HANBBOQKSforSiiidentsundGcneral Readers ZOOLOGY MACALISTER John 3\vett rr HANDBOOKS for Students and General Readers IN SCIENCE, LITERATURE, ART, AND HISTORY. Messrs. HENRV HOLT & Co. have begun the publication of a Series of brief Handbooks in various departments of knowledge. The grade of the books is intermediate between the so-called "pr'mers" and toe larger works professing to present quite detailed views. Generallv, thijy will be found available by upper classes in schools which can not give much time to the subjects and by mature persons of little leisure who wish to enlarge or revise their knowledge. The subjects and authors, so far as selected, are as follows : VOLUMES PUBLISHED. Zoolosry of the Invertebrate Animals. By ALEX. MACAUSTER, M.D., Professor of Zoology and Comparative Anatomy in the University of Dublin. Special! v revised tor America by A. S. PACKARD, JR., M p., Professor of Zoology and Geology in Brown University. 60 cts. 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F.L.S., Professor of Botany, Royal College of Science for Ireland, Dublin. Revised by C. E. BESSEY, M.S., Professor of Botany in the Iowa Agricultural College. Botany. Classification of Plants. By W. R. McNAB. Revised by C. E. BESSEY. English Language. By T. R. LOUNSBURY, Professor in Yale College. English Literature. By French Literature. By FERDINAND BOCHER, Professor in Harvard University. German Literature. By History of American Politics. By ALEXANDER JOHNSTON, A.M. Jurisprudence. By JOHNSON T. PLATT, Professor in the Law Department of Yale College. Practical Physics Electricity and Magnetism. By Prof. F. GUTHRIE, Ph.D. Practical Physics Heat and Light. By Prof. F. GUTHRIE, Physical Geography. By CLARENCE KING, Director of the U. S. Government Surveys. Political Economy. * By FRANCIS A. WALKER, Ph.D., Professor in Yale College. HANDBOOKS for Students and General Readers ZOOLOGY BY ALEX. MACALISTER, M.D. Professor of Zoology and Comparative Anatomy in the University of Dublin Specially Revised for America A. S. PACKARD, JR., M.D. Professor of Zoology and Geology in Brotvit University TWO VOLUMES IN ONE NEW YORK HENRY HOLT AND COMPANY 1879 HANDBOOKS for Students and General Readers. ZOOLOGY OF THE INVERTEBRATE ANIMALS BY ALEX. MACALISTER, M.D. Professor of Zoology and Comparative Anatomy in tke University of Dublin. Specially Revised for America A. S. PACKARD, JR., M.D. Professor of Zoology and Geology in Brown University. NEW YORK HENRY HOLT AND COMPANY 1879. COPYRIGHT, 1879, BY HENRY HOLT & CO. PRINTED BY TROVES PRINTING AND BOOKBINDING CO., NEW YORK. EXPLANATORY. THIS Series is intended to meet the requirement of brief text-books both for schools and for adult readers who wish to review or expand their knowledge. The grade of the books is intermediate between the so-called "primers" and the larger works professing to present quite detailed views of the respective sub- jects. Such a notion as a person beyond childhood re- quires of some subjects, it is difficult and perhaps impossible to convey in one such volume. Therefore, occasionally a volume is given to each of the main departments into which a subject naturally falls for instance, a volume to the Zoology of the vertebrates, and one to that of the invertebrates. While this ar- rangement supplies a compendious treatment for those who wish, it will also sometimes enable the reader interested in only a portion of the field covered by a science, to study the part he is interested in, without getting a book covering the whole. Care is taken to bring out whatever educational value may be extracted from each subject without ira- vi Explanatory, peding the exposition of it. In the books on the sciences, not only are acquired results stated, but as full explanation as possible is given of the methods of inquiry and reasoning by which these results have been obtained. Consequently, although the treatment of each subject is strictly elementary, the fundamental facts are stated and discussed with the fulness needed to place their scientific significance in a clear light, and to show the relation in which they stand to the general conclusions of science. Care is also taken that each book admitted to the series shall either be the work of a recognized author- ity, or bear the unqualified approval of such. As far as practicable, authors are selected who combine knowledge of their subjects with experience in teach- ing them. PREFACE. THE STUDENT who would acquire a satisfactory knowledge of the principles of Zoology is recom- mended to commence by learning the elementary principles of General Biology ; and having mastered these he should then study the groups of the Inverte- brates as here detailed, coupling his study with a practical examination of such common types as are easily to be obtained. A jellyfish, or a hydra, an earthworm, an oyster, a snail, a cockroach and a lobster, are forms everywhere procurable, and, if examined, will give the student a good general idea of the structure of Invertebrate Animals. It must be borne in mind that without some such practical study, no amount of reading will suffice to convey accurate and adequate ideas of animal organisation. ALEXANDER MACALISTER. CONTENTS. CHAPTER I. PAGE Nature of Animals Processes of Life Tissues and Organs Symmetries of Animals I CHAPTER II. Classification of Animals Method of naming Resem- blances of Relationship and of Adaptation Mimicry Parasites The Seven Sub-kingdoms of Invertebrate Animals Each Animal has a Life History, not a mere Growth Rudimental Organs Tendency to Individual Variety 6 CHAPTER III. Conditions of Distribution in Time and Space Freshwater, Marine, and Terrestrial Life Methods of Study of Zoology 13 CHAPTER IV. Sub-kingdom i. Protozoa : Rhizopods Amoebae Sun- Animalcules Gregarines and Radiolarians . . .18 Contents. CHAPTER V. PAGB Infusion-Animals Luminous Animalcules Summary of the Forms in Sub-kingdom I 25 CHAPTER VI. Sub-kingdom 2. Sponges ...... 28 CHAPTER VII. Sub-kingdom 3. Ccelenterate Animals : Hydras Sea-Firs, Medusae 52 CHAPTER VIII. Sea- Anemones Corals ' Dead Men's Toes ' Sea-Pens . 41 CHAPTER IX. Sub-kingdom 4. Echinodermata : Stone-Lilies Feather- StarsStarfishes 47 CHAPTER X. Sea Urchins Sea Cucumbers Summary of Forms in- cluded in Sub-kingdom 4 52 CHAPTER XL Sub-kingdom 5. Worms : Turbellarians Tape- Worms- Flukes Round and Thread- Worms .... 57 CHAPTER XII. Wheel-Animalcules Spoon-WormsLeeches. . . 66 Contents. xi CHAPTER XIII. PACK Bristled- Worms Earth-Worms Summary of Normal Worms 70 CHAPTER XIV. Aberrant- Worms Moss-Polyps and Tunicated Animals . 74 CHAPTER XV. Sub-kingdom 6. Mollusca or Soft-bodied Animals : Class I. Arm-footed Molluscs; Class 2. Bivalves . . 78 CHAPTER XVI. Class 3. Head-bearing Molluscs : Whelks, Snails, &c. . 84 CHAPTER XVII. Class 4. Cuttle-FishesNautili and Squids Summary ot Characters of the Classes of Mollusca .... 90 CHAPTER XVIII. Sub-kingdom 7. Jointed Animals or Arthropoda . . 96 CHAPTER XIX. Class I. Crustacea : Crabs, Loboteis, Shrimps, &c. . 98 CHAPTER XX. Class 2. Spiders, Mites, and Scorpions . . . 108 xii Contents. CHAPTER XXI. PACK Class 3. Myriopoda, Centipedes, and Gaily- Worms . 112 CHAPTER XXII. Class 4.. Insecta : Insects General Characters and Struc- ture 115 i CHAPTER XXIII. ./ Orders of Insects whose Metamorphoses are Imperfect Aphides, Bugs, Straight-winged Insects and Dragon- Flies 123 i / \ , . CHAPTER XXIV. Insects whose Metamorphoses are complete . 127 INDEX and GLOSS4RY , . 137 INVERTEBRATA. CHAPTER I. GENERAL CHARACTERS OF ANIMALS. Physical Conditions of life. An animal, chemically considered, consists of a few elements l united into extremely unstable combinations, which are at every moment undergoing chemical change. The consti- tuent materials are constantly becoming grouped into more simple and stable compounds, and in that state they are either eliminated or retained in an inactive condition, while other materials from without are being taken in, and so modified that they replace the molecules removed by the previous decomposition. As long as life lasts, these conditions of waste and re- pair continue ; so that the particles of the bodies of al lanimals are in a state of constant change. The food of animals contains carbon, hydrogen, nitrogen, and oxygen, which must be grouped into complex molecules before the animal can use them for his nutrition. Combinations of the requisite com- plexity can be derived only from previously organised 1 Carbon, hydrogen, oxygen, and nitrogen. B 2 Invertebrate*. ^materials either iiiimal or vegetable. In most vege- tables the forces concerned in assimilation are suffi- ^ q^it , to^ bre^ uj> originally stable compounds, such 'as carbonic" acid, ahcTto induce the elements to combine into the unstable combinations of which living textures consist The process of repair in animals has three stages, ist, the taking in of material as food; 2nd, the chang- ing of food into a substance capable of forming part of the living organism, i.e. blood ; and 3rd, the laying down of this assimilated material in the tissues of the body of which it thus becomes a constituent, replacing the losses sustained by each organ in each discharge of its function. For the life-processes of animals oxygen is necessary, and special structures, called respiratory or breathing organs, are often provided for taking it in. The car- bonic acid formed from the waste of the tissues is usually got rid of by these organs. The material with which the vital properties are connected is of the same nature in all animals and is called protoplasm. The simplest animals are mere masses of this substance, which in them discharges all the fjnctions needful for the maintenance of life ; the more complex are built up of aggregations of particles of the same material, or of substances derived from it in the course of growth. Each of these constituent particles or cells, as they may conveniently be called, usually consists of a mass of protoplasm surrounded by an envelope of some material derived by chemical action from protoplasm. , Ceils continuously grouped make up tissues, and a group of tissues which General Characters of Animals. 3 performs any special duties in the life of an animal is called an organ.// While there are thus varying degrees of complexity among animals, yet the parts of a simple animal have to perform as many essential functions as those of a more complex animal, the in- crease in complexity of an organism being correlated not with an increase in the number of essential functions but with the need for the more perfect fulfilment of existing duties. Increase in complexity thus results from division of labour, and, with each increase, the sphere of the functional activity of each part becomes narrowed. For example, in jelly-fishes one set of cavities act as organs of digestion and of circulation, while in higher animals these functions have separate organs, and even subsidiary portions of these great functions have for their accomplishment distinct parts. Functions. Three sets of functions are discharged by organs in the body of an animal : namely, ist, those of Relation ; 2nd, those of Nutrition ; 3rd, those of Reproduction. The organs appropriated to the functions of Rela- tion are those which connect the animal with its environ ng conditions, informing it about its surround- ings, and enabling it to avoid disagreeable or to court agreeable external influences. These organs are of two kinds : (A) those of sensation, such as the skin, or organ of touch, and the special sense organs (eye, ear, nose, tongue), and (B) those of motion, which may be of three kinds, (a) inconstant processes of protoplasm called pscudopodia (fig. 8), (b) minute, constant, hair- like processes having the power of waving to and fro, called cilia, or (c] contractile cells and fibres in B 2 4. Invertebrates bundles called muscles. The first kind occur in the lowest animals and in naked protoplasmic particles ; the second in infusorial animals (fig. 14) ; the third in all but the simplest animals. Connected with the organs of relation we find a system of fine white threads called nerves, whose endings occur in these organs, and whose starting-points are central clusters of nerve- cells, called ganglia. These threads convey the variously received stimuli from the sense organs to the ganglia, and carry the command for motion from the ganglia to the muscles. The function of Nutrition is discharged by four sets of organs : ist, those of feeding, consisting of a cavity or stomach, for the reception of the food, with glands appended thereto, which secrete fluids to assist in assimilation ; 2nd, organs of circulation, which carry FIG. Euplotes Charon, a ciliated infusorium showing the stages of division. the assimilated matter, or blood, through the body for the nutrition of the tissues ; 3rd, organs of respiration, by which oxygen is taken in ; and 4th, organs of excretion whereby the waste products are eliminated. General Characters of Animals. 5 There are three stages in the contest between waste and repair which is characteristic of life. In the first, repair is in excess of waste, and individual growth proceeds until a definite limit, constant within certain bounds for each specres, is reached. When this is attained, excess of nutrition still continues but tends to become separate and independent ; by such dis- continuous modes of growth, the third set of functions, or Reproduction, is accomplished. Of this there are three chief forms : (A) either the whole body of the parent may split into two or more, each becoming a perfect animal like its parent ; this process is named fission. (B) In the second mode of reproduction a small portion of the body of the parent animal enlarges and becomes detached as a bud, which develops directly into an organism like its ancestor ; this is called gem- mation, (c) In the third mode small particles FIG. 2. called eggs arise from the tissues of the parent, and on being fertilised, are capa- ble of developing into new individuals ; this is called ovulation. The second stage of existence having for a time continued, the organism reaches a third stage, in which waste exceeds repair, and as, by degrees, the assimilated material becomes insufficient to keep up Gemmation ; n the processes of life this stage terminates Hydra viridit. in death. Summary. Animals consist for the most part of protoplasm, are constantly undergoing waste, and being built up by the assimilation of food. They differ from plants in being usually capable of loco- 6 Invertebrate motion (though this has exceptions), in being only capable of assimilating organic matter (except in the case of water and oxygen), and in having their cell- walls composed of nitrogenous matter, while in plants non-nitrogenous matter abounds. Higher animals are strongly differentiated from plants ; the lower forms are often of doubtful position. Animals may be simple or complex, complexity depending on division of labour, and the consequent specialisation of function in organs which become differentiated from each other. The chief functions are Relation, Nutrition and Reproduc- tion, the latter taking place during the stage when individual growth has ceased and while as yet repair exceeds waste. CHAPTER II. ORGANS AND CLASSIFICATION OF ANIMALS. Method of Study. The first branch of zoology necessary to be studied is the anatomy of the organism, and the best method of study is the examination of some of the commoner types of each class. As many of these are small, and optical assistance necessary, the student should provide himself with a good pocket lens. For dissection, the instruments required are, a scalpel, a fine-pointed pair of dissecting forceps, and several sharp-pointed needles fixed in wooden handles and with their extremities ground flat, so as to cut as well as tear. As many small animals can be most easily dissected under water it is convenient to have a shallow Organs and Classification of Animals. f wooden tray lined with sheet lead for the purpose, while it often facilitates dissection to have a thin sheet of cork weighted with lead, so as to retain its position at the bottom of the fluid upon which the various parts may be pinned down. To preserve animal organs the best materials are, spirits of wine, or a weak (2 per cent.) solution of bichromate of potassium. The study of the forms, nature and relations of organs to each other and to the organism in general, FIG. Common orange Star-fish (Astropecten aurantiacus). and the laws deduced therefrom is known as Morpho- logy ; the study of the uses of parts is called Physiology. 8 Invertebrata. Morphology. Groups of organs are generally sym- metrically disposed in animals ; either they are arranged in order around a central point in one plane, or else each individual consists of a succession of similar segments, as in a centipede. In the first case the symmetry is said to be radial as in the star-fish (fig. 3) ; in the second the segments are each made up of two sym- metrical halves, and the symmetry is said to be bilateral In a perfectly symmetrical animal all the organs should be proportionally developed, but as the vary- ing conditions of animal existence often require the more extensive performance of some duties than of others, we always find that some organs are larger, others smaller. In fact animals are so perfectly fitted to their surroundings that could we know all the con- ditions under which a given animal existed, we could form a good conception of its structure and vice versd. The Embryo. To understand the true relations of structures in animals it is necessary to watch the growth of the organism from the earliest stages of its produc- tion in the egg until it attains its adult condition. The embryo is not a simple miniature of the full grown animal, but reaches its perfect state by undergoing a series of changes, which follow each other in a definite order. In this process, parts and organs start into being which were before unnoticeable, and some of these have only a transient existence fading off into nothingness. Thus the common acorn shell emerges from its egg as a little free-swimming larva (fig. 4), with eyes and feelers, but these totally vanish in the adult (fig. 5) ; such organs are known as provisional organs, and occasionally they Organs and Classification of A nimals. 9 leave traces behind when their functions have ceased, like the cord-like obliterated embryonic blood-vessels in mammalia. In some animals, during their develop- ment, organs spring into being for a shorter or longer period, but never perform any function and either vanish FIG. 4. Larva of common Acorn-shell (Balanus porcatus), showing antennae (), limbs (b\ and eye (d). or remain permanently in an undeveloped condition ; such organs are called rudimental, and they are always such as in some kindred form discharge an important duty. Thus most cuttle-fishes have a groove in their body during their embryonic life, which closes in and forms a cavity wherein the internal shell is secreted; but 10 Invertebrate* FIG. 5. the octopus or sea-spider, a closely allied form, has a similar groove which vanishes, leaving no trace behind. Instances of the kind might be multiplied, as there is scarcely an individual form in the higher sub-kingdoms which does not in its life history exhibit instances of provisional and rudimental organs. Characters Essential and Adaptive. In each animal we can divide the characters into two groups, essential and adaptive; the former of these are those whereby we can learn the relations of animals among them- selves, and these are of primary importance in classification ; the latter show the relations of the animal to its sur- roundings, but these in the adult often so overlie the essential characters as to obscure them. A study of the embryogeny of the animal will enable us to understand its relation- ship, for the adaptive characters are of later origin than the essential and may be traced as they are becoming superinduced. Thus among the parasitic mites of the genus Pentastoma, we could not know the true relations of the worm-like adults if we were not acquainted with the limb-bearing larva. Classification and Nomenclature. The animal kingdom is a vast assemblage of individuals, and we require to arrange these in larger categories for Adult form of Balanus porcatus. Organs and Classification of Animals. II purposes of study. Those individuals which are so far identical in- structure as to lead us to believe that they are descended from common parents we speak of as belonging to the one species. Species is thus our unit in systematic zoology, but as two in- dividuals are seldom absolutely identical in all respects specific distinctions must be more or less arbitrary. A group of allied species embodying the same structural ideas is called a genus. An assemblage of allied genera is a family ; a group of related families make up an order ; while related orders make up a class, and the several classes included in the animal kingdom are united in certain primary categories called sub- kingdoms. Systematic zoologists give a Latin name to each of these, and for convenience each species is designated by a Latin word to which is prefixed the name of the genus. The specific name is generally an adjective, the generic is a substantive, and should be written with a capital letter. Thus the dog is called by zoologists Canis familiaris, Canis being the generic, familiaris the specific name. Canis aurats is the jackal, Canis lupus the wolf. That species in a genus which most strikingly embodies the generic characters is the type of the genus. We also speak of the type of a family, of an order, or of a class, the type being that species which displays most clearly the characters of the group ; and for convenience we attribute certain characters to ideal types to illustrate truths in classifi- cation. The type genus usually gives its name to the family , thus the dog-family is called Canidae. Homology. In comparing animals, the most im- 12 Invertebrata. portant resemblances are those which depend on common relationship to the types of the class to which they belong. These likenesses are called resemblances of morphological type. Thus if we compare a dog and a crow, we find in both a skeleton, a brain, a skull, four limbs, a heart &c., and we refer them both to the vertebrate type, inasmuch as they both embody the ideas of structure characteristic of vertebrate animals. Each part in one is said to be homologous with the corre- sponding part in the other, the wing with the fore leg, &c. Homology is thus identity of structure irrespec- tive of function, and parts are homologous which represent the same parts in the ideal type of the class. Such resemblances are the bases of classification. Analogy. Likenesses of parts may also depend on similarity of function ; thus the wings of insects and the FIG. 6. ^ wings of birds are used for the same purpose, and have certain resemblances. These similarities are called resem- blances of analogy, and they tell us nothing as to the nature of the organs compared. Mimicry. Animals of de- finite geographical areas often resemble each other in some . respects : thus they may be Leaf insect (Phylhwn siccifo- ' . . . J J Hum). mostly similar in colour, mostly white, or spotted, or striped, or brightly coloured. Sometimes animals mimic in shape or colour the leaves and twigs on which they live (fig. 6), or the prevalent colour of the heibage. Thus the Kakapo Classification and Distribution of Animals. 13 or ground parrot of New Zealand, which can hardly fly, is in plumage like the mottled green vegetation among which it lives. The ptarmigan and other birds become white in winter, so as to become inconspicuous among the snow. Sometimes an insect mimics in appearance another of different nature living in the same district. In such cases the insect imitated is one which, from its disagreeable secretions or sting, is not a favourite prey of insect-eaters. Hence the mimicry protects the imitator, who is usually rarer than the insect imitated. Organs which are homologous consist of homo- logous parts ; and as this is not the case in organs re- sembling each other only in function, we must be careful to discriminate morphological from physio- logical likeness. In animals which consist of successive segments in a chain, like centipedes or lobsters, each segment is composed of parts similar to those of its neighbouring joints. Such parts are said to be serial homologues, as for example the fore and hinder limbs of quad- rupeds. CHAPTER III. CLASSIFICATION AND DISTRIBUTION OF ANIMALS. Sab-Kingdoms. THE animal kingdom includes eight sub-kingdoms. In these we observe a certain pro- gressive increase in complexity, from one end of the series to the other ; but they do not make a linear series, as the highest organism of each is in no degree related to the lowest organism of the next sub-kingdom, being usually much more advanced and specialised, so , 14 Inverlebrata. that in point of complexity the sub-kingdoms overlap each other. The first sub-kingdom, Protozoa, includes those animals which have neither body-cavity nor nervous system, and are single celled. Sub-kingdom 2. Polystomata, includes sponges, which have an internal cavity with a three layered wall, one outlet, and usually many inlets, but no differ- entiated organs, though consisting of many cells. Sub-kingdom 3. Coslenterata, includes jelly-fishes and sea anemones, having a stomach cavity and a body cavity as an outgrowth therefrom, and a radiate symmetry. Sub-kingdom 4. Echinodermata, includes star- fishes and sea-urchins, with a body cavity separate from the stomach, a nervous system, and a system of water-tubes which are agents in locomotion. Sub-kingdom 5. Vermes, includes worms which are bilaterally symmetrical, and composed of successive similar segments, with no jointed limbs, and with a water- vascular system which has no locomotory func- tion. Sub-kingdom 6. Mollusca, includes oysters, snails, &c., possessing soft bodies enveloped in a leathery mantle, no jointed limbs, a circulating system, often an external shell and often an unsymmetrical nervous system. Sub-kingdom 7. Arthropoda, includes crabs, lobsters, spiders, and insects, which have bodies made up of successive joints, with a symmetrical nervous system, an external skeleton and jointed limbs. Sub-kingdom 8. Vertebrata, including fishes, Classification and Distribution of Animals. 15 reptiles, birds and quadrupeds, which have an internal skeleton, a brain and vertebral column. This one sub-kingdom includes the most complex of animals whose structure requires more minute examination than does that of the other sub-kingdoms. We will in the present volume consider the seven invertebrate sub-kingdoms. In comparing these sub-kingdoms, we speak of forms as being high or low in organisation according to the degree in which special parts are appropriated for the discharge of special functions. We also notice that no organ appears for the first time in animals in a. state of complexity, but on the contrary, there is always in lower forms a prophetic foreshadowing of it in the modification of some part already existing. Distribution. Every species of animal is limited to a definite geographical area. Thus the earth's surface may be divided into regions, each characterised by special inhabitants, and the collected animals of any region we speak of as its fauna. As a rule, life increases in amount in any country with increasing, and dimi- nishes with diminishing temperature. Thus the fauna of a tropical exceeds that of a temperate region. The number of animals is also larger when the difference between the winter and summer temperature is small, than in a country with the same mean temperature but with a greater range between maximum and minimum. Moisture is also favourable to animal life, and the fauna of a moist exceeds that of a dry region, other things being equdl. Many animals live in places from which light is excluded, as in caves ; these have rudimental eyes, and 1 6 Invertebrate. are white or colourless. Many large caves, like those of Kentucky, Adelsberg c., have thus peculiar blind faunae. Sometimes the presence of one animal prevents the diffusion of others ; thus in Africa the tzetze fly renders whole tracts uninhabitable by oxen and deer, which are destroyed by its poisonous bites. The fauna of a limited area of a continent usually exceeds that of an island of equal size in its number of specific forms ; and the fauna of an island lying near a continent resembles that of its neighbouring con- tinent. Oceanic islands or those isolated by very deep straits have often remarkable faunae of their own, e.g., the Galapagos and New Zealand. Tropical species are, as a rule, more limited in range tnan are those of temperate climates, and simpler animals are usually more widely distributed than are the more complex. Fresh-water inhabitants are the fewest specifically, and as a rule are simpler in organisation than allied forms inhabiting other media. The fourth sub-kingdom has no fresh-water representatives ; the second has only two, and the third only five species living in this medium ; while the others are not very numerously represented in fresh-water. The sea is the home of nine-tenths of the inver- tebrates (if we exclude insects), and there are also definite ranges of extension to be noticed in the cases of marine species. The conditions limiting specific life in the sea are depth, cunents, and tem- perature. Terrestrial animals are the most specialised, and Classification and Distribution of Animals. 