CLASS REPTILIA. d 



ing the course of the blood ; accordingly, they dive 

 more easily, and for a longer time, than mammifera 

 or birds : the cellules of their lungs being less 

 numerous, because they have fewer vessels to lodge 

 on their parietes, are much wider, and those organs 

 have sometimes the form of simple sacs, which are 

 scarcely cellular. 



Reptiles are provided with a trachea and larynx, 

 though the faculty of an audible voice is not accorded 

 to them all. 



Not possessing warm blood, they have no occasion 

 for teguments capable of retaining the heat, and they 

 are covered with scales, or simply with a naked 

 skin. 



The females have a double ovary, and two ovi- 

 ducts. The males of many genera have a forked or 

 double organ of generation. In the last order — that 

 of the batracians — they have none. 



No reptile sits upon its eggs. In many genera of 

 batracians, the eggs are not fecundated until after 

 they have been laid; and hence they have only a mem- 

 branous envelope. The young of this last-men- 

 tioned order, on issuing from the egg, have the form 

 and the gills of fishes ; and some genera preserve 

 these organs, even after the development of their 

 lungs. In many of the reptiles which lay eggs, 

 especially in the colubri, the young one is already 

 formed, and considerably advanced in the egg at the 

 moment when the mother lays it ; and it is the same 



B 2 



