React 1 0)1 s of I so pods i^.'J'J 



darkened and the upper end illuminated afforded conditions 

 somewhat resembling conditions in caves which are entered by- 

 streams from the outside. Under such conditions, judging from 

 the results of the experiments, Asellus, when carried to the inlet, 

 would tend to leave the cave because of its relatively stronger 

 rheotaxis. In addition to this factor, however, the positive pho- 

 totaxis of Asellus after having been in darkness would also aid. 

 Caecidotea, on the contrary, is always negatively phototactic, and 

 while it shows a tendency under these circumstances to enter the 

 light because of its rheotaxis, it is probable that this form of 

 reactions is always subordinate to its negative phototaxis. 



III. STUDY OF THE FOOD 



Attempts were made to ascertain if a difference in the food of 

 Asellus and Crecidotea was possibly an important factor in deter- 

 mining the habitats of the two species. To this end specimens 

 of Caecidotea were taken direct from the caves in Indiana and pre- 

 served in formaline before they had an opportunity to feed upon 

 other substances than those they might get in their normal sur- 

 roundings and the same was done with Asellus communis ob- 

 tained near Cambridge, Mass.^" 



The digestive tracts of each w^ere then carefully examined to 

 determine their contents. 



Afterward several individuals of each species were kept in 

 clean tap water without food for several days and then placed in 

 separate jars with bits of decayed leaves and living Ceratophy- 

 lum and subsequently examined to determine what was taken for 

 food when living and dead plant tissue were equally present. 



With Caecidotea the evidence pointed to the conclusion that 

 the animal in the cave collects for food whatever decaying or- 

 ganic matter it happens upon. Naturally dead plant tissue forms 



''Mancasellus tenax dilata. the common and extremJy abundant Asellid from southern Indiana, 

 was similiarly treated and examined. It was found that the food of this species from the region 

 about the cave in Indiana is practically the same as that of Asellus communis near Cambridge, 

 Mass. 



