CLASSIFICATION 



657 



Family I. Ornithorhynchidae. (The duck-bill of Australia.) 



There is no corpus callosum (Fig. 471), and the brain is the most 

 primitive of all living mammals. 



The eggs, two or three in number, and covered with a hard shell, 

 are reptilian in form and are laid in a nest of grasses. The heat of the 

 mother's body hatches them. 



Family II. Echidnidae. 



These are the Australian Ant-Eaters. There is a temporary mar- 

 supial pouch. Only one egg, about half an inch long, is laid at a time 

 and placed in the marsupial pouch by the mouth of the mother. Here 

 the young hatch in a very immature condition, the mother being obliged 

 to remove the egg-shell after the young has come forth. The young 

 Echidna obtains its food by licking the milk-like secretion exuding from 

 the hairs in the pouch. 



Sub-Class II. Eutheria. 



These are the viviparous mammals which are divided into two divi- 

 sions. 



Division I. Didelphia (Metatheria) (Fig. 384). 

 These are the marsupials. 



Order I.. Marsupialia. Mammals having a pouch to carry their 

 young which are born in a rather immature condition. There is usually 



Didftphyt dorsiyeru (South American opossum) 



Petrogale xanthopus (rock wallaby 

 with young in pouch) 



Fig. 384. Didelphia. 



(A, after Vogt Specht ; B, after Nicholson.) 



