7 8 REPTILES 



transversely, rather than longitudinally, on a cylindrical body. 

 As to the question why any of these lizards retain their longi- 

 tudinal striping, seeing that it is the natural course of evolution 

 that they should be lost, it has been suggested this may be due 

 to the circumstance that small-bodied reptiles living among sparse 

 tufts of grass have their colour-pattern less interfered with than 

 is the case with their larger relatives, or even that the incidence 

 of sunlight enhances the effect of their linear marking. It 

 appears indeed that these lizards cannot retain their stripes 

 unless they live in situations where such a type of coloration 

 tends to render them in harmony with their surroundings ; 

 any more than they keep their pale spots amid desert sur- 

 roundings. For it is a well-ascertained fact that when spots 

 occur in desert-dwelling animals they are dark on a light 

 ground, as is exemplified among reptiles by some of the sand- 

 skinks (Chalcides) and among mammals by leopards and 

 servals ; while among forest-dwellers light spots on a dark 

 ground are the fashion, as in the fallow-deer and the Indian 

 spotted deer. 



It may be taken, then, as probable that most of the uni- 

 formly coloured or dark-spotted reptiles inhabiting desert 

 districts, where their coloration is eminently protective, are 

 derived from white-striped or white-spotted ancestors dwel- 

 ling in situations where vegetation was more or less abundant. 

 And if this be true, it follows that chameleons and tree-snakes 

 which have acquired a green livery to harmonise with the 

 surrounding foliage have in all probability been evolved from 

 striped or spotted ancestors by an analogous modification. Be 

 this as it may, such green coloration in arboreal reptiles is evi- 

 dently a specialised protective adaptation, as is likewise the 

 colour-charge of chameleons and certain lizards. 



Exemplifying somewhat more fully the variations in colour 

 and pattern which occur in many reptiles, it may be shown to 

 what extent these are connected with sex and age in species 

 other than those already mentioned. 



As an example of sexual colour-difference may be cited the 

 terrestrial iguanas of the genus Sceloporus. In most of the 

 numerous representatives of the group the males are larger and 

 more brilliantly coloured than the females, from which they are 

 further distinguished by the presence of bright blue blotches 



