MAMMALS 



197 



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 



FlG. 361. OPOSSUM (Didelphys Virginianus}. 



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 ? 



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 sug- 

 gested ? As shown by its grinning, its lips are not well de- 