17 have organs in a more concentrated condition than in their aquatic allies. Parasitism. Some animals pass their lives within or on the bodies of others, and this condition induces striking alterations in structure. In some cases the intruder collects its own food independently of his host, being thus only indebted to him for house room ; of this nature are the sponges which live rooted on crabs, or the barnacles on the skin of the whale. The second series of intruders are fellow commoners with their hosts, feeding on the food which their entertainer collects ; while in a third class the parasite is a pen- sioner on the body of his host, feeding on his sub- stance. Such forms are true parasites. In all these conditions there is a diminished necessity for locomotion and for food-capture on the part of the parasite ; so the organs of motion, of sense, and of nutrition retrograde, but as the parasitic condition involves difficulties in the continuance of the species, the organs of multiplication are enor- mously increased in size and complexity. Extension in Time. Species of animals have limited ranges in time as well as in space, for they are dependent on the constancy of physical conditions for their specific longevity, and such alterations in these as are constantly occurring will tend to extinguish species ; hence the history of life in the past is a con- tinual record of the dying out of types of life. 18 Invtrtebrata. CHAPTER IV. SUB-KINGDOM PROTOZOA. General Characters. The constituent animals of this sub-kingdom are animals of extreme simplicity, con- sisting for the most part of undifferentiated protoplasm. None of them possess a nervous system, sense organs, nor a body cavity, nor do we find differentiated organs present in any of them. Among these there are five chief types forming five classes. FIG. 7. One of the minute Foraminifera, Globige* ina bulloides, magnified seven; y diameters. Certain forms, called Monera, are even simpler than the Rhizopods, as they not only want the power Protozoa. 19 of house-building but have no nuclei, and are thus the simplest conceivable living beings, mere specks of living jelly (fig. 9). Of these naked forms, some authors make a separate class under the name Monera. Class 1. Rhizopoda. In the fine white sand on the sea-shore or in the mud of the sea-bottom there are to be found minute calcareous shells of varying forms, ranging from -yj-g-th to -j^th of an inch in diameter. Each shell consists of many separate chambers, arranged either one after another in a straight line or in a single or double spiral, or even grouped in more complex fashions. Each chamber is separated from its neighbours by a partition which is pierced with one or many holes whereby the several chambers communicate with each other. The shell-substance is either white and porcelain-like, or glass-like and more brittle, and pierced not only in the partitions but over its whole surface by numerous holes. On ac- count of these perforations these little shells are called Eoraminifera (hole bearing). The animals which build these wonderful houses are exceedingly simple in their structure. The interior of each chamber in a fresh state is filled with proto- plasm which is jelly-like, highly contractile on being irritated, and not only extends through the holes in the shelly wall but coats the outside of the shell with a glairy external living layer. This layer has no defi- nite uniformity of outline, but is constantly changing its shape by sending into the surrounding water radiating protoplasmic processes which are incon- stant, rapidly retracted, disappearing by being taken into the homogeneous matter of the animal's body, C2 20 Invertebrata. and coalescing when they touch each other. To these the name pseudopodia (false feet) has been given. These little creatures live on any minute organic particles with which they come in contact, and their mode of feeding is simple ; when the ray-like pseudo- podia touch a particle of which they seem to approve as a prospective meal they converge around it, and FIG. 8. Rotalia. Veneta, a Rhizopod, showing the pseudopodia. touching each other coalesce, and draw the particle within the body proper, in which it is digested. As these creatures are homogeneous or nearly so, any one spot is as suitable for the protrusion of pseudo- podia or for the taking in of food as another, but usually the processes are most numerous opposite the holes in the shell. Protozoa. 2 1 As the protoplasm includes its food in the manner described, foreign particles and fine granules become enclosed in it derived from the undigested parts of the food. Sometimes drops of water or of thin fluid may be seen in the protoplasm like little bubbles ; these are called vacuoles (fig. 14), and they with the gran- ules circulate actively in the body mass ; obscure con- densed points or nuclei also exist, and the name of the class is derived from the root-like spreading of the pseudopodia. Mode of Growth of Rhizopoda. Those Rhizo- pods that separate lime from the sea-water to form shells, begin the process while they are young single masses, and they increase by budding, each bud forming on the newest FIG. 9. end of the last bud ; consequently the perfect animal con- sists of a rod-like or spiral set of chambers, each chamber being a new, undetached bud. Two forms of Protozoa. Protamceba pri- DUOS DeCOme mltiva, the simplest living animal ; Mago- , sphtera planula, a compound form. quite separate and grow into new individuals. In a few cases each bud becomes detached, so that the animals always remain of one chamber. Shell-forming Rhizopods are occasionally aggre- gated in great masses and sometimes at great depths in the ocean. Such seems to have been their habit in past times, and many of the chalky limestones consist of the accumulated shells of Foramimfera. Invertebrate. Fig. 10. Class 2. Protoplasta. In the slowly running waters of ditches, or in bog pools, are found curious creatures in many respects reminding us of the naked Rhizopods. These amoebae as they are called, are little masses of protoplasm, moving and taking food by means of pseudopodia. On close inspection many particulars will be noticed, in which they differ from those simple creatures which we have already ex- amined. Thus their pseudopodia are blunt, and do not freely coalesce, on touching each other ; the granules and vacuoles are not uniformly distributed through the protoplasm, but are for the most part in the central region, while the outer protoplasm is firmer. We also notice a denser central spot in the body, to which the name nucleus is given, as can be seen in each component mass of Magosphsera (fig. 9) ; and one or more little clear spaces may be seen occasionally to contract and ex- pand alternately. Thus in the group of organisms of which Heliophrys variabilts. One of the Sun , . , animalcules showing the pseudopodia, am Ox ytrichaf>ibba. B. Trachelocerca clothe, either the whole bice * s - c - Vorticella ' citrin - FIG. 13. 26 Invcrtebrata. surface; or else special areas of it ; sometimes a few of these processes are rigid and act like little feet, or else they are all equal and fine, invisible during their active exercise owing to their rapid rate of motion. The outer layer of their body is a firm cuticle which covers a differentiated protoplasmic lamina con- FIG. 14. Paramcecium aurelia, an infusorian, showing the contractile vesicles (i') cilia and vacuoles (a). taining one or more clear spaces or contractile vesicles, which when watched can be seen to expand and con- tract regularly, pulsating like a heart. Within this layer is a more fluid mobile protoplasm containing granules, vacuoles and a pair of singular solid bodies called re- spectively nucleus and nucleolus. Protozoa. 27 Near one end of the body there is usually a funnel- shaped mouth opening into the inner protoplasm, where digestion takes place, as in Rhizopods ; the un- digested particles are ejected at a spot where the outer wall seems deficient, and which sometimes is a distinct opening. These animals multiply either by fission like most of the other Protozoa, or else the nucleus breaks up into egg-like masses which seem to develop into new infusoria. This condition is preceded by the forma- tion of a mucous mass around the animalcule, which becomes quiescent, losing its cilia. The Vorticella, or bell animalcule (Fig. 13, c) is a common form fixed by a slender footstalk, which on FIG. 15. Noctiluca miliaris, a marine luminous Atineta mystacina* animacule. showing its flagellum. irritation instantly contracts into a spring-like spiral and the ciliary crown around the mouth of the bell becomes introverted. Another common form, Ophry- dium, has an outer gelatinous envelope, and as division proceeds, this keeps the broods together so that they 28 Invertebrata. sometimes form masses of more than an inch in diameter, which ay^ often found floating on standing water. The commonest forms are the slipper animal- cule (fig. 14), the boat-like animalcule or Evplotes (fig. i), and the hay infusion animal or Colpoda, but almost every infusion has its own form of animal. Several groups of microscopic animals are allied to the Infusoria. Some of these are called monads and are mouthless nucleated bodies with one long cilium. Another of these is Noctiluca (fig. 15), a globular creature about ^th of an inch long, with a short obtuse vibrating flagdlum or filament and a mouth, but whose interior consists of netted protoplasmic threads whose meshes are filled with water. These organisms are among the commonest of those to which the sea owes its phosphorescence. Other minute forms, called Acinetse (fig. 16), are small, stalked masses whose surface is studded with radiating, retractile tubular suckers, through which they suck the juices of their prey. CHAPTER VI. SUE-KINGDOM II : SPONGES (POLYSTOMATA). Metazoa. All animals above the Protozoa possess an internal body-cavity, the wall around which is made up of three primary layers, often with difficulty discriminable in the lowest forms ; and there is either one terminal mouth into the cavity, or, as in the case of the sponges, many lateral pores communicate there- with. Polystomata. 29 Characters of Sponges. The common toilet sponge is a representative of a group of animals whose affinities are not easily understood. On ex- amination with a magnifying glass it will be found to consist of irregularly branching and re-uniting threads of a highly elastic material, so arranged that the inter- spaces between the finer branches appear as pores or canals, which, from the nature of their walls, freely communicate with each other. On examining the surface of a sponge, some large holes will be seen, which, on being cut into, are found to be the extremities of wide FIG. 17. spaces or tubes ; these divide within the sponge-mass into smaller canals, which again divide and subdivide until finally they end in the fine canals whose terminations are the minute sur- face pores between the superficial fibres of the mass. The walls of these spaces are themselves full of small pores in the interstices of the fibres which form the sub- stance. This horny mass is really the sponge skeleton, having the same relation to the sponge animal that the spicules of Radio- A calcareous sponge, larians bear to the soft parts of those creatures. We can most easily understand the nature of a sponge animal by examining such simple forms of the group as may be found encrusting sea-weeds or stones on our own shores. These are nearly cylindrical, 3O Invertebrata. rooted by a flat protoplasmic expansion below (fig. 17), and have a single wide opening above, which is named the osculum. Its walls are pierced by numerous fine apertures or pores, which open di- rectly into the central cavity. The wall consists of a cluster of Monad-like cells, provided with a collar, each sending out a pseudopod. In the wall and around each of the lateral pores are needle-like spicules of carbonate of lime usually united in threes, and arranged in a radiated manner. Sometimes they are in pairs or in twos. Others are like anchors, with two flukes. As in most sponges the wall of the body-cavity below each mouth is thick, not simple and membranous, the pores elongate into canals. Most sponges also grow in tufts or clusters arranged so close together that the outer pores of the neighbouring, and closely united animals communicate with each other ; thus a complex canal system grows up, according to the degree of thickening of the wall and coalescence of separate elements of the clusters, as well as by the superaddition of interspaces, which are often branched, between the separate individuals or elements. In a living sponge, currents of fluid set in through the minute pores on the surface, setting out in large streams through the oscula ; thus there are many mouths and few outlets. These currents are kept up by the waving of the flagella which bedeck the pro- toplasm masses that line the canals and cover the skeleton, and as these currents traverse the canals the small organic particles which they carry in are taken up by the cells of the wall in the same manner as food particles are swallowed by Rhizopods. Polystomata. 3 1 Spicules. The skeleton of most sponges consists not only of the horny material with which we are familiar in the toilet sponge, but ofspicules of silica of various shapes embedded in the horny mass, resembling pins, needles, clubs, crosses, anchors, hooks, wheels, &c. In others, siliceous spicules alone make up the skeleton, which has no horny matter. There is a calcareous skeleton in another group. Reproduction and Classification. Sponges multiply by division, either natural or artificial. That is, if we cut up a living sponge into many small pieces, each can grow into a perfect sponge! Other modes of growth or reproduction are by contin- uous budding, by the formation of free buds, usually arising in autumn and growing in the ensuing spring, or else by the formation of eggs which have been found in summer in many forms, and which develop in the following year Sponges are classified according to the material of the skeleton and the shapes of the spicules. Thus there are calcareous, horny, and siliceous sponges. The last class is the largest and includes some remarkable forms, such as the . boring sponge (Cliona celata), which pierces holes in old oyster shells on our sea-shore, and is known by its pin- shaped spicules. The remarkable Neptune's cup (Raphwphora) is closely allied, though very dissimilar in shape and size. Hyaloncma, the glass- tope, from Japan and Portugal, has long twisted siliceous spicules. Etipleetella, the exquisite Venus's flower-basket, from the Philippines, is now well known as an ornament, and exhibits .1 most wonderful interweaving of siliceous spicules. Sj>ongi B> Head of Ttenia mediocanel- each of which lata ' joints contains a complete egg-producing apparatus. When we remember that these worms may attain the length of 25 feet, and that there are at least twenty perfect joints in a foot, and that each joint can produce many scores if not hundreds of ova, we can form some idea of the amazing fecundity of these parasites. The growth of the individual takes place from the head, so that the oldest segments are those which are most remote from it and the newest are the fine joints close thereto. The life history of the tapeworm is curious. The eggs are protected by a very firm horny capsule and thus they can maintain their vitality for long periods of time, and can resist maceration and even short 62 V Invertebrata. exposures to high temperature. On entering the digestive organs of some animal with its food or diink, the embryo is set free and travels through the tissues of its new host as a little oval body armed in front with weak hook-like or boring spines. On reaching a suitable site it anchors, and the body dilates into a sac full of water. In this cystic condition the animal may remain stationary for a length of time, and by budding the number of cysts is capable of a rapid increase. When the flesh of an animal containing such cysts is eaten by another, the liberated saccular worm has its outer wall dissolved away, and its inner portion lengthens and in a short time becomes a true tapeworm. In most cases it requires two animals as hosts for the proper perfection of the worm. Thus the human tapeworm has its cystic stage in the flesh of the pig, the condition of pork called ' measly ' being due to these little cysts in the muscles of the pig. Similarly, the tapeworm of the dog develops from cysts found in the hare ; that of the cat from cystic worms in the mouse, that of the fox from cysts in the field-mouse, &c. In Ireland, the commonest human tapeworm has four suckers but no hooks on its head (fig. 36 B), and is known as Tcznia mediocanellata ; its larva inhabits the ox. In Russia and Switzerland, the human tapeworm is quite a distinct species, with very flat body, no hooks, and two long grooves on its head in place of suckers ; its larvae live in the waters of certain lakes, and it has been supposed that it is through these waters being used for drinking purposes that they gain entrance into the human body. Flukes. Trematodes or Flukes. The second order of sucker-bearing parasitic worms consists of the ' flukes/ FIG. 37. FIG. 38. Dittoma lanceolatum^ the liver fluke, a, mouth ; b, sucker ; c, digestive canal; d. e, water-vascular sys- tem ; A, k t reproductive organs. Oxyuris vermiciilaris, the common threadworm of children. met with in the liver of the sheep, and of allied forms ( n g- 37) ; these are not united in chains as in the 64 Invertebrate tapeworms, but each consists of a single segment bear- ing one or two suckers (a, b). In many respects they resemble the Turbellarian worms, but are not ciliated and often present formidable armatures of recurved hooks. They are like tapeworms in the development and complexity of their ovaries, and many of them show in their history alternations of generations as curious as those of their relatives the tapeworms ; for example, the larvae of some liver flukes live for a time free, in water,- and develop within their bodies little cylindrical worms, which are set free on the bursting of the wall of the parent, and in turn enjoy an inde- pendent life. Within these worms again there may form another brood of internal buds, which also grow, burst their envelope, and become for a time free, but soon attach themselves to some soft aquatic animal in whose body they become encysted, to develop finally into the mature forms when their first host is eaten by some larger animal. Thus the flukes found in" water-fowl have their larvae in water molluscs, &c. To these flat sucker-bearing parasites the name Trematoda is given. CLASS TIL Nematelmia. These, the commonest forms of parasitic worms, are cylindrical, tapering to each end, and possessing a body cavity (fig. 38.) They are never divided into successive joints, although their surface may be finely ringed, and there is always a digestive canal with an outlet, as well as a mouth. The round worm, often found in the small intes- tines of children, is a good example of the order. It is about seven or eight inches long, ringed on its surface, with the mouth at its anterior end, surrounded by three little lobes j from this, a tube, the oesophagus, passes Thread-worms. 65 to the stomacl , which is a small suctorial muscular cavity, communicating by a straight intestine with an outlet which is not terminal. Beside the common round A scar is lumbricoides, the human digestive canal is the occasional dwelling-place of two other worms, one of which, Oxyuris vermicularis, is a small thread- like worm (fig. 38), the other Trichocephalus dispar^ much more common, has a very slender neck and a thicker body. A species closely allied to the last named is the Trichina spiralis, a minute worm found in the flesh of pigs, calves, &c., which when introduced into the human body, often multiplies rapidly in the voluntary muscles of the system, causing dangerous and even fatal symptoms. These worms are as prolific as their fellow parasites, and the early stages of many live for a time in water, from whence they enter into the bodies of their hosts, and in those whose life-history we know, the free and parasitic conditions appear very dissimilar. It has been supposed and with reason that most of the free Ne- matelmians found in stagnant pools are early stages of parasitic species. Gordiacca. The horsehair-like thread - worm which is found in rainwater pools is an example of a second order 01" round worms. This remarkable animal begins life as a little larva living in mud or in water pools ; it is armed with boring spines, whereby it pierces into the body of a beetle or other aquatic or terrestrial insect ; here it becomes encysted, and, having grown in this condition to a considerable length, often ten times as long as its host, it becomes free and aquatic and produces its eggs. So rapidly do some F 66 Invertebrata. of these multiply, as, for example, the common Mermis aloicans, that they have given rise to the belief that they have fallen as ' worm-ra.ins.' These worms are called Gordiaceae and are distinguished from the other round-worms by the rudimentary condition of their digestive canal. They are also remarkable for their extreme tenacity of life, as they can be dried into hard brittle threads and yet appear lively and active on being moistened. CLASS IV. Acanthocephala. The ' thorn-headed ' worms are rounded, or cylindrical, each with a pro- trusible proboscis armed with many recurved hooks. They are remarkable for the total absence of the mouth and intestine in their adult condition. The common- est species are found in the intestines of swine, &c., with their heads buried in the substance of the wall of the digestive tube. CHAPTER XII. NON-PARASITIC WORMS. CLASS V. Wheel- Animals, Rotatoria. On tracing the development of the more complex free worms we find that the larva, after emerging from the egg, ap- pears as a free-moving creature, with circlets of vibrat- ing cilia aiound its extremities, these ciliary lobes being in some forms large and rounded (fig. 47, A). In rain pools and ditches, small creatures are fre- quently met with which resemble the larvae of worms, Spoon-worms and Leeches. FIG. 39. but which remain permanently in this ciliated condi- tion. In these, the ciliary lobes are prominent and rounded, acting as locomotory organs, and from the rapid vibration of the cilia which clothe them they seem like rotating wheels, hence these little creatures are called Rotatoria. They are microscopic in size varying from 3-^o tn to Jth of an inch in length, but from the exquisite transparency of their bodies the details of their organisation can be seen by the aid of the microscope. The male rotifers are few and small and have no digestive canal ; the females have a com- plex nutritive system, and many species are provided with an organ of mastication like an anvil acted on by two hammers. These animals can bear much ill usage, and are capable of reviving again on being moistened, after having been almost com- pletely dried up. On irritation the trochal disks (fig. 39, c] can be retracted into the cavity of the body, from which they are gradually protruded again on the cessation of the stimulus. Some rotifers are rooted ; others possess a forceps posteriorly, whereby they can hold on to foreign bodies ; others again are contained in sheath, into which they being irritated. CLASS VI. Spoon- worms or Squirt- worms, Gephyrea. These are interesting marine worms whose F 2 a vase-like can retract themselves, on 68 Invertebrate elongated or sac-like bodies contain a long tortuous in- testine, ciliated inside and outside. They rarely exhibit a division into segments, nor have they locomotory pro- cesses of any kind, and they never have any calcareous FIG. 40. FIG. 41. Tooth and Muscles of Leech. Embryo Leech. Adult Leech. Mouth of Leech. or siliceous spicules in their skin, although sometimes there are a few bristles scattered on the surface. The mouth is at the anterior end, and it is provided with a protrusible proboscis, sometimes of great length. CLASS VII. Leeches. The next group of worms is exemplified by the common horse-leech or by the medicinal leech. They are soft-bodied annulated worms which live parasitically on the outside of verte- brated animals, from which they draw their nourish- ment. Their bodies are composed of segments, which are indistinctly or not at all marked from each other Leeches. 6 9 on the surface, but can easily be distinguished within, as the organs of the body are arranged in successive groups. Leeches have at their front end a sucker, and some have a second suctorial disk at the hinder ex- tremity, and several species are even pro- vided with lateral suckers. The mouth is generally situated in the front sucker, and it is armed with three horny jaws or plates (fig. 41) with serrated edges. These plates act as teeth, enabling the leech to make incisions in the skin of its host through which to suck the blood. The digestive canal is straight and consists of a central tube with a row of blind pouches along each side (fig. 42, B) which can become distended, hence the body can take in a great quantity of blood. There is a nerve-ganglion in each segment of the body, the first (fig. 42, c) of these is comparatively large and made up of several smaller ganglia grouped together; the successive ganglia are united into a chain by fine filaments and they lie on the ventral or under side of the digestive organs. Leeches possess proper blood-vessels in which their own nutritive fluid circulates. Their water- vascular system takes the form of a series of segmented A Reproductive organs of leech. B Di- gestive canal of leech, c Nervous sys- tem of Malacobdella. 70 Invertebrata. organs or tubes opening laterally, one on each seg- ment. The egg-producing organs are very complex. Locomotion takes place by the suckers : the hinder one being fixed, the animal elongates itself and, fixing its front sucker, sets free the hinder one, then shortening its body it proceeds in a similar manner. Leeches can also swim, and when so progressing the body becomes flattened by the contraction of vertical muscular fibres which run from the dorsal to the ven- tral surface, and then by undulating movements it advances like a wavy ribbon. Medicinal leeches are principally imported from Hungary and Sardinia. CHAPTER XIII. NON-PARASITIC WORMS. CLASS VIII. Bristle-footed Worms (Chsetopoda). We can scarcely turn over a stone on the sea shore FIG. 43. Transverse section of a Worm, of Amphioxus, and of a Vertebrate contrasted. a, outer or skin layer ; b, dermal connective layer ; c, muscle plates ; d, segmental organ ; h, arterial, and i, venous blood-vessel ; g, intes- tine ; /, notochord. without finding under it some species of the group of Worms. bristle-bearing worms, a class of which the lug-bait or the hairy- bait of fishermen may be taken as represen- tatives. These worms have bodies made up of a succession of simi- lar joints, and their locomotion, either creeping or swimming, is accomplished by means of little stumpy bristle-bearing eminences, with which their bodies are pro- vided. Each joint of the body exhibits two pairs of these pro- cesses, two of which are on the upper or dorsal surface, and two are on the ventral or under sur- face, oae on each side of each surface ; these are known as dorsal and ventral oars. The mouth is on the second segment, and is often armed with sharp teeth. The intestine is usually straight and very often has lateral pouches appended to it like those in the leeches. There is a vascular system consisting of long tubes, dorsal, ventral and lateral, and the blood contained in these is often red, green, or white. The gills are usually arranged along the dorsal surface of the body spring- ing close to the root of the dorsal oar, and in these the blood is purified by being exposed to the oxygen held in solution in the sea-water. Arenicola piscatorutit Lug-bait worm. 72 Invcrtebrata. There are also segmental tubes opening one on each side of each segment, and sometimes the eggs, which are produced within the body, escape through these canals. The chain of nervous ganglia is also well- developed. Some worms secrete a glutinous material from their surface, which cements together sand-grains and other foreign bodies into a tube wherein the animal lives. Other worms secrete from their surface cal- careous matter which makes up a tube as a dwelling- house, in which the animal is permanently contained. Such forms have the gills developed only on the fore- most segments of the body, and have the dorsal and ventral oars of all the other joints rudimentary ; but they possess tentacle-like, branching processes about the head. Of these the common Serpula, whose white calcareous snake-like concretions are so common on the stones and shells on the sea shore, and the Spirorbis, whose minute white whorled shells dot the surface of the shore-tangles, are examples. A few worms are phosphorescent ; many others, ike the sea-mouse, are clad with iridescent scales and bristles. The common earthworm has much smaller and fewer bristles, which are in the form of recurved hooks, not elevated on stumpy processes of the sur- face. The body is closely ringed and tapers from the middle forwards to an acute point in front. Each ring bears its armature of hooks, which can easily be felt by drawing the body of a worm between the fingers from tail to head, although they are scarcely to be detected when we feel the body in the reverse direction. In beginning to burrow, the worm lengthens Worms. 