The Elegant Opossum (_Didelphys elegans_), of Chili, is still smaller than the last, and frequents the thickets growing on the rocky hills near Valparaiso. They are numerous, or were so when Mr. Darwin observed them, and are easily caught in traps baited with cheese or meat. The tail appeared to be rarely, if at all, used as a prehensile organ; yet they could run up trees with some degree of facility. It is an interesting fact that some of the smallest Opossums prey upon Lizards and Snakes as large, and even heavier, than themselves. 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. { Genus Macropus Kangaroos.[128] Family MACROPODIDÆ { „ Dendrolagus Tree Kangaroos. { „ Hypsiprymnus Potoroos. { „ Hypsiprymnodon The Hypsiprymnodon. „ PHASCOLOMYIDÆ „ Phascolomys The Wombat. { „ Phascolarctus The Koala. { { The Cuscus. „ PHALANGISTIDÆ { „ Phalangista { Dormouse Phalanger. { { Phalangers. { „ Petaurus Flying Phalangers. { „ Tarsipes Tarsipes.