other classes, birds, reptiles, and fishes together, makes up the back-boned or vertebrate primary division of the whole animal kingdom,
What, then, is the relation of the kangaroo's order—the Marsupialia—to the other orders of the class Mammalia?
Now, these orders are:
1. The order which contains man and apes.
2. That of the bats.
3. That of the mole, shrew, hedgehog, and their allies—all insectivorous.
4. That of the dog, cat, weasel, and bear—all carnivorous.
5. That of the gnawing animals, such as the rat, squirrel, jerboa, and guinea-pig—all with cutting-teeth 2/2, with permanent pulps. They are called Rodents.
6. The order containing the sloths.
7. That of the grazing, hoofed quadrupeds—deer, antelopes, and their allies.
Besides three orders of aquatic beasts (seals, whales, and the manatee order), with which we need not be now further concerned.
Fig. 18.—The Yapock (Chironectes).
Now, in the first place, very noticeable is the much greater diversity of structure found in the kangaroo's order than in any other order of mammals. While each of the latter is of one predominate type of structure and habit, we have found in the marsupials the greatest diversity in both.
Some marsupials are, we have seen, arboreal, some are burrowing, some flit through the air, while others range over and graze upon grassy plains. Some feed on vegetable food only, others are as exclu-
