of the Fishery Board for Scotland. 



2 I I 



We thus have three possible and plausible explanations of the altera- 

 tion in the combination of characters in the plaice. The evidence 

 required to bring us nearer to a more exact explanation will come from 

 two directions. We require a more exact measure of the reproductive 

 fertility — mass of reproductive organs, or number of eggs — in the 

 different regions, and thence some notion of the so-called " reproductive 

 selection"* within those regions, and at different ages or sizes. Secondly, 

 we require some knowledge of the meteorological, physical, and chemical 

 conditions over the North Sea area, together with a more exact determina- 

 tion of the seasonal fluctuations and their averages in the life-cycle of the. 

 plaice, especially of the southerly regions. 



* \'ide Pearson, K. : " Chances of Death," 1897. 



