102 INTRODUCTION 



open mouth, but very seldom bites; its principal 

 defensive action when caught consists in voiding a 

 most repulsive secretion from its anal glands, which 

 it evidently controls, as it ceases doing so when 

 accustomed to being handled. The same snake also 

 produces, during the spring, an oily exudation from 

 the skin which has the same repulsive smell. 

 Mr. H. N. Ridley has observed a Malay snake 

 allied to Tropidonotus, Macropisthodon rhodomelas, to 

 exude drops of a white viscid liquid from the skin of 

 its neck, which is flattened out like that of a Cobra 

 when in an attitude of defence, and he noticed that 

 his dog, seizing the snake to worry it, foamed at the 

 mouth as if he had been biting a toad. 



The hissing is produced by the rapid expulsion of 

 air from the lungs through the trachea and the notch 

 at the end of the mouth, which is kept shut at the 

 time. Snakes provided with an epiglottis (see p. 79) 

 produce a much louder hissing. Other sounds are 

 produced by some snakes. Thus, the Indian and 

 African Vipers of the genera Echis and Cerastes make 

 a curious, prolonged, rustling noise, by rubbing the 

 folds of the sides of the body against one another. 

 This sound is produced by friction between the 

 serrated keels of the lateral scales, which are dis- 

 posed obliquely with their tips directed downwards 

 and backwards ; the noise can even be repeated 

 after the death of the animal, by twisting the body 

 and thus rubbing or rasping these little saws against 



