The Project Gutenberg EBook of The Cambridge Natural History, Vol X., Mammalia, by Frank Evers Beddard This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org Title: The Cambridge Natural History, Vol X., Mammalia Author: Frank Evers Beddard Release Date: June 1, 2012 [EBook #39887] Language: English Character set encoding: ISO-8859-1 *** START OF THIS PROJECT GUTENBERG EBOOK CAMBRIDGE NATURAL HISTORY *** Produced by Chris Curnow, Joseph Cooper, Keith Edkins and the Online Distributed Proofreading Team at http://www.pgdp.net Transcriber's note: A few typographical errors have been corrected. They appear in the text like this, and the explanation will appear when the mouse pointer is moved over the marked passage. THE CAMBRIDGE NATURAL HISTORY EDITED BY S. F. HARMER AND A. E. SHIPLEY VOLUME X M A M M A L I A by F. BEDDARD Reprint Edition 1958 CODICOTE, ENGLAND WHELDON & WESLEY, LTD. WEINHEIM, GERMANY H. R. ENGELMANN (J. CRAMER) NEW YORK HAFNER PUBLISHING CO. © 1902, by Macmillan & Co., Limited Authorized reprint by Wheldon & Wesley, Ltd. and H. R. Engelmann (J. Cramer) Printed in Germany {iii} PREFACE Inasmuch as Sir W. H. Flower and Mr. Lydekker could not profess to treat the Mammalia exhaustively within the limits of nearly 800 pages, in their Introduction to the Study of Mammals, it is obvious that the present volume, which appears ten years later and is of rather less size, can contain but a selection of the enormous mass of facts at the disposal of the student of this group. Thus the chief question for myself was what to select and what to leave aside. It will be observed that I have reduced the pages of this book to conformity with those of other volumes of the series by treating some groups more briefly than others. It has appeared to me to be desirable to treat fully such groups as the Edentata and the Marsupialia, and permissible to be more brief in dealing with such huge Orders as those of the Rodentia and Chiroptera. Lengthy disquisitions upon such familiar and comparatively uninteresting animals as the Lion and Leopard have been curtailed, and the space thus saved has been devoted to shorter and more numerous accounts of other creatures. As there are nearly six hundred genera of living Mammals known to science, omission as well as compression became an absolute necessity. I have given, I hope, adequate treatment from the standpoint of a necessarily limited treatise to the majority of the more important genera of Mammals both living and extinct; but the length of this part of the book had to be increased by the discoveries, which give me at once an advantage and a disadvantage as compared with the two authors whose names I have quoted, of a considerable number of important new types in the last ten years. Such forms as Notoryctes, Romerolagus, Caenolestes, "Neomylodon," and Ocapia could not possibly have been omitted. In preparing my accounts of both living and extinct forms I have nearly invariably consulted the original authorities, and have often supplemented or verified these accounts by my own dissections at the Zoological Society's Gardens. My rule has not, however, been invariable in this matter, inasmuch as there exist two recent and trustworthy text-books of Mammalian Palaeontology—Professor Zittel's Handbuch der Palaeontologie, and Dr. A. Smith Woodward's manual, Outlines of Vertebrate Palaeontology, in the Cambridge Biological Series. Where the name of a genus only or its range, or merely one or two facts about it, are mentioned, I have not thought it necessary to go further than these two works. But a good deal has been done even since the appearance of these two volumes which it will be found that I have not ignored. I have to thank my editors for the trouble which they have taken in the revision of the proofs and for many suggestions. To Professor Osborn, of Columbia University, New York, I am indebted for some kind suggestions. My daughter Iris has assisted me in various ways. Finally, I desire to express my indebtedness to Mr. Dixon and to Mr. M. P. Parker for the care which they have taken in the preparation of the figures which were drawn by them especially for this work. Frank E. Beddard. London, February 28, 1902. CONTENTS Page Preface iii Scheme of the Classification adopted in this Book ix CHAPTER I Introductory 1 CHAPTER II Structure and Present Distribution of the Mammalia 5 CHAPTER III The Possible Forerunners of the Mammalia 90 CHAPTER IV The Dawn of Mammalian Life 96 CHAPTER V The Existing Orders of Mammals: Prototheria—Monotremata 105 CHAPTER VI Introduction to the Sub-Class Eutheria 116 CHAPTER VII Eutheria—Marsupialia 122 CHAPTER VIII Edentata—Ganodonta 161 CHAPTER IX {iv} {v} {vi} Ungulata—Condylarthra—Amblypoda—Ancylopoda—Typotheria— Toxodontia—Proboscidea—Hyracoidea 195 CHAPTER X Ungulata (continued)—Perissodactyla (Odd-toed Ungulates)—Litopterna 235 CHAPTER XI Ungulata (continued)—Artiodactyla (Even-toed Ungulates)—Sirenia 269 CHAPTER XII Cetacea—Whales and Dolphins 339 CHAPTER XIII Carnivora—Fissipedia 386 CHAPTER XIV Carnivora (continued)—Pinnipedia (Seals and Walruses)—Creodonta 446 CHAPTER XV Rodentia—Tillodontia 458 CHAPTER XVI Insectivora—Chiroptera 508 CHAPTER XVII Primates 533 Index 591 Scheme of the Classification Adopted In This Book Sub-Class Prototheria (p. 105). Order. Sub-order. Family. Sub-family. MONOTREMATA (p. 106) Echidnidae (p. 110). Ornithorhynchidae (p. 112). ?ALLOTHERIA (p. 96). Sub-class Eutheria (p. 116) MARSUPIALIA (p. 122) Diprotodontia (p. 128) Macropodidae (p. 129) Macropodinae (p. 132). Potoroinae (p. 137). Hypsiprymnodontinae (p. 138). Phalangeridae (p. 138) Phalangerinae (p. 140). Phascolarctinae (p. 142). Phascolomyinae (p. 144). Tarsipedinae (p. 145). Epanorthidae (p. 145). Polyprotodontia (p. 149) Dasyuridae (p. 149). Didelphyidae (p. 155). Peramelidae (p. 156). Notoryctidae (p. 158). {vii} EDENTATA (p. 161) Xenarthra (p. 166) Myrmecophagidae (p. 166). Bradypodidae (p. 170). Dasypodidae (p. 173). Mylodontidae (p. 179). Megalonychidae (p. 183). Megatheriidae (p. 183). Glyptodontidae (p. 184). Nomarthra (p. 186) Orycteropodidae (p. 187). Manidae (p. 188). GANODONTA (p. 190) Stylinodontidae (p. 