DESICCATION IN PHILODINA ROSEOLA. 387 



nuclear membrane. This karyosome is of course not a true 

 nucleolus since it is made up of chromatic material. This type 

 of nucleus has been given the name of "nucleoles noyau" by 

 Carnoy and it has been described by numerous authors in the 

 cells of several kinds of unicellular animals. Nucleoli showing 

 apparently all grades of morphological and chemical properties 

 between true plasmasomes and karyosomes have been described 

 by various authors (see Montgomery, '98) so that it cannot be 

 said that there are no intermediate conditions to be found. 

 Montgomery says: 'The existence of Carnoy 's 'nucleoles 

 mixtes' and 'nucleoles-noyaux' in cells of metazoa appears to 

 be doubtful" yet the " pseudonucleoli " which he describes in 

 the ova of the mollusc Montagua pilata have many of the proper- 

 ties of a chromatin nucleolus or karyosome. 



The significance of the peripheral chromatic ring in the dried 

 rotifer nucleus is a point w r hich requires explanation and correla- 

 tion with the other conditions incident to the adaptation of the 

 rotifer to its dried condition. The chromatin ring undoubtedly 

 represents a stage of chromatin migration. There are two 

 possibilities regarding the extent of this migration. The chro- 

 matin may merely leave its place in the center of the nucleus 

 and, by taking a position next to the nuclear membrane, remain 

 within the nucleus proper during the entire dry period. On 

 the other hand, some of the chromatic elements might be of 

 such nature as to pass readily through the nuclear membrane 

 while the latter might be impermeable for others. That ma- 

 terials may be changed chemically within the nucleus is admitted. 

 In nuclei of cells which have just completed mitotic division the 

 nucleus imbibes substances from the cytoplasm and changes 

 them into nuclear material. It is also a matter of common 

 knowledge that at the beginning of mitotic activity much ma- 

 terial is cast out of the nucleus into the cytoplasm. However, 

 it is not commonly contended that materials pass from the 

 nucleus into the cytoplasm without a rupture of the nuclear 

 membrane. That the latter condition is a possibility in the 

 rotifer nucleus will appear shortly. 



The karyosome of the rotifer nucleus being almost pure 

 chromatin, the reason for its migration might be sought in a 



