76 



ANIMAL LIFE IN DESERTS 



members are modified in the same direction as the 

 Jerboa, though not all to the same extent. In 

 AUactaga, for instance, five toes are present on the 

 hind-foot, though two are vestigial ; in Scarturus 

 the first digit is absent, and the fifth vestigial ; in 

 Dipus and Jaculus only three toes are present, 

 and the two which are lacking are not represented 

 by any vestige externally (Fig. 32). 



Fig. 32. — UNDER'SURrACE or Right Foot of Allactaga indica {A), Scar- 

 turus tetradactyla {B), and Jaculus jaculus (C). 

 {After R. I. Pocock.) 



These genera are characteristic of the Great 

 Palaearctic Desert and of the steppes on its fringe ; 

 the closely related Zapus is American, and is inter- 

 esting because it is intermediate in habit and 

 anatomy between the ordinary running quadruped 

 mice and the biped jumping Jerboas. In another 



