24 



The iris is often tinged with various colours, yellow and 

 green being frequent ; in Lycodon, it is so black that the 

 shape of the pupil is most difficult to see. 



In the Typhlopidce, the eye is hardly visible at all, being 

 very minute and covered by the lateral head-shields. 



The tongue is probably a tactile organ; and in some 

 snakes there is a prolongation of the snout apparently acting 

 as an organ of feeling (Passerita, Herpeton). 



CHAPTER VI.— The Integuments. 



The skin of snakes is a smooth soft tissue, generally 

 white, sometimes coloured, giving off numerous scales 

 {squamce) which are generally contiguous and often im- 

 bricate or overlapping one another to some extent. In 

 snakes which can expand the neck this skin is seen dotted 

 over with separate scales at some distance from one another. 

 In most viperine snakes the scales are dull, stiff and suffi- 

 ciently imbricate to make a rustling noise if the skin is 

 crumpled; in the burrowing snakes, a cuirass of smooth 

 polished scales leaves hardly any interval visible ; in the 

 sea-snakes, the scales become tuberculated. In most snakes 

 the skin is shown between the interstices of the scales 

 during the respiratory movements. 



On the lower parts of the body the scales become broad 

 (in the higher types), expanding into ventral shields (aeutoe) 

 and, beyond the anus, into subcaudal shields (scutelloB). 



On the head a few snakes, Erycidce, AcroehordidcB, 

 Viperidce and others, have scales like on the rest of the 

 upper parts, but the majority have the head covered with 

 plates (non-imbricate shields) varying but little from a 

 normal pattern, and, when varying, doing so with sufficient 

 regularity to form characteristic distinctions. 



