LARVAL TREMATODES 
207 
Cuticular spines are present on both the dorsal and ventral surfaces in 15 out of the 22 specimens; in 
the others the spines are evident only on the ventral surface. In some specimens the spines on the dorsal 
surface extend as far back as the posterior border of the posterior testes. The spines behind the level of 
the ventral sucker become progressively smaller and more widely spaced till they disappear. Sprehn 
(1932) and Ben Dawes (1946) consider that Echinostoma differs from Echinoparyphiwn in the absence of 
dorsal cuticular spines. However, Tubangui (1932) and Beaver (1937) mention the presence of cuticular 
spines on the dorsal surface of Echinostoma revolutum although the latter finds in his series that the dorsal 
cuticular spines are lost after reaching a length of about 8 mm. in ducks and bird hosts. 
It was noticed that in the adult worm the cuticular spines (Fig. 8c and d) tend to be more scale-like 
with a longitudinal thickening and not so sharp-pointed as illustrated by Johnson. Seen in profile, as the 
spines on the sides appear in toto mounts, they are more spine-like with blunt rounded points. In the 
area between the two suckers they measure 270. long by 22\x wide. 
The testes are oval or slightly lobate with smooth outline. The larger specimen was flattened 
between two glass slides and fixed and it was noted that the lobulation of the testes which was not evident 
in the living specimens became noticeable. 
Second Batch of Snails 
On 17th August, 1949 a second batch of 25 Lymnaea crosseana was received four days 
after it had been despatched by plane from Malaya. All were found dead on arrival. 
Dissection of Snails 
On dissection eleven snails were found to contain globular metacercariae in numbers 
varying from about ten to twenty. Some were very dense, others translucent and obviously 
dead. 
On examination, these metacercariae proved to belong to the Echinostome group with about 50 or 
more collar spines in two rows and therefore different from the two species seen previously. The cysts 
are provided with a double thick wall which measure iiji. across. The outer wall is wider and more 
transparent than the inner wall which is dark and thin. The outer wall breaks off readily but the inner wall 
is tough and it is difficult to rupture it without injuring the contained agamodistome. The metacercaria 
appears dense and the collar spines cannot be counted accurately. The diameter of the cyst is 0.15 to 
0.16 mm. 
Feeding Experiments 
These metacercariae were fed to one duckling, two rats, two mice and one guinea-pig. 
None of them became infected judging by the examination of faeces and subsequently of the 
gut when they were killed one by one after the sixth week. 
Third Batch of Snails 
On 20th August, 1949, a third batch of snails arrived by air from Malaya. They had 
taken five days in the travel and consisted of six Lymnaea crosseana and two Planorbis exustus. 
Of these only three Lymnaea and one Planorbis were alive. 
Dissection of Snails and Feeding Experiments 
The dead snails were dissected and Echinostome metacercariae were present in both 
species of snails but there were no rediae or sporocysts. Examination of a few metacercariae 
from each of the snails showed that they all belonged to the 37 collar-spine variety. They 
were divided into two lots and one was given to a duck and the other portion to a rat. 
A month later both animals were killed and examined. The rat was negative but the 
duck had one Echinostoma revolutum in the large intestine. 
Description of Xiphidocercariae {Fig. 9) 
Of the live snails, one Lymnaea discharged a few xiphidocercariae with a stylet. These are poor 
swimmers being found mostly at the bottom of the glass container. When swimming the body is doubled 
up ventrally while the tail lashes in all directions. On a glass slide they are capable of crawling with the 
aid of suckers. 
MALAYA , No. 26 , 1953 
