38 MANUAL OF HUMAN PROTOZOA 



nucleus is located very close to the anterior tip. It is char- 

 acterized by a distinct membrane to which chromatin 

 granules are attached. The three flagella arise from a 

 point anterior to the nucleus, and are of the same length 

 (about 7-10m long). The fourth flagellum is about one-half 

 the length of the other flagella and lies in the cytostomal 

 cleft. The ridge of the cytostome is supported by two 

 fibrils of which one on the right side is usually longer 

 and makes a loop at the posterior margin. 



Cysts 



1. Living specimens. The cyst (Fig. 9, 5) usually occurs 

 with the trophozoite. It is pyriform and resembles a melon 

 seed. It is about 7-10|j long. Its contents appear homo- 

 geneous except a few coarse granules. In general appear- 

 ance, it is similar to the cyst of RetoHamonas intestinalis 

 (p. 31), but noticeably larger than the latter. 



2. Stained specimens. The uniformly thin, but distinc- 

 tive cyst wall is clearly recognized (Fig. 9, 6). The reticu- 

 lated cytoplasm contains a spherical to ovoid nucleus 

 located near the narrow end. The chromatin material is 

 usually concentrated on a portion of the nuclear mem- 

 brane. Surrounding or near the nucleus, may be seen the 

 two cytostomal fibrils and the short flagellum. 



5. Trichomonas hotninis (Davaine 1860) 



This is one of the commonest flagellates of the human 

 intestine. It appears to inhabit the lumina of the colon and 

 ileum. The organism frequently appears in large numbers 

 in diarrhoeic faeces, but its presence is considered as a 



