20 THE SNAKES OF SOUTH AFRICA. 



At the old Port Elizabeth Museum the sun only shone for an 

 hour or so daily into the cages, owing to their situation. In con- 

 sequence the female puff adders frequently produced their young 

 in an incomplete state of development. In others, the embryo 

 died and the egg hardened resulting in the death of the parent. 



The incubation period is about three months. In oviparous 

 species the baby snake is provided with an egg-tooth for making 

 a slit in the shell. The tooth then disappears. 



Sense of Smell and Breathing Apparatus. 



The sense of smell in snakes is very well developed, as will 

 be seen on dissection of the apparatus of the nose. In the family 

 of grass snakes this sense of smell is particularly good. 



Snakes are thus enabled to find their prey and guard against 

 their enemies by the senses of sight, touch, smell, and hearing. 



Snakes breathe by means of lungs. The left lung is much 

 smaller than the right one, and in most cases it is rudimentary, 

 or entirely absent.* The right or functional lung often reaches 

 to the centre part of the body. The lung is a sort of long hollow 

 tube or bag, with thin walls, in which are embedded the honey- 

 comb-Uke respiratory "cells" and blood vessels which take up 

 the oxygen of the inspired air. Snakes, owing to their low 

 temperature and slow blood circulation, do not require to breathe 

 as frequently, or inhale such pure air as birds or mammals. The 

 breathing is slow and quiet, except when the serpent is alarmed 

 or enraged, when it will inhale a great volume of air and expel 

 it forcibly, producing the characteristic hiss. 



Hissing, Progression, and Sex. 



The hissing of a snake is caused by the long sac-like lung 

 being inflated with air, which is forcibly expelled through the 

 glottis and nostrils, causing that well-known hissing sound which 

 warns us of the proximity of a snake. 



The Puff Adder makes the loudest and most prolonged hiss of 

 any South African snake. Hissing is the only sound snakes are 

 capable of producing, except the American Rattle Snakes, which 

 have a horny substance in loose sections or segments at the end of 

 the tail, which, when shaken, emits a hollow kind of rattling noise. 



* A few snakes, such, for instance, as the Herald Snakes, Pythons, and 

 Boas, have two functional lungs^the right in all instances being the larger. 



