228 BATE OF GROWTH OF SOME SEA FISHES. 



criterion by whicli to find out whetlier it has spawned before or not ; 

 it may be sexually immature, or it may have spawned previously, its 

 sexual organs being merely in an inactive state at that particular 

 time of tbe year. 



Now it was, a priori, improbable that the sexual maturity of a 

 fish should depend simply on its size. This could only be the case 

 if every specimen grew to exactly the same size in the same time, 

 if there were no individual variation in the rate of growth. That 

 such a variation exists is obvious from the examination of fishes 

 taken at sea, and my observations on flounders, &c., in captivity, 

 liave shown how great the variation may be. Thus, when Fulton 

 finds the smallest ripe flounder to be 7 inches long, it by no means 

 follows that all specimens larger than this have begun to breed. I 

 have given above the lengths of the twelve of my captive speci- 

 mens which were found to be ripe males in February and March 

 this year. The smallest of them is 6 '4 inches long, the largest 

 9-2 inches. Therefore even a male flounder may be more than 9 

 inches long before it begins to breed — before it spawns for the first 

 time. Eight out of the twelve ripe males are over 8 inches long. 

 If these had been taken at sea last November, they would have 

 been over 7 inches long, and would, according to Fulton^s method, 

 have been classed as mature, while, as a matter of fact, they had not 

 begun to breed, had never yet produced milt. Similarly, with the 

 females there are only four ripe among my captive specimens, and 

 their lengths are from 8-4 inches to 10*5 inches, so that a female 

 flounder may be more than 10 inches long before it breeds for the 

 first time. 



The results thus obtained for the flounder probably apply more 

 or less exactly to other kinds of flat-fishes. Hence we may 

 conclude that, when the smallest size of the mature female in a 

 given species has been ascertained, many females do not reach 

 maturity until they are somewhat larger than this. Therefore, in 

 order to exclude all immature individuals, a limit of size must be 

 taken which is above the minimum size of mature females. 



Pleuronectes limanda, the Dah. 



In the autumn of last year I collected from Cawsand Bay, and 

 other parts of Plymouth Sound, a number of small dabs Avhich I 

 judged to be derived from the spawning of the spring of the same 

 year. 



The dates of collection and lengths of these were as follows : 



