406 
Digenetic Trematodes in Japan 
canal broad and terminating blindly (?) near the dorsal surface. Uterus with 
several irregular loops lying within and without the intestinal caeca, in the 
posterior half of body. Eggs 0-04 mm. x 0-02 mm. Habitat: in the intestine 
of Parasilurus asotus. 
Description. This parasite is found abundantly in the duodenum and 
the anterior part of the small intestine of Parasilurus asotus. The species 
occurs very commonly in the fish from various parts of Okayama and Tokyo. 
Various stages of the species are found in one host. The average size of 
mature examples is 02-03 mm. in length and 0-26-0*28 mm. in breadth 1 . 
Generally the body is slightly broader than long. Both anterior and posterior 
ends are round, the anterior part often narrowing slightly. It is compressed 
dorso-ventrally. It appears as a brown dot to the naked eye, the colour being 
derived from the eggs in the uterus. 
The cuticle is relatively thick, measuring 0-003-0-004 mm. In fresh speck 
mens closely-set, fine spines are found in the cuticle, excepting on the posterior 
part of the body. In sections, however, these spines appear indistinct, being 
represented as small protuberances on the surface. Several cephalic glands 
lie in the anterior end of the body near the oral sucker. 
The oral sucker is situated at the anterior end, facing ventrally. In 
moderately extended specimens, the ventral sucker lies at the anterior third 
of the body and it is smaller than the oral one, the diameters of the oral and 
the ventral suckers being 0*055-0*077 mm. and 0-04 mm. respectively; the 
ventral is deeply depressed. 
A pair of round, brown eve-spots are present at the anterior dorsal part 
of the body, laterally to the oral sucker. There is another median pigment 
spot lying slightly anterior or posterior to the paired eye-spots. In mature 
specimens they are indistinct and in some cases they are found disintegrating 
into several pigment granules. 
The pharynx is small. Its breadth is 0-03 mm. The intestinal caeca turn 
first laterally and then posteriorly along the lateral body margin and terminate 
near the posterior end of the body, where they turn mesially. 
The excretory vesicle is V-shaped, opening at the posterior end of the 
body. The arms are very broad and lie between the intestinal caeca and 
anteriorly they reach a point immediately posterior to the oesophagus. 
Both testes lie near the middle part of the body on the same level, either 
on the dorsal side of, or lateral to, the intestine as the case mav be. The 
shape is round or elliptical. The vesicula seminalis is very large and lies 
dorsally to the ventral sucker. It is 0-15 mm. x 0-05 mm. and its dorso- 
posterior end almost touches the dorsal body wall. Slightly distal to the 
middle part, the organ is constricted, the constriction dividing the organ into 
two unequal parts. Antero-ventrally it narrows into a short ductus ejacula- 
torius which unites with the vagina and forms a tube-like genital sinus. It 
opens at the anterior border of the ventral sucker. It is destitute of a cirrus- 
1 As measured in a preserved specimen. 
