16 SCIENCE PROGRESS 



compounds are present in considerable proportion in the Bay 

 of Naples within rather close proximity to the land. 1 We know 

 that a considerable quantity of carbon dioxide is present in 

 solution, but there are also other carbon compounds. One 

 litre of water in Naples Bay contained : 



Carbon dioxide 99 mg. 



Volatile organic acids 36 ,, 



Carbohydrates, higher organic acids, etc. . 70 ,, 



Here there is a considerable food supply, and a review of 

 the evidence afforded by Putter's experiments appears to justify 

 us in regarding these carbon compounds as food-stuffs for 

 such animals as Suberites and Cucumaria. We have seen that 

 the sponge must pass about 242 litres of water per hour through 

 its canal system in order to obtain sufficient food, and that it 

 is impossible that it can circulate this volume of water. But 

 it can pass about \ litre of water per hour through its osculum, 

 and taking the above figures as representing the average com- 

 position of the sea-water, so far as concerns soluble carbon 

 compounds, it is evident that this latter volume is enough if 

 we suppose that these substances can be utilised as food-stuffs. 

 For \ litre contains about 50 mg. of carbon in the form of 

 soluble compounds other than carbon dioxide, and only 

 0'92 mg. of carbon is required for the hourly metabolism of 

 the sponge. So even if we assume that not all these carbon 

 compounds present in solution in the sea are suitable food- 

 stuffs, and if we assume that the coefficient of absorption is 

 not a very high one, it may still be the case that the sponge 

 finds sufficient nutriment in the dissolved food-stuffs. 



These soluble carbon compounds probably originate as 

 products of the katabolism of the protophyta and bacteria of 

 the plankton. These are the smallest organisms found in the 

 sea, and their mass is to be regarded as small compared with 

 that of the larger planktonic organisms, such as the larger 

 protozoa, micro-crustacea, or the ccelenterates and worms. 

 But the conclusion is not so strange as it at first appears to be 

 when we reflect that the protophyta and bacteria are much more 

 numerous than all the other groups of animals which make up 

 the marine plankton, and that the intensity of metabolism in their 



1 Stofthaushalt des Meeres, p. 328. 



