208 
A. A. SANDOSHAM 
They are distomes with a straight tail which is narrower than the body. Eyes are absent. The 
anterior extremity is rounded and provided with a stylet which is about 19 to 22[jl long. It has a single 
needle-like point and has a lateral thickening about a third of the way behind its tip. The stylet lies 
dorsal to the oral sucker in the long axis of the body. The body is about 0.09 mm in length and about 
0.08 mm in maximum width which is at the level or slightly in front of the ventral sucker. The tail is 
about 0.14 mm in length and 0.023 mm in width. There are no fin folds to the tail. 
The ventral sucker which is smaller than the oral, is just behind the middle of the body. The cuticle 
is spinous being particularly dense in the anterior part of the body. A pharynx is present about midway 
between the two suckers. The interior of the body is filled with uniformly rounded cells and a little 
anterior to the side of the ventral sucker are seen two pairs of penetration glands. The excretory bladder 
is of the simple bicornuate type with a median extension down the tail. 
Dissection of Snail discharging Xiphidocer car iae 
The Lymnaea crosseana discharging xiphidocercariae died and dissection showed the 
presence of cysts and cercariae in elongated sporocysts in the digestive gland. The cysts 
are oval in shape measuring 0.16 by 0.12 mm and contain an extruded stylet of the same type 
as above. There is a mass of dark substance close behind the ventral sucker. The agamodis- 
tome released from the cyst wall was similar to the one described earlier from the first batch 
of snails. 
Exposure of Snail to Xiphidocercariae 
A number of these xiphidocercariae freshly released were placed in the same tube with 
three Lymnaea natalensis. There was a reduction in the numbers of the cercariae and dissection 
of the snails, all of which had died in the course of two weeks, showed two with metacercariae 
with extruded stylets. 
Dissection of Planorbis exustus 
The two snails on dissection showed the presence of Echinostome metacercariae of the 
37 collar spine type and presumably of E. revolutum. The live snails not discharging cercariae 
died within 10 days and dissection of these showed no larval trematodes. 
Summary 
This can only be considered as a preliminary study of some Malayan larval trematodes. 
The snails had been sent for while the author was working in London in order to study in 
greater detail the dermatitis-producing Cercaria malayi I which had been described earlier. 
Its absence in these batches of snails sent from the same locality may suggest a seasonal pre- 
valence of infection. 
A high incidence of infection of Lymnaea crosseana and Planorbis exustus exists and a high 
mortality takes place during the transport of these by air. 
The occurence of mixed infections in these snails is noted, two snails discharging an 
echinostome and a furcocercous cercaria and one snail discharging two species of echinostome 
cercariae. 
The experimental infections have been, on the whole, unsatisfactory. The 
inadequate numbers of metacercariae used and the doubt as to their ability to infect should be 
taken into consideration in interpreting the negative findings. 
The identity of the cercaria with 37 collar spines has been established as Echino stoma 
revolutum by experimental feeding of ducks. The development of the egg and the formation 
of mother rediae in Lymnaea natalensis are described. 
STUD. INST. MED. RES. 
