IS!! 1 ] McCullock: Life Cycle of Crithidia and Trypanosoma 145 



the crithidial forms the extranuclear complex of organelles is anterior 

 to the nucleus (fig. A, 1, 2) and the body has a tendency to be 

 cylindrical in cross-section and to show only a slight undulating mem- 

 brane (und. m.. fig. A). These crithidial forms are common to the 

 life cycle of both Crithidia and Trypanosoma. The next step in our 



l 



Fig. A. Typical crithidial forms of: (1) Crithidia leptocoridis ; (2) C. 

 euryophthalmi ; (3) Trypanosoma lewisi (after Minchin and Thomson, 1915, pi. 

 37, fig. 66); (4) T. triatomae; (5) Schizotrypanum cruzi (after Chagas, 1909, 

 pi. 13, fig. 16); showing the similarity of the several flagellates in size, form 

 and structure. X 3500. bl., blepharoplast; fl., flagellum; n,., nucleus; pb., para- 

 basal body; pb. rh., parabasal rhizoplast; ft. rh., nuclear rhizoplast; und. m., 

 undulating membrane; vac, vacuole. 



discussion will be directed to the demonstration of the close resem- 

 blance of the crithidial forms of the genus Crithidia to those of 

 Trypanosoma in the invertebrate host. 



A series of typical crithidial flagellates (fig. A) has been selected 

 from the stomach phase of the life histories of both Crithidia and 



