196 
the ova dehisce is a closed portion of the celom. The 
cavity of the oviduct is also a portion of the celom. It 
does not appear to be a Miillerian duct like the oviduct of 
all other vertebrata, and its morphology is exceedingly 
obscure. It has no homologue among the genital struc- 
tures of the male fish. ‘The external opening of the oviduct 
(Od., fig. 20, pl. V.) lies just within the lip of the anus on 
the posterior side of the latter. It may appear to be out- 
side the anus on the ventral body wall, and its variable 
situation is due to the extent to which the terminal por- 
tion of the rectum is contracted. In the immature fish 
the opening does not apparently exist, and even in the 
mature but unripe individual we have been unable to 
satisfy ourselves of its existence. If in a ripe female 
Plaice the body over the region of the ovaries be gently 
pressed, the mature eggs issue in a thick stream, and the 
opening can then be easily seen as a transverse slit behind 
the anus. After extrusion of all the eggs this slit seems 
to close up by the adhesion of its edges, and in dissecting 
such a spent specimen, though the terminal part of the 
oviduct can be traced to just behind the anus, some little 
pressure with a blunt seeker is required to force a passage. 
In the nearly ripe fish which has not yet spawned even a 
moderate pressure on the abdomen may not cause the 
extrusion of any eggs, though dissection may shew that 
inature ova are present in considerable number lying loose 
in the cavity of the ovary. The more nearly ripe the fish 
is, the more easily are the eggs expelled, until in some 
cases merely lifting it from the water in which it is lying 
may cause the eggs to run from it. There is generally no 
bleeding from the edges of the forced opening in a nearly 
ripe fish, and sections of the region of the body wall 
behind the anus shew that it is formed almost entirely of 
dense fibrous connective tissue without many blood 
