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STUDIES ON THE CERCARIAL FAUNA
[Vol. XXV, Part II,
opening which is guarded by the anterior piercing spines. The organ measures 36
by 24 microns. The highly muscular ventral sucker is situated at the junction of
the middle and posterior third of the body, with an average diameter of 25 microns.
Its free edge is furnished with two or three rows of spines.
The anteriorly situated mouth opening measures 10 microns across and leads
into a narrow vestibule, the prepharynx which traverses the anterior penetrating
organ. This is followed by a well-defined muscular pharyngeal bulb measuring 6.5 by
4.5 microns and a short oesophagus which divides at a point midway between the
two suckers into two intestinal caeca. From the point of bifurcation, the caeca
run outwards and backwards dorsal to the penetration glands. They encircle the
lateral borders of the acetabulum, slightly converge behind the sucker and then
turn outwards and run posterior to end just a little beyond halfway between the
acetabulum and the excretory vesicle. The caeca gradually become broader as they
run backwards.
The penetration or secretory glands are four in number arranged in pairs on
either side of the median line in front of the ventral sucker and bounded laterally
by the intestinal forks. In each pair, the outer one is situated posterior and the inner,
anterior. All the glands are of the same size and contain finely granular protoplasm
which takes neutral red stain very readily. Their ducts run in pairs on either side
towards the mouth. At about the level of the caecal bifurcation the duct of the
inner gland crosses that of the outer one and comes to lie lateral to it. Thereafter,
the lumen of the duct increases slightly. On reaching the posterior border of the
anterior penetrating organ, the ducts get again constricted and then pierce the
anterior organ in which they run as dilated tubes to open through paired pores
situated lateral to the mouth opening.
At the posterior extremity of the body is situated the bladder which is globular
in shape with a slight constriction in the middle. The bladder opens out dorsally
through a minute pore located at the point of attachment of the tail to the body.
From the antero-lateral aspect of the bladder on either side is given off the main
excretory trunk which has a bulbous origin. The basal dilatations of these vessels
are so prominent that they together with the bladder assume the appearance of a
triglobular or tripartite structure which is quite characteristic in the present cercaria.
Each main canal runs forwards lateral to the distal portion of the caecum of the
corresponding side and forms at the postero-lateral angle of the acetabulum a tangle
from which arise the anterior and posterior collecting tubules. The transverse
excretory tube or commissure connecting the main canals is placed anterior to the
acetabulum. The anterior collecting tubule proceeds forwards and divides at the
level of the eye-spot into two branches. The shorter branch traces its course back-
wards for a short distance to divide into two capillaries capped with flame cells
which are located anterior and lateral to the acetabulum. The other branch con-
tinues its course cephalad and splits up into capillaries which drain the two flame
cells present in the anterior region of the body behind the penetrating organ. The
posterior collecting tubule during its backward course gives off two branches, one
receiving the capillaries from the two flame cells found behind the tangled mass of
the main vessels and the other from two cells located at the posterior end of the
body near the bladder. The backward continuation of the posterior collecting