Cambridge Natural History Mammalia/Chapter VII

by Frank E. Beddard

CHAPTER VII

EUTHERIA—MARSUPIALIA

Order I. MARSUPIALIA^[1]

The Marsupials may be thus defined:—Terrestrial, arboreal, or burrowing (rarely aquatic) mammals, with furry integuments; palate generally somewhat imperfectly ossified; jugal bone reaching as far as the glenoid cavity; angle of lower jaw nearly always inflected. The clavicle is developed. Arising from the pubes are well developed and ossified epipubic bones. Fourth toe usually the most pronounced. Teeth often exceed the typical Eutherian number of forty-four; molars generally four on each side of each jaw. As a rule but one tooth of the milk set is functional, which is (according to many) the fourth premolar. Teats lying within a pouch, in which the young are placed. Young born in an imperfect condition, and showing certain larval characters. There is a shallow cloaca. The testes are extra-abdominal, but hang in front of the penis. In the brain the cerebellum is completely exposed; the hemispheres are furrowed, but the corpus callosum is rudimentary. An allantoic placenta is rarely present.

Structurally the Marsupials are somewhat intermediate between the Prototheria and the more typical Eutheria, with a greater resemblance to the latter.

The name Marsupial indicates what is perhaps the most salient character of this order. The pouch in which the young are carried is almost universally present. It is less developed on the whole in the Polyprotodont forms, such as the Thylacine, Dasyures, etc., but is found in so many of them that the two divisions of the Marsupials, the Diprotodonts and the Polyprotodonts, cannot be raised to distinct orders on this and other grounds. The marsupial pouch of the Marsupials must not, as has been already pointed out, be confounded with the pouch of the

Fig. 59.—Rock Wallaby (Petrogale xanthopus), with young in pouch. × ¹⁄₇. (After Vogt and Specht.)

Monotreme mammals. Distinct teats are found in the marsupium of the Marsupials, while there are none in the mammary pouch of the Monotreme, the pouch itself indeed representing an undifferentiated teat, of which the walls have not closed up. The pouch opens forward in the Kangaroos, and backwards in the Phalangers and in the Polyprotodonts. Its walls are supported by a pair of bones diverging from each other in a -shaped manner; these are cartilaginous and vestigial in the Thylacine. They are the precise equivalents of similar bones in the Monotremata. It has been held, but apparently erroneously, that these bones are mere ossifications in the tendons of the external oblique muscle of the abdomen, or of the pyramidalis of the same region; and vestiges have been asserted to exist in the Dog. Such bonelets are undoubtedly present in the Dog; but it seems clear from their development in Marsupials, as structures actually continuous with the median unossified portion of the symphysis pubis, that the "marsupial bones" belong to that part of the skeleton, and that they correspond with the epipubis of certain amphibians and reptiles. The pouch, it may be remarked, exists in a rudimentary form in the males of many Marsupials.

Fig. 60.—Ventral surface of innominate bone of Kangaroo (Macropus major). × ⅓. a, Acetabulum; ab, acetabular border of ilium; is, iliac surface; m, "marsupial" bone; pb, pubic border; pt, pectineal tubercle; s, symphysis; si, supra-iliac border; ss, sacral surface; thf, thyroid foramen; ti, tuberosity of ischium. (From Flower's Osteology.)

Fig. 61.—Mammary foetus of Kangaroo attached to the teat. (Nat. size.) (From Parker and Haswell's Zoology.)

The most salient feature in the life-history of the Marsupials is the imperfect condition in which the young are born. The egg is no longer laid, as in the Monotremes; but curiously enough the ovum, which has the small size of that of the Eutheria, divides incompletely at the first division (as Mr. Caldwell has shown), and this developmental feature may perhaps be looked upon as a reminiscence of a former large-yolked condition. The young when born are small and nude; the newly born young of a large Kangaroo is perhaps as large as the little finger. The young are transferred by the lips of the mother to the pouch, where they are placed upon a teat. It is an interesting fact that they are not merely imperfect foetuses, but that they are actual larvae. They possess in fact at any rate one larval organ in the shape of a special sucking mouth. This sucking mouth is an extra-uterine production, and is of course an adaptation to the particular needs of the young, just as are other larval organs, such as the chin-suckers of the tadpole, or the regular ciliated bands of the larvae of various marine invertebrate organisms.

There are a number of other features which distinguish the Marsupials from other mammals.

The cloaca of the Marsupials is somewhat reduced, but is still recognisable. Its margins in Tarsipes are even raised into a wall, which projects from the body.

The tooth series of the Marsupials was once held to consist of one dentition only, with the exception of the last premolar, which has a forerunner. The interpretation of the teeth of Marsupials are various. Perhaps most authorities regard the teeth as being of the milk dentition, with the exception of course of the single tooth that has an obvious forerunner. But there are some who hold that the teeth are of the permanent dentition. In any case it is proved that a set of rudimentary teeth are developed before those which persist. Those who believe in the persisting milk dentition describe these as prelacteal. Another matter of importance about the teeth of this order of mammals is that their numbers are sometimes in excess of the typical Eutherian 44. This, however, holds good of the Polyprotodonts only.

It was for a long time held that the Marsupials differed from all other mammals in having no allantoic placenta. But quite recently this supposed difference has been proved to be not universal by the discovery in Perameles of a true allantoic placenta. The Marsupials have been sometimes called the Didelphia. This is on account of the fact that the uterus and the vagina are double. Very frequently the two uteri fuse above, and from the point of junction an unpaired descending passage is formed (see Fig. 48 on p. 74).

A character of the brain of Marsupials has been the subject of some controversy. Sir Richard Owen stated many years ago that they were to be distinguished from the higher mammals by the absence of the corpus callosum. Later still it was urged that a true corpus callosum, though a small one, was present; while, finally, Professor Symington^[2] seems to have shown that the original statement of Owen was correct, at least in part. It is at most feebly developed (see Fig. 58, p. 118).

As to skeletal characters, the Marsupial skull has on the whole a tendency towards a permanent separation of bones usually firmly ankylosed. Thus the orbitosphenoids remain distinct from the presphenoid. The palate is largely fenestrated, a return as it were—says Professor Parker—to the Schizognathous palate of the bird. The mandible is inflected; this familiar character of the Marsupials goes back to the earliest representatives of the order in Mesozoic times (see p. 96); but it is not absolutely universal, being absent from the much weakened skull of Tarsipes. On the other hand, the inflection is nearly as great in certain Insectivores, in Otocyon, etc. The malar always extends back to form part of the glenoid cavity. The shoulder girdle has lost the large coracoid of Monotremes; this bone has the vestigial character that it possesses in other Eutheria. The clavicle is present except in the Peramelidae. A third trochanter upon the femur seems to be never present.

Fig. 62.—Skull of Rock Wallaby (Petrogale penicillata). (Ventral view.) ali, Alisphenoid; bas.oc, basi-occipital; bas.sph, basi-sphenoid; ex.oc, ex-occipital; ju, jugal; max, maxilla; pal, palatine; par.oc, paroccipital; p.max, premaxilla; pr.sph, presphenoid; pt, pterygoid; sq, squamosal; ty, tympanic. (From Parker and Haswell's Zoology.)

The Marsupials cannot be regarded as an intermediate stage in the origin of the Eutheria for a number of reasons. In the first place, the nature of their teeth shows them to be degenerate animals; one set, whether we regard it as the milk or permanent dentition, has become vestigial. The recent discovery of a true allantoic placenta in Perameles removes one reason for regarding the Marsupials as primitive creatures. It implies on the whole that the Marsupials have sprung from a stock with an allantoic placenta. The alternative is to assume the independent development of an allantoic placenta in both groups of the Mammalia; unless indeed the genus Perameles is to be held to be the most primitive race of Marsupials living, a hypothesis which does not appear on the face of it likely. So long as it was believed that the mammary pouch of the Monotremes was the equivalent of the marsupium of the Marsupials, the persistence of this structure seemed to be a bond of union between the groups. But it is now known that the marsupium is a special organ confined to the Marsupials, an argument which is rather in favour of their being a lateral development of the mammalian stem. It is to be remarked also that the marsupium is feeblest in the Polyprotodonts, which may perhaps be looked upon as the most primitive of the Marsupials, owing to their more numerous teeth and other points to be referred to immediately.

