230 University of California Publications in Zoology [Vol. 19 



uniformity of size and shape, being ovoid, from 1.5 to 2/j. in length, 

 0.5 to 0.75/m wide; with one exception, namely that one chromosome 

 is but half so long and hardly so wide. These are arranged equatori- 

 ally with very slight tendency to V-shape or crescent-shape. Their 

 elongated axes are meridional to the spindle. 



In division (pi. 12, fig. 50) all the chromosomes but one in this 

 spindle appear to have parted transversely. The spindle fibers are 

 attached to the ends and not to the centers or sides. This parting 

 may be fundamentally similar to the parting of the chromosomes as 

 found by Tschenzoff (1916) in Euglena. The precocious splitting 

 is evidently not so far removed from the metaphase, however, since 

 in Euglena it apparently takes place in the preceding telophase of 

 the parental individual, while in Collodictyon it takes place no farther 

 back than the late prophase just preceding the metaphase. 



In the most satisfactory metaphase I have found (pi. 12, fig. 50), 

 the small chromosome has not as yet divided. No constriction can 

 be found in it in this figure. It may best be interpreted as a lagging 

 chromosome. In such a case it would probably divide later on in the 

 metaphase or early anaphase, though there is no available material 

 to determine this matter. 



In one anaphase (pi. 12, fig. 51) there are obviously unequal 

 chromatin masses. These are either so deeply stained as to prevent 

 an accurate chromosome count or else the chromosomes were con- 

 tracted and massed in the killing and fixation. It is barely possible 

 that this inequality of mass is due to the failure of the lagging 

 chromosome to divide, thus giving an unequal qualitative as well as 

 quantitative division comparable to the sex chromosome ; but we have 

 as yet no evidence of gamete formation in this genus. Such in- 

 equality may also be explained by the passing over to one of the 

 daughter nuclei of the remnants at least of the macrokaryosome 

 (pi. 12. figs. 48. 56). Any inequality of mass which is evident in 

 early anaphase is soon obscured by the growth of chromatin, which 

 is proceeding rapidly. I regret that I have not found a sufficient 

 number of metaphase stages to warrant a detailed study. Of the 

 many thousand individuals studied I have seen but three or four 

 equatorial plates. 



As suggested above, the indication of a peculiar splitting of cer- 

 tain peripheral chromatin granules is a prophase, not a metaphase 

 phenomenon, related rather to the precocious splitting of the seg- 

 mented spireme. I have found no indication of a division of the 