191). Conoryctidae (p. 193). UNGULATA (p. 195) Condylarthra (p. 202). Amblypoda (p. 205). Ancylopoda (p. 211). Typotheria (p. 212). Toxodontia (p. 214). Proboscidea (p. 216) Elephantidae (p. 217). Dinotheriidae (p. 231). Hyracoidea (p. 232). Perissodactyla (p. 235) Equidae (p. 237). Lophiodontidae (p. 247). Palaeotheriidae (p. 247). Tapiridae (p. 260). Rhinocerotidae (p. 253). Titanotheriidae (p. 264). Litopterna (p. 267) Macraucheniidae (p. 267). Artiodactyla (p. 269) Hippopotamidae (p. 273). Suidae (p. 275). Dicotylidae (p. 278). Tragulidae (p. 282). Proceratidae (p. 284). Camelidae (p. 285). Cervidae (p. 291) Cervinae (p. 293). Moschinae (p. 299). {viii} Giraffidae (p. 301). Antilocapridae (p. 306). Bovidae (p. 307). Anthracotheriidae (p. 328). Caenotheriidae (p. 329). Xiphodontidae (p. 329). Oreodontidae (p. 330). Anoplotheriidae (p. 332). SIRENIA (p. 333). CETACEA (p. 339) Mystacoceti (p. 353) Balaenopteridae (p. 355). Balaenidae (p. 358). Odontoceti (p. 362) Physeteridae (p. 362) Physeterinae (p. 363). Ziphiinae (p. 367). Delphinidae (p. 372). Platanistidae (p. 380). Squalodontidae (p. 384). Archaeoceti (p. 384) Zeuglodontidae (p. 384). CARNIVORA (p. 386) Fissipedia (p. 387) Felidae (p. 390). Machaerodontidae (p. 401). Viverridae (p. 403) Euplerinae (p. 403). Galidictiinae (p. 404). Cryptoproctinae (p. 404). Viverrinae (p. 405). Herpestinae (p. 409). Hyaenidae (p. 411). Canidae (p. 413). Procyonidae (p. 426). Mustelidae (p. 431) Melinae (p. 432). Mustelinae (p. 433). Lutrinae (p. 439). Ursidae (p. 442). Pinnipedia (p. 446) Otariidae (p. 450). Trichechidae (p. 451). Phocidae (p. 452). CREODONTA (p. 455). Anomaluridae (p. 462). Soiuridae (p. 463). Castoridae (p. 467). Haplodontidae (p. 469). Gliridae (p. 470). {ix} RODENTIA (p. 458) Simplicidentata (p. 462) Muridae (p. 471) Murinae (p. 471). Phlaeomyinae (p. 473). Hydromyinae (p. 474). Rhynchomyinae (p. 474). Gerbillinae (p. 475). Otomyinae (p. 475). Dendromyinae (p. 476). Lophiomyinae (p. 476). Microtinae (p. 477). Sigmodontinae (p. 479). Neotominae (p. 480). Bathyergidae (p. 480). Spalacidae (p. 482). Geomyidae (p. 483). Heteromyidae (p. 484). Dipodidae (p. 484). Pedetidae (p. 486). Octodontidae (p. 487) Octodontinae (p. 487). Loncherinae (p. 488). Capromyinae (p. 489). Ctenodactylidae (p. 490). Caviidae (p. 491). Dasyproctidae (p. 493). Dinomyidae (p. 495). Chinchillidae (p. 496). Cercolabidae (p. 497). Hystricidae (p. 499). Duplicidentata (p. 502) Leporidae (p. 502). Lagomyidae (p. 505). TILLODONTIA (p. 506). INSECTIVORA (p. 508) Insectivora Vera (p. 509) Erinaceidae (p. 509). Tupaiidae (p. 511). Centetidae (p. 511). Potamogalidae (p. 513). Solenodontidae (p. 513). Chrysochloridae (p. 514). Macroscelidae (p. 515). Talpidae (p. 516). Soricidae (p. 518). Dermoptera (p. 520) Galeopithecidae (p. 520). CHIROPTERA (p. 521) Megachiroptera (p. 524) Pteropodidae (p. 524). Microchiroptera (p. 526) Rhinolophidae (p. 527). Nycteridae (p. 527). Vespertilionidae (p. 528). Emballonuridae (p. 530). Phyllostomatidae (p. 531). {x} PRIMATES (p. 533) Lemuroidea (p. 534) Lemuridae (p. 538) Indrisinae (p. 538). Lemurinae (p. 540). Galagininae (p. 542). Lorisinae (p. 545). Chiromyidae (p. 548). Tarsiidae (p. 550). Anaptomorphidae (p. 552). Chriacidae (p. 552). Megaladapididae (p. 554). Anthropoidea (p. 554) Hapalidae (p. 556). Cebidae (p. 557). Cercopithecidae (p. 562). Simiidae (p. 570). Hominidae (p. 585). CHAPTER I INTRODUCTORY The Mammalia form a group of vertebrated animals which roughly correspond with what are termed in popular language "quadrupeds," or with the still more vernacular terms of "beasts" or "animals." The name "Mammal" is derived from the most salient characteristic of the group, i.e. the possession of teats; but if the term were used in an absolutely strict etymological sense, it could not include the Monotremes, which, though they have mammary glands, have not fully-differentiated teats (see p. 16). There are, however, as will be seen shortly, other characters which necessitate the inclusion of these egg-laying quadrupeds within the class Mammalia. The Mammalia are unquestionably the highest of the Vertebrata. This statement, however, though generally acceptable, needs some explanation and justification. "Highest" implies perfection, or, at any rate, relative perfection. It might be said with perfect truth that a serpent is in its way an example of perfection of structure: not incommoded with limbs it can slip rapidly through the grass, swim like a fish, climb like a monkey, and dart upon its prey with rapidity and accuracy. It is an example of an extremely specialised reptile, the loss of the limbs being the most obvious way in which it is specialised from more generalised reptilian types. Specialisation in fact is often synonymous with degradation, and, this being the case, implies a restricted life. On the other hand, simplification is not always to be read as degeneration. The lower jaw, for instance, of mammals has fewer bones in it than that of reptiles, and is more concisely articulated to the skull; this implies greater efficiency as a biting organ. The term highest, however, includes increased complexity as well as simplification, the two series of modifications being interwoven to form a more efficient organism. It cannot be doubted that the increased complexity of the brain of mammals raises them in the scale, as does also the complex and delicately adjusted series of bonelets which form the organ for the transmission of sound to the internal ear. The separation of the cavity containing the lungs, and the investment of the partition so formed with muscular fibres, renders the action of the lungs more effective; and there are other instances among the Mammalia of greater complexity of the various parts and organs of the body when compared with lower forms, which help to justify the term "highest" generally applied to these creatures. Complexity and finish of structure are often accompanied by large size; and the Mammalia are, on the whole, larger than any other Vertebrates, and also contain the most colossal species. The huge Dinosaurs of the Mesozoic epoch, though among the largest of animals, are exceeded by