FEOGS 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 to 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 cither 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 
skin. A Frog has boon 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 
