386 
Herpetomonas jaculum (Leger) 
no undulating membrane, such as H. lygaei, H. jaculum, H. culicis 
and II. muscae domesticae. 
Regarding the systematic position of the Herpetomonads among 
the flagellates, consideration of their life-cycle with its three phases, 
places them with the Crithidia, and the latter are united on morpho¬ 
logical grounds with the Trypanosomes. It is possible that when the 
full life-cycle of the latter organisms is known, it will be on the 
Crithidial plan, showing pre- and post-flagellate phases. 
The genus IIerpetomonas would then be the lowest in organisation 
of these three great genera. In Herpetomonas an undulating membrane 
does not exist (Text-fig. 1, a). In Gritliidia it is present but is 
relatively small (Text-fig. 1, h), while the Trypanosomes possess well- 
marked membranes (Text-fig. 1, c). The blepharoplast is in the 
anterior (pre-nuclear) region of both Herpetomonas and Crithidia. The 
flagellum arises near it, and in Crithidia, as it passes outwards, it draws 
out the body in the form of a membrane which becomes lengthened as 
the body elongates. 
The family Trypanosomatidae, then, contains forms varying some¬ 
what in detail among themselves, but having the same general principle 
underlying their organisation, the simplest members being that to which 
H. jaculum belongs, the Herpetomonads. 
With regard to the phylogeny of the Trypanosomatidae, I feel that 
there is far too little evidence at present to justify hypotheses on the 
subject. (See Patton and Strickland (1908), p. 340.) 
In conclusion, I would again point out the need for the study of the 
living organism, at every stage of its life-history. While H jaculum is 
purely a parasite of an arthropod, its study, like that of H. muscae 
domesticae, is a clue to the mode of life and reproductive processes of 
other, possibly pathogenic, organisms to which it is nearly allied. 
Summary. 
(1) Herpetomonas jaculum is a parasite of Nepa cinerea, occurring 
in the alimentary tract of its host. 
(2) The life-history of the parasite may be conveniently divided 
into three stages, the pre-flagellate, flagellate and post-flagellate stages, 
which gradually merge into one another. 
(3) The movements of the parasite are less flexible than those of 
Crithidia, as Herpetomonads have no undulating membrane. The 
flagellum is the most active agent in effecting motion. 
