DESICCATION IN PHILODINA ROSEOLA. 357 



appear but the puckering due to the contraction of the circular 

 muscles is evident. Jacobs has pointed out this fact and my 

 Fig. 16, a longitudinal section through a dried animal, shows the 

 sides as being free from folds while the ends show prominent and 

 regular wrinkles. 



Frequently several animals are carried together by the dimin- 

 ishing drop as it evaporates. In this case each rotifer tends to 

 assume a hexagonal shape as a result of mutual pressure. Fig. 5, 

 Plate II., shows an animal which was dried on a clean slide at 

 room temperature and drawn nine days after the desiccation 

 began. It will be seen at once that the integument has become 

 much folded and the internal organs indistinct, but the vitel- 

 larium, foot and stomach are still recognizable. 



E. Animals Recovering from Desiccation. When water is added 

 to dried animals, such as that described in the last section, they 

 usually regain their normal size within ten minutes, often before. 

 The rapid swelling of the animal causes any wrinkles which 

 may be in the integument to disappear. Active movements 

 may occur within a short time if the conditions under which they 

 are dried are favorable. Sometimes movements may not occur 

 for several hours, even a whole day. This fact may account for 

 the negative results of the desiccation experiments of some of 

 the older authors. These investigators probably did not give 

 their rotifers sufficient time to recover, as Jacobs points out. 



As the animals recover they resume their usual activities. 

 I have noticed that rotifers recovering from desiccation are 

 lighter in color than they were before the process began. Further 

 comment will be made upon this point in a later paragraph. 



2. Study of Sections. 



The cytological details of the structure of rotifers has been 

 described in comparatively few cases. Of the Bdelloidese, 

 Discopus synaptce has been described by Zelinka ('86). From 

 the study of the figures of sections through the principal body 

 regions as represented by Zelinka one can see many points of 

 similarity between this form and P. roseola. In the case of 

 P. roseola I find no record in the literature which tells of the 

 cytological structure of its tissues. The accompanying figures 



