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Part III. — Thirteenth Annual Beport 



proceed. In other words, the matured state of .the reproductive 

 organs is the only criterion by which we may pronounC© on the 

 maturity (arrival at adult state) of any given specimen, al]d the 

 connection between this stage and the size then attained seems to be 

 very variable. It follows from this that the term "immature" if it is iC 

 signify anything definite whatever, must apply only to the fish which 

 have not yet ripened their sexual organs. If a mean average length 

 could be fixed by scientific observers, under which the individuals of 

 the species under consideration are not sexually mature, and above which 

 they are sexually mature, then one would have a scientific basis for 

 prohibitive legislation. To fix any other significance to the terms 

 "immature" and "mature," is to make these terms absolutely meaning- 

 less, and to make apparent a scientific distinction where none such 

 exists.* 



If the maturation of the sexual organs takes place in a certain district 

 at a smaller size than is the case with the average, then a "race" or 

 variety of smaller fish ensues. Thus the plaice in the south of England, 

 as far as statistics go, appear to be smaller on an average on attaining 

 maturity than those, e.g., on the east coast of Scotland ; and Petersen f 

 deduces facts to show that a smaller " form " J is present in the Baltic than 

 in other Danish waters ; whilst in Iceland a " giant race " predominates. 

 If we assume that in all these " forms " the sexual organs mature at the 

 same lapse of time from the hatching date, then the different rate of 

 growth, due to the different environment, would account for the smaller 

 size. 



The other alternative is to assume an approximately constant rate of 

 growth in each case, and an earlier (in time) maturation of the sexual 

 organs. 



Further investigation alone can show whether one has to deal with a 

 case of a hastening of sexual development (paedogenesis) or a retardation 

 of growth. Petersen is led to find that the period of attainment 

 of maturity (roughly three years) in the Danish corresponds with 

 that of our East Coast "form" of plaice, which rather indicates the 

 latter. 



The attainment of maturity also takes place at a different size in the 

 two sexes, the male pretty generally being the smaller amongst Teleostei. 

 Occasionally, as in the long rough dab and the salmon, this is very 

 marked, Here again we have the same two alternatives by which to 

 explain the faots. Does the male grow more slowly than the female, 

 both maturing at the same time ? or does the male mature at an earlier 

 age, the rate of growth for the two sexes being the same? In 

 other words, which varies — the rate of growth, or the period of develop- 

 ment? 



Here we have data which distinctly point to a variation in the duration 

 of the development, the male sexual organs maturing at an earlier date 



* It is difficult to understand the term ' fully-grown ' as used by Cunningham 

 Journ. Mar. Biol. Assoc. 1890-91). One would naturally suppose that a fish which 

 s ' fully -grown ' must have reached a size beyond which further growth does not 

 take place, but there is no proof that such a state is ever attained by fish. In the 

 higher vertebrata, in which there is a definite limit of growth, the maturation of 

 the sexual organs is more or less correlated with its attainment, and hence a 

 ' mature ' animal in these groups may be roughly defined either as ' fully-grown ' or 

 as ' sexually ripe.' The latter only of these standards can be applied in the case of 

 fish, and the former term as applied to them has no meaning whatever, 

 t Petersen, Rep. Danish Biol. Stat., 1893. 



+ Petersen goes over the grounds for and against regarding the " form " peculiari- 

 ties as racial — he appears inclined to attribute them to direct influence of the differ- 

 ent environments in each generation. 