Not only are the Marsupials interesting from the point of view of their structure; their present and past distribution is of equal interest. During the Mesozoic epoch they occurred in Europe and North America; but not, so far as negative evidence means anything, in Australia, which is now their headquarters. In Europe Marsupials lingered on into the Tertiary period, when they finally became extinct. In America, of course, the group has persisted to the present day. Now it is important to notice that the two main subdivisions of the Marsupials, the Polyprotodontia and the Diprotodontia, exist to-day in both Australia and South America. These two divisions, it should be explained, differ principally in that one has numerous, the other rarely more than two,^[3] incisors in the lower jaw. It is perhaps the more widely distributed opinion that the Polyprotodontia are the more archaic group; this opinion rests upon one or two facts in addition to the absence of specialisation in the incisor teeth. Among the Polyprotodontia the total number of teeth is greater—a clearly primitive character; secondly, the general form of the body of these animals, with four subequal limbs and carnivorous or omnivorous diet, contrasts with the purely vegetarian and much specialised Kangaroos at any rate. Finally—and sufficient stress has perhaps not been laid upon this matter—the brain among the Polyprotodonts is less convoluted than among the genera of the other division. This statement is of course made with due regard to parallelism in size (see p. 77). It is well known that the complexity of a brain bears a distinct relation to the size of its possessor within the group. Now the most ancient Marsupials are decidedly more Polyprotodont-like. No European form from the earlier periods is distinctly to be referred to the Diprotodonts. But both divisions now exist in America and Australia.

We must assume, therefore, one of three hypotheses. Either the differentiation into the two great divisions occurred in Jurassic or Cretaceous times before the migration of the order southwards; or the Diprotodont type is only a type, and not a natural group, i.e. it has been separately evolved in America and Australia; or, finally, there was formerly a land-connexion in the Antarctic hemisphere, along which the Diprotodonts of Australia wandered into South America. The middle hypothesis has this to commend it, that syndactylism occurs in both divisions, and that in some Diprotodonts the pouch opens backwards as it does in the Polyprotodonts. So great are the resemblances that but little difference is really left—of great importance that is to say. Hence it is not difficult to imagine the reduction of the incisors having taken place twice. In favour of the first hypothesis there are no positive facts. Finally, in favour of the last, which is so strongly supported by the facts of distribution derived from the study of other groups of animals,^[4] there is at least this striking fact or rather series of facts: that some of the South American fossil Polyprotodonts have a "strictly Dasyurine relationship."^[5] If there has not been a direct migration, then the Dasyurine type has been twice evolved, an improbability that few will attempt to explain away. In any case we shall adopt here the usual division of the Marsupials into Diprotodontia and Polyprotodontia.

Sub-Order 1. DIPROTODONTIA.

This group includes the herbivorous Marsupials. The incisors are as a rule three above, but one only in the Wombats. Below is one strong pair, with occasionally one or two rudimentary incisors. The upper canines, if present, are not large. The molars are tuberculate or ridged. All Marsupials (except the Wombats) to some extent, and the Macropods especially, are characterised by the prolongation of the tubes of the dentine into the clear enamel. The significance of this fact is, however, lessened by the fact that the same penetration of the enamel by dentinal tubes occurs in the Jerboa, the Hyrax, and some Shrews. The feet have two syndactylous toes,^[6] less marked in the Wombats than in the Kangaroos and Phalangers.

Fig. 63.—Skull of Wombat (Phascolomys wombat). (Lateral view.) ang, Angular process; cond, condyle of mandible; ext.aud, opening of bony auditory meatus; ex.oc, exoccipital; ju, jugal; lcr, lachrymal; max, maxilla; nas, nasal; p.max, premaxilla; sq, squamosal; ty, tympanic. (From Parker and Haswell's Zoology.)

This order is mainly Australian at the present day, using the term of course in the "regional" sense (see p. 84); the only exception indeed to this statement is the occurrence of the genus Caenolestes in South America. But it is now known that Diprotodont Marsupials formerly existed in the same part of the world.

Fig. 64.—Bones of right foot of Kangaroo (Macropus bennetti). a, Astragalus; c, calcaneum; cb, cuboid; e³, ento-cuneiform; n, navicular; II-V, second to fifth toes. (From Flower's Osteology.)

Fam. 1. Macropodidae.—This family contains the Kangaroos, Wallabies, Rat-Kangaroos, and Tree-Kangaroos. With the exception of Dendrolagus the family is terrestrial, and its numerous species progress by leaps effected by the long hind-limbs, which are

Fig. 65.—Skeleton of Wallaby (Macropus ualabatus). The scapula is raised somewhat higher than in nature. The end of the tail is omitted. The head of the femur has been separated from the acetabulum. acet, Acetabulum; acr, acromion process; ast, astragalus; cal, calcaneum; cbd, cuboid; chev, chevron-bones; cl, clavicle; cun, cuneiform of carpus; epi, epipubis; fb, fibula; fem, femur; hd, head of femur; hu, humerus; il, ilium; isch, ischium; obt, obturator-foramen; orb, orbit; pis, pisiform; pub, pubis; rad, radius; rb¹, first rib; rb¹³, last rib; sc, scapula; st, sternum; tb, tibia; troch, great trochanter of femur; uln, ulna; unc, unciform; IV, fourth toe. (From Parker and Haswell's Zoology.)

decidedly, often greatly, longer than the fore-limbs. In the hind-limb the fourth toe is very long and strong; the fifth moderately so; the second and third are slender and united by skin. The tail is always long, but differs in its characters from genus to genus. The stomach is much sacculated. The dental formula is I 3/1 C (1 or 0)/0 P 2/2 M 4/4. The atlas is often open below, forming thus an incomplete ring.

Though the number of the incisor teeth in the adult Diprotodonts is never more than three on each side in each jaw, more numerous rudiments are present. Mr. M. Woodward^[7] has lately investigated the subject with interesting results. He finds that many species present decided traces of two additional incisors, raising the total to that which characterises the Polyprotodontia; but in two cases, viz. Macropus giganteus and Petrogale penicillata, a sixth is present, the total number being thus in excess of that found in any other Marsupial. This, as the author himself admits, proves too much. No mammal is known which in the adult condition has so many incisors; nor do the fossil Mammalia help us to get over the difficulty; even among reptiles it is not usual for so many teeth to occur upon the premaxillaries.

It is a curious fact that the two long lower incisors can be used after the fashion of a pair of scissors, or rather a pair of shears. Their inner edges are sharpened, and they are capable of some motion towards and away from each other; by their means grass is cropped.

The stomach of Macropus (and of other allied genera) is peculiar by reason of its long and sacculated character; the oesophagus enters it very near the cardiac end, which is bifid. Messrs. Schäfer and Williams^[8] have shown that the squamous, non-glandular epithelium of the oesophagus extends over the greater part of the stomach, only the pyloric extremity and one of the two cardiac caeca being lined with columnar epithelium.

The Macropodidae are clearly divisible into three sub-families, which are distinguished by marked anatomical characters.

In the sub-family Macropodinae (including the genera Macropus, Petrogale, Lagorchestes, Dorcopsis, Dendrolagus, Onychogale, and Lagostrophus) there is no hallux, and the tail is hairy. The oesophagus enters the stomach near the cardiac end. The caecum when short has no longitudinal bands; the liver has a Spigelian lobe.

