CHELONIA 251 



while others are omnivorous. Predacious species probably 

 lie in wait for their prey. 



The respiration is unique. The large spongy lungs reach to 

 the pelvis. In breathing the neck and limbs act like pistons in 

 being drawn in and out. The throat is alternately inflated and 

 emptied by the hyoidean apparatus when the neck is stretched 

 out, thus the air is swallowed or pumped into the lungs. Since 

 the lungs are so roomy and the animals poikilothermal, most 

 turtles can live for a long time without breathing, sometimes 

 remaining under water for hours or even days. 



Special Senses. — Their eyes, though comparatively small, 

 are their most highly developed sense organ. They are situ- 

 ated far forward on the head and protected by two lids and a 

 nictitating membrane. The nostrils are terminal; thus by ex- 

 posing a minimum portion of the head above water they are 

 able to breathe and see what is going on about them, compara- 

 tively free from danger. The sense of smell is well developed, 

 many species showing a choice of certain kinds of food which 

 they distinguish by smell. The sense of hearing is not well 

 developed. That they distinguish sounds is evident from 

 their voice, which Gadow declares is very tiny and piping during 

 the pairing season. Some species, at least, snap their jaws 

 together when angry, and when the head and limbs are with- 

 drawn they make a hissing sound. Holder says the male 

 " elephant turtle " of the Galapagos Islands " utters a hoarse 

 croak or bellow during the breeding season." They are fright- 

 ened by noise. The tympanic membrane in most water forms 

 is thin and quite exposed. In land tortoises it is often thick and 

 covered with the skin. Turtles, contrary to the notion of small 

 boys, are very sensitive to the touch, both upon the shell and 

 upon the soft parts. 



Multiplication. — Turtles lay their eggs at night in the sand, 

 cover them carefully, and leave them for the heat of the sun- 

 warmed sand to hatch. 



The young are like the adult in general, but differ somewhat 

 in color. 



Enemies and Defense. — They are preyed upon by carnivo- 

 rous birds, fishes, alligators, and by men. They defend them- 

 selves by closing up their shell, as the box turtle; by snapping 



