MAMMALS 



481 



numerous orders, which include the vast majority of mammalian 

 species. Though Marsupials appear to have diverged early from 

 the m.ain line of descent, and have since specialized in so many 

 directions that they give us but little idea of what the remote 

 ancestors of the Eutheria were like, there are good reasons for 

 thinking that these last are descended from pouched forms. At 



Fig. 999. — Three-toed Sloth {Bradypiis tridactylus) carrying her Young 



any rate, traces of a pouch have been found in some of the higher 

 Mammals, even in adults. 



The young of higher Mammals are always born in a more 

 perfect condition than those of Marsupials, but the amount of 

 parental care they require varies gready in different forms. 

 There are also marked differences as to the number of young 

 produced, and, broadly speaking, a corresponding variation in the 

 number of milk-glands and teats, the actual position of these 

 organs depending upon the species. Our purpose will be here 

 sufficiently served by a review of some of the more interesting 

 and important facts. 



