1919] McCulloch: Life Cycle of Crithidia and Trypanosoma 147 



icular type of structure, having a relatively large karyosome, a light 

 area outside of this, and a clearly defined nuclear membrane. In 

 figure A, 3 a slightly different condition exists; the nucleus of C. < uryo- 

 plitlialmi is of the vesicular type, but the nuclear membrane is en- 

 crusted with considerable chromatin, and the central karyosome is 

 somewhat reduced as compared with that of C. leptocoridis in figure 

 A, 1. An examination of plate 5 indicates that the nucleus of this 

 flagellate (C. euryophthalmi) is characterized by the heavily encrusted 

 nuclear membrane, the small central karyosome, and the broad, clear 

 area between the membrane and karyosome. 



In the trypanosomes (fig. A, 3, 4, 5) the nucleus is slightly poste- 

 rior to the center of the body, which has a tendency to be shorter and 

 more club-shaped at the posterior end than is that of the crithidias 

 (fig. A, 1, 2). The nucleus of Trypanosoma lewisi (fig. A, 3) shows 

 a peculiar structure. In this particular form it is difficult to demon- 

 strate the nuclear membrane, since the light area encircling the more 

 deeply stained portion could be interpreted as either intranuclear 

 or extranuclear. However, taking into consideration other figures of 

 T. lewisi (cf. Minchin and Thomson, 1915, pis. 37, 42) this light area 

 has been regarded as being extranuclear and the diameter is 1/x 

 instead of 1.4/x. Within this relatively deep-staining nucleus the 

 chromatin is divided unequally into a large, irregularly shaped granule 

 and a smaller one. The nucleus of T. triatomae (fig. A, 4) resembles 

 that of C. euryophthalmi. It is also characterized by the chromatin- 

 encrusted nuclear membrane, the wide clear area, and the small cen- 

 tral karyosome, as in C. euryophthalmi. A nucleus of a somewhat 

 more complex type is found in Schizotrypanum cruzi (fig. A, 5). A 

 faint nuclear membrane limits the clear nuclear space which sur- 

 rounds the central karyosome containing a centriole at the base of 

 the rhizoplast. This nucleus is 1.7/x. in diameter and somewhat larger 

 than that of any other flagellate in the series. 



Blepharoplast. — This structure is of great interest since it is the 

 center of the extranuclear organelles, or neuromotor apparatus. In 

 the crithidias this structure is not a sharply defined basal granule at 

 the base of the flagellum. For instance, in Crithidia leptocoridis a 

 slight enlargement at the base of the flagellum is noted (fig. A, 1). 

 Since this slight enlargement stains with almost the same intensity as 

 does the flagellum it is exceedingly difficult to get a satisfactory concep- 

 tion of its structure. By careful focusing of the binocular microscope 

 with Watson's no. 20 holoscopic oculars, however, the small enlarge- 



