DESICCATION IN PHILODINA ROSEOLA. 369 



before actual drying occurs. At this time the tissues contain 

 the usual amount of moisture but the approach of the dry con- 

 dition is, at the same time, apparent to the animals. That 

 there can be no doubt about the preparation of the animals for 

 the dry state is evidenced by their behavior at the onset of 

 desiccation, before described. 



Sections of animals killed at the moment when the last visible 

 traces of moisture were disappearing, confirm the supposition 

 outlined above. The nuclei of the cells of the different tissues 

 plainly show the remarkable changes which are going on and 

 which I have described in an early part of this section. While 

 in many cases the rearrangement of chromatin is not so com- 

 plete as in some of the sections of dried animals here shown, yet 

 it was definite and uniform in the different tissues and indicates 

 beyond question that the transitional period for chromatic re- 

 arrangement occurs just before the last traces of moisture are 

 removed. 



The movement of chromatin just before drying is interesting 

 for the light it throws upon the question of the lability of the 

 nuclear material. Chromatin undergoes changes of form, posi- 

 tion and chemical structure at the time of mitotic activity but 

 there are few cases recorded where such changes occur during 

 the resting condition. In the present instance, however, we 

 have a marvelous rearrangement of the nuclear materials which 

 occurs as a vegetative rather than a reproductive process, the 

 essential steps of which may take place in a few minutes and the 

 new internal conditions so established enabling the animal to 

 resist an unfavorable environment for years. 



In this connection also lies a clue to the solution of the question 

 of mortality among rotifers which have been dried. Since under 

 the most favorable conditions of drying some few animals never 

 survive, it seems that there should be some definite cause to 

 account for the fact. Comment has been made concerning the 

 tearing of the organs of a rotifer which might result from too 

 rapid drying. In cases where this last factor cannot enter there 

 are still some fatalities and these cases seem to admit of explana- 

 tion upon the basis of lack of time or vitality to bring about the 

 internal rearrangement of cell elements necessary in resisting 

 the dried condition. 



