318 FOUNDERS OF OCEANOGRAPHY 



cient to provide food for the larger animals if these merely 

 filter the water as it comes. In fact, according to the 

 latest investigations, the organic matter in solution and the 

 generally distributed plankton taken together do not seem 

 sufficient for the nutrition of actively swimming marine 

 animals, although they may suffice for the fixed or sedentary 

 forms, such as sponges, ascidians and lameUibranch molluscs. 

 Moore estimates that the sedentary sponge requires to 

 filter only fifteen times its own volume per hour, while the 

 active Crustacean requires 250 times. The active animals, 

 however, such as Crustacea and fishes, probably hunt their 

 food and follow up shoals of plankton or frequent those 

 zones in which the plankton is especially abundant, and so 

 are able to obtain a great deal more than the average amount 

 which is distributed through the water in general at the time. 

 This result accords well with our many observations at 

 Port Erin on the irregularity in the distribution of the plank- 

 ton, and the corresponding variations in the occurrence of 

 the migratory fishes which may be regarded as following 

 and feeding upon the swarms of planktonic organisms. 



We have, moreover, direct evidence that the larger and 

 more active members of the plankton, such as Copepoda, 

 do feed upon the minute algae of the plankton. W. J. 

 Dakin's original observations made at Kiel have been 

 corroborated and extended by Esterly in California, who has 

 shown conclusively that in a number of different species of 

 Copepoda he examined, particles such as Diatoms and other 

 minute members of the plankton are ingested and can be 

 traced through the intestine. Some individual Copepoda 

 may be found with the alimentary canal empty, or containing 

 only a greenish amorphous mass, but that may weU be 

 because soft-bodied organisms have been eaten and have 

 been or are being rapidly digested. Further observations 

 must, however, be made into the food and the feeding habits 

 of all plankton feeders in the living condition, and when 

 actually feeding. I may add that during the last twenty 



