HtU)] Kofokl-ilci'uUiicli : Trijpniiosoiiia tiiafoiiHic 11!) 



occurrence in the same stomach with these of an occasional individual 

 with an oval, but still diffusely granular, nucleus and a parabasal 

 which liad almost reached the anterior position characteristic of the 

 crithidial phase (pi. 14, fig. 13). 



2. The structure of the crithidial form. — The crithidial form has 

 a length of 8^0/x and a diameter of 1.8-2.5/i, rarely as much as 4//. 

 It is widest posteriorly and the posterior end is more or less abruptly 

 subeonical. Anteriorly the body is slender and tapering (pi. 14, figs. 

 14-19, pi. 15, tigs. 22-26). It is less sinuous in locomotion, the pos- 

 terior part being more rigidly held in one form than in the trypano- 

 some stage ; hence in the pictures which it affords the body is more 

 nearly straight, or more regularly curved than in those of the trypano- 

 some phase. It also moves with a more darting motion. The undu- 

 lating membrane is much reduced and no differentiated zone is evident 

 along the flagellum. 



The nucleus is spherical, posteriorly located, 1.2-2ft in diameter, 

 with chromatin-encrusted membrane, central karyosome in diameter 

 aljout 0.35 that of the nucleus. The tlagellum terminates in a very 

 minute blepharoplast (pi. 14, fig. 19), immediately above the level of 

 the bilobed, transversely located parabasal, whose length is 0.5-0.7 

 the diameter of the nucleus. The parabasal often lies adjacent to 

 the nuclear membrane, and appears to be suspended from the ble- 

 pharoplast by a fan-shaped parabasal rhizoplast. The parabasal is 

 often seen to be distinctly lateral in attachment (pi. 14, figs. 14, 15). 

 In rare cases a nuclear rhizoplast appears to run from the blepharo- 

 plast to the nuclear membrane (pi. 15, fig. 23), or even to the central 

 karyosome (figs. 21, 22). Occasionally traces of a chromatic fiber 

 run posteriorly from the blepharoplast to the posterior end as a sort 

 of a feebly developed axostyle (pi. 14, figs. 14. 15. pi. 15, figs. 23. 29). 

 Traces of a myoneme anterior to the nucleus are sometimes to be 

 found (pi. 14, fig. 14, pi. 15, figs. 22, 23). 



There appears to be among the crithidial forms in the stomach 

 two types representing two tendencies. The first is a progressive 

 rolling up (or unrolling?) of the flagellate and the second may in- 

 clude a progressive decrease (or increase?) in size. We will now 

 consider these two series. 



3. The rolled-up type. — There ajipears among the crithidial forms 

 of the stomach a series of large individuals 20-30/u, in length with 

 elaviform body and posteriorly located nucleus (pi. 14. figs. 16-19, 

 pi. 15, figs. 20, 21). It is not unlike, in its progress and result, the 



