REPTILES. 205 



them. They differ from them in some respects, a few of 

 which I 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- 



