached to the gulf-weed, show the same traits of coloration. In the black rocks about Tahiti is found the black noki or lava-fish (Zmmydrichthys vul- canus) (Fig. 167), which corresponds perfectly in color and form to a piece of lava. This fish is also noteworthy for having envenomed spines in the fin on its back. The. slender grass-green caterpillars of many moths and butter- flies resemble very closely the thin grass-blades among which they live. The larve of the geometrid moths, called inch-worms or span-worms, are twig-like in appearance, and have the habit, when disturbed, of standing out stiffly from the twig or branch upon which they rest, so as to re- semble in position as well as in color and markings a short or a broken twig. One of the most striking resemblances of this sort is shown by the large geometrid larva illus- trated in Fig. 216, which was found near Ithaca, New York. The body of this caterpillar has a few small, irregular spots or humps, resembling very exactly the scars left by fallen 356 ANIMAL STUDIES buds or twigs. These caterpillars have a special muscular development to enable them to hold themselves rigidly for Fie. 216.—A geometrid larva ona branch. (The Fie. 217.—A walking-stick insect larva is the upper right-hand projection from (Diapheromera Jemorata) on the stem.) twig. long times in this trying attitude. They also lack the middle prop-legs of the body, common to other lepidopter- PROTECTIVE RESEMBLANCES, AND MIMICRY 357 ous larve, the presence of which would tend to destroy the illusion so successfully carried out by them. The common walking-stick (Diapheromera) (Fig. 217), with its wingless, greatly elongate, dull-colored body, is an excellent example of special protective resemblance. It is quite indistinguish- able, when at rest, from the twigs to which it is clinging. Another member of the family of insects to which the walk- ing-stick belongs is the famous green-leaf insect (PA yllium) (Fig. 218). It is found in South America and is of a bright green color, with broad leaf-like wings and body, with markings which imitate the leaf veins, and small irregu- lar yellowish spots which mimic decaying or stained or fungus-covered spots in the leaf. There are many butter- flies that resemble dead leaves. All our common meadow browns ((Grapta), brown and reddish butter- flies with ragged-edged wings, that appear in the autumn . and flutter aimlessly about ex- Fig. 218.—The Birch) insect actly like the falling leaves, (Phyllium). show this resemblance. But most remarkable of all is a large butterfly (Aallima) (Fig. 219) of the East Indian region. The upper sides of the wings are dark, with purplish and orange markings, not at all resembling a dead leaf. But the butterflies when at rest hold their wings together over the back, so that only the under sides of the wings are exposed. The under sides of Kallima’s wings are exactly the color of a dead and dried leaf, and 008 ANIMAL STUDIES the wings are so held that all combine to mimic with ex- traordinary fidelity a dead leaf still attached to the twig by @ short pedicle or leaf-stalk imitated by a short tail on the N \ \ ‘ \ ‘ Fie. 219.—allima, the “‘ dead-leaf butterfly.” hind wings, and showing midrib, oblique veins, and, most remarkable of all, two apparent holes, like those made in leaves by insects, but in the butterfly imitated by two small circular spots free from scales and hence clear and trans- PROTECTIVE RESEMBLANCES, AND MIMICRY 9399 parent. With the head and feelers concealed beneath the wings, it makes the resemblance wonderfully exact. There are numerous instances of special protective resemblance among spiders. Many spiders (Fig. 220) that Fie. 220.—Spiders showing unusual shapes and patterns, for purposes of aggressive resemblance. live habitually on tree trunks resemble bits of bark or small, irregular masses of lichen. A whole family of spiders, which live in flower-cups lying in wait for insects, are white and pink and party-colored, resembling the markings of the special flowers frequented by them. ‘This is, of course, a Fig. 221.—A pipe-fish (Phyllopteryx) resembling sea-weed, in which it lives. special resemblance not so much for protection as for ag- gression ; the insects coming to visit the flowers are unable to distinguish the spiders and fall an easy prey to them. 283. Warning colors and terrifying appearances,—In the cases of advantageous coloring and patterning so far dis- 360 ANIMAL STUDIES cussed the advantage to the animal lies in the resemblance between the animals and their surroundings, in the incon- spicuousness and concealment afforded by the coloration. But there is another interesting phase of advantageous coloration in which the advantage derived is in render- ing the animals as conspicuous and as readily recogniz- able as possible. While many animals are very inconspicu- ously colored, or are manifestly colored so as to resemble their surroundings, generally or specifically, many other animals are very brightly and conspicuously colored and patterned. If we are struck by the numerous cases of imi- tative coloring amoug insects, we must be no less impressed by the many cases of bizarre and conspicuous coloration among them. Many animals, as we well know, possess special and effective weapons of defense, as the poison-fangs of the venomous snakes and the stings of bees and wasps. Other animals, and with these cases most of us are not so well acquainted, possess a means of defense, or rather safety, in being inedible—that is, in possessing some acrid or