73 its body and pushes its sharply pointed head into the mass of soil which it is about to perforate, then having insinuated the few foremost rings of its body into the mould, the whole animal contracts in length, thus swelling the front of the body in thickness and for- cibly dilating the opening made by its fore part, the worm being prevented by its hooks from slipping out of the opening ; then it again lengthens its body in front, its hooks giving it a fixed point from which to act, and by a succession of such elongations and thickenings it can ' worm ' its way through even a hard gravel walk. The mouth of an earthworm is placed on the second segment, near the apex of the body, and from it the digestive canal extends as a straight tube through the body. This tube is very wide and is always found full of earth, as these animals devour large quantities of the soil for the sake of the organic particles con- tained in it, the remaining part being passed out, and heaped by the worms at the outlet of their burrows, as * wonn casts.' For the better division of the mate- rial swallowed, the digestive canal is provided with a muscular gizzard about fifteen rings behind its mouth. The eggs in earthworms are produced in the body cavity beginning at a point about seven rings rom the mouth, and they usually fill the body for ibout seven segments, distending it and producing a thick white band or ring which we often notice in the body of worms during early autumn. Worms are propagated exclusively by eggs, the common belief that, when cut in pieces, each part is capable of inde- pend'.nt life not being strictly true. If we divide an *4 Invertebrata. earthworm about its middle, the hinder segment dies after a short time ; the fore segment will probably live and its wound heal. Similarly, if we cut the anterior four or five segments away the small fore fragment will soon die, while the large hind mass will recover. CHAPTER XIV. MOSS POLYPS AND TUNICARIES. CLASS IX. Moss Polyps (Bryozoa). The broad leathery fronds of the tangles along our shores are often encrusted with beautiful lace-like patches of regular and minute patterns. If we put a fresh, living piece of this into a vessel of sea-water, we find that each of the cell-like spots is the home of an elegant little organism which may be seen to protrude through the mouth of its cell a delicate little crown of tentacles. Each colony of these animals consists of a common stock, bearing numerous little cells, and each cell contains its delicately organised inhabitant. Some of the little creatures become modified into bird's-beak-like graspers with two horny jaws, for the protection of the colony (fig. 45, B) ; others become altered into globular pouches for the reception of the eggs after their extrusion. Each of the dwellers in these little cells consists of a saccular body containing a looped digestive canal, in the bend of which a nerve ganglion is placed, and it is provided with a crown of hollow tentacles guarding the mouth. Most of these moss-polyps are marine and have Tunicata, a circular protrusible basis, supporting the tenta- cles ; some few are inhabitants of fresh water, and these have the tentacles on a horse-shoe-shaped basis ; these also have a little valve to shut the mouth, which is present in only two of the marine forms. Each of the little constituent animals of one of these colonies has its own digestive canal, its own nervous system, FIG. 45. A. Natural size of Acamarchis avicuJaria, one of the Moss Polyps ; B. Magnified view of one Polype, showing its 'bird's head.' and its own egg-producing apparatus, and these are essentially like the corresponding organs in worms. CLASS X. Tunicata. These also are marine soft- bodied animals, met with in abundance attached to shells and stones among the tangles on our sea shores. They are often called sea- squirts, on account of their ejecting little jets of water from their terminal open- ings when irritated. They appear as irregular or oval 7 6 Invertebrata. cated worm . A, Pharynx, or re^pira tory body ; masses of semi-transparent, often gristly material, and of a whitish, pink, or brownish colour. They vary in length from i to 6 inches. In each tunicary there are two apertures on the surface; one of these (c, fig. 46) opens into a large chamber whose wall (e) is a vascular mem- brane, and at the bottom of which is the mouth (k). The digestive canal ends at the bottom of a second chamber (/"), of which the lower or hinder opening is the outlet. Be- tween these two chambers, which thus lie over the digestive canal, there is a partition wall which is pierced by many small holes whereby the water which enters into one can pass into the other, thus bathing the surface of the lining membrane, and enabling the blood contained in the spaces in its texture to become aerated. The first chamber (fig. 46) is called the branchial chamber, the second is called the atrial. Between the opening of the branchial chamber and the atrial ori- fice there is a nerve ganglion send- a tuni- m g a fi ne 1P of branches around the mouth. The heart lies at the ocy Bstmac c egg-producing organ! it the vessels pass into the wall of Summary. yj the branchial chamber. In the action of this heart a curious appearance is observed ; the blood is driven by this vessel first from one end to the other, for a second the action stops, then it is resumed in the opposite direction, again another cessation, and another reversal, &c. The * tunic/ or outer wall (/) contains a starch-like compound which is interesting as it is almost the only instance of the occurrence of a starch-like compound in the Animal Kingdom. Young tunicates as they emerge from the egg appear as small, tailed larvae, with bodies consisting of two cavities. The axis of the tail consists of a cartilaginous or gristly rod : in one cavity of the body the nerve ganglion is developed, in the other space the viscera are formed. Thus they foreshadow the struc- ture of vertebrate animals. Tunicaries are sometimes solitary, but many species are found united into social assemblages, and this union may go as far as the perfect union of the blood-vessel systems, a single vascular apparatus sup- plying the whole colony. In one group, the Salpae, there is an alternation of generations, solitary and colonial forms succeeding each other in a cycle. Many of the tunicates are phosphorescent, Pyrosoma, a compound form inhabiting the Atlantic ocean, being the most vividly luminous animal met with in the seas. Summary. The chief types of worms may be tabulated thus : i. Unjointed, ciliated, non-parasitic forms without ciliated head-lobes = Class Turbellaria, 78 Invertebrata. 2. Unjointed or obscurely segmented minute forms, with ciliated head-lobes = Class Rotatoria. 3. Parasitic, flat-bodied forms, with no body cavity, and provided with suckers = Class Cotylidea. 4. Parasitic forms with no suckers nor digestive canal, and with a hook-bearing proboscis = Class Acanthocephala. 5. Cylindrical, unjointed, non- ciliated forms, with digestive canal and body cavity, mostly para- sitic = Class Nematelmia. 6. Segmented forms with a proboscis, and convoluted intestine, non-parasitic = Class Gephyrea. 7. Segmented, bristle-clad worms with no suckers. moderate intestine, non -parasitic = Class Chaetopoda. 8. Segmented, unbristled, sucker-armed, external parasites = Class Hirudinea. 9. Sessile, one-jointed, colony-building worms living in cells and with a crown of protrusible tenta- cles = Class Bryozoa. 10. Sessile or free, one-jointed worms, with one nerve ganglion but no protrusible crown of tentacles = Class Tunicata. CHAPTER XV. SUB-KINGDOM VI. MOLLUSCA, SOFT-BODIED ANIMALS. THIS division includes all such forms as oysters, whelks, snails, and cuttlefishes. Most of these are aquatic and in none is there an inner skeleton (except some small gristly organs in cuttlefishes) nor are there Molluscs. 79 any limbs, properly so called, in the whole group The outer tunic of the body is generally thick and extended to form a leathery envelope or mantle, the outer surface of which secretes a shell of carbonate of lime for the protection of the animal. The earliest condition of existence of a mollusc, after it has left the egg-stage, is as a small ciliated, worm-like body having at its head an expanded lobe, richly clothed with cilia and resembling the trochal Larval forms of Worms and M olluscs. A, Larva of a Gephyrean Worm ; B, c, Larvae of Molluscs, showing the ciliated velum v, and the rudi- mental foot, f. discs of a rotifer, or the tentacle-bearing basis of the moss-polyps (fig. 47, B). This process is lost in the adult in general, but is interesting as one of the many eviden- ces of the relationship between worms and molluscs. The shells secreted by molluscs consist of one, two, or several valves, or pieces, and are very various So Invcrtebrata. in shape, and often brightly coloured. All molluscs have a digestive canal, and sometimes a complex arrangement of teeth. They have like- wise a nervous system consisting of a ring around the fore-end of the diges- tive canal, on which are formed ganglia over and under the tube ; besides this there are often other nerve masses and organs of sense. There is a heart which propels the blood, but there are few or no blood-vessels, the circulation Lamp-shell or Te- . . ... rebratuia, one being chiefly carried on in the inter- of the Brachio- - . . , , pods, dorsal sur- spaces of the tissues. I here is rarely much of the body-cavity to be found free, with the exception of a small space around the heart, which is called the pericardium, and from this two short tubes pass out representing the segmental organs of worms. Four classes are included in this sub-kingdom. CLASS I. Brachiopoda. Of this class compara- tivey few representatives are now living, and these in few places, usually at considerable depths in the sea ; but at an earlier period of the world's history they were very abundant. They possess shells of two valves, one of which is large, placed ventrally or down- wards, and having a beak pierced with a hole, through which a foot-stalk projects whereby the animal is anchored. The other valve is smaller and placed dor- sally ; it bears on its inner surface a delicate shelly loop for the attachment of the peculiar arms from which the name of the class is derived. The valves are joined, either by horny matter as in the duck-bill Shells of Bivalves. 8 1 shells (Lingula) of Australia, or by tooth-like hinges, as in the lamp-shells (Terebratu/a), and there are several muscles for opening and others for closing the valves. The mantle in Brachiopoda is full of blood-spaces, which are the only breathing organs in these animals, and there is said to be a heart lying on the stomach for driving on the blood. Some anato- mists dispute the presence of a heart, and claim that the blood is impelled through the body by ciliary ac- tion alone. The larvae of Brachiopoda are freely locomotive and possess eyes and ear-sacs, but the eyes disappear in the fixed adult in which the ciliated head lobe of the embryo becomes converted into the basis of the arms. These arms are long and hollow, usually spiral and clothed with tentacles, and their to-and-fro mo- tions cause currents which bring the food within the reach of the mouth of the stationary animals. CLASS II. Lamellibranchiata. More familiar to us are the representatives of the second great group of molluscs, oysters, mussels, cockles, &c. These are easily recognised by their bivalve shells, and by the two-lobed mantle under whose folds are the gills or breathing organs arranged in layers or lamellae. The freshwater mussel, or the large Mya or clam, easily found along our coasts buried in the sand, out of which the tips of their long siphonal tubes project, are good examples. The shell of one of these ex- hibits to us a beak or point on each valve, and is marked by numerous lines parallel to its margin ; the inner surface also differs in texture from the outer, being whiter and often exhibiting a mother-of-pearl 82 Invertebrata. lustre. The cause of the difference in appearance is seen on making a microscopic section through a shell, as the outer surface is composed of long, nearly ver- tical, prisms, while the inner surface consists of fine layers whose edges overlap each other. These edges Diagram of the anatomy of a Lamellibranch, or Bivalve Mollusc, g, stomach ; i intestine surrounded by the liver, the two tubes on the left marked by arrows are the canals of the siphon, a, the anus ; b, hinder adductor muscle ; c, heart ; d, nerve ganglia ; e, fore adductor muscle f t mouth ; h, gills. are often finely waved, and so decompose the rays of light which fall on them, thus producing the iridescent appearance seen in so many shells. The nacreous or mother-of-pearl layers are secreted by the surface of the mantle, while the prismatic material is formed by the margin of that structure. Thus the shell is con- stantly increasing in size by the formation of new prismatic matter, the lines of growth being the con- centric curves before noticed. The edge of the mantle Structure of Bivalve Molluscs. FIG. is sometimes fringed, and the irregularities secrete corresponding processes on the shell in the forms of ridges, spines, c. On the inside of the shell a line of demar- cation shows where the nacre-secreting surface ends, and the prism- secreting por- tion begins, this is called the pallial line ( fi g- 5)- Hinge. The two Valves Of the Shell Shell of Galathea, showing the hinge, mantle inLamellibranchsare usually similar to each other; they are disposed late- rally, one on the right and one on the left, and are united by a hinge of interlocking teeth at the dorsal margin. A highly elastic ligament unites the valves outside to the hinge, and is so arranged that it keeps the valves slightly open. On the inside of , abdomen. in almost every conceivable locality on the earth's I 2 1 1 6 Invertebrata. surface. Scarcely a plant exists but it harbours some one of the tribe, and many animals, living or dead, supply food for other species. Insects are usually of small size and have the six foremost segments united to form a head. The three succeeding segments form a thorav, which alone bears the legs, one pair on each of its rings, and when wings are present they are borne by the middle and hindmost of these thoracic rings. The abdomen consists of seven segments not bearing any limbs, and followed by one, two or three abdom- inal rings, to which are appended the sting or its equivalent, the ovipositor. A black beetle, a blue- bottle fly, and a butterfly may be taken as types of the class. Organs of Sense. The head of an insect bears a pair of compound eyes, and often several simple eyes in a cluster. The former have a cornea or transparent surface divided into many facets, each of the nerve rods having its own pigment mass and its own cornea. In the common house-fly there are 2000 such facets in each eye, and in the dragon-fly there are 28,000. The head of an insect also bears one pair of antennce or feelers, jointed organs which vary much in shape and structure, being sometimes simple, filiform, comb-like, or lamellar. These are organs of touch and hearing, possibly of smell and taste, and also of communication between one insect and its fellow. Month. The mouth is on the fore and under part of the head and varies in shape according to the method whereby the insect obtains its food. In beet- les, dragon-flies, &c., the mouth is armed with chew- ing jaws. There are two lips, an upper or iabrum (fig. Mouths of Insects. 117 65, e) and lower or labium. The lower (/) represents the second pair of max- illae in the lobster and crayfish, which here are united together, but sometimes as in cock- roaches (fig. 64) and locusts remaining sepa- rate. The labium bears a pair of feelers called labial palps (k). Between the and the labium Under side of mouth of Cockroach. f . maxillary palp ; i, ligula ; * para- are tWO pairs Of ja\VS gloss* ; k, labial palp ; i, cardo of placed vertically, so that FIG. 65. hinge ; 2. stipes ; 5, maxilla ; 6, galea, or sensitive process of maxilla. FIG. 66. Upper side of head of Cockroach. I, epicranium, or top of the head ; d, clypeus; e, labrum ; f, mandibles : A, antennae. Mouth of Flea. Showing the slender style- like labrum between the long mandibles medially, and the labial and max. illary palps laterally. in acting they move in a horizontal plane. The uppei 1 1 8 Invertebrata. pair are named mandibles or biting jaws, the lower pair maxillae or chewing jaws. The last-named have usually appended to them on each side a pair of small jointed feelers or maxillary palps. In the bluebottle and house-fly the lower lip is lengthened into an elon- gated gutter-like sheath in which are contained the maxillae and mandibles, which are reduced to mere bristle-like processes. In the bee (fig. 77, p. 132) the upper lip and mandible are strong and fitted for chewing, while FIG. 6 7 . tne rnaxillae and lower lip are long and channelled, so that when placed in apposition they make a tube through which the insect sucks in honey. In these crea- tures the lower lip consists of two parts, an upper or tongue and a hinder part or mentum. In the butterfly, the mouth has lost all trace of its chewing func- tion and the maxillae form two half tubes, and when opposed as Head and proboscis of But- , . . , terfly, showing antennae they always are they make up a canal, and being very long and curved, this is sometimes called the proboscis. Each of these maxillae has within it also a fine tube, and thus a transverse section through the proboscis shows three tubes, one medial between the maxillae and one lateral on each side within each maxilla. Behind this proboscis lies the labium, which has usually large palps between which the proboscis lies when retracted ; for, unlike the tube in the bee, this proboscis is freely retractile. Nervous System of Insects. 119 Body. The head is joined to the thorax by a nar- row neck, and this region is generally strong, and the limbs are attached to the under part of the side of each of its three rings. Each limb is composed of five joints : hip (coxa ), a ring segment (trochanter), thigh (femur, fig. 63, k], a shin (tibia], and a tarsus of seve- ral joints ending in the claws to which sucking cushions or pads may be appended. The wings are jointed to the middle and hinder rings of the thorax ; these are modified lateral flaps of the body wall, such as exist in some crustaceans ; the thin skin folds of which they consist are supported by chitinous ribs (costa) con- taining branches of the tracheae. Internal Structure. On the sides of each abdo- minal ring are the apertures of the long, finely branch- ing tracheae, which sink into the body and are distri- buted widely among the tissues. Each tube has a membranous wall strengthened by a coiled spiral chitinous thread which keeps it open for conveying air from the surface through the body. Each motion of the body by altering the tension of the vessels pro- motes this method of respiration. The dorsal tubular heart placed in the abdomen, consists of a chain of chambers separated the one from the other by valves. This receives the impure blood and the new blood from the intestines, and propels it by the chief blood- vessels into lacunae or interspaces between the tissues which are thus nourished. The blood is colourless, or green, rarely red. Insects have two large and complex nerve ganglia in the head, and ganglia in all the segments from the head backwards. The head ganglia send branches 120 Itivertebrata. to the eyes and appendages, while the thoracic ganglia supply the limbs. Some cave-dwelling insects have no eyes, others have these organs rudimental. The digestive canal of insects consists of a stomach to FIG. es. which the long oesophagus or gullet leads from the mouth ; to this a thin walled sac or sucking stomach may be ap- pended as in butterflies, in others there is a gizzard with hard horny tooth-like pro- cesses, and this is followed by the glandular thin- walled true digestive stomach which ends in an intestine, whose length depends on the nature of the food, being longer in Nervous system of Beetle, f showing central double nerve thOSC that feed On SOlld than cord and chain of ganglia. matter, and longer in the herbivorous than in the predaceous forms. Glandular tubes opening into the end of the intestine exist in many insects, and from their first describer are known as Malpighian. Some insects are luminous. In the glow-worm (Lampyris noctilucd] there is a large fatty body in FIG. 69. the abdomen richly supplied with tracheae and nerves from which a bright light is emitted. The fire-fly (Elater noctilucus) sends out light from two oval spots on the thorax. Grasshoppers and crickets emit sounds by rubbing one part of the Metamorphoses of Insects. 121 body against another, and such have usually a special hearing organ which in crickets and locusts is placed under the knee on the outside of the foremost pair of limbs. Development and Metamorphoses. Insects' eggs have often a sculptured shell, and are laid in such places as are suitable for the supply of food to the newly hatched larvae. For this egg-laying the parent has often an organ formed of the modified append- ages of the abdomen. These organs are in the form of bristles, pincers, or saws, and by these the insect prepares the place for and deposits its eggs ; hence, the organ is called an ovipositor. The young of most insects emerge from the eggs as worm-like animals called caterpillars or larvae. These are little jointed creatures, having a head which bears eyes and a pair of antennae. Its mouth is armed with strong jaws, and the surface is often covered with bristles. Each of the three anterior segments of the body of a caterpillar is usually provided with a pair of little stumpy feet, and sometimes, as in the larvae of butterflies, flies and saw-flies, the hinder joints have also foot- like processes. Caterpillars are most voraci- ous in their habits and grow rapidly, frequently moult- ing or shedding their skin. On reaching the limit of size, many caterpillars begin to spin for themselves a case or cocoon. The glands from which this pro- ceeds are two long tubes placed behind the head, but opening on the lip, and the material of the cocoon is silk. When caterpillars are fully fed they give up eating, and their skin thickening they become fixed and rigid and are known as pupae, or from 1 22 Invertebrata. their occasional metallic lustre, chrysalides. In this pupa stage the animal lies for a considerable time; this skin then bursts and the perfect insect emerges, at first soft and moist but soon becoming firm and fit for independent life. Caterpillars differ much in structure from the adult insect; thus the digestive canal of the cater- pillars of butterflies is fitted for the digestion of solid food, while that of the imago or perfect insect is only fitted for sucking the juices of plants. The antennae likewise of caterpillars are attached to the front edge of the forehead shield, and outside the articulation of the mandible, whereas the antennae of the imago or perfect insect is articulated further forward, and on a plane with the joint at the base of the mandible ; thus the antennae of the caterpillar represent the long antennae of the crab and lobster, while those of the perfect insect represent the anten- nule of crustaceans. Insects display an amount of intelligence far superior to that of the lower verte- brates; ants, wasps, and bees, the most highly or- ganised as well as the most intelligent of the class, exhibit a wonderful power in the mode of ordering and governing their communities, and the skill shown in the construction of their habitations is scarcely inferior to that of man himself. There are at least thirteen orders of insects known to the naturalist, a few of the commoner and more interesting representatives of which are shortly de- scribed in the next two chapters. Bugs. Spring tails. Eat wigs. 123 CHAPTER XXIII. ORDERS OF INSECTS. ORDER I. Bhynchota. This group consists of those insects which either undergo no metamorphoses or a very slight change in FIG. 70. the process of growth. They have almost all suctorial mouths (fig. 70), consisting of a long tubu- lar labium, whose base is open or covered by the labrum like a little lid. The mandibles and maxillae are altered into piercers or bristles which work within the tube. A few, however, like the bird-lice, have hook-like mandibles and chewing mOUths. Many Of the Showing the median elongated labium, incf^tc r\f tVn'c rvrrl^r arp tne f ur bristle-like mandibles and insects ot this order are maxillaet also , at ^ sideSj Ac an _ parasites and wingless, tennae and * such as lice and bugs ; others, the aphides, the small green insects which are so abundant on roses, gera- niums, &c., are plant parasites. These aphides are marvellously prolific, a single pair being capable in one year of producing a progeny of twenty thousand millions or even more. Some aphides have glandular tubes on the abdomen which secrete a sweet honey-like fluid. This fluid is used 124 Invertebrata. as food by some species of ants, especially in this country by the red and yellow ants, which can be seen to 'milk' the honey tubes with their antennae and swallow the fluid. Several species of aphides appear to be kept as ' milch kine ' by these ants, and are fed by them apparently for this secretion. Other representatives of this order are the cochineal and lac insects, the * water boatmen 'and ' water scorpions/ as well as the numerous and often brightly coloured field bugs. ORDER II. Thysanura. Spring- tails, an unim- portant group, consisting mostly of very small crea- tures, sugar-lice and spring-tails, which live in dark, damp cellars, or in sugar stores, and can be seen hopping or springing about and shunning the light. They scarcely undergo metamorphoses, and their mouths are suited for chewing. The extremity of the abdomen is prolonged into a pair of bristles or a forked tail, whereby the animal is enabled to progress by leaping. The scales of the bodies of some of these Podurae or spring-tails are marked with very minute furrows. ORDER III. Euplexoptera. This order includes the earwigs, which are remarkable for their curiously folded hind wings, that lie folded like a fan under cover of the hard-shielded forewings. They have a masticating mouth, and posteriorly there is a pincer- like long abdominal appendage in both male and female. The earwig is remarkable for sitting on her eggs to hatch them, and for the maternal protection which the female exercises over her young which resemble her except in the absence of wings. p-r Thrips. Cockroaches. Locusts. 12$ ORDER IV. Thysanoptera, or fringe-winged in- sects, including a not uncommon little fly, named Thrips, whose contact with the face in warm weather is often a source of considerable itching from the titilla- tion caused by its plumose wings and bristled body. One species of this order by piercing the immature wheat grain with its bristle-like mandibles causes the seed to shrivel, and occasionally destroys even the corn stalks. ORDER V. Orthoptera, straight-winged insects, includes cockroaches, grasshoppers and locusts. These have four wings, of which the often parchment- like front pair are the smaller ; the second pair are usually large, and when at rest are folded like a fan. The mouth is masticatory and both pairs of maxillae are free. Some of the tropical forms of this order are wingless and assume extraordinary forms, the walking leaves, mantis, and walking stick (Bacterium) sometimes resembling dry twigs or bits of branches. In the common cockroach (Periplaneta orieiitalis) which is a native of the East, the legs are fitted for running and have spiny tibiae, the head is over- lapped by the front segments of the thorax and bears long antennae, and the parts of the mouth are distinct (figs. 64, 65). The wings are very small, especially in the females. The Drummer Cockroach of the West Indies adds to its other disagreeable qualities that of making a knocking noise, which is sometimes sufficiently loud to keep awake the inhabi- tants of houses infested with these insects. Troctes pulsatorius, a minute insect found in books, old pic- tures, &c, also produces a sound which has earned for it the name ' death-watch ; or ' death-tick.' 126 Invertebrata. Locusts are terrible scourges in tropical countries, devouring all vegetation and leaving bare the regions over which they pass. Their body is long and laterally compressed and the long hind legs act as leaping organs. They produce a chirping sound by rubbing the thighs against the elevated ribs of their wings. In the grasshopper and cricket a similar sound is produced by the rubbing together of spots on the wings provided with raised ridges. The white ants or Termites of tropical regions also belong to this order, and build ant-hills of extra- ordinary size and hardness. Their colonies are very complex, and consist of several kinds of inhabitants, females, males, workers and soldiers. The dragonflies, which also belong to this order, have aquatic larvae, breathing by means of tracheal FIG. 71. Larva of Dragonfly, showing the ' Mask.' gills or tuft-like processes of their body- wall contain- ing tracheae, but with no openings. These processes are lost in the perfect insect ; in one American genus, however, these appendages are retained during life. The larva of the common dragon-fly has a long and jointed under lip, which is folded over the face when at rest and is called the mask, but when the animal is feeding it becomes extended as a formidable tongs- like weapon for the grasping of prey (tig. 71). Fleas. Flies. 127 CHAPTER XXIV. INSECTS WHICH UNDERGO PERFECT METAMORPHOSES. THE four orders of insects which follow are small, but contain some interesting forms which deserve a passing notice. FlG ?2 ORDER VI. Neuroptera, nerve-winged insects, including the scorpion-flies (fig. 7 2 ^snake- flies, and ant-lions. These in their perfect stage possess a mouth fitted for chewing, and four equal membranous wings, Pan n. or Scorpion-fly, of which the hinder pair are never folded. Few of these insects are natives of this country. ORDER VII. Trichoptera, including the caddis- flies which have hair-clad or scaly unequal wings, the hinder of which are folded. Their larvae agglutinate small shells, stones, straws &c. by silken threads secreted by a small spinning gland placed on the lower lip, and of these they make cases in which they live. Having attained its full size, the pupa fixes its case under water and spins a silken network or grating over each end of it, thus shutting itself in for its pupa sleep, while it does not exclude the water which it requires for breathing. After this stage of rest the pupa by its strong jaws bites through its prison, and after moulting assumes its adult form. ORDER VIII. Strepsiptera includes the curious 128 Invertebrata. parasites which live on the abdomen of bees and wasps. In these the males have four wings, two in front, small and twisted, from which the order is named, two behind, large and fan-like ; the females never lose their last pupa-skin, and are wingless, with a worm-like abdomen and are viviparous. ORDER IX. Aphaniptera. Includes fleas which have laterally compressed bodies and exceedingly rudimental wings, the scale-like traces of which are with difficulty noticeable. The suctorial mouth (fig. 66), without upper lip, has long slender saw-like mandibles, which are sheathed by the three-jointed labial palps at their base. The antennae are very small and lie in a groove, but the maxillary palps are large and prominent. The hindmost pair of limbs are long, muscular, and well- fitted for leaping. The larvae are white footless grubs which feed on animal matter for about twelve days, spin for themselves a cocoon, and pass to the pupa stage. After about fourteen days' quiescence in this stage the perfect insect emerges. In many respects the flea is closely allied to the next order. ORDER X. Diptera, two winged flies, including flies, gnats, mosquitoes, &c. In this order the hind pair of wings is rudimental and represented by scale- like or pin-like processes under the developed pair of wings, and the mouth is a proboscis. The larvae are footless, often headless maggots, such as are found on putrid meat. Some forms of Diptera, like the gnats and mosquitoes, are provided each with a long pro- boscis enclosing six long sharp bristles. The larvae of the gnats are aquatic and breathe air by means of a Moths. 