A. Porter 
381 
that the Nepa take up the cysts of the flagellate by ingesting the 
faeces of their fellows. 
Another method of infection is that due to the cannibalistic habit of 
Nepa cinerea. These insects are not only blood-suckers and coprophagous, 
but I have seen young nymphs and weakly adults seized and killed by 
stronger Nepa, and have seen them drag out and devour the entire 
viscera of their victims. The attacks were usually made at the meta¬ 
thorax, and the viscera were drawn out, either from the wound or else 
from the anus. As this feeding habit is common, there is the possibility 
of the Nepa acquiring all stages of Herpetomonas jaculum by way of its 
food. 
The Evolution of Hereditary Infection. 
The occurrence of Herpetomonas jaculum in the ovaries of Nepa 
cinerea has already been mentioned. The parasites have been seen to 
pass through the wall of the gut near the ovaries and to penetrate 
them. The Herpetomonads having entered the ovaries rapidly lose 
their flagella (PI. Y, Fig. 46) and become very broad and large 
(Figs. 47, 48). Occasionally groups of these non-flagellated forms 
(Fig. 49) are found in preparations. The nucleus and blepharo- 
plast of each Herpetomonas is fairly distinct. Large granules of 
chromatin are present in the general body protoplasm, and the latter is 
much more alveolar than in the forms in the gut (Figs. 46—49). 
It seems, therefore, that the flagellates degenerate in the ovaries of 
Nepa cinerea. Though I have examined many ova and embryos of the 
host, I have failed to find infected ones. Nevertheless, the occurrence 
of the parasites in the ovaries seems to be a step on the way to 
hereditary infection. But the Herpetomonads have not yet fully 
adapted themselves to this form of parasitism, consequently degeneration 
ensues and the Herpetomonads die. The phenomenon of hereditary 
infection “ in the making ” has also been observed by me in the case of 
Crithidia gerridis, while Grithidia melophagia, on the other hand, is 
capable of infecting the ova of Melopliagus ovinus. 
Environmental Effects. 
In the course of the investigation of H. jaculum, some experiments 
were performed on the effects of certain changes of environment on 
the parasite. 
