396 THE POPULAR SCIENCE MONTHLY. 



Cave and a few adjoining caves the only species in this country 

 of the genus is blind, but possesses rudiments of the outer eye, 

 several corneal lenses surviving. On the other hand, the species 

 of this or the closely allied representative genus Bathyscia, to 

 which they are now referred by Dr. Horn, are very numerous in 

 Europe, and are scavengers in habit. Bedel, in his list of the cave 

 insects of Europe (1875), states that sixty-five species are known, 

 and that several others were known but not described, and that 

 probably further explorations in the region of the Pyrenees, both 

 in France and Spain, will lead to further discovery of species. It 

 appears that not all the species live in caves, but occur in the open 

 air under large stones, moss, vegetable detritus, or at the entrances 

 to caves. It is apparent, then, that the cave animals are emigrants 

 from out of doors, and that the cave species, by isolation from the 

 light and from interbreeding with out-of-door forms, as well as by 

 adaptation to total darkness, have become fixed species with sepa- 

 rate generic characters. 



Equally instructive and explanatory of the origin of cave ani- 

 mals in general is the genus Ariophthalmus. In the caverns of the 

 central United States there are only eight species, and none occur 

 elsewhere in America, though we have two or three species of 

 Trechus, one at least not infrequent, and Trechus micans is com- 

 mon to both hemispheres. Not alone loss of sight and eyes, but 

 other modifications of the body, legs, and antennae, evidently the 

 result of loss of sight, occur, so universal is the modification of the 

 organism. It is evident that southern Europe is the zoogeo- 

 graphical center of this subgenus, for sixty-four species of com- 

 pletely eyeless beetles referred to this genus have already been 

 discovered in the caves of Austria, Italy, France, and Spain. 

 Lately, however, owing to the studies of Putzeys, and especially 

 of De Perrin, the genus Anophthalmus has been united to Trechus, 

 since there is a series of forms with more or less rudimentary 

 eyes connected with the eyed species of Trechus. Bedel also tells 

 us that in all the species of Trechus there is a natural tendency to 

 penetrate into grottoes, even when ordinarily they live in the open 

 air buried in the earth under stones. 



It seems reasonable to conclude that the cave species, which 

 are without optic ganglia, optic nerves, and any traces of eyes, had 

 originally, by adaptation to total darkness, become isolated, and 

 that their characteristics after being fixed by heredity have been 

 transmitted for generations, becoming as unchanging in their way 

 as the physical conditions of darkness and uniform temperature 

 surrounding them. Those living in the open air in the soil under 

 stones, or at or just within the entrances to caves, vary most as 

 regards the eyes, as we have found to be the case with the other 

 forms previously mentioned. 



