CH. Vl] QUANTITATIVE PLANKTOX INVESTIGATIONS 137 



Miillergaze, but many invertebrate larvae and eggs were lost. The 

 larger protozoa were retained by the net but the smaller forms 

 were almost entirely lost. Large diatoms were caught by the net, 

 but here again a great number of the smaller ones were passed 

 through to be caught by the filter paper. 



These results seemed to justify further investigation and so, 

 armed with the sinews of war by the University of Kiel, Lohmann 

 made a very searching examination of the various methods of 

 determining the richness of the sea in planktonic life, and his 

 paper ^ describing his results is the most important contribution 

 to the literature of planktology which has appeared since the 

 publication of Hensen's original memoir in 1887. It is one of 

 those papers which stimulate thought by reason of the novelty of 

 the results obtained, and help on new discovery by the development 

 of a new method of research. No one method, we see, is 

 sufficient to give us samples of the planktonic life of the sea. 

 Just as we are compelled to employ half-a-dozen nets if we wish 

 to obtain a true representation of the distribution of any one fish 

 in the sea, so it is necessary to employ several different methods of 

 research if we are to obtain a true picture of the nature and rich- 

 ness of planktonic life in a sea area. If we desire to estimate the 

 abundance of the larger planktonic or pelagic animals in a sea 

 area then it is necessary to fish with wide meshed seine nets and 

 to pass, it may be, hundreds of cubic metres of water through 

 the meshes of this net before the adequate sample of water has 

 been filtered. For fish eggs we must employ an ordinary quanti- 

 tative vertical net with a comparatively wide mesh, and three or 

 four cubic metres of water will afford a sufficient sample. For 

 copepods we may use the net of ordinary mesh and less than one cubic 

 metre will be enough water to filter. Diatoms and protozoa can 

 only be caught when we employ either the very finest silk cloth which 

 can be made, or still better, the much finer filters constructed of 

 paper or densely woven silk cloth ; and for such organisms even 

 i litre of water may be a big enough sample. For bacteria quite 

 special methods of culture must be employed, for no filter is fine 



^ Lohmann, " Neue Untersuchungen u. d. Eeichtumd. Meeres an Plankton und 

 u. d. Brauchbatkeit d. verscbeidenen Fangmethoden," Wi-s. Meeresuntersuch. Kiel 

 Komm. Bd. vii. Abth. Kiel, 1903. 



