SEA-FISHERIES LABORATORY 



133 



single plankton net can be expected to collect a represen- 

 tative sample, so no one trawl-mesh gives ns a representa- 

 tive catcli of the fish resident on the sea-bottom. 



Three groups of plaice caught during 1909 have been 

 examined statistically in order to see whether the 

 distribution of the length followed the normal law. The 

 results of these examinations are given in Tables on 

 pp. 181-182, and the curves (figs. 10 and 18) express the 

 distribution graphically. It will be seen that the 

 correspondence is in no case a close one, and that it is 

 probable that the distribution would be better repre- 

 sented by a skew curve. 



■Integral curv, 



Frequency curve. 



■Curve of error. 



Fig. 16. Catcli of 44 plaice from Barrow Channel, 12 July, 1909, Gp. II cf • 

 Correspondence with curve of error. 



I thought it might be possible to decide whether or 

 not the deviations from the modal length in a number of 

 young plaice, of very approximately the same age, were 

 distributed according to the normal law of error. For 

 this purpose a number of measurements made by Mr. 

 H. C. Chad wick were available* The fish had been 



* Eeferred to in Annual Report of Liverpool Marine Biology 

 Committee for 1907, p. VS. 



