CH. Vl] QUANTITATIVE PLANKTON INVESTIGATIONS 135 



to beadapted for quantitative treatment. The general results of the 

 Plankton-Expedition were severely criticised and, without adducing 

 any other evidence than the general impressions of a naturalist 

 who had fished with the older qualitative nets, he denied one of 

 the chief conclusions of the work of the National Expedition, viz. 

 that the plankton was more abundant in the colder, or temperate 

 seas than in the warmer regions. He also laid great stress on the 

 variability of the plankton, and emphasising the importance of 

 swarms or streams of microscopic life in the sea (Zoorema, or 

 animal streams, he called these), he contended that this apparently 

 fortuitous distribution of the plankton militated against any 

 attempts to estimate its abundance in a precise manner. In some 

 respects Haeckel completely misunderstood Hensen's methods. 



Then Kofoid^ struck the next note of dissent. In a series of 

 experiments carried out in the lakes of Illinois by means of a 

 Hensen quantitative net he obtained results which led him to the 

 conclusion that the catches made with this apparatus gave a very 

 distorted picture of the actual conditions. Kofoid's first objection 

 was that the meshes of the Mullergaze became stopped up with 

 the smaller organisms in the water and that this closure of the pores 

 caused the net to fish in an uncontrollable manner. His second 

 objection was that many of the smaller organisms actually passed 

 through the meshes and that the catch was therefore smaller than 

 it ought to be. In order to remedy these defects of the Hensen 

 method Kofoid proposed to substitute a pump and filter for the 

 net of Mullergaze. 



In 1899 Lohmann- undertook a critical investigation of the 

 method of quantitative fishing by means of nets made of Mullergaze 

 No. 20. Dealing with Kofoid's first objection he had no difficulty 

 in shewing that the latter had misunderstood the nature of the 

 method which he had criticised, and that his objection had no 

 validity. Hensen and Apstein had shewn previously that the 

 net had to be designed for the nature of the plankton which it 

 was desired to catch. Generally speaking fresh water contains a 

 greater mass of plankton in the same volume than does the water 

 of the sea. To guard against the possible danger of a partial 



1 Kofoid, Science (N.S.), Vol. vi. p. 829. 



2 Wiss. Untersuch. Kiel Komm. Bd. v. Abteil. Kiel, Heft ii. Kiel, 1901, 



