478 A. M. Bauta 



the main part of its food. The digestive tracts contained rela- 

 tively small amounts of mineral matter. Those placed with liv- 

 ing and decaying plant tissue ate relatively small amounts of green 

 algae, probably only that taken in with the decayed plant tissue. 



From the evidence obtained from the series of examinations of 

 Asellus it seemed probable that it takes its food either from sur- 

 faces of dead plant tissue or from living plants. In cases where 

 material apparently quite recently taken as food was found in the 

 digestive tract there was always more or less fresh plant tissue 

 and those individuals which were deprived of food for a time and 

 then placed with both the decaying leaves and the living Cera- 

 tophyllum seemed to have collected nearly all their food from the 

 Ceratophyllum. There was, however, no evidence to prove that 

 green plant tissue was a necessary portion of the food of Asellus. 

 It probably could live upon decaying organic matter exclusively, 

 as Caecidotae does, but it partakes of both kinds of food and will 

 use living plant tissue largely when both living and dead are 

 present. 



In every case the digestive tracts of those Asellus examined con- 

 tained a large percentage of mineral matter, in most cases as much 

 as 85 per cent of the contents being inorganic. It will be remem- 

 bered that the digestive tracts of even those Caecidotea which 

 were taken directly from the caves contained very little mineral 

 matter. 



The difference between the amounts of mineral matter taken 

 with the food in the two species is remarkable in caves where 

 Caecidotea obtains its food, organic matter is extremely scarce, 

 while, where Asellus lives, the proportion of organic to mineral 

 matter is very many times as great. This difference sug- 

 gests that Caecidotea possesses a superior discriminative power in 

 selecting its food. Such ability would be of immense advantage 

 to an animal in a cave. The lack of discrimination in selecting 

 food clearly indicates, I believe, that Asellus is incapable of meet- 

 ing the food conditions within caves. 



