118 BRITISH LIZARDS 



colour variation, since the variations in the climate in 

 such a limited area are not sufficient. The same 

 remark applies to some of the other factors, and, as 

 a matter of fact, the list of those which are really 

 responsible is found to be a comparatively short one. 

 Fortunately, the problem has been very fully worked 

 out in some countries which possess far more species 

 of lizards than does Great Britain, and we may safely 

 assume that the same factors produce colour variation 

 in one family of lizards as in another. The colours 

 themselves, of course, may be entirely different, and 

 do not affect the question. We may therefore briefly 

 note what has been observed in American lizards, 

 where the number of species allows of more accurate 

 conclusions being drawn than could be done from a 

 restricted collection of our indigenous species. 



The following examples of colour variation are 

 quoted from Professor Cope's great work on The 

 Crocodiles, Lizards, and Snakes of North America, a 

 work which abounds in references to this question as 

 affecting both snakes and lizards. 



The genus Scelojyorus consists of terrestrial, and 

 therefore depressed Iguanid?e. Its especial habitat is 

 Mexico and Central America, the south-western parts 

 of the United States and California. The species are 

 rather numerous, and in all the species the males are 

 generally more brilliantly coloured and larger than the 

 females ; moreover, the males have a blue blotch on 

 the under surface and on the sides of the belly. But 



