1916] Esfcrlij: Feeding Habits of Pelagic Copepods 177 



It must be kept in mind, however, that there are large quantities 

 of plankton consisting of organisms so small that the finest nets do 

 not capture them. This is the so-called nanno- or centrifuge plankton 

 of Lohmaun (1911), and Lohmann believes that organisms like these 

 comprise most of the food of such forms as the microcrustacea and 

 the appendicularians. Unless special methods of collecting are em- 

 plo.yed, this part of the plankton will be neglected in an estimate of 

 the amount of food available. 



This paper is not intended as a review or criticism of Piitter's 

 work, although it must necessarily be mentioned. One way of answer- 

 ing in a measure the questions he raises, as he himself suggests (Piitter 

 1909, p. 51), is by determining, through an examination of the con- 

 tents of the intestine, what organisms and how many of them are 

 eaten by the plankton feeders. 



The important group of the Copepoda has been examined in this 

 way by Dakin (1908), who studied the contents of the gut in several 

 species. He found that diatoms are the most abundant organisms in 

 the tract, especially specimens of Thalassiosira or Coscinodiscus so 

 small that they would pass through a no. 20 net. Peridinium divergens 

 and P. cerasus were next in frequency. Silico-flagellates did not occur 

 in large numbers, the Tintinnidae were rare and Ceratium appeared 

 to be absent (Dakin, 1908, pp. 771-179). Dakin noted that in many 

 cases the tract was full of a green mass, as Hensen (1893, p. 94) had 

 found, and the former states (Dakin, 1908, p. 777) that, in his opinion 

 "it is the micro-organisms, many of which pass through even a no. 

 20 ' Miillergaze ' that play the most important role." 



So far as I am aware, Dakin 's paper is the only one that deals 

 especially with the food of marine copepods. Hensen (1893, p. 94) 

 states that repeated searching revealed only one shell of a Cyclotella, 

 although the tract was always full of a green mass which he regarded 

 as derived from diatoms. 



I have recently examined the intestinal contents of several hun- 

 dred copepods of different species, taken at different seasons and at 

 different depths. All had been preserved in formalin. The animals 

 were divided with a scalpel into right and left parts, the section being 

 a little to one side of the middle line. The entire digestive tract was 

 removed by means of a needle, and mounted by itself in glycerine. 

 Such preparations are very easy to make, and can be examined with 

 the oil-immersion. 