129 tube with which they are provided which opens at the surface of the water. Some of these insects are very destructive to vegetation ; the larvae of the common daddy-longlegs for instance, feeds on the roots of grass and will thus sometimes destroy large patches of meadow. The Hessian fly is still more formidable, often destroying whole fields of wheat by attacking the young plants before they are in flower. ORDER XI. Lepidoptera, is also a large order, and includes those most beautiful of all insects, the but- terflies, characterised by possessing four wings covered with fine dust-like scales. These microscopic scales overlap each other on the surface of the wings, and are of different shapes in different species. Butterflies have suctorial mouths (fig. 67), the proboscis-like sucker being rolled up when not in use. The larvas or cater- pillars consist of thirteen joints and are very unlike in mouth, structure, and general appearance to the perfect forms which emerge from them. On the lower lip in the larvae of some moths there is the outlet of two spinning glands, which when the larva has reached its full size secrete the material for a silken cocoon within which it is enclosed in the pupa state. These insects vary in size ; some, as the clothes moths and fur moths, are very small. The larvae of the leaf-rollers, a form nearly allied to the clothes-moth, roll up the leaves of plants on which they feed into tubes, within which they live and pass their pupa sleep, and whence they emerge in due time as little broad-winged moths. Another related form often found on apple trees is 130 Invertebrata. the looper or canker-worm moth, named from the pecu- liar looped attitude which the larva assumes in walking. The silkworm moth, a native of North China, secretes by its two glands the silk of commerce. The sphinx moths, called so from the attitude in which the cater- FlG. 73- FIG. 74- Chrysalis. Deilephila Elpenor, Hawk Moth. pillars are often found, with their heads and fore parts raised, are known by their prismatic antenna? and by the long horn on the tail end of the caterpillar. One of these, the tomato or tobacco sphinx moth (whose large green larva feeds on leaves of those plants) bears on each side of its abdomen five large yellow patches. While nearly all moths are nocturnal, the true butterflies, recognised by their brighter colours and their club-shaped antennae, are diurnal in their habits. The best known examples are the white cabbage butterfly, the nettle tortoiseshell, and the thistle painted Beetles. 131 lady butterflies. The larvae of the true butterflies do not spin a cocoon. ORDER XII. Coleoptera. Beetles form numeri- cally the largest sub-division of the animal kingdom, there being over seventy thou- FIG. 75. sand species. In these the fore wings are converted into a hard thick pair of wing-covers or elytra overlapping the hinder pair, which are membranous, folded, and usually capable of flight. Beetles are found in almost every condition and feed on almost every kind of material ; cayenne pepper, can- tharides, medicinal rhubarb, animal and P u ? a - effete matter, putrid flesh and decaying vegetables are the favourite nourishment of some forms. There are forty-eight families included in this * polymorphic ' order ; one of these contains the little ladybird or Coctinella, whose spotted bodies are often seen on nettles in pursuit of the aphides on which they feed. It has only three large joints in the tarsus of each foot. The destructive Colorado or potato beetle (Doryphora) somewhat resembles the ladybird but is ten-striped and not spotted. Many beetles are ex- tremely destructive to vegetation, both in their larval and perfect states, the strong mandibulate mouths being able to cut even hard woods. Of these, the turnip-fly, the wire-worm (which is the larva of the beetle called Agriotes), the pine-beetle, the typographic beetle, Scolytus the elm-beetle, Lymexylon the oak- beetle, are illustrations. KJ 132 Invert cbrata. Other beetles are found in articles of food, such as Tenebrio, the meal-worm often found in ships' biscuits, FlG ?6 Dermestes, or the bacon grub; others are the pests of museums, like the little Anthrenus or Ptinus the herbarium beetle, and The blistering \* The animal is supposed to be placed with its length hori- zontal and its mouth forwards. General Characters of Vertebrates. 3 The chain of these rings or disks, around or replacing the notochord, which forms the axis in the adult stage of all but the lowest of the vertebrates, is called the vertebral column, and each disk, with the parts im- mediately joined to it, is called a vertebra (fig. 2). Each vertebra has attached to it behind a ring or arch (made up of two lateral projections or processes) which surrounds the spinal marrow, and forms the wall of the neural cavity. This arch is called the neural arch. The mouth opens at the foremost end of the body in all vertebrates, and communicates internally with a cavity called the pharynx, on whose walls, directly or indirectly, the blood-vessels are arranged for the purposes of respiration. This part of the digestive canal ! is pierced by slits at some period hi the life of each vertebrate. Below the pharynx is a narrow part of the diges- tive canal, called the oesophagus, which passes between the spinal column above and the heart below, and leads into the stomach, from whence the intestinal canal is continued, to open at the posterior end of the body ; directly below the stomach the duct of the liver opens in all vertebrates, and this organ is peculiar in this sub-kingdom, in that the vein which conveys the impure blood back from the digestive organs enters this gland and breaks up within it into a network of fine vessels, which, reuniting, pass back from hence to the heart. The vessel which thus 1 The digestive or alimentary canal is a tube traversing the whole length of the body, in which the food is digested, and its nourishing part taken into the blood. B 2 4 Vertebrata. conveys the blood from the alimentary canal to the liver is called the vena portce. 3. Primary divisions of vertebrates (headless form). There are two primary divisions of vertebrate animals ; the first of these includes only one form, and that the smallest and simplest in the sub-kingdom, remarkable principally for its extremely simple organ- isation. This little creature is named the lancelet, or technically the Amphioxus lanceolatus, and is so called on account of its lancet-like shape, and from its being pointed at both ends. It is a small, flattened, fish-like animal, about an inch and a half long, about a quarter of an inch in depth and an eighth in thickness, found in sandbanks in our own seas. It has been taken in abundance off the coasts of North Carolina and Florida, off the S.W. coast of Ireland, in the Mediter- ranean, and in the Indian and Pacific Oceans. This animal has no head, and the notochord stretches from the front to the hinder point ; the neural canal and its enclosed spinal marrow likewise extend for the whole length. The mouth is a longi- tudinal slit, bordered with stiff, bristle-like filaments ; ' >' T=-T5- Diagram of Amphioxus. a, mouth; 6, f, g, respiratory region ; c, body cavity ; d, liver ; e, heart; /&-/, digestive canal ; /, notochord ; **, spinal marrow. and the pharynx has many lateral slits in its wall, The Lancclet. 5 through which the water which enters the mouth escapes into the space between the wall of the body and that of the pharynx. To this space the name ' atrium ' is given, and it opens externally by a median pore or outlet placed on the under edge, and in front of the end of the intestine (fig. i,. The liver is a simple sac, and the heart is a single di- lated tube(^), like that of some worms; it sends branches backwards to the pharyngeal wall, one along each slit, and these join dorsally below the notochord, making a dorsal aorta or large blood-vessel, which gives off branches to the different parts of the body. Though there is no brain, yet two of the foremost of the many nerves emitted from the spinal marrow supply structures which may be regarded as rudimen- tary sense-organs. Thus there is in the middle of the foremost end of the animal a small pit, possibly an organ of smell, and two or more lateral pigment-spots in front of and above the mouth, which may be organs of sight There is a narrow membranous fringe or fin around the tail, but there are no limbs, and the blood is colourless. The division of Vertebrata which contains this sin- gularly aberrant form is named Acrania (headless), to distinguish it from that which includes the entire re- maining series, which is called Craniola (head-bearing), 6 Vertebrata. CHAPTER II. CRANIOTA. 4. General characters of head-bearing vertebrates. The head-bearing vertebrates are characterised by the enlargement of the anterior end of the central axis of the nervous system into a series of swellings which collectively make up the brain. To contain this brain the fore part of the neural canal is enor- mously dilated, and its walls are converted into a gristly, membranous, or bony case, called the skull, and in this part of the body the organs of sense are chiefly seated. The brain in its simplest form con- sists of three thick-walled cavities in a series from before backwards, the walls of the three being named respectively the fore, mid, and hind brain. The rest of the neural canal behind the skull remains as a narrow tube enclosed in the canal, which is bounded by the neural arches of the vertebrae. In the sides of the wall of the cranial or skull cavity the organs of the special senses are placed in a series from before backwards ; foremost of them is the organ of smell ; secondly, that of sight ; thirdly, that of hearing. Each of these organs consists primarily of a pouch of skin bulging towards the inside of the body, and receiving a nerve from the brain. Passing out from the brain there are also other nerves, which are distributed to the parts of the foremost end of the body. Around these organs and nerves the cartilage which forms the primi- tive skull becomes disposed so as to protect them; and Visceral Arches. 7 when, as is often the case, the cartilage becomes con- verted into bone, the several pieces of which the osseous skull consists are so grouped around these nerves and sense organs that the bony cranium appears as if its bones were arranged in a succession of segments. These have been mistaken for true vertebral divisions, but are really due to a secondary grouping of parts in the course of growth, and are not primary morpho- logical elements. Appended to the under or mouth side of the cranium, and to the fore part of the vertebral column, we find a series of lateral arches, which unite below in the medial line, and thus close in the sub- vertebral cavity in front To these arches the name 'visceral arches/ is given ; and very often between these arches there a r e slits opening inwards ; these are called visceral slits. The number of these arches varies in many vertebrates, but there may be as many as ten or twelve. The foremost is in front of the part of the skull which begins at the front end of the notochord (for this structure does not in craniotes extend beyond the region of the mid-brain), and its two elements pass forwards in the middle line to unite in front; to these the name cornua trabeculcK is given. The second arch lies behind, below, and a little outside the cornua trabeculse, and forms part of the deeper or palatine portion of the upper jaw in most vertebrates (or the whole upper jaw in sharks) ; its lower end forms the lower jaw, or parts thereof. The third or hyoid arch is that bony system on which the tongue is based ; and the suc- ceeding ones can be easily distinguished in fishes as the arches of bones which bear the gills, but, except 8 Vertebrata. the foremost of this set, the others are rudimental in the higher animals. The visceral slit between the first and second of these arches is the mouth ; the other visceral slits remain either as the gill fissures in fishes, or else become closed at an extremely early period of embryonic life. The remnant of the first pair of visceral slits behind the mouth we find in the form of the ear passages in higher vertebrates. These visceral arches never extend backwards behind the heart. 5. Limbs and ribs. Vertebrate animals have never more than four limbs, which are placed two in front and two behind. The fore limbs are usually placed a short way behind the head ; the hind limbs at or immediately behind the posterior end of the visceral cavity. Each limb has a bony or gristly axis or skeleton, and this consists of two parts first, a girdle or half-zone of bone, which is embedded in the lateral muscles, and is often attached to the vertebral column ; secondly, a limb ray or projecting part made up of several sets of cartilages in a series. Some vertebrates, like whales and some lizards, have only two fore limbs and no hind limbs ; others, like boas and pythons, have rudimentary hind limbs and no fore limbs; others, like most of the snakes, have no limbs at all. These limbs are always turned towards the haemal or ventral side of the body. In the wall of the visceral cavity, following the visceral arches, but quite separate from them, there are usually long slender bones, jointed at the back to the vertebral column, and forming supports for the wall of this space. These bones are named ribs, and the part of the body surrounded by them Ribs and Secreting Organs. FIG. 2. Diagram of a vertebra, with its body (5 , rib (7), and breast bone (6). is called the thorax ; the region between the thorax and the head is called the neck a very short space in fishes and whales, long in many birds. The part of the vertebral column which projects behind the visceral cavity is named the caudal or tail region, and in it there are usu- ally V-like bony arches, suspended to the lower surface of the vertebral bodies, within which a caudal blood-vessel is pro- tected. 6. Secreting 1 organs. All vertebrate animals of this division have a solid glandular liver for secreting the bile, an important fluid used in the process of digestion. They have all red blood, the colour de- pending on the presence of certain minute coloured corpuscles. The circulation of the blood is maintained by a muscular heart, which never possesses fewer than two chambers, one of which is for the collection and reception of the blood from the veins, and is called the auricle ; the other, which is named the ventricle, propels the blood into the large blood-vessels or aortic arches, of which there are usually (in some period of life at least) more than three pairs. In vertebrates the lining membrane of the mouth (which is named the mucous membrane), clothing the upper and lower jaws, and sometimes the similar membrane over other bones, developes processes or io Vertebrata. papillae, which become converted into a very hard kind of bones for the purpose of seizing and dividing their food ; these are known as teeth. In higher forms these become rooted in the subjacent bones, but in all cases they arise as papillae of the mucous membrane. The products of waste (which is constantly taking place) are got rid of by means of certain purifying organs. The skin, by means of its glands, removes some of these effete matters ; so do certain areas of the pharynx, richly supplied with blood-vessels from the aortic arches, and which are called the respiratory organs. There are also developed certain glandular tubes in the hinder portion of the visceral cavity, of the same nature, and built on the same plan, as the segmental tubes of worms, which eliminate from the blood the nitrogenised waste products ; these organs are called kidneys. 7. Primary and secondary segments. In the body of a vertebrate animal there is to be seen the remains of a primary segmentation into a chain of successional divisions ; thus many organs or parts are repeated in a series, such as the vertebrae, the nervous system, the muscle masses (as can be seen in fishes), and the tubes which constitute the kidney. At the same time there is such a tendency to con- centration noticeable that this segmental symmetry is only to be seen in the lower forms, or in the embryonic stages of the higher, secondary modes of aggregation of parts masking completely the original systems of segments. For example, while in the embryo the primitive vertebrae can be distinguished clearly from Cephalization. 1 1 each other, in the adult what appear to be the verte- bral segments are really due to a secondary cleaving occurring in a later stage, after the originally separate primary segments have become fused. As we ascend in the scale of complexity among vertebrates, we find as a rule that the head becomes more and more highly organised, and that there is a tendency towards the concentration of its elements, and that the fore parts of the body become more and more subservient to it This reaches its climax in man, where we find the anterior pair of limbs entirely set apart to wait on the head. There are five classes of vertebrate animals fishes, amphibians, reptiles, birds, and mammals. CHAPTER III. CLASS i, PISCES (FISHES). 8. General characters of fishes. Fishes consti- tute the first and simplest class of the head-bearing vertebrates, and, like the simplest forms of all the other sub- kingdoms, they are aquatic in habit, and all their organs are adapted for a watery home. Thus in shape they are for the most part of an elongated flattened outline, pointed in front, tapering behind, so as to afford as little resistance as possible in traversing the water ; the fore part of the body, or head, is joined to the trunk directly, without the inter- vention of a narrow neck, and to the hinder ex- 12 Vertebrata. tremity of the vertebral column is appended a flattened tail, which, by moving like a scull or screw-propeller, can drive the body forward. The limbs are also, in fishes, developed into fanlike bars, the fins. -^ 9. Scales. The surface of the body in fishes has only a scanty epidermis, or outer layer of skin, which is generally of a mucous or slimy consistence; beneath this is the dermis, or inner skin, whose surface consists of numerous thin, flattened scales. These structures, so characteristic of fishes, are composed of bony plates, which are ossifications of flat dermal processes, often containing or bearing little tooth-like points, composed of the same material as true teeth. In some fishes, like sharks, the entire scale consists of this dentine or tooth FIG. 3. Placoid scale of dog-fish (vertical section magnified). , enamel layer ; b, dentine of spine on scale. structure (fig. 3) ; in others the bony element, which forms around the tooth, covers or entirely supersedes the dentinal, but in its essential nature the coating of scales or dermal exoskeleton of fishes may be regarded as consisting of or containing ossified papillae, which in their structure are identical with the tissue of ordi- Scales and Fins. 1 3 nary teeth. 1 Many scales are of beautiful forms, and they vary very much in outline and surface, some- FlG. 4. Cycloid scale of roach magnified ; seen in section A, and on surface B. times being flat and smooth-edged (fig. 4), or else spinose, ridged, or comblike (fig. 5). These structures can be examined and their varieties observed with the aid of a pocket-lens. The scales of the pike, sole, and perch are especially characteristic forms. 10. Fins. Along the middle line of the body of a fish there are usually developed extensions of the dermal 1 It would perhaps be more correct to say that teeth are really in nature a special set of dermal papilla? of the same nature as those which cover the surface of the skin in some fishes, ?nd which, covering the jaw arches, are set apart for grasping and dividing food ; but the relationship is put con- versely, as the tooth form is the more familiar. 14 Vertebrata. exoskeleton in the form of median fins. Of these one extends along the upper or dorsal edge, and is named F the dorsal fin, consisting of a suc- cession of soft and branched or spiny and hard fin-rays connected by membrane. The other is pre- sent on the under or ventral side of the body behind the terminal opening of the intestine ; this is called the anal fin. These median fins, though apparently single and Ctenoid scale. > . * central, are in reality composed of two lateral layers placed in close apposition. 11. Sense-organs of the lateral line. Along the line of greatest convexity of each side of the body of a fish there is a lateral line, extending from be- hind the eye to the side of the tail. This con- sists of a row of scales, each pierced by a minute tube leading into a small simple or branched sac filled with a gelatinous material, in which the extremity of a nerve is embedded. These are organs of sense, and are probably capable of being impressed by several forms of vibration. 1 2. Backbone and tail. The vertebral column of fishes usually consists of a chain of biconcave vertebral bodies, bearing on their upper surfaces neural arches which are surmounted by long neural spines. On the under side the vertebrae bear ribs towards the front, and V-shaped bones towards the hinder part of the body. The hindmost of the tail vertebrae may either gradually diminish to a point, as in the African mud- fish (fig. 14), or they may undergo modification, being re- placed by a rodlike bone which turns sharply upwards, The Sole. as in the tails of most of the bony fishes. The median fin is continued around the tail end of the vertebral >. I/! ' ?i *2 g-c o "Sr i6 Vertebrata. I 1 I i column, and sometimes appears as a simple uniform fringe evenly distributed around the pointed vertebraj axis, or else the whole caudal area of the vertebral column becomes upturned and the tail fin forms a large lobe on the under surface of the axis while simply margining the end of the caudal vertebrae ; such a tail is spoken of as* an unequally lobed tail. When, as in bony fishes, the extremity of the spinal column becomes con- verted into a single bone, then the fin borne by it is usually an evenly bilobed tail, such as that of a herring or salmon or sole. It is, however, an in- teresting fact in relation to this that the young fry of the salmon or other bony fish has origi- nally a tail of the unevenly ^ l ^ 6 ^ character, which by the &y \? I 5 snor tening f tne upper part, and the expansion of the lower lobe, becomes even, as we find it in the adult. In the simplest fishes the notochord persists through life, and such fishes have generally a uniformly fringed tail, as in the lampreys. The structure of the skull differs in the various subdivisions of the class : in some it is a simple carti- Skull of Fishes. 17 laginous box, as in lampreys and sharks; in others this cartilaginous box is covered and protected by a series of bony dermal plates, as in the sturgeon, or the whole skull may be made up of a number of closely articulated and perfectly united bony pieces as in the cod (fig. 8). In this case it must be re- membered that these bones are of a twofold nature first, the ossified pieces of the cartilage of which the primitive skull consists, and which surrounds the dif- ferent apertures and nerves, forming principally the lateral walls of the skull ; secondly, the ossified plates of membrane which are the equivalents of the dermal bony plates of the sturgeon, and which chiefly make up the roof and floor bones. Besides the skull or brain-case proper, the head of a fish consists of four other series of bones, as can be seen in fig. 8. These are, first, those of the upper jaw arch, sometimes seven in number on each side ; secondly, those of the lower jaw arch, sometimes four or five pairs ; thirdly, those of the gill arches, four, five, or six pairs of arches on each side, each consisting of about four pairs of bones, and bearing the gills These three series are chiefly ossifications in the system of visceral arches before referred to. Besides these, there is a fourth group of bones, those of the operculum or gill cover, which overlap and cover the gill arches ; of these there are four or more, making up the gill cover on each side. It is thus not to be wondered at that the skeleton of the head of a fish presents an appearance of great complexity. The limbs of fishes are converted into fins, and of these there are usually two pairs. The fore limbs, or c i8 Vertebrata. pectoral fins, are placed directly behind the head, to which indeed the shoulder girdle is in most fishes united by small dermal ossifications. The hind limbs are called the ventral fins, and are rarely as well de- Skull of Cod. 3, supra-occipital bone ; 4, opisthotic ; 8, post-temporal : n, frontal ; 9, parasphenoid bone ; g, g, sub-orbital bones ; 22, premaxilla ; 21, maxilla ; 24, pterygoid ; 28, hyomandibular ; 29, articular piece of lower jaw ; 23, dentary bone ; 39, 40, 41, 43, hyoid arch ; 44, branchio-stegal rays; 34, 35> 36, 37, opercular bones. veloped as the fore limbs, and the pelvic girdle is seldom attached to the vertebral column. The fins are of use in directing the motion of fishes, while the tail is the principal organ of propulsion. Brain and Heart of Fishes. 13. Internal organs of fishes. The brain of fishes (fig. 9) is small, not filling the cranial cavity. It consists of a succession of little knobs or ganglia arranged in a chain from before backwards. Of these the foremost are connected with the sense of smell, the second consist of the fore- brain hemi- spheres or cerebrum, the third are the optic lobes from which the nerves of sight arise, the fourth con- stitute the mid-brain and the fifth the hind brain. Beneath and behind the head lie the gills (fig. 10), which consist of nume- rous vascular fringes ar- ranged in platelike layers attached to the visceral arches, and bathed by the water which enters the mouth and escapes through the visceral slits. The heart is situated in the middle Brain of Cod. Of What We might Call the /, nerves of sight; k, nerves of smell; . ... a, foremost lobe of brain ; c. se- throat, a Very Short distance cond lobe or cerebrum ; / cere u U' J it. i bellum; A, hind brain or medulla behind the lower jaw. oblongata ; , fifth pair of nerves ,; This nrain rnndstc; nf a , nerves of hearing ; 0, ninth pair >1SIS 01 a of nerves; /.tenth or vagus nerve. thin-walled auricle, receiv- ing the veins which convey to it the impure blood from the body, and a large thick-walled ventricle for propelling the blood into the gills. This latter is ca 2O Vertebrata. sometimes prolonged at its outlet into a conical part FIG. 10. full of valves, called the arterial cone, which ends in the large main blood- vessel, or aorta. The arterial cone is well de- veloped in sharks. Sometimes, as in most of our common fishes, the aorta at its A, the aortic bulb ; H. heart : B, branchial arches ; b, branchial veins returning the blood to A, the aorta ; v, v, the ve.ns. B shows the structure of one of the branchial arches, with its ap- pended gill filaments, be. The blood from the aortic bulb passes through B, the branch- ial artery, is aerated in the fila- ments be, collected and returned by b, the branchial vein, into A, the dorsal aorta. 8 Diagram of the circulation in a fish. Circulation in Fishes. 21 commencement is swollen into an aortic bulb, from which come off at least three pairs of branchial or gill arteries ; these pass in the form of arches, right and left, to the gills, and there break up into fine branches in the soft, fringe-like folds. Here the blood, being exposed to the air dissolved in the water, absorbs oxygen and gives out carbonic acid, and is thus purified. The purified blood, returning from the gills by the branchial veins , enters the dorsal vessel or aorta, which sends it to the different organs of the body to supply the viscera. The blood of fishes is generally of the same temperature as the medium wherein they live, or only slightly warmer, and hence it usually feels cold to the touch. It contains corpuscles, or little micro- scopic bodies, of an oval shape and with a central nucleus. Though the respiration of fishes is accomplished by means of the air which is dissolved in water, yet it is supplemented in some of them by direct exposure of the gills to the atmosphere, and some fishes are killed if prevented from rising to the surface. In most fishes there is a large sac filled with air, placed beneath the vertebral column at the anterior part of the body cavity, and communicating by a duct with the digestive organs. This is called the swimming- bladder, or the air-bladder, and, by expanding or compressing it, the fish can rise or sink in the water. This sac commences its existence in the embryo as an outgrowth from the neck end of the alimentary canal. 