LARVAL TREMATODES 
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species is also slightly smaller but the variations in size of these two species allow for overlapping and the 
difference in size alone cannot be used to sort them out. The cuticular spines are more easily made out 
in this species. No other difference was noticeable between the two species of cercaria. 
Furcocercous Cercariae (Fig. 2) 
These are pharyngeal, longifurcate distome cercariae without eye-spots. They are very active and 
swim almost incessantly tending to collect near the surface towards the darker side of the container. 
They swim tail foremost with the furcae fully extended and give the impression of a rotating spindle 
moving upwards. When they come to the surface the swimming ceases, the furcae are spread out and the 
cercariae tend to sink slowly. The activity of these cercariae slows down in 6 to 7 hours and most of 
them are dead in 20 hours. When dead, the tail is usually found lying separate from the body and a 
mass of fine globules collects in the neighbourhood of the oral sucker. 
The body, which is somewhat flattened dorso-ventrally, expands and contracts considerably. The 
tail stem is stout and is of the same thickness as the body when the latter is fully expanded. The furcae 
are also stout and are as long as the tail stem. The ventral sucker is situated at about the middle of the 
body or slightly posterior to it. In freshly-dead specimens, the body measures 0.14 to 0.15 mm in length 
and 0.045 to 0.056 mm in maximum width. The tail stem measures 0.08 to 0.1 mm in length and the 
furci are 0.1 to 0.12 mm long. 
The cuticle in the anterior region is beset with minute spines arranged in transverse rows. Spines 
are also present over the ventral sucker, being most marked round the margin. The rest of the cuticular 
surface is smooth. 
The anterior organ is globular and is larger than the ventral sucker. There is a short prepharynx 
followed by the oval or globular pharynx and a short oesophagus which divides in front of the ventral 
sucker into two long caeca. A mass of granular gland cells are present behind the ventral sucker. 
The excretory vesicle is bilobed, the two main collecting canals extending forwards to the front of the 
ventral sucker. At this level, they meet the lateral ducts and give off on each side a transversely-running 
duct. The caudal excretory tube sends a branch into each furcal ramus which opens by a pore at about 
half way down the length of the ramus. The tail stem contains 8 conspicuous pairs of large rounded cells. 
Dissection of Snails 
Forty dead snails were dissected and eleven had metacercariae and or rediae in the tissues 
of the body. Four had tetracotyles. 
Description of Rediae 
Mature rediae (Fig. 3A) containing about 7 to 10 echinostome cercariae in each were present in 
large numbers. These rediae are tinged a fight orange yellow, possess a collar and locomotory organs. 
They measure about 1.5 to 2.75 mm long by 0.2 to 0.3 mm broad. The pharynx is about 0.09 mm long 
by 0.06 mm broad. None of the rediae contained cysts within them. 
Description of Metacercariae 
In the digestive glands were seen large numbers of free echinostome cercariae some of them without 
tails probably preparatory to encystment. In the snails with double infection both types of echinostome 
cercariae were seen lying free in the fiver tissues. 
There were also present numerous echinostome metacercariae. These are of two types but both 
are globular and measure 0.17 to 0.19 mm in diameter. The cyst wall is thick and two-layered. The 
two types of metacercariae though similar in size and general appearance can be distinguished by the collar 
and cuticular spines. The one with 37 collar spines (Fig. 3B) shows no evident cuticular spines while in the 
other with 43 collar spines (Figs. 4A and b), these are prominent. The one with 37 collar spines has five 
corner spines while the other has only four on each side. Of the eleven snails containing encysted 
metacercariae, six had both types and five had only one type or the other. The number of metacercariae 
in the dissected snails varied from about a dozen to a few hundreds in each. A few of the metacercariae 
were dead, as evidenced by the marked translucency or by their taking on a pinkish stain from the shell 
of the snail. 
Description of Agamodistomes 
The agamodistomes (Fig. 4c) released by rupture of the echinostome metacercariae are similar except 
for the differences in the collar and cuticular spines noted in the encysted forms. The movement is 
sluggish and consists of expansion and contraction of the body. It measures about 0.5 by 0.1 mm. 
Description of Sporocyst 
The parthenitae of the furcocercous cercariae are long sporocysts with irregular constriction. These 
are present in the digestive glands and contain large numbers of cercariae in various stages of development. 
MALAYA , No. 26. 1953 
