230 THE CONDITIONS OF LIFE IN THE SEA [PART III 



metabolism of the lower marine animals. Without sufficient 

 reflection we assume that the oxidation process characteristic of 

 the mammal also obtains in all animals living in the sea. We 

 naturally assume that the proteid, carbohydrate and fats of the 

 bodies of animals are ingested, converted into peptones, sugars and 

 dissociated fats, are absorbed and built up into tissue ; and that 

 the constituents of the latter are then oxidised by the oxygen 

 taken up by the gills and excreted as carbon dioxide, water, and 

 nitrogenous waste products like urea or uric acid. 



Do marine animals always obtain their food supply by ingesting 

 the bodies of other animals and plants ? One naturally assumes 

 that this is universally the case and so encounters difficulties, such 

 as I have often experienced in attempting to demonstrate the food 

 of a cockle to a class of sceptical fishermen. Repeatedly one 

 searches among the mud and sand that fill the alimentary canal 

 of this mollusc for traces of planktonic organisms, and it is only 

 the magnifying power of a ^th inch objective, when applied to 

 one or two Naviculae, that makes the demonstration a partial 

 success. It is often with great difficulty that one succeeds in 

 finding food in the alimentary canal of some invertebrates. Dohrn 

 failed to demonstrate the food of Pycnogonids, and Rauschenplatz, 

 in an extensive study of the foods of marine invertebrates of the 

 Bay of Kiel failed, in some cases, to find satisfactory evidence of 

 the food organisms^. We can hardly ever find visible food within 

 the alimentary canal of a mature plaice during the winter months, 

 and yet it is just during these months that the reproductive 

 organs of the fish are maturing for the spawning act in the 

 following spring. Often one may observe that fishes and other 

 animals may live for a long time in aquaria without obvious food. 

 Do they really cease to feed during this time ; and if so why is 

 the plentiful supply of oxygen in the water conveyed to them 

 quite essential ? 



Putter seeks to answer these questions b}^ suggesting that the 

 sea is an immense reservoir of food-stuffs in the form of dissolved 

 organic carbon and nitrogen compounds. We have already seen 

 that there is evidence that these substances exist in the sea — 

 at least in the water of the Bay of Naples. He suggests that 

 ^ See also Shipley, "Gephyrea," Cambridge Nat. Hist., vol. 2. 



