A. Porter 
351 
have been found in the ovaries, and I have seen parasites pass out from 
an unruptured gut at that part of the gut adjacent to the ovaries, and 
make their way into the latter organs. Though very careful search has 
been made, the passage of the flagellate into the ova has never been 
seen. I may add that Crithidia are often less abundant in male Gerris 
than in females. 
General Description. 
The adult Crithidia are flagellates each possessing a long, narrow, 
tapering, fusiform body, which has its ectoplasm or periplast produced 
outwards as a thin, narrow membrane, whose edge, thickened as a 
chromatic border, passes on as the flagellum (PI. IV, Figs. 21—46). In 
life, the flagellum and membrane can be readily seen, the lashing move¬ 
ments of the former making it more conspicuous. 
The adult parasites measure from 16/a to 80/u. in total length 1 and 
are 2/x to 4>/a broad, while the flagellum from its basal granule to its tip 
may be 8/x to 40/r long. The flagellum even in life is seen gradually to 
taper from its origin to its free extremity. As the organism moves with 
its flagellum forwardly directed, this end of the organism is the anterior 
end. 
The nucleus of the parasite in life apjiears as a bright, retractile 
spot. It is usually oval in contour. Near to it a much more highly 
retractile, rod-like body, the blepharoplast is seen. Other granules, also 
having great refringency, are scattered through the general body 
substance. Staining reactions show that some of these granules are 
composed of chromatin and so are chromidia (PI. IV, Figs. 28, 34). 
The organism has a richly granular, highly alveolar endoplasm 
(Figs. 26, 28, 44), and very occasionally in life the granules are so 
arranged that a clear central space is left somewhat suggestive of a 
cytopharnyx (Fig. 31) such as Leger mentions in Herpetomonas 
jaculum. But such cases are few, and as there is no evidence of the 
food-assimilating nature of such a space, I think it would be better to 
consider this arrangement as a more or less unusual, rather than as 
a normal, feature of the cell. 
Stained preparations show the features mentioned before more clearly. 
They also show that the ectoplasm is thin and that the end of the body 
near the flagellum contains but little endoplasm in many cases. 
1 This total length is measured from the extreme free end of the flagellum to the 
extreme posterior end of the body. There is much variation in the length of the body, 
but the flagellum is always about half the total length of the body. 
