RECENT WORK ON MARINE METABOLISM 5 



animals are almost entirely sedentary in their habits, and one 

 fails to see the necessity for such an intensity of oxidation as 

 would be indicated if we supposed that the function of the gills 

 is that of the absorption of oxygen from the sea-water. Then 

 when we examine the alimentary canal in order to determine 

 what are the characteristic food organisms we often have diffi- 

 culty in finding that such are really present. The intestine of 

 a cockle, or a lugworm, is filled with sand and mud, but among 

 this one finds very few food organisms ; certainly the latter are 

 not present in such number as would justify us in assuming 

 that they formed the entire food supply of the animal. Yet one 

 is impressed with the enormous food contents of the stomachs 

 of many carnivorous marine animals, the cod and herring, for 

 instance; and in these animals the gill surface is not so great 

 relatively to the general surface of the body as in the sedentary 

 mollusc, where the food contents of the intestine are not at all 

 obvious. So also in other cases. Indeed we know very little 

 about the food, or the feeding habits, of many marine animals, 

 and what knowledge we do possess relates principally to the 

 fishes and other animals of economic importance, for in such 

 cases bionomical investigations have a certain practical value. 

 Most zoologists who have written comprehensive memoirs on 

 marine animals say, as a rule, very little about the food of their 

 types ; and their attitude towards the latter is often that of the 

 Cambridge man to whom an animal was only an animal when 

 it was dead and preserved ! So, just because the living organism 

 is not always studied, suggestions as to the purpose of organs 

 must often have been neglected, and functions have usually 

 been interpreted from the results of morphological comparisons. 

 There can be no better example than that of the eyes of Pecten. 

 The structure of these organs suggests irresistibly that their 

 function is a visual one, and no doubt this is the view that is 

 taught in lecture-rooms and laboratories. Yet one is inclined 

 to doubt this when he reflects on the possible reasons for the 

 possession of such a battery of highly complex eyes in an animal 

 which is not predatory; which (in its adult phase at least) is not 

 greatly preyed upon by other animals ; and obtains its food in 

 a perfectly automatic manner, just as does the mussel, where 

 the eyes are practically non-existent. So Patten suggested 

 that the eyes were really organs for the utilisation of solar 

 energy; and though this source of energy is utilised by more 