the Whales; and the latter group includes the mightiest creature that exists or has ever existed, the eighty-five-feet-long Sibbald's Rorqual. Confining ourselves rigidly to facts, and avoiding all theorising on the possible relation between complexity and nicety of build and the capacity for increase in bulk, it is plain from the history of more than one group of mammals that increase in bulk accompanies specialisation of structure. The huge Dinocerata when compared with the ancestral Pantolambda teach us this, as do many similar examples. Within the mammalian group, as in the case of other Vertebrates, difference of size has a certain rough correspondence with difference of habitat. The Whales not only contain the largest of animals, but their average size is great; so too with the equally aquatic Sirenia and very aquatic Pinnipedia. Here the support offered by the water and the consequent decreased need for muscular power to neutralise the effects of gravity permit of an increase in bulk. Purely terrestrial animals come next; and finally arboreal, and, still more, "flying" mammals are of small size, since the maintenance of the position when moving and feeding needs enormous muscular effort. The Mammals are more easily to be separated from the Vertebrates lying lower in the series than any of the latter are from each other in ascending order. A large number of characters might be used in addition to those which will be made use of in the following brief catalogue of essential mammalian features, were it not for the low-placed Monotremata on the one hand and the highly specialised Whales on the other. Including those forms, the Mammalia are to be {1} {2} {3} distinguished from all other Vertebrates by the following series of structural features, which will be expanded later into a short disquisition upon the general structure of the Mammalia. The class Mammalia may, in fact, be thus defined:— Hair-clad Vertebrates, with cutaneous glands in the female, secreting milk for the nourishment of the young. Skull without prefrontal, postfrontal, quadrato-jugal, and some other bones, and with two occipital condyles formed entirely by the exoccipitals. Lower jaw composed of dentary bone only, articulating only with the squamosal. Ear bones a chain of three or four separate bonelets. Cervical vertebrae sharply distinguished from the dorsals, and if with free ribs, showing no transition between these and the thoracic ribs. Brain with four optic lobes. Lungs and heart separated from abdominal cavity by a muscular diaphragm. Heart with a single left aortic arch. Red blood-corpuscles non-nucleate. The following characters are also very nearly universal, and in any case absolutely distinctive:—Cervical vertebrae, seven; vertebrae with epiphyses. Ankle-joint "cruro-tarsal," i.e. between the leg and the ankle, and not in the middle of the ankle.[1] Attachment of the pelvis to the vertebral column pre-acetabular in position. The Mammalia since they are hot-blooded creatures are more independent of temperature than reptiles; they are thus found spread over a wider area of the earth's surface. As however, though hot-blooded, they have not the powers of locomotion possessed by birds, they are not quite so widely distributed as are those animals. The Mammalia range up into the extreme north, but, excepting only forms mainly aquatic, such as the Sea Lions, are not known to occur on the Antarctic continent. With the exception of the flying Bats, indigenous mammals are totally absent from New Zealand; and it seems to be doubtful whether those supposed oceanic islands which have a mammalian fauna are really oceanic in origin. The continents and oceans are peopled by rather over three thousand species of Mammalia, a number which is considerably less than that of either birds or reptiles. It seems clear that, so far at any rate as concerns the numbers of families and genera, the mammalian fauna of to-day is less varied than it was during the Mid-tertiary period, the heyday of mammalian life. It is rather remarkable to contrast in this way the mammals and the birds. The two classes of the animal kingdom seem to have come into being at about the same period; but the birds either have reached their culminating point to-day, or have not yet reached it. The Mammalia, on the other hand, multiplied to an extraordinary extent during the Eocene and the Miocene periods, and have since dwindled. The break is most marked at the close of the Pleistocene, and may be in part due to the direct influence of man. At present man exercises so enormous an effect, both directly and indirectly, that the future history of the Mammalia is probably foreshadowed by the instances of the White Rhinoceros and the Quagga. On the other hand, the economic usefulness of the Mammalia is greater than that of any other animals; and the next most important era in their history will be probably that of domesticity and "preservation." CHAPTER II STRUCTURE AND PRESENT DISTRIBUTION OF THE MAMMALIA External Form.—It would be quite impossible for any one to confuse any other quadrupedal animal with a mammal. The body of a reptile is, as it were, slung between its limbs, like the body of an eighteenth century chariot between its four wheels; in the mammal the body is raised entirely above, and is supported by, the four limbs. The axes of these limbs too, as a general rule, are parallel with the vertical axis of the body of their possessor. There is thus a greater perfection of the relations of the limbs to the trunk from the point of view of a terrestrial creature, which has to use those limbs for rapid movement. The same perfection in these relations is to be seen, it should be observed, in such running forms among the lower Vertebrata as the Birds and the Dinosaurs, where the actual angulation of the limbs is as in the purely running Mammalia. These relations are of course absolutely lost in the aquatic Cetacea, and not marked in various burrowing creatures. The way in which the fore- and hind-limbs are angulated is considerably different in the two cases. In the latter, which are most used and, as it were, push on the anterior part of the body, the