A. Porter 
355 
The flagellum forms a chromatic border to the membrane. It appears 
thicker as the border of the membrane than it is as the free flagellum, 
for it gradually becomes more tenuous towards its free extremity 
(Figs. 33, 37, 46). The flagellum of G. gerridis does not originate from 
the blepharoplast. There is commonly a space between the two 
(Figs. 21, 25, 27) and one or more chromatic grains may be present in 
the intervening space. Sometimes one of these grains is so near 
the flagellum that the latter appears to arise from it (Figs. 22, 30, 
32, 34, 43). Such a granule may be called a basal granule. No 
structure of the nature of a diplosome as described by Prowazek in 
Herpetomonas muscae domesticae , has been observed in this parasite. 
The nucleus is usually oval (PI. IV, Figs. 24, 25) or round 
(Figs. 35, 38). It may occupy the full breadth of the body of the 
parasite (Figs. 25, 31, 39) or not extend quite across (Figs. 21, 27, 
32). Large chromatin granules (Figs. 34, 43, 45), occasionally eight in 
number (Fig. 31) are present. Usually the chromatin of the nucleus 
is arranged in slightly irregular masses (Fig. 27). Finer granules 
are found in the nuclei of parasites about to divide. Around the 
periphery of the nucleus is a chromatin condensation. 
The blepharoplast. In addition to what has been previously stated, 
the following points with regard to the blepharoplast may be noted. Its 
chromatin stains very heavily with all the stains I used. The chromatin 
is much concentrated and usually the blepharoplast shows no sign of 
differentiation. The position of the blepharoplast is usually anterior to 
the nucleus (PL IY, Figs. 27, 39, 40) but very rarely it is laterally 
placed with regard to the nucleus. A clear area is not uncommon 
around the blepharoplast (Figs. 23, 44). The flagellum arises in the 
vicinity of the blepharoplast, often from a basal granule (Figs. 32, 
43, 44). 
Extra-nuclear chromatin — Chromidia. Chromidia are scattered at 
intervals in the general protoplasm of most of the Crithidia that I have 
examined (Figs. 26, 39, 44, 46). The chromidia seem more or 
less isolated in the alveolar protoplasm (Figs. 28, 39, 44). There 
is no indication of meta-chromatin being present such as Swellengrebel 
(1908) described for Trypanosomes. 
The Post-flagellate Stage. 
When the rectum of an infected Gerris paludum is examined, a 
certain number of flagellates are always to be found moving actively in 
