208 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



was suspended here for the period of the war and we have 

 only the years 1909, 10, 11, 12, 13, and 1920 for comparison 

 with each other. The distributions considered are those for 

 August and September (the best ones), and the data are taken 

 from Tables 5, 23, 24. What we can compare is the pre-war 

 period, 1909-13, with the post-war one, 1920, and it is to be 

 noted that we know nothing of the years 1914-19 : possibly 

 1919 was a year in which the plaice here ran bigger than they 

 did in 1920. Now which of the pre-war years ought we to 

 set over against 1920 ? 



The last pre-war year, 1913, is the one with which we 

 naturally compare the first post-war year, 1919 (or 1920, for 

 we have no data for 1919). But we see, from Fig. 16, that 1913 

 appears to have been a year of minimum abundance of plaice, 

 while 1910 was situated near a maximum. It is well, then, 

 to see if there are differences between the prevalent sizes of 

 plaice as they occurred on the Liverpool Bay grounds, and so 

 Fig. 18 was prepared. 



Evidently, if we compare 1920 with 1913, we find that 

 the post-war plaice ran bigger than did the pre-war ones ; 

 but if we compare 1920 with 1910 we find that there is little 

 (if any) significant difference. If we take the average lengths 

 for the years 1913-1909 we shall find that the plaice of 1920 

 are, on the whole, bigger than in the years immediately pre- 

 ceding the war ; but it would be wrong to associate the increase 

 so indicated with the restrictions on fishing of the years 1914-18. 

 It is necessary to consider also the deviations from the average 

 of 1909-1913, and we see that the good year 1920 is not any 

 better than the best of the pre-war years with which it is 

 contrasted. The fact is that these length-frequency data are 

 very difficult to interpret in some cases : to make the best 

 use of the information that they give requires also a knowledge 

 of the migrations. We should want to know, rather closely, 

 in what months the crises of the migrations occurred, because 