femur has its lower end directed forwards, the tibia and the fibula project backwards at the lower end, while the ankle and foot are again inclined in the same direction as the femur. With the fore-limbs there is not this regular alternation. The humerus is directed backwards, the fore-arm forwards, and the hand still more forwards. This angulation seems to facilitate movement, inasmuch as it is seen in even the Amphibia and the lower Reptiles, in which, however, the differences between the fore- and hind-limbs are less marked, indicating therefore a less specialised condition of the limbs. It is an interesting fact that the angulation of the limbs is to some extent obliterated in very bulky creatures, and almost entirely so in the elephants (see p. 217), which seem to need strong and straight pillars for the due support of their huge bodies. The alertness and general intellectual superiority of mammals to all animals lying below them in the series (with the exception of the birds, which are in their way almost on a level with the Mammalia) are seen by their active and continuous movements. The lengthy periods of absolute motionlessness, so familiar to everybody in such a creature as the Crocodile, are unknown among the more typical Mammalia except indeed during sleep. This mental condition is clearly shown by the proportionate development of the external parts of all the organs of the higher senses. The Mammalia as a rule have well-developed, often extremely large, flaps of skin surrounding the entrance to the organ of hearing, often called "ears," but better termed "pinnae." These are provided with special muscles, and can be often moved and in many directions. The nose is always, or nearly always, very conspicuous by its naked character; by the large surface, often moist, which surrounds the nostrils; and again by the muscles, which enable this tract of the {4} {5} {6} integument to be moved at will. The eyes, perhaps, are less marked in their predominance over the eyes of lower Vertebrates than are the ears and nose; but they are provided as a rule with upper and lower eyelids, as well as by a nictitating membrane as in lower Vertebrates. The apparent predominance of the senses of smell and hearing over that of sight appears to be marked in the Mammalia, and may account for their diversity of voice as well as of odour, and for the general sameness of coloration which distinguishes this group from the brilliantly-coloured birds and reptiles. The head, too, which bears these organs of special sense, is more obviously marked out from the neck and body than is the case with the duller creatures occupying the lower branches of the Vertebrate stem. Fig. 1A. Fig. 1.—A, Section of human skin. Co, Dermis; D, sebaceous glands; F, fat in dermis; G, vessels in dermis; GP, vascular papillae; H, hair; N, nerves in dermis; NP, nervous papillae; Sc, horny layer of epidermis; SD, sweat gland; SD1, duct of sweat gland; SM, Malpighian layer. B, Longitudinal section through a hair (diagrammatic). Ap, Band of muscular fibres inserted into the hair- follicle; Co, corium (dermis); F, external longitudinal; F1, internal circular, fibrous layer of follicle; Ft, fatty tissue in the dermis; GH, hyaline membrane between the root-sheath and the follicle; HBD, sebaceous gland; HP, hair-papilla with vessels in its interior; M, medullary substance (pith) of the hair; O, cuticle of root-sheath; R, cortical layer; Sc, horny layer of epidermis; Sch, Hair shaft; SM, Malpighian layer of epidermis; WS, WS1, outer and inner layers of root-sheath. (From Wiedersheim's Comparative Anatomy.) Fig. 1B. THE HAIR.—The Mammalia are absolutely distinguished from all other Vertebrates (or, for the matter of that, Invertebrates) by the possession of hair. To define a mammal as a Vertebrate with hair would be an entirely exclusive definition; even in the smooth Whales a few hairs at least are present, which may be reduced to as few as two bristles on the lips. The term "hair," however, is apt to be somewhat loosely applied; it has been made use of to describe, for example, the slender processes of the chitinous skin of the Crustacea. It will be necessary, therefore, to enter into the microscopical structure and development of the mammalian hair. Hair is found in every mammal. The first appearance of a hair is a slight thickening of the stratum Malpighii of the epidermis, the cells taking part in this being elongated and converging slightly above and below. Dr. Maurer has called attention to the remarkable likeness between the embryonic hair when at this stage and the simple sense-organs of lower Vertebrates. Later there is formed below this a denser aggregation of the corium, which ultimately becomes the papilla of the hair. This is the apparent homologue of the first formed part of a feather, which projects as a papilla before the epidermis has undergone any modification. Hence there is from the very first a difference between feathers and hairs—a difference which must be carefully borne in mind, especially when we consider the strong superficial resemblance between hairs and the simple barbless feathers. Still later the knob of epidermic cells becomes depressed into a tubular structure, which is lined with cells also derived from the stratum Malpighii, but is filled with a continuation of the more superficial cells of the epidermis. This is the hair- follicle, and from the epidermic cells arises the hair by direct metamorphosis of those cells; there is no excretion of the hair by the cells, but the cells become the hair. From the hair-follicle also grows out a pair of sebaceous glands, which serve to keep the fully-formed hair moist. Fig. 2. Fig. 2.