REPTILES. 205 
them. They differ from them in some respects, a few of 
which [ will notice. Prominent among these is the se- 
ries of changes in passing to their mature state, of which 
I have just spoken. The reptiles of the other orders are 
covered with plates, or shields, or scales; but the Am- 
phibia have a smooth skin, with the exception of a few 
species, whose scales are much like those of a fish. This 
skin is in many cases moist, and in some the secretion 
which makes it so is irritating to one who handles the 
animal. The Amphibia have no ribs, and therefore, not 
having the means of dilating the chest, must swallow air 
as they swallow food, directing the one to the lungs and 
the other to the stomach. You can therefore suffocate a 
Frog or any animal of this order by wedging its mouth 
wide open; that is, you prevent the air from going into 
its lungs as effectually as it is done with most other an- 
imals by closing the passage to the lungs. There is one 
other order of reptiles of which the same is true—the 
Tortoises. This is partly because the ribs are joined to 
the carapace (§ 314), and therefore are not movable, and 
partly because the plastron below does not permit that 
protrusion of the abdomen which we see always pro- 
duced by the action of a diaphragm. No reptiles have 
a diaphragm, but all except the Tortoises and the Am- 
phibia can dilate the lungs by means of their ribs. The 
feet of the Amphibia are without claws. Their eggs 
have no hard covering or shell. They are usually de- 
posited in the water, even in the case of those that live 
mostly on the land. They are enveloped in a glutinous 
matter, which unites them in masses, or in chains, the 
latter looking like necklaces of black beads. 
341. The tongues of the Batrachians are commonly 
large and fleshy. In the Frogs and Toads there is a very 
peculiar arrangement. The tongue is fastened to the 
front of the jaw, and its tip extends backward toward 
the throat. It is covered with a slimy substance, as the 
end of the Chameleon’s tongue is (§ 324), and for a sim- 
