SNAKES. Ill 



at once arrested, being caught on the needle 

 points. Thus it is that snakes are obliged to 

 swallow their prey whole. Broken teeth have 

 no terrors for snakes, since provision is made 

 by Nature for a constant renewal of those which 

 are lost. 



The lungs of snakes are peculiar in that owing 

 to the great elongation of the body cavity, the 

 left lung is much smaller than the right. The 

 latter is, furthermore, remarkable in that it 

 consists only of an exceedingly thin-walled bag, 

 only the anterior portion of which is used for 

 respiratory purposes, the hinder end serving 

 merely as a reservoir of air. 



Having now considered the principal charac- 

 teristics of snakes, we may proceed to enquire 

 into the factors which have given these creatures 

 their peculiar features. Probably the most im- 

 portant influence at work has been the method 

 of securing prey. Originally, like the lizards, 

 four-footed, they seem to have been essentially 

 hunters on the ground, taking their prey by 

 stealth. This led, as in the case of many lizards, 

 to the loss of the limbs and the enormous elonga- 

 tion of the body. Simultaneously with the dis- 

 appearance of the limbs they developed new 

 organs of locomotion, pressing the ribs into this- 

 service. The fact that every rib in the body, 

 save only the very hindmost, takes part in this 

 exercise, shows that this peculiar adaptation must 

 have taken place quite early in the history of 

 the group, before the ribs of the neck vertebrae 

 became reduced to the dimensions which they 

 present in the majority of other forms. The 



