256 SCIENTIFIC ILLUSTRATIONS |0rs 



stance of a somewhat extensive series of animals inhabiting vast 

 and gloomy caves and deep wells, and perfectly deprived even 

 of the vestiges of eyes. Enormous caves in North America, 

 some of which are ten miles in length, and other vast and 

 ramified grottoes in Central Europe, have yielded the chief of 

 these ; but even in this country we possess at least four species 

 of minute shrimps, three of which are absolutely blind, and the 

 fourth (though it has a yellow speck in the place of an eye) 

 probably so. All these have been obtained from pumps and 

 wells in the southern counties of England, at a depth of thirty 

 or forty feet from the surface of the earth. The Mammoth 

 Cave in Kentucky consists of innumerable subterranean galleries 

 in the limestone formation, some of which are of great extent. 

 The temperature is constantly throughout the year 59 degrees 

 Eahr. A darkness, unrelieved by the least glimmer of light, 

 prevails. Animals of various races inhabit these caves, all 

 completely blind : for though some have rudimentary eyes, they 

 appear useless for purposes of vision. Among these are two 

 kinds of bats, two rats (one found at a distance of seven miles 

 from the entrance), moles, fishes, spiders, beetles, Crustacea, and 

 several kinds of infusoria. Mr. Charles Darwin has alluded 

 to these singular facts in confirmation of his theory of the origin 

 of species by means of natural selection, or the preservation of 

 favoured races in the struggle for life. He takes the 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 footstalk 

 remains, though the eye is gone ; the stand for the telescope is 

 there, though the telescope with its glasses has been lost. As 

 it is difficult to imagine that eyes, though useless, could be 

 in any way injurious to animals living in darkness, we attribute 

 their loss wholly to disuse. On Mr. Gosse's view, we must 

 suppose that American animals, having ordinary powers of 

 vision, slowly migrated by successive generations from the outer 

 world into the deeper and deeper recesses of the Kentucky 

 caves, as did European animals into the caves of Europe. "We 

 have some evidence of this gradation of habit ; for as Schioclte 

 remarks, animals not far remote from ordinary forms, prepare 

 the transition from light to darkness. By the time that an 



