VERTEBRATED ANIMALS. 
268 
and their flesh preserves its irritability much longer, after having been separated from 
the rest of the body, than is the case with the preceding classes. Their heart pulsates 
for many hours after it has been detached, and its loss does not deprive the body of 
' mobility for a still longer period. It has been remarked of some which have the 
cerebellum extremely diminutive, that this circumstance has some reference to their 
disinclination to move. 
The smallness of the pulmonary vessels enables Reptiles to suspend their respiration 
without arresting the course of the blood, and thus to remain submerged with less 
difficulty, and for a longer time, than Mammalia or Birds. The cells of their lungs 
are not so numerous, as they contain fewer vessels within their precincts, and they are 
also much larger, these organs having sometimes the form of simple sacs, merely a 
little cellular. 
For the rest. Reptiles are provided with a trachea and larynx, although they have 
not all the power of emitting an audible voice. 
Their blood not being warm, they consequently do not require teguments capable 
of retaining heat ; and they are accordingly covered with scales, or simply with a 
naked skin. 
The females have a double ovary and two oviducts, and the males of several genera 
have a forked or double penis, but in the last order (that of the Batrachians), they 
have [mostly] none at all. 
No Reptile incubates its eggs. In several genera of Batrachians, these are not 
fecundated until after they have been excluded ; they have merely a membranous 
envelope. The young of this last order have, on quitting the egg, the form and gills 
of Fishes ; and certain genera retain these organs even after the developement of their 
lungs. In other Reptiles which produce eggs, the Snake, for example, the young is 
already formed and considerably advanced within the egg at the time the parent 
deposits it ; and there are even some species which may be rendered viviparous at will, 
by retarding the deposition of their eggs, as M. Geoffroy exemplified by depriving 
the common Snake of water. 
The amount of respiration in this class is not fixed, as in the Mammalia and Birds ; 
but it varies according to the relative proportion of the diameter of the pulmonary 
artery, as compared with that of the aorta. Thus, Tortoises and Lizards respire much 
more than Frogs, &c. [though the latter, it should be observed, respire in part over the 
whole damp skin, as conclusively ascertained by the experiments of Dr. Milne 
Edwards] . Hence, the differences of energy and sensibility are very much greater than 
those between one Mammalian and another, or one Bird and another. 
Reptiles also present more varied forms, characters, and modes of gait, than the 
two preceding classes ; and it is in their production more especially, that Nature 
‘ seems to have tried to imagine grotesque forms, and to have modified in every possible 
way the general plan adopted for all vertebrated animals, and for the oviparous classes 
in particular. 
A comparison of the extent of their respiration with their organs of movement has 
led M. Brongniart to divide them into four orders, which are as follow : — 
The Chelonians (or Turtles and Tortoises), which have a heart with two auricles, 
and the body of which, supported by four limbs, is enveloped by two plates or buck- 
lers formed of the ribs and sternum. 
