80 



ANIMAL LIFE IN DESERTS 



course the full number of digits in either the fore- 

 or the hind-foot. " 4 and 1 " or " 3 and 2 " indi- 

 cate that 4 (or 3) normal digits are present and 1 

 (or 2) which is reduced in size. Toes are only 

 shown as " vestigial " when they are minute, and 

 probably not used : thus Perognathus has five 

 digits on the hand, of which one is small : on the 

 foot it has either three normal toes and two small 

 ones, or else (in another species) three normal toes, 

 one small and one vestigial. A zero in the " ves- 

 tigial " column indicates that no external trace of 

 digit can be found. In Dipus and Jaculus the 

 reduction has gone so far that two toes are not 

 even represented by a vestige. 



Genus. 



Dipus, Jaculus . 



Scarturus 



AUactaga 



Gerbillus 



Zapus 



Perognathus, either 



or 

 Conilurus 

 Notomys ... 

 Antechinomys 

 Phascogale hillieri 

 Pedetes . 



Number of Toes. 



Fore -foot. 



4 & 



Hind-foot. 



Functional. Vestigial, 



