BLIND FAUNA OF CAVEHNS. 79 



of the vertebrate creatures of the Kentucky cave, the 

 optic nerve is found to exist, though the eyes are 

 wanting. 



Of the true relations of these remarkable beings with 

 those which inhabit the sunny world without, there are 

 various opinions. Some have thought it possible that 

 they are the descendants of unfortunate individuals that, 

 in unknown ages past, wandered into the caves, and were, 

 unable to find their way out again ; the total absence of 

 light, and the consequent disuse of the visual organs, in- 

 ducing an obliteration of the organs themselves, or at least 

 of the function. Others suppose that the animals were 

 at the first assigned to such situations, and fitted for them 

 at their creation. Others again, among whom may be 

 reckoned the late Mr Kirby, in his " Bridgewater Treatise," 

 contend that they form no portion of the fauna now in 

 existence on the surface of the earth, but belong to a 

 creation as distinct as we may suppose that of Venus or 

 Jupiter to be. The data, however, scarcely warrant such 

 a conclusion as this. 



Mr Charles Darwin has lately alluded to these singular 

 facts in confirmation of his theory of the origin of species 

 by means of natural selection, or the preservation of fa- 

 voured races in the struggle for life. He takes the first- 

 named view, that in the subterranean animals the organs 

 of sight have become (more or less completely) absorbed, 

 in successive generations, by disuse of the function. " In 

 some of the crabs the foot-stalk remains, though the eye 

 is gone ; the stand for the telescope is there, though the 



