DESICCATION IN PHILODINA ROSEOLA. 373 



sections of the ovary of animals in the free-swimming condition. 

 Since, as we have seen, chromatic material passes from the nuclei 

 of the vitellarium and of other tissues into the cytoplasm of the 

 same structures it is not improbable that a similar movement 

 would occur in the ovary. In the latter case, however, the ele- 

 ments are so small that one detects minute changes with difficulty 

 even under the highest powers of the microscope. 



This condition in the ovary of the recovering rotifer seems to 

 indicate the time and manner of the increase of the ovarian 

 nuclei. 



It is well known that periods of great reproductive activity 

 always follow periods of desiccation. Reproductive activity 

 under normal conditions in most animals would involve an in- 

 crease in the number of the sex cells. Now in the rotifer this 

 increase might be looked for just before drying, for, if the cells 

 of the other tissues prepare themselves for the new conditions by 

 rearranging their elements it is not inconceivable that the sexual 

 elements might likewise prepare for a season of unusual activity. 

 Such, however, is not the case. By counting the nuclei in several 

 hundreds of sections of ovaries in normal, dried, and recovering 

 animals, I find that the average number in the first two con- 

 ditions is about the same. Likewise in sections of ovaries of 

 animals to which water had just been added there is no noticeable 

 increase. But in sections of animals killed several hours after 

 the addition of water one is struck by the increase in the number 

 of the ovarian nuclei. 



It would be desirable to make a definite statement as to the 

 exact time which must elapse before the multiplication takes 

 place but this is impossible since the time varies among different 

 individuals. In animals dried several weeks the increase does 

 not become apparent in any case before one and one half to two 

 hours has elapsed subsequent to adding water to the dried 

 animals. This time may be too short for animals whose proc- 

 esses go on at a much slower rate. 



In connection with the observation regarding the position of 

 chromatic bodies in the cytoplasm of the vitellarium it is inter- 

 esting to note that Janson ('93) comments upon, but gives no 

 figures of similar cases. He says: "Only twice in P. roseola 



