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THE AMERICAN NATURALIST [Vol. LVI 



A result of extraordinary interest in connection with 

 the food-chain has recently been brought to light by two 

 sets of investigators working independently. In seeking 

 to explain certain features which he had found in connec- 

 tion with the growth of the cod, Hjort^^ undertook a 

 study of the distribution in marine organisms of the 

 growth stimulant known as vitamin. Fat-soluble vitamin 

 was already known to be present in large quantities in 

 cod-liver oil, and is what probably gives the oil its medic- 

 inal value. Hjort was able to trace the vitamin, by 

 means of feeding experiments on rats, in the ripe ovaries 

 of the cod, in shrimps and prawns, which resemble the 

 animals on which the cod feeds, and in diatom plankton 

 and green algse. Jameson, Drummond and Coward^* 

 cultivated the diatom NitzscMa closterium, and by a simi- 

 lar method to that used by Hjort showed that it was 

 extraordinarily potent as a source of fat-soluble vitamin. 

 We thus conclude that this substance, so essential to 

 healthy animal growth, is produced in large quantities 

 by plankton diatoms, and passed on unchanged to the fish 

 through the crustaceans which feed on the diatoms. In 

 the fish the vitamin is first stored in the liver, and with 

 the ripening of the ovary passes into the egg, to be used 

 to stimulate the growth of the next generation. Again 

 we see the fundamental importance of the food-producing 

 activities of the lowest plant life. 



Attention has already been drawn to the suggestion that 

 fishes developed their remarkable swimming powers in 

 rivers, in response to a need to overcome the currents, 

 and that they afterwards returned to the sea, where they 

 preyed upon a well-developed and highly complex inverte- 

 brate fauna already fully established there. Their speed 

 enabled them to conquer their more sluggish predecessors, 

 whilst they themselves were little open to attack. With 

 the exception of the larger cephalopods, which are of 

 comparatively recent origin, and were probably evolved 

 after the arrival of the fishes, there are few, if any, in- 

 vertebrates which capture adult fishes as part of their 



23 Proc. Boy. Soc, May 4, 1922. 

 2* Biochemical Journal, 1922. 



