FROGS AND TOADS. 



283 



faculty of sight would be thrown away upon the Proteus. 

 Accordingly it is found that though it possesses the 

 rudiments of eyes, they are reduced tc specks of excessive 

 minuteness, and are, besides, covered by the common 

 skin of the head. And this leads us to mention the 

 curious fact that there exists a subterranean fauna, existing 

 chiefly in mines and caves, every individual of which is 

 totally blind by nature. Numerous species have been 

 lately brought under the notice of naturalists, especially 

 from the great caverns of North America, none of 

 which can be identified with any known supraterranean 

 species, and every one of which is sightless. 



We have hitherto spoken only of that measure of re- 

 spiration which is effected either by means of gills, or of 

 lungs, or of both together. But experiments have shewn 

 that the adult Amphibian needs yet a further supply of 

 oxygen, which it obtains through the whole surface of the 

 skm. A Frog has been kept alive for forty days after 

 having been subjected to the total privation of its lungs. 



In order, however, that the skin should be fit for the 

 performance of this function, it is absolutely essential that 

 it be maintained in a moist state : dryness of the skin is 

 speedily fatal, A beautiful provision is made for the 

 supply of the requisite superficial moisture, by a secretion 

 from the skin itself. " The extent of the skin is, however," 

 observes Professor Bell, " so great that the whole internal 

 moisture of the animal would speedily be exhausted, 

 unless a reservoir were provided for an extraordinary 

 demand ; and I now proceed to shew what this reservoir 

 is, and by what means it is replenished. Every one 

 knows that when a Frog is hastily seized, or even quickly 



