Timherlake — Swarm-Sporcs of Hydrodictyon. 503 



torial plates in. which the chromatin mass always appears, so 

 far as my preparations show, to be nearly equal in its length 

 and breadth. The equatorial plate in the larger spindle con- 

 sists of a greater amount of chromatin than that of the smaller 

 one. Whether the number of chromosomes varies in the two 

 cases is an important point that I could not determine, as I was 

 unable to find the stages of division in which the chromosomes 

 could be distinguished from each other. It is quite probable 

 that the different sized nuclear figures are derived from nuclei 

 that differed in the same respect before division commenced, 

 though I have not yet succeeded in finding the stages that would 

 confirm this suggestion. The largest spindles are somewhat 

 multipolar with the chromatin arranged in such a way as to form 

 a branched equitorial plate (Figs. 17a and 10a), so that the en- 

 tire figure has the appearance of the well kno^vn cases of poly- 

 centric nuclear fio-ures in cells treated with certain Doisons or 

 subjected to other unusual stimuli. But there was no otlier evi- 

 dence of abnormality either in the structure of the cytoplasm or 

 that of the nuclear figures themselves. 



So far as I could determine there was no particular time 

 during the day when nuclear division was most likely to take 

 place. Material in which I have found it was in part killed 

 at various hours during the forenoon and in part in the after- 

 noon. In a small amount of material killed at different times 

 during one night, I w^as unable to find any indications of 

 division, but of course so small an amount of material would 

 not show conclusively that it never takes place at night. Still 

 it seems quite evident that there is no regular daily period 

 to which division is confined. This is made the more cer- 

 tain by the fact that in a single net one cell alone may show 

 nuclear division while in the other cells the nuclei seem to 

 1)0 in a resting condition. That, however, the divison de- 

 pends upon conditions common to the whole cell is shown by 

 all of the nuclei of a single cell dividing at the same time though 

 without being in the same stage. Very often all stages from 

 the early prophases to the late anaphases can be found in a 

 single cell in a more or less regular succession from one end 

 of the cell to the other. (Figs. 15 and 10.) This fact is in- 



