THE RATE OF GROWTH OF FOOD-FISHES. 109 



Female. 

 Inches. 

 8i-18 

 5-16i 

 20—28 

 11—19 



H-n 

 r-i7i 



By this method one important fact has been brought to 

 light, namely, the difference in size between the sexes. It 

 appears to be the rule that the attainment of maturity takes 

 place at a different size in the two sexes, the male pretty 

 generally being the smaller among Teleosteans. 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 facts. 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 development ? 



We have data which distinctly point to a variation in the 

 duration of the development, the male sexual organs maturing 

 at an earlier date than the female. This is undeniably the 

 case in Myxine, and also in the salmon. Thus we may assume 

 that the rate of growth in the two sexes is closely similar. 

 Both sexes are placed under the same environmental conditions, 

 and hence a different rate of growth would be at least im- 

 probable, whereas the more rapid maturation of the male 

 elements may be traced to a deep-seated origin which may be 

 best explained by the following remarks by one of us^ 



" There are numerous facts in the ontogeny and structure of 

 the Vertebrata which point to a hermaphrodite chordate 

 ancestor. 



"Amongst these we may cite Nansen's observation of 

 the protandric hermaphrodite condition of Myadne^ and the 



1 A. T. M. ' Hermaphroditism in the Cod,' 13th Scot. Fish. Board Report, 

 p. 298. 



2 Aarsber. Bergens Mm. 1887, op. vii. 



