1916] Estcrlfj: Feeding Hahifs of Pflagir Coprpods 181 



He has estimated that a ''Calanus spec." will require 15,800 Coscino- 

 discus of medium size daily, or 9,750,000 Thalassiosira nana, to cover 

 its food needs. If these figures are even approximately correct, it 

 must be evident that the needs of a Calamis in the San Diego region 

 are either far from satisfied or else there is some other source of food 

 than that which appears in the intestinal contents. Dakin (1908, p. 

 777) counted 200 diatoms as a maximum number, while many animals 

 did not have anything in the alimentary canal, and in a review of 

 Putter's work (Dakin, 1910, p. 214) he states that if the figures given 

 by Piitter for the food requirements of copepods are correct, he does 

 not see how they get enough food in diatoms or flagellates. He will 

 be ready to accept, then, Piitter 's theory that dissolved substances 

 form an additional source of food. 



If the unicellular plants and animals comprising the centrifuge 

 plankton are taken in large enough numbers, the problem is solved 

 so far as the eopepod is concerned, and such organisms will not leave 

 definite traces. But if the green matter noted so often is derived 

 from such food organisms, they are not taken in large numbers in 

 these waters, if one may judge from the amount of that material that 

 shows in the tracts of animals preserved in formalin. 



Although the part taken by the centrifuge plankton in the nutri- 

 tion of the marine copepods is not known, it is probable that those 

 unicellular forms are most important, and that the ingested numbers 

 could be ascertained from a study of living eopepod material. Loh- 

 mann (1909, p. 24) states that the forms of the nannoplankton like 

 chrysomonads or Rhodomonas can be recognised in living Tintinnidae 

 or naked ciliates, while in preserved material only the skeletons of 

 silico-flagellates and diatoms or the remnants of Peridinmm can be 

 seen. The same may be true of the intestinal contents of the cope- 

 pods. As things are, it is largely a matter of opinion what forms 

 other than those with skeletons are present. 



In the case of some of the fresh-water Cladocera, however, Wolte- 

 reck (1908) showed that the centrifuge plankton has an important 

 role. He found that these crustaceans are better nourished in the 

 upper lake at Lunz than in the lower lake, though the net-plankton 

 is mlich greater in the latter. The upper lake, however, contains a 

 richer centrifuge plankton, and these are the organisms that are re- 

 garded as of first importance in the nutrition of the Cladocera. 



The answer to the important questions raised by Piitter 's investi- 

 gations will be most readily obtained, probably, by ascertaining what 



