GERMAN PLANKTON INVESTIGATIONS. 317 



In order to determine whether or not the Copepoda lived 

 on Peridinese and Diatoms, Hensen made three experi- 

 ments. The catch from a single net was divided into two 

 parts. One part was immediately killed and preserved. 

 The organisms in the other part were allowed to live for 

 from 7 to 9 hours, and then killed and preserved. In 

 each case the number of Diatoms and Peridinese were in 

 excess in the part that had been fixed and preserved imme- 

 diately after capture. From this it is concluded that the 

 Copepoda in the part allowed to stand for from 7 to 9 

 hours had devoured a certain number of Diatoms and 

 Peridinese. The number of consumed Peridinese was in 

 all cases in excess of the number of Diatoms consumed. 

 From this it may be deduced with a fair amount of 

 certainty that the Copepoda devour the Peridinese. Pro- 

 bably the hard shells of the latter are not devoured, but 

 are broken up by the complicated masticatory apparatus 

 posessed by the Copepoda, and the edible contents 

 extracted by means of the hair-like bristles. 



Hensen endeavoured from the above experiments to 

 determine the average number of Peridinese annually 

 devoured by a Copepod, and he concluded the number was 

 4,730. On the calculation that each square metre of 

 surface water in the Baltic covers one million Copepoda, 

 we see that 4,730 million Peridinese are annually used up 

 by these as food. A million Peridinese yield 0*031245 

 grams of dry organic substance, so that the Copepoda of 

 the Baltic use, per square metre of surface water, dry 

 organic matter in the form of Peridinese to the annual 

 amount of 133'35 grammes. 



The number and mass of Diatomacese probably exceeds 

 all the other constituents of the plankton taken together. 

 On account of their extraordinary minuteness, the capture 

 and enumeration of these organisms is attended with no 