The second sub-family, Potoroinae or Hypsiprymninae (including the genera Potorous, Aepyprymnus, Bettongia, and Caloprymnus), consists of smaller animals than the Macropodinae, which, however, resemble them in having no hallux, but a hairy tail. The oesophagus enters the stomach near the pyloric end of that organ. The caecum, though short, has lateral longitudinal bands. The liver has no special Spigelian lobe. The canines are always present, being rarely so in Macropodinae, and are usually well developed.

The third sub-family, that of the Hypsiprymnodontidae, is doubtfully referable to the family; it consists of but one genus Hypsiprymnodon, which is in many points more like a Phalanger than a Kangaroo. It has an opposable hallux and a non-hairy, but scaly, tail. It has canines in the upper jaw.

Fig. 66.—Red Kangaroo. Macropus rufus. × ¹⁄₁₈.

Sub-Fam. 1. Macropodinae.—The genus Macropus includes not only the Kangaroos but also the Wallabies, which are really indistinguishable, though they have sometimes been placed in a separate genus Halmaturus. The genus thus enlarged contains twenty-three species. It may be thus characterised: the ears are long, the rhinarium is usually naked, but in M. giganteus and others a band of hairs descends to the upper lip; a naked band extends from the ankle to the pads on the digits, which is interrupted in M. rufus by a band of hairs just in front of the digits. The mammae are four. The tail is not bushy, but is crested in M. irma. They are for the most part found on the Australian continent, but some species are found in the islands to the north which belong to the Australian region. Thus M. brunii, which is of interest as the first Kangaroo seen by a European, is a native of the Aru islands. A specimen of this animal, which was then living in the garden of the Dutch governor of Batavia, was described by Bruyn in the year 1711. M. rufus, the largest member of the group, is remarkable for the red secretion which adorns the neck of the male. It is caused by particles which have the appearance and colour of carmine. M. giganteus is not, as its specific name might imply, the "giant" of the race; its dimensions are given as 5 feet, while M. rufus is said to attain a length of 5 feet 5 inches, exclusive (in both cases) of the tail.

The account which Sir Joseph Banks gives^[9] in his diary of the Kangaroo is interesting, since he was one of the first naturalists to see that creature. In July 1770 it was reported to him that an "animal as large as a greyhound, of a mouse colour, and very swift" had been seen by his people. A little later he was surprised to observe that the animal "went only upon two legs, making vast bounds just as the jerboa does." The second lieutenant killed one of these Kangaroos, of which Sir Joseph Banks wrote that "to compare it to any European animal would be impossible, as it has not the least resemblance to any one I have seen. Its fore-limbs are extremely short and of no use to it in walking; its hind, again, as disproportionately long; with these it hops seven or eight feet at a time, in the same manner as the jerboa, to which animal indeed it bears much resemblance, except in size, this being in weight 38 lbs., and the jerboa no larger than a common rat." The beast was killed and eaten, and proved excellent meat. Sir Joseph Banks' observations upon the leaping of the Kangaroo are of interest, because it is often asserted that the tail is largely made use of as a third foot or as a support. Mr. Aflalo declares in the most positive way that after repeatedly examining the tracks upon soft sand immediately after the animal had passed, not the very faintest trace of the impression of the tail could be discovered. The leaps of a big Kangaroo seem to be somewhat greater than is recorded by Banks. It is said that 15 or even 20 feet are covered at a bound, and in bound after bound. But in walking slowly it can be readily seen from an inspection of Kangaroos at the Zoological Society's Gardens that the animal does rest upon its tail, which with the hind-legs forms a tripod.

Petrogale with six species comes next to Macropus, and is indeed only to be differentiated from it by the thickly-haired and more slender tail, which is not used, as it is sometimes in the Kangaroos, as an extra hind-limb. The Rock-Kangaroos live among rocks, which they climb, and from which they leap; and the tail acts rather as a balancing pole. The most elaborate account of the anatomy of Petrogale known to me is by Mr. Parsons.^[10] The dentition as given by Mr. Thomas is I 3/1 C 0/0 Pm 2/2 M 4/4—that of Macropus without the occasionally occurring canine of the upper jaw. The osteological characters which separate it from Macropus are quite insignificant. Mr. Parsons mentions a wormian bone, "os epilepticum," at the junction of the coronal and sagittal sutures. It was found to occur in two out of five skulls examined, and appears not to occur in other Kangaroos. The palatine foramina of Petrogale are so large that the posterior part of the bone is only a narrow thickened ridge. The small intestine of P. xanthopus is 102 inches long, the large intestine 44 inches. The caecum has a length of 6 inches, and is not sacculated, differing in this from the caecum of Macropus major. The best known species are P. xanthopus and P. penicillata. The genus is confined to Australia itself, and does not enter Tasmania.

Onychogale includes the so-called "Nail-tailed Wallabies," which have a thorn at the end of the tail, reminding one of the Lion and the Leopard, whose tails have a similar armature. The muffle is hairy. Three species are allowed by Mr. Thomas.

Lagorchestes has, like the last genus, the rhinarium, i.e. that part of the nose immediately surrounding the nostrils, hairy instead of smooth as in the Kangaroos proper. It is distinguished from Onychogale by the absence of the terminal callosity to the tail, which is rather short. The name Hare-Kangaroo is given to the members of this genus (three species) on account of their exceeding fleetness. This genus is limited to Australia itself. L. conspicillatus is said to present "a remarkable resemblance to the English hare," and L. leporoides was so called by Gould on account of general appearance as well as face.

Dorcopsis has shorter hind-legs than Macropus, and a naked muffle. The ears are small. The structure of D. luctuosa has been studied by Garrod,^[11] who pointed out the existence of four enlarged hair follicles on the neck near the mandibular symphysis. These are, however, represented in the next genus Dendrolagus, and occur also in Petrogale. The limbs are not so disproportionate as in Macropus, and the tail is naked at the tip.

Dorcopsis and the next genus to be described, Dendrolagus, differ from Macropus and its immediate allies, Petrogale and Lagorchestes, in a number of anatomical points. In the first place, the premolars are twice the size of those of Macropus, and they have a characteristic pattern not observable in the Kangaroos. This consists of a median ridge (the whole tooth being rather prismatic in shape), with lateral ridges at right angles to it. The upper canines are developed, but are minute.

The stomach is not quite like that of Macropus, though built upon a similar plan. The blind cardiac extremity is a single, not a double cul-de-sac; in this it is like that of Petrogale. The distribution of the squamous, white, oesophageal epithelium is very much like that of Dendrolagus. In both genera the orifice of the oesophagus into the stomach is guarded by two strong longitudinal folds, which run for some distance towards the pylorus. In Dendrolagus, at any rate, this tract is bordered on each side by glandular patches. In Dendrolagus, moreover, the squamous epithelium does not extend into the cardiac cul-de-sac. This latter is separated from the rest of the stomach by two slightly diverging folds, which are faintly represented in Petrogale and in Halmaturus. In the last two genera the folds surrounding the oesophageal orifice are but slightly represented; better in Halmaturus than in Petrogale. But there are not the patches of glands already referred to. The small intestine of Dorcopsis is 97 inches in length, the large being 32, i.e. proportionately long, as in Marsupials generally. The small caecum (2½ inches) is not sacculated.

The spleen is Macropodine, being -shaped or -shaped. The differences between Dorcopsis and the evidently closely allied Dendrolagus will be further considered under the description of the latter. Dorcopsis is confined to New Guinea, and contains three species, viz. D. muelleri, D. luctuosa, and D. macleani. D. muelleri has a striking resemblance to Macropus brunii, with which it has been confounded. Though intermediate between Macropus and Dendrolagus, these Kangaroos are not arboreal.

The genus Dendrolagus is remarkable for its un-kangaroo-like habit of living in trees. In accordance with this change of habit is a relative shortening of the hind-limbs, a feature which begins to be observable in Dorcopsis. "The general build," writes Mr. Thomas, "is of the ordinary mammalian proportions, not macropodiform at all." The muffle is not naked for the greater part, though the shortness of the hairs gives that effect. As in Dorcopsis, but not as in Macropus, the bulla tympani is not swollen. There are altogether five species, the fifth, D. bennetti, having been lately described from specimens living in the Zoological Society's Gardens.

