1919] McCulloch: Life Cycle of Crithidia and Trypanosoma 153 



of C. euryophthalmi, notwithstanding the fact that the initial stages 

 of the two life cycles are entirely different in the insects. The initial 

 stages of the crithidial life cycle are small, oval spores, which develop 

 into elongate Crithidial flagellates, whereas the initial stages of the 

 trypanosome are trypanosomes from the blood of a rat, which indirectly 

 by a process of multiple fission, produce very similar elongate crithidial 

 flagellates. Subsequently all of the rectal stages in each life cycle are 

 very similar. 



Fig. B. Five figures of Crithidia euryophthalmi to show the relation of the 

 parabasal body to the flagellum, blepharoplast, rhizoplast, and nucleus. X 3500. 

 Abbreviations same as in figure A. 



The developmental or infective series of Crithidia euryophthalmi 

 consists of the stomach phase or the crithidias of the ''crop," mid- 

 stomach and upper part of the pyloric expansion. The degenerative 

 series includes the late rectal phase or the attached crithidias of the 

 pyloric expansion. 



THE DEVELOPMENTAL SERIES 

 STOMACH PHASE 



The stomach phase of Crithidia euryophthalmi is apparently init- 

 iated when the small, oval spores (pi. 2, figs. 1, 2) casually ingested- 

 with food begin to develop in the "crop." Such initial infective 

 spores develop rapidly into a swarm of multiplying crithidias (pi. 2, 

 figs. 2-7). Later as mature flagellates (pi. 2, figs. 9, 10) the crithidias 



