FOOD-MATTERS IN THE SEA 319 



years I have myself examined in the living condition about 

 10,000 samples of freshly caught plankton, and I have no 

 doubt whatever, from what I have seen, that the Copepoda 

 and other larger and more active animals are habitually 

 feeding upon the smaller forms. 



Putting aside the detritus or demerson, and other plant 

 and animal food on the sea-bottom, and considering only 

 what is free in the water, as yet we have discovered no other 

 more abundant source of food for larger marine animals 

 than the organisms of the plankton, and if this is really 

 insufficient, as Piitter and others have tried to prove, then 

 we have here one of the most important problems of marine 

 biology still unsolved, and one which requires further 

 research, both observational and experimental, upon the 

 feeding habits of many common animals — work which can 

 only be carried on at sea or in the laboratories of marine 

 biological stations. 



The problem is, in part, a bio-chemical one ; and that 

 brings us to Piitter' s further assertion that, as he was able 

 to keep large invertebrates and even fish in water containing 

 no obvious or particulate food during long periods when they 

 were daily absorbing oxygen and losing carbon, they must 

 have been living on dissolved carbon in the water. This 

 has been answered by Moore and his fellow-workers at 

 Port Erin, who have conducted a long series of experiments 

 ranging over seven months (235 days) on the nutrition and 

 metaboHsm of various marine animals, during which they 

 kept such large animals as lobsters, octopus and fish. Each 

 experiment ran for a long period, during which the animals 

 were not fed, but their consumption of oxygen and output 

 of carbon-dioxide was determined daily. At the end the 

 animals showed no serious result and no loss in weight. 

 They were apparently healthy and lively. The explanation 

 was found to be that the loss of organic matter from the 

 tissues is made good or replaced by an equivalent amount 

 of sea-water taken in. The proteins of the animals' tissues 



