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is shown by the abdominal testes, the single cloacal outlet, the low cerebral development, the absence of medullary canals in the long bones in the Sloths, and by the great tenacity of life and long-enduring irritability of the muscular fibre, in both the Sloths and Anteaters1.

The order Bruta is but scantily represented at the present period. One genus, Manis or Pangolin, is common to Asia and Africa; the Orycteropus is peculiar to South Africa; the rest of the order, consisting of the genera Myrmecophaga, or true Anteaters, Dasypus or Armadillos, and Bradypus or Sloths, are confined to South America.

Having defined the orders or subdivisions of the two foregoing subclasses, I may remark that the Lyencephala cannot be regarded as equivalent merely to one of the orders, say Rodentia, of the Lissbncephala, without undervaluing the anatomical characters which are so remarkable and distinct in the marsupial and monotrematous animals. The anatomical peculiarities of the edentulous Lyencephala2 appear to me to be, at least, of ordinal importance. In these deductions I hold the mean between those who, with Geoffroy St Hilaire, would make a distinct class of the Monotremata, and those who, with Cuvier, would make the Monotremes a mere family of the Edentata. In like manner, whilst I regard the Lyencephala as forming a group of higher rank than an order, I do not consider it as forming an equivalent primary group to that formed by all the placental Mammalia.

The true value of the Lyencephala is that of one of four

1 This latter vital character attracted the notice of the earliest observers of these animals. Thus Marcgrave and Piso narrate of the Sloth :—'Cor motum suum validissime retiuebat, postquam exemptum erat e corpore per semihorium :—exempto corde caeteris visceribus multo post se movebat et pedes lente contrahebat sicut dormituriens solet.' Buffon, who quotes the above from the Historic/, Naturalis Brasilia, p. 322, well remarks, 'Par ces rapports, ce quadrupede se rapproche non seulement de la tortue, dont il a la lenteur, mais encore des autres reptiles et de tous ceux qui n'ont pas un centre du sentiment unique et bien distinct.'—Hist. Natwelle, 4to, Tom. xm. p. 45.

2 See my article Monotremata, in the Cyclcpadia of Anatomy, part xxvi. 1841.

primary divisions or subclasses of the Mammalia; its true equivalency is with the Lissencephala, and all its analogical relations are to be found more directly in that smooth-brained subclass than in the Placentalia at large.

The following Table exemplifies the correspondence of the groups in the Lyencephalous and Lissencephalous series:—

Lyencephala. Ijissencephala.

Rhizophaga1 Burrowing Rodentia.

Poephaga1 Dipodidce and Leporidce.

Petaurus Pteromys.

Phalangistidce Sciuridce and prehensile-tailed

arboreal Rodents.

Phascolarctos Bradypus.

Perameles and Myrmecobius. Erinaceidce.

Chceropus Macroscelis.

Didelphys and Phascogale . Soricidce.

Dasyuridce Centetes, Gymnura.

Echidna Manis.

Besides the more general characters by which the LissenCephala, in common with the Lyencephala, resemble Birds and Reptiles, there are many other remarkable indications of their affinity to the Oviparous Vertebrata in particular orders or genera of the subclass. Such, e. g., are the cloaca, convoluted trachea, supernumerary cervical vertebrae and their floating ribs, in the three-toed Sloth; the numerous trunk-ribs in the two-toed Sloth; the irritability of the muscular fibre, and persistence of contractile power in the Sloths and some other Bruta; the long, slender, beak-like edentulous jaws and gizzard of the Anteaters; the imbricated scales of the equally edentulous Pangolins, which have both gizzard and gastric glands like the proventricular ones in birds; the dermal bony armour of the Armadillos like that of loricated Saurians; the quills of the Porcupine and Hedgehog; the brilliant iridescent colours of the fur of the Cape-mole (Chrysochlora aurea); the proventriculus of the Dormouse and Beaver; the pre

1 On the Classification of the Marsupialia, Trans, of the Zool. Soc. Vol. II. p. 315, '839.

valence of disproportionate development of the hind limbs in the Bodentia, coupled, in the Jerboa, with confluence of the three chief metatarsals into one bone, as in birds; the keeled sternum and wings of the Bats; the aptitude of the Cheiroptera, Insectivora, and certain Bodentia to fall, like Reptiles, into a state of true torpidity, associated with a corresponding faculty of the heart to circulate carbonized or black blood:— these, and the like indications of coaffinity with the LyenCephala to the Oviparous air-breathing Vertebrata, have mainly prevailed with me against an acquiescence in the elevation of different groups of the Lissencephala to a higher place in the Mammalian series, and in their respective association, through some single character, with better-brained orders, according to Mammalogical systems which, at different times, have been proposed by zoologists of deserved reputation. Such, e. g., as the association of the long-clawed Bruta with the Ungulata1, and of the shorter-clawed Shrews, Moles and Hedgehogs, as well as the Bats, with the Carnivora*; of the Sloths with the Quadrumana3; of the Bats with the same high order*; and of the Imectivora and. Bodentia in immediate sequence after the Linnean 'Primates,' as in the latest published 'System of Mammalogy,' from a distinguished French author5.

