Page:First course in biology (IA firstcourseinbio00bailrich).pdf/435

 in a fold of the skin until hatched. Since it is pouched it could be classed with the pouched mammals (next order), but it is egg-laying. Suppose the two animals in this order did not nourish their young with milk after hatching, would they most resemble mammals, birds, or reptiles?

Write the name of this order. (See Table, p. 193.) Why do you place them in this order ? See p. 193.) The name of the order comes from two Greek words meaning "one opening," because the ducts from the bladder and egg glands unite with the large intestine and form a cloaca. What other classes of vertebrates are similar in this?

(Didelphys Virginianus).

Pouched Mammals.—These animals, like the last, are numerous in the Australian region, but are also found in South America, thus indicating that a bridge of land once connected the two regions. The opossum is the only species which has penetrated to North America (Fig. 361). Are its jaws slender or short? What kinship is thus suggested? As shown by its grinning, its lips are not well de-