BLIND CAVE-ANIMALS 323 
such light, and are thus able to see and capture their prey 
with ease. In the absence of such artificial light and special 
modes of vision, cave-animals are of course compelled to 
rely solely on their organs of touch, hearing, and perhaps 
of smell; and, to our thinking at least, their life must be 
far more dreary and devoid of pleasure than is that of the 
inhabitants of the deep sea. Possibly, however, there may 
be other compensating advantages unknown to us; and, 
in any case, they lead a life of peace unmolested by the 
various carnivorous tyrants of the outer world, It is, 
however, very noteworthy that there is one blind fish 
inhabiting the ocean at great depths, and that a member 
of the same family is also found in the caves of Cuba; 
and this instance seems to indicate that certain families 
of fishes are better suited than others for taking to a 
subterranean existence. 
Caves or subterranean channels containing the typical 
blind fauna are met with in many countries, apparently 
invariably in limestone rocks, and mostly in those belong- 
ing to the Carboniferous epoch; the latter, from their 
massiveness, being especially adapted for the formation of 
such chambers by the action of water. Needless to say, 
the formation of a cavern of any size in solid limestone 
rock is a process involving an enormous length of time 
for its accomplishment, and it is therefore essential that 
the rock should be of very considerable geological age. 
Indeed, it is believed that the formation of the celebrated 
Mammoth Cave was commenced at a comparatively early 
date in the Secondary era, although it was not completed 
till the Pleistocene. The reader must not, however, be 
led to suppose that cave-animals belong to an older epoch 
than those of the outside world, as it is probable that 
many of them have not taken to their present mode of 
