180 University of California Publications in Zoology [Vol. 16 



Gaidius pungens. — Sixteen were examined, and only two of them 

 were entirely empty. Eight showed the green color. The organic 

 remains consisted of broken Coscinodiscus, Dictyocha and a radio- 

 larian ; in addition nine of the animals contained broken bristles, bnt 

 I could not determine their source. On the whole, judging from these 

 specimens, this copepod may be said to get an abundance of food. 



Vndeuchaeta hispinosa. — Six of the twelve specimens had nothing 

 in the tract; four of the others showed a bit of green material, one 

 contained several copepod feet, and the remaining one had a Chaeto- 

 ceras bristle and a large amount of stuff with the appearance of 

 mineral debris. 



Since the copepods form an important group because of their 

 numbers in the plankton and because they are used as food by higher 

 organisms (Peck, 1896, p. 353), the food of the copepods is of more 

 than incidental interest. It seems plain enough that the copepods 

 feed principally upon the small forms of the plankton, such as the 

 diatoms, so far as one can judge from an examination of the intestinal 

 contents. But, as has been pointed out by Lohmann (1909), and 

 Biedermann (1911, pp. 650, 651), this method involves a certain 

 amount of error, which may be considerable. Only the indigestible 

 portions of the food can be recognised, and it is certain that forms 

 are ingested which do not have shells or skeletons. To determine ac- 

 curately what is eaten and how much, it is necessary to be able to 

 observe the animals alive and while feeding (Lohmann, 1909, p. 26). 

 This would permit one to determine how much food material passes 

 through the gut in a given time, which, as Biedermann has pointed 

 out (1911, p. 650), it is more important to ascertain than to estimate 

 from the intestinal remains how much was eaten. 



It is interesting to note, however, that many of the intestinal canals 

 examined were devoid of contents. We may reasonably assume, under 

 such conditions, that food either has not recently been ingested or 

 that it consists of exceedingly delicate forms that are soon broken up 

 without leaving traces. The amount of material in the intestine ought 

 to furnish some clue as to the amount of food eaten. The specimens 

 of Gaidius and of Scolecithrix persecans which I saw appeared to 

 have had an abundance, but only one Calanus could be said to be in 

 that condition and it had over sixty cells of Prorocentrum. Eucalanus 

 never has solid contents in the tracts so far as my observation goes. 



With these matters before us, it is interesting to consider the 

 figures given by Piitter (1909, p. 63) as to the needs of a Calanus. 



