December, 1955 ]
C.
T.
PETER
337
one-third length from the tip. The ' shoulder ' actually is made up of two promi-
nences, a larger and rounded posterior one and a smaller and pointed anterior one.
The mouth is subterminal and leads back into the cavity of the oral sucker, the
latter being connected by a short pre-pharynx to a spherical pharynx measuring
0.018 mm. across in living specimens. Beyond the pharynx, no other structures
constituting the gut could be detected. The penetration glands located antero-
lateral to the acetabulum are composed of 8 cell units in each, containing well-
marked nuclei and finely granular protoplasm. Narrow ducts arising from these
cells pass forwards to the sides of the oral sucker, where they exhibit a certain amount
of dilatation and then turn inwards around the dorsal aspect of the oral sucker to
open out on the anterior border of the mouth. Surrounding the pharynx and occupy-
ing the region behind the oral sucker is a mass of cells which stain dark with haema-
toxylin. The exact nature of this cellular structure is not known. The excretory
bladder situated at the posterior end of the body is a Y shaped thick-walled organ
consisting of a bulbous posterior or caudal vesicle and a cornuated anterior vesicle.
The bladder opens out through an orifice on the dorsal aspect of the body at the
point of attachment of the tail. The main excretory tubes originate from the
antero-lateral aspects of the bladder and extend forwards to divide at the acetabular
region into the anterior and posterior collecting tubules. The anterior branch divides
into three capillaries each ending in a flame cell, one located at the antero-lateral
aspect of the acetabulum, another at a point midway between the two suckers and
the third in the neighbourhood of the oral sucker. The posterior collecting tubule
also divides in a similar manner, receiving capillaries from three flame cells, two
of which are found in the region between the ventral sucker and the anterior arm of
the bladder, and the other lateral to the base of the bladder. Thus, there are six
pairs of flame cells, of which three are pre-acetabular and three post-acetabular.
The flame cell formula can be represented as 2 [(l+l+1)+(l+l+1)]=12.
The genital system is located dorsal to the acetabulum and it has more or less the
shape of the letter ' C ', which can be roughly divided into three parts. The posterior
portion found behind the acetabulum is horizontally placed and consists of a main
mass, representing the ovary and two lateral extensions which are probably the
rudiments of the Laurer's canal and the vitelline duct. The ovarian mass continues
forwards on the left side of the acetabulum to form the vertical portion—the uterine
anlage—which in its turn curves to the right and forms in front of the ventral sucker
a coiled structure constituting the rudiments of the genital aperture. The male
genital fundament consists of two cord-like structures—the vasa efferentia—which
start from the ovary and end posterior to it in two globular structures—the testis.
The cercariae develop in thick-walled, sausage-shaped sporocysts infecting
the digestive gland of the host. The sporocyst-sac is incapable of independent
movement and does not possess a birth-pore. Its length ranges from 0.667 to
1.750 mm. and breadth from 0.218 to 0.250 mm. Ten live individuals measured on
an average 1.198×0.233 mm. The cercariae are found in varying stages of deve-
lopment within the sporocyst and come out only after attaining full growth.
The present cercaria belonging to ' Cercariae armatae ' possesses all the diagno-
stic characters of the ' Polyadena ' group created by Cort [1915]. Brooks [1943]
recognised that some of the polyadenous type of xiphidio-cercariae would allow of a