RECENT WORK ON MARINE METABOLISM u 



that i cubic metre of sea-water in the sea off Syracuse 

 contained : 



Metazoa 17,325 



Protozoa 325,510 



Protophyta 2,082,860 



Bacteria 785,000,000 



These numbers represent a total volume of about 53*63 c.c. of 

 plankton organisms, and a total weight of about 55*6 milli- 

 grammes. Utilising Brandt's tables in order to convert this 

 mass of plankton organisms into food values, we find that the 

 total mass of carbon in 1 cubic metre of sea-water was : 



Metazoa 



Protozoa 



Protophyta 



Bacteria 



Total 3*84 mg. 



And again making use of Brandt's tables l of the composition of 

 planktonic organisms, it is found that the dry organic matter in 

 1 litre of sea-water contained : 



Carbon as proteid 0*00129 mg. 



Carbon as carbohydrate and fat . . 0*00255 „ 



Total carbon .... 0*00384 mg. 

 Total nitrogen. . . . 0*00039 ,, 



Thus 1 litre of water contained 0*0038 mg. of carbon in the 

 form of microscopic animals and plants. If then we assume 

 that the sponge obtains its food from such a source we can 

 easily calculate what quantity of water must be circulated 

 through its canal system in order to supply its requirements. 

 We only have to divide 0*92 (the mass of carbon required) 

 by 0*0038 (the mass of organised carbon present per litre) in 

 order to find that the sponge must pass through its canal system 

 about 242 litres of water per hour, or some 4,000 times its- 

 own volume. And in so doing we assume that every plankton 

 organism is removed from this volume of water by the choan- 

 cytes of the flagellated chambers — an exceedingly improbable 

 assumption. 



1 " Chemische Zusammensetzung des Planktons," Wiss. Meeresunt. Kiel 

 Kommission, Bd. iii. Abth. Kiel, 1898. 



