Fig. 62.
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'sZoology.)
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 inPeramelesremoves one reason for regardingthe 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 genusPeramelesis 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,[69]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 stresshas 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,[70]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."[71]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.
This group includes the herbivorous Marsupials. The incisors are as a rule three above, but one only in the Wombats. Belowis 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,[72]less marked in the Wombats than in the Kangaroos and Phalangers.
Fig. 63.
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'sZoology.)
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 genusCaenolestesin South America. But it is now known that Diprotodont Marsupials formerly existed in the same part of the world.
Fig. 64.
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'sOsteology.)
Fig. 65.
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'sZoology.)
Fam. 1. Macropodidae.—This family contains the Kangaroos, Wallabies, Rat-Kangaroos, and Tree-Kangaroos. With the exception ofDendrolagusthe family is terrestrial, and its numerous species progress by leaps effected by the long hind-limbs, which are 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 fromgenus 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[73]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 giganteusandPetrogale 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 ofMacropus(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[74]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-familyMacropodinae(including the generaMacropus,Petrogale,Lagorchestes,Dorcopsis,Dendrolagus,Onychogale, andLagostrophus) 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,PotoroinaeorHypsiprymninae(including the generaPotorous,Aepyprymnus,Bettongia, andCaloprymnus), 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 theHypsiprymnodontidae, is doubtfully referable to the family; it consists of but one genusHypsiprymnodon, 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.
Fig.66.—Red Kangaroo.Macropus rufus.×1⁄18.
Sub-Fam. 1. Macropodinae.—The genusMacropusincludes not only the Kangaroos but also the Wallabies, which are really indistinguishable, though they have sometimes been placed in a separate genusHalmaturus. The genus thus enlarged contains twenty-three species. It may be thus characterised: the ears are long, the rhinarium is usually naked, but inM. giganteusand 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 inM. rufusby a band of hairs just in front of the digits. The mammae are four. The tail is not bushy,but is crested inM. 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. ThusM. 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. giganteusis not, as its specific name might imply, the "giant" of the race; its dimensions are given as 5 feet, whileM. rufusis said to attain a length of 5 feet 5 inches, exclusive (in both cases) of the tail.
The account which Sir Joseph Banks gives[75]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 recordedby 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.
Petrogalewith six species comes next toMacropus, 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 ofPetrogaleknown to me is by Mr. Parsons.[76]The dentition as given by Mr. Thomas is I 3/1 C 0/0 Pm 2/2 M 4/4—that ofMacropuswithout the occasionally occurring canine of the upper jaw. The osteological characters which separate it fromMacropusare 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 ofPetrogaleare so large that the posterior part of the bone is only a narrow thickened ridge. The small intestine ofP. xanthopusis 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 ofMacropus major. The best known species areP. xanthopusandP. penicillata. The genus is confined to Australia itself, and does not enter Tasmania.
Onychogaleincludes 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.
Lagorchesteshas, 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 fromOnychogaleby 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. conspicillatusis said to present "a remarkableresemblance to the English hare," andL. leporoideswas so called by Gould on account of general appearance as well as face.
Dorcopsishas shorter hind-legs thanMacropus, and a naked muffle. The ears are small. The structure ofD. luctuosahas been studied by Garrod,[77]who pointed out the existence of four enlarged hair follicles on the neck near the mandibular symphysis. These are, however, represented in the next genusDendrolagus, and occur also inPetrogale. The limbs are not so disproportionate as inMacropus, and the tail is naked at the tip.
Dorcopsisand the next genus to be described,Dendrolagus, differ fromMacropusand its immediate allies,PetrogaleandLagorchestes, in a number of anatomical points. In the first place, the premolars are twice the size of those ofMacropus, 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 ofMacropus, 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 ofPetrogale. The distribution of the squamous, white, oesophageal epithelium is very much like that ofDendrolagus. 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. InDendrolagus, at any rate, this tract is bordered on each side by glandular patches. InDendrolagus, 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 inPetrogaleand inHalmaturus. In the last two genera the folds surrounding the oesophageal orifice are but slightly represented; better inHalmaturusthan inPetrogale. But there are not the patches of glands already referred to. The small intestine ofDorcopsisis 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, beingT-shaped orY-shaped. The differences betweenDorcopsisand the evidently closely alliedDendrolaguswill be further considered under the description ofthe latter.Dorcopsisis confined to New Guinea, and contains three species, viz.D. muelleri,D. luctuosa, andD. macleani.D. muellerihas a striking resemblance toMacropus brunii, with which it has been confounded. Though intermediate betweenMacropusandDendrolagus, these Kangaroos are not arboreal.
