5'40 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



might be estimated. Hensen lias suggested a method for 

 converting star fish into manure. 



While the present paper was in tne press, there 

 appeared the preliminary announcement of a work on 

 Plankton Methods, by Yolk, 1 who has investigated the 

 Plankton of the Elbe and its tributaries and the harbour 

 at Hamburg. He found that he obtained no exact results 

 by the Hensen-Apstein method, though no reason is given 

 for the supposed inexactitude. He therefore suggests a 

 new method, which consists in the employment of a rotary 

 pump, with a contrivance for pumping up water from 

 different layers. To the pump is attached an apparatus 

 by means of which the volume of water can be measured, 

 and the depth to which the lower opening of the pump is 

 sunk can also be ascertained. The water is first of all filtered 

 through an Apstein net, the meshes of which are however 

 not small enough to capture the smaller organisms. The 

 water is therefore subsequently mixed with formalin, and 

 carefully filtered. For the purpose of filtration either 

 porcelain, burnt clay, silica or charcoal may be used. 

 The organisms were, for the purpose of quantitative 

 estimation, shaken up in a viscous fluid consisting largely 

 of formalin, and a given portion of the fluid was weighed 

 out on to a glass plate and the organisms counted. Volk 

 says that he has such solutions which after 10 months' 

 standing have no deposit. 



1 Zur Plankton-Methodik (Vorlaufige Mittheilung). Zool. 

 Anz. 1901. p. 278. 



