176 VHivcrsifij of California Publications in Zoology [Vol. 16 



the water. Putter (1909, p. 4ff.) gives figures which, he states, indi- 

 cate the amount of food needed by variovis forms, and he shows (1909, 

 pp. 105-107) that there is a much larger quantity of soluble organic 

 compounds in a volume of water than there is of solid food as found 

 in the plankton organisms. He shows, furthermore (1909, p. 49), that 

 to satisfy the food requirements by the ingestion of plankton or- 

 ganisms, it would be necessary for an animal to filter an unbelievably 

 large volume of water if the volume of the animal itself is considered. 

 It follows, therefore, that the substances in solution, though but 

 slightly concentrated, form an additional source of food, and Putter 

 (1909, pp. 44—53) gives instances to show that such substances really 

 are used. His general conclusion is as follows (1909, p. 147) : 



Die Erniihrung eines grossen Teiles der Formen aller Stamme vollzieht sicU 

 nicht in tier Weise, wie man bisher, in grober Analogie mit den Saugetieren und 

 Vogeln annahm; il. h. dass geformte Nahrung aufgenommen, durch die Ver- 

 dauung gelost und gespalten und in diesem Zustande resorbiert wird, sondern 

 eine grosse Anzahl von Tieren, speziell die absolut kleinen Formeu aller 

 Stamme, nehmen, so weit sie im Wasser leben, ihre Nahrung direkt in geloster 

 Form aus dem Wasser. 



This view was apparently retained in 1913 (Piitter, 1913). 



While Piitter 's presentation of data is impressive, his contention 

 as to dissolved food substances is not supported by subsequent in- 

 vestigation. The recent studies of Moore, Edie, Whiteley and Dakin 

 (1912, 1913) led them to agree with Piitter so far as to say that 

 uniformly distributed plankton is not sufficient to maintain nutritive 

 equilibrium. These investigators found (Moore et al.. 1912, pp. 260, 

 281) that the organic material contained in the plankton obtained by 

 passage through a no. 20 net and a Chamberland filter is, on the 

 average, one part in a million. Under such conditions, only forms 

 with slow metabolism (such as sponges or ascidians) can possibly be 

 nourished upon the plankton. Piitter 's results as to the amount of 

 dissolved organic compounds are not confirmed, however, and Moore 

 and his co-workers attribute his high figures to faulty methods of 

 analysis, their results (p. 280) being that the soluble material does 

 not exceed one part in a million. Piitter (1909, p. 145) gives 10 to 

 20 mg. per litre as a rough estimate of the average content of sea 

 water in dissolved organic compounds. 



The answer of Moore and the others (1912, p. 260) to the question. 

 What is the food supply, then? is that it is the plankton but only when 

 it occurs in rich shoals; that is, the swimming plankton feeders must 

 seek the best grounds in order to get enough food to maintain nutri- 

 tive equilibrium. 



