146 ANIMAL LIFE IN DESERTS 



that mice, wood-rats, and other small mammals 

 which inhabit areas of blackish lava as well as other 

 parts of the desert are often darker on the lava than 

 elsewhere. It is fair to mention that this has 

 recently been controverted by Sumner, who has 

 shown that in some cases, at any rate, the darker 

 colour may be due not to living on lava, but to 

 differences in other environmental factors, such as 

 rainfall. In the case of one animal (the deer-mouse, 

 Peromyscus crinitus), he was able to show that if 

 long series of this mouse living on black lava and on 

 " pale grey, buff, and pinkish " rock were compared, 

 no difference in tone could be detected either by eye 

 or by photometer. 



Other cases occur in which the resemblance of 

 animals which are, broadly speaking, " desert- 

 coloured " to their particular type of desert, is by 

 no means very close. I remember obtaining four 

 species of mammalia at Qazvin in North- West 

 Persia : the local fox was greyish sandy with a 

 reddish saddle ; the hare was pinkish buff ; the 

 gerbil {Meriones hlachUri lycaon) was yellowish buff ; 

 and the dwarf hamster (Cricetulus) pure pale grey 

 without any trace of yellow or buff colour. All 

 these occurred on the same ground, and any one of 

 them was a good example of " desert coloration," 

 but none of them resembled the exact shade of the 

 soil at all closely. 



In Mesopotamia downy young of the Sandgrouse 

 Pterocles senegallus and P. exustus have been obtained 

 in the same type of pebble and clay desert, but they 

 differ widely both in pattern and colour. 



