42 I'tiivcrsity of California Publications in Zoology [Vol. 16 



tion between this plane of constriction and the previous one of pre- 

 cocious splitting except in figure 26 in which there are four pairs, 

 possibly not yet arranged in the equatorial plate. The cleft in these 

 is perpendicular to the equator. The number of chromosomes at this 

 stage is always four and there is little differentiation among them and 

 no marked lagging pair as in Trichomonas. 



The anaphase (pi. 6, figs. 27-29) is brief. In this the chromosomes 

 move apart toward, but not to, the pole, either in one plane (fig. 27), 

 or irregularly (fig. 28). and tend to group themselves in two coalescing 

 pairs (fig. 29) suggestive of two ancestral sources as in some Metazoa. 



The telophase is accomplished after the constriction of the nucleus 

 (fig. 29) into two spherical nuclei (fig. 30) within which the four 

 chromosomes mass themselves into the central karyosome. 



Plasmotomy or constriction of the cytoplasm occurs after mitosis 

 is completed (pi. 7, figs. 31-34). It is possible that these figures 

 represent the first division of a phase of multiple mitosis since in each 

 case the axostyles and nuclei are in the prophase of an ensuing division. 

 We have little evidence as to the direction of the plane of division 

 having found only one (fig. 32) stage intermediate between the com- 

 pletion of mitosis (fig. 30) and the late stage of plasmotomy (figs. 31, 

 33, 34) in which the two zooids have so far pulled asunder that their 

 anterior ends are nearly 180° apart. As shown in the discussion of 

 the division of the peristome, there is a little evidence that the plane 

 is longitudinal, parting the peristome in the median line. Such a plane 

 in the middorsal-veutral position would part not only the peristome 

 but the daughter axostyles and leave sisster nuclei in each of the result- 

 ing organisnLS. In figure 32 the left sister has moved anteriorly, 

 detaching itself from the right along such a plane. Persistence of a 

 connecting strand of cytoplasm at the posterior end and a shifting of 

 the daughters to an end to end position as in Trichotnonas is suggested 

 by figures 31, 33, 34. 



Our material has not furnished a full series of stages illustrating 

 both the development and disintegration of the multinuclear Plas- 

 modium such as was foimd in Trichomonas (Kofoid and Swezy, 1915 

 h). but enough of the stages have been found to determine that this 

 organism also forms an 8-zooid plasmodium, which because of the 

 binucleate nature of the individual will in this species contain sixteen 

 instead of eight nuclei. A 4-nucleate stage in the prophase of the 

 next division leading to the 8-nucleate with four potential individuals 



