RATE OF GEOWTH OF SOME SEA FISHES. 227 



Of course it may be objected that it is unsafe to draw inferences 

 from what takes place under artificial conditions ; that fish kept in 

 captivity in tanks may grow at a different rate and breed at differ- 

 ent ao-es from those in their natural state. But the degree to which 

 such differences occur may be ascertained with sufficient certainty 

 by comparing observations made on specimens taken at sea with 

 those made on captive specimens. In my last paper I showed that 

 specimens living under natural conditions are taken at the spawn- 

 ing season, which must be one year old, and yet which are consider- 

 ably smaller than the smallest ripe specimen recorded. Thus there 

 is here some evidence that the development of the reproductive 

 organs is not greatly modified by confinement. 



Dr. Fulton's investigation of the question of immature fish was 

 of a statistical character, and his criterion of immaturity for each 

 species was a criterion of length. He ascertained the length of the 

 smallest ripe fish among a very lai'ge number examined and mea- 

 sured, and he regarded all specimens smaller than this as sexually 

 immature, all larger specimens as mature. Mr. Holt in the course 

 of his observations on the west coast of Ireland introduced a new 

 and important consideration, namely, the distinction of the sexes. 

 Dr. Fulton spoke merely of a ripe specimen without reference to 

 the question whether it was male or female, but it had long been 

 known, e. g. in the case of the salmon, that a male fish may be 

 sexually ripe when very small indeed, while the smallest ripe female 

 is a great deal larger. Mr. Holt, therefore, records the sex as well 

 as the size of ripe specimens, and finds the smallest ripe female to 

 be considerably larger than the smallest ripe male. The importance 

 of this distinction had been also present to my own mind long before 

 Mr. Holt's results were published. In fact, in my previous paper, 

 which appeared in November, 1891, I have in all cases given the 

 sex of the smallest ripe specimen observed, and in the case of the 

 dab have given the length of the smallest ripe specimen of each 

 sex. My knowledge of Mr. Holt's observations is derived from a 

 proof copy of his reports in the Report of the Council of the Royal 

 Dublin Society for 1891. 



In the statistical inquiries of both Holt and Fulton, it is tacitly 

 assumed that the sexual maturity of a fish of a given species 

 depends only on its size. The smallest ripe specimen is found, and 

 it is assumed that all specimens above this size are to be considered 

 as mature. The method of these inquiries naturally involved such 

 an assumption, for while the minimum size of ripe or ripening speci- 

 mens was ascertained, no attempt was made in them to ascertain 

 the maximum size of immature specimens. In fact, when a speci- 

 men caught at sea is not ripe or ripening, we have at present no 



