332 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



to substitute pump and filter for the Heusen vertical net, 

 which he considers useless. 



It may be stated as a general proposition that no 

 scientific method is perfect and incapable of being 

 improved upon. Hensen himself is well aware of the 

 defects of the method. With a view of confirming or 

 rejecting the use of the net for such purposes as fish-egg 

 enumeration and determination of the most important 

 constituents of the plankton, for which it was primarily 

 intended, Lohmann (10) has recently undertaken a number 

 of observations on the Stollergrund (Baltic Sea), the results 

 of which have just been published, and are of considerable 

 interest and importance. 



On the 8th November, 1899, Lohmann obtained 76 litres 

 of water from the Stollergrund, and carefully filtered it, 

 first of all through the silk bolting cloth No. 20, and sub- 

 sequently through filter paper. The results were then 

 tabulated, and the most important are here quoted. For 

 plants, the auxospores of Chcetoceros and small species of 

 Naviculacese entirely escaped through the meshes of the 

 net. Of small forms of Coscino discus, 98*6 per cent, in a 

 like manner escaped. The percentage of forms in the 

 case of the Diatomacese was almost invariably large, in the 

 case of Cocconeis, Nitschia, and Scehtonema costatum being- 

 over 90 per cent. But of the most important Diatom, that 

 is the largest form of Coscinodiscus (208^), all specimens 

 were retained by the silk cloth. Of the Peridineae, 100 per 

 cent, of Dinojdiysis rotundata and 98'7 per cent, of Proro- 

 centrum micans escaped capture. Of Ceratium tripos var. 

 tergestina and var. baltica 96'8 and 99"3 per cent, were 

 respectively retained. 



The whole of the specimens of Peridinium divergens were 

 also retained as were the Oscillaria threads. Of the 

 Tintinneaa, 97 per cent of Tintinnus acuminatum escaped, 





