of the Fishery Board for Scotland. 



223 



the lowest average in the Solway Firth specimens being only *06 less than 

 the highest in the Aberdeen and Baltic specimens. This means that the 

 size of the abdominal cavity is probably the same in all. 



The case is different with the caudal vertebrae, and these may be con- 

 sidered before proceeding to the total number of vertebras. The Table 

 shows that the averages of the caudal vertebras for the whole of the North 

 Sea differ very little between themselves, the lowest, in the Helder 

 specimens, being only *125 less than the highest in the Heligoland 

 specimens. The fluctuations of the averages, again, greatly overlap in 

 these, and the only conclusion is that they are all identical in regard to 

 this character. The specimens from the Solway Firth also have an 

 average but little smaller than those from the North Sea, and the fluctua- 

 tions of the averages overlap as before. On the other hand, the specimens 

 from the Baltic differ greatly from the above. The average differs from 

 the lowest of the others by *48, and the fluctuations barely overlap. If 

 it be considered that the number of specimens from the Baltic is com- 

 paratively small, and that this has the effect of increasing the size of the 

 fluctuations, it may be admitted that a similar number of specimens from 

 the Baltic, as from the other regions, would have reduced the fluctuations 

 of the average so much that they would not overlap those of the other 

 regions. 



If we turn to the total number of vertebras the same conclusions are 

 forced upon us. The average for the whole North Sea is practically 

 43*00, and very little difference exists between the different regions. 

 Helder has the lowest value, its average being *1 less than those of the 

 others. The standard deviation is, however, the greatest here, and this 

 causes a bigger fluctuation of the average. Whether, if a much 

 larger number of specimens from Helder was examined, this difference in 

 the averages would remain constant, and thus tend to show that the plaice 

 from Helder were really a distinct group from those of the other regions, 

 it is difficult to say. There is a certain amount of probability, but it is at 

 present small. 



Table VI. — Vertebral. 



Average, M. ; probable fluctuation, P.F. ; standard deviation, o*. 



Region. 



No. of 

 Specimens. 



M. 



P.F. 



<j 



Heligoland, .... 



341 



43-032 



42-932-43-132 



•56 





200 



42-90 



42-74 -43-06 



•675 



Lowestoft, .... 



170 



43-05 



42-91 —43-19 



•54 



Grimsby, .... 



120 



43-02 



42-84 —43-20 



•59 



Total, Southerly North Sea, . 



831 



43-002 







Aberdeen, .... 



254 



42-996 



42-882—43-110 



•54 



Solway Firth, .... 



197 



42-85 



42-71 —42-99 



•62 





47 



42-42 



41-97 —42-87 



1-02 



[Table. 



