268 
Herpetomonads 
forward, and the flagellum going over to one of the daughter halves 
without a second flagellum being formed : the halves hung together for 
a long time and I did not see them finally separate. The organisms all 
died at this stage, and I never saw the encystment completed. 
While the flagellum is being withdrawn, and the body is assuming 
its pear-shaped form, the cytoplasm becomes rather sticky, and I noticed 
a strong tendency for flagellates to adhere to one another side by side, 
either in groups or in pairs. This was often suggestive of the pre¬ 
liminaries for conjugation, but though watched for a long time, these 
chance groupings never went any further: the organisms either separated 
after a brief struggle, or else died. It is not infrequent for individuals 
in this condition to become bent on themselves, the adjacent portions of 
the body-wall then adhering to one another (see text-fig. 3, a and b) and 
producing an appearance not unlike the first stages in the rounding off" 
Fig. 3. 
Fig. 4. 
of Trypanosoma vittatae as observed by Robertson (1909). I never 
found, however, that they developed further. Another instance of 
the “stickiness” of the cytoplasm was sometimes shown, where the 
flagellum had got bent back along the body, and adhered firmly to it. 
Where the flagellum was still pretty long and active, its efforts to 
continue movement under these abnormal conditions resulted in the 
gradual lifting up from the cytoplasm of the body of a sort of pseudo 
undulating membrane (text-fig. 4, a and b). The movements of this 
structure were so exactly those of a true undulating membrane that it 
was difficult to believe one was not dealing with a small, blunt try¬ 
panosome : observation of the earlier stages of course explained the true 
nature of the case. 
I starved several young larvae of Homalomyia, and on examining 
them found that the parasites had all collected in the hind-gut and were 
in process of rounding up. 
