1. The MARSUPIATA include the Kangaroos and Opossums (fig. 59). They are characterised by the possession of a pouch at the lower part of the abdomen, into which the young enter as soon as born, for they are born in a very imperfect state, and when in the pouch they adhere to the teat of the mother, where they remain till more fully developed. In these animals the hind legs are greatly developed, and the fore legs but little. They progress by enormous leaps, resting on the hinder legs and tail, both of which are very strong. They belong exclusively to Australia, which appears to produce many forms having peculiarities not met with elsewhere, and among the lowest of their type; this and the next order appear somewhat to partake of the form of the Bird, the undeveloped state of the young in the Marsupiata, being an approach to the egg of the Oviparous animals. * * * * * [Illustration: FIG. 60.--PLATYPUS, OR DUCK-BILL (Ornithorynchus).] 2. The MONOTREMATA includes the Duckbill, called also "Platypus," and "Ornithorynchus paradoxus," (fig. 60), a most singular combination of the forms of the mammal and the bird. It has a mouth resembling the bill of a Duck, and several other peculiarities, which lead to the consideration of it as one of the connecting links between the forms of the Mammalia and Birds. * * * * * [Illustration: FIG. 61.--BEAVERS (Castor fiber).] 3. The RODENTIA comprise the Rat, Beaver, Rabbit, Hare, Mouse, &c. They live upon almost any kind of vegetable matter; the Rat and Mouse will eat anything they can get. Their incisor teeth are two in front of each jaw, and are chisel shaped and very sharp; they are so constructed that they shall be kept sharp by being used, which is effected by the hardest part or enamel being in front in a thin layer, so that it is not so easily worn away as the bony part. If these animals be fed on soft food, their teeth continue to grow nevertheless, and protrude from their mouths in a most singular way. The Beaver (fig. 61) is almost aquatic in its habits, it gnaws through the stems of trees, and uses them to dam up the water of the stream they inhabit, so as to secure a constant supply. They build houses or huts of wood, mud, and stones, which they unite in constructing. These houses have their entrances beneath the water, so that the Beavers dive to enter them; they have two divisions or rooms in them, and are sufficiently large to lodge several families. The Rat is too well-known to need much description. The brown or Norway Rat has only been an inhabitant of this country about forty years, the black Rat being before that time the usual house Rat, but it is now almost exterminated, specimens being very rare. There are several other species of Rats; the best known is the Water Rat, who burrows in brooks and ditches, and partly lives in the water. Of the Mouse there are also several species.