3<S6 SYSTEMATIC ZOOLOGY 



cavities in rocks and trees in Africa, Arabia, and Syria, and is 

 believed to be the " cony " referred to in the Old Testament. 



Order 5. Rodentia 



The Rodentia (Lat. rodere, to gnaw), or gnawing mammals, 

 constitute a sharply defined group of small animals, which may 

 readily be distinguished by the incisor teeth ; these are long, 

 never more than two in the lower jaw, and in most cases only 

 two in the upper jaw. Although they are continually being 

 worn away at their free ends, the length remains constant, since 

 they grow continually at the root. Canine teeth are always 

 absent and, except in the hares and their immediate relations, the 

 premolars are likewise usually lacking ; thus there is a long tooth- 

 less interval, or diastema, between the incisors and the molars. 

 The food consists chiefly of seeds, fruits, roots, and stalks of 

 plants. The toes are provided with claws, and there are usually 

 five digits. The body is covered with soft fur in most of the 

 Rodentia, sometimes with stiff contour hairs as well ; in some 

 the hairs are scanty and bristlelike, and in others some of the 

 hairs may be modified into stiff spines or "quills." The testes 

 may lie in the abdomen or in a scrotum, and the teats vary from 

 two to ten ; the uterus is two-horned. 



As a rule the rodents are very prolific, producing several young 

 at a birth, and some species have from four to six litters a year. 

 Many build nests or burrows, and some lay up food in large 

 quantities for the winter months ; the latter generally have 

 cheek pouches in which the food may be carried to the nest. 

 Some rodents pass into an interrupted or a continuous winter 

 sleep, and others migrate in large numbers. There are numer- 

 ous fossils, some larger than any existing species. The order is 

 a large one, containing some nine hundred living species, which 

 may be grouped under four types represented by the squirrel, 

 the rat, the porcupine, and the rabbit. Thus we have four sub- 

 orders, under which we may best consider some of the more 

 important representatives. 



Suborder 1. Sciuromorpha 



The Sciuromorpha (Lat. sciurus, squirrel, and Gr. nop<pij, 

 form), or squirrel-like rodents, include some animals which 



