COLORATION 37 



districts the desert individuals are paler, without or 

 with less distinct markings, as compared to their 

 fellows among other surroundings. In addition to 

 their markings, some snakes are adorned with a 

 metallic iridescent gloss, due to a fine striation of 

 the scales. 



The iris is often metallic, gold, bronze, or copper- 

 red, and the black streaks of the head sometimes 

 extend over it. 



Although, unlike many lizards, snakes are unable 

 to rapidly alter their colours, some produce a 

 semblance of this phenomenon when inflating their 

 neck or body ; this is due to the presence of dark 

 and light markings or of a bright pigment in the 

 interstitial skin, which is not seen when the scales 

 overlap. Thus, in the Indian Tree-snake Dryophis 

 mycterizans the skin between the green or brown 

 scales in the anterior part of the body is black 

 and white, producing a striped pattern when the 

 neck is inflated; the skin of the same region is 

 bright vermilion in the Malay Tropidonotus sub- 

 mini atus ; many more examples could be quoted. 

 The spectacle marking on the hood of the Indian 

 Cobra involves the scales as well as the interstitial 

 skin. 



As a rule there are no sexual differences in colour. 

 Yet these are so marked in our Common Adder that 

 the sex of a specimen can nearly always be recog- 

 nized by the coloration. This is, however, the 



