RAPPORTS. XIII C4: MASTERMAN _ lo — 



reached a certain age or because it has attained a certain size ? The author, by dividing 

 up the age-groups into sizes, has obtained evidence which appears to point to the attain- 

 ment of a certain size, as determined by length, as being the all-important feature rather 

 than age. "Whether this is attained in a longer or shorter period by slower or more rapid 

 growth, would appear to be of secondary importance". This conclusion may be compared with 

 the already well-known fact that the gradual growth-movement seawards of the young 

 plaice is determined, not according to age so much as according to size. As the plaice 

 naturally distributes itself seawards in size-zones, the zone comprising the average size-at- 

 flrst-maturity would constitute itself a spawning zone, provided other features of distribution 

 did not intervene. 



These results may be compared with those of Johansen (4). Numerous individuals 

 were examined in the period between the middle of September and the end of April. It 

 was found that signs of approaching ripeness, as given by previous observers for the 

 female were reliable, whilst the testes of males approaching maturity showed a total length 

 of over 5 mms. Only in isolated cases were fish with testes of 3 to 4 mms. in length 

 found by microscopical examination to be ripe. 



Further, it was found that, in the male, a ciliation of the head-scales makes its 

 appearance simultaneously with maturity. Only about 1 — 2% of the plaice landed at 

 Esbjerg from the North Sea were mature. 



The critical sizes may be given here for comparison with those of Wallace. 



The males reach maturity at an age of 3 to 7 years and the females 4 to 7 years. 

 The data for mature individuals were not sufficiently extensive to give more definite re- 

 sult, e. g. as to the age at which the majority of individuals become mature, though this 

 is evidently later than the third year for males and later than the fourth for the females. 



*Hefford's work (3) is based upon the experimental hauls of the Huxley, and upon 

 materia] obtained from commercial sailing vessels in the Flemish Bight. It consists of a 

 detailed enquiry into the occurrence of a high proportion of males, in relation to locality 

 and season. For the purpose in hand, the author divides the North Sea into six sub-regions, 

 subdivided into thirteen areas. These divisions can only in a limited degree be] compared 

 with the International Plaice areas or with those adopted by Lee in the report already 

 referred to. 



If the whole of the data from a research vessel be arranged under sizes and sexes 

 it is found that there is about the same number of each sex. Below 15 cms. in length 



