DESICCATION IN PHILODINA ROSEOLA. 361 



staining granules which are masses of reserve food material. 

 Janson ('93) says that these masses are kept by the rotifer for 

 use during the dry periods when feeding must of necessity cease. 

 Beauchamp ('09) shows sections of the stomach of Hydatina 

 senta in which these granules appear. He shows further that 

 in a section of the stomach of an individual of the same species 

 which had been starved for twenty-two days, these granules had 

 disappeared and were replaced by vacuoles. In sections of 

 very young Philodinas no such granules are present and I shall 

 show later that after periods of desiccation in Philodina these 

 granules become fewer or disappear entirely, thus furnishing 

 cytological evidence in support of the theory of Janson and 

 Zelinka, which by them was based entirely upon observations 

 upon the entire, living rotifers. 



The stomach tissue is most pliable and the lumen seems 

 normally to be able to occupy almost any position in it. This 

 fact has been remarked by Beauchamp in Callidina socialis. 



The stomach tissue of Discopus as figured by Zelinka lacks 

 some of the elements which I find in Philodina. I refer to the 

 granules of reserve food material just mentioned. In none of 

 his figures does he show these deeply staining aggregations. It 

 may be that the digestive processes of Discopus differ from 

 those of Philodina. The difference in the habits of the two 

 forms might account for this. On the other hand these elements 

 might have been present but not differentiated by the stain. 

 The latter condition does not seem probable, however, for I 

 have found that most of the nuclear stains have an affinity for 

 the food granules. 



Another point of difference is in the structure of the ground 

 substance of the stomach tissue. In Discopus this ground 

 substance is represented by Zelinka as being made up of fine 

 granules loosely packed together. In Philodina the ground 

 substance of the stomach tissue is composed of alveoles closely 

 apposed. This difference could perhaps be accounted for upon 

 the basis of fixation. 



Fig. n, Plate III., shows a section through the most posterior 

 part of the trunk at the point where the stomach-intestine joins 

 the "blasendarm.' The contrast in the structure of the two 



