370 
Herpetomonas jaculum (Leger) 
duction usually of four small flagellates from one. These forms 
gradually lose their flagella, become rounded off and are passed out 
along with the faeces of the Nepa , as small, post-flagellate cysts which 
are specially adapted for resisting desiccation and serve to infect new 
hosts (Figs. 57—68). 
Movements. 
Herpetomonas jaculum possesses a single flagellum and this is very 
noticeable when the organism is moving. The adult flagellates are 
either fixed by their flagellar ends to the gut wall of their host or else 
they swim actively in the gut contents. The attached forms are usually 
in clusters or aggregation rosettes (Fig. 45), and their movement is 
suggestive of that of ciliated epithelium. The body of each flagellate 
bends slightly and rhythmically sways to and fro, and at the same time 
it twists on itself, so that what was at first the upper surface becomes 
the under one, and the previously under one becomes exposed to view. 
(Cf. Fig. 23.) There is no definite direction for this twist; I have seen 
forms twist from right to left, then reverse their motion and twist from 
left to right. This rolling movement of Herpetomonas has been men¬ 
tioned by other writers (Leger, Patton, Berliner) but has not been 
described in detail. 
The movements of free flagellates may next be considered. These 
are far more rigid and jerky in character than those of Crithidia. This 
is to be expected, seeing that they possess no undulating membrane, 
the presence of which tends to produce smoothness of motion. The 
same rolling movements as are seen in attached flagellates, can be 
observed in free forms. But in addition there are the rapid lashing 
movements of the flagellum. The flagellum lashes from side to side 
and frequently is thrown into coils, so that it bores its way spirally 
through the medium in which the flagellate swims, and much focussing 
is necessary to observe the full length of the flagellum. As a rule, the 
flagellar end of the organism moves in the forward direction, the 
flagellum then functioning as a tractellum, but on occasions, I have 
seen the Herpetomonas moving fairly rapidly, its flagellum trailing as a 
feeble pulsellum and its blunt, posterior end moving forwards. The 
rapidity of progression under these circumstances is not so great as 
when the anterior (flagellar) end is forwardly directed. 
A further aid to movement forwards is afforded by the contractions 
of the body itself, for myonemes are present. Waves of contraction 
