222 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



fat-contents and sea-temperature, that is, metabolism is more 

 intense the higher the temperature of the medium. Still the 

 correspondence is not very close and we must find some other 

 factor governing the variation in fat contents. 



This latter factor is the reproductive cycle. The period 

 preceding the final maturation of the genital products is 

 marked by a large increase in fat- contents of the tissues of 

 the fish, and the act of spawning is accompanied by a fairly 

 rapid decrease in this fat-contents. We might generalise these 

 facts by saying that the fish accumulates fat in its tissues in 

 order that this stored nutritive matter might be drawn upon 

 for the maturation of the eggs and spermatozoa (in the herring 

 the masses of these products are about equal) : the protein 

 and fat present in the reproductive glands must come from 

 somewhere. Now this generalisation cannot be quite true. 

 The ratio of protein to fat in the ovaries increases greatly as 

 the genital organs ripen, and the increase in mass of these 

 organs is, therefore, not altogether due to the transference of 

 fat from the muscular tissues to the genital organs. Further 

 the greatest decrease in fat-contents occurs after spawning, 

 when this stored nutritive material is no longer required in 

 the reproductive process. Yet again there must be some 

 relation between the spawning operation and the general 

 metabolism of the animal in order that this change may occur. 

 Evidently there are two independent factors which influence 

 the metabolism of the fish (1) the variations of sea temperature, 

 and (2) the reproductive cycle. It is certain that even virgin 

 herrings would show as well marked a rise and fall of fat- 

 contents as do sexually mature fish, thus virgin plaice do 

 certainly show marked variations in " condition " which 

 corresponded with seasonal changes in the sea. But, all the 

 same, the maturation of the ovaries and testes and act of 

 spawning do certainly influence the general metabolism of 

 the animals. The rapid decrease of fat at the time of spawning 



