COLOUR VARIATION IN LIZARDS 119 



while the species of Sceloporus possess brilliant colours, 

 these are generally on the inferior surfaces and are 

 therefore concealed. The throat and sides of the belly 

 are usually of some shade of blue (sometimes purple), 

 while the dorsal regions are, in the majority of species, 

 different shades of brown. When the animal raises 

 the head, as it habitually does, the brilliant colours of 

 the throat are visible, but those of the sides are much 

 less apparent. All these colours are most conspicuous 

 in the males, and in many species they are absent from 

 the females. They are to be regarded as secondary 

 sexual characters. In the species S. undulatus the 

 males are cross-barred, while the females are banded, 

 the species being found all over the continent south of 

 the Canadian district. In the species >S'. dugesii, the 

 females resemble the males in the colour of the upper 

 surface, but have the under parts yellow. In still 

 another species of this genus (S. joyrrhocephaliis) a 

 marked distinction in colour is to be observed in the 

 two sexes. The males are greenish brown with a 

 broad black band extending from the shoulder to the 

 groin, the sides being bluish. The females, on the 

 other hand, have the head brown above, the lateral 

 stripe is obsolete, and the blue marks on the sides are 

 replaced by brown. 



In several other species of the same genus we find 

 a similar sex variation, the males exhibiting a blue 

 colour on the chin and sides which is wanting in the 

 females. In some other species the variations are 



