SEA-FISHERIES LABORATORY. 337 



G._THE REPRODUCTIVE ORGANS. 



Some difficulty will be experienced in determining 

 the anatomy of the reproductive organs, on account of the 

 fact that sexual maturity does not occur until the Plaice 

 has grown to a relatively large size, and that to examine 

 the varying relations of the system in a really satisfactory 

 manner fishes in various phases of reproductive activity 

 must be examined. The ordinary marketable Plaice is as 

 a general rule an immature fish. There is some consider- 

 able difference in the size and age at which it becomes 

 sexually mature in different localities, but it will be suffi- 

 cient for our present purpose to say that under 17 inches 

 of total body length in the female, and 14 inches in the 

 male, the reproductive organs are generally immature. Only 

 fishes of those sizes should therefore be dissected for these 

 organs, and they are best examined some little time prior to 

 the spawning season, that is daring November to January. 

 We may here define several terms used in the follow- 

 ing pages. The Plaice is spoken of as " mature " when it 

 first begins to produce eggs capable of fertilization, or, in 

 the male, functional spermatozoa. It is " ripe " when the 

 ovary becomes distended with mature ova, that is imme- 

 diately before the spawning season. It is " spent " or 

 " shotten " when all the ova have been extruded in the 

 act of spawning. The same terms with the same signifi- 

 cance are applied to the various phases of the male in 

 respect to the conditions of the testes. 



Considerable differences in the condition of the repro- 

 ductive organs may th*m be expected in Plaice of different 

 sizes or of mature fishes captured at different times in the 

 year. In the female fish of about 1J inches long ovaries 

 and ovarian eggs are certainly developed, but the organs 

 are represented by very minute structures situated in the 



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