120 BRITISH LIZARDS 



still more striking, and Professor Cope thinks that 

 S. variabilis was probably so named on account of the 

 wide difference between the colouring of the males and 

 the females. 



Taking next another family of lizards, the Scincidae, 

 it is found that similar variations obtain in them. In 

 some members the differences are so marked that they 

 have been supposed to represent distinct species, but 

 careful examination shows them to be attributable to 

 age and sex. In these particular species (Scincus 

 erythrocephalus, qicinquelineatus, and fasciatus) Professor 

 Cope says that it is probable, or even almost certain, 

 that the females retain their stripes and other mark- 

 ings longer than the males, and have a much less 

 tendency, if they exhibit it at all, to reddening and 

 wideningr of the head. It is almost certain that 

 females never entirely lose their stripes. All those of 

 the largest size, with narrow head and distinct stripes, 

 are females ; all those of the same or even less size, 

 with very broad red head and obscure markings, are 

 males. Similar variations are found to characterise 

 other species besides those named. 



Examples such as those quoted might be multi- 

 plied almost indefinitely, but enough has been said to 

 show that, from the point of view of sex, we have 

 one powerful factor operating to produce colour 

 variation. 



The field naturalist will doubtless call to mind the 

 fact that sexual colour variation is common in other 