Fig. 67.—Tree-Kangaroo. Dendrolagus bennetti. × ¹⁄₁₂.

The anatomy of this genus has been described by Owen for D. inustus,^[12] and by myself for D. bennetti. The stomach, which has a single, not bifid, cul-de-sac, is sacculated by two principal bands and other subsidiary ones. Its internal structure has already been to some extent described. The spleen of D. bennetti is remarkable for the fact that it is not -shaped, whereas D. inustus agrees with other Macropodines in the form of this organ. The small intestine of D. bennetti is 95 inches long, the large 38. The caecum appears to differ in the two species; it is smaller in D. bennetti, where it is only 2 inches in length. The most remarkable feature of the liver is the large size of the left lateral lobe and the bilobed condition of the Spigelian lobe; this at least was the case with D. bennetti. A recently-described species^[13] has been attentively studied in its native haunts by Dr. Lumholtz.^[14] It lives in the highest parts of the mountainous scrubs of Queensland, where it moves quickly on the ground as well as among the trees. It is hunted with Dingos by the "blacks," and is eaten by them.^[15]

Lagostrophus is a generic name that has been proposed by Mr. Thomas for a small Wallaby 18 inches in length, which is distinguished by the fact that the long claws of the hind-limbs are entirely hidden by long and bristly hairs; the muffle is naked; there is no canine. The bullae are swollen. There is but one species of the genus, L. fasciatus, a native of West Australia.

Sub-Fam. 2. Potoroinae.—Aepyprymnus and the other genera placed in this sub-family are known by the vernacular name of Rat-Kangaroos, or sometimes Kangaroo-Rats. The latter term has been called "incorrect," though it is just as good as the former, both of them in fact being inaccurate as implying some likeness to or relation with a Rat. The present genus has a partially hairy rhinarium; the auditory bullae are not swollen. It contains but one species, Ae. rufescens, a native of Eastern Australia, which is distinguished by its very long hind-feet.

Bettongia has long hind-feet as in Aepyprymnus, but the rhinarium is entirely naked instead of being partially hairy, while the ears are much shorter. The genus, which contains four species, is remarkable as being the only ground-living mammal with a prehensile tail, which it uses to carry grass, etc. B. lesueuri burrows in the ground, often to so great a depth as 10 feet. The genus occurs in Tasmania as well as in Australia.

Caloprymnus, with one species, is a genus instituted by Mr. Thomas in his Catalogue of Marsupials for a form (C. campestris) which combines in a remarkable way the characters of Aepyprymnus, Bettongia, and Potorous. The external characters and the general shape of the skull are as in Bettongia, while the molars have the structure of those of Aepyprymnus. The last premolar is as in Potorous.

Of the genus Potorous there are three species, which are Tasmanian as well as Australian. Unlike the other Rat-Kangaroos, the hind-feet are comparatively short, and the animal is therefore less addicted to jumping than its relatives. The rhinarium is naked, and the ears are of fair length.

Sub-Fam. 3. Hypsiprymnodontinae.—The Musk-Kangaroo, Hypsiprymnodon, is the last genus of the present family, and the only genus of this sub-family. It is intermediate between the Macropodidae and the Phalangeridae, the annectant character being mainly the hind-feet, which though they have the same long fourth digit as the Kangaroos, have it more feebly developed, and possess also an opposable hallux, which is one of the salient features in the structure of the Phalangeridae. The tail is naked and scaly; the rhinarium is entirely naked. The ears are large and not furry. The single species, H. moschatus, appears to feed upon insects as well as vegetables.

"Its habits are chiefly diurnal, and its actions when not disturbed by no means ungraceful. It progresses in much the same manner as the Kangaroo-Rats (Potorous), to which it is closely allied, but procures its food by turning over the débris in the scrubs in search of insects, worms, and tuberous roots, frequently eating the palm berries, which it holds in its fore-paws after the manner of the Phalangers, sitting up on its haunches, or sometimes digging like the bandicoots." This is Mr. Ramsay's description of the animal, which he was the first to discover.^[16]

Fam. 2. Phalangeridae.—The genus Hypsiprymnodon bridges over the not very wide gap which separates the Kangaroos from the Phalangers. The Phalangers are Marsupials with five fingers and toes; the second and third toes are bound together by a common integument as in the Macropodidae. The hallux is opposable and nailless. The tail is nearly always long and prehensile. The pouch is well developed; the stomach not sacculated; a caecum is present (except in Tarsipes). These are really the principal distinctions between the two families. In addition, it may be mentioned that the lower incisors have not a scissor-like action as in the Kangaroos.

The Phalangers may be divided into four sub-families.

The first of these, that of the Phalangerinae, contains the genera Phalanger (including Cuscus), Acrobates, Distaechurus, Dromicia, Gymnobelideus, Petaurus, Petauroides, Dactylopsila, Pseudochirus, and Trichosurus.

These genera agree in the following generalities:—Tail well developed, often very long; three incisors above, and at least two premolars both above and below; caecum long and simple; stomach without a cardiac gland; liver not very complicated by secondary furrows, with a distinct caudate lobe; the vaginal median culs-de-sac often coalesced; lungs with an azygos lobe.

Fig. 68.—Bones of leg and foot of Phalanger. ast, Astragalus; calc, calcaneum; cub, cuboid; ect.cun, ecto-cuneiform; ent.cun, ento-cuneiform; fb, fibula; mes.cun, meso-cuneiform; nav, navicular; tib, tibia; I-V, first to fifth toes. (After Owen.)

The second sub-family, Phascolarctinae (with the Koala only), is thus characterised:—Tail rudimentary; cheek-pouches present; superior incisors three, but only one premolar above and below; caecum extraordinarily long; stomach with a cardiac gland; liver complicated by additional furrows, without a free caudate lobe; no azygos lobe to lungs; vaginal culs-de-sac free.

The third sub-family, Phascolomyinae, contrasts with the others as follows:—Tail rudimentary; cheek-pouches present, but rudimentary; one incisor on each side above, but no additional premolars; all the teeth rootless; caecum not peculiar in shape; stomach with a cardiac gland; liver complicated by secondary furrows, without a free caudate lobe; lung with an azygos lobe; vaginal culs-de-sac free.

The last sub-family, Tarsipedinae, is thus defined:—Tail long; tongue extensile; only one premolar; molars reduced; caecum absent.

Fig. 69.—Vulpine Phalanger. Trichosurus vulpecula. × ¹⁄₆.

Sub-Fam. 1. Phalangerinae.—The genus Phalanger embraces five species, sometimes called by the generic name of Cuscus. They are largish animals with short ears; only the end of the tail is naked. Of these animals only one species is found in Australia itself, the rest inhabiting the islands lying to the north. The Spotted Cuscus, Ph. maculatus, is in spite of its vegetarian diet, and perhaps on account of its spots, spoken of as the "Tiger Cat." Mr. Aflalo remarks of it that though provided with a prehensile tail, it is little better as a climber than the tailless Koala.

Trichosurus, including the "True Phalangers," includes largish species, which can be distinguished from the last genus by a chest-gland similar to that which occurs in Myrmecobius and some other Marsupials of the present group. There are but two species, which are purely Australian. The "Brush-tailed Opossum," T. vulpecula (perhaps better known as Phalangista vulpina), like its American pseudo-namesake (a true Opossum, genus Didelphys), "plays 'possum" on occasions. The dental formula is I 3/2 C 1/0 Pm 2/3 M 4/4. The ears are shortish.

