(137) 



378 0. GORDON HEWITT. 



contains a trophonucleus and kinetonucleus. Division takes 

 place by simple longitudinal division or multiple segmenta- 

 tion, and in this manner a large number of individuals are 

 formed (II b and III) . These develop into the flagellate stage : 

 a vacuole, the flagellar vacuole (III, f-v.) appears between the 

 kinetonucleus and the rounded end of the pre-flagellate form, 

 and in it the flagellum appears as a single coiled thread, which 

 is extended when the vacuole has approached the surface. 



The flagellate form has already been described, and in the 

 concluding portion of the flagellate stage, which, according 

 to Prowazek, is found in starved flies, these forms are found 

 collecting in the rectal region, and attaching themselves by 

 their flagellar ends in rows to gut epithelium. The more 

 external ones begin to shorten, during which process the 

 flagella degenerate (IX) and are shed. Thus a palisade of 

 parasites is formed, the outer ones being rounded and devoid 

 of flagella, and some of them may be found dividing (X). 

 Leger (1902) terms these the "formes gregariennes," and 

 maintains that the existence of these "gregarine" forms is a 

 powerful argument in favour of the flagellate origin of the 

 Sporozoa, which he had previously suggested, and which 

 Biitschli had put forward in 1884. After the degeneration of 

 the flagellum a thickened gelatinous covering is formed, con- 

 taining a double row of granular bodies (Xa), and these cysts 

 are regarded by Patten as the post-flagellate stage. They 

 pass out with the faeces, and dropping on the moist window- 

 pane or on food, are taken up by the proboscides of other flies. 



Prowazek describes dimorphic forms of the flagellate stage, 

 which he regards as sexually differentiated forms, but Patton, 

 in a letter to me, says that he is unable to find any of these 

 complicated sexual stages. According to Prowazek, one of 

 these forms is slightly larger than the other, and has a greater 

 affinity for stain. The dimorphic forms conjugate; their cell 

 substance and nuclei fuse, and a resting-stage cyst is formed, 

 but the subsequent stages have not been followed. He 

 further states that the sexually differentiated forms may force 



