320 
Oriental Sore 
applied to that surface of the vacuole which is nearest the basement 
membrane. I have used the word suction, but it must be admitted 
that there is no indication of a stress being produced in the protoplasm 
which one would expect to find if a suction force were being exerted. 
In the case of tape worms fixed to the gut it is easy in sections to see 
that such a suction is taking place, for the tissues in the neighbourhood 
are dragged, as it were, towards the sucker. If we can compare a 
gregarine with such a large organism as a tape worm we might expect 
to find some signs of stress though on a smaller scale. Nothing of the 
kind can be detected, so it is possible that the peculiar organ which 
has been called a sucking organ, merely secretes some adhesive 
substance which will hold the gregarine in its place. As in Lankesteria 
ascidiae, immediately below this fixation organ is a deeply staining area 
from which pass fan-wise the fibres which run through the anterior 
part of the body of the gregarine (PI. XV, figs. 5 and 8). These fibres 
are evidently contractile and possibly enable the gregarine to bring into 
action the fixation oi’gan at its anterior end. 
When the gregarine is about 50/a in length, the epithelial cell 
ruptures and the gregarines remain attached to the epithelial remnants 
for some time. They then become detached and fall into the gut cavity 
where they exist for a while as free gregarines. After the passage of 
the Stegomyia larva into the pupa, as pointed out by Ross, the 
gregarines migrate into the malpighian tubes. The stimulus acting 
upon the gregarines is probably the sudden cessation in the intake of 
food by the Stegomyia. 
Encystment. Within the malpighian tubes the gregarines associate 
in pairs, becoming attached to one another by the anterior ends, the 
two sucking organs coming into apposition. Tlie point of contact of 
the two gregarines appears in the stained sections as a deeply staining 
area (PI. XV, figs. 8 and 7). A similar appearance is shown by 
Siedlecki in the case of Lankesteria ascidiae. The two gregarines 
become enveloped by a thin membrane forming spherical cysts. The 
cells of the malpighian tubes become excavated to accommodate these 
comparatively large gregarine cysts. PI. XV, fig. 9 is a longitudinal 
section of a malpighian tube of a Stegomyia pupa, shoAviug the 
gregarine cysts and the alteration produced in the cells. Though in a 
single section it may appear that a single gregarine occupies one cyst, 
by following the sections through the series it is seen that there are 
always two. I have not encountered a case of a gregarine encysted 
singly. 
