342 H. S. DAVIS 



can be distinguished at one side of the spindle. In many cases 

 as in figure 53 the nucleolus has entirely disappeared at this 

 time and I have never been able to distinguish it at a later stage. 

 In all cases, when present, the nucleolus lies at one side, and at 

 some distance from the spindle, never on it. Figure 55 shows a 

 telophase in which the interzonal filaments can be plainly dis- 

 tinguished and there is a slightly developed 'zwischenkorper.' 

 In some cases the interzonal filaments may persist for a short 

 time after the daughter cells have otherwise entirely separated. 



2. Polysporous form 



a. Living trophozoites. In addition to the forms described 

 above there are almost invariably present a number of tropho- 

 zoites which have a very different appearance. These tropho- 

 zoites, which are usually much larger than the disporous form, 

 are sometimes relatively rare, in other cases they were found to 

 be equally, if not more abundant than the smaller form. I 

 am uncertain whether or not they are ever entirely absent. Ac- 

 cording to my notes a few fish examined during the early part 

 of the investigation contained none of this type, but I do not 

 feel at all certain that they were not present in small numbers, 

 since in that case they could easily be overlooked. At first I 

 considered that the larger trophozoites were specifically distinct, 

 but was later forced to the conclusion that both the large and 

 small types of trophozoites are but different forms of the same 

 species. The reasons for this conclusion will be given later. 



The polysporous trophozoites have a very characteristic ap- 

 pearance, and in all but the youngest stages can readily be dis- 

 tinguished from the disporous form already described. When 

 attached to the inner lining of the bladder they are usually elon- 

 gated and cylindrical, but considerably larger at the base where 

 they are attached to the epithelium (figs. 61 and 62). The free 

 end of the body is commonly drawn out a long, tail-like process, 

 rounded at the end (fig. 56). The size varies greatly. Some 

 are no larger than the disporous trophozoites while one of the 

 largest measured was 575 m long with a maximum diameter of 



