CLASS OF EEPTILES. 



361 



467. Respiration is not active in reptiles ; they consume 

 but little oxygen, and can remain alive for a long time without 

 air ; but this activity differs according to the temperature of 

 the season. The lungs are composed of large cells, and in 

 consequence are not very vascular. The tortoise and turtle 

 swallow the air, as it were, the ribs 

 being immovable; there is no ao c c a 



natural division between the chest 

 and the abdomen, and respiration 

 is not regular ; in serpents one lung 

 is rudimentary (Fig. 363). 



468. All reptiles are cold- 

 blooded animals, and the tem- 

 perature of their bodies rises and 

 falls with that of the surrounding 

 medium . A heat of from 40 to 50 

 (Centigrade scale) is quickly fatal 

 to most of them, and the effects of 

 cold are well known, for during 

 winter most reptiles eat no food, and 

 do not even digest what happens 

 to be in their stomachs ; the respiration becomes slower, and 

 their whole state resembles hybernation. 



469. Like birds, they lay eggs, and their young do not 

 suckle ; they have no mamma? ; but there is this peculiarity, 

 which also happens in some fishes, that in some the young are 

 hatched before being born, as in the viper ; and such animals 

 are called ovoviviparous. 



The young reptile, on quitting the egg presents nothing 

 anormal ; it resembles its parent in its mode of respiration, 

 general structure of the body, and external form. 



470. Reptiles generally abandon their eggs when laid, 

 and the young are developed by the heat of the external 

 atmosphere; but there is one remarkable exception in the 

 great Indian serpent, called python, which hatches its eggs, 

 during which period its own temperature will rise to 40. 



Fig. 362.* 



* Heart and large vessels of the Crocodile : -v, v, veins which bring back 

 blood from different parts of the body to the right auricle (od) ; vt, the two 

 ventricles, internally separated by a partition ; ap, the two pulmonary 

 arteries proceeding from the right ventricle to the lungs ; a, a vessel pro- 

 ceeding from the same ventricle to the descending aorta ; vp, pulmonary 

 veins carrying the arterial blood from the lungs to the left auricle (og), from 

 whence it passes into the left ventricle, and tnus enters the aorta (ao) and 

 into the two arteries (c c) which proceed to the head, &c. 



