A. Porter 
387 
(4) The pre-flagellate stages of the parasite (PI. Y, Figs. 1—18) 
are best observed in the crops of nymphs of Nepa cinerea. The parasites 
at first are oval (Figs. 1—6). They vary in size from about 4 /a to 
5 /a long and from 2 /a to 2'5/a broad. They show nucleus and blepharo- 
plast, and may divide longitudinally before flagella are acquired (Figs. 
2 —4). The flagellum of each parasite arises from a region near to 
the blepharoplast but not directly from it (Figs. 5—9). 
(5) The flagellate stage of the organism (PI. V, Figs. 19—36) is 
that best known. H. jaculum is from 13/a to 33 /a long and from 1/a 
to 4 fjb broad, the size varying according to the recency or otherwise of 
longitudinal division. Myonemes (Figs. 20, 21, 38) are present on the 
body. The flagellum is at least as long again as the body. The 
nucleus contains a number of grains of chromatin (Figs. 28, 34), some¬ 
times in the form of eight large grains (Figs. 34, 36), sometimes as 
very fine granules (Figs. 22, 31). The blepharoplast is in the anterior, 
pre-nuclear, region of the parasite, and is usually rod-like (Figs. 19, 20, 
21). The single flagellum (Fig. 19) arises near it but not from it. 
A basal granule (Figs. 22, 33, 34) is present at or near the origin of the 
flagellum. Chromidia are present as scattered granules in the body 
(Figs. 28, 32, 33). 
(6) The post-flagellate stage is the form assumed by the parasite 
for life outside the body of the host. Preceding encystment, the 
organism divides twice longitudinally, giving rise to four daughter forms 
(PL Y, Figs. 51—54) each of which ultimately loses its flagellum, rounds 
itself off and forms a cyst (Figs. 57—68). These cysts are from 2 5 /a 
to4 - 5/A long and from 1'4/a to 2'6/a broad. They occur in the rectum 
of Nepa cinerea and are voided with the faeces, being ingested later 
by other bugs. 
(7) Longitudinal division is the common method of multiplication 
of H. jaculum. The flagellum may divide precociously, but usually 
division is initiated by constriction of the blepharoplast (PI. Y, Fig. 37) 
almost simultaneously with division of the flagellum and followed by 
that of the nucleus (Figs. 39, 40). A split occurs (Figs. 40—42) and 
the active movements of the two flagella aid in the divergence of the 
daughter organisms (Figs. 43, 44), which ultimately separate. 
(8) I have no evidence whatever for ascribing sex to any form of 
Herpetomonas, but consider the occurrence of long and short and of thin 
and stout forms to be explicable as the results of growth and division. 
Also, I have shown experimentally that richly granular protoplasm is 
the result of a physiological condition and is not necessarily fixed as an 
attribute of the female sex. 
