THE COLOURS OF DESERT ANIMALS 141 



when a specimen is examined closely it will often 

 be found that the general unicolorous effect is 

 produced by fine mottHng. In the Palsearctic 

 region we have many examples of this ; among the 

 birds the Egyptian Nightjar (Caprimulgus cBgyptius), 

 many Sandgrouse (Fig. 34), especially females, Hey's 

 and See-See Partridges (Ammoperdix) ; among the 

 mammals several foxes and gerbik, in which a 

 general sandy tone is produced by the presence of 

 black hairs or black-banded hairs among the pale 

 hairs ; many moths, especially Geometridse, in 

 which a unicolorous appearance is produced by fine 

 and inconspicuous banding or mottling ; in fact, 

 fine vermiculation, producing a general impression 

 of " self -colour," is common. 



In many desert mammals the under-surf ace is very 

 pale or quite white. It is a fact that desert species 

 and sub-species differ from their near relatives from 

 other environments just as much in their pale 

 ventral surface as in their buff or sandy backs. 

 Moreover, the pale ventral area is often more 

 enlarged up the flanks of a desert mammal than it 

 is in its relatives from other environments. This 

 paleness of parts of the animal which cannot normally 

 be seen extends even to the sole of the feet : Sumner 

 states that "the soles of the feet of desert deer-mice 

 are nearly or quite lacking in pigment, while those 

 of mice from the more humid coastal regions vary 

 from purplish to nearly black." 



This type of coloration is found in all groups of 

 animals which inhabit deserts ; in spiders and 

 centipedes and wood-lice; in moths, bugs, beetles. 



