BLIND CAVE-ANIMALS 323 



such light, and are thus able to see and capture their prey 

 with ease. In the absence of such artificial hght 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 soHd 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 



