100 FAUNA OF MAYFIELD'S CAVE. 



creatures. This view was set forth by Spencer (1893, 758; 477-478) 

 as follows: 



The existence of these blind cave animals can be accounted for only by supposing 

 that their remote ancestors began making excursions into the cave, and, finding it 

 profitable, extended them, generation after generation, further in, undergoing the 

 required adaptations little by little. 



This class of immigrants into caves is nicely exemplified by the 

 spiders living about the mouth of Mayfield's Cave. 



On the other hand, cave faunas may be formed directly through 

 colonization by animals already highly modified and entirely suited to the 

 rigid conditions of remote portions of caves. This is in accord with H. 

 Carman's view (1892, 240) : 



It is to species such as these, already fitted for life in caves, that we should look, 

 it seems to me, as representing the ancestors of cave species; certainly not to ordinary 

 species with well-developed eyes. The originals of the cave species of Kentucky were 

 probably already adjusted to a life in the earth before the caves were formed, and it 

 seems probable from some facts mentioned below that they were not very different 

 in character from the animals now living in the caves. I can not believe that there 

 has been anything more than a gradual assembling in the caves of animals adapted 

 to a life in such channels. 



WHAT WERE THE CONDITIONS OF CAVE ANIMALS WHEN THEY ENTERED CAVES? 



From the foregoing discussion it will be seen that some animals 

 take up their abode within caves when (e. g. , Theridium kentuckyense, 

 Cambarus bartoni, and Crangonyx gracilis) they are little or apparently 

 not at all different from outside forms. Others, such as the geodepha- 

 gous beetles and the Amblyopsidae, before becoming cave inhabitants 

 at all were probably suited even to the rigid conditions of the remote 

 portions of caves. Animals which take up their abode in caves are not 

 necessarily all in the same grade of adaptation. On the contrary, it has 

 been seen that all grades of adaptation between extremes of little or 

 no adaptation and perfect adaptation may lead to cave life. 



This opens the way for the conception that there is no sharp dis- 

 tinction between cave faunas and other dark and shade inhabiting 

 faunas. This conception is abundantly justified by the blind and white 

 goby (Eigenmann, 1890) of the California coast, the Chologaster papilli- 

 ferus (Forbes, 1882) living in a spring in Illinois, the blind beetle 

 (Carman, 1892, 24) living about crevices in open quarries in Kentucky, 

 the blind amphipods and isopods (Sayce, 1901) found among driftwood 

 in a shaded stream in Australia, and even the very highly modified 

 Cascidotea stygia, which occurs sometimes under stones or leaves in 

 shaded ravines and about the mouths of springs in the Ohio Valley, 

 not to mention the occurrence throughout the world of blind and color- 

 less animals in wells and springs. 



