CH. X] 



THE CONDITIONS OF LIFE IN THE SEA 



243 



spring is to be traced to the accumulation of food-stuffs in the 

 water ; no doubt also to the increase in the intensity of sunlight, 

 which raises the intensity of photo-synthesis ; and also to the rise 

 in temperature. But the spring spawning habit of the larger 

 marine animals is perhaps the outcome of a long series of seasonal 

 changes in the general external life-conditions of these organisms. 

 Fluctuations in temperature, food supply, &c., have, in the course 

 of time, so operated that a spawning habit has been formed ; and 

 heredity has ultimately stamped this seasonal reproductive act 

 on the life-histories of these animals. It has become a periodic 

 habit and is now only indirectly affected by changes in the life- 

 conditions. 



There are comparatively few series of observations on the 

 effect of temperature changes on the intensity of marine meta- 

 bolism, but whatever indicator of the latter process we may take, 

 the intimacy of the connection is well shewn. The pelagic eggs 

 of a teleostean fish hatch out in from one week to three, and the 

 development of the embryo is always hastened by an increase in 

 temperature. So close is the relation between temperature and 

 incubation period that it might almost be expressed mathe- 

 matically^. More precise measurements of the variation of the 

 rate of metabolism with temperature changes are given by estima- 

 tions of the exchange of oxygen and carbon dioxide between the 

 organism and its medium, and several such series of observations 

 have been made by Putter. Thus in the case of the metabolism 

 of marine bacteria the following figures were obtained-: 



Oxygen absorbed by the bacteria contained in one litre of water from 

 Naples Bay, kept in the dark in sterilised vessels. 



^ Eeibisch, Wiss. Meeresiint. Kiel Komin. Bd. vi. Abth. Kiel, 1902, 

 ^ Stoffhaushalt des Meeres, p. 338. 



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