DIVISION OF COLLAR-CELLS OF CLATHRINA CORIACEA. 627 



in all cases the protoplasmic pi-ocess in question is very 

 short in proportion to the length of the original flagelluiu. 



The division of the blepharoplast takes place with forma- 

 tion of a distinct centrodesmose connecting the two daugrhter- 

 blepharoplasts (figs. 6, 1, 13). 



During these changes the collar remains practically unal- 

 tered, except that it begins to show more or less cleai-ly the 

 appearance of shrinkage and degeneration characteristic of 

 the succeeding stages of the division. 



(3) The Mitosis. — The general course of the mitosis in 

 the collar-cell is similar to that known to occur in the cells of 

 other Metazoa generally, and described for sponges by Maas 

 (10, 11) and Jorgensen (9). It is unnecessary, therefore, 

 to do more than describe its most characteristic features. 



As already stated in a previous section, the nucleus of a 

 collar-cell about to divide, but before any changes prepara- 

 tory to division have begun in the chromatin contents, is of a 

 pale type — that is to say, the granules of chromatin dis- 

 tributed over the general framework ai-e very fine and 

 scattered evenly, so as to give the nucleus an almost homo- 

 geneous appearance relieved only by the karyosome, stained a 

 deep black, after iron-h£ematoxylin, in contrast with the pale 

 grey tint of the remainder of the nucleus (figs. 1 , 10, 11). The 

 nucleus at this stage is also distinctly larger than the average 

 nucleus of a resting" cell. 



The first changes to be observed in the chromatin contents 

 of the nucleus are that they stain darker and become more 

 blotchy and uneven in appearance, apparently as the result of 

 the minute granules of chromatin being clumped together to 

 form coarse grains or masses. Figs. 6 and 7 show early 

 stages in this process ; the masses of chromatin still stain 

 faintly, appearing to be loose in texture and ill-defined in 

 outline, and the karyosome stands out sharply. In later 

 stages (figs. 8, 12) the chromatin masses become more definite 

 in outline and somewhat smaller, and the deep stain they 

 take gives the impression that they are more closely knit and 

 of denser texture ; the karyosome, however, is still distinct. 



VOL. 55, PART 4. NEW SERIKS. 42 



