SEA-FISHERIES LABORATORY. 247 



so that there is apparently an increment of growth of 

 about 10 cms. between Groups and I, and an increment 

 of only 2 cms. between Groups I and II. After examining 

 some of my figures, Professor D'Arcy Thompson 

 suggested that a complete year had been omitted in 

 these estimates : if this were really the case, it would seem 

 that the method of age-determination by the examination 

 of the growth of the otolith is unreliable. Scrutiny of 

 the table shows, however, that the cause of the apparent 

 irregularity really lies in the method of sampling which 

 had to be employed. 



The ranges in the cases of Groups I to III are pro- 

 bably very approximately given by the table. Group IV 

 has, doubtless, a more extended range than that shown, 

 since very few fish over 40 cms. in length have been 

 examined, and a larger number would probably show that 

 plaice of this age may be much larger than 415 cms. The 

 lower limit of plaice of Group is, of course, at zero 

 length. In the case of Groups I to IV the lower limits 

 are probably as they are shown in the table. In Group II 

 the distribution is markedly skew, and this is also 

 apparent in Group III, but not to the same extent, while 

 in Group IV the distribution about the mean is probably 

 symmetrical. Group I ought to be still more asymmetrical 

 than Group II, and obA r iously in Group the mode will 

 be at infinity. Yet the actual figures show that the dis- 

 tribution of frequencies in Group I is very nearly sym- 

 metrical. 



The reason of the irregularity in the case of plaice of 

 Group I is that the ordinary 6-inch trawl mesh does not 

 give a catch of plaice representative of those resident on 

 the sea bottom in shallow waters, such as those of 

 Lancashire. Thus there are far too few at lengths of 8 to 

 about 15 cms., fish of these sizes escaping through the 



