2 REPTILES. 



The connexion with the nervous system is also much less necessary to 

 the contraction of their fibres, and their muscles preserve their irritabi- 

 lity after being severed from the body much longer than those of the pre- 

 ceding classes; their heart continues to pulsate for hours after it has 

 been torn away, nor does its loss prevent the body from moving for a 

 long time. The cerebellum of several has been observed to be extremely 

 small, a fact which tallies with their slight propensity to motion. 



The smallness of the pulmonary vessels permits Reptiles to suspend the 

 process of respiration without arresting the course of the blood; thus 

 they dive with more facility, and remain longer under water than either 

 the Mammalia or Birds. The cells of their lungs, being less numerous, 

 because they have fewer vessels to lodge on their parietes, are much 

 wider, and the organs themselves sometimes have the form of simple and 

 scarcely cellular sacs. 



Although some of them are incapable of producing audible sounds, they 

 are all provided with a trachea and larynx. 



Their blood not being warm, there was no necessity for teguments capa- 

 ble of retaining heat, so that they are covered with scales or simply with 

 a naked skin. 



The females have a double ovary and two oviducts; the males of seve- 

 ral genera have a forked or double penis, those of the last order, the 

 Batrachians, have none. 



No Reptile hatches its eggs, and in several genera of the Batrachians, 

 they are fecundated after their exclusion from the female, in which case 

 the egg is enveloped by a membrane only. The young of this latter 

 order, on quitting the egg, have the form and branchiae of Fishes, and 

 some of its genera preserve these organs even after the development of 

 their lungs. In several oviparous Reptiles, the Colubers particularly, the 

 young animal in the egg is formed and considerably advanced at the mo- 

 ment of its exit from the mother ; and there are even some species which 

 may be rendered viviparous by simply retarding that epoch*. 



The quantity of respiration in Reptiles is not fixed like that of the 

 Mammalia and Birds, but varies with the proportion of the diameter of 

 the pulmonary artery compared to that of the aorta. Thus Tortoises and 

 Lizards respire much more than Frogs, &c. ; and hence results a much 

 greater difference of sensibility and energy than can exist between one of 

 the Mammalia and another, or between Birds. 



Reptiles accordingly present an infinitely greater variety of forms, mo- 

 tions, and properties than is to be found in the two preceding classes ; 



* The Colubers, for instance, when deprived of water, as proved by the experi- 

 ments of M. Geoftroy. 





