292 
Flagellates in Fleas 
apparently broken up into a number of small granules scattered through 
the cell. The flagellum is never seen “ cast off.” The distal portion 
which attaches the parasite to the wall of the gut becomes reduced to 
a little circular mass of pink-staining material, persisting through the 
early stages of encystment: later on this is completely absorbed. The 
portion of the flagellum within the cell sometimes shows as a faintly 
reddish streak running down towards the blepharoplast, but more often 
is simply indicated by a pink-staining area. All trace of this disappears 
in the later stages. The cytoplasm shows great variability in its staining 
properties. Early in the encystment it stains a pale, clear blue and is 
markedly free from granules: in the neighbourhood of the flagellum- 
root it has a pinkish tint. Other cysts stain a deep purplish-pink, and 
contain minute darker-staining granules. Generally there are one or 
two large, indefinitely-outlined vacuoles, but the later stages often show 
numerous, small, round vacuoles all through the cell (Fig. 11). In no 
instance was anything seen resembling a well-developed cyst-wall, such 
as Prowazek and other authors have described in the “ Dauercysten ” of 
Herpetomonas. 
II. Crithidia hystriciiopsyllae, n. sp. 
Only one flea was infected with this parasite. The hind-gut con¬ 
tained numerous encysting stages, and, judging from these alone, it 
would be impossible to say that one was not dealing with a Herpetomonas. 
But though free adult flagellates w 7 ere few, they were unmistakeably 
crithidian in character. 
(1) Pre-flagellates. I saw no stage that could be so interpreted. 
(2) Flagellates. The adult flagellates vary extraordinarily in size, 
and in general appearance. The following are the chief types: (a) Large 
forms (18/z. x 4/z., without the undulating membrane) with broad, rounded 
posterior portion, and a well-marked undulating membrane, staining pink 
with Giemsa (Plate III, Figs. 16 and 17). The nucleus is situated in the 
posterior half of the body; it is rather large, and stains deep rose-red, 
but is much obscured by granules in the surrounding cytoplasm. The 
blepharoplast is situated close to the nucleus—slightly anterior or 
lateral: it is relatively large, and is broadly rod- or crescent-shaped: it 
takes on a deep purplish-black stain. The undulating membrane arises 
close to the blepharoplast, but its exact origin is difficult to make out: 
the free flagellar portion is very short. The cytoplasm stains pink 
in the neighbourhood of the undulating membrane: near the nucleus 
