338 KOFOID AND SWEZY. 



anteriorly (PI. 5, Fig. 46), but the nucleus is not in a constant position 

 with respect to the concavity (Plate 5, Figs. 46, 48, 50, 52), indicating 

 some intracytoplasmic mobility of these organelles. 



Binary fission in Trichomonas muris. 



The dense karyosome resulting from the fusion in the telophase 

 of the clu'omosomes in one central mass is followed by a stage in 

 which the chromatin is dispersed in numerous subequal spheroidal 

 and ellipsoidal granules, with a delicate connecting achromatic net 

 (PI. 5, Fig. 47). As mitosis approaches a faint intranuclear cloud 

 gives a dark homogeneous (PI. 5, Fig. 49) appearance to the nucleus 

 and seems to emerge thence into the cytoplasm where it is dissipated. 

 The equidistant subequal chromatin granules, at first over twenty 

 in number, are then arranged in a more or less connected, sometimes 

 spiral (PI. 5, Fig. 50) skein in which the number of separate chro- 

 matin units becomes reduced (PI. 5, Figs. 50-52) until finally there 

 are but five groups (^Fig. 53) which present the appearance of five 

 pairs of chromosomes in parasynapsis, or as we interpret it in the 

 light of our results in T. augusta, in five chromosomes split longitudi- 

 nally. These chromosomes are somewhat unequal in size. There is a 

 pair of small ones, overlooked by Kuczynski (1914) which in the five 

 nuclei in this stage found by us is always located near the anterior 

 surface of the nucleus (PI. 5, Figs. 53-55). This pair, as in T. augusta, 

 also lags in division in the equatorial plate. There is a large pair and 

 three pairs of medium size, one of which is a trifle smaller than the 

 others. They do not divide synchronously in the equatorial plate 

 (PI. 5, Fig. 56). 



Kuczynski (1914) concludes that there are but four of these groups 

 and regards the granules seen in an earlier stage as the true chromo- 

 somes and these as plurivalent aggregates. However, since these are 

 the actual masses parted in the equatorial plate (PI. 5, Fig. 56) it 

 seems more in keeping with the terminology of mitosis generally to 

 regard these as the true chromosomes and the earlier subdivisions as 

 chromomeres, whatever these may be. These pairs of chromosomes 

 which lie with their long axes parallel and rather closely appressed, 

 appear almost to merge into a single unit just before entering the 

 equatorial plate (PI. 5, Fig. 54). The indications are that they lie 

 in this plate in an end-to-end position as in T. augusta (Fig. 56) parting 

 in any event at a median transverse constriction which we assume 