22 Vertebrata. Fishes are oviparous, that is, their .young are produced from eggs, and for the most part they are enormously prolific. The egg-organ of the cod some- times contains over a million eggs, and some other fishes are equally fruitful ; the eggs are of small size, and contain very little food yolk. The majority of fishes are marine ; those found in fresh water are, as a rule, simpler in organisation and retain many of the embryonic characters of the class. About 13,000 different species of fish are known, and they are divided into five orders. CHAPTER IV. 14. Order 1, Marsipobranchii (Lampreys). This, tb sostome fishes. The most familiar examples are the perches of our streams ; the bull-heads and gur- nards, known by their spiny heads, found along our coasts ; the sticklebacks, so interesting on account of the nests constructed by the males for the protection of the young : the mullets, which have the singular property of changing colour when they are dying ; the mackerels, bi earns, braizes, blennies, gobies, &c. Some of these fishes are laterally compressed, like flat fish, but without showing any distortion of the heads, such as the John d ; Ory and Archer fishes ; the latter are East Indian fishes, and owe their name to their habit of shooting at flies by forcibly ejecting drops of water from their long snouts. The sword- fish, which sometimes attains the length of sixteen feet, is closely allied to the mackerel, and is remarkable for the long, swordlike upper jaw. The common lump- sucker, the little red or brown Lepadogaster of En- gland, and the tropical Remora are remarkable as being provided with sucking disks, whereby they can adhere with great tenacity to foreign bodies. Fistularia (the tobacco-pipe fish) is remarkable for his long tubular snout, as is also the allied trumpet- fish. Trachinus (the weever) is said to be able to inflict poisonous wounds. There are three aberrant groups of spiny-fmned fishes, which constitute the remaining three sub-orders. The first of these, or sub-order 4, is called Pharyn 32 Vertebrata. gognathi, or pharynx-jaw-bearing fishes, on account of the presence of a single medial tooth-bearing bone in the pharynx, made up of the united lateral remains of one of the hindmost of the visceral arches, which does not bear gills. The flying fishes, distinguished by their long pectoral fins ; the gar-pikes and parrot fishes ; the cunners and tautogs, so common along our shores, are the most familiar examples of the group. They are small or moderate-sized hshes, with spiny fins, and often with strong conical teeth in the jaws. Sub-order 5 consists of the sea horses and pipe fishes, which differ from all other fishes in having the gill filaments in symmetrical clusters or tufts on the gill arches, not in comblike plates ; hence they are called Lophobranchii, or tufted-gilled fishes. Their bodies are clad with bony plates, and are often of eccentric angular shapes. They have no ribs, their jaws are toothless, and the males in some species are provided with pouches on the front of the abdomen, into which they collect the eggs on their being laid by the females, and within which the young are hatched. The sixth sub-order, PUctognathi, or soldered jaws, consists of spiny-finned fishes in which the bones of the upper jaw are consolidated together instead of remaining separate ; these are the singular globe-fishes, whose spiny bodies are capable of inflation, and whose bare, ivory-like teeth give them such a remarkable appearance. The file fishes also, with their rough, branched spines and tough skin and the angular box- fishes, which belong to this order, are likewise among Mud Fishes. 33 the most singularly shaped of tropical fishes. One remarkable species the sun fish a large globular fish with an extraordi- narily thick skin, sometimes reaches the weight of 400 pounds. 1 8. Order 5, Dipnoi.- This, the last and in some respects most interesting order, includes three living fishes, which form a transition to the next class. These fishes differ from all the foregoing in having the swim- ming-bladder developed as an accessory respiratory organ ; the blood returning from it being received into a small additional auricle of the heart placed to the left of the main auricle. They have a covering of horny scales, and the alimentary canal has a spiral valve. They also exhibit the peculiarity of pos- sessing tubular nasal passages which perforate the upper lip, opening into the mouth. One of the fishes of this order is the African mud fish, or Protopterus of the Gambia ; another is the Lepidosiren (fig. 14), of South America ; and the third is the (The mud fish D 34 Vertebrata. Ceratodus, of the rivers of Queensland. In several respects these fishes present characteristics which are identical with the embryonic conditions of many of the higher groups of animals. The characters of the skeleton can be seen in fig. 7. CHAPTER VI. CLASS 2, AMPHIBIA. 19. Characters of Amphibia.^-The class Am- phibia, to which we are structurally conducted by the last order of fishes, consists of cold-blooded animals, usually of small size. This is at present the poorest in species of all the classes of vertebrata, yet, as in the case of the ganoid fishes, at earlier periods in the world's history the animals of this class vastly ex- ceeded their present representatives in number, size, and complexity. Like fishes, they are characterised by having a feeble development of the outer skin, or epidermis, but, unlike them, they have no dermal clothing of scales, and the surface is generally smooth, naked, and often glandular. Some of them, in the embryonic or tadpole stage of their existence, possess rudiments of the system of sense organs, like those of the lateral line in fishes, but none of them are retained in the adult state. Amphibians, moreover, have no functional fin-rays, though sometimes they have marginal membranous fringes, as in the common newt or tadpole, and even rudimentary rays, as in the Characters of A mphibians. 3 5 toe-webs of some salamanders. They also undergo regular metamorphoses, beginning life as little fish- like creatures with large flat heads and external gills. To this stage the name tadpole is commonly given. Then, as development progresses, the air sacs (which correspond to the swimming-bladder in fishes) grow, become large, vascular, and capable of acting as FIG. 15. Skeleton of frog. *, skull ; b, vertebrae ; c. sacrum ; d, ilium ; e, urostyle ; /, suprascapula ; g, humerus ; h, fore-arm bones ; ', wrist bunes ; m, thigh bone ; n, leg bones ; o, elongated first pair of ankle bones ; /, q, foot bones. breathing organs, which are then called lungs ; and ultimately, in the adult state, a pulmonary or direct air-breathing system supplants the gill or branchial system of earlier life. The two-chambered larval heart at the same time becomes three-chambered, developing a special auricle in the left side for the reception of the blood which has been purified in D 2 36 Vertebrata. the lungs, and is returned from hence into the heart. It may also be noted that, during this process of development in the common frog the digestive canal, which in the tadpole is long and spirally coiled, becomes shorter and straighter The blood of amphi- bians is remarkable for the large size of the oval red corpuscles which it contains, those in Proteus being of an inch in diameter, those in the frog being The vertebral column in the simplest of the amphibians consists of rudimentary or biconcave vertebrae ; in frogs (fig. 15), however, it consists of a chain of a few solid disks whose surfaces fit into each other by ball and socket joints. Ribs are either very short or, as in frogs, absent. The skull articulates to the foremost vertebra by means of two lateral arti- cular surfaces which are called condyles. The skull 12 also, as a rule, much more consolidated than the skull in fishes, but resembles the latter in having, as the most conspicuous bone in its base, a long ossifi- cation in the membrane underlying the middle of the cartilage of the base of the skull, which is known as the parasphenoid bone, a bone which is rudimental or absent in all higher forms. Amphibians also differ from fishes in having a middle ear, closed by a tym- panic membrane, and not merely the internal ear cavity which constitutes the ear in fishes. Their nasal cavities open posteriorly into the pharynx. They have usually four limbs, which consist of parts com- parable with those in higher animals, and very unlike the fins in fishes. There are three orders of amphibians at present represented by living forms on the globe. 37 CHAPTER VII. CLASSIFICATION OF AMPHIBIA. 20. Order 1, Gymnophiona. A small group of worm-like forms, with no limbs, rudimental eyes (hence they are called C(Kcilia\ which are found in tropical countries burrowing in the ground. These, with one exception, have the body provided with dermal scales. They are usually marked with super- ficial rings like an earth-worm, and range in size from one to two feet, rarely exceeding this length. At present only a few species exist, but many fossil forms have been found which probably resembled these in structure. A large and structurally complex order of fossil amphibians, named Labyrinthodonts, formerly in- habited the earth, which in some respects seem to have been related to the Ccecilians, but were much larger, and many of them were defended by dermal coats of bony mail something like the armour clothing of a crocodile. 2 1 Order 2, TIrodela. Limb-bearing amphibians provided with a permanent tail, which is retained during life. There are two sections in this order, in one of which the animals retain their embryonic gills through their whole existence, and are thus peren- nially or permanently branchiate, while in their adult condition they also possess lungs, which become de- veloped gradually in process of growth. In the other section the gills are only transitory or caducous, Vertebrata. FIG. wasting and disappearing on the development of the lungs. Of the former, we perennibranchiate section we have interesting examples in the sirens or mud .eels of Carolina, which are provided with only two limbs represent- ing the fore limbs of other verte- brates. Another form, the proteus, inhabits the Cave of Adelsberg and other caves in Ca- rinthia, &c., and is, like all other cave- dwellers, blind and blanched ; its weak fore legs are pro- vided with three toes, while the hind limbs possess only two. The curious axolotl (fig. 1 6) of Mexico is an inte- resting form, as it has proved to be a permanent tadpole which in certain conditions only un- dergoes its further metamorphosis into the salamander- like form of its adult state. Jn some perennibranchs the outer gills disappear, Diagram of the axolotl, showing its gills, 6, and lungs, v. Frogs. 39 and are replaced by an internal series, or gills of the type of those developed in fishes. This modification in the structure of these organs is of considerable inte- rest from a morphological point of view, when we re- member that in sharks there are originally in the embryo distinct external gills, which are lost as the shark attains his more perfect organisation, and are replaced by the permanent gills, which are formed directly on the aortic arches. From these conditions it seems as if external gills were a more primitive or embryonic form, and internal gills a more specialised modification of respiratory organs. The amphibians which show these internal gills are the giant Sieboldia of Japan, which reaches a length of four feet, and the amphiuma and menopoma of North America. The caducibranchiate tailed amphibians are the sala- manders and newts, the latter of which are common in our ditches, where their metamorphoses ^an easily be traced. The common newt is interesting on ac- count of the bright colours which it exhibits at certain stages, and for the remarkable dorsal crest which it also occasionally possesses. 22. Order 3, Annra. The largest group of the Amphibia consist of the frogs and toads, or the tailless forms. In these, the larva or tadpole loses during its development all traces not only of its gills, but also of its tail ; the hinder limbs are also in these more perfectly developed than the fore, and the two proxi- mal bones of the ankle are elongated, so as to make what appears to be an independent third portion of the hind limb. The fore arm and the leg proper also differ from those of urodeles and of the higher verte- 4O Verlebrata. brates in that there are only single bones in these regions, the separate bones, radius and ulna, which are present in these parts of other vertebrates being here united. The frogs, toads, pipas, and tree frogs are the most striking examples of this order. CHAPTER VIII. CLASS 3, REPTILES. 23. Characters of Reptilia. Tortoises, lizards, snakes, and crocodiles are the leading forms included in this large third class of vertebrate animals, a class often confounded with the amphibians, but differing therefrom in many striking and characteristic respects. Reptiles are invariably provided with a very distinct epidermic clothing of scales which differ essentially from the dermal scales of the foregoing groups. The scales of reptiles being epidermal, and not parts of the derm is or true skin, are often shed and replaced, as in snakes, and they are sometimes hard and thick, as in the tortoise shell of commerce and in the mail clothing of the crocodile. This firm covering may be supplemented by a dermal bony layer, as in croco- diles or tortoises, but these indurations of the dermis are never superficial. The blood is cold ; the aortic arches never bear gills, nor is there ever branchial respiration in any stage of existence among the animals of this group. The heart consists of three cavities, two auricles and one ventricle j but the latter is often CJiaracters of Reptiles. FIG. 17. more or less perfectly divided by a septum, so as to act as if it were a double chamber (fig. 17). There are always at least two aortic arches, right and left, which usually unite sub vertebral ly to form one dorsal aorta. The notochord never per- sists in the adult, and in most living reptiles the vertebral bodies unite witn each other by ball and socket joints, and are very rarely biconcave. The skull joins the vertebral column by a single me- dian articular eminence or condyle, and there is no parasphenoid bone, the bones of the middle of the base of the skull being developed in the cartilage of the base itself, not in the membrane be- neath the cartilage. The lower jaw articulates, as in the amphibians, with the end of the preceding visceral arch ; and a bone at its extremity called the quadrate bone is interposed between the palatine part of that arch and the skull. Many reptiles are ovoviviparous ; others are ovi- parous. Like the amphibians, the reptiles at the present day, though still numerous, give us a very faint idea of their former grandeur of size and complexity. In the Mesozoic age they held the same position on the globe Heart of turtle. H, ventricle ; h, h 1 . auricles. 42 Vertebrata. that the Mammalia do at the present period. Only four orders of reptiles are represented in the existing terrestrial fauna ; at least five orders, and these in- cluding the giants of the class, have perished. CHAPTER IX. LIZARDS AND SNAKES. 24. Order 1, Lacertilia. The lizards are scale- clad, and at least forelimb-bearing reptiles, with a heart possessing a single ventricle, and with a lower jaw of firmly united segments. The eyes are provided with movable and functional eyelids, and the teeth are not in sockets, but are disposed in rows either around the edge or along the side of the jaws. The cloaca, or cavity into which the digestive canal and excreting orifices open, has usually its outlet placed transversely. Like most of the lowly organised vertebrates, lizards display a remarkable power in restoring lost parts, and in connection with this we perceive in them a facility for making their escape from capture by breaking off their extremities. Thus a lizard taken by the tail will often break off that process and escape, the fracture taking place not between two of the vertebrae which make up the organ, but actually through the middle of a vertebra, as there is a medial cartilaginous plate in the caudal vertebrae of some. In one specimen in the writer's possession a lizard whose tail was cracked, but not Lizards. 43 broken off, developed at the crack an accessory tail, while the original tail yet remained and became re- paired at its injured part, thus giving a bifid extremity to the tail. Some lizards are snakelike and ringed, like the amphisbaenas, with no projecting limb-rays, but in all these traces of the limb girdles are persistent, although they may not show superficially, as in the blind worm a pretty and innocent, though much maligned, native of Great Britain, whose scientific name Anguis fragilis, expresses the brittleness before referred to. The common wall-lizards are typical examples of the long fork-tongued division of the order. The monitors and teguexins, or safeguards of the tropics, are so called because they are supposed to give warning of the presence of crocodiles. They reach the length of six to eight feet, and are among the largest of living lizards, although they are but pigmies when compared with the extinct forms of which fossil remains have been found, sometimes exceeding thirty feet in length. The American iguanas are large-sized lizards which are used as food ; they usually bear tufted crests on the back, and have thick short tongues. Some lizards have large lateral flaps of skin : thus the frilled lizard of Australia bears on each side of the neck a wide fold of skin like a ruff or Queen Eliza- beth collar ; others, like the little flying dragon, bear on each side a winglike fold, supported on extended ribs, and these, together with the long conical chin- pouch, give this creature a very extraordinary appear- ance. The appropriately named Moloch Jwrridus of Australia bristles most repulsively with conical spines, 44 Vertebrata. as do many other genera. The geckos of India are remarkable for the suckers which they bear on the ends of their fingers, whereby they can walk up per- pendicular walls and along ceilings. The last group of lizards, the chameleons, are interesting for their proverbial quality of changing colour, due to the ex- pansion and contraction of certain pigment-bearing connective tissue bodies in the skin. They also FIG. 18. Head of chameleon, with protruded tongue. possess circular eyelids, and a very long tongue (tig. 1 8) capable of being protruded with lightning-like rapidity. 25, Order 2, Ophidia (Snakes). These dreaded animals may be regarded in some respects as special modifications of the lizard type. They are scale-clad and limbless, not having even a remnant of the shoulder girdle persistent. The sternum and sternal apparatus have also vanished, and the skeleton consists of a long vertebral column, often of several hundred joints or vertebrae, each of which bears two ribs, one on each side. Serpents. 45 The vertebrae have each a concavity on the anterior side of each body, into which the ball or convexity of the hinder surface of the foregoing body fits. There are also two pairs of articular facets on the processes of each vertebra, so that the entire spine combines flexibility with amazing strength. The ribs are capable of being moved forwards and backwards, and the ventral surface of the animal's body is covered with flat, horny shields, into which muscles run from the tip of each rib. The rapid, even, gliding motion in serpents is accomplished by the successive advances of these ventral scutes, and the drawing of the body forwards towards them, while the slightly projecting hinder edges of the scutes serve as fixed points by catching the surface of the ground. The brain case is firmly built up of sin- gularly united bones ; but the bones of the upper and lower jaw-arches are loose, united together by means of fibrous tissue, and hence capable of an extreme degree of stretching during the swallowing of food, which these animals bolt in large masses. The teeth are recurved and solidified to the jaw, not set in sockets, and they can only act as organs of prehension. The tongue consists of a long, bifid muscular organ, capable of being rapidly protruded, or of being drawn back into a sheath when not in use. The windpipe is long and protected by complete gristly rings ; only one lung is usually large and developed, the other is rudimental or simply saccular, and they are never symmetrical. The digestive canal is capacious and short, and the cloacal opening is transverse. The 4 6 Vertebrata. eyelids are confluent and transparent, forming the clear glassy surface of the eye, and thus giving to the serpent the stony, unwinking stare peculiar to them. The boas of the New World, and pythons of the East, are remarkable among snakes for their size and for the strength of their teeth, as well as for the pos- session of two rudimentary hind limbs in the form of spur-like processes placed one on each side of the cloaca. Some of these serpents, like the anaconda of FIG. 19. Poison fangs showing their internal hollows. America, have been known to reach the length of forty feet, and even larger specimens are described. The Colubrine snakes, such as the common Amer- ican striped snake (Eutcemia sertalis), are all harmless creatures, mostly of small size, and having all the teeth solid, not grooved. Poison Fangs of the Viper. 47 26. Poisonous Snakes. The most remarkable, though not the most numerous group of serpents, are those provided with poison-fangs, the vipers and rattlesnakes. Of these the best known is the rattle- snake, in which animal the epidermal clothing of the last few tail-joints is loose, and consists of hard, horny rings loosely embracing each other ; these cause the rattling noise, when the animal's tail is shaken, which nas given rise to the name of this dreaded American snake. Like most other poisonous snakes, it has FIG. Poison apparatus of rattlesnake. a, poison bag and duct ; e, i, g, t, v, muscles of jaw. a flat triangular head, and in its mouth there can be seen the two long grooved maxillary teeth in which are the channels for the poison. These are the only large teeth in the mouth, all the others being small and obscure. They are placed far forwards in the upper jaw, and are movable along with the movable maxilla, being bent upwards towards the palate in the 48 Vertebrata. closed position of the mouth,while in the gaping state they project, being arched downwards, ready to be inserted into the victim about to be struck. The groove in the tooth leads into a canal which traverses the base of the poison fang, and is continued by a duct into a cavity or sac, which receives the tubular ducts of the poison gland (fig. 20). In the act of striking, the muscles which close the jaws squeeze the poison sac and drive the poison through the duct into the tooth, and thence into the wound. The poison apparatus is constructed on the same plan in the common viper (Pelias berus\ not uncom- mon in Central and Southern Europe, and easily re- cognised by its dark green colour, and by the zigzag black line in the middle of the back. Other poisonous snakes like the asp, the cobra di capello, and the coral snake, have other solid teeth coexisting with the poi- son fangs, and some, like the dipsads, tree snakes, 'and sand snakes, have some of the hinder teeth grooved. The poison of snake-bites is rapidly fatal, death taking place within an hour in general, and it is com- puted that over 10,000 deaths take place annually from this cause among human beings. The water snakes inhabit the Pacific and Indian Ocean, and have flat tails. They possess strong un- grooved teeth behind the true poison fangs. In one species, allied to the coral snake ( Callophis inttstinalis), the poison gland extends into the abdomen. One curious group of non-poisonous snakes pos- sess teeth on the anterior surface of the neck vertebroe in addition to feeble jaw teeth. These animals feed on eggs, and use these teeth for breaking them while Tortoises. 49 in the act of swallowing, so that all the material of the egg may be saved for food. Snakes are rare in cold and more abundant in warm climates ; they are also more numerous in continental than in insular regions. CHAPTER X. TORTOISES AND CROCODILES. 27. Order 3, Chelonia (Tortoises). This order consists of those reptiles whose bodies are enclosed in a bony case composed of a dorsal or upper convex shield, called the carapace and a flat ventral or under shield, the plastron. The carapace is notched in front and behind, and between it and the plastron project the head and neck, the limbs, and the tail. These parts can be retracted under cover of the bony case. Each shield consists of a layer of epidermis or tortoise-shell, and a layer of bone, which in the cara- pace consists of dermal plates added to the tops of the spines of the vertebrae, the surfaces of the ribs, and a row of marginal bony plates below these. The plastron also consists of nine plates of ossified dermis covered by a symmetrical series of horny laminae. The skull is short, rounded, and not armed with teeth, which are replaced by horny beak-like jaws. The lower jaw is in one piece in the adult The shoulder-girdle consists of three bony rods, two in 50 Vertebrata. front, and one behind ; these are included within the carapace, as also is the pelvic girdle. FIG. 21. Skeleton ol European tortoise, the plastron or under-shell removed. Crocodiles. 5 1 The land forms included under this order are tortoises, such as the common Greek tortoise, which live on land and have stumpy feet with short nails. The aquatic forms or turtles, such as the green turtle used in making turtle soup, and the hawks-bill turtle used for its ' tortoise shell,' are known by their webbed feet The largest tortoises of the present day only measure a few feet in length, but in ancient days tortoises reached enormous sizes ; thus the Colosso- chelys, or .giant fossil tortoise of India, sometimes reached a length of over thirteen feet Tortoises are slow in growth, and attain to extraordinary ages. They are for the most part vegetable feeders, differ- ing in this respect from most other reptiles. 28. Order 4, Crocodilia. These, the highest in organisation of the entire class, are inhabitants of the rivers of tropical countries, and are among the largest of living reptiles. T^ey have a rough, hard, scaly coat of epidermis which is placed dorsally on a dermal bony surface. The vertebral column is pro- vided with ribs, and is composed of vertebrae hollow in front and convex behind. The skull is long, and covered with peculiar sculptured markings. The teeth are seated in sockets in one row, and are renewed several times in succession. The heart has a com- plete septum or partition in the ventricle dividing it into two distinct cavities, but the aortic arches still communicate with each other at their bases. The feet are webbed and possess strong claws, and there are dermal glands in the throat secreting a peculiar musky material The forms included are the croco- diles of the Nile and Indian rivers, with their long 2 52 Vertebrata. tapering snouts, in which the longest teeth of the lower jaw notch the sides of the upper jaw. The alligators of the New World have heads oval or rounded in front, and in all of them the lower jaw teeth are hidden by the edge of the upper, when the mouth is closed. The gavial of the Ganges has a long, slender- pointed head, and is the smallest of the group. Of all the reptiles the crocodiles are those which in point of structure approach most closely to the birds. They have a gizzard-like stomach, a nictitat- ing membrane in the eye, an immovable joint between the tibia or leg bone and the first bone of the tarsus or ankle, a single carotid or neck-artery, and many other structural peculiarities which show their super- iority over other reptiles. Among the orders of the reptile class now extinct, there was one which in- cluded bipedal forms which had possibly a kangaroo- like mode of progression, and one of flying reptiles, which indicated a still closer relationship to the birds. CHAPTER XI. CLASS IV. AVES (BIRDS). 29. General Characters. These familiar verte- brates are characterised by possessing an epidermal clothing of feathers, warm blood, a four-chambered heart, no teeth, and in general an adaptation for aerial locomotion. The mode of progression on the earth Feathers. 53 is strictly bipedal, as the fore-limbs never touch the ground, being modified into wings. Like reptiles they are oviparous and their eggs Fig . 22- are of large size ; in most cases also the young are for a certain period under the care of the mother, by whose agency they are provided with food. 30. Feathers. Feathers are epidermal processes se- creted by long grooved papillae and they are of several sorts. The strong distinct feathers, which have a central axis and lateral expansions or vanes, are called contour-feathers, while the smaller soft feathers which clothe the intimate surface of the skin, which have soft or woolly processes and no axis, are called down-feathers. In each contour-feather we notice, firstly, the hole at the base (fig. 22, e) where it is thickened around the base of the papilla ; secondly, the slit-like hole, f, marking the region above which the sheath of the papilla has split ; thirdly, the rachis, or the square solid axis, b ; fourthly, the flat expanded* lamina, Or , barrel; b, rachis; c, vanes; vane, c, composed of separate barbs, the margins of each of Contour-feather. 54 Vertebrata. which are joined to their neighbours by numerous booklets. In this respect contour-feathers differ from down, in which the barbs are all discontinuous. In young birds the entire plumage consists of simple down- feathers covering the whole surface almost uniformly, and in some birds which do not possess the power of flight, this condition is more or less perpetuated, and thus all the feathers have discontinuous barbs, as in the ostriches. In the great majority of birds, how- ever, this primitive surface clothing is shed and be- comes replaced by a second growth of feathers, which differs from the first in that the component feathers are for the most part contour-feathers, arranged in definite tracts, and between these pterylce, or feather tracts, there are spaces quite devoid of contour-feathers. In the course of life, many birds change their feathers several times, the process being called ' moulting.' To defend the feathers from the influence of moisture there is a gland situated on each side of the tail bone which secretes an oily material of use in lubricating the plumage. The largest feathers are those of the wing, and they are grouped into primaries, secondaries, and tertiaries, according as they are borne respectively by the hand, the lower, or the upper end of the fore- arm ; over these are the scapulars, and on the rudi- mental thumb is the alula. The tail feathers are also long, and as they are used in steering they are named rectrices to distinguish them from the oar- feathers of the wing. The papillae which secrete the feathers are long, vascular, and deeply grooved on the surface ; the Plumage and Skeleton of Birds. 5 5 protoplasmic matter exuded by the surface of the papillae is collected into these channels, it then hardens and forms in the first place a hollow cylinder of horny matter, with ridges fitting into the papillary grooves and thin areas between. As growth takes place most actively at the base of the papilla, this horny sheath is pushed off the surface of the papilla, upon which it shrinks still more, and the horny cylinder splits along its thinnest side, whereupon the two lateral laminae flatten out as the vanes, while the rib which corre- sponded to the main groove of the papilla becomes the rachis. The feathers of many birds are of brilliant colours, usually brighter in the males than in the females. 