328 Entozoa of Fishes 
of P. commune showing the same condition. It is suggestive of self¬ 
fertilisation. 
The testes are situated in the posterior third of the body, the post- 
testicular space being fths of the body length. They are always 
directly tandem and contiguous. The shape is somewhat irregular but 
approaches a transverse oval, the breadth being always greater than 
the length. In size they vary considerably but the longer diameter 
is usually about -|th of the body length. 
The ovary is situated immediately in front of the anterior testis, 
generally separated from it by the yolk-reservoir. It is on the right 
side of the middle line, of globular shape and somewhat smaller than 
the testes. The receptaculum seminis is of large size and lies slightly 
behind and dorsal to the ovary. It is in intimate connexion with the 
oviduct, there being no intervening receptacular duct. Laurer’s canal 
is given off directly from the receptaculum. 
The yolk-glands are unusually voluminous and of rather character¬ 
istic distribution. They fill up the post-testicular space and the lateral 
margins of the body as far forward as the posterior border of the 
ventral sucker, overlapping the testes and ovary to a slight extent. 
At the level of the ventral sucker they are entirely absent on each side 
but they again become voluminous in the neck, forming a continuous 
wedge-shaped mass in front of the ventral sucker, and extending 
forward to the level of the posterior border of the pharynx. The 
follicles are of moderate size, about 0'04 mm. in diameter. 
The uterus is short and never contains more than 30 ova. The 
vagina is well marked and begins about the posterior border of the 
ventral sucker. The ova are rather large and broad, light yellow in 
colour and the shell is slightly thickened at the anopercular pole. The 
size varies considerably, i.e. 0'080—0'088 mm. in length and 0044 
—0 - 056 mm. in breadth. The average size is 0'0845 x 0 - 051 mm. The 
rather great amount of variation in the breadth may possibly be due 
to the fact that the eggs are not completely circular in section but 
are flattened slightly from side to side. 
Species 2. Peracreadium commune (Olsson 1868). 
This species was also confined to Labrus berggylta, occurring along 
with, but much less frequently than Peracreadium genu. Only two 
specimens were obtained altogether. It bears a very close resemblance 