The Ring-tailed Phalangers, Pseudochirus, are more widely distributed than the last two genera; they range from Tasmania in the south to New Guinea in the north. They are not, however, ring-tailed, though the tip of the tail is generally white. As in the last genera, which have prehensile tails, the end of this appendage is naked. The mammae are four. The tooth formula is I 3/2 C 1/0 Pm 3/3 M 4/4. There are some ten species of the genus.

The Striped Phalanger, Dactylopsila trivirgata, is an animal about a foot long, whose identity can be ascertained by its striped, black and white skin. It is an arboreal creature that lives apparently both on leaves and grubs like so many arboreal creatures of quite different groups—Squirrels, for instance, and New-World Monkeys. The tooth formula is I 3/3 C 1/6 Pm 3/2 M 4/4.

Gymnobelideus leadbeateri is a small creature with a body 6 inches in length. It is restricted to the colony of Victoria. The general look is that of Petaurus; the ears are naked.

Dromicia is a genus of Phalangers which although devoid of a parachute, such as is possessed by certain genera that will be considered immediately, is able to leap with great agility from branch to branch. The ears are large and thin and almost naked; the tooth formula is I 3/2 C 1/0 Pm 3/3 M 4/4. They are minute creatures, the longest measuring, with the tail, but 10 inches. Dormouse-Phalanger is a name sometimes given to them. There are four species, ranging from Tasmania to New Guinea. The name Dormouse as applied to the genus seems to be owing to the way in which they hold a nut in the paws when feeding. D. nana is 4 inches long, with a tail of nearly the same length. It is thick at the base.

Distaechurus is the last genus of non-flying Phalangers. Its name refers to the arrangement of the hairs on the tail, which are disposed on either side in a row like the vane of a feather. The tooth formula is I 3/2 C 1/0 Pm 3/2 M 3/3, very nearly as in Acrobates. The ears are as in that genus.

Petaurus is the first genus of the Flying Phalangers, all of which are provided with a parachute-like expansion of the skin between the fore- and hind-limbs; the ears are large and naked; and the tooth formula is I 3/2 C 1/0 Pm 3/3 M 4/4. There are three species of the genus, which extend through pretty well the entire Australian region. The term "flying" as applied to these and the other "flying" genera is of course an exaggeration. The animals cannot fly upwards; they can only descend in a skimming fashion, the folds of skin breaking their fall. P. breviceps is perhaps the best-known species. The body is 8, the tail 9 inches long.

Petauroides seems to be chiefly distinguished from Petaurus by the fact that, as in its ally Dactylopsila, the tail is partly naked terminally. In Petaurus and Gymnobelideus the tail is bushy to the very end, including its extreme tip below.

A third genus of Flying Phalangers is the minute Acrobates, which has a distichous tail like that of Distaechurus. It is not more than 6 inches in length including the tail. As to these Flying Phalangers it is exceedingly instructive to observe that the same method of "flight" has been apparently evolved three times; for the three genera are each of them specially related to a separate type of non-flying Phalanger. The same observation can be made about the Flying Squirrels, Anomalurus and Sciuropterus. The dental formula is I 3/2 C 1/0 Pm 3/3 M 3/3. The ears are thinly clad with hair. There are four teats.

Sub-Fam. 2. Phascolarctinae.—The Koala, or Native Bear, Phascolarctos cinereus, is the only representative of its sub-family. It is, like the Wombat, aberrant in the lack of an obvious tail. The absence of this appendage is curious in an arboreal creature whose near allies have a long and prehensile one. The structure of the Koala was investigated by the late Mr. W. A. Forbes.^[17] There are some unexpected points of likeness to the Wombat: thus they agree in the absence of the tail, in the structure of the stomach, and in the great subdivision of the lobes of the liver. The brain, however, is smooth, and the caecum is exceedingly large and complicated in structure, that of the Wombat being short. That both animals have cheek-pouches is perhaps due to similar habits of temporarily storing masses of food. This animal has only eleven pairs of ribs. The tail has only seven or eight vertebra, and these have no chevron-bones.

A peculiarity of the skull is seen in the great size of the alisphenoid bulla, which is comparable in size and appearance with that of the Pig. As in the Kangaroos, the atlas is incomplete below.

The tooth formula of the genus is I 3/1 C 1/0 Pm 1/1 M 4/(4 or 5). The additional lower molar seems to be exceptional, and has been found in one specimen only.

In the alimentary tract the most remarkable structure is the large intestine, which is very capacious for the first 28 inches or so of its course. This section of the colon is lined with rugae precisely like those which are found in the caecum. These folds, which at first are some twelve in number, fuse lower down, and by the time that the colon approaches the external orifice are reduced to five. Similar folds, as already stated, occur in the caecum, but do not extend as far as its blind end. The caecum is proportionately and actually larger than in any other Marsupial. The gall-bladder is unusually elongated.

Fig. 70.—Koala. Phascolarctos cinereus. × ¹⁄₉.

The Koala is mainly crepuscular or nocturnal in its habits. It feeds so exclusively upon the leaves of the gum-tree (Eucalyptus) that it is impossible to keep the creature long in captivity in lands where that particular kind of food is not available.

The female, though she seems to bear but a single young one, which is carried on the back after the fashion of some Opossums, has two nipples. The animal's slow habits seem to require a nocturnal and retired life. It is about as lethargic as the Sloth, and it is said to further resemble that animal in clinging firmly to a branch even after it is shot.

Fig. 71.—Wombat. Phascolomys wombat. × ¹⁄₁₂.

Sub-Fam. 3. Phascolomyinae.—Phascolomys, the Wombat, is the only genus of this sub-family. This animal has the appearance of a heavily-built Marmot, like which it has a mere stump for a tail, and a pair of strong chisel-shaped and Rodent-like incisors, which, however, differ from those of Rodents in having a complete coating of cement. All the teeth of the animal are rootless, and there are no canines. The incisors have enamel on the front and lateral faces only. The dental formula is I 1/1 C 0/0 Pm 1/1 M 4/4. The affinities with other Diprotodont Marsupials are shown by the commencing syndactyly of the second and third toes. The rhinarium is naked or hairy. There is a rudimentary cheek-pouch, as in Phascolarctos. The Wombat has, like the Koala, and also the Beaver—which does away with some of the value of the comparison—a peculiar gland-patch in the stomach, a raised area of collected glands. In no other Marsupial is such a structure found, "whilst in the two forms under consideration its identity is almost precise. That such a unique structure should have been independently developed in two forms unrelated to each other, appears to me to be in the highest degree improbable." This is Mr. Forbes' opinion. It might be strengthened by adding the observation that, as there are other points of likeness between the Wombat and the Koala, it seems more unlikely that a structure so nearly identical should have been twice developed in two not very distant forms. As in the Kangaroos, the atlas is open below. Ph. ursinus has 15 ribs; the other species the normal (for Marsupials) 13. Other points of likeness will be mentioned under the description of the Koala. These animals mainly feed upon roots; they live in companies in burrows. There are three species—Ph. ursinus, Ph. latifrons, and Ph. mitchelli. Ph. ursinus is Tasmanian in range, the other two species South Australian.

Fig. 72.—Skull of Wombat. Phascolomys wombat. (Lateral view.) ang, Angular process; cond, condyle of mandible; ex.oc, exoccipital; ext.aud, opening of bony auditory meatus; ju, jugal; lcr, lachrymal; max, maxilla; nas, nasal; p.max, premaxilla; sq, squamosal; ty, tympanic. (From Parker and Haswell's Zoology.)

Sub-Fam. 4. Tarsipedinae.—The genus Tarsipes ought perhaps to be removed from the present family. There is but a single species, which is a small creature of 7 inches in total length, of which the tail measures 4 inches. The teeth are much dwindled, the formula being I 2/1 C 1/0 Pm 1/0 M 3/3 = 22. The lower incisors are procumbent. The lower jaw, moreover, has not the characteristic Marsupial inflection. The intestinal canal is without the caecum present in the remaining Phalangeridae. It is a curious fact that this aberrant little Phalanger should come from Western Australia, like the even more aberrant Myrmecobius. Like the latter also, Tarsipes has a long exsertile tongue, with which, however, it extracts honey from flowers. Probably it also catches minute insects in the corollas of the flowers. It has been proved, in fact, that in captivity at any rate the animal is insectivorous; for it has been known to eat moths.

