372 LOUIS MAX HICKERNELL. 



represented in Fig. 15 for it had already partially unfolded at 

 the time it was killed. The nuclei here show several chromatic 

 patterns not figured in the other sections but they are all stages 

 incidental to the resumption of the typical nuclear form. 



Fig. 22 shows a transverse section of the vitellarium of an 

 animal dried at room temperature, then placed in an evacuated 

 desiccator for six days, then in water for one hour and finally 

 killed and sectioned. The nuclei here show almost complete 

 recovery, while the cytoplasmic part of the structure has not 

 regained the characteristic regular pattern. 



Another condition found frequently in the cytoplasmic portion 

 of the vitellaria of rotifers recovering from desiccation is that 

 represented in Fig. 20. The vitellarium nuclei are found in 

 various stages of recovery, while entirely outside of the nuclear 

 membrane and indistinguishable in appearance from ovarian 

 nuclei are round chromatic particles. This condition is important 

 for I believe it shows what we have not been able to demonstrate 

 visually before, namely, that the withdrawal of water causes the 

 chromatin in the vitellarium nucleus to diffuse into the cytoplasm, 

 but the very withdrawal of water initiates a chemical change 

 which causes the chromatin to lose its staining power. The 

 addition of water causes this same chromatic material, scattered 

 about through the cytoplasm to resume its normal staining reac- 

 tion and in that way its actual presence is for the first time 

 visually demonstrated. Gradually this extranuclear chromatin 

 in the vitellarium disappears and it is probable that its dis- 

 appearance is due to some chemical change which again causes 

 it to assume the appearance or become a part of the regular 

 cytoplasmic structure. 



In Fig. 23 the cytoplasm of the ovary shows that it has re- 

 gained its clear, homogeneous appearance. The number of 

 ovarian nuclei is also greater than in sections of that organ which 

 have not been recently dried. I have found this condition 

 repeatedly in sections of animals recovering from drying. This 

 is clearly one of the steps incident to increased reproductive 

 activity. There are several factors involved in this process. 

 It will be recalled that in drying the cytoplasm of the ovary 

 becomes dense and takes chromatid stains more readily than do 