31. Bones. The skeleton of birds is well adapted for their aerial existence. The skull is early consoli- dated, and articulates with the spine by one occipital condyle. The ten or twelve parts of the lower jaw are also early united into a single piece and the front of the jaw is enclosed in a horny sheath ; it articulates to the skull by means of a movable quadrate bone which is kept in its place by two rods of bone, one on the outside stretching from the base of the upper beak (the jugal arch), the other on the inside stretch- ing from the palate (the pterygoid arch). The upper mandible, or beak, is also encased in a horny layer at whose base are the nostrils, very often surrounded by a thick leathery skin, which is called the cere. The neck is usually long and exceedingly flexible, made up of from nine to twenty- three vertebrae ; its length and that of the bill usually bears some propor- tion to the length of the legs. The breast-bone bears 56 Vertebrata. in front a prominent keel, to which the muscles which elevate and depress the wing are attached, and this is only absent in such birds as do not fly, as the ostrich, emu, and New Zealand ground parrot. The wings are fastened to a very strong shoulder-girdle, which consists of three parts ; firstly, of a V-shaped furculum, or merrythought, which consists of the two collar- bones united together in the middle line ; secondly, FIG. 23. of the coracoid bone, a stout bony rod which fits into a groove in the top of the breast-bone and stretches from thence upwards and backwards to the shoulder joint ; thirdly, the scapula, or scythe-blade-like bone, which j joints with the coracoid at the shoulder, and descends backwards over the dorsal ribs, slung in its place by muscles. The wing bones consist of, firstly, an arm bone, or humerus ; secondly, Pelvis of bird. two forearm bones ; thirdly, a, sacrum ; b, lumbar vertebras ; i i j i i d, ilium ; /, pubis ; g, sciatic a consolidated hand made up of several (never more than four) united fingers, of which only the thumb in general bears a claw, rarely the thumb and index fingers, as in the cassowary. The ribs are few and are fastened together by lateral spurs, or processes. The portions of the ribs which articulate with the vertebral column are separate from those that unite with the breast bone. Feet of Birds. 5 7 The tail bones are short and compressed, forming a ploughshare-like process ; the pelvic bones are long, and stretch along the spine fore and aft to an extent proportionally unmatched in the rest of the sub-king- dom (fig. 23). The two pubic bones do not unite in the middle line in front of the pelvis except in the ostrich, but always remain separate and open. The thigh bones are short. The leg-bone consists of two parts, which in adult birds are indistinguishably united. Of these the largest part is the tibia, or leg-bone proper, the lower end consists of the astragalus, or first bone of the tarsus or ankle. The lower part of the shank of a bird consists of the remaining tarsal and metatarsal bones elongated into a single shaft, and below this are the toes, of whiqh usually four are developed. The innermost of these or the hind .toe consists in general of two joints or phalanges, the second (inner) toe is made up of three, the middle or longest toe, of four, and the outermost toe of five phalanges. The shapes and dispositions of the toes vary with the habits of the birds ; thus, birds of prey have stout, grasping feet, with sharply hooked claws. Climbers, like woodpeckers and parrots, have the outer and inner toes turned backwards and the other two forwards. In swimmers, all the forward toes are webbed, while in the scraping birds the toes are short, stout, and armed with blunt nails. Many of the bones in the body of a bird are hollow, and in- stead of containing marrow they are lined by a deli- cate membrane and contain air, which is conducted into them from the respiratory organs by thin walled canals. This condition is specially exhibited in the 58 Vertebrata. birds of most powerful flight, but the bones of very young birds contain marrow. 32. Muscles and Viscera. The muscle or flesh of birds consists of very close fibres, and the sinews or tendons are often converted into bone. There is an enormous muscle on the front of the breast, the great pectoral, whose action is to depress the wing ; beneath this is a smaller, or second pectoral muscle with oblique fibres, arranged like the barbs of a feather, and converging to a tendon which, winding round a pulley at the top of the coracoid, is inserted into the top of the humerus and raises the wing ; this is the second pectoral. In the legs of many birds there is to be found superficially on the front of the thigh a slender little muscle, which, starting from the front of the pelvis, passes down the upper or front surface of the thigh, winds round to the back of the knee and runs by a tendon into the superficial flexor (or bender) muscle, for the longest toe (plantaris) ; a second muscle (the peroneus), from the outside of the leg can generally be traced into the same toe-muscle. These muscles are supposed to be of importance in the action of perching, and as their tendons pass over several joints they probably have a complex action. The digestive system of birds consists of the fol- lowing parts : first, the bill or prehensile organ, vary- ing in shape and texture according to the nature of, and mode of obtaining, the food upon which the bird subsists ; secondly, the tongue, rarely soft, usually hard and horny, often barbed ; thirdly, the long food- passage, or oesophagus, which, above the furculum, usually dilates into a crop (fig. 24, #), below which is Viscera of Birds. 59 a glandular stomach (c) communicating with the gizzard, or true muscular stomach (c). This cavity has a thick muscular wall consisting chiefly of two masses of muscle united by a strong tendon, and lined by a rough horny cuticle ; into this birds fre- quently introduce small stones which assist in tri- turating or grinding the food, as this organ is chiefly the place where the material of the food is reduced FIG. 24. b, crop : i; c, glandular stomach and gizzard. mechanically to a condition of pulp to prepare it for further digestive changes. The gastric juice secreted in the glandular stomach is here thoroughly mixed up with it, and the food mass is thus prepared for the intestinal canal. The gizzard is especially strong in grain, or fruit-eaters, weak or absent in flesh-eaters. Birds have two separate ventricles in the strong muscular heart ; one on the right side for propelling 6o Verlebrata. the impure or venous blood of the right auricle into the lungs, and the other, or left ventricle, for driving the purified blood after its return from the lungs, through the body ; the opening into the right ventri- cular cavity from the auricle is guarded by a muscular flap. There is only one aortic arch developed in the adult bird, and it arches to the right side, and in many birds there is only one artery developed in the neck for the supply of the head. The lungs are large, and surrounded on their lower surfaces by large air-sacs, into which the bronchial tubes distinctly open ; from these cavities pass the membranous canals, which convey the air to the principal bones. There is no muscular layer underlying the ' lungs for the purpose FIG. 25. Organ of voice of the raven. A, front view ; B, side view showing the muscles of vocalisation. of directly acting on them in respiration, except in the ostrich and apteryx ; but as the sternal and vertebral Voice and Senses of Birds. 6 1 ribs can move on each other, the bony wall of the thorax or chest cavity is susceptible of a large range of motion for breathing. As, from the activity of their motion, birds require a more perfect system of nutrition for their ultimate tissues and organs than reptiles, their respiratory apparatus is very highly developed, and hence their temperature is higher than that of any other group of animals. An organ of voice is usually developed in the air-passages of birds, most commonly at the point where the windpipe or trachea bifurcates to send an air-tube to each lung (fig. 25). At this spot there is a drum-like cavity or syrinx (g), in which certain tense membranes can be made to vibrate, and can be acted on by muscles (a, b, c, */, e\ attached to the windpipe. Thus the organ differs from that in mammals, in which the seat of voice is the larynx or upper end of the windpipe. In the wild swan the long and sinuous windpipe is contained in a hollow which is provided for its reception in the keel of the sternum. The blood of birds contains small elliptical cor- puscles which are nucleated. The eye of birds is remarkable for possessing bony plates in its ' white/ as well as a curious folded vascular projection at the bottom of the eyeball, which projects forwards towards the crystalline lens. There is also a third eyelid, or nictitating membran", placed below and within the two ordinary lids, and moved by two little muscles on the back of the eyeball, and there is an additional gland whose secretion keeps this accessory lid moist The senses of smell and 62 Vertebrata. hearing are also largely developed in some birds, notably in vultures and owls, the latter being pro- vided with a distinct external ear. Most birds have but one oviduct, and that is on the left side ; in its lining there are glands which secrete the white of the egg, its membrane, and the shell, during the downward passage of the yolk. The embryonic bird is provided with a rudimental knob on its pre-maxillary bones, which it uses in breaking the egg-shell wherein it is contained. CHAPTER XII. CLASSIFICATION OF BIRDS. 33. Primary Divisions. About 8,000 species or birds are known to the naturalist, and these are divided into two primary sub-classes. The first sub-class is called Ratidce, and includes all those birds which have a sternum without a keel, a rudimentary furculum and wings, feathers with discon- tinuous barbs and not distributed in feather tracts, and with no oil gland. They are all natives of warm or temperate climates, and strictly limited in their range. Several gigantic forms which existed until recently, are now extinct, such as the moa of New Zealand and the sepyornis of Madagascar. The ostrich of Africa is a familiar instance, and is pro- vided only with two toes. The American ostrich or rhea is smaller, and inhabits South America. Parrots and Cuckoos. 63 The cassowary is a native of the East Indian archi- pelago, and the emu of the Australian continent. The apteryx of New Zealand is the most remarkable of these birds, as it has perfectly rudimentary wings and a long slender bill, and there is a remarkable disproportion between the size of the egg, which is very large, and that of the bird. The second sub-class of birds is called Carinata and includes all those birds which have a keel on the breast -bone, a merrythought, usually functional wings, whose feathers are in tracts (except in the penguins) and have the barbs united along their margins. This includes fourteen orders of birds, of many of w r hich there are familiar illustrations easily obtainable. 34. Order 1, Parrots (Psittaci). The most in- telligent and most highly organised of birds ; easily known by their sharply FIG. 26. hooked beaks, both the upper and lower part of which are movable, and by their brightly-coloured feathers. Their feet are prehensile, the outer and inner toes being turned ~^ kull of ~ backwards, while the tWO Mj nostril ; e, quadrate bone ; v. lower middle toes are turned forwards, and thus they are enabled to grasp in climb- ing. The tongue is soft, and the muscles which move it are more distinct thai* those of most birds, and hence the singular power of mimicking sounds pos- sessed by many of them. They are natives of the 64 Vertebrata. \ tropics, the cockatoos being mostly from the East Indian archipelago, the macaws from South America, the common parrots from Africa and Madagascar. One curious genus, Strigops, the ground parrot of New Zealand, is exceptional in having no keel on its sternum, and some parakeets from Australia have no merrythought. They are vegetable-feeders, princi- pally subsisting on fruits, but often eating honey. Many species live long in confinement, and they are all easily domesticated. 35. Order 2, Cuckoos, &c. (Coccygomorphae). These are usually long-beaked birds with small flat tongues, having the toes arranged either permanently or temporarily like those of parrots, with the outer and inner turned backwards. The wings have long covering feathers. Some of these birds have enor- mous beaks thrice as long as the head, like the little toucans of America ; in others the beaks are sur- mounted with great horns, made of spongy bony tissue covered with horn, as in the hornbills of the Eastern tropics. Other examples of this order are the cuckoos, so familiar for their peculiar note and for their habit of laying eggs in the nests of other birds ; the kingfishers, bee-eaters, hoopoe, rollers, &c. Some are remarkable for their colours, like the plantain - eaters of Africa. The tongues are hard, often bristled, as in the toucans; few have much vocal power. They are for the most part feeders on insects and animal substances. 36. Order 3, Woodpeckers (Pici), Mostly brightly-coloured birds, with straight, strong, conical beaks, and slender and actively protrusible tongues. Swifts and Humming Birds. 65 The wings have short coverts. The middle toes are united at the base ; the inner toe is small, directed backwards, as is also the outer r, G . 27 . toe. The tail feathers are short, stiff, and serve as organs of support. These are insect-eat- ing birds like the last group, and they derive their name from their efforts after the capture of their prey, fn these the tongue bone is specially elon- gated, and its lateral processes coiled and disposed to allow of the rapid protrusion of the , IT j i Foot of woodpecker. barbed tongue. Woodpeckers exist everywhere but in Madagascar and Australia. 37. Order 4, Swifts and Humming-Birds (Macro- chires). A small order of birds, mostly of very minute size, and almost all of powerful flight. Some of these, like the swifts, have flattish beaks; others, like the humming-birds, have long tubular bills. In each wing the forearm and hand greatly exceed in length the upper arm, hence the I,atin name given to the order. The feet are very weak, scarcely able to support the weight of the body, and the inner toe may in some be turned forwards or backwards. They have a very simple syrinx, and little or no voice. They are mostly tropical birds, and vary much in size, the goatsuckers being the largest, sometimes of comparatively large size ; while the swifts are much smaller and somewhat swallow-like. One of these, the Collocalia of the Malay archipelago, secretes, by 66 Vertebrata. means of glands in the throat, a glutinous material of which it constructs its nests, which are the edible birds' nests of Eastern commerce, used as food in China. The humming-birds of Brazil, of which there are very numerous species, are also examples of this order, and include the smallest forms of the entire class of birds; thus Mclisuga minimus, from the island of San Domingo, only weighs about nine grains, and measures two inches in extreme length ; its nest is about the size of a walnut, and it contains two eggs each nearly as large as a pea. 38. Order 5, PercMng birds (?asseres.) This large order includes all our small birds, with the ex- ception of those hitherto mentioned. They may be recognised by possessing short wing coverts, a tarsus FIG. 28. covered in front with seven large scales, and slender toes, of which the first joints of the two outer are united. They have a well-deve- loped syrinx or organ of voice, and many of them can sing. These birds are very numerous, and make up Foot of passerine bird. , ..... . about twenty-one families. The best known of these are the following : The thrushes, known by their slightly curved bill, with a notch or tooth on each side near the tip, and with bristles at the angles of the gape of the mouth. They are insect-eaters for the most part. The commonest species are the song thrush; the blackbird, known by its yellow bill and eyelid-edge and its black body ; the missel thrush, known by its white-tipped three outer tail feathers ; the fieldfare, the redwing. Passerine Birds. 67 To this family belongs the mocking bird of America, which can mimic the song of any other bird. The birds of the wagtail family are recognisable by their slender forms, long legs, long tails, and moderate wings with nine primary feathers. They include the common pied wagtails, the yellow-breasted wagtail ; closely allied to which are the hedge-sparrows (Ac- centor) with strong, sub-conical, straight bills, and wings with a very short first quill, the third and fourth primaries being the longest. The warbler family, consisting of small singing birds with awl- shaped beaks flattened at base, are also closely allied ; of these the most familiar examples are the nightingales (Philomela] ; robin red-breasts of Europe ; red-starts (Phanicura) ; sedge and grasshopper warblers (Sal- icaria) ; white-throats, black-caps (Curruca) ; and willow-wrens (Sylvia). The gold-crested kinglet (Regulus) is the smallest American bird of this order, its length being under 4 inches. The pipits (Anthus), have awl-shaped bills, keeled at the base above, with two long scapular feathers and long hind claw. In North America the warblers (Silviidce) of Europe are represented by the Sihricolida or American warblers. The crow family (Corvida) constitute a group of much larger birds ; they have strong conical bills with no notch, and robust feet. This family includes the jackdaw, crow, raven, jay, and magpie, and the star- ling is a nearly related form. These have ten pri- mary feathers, while the birds of the conical-billed finch family possess only nine. This family consists of the house-sparrows, hawfinches, linnets, bullfinches, and nearly related are the larks and buntings. F 2 68 Vertebrate. Among the most remarkable tropical forms are the lyre-birds of Australia, the oven-builders of Brazil ; the sun-birds, nuthatch, wax-wings, &c. 39. Order 6, Birds of Prey (Raptores). This order consists of eagles, owls and vultures, which feed on animal food, and are armed with strongly hooked bills (fig. 30), and with strong, sharp and curved claws (fig. 29). At the base of the bill is a Fig. 29. FIG. 30 Foot of eagle. Head of eagle. cere or skin, which is pierced by the nostrils. The gizzard is weak, the digestive tract short, the sense organs are acute and powerful. Their strong wings have ten primary feathers, and the tail has twelve rectrices. Owls are mostly nocturnal, round-faced birds, with short beaks, and with eyes directed for- wards. They have no crop, and peculiarly soft plu- mage. Some have tufts of feathers above the ears, such as the horned owls. Vultures are carrion-eaters, most abundant in warm climates, with naked or down- clad head and longer bills. Eagles have feather- clad heads, and short, sharply-hooked bills, and they for the most part feed on prey which they kill for Pigeons and Poultry. 69 themselves. To this family belong the hawks, kites, buzzards and harriers, as well as the larger eagles, ospreys, and falcons. CHAPTER XIII. CLASSIFICATION OF BIRDS CONTINUED. 40. Order 7, Pigeons (Gyrantes). This well- marked group consists of the doves and pigeons, characterised by having a gristly plate covering the base of the upper mandible, pierced in front by the nostrils. They are vegetable-feeders, with a large glandular crop which sometimes secretes a milky fluid with which the parents nourish the young birds. They have a strong gizzard, shielded or feathered tarsi, and four usually free toes all on the same level, with short, slightly-hooked claws. They are mostly birds of powerful flight, and have ten primary quill feathers in their long pointed wings, and twelve or rarely sixteen rectrices. They are mostly social birds, often living in great societies. The pigeons, wood- quests, and doves are familiar instances, as also are the passenger pigeons of North America, which mi- grate in millions, darkening the air by their flocks. Our common pigeons, in all their varieties, are de- scended from the rock-dove, Columba livia. The curious dodo of Mauritius was an aberrant large pigeon incapable of flight, and hence it was easily 70 Vertebrata. captured by the early voyagers, and was extirpated in the seventeenth century. 41. Order 8, Scraping birds (Rasores). This large and economically important order includes the FIG. 31. poultry, turkeys, pheasants, grouse, partridge, &c., heavy plump-bodied birds, with com- paratively small rounded wings, weak in flight, and with a mode- rate length of beak and legs; they have stout blunt claws, the hind toe being raised above the level of the others. The name of the order is derived from the habit common to most of them of scraping in searching for their food in or on the ground. The tarsus often bears spurs, especially in the males, and the plumage is close and often brilliantly coloured, as in the peacocks and pheasants. Many of them have naked areas on the head, where the skin is soft and vascular, forming wattles or crests. As they are mostly grain-eaters, they have large muscular gizzards, capacious crops, and long intestines. Our common domestic fowls are natives of India, as also is the peacock and that most gorgeously coloured bird the Impeyan pheasant, whose plumage has a rich metallic lustre. The golden pheasant is a native of China, the turkey of America. In Australia the order is repre- sented by the mound-birds and brush turkeys, which hatch their eggs in ' hot-beds ' formed of large masses of decaying vegetable matters which they heap together for the purpose. 42. Order 9, Grallae. This group consists of long- Storks and Ducks. 7 1 legged birds which are often waders in habit, and are characterised by possessing small hind toes and long bills. They feed on worms, molluscs, and fish, rarely on vegetables. The side of the head presents no bare patch between the angle of the mouth and the eye, and the palate exhibits a long cleft between the two lateral halves of the upper jawbones. To this order belong the plovers and peewits, coots and waterhens, corncrakes and snipe, the cranes and bustards, oyster-catchers, herons, and bitterns. 43. Order 10, Storks (Ciconise). This group also consists of birds with long legs and bills, which in habit resemble the last, but differ from them essen- tially in their structure. Thus they have the two FIG. 32. B Head of ibis. Foot of ibis. lateral sides of the upper-jaw united along the middle line of the palate ; the lore or space between the angle of the mouth and the eye is bare, and the hind toe is long and functional. The best known examples 72 Vertebrata. are the ibises, spoonbills, storks, and jabirus, some of which are distinguished for their brilliant colours, like the scarlet ibis, the straw-necked ibis, and the scarlet spoonbill. The loose feathers of the lepto- ptilus of India are used for ornamenting bonnets, under the name Marabou feathers. 44. Order 11, Ducks and Geese (Lamellirostres). The birds belonging to this order make a very natural assemblage characterised by possessing webbed feet and long flattened bills, which on the under surface of the upper mandible exhibit a series of close transverse lamellae ; these act as sensitive prehensile surfaces in feeding, and large nerves are distributed on them. They have large fleshy tongues, and the hind toe is free and small. The wild swan presents a curious arrangement of its very long and sinuous windpipe, a coil of which lies within the hollow keel of the sternum. The best known forms are the ducks, geese, mergansers, swans, teals, widgeon, c. 45. Order 12, Longipennes. These are also web- footed marine fish-eating birds, with long pointed wings well fitted for flight They have long com- pressed beaks, with the nostrils either slit-like, as in the common gull, or tubular, as in the petrel. The hind toe is free, and usually of small size. The gulls, terns, petrels are the best known examples, the largest species in the order being the famous albatross, found on the ocean about the equator, which is allied to the small petrels or Mother Gary's chickens. 46. Order 13, Pelicans (Steganopodes). A curious order of water birds which have all the four Penguins. 73 toes included in the broad web, hence the feet have a singularly inturned appearance (fig. 33). Many of them have long bills and throat FIG. 33 . pouches, like the pelicans and fri- gate birds ; other and better known forms are the gannets, cormorants, and long-tailed tropic birds. 47. Order 14, Pygopodes. The last order of birds includes a singular assemblage of seabirds, whose wings are small and sickle- shaped, scarcely fitted for flight, and sometimes with scale-like fea- thers, as the penguins of the Ant- arctic Ocean. They have the hind limbs even farther back than in the generality of seabirds, and hence the curious erect position assumed by these birds when standing ; they have hard pointed compressed bills, and a small hind toe, the three anterior toes are closely webbed. The auks of the northern seas, the puffins, guillemots, and razorbills of our shores, are the most familiar examples. The great auk of the northern seas, is wingless, and like the dodo has become extinct. 48. Migration of Birds. Among birds, as among fishes, we notice the curious habit of periodical mi- gration ; the travelling at regular periods into districts wherein suitable food is abundant, and their return on change of season ; thus the swallows, swifts, rice birds and warblers visit the north about the middle of April, breed there, and then return to their winter quarters in the Southern States and the West Indies 74 Vertebrata. on the advent of cold weather, about the first week of October. CHAPTER XIV. CLASS 5, MAMMALIA. 49. General Characters. This, the highest class of vertebrate animals, includes all those viviparous, warm-blooded animals which are provided with super- ficial dermal glands for the purpose of secreting a fluid called milk for the nutrition of the young until they are able to seek out other nutriment for them- selves. They are for the most part terrestrial in habit ; they are all provided with epidermal covering in the form of hairs ; and the lower jaw in them articulates directly with the base of the skull, the quadrate bone being very small and included in the ear cavity, so that it is of use only in conveying sound-waves to the nerves of hearing. Man, all quadrupeds, seals, whales, and bats are examples of this class. The superficial clothing of hairs characteristic of the class may be only transitory, as in whales and some thick-skinned animals, or the hairs may be thick and spine-like, as in the porcupine and hedge- hog, or they may be united into scales, as in the manis and armadillo, or on the tail of a rat. Each hair is the epidermal secretion of a single papilla, and is a solid cylinder composed of long cortical or super- ficial cells, and rounder central cells. The hairs arise Skeleton of Mammalia. 75 in pits or follicles, and into these follicles there open sebaceous glands, which secrete an oily material for the lubrication of the hairs. The neck-region of the vertebral column or back- bone in all mammals consists of seven vertebrae, except in three cases; 1 the back region consists of about twenty, but the number is more variable; the shoulder girdle is never connected directly to the spine, but the pelvic girdle always is so, and hence there are always certain vertebrae thickened and united for the purpose of supporting the pelvis; these are "known as the sacrum, and behind this in most mammals is the tail, which varies extremely in length, sometimes, as in the long-tailed manis of Western Africa, having over forty vertebrae, in others, as in some bats, having only three. In man there are four very small rudimental tail vertebrae, and the same number exists in the gorilla, chimpanzee, and orang- outang. In many mammals, as the South American monkeys, opossums, and kinkajous, the tail is prehen- sile and is used as an additional hand in climbing. 50. Skeleton. The skeleton consists of two classes of bones, some with an interior of spongy cells, others with an internal cavity. In both cases the hollow spaces are filled with marrow. The skull in mammals is a solid box to which the upper jaw is immovably fixed, and it articulates with the first vertebra of the neck by means of two articular knobs or condyles. The lower jaw is composed of two pieces only, one on each side, and it forms a joint directly with the 1 These are two sloths, one having 9, the other 6 vertebrae, and an aquatic American animal, the manatee, which has 6. 76 Vertebrata. skull, beneath the ear. The shape of the articular surfaces which form this joint is variable, and de- pends on the nature of the food and the character of the motions which are necessary for mastication. Thus, in flesh-eating animals the lower jaw has a transversely elongated, cylindrical condyle, which can allow only of a vertical motion, while in gnawing animals the lower jaw slides forwards and backwards. 51. Teeth. The jaw arches, and they alone, bear teeth, which are arranged in one row ; no accessory teeth are developed on the palate as in reptiles and fishes. The teeth are always in sockets, and are FIG. 34. Skull of anteater, a perfectly toothless mammal. rarely absent, as in the ahteaters (fig. 34), though sometimes they are rudimental and disappear early, as in whales. There are usually two sets of teeth ; one an early developed or milk set, which soon drop out and are succeeded by a second or permanent set ; thus reminding us of what we found in crocodiles, where successively growing teeth follow each other in the one row almost indefinitely as long as growth continues. Those teeth in the upper jaw which are rooted in the foremost bone, or premaxilla, are called incisor teeth, and have usually a cutting edge and a single root. When the first tooth in the maxilla or jaw proper, is placed near the suture or line of con- tact between that bone and the premaxilla, it is Teeth of Mammals. 