RAPPORTS. XIV: MASTERMAN - 24 



Proportion of each sex at each age. 



If the proportions of the two sexes be calculated for each age group it is found that 

 the number of males predominates in the earlier years and the females in the later years. 

 The change is continuous so that at a critical age a point is reached at which the number 

 of each sex is approximately equal. This point for the North Sea is at five years old, 

 and for the English Channel it is between two and three-years-old. These points are in 

 approximate aggreement with the age-of-first-maturity of the male sex in each instance. 

 Wallace has already indicated, as quoted in my Second Report, that in the Dogger region 

 the majority of male plaice probably become mature when five years old and in the 

 Flemish Bight when four years old. They attain maturity in the English Channel when 

 two years old. This correlation enables the author to formulate the following rule: — 

 "In each region, males are more numerous than females up to the age at which the 

 majority of males become mature for the first time, after which, or soon after which, 

 females begin to preponderate, the number of males diminishing somewhat rapidly". 



Future research will no doubt throw more light upon the causes underlying this 

 correlation. It is possible that a study of the proportion of the sexes at each size may 

 help to effect this. 



Habits of the sole. 



In the Report by Redeke and Tesch already referred to, there are given some notes 

 concerning the biology of the sole. As regards the spawning grounds more knowledge 

 is still required. The eggs appear first in quite fresh water and thence the operation of 

 spawning spreads to greater depths till the 40-metre line is reached. No great concentration 

 upon specific grounds is found, as is the case, e. g. with the plaice. The period of 

 spawning appears to last from mid April to end of June, with a zenith in May. The 

 young soles are found close inshore, along with young plaice, and the transformation is 

 completely effected at a length of 15 mms. The authors are inclined to regard these 

 inshore waters as the normal habitat of the young sole of the first year, their comparatively 

 rare occurrence in the nets being perhaps ascribed to their great activity. The small 

 data which are known seem to indicate that in the early years of its life the sole frequents 

 the shallow inshore waters. 



As regards the age of soles, the authors have employed the method of age-determination 

 by examination of the vertebrae which were found to give clear indications of annual 

 rings. Only a small number of fish were examined by this method, but further investigations 

 are promised. 



