of the Fishery Board for Scotland. 



193 



(381mm.) was the size at which all or nearly all were mature. This 

 size was contrasted with that given by Holt (17in.), and was considered 

 as indicating a racial difference in the plaice of the North Sea and of the 

 English Channel. The borderland between the altogether immature and 

 the altogether mature was found to be from 9-1 2in. (229-305mm.) for the 

 males and from 9-14|in. (229-368mm.) for the females. The averages 

 for these borderlands were considered to be about lOin. (254mm.) for 

 the males and 12-13in. (305-330mm.) for the females. 



At a later date the same naturalist continued the work of Holt on the 

 east coast of England, but while Holt had studied for the most part the 

 forms from the North Sea north of Grimsby, Cunningham investigated 

 those from the southerly portions of the North Sea mostly, and more 

 especially those from around Lowestoft. There is consequently a consider- 

 able difference in their results, the sizes given by the latter being much 

 smaller than those given by Holt. Fortunately, the data recorded by 

 Cunningham are sufficiently numerous and representative to be restated 

 according to the method here proposed. 



The following Table represents the totals of five different lots of plaice* 

 collected from the same region — the southerly portion of the North Sea, 

 and about the same time — from October to December. The specimens 

 obtained by Cunningham from Geestemunde are omitted, as they came 

 from another part of the North Sea, and do not seem representative. 



Table I. 



Proportions of Mature to Immature Plaice at Different Sizes. 



Sex. 



Condition of 

 Reproductive 

 Organs. 



Size in Inches. 



8 



9 



10 



11 



12 



13 



14 



15 



16 



17 



Males 



Immature . 



1 



10 



27 



20 



12 



11 



2 



1 









Mature 





6 



17 



30 



26 



10 



2 



5 



14 





Do. in percentage 



Immature . 



100 



63 



61 



40 



32 



52 



50 



17 









Mature 





37 



39 



60 



68 



48 



50 



83 



100 





Females . 



Immature . 





8 



46 



74 



67 



30 



18 



6 



3 



1 





Mature 





1 



2 



18 



24 



21 



7 



9 



13 



9 



Do. in percentage 



Immature . 





89 



96 



80 



74 



59 



72 



40 



19 



10 





Mature 





11 



4 



20 



26 



41 



28 



60 



81 



90 



The proportions of immature and mature at each size are arranged in 

 percentages, because by so doing the inequalities in the numbers of speci- 

 mens at the different sizes are done away with. A comparison can then 

 be drawn between the number of mature specimens at the different sizes, 

 and similarly for the immature. In calculating the percentages the 

 nearest whole numbers are always taken. 



* " North Sea Investigations : " Jour. Mar. Biol. Ass., Vol. IV., 1895, p. 106 et seq. 



