228 
Herpetomonas Ivciliae n. sp. 
cells none of the organella may be divided, a unicellular biflagellate 
creature being the result, but these forms are very rare. In yet other 
cells we find a cell, incompletely divided, with ybz<r chromatin filaments 
in the flagellum, which must be interpreted as cells in which redivision 
is taking place prior to the separation of the daughter cells. 
(/) The chromidia are scattered throughout the cell. Relatively 
to the other structures they are very much smaller than in the ‘ crop 
forms. The more actively dividing parasites seem to contain the most 
granules. 
The structure of the parasites in this region is therefore very 
variable, in that they do not form a gradual series of forms. This 
indicates that the sequence of division of the various organella is not 
uniform; for instance in some cells only the flagellum has divided, in 
others only the rhizoplast. (PI. IX, figs. 1-14.) 
III. The parasite in the hindgut and rectum. 
In this region the forms of the parasite fall into three main groups, 
which are connected by intermediate forms: (i) large oval flagellates, 
(ii) round flagellates, (iii) small oval forms, or ‘ cysts.’ None of these 
show any signs of multiplication, either in living or stained preparations. 
(i) The large oval forms are found in the hindgut immediately 
below the opeiring of the Malpighian tubes. They are less numerous 
than the other types, probably because this stage is very transitory. 
They measure 8 to 10/ix2to3ya. The cytoplasm, as in the midgut 
forms, is not differentiated into periplast and cytophai’ynx, and stains 
pale-blue. The nucleus, blepharoplast, and flagellar apparatus contain 
less chromatin than the corresponding structures in the midgut forms, 
and the matrix of the nucleus, which stains pale-pink, is more evident. 
The blepharoplast still occupies the same relative position to the 
nucleus as in the midgut forms, that is, well in the front end of the 
cell. The flagellum is much shorter than in the midgut forms, and 
stains less deeply owing to its being partly dechromatinised. The 
chromidia have a tendency to become grouped in the posterior end of 
the cell. (PL IX, fig. 7.) 
(ii) The round forms are chiefly found in the posterior part of the 
hindgut, and in the rectum. In this category we include forms which 
are not round but oval, for the only difference between them is their 
shape. They are of the same length, about 5 g, but whereas the round 
cells are about 5 /a in breadth, the oval cells have contracted to about 
