ii] RHYTHMICAL CHANGE IN THE SEA 41 



and shrimp hibernate, burying themselves beneath 

 the surface of the sand while the temperature of the 

 sea is at its lowest. Nearly all marine animals 

 become sluggish and inert at this time : they do not 

 migrate much; they do not feed so actively as at 

 other times, or perhaps they refuse to feed altogether. 

 Reproduction does not take place, or if it does occur 

 it is mimimal in degree. 



What we call functional metabolism, that is the 

 assimilation and oxidation of food for the purposes of 

 keeping up the life-processes of the animal, is reduced 

 to a. minimum; the animal uses up as little of its 

 tissues as possible. But morphogenetic metabolism, 

 that is the formation of new substance in the shape 

 of the genital products the eggs or spermatozoa 

 increases to a maximum during the resting stage of 

 the cold winter months. During this time the animal 

 is using its own reserve food-stuff, that is, the fats, 

 carbohydrates, and proteids stored in its flesh, for the 

 purpose of manufacturing the generative substances. 

 The ovaries and testes thus increase largely in weight, 

 but the general tissues of the body lose in weight. 

 This of course only occurs in sexually mature animals : 

 if the fish is immature the whole weight of the body 

 falls off. If it is mature the ' condition' is worst of 

 all just after the time of spawning, and the fish is 

 then thinner than at any other time in the year. 



The reproductive phase, that is the actual spawning 



