232 



THE HAEMOFLAGELLATES 



or even behind it (i.e. nearly terminal at the afiagellar end), though 

 it is not often in the last position. Minchin thinks this last form 

 most nearly represents that in which T. grayi occurs in its Vertebrate 

 (probably Avian) host. The second type (b} is constituted by 

 slender, often greatly elongated individuals, with well-developed 

 undulating membrane and flagellum. Minchin was at first inclined 

 to regard these as male forms ; but from their occurrence in one 

 case in remarkable numbers in the proctodaeum, to the exclusion 

 almost entirely of any other kind, he has since thought this view 

 to be unlikely. The primary habitat of the slender type is the 

 proctodaeum, from which region it may extend forward through 

 the intestine and stomach of the fly. (c) Small, very narrow forms, 

 of a typical Herpetomonas-Yike structure, practically lacking any 



undulating membrane (Fig. 

 22, a), which stain more 

 faintly and appear much 

 more delicate than parasites 

 of type (b); the kinetonucleus 

 is often relatively large. 

 These individuals were found 

 in the proctodaeum, and, 

 rarely, in the hinder intes- 

 tine ; they are apparently 

 derived from young forms of 

 the indifferent type, pro- 

 duced by rapid multiplication 

 in the hinder part of the 

 intestine. 



It is this Herpetomonad 

 type which undergoes en- 

 cystment. In cyst-formation 

 the flagellum becomes 

 shortened and at the same 



time apparently thickened. The cyst begins to appear as a layer 

 of substance, probably of a slimy or mucoid nature (cf. Prowazek's 

 " Schleimcysten " in the case of Herpetomonas muscae-domesticae 

 [69]), which forms a cap at the aflagellar end (Fig. 22, b). These 

 two processes continue until, on the one hand, the flagellum is 

 completely retracted, and, on the other hand, the body is enveloped 

 in a pear-shaped cyst (c), which is at first incomplete at the pointed 

 end. The flagellum appears next to become retracted into a pink- 

 staining vacuole (cf. the opposite process in the formation of the 

 flagellar phase of Leishmania (Piroplasma) donovani) ; finally, the 

 flagellar vacuole fades away, the cyst meanwhile closing up. 

 Eventually there results an oval or circular cyst, containing hyaline 

 cytoplasm and the two chief nuclear masses (d). In this guise, 



FIG. 22. 



Encystrnerit of the narrow, Herpetomonad form 

 of Trypanosoma grayi. (After Minchin.) 



