ISO RODENTIA 



of America and the Middle Eocene of Europe, and possibly- 

 had its origin in the Northern Hemisphere (Osborn). 



Its members are now found naturally throughout the whole 

 world, excepting only New Zealand and Oceanic Islands, where, 

 however, many introductions have taken place of Oryctolagus, 

 Epimys, and Mus. 



Although sharply defined as regards structure, the order 

 includes a great variety of types, displaying very different habits 

 and existing under a great diversity of conditions. Some are 

 burrowers, climbers, swimmers, or jumpers ; others are cursorial, 

 sedentary, or, being provided with parachutes of skin, appear to 

 be in a fair way to attack the problems of flight. With the 

 exception of the actual oceans, there are few parts of the 

 world's surface where rodents have not secured a foothold, and 

 they exist in one form or another in almost all types of country ; 

 being found from the eternal snows of the lofty mountain 

 ranges to the swamps of the great rivers, and from the frozen 

 lands of the north polar basin to the vast burning sand deserts. 



By nature primarily herbivorous, they differ from the other 

 great order of herbivorous mammals, the Ungulata, in the fact 

 that they rarely attain to any considerable size. To this fact, 

 together with their extreme fertility and their general readiness 

 to adapt themselves to an omnivorous, to an insectivorous, or 

 even a carnivorous diet, they probably owe the secret of their 

 success as an order, but it should be noted that some species 

 are absolutely restricted to vegetarianism. 



All the British representatives give birth to several young 

 at a time, and, usually, to more than one litter in a season, 

 so that, under favourable conditions, their increase is rapid. 

 Except in the case of the hares, all British rodents are born in 

 an undeveloped and helpless state, and are at first well cared for 

 in a warm nest, placed often in an underground tunnel con- 

 structed by the mother, and frequently lined with wool or hair 

 plucked from her own belly. The cavies or guinea-pigs, only 

 known in Britain in captivity as domesticated varieties, 

 probably represent the extreme of mammalian precocity, since 

 they will eat cabbage within half an hour of their birth. All 

 grow with great rapidity, and breed as soon as, or before, they 

 are full grown. 



