1919] McCulloch: Life Cycle of Crithidia and Trypanosoma 165 



and in the somatella of Crithidia euryophthalmi either the extra- 

 nuclear or the nuclear organelles may divide first. The ultimate 

 number of nuclei is equal to the number of parabasal bodies and of 

 the blepharoplasts. 



The stage of development of the merozoites when plasmotomy 

 occurs, is variable. Usually the rupture of the somatella occurs when 

 the merozoites are just beginning to elongate, as in figure 31. All 

 the organeles of these merozoites are definitely outlined, and the 

 flagella are free for a certain distance of their length. In a few 

 instances extremely elongate flagellates have been observed wriggling 

 about within the spherical structures. There is no evidence of a 

 residual mass of cytoplasm. 



A comparison of these two methods of multiple fission in the 

 life cycle of Crithidia euryophthalmi reveals the fact that they are 

 fundamentally different, In the first place, the former method, endo- 

 genous budding, involves only one organelle of the crithidia, namely, 

 the nucleus. In the latter method a somatella results from a repeated 

 division of the nucleus, blepharoplast, parabasal body, and, in all 

 probability, the nuclear and parabasal rhizoplasts. The flagella, how- 

 ever, in each case are new outgrowths from the newly formed blepharo- 

 plasts in endogenous buds or from the daughter-blepharoplasts in the 

 somatella. Secondly, the flagellates undergoing endogenous budding 

 retain their normal shape as elongate or pear-shaped crithidias. In 

 some instances their size increases as the buds develop. The flagellates 

 forming somatellas round up into spheres. The comparative efficiency 

 of the two processes from the standpoint of the multiplicative phase 

 in the host cannot be estimated. The length of time necessary 'to com- 

 plete each process and the conditions under which each occurs are at 

 present unknown. On the whole, the number of individuals resulting 

 from an equal number of endogenous flagellates or of somatellas is 

 approximately the same. Our conclusion, however, concerning the 

 two methods is that the endogenous budding is of greater importance 

 in the life cycle of C. euryophthalmi since in the preparations there 

 are relatively many more evidences of the endogenous budding than 

 of the somatella. 



BINAEY FISSION 



Another method of multiplication of Crithidia euryophthalmi in 

 the "crop" is binary fission. This process has also been observed in 

 the pyloric expansion. While the number of crithidias found dividing 



