Changing Colour in Reptiles. 401 



change of colour that takes place in many lizards in the male 

 sex for the purpose of exercising an attraction over the females 

 at the pairing-season. The occurrence in the Lacertilia of a 

 power of changing colour in this direction is already in itself 

 a proof of the higher development of these animals as com- 

 pared with the snakes. Among the Ophidia we find little 

 divergence in the colour of the sexes and in the shape of the 

 body, indeed, apart from the length of the tail, scarcely any 

 difference at all. In the Lacertilia, on the contrary, the 

 difference between the sexes is frequently very strongly 

 marked ; I need only allude to the throat-sacs and crests. 



Well-known examples of the power of changing colour 

 which have probably arisen through sexual selection are 

 afforded by Agama inermis and ISceloporus undulatus. In 

 respect of the Darwinian theory these species are so much the 

 more interesting in that in them, simultaneously witli the 

 colour-changing faculty, quite peculiar habitual movements 

 have been developed. In order to remain invisible to the 

 eyes of their enemies — probably in the majority of cases 

 birds — when looked at from above it was necessary that the 

 change of colour should be confined to the throat and sides of 

 the belly. Lest, however, the beauty of their wooers should 

 escape the glances of the females, the former had to adopt 

 their peculiar nodding and bobbing up and down movements, 

 in order to render their chief adornment visible. The splendid 

 blue coloration of the throat and sides of the belly in Agama 

 inermis and Sceloporus undulatas is, moreover, not so much 

 spontaneous as dependent on the temperature. In the case of 

 Agama the blue colour disappears entirely in cool weather or 

 persists upon the throat only in the form of a blackish 

 marbling; in Sceloporus during cold the blue passes into 

 black, but generally allows a blue metallic sheen to be 

 detected. I am not aware whether Chamceleon arrays itself 

 in especially vivid colours at the breeding-season. I am 

 inclined to think, however, that the species employs its pecu- 

 liarly well-developed power of changing colour also as a 

 means of attracting the female sex ; and I do so because the 

 extremely quarrelsome males at once assume vivid colours on 

 catching sight of one another. 



Our knowledge of colour-change in Lacertilia is probably 

 exceedingly small in comparison with that which has still to 

 be discovered. Most of the species which change colour are 

 small and delicate animals that never reach Europe alive at 

 all. That the large powerful species are less in need of a 

 protection derived from colour is evident ; they will therefore, 

 in the majority of cases, have fixed colours. Anyone who 

 Ann. & Mag. N. Hist. Ser. 7. Vol. iii. 29 



