LARVAL TREMATODES 
205 
Penetration of Miracidia into Snail Hosts 
To a small petri-dish with water containing ten miracidia, a Lymnaea natalensis was trans- 
ferred. This was placed on the stage of a Greenough’s binocular microscope and kept under 
observation. If a miracidium hits the shell it quickly turns round and swims away. If it 
strikes one of the soft spots it seems to rotate on its long axis as if it was boring into the tissues 
of the snail. After one or two minutes of this boring motion, it remains quiescent and attached 
until it is brushed off by the friction against the shell when the snail retracts its body. This 
brushing off occurred in a few minutes in the case of the miracidia that became attached to the 
tentacles or head. The miracidia that became attached to the mantle and dorsum of the foot, 
however, remained fixed and motionless for the twenty minutes during which they were 
observed. No further attempt was made to study the further penetration and route of migration 
inside the body of the snail. 
As miracidia hatched out they were placed in 3 " x 1 " tubes with Lymnaea natalensis , allowing 
about half-a-dozen larvae for each snail. These snails were ultimately transferred to jars with 
well-aerated water in a room at a constant temperature of 22 c C and fed on boiled lettuce. 
Rediae (Fig. 7) 
These same snails died from three to seventeen days after exposure to the miracidia and they were 
dissected and examined for developmental stages. Only young rediae with undifferentiated germ balls 
and mother rediae with developing daughter rediae were observed in these. No sporocysts were seen 
even in the snail which died three days after exposure and no daughter rediae with cercariae were seen 
even in the snail which had been infected seventeen days. These rediae occupy a superficial position in 
the digestive gland and when the shell was removed they were seen projecting on the surface and were 
easily teased out. 
The rediae are colourless and capable of some sluggish movement of extension and contraction. 
The collar, locomotor appendages and the rhabdocoele gut are prominent. 
The young rediae are of varying shapes, some being oval, others elongated. They measure from 
0.2 mm by 0.12 mm to 0.4 mm by 0.08 mm. The mother rediae with enclosed daughter rediae are also 
free of pigmentation and measure 0.8 mm by 0.15 mm. 
Description of Adults (Fig. 8) 
Adults recovered from Ducks A and C proved to be Echinostoma revolutum (Froelich 1802), Dietz, 
1909. 
There was a noticeable difference in the size and stage of development between the single specimen 
obtained in the small intestine and the twenty-one obtained from the caecum of Duck A, the former 
being larger and more mature. 
The adult has been described previously but Johnson (1920) maintains that Looss, Luhe and others 
have undoubtedly placed two species, perhaps more, under the name E. revolutum. Beaver (1937) shows 
that the mature worm of this species varies from 4 to 30 mm in length and that the proportionate 
measurements between the various organs and structures (previously used in species determination) are 
not constant for all sizes. In addition to E. echinatum, which had already been reduced to synonymy, he 
considers eight others to be synonyms and eight more to be probably synonyms or species of dubious 
standing. He has emphasised the importance of the number and arrangement of the cephalic spination 
in the diagnosis of the adult worm. These adults were examined in the light of Beaver’s work and the 
following comments are made. 
Although the adults from Duck A are all of same age having been secured 26 days after feeding with 
metacercariae the specimen from the small intestine is larger and more mature. It measures 15 mm long 
by 4 mm broad at the widest point, the testes are distinctly lobed and the uterus is a dense mass of 
transversely coiled tubes packed with numerous eggs. The specimens from the caecum, however, measure 
only from 5 to 10.2 mm in length by 1.2 to 1.7 mm at the widest point and the uterine coils vary from six 
to twelve containing 20 to 45 eggs. This finding is interesting in view of the statement of Sandground 
and Bonne (1940) that the marita of E. lindoensis grows to more substantial proportions, especially in 
width, and that the testes are almost invariably deeply lobed. The findings of eggs in the faeces of Duck A 
as early as the eighth day is probably due to the quicker development of the adult in the small intestine. 
It is possible that the more rapid development of the one in the small intestine was due to the ready 
availability of digested food there as compared with the caecum. 
The collar spines number 37 in 19 out of the 22 specimens and 36 in two specimens; one specimen is 
too badly damaged to allow the counting of spines accurately. In both those specimens with only 36 
spines, one of the corner spines has become detached. The arrangement of the collar spines is, as Beaver 
first pointed out, in the (3+2)+ (0+6)-)- (8 — 7) — (6+0) — (2 — 3) fashion 
MALAYA , No. 26 . 1953 
