96 FAUNA OF MAYFIELD'S CAVE. 



Packard (1894, 744-745) also introduces the element of accident, but 

 in a much more plausible way: 



Where, however, individuals with more or less defective eyes should breed with 

 normal mates, any tendency to the transmission of such defects would be wiped out 

 by the swamping effects of crossing, owing to the immense preponderance of normal, 

 vigorous forms with perfect vision. The whole tendency in nature in the upper 

 world of light is to weed out such sporadic, defective forms. But in limestone regions 

 honeycombed with caves and permeated with subterranean streams, like those in the 

 Mediterranean regions, France, Spain, and Australia, or in those of Southern Indiana, 

 Virginia, Kentucky, and Missouri * * * in such regions as these, there exist the 

 conditions favorable to the origination and perpetuity of blind forms. To give an ex- 

 ample, eyed geodephagous beetles, such as the species of Trechus, of which there are 

 so many in Southern Europe, accustomed to burrowing in the soil under stones, when 

 carried down by various accidents into dark crevices or into caves from which they 

 are unable to extricate themselves, and too hardy and vigorous to succumb to the 

 deadly effects of a life in perpetual darkness, and with, perhaps, already partially 

 lucifugous habits, such forms under these changed conditions survive, breed, and mul- 

 tiply, finding just enough vigor to propagate their kind. We can easily imagine that 

 in time, and indeed no very long period, the newcomers would soon become adapted to 

 their new surroundings, an environment abnormal both from the absence of light, 

 and from the lack of predaceous forms to devour them; and they would live on, weak, 

 half -fed, half -blind, forced to make their asylum in such forbidding quarters. 



But even this is not the most plausible method of explaining the 

 origin of cave species. Animals such as the geodephagous beetles men- 

 tioned above, if accidentally carried into caves, would probably establish 

 themselves there and I see'no objection to the possibility of the occasional 

 introduction into a cave by a flood or other means of a species fitted for 

 cave life. 



The beetles referred to are light-shunning creatures and constantly 

 crawl about under stones and in crevices in the earth. Certainly in a 

 limestone region ' 'honeycombed with caves and permeated with subter- 

 ranean streams," as Packard suggests (and there are perhaps more 

 passages, many of them opening to the surface, no longer followed by 

 streams except in times of considerable rain, than there are passages that 

 always contain water), these beetles would have every opportunity to 

 enter underground channels in their ordinary search for food, and there 

 can be no reason for supposing that they would be more likely to reach 

 underground passages by accidental bodily transportation rather than 

 by migration in following their usual habits. Without denying the 

 possibility of the former method, it must be said that it can, at best, 

 be but an unusual method of the origin of cave forms, while the latter 

 method of entry into caves is not only the more plausible, but is sup- 

 ported by good evidence. 