The genusDendrolagusis 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 inDorcopsis. "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 inDorcopsis, but not as inMacropus, 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.
Fig.67.—Tree-Kangaroo.Dendrolagus bennetti.×1⁄12.
The anatomy of this genus has been described by Owen forD. inustus,[78]and by myself forD. bennetti. The stomach, whichhas 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 ofD. bennettiis remarkable for the fact that it is notT-shaped, whereasD. inustusagrees with other Macropodines in the form of this organ. The small intestine ofD. bennettiis 95 inches long, the large 38. The caecum appears to differ in the two species; it is smaller inD. 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 withD. bennetti. A recently-described species[79]has been attentively studied in its native haunts by Dr. Lumholtz.[80]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.[81]
Lagostrophusis 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.—Aepyprymnusand 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.
Bettongiahas long hind-feet as inAepyprymnus, 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. lesueuriburrows 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 ofAepyprymnus,Bettongia, andPotorous. The external characters and the general shape of the skull are as inBettongia, while the molars have the structure of those ofAepyprymnus. The last premolar is as inPotorous.
Of the genusPotorousthere 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.[82]
Fam. 2. Phalangeridae.—The genusHypsiprymnodonbridges 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 acommon 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 inTarsipes). 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 thePhalangerinae, contains the generaPhalanger(includingCuscus),Acrobates,Distaechurus,Dromicia,Gymnobelideus,Petaurus,Petauroides,Dactylopsila,Pseudochirus, andTrichosurus.
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.
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.
Fig.69.—Vulpine Phalanger.Trichosurus vulpecula.×1⁄6.
Sub-Fam. 1. Phalangerinae.—The genusPhalangerembraces five species, sometimes called by the generic name ofCuscus. 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 inMyrmecobiusand 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 asPhalangistavulpina), like its American pseudo-namesake (a true Opossum, genusDidelphys), "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 leadbeateriis a small creature with a body 6 inches in length. It is restricted to the colony of Victoria. The general look is that ofPetaurus; the ears are naked.
Dromiciais 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. nanais 4 inches long, with a tail of nearly the same length. It is thick at the base.
Distaechurusis 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 inAcrobates. The ears are as in that genus.
Petaurusis 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 threespecies 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. brevicepsis perhaps the best-known species. The body is 8, the tail 9 inches long.
Petauroidesseems to be chiefly distinguished fromPetaurusby the fact that, as in its allyDactylopsila, the tail is partly naked terminally. InPetaurusandGymnobelideusthe tail is bushy to the very end, including its extreme tip below.
A third genus of Flying Phalangers is the minuteAcrobates, which has a distichous tail like that ofDistaechurus. 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,AnomalurusandSciuropterus. 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.[83]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.
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.
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 inPhascolarctos. 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 twicedeveloped in two not very distant forms. As in the Kangaroos, the atlas is open below.Ph. ursinushas 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, andPh. mitchelli.Ph. ursinusis Tasmanian in range, the other two species South Australian.
Fig. 72.
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'sZoology.)
Sub-Fam. 4. Tarsipedinae.—The genusTarsipesought 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 aberrantMyrmecobius. Like the latter also,Tarsipeshas 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 ofPatagonia are represented to-day by a small Marsupial which has been rediscovered within the last two or three years. This little animal, formerly calledHyracodon(a pre-occupied name), is now termedCaenolestes, and is a native of Colombia and Ecuador. There are two species, and of theseC. obscurusis 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 AustralianDromicia.[84]
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 aMacropusorPhalanger, with long and forwardly projecting incisors.
Extinct Diprotodonts.—The greatDiprotodonis a creature with a skull a yard long, which must have been of the size of a large Rhinoceros. Though closely allied toMacropus, 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 ofDiprotodonhave 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 havebeen syndactylous, and the authors of the account[85]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,Diprotodonwas 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 theDiprotodoncould not be more unlike that of a Kangaroo than it actually is.
Fig. 73.
Fig. 74.
Fig.73.—Diprotodon australis.(After Owen.)
Fig.74.—Thylacoleo carnifex.Side view of skull. (After Flower.)
Another giant among these Marsupials was the genusThylacoleo, 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 andCuscuses.[86]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 ofPotorous.
Nototheriumwas a creature smaller thanDiprotodon, but still of large size; it is believed to have been a burrowing creature, and to connect the Wombats withDiprotodon. More certainly allied to the existing Wombat wasPhascolonus, a Wombat as big as a Tapir.