376 SYSTEMATIC ZOOLOGY. 



gophers and pocket-rats, which burrow through the soil in 

 the western states; the familiar muskrat, and the less 

 familiar jumping mice, which resemble the kangaroos in 

 their locomotion. 



Another series of rodents contains the beaver, common 

 to the Old World and the New, which furnishes furs of 

 great value. These live most of their lives in the water, 

 building dams so that they may always have plenty of 

 it; while their near relatives, the woodchucks, and their 

 western representatives, the prairie-dogs, have no such de- 

 pendence upon water. Highest of all the rodents are 

 the ground-squirrels, the true squirrels, and the flying 

 squirrels. 



ORDER IV. INSECTIVORA (Insect-eaters). 



These are small mammals, in which all four types of 

 teeth are developed, and which are marked off from all 

 other orders by characters rather difficult of expression. 

 As their name implies, they feed largely upon insects, but 

 worms and other small animals are not despised. The 

 species are largely tropical, but the shrews and moles are 

 found in cooler climates. Most of the species are noctur- 

 nal and burrowing animals, consequently their eyes are 

 small and degenerate while their fore legs are adapted for 

 digging. 



ORDER V. CHIROPTERA (Bats). 



The bats are the only mammals which truly fly. In the 

 case of the flying squirrel and the rest, the animals glide 

 through the air on the plane formed by the lower surface 

 of the body, the tail, and the broad membrane which 

 extends between the limbs; and they can never ascend to 

 the level from which the flight started. With the bats, 



