1919] McCulloch : Life Cycle of Crithidia and Trypanosoma 151 



panosome rounds up for the process of multiple fission no nuclear 

 rhizoplast is in evidence, but after the complete transition into the 

 crithidia! form the nuclear rhizoplast can be readily demonstrated 

 with the high power binocular microscope and Watson's holoscopic 

 eyepiece. It is also possible that further work will show that the 

 centrosomic structure of the trypaniform flagellate differs from that 

 of the crithidial form, and consequently that the rhizoplasts are absent 

 in the former. 



In Schizotrypanum cruzi (fig. A, 5) the parabasal body is slightly 

 bilobed in appearance, and is suspended from the blepharoplast by a 

 clearly defined, fibrous rhizoplast. The suspensory apparatus of the 

 parabasal body is here relatively larger and apparently more highly 

 developed than in any of the other flagellates. A few of the trypani- 

 form stages also show a similar parabasal rhizoplast, according to the 

 figures of Chagas (1909). In the crithidial stages of this trypano- 

 some, as shown in figure A, 5, there is a sharply defined nuclear rhizo- 

 plast passing from the centriole of the nucleus to the blepharoplast. 

 The position of the parabasal body in 8. cruzi is similar to that of 

 Crithidia < ury&phthalmi and is situated apparently to one side of the 

 nuclear rhizoplast. 



One of the most important discoveries in connection with the study 

 of these organelles is the fact that the parabasal body, or the so-called 

 kinetonucleus, is not axial in position in Crithidia euryophthalmi 

 (figs. B, 1-4) and apparently not in the other flagellates (figs. A, 

 1, 3-5). With the evidence at hand to show definitely that this body 

 is not axial but a lateral appendage of the blepharoplast in ('. < uryo- 

 phthalmi it is necessary to look upon this organelle as something other 

 than a second nucleus or a kinetonucleus. Reference has already 

 been made to the work of Dr. Kofoid (1916) concerning the homology 

 of this organelle with the parabasal body of other flagellates. The 

 observations concerning the origin of this structure, the location 

 and relation of the parabasal body to the other organelles as found 

 in the study of C. euryophthalmi offer some of the best evidence against 

 the binuclear conception of these flagellates (Hartmann, 1911). 



Flagellum and undulating membrane. — Owing to the relationship 

 which exists between the flagellum (//.) and undulating membrane 

 (unci, m.) it is convenient to describe these two organelles together. 

 The flagellum consists of an outgrowth from the blepharoplast and is 

 surrounded by a cytoplasmic sheath which is continuous with the sack- 

 like sheath covering the parabasal body. In the ordinary preparations 

 no distinction can be made between this central portion originating 



