PLANKTON 275 



which they feed, there are marked fluctuations in the number 

 of young produced in different seasons, and that it is only 

 at intervals of years that a really large stock of young is added 

 to the population. 



The prospects of a year's fishery may therefore depend, 

 primarily, upon the rate of spawning of the fish, affected no 

 doubt by hydrographic and other environmental conditions ; 

 secondarily, upon the presence of a sufficient supply of phyto- 

 plankton in the surface layers of the sea at the time when 

 the fish larvse are hatched, and that in its turn depends upon 

 photosynthesis and physico-chemical changes in the water ; 

 and, finally, upon the reproduction of the stock of molluscs or 

 worms at the bottom, which were all transitory members of 

 the plankton in their embryonic and larval stages, and which 

 constitute the fish food at later stages of growth and develop- 

 ment. 



The question has been raised of recent years — Is there 

 enough plankton in the sea to provide sufficient nourishment 

 for the larger animals, and especially for those fixed forms, 

 such as Sponges, that are supposed to feed by drawing currents 

 of plankton-laden water through the body ? In a series of 

 papers from 1907 onwards Piitter and his followers put 

 forward the views (1) that the carbon requirements of such 

 animals could not be met by the amount of plankton in the 

 volume of water that could be passed through the body in a 

 given time, and (2) that sea-water contained a large amount 

 of dissolved organic carbon compounds which constitute the 

 chief, if not the only, food of a large number of marine animals. 

 These views have given rise to much controversy, and have 

 been useful in stimulating further research, but I believe it is 

 now admitted that Piitter' s samples of water from the Bay 

 of Naples and at Kiel were probably polluted, that his figures 

 were erroneous, and that his conclusions must be rejected, 

 or at least greatly modified. His estimates of the plankton 

 were minimum ones, while it seems probable that his figures 

 for the organic carbon present represent a variable amount of 



