166 University of California Publications in Zoology [ VoL - 19 



in this way is relatively small, on the whole, yet crithidias of almost 

 any stage of development apparently may thus increase their number. 

 Some conception of the prevalence of the process throughout the 

 life cycle may be gained by studying figures 33 to 37. In addition 

 to these smaller crithidias in various stages of development many 

 instances of binary fission have been observed among the elongate or 

 mature flagellates. 



The blepharoplast or the centrosome of the nucleus may initiate 

 the division of the several organelles. In figure 33, plate 3, the 

 centrosome of the nucleus is in the process of binary fission and there 

 are present two daughter-nuclei. In each of the nuclei the chromatin 

 is peripheral on the nuclear membrane. The blepharoplast and the 

 parabasal body have not yet begun to divide. The general appear- 

 ance of this binary fission form is very similar to that of the smaller 

 somatella. In the unflagellated crithidia shown in figure 34, plate 3, 

 the blepharoplast and parabasal body have divided but the nucleus 

 is still intact. A more advanced stage of binary fission is found in 

 figure 35. In this small, unflagellated crithidia the blepharoplast, 

 parabasal body, and the nucleus have divided, and a light, thin area, 

 which is preliminary to the cleft in the cytoplasm, extends longi- 

 tudinally between the two sets of organelles. The flagella can also 

 be observed. The longer, more clearly defined flagellum is evidently 

 that of the parent since the second is shorter and less distinct. The 

 last stages of binary fission are shown in figures 36 and 37. In figure 

 36 the cleft in the cytoplasm can be traced from the anterior to the 

 posterior end, and the daughter flagellum has also attained a greater 

 length. ' The two flagella in figure 37 are the same length; the separa- 

 tion of the two daughter individuals is more marked and almost com- 

 plete in figure 38. The posterior ends are the last to remain attached 

 and the lashing about of the anterior ends assists efficiently in the 

 final tearing apart. 



One of the most interesting problems in connection with this 

 method of reproduction has always been the origin of the daughter- 

 flagellum. Is it due to the division of the flagellum of the parent or 

 to a new outgrowth from the daughter-blepharoplast ? A review 

 of the work already done on this genus indicates that with the excep- 

 tion of Porter (1909, 1910) all authors regard the daughter-flagellum 

 as a new outgrowth and consider that the parent-flagellum does not 

 split to form two daughter flagella. My work on Crithidia leptocoridis 

 and C. euryophthalmi, unlike that of Porter, is an agreement with 



