196 



tlie ova dehisce is a closed portion of the coelom. The 

 cavity of the oviduct is also a portion of the coelom. 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, pi. V.) lies just within the lip of the aniis 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 immatiire 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 

 mature 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 exjielled, 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 nearlj^ 

 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 



