GERMAN PLANKTON INVESTIGATIONS. 339 



4. Owing to the organisms becoming embedded in the 

 pores of the net and to the drying of slime on it, it 

 becomes ultimately permanently stopped np. 



Practical Applications of the Hensen Method. 



It cannot be denied that the application of this method 

 has yielded valuable and important results, in the shape of 

 additions to our knowledge of the conditions of life in the 

 sea, and more particularly that portion of the life which 

 comes under the heading of plankton. In this way a 

 great step forward has been made. The plankton 

 undoubtedly forms the sole food supply of many of our 

 most important food fishes, for example, the herring, sprat 

 and mackerel. For the solution of the problem of the 

 migration of the herring we must probably seek further 

 in this direction, as it is in all likelihood connected with 

 the variation in their food supply, that is, in the variation 

 of the plankton, or more particularly the variation 

 in the Copepod constituents of the same. In like manner 

 the estimation of the number of floating fish eggs in the 

 sea gives us an idea of the total number of spawning 

 fishes present at that time in the portion of the sea 

 investigated. 



The quantitative method thus started for plankton work 

 might be capable of extension in other directions. It 

 might be possible to estimate how much valuable human 

 food in the shape of fish is annually consumed by por- 

 poises and dogfish around our coast. These destroyers 

 of fish are undoubtedly our most formidable competitors, 

 and should be ruthlessly destroyed. Another animal 

 which might be quantitatively investigated is the starfish. 

 The amount of damage done by this pest in the way of 

 destruction of mussel, oyster and other shell fish beds 



