474 



RODENTIA 



Ears and eyes large ; muzzle naked at the extremity. Fur soft, in 

 some cases intermingled with spines. Pollex with a short nail in 

 place of a claw. No cheek -pouches. Tail long, nearly naked, 

 with rings of overlapping scales. Vertebrae : C 7, D 1 3, L 6, S 4, 

 C 26-32. 



This genus is the largest in the whole mammalian class, com- 

 prising not less than 130 species, ranging over the whole of 

 the Old World, with the noteworthy exception of Madagascar. 

 On the whole, the species are more numerous in tropical than 

 in temperate regions, and very few occur in cold countries. 

 Many of the species living in warm climates have flattened spines 

 mingled with the fur ; these spines being shed in winter, when a 

 warmer covering is necessary, and replaced by hair. Five species 

 occur in England, which are briefly noticed below ; and it may be 

 observed that none of the species are much larger than M. decumanus 

 or smaller than M. minutus. As a rule the habits of the species 

 are similar to those of the English forms, but a few are arboreal, 

 while others again, like the one represented in Fig. 211, are 

 aquatic. The earliest known representatives of the genus (exclud- 

 ing Acanthomys gaudryi of the Lower Pliocene Pikermi beds of Attica) 

 occur in the Pleistocene of Europe. 



The Brown or Norway Rat (M. decumanus) is a heavily built 

 A animal, growing to 8 or 9 



inches in length, with a 

 bluff rounded head, small 

 ears (Fig. 212, A}, and a 

 comparatively short tail, 

 which is always shorter 

 than the head and body 

 combined, and generally 

 not longer than the body 

 alone. The colour is a 

 uniform grayish - brown 

 above and white below, 

 the ears, feet, and tail being 

 flesh coloured. Black 

 varieties, which are often 

 mistaken for true Black 

 Rats, are by no means rare, 

 but the differences in size 

 and proportions form a 

 ready means of distinguish- 

 ing the two. The Brown 



Rat is believed to be a native of Western China, where a race 

 (M. humiliatus) has been discovered so like it as to be practically 

 indistinguishable. Both this, and the next species agree in their 



Fio. 212. A, Head of Brown Rat (M. decumanus). 

 B, Head of Black Rat (Mus rattus). 



