376 LOUIS MAX HICKERNELL. 



an earlier paragraph, the addition of water causes a swelling to- 

 gether w T ith an increase in staining capacity in the nuclear ma- 

 terial with the result that the position of the chromatin is most 

 plainly seen not in the dry period but just subsequent to that 

 and before a sufficient time has elapsed to permit a normal 

 arrangement to be brought about. 



The observations upon the tissues of the dried animals re- 

 corded in the preceding paragraphs show that they react simi- 

 larly, with very few exceptions, to the drying stimulus. The 

 cytoplasm becomes denser. This is of course to be expected. 

 The nuclei, all of which have a very definite and similar chromatic 

 pattern, undergo a chromatic rearrangement which is striking 

 and uniform. That this chromatic movement is the visible 

 expression of an adaptation to a new sort of environment can 

 hardly be doubted. The resumption of normal conditions in 

 nucleus and cytoplasm is likewise uniform in the elements of the 

 different tissues. If any doubt existed as to the nature of the 

 adaptive response in the desiccated condition that uncertainty 

 would be removed upon observing the return to normal con- 

 ditions as shown in sections of recovering rotifers. The sig- 

 nificance of the chromatic movement and its interaction with the 

 cytoplasm in the different tissues will be discussed fully in a 

 later section. 



IV. REVIEW AND DISCUSSION. 



The literature relating to the cytology of desiccation is, in the 

 case of animals, very sparse, and, relating to rotifers, almost 

 nothing. While rotifers have been studied since the invention 

 of the microscope, the chief interest has been along anatomical 

 lines. Along with the anatomical studies, the Bdelloidese have 

 received consideration in discussions as to whether they actually 

 dry up and recover from the desiccation, but apparently no one 

 thought to examine the cytological changes underlying the 

 process. 



Pfeffer, in his "Physiology of Plants," makes numerous ob- 

 servations upon the subject of desiccation among members of 

 the plant kingdom. His point of view is, of course, physiological 

 rather than cytological. 



