ORIGIN OF CAVE LIFE. 97 



Cambarus bartoni and Crangonyx gracilis as shown before, have 

 selectively entered Mayfield's Cave and without constraint have remained 

 there. They can escape at any time. They remain within the cave 

 because conditions are suitable to their existence. Such is also true of 

 Theridium kentuckyeTise, Theridium porteri, and Meta menardi, which 

 live in twilight never far from the mouth, while Nesticus carteri,Phanetta- 

 svhterranea, and Erigone infernalis, while occasionally found in twilight, 

 are less abundant there than in absolute darkness far within the cave. 

 These spiders enter caves and remain there because they find conditions 

 favorable. No physical barrier prevents their escape from caves. 

 Crangonyx gracilis and Cambarus bartoni could not have been introduced 

 into Mayfield's Cave by accident, since to get into the cave from outside 

 they must migrate against the current. It might be said that these 

 forms became cave inhabitants through chance introduction into another 

 cave and extended their distribution to Mayfield's Cave. I consider 

 this very improbable and even impossible. It is certainly impossible 

 that Theridium porteri and Theridium kentuckyense should have arisen 

 as cave inhabitants elsewhere by chance and migrated to Mayfield's. 

 In their present condition they could not exist far within a cave, and if 

 they remain near the mouth escape is always easy. 



On the contrary, the fact that widely distributed species found in 

 epigean streams enter caves wherever such exist is strong evidence 

 that caves become populated by voluntary immigrants. 



That species which live in caves belong to groups which are given 

 to life in dark and damp places is further evidence that caves become 

 inhabited by voluntary immigration. The Carabidse and Staphylinidse 

 compose nearly the whole of the coleopterous cave fauna. Many species 

 of both of these families live under stones and in damp ravines and in 

 crevices in the earth, under logs, and in similar places. The Carabid 

 genus Platynus, with 4 species taken occasionally in Indiana caves, is a 

 good illustration of the tendency of certain adapted groups to enter 

 caves and become cave inhabitants. Species of this genus live habitually 

 in retired places along ravines and in similar situations out of doors. 

 A closely related genus, Pristonychus, has 6 representatives in Euro- 

 pean caves. 



A similar case is seen in the family Theridiidse, 12 species of which 

 have been taken in Mayfield's Cave alone. Three other species have 

 been taken in other Indiana caves, 5 others from caverns of Kentucky, 

 while 20 species of this same family are recorded from European caves. 

 Of this family the genus Nesticus has 2 representatives in Kentucky, 1 

 in Indiana, and 3 in European caves. The old genus Linyphia has 1 

 Indiana, 3 Kentucky, and 10 European cave species. This family "con- 



