320 KOFOID AND SWEZY. 



chromidial cloud accumulates and then passes to the exterior in the 

 extranuclear cloud. This is a period of considerable increase in the 

 total amount of chromatin in the nucleus and in deeply staining 

 material outside of it. Within the nucleus it aggregates at first into 

 a ragged gradually thickening skein (PI. 1, Fig. 9) which at least 

 approaches the appearance of a continuous thread. This occurs 

 prior to the division of the blepharoplast and after that of the undu- 

 lating membrane. This is of brief duration and is followed by the 

 aggregation of the chromatin into somewhat elongated chromosomes 

 (PL 1, Fig. 10) resembling grains of rice in proportions. The number 

 of these is as a rule five, of which one is large, two of medium size, 

 and two small. During the transition from skein to chromosomes 

 the number of masses often exceeds five, possibly as the last step in 

 chromosome aggregation, although it is not always easy to distin- 

 guish these from following phase of division. Some instances of four 

 masses are resolved into five on close scrutiny. In other words the 

 evidence of a constant number of chromosomes in Trichomonas 

 augusta is of the same character as that for the normal number in 

 most metazoan cells. 



Splitting of the chromosomes follows soon after their organization, 

 in fact the numbers of individuals found in smears with five unsplit 

 chromosomes is much less than those with split or ten chromosomes. 

 The splitting occurs prior to the arrangement of the chromosomes 

 in an equatorial plate (PI. 2, Figs. 11-19) and is not synchronous. 

 There is a little evidence that the largest chromosome is slow in divid- 

 ing and that its division is unequal in an x-y fashion (Figs. 16, 23). 

 There is, however, no evidence that we are dealing here with matura- 

 tion divisions or sex chromosomes. It appears too frequently, in six 

 out of eleven figures on Plate 2 to be a chance inequality. The 

 direction of splitting is in each case longitudinal, though the parallel 

 position of the sister chromosomes (PI. 2, Fig. 15) is soon shifted to an 

 end-to-end one resembling a telosynapsis. The evidence (PI. 2, 

 Figs. 15-19) points toward the assimiption of the end-to-end posi- 

 tion by the swinging of the ends at one pole apart, while those in the 

 other remain together, rather than by a sliding of one chromosome 

 along the other till two poles originally at opposite ends of the pair 

 meet. Some suggestions of such sliding are, however, present in our 

 preparations and figures (PI. 2, Figs. 11, 17). 



The precise equivalent of the metaphase of metazoan mitosis, in so 

 far as it is represented by the splitting of the chromosomes has already 

 been accomplished before the amphiaster is formed in Trichomonas 