—Four diagrams of stages in the development of a hair. A, Earliest stage in one of those mammals in which the dermal papilla appears first; B, C, D, three stages in the development of the hair in the human embryo. blb, Hair-bulb; crn, horny layer of the epidermis; foll, hair-follicle; grm, hair-germ; h, hair, in D, projecting on the surface; muc, Malpighian layer of epidermis; pp, dermal papilla; seb, developing sebaceous glands; sh.1, sh.2, inner and outer root-sheaths. (After Hertwig.) Dr. Meijerle[2] has lately described in some detail the particular arrangement of the individual hairs among mammals; they are not by any manner of means scattered without order, but show a definite and regular arrangement, which varies with the animal. For instance, in an American Monkey (Midas), the hairs arise in threes—three hairs of equal size springing from the epidermis close together; in the Paca (Coelogenys) there are in each group three stout hairs alternating with three slender hairs. In some forms a number of hairs spring from a common point: in the Jerboa (Dipus) twelve or thirteen arise from a single hole; in Ursus arctos there is the same general plan, but there is one stout hair and four or five slender ones. There are numerous other complications and modifications, but the facts, although interesting, do not appear to throw any light upon the mutual affinities of the animals. Allied forms may have a very different arrangement, while in forms which have no near relationship the plan may be very similar, as is shown by the examples cited from Dr. Meijerle's paper. The groups of hairs, moreover, have themselves a definite placing, which the same {7} {8} {9} anatomist has compared with the disposition of the bundles of hairs behind and between the scales of the Armadillo, and which has led him to the view that the ancestors of mammals were scaly creatures—a view also supported by Professor Max Weber,[3]and not in itself unreasonable when we consider the numerous points of affinity between the primitive Mammalia and certain extinct forms of reptiles.[4] The hairs are greatly modified in form in different mammals and in different parts of their bodies. It is very commonly the case that a soft under-fur can be distinguished from the longer and coarser hairs, which to some extent hide the latter. Thus the "sealskin" of commerce is the under-fur of the Otaria ursina of the North. The coarser hairs may be further differentiated into bristles; these again into spines, such as those of the Hedgehog and of the Porcupine. Again, the flattening and agglutination of hairs seems to be responsible for the scales of the Manis and for the horns of the Rhinoceros. It is a matter of common knowledge that upon the head of various animals, e.g. the Domestic Cat, long and sensitive hairs are developed, which are connected with the terminations of nerves, and perform a sensory, probably tactile function. These occur on the snout, above the eyes, and in the neighbourhood of the ears. It is an interesting fact that a tuft of quite similar hairs occurs on the hand of many mammals close to the wrist, which, at least in the case of Bassaricyon, are connected with a strong branch from the arm-nerve. These tufts also occur in Lemurs, in the Cat, various Rodents and Marsupials, and are probably quite general in mammals who "feel" with their fore-limbs; —in which, in fact, the fore-limbs are not exclusively running organs. That the last remaining hairs of the Cetacea are found upon the muzzle, is perhaps significant of the importance of these sensory bristles. The entire absence of hairs is quite common in this order, although traces of them are sometimes found in the embryo. The Sirenia, too, are comparatively hairless, as are also many Ungulates. Whether the presence of blubber in the former case and the existence of a very thick skin in the latter animals are facts which have had anything to do with the disappearance of hair or not, is a matter for further inquiry. The intimate structure of the hair varies considerably. The variations concern the form of the hair, which may be round in transverse section, or so oval as to appear quite flat when the hair is examined in its entirety. The substance of the hair is made up of a central medulla or pith with a peripheral cortex; the latter is scaled, and the scales are often imbricated and with prominent edges. The amount of the two constituents also differs, and the cortex may be reduced to a series of bands surrounding only tracts of the enclosed pith. In the hair is contained the pigment to which the colour of mammals is chiefly due. Tracts of brightly-coloured skin may exist, as in the Apes of certain genera; but such structures are not general. The pigment of the hair seems to consist of those pigmentary substances known as melanins. It is remarkable to find such a uniform cause of coloration, when we consider the great variety of feather-pigments found in birds. The variations of colour of the hair of mammals are due to the unequal distribution of these brown pigments. There are very few mammals which can be called brightly coloured. The Bats of the genus Kerivoula have been compared to large butterflies, and some of the Flying Squirrels have strongly-marked contrasts of reddish brown, white, and yellow. The same may be said of the spines of certain Porcupines. But we find in the hair no bright blues, greens, and reds such as are common among birds. There are certain general facts about the coloration of mammals which require some notice here. Next to the usually sombre hues of these animals the general absence of secondary sexual coloration is noteworthy. In but a few cases among the Lemurs and Bats do we find any marked divergences in hues between males and females. Secondary sexual characters in mammals are, it is true, often exhibited by the great length of certain hair-tracts in the male, such as the mane of the Lion, the throat- and leg-tufts of the Barbary Sheep, and so forth; but apart from these, the secondary sexual characters of mammals are chiefly shown in size, e.g. the Gorilla, or in the presence of tusks, e.g. various Boars, or of horns, as in the Deer, etc. The coloration of mammals frequently exhibits conspicuous patterns of marking. These are in the form of longitudinal stripes, of cross-stripes, or of spots; the latter may be "solid" spots, or broken up, as in the Leopard and Jaguar, into groups of smaller spots arranged in a rosette-fashion. We never find in mammals the complicated "eyes" and other markings which occur in so many birds and in other lower Vertebrates. It is important to note that in the Mammalia