77 generally long and pointed and has but one root To it the name canine is given, while the other maxillary teeth have in general two or more fangs, and are called grinding teeth or molars. The milk teeth are usually fewer than the permanerft teeth, and hence some of these grinders have had predecessors while others have not ; those which are secondary are called premolars, while those which are primary (the hindermost), are called molars. Similar names are given to the corresponding teeth in the lower jaw. As the teeth vary in number and size in the different orders of mammals, they afford a good and easy system whereby the different forms can be discrimi- nated ; and in order to be able briefly to describe the characteristic dentition of any animal, zoologists are in the habit of tabulating the number and arrange- ment of the teeth of animals in a set formula : thus FIG. 35. Teeth of Tasmanian devil. to write the dental formula of an animal we first put down the initials of the sets of teeth, and follow each initial by the number of teeth of that sort in the two jaws, those of the upper jaw being written like the 78 Vertebrata. numerator of a fraction, while those of the lower are placed as the denominator; thus, in an adult man the dental formula is /- , C^=, P^^, M^^ ; 22 i i 22 33' that is, on each side of each jaw there are two in- cisors, on each side of each jaw one canine, two pre- molars, and three molars. The jaws are almost always protected by fleshy lips, except in the first order. 52. Viscera. Mammals have well developed brains, and usually acute sense-organs. The lungs and heart are separated from the intestine and other digestive organs by a muscular partition, called the diaphragm, which is an important agent in breathing. The heart consists of four cavities, and the opening between the right auricle and right ventricle is guarded by a membranous valve consisting of three flaps. There is but one aortic arch in the adult, and it arches to the left side ; there are two carotid arteries for conveying blood to the brain. The blood con- tains round, non-nucleated corpuscles, and therein differs from that of any of the foregoing classes. There are seventeen orders of mammals at pre- sent living, but representatives of several additional and most remarkable intermediate orders have been found in a fossil state, especially in the tertiary beds in America. 79 CHAPTER XV. CLASSIFICATION OF MAMMALS. 53. Order 1, Monotremata. The first order of mammals is called Monotremata, and includes two remarkable Australian forms, the platypus and the spiny anteater. They are both small animals, being about a foot in length. Both have long coracoid bones separate from the shoulder-blade or scapula, which, bird-like, reach as far as the sternum, and the two collar-bones unite into a single T -shaped merry- thought-like bone. In both forms there are two long spur-like bones articulated to the front of the pelvis and embedded in the abdominal muscles, and in both the bones of the skull unite at an early period to form a perfectly continuous braincase. They are also characterised by the intestine and excretory organs opening, as in the birds, into a common cloaca (hence the name of the order). The platypus, or OrnithorhynckuSy is aquatic, and has a duck-like bill and two small, flat, horny teeth in each jaw. The male has a strong hollow spur on the ankle which communicates with the duct of a poison gland and is a weapon of offence. The spiny anteater, or Echidna (fig. 36), is toothless, and has a long slender horny bill, a worm-like tongue, and a dermal covering of strong stout spines. The young of both these forms are born in a very imperfect state of development 54. Order 2, Marsupialia. The second order of mammals is named Marsupialia, and includes kanga- 8o Vertebrata. roos and opossums, and all those other Australian forms in which the females bear on the under surface Kangaroos. 81 of the body a pouch wherein the young are received and sheltered after their birth. This pouch is sup- ported by two bones (fig. 37, ///,) FIG. 37 . similar to those described in connection with the pelvis of the Monctremes ; to these bones the name marsupial bones has been given, but they exist in the pouchless males as well as in the pouch-bearing females. All the marsupials are clad with thick fur, and they are armed with claw-bearing toes, two of which on the hind foot tend to become very small and united within a common web of skin. They exhibit many characters of inferiority to the other mam- mals ; thus the two lateral lobes of the fore -brain are nearly smooth on the surface and are imperfectly united together, and the young are born in an exceedingly rudimental state. The marsupials vary very much in habit, and are modified to suit these habits. Thus, the Tasmanian devil and Tasmanian wolf are flesh-eaters, with sharp claws and sharp strong teeth (fig. 35). The opossums of America are insect-eaters, and have sharp and numerous teeth ; they are the only marsupials which live outside the great Australian region, to which all the others are confined, and of which they are almost the sole mammalian inhabitants. Some of G Pelvis of kangaroo, marsupial bones; 62, ilium. 82 Vertebratd. ftie opossums have the pouch rudimental, and the mother carries her young ones on her back, often with their prehensile tails coiled round her tail. Others, like the yapock of South America, are amphibious, and have webbed feet The kangaroos proper (fig. 38) are characterised by the enormous dispropor- tion of the fore and hind limbs ; the former are short, five-fingered, while the latter are very long with long feet, the middle or third toe (which corresponds to our fourth, as they have no great toe) being enormous in length, the fourth being a little smaller, while the first and second are united and excessively Kangaroos, Phalangers. 83 slender. The tail is thick and with the hind legs makes a tripod whereupon the animal rests when standing. In feeding, the animal bends down so as to rest on the short forepaws, and in running it pro- gresses by a series of long leaps or bounds in which it uses only its hind legs. The largest living kangaroos are about five to six feet high when standing ; but the majority of the species are small, some being not larger than a rat FIG. 39. Teeth of kangaroo rat. These true kangaroos are herbage -feeders, and they have a complexly-pouched stomach to enable them to digest green food. Their teeth generally are : The phalangers, or Australian opossums, are fruit- eaters for the most part, and like the opossums of America they have an opposable thumb on the hind foot, which thus is able to act in grasping like a hand. Some of these phalangers have wing-like side folds of skin stretching from the fore to the hind limbs, where- by they are able to take long flying leaps. 84 Vertebrata. The wombat is a burrowing and gnawing mar- supial, whose chisel-shaped incisor and other teeth continue permanently to grow, and thus the waste of tooth-tissue which takes place in the process of grind- ing the roots and twigs which constitute its food, is restored. This animal is about 2\ feet long, and, like the koala or native bear of Australia, has an accessory gland in the stomach, and a long caecum or pouch, where the large and small intestines unite. They are both also almost tail-less, and the koala has its thumb and index fingers capable of being opposed to the others. Some fossil kangaroos, like the Diprotodon, were of great size ; one thigh bone of this animal in the museum of the University of Dublin, must have been at least two feet in length when complete. It is also interesting that the earliest fossil mammals which have as yet been discovered are marsupials. The bones of marsupials are, in general, easily recognised ; thus the lower jaw has an inflexed angle, whereby it can be distinguished from that of any other mammal. The dentitions of marsupials are very variable, as can be seen from the four subjoined examples : Kangaroo (fig. 37) * /i^4 4 i i Myrmecobius or) 7 4~ 4 r I ~ I p 2 ~ 2 *f55 banded anteater) 33' i i' 33' 66' Tasmanian devil) r 4 4 r i i P 2 2 ,,-4 4 (fig. 35) J3^3 i=?^J=?. ' 4=? CHAPTER XVI. PLACENTAL MAMMALS. 55. The Placenta. In all the succeeding orders of mammals the young are not born until their internal organisation has become much more perfectly developed than in the case of the young of the mar- supials and monotremes ; and in order to provide for their nutrition while they are thus growing, a peculiar vascular organ, called the placenta, is developed, whereby blood is supplied to the embryo for its nourishment; hence they are called placental mam- mals to distinguish them from the marsupials, which are named non-placental mammals. Order 3, Edentata. The third mammalian order is known as Edentata^ and includes the anteaters and armadillos, which are easily recognised by the absence of incisor teeth, at least in the middle of the jaws, so that the front of the long, snout-like mouth appears toothless, hence the name. They are all armed with strong, usually sharp claws, and are clad with coarse hair, or else with hard scales, and feed on insects, small animals, or carrion. The true anteaters are natives of South America, and are quite toothless (fig 34). They have exceedingly long, worm-like tongues, which they can protrude for the purpose of entrap- ping the insects whereon they feed ; and they have an enormous pair of glands in the neck which secrete a glutinous fluid to render the surface of the tongue sticky. This long tongue they can retract rapidly, 86 Vertebrata. FIG. 40. and in order to enable them to accomplish this, the retractor muscle extends back to the hinder end of the breast-bone, which itself is often enormously elongated. Some anteaters are over five feet in length, others are much smaller. The great Cape anteater of South Africa is closely allied, but has a strap-like tongue and grinding teeth, which are peculiar in their struc- ture, as each tooth con- sists, not of a single papilla like the teeth of most other animals, but of a closely united bundle of separate papillae (fig. 40). The pangolins of Africa and Asia are covered with overlap- ping epidermal scales, and are also toothless \W3W and insect-eaters. They Tooth of Orycterope or Cape Ant- all have CHOrmOUS claWS eater magnified, showing the sepa- ... , ate papiii^,/, of which each tooth on their hands for tear- is made up ; d, dentine, or tooth- , , i -11 substance ; c, cement. mg Open the ant-hills SO as to reach their prey. The second family, or the armadillos, are South American, scale-covered burrowing animals, with grinding teeth and a short tongue. They feed chiefly on carrion or small animals, and their dermal armour is arranged in transverse girdles or bands which may be movable on each other. A rmadillos. 87 The Edentates now existing are all of moderate or small size, but from the remains of fossil forms we know that some of them must have been of gigantic proportions. 88 Vertebrata. 56. Order 4, Bradypoda, or Sloths. These are tail-less animals inhabiting South America. They are often united with the Edentates, from which they Sloths and Manatees. 89 differ in the possession of short round heads, not pro- longed into a snout, with a lower jaw of one piece, even from a very early age, and also by having a very remarkable down-directed process of the malar or cheek-bone. They are strictly vegetable-feeders, and have sacculated stomachs. Their whole organisation is adapted to an arboreal life, and they live suspended from the branches of trees by their long and strong hook-like claws. They are clad with coarse hair of a dirty white or brownish colour, and have two or three toes only. The peculiarity of their neck verte- brae has been alluded to before ( 49). They have no incisor teeth and ^^- molars, which are simple and nearly flat-topped. The Megatherium, a fossil sloth from South America, must have been little less in size than a large hippopotamus. In many respects it and its allies seem like passage forms from the sloths to the armadillos. 57. Order 5, Sirenia or Manatees, constitute a small group of sea-weed-eating marine animals, of a somewhat fish-like habit and form, usually found near the mouths of rivers. They have a thick skin, sparsely covered with bristles, and flat-crowned grinding teeth. They have no hind limbs, and the fore-limbs are converted into paddles. The heart in some is deeply cleft, the right and left ventricles being nearly separate from each other (fig. 43). One animal of this group, the Rhytina, which inhabited some islands in Behring's Strait, has become extinct within the last century. Another, the dugong, inhabits the Indian Ocean, QO Vertebrata. while the manatee or mermaid is a native of the opposite shores of the South Atlantic, extending from South America to Africa. These are often confounded with whales, but can be known therefrom by their FIG. 43. Heart of dugong, showing the separation of the ventricles. n, right auricle ; d, left auricle ; b, right ventricle ; e, left ventricle ; f, aorta ; c, pulmonary artery. possessing a neck, a movable elbow-joint, a trace of nails, and nostrils far forward and not at the top of the head. They also, except the extinct Rhytina, possess teeth. 58. Order 6, Ungulata, includes all those herbi- vorous mammals whose extremities are used solely as organs of progression, and not of prehension, and in which each toe ends in a hoof or broad case of horny epidermis. They are usually animals of large size, and they have no collar-bones. Their brains, however, are small in proportion to the bulk of the body, and Horse, Ass, and Tapir. 91 the intestinal canal is of very great length. There are two chief sub-orders of these hoofed animals, the first consisting of such as have odd toes on their hind feet, and unsymmetrical toes on the fore feet. Of these odd-toed mammals, there are three living types horses, tapirs, and rhinoceroses. The horse and ass have only a single toe developed on each limb, which corresponds to the third toe of ordinary mammals. They have also a dentition of , 9 6 i i 44 33 The two best known forms are the horse and the ass ; the former is characterised by its tail, hairy from its base, and by the wart-like callosities on the inner surface of its legs. Remains of horses are found in the bone caves of Britain and of South America, as well as in those of Continental Europe. The striped races of the genus Equus are confined to Africa ; they are the zebra, the quagga, the dauw, &c., and are scarcely tameable. The wild asses inhabit Western Asia, Fossil horses are known, exhibiting all the intermediate grades of development of feet from the single hoof of the common horse to the Eohippus with four functional toes and a fifth rudi- mentary one on the fore feet, and three toes behind. The tapirs, natives of Malaya and of South America, are also uneven-toed ungulates, possessing three toes on their hinder, and four (but laterally unsymmetrical) toes on their fore feet They are characterised by possessing a proboscis- like snout, and rather long legs. In number the teeth are equal to those in a horse. 9 2 Vcrtebrata. The rhinoceros (fig. 44) is the third type of this sub-order, and is a native of Africa and the Malay / /-' archipelago; the foot is three-toed, and the skin of Rhinoceros, Swine. 93 enormous thickness and often folded. The leading characteristic is the long epidermal horn which is rooted in the dermis on the upper surface of the nose. This in structure consists of a tuft of confluent hairs, and sometimes grows to several feet in length, and is of great hardness; the horn is always medial, and usually single, when two exist they are placed one in front of the other. At one time a species of rhino- ceros clothed with a woolly coating inhabited Great Britain and the northern parts of Europe and Asia, but it became extinct in prehistoric times. All these odd-toed ungulates have at least twenty- two vertebrae in their trunk, interposed between the neck and the sacrum, and they all have a bony knob or third trochanter on the outside of the shaft of the thigh bone for the attachment of muscles. See fig. 44, also fig. 41. The second sub-order of hoofed animals includes those whose toes are. in even numbers, two or four, and are laterally symmetrical (when there are four, two are in front and two behind). They have for the most part nineteen dorso-lumbar vertebrae, and none of them have the protuberance on the thigh-bone referred to above. Many of them have horns, but these are always on the forehead, and one on each side, never median as in the rhinoceros. 59. Swine and Hippopotami. There are two very well-marked divisions of these even-toed ungulates. In one of these the animals have simple stomachs, and the grinding teeth have little knobs or protuber- ances on their surfaces, hence these are called Buno- donts j in the other group the stomachs are complex, 94 Vertebrata. and the hardest layer of the teeth (the enamel), is arranged in crescents; these are known as Ruminants. FIG Of the btmodonts the pigs are the most familiar examples. Our domes- tic pigs are derived from the wild boars of Southern Europe and Asia, animals which formerly inhabited Great Britain in a wild state. The babyroussa of the Malay Islands is Crown of the tooth of a singular pig whose upper canine Lf m e e r ic s resfs. the teeth grow upwards and arch back- wards so as to reach the forehead where they end in a curled point. Most of the pigs have large tusk-like canines, and their teeth are usually represented by the formula 33 i -i 33 33 The hippopotamus of the rivers of Africa is an enormous pig-like creature, with very short legs and a heavy body, and with long tusk-like incisors, two in each jaw ; it sometimes reaches a length of nine feet. 60. Ruminants. The ruminants are so called because they chew the cud, that is, they subject their food to a second chewing after it has been swallowed. They are, for the most part, large soft-fleshed animals, the favourite prey of large carnivores, and as the food which they require for their nourishment is bulky, being green herbage, and only to be obtained in open places of pasturage, where they would be exposed without shelter to the assaults of their enemies, it becomes a matter of vital importance for their well- Stomachs of Ruminants. 95 being that the process of mastication, a long and tedious one in the case of such food, should be kept over until the animal has laid in its store of provisions and retired to a sheltered hiding-place. Accordingly the stomach of a ruminant is divided into four com- g6 Vertebrata. partments, and into the first of these (called the paunch} the food is taken when first swallowed ; then it passes into the second division, which consists oi many large hexagonal cells or little chambers ; here it becomes divided into masses for re-chewing, and these pass up the oesophagus back into the mouth, where it is carefully and slowly masticated, and mixed with saliva, after which it is re-swallowed, but this time as a semi-fluid soft material, which on reaching the stomach is conducted along a gutter made by a mucous fold, into the third stomach or liber, which consists of many layers of mucous membrane arranged like the leaves of a book. Here the materials are still farther mixed up with the secretions of gastric glands, and pass on into the fourth stomach, where digestion finally takes place. The camels of Arabia and Africa differ from the other ruminants in having no third stomach, in possessing canine teeth in each jaw, and two lateral incisor teeth in the upper jaw. They have also nails rather than hoofs on their large and well- padded toes. The hump on the camel's back consists of fat and cellular tissue. There is a single hump on the dromedary, but there are two on the back of the Arabian or Bactrian camel. The second stomach of the camel has deep cells or compartments, which has given origin to the fables about the capacity of camels to store water in their stomachs. The llamas of the Andes in South America are closely allied to the camels, and agree with them in most of their peculiarities, but have no humps. The musk-deer, which inhabit the mountainous regions between the Himalaya and the Altai mountains, have The Cow. 97 also canine teeth, and are distinguished by the presence of a pair of odour-secreting musk-glands. 98 Vertebrata. The other ruminants have neither canine nor incisor teeth in the upper jaw, and most of them possess horns. In the giraffe, the tallest and longest- necked of the mammals, these horns are short pro- cesses of the frontal bone covered with hairy skin. In the cows, antelopes, goats and sheep, these horns are made up of an outer hard, horny sheath, placed over a bony core or process of the frontal or forehead bone. In the ox and cow group, the horns are directed forwards, and are smooth, while in the antelopes, which are mostly natives of Africa, the horns are directed backwards, and are often ringed or waved. One American species, the pronghorn, sheds its horns periodically like the true deer. The goats and sheep have compressed angular wrinkled horns, often coiled. Our domestic sheep are possibly derived from the mountain sheep of South Europe and Asia. The deer family possess solid horns composed of bony processes of the frontal bone, often branched in various ways. These antlers are annually shed and renewed, each new growth being usually larger than its predecessor. The best known examples are the Virginian deer, the fallow deer, and the roebuck. In most of these ruminants the dentition is repre- sented by the formula /2 -o ^-o 3-3 33 i i 33 33 99 CHAPTER XVII. CLASSIFICATION OF MAMMALS continued. 6 1. Order 7, Cetacea (Whales). These, like the Sirenia, are marine mammals with no hind limbs, and having the fore limbs converted into fins. They are fish-like in shape, without necks, and have a smooth thick skin beneath which is a thick layer of fat known as blubber. The nostrils are situated on the upper surface of the head, and are called blow-holes, and are well protected by dermal folds so as to prevent the entrance of water into the air-passages while the whale is beneath the surface of the sea. These animals require to rise to the surface to breathe, and on doing so they forcibly eject a shower oi spray, consisting of the mucus secreted by the membrane of the nasal passages, the vapour of the breath, and whatever sea water lurks in the crevices about the nostril ; this process is called blowing, and it is in reality somewhat like a forcible sneeze preparatory to a deep inspiration. The sense of smell is almost or altogether absent. There are seven cervical vertebrae, but they are usually united together so as, in old whales, to form one bone. The tail in whales consists of two lateral, hori- zontally-placed lobes consisting of folds of skin and connective tissue appended to the end of the vertebral column ; this is the chief instrument of locomotion. The mouth in true whales is of enormous capacity, and as theii food is mostly small fish, cuttlefishes and ioo Vertebrate. molluscs, they require to take in very large quantities of this material for their nourishment, which they do in the following way. The jaw arches are covered all around their edges with horny plates of * whalebone,' fringed with bristles in place cf teeth, and these act as strainers. In feeding, the animal opening its mouth, takes in a mouthful of sea-water and its animal FIG. 48. Head and tongue of whale. a, tongue (represented much too large) ; b, whalebone plates. contents, and then by closing the jaws and pressing the tongue against the palate, expels the water through the slits between the whalebone plates, which by their opposition and by their bristly margin retain the solid materials to be subsequently swallowed. In some whales there are exceedingly minute rudiments of the hind limbs, in the form of small ischia or pelvic bones, embedded in the muscles of the abdomen, and not visible on the surface. Whales have usually complex stomachs, often with four chambers; they have also a moderately long alimentary canal, large and tortuous networks of blood- vessels along the ribs, and a thick fleshy diaphragm. Seals and Walruses. 101 The large-headed sperm whales are often as much as sixty to eighty feet long. One third of the whole length is formed by the head, whose anterior bones, enormously dilated, are hollowed into a chamber which contains the substance called spermaceti, used in making ointments and cosmetics. These whales possess from fifty to sixty large conical teeth in the lower jaw, and therein differ from the baleen whales, which in some cases possess small embryonic teeth that disappear early and are replaced by the whale- bone plates. The common porpoises, bottle-noses, and dolphins have numerous simple teeth in both jaws, and the narwhal has one enormous front tooth which sometimes grows to a length of 5^ or 6 feet, forming a horizontal tusk. Whales are the largest of animals, and have been seen over ninety feet in length. 62. Order 8, Pinnipedia. This small order con- sists of the seals and walruses, and forms a connecting link between the whales on the one hand and the bears on the other. They are aquatic, fish-eating, hair-clad mammals, with four fin-like limbs, each provided with five webbed digits. The hind-limbs are stretched horizontally backwards on the same line as the tail, to which they are very closely united. They have roundish heads provided with numerous sensitive bristles, large eyes, and loosely united facial bones. They have valvular nostrils, no external ears, simple stomachs, and large venous cavities to hold the impure blood while respiration is suspended during diving. Most seals are marine, but some live in fresh- IO2 Vertebrate water lakes as in Lake Baikal. Our common seal is inoffensive and easily tamed. The walrus, known by its huge tusks or canine teeth, used for digging up the molluscs on which it feeds, sometimes reaches twenty feet in length. The fur seals, whose beautiful sk ns are of such commercial importance, are natives of the Southern Atlantic and Pacific Oceans. The dentition of the common seal is 2 - 2 I I 3 - 3 2 - 2 63. Order 9, Carnivora. The flesh-eating mam- mals are the cats, dogs, weasels and bears, known by possessing sharp claws, long pointed canine teeth, a simple stomach, and a short intestine. The lower jaw is constructed to move only in the vertical plane up and down, having no lateral motion, the condyle FIG. 49. Skull of lion. 7, median temporal crest ; 12, post-orbital process ; 15, nasal bone. being transversely lengthened. The molar teeth are ridged and sharp, so as to be fitted for dividing flesh. Cats, Dogs, Lions. 103 They never have collar-bones. The skull of a carnivore can be easily known by the prominent medial crest for the attachment of the powerful muscles which move the lower jaw (fig. 49, 7). The dog is a typical carnivore, whose teeth are represented by the formula 33 i i 44 33 In progression dogs are digitigrades, that is they only rest on the last joint of their toes in walking, and their claws are blunt, not capable of being retracted. The numerous races of dogs cannot be sharply marked off from each other, nor can some of the varieties of the dog be sharply differentiated from wolves. The wolf has usually erect ears and larger teeth, but no absolute point of difference can be relied upon. The fox has an oval pupil and a more bushy tail. All the true dogs have comparatively smooth tongues. The family Felidcz, or cats, are also digitigrade carnivores, but they differ from the Canidce, or dogs, in having the claws capable of retraction when not in use, and thus they are preserved from undue friction and are sharp ; the retraction is accomplished by mean 3 of lateral elastic ligaments. The cats are more purely flesh-eaters than the dogs, and usually hunt and kill their prey ; their dentition is 33 I I 22 I -I The lion is a native of Africa and Asia, the tiger, the 104 Vertebrata. strongest of the carnivores, is confined to Asia, Other forms are the panthers and leopards, the ounce, the jaguar or American leopard, the puma or American lion, the tiger-cats, ocelots, lynx, and domestic cats. This last-named is probably the descendant of the wild cat of Abyssinia tamed by the ancient Egyptians. The wild cat of this country (Lynx canadensis), ranges over the entire continent south of the Arctic circle. The cheetah, or hunting leopard of India, has only partially retractile claws. The cats have all rough tongues armed with numer- ous sharp, recurved papillae. The hyaenas are intermediate in some respects between the dogs and the cats. They have the dentition and rough tongues of the cats, with a more doglike form and non-retractile claws. They are nocturnal, and can be known by the peculiarly low hind-quarters in comparison with the fore. Civets and mongooses make another family called Vtverridtz, which usually possess odorous glands, rough tongues, short legs, and a semi-plantigrade mode of progression. The weasel and otter family, Mustelida, differ from these in their shorter, rounder heads, smooth tongues, and longer bodies. Many of these are sought for on account of their skins, such as the vison, ermine, sable, mink, &c. Others, like the weasel, skunk and pole-cat, are well-known vermin ; the Mustela foina, or marten, was the domestic cat of the classic authors. The plantigrade carnivores are those that bring their whole foot- sole to the ground when walking; they are bears, badgers, and kinkajous. The badgers Bears, Badgers, Kinkajoiis. 105 have scent glands, whereby they are easily distin- guished. The kinkajou, a native of South America, has a prehensile tail and retractile claws. The best io6 Vertebrata. known of the bears are the polar or white beai of the Arctic regions, the black bear of America, the brown bear of Europe, and the grizzly bear of the Rocky Mountains, possibly the same as the giant cave bear, now extinct in these countries. The brown bear formerly inhabited the British Islands, but was extir- pated in Scotland in the eleventh century. The bears differ from the other carnivores in the possession of tubercled teeth which can be used for masticating vegetable matters, and many of them are capable of partaking of a mixed diet. 64. Order 10, Hyraooidea. A small order inclu- ding a few little tail-less animals, natives of Africa and Syria, one of which is the cony, mentioned in the Bible. They are somewhat rabbit-like in habit, with four toes on the fore feet, and three on the hinder, each toe being armed with a flat nail. The molar teeth have been compared in pattern to those of the rhinoceros, and there are no canines. They have sacculated stomachs and no collar-bones. 