44 LIFE IN THE SEA [CH. 



their time of gorging is after the end of the spawn- 

 ing period. From then till about midway between 

 the time of the annual temperature maximum and 

 that of the minimum both functional and morpho- 

 genetic metabolism are most intense. The animal 

 lives at a more rapid pace during the summer months 

 and takes in more food and more oxygen and gives 

 off more carbonic acid during that time. But the 

 type of constructive metabolism undergoes change, 

 for instead of the development of the reproductive 

 organs we find that a rapid growth of the tissues takes 

 place. The fish increases in size, and assimilated 

 food reserves are stored up in its flesh. All the 

 growth of the year occurs during this phase, and 

 the greatest amount of growth takes place at the 

 time when the temperature is at its highest. Growth 

 in a marine animal is a strictly 'periodic function' 

 and is capable of representation by a mathematical 

 expression. In the case of most marine fishes the 

 rate of growth can often be represented by a ' damped 

 sine curve/ that is it is higher than the mean, and 

 maximal, during the warm months, and it is less 

 than the mean, and minimal, during the cold months. 

 The period is an annual one, and the amplitude 

 decreases as the fish becomes older, following an 

 exponential law. Such an expression for yearly growth 

 may also apply to most mollusca, but not to Crustacea, 

 for in the latter animals the growth takes place 



