334, REPTILES. 



ing for the class, as fur for the quadrupeds, or feathers for the 

 birds. Their low temperature, not differing much from the 

 medium in which they live, renders such a covering to re- 

 tain the heat unnecessary. The skin is naked in Frogs, scaly 

 in Lizards and Serpents, and covered with a shelly plate in 

 the Tortoises. 



The brain in Reptiles is small, their nerves are very solid, 

 and the relation of their sensations to a common centre seems 

 less necessary to their animal and vital functions than in the 

 higher classes. They continue to live 'and possess voluntary 

 motion for a considerable time after the brain has been remov- 

 ed, and even when their head is cut off. The connection of the 

 nervous system with the muscular fibre is also less necessary 

 to its contraction ; and their muscles preserve their irritability 

 longer after being separated from the body, than in the previous 

 classes. Even in some species the heart beats many hours after 

 it has been taken from the body, and the body itself to move 

 for a still longer period, after the removal of this essential organ. 



Reptiles possess five senses, but none of them in great per- 

 fection. Thus their sense of touch is obtuse, from the scales, 

 plates, or shells of some species ; and even when the skin is 

 naked it is not adherent to the body, but envelopes it like a bag, 

 as is seen in the frog. Sometimes, as in the serpents, their eyes 

 have no eyelids, are often immoveable, and covered with a cor- 

 neous substance ; in some three eyelids are to be distinguished ; 

 while some again appear to be destitute of sight. They have no 

 cochlea, and but a small bone under the tympanum. Their 

 nostrils are small, and their sense of smell appears weak. 

 Their taste is not delicate, for the greater number swallow their 

 prey whole, and in those which have the tongue soft and flexible, 

 this organ serves chiefly for the seizure of their food. 



Many species of Reptiles have no ribs, as the Frogs ; among 

 others, as the Serpents, these ribs are free and without a ster- 

 num ; in the Tortoises they are all fixed together ; and in the 

 Lizard family the ribs are disposed nearly as in birds. The 

 lungs are always included in the same cavity as the intestines. 

 The smallness of the pulmonary vessels permits reptiles to 

 suspend their respiration without stopping the circulation of 

 the blood ; and thus they can remain for a long time under 

 water with ease. The cells of their lungs are few in number, 



