NUTRITION 89 



over recalls Keeble's researches on the supposed symbiosis 

 between the turbellarian Convoluta and the Chlamydomonad 

 which infests its subintegumentary tissues and is ultimately 

 destined to be absorbed by intracellular ingestion in the body 

 of its host after degeneration of the alimentary tract in the 

 latter. Reference may be made here to an hypothesis put 

 forward some years ago by Putter (1907) who maintained that 

 many aquatic organisms absorb dissolved organic matter from 

 the water as a source of food. This view is provocative, 

 because as Dakin rightly points out, though structures resem- 

 bling the alimentary tract of land animals exist throughout the 

 animal phyla, it is largely on the basis of analogy that these 

 have been regarded as the only avenue through which food 

 passes into the organism. Putter's hypothesis was based on 

 three lines of reasoning : (i) that there exists in sea- water 

 a comparatively large available quantity of dissolved organic 

 matter ; (ii) that the quantity of solid food present in sea- 

 water is insufficient to account for the rate of respiration of 

 marine organisms ; (iii) that certain animals — e.g. goldfish — 

 do not lose weight if amino-acids, glycerine, etc., are dissolved 

 in the water, but do so if kept without food in water containing 

 no dissolved organic matter. As regards the first, later in- 

 vestigation has not as yet fully confirmed Putter's analyses, 

 but recent observations of Harvey (1925) and of Atkins (1925) 

 point to the conclusion that appreciable quantities of dissolved 

 organic matter exist in sea- water. The data on which the 

 second conclusion is based are questionable. Experiments 

 of Putter on absorption of nitrogenous solutes by goldfish 

 and axolotls have recently been repeated by Dakin and 

 Dakin (1925) with negative results. There seems, therefore, 

 insufficient reason for abandoning the view accepted by most 

 students of the plankton, that marine organisms prey on one 

 another, the smaller organisms providing food for larger ones, 

 as in the following series (Johnstone's " Life in the Sea ") : 

 Peridinians — Copepoda — Sprats — ^Whiting — Cod — Man. 



Feeding Mechanisms. — Appropriate devices (jaws, beaks, 

 etc.) for the trituration of food in animals which actively 

 select their diet are described in text-books of zoology. A 