whose sense of sight is quite keen there should be a practical absence of secondary sexual colours. As to the relationship of the various forms of marking that do occur, it seems clear that there has been a progression from a striped or spotted condition to uniform coloration. For we find that many Deer have spotted young; that the young Tapir of the New World is spotted, while its parents are uniform blackish brown; the strongly-marked spotting of the young Puma contrasts with the uniform brown of the adult; and the Lion cub, as every one knows, is also spotted, the adult lioness showing considerable traces of the spots. The seasonal change in the colours of certain mammals is a subject upon which much has been written. The extreme of this is seen in those creatures, such as the Polar Hare and the Arctic Fox, which become entirely blanched in the winter, recovering their darker coat in the spring. This is, however, only an extreme case of a change which is general. Most animals get a thicker fur in winter and exchange it for a lighter one in summer. And the hues of the coat change in correspondence. GLANDS OF THE SKIN.—The great variety of integumental glands possessed by the Mammalia distinguishes them from any group of lower Vertebrates. This variability, however, only concerns the anatomical structure of the glands in question. Histologically they are all of them apparently to be referred to one of two types, the sudoriparous or sweat gland and the sebaceous gland. Simple sweat and sebaceous glands are abundant in mammals, with but a few exceptions. The structures that we are now concerned with are agglomerations of these glands. The mammary glands will be treated of in connexion with the marsupium; they are either masses of sweat glands, or of sebaceous glands whose secretion has been converted into milk. {10} {11} {12} Many Carnivora possess glands opening to the exterior, near the anus, by a large orifice. These secrete various odoriferous substances, of which the well-known "civet" is an example. Other odoriferous glands are the musk glands of the Musk-deer and of the Beaver; the suborbital gland of many Antelopes; the dorsal gland of the Peccary, which has given the name of Dicotyles to the genus on account of its resemblance in form to a navel. This gland may be seen to secrete a clear watery fluid. The Elephant has a gland situated on the temple, which is said to secrete during certain periods only, and to be a warning to leave the animal alone. Very remarkable are the foot glands of certain species of Rhinoceros; they are not universally present in those animals, and are therefore useful as specific distinctions. On the back of the root of the tail in many Dogs are similar glands. The Gentle Lemur (Hapalemur) has a peculiar gland upon the arm, about the size of an almond, which in the male underlies a patch of spiny outgrowths. In Lemur varius is a hard patch of black skin which may be the remnants of such a gland. It is thought that the callosities on the legs of Horses and Asses are remnants of glands. One of the most complex of these structures which has been examined microscopically exists in the Marsupial Myrmecobius.[5] On the skin of the anterior part of the chest, just in front of the sternum, is a naked patch of skin which is seen to be perforated by numerous pores. Besides the ordinary sebaceous and sweat glands there are a series of masses of glands, opening by larger orifices, which present the appearance of groups of sebaceous glands, and are of a racemose character; but the existence of muscular fibres in their coats seems to show that they should be referred rather to the sudoriparous series. Beneath the integument is a large compound tubular gland quite half an inch in diameter. In Didelphys dimidiata there is a precisely similar glandular area and large underlying gland, the correspondence being remarkable in two Marsupials so distant in geographical position and affinities. Even among the Diprotodont genera there is something of the kind; for in Dorcopsis luctuosa and D. muelleri is a collection of four unusually large sebaceous follicles upon the throat, and in the Tree Kangaroo (Dendrolagus bennettii) there is the same collection of enlarged hair-follicles, though they are apparently somewhat reduced as compared with those of Dorcopsis. These are of course a few examples out of many. It seems to be possible that the functions of these various glands is at least twofold. In the first place, they may serve, where predominant in one sex, to attract the sexes together. In the second place, the glands may be useful to enable a strayed animal of a gregarious species to regain the herd. It is perfectly conceivable too that in other cases the glands may be a protection, as they most undoubtedly are in the Skunk, from attacks. In connexion with the first, and more especially the second, of the possible uses of these glands, it is interesting to note that in purely terrestrial creatures, such as the Rhinoceros, the glands are situated on the feet, and would therefore taint the grass and herbage as the animal passed, and thus leave a track for the benefit of its mate. The same may be said of the rudimentary glands of Horses if they are really glands. The secretion of the "crumen" of Antelopes is sometimes deposited deliberately by Oreotragus upon surrounding objects, a proceeding which would attain the same end. One may even perhaps detect "mimicry" in the similar odours of certain animals. Prey may be lured to their destruction, or enemies frightened away. The defenceless Musk-deer may escape its foes by the suggestion of the musky odour of a crocodile. It is at any rate perfectly conceivable that the variety of odours among mammals may play a very important part in their life, and it is perhaps worthy of note that birds with highly-variegated plumage are provided only with the uropygial gland, while mammals with usually dull and similar coloration have a great variety of skin glands. Scent is no doubt a sense of higher importance in mammals than in birds. The subject is one which will bear further study. NAILS AND CLAWS.