120 
Herpetomonas and Crithidia 
loses a part of its achromatic substance and consequently becomes 
much smaller (Figs. 2-5). The flagellate Anally becomes very short 
with only an internal flagellum, or no flagellum (Figs. G-11). Some¬ 
times a double rhizoplast may be seen (Figs. 9, 10). These forms 
cannot be considered as real cysts as a well-developed cyst-wall was not 
observed. 
Sometimes a peculiar radiated zone was seen surrounding the cell 
and staining pinkish with Giemsa (Fig. 11). Similar observations were 
made by Minchin (1908) and Prowazek (1904); the latter considers this 
formation a cyst-wall. I think these radiated zones do not really exist 
but are artefacts due to the precipitation of staining substance around 
the cell, as may be often observed when Giemsa solution comes in 
contact with gelatinous substances, but after all these artefacts may be 
an indication that there is a gelatinous envelope present. 
The post-flagellate stages are 7-9 /a long and 4-5 broad, the 
gelatinous envelope is 1‘5-1'8 /a broad. 
In the same way as the preflagellate stages, the post-flagellate 
stages may be found in the inidgut, often without any other develop¬ 
mental form of this parasite (Diagram X). They are small flagellates 
Diagram X. 
Transitional forms between the flagellate and post-flagellate stages of Herpetomonas 
calUphorae, from the midgut of the fly. 
with a short flagellum and are actively motile, often uniting into large 
clusters. Sometimes stages of division are to be seen (Fig. 3). 
Similar forms occurring in the house-fly {Musca domestica) have been 
probabl}' mistaken by Werner (1908) for an independent species 
{Crithidia muscae-domesticae). 
4. Degenerating forms. 
These forms (Diagram XI) are frequent in flies which have been fed 
on fruit-juice or on honey, especially in autumn. Sometimes the 
nucleus degenerates (Fig. 6) so that only the blepharoplast remains 
(Fig. 5); or the nucleus and the blepharoplast may both be reduced to 
