168 University of California Publications in Zoology [Vol. 19 



panosoma lewisi as being due to a repeated binary fission wherein the 

 resulting individuals failed to separate immediately. Kofoid and 

 Swezy (1915) have described in detail the process of binary fission and 

 of multiple fission for the trichomonad flagellates, and these authors 

 found the increase of organelles in multiple fission to be due to thrice 

 repeated mitosis. The larger size of those flagellates together with 

 the correspondingly increased size of the organelles presents better 

 material for the study of binary and multiple fission than do the 

 trypanosomes or the crithidias. In C. euryophthalmi the minute size 

 of the flagellates undergoing either process have made accurate inter- 

 pretation thus far impossible. For this reason the relation of binary 

 fission to multiple fission in a somatella must remain an open question 

 for the present. 



INTRACELLULAR CRITHIDIAS 



Another salient similarity between the life cycle of Critkidia 

 euryophthalmi and the life cycle of Trypanosoma lewisi in the inverte- 

 brate host is the appearance in each life cj-cle of a stage of intra- 

 cellular multiple fission. In C. euryophthalmi there is figured for 

 the first time an epithelial cell in the life cycle of a crithidia taken 

 from a "crop" containing numerous crithidial parasites. Careful 

 examination of this infected cell shows that there are three distinct 

 groups (pi. 3, fig. 39, a, b, c) of parasites and a number of scattered 

 crithidias. Altogether there are approximately seventy parasites in 

 this one epithelial cell. In figure 39a the crithidias are of two sizes: 

 long, slender flagellates, and short, non-flagellated forms. Since mul- 

 tiple fission of either the endogenous or somatella type produces zooids 

 or merozoites of approximately the same size, it appears that several 

 infections have occurred in this cell. It is conceivable that all the 

 elongate flagellates are due to one infection while the short, non-flag- 

 ellated crithidias are due to a second infection. In figure 39& there 

 are ten small oval forms. In structure they show a diffuse nucleus, 

 as do the other parasites within this host-cell, which is probably due 

 in part to the thickness of the cell. A nuclear rhizoplast can be 

 observed passing from the nucleus to the blepharoplast, and a short 

 intracellular flagellum extends forward to the anterior end of the 

 body. The parabasal body of each is a relatively small and deeply 

 staining structure. At c and e of figure 39 are more of the small oval 

 forms. In the former region the cytoplasm of the host-cell has been 



