WHAT EVOLUTION IS 49 



commonly characterized by the pres- 

 ence of a pouch on the abdomen. This 

 pouch, which contains the milk glands, 

 serves as a receptacle for the young 

 after their birth. Most persons have 

 seen in our zoological gardens the 

 female kangaroo with her offspring 

 and have noticed how the young, when 

 alarmed, run to the pouch, enter it, 

 and are carried oft' by the mother. 

 The marsupials, like the monotremes, 

 are very primitive mammals. Ex- 

 cepting the American opossums and 

 one other pouched mammal in South 

 America, all marsupials are limited 

 to the Australian region. No mar- 

 supial occurs in Eur-Asia or in Africa. 

 Thus the marsupials, like the mono- 

 tremes, illustrate a common peculiar- 

 ity of animal distribution, namely, that 

 many large and important groups are 

 limited to well circumscribed and often 

 relativelv small areas of the earth. 



