250 



THE CONDITIONS OF LIFE IN THE SEA [PART III 



also be an optimum intensity of light in the case of the marine 

 protophyta. It may sometimes be observed that a culture of 

 marine diatoms in sea water mud exposed to strong sunlight does 

 not shew the same obvious indications of rapid multiplication as 

 when the same culture is shaded from the direct rays of the sun. 

 Neither must we assume that photo-chemical reactions — the 

 power of making use of solar radiations — are exhibited only by 

 marine plants, or at least by those organisms possessing chlorophyll 

 plastids. Patten^ suggested long ago that the "eyes" of the 

 scallop (Pecten) were not solely visual organs, but also constituted 

 an apparatus for the utilisation of the energy of sunlight; and 

 there is a fair amount of experimental evidence in favour of this 

 hypothesis I It must have occurred to many zoologists that if a 

 principle of " economy of effort " is to be assumed in morphological 

 speculations, the explanation of the functions of a battery of 

 highly developed visual organs in such an animal as Pecten is 

 rather difficult to find. But however this may be we have direct 

 evidence that the intensity of metabolism in some marine animals 

 may be influenced by the amount of light which falls on their 

 surface. I quote here some results obtained by Piitter^ in the 

 course of a research on the amount of oxygen used by the sponge 

 Suberites in conditions of light and darkness : 



Amount of oxygen used jyer hour, and per kiLogrwnime of weight. 



There can apparently be no doubt of the existence of a photo- 

 chemical activity in the metabolic processes of Suberites. The 

 adult sponge is an organism possessing no powers of locomotion, so 



1 Mitth. Zool. Stat. Neapel, Bd. vi. 1886. 



' See Herlet, " Uber die Bedeutung d. Pigments f. d. physiol. Wirkung der 

 Lichtstrahlen," Zeitschr. Allgem. Phys. vol. vi. 1907, p. 44. 



2 Vergleich. Phys. Stqfxvechsel, p. 30. 



