224 
Herpetomonas luciliae n. sp. 
(iii) the hindgut and rectum, although intermediate forms between 
the predominant types occurring in each region are occasionally found. 
The scarcity of such intermediate forms probably depends upon rapid 
and marked changes of form occuri’ing in the parasites as they pass 
from one region of the intestine to another. 
I. The parasite in the oesophageal diverticulum. 
In this region, we find (1) small truncate 'pyriform bodies (the so- 
called cysts), (2) oval forms ivithout a flagellum, and (3) oval forms 
with a short flagellum. These forms are connected by intermediate 
stages, and none of them show any signs of division. They have the 
following characters: 
(1) The cysts, as seen alive, are small truncate pyriform bodies about 
3'5 X 1'5 /u. in size. Their truncated appearance is due to a small cup¬ 
shaped depression in the protoplasm, at what we consider to be the 
anterior extremity of the cell. The protoplasm can readily be seen to 
consist of an inner core of endoplasm, invested by a layer of ectoplasm, 
which however does not cover in the endoplasm at the site of the 
above-mentioned depression at the anterior end of the cell. 
In stained prepai’ations, the ectoplasm, or ‘ periplast,’ appears as a 
dense blue-staining coarsely sponge-like structure, while the endoplasm 
is more homogeneous, and appears pale-blue through the periplast, but 
in cells which have ruptured it can be seen to be stained pale-pink. 
As was seen in the living cell, the periplast does not completely cover 
in the endoplasm, but leaves a tiny area where the latter comes to the 
surface at the truncated end of the cell. The pale-staining endoplasm 
may be called the cytopharynx, and its cup-shaped entrance the 
cytostome. The lip of the cytostome consists of periplast. In those 
cysts which have the most differentiated protoplasm, the lip of the 
cytostome is inverted, probably by the action of the retracting endoplasm, 
so that only a minute aperture, or inicropyle, is left opening into the 
cytostome. The periplast is thus made to fold over the exposed 
endoplasm. Embedded in the ectoplasm are the nucleus, blepharoplast, 
and ‘ chromidia ’; and in the endoplasm traces of a flagellar apparatus 
can sometimes be seen as a faintly-staining red line. (See PI. VIII, 
figs. 1-2, 23-25.) 
The nucleus is round and placed eccentrically against the side of 
the cell. It consists of a delicately reticular matrix, which stains 