—Except for the Cetacea (where rudiments have been found in the foetus), the extremities of the fingers and of the toes of mammals are covered by, or encased in, horny epidermic plates, known as nails, claws, and hoofs. The variety in the shape and development of these corneous sheaths to the digits is highly characteristic of mammals as opposed to lower Vertebrates. If we take extreme cases, such as the nail of the thumb in Man, the hoof of a Horse, and the claw of a Cat, it is easy to distinguish the three kinds of phalangeal horny coverings. But the differences become extinguished as we pass from these to related types. The nail of the little finger in Man approaches the claw-like form; and the hoofs of the Lama are almost claws in the sharpness of their extremities. On the whole it may be said that claws and hoofs embrace the bone which they cover, while nails lie only upon its dorsal surface. The form of the distal phalanx which bears the nail shows, however, two kinds of modification which do not support such a classification. When those phalanges are clad with hoofs or covered by a nail they end in a rounded and flattened termination. On the other hand, when they bear a claw they are themselves sharpened at the extremity and often grooved above. THE MARSUPIUM.—It may appear to be unnecessary at this juncture to speak of the marsupial pouch, which is so usually believed to be a characteristic of the group Marsupialia. Rudiments of this structure have, however, been recently discovered in the higher mammals, and, as Dr. Klaatsch[6] has remarked, all researches into the "history of the mammals culminate in the question whether the placental mammals pass through a marsupial stage or not." We cannot, therefore, look upon the marsupial pouch as a matter affecting only the Marsupials, though it is true that this organ is at present functional only in them and in the Monotremata. Fig. 3. Fig. 3.—Echidna hystrix. A, Lower surface of brooding female; B; dissection showing a dorsal view of the pouch and mammary glands; ††, the two tufts of hair in the lateral folds of the mammary pouch from which the secretion flows, b.m, Pouch; cl, cloaca; g.m, groups of mammary glands. (From Wiedersheim's Comparative {13} {14} {15} Anatomy, after W. Haacke.) In the Marsupials the pouch shelters the young, which are born in an exceedingly imperfect state, minute, nude, and blind, with a "larval" mouth fitted only to grasp in a permanent fashion the teat, upon which they are carefully fixed by the parent. But even later the pouch is made use of as a temporary harbour of refuge: from the pouch of female Kangaroos at the Zoological Gardens may frequently be observed to protrude the tail and hind-legs of a young Kangaroo as big as a Cat, and perfectly well able to take care of itself. In the Monotremata (in Echidna) there is a deep fold of the skin which lodges the unhatched egg, and into which the mammary glands open, one on either side. This structure is only periodically developed, and arises from two rudiments, one corresponding to each mammary area; but in the female with eggs or young there is but a single deep depression, which occupies the same region of the body as the marsupial pouch of the Marsupials.[7] It is usually held that this structure is not of precisely the same morphological value as the pouch of the Marsupial; and the difference is expressed by terming the one (that of Echidna) the mammary pouch, and the other the marsupium. At first sight it may appear to be an unnecessary refinement to separate two structures which have so many and such obvious likenesses. It is not quite certain, however, that the difference is not even more profound than later opinions seem to indicate. The Monotremata not only have no teats, as has already been pointed out, but the mammary glands themselves are of a perfectly different nature to those of the higher mammals, including the Marsupials. There is therefore no a priori objection to the view that the accessory parts developed in connexion with the mammary glands should also be different. The teat of the higher Mammalia grows up round the area upon which the ducts of the mammary glands open; it is a fold of skin which eventually assumes the cylindrical form of the adult teat, and which includes the ducts of the milk glands. It has been suggested that the two folds of skin which form the mammary pouch of Echidna are to be looked upon as the equivalent of the commencing teat of the higher mammal.[8] In this case it is clear that the marsupial folds of the Marsupial cannot correspond accurately with the apparently similar folds of Echidna, because there are teats as well. It is the teats which correspond to the marsupial folds of Echidna. This view is in apparent contradiction to an interesting discovery in a specimen of a Phalanger by Dr. Klaatsch.[9] This Marsupial, like most others, has a well- developed marsupial pouch, in which the young are lodged at birth; but round two of the teats is another distinct fold on either side, the outer wall of which forms the general wall of the pouch. Dr. Klaatsch thinks that these smaller and included pouches are the equivalents of the mammary pouches of Echidna. They contain teats, but this comparison does not do away with the validity of Gegenbaur's suggestion already referred to, because the teats are (see above) secondary. If this fact be fairly to be interpreted in the sense which Dr. Klaatsch attaches to it, we have an interesting case of the growth of a new organ out of and partly replacing an old organ. In the Monotremes there is a pouch which facilitates or performs both nutritive and protective functions; in the Phalanger these two functions are carried on in separate pouches; finally, in other Marsupials, there is a return to the undifferentiated state of affairs found in the Monotremata, but with the help of a new organ not found in them. Fig. 4. Fig. 4.