CLASS THIRD. 
REPTILES. 
Vertebrated animals with cold red blood, the skin either na¬ 
ked or protected by scales. 
OF REPTILES. 
The skin of this class is either naked or covered with scales. 
It is periodically renewed among many of the tribes. The se¬ 
cretions of the cuticle are insufficient to moisten it. 
The temperature of reptiles usually corresponds with that of 
the medium where they are situated: they become torpid when 
the temperature sinks to the freezing point; and so essential is 
a warm temperature to these animals, that we find the greater 
number of the class destined to inhabit the hotter portions of 
the earth. 
The bones of reptiles, with the exception of the larger kinds, 
seldom attain the same degree of hardness as in quadrupeds and 
birds. These vary exceedingly in their connection and number, 
in different tribes. Frogs and their congeners have no ribs ; 
in serpents the ribs are detached, without a sternum; in tor¬ 
toises they all adhere together; and in lizards they are like that 
of birds. Their limbs are fitted for performing progression in 
a variety of ways. Some have two, and others four, feet; either 
webbed for swimming, or cleft for walking and climbing. Many 
are inhabitants of the water, and others exist entirely upon land. 
Those which live in the former element are often formed some- 