Fam. 3. Epanorthidae.—The extinct Epanorthidae of Patagonia are represented to-day by a small Marsupial which has been rediscovered within the last two or three years. This little animal, formerly called Hyracodon (a pre-occupied name), is now termed Caenolestes, and is a native of Colombia and Ecuador. There are two species, and of these C. obscurus is called by the inhabitants "Raton runcho," which means opossum-rat. It lives apparently upon bird's eggs and small birds, though it belongs to the Diprotodont division of the Marsupials. Caenolestes, however, although diprotodont, has not the syndactylous character of the digits of the feet already referred to in the Kangaroos and their allies. The pouch is small and rudimentary. The dentition is I 4/3 C 1/1 Pm 3/3 M 4/4 = 46, and the teeth are said by Mr. Thomas to be much like those of the Australian Dromicia.^[18]

In the skull a peculiarity which does not bear upon its affinities to other Marsupials, but is still interesting, is mentioned by Mr. Thomas. The nasals are not sufficiently prolonged to meet the upper edge of the maxillae, and so a vacuity is left, as in the skulls of many Ruminants (e.g. the Sable Antelope). The palate is very imperfect; the foramina, which render it so, reach as far forward as the last premolar. The lower jaw has quite the appearance of that of a Macropus or Phalanger, with long and forwardly projecting incisors.

Extinct Diprotodonts.—The great Diprotodon is a creature with a skull a yard long, which must have been of the size of a large Rhinoceros. Though closely allied to Macropus, it seems that this great beast did not hop after the fashion of a Kangaroo, its limbs being of a more equal size than in the Kangaroo. Recently some further remains of Diprotodon have been discovered in a lake known as Lake Mulligan, where they had apparently been bogged. Professor Stirling has contributed an account of these remains, which fills up a considerable gap in our knowledge. He has been able to state the structure of the fore- and hind-limbs. Both limbs are pentadactyle, the fingers of the fore-limb being approximately equal in length and general development. In the hind-limb the hallux is small, and consists of the metatarsal only. This bone is fixed in the position of "extreme abduction," and is suggestive of an arboreal limb. Digits two and three may have been syndactylous, and the authors of the account^[19] of these bones think that the fourth toe may have shared in this syndactyly. The metatarsal of the fifth digit is enormously expanded at its edge, and seems to have furnished a strong support to the creature; this is also seen in the metacarpal of the fore-limb. Probably, therefore, Diprotodon was quadrupedal in its mode of progression, with the emphasis laid upon the little finger and the little toe instead of, as in ourselves, the first toe. The hind-foot of the Diprotodon could not be more unlike that of a Kangaroo than it actually is.

Fig. 73.—Diprotodon australis. (After Owen.)	Fig. 74.—Thylacoleo carnifex. Side view of skull. (After Flower.)

Another giant among these Marsupials was the genus Thylacoleo, whose name was given to it by Sir Richard Owen on the view that it was a Marsupial Tiger. Sir W. Flower has, however, controverted this opinion, and the genus is in fact, in spite of its large size, closely allied to the Phalangers and Cuscuses.^[20] The dental formula is I 3/1 C 1/0 Pm 3/1 M 1/2; the last premolar is a great blade-shaped tooth like that of Potorous.

Nototherium was a creature smaller than Diprotodon, but still of large size; it is believed to have been a burrowing creature, and to connect the Wombats with Diprotodon. More certainly allied to the existing Wombat was Phascolonus, a Wombat as big as a Tapir.

Fig. 75.—Nototherium mitchelli. Side view of skull. × ¹⁄₆. (After Owen.)

Of extinct American Diprotodonts the Epanorthidae, already referred to in connexion with the living Caenolestes, were the most prominent forms. The genus Epanorthus occurs in the Santa Cruz formation of Patagonia, which is believed to be Miocene. The incisors are three in the upper jaw; and the single incisor of each ramus of the lower jaw is a great chisel-shaped, cutting instrument.

Abderites is also typically Diprotodont by reason of the large projecting incisors of the lower jaw. It has a large cutting tooth in the lower jaw, which appears to be the last premolar, and is thus comparable to the great cutting tooth of the lower jaw and of the upper jaw of the extinct Phalanger, Thylacoleo. It may also be comparable to the great premolar of such Multituberculata as Ptilodus and Plagiaulax. It is, moreover, marked with vertical grooves.

An interesting form, which is unfortunately but little known, is the Australian and Pleistocene genus Triclis, with one species, T. oscillans. In having a minute canine tooth in the lower jaw it agrees with some Phalangeridae, and being otherwise closely allied to Hypsiprymnodon, it unites the Macropodidae with the Phalangeridae.

Sub-Order 2. POLYPROTODONTIA.

In this mainly carnivorous or insectivorous division of the Marsupials the incisors are four or five on each side of the upper jaw, and one or two fewer in the lower jaw. Figs. 76 and 77 illustrate the Polyprotodont and Diprotodont dentitions. The canines are those of flesh-eaters and so are the molars, being as a rule sharply cuspidate. As a rule, which has an exception in the Peramelidae, there is no syndactylism of toes in the hind-foot. This sub-order is at the present day Australian and American in its range.

Fig. 76.—Front view of the skull of Tasmanian Devil (Sarcophilus ursinus), showing Polyprotodont and carnivorous dentition. (After Flower.)

Fam. 1. Dasyuridae.—This family consists of Marsupials which are generally pentadactylous, but with occasionally the hallux missing. The tail is long but not prehensile. The pouch is present or absent. The teeth vary in the different genera, but the upper incisors are never less than three, and may be as many as five in the upper jaw and six in the lower. The canines are trenchant. There is no caecum.

Fig. 77.—Front view of skull of Koala (Phascolarctos cinereus), illustrating Diprotodont and herbivorous dentition. (From Flower.)

Fig. 78.—Longitudinal section of the skull of the Thylacine (Thylacinus cynocephalus). × ½. a, Angular process of mandible; AS, alisphenoid; BO, basioccipital; BS, basisphenoid; cd, condyle of mandible; ET, ethmoturbinal; Ex.O, exoccipital; Fr, frontal; ME, ossified portion of mesethmoid; MT, maxilloturbinal; Mx, maxilla; Na, nasal; OS, orbitosphenoid; Pa, parietal; Per, periotic; Pl, palatine; PMx, premaxilla; PS, presphenoid; Pt, pterygoid; SO, supraoccipital; Sq, squamosal; Vo, vomer. (From Flower's Osteology.)

The genus Thylacinus contains but a single species, which is now limited to Tasmania, and is generally known as the Tasmanian Wolf. It has the build of an ordinary Wolf, and is of about the same size. The hinder part of the body is marked with a series of black transverse bands. The hallux is entirely wanting; the pouch opens backwards. The marsupial bones are minute and unossified. The dental formula is I 4/3 C 1/1 Pm 3/3 M 4/4 = 46. There are four mammae. This animal, now confined to Tasmania, is getting rarer on account of its sheep-killing propensities, and the consequent war of extermination declared upon it by the colonists. It will, however, feed upon other animals; and it is related that the first specimen ever captured had in its stomach the remains of an Echidna! Mr. Thomas thinks that the persistence of this and of some of the other larger carnivorous Marsupials in Tasmania after their extinction in Australia is not unconnected with the advent of the Dingo. But it is stated that the Thylacine is quite capable of keeping even a pack of dogs at bay.

Fig. 79.—Tasmanian Devil. Sarcophilus ursinus. × ¹⁄₁₀.

