222 STUDIES ON THE CERCARIAL FAUNA [Vol. XXV, Part III,
Both the body and tail are aspinose, except for the presence of 'collar-spines'.
Eye-spots are absent. Beneath the cuticle of the body are present rounded or nearly
ovoid cystogenous glands filled with rod-like bodies arranged in two or three bundle-
like formation. The cercaria is provided with well-developed oral and ventral
suckers. The oral sucker which occupies the anterior bluntly rounded extremity
of the body is smaller than the ventral and is spherical in shape with a diameter of
0.045 mm. The anteriorly directed acetabulum is a large, heart-shaped highly
muscular organ, situated at about two-thirds to three-quarters of the total body
length from the anterior end. The radiating muscle fibres at the margin of the sucker
give the appearance of a fencing or a frill. The organ is wider horizontally than
antero-posteriorly and measures 0.050 by 0.059 mm.
At the anterior end of the body behind the region of the oral sucker is a ridge
which is in the form of a distinct collar, carrying a number of spines alround it except
on the ventral aspect. There are 41 spines in all—15 dorsals of equal size, arranged
in two alternating rows (eight orals and seven aborals), eight laterals on either side,
which are continuous with the dorsal aborals, and 5 'angle' spines placed on each
ventro-lateral lappet. The 'angle' spines are slightly larger than the rest, and are
set at an angle to the others. On the dorsal surface, at about the level of the posterior
border of the oral sucker, are found two irregularly conical bodies set in close apposi-
tion. The entire structure measures 0.011 mm. long and 0.014 mm. broad at the
base, and contains highly refractile granules.
The tail is fitted into a concavity at the posterior end of the body. The distal
end of the tail forms a narrow conical process which is capable of contraction and
extension independent of the stem. The cuticle of the tail expands on the median
dorsal aspect at the posterior third into a cuticular fold or fin which extends back-
wards to about half the length of the conical projection. Beneath the cuticle are
the circular and longitudinal muscular layers. Numerous rounded nuclei are found
scattered in the tail parenchyma.
The mouth-opening is situated slightly sub-terminally and leads back into the
cavity of the oral sucker. It is followed by a short pre-pharynx and a somewhat
pyriform muscular pharynx, measuring 0.018 X 0.014 mm. The narrow oesophagus
divides anterior to the acetabulum into two caeca. As in most of the echinostome
larvae, the oesophagus and caeca are solid in nature. The caeca pass round the sides
of the acetabulum and extend up to the antero-lateral aspects of the bladder. An-
terior to the acetabulum and on either side of the oesophagus, occupying the space
between it and the main excretory trunks, are located the secretory glands com-
posed of three pyriform cells arranged longitudinally. The gland cell contains a
round nucleus and finely granular protoplasm which takes the neutral red stain
readily. The ducts arising from the cells pass forward and are continued around the
sides and dorsum of the oral sucker to open through separate minute orifices arranged
in linear series on the anterior border of the mouth opening.
The excretory system consists of an excretory bladder, two main excretory
trunks or siphons, 15 pairs of flame cells and their connecting capillaries and a caudal
canal with two lateral outlets. The system of tubes and the terminal organs are
bilaterally symmetrical. The excretory bladder is situated at the posterior end of