ill- tasting substance in the body which renders them unpala- table to predaceous animals. Many caterpillars have been found, by observation in Nature and by experiment, to be distasteful to insectivorous birds. Now, it is obvious that it would be a great advantage to these caterpillars if they could be readily recognized by birds, for a severe stroke by a bird’s bill is about as fatal to a caterpillar as being wholly eaten. Its soft, distended body suffers mortal hurt if cut or bitten by the bird’s beak. This advantage of being readily recognizable is possessed by many if not all ill- tasting caterpillars by being brilliantly and conspicuously colored and marked. Such colors and markings are called warning colors. They are intended to inform birds of the fact that the caterpillar displaying them is an ill-tasting insect, a caterpillar to be let alone. The conspicuously black-and-yellow banded larva (Fig. 147, 0) of the common PROTECTIVE RESEMBLANCES, AND MIMICRY 361 Monarch butterfly is a good example of the possession of warning colors by distasteful caterpillars.. These warning colors are possessed not only by the ill- tasting caterpillars, but by many animals which have spe- cial means of defense. The wasps and bees, provided with stings—dangerous animals to trouble—are almost all con- spicuously marked with yellow and black. The lady-bird beetles (Fig. 222), composing a whole family of small beetles Fia. 222.—Two lady-bird beetles, conspicuously colored and marked. which are all ill-tasting, are brightly and conspicuously col- ored and spotted. The Gila monster (/Heloderma), the only poisonous lizard, differs from most other lizards in being strikingly patterned with black and brown. Some of the venomous snakes are conspicuously colored, as the coral snakes (Zaps) or coralillos of the tropics. The naturalist Belt, whose observations in Nicaragua have added much to our knowledge of tropical animals, describes as follows an interesting example of warning colors in a species of frog: ‘In the woods around Santo Domingo (Nicaragua) there are many frogs. Some are green or brown and imitate green or dead leaves, and live among foliage. Others are dull earth-colored, and hide in holes or under logs. All these come out only at night to feed, and they are all preyed upon by snakes and birds. In contrast with these obscurely colored species, another little frog hops about in 24 362 ANIMAL STUDIES the daytime, dressed in a bright livery of red and blue. He can not be mistaken for any other, and his flaming breast and blue stockings show that he does not court con- cealment. He is very abundant in the damp woods, and I was convinced he was uneatable so soon as I made his acquaintance and saw the happy sense of security with which he hopped about. I took a few specimens home with me, and tried my fowls and ducks with them, but none would touch them. At last, by throwing down pieces of meat, for which there was a great competition among them, I managed to entice a young duck into snatching up one of the little frogs. Instead of swallowing it, however, it instantly threw it out of its mouth, and went about jerk- ing its head, as if trying to throw off some unpleasant taste.” Certain animals which are without special means of defense and are not at all formidable or dangerous are yet so marked or shaped and so behave as to present a threat- ening or terrifying appearance. The large green caterpil- lars (Fig. 223) of the Sphinx moths—the tomato-worm is a familiar one of these larve—have a formidable-looking, Fig. 223.—A ‘‘tomato-worm”™ lurva of the Sphinx moth, Phlegethontius carolina, showing terrifying appearance. sharp horn on the back of the next to last body ring. When disturbed they lift the hinder part of the body, bear- ing the horn, and move it about threateningly. As a mat- ter of fact, the horn is not at all a weapon of defense, but is quite harmless. Numerous insects when disturbed lift the hind part of the body, and by making threatening mo- PROTECTIVE RESEMBLANCES, AND MIMICRY 363 tions lead enemies to believe that they possess a sting. The striking eye-spots of many insects are believed by some entomologists to be of the nature of terrifying appearances. The larva (Fig. 224) of the Puss moth (Cerwra) has been often referred to as a striking example of terrifying appear- ances. When one of these larve is disturbed, “it retracts its head into the first body ring in- flating the mar- gin, which is of a bright red color. There are two in- tensely black spots on this margin in the appropriate position for eyes, and the whole ap- pearance is that of a large flat face extending to the outer edge of the red mar- gin. The effect is an in- tensely exaggerated cari- Fig. 224.—Larva of the Puss moth (Cerura). cature of a vertebrate Upper figure shows the larva as it appears face, which is probably when undisturbed ; lower figure, when dis- : turbed.—After PouLTon. alarming to the verte- 7 brate enemies of the cat- erpillar. . . . The effect is also greatly strengthened by two pink whips which are swiftly protruded from the prongs of the fork in which the body terminates. ... The end of the body is at the same time curved forward over the back, so that the pink filaments are brandished above the head.” 284. Alluring coloration—A few animals show what are called alluring colors—that is, they display a color pattern so arranged as to resemble or mimic a flower or other lure, and thus to entice to them other animals, their natural prey. This is a special kind of aggressive resemblance.