W. S. Patton 
313 
intestinal tracts of insects, non-blood-sucking and blood-sucking, and it 
should be clearly understood that those species occurring in the latter 
have no connection with any blood parasite, nor are they cultural 
trypanosomes; they have a characteristic developmental cycle which 
may be conveniently divided into three stages, pre-flagellate, flagellate 
and post-flagellate. 
In their pre-flagellate stages they are round or oval bodies of varying 
size, and contain two characteristic chromatic bodies, the nucleus and 
blepharoplast. In this stage they multiply by simple longitudinal 
fission or by multiple segmentation, and are found in the midguts of their 
insect hosts, except in the case of the three human parasites. I have 
been able to show that this stage in a known species occurring 
in Gulex mosquitoes is exactly similar to that of the human parasites. 
The flagellate stage is characterised by the formation of a single 
flagellum and the multiplication of the resulting flagellates by equal or 
unequal longitudinal division. The adult forms are long, spindle- 
shaped organisms, with a single flagellum, but no undulating membrane. 
This stage occurs in the mid- and hindgut of their hosts, but in the 
case of Herpetomonas donovani it takes place naturally in Gimex 
rotundatus. The post-flagellate stage is characterised by the massing 
together of the flagellates in the midgut, their shortening and rounding 
up, the resulting cysts are passed out in the faeces and are accidentally 
sucked up by fresh hosts. It is not known yet whether H. donovani 
undergoes this stage in the bed-bug. 
It is important to remember that many of these Herpetomonads are 
indistinguishable in their pre-flagellate stages, and therefore if this stage 
alone is studied two distinct species may be classed as one. Further, I 
wish to point out here that a partial study of the stages of these 
flagellates is very apt to lead to confusion, so that what are true Herpeto¬ 
monads may quite easily be mistaken for Grithidia or young Trypano¬ 
somes ; a reference to receut literature will show that this has actually 
occurred in more than one instance. 
As the life-cycles and general structure of the three human 
parasites are similar to those of well-known Herpetomonads, I see no 
reason for placing them in a distinct genus. The differences in their 
development, such as the formation of the flagellum, methods of 
division and the fact that their pre-flagellate stages are passed in man 
only justify their being regarded as specifically distinct from such 
species as H. muscae domesticae, H. sarcophagae, H. culicis, H. lygaei, 
and many others. 
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