STRUCTURE AND DIVISION OF TRICHOMONAS 135 



reticulum of the nucleus (figs. 10 to 17 and 21). Occasionally 

 the six elements become arranged in the form of a chain, recalling 

 the chains of split chromomeres sometimes seen in metazoan 

 prophases (fig. 15). In cases where the fixation has not been 

 good, the two parts of each element appear to be fused together, 

 so that the nucleus seems to have six single granules in it in 

 addition to the caryosome. This condition seems to be more 

 prevalent in the later than in the earlier prophases (fig. 19). 

 Since in the earliest stage in which the prophase chromosomes 

 can be distinguished they are already double, it has been im- 

 possible to determine whether or not the doubling is the result 

 of antecedent splitting. 



In the earlier stages the six chromosomes are always outside 

 the clear area surrounding the caryosome, but later the boundary 

 of the clear area disappears, and the caryosome then seems to 

 be more directly connected with adjoining chromosomes by the 

 non-chromatic reticulum (fig. 15). In cases where the chromo- 

 somes appear to be single, due to fusion, and where the peri- 

 caryosomal space can no longer be defined there seem to be 

 seven chromosomes instead of six, since the caryosome is not 

 always easily distinguishable from the chromosomes. In all 

 such cases, however, careful study has resolved the group of 

 seven into six chromosomes and one caryosome. During the 

 progress of the prophase changes the caryosome gradually loses 

 its staining power just as do nucleoU of metazoan cells, and at 

 the metaphase no trace of it is visible. Figure 22 shows a very 

 late prophase or early metaphase with the spindle partly formed 

 and a faintly defined vestige of the caryosome. 



Number of prophase chromosoines. Wenyon ('07) reports the 

 number of prophase chromosomes as six and says that they early 

 divide into two, giving six pairs of granules. In his figure 2, 

 plate 11, for example, he shows six pairs of granules besides a 

 caryosome. My results are thus in agreement with his. Kuc- 

 zynski ('14) describes eight prophase and four metaphase chromo- 

 somes and again insists on these numbers in his later paper 

 ('18). In this later paper, however, he admits (p. 128) that 

 "Over 70 per cent of the observed prophase nuclei of the Tri- 



JOURNAL OF MOKPHOLOGT, VOL. 36, NO. 1 



