376 
Herpetomonas jaculum (Leger) 
bodies, that stain very deeply on account of the large amount of 
chromatin that they contain (Figs. 57—68). The post-flagellate cysts 
measure from 2 - 5/a to 4'5/a long and T4/a to 2'6/a broad. 
The tiny, oval, very resistant cysts become detached from the rectal 
walls, and pass out with the insect’s faeces, that form minute, blackish 
patches on the leaves of water plants. 
A form of the post-flagellate stage occurs in the ovaries of the host. 
Thus very large, broad, non-flagellated parasites (PL V, Figs. 46—49) 
were found in the ovaries of most of the female Nepa cinerea that I 
examined. These forms have a well-marked nucleus and blephai’oplast 
(Figs. 47, 48, 49). Their protoplasm is very alveolar (Figs. 46, 49) and 
chromidia (Figs. 46—49) are much more numerous than in parasites 
inhabiting the gut. I have seen H. jaculum pass through the walls of 
the gut, and swim towards and penetrate the ovaries. The parasites 
appear then to lose their flagella, and to assume the form described 
above. Since careful examination of both ova and embryos has never 
shown the presence of H. jaculum, it is likely that these very large 
parasites simply undergo degeneration in the ovaries; the abundance 
of chromidia in the general protoplasm tends to confirm this supposition. 
Nevertheless, the occurrence of H. jaculum in the ovaries is of in¬ 
terest, representing, as it does, an attempt at the evolution of hereditary 
infection. It is of interest to note that Prowazek (1904) found 
II. muscae domesticae in the ovaries of Musca domestica. 
Division. 
Longitudinal division is the means of rapid multiplication of 
H. jaculum. It occurs either in the pre-flagellate stage, whereby the 
present host is primarily infected (PI. V, Figs. 2, 3, 4), or in the 
flagellate stage (Figs. 37—44), or in the post-flagellate phase (Figs. 
51—54). In the case of post-flagellates very rapid longitudinal division 
of a single organism gives rise to several—usually four—small daughter 
forms that proceed to encyst. 
The division of the pre-flagellate forms begins with the division of 
the blepharoplast. This becomes dumb-bell shaped and gradually 
constricts into two (PI. Y, Fig. 2), the daughter halves migrating 
frequently to the opposite sides of the organism. Vacuoles appear in 
the general protoplasm, and gradually fuse in the mid-line, so that in 
the living specimens a clear area is seen posterior to the nucleus 
(Figs. 2—4). Most of the chromatin of the nucleus, meanwhile, has 