—Diagram of the development of the nipple (in vertical section). A, Indifferent stage, glandular area flat; B, elevation of the glandular area with the nipple; C, elevation of the periphery of the glandular area into the false teat, a, Periphery of the glandular area; b, glandular area; gl, glands. (From Gegenbaur.) Though so characteristic of Marsupials, the marsupial pouch is not always developed in them. It is present in all the Kangaroos, Wallabies, and Wombats, in fact in the Diprotodonts. It is also present in a number of the carnivorous Polyprotodont Marsupials; but in Phascologale it is only present in rudiment, and in Myrmecobius it is entirely obsolete. In the American Opossums the state of the pouch is variable. "Generally absent, sometimes merely composed of two lateral folds of skin separate at each end, rarely complete," is Mr. Thomas' summary in his definition of the family Didelphyidae.[10] Another curious feature of the pouch in the Marsupials is the variability in the position of the mouth of the pouch: in all the Diprotodonts it looks forward; but in many Polyprotodonts it looks backward. This, however, has some connexion with the habitual attitude of the possessor: in the Kangaroo, leaping along on its hind-legs, it is requisite that the pouch should open forwards; but in the dog-like Thylacine, going on all fours, the fact that the pouch opens backwards is less disadvantageous to the contained young. The male Thylacine has a pouch which is quite or very nearly as well formed as in the female. There are also rudiments of a pouch in the male foetuses of many Marsupials, especially of those belonging to the Polyprotodont section of the order, though these rudiments are by no means confined to that subdivision. Up to so late a period as the age of four months (length 19.8 cm.) the male Dasyurus ursinus has a pouch. We have now to consider the interesting series of facts relative to the permanence—in a rudimentary condition it is true —of the mammary pouch in the higher Mammalia, facts which seem to be an additional proof that they have been derived from an ancestor in which the pouch was an organ of functional importance. The first definite proof of the occurrence of a pouch in any mammal not a Marsupial or a Monotreme was made by Malkmus, who found this structure in a Sheep. It seems, however, that the structures found in the higher mammals are not always comparable to the marsupium of the Marsupials, but sometimes to the mammary pouch of the Monotreme. That the Marsupials are a side line, and not involved in the ancestry of the Eutheria, is an opinion which is at present widely held. At the same time it is reasonable to suppose that the original stock lying between the Prototheria and the Metatheria, whence the latter and the Eutheria have arisen, preserved both the mammary pouch of the lower mammal and the marsupium of the further-developed stage, as does Phalangista occasionally at the present day. Hence to find remnants of both {16} {17} {18} structures in existing mammals would not so incredible. This is what Dr. Klaatsch believes to be the case. In certain Ungulates, including two species of Antelope, Dr. Klaatsch found very considerable rudiments of folds provided with unstriated muscular fibre; there were in the adult Cervicapra isabellina a pair of pouches, one on each side, and a rudiment of a second on either side; possibly this multiplication of the pouches has relation to the number of young. That there is more than one pouch makes a comparison with the mammary pouch rather than with the marsupium probable. The Ungulate teat, it must be remembered (see p. 16), is a secondary teat; hence there is no difficulty in the comparison from this point of view. A pouch containing a primary teat would of course be absolutely incomparable with a mammary pouch, because in that case the wall of the teat itself would be the pouch. Mammals belonging to quite different Orders show traces more or less marked of a marsupium. In young Dogs the teats are borne upon an area where the skin is thinner, the covering of hair less dense than elsewhere—all points of resemblance to the inside of the pouch of a Marsupial; in addition to this there are traces of the sphincter marsupii muscle. In other Carnivora there are similar vestiges. In Lemur catta a more complete rudiment of a marsupial pouch is to be met with. In this Lemur the teats are both inguinal and pectoral; the skin in these regions is thin and but slightly hairy, and extends forwards as two bands of the same thinness and smoothness on each side of the densely hairy skin covering the sternum. This area is sharply separated from the rest of the integument by a fold which runs parallel to the longitudinal axis of the body, and can be comparable with nothing save the rudiment of the marsupial fold. One is tempted to wonder how far the habit which certain Lemurs have of carrying their young across the abdomen with the tail wrapped round the body of the mother is a reminiscence of a marsupial pouch. Skeleton. The skeleton of the Mammalia consists almost solely of the endoskeleton. It is only among the Edentata that an exoskeleton of bony plates in the skin is met with. As in other Vertebrates, the skeleton is divisible into an axial portion, the skull and vertebral column, and an appendicular skeleton, that of the limbs. The bones of mammals are well ossified, and in the adult there are but few and small tracts of cartilage left. Vertebral Column.—The vertebral column of the mammals, like that of the higher Vertebrata, consists of a number of separate and fully-ossified vertebrae. The constitution of a vertebra upon which all the usual processes are marked is as follows:—There is first of all the body or centrum of the vertebra, a massive piece of bone shaped like a disc or a cylinder. The centra of contiguous vertebrae are separated by a certain amount of fibrous tissue forming the intervertebral disc, and the apposed surfaces of the centra are as a rule nearly flat. In this last feature, and in the important fact that the centra are ossified from three distinct centres, the anterior and posterior pieces ("epiphyses") remaining distinct for a time, even for a long time (as in the Whales), the centra in the mammals differ from those of reptiles and birds. The epiphyses are not found throughout the vertebral column of the lowly-organised Monotremata, and they do not appear to exist in the Sir...