THE COLOURS OF DESERT ANIMALS 161 



and their counterparts in the American deserts and 

 Australia (pages 74-80), are strictly nocturnal, and 

 one may weU question whether their beautiful sandy 

 tints have much protective value. By moonlight, to 

 the human eye they appear nearly white and rather 

 conspicuous. Most of them, it should be remem- 

 bered, are very strictly nocturnal : Jerboas {Jaculus) 

 and Dwarf Gerbils (Dipodillus) may occasionally be 

 seen when the dayhght has nearly gone, but many 

 other forms never come above ground until night 

 has definitely faUen. In the summer and autumn 

 of 1919 I was camped for four months outside 

 Qazvin in the semi-desert of North- West Persia. All 

 around us were the burrows of the Gerbils {Meriones 

 blackleri lycaon and M, erythrurus), but never once 

 did I see either of these animals by dayhght, either 

 in the dawn or after sunset : every night I was in 

 the desert between 8 and 9 p.m., and I always saw 

 Gerbils crossing the beam of my lamp. Without 

 a lamp I found it impossible to see them except when 

 the moon was bright, and then they appeared white 

 and conspicuous. Devout supporters of the theory 

 of protective coloration claim that animals, both 

 predators and prey, are rendered iaconspicuous even 

 at night, perhaps by moonlight, by their pale colour ; 

 the claim seems to me to be more ingenious than 

 probable, but I cannot disprove it. The whole 

 question of visibiHty at night, with or without moon, 

 is beset with difficulties, because we have only the 

 vaguest knowledge of the extent to which habitually 

 nocturnal animals rely upon their eyes in obtaining 

 their food. 



