226 University of California Publications in Zoology [Vol. 19 



the above interpretation still tentative. Much work is still needed 

 upon CollocUcty&n and related forms to clear up fully the question 

 of the division center. 



The time at which the blepharoplast divides has not been definitely 

 determined. There is evidence of its division as early as the middle 

 of the prophase (pi. 11, figs. 40, 40a). It seems, from the figures 

 just referred to, that the method is one of doubling of the basal 

 granules, thus making two pairs, which gradually separate (pi. 11. 

 fig. 46, pi. 12, figs. 48, 53, 54). No splitting of the flagella has been 

 observed, but since only equal flagella have been found in these 

 stages, it seems safe to conclude that the flagella split longitudinally 

 or new ones grow out at about the same time as the doubling of the 

 paired basal granules. At the metaphase the doubling is complete 

 (pi. 12, fig. 48). 



PROPHASE 



"With the unequal constriction of the karyosome. sometimes even 

 before this differential division has been completed, the microkaryo- 

 some organizes about itself a membrane, which seems to have a kinetic 

 or metabolic function and which I shall designate as the kinetic 

 membrane. The macrokaryosome is passive in behavior and remains 

 outside of this active membrane. The kinetic membrane does not 

 simply bound the hyaline area, but is almost surrounded by such a 

 zone (pi. 10, fig. 32). At first the space between the microkaryosome 

 and the membrane is hyaline, but it is soon filled with a dense 

 chromatin cloud (pi. 11, figs. 37, 38, 41, 42, 44). This kinetic mem- 

 brane seems somewhat less chromatic than the nuclear membrane. 

 Usually it is spherical or irregularly globular, but in two or three 

 instances angular, almost polygonal (pi. 10, figs. 32, 33), which is 

 probably an artifact. As it enlarges, however, it may elongate and 

 its shape become modified by the organizing spindle. 



When the organization of the microkaryosome is begun, the 

 chromatin outside the kinetic membrane tends to accumulate in 

 granules or masses which are linked together by slightly chromatic 

 strands (pi. 10, figs. 30. 32, 36). Much of it is encrusted upon the 

 nuclear membrane (pi. 10. fig. 32) ; much forms immediately around 

 the hyaline area surrounding the kinetic membrane (pi. 10. fig. 30). 

 frequently also about the macrokaryosome (pi. 11, fig. 40). The 

 whole peripherial zone becomes thus involved and with the expansion 

 of the active hyaline area is more and more encroached upon until 



