MECHANICS OF SNAKES — LEUTSCHER 307 



tion that is at an angle to that in which it is facing. The body does 

 not follow the course of the head but, as it were, tacks away from a 

 base line. 



In burrowing snakes, of which Typhlo'ps is a typical example, there 

 are no broad belly shields, and the body is uniforml}^ covered with 

 polished and closely united scales of more or less equal size. This is 

 also found in the slowworm, a legless lizard that ^s fond of burrow- 

 ing. There is no risk of earth particles becoming caught up in the 

 skin, and the scales play no part in locomotion. Instead, the body 

 twists and turns in all directions, pushing its curves against resisting 

 bodies, such as stones, plants, and the walls of burrows to propel itself 

 forward. In some burrowing snakes (e. g., Uropeltis) the short tail 

 ends abruptly in a broadened oblique surface, which is covered with 

 large scales, and this operates somewhat like a digging implement. 



The highly poisonous sea snakes, which constitute the subfamily 

 Hydrophiinae (these are the only "sea serpents" at present recognized 

 by science), are entirely divorced from the land, being viviparous 

 and adapted for swimming. They have strongly compressed bodies 

 and oarlike tails which present a broad surface to the water as they 

 progress with lateral undulations. This compares with the move- 

 ment of fishes and is thought to be a relic of their fish ancestry. 

 Even a land snake, such as the grass snake, will swim in this manner 

 over a pond — and for that matter "swim" through the grass. 



Yet another remarkable feat of some serpents is to be seen in the 

 action of a "flying" snake. This is much more in the nature of a 

 glide but is nonetheless extraordinary. The ventral surface can be 

 pulled in to form a deep concavity, accompanied by a slight flattening 

 of the body, the kind of flattening one would find if the body were 

 squashed by a pressure applied above and below. The hollow under 

 surface gives the snake the necessary buoyancy in the air for its 

 parachutelike descent into a lower branch, in a glide of some 

 considerable distance. 



In general, snakes that are well able to take care of themselves, 

 such as the poisonous kinds and the large constrictors, are by nature 

 sluggish, and many have squat clumsy bodies. They may even possess 

 peculiar mechanical devices that are used to warn away enemies. 

 There is, for instance the "hood" of certain cobras produced by the 

 flattening of the ribs behind the head when the animal is annoyed. 

 Then there is the warning "rattle" of the American pit viper, or 

 rattlesnake; the rattle is composed of a series of rounded, homy 

 sheaths at the end of the tail which is added to with each successive 

 molt of the skin, and vibrates at high speeds to produce a whirring 

 sound intimidating to its enemies. 



