H. Kobayashi 
403 
0-14-0*24 mm. respectively. The elongated pharynx measures 0-45-0-625 mm. 
x 0-12-0-25 mm. There are no cervical papilla-like process or fringes. The size 
of the egg is 0-016 mm. x 0-008 mm. 
This species appears to be new. 
Some of the specimens were parasitised by a sporozoan (Haplosporidia?). 
The parasites infest only the parenchyma cells of the host. 
(23) Didymozoon sp. (PL XXVI, fig. 4). 
This species infests the gill of Sconiber japonicus. The cyst has an ellipsoidal 
form, measuring 2 mm. x 1-2 mm. Two individuals are present in one cyst. 
Both are hermaphrodite and have the same structure. The body is composed 
of two parts, a narrow anterior and the greatly enlarged posterior part. The 
anterior part has a length of about 0-7 mm. and a breadth of 0-08 mm. The 
posterior part measures 1-1*3 mm. in length and 0-55 mm. in breadth. At 
the junction of the two parts, the posterior part protrudes in two lateral lobes 
which overlap the anterior part. As Odhner 1 has observed, its form is com¬ 
parable to that of a mammalian stomach, the anterior part corresponding 
to the oesophagus. 
The oral sucker lies at the anterior end of the body, being placed in a 
depression. It is pyriform, the length and the width at its widest part being 
0-035 mm. and 0-02 mm. respectively. The pharynx is spherical, being 
0-025 mm. in diameter. The prepharynx is lacking. The oesophagus is relatively 
slender; it is divided into two intestinal caeca about at the middle of the 
anterior part. The intestinal caeca extend almost to the posterior end and they 
widen in their posterior parts. 
The testes, the ovary, the vitellarium and the uterus lie in the posterior 
portion of the body. They are all very long and make numerous loops. The 
oviduct arises from the middle of the ovary. The vitellarium has two main 
trunks which each divide at least twice. The vitellarium extends throughout 
the whole peripheral part of the posterior portion, while the central part is 
occupied by the uterus. The ovary lies near the base of the anterior part. 
There is a Laurer canal, which ends blindly, being surrounded by a group 
of peculiar cells. Near the basal portion of the anterior part, the uterine 
walls become abruptly thickened to form a vagina, which runs straight 
forwards and opens at the anterior end of the body, near the mouth. The 
eggs are very numerous. They are small, being 0-018 mm. x 0-007-0-009 mm. 
Two testes lie near the base of the anterior part of the body. Each of 
them makes a single loop. At the anterior end the vas efferens arises which 
soon unites with the vesicula seminalis. The vesicula seminalis is a thick 
tubular organ running anteriorly between the intestinal caeca and later along 
the oesophagus. There is a short ductus ejaculatorius which opens at the 
anterior end, uniting with the vagina. 
1 Odhner, T. (1907). Zur Anatomie der Didymozoon, etc. SarlrycJc ur Zoologislca Sludier 
ilia gnadc Professor T. Tullberg. 
