March, 1950]
BIPIN
BEHARI
SINHA
7
appendages. A fully developed redia was observed to contain 10 to 17 developing
cercariae inside. No case of a daughter rediae inside the parent was observed.
CERCARIAE
The snails generally begin shedding fully developed cercariae on the 30th day of
infection. They are quite active when shed and swim in water by lashing movements
of their tail. It is not easy to take the measurements in the living condition but
when the movements are properly restricted, it was found to be 0.456-0.472 mm. in
length and 0.141-0.149 mm. in greatest breadth (Fig. 9). They are, however,
0.319-0.43 mm. in length and 0.269-0.298 mm. in breadth in fixed condition. The
tail varies from 0.46-0.51 mm. in the fixed condition and 0.61-0.67 mm. in the living
condition, so that it appears that cercaria is extremely contractile. The entire body
of the cercaria, particularly the anterior third, is thickly pigmented and does not
easily permit the study of the internal structures in the living condition. A pair of
conical eye spots, however, are easily observed situated immediately behind the
oral sucker, with their apices directed antero-posteriorly and the bases mounted
with a clear refractile lens. The body is covered over with a thick cuticle while
underneath it rows of cystogenous cells are easily seen.
The oral sucker is oval in shape and is situated terminally at the anterior end.
The acetabulum is oval, being broader than long and is situated at the posterior
end of the body. The oesophagus runs posteriorly and bifurcates behind the eye
spots into two intestinal caeca. Caeca are small in diameter and terminate a little
in front of the (ventral sucker) acetabulum. The reproductive organs are
represented by two groups of cells, connected by a single cord of cells. One group
of these cells is situated just in front of the acetabulum while the other just behind
bifurcation. The posterior mass represents the ovary and the testes, while the
anterior one, the genital pore and genital sucker, the cord representing the uterus
and vas deferens.
The excretory system consists of an excretory bladder, situated dorsally over
the acetabulum and the posterior reproductive mass of cells. A small duct running
dorso-anteriorly from it opens at the excretory pore while two large excretory ducts
meet it laterally. The large lateral ducts were seen to run from the bladder
outward towards the anterior end. Near the middle of the body they loop inward,
and again pass forward and outward up to the oral sucker. Here again the ducts
make a loop behind the eye spots, between it and the oesophagus and then turn
outward and backward to run down to the sides of the acetabulum. At the middle of
the body, the lateral ducts give out inwards one branch each which run inward and
meet each other. From this junction a small duct is sent forward as a median
diverticulum. On account of the heavy pigmentation of the body and the presence
of cystogenous cells, the flame cell pattern could not be studied. The main ducts,
the cross connections and the median diverticulum, are all filled with refractile
excretory granules. The tail possesses a central excretory duct which joins the
bladder posteriorly. The central duct runs down towards the tip of the tail and a
little in front of it swells up into a small vesicle. Two small ducts arise from this
and run latero-posteriorly to reach the surface.