DESICCATION IN PHILODINA ROSEOLA. 371 



warrant, change chemically so as to become able to pass through 

 the nuclear membrane. When moisture is again available the 

 reverse process could take place and new chromatic material be 

 built up from cytoplasmic substance. This certainly would fit 

 in with the changes which one is able to observe in the different 

 stages under the microscope. 



The changes in the chromatin just mentioned are not unlike 

 those which Heidenhain ('94) has described. His oxychromatin 

 and basichromatin could be demonstrated by staining reactions. 

 In the rotifer cells, however, the staining is not nearly so precise 

 and delicate in the dried tissues so that it would be difficult to 

 say whether or not the chromatin exists in the condition just 

 mentioned. Certain it is, however, that there is a change in 

 the chemical nature of some of the chromatin at the time of 

 drying and a return to normal conditions when moisture is added- 



D. Animals Recovering from Desiccation. The condition of 

 the organs in rotifers recovering from desiccation is shown in 

 Fig. 15, Plate IV. This section was made from an animal which 

 after drying thoroughly had been put into water and then killed 

 four hours subsequent to the addition of water. This perhaps 

 represents a case where recovery was slower than usual, but the 

 condition of the tissues shows that it certainly would have re- 

 covered completely. 



In this same section the vitellaria are seen to be resuming their 

 normal condition. The cytoplasm is not different from that of 

 the normal tissue. One of the nuclei has completely recovered 

 while the other two which appear in the section are rapidly 

 assuming typical structure. One of the first changes noticeable 

 in the nuclei of cells of dried animals subjected to moisture is 

 the increase in thickness in the chromatic ring in the nucleus 

 and the greater affinity for stains exhibited by it. This is well 

 shown in these vitellarium nuclei. The two conditions of the 

 nuclei shown are therefore two stages in the process of recovery. 

 Fig. 23 represents a longitudinal section through the ovary- 

 vitellarium of an animal which had been kept in an evacuated 

 desiccator for fifteen days, then placed in water and killed one 

 hour and fifteen minutes after the addition of water. The re- 

 covery of this animal was more rapid than was that of the one 