So far as their ordinal affinities are known, the most ancient Mammals, the fossil remains of which have been found in secondary strata, are either ly- or liss- encephalous, and belong either to the Marsupialia or the Insectivora. (Appendix A).

In the Gyrencephala we look in vain for those marks of affinity to the oviparous vertebrate animals which have been instanced in the preceding subclasses; although, it is true, that when we proceed to consider the subdivisions of the Gyren

1 Macleay, Linn. Trans. Vol. xvi. (1833); Gray, Dr. J. E., Mammalia in the British Museum, nmo, 1843, p. xii. 3 Cuvier, Rigne Animal, 1829, p. 110.

3 De Blainville, Ostgographie, 4to, Fasc. 1. p. 47 (1839).

4 Linnaeus, Systema Naturm, Ed. 12, Tom. 1. p. 26.

"Prof. Gervais, Zoologk et PaUontdlogie Francois, 4to, 1852, p. 194.

Cephala, we seem at first to descend in the scale by finding in that wave-brained subclass a group of animals, having the form of Fishes: but a high grade of mammalian organization is masked beneath this form.

The Gyrencephala are primarily subdivided, according to modifications of the locomotive organs, into three series, for which the Linnean terms may well be retained; viz. Mutilata, Ungulata and Unguiculata, the maimed, the hoofed, and the clawed series.

These limb-characters can only be rightly applied to the gyrencephalous subclass; they do not indicate natural groups, save in that section of the Mammalia. To associate the Lyencephala and Lissencephala with the unguiculate GyrenCephala into one great primary group, as in the Mammalian systems of Ray, Linnaeus and Cuvier, is a misapplication of a solitary character akin to that which would have founded a primary division on the discoid placenta or the diphyodont dentition. No one has proposed to associate the unguiculate Bird or Lizard with the unguiculate Ape; and it is but a little less violation of natural affinities to associate the Monotremes with the Quadrumanes in the same primary (unguiculate) division of the Mammalian class.

The three primary divisions of the Gyrencephala are of higher value than the ordinal divisions of the Lissencephala; just as those orders are of higher value than the representative families of the Lyencephala.

The Mutilata, or the maimed Mammals with folded brains, are so called because their hind limbs seem, as it were, to have been amputated; they possess only the pectoral pair of limbs, and these in the form of fins: the hind end of the trunk expands into a broad, horizontally flattened, caudal fin. They have large brains with many and deep convolutions, are naked, and have neither neck, scrotum, nor external ears.

The first order, called Cetacea, in this division are either edentulous or monophyodont, and the latter have teeth of one kind and usually of simple form. They are 'testiconda,' and

D2

have no 'vesiculae seminales.' The mammae are pudendal; the placenta is diffused; the external nostrils—single or double—are on the top of the head, and called spiracles or 'blow-holes.' They are marine, and, for the most part, range the unfathomable ocean; though with certain geographical limits as respects species. The 'right whale' of the northern hemisphere {Balcena mysticetus) is represented by a distinct species (Balcena australis) in the southern hemisphere: the high temperature of the waters at the equatorial zone bars the migration of either from one pole to the other. True Cetacea feed on fishes or marine animals.

The second order, called Sirenia, have teeth of different kinds, incisors which are preceded by milk-teeth, and molars with flattened or ridged crowns, adapted for vegetable food. The nostrils are two, situated at the upper part of the snout; the lips are beset with stiff bristles; the mammae are pectoral; they are 'testiconda,' but have 'vesiculae seminales.' The Sirenia exist near coasts or ascend large rivers; browsing on fuci, water plants, or the grass of the shore. There is much in the organization of this order that indicates its nearer affinity to members of the succeeding division, than to the cetaceous order.

The Dugongs (Halicore) inhabit the Red sea, the Malayan Archipelago, and the soundings of the Australian coasts: the Manatees (Manatus) frequent the shores of tropical America and Africa.

In the Ungulata the four limbs are present, but that portion of the toe which touches the ground is incased in a hoof, which blunts its sensibility and deprives the foot of prehensile power. With the limbs restricted to support and locomotion, the Ungulates have no clavicles; the two bones of the fore leg are fixed together in the position anatomists call 'prone;' as a general rule hoofed quadrupeds feed on vegetables.

A particular order, or suborder, of this group is indicated by fossil remains of certain South American genera, e. g. Toxodon and Nesodon, with long, curved, rootless teeth,

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