65. Order 11, Bodentia. Gnawing animals, the largest order in the entire class, including the rats, mice, squirrels, &c. They are all small and claw-bearing, and have a most remarkable dentition. There is usually but one incisor on each side of each jaw, and this tooth is chisel-shaped ; it consists of two materials, one a hard substance or enamel on the outside or front, the other a softer dentine or bone-like substance behind. In their growth the upper and lower teeth oppose each other, and the constant friction during feeding wears away the surface of the tooth, which however is constantly growing, but as the soft dentine Teeth of Gnawing Mammals. 107 wears away more quickly than the harder enamel, the tooth is kept constantly sharp ; hence when one incisor in a rodent is broken, the one that should FIG. 51. Flying squirrel. oppose it grows on continuously, and sometimes this mode of growth locks the jaws together. There are no canine teeth in rodents, and the io8 Vertebrata. molars are separated from the incisors by a long interspace. The lower jaw is large, and its condyle is so articulated as to permit it to slide backwards and forwards in mastication, thus giving the power of gnawing. FIG. 52. Skull of porcupine, showing v, the large infra-orbital cavity. Rodents have small, smooth brains, usually a simple or saccular stomach, and a long caecum or blind pouch from the intestine (except in dormice). Some genera, like guinea-pigs, hares, and rabbits, have no collar-bones, others, like squirrels and beavers, have these bones well marked. The hares and rabbits have a thin layer of enamel surrounding the backing of dentine on the incisor teeth, and have two small incisors behind the large ordinary pair in the upper jaw. The squirrel family are usually long-tailed elegant creatures, and in one genus, the flying squirrel (fig. 5 1 ), there is a lateral parachute of skin stretching from the fore to the hind limbs. The beavers have flat scaly- tails and webbed hind feet. The rats and mice Gnawing Animals. 109 are known by their long cylindrical scaly tails, and usually rooted teeth (except in the voles). The common grey rat, introduced from the banks of the FIG. 53- ihe spaiax, or blind rat. Volga in 1727 into Western Europe, has now nearly exterminated the black rat. Spaiax (fig. 53), the rat- mole of SE. Europe and NW. Asia, has rudimental eyes covered by the skin, and Dipus, the jerboa of the East, has long, kangaroo-like hind legs and very small fore legs. The porcupines have a covering of quill-like hairs, and have an enormous hole in the front of the skull wall, directly under the eye (fig. 52), which is partly occupied by a muscle of mastication. The chinchillas, coypu, &c. which are sought for their fur, are also examples of this order. Hybernation. Many rodents, like some mam- mals of other orders, bears, bats, &c., spend their winter in a condition of sleep : this process is called hybernation. Previous to retiring to this rest, these animals store up fat in different regions of the body, 1 10 Vcrtebrata. especially in a large gland called the thymus, placed in the thorax, or cavity of the chest, in front of the heart. This fat is absorbed during the winter, and the animal arises next spring lean and hungry. The lemmings extend far north into the Arctic regions, some having been captured at the winter quarters of the 'Alert ' in 1875, in N. latitude 82. 66. Order 12, Proboscidea (Elephants). No groups of mammals appear more diverse from each other, in size at least, than do the rodents and the elephants, and yet the latter are structurally more FIG. 54- Skull of young elephant. 22, the premaxillary bone, containing the root of the tusk k ; 15, nasal bone ; 7, tempora region: 26, zygomatic arch ; i, lower jaw; c, upper jaw. closely allied to the former than to any other order of mammals. The elephants are the giants among Elephants. in living land animals of the tropics, and are covered with a thick naked, or sparsely haired skin. They have five hoof-covered toes on each foot, though sometimes two toes are included in one hoof. The proboscis, or trunk, is a muscular and exceedingly movable double-barrelled tube appended to the nose, FIG 55- Section of the skull of the elephant, showing the small size of the brain- case, e, and the large size of the air spaces. b, marks the posterior nostrils ; 13, the cavity of the nose ; a, the front opening of the bony nostrils to the edge of which the trunk is attached. in fact an extension of that organ, which, by means of a finger-like appendage at the tip, can pick up even 112 Vertebrate exceedingly small objects. The teeth of an elephant consist of two tusks or incisors in the upper jaw, which grow continuously, sometimes to enormous sizes, and furnish the ivory of commerce. There are no incisors in the lower jaw, but there are on each side of each jaw two large, rough-crowned, quadrate teeth, whose crowns are marked by transverse enamel ridges, used in grinding the twigs and shoots of trees on which these animals feed. There is a constant succession of these molars, seven of which are de- veloped during the life of the animal on each side of each jaw, but never more than two, or at most three, are laterally functional at one time. The skull is enormous, most of its bulk consisting of huge air- cells, and the brain is large and convoluted on the surface. Two species of elephants are now living, confined to the tropics : one in Africa, known by its convex forehead and flapping ears ; one in India, which has a concave forehead and smaller ears. Formerly several species of elephants lived in Europe, and remains of one form have been abundantly met with in some parts of the British Islands. In Siberia, also, there exist numerous remains of a hair-clad ele- phant, the mammoth, which had probably existed down to a comparatively modern time. H3 CHAPTER XVIII. LEMURS, MOLES, AND EATS. 67. Order 13, Prosimii. The lemurs, which constitute this little order, are monkey-like animals, chiefly confined to the Island of Madagascar, and to other islands in the Indian Ocean. They are arbo- real, fruit- or insect-eating animals, with an opposable thumb on the fore foot, and sometimes on the hind foot as well, the second toe of which always bears a long claw, while all the others usually have flat-nails like those on the human fingers. In some respects the animals resemble the sloths of the New World, and many of them are nocturnal. Their teeth are always of the four kinds, and are more numerous than those of man. They are clad in an exceedingly soft and thick fur, and many of them have bushy tails, while others, like the Loris, or slow lemurs, are per- fectly tailless. The largest forms measure about three feet in length, but some are much smaller, being only a few inches long. Many zoologists regard them, on account of their opposable thumbs, as closely allied to the monkeys ; but in their simple brains and in the structure of some of their internal organs, they represent a much lower grade of organisation than that of the monkeys. The aye-aye of Madagascar, a strange little animal, about the size of a rabbit, has nails only on its thumbs, and claws on the other fingers. One singular genus from the Philippine and Vertebrata. FIG. 56. Malay Islands, Tarsius, has the tarsus or ankle-bones of the foot exceedingly long, like the corresponding bones in the frog, so that it appears to have two ankle joints. 68. Order 14, Insectivora. This order of -mam- mils consists of the shrews, moles, and hedgehogs, which, as their name implies, feed on insects and worms, and other small animals. They are all of small size, and possess strong claws, long tapering snouts, and numerous sharply pointed teeth, the canines being small or absent. They all possess complete collar bones, a character which distinguishes them from Carnivores, and gives to the fore- limbs a fixity and defi- niteness of action that would be otherwise wanting. Their brains are usually small and smooth, not unlike those of rodents. In habit they are planti- grade, terrestrial, and usually active. The moles are familiar in- stances, and present in the highest degree the character of a fossorial or digging animal ; the paddle- like hand the square arm-bone or humerus (fig. 56, 53), and the enormous muscularity of the fore-limb enable it to dig with wonderful celerity in pursuit of the worms and insects on which it feeds, while the Bones of fore-limb of mole. 52, scapula ; 53, humerus ; 54, 55, fore-arm bones. Moles and Bats. 115 velvety skin, and the rudimental eyes and outer ears, give it the greatest degree of fitness for its subter- ranean life. Moles are common in America and Great Britain, but are absent from Ireland. The shrew-mouse and the hedgehog are equally common types ; the former can be easily distinguished from the true mice by the structure of the teeth. The pigmy shrew of S.E. Europe is the smallest known mammal, being only about two inches long. The flying lemurs of the East Indian archipelago, which form the last family of this order, have a wide parachute-like mem- brane stretching from the fore-limbs to the hind, and thence to the tail. They form a connecting link be- tween this order and the next. 69. Order 15, Cheiroptera (Bats). This curious group of mammals includes the only forms in the entire class which have any true powers of flight, the so-called flying phalangers, flying squirrels, and flying lemurs having only the power of taking long leaps, In the bats the fore limbs are very long, the fingers are enormously lengthened, and are united togethei by an extensive and thin membrane, which stretches from finger-tip to finger-tip, and from thence to the hind limb; the thumb alone is free, and it is always armed with a claw. The outline of this membrane is shown by the dotted line in fig. 57. They are mostly nocturnal, with smooth brains and feeble powers of sight, and are rarely of large size. To move the wings they are provided with powerful pectoral, or breast muscles, and there is often an im- perfect keel on the sternum, for muscular attachment They have also long and strong clavicles. Their hind I 2 Vertebrata. limbs are turned outwards in a peculiar manner, so that the knees bend backwards, and the great toes are Bats. 117 thus twisted to the outer side of the foot, which has five equal claw-bearing toes. Many bats have enor- mous ears, others, like the vampires of South America, have sensitive leaf-like organs on their noses, made up of complicated folds of skin overlying processes of gristle. The body is covered with soft hairs whose surface presents a peculiar and characteristic scaly appearance under the microscope, and the fronts of the wings are extremely sensitive. They rest by hooking on to branches or ledges by the Curved claws of their hind toes, and many of them thus feed with their heads downwards. They are extremely awkward in progression on the ground, and rarely resort to this method of locomotion. Most of the bats of temperate climates hybernate, and these are almost all insecti- vorous, having sharp-pointed teeth like those of the Insectivora. In warmer regions of the New World there are numerous large species, such as the vam- pires, which are suctorial in habit, sucking the blood of large animals, for which purpose they have sharp lancet-like teeth, and a long suctorial stomach. In the tropics of the Old World there are the largest individuals of the order, the fruit bats or Pteropi, which inhabit the Asiatic and insular shores of the Indian Ocean. They have blunt teeth, moderate ears, and, in one species, the distance from tip to tip of the wings is often as much as five feet. They are sometimes called flying foxes, from their prevailing colour and the shape of their heads. Ii8 Vertebrata. CHAPTER XIX. MONKEYS. MAN. 70. Order 16, Primates. This, the last and highest order of mammals, includes the most highly organised members of the entire animal kingdom the monkeys, apes, and mankind. They all possess opposable thumbs on some of the extremities, and (except among the marmosets) flat nails in place of claws. The face is mostly naked though fringed with hairs. The teeth are of three kinds and thirty-two in number, the formula being usually 2 - 2 I - 1 2 - 2 3 - 3 They have the highest proportional development of brain of all animals, and the fore-limbs are chiefly set apart to wait on the head. There are four sub-orders included: 1. The marmosets of South America, gregarious small monkeys of a squirrel-like habit, which have sharply tubercled teeth, claw-like nails on all the digits, except the great toe, which alone bears a flat nail. The long fur-clad tail is incapable of grasping, and the thumb is scarcely opposable. 2. The American monkeys, which differ from all others in having an additional premolar tooth on each side of each jaw (P ^ *). They have for the o 3 most part prehensile tails, and the thumb of the Monkeys. 119 hand is not well developed, or is absent as in the spider monkeys : on all their fingers they have thick convex nails. Most of these live in the woods of Brazil, and are found in troops. The howling monkeys have a drum-like enlargement of the tongue bone at the top of the larynx or organ of voice, and with it they can produce a loud booming sound, audible for nearly a mile. In all the American monkeys the nostrils are separated by a very broad partition, their ear-drums or tympanic bones in the skull have also wide oval mouths. 3. The Old World monkeys and apes are charac- terised by having a narrow nasal septum, and the ear- drums have a long tubular mouth. The dentition is similar to that of man, the premolars being - - 2 . They have almost always an opposable thumb on the hand as well as on the foot, though it is rarely as perfect, and the muscle which bends it is never sepa- rate from the common flexor muscle of the other fingers. The baboon family may be known by pos- sessing cheek pouches, and callous patches whereon they sit, as well as by their elongated jaws. The true baboons have dog-like muzzles and very short tails ; they are confined to Africa and Arabia, and some of them have curiously coloured faces; thus the mandrill, with its blue, deeply-grooved cheeks, its brilliant scarlet lips and nostrils, and its white beard, is a most striking-looking creature. Some, like the Bar- bar} 7 ape, the only species which now lives in Europe, have no visible tails ; others, like the cercopitheci or green monkeys, have long tails, but these organs are 120 Vertebrata. FIG. 58. Skeleton of siamang. never prehensile. Many, like the macaques of East- ern Asia, have long and promi- nent canine teeth, but these are wea- pons of offence, not indicative of a carnivorous diet. The sacred mon- key of India (Sem- nopithecus), and the thumb-less Colobus of Africa, have no cheek- pouches, but pos- sess long tails and callosities, while the highest group of the sub-order, the so-called an- thropoids, have no tails, callosi- ties, nor cheek pouches. The chimpanzee is a black-haired ape, a native of Guinea, which sometimes reaches a height of five feet. The Man. 121 orang-utan, a larger brown-haired species, with longer arms and a larger, rounder head, is found in Borneo and Sumatra. The gorilla, the largest of the anthro- poids, is a native of Senegambia, and is nearly as tall as, but much stouter than, a man. The gibbons of Southern Asia differ from the anthropoids in having callosities, and resemble the orangs in the enormous length of their arms (fig. 58). 4. Man is the last and highest type included in the order, and though in an anatomical point of view there are not a sufficiently numerous series of differ- ences of kind to lead us to form of him a separate order, yet there are enormous differences of degree, even of such kinds as are cognisable by the zoologist, who, from the difficulties incident thereto, cannot easily take psychological considerations into account in constructing a classification. Man has a rudimentary (though an almost com- plete) hair clothing, and a perfectly opposable thumb on the hand, moved by independent muscles, while the great toe is only capable of grasping by approxi- mation, not by opposition, and even this power, though great in some savage tribes, is almost des- troyed, in civilised races, by the habit of wearing shoes. The arms in man are shorter, and the hind limbs longer and stronger than in any of the apes. Progression is bipedal, and the feet are plantigrade, while the arms are specially and solely set apart for waiting upon the head. The muscles which keep the body erect, such as those of the back, the ex- tensors of the hip-joint, and the muscles of the calf are enormously greater than are the corresponding 122 Vertebrata. FIG. 59. parts of monkeys, while the spinal column exhibits a series of curves so constructed that the centre of gravity falls between the feet. The brain of man is larger in relative size and complexity than t'nat of any other animal, being on an average fifty ounces in weight, while that of the orang-utan weighs only about sixteen ounces. Man is also capable of articulate speech, and, psychologically, man is susceptible of education, which, in kind as well as in degree, is utterly unknown among the lower animals. Man also is capable of fitting himself for residence in any climate, and having been thus long scattered over the face of the earth, the single human species pre- sents to us numerous varieties, none of which, however, ex- hibit any approach to true specific distinct- ness. These varieties may be classed as follows : i. Woolly-haired races, such as the Negroes, Andamanese, and the Negritos of the Malay Archipelago. 2. Straight-haired races, which may be, a. Australioid or dark-skinned, small-headed races, such as the aborigines of Australia, the abo- riginal or hill tribes of India and Ceylon, possibly the ancient Egyptians, and the aboriginal races of the stone age. Skull of negro. Man. 123 b. Turanian races, yellow or red-skinned, mostly broad-headed races, like the Mongols, Chinese, the American Indians, &c. c. Iranian or Indo-Germanic races, pale or olive races, usually bearded, and usually with longer heads and straighter features. INDEX AND GLOSSARY. ABO A BOMASUS, the fourth stomach * in ruminants, 96 Acanthopteri, spiny-finned fishes, 30 Accessory eyes in Scopeline fishes, 29 Acrania, headless vertebrates, 5 sEpyornis, a gigantic extinct bird ol Madagascar, 62 African mud-fishes, 14-33 Aftershaft, 53 Air in bones of birds, 57 Albatross, 72 Allantois, a membrane surrounding the young of reptiles, birds, and mammals before birth. Alligators, 52 Alula, the bastard wing, or feathers borne on the thumb in birds, 54 Alveoli, the sockets of the teeth in vertebrate animals, A ntblyopsis, or blind-fish, 29 American monkeys, 118 Amphibia, 34 blood of, 36 Amphicoelous vertebras, bones of the vertebral column which are hollow on both surfaces, 15 Amphioxus lanceolatus, 4 A mphiuma, one of the amphibia, 39 Anacanthini, soft-finned fishes witn no swimming bladder, 29 Anal fin, 14 Anatomy of amphioxus, 4 Angiiisfragilis, 43 Animals, vertebrate, characters of, i Anteaters, 80-85 Antelopes 100 Anthropoid apes, 120 BAB Anura, tailless amphibians, such as frogs, 39 Aorta, the large bloodvessel which conveys the pure blood from the heart, 21 Aortic arches, 9 ; in reptiles, 40 ; in birds, 60 ; in mammalia, 78 Aplacentalia, such mammals as have no placentae. Apteryx, wingless bird of New Zealand, 63 Arch, neural, 3 Arch, hyoid, 8 Arches, aortic, 9 branchial or gill, 18 visceral, 7 Armadillos, 86 scales of, 74 Arterial cone in fishes, 2 Arteries, branchial, 21 Articulation, a joint between two bones. Artiodactyla, even-toed hoofed ani- mals, 93 Asymmetry of flat-fishes, 31 Atlas, the first bone of the vertebral column, which supports the head. Atrium in amphioxus, 4 Auricle of heart, 9 Australioid races of man, 122 Aves, birds. 52 Axolotl, a Mexican amphibian, 40 Aye Aye, 113 DABOONS, 119 LJ Babyroussa, a kind of pig from the Malay Islands, 94 126 Index and Glossary. BAD Badger, 104 Barbary ape, 119 Barbel, a river fish, 28 Basking shark, 25 Bats, 115 Bears, 104 Beavers, 108 Bee-eaters, 64 Birds, 52 Bitterns, 71 Blackbird, 66 Blackcap, 67 Blennies, 31 Blind amphibians, 37 fishes, 29 rats, 109 worms, 43 Blood of amphibians, 36 of fishes, 21 -- vertebrates, 9 corpuscles of fishes, 22 -- of birds, 61 vessels of birds, 60 -- of fish-gills, 20 Blowing and blowholes of whales, 99 Boa, 8, 46 Body of vertebrate animal, 2 Bones, formation of, 17 Bony pike of California (Lepidos- teus), 27 Bony skull, 7, 17 Bottlenose whales, 101 Box fishes, 32 Bradypoda, the sloth family, 88 Brain of cod, 19 -- craniota, 19 -- fishes, 19 Branchial, pertaining to the gills. arteries of fishes, 21 Breathing, 10-35 Bullfinch, 67 Bullhead, 31 Bunodonts, hoofed animals with tu- berculated teeth, 93 Bustard, 71 Buzzard, 69 pADUCOUS gills, gills which ^ fall off before the animals reach maturity. Caecum, the first part of the large intestine. Caecilians, worm-like amphibians, 37 COB Calamoickthys, African reed fish, 27 Callopkis, snake, poison gland of, 48 Camels, 96 Canine teeth, the eye-tooth, the foremost tooth in the maxillary bone, when it is single-fanged, and the corresponding tooth in the lower jaw. Carapace, the upper shield of a tor- toise, 49 Carnivont, flesh-eating mammals, 102 Carp, 28 Cannate birds, those with a keel on the breast-bone, 63 Carotid arteries, neck bloodvessels, 78 Carpus, the bones of the wrist-joint. Cartilage bones, such as begin their existence as masses of gristle, 17 Cassowary, 62 Catarrhine monkeys, old world mon- keys with a narrow partition be- tween the nostrils, 119 Cats, 103 Cave amphibians, 38 Cave bir, 106 Cavities in the vertebrate body, 2 Cebus, South American monkeys. 118 Cephalic, pertaining to the head. Cephalisation, subordination in func- tion of limbs to the head, n Ceratodus, Australian fish, 34 Cercopithecus, green monkeys, no Cere, soft skin at the base of the horny beak in birds, 68 Cerebrum, the greater or anterior lobes of the brain, 20 Cetacea, whales, 99 Chameleons, 44 Cheetah, hunting leopard of India, 104 Cheiroptera, 115 Chelonia, tortoises and turtles, 49 Chewing the cud, 95 Chimpanzee, 120 Chinchilla, 109 Ciconiee, storks, 74 Circulation in fishes, 20 Civets, 104 Clavicle, the collar-bone. Claws of cats, 10? Cloaca, the cavity into which the intestine and excretory organs open, 79 Cobra, hooded snake, asp, 48 Index and Glossary. 127 coc Coccygomorpha, the cuckoo order of birds, 64 Coccyx, the rudimental tail in the higher mammals. Cockatoos, 64 Cod, 17, 18, 29 Collocalia, the swallow which se- cretes the 'edible bird's nest,' 65 Colobus, 120 Colossochelys, a giant extinct tor- toise, 51 Colubrine snakes (non-poisonous), 46 Concentration of segments charac- teristic of vertebrates, 10 Condyles, knobs of bone by which one bone forms a joint with an- other, 38 Contour feathers, the strong quill- feathers on the surface of a bird, 53 Coots, 71 Coracoid bone, one of the bones of the fore part of the shoulder- girdle, 56, 79 Coral snake, 48 Cormorants, 73 Corncrake, 71 Corpuscles, microscopical bodies found floating in blood. of blood in amphib.a, 36 birds, 61 fishes, 22 CorvicUe, the crow family, 67 Cows, 97 Coypu, 109 Cranes, 71 Craniota, skull-bearing vertebrates, Cranium, the skull of a vertebrate animal, 7 Crocodilia, 51 Crows, 67 Ctenoid scales, fish-scales with a comb-like hinder edge, 14 Cuckoos, 64 Curruca, black-caps, 67 Cuticle, the outer layer of the skin. Cycloid scales, thin bony fish-scales with a smooth rounded margin, 13 DAB, flat-fish, 30 Dasypeltis, snake, teeth in the gullet of, 48 Dasyurus, Tasmanian devil, 81 EEL Dasypus, armadillo, 87 Deer, 98 Dental formulas, 77 formula of cat, 103 dog, 103 horse, 91 kangaroo, 84 man, 78 marsupials, 84 pi g> 94 ruminants, 98 seal, 102 sloths, 89 _ Tasmanian devil, 77 Dentine, the ivory substance o' teeth, 13, 25 Dentition, the arrangement of teeth in an animal. Dennis, or true skin, of fishes, 12 reptiles, 40 Diaphragm, the muscular partition between the cavity of the ches' and that of the abdomen, 60, 78 Digestive system of birds, 58 frogs and tadpoles, 36 sharks, 25 Diphycercal tails, tails in fishes with an even marginal fringe of fin rays. Dipnoi, fishes whose swimming bladder acts as a breathing organ, Diprotodon, giant fossil kangaroo, 84 Dipus, the jerboas, or jumping rats, 109 Dodo, the extinct gigantic pigeon of Madagascar, 69 Dog, 103 Dog-fishes, 15, 26 Dolphin, 101 Domestic fowl, 70 Dormouse, 108 Dorsal fin, 14 Doves, 69 Dragon, 43 Ducks. 72 Dugong, 89 RAGLES, 68 *-' Ear passage, nature of, 8 Echidna, the spiny anteate o) Australia, 79 Edentata, toothless mammals, 85 Edible birds' nests, 65 Eels, 28 128 Index and Glossary. EGG Egg cases of sharks, 25 Egg pouches of pipe fishes, 32 Eggs of birds, 65 fishes, 22 Elasmobranchs, sharks so called from their laminar gills, 23 Electric organ of gymnotus, the electric eel, 28 malapterurus, 28 mormyrus, 28 torpedo, 26 Elephants, no Embryonic characters in vertebral column of sharks, 24 Embryos of flat fishes, 30 Emus, 62 Enamel, the hardest portion of a tooth, formed by the calcification of the outer layer or epidermis of the tooth papilla. Epidermis, or surface layer of the skin of fishes, 12 of reptiles, 40 Eqwus, the horse and ass genus, 91 Ermine, 104 Erythacus, robin redbreast, 67 Exoskeleton, bony deposits in the skin or surface tissues, 14 Extensor, a muscle which straightens a joint. External gills in sharks and am- phibians, 39 Extinct reptiles, 52 Eye of amphioxus, 5 Eyes of birds, 61 snakes, 46 T7ALCONS, 69 Fallow-deer, 98 Fauna, the collective name applied to the animals of a country or district. Feathers, 53 Feeding of whales, 100 Feet of birds, 59 Felidce, 103 Femur, the thigh-bone. Fieldfare, 66 Fierasfer (a parasitic fish), 30 Filefishes, 32 Finches, 67 Fin rays, the bony filaments and spines which are included in the fins of fishes. Fins of fishes, 14-19 Fish, epidermis of, 12 GIL Fish, gills of, 8 head of, 17, 18 lateral line of, 15 notochord in, 17 scales of, 12 shape of, 12 tail of, 12-15 Fistularia, or tobacco-pipe fish, 3 Flat fishes, 30 Flounders, 30 Flying fishes, 32 foxes, 117 lemurs, 115 squirrels, 107 Forelimbs, iiC Quagga, 91 D ABBIT, 108 AX - Rachis, the central axis of a feather, 53 Radius, the outer bone in the fore- arm, 40 Raptores, birds of prey, 68 Rasores, scraping birds, poultry, 70 Rat, 108 Ratidcz, running birds with no keel on the breast-bone, 62 Rat-mole, 109 Rattlesnake, 47 Raven, 67 Rays, 26 Razorbill, 73 Rectrices, the strong tail-feathers, Red deer, 98 Redstart, 67 Reed-fish of Africa, 27 Regulus, wrens, 67 Remora, sucking-fish, 31 Rennet, 96 Reptiles, 40 Respiration, 3, 22 Restoration of lost parts in reptiles, 42 Reticulum, 96 Rhea, 62 Rhinoceros, 92 Rhinodon, gigantic shark, a6 Rhytina, extinct sea-cow, 89 Ribs, 9 Roach, 28 Index and Glossary. 133 ROB Robin, 69 Rodentia, 106 Roebuck, 98 Rollers, 64 Rook, 67 Ruminant ia, animals which chew the cud, 94 Ruminating, 95 CABLE, 104 ^ Sacrum, the united vertebrae which enter into the pelvis, 75 Saith, fish, 29 Salamander, 38 Salicaria, warblers, 67 Salmon, 28 Sawfish, 26 Scales of amphibians, 39 fishes, 12, 25, 28, 29, 32 reptiles, 43 Scapulars, feathers on the shoulder, Sclerotic plates, 61 Scopelidae, accessory eyes of, 29 Scraping birds, 70 Screw propeller, principle of, 12 Sea-cows, 89 Sea-horses, 32 Seals, 101 Sebaceous glands, 74 Segments of skull, 7 body, 10 Segmental ducts, 10 Seltuhia, sharks, 24 Semnopitheci, 120 Sense organs in tadpoles, 36 6, 15 Shape of fishes, 12 Sharks, 7, 13, 17, 24, 25 external gills of, 39 Sheep, 98 Shrews, 115 Sieboldia, giant salamander, 39 Siren, mud-eel, 38 Sirenia, sea-cows, 89 Skate, 26 Skeleton of bird, 55 1 frog, 37 lepidosiren, 10 mammals, 75 sole, 15 tortoise, 50 Skin, action of, in respiration, 10 of amphibia, 34 Skull, 6 of amphibian, 36 TEA Skull of bird, 55 elephant, no fishes, 17, 18 mammal^ 75 reptile, 41 Skunk, 104 Slits, visceral, 3-6 Sloth, 75, 88 Smell, 20 Snake-like lizards, 43 Snakes, 44 Snipe, 72 Sole, 15-29 Song thrush, 66 Spalax, the blind rat-mole of S. Europe, 109 Sparrow, 67 Species of fish, number of, 22 Spermaceti, 101 Sperm whales, 101 Spider monkeys, 119 Spiral valve in shark's intestine, 25 Spoonbills, 72 Squirrels, 108 Stag, 98 Starling, 67 , Steganopodes, pelicans and cormo- rants, whose fourth toe is included in the web, 72 Stickleback, 31 Stomach of camel, 96 ruminant, 95 sheep, 95 whales, ico Storks, 71 Strigops, the New Zealand ground parrot, 64 Sturgeons, 17, 27 Sucking fishes, 31 Sunbirds, 68 Sunfish, 32 Swans, 72 Swifts, 65 Swimming bladder in fishes, 22, 29 Swordfish, 33 Syhna, wood warblers, 67 Syrinx, the organ of voice in birds, 61 TADPOLE, 36-38 A Tails, 9, 15, 19, 78, lox Tapirs, 91 Tarsius, 114 Tasmanian devil, 77, 8z wolf, Si Teal, 74 134 Index and Glossary. TEE Teeth, 10-14 of elephant, in lamprey, 23 mammals, 76 rodents, 107 snakes, 46 Teguexins, 47 Teleostei, bony fishes, 27 Tench, 28 Terns, 72 Thorax, the cavity of the chest, 8 Thrushes, 67 Thymus gland, 1 10 Tiger, 103 Titmouse, 67 Toads, 39 Toes, 57, 82, 91 Tongue, 8, 44 , 45, 58, 79 lorpedo, 27 Tortoises, 49 Toucans, 64 Trabeculce, processes of gristle at ^ the base of the embryo skull, 7 Trachinus, weaver fishes, 31 Tree frogs, 40 Tropic birds, 73 Tropj'donow, the ringed snake, 46 Trout, 28 Trumpet fish, 31 Trunk of elephant, in Tunicated worms, relation of to ver- tebrates, 2 Turanian races of mankind, 123 Turkey, 70 Turtles, 49 TTLNA, the inner bone of the ^ J forearm, 40 Ulotrichi, woolly haired races of man, 122 Umbilicus of feather, 53 Ungulates, hoof-bearing mammals, Urodela, tailed amphibians, 38 \7AMPJRES, 117 v Vanes of feathers, 53 Veins of the liver, 3 Vena portse, the vein that carries th<; blood from the intestines to the liver, 3 ZEB Venomous snakes, 47 Ventral fins, 19 Ventricles of heart, 9 Vertebra, one of the detached cle- ments of the backbone, 3 Vertebral column, 24, 29, 36, 41, 45 Vertebrata, characters of, i Vipers, 47 Visceral arches and slits, 3, 10 Viscera, organs of the body. Vison, 104 Viverridte, 104 Voice in birds, 60. 61 Voles, 108 Vultures, 68 WAGTAILS, 67 Walrus, io2 Warbler, 67 Waste of living bodies, 10 Water hens, 71 Water snakes, 48 Wattles, 70 Waxwings, 68 Weasels, 104 Weevers, 31 Whalebone, 100 Whales, 99 limbs of, loo teeth of, 76 Wheatears, 67 Whinchat, 67 Whiting, 29 Widgeon, 72 Wild cat, 104 Wild swan, windpipe of, 72 Wings of bats, 117 Wolf! 103 Wombat, 84 Woodpecker, 64 Woodquest, 76 Wrasse, 32 Wren, 69 YAPOCK. fe EBRA. 91 , A A , Ml -^ ^Z ^--^- . 14 DAY USE RETURN TO DESK FROM WHICH BORR OWED This book is due on the last date stamped below, or on the date to which renewed. 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