482 ANIMAL LIFE-HISTORIES 



Mammals Poor in Tep:th (Edentata). — The Sloths of 

 South America have a pair of mills;-glands situated on the 

 chest, and produce a single young one at each birth. This is 

 sufficiently well-developed to cling firmly by its curved claws 

 to its mother's back, on which it is carried about (fig. 999). 

 Similar facts have been determined in the case of the Great 

 Ant- Eater {^Mynnccophaga jubattx), native to the same part of 

 the world. 



In most of the Armadilloes, which are inhabitants of South 

 and Central America, the young are from two to four in number, 

 although in such species there are but two milk-glands, situated 

 as in Sloths. When born they are blind and helpless, as usually 

 in burrowing mammals, but after being suckled and tended for a 

 few weeks are able to take care of themselves. 



Gnawing Mammals (Rodentia). — The members of this large 

 and widely-distributed order differ greatly from one another as 

 regards the number of young, their condition at birth, and the 

 arrangements made for their welfare. 



Here again we find, as in Edentates, that helpless young 

 are associated with the existence of burrows or other shelters 

 in which the earliest part of life can be passed in comparative 

 security, while in the absence of such dwellings the condition at 

 birth is decidedly more advanced. This is well illustrated by 

 comparing the Rabbit [Leptis cunicitlus) and Hare (Z. timidus), 

 two closely allied species. The former is a typical burrowing 

 animal, and the doe excavates a special dwelling by way of 

 nursery for her blind and helpless young, which number from 

 five to eight as a rule. There is but one opening into this 

 nursery, in which respect it differs from the ordinary burrow, 

 and the mother lines the end of it with some of her own fur, 

 for the greater comfort of her offspring. Like the Duck-Bill 

 (see p. 478) she safeguards them in her absence by throwino- 

 up a rampart of earth to hinder weasels and other enemies 

 from approaching the nest. We have elsewhere had occasion 

 to note that extreme fecundity is an important means of pre- 

 venting ill-defended species from becoming extinct (see vol. ii, 

 p. 345), and the Rabbit is almost proverbial in this respect, 

 littering several times in the same year. The young in their 

 turn often become parents when they are only six months old. 

 In this country there are so many checks to increase that in a 



