The last section of the Opossums contains the Water Opossum.
THE YAPOCK.[127]
This animal has a perfect pouch, and has large hind feet, the toes of which are united by a web. The fore feet are moderate-sized, and the pisiform bone is unusually long. Its habits are aquatic. The Yapock has large naked ears, and a long, almost naked, tail, and is altogether rather larger than the common Rat. Its method of life is very much the same as that of the Otter. It is a good diver, and feeds upon crustaceous and other aquatic animals. It is a native of Guiana and Brazil.
The Marsupial animals assume the general shape and habits of many orders of Mammalia which have no marsupium, and which live in the other great natural history provinces. Thus there are Marsupial animals like Dogs, Rats, Squirrels, Flying Squirrels, Deer, &c. They have, therefore, many methods of life as a group, and, as might be expected, the brain and nervous system present many differences in them. In all, the front lobes of the brain which deal with the sense of smell are very large, and in some, such as in the Carnivorous Marsupials, they are exposed, and not covered by the main mass of the brain. In the Kangaroos, however, these olfactory lobes are hidden more or less. These last also have well-marked convolutions on the brain which are nearly wanting in those first mentioned.
The Marsupial animals just considered have been classified to a certain extent during their descriptions, but it is necessary to recapitulate. They are arranged in groups of genera or species, or into families. They are as follows:—
ORDER MARSUPIALIA.—SUB-ORDER MARSUPIATA.
Family | MACROPODIDÆ |  | Genus | Macropus |
| Kangaroos.[128] |
„ | Dendrolagus |
| Tree Kangaroos. | |||
„ | Hypsiprymnus |
| Potoroos. | |||
„ | Hypsiprymnodon |
| The Hypsiprymnodon. | |||
„ | PHASCOLOMYIDÆ |
| „ | Phascolomys |
| The Wombat. |
„ | PHALANGISTIDÆ |  | „ | Phascolarctus |
| The Koala. |
„ | Phalangista |  | The Cuscus. | |||
Dormouse Phalanger. | ||||||
Phalangers. | ||||||
„ | Petaurus |
| Flying Phalangers. | |||
„ | Tarsipes |
| Tarsipes. | |||
„ | PERAMELIDÆ |  | „ | Perameles |
| Bandicoots. |
„ | Chœropus |
| Chœropus. | |||
„ | DASYURIDÆ | | „ | Myrmecobius |
| Ant-eaters. |
„ | Phascogale |
| Phascogale. | |||
„ | Dasyurus |
| Dasyures. | |||
„ | Thylacinus |
| Dog-headed Thylacinus. | |||
„ | DIDELPHIDÆ | | „ | Didelphys |
| Opossum. |
„ | Chironectes |
| Yapock. |
The Macropodidæ, Phalangistidæ, Peramelidæ, and Dasyuridæ are found living somewhere or other in the Australian distributional province, which includes the mainland, Tasmania to the south, and the Molucca and Arru Islands to the north, bounded by the Straits of Lombok, and Celebes, New Guinea, New Ireland, Timor, Amboyna, Banda, and Waigeoe. Each family is not represented fully, however, in all the remarkably separated divisions of the province. Thus the genera Macropus and Dendrolagus of the first family, Petaurus and Phalangista of the third, Perameles of the fourth, and Phascogale of the Dasyuridæ have been found in New Guinea; but in other islands, such as Celebes, and in those from Lombok to Timor, the genus Cuscus alone is represented. In the Moluccas, Cuscus and the genus Petaurus are found. In Van Diemen’s Land about one-half of the species are peculiar to the island, and the remainder are found also on the eastern districts of the mainland. It has Kangaroos, Potoroos, Wombats, Phalangers, Bandicoots, and three out of the four genera of Dasyuridæ. Western Australia, which is such a remarkable botanical province, and is so separated by desert and sand from the east, has numerous Kangaroos, Potoroos, Phalangers, Bandicoots, Phascogales, Dasyures; and, in common with South Australia, a Chœropus, whilst the genus Tarsipes is peculiar to it. The Wombat is found in Van Diemen’s Land and some of the islands in Bass Strait. It is found in the south and east of the mainland of Australia, but not to the west and north. Mr. Waterhouse notices that the Marsupials of the eastern districts are for the most part distinct from those of the opposite side of the continent, there being, when his great work, which has been so constantly referred to in this description, was written, but eight species out of upwards of sixty inhabiting the two provinces. South Australia is the habitat of more common species than elsewhere. The northern part of Australia has more species peculiar to it than the other divisions, and some of its Dasyuridæ especially, and species of Cuscus also, are found in the Arru and other islands to the north. The metropolis of the sub-genus Cuscus is in the Moluccas, where two species are widely distributed, or one is restricted to certain islands.
The other divisions of the genus are represented by the Vulpine Phalanger, an animal with long loose fur, which inhabits New South Wales, Western Australia, and North Australia; by Cook’s Phalanger, of New South Wales and Van Diemen’s Land. The genus Perameles, the Bandicoots, has species in Van Diemen’s Land, Australia, New Guinea, and in the Arru Islands, and the genus Petaurus has a corresponding distribution. The Didelphidæ are found in the United States, California, Mexico, Peru, Guiana, Brazil, Paraguay, Banda Oriental, and Chili; and Brazil is the country where they abound the most in species and individuals, the number diminishing to the north and south.
The Marsupials have a great ancestry, and some of them lived when the continents and oceans of the earth were in very different relative positions to those they now occupy. Indeed, it is most probable that the fossil remains of the most ancient mammal belong to this order. There is a small double-fanged molar tooth of a mammal which was found by Plieninger, in 1847, contained in a jumble of shells and of the remains of reptiles and fishes in strata beneath the Lias formation of Diegerloch, near Stuttgart. It and another which was discovered close by, by the same professor, belonged to animals which were dead when this topmost stratum of the Trias, immediately beneath the Lias, was being formed. They are Triassic in age, therefore, and they somewhat resemble the back teeth of a fossil which was found subsequently in the Purbeck strata of England, and which evidently belonged to a Marsupial more or less resembling the existing Kangaroo-Rats or Potoroos, of the genus Hypsiprymnus. Later on, Professor W. Boyd Dawkins, F.R.S., discovered a small tooth belonging to the same extinct genus as that which included Plieninger’s fossil, namely, Microlestes; and its resemblance to one of Hypsiprymnus is even greater. Its position was high up in the Trias of Watchet in Somersetshire. Mr. Charles Moore, of Bath, had previously found many specimens of teeth of the same family in a fissure, down which they had been washed by the Triassic sea.