RODENTIA. 621 



The three first are also common in North America. Closely 

 allied to the true Rats are the Hamsters (Cricetus, fig. 265), 

 and the Voles (Arvicola); the latter represented by many species 

 in both Europe and America. 



A less familiar example of this family. is the Lemming (Myodes 

 lemmus). This curious little Rodent is found inhabiting the 

 mountainous regions of Norway and Sweden. It is chiefly re- 

 markable for migrating at certain periods, generally towards the 

 approach of winter, in immense multitudes and in a straight 

 line, apparently in obedience to some blind mechanical im- 

 pulse. In these journeys the Lemmings march in parallel 

 columns, and nothing will induce them to deviate from the 

 straight line of march. 



Fam. 6. Dipodidcz. The sixth family of the Rodents, which 

 is sufficiently important to need notice, is that of the Dipodid<z 



Fig. 265. Common Hamster (Cricetus -vulgaris). 



or Jerboas, mainly characterised by the disproportionate length 

 of the hind-limbs as compared with the fore-limbs. The tail 

 also is long and hairy, and there are complete clavicles. The 

 Jerboas live in troops, and owing to the great length of the 

 hind-legs, they can leap with great activity and to great dis- 

 tances. They are all of small size, and inhabit Russia, North 

 Africa, and North America. The best-known members of this 

 family are the common Jerboa (Dipus sgypticus\ which lives 

 in societies and constructs burrows ; the Jumping Hare (Pedetes 

 Capensis) of South Africa, and the Jumping Mouse (Meriones 

 Huasonicus) of North America. Here also may be placed the 

 Gerbilles (Gerbillus] of the Old World. 



Fam. 7. Myoxidce. The members of this family are com- 

 monly known as Dormice, and they are often included in the 

 following family of the Squirrels and Marmots. They only 



