244 A- ^^- Banta 



This study was undertaken in the Zoological Laboratory of the 

 Museum of Comparative Zoology at Harvard College. The first 

 part, dealing with reactions to light, was carried out under the 

 direction of Prof. E. L. Mark, to whom I am greatly indebted 

 for providing exceptional facilities for conducting the research and 

 for excellent suggestions and stimulating criticism. 



Cave animals have long been a source of interest to men of 

 science as well as to others. Their origin was long considered a 

 matter of accident. Some animal, it was assumed, having wan- 

 dered into a cave, or having been carried into it by a flood, was 

 hardy enough to withstand the unusual conditions there, and, suc- 

 ceeding in finding a mate in a like straggler, was enabled to found 

 a race. This race, as time went on, became more and more 

 adapted to the unusual conditions and permanently established 

 itself within the cave, ultimately producing a new and distinct 

 species of cave animal. This "accident" hypothesis of the origin 

 of cave life was well set forth and defended by Lankester ('93). 



Eigenmann ('00, pp. 55-58), in discussing cave fishes, pointed out 

 these objections to Lankester's hypothesis, — first that so many 

 fishes of a single, extremely restricted small family should have 

 "accidentally" become cave inhabitants, while no others in the 

 same region (a region abounding in families and species of fresh- 

 water fishes) became cave species; secondly the manifest impos- 

 sibility of the survival of a species accidentally swept into a cave, 

 unless it were already fitted for life in subterranean abodes; thirdly, 

 that cave animals are negatively phototactic, a fact not to be 

 harmonized with that part of Lankester's explanation which main- 

 tained that of those individuals which were accidentally swept into 

 caves, the ones with the better eyes would follow the "glimmer of 

 light and escape," leaving those with poorer eyes behind to be- 

 come the progenitors of a blind cave race. Garman ('92, p. 240), 

 Eigenmann ('90, and '00, p. 57), and the author (Banta '07, p. 98) 

 have shown that animals undergo modifications suiting them for 

 cave life in situations other than caves. In a former paper I ('07, 

 p. 97) have laid stress upon the fact that cave animals belong to, 

 and have originated within, families and genera which show a 

 tendency to live in situations where the conditions resemble those 

 of a cave, as regards darkness, moisture, etc. 