The genus Sarcophilus has been frequently confounded with the next, but it is kept apart by Mr. Thomas, who follows Cuvier in this. An alternative generic name is Diabolus, which, like the first name, refers to the habits and character of the single species which this genus contains. The genus is more like Thylacinus than is Dasyurus. The hallux is wanting, and the teeth, though fewer in number (42), resemble those of the Thylacine more closely than do those of the Dasyure. The species is called S. ursinus, the popular name being Tasmanian Devil. It is black with a variable number of white patches on the body. It is of about the size of a Badger, and is, like the Thylacine, a nocturnal animal. The Tasmanian Devil is said to be one of the most ferocious of animals, and to express its ferocity by a "yelling growl."

The next genus of this family, Dasyurus, comprises five species, which range over the whole of the Papuan and Australian sub-regions. The general form is Viverrine, and the hallux is sometimes present though small. The dental formula is as in the

Fig. 80.—Skull of Dasyurus. (Lateral view.) al.sph, Alisphenoid; ang, angular process of mandible; fr, frontal; ju, jugal; lcr, lachrymal; max, maxilla; nas, nasal; oc.cond, occipital condyle; par, parietal; par.oc, paroccipital process; p.max, premaxilla; s.oc, supraoccipital; sq, squamosal; sq′, zygomatic process of squamosal. (From Parker and Haswell's Zoology.)

Fig. 81.—Dasyure. Dasyurus viverrinus. × ¹⁄₅. (After Vogt and Specht.)

last genus, but the teeth "are more insectivorous in their character." There are six or eight mammae. The members of this genus are grey or brown, and spotted with white; they are all arboreal, and feed largely upon birds and their eggs. Mr. Thomas has pointed out that in two species, D. viverrinus and D. geoffroyi, the striae upon the foot-pads are absent, and that therefore these at least are probably not so purely arboreal as the rest. The animals are not diurnal, and during the day hide themselves in the hollow trunks of trees. They are spoken of as "Native Cats," but have the general habits of Martens. D. maculatus is common in Tasmania, but is rare in Australia, thus "approaching the condition now exhibited by the Thylacine and Tasmanian Devil, namely, complete extermination in Australia, where both once lived." D. hallucatus shows an approach to Phascologale in its five-toed hind-feet and slender build.

Phascologale is a genus which, like the last, is usually arboreal (although not P. virginiae of North Queensland), but is of much smaller size, the species not exceeding the dimensions of a rat. They have no spots, but there is sometimes a stripe down the back. There are thirteen species, which have the same range as the last genus. The hallux is present though small, but the pouch is "practically obsolete," though there is a small fold of skin behind the teats. The rhinarium is naked; the tail is long, "bushy, crested, or nearly naked." The mammae are four to ten in number. The dental formula is as in Dasyurus, and the teeth are not very different in form; sometimes the last premolar is wanting. "The members of this genus," remarks Mr. Thomas, "evidently take the place in the Australian region filled in the Oriental by the Tupaiae, and in the Neotropical by the smaller Opossums."

The genus Sminthopsis comprises not more than four species, even smaller than the last. The largest species, S. virginiae, is only 125 mm. in length. The hallux is present, and there is a well-developed pouch. There are forty-six teeth, as in the Dasyures. The feet are narrow with granulated or hairy soles, whereas in Phascologale they are broad with smooth soles. The mammae are eight or ten. The genus ranges through Australia and Tasmania.

The genus Antechinomys has but a single species, which is a native of Queensland and New South Wales. The build is Jerboa-like, and the animal is, as might be inferred, terrestrial. The ears are very long, and the limbs elongated; the hallux is absent; the teeth are exactly as in Sminthopsis.

Antechinomys has thirteen dorsal and seven lumbar vertebrae; three sacrals and twenty-five caudals, the latter number being in excess of that of its allies. The stomach is nearly globular, with approximated orifices; the intestine measured 6.8 inches, a little more than twice the length of the animal itself. A. lanigera is a native of East Central Australia, and appears to be entirely terrestrial in habit, and to progress by a series of leaps—at any rate when going at full speed.

Professor Spencer, who found examples of this rare species, gives an interesting description of its habits. Antechinomys has much the look of the Australian Rat, Hapalotis mitchelli; and as the two animals lead a similar kind of life, the resemblance is not unexpected. Professor Spencer wonders why these creatures are saltatory in habit. The country which they inhabit is arid, but with patches of grass and shrubs. For a big kangaroo the advantage of the power of leaping over such obstacles may be obvious, but not for the small and slender Antechinomys. The chief foes of this rare Marsupial appear to be predatory birds; and Professor Spencer thinks that the saltatory mode of progression may be more baffling to such pursuers than even a rapid run.

The genus Dasyuroides has been lately instituted by Professor Spencer for a Marsupial from Central Australia somewhat intermediate between Sminthopsis and Phascologale. As there is but one species, the generic will be considered with the specific characters. D. byrnei is an animal of about the size of the Common Rat. The hallux is absent. The tail is fairly thick, but not "incrassated." There are six mammae, and the pouch is but slightly developed, with two low lateral folds. The dentition is I 4/3 C 1/1 Pm 3/2 M 4/4. This Marsupial is nocturnal, and burrowing in habit. Its food consists of insects.^[21]

Myrmecobius is so different from the last-described genera (Dasyurinae) that it is usually separated from them as a sub-family Myrmecobiinae. The animal is of a bright rufous colour, banded posteriorly with white. There is no hallux, though the metatarsal belonging to that digit is present. There are four mammae.^[22] On the chest is a naked patch of some extent, upon which open the ducts of a complex gland, which has been described and figured by myself.^[23] There is no pouch, but a tract of skin shows indications of a pouch-like structure. The teeth are extraordinarily numerous, fifty to fifty-four; the formula being I 4/3(4) C 1/1 Pm 3/3 M 5/6. Their resemblance to those of certain Jurassic Marsupials is dealt with on p. 100.^[24] In this matter lies of course the chief interest of the genus, which may be "an unmodified survivor from Mesozoic times, and therefore from a time long before the Didelphyidae, Peramelidae, and Dasyuridae were differentiated one from the other." Another ancient feature (found in Jurassic mammals) is a mylo-hyoid groove upon the lower jaw, which, however, is not always present, and its existence has therefore been denied. The single species, M. fasciatus, is partly arboreal and partly terrestrial in habit, and feeds upon ants. It is a Western and Southern Australian form.

Fig. 82.—Banded Australian Anteater. Myrmecobius fasciatus. × ¹⁄₅.

Fam. 2. Didelphyidae.—All the members of this family are pentadactylous. The teeth are fifty in number, arranged thus: I 5/4 C 1/1 Pm 3/3 M 4/4. The caecum is small; the pouch is generally absent; the tail generally long and prehensile.

Fig. 83.—Virginian Opossum. Didelphys virginiana. × ¹⁄₅. (After Vogt and Specht.)

The genus Didelphys contains most of the forms belonging to this family, including as it does some twenty-three species. The Opossums are mainly arboreal animals, insectivorous in their food; but the larger species eat reptiles, birds, and their eggs. Several of the small species carry their young, when able to leave the teats, on their back, the tails of the young being wrapped round that of the mother. It is not only the pouched species which carry their young in something of this fashion. Azara's Opossum, an animal as big as a cat, is said to carry its eleven young ones (themselves as large as rats) on the back, though their foothold does not appear to be strengthened by intertwining the tails. Even with this huge family on her back, the mother can climb trees with considerable alacrity. The mammae are seven to twenty-five in number. The genus has been lately split up into a number of genera, Marmosa, Dromiciops, Peramys, etc.

Fig. 84.—Thick tailed Opossum. Didelphys crassicaudata. × ¹⁄₅.

Chironectes is hardly different from Didelphys. It has webbed hind-feet, and is aquatic in habit. The one species of the genus is known as the Yapock, and is a Central and South American form. It is of about the size of a large rat, and appears to be an expert diver after the fish upon which it lives.

