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Part III. — Eighteenth Annual Report 



A few "precocious" specimens become mature at a small size, from 9 to 

 llin. (22*9 to 27"7cm.); then the number of the mature increases 

 rapidly, showing that the great majority become mature between 11 and 

 loin. (27'9 and 38*lcm.). This means that they become mature at the 

 same average-age, which, if Dannevig's calculation be taken, is probably 

 at five years old. According to Petersen's and Masterman's calculations, 

 this average-age may be four years. The males become mature a year 

 younger. 



If the curves between 12 and 15in. (30-38cm.) be again considered, 

 it will be noticed that they approximate, in the case of the females, very 

 closely to two straight lines. This agrees with the notion that we have 

 a single year's group between these sizes. The variation in the size of 

 these mature specimens probably arises from the initial difference in age, 

 to be referred to later in the section on " Variability," and this being so, 

 the relative proportions of the mature and immature specimens should 

 alter so rapidly and uniformly as to be represented best by two straight 

 lines. 



At the upper limits, on the other hand, we have to consider the 

 presence of large immature specimens. From my own observations, the 

 largest immature was 15in. (38cm.) for the females and 14in. (35*5 

 cm.) for the males ; but the general trend of the curves admits the possi- 

 bility of finding immature specimens at a larger size than this. And 

 Cunningham's data shows that these may occur up to 17in. for the 

 females and 15in. for the males. As with the earliest mature specimens, 

 these are scattered examples, though probably of constant occurrence. 

 If we suppose that they become mature in the following year, then we 

 are perhaps justified in declariug that all the females are mature in their 

 sixth year, and all males in their fifth at the latest. The exact upper 

 limit in size is hard to fix, but may be taken as about 17in. for the 

 females and 15in. for the males. The ranges of variation would, 

 therefore, appear to be from 9 to 17in. for the females and 6 to 15in. 

 for the males, and three years would be the range in time. Such seem 

 to be the facts, although the reasons for these great ranges of variation are 

 not yet evident. 



We may turn now to the specimens from the northerly portion of the 

 North Sea, which include those from Aberdeen and from St. Andrews. 

 In Table III. they are arranged according to size, in the same manner as 

 those of the southerly North Sea in Table II. The numbers of specimens 

 are not so great as were those of the latter region, and more especially is 

 this the case with the females. Consequently, when the numbers are 

 divided into eight divisions, there are very few in certain of the 

 divisions— from 320 to 420 mm. — and the value of the observed propor- 

 tions of the immature and mature is therefore seriously affected. The 

 multipliers that require to be employed in order to obtain the percentages 

 lie between 3 and 8 in the case of the males, but between 3 and 20 for the 

 females. No definite conclusions can be drawn in the latter case, and 

 only the one set of curves, representing the male specimens, has been 

 drawn. (Plate X.) 



[Table. 



