MAMMALIA 291 



out at night to hunt for insects, berries, nuts, small birds, 

 mammals, eggs, etc. Two or three litters of four to six are 

 produced annually. The young remain with the mother 

 for a couple of months; at first in the pouch, then clinging 

 to her back. 



Order 3. Edentata. As the name of this order indi- 

 cates, the animals included are without teeth. The 

 sloths, armadillos, and the American ant eaters are com- 

 mon representatives. The only species entering the United 

 States is the nine-banded armadillo which occurs along the 

 Mexican border. This interesting animal bears four young 

 in each litter which are always of the same sex and result 

 from the fragmentation of a single embryo. Such multipli- 

 cation of the individuals from a single fertilized egg is 

 known as polyembryony. 



Order 4. Insectivora. The insectivores are all small 

 in size and live for the most part ^n or in the ground. The 

 moles and shrews are common representatives in North 

 America. The moles (Family Talpidce) are stout, with 

 powerful forefeet suited for digging, rudimentary eyes, 

 and no external ears. The common mole, Scalops aquations. 

 burrows just below the surface of the soil and, though it 

 sometimes disfigures lawns, does considerable good by 

 destroying insects. The shrews are tiny, shy, mouse- 

 like creatures with pointed heads. Some species are among 

 the smallest of mammals. Their food consists of insects, 

 snails, worms, and other suitable objects. 



Order 5. Chiroptera. The bats belong here. The fly- 

 ing squirrels, and a few other hairy animals are able to sail 

 snort distances, but the bats are the only mammals which 

 really fly. The digits on the fore limbs are spread out to 

 support the thin wing membranes, the breast bone has a 

 keel for the attachment of wing muscles, and there are 

 other adaptations for aerial locomotion. Bats have re- 

 markable ability to avoid obstacles while on the wing. An 

 individual in which the eyes have been destroyed is able 

 to fly about in a room crossed by a number of strings with- 