Fam. 3. Peramelidae.—The Bandicoots, although clearly belonging to the Polyprotodont Marsupials, yet agree with the Diprotodonts in the fact that the second and third toes of the feet are bound up in a common integument, which is not the case with the Diprotodont Caenolestes. The hind-feet are longer than the front; of the former limb, two or three of the fingers alone are long and functional; the others are rudimentary or absent. Tail long, hairy, and non-prehensile. Dentition I 5/3 C 1/1 Pm 3/3 M 4/4 = 48, or sometimes, owing to the absence of a pair of upper incisors, 46. There is a caecum.

The genus Peragale, the Rabbit-Bandicoots, consists of two species entirely Australian in range. The enormous ears (whence

Fig. 85.—Bones of manus. A, of Choeropus castanotis. × 2. B, of Bandicoot (Perameles). × 1½. c, Cuneiform; l, lunar; m, magnum; R, radius; s, scaphoid; td, trapezoid; tm, trapezium; u, unciform; U, ulna; I-V, digits. (From Flower's Osteology.)

Fig. 86.—Rabbit Bandicoot. Peragale lagotis. × ¹⁄₅.

"Rabbit" Bandicoot) distinguish this genus from Perameles. The pouch opens backwards, and there are eight mammae. P. lagotis, the only species about whose ways of life anything is known, burrows in the soil, whence it extracts grubs; it is also a grass-feeder, and it is said that its likeness to a Rabbit in appearance is strengthened by its similarity in flavour!

Perameles is a genus consisting of twelve species, which are found in Tasmania, Australia, and New Guinea. Like the last genus, from which it does not widely differ in other points, Perameles consists of species which combine insectivorous and vegetarian habits. One species is said to become in captivity an expert in catching mice. The pouch opens backwards, and there are six or eight mammae.

Fig. 87.—Pig-footed Bandicoot. Choeropus castanotis. × ⅓.

The last genus of this family is Choeropus, containing but one species, Ch. castanotis. It is confined to the Australian continent. It is to be distinguished from the last two by the fact that there are only two functional digits, the second and third, in the fore-limb; the fourth is rudimentary; the other two are absent. It burrows, and is omnivorous like its allies. The two metacarpals that are developed are very long and closely apposed; they have hence a remarkably pig-like aspect, and justify its name. The pouch opens backwards, and there are eight mammae.

Fam. 4. Notoryctidae.—This family contains but a single genus and species, the recently-discovered Notoryctes typhlops.^[25] We may regard as family-characters the pentadactyle limbs, the existence of three pairs of incisors in the lower and four in the upper jaw; and the tritubercular nature of the upper molars. Notoryctes typhlops, the "Marsupial Mole" as it has been termed, was originally discovered by Professor Stirling in Central South Australia. It is a burrowing creature, clothed in a silky fur of a pale golden red, without external ears. It has been compared in appearance with Chrysochloris, the Cape Golden Mole, and the eminent palaeontologist, Professor Cope, has even insisted upon a real genetic affinity. Edentate affinities have also been suggested. But Notoryctes has a small pouch opening backwards as in other Polyprotodonts,^[26] and as it also possesses marsupial bones it must undoubtedly be referred to the Marsupialia. The animal shows many curious adaptations to its underground mode of life. Certain of the vertebrae in the neck and in the lumbar region are firmly welded together, giving of course a strength of push, and suggesting the Armadillos; the claws of the third and fourth front-toes are greatly enlarged, and must be efficient digging organs. The track of the animal is like that of a railway in mountainous country; it burrows for a short distance, emerges, and then descending beneath the surface re-emerges. The red colour of the fur is said to be in harmony with the arid soil in which it lives. The native name of the creature is "Urquamata." It feeds upon ants and other insects.

Fig. 88.—Australian Marsupial Mole. Notoryctes typhlops. × ¼.

Extinct Polyprotodonts.—Of extinct Polyprotodonts (apart from those Mesozoic forms which are considered on p. 100) extinct species of Thylacinus and Dasyurus are known from Australia. The most interesting fact in connexion with the Tertiary Polyprotodonts is the existence in South America of such genera as Prothylacinus and Amphiproviverra, which are not merely Polyprotodonts but definitely Dasyures, and not referable to the Didelphyidae.

These forms have been included in an order, Sparassodonta. But it is not by any means certain whether these forms are rightly placed in the neighbourhood of the carnivorous Marsupials; it is possible that they ought to be relegated to the Creodonta or to their allies. Their structure is in fact somewhat intermediate between those two groups. The teeth seem to be carnivorous and Marsupial-like in form; but as already mentioned, in connexion with the general structure of teeth, more than a single premolar is replaced. These animals in fact, in so far as regards their teeth, are midway between the Marsupials and the typical Eutheria. The angle of the lower jaw is inflected, but the palate is not marked by deficient ossification. At least this is not the case with all the members of the group. Whether the small Microbiotherium, which is made the type of a family, is rightly referred here is not certain. This animal had palatine vacuities as well as an inflected angle to the lower jaw.

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1. Works dealing exclusively with the Marsupials are: Lydekker, in Allen's Naturalists' Library, 1894; Aflalo, Natural History of Australia, Macmillan and Co. 1896; Waterhouse, Natural History of Mammalia, i. London, 1848; Oldfield Thomas, British Museum Catalogue of Marsupialia and Monotremata, 1888.
2. "The Cerebral Commissures in the Marsupialia and Monotremata," Journ. Anat. Phys. xxvii. 1893, p. 69.
3. When there are more than two, two are especially developed. See Figs. 76, 77 (pp. 149, 150).
4. See for a further discussion of this subject the zoogeographical handbooks of Mr. Lydekker and myself, quoted on p. 78 (footnote).
5. To this may be added Mr. Thomas' observation that the family of American Opossums is "very closely allied to the Dasyuridae, from which, were it not for its isolated geographical position, it would be very doubtfully separable."
6. Except in the South American Diprotodonts.
7. Proc. Zool. Soc. 1893, p. 450.
8. Ibid. 1876, p. 165.
9. Journal of the Rt. Hon. Sir Joseph Banks, Bart., K.B., P.R.S., edited by Sir Joseph Hooker, London, 1896.
10. Proc. Zool. Soc. 1896, p. 683.
11. Proc. Zool. Soc. 1875, p. 48.
12. Proc. Zool. Soc. 1852, p. 103.
13. Proc. Zool. Soc. 1895, p. 131.
14. Ibid. 1884, p. 387.
15. Ibid. 1884, p. 407.
16. Proc. Linn. Soc. N.S. Wales, i. 1877, p. 34.
17. "On some Points in the Anatomy of the Koala," Proc. Zool. Soc. 1881, p. 180.
18. Thomas, "On Caenolestes, a still existing survivor of the Epanorthidae of Ameghino, and the representative of a new family of recent Marsupials," P.Z.S. 1895, p. 870.
19. Stirling and Zietz, Mem. Roy. Soc. South Australia, i.; see also a notice in Nature, January 18, 1900.
20. Quite recently (Proc. Linn. Soc. N.S.W. 1898, p. 1) the carnivorous character of Thylacoleo has been reasserted by Mr. Broom.
21. Horn Scientific Expedition, pt. ii. Zoology, 1896, p. 36.
22. Leche found five, and Waterhouse stated eight to be the number.
23. Proc. Zool. Soc. 1887, p. 527. See also Leche, Biol. Fören. Förhandl. 1891, p. 136, and literature quoted.
24. Traces of horny pads, like those of the Duck-bill, have been asserted to exist in this animal. This is exceedingly interesting when regarded in conjunction with its multituberculate molars.
25. See for an account of this animal, Professor Stirling's Memoir in Trans. Roy. Soc. S. Australia, 1891, p. 154, and Gadow, Proc. Zool. Soc. 1892, p. 361.
26. The male, according to Professor Spencer, has a rudimentary pouch.