280 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



is due to Hensen (1),* differ from and mark an advance 

 on the methods hitherto employed in England, inasmuch 

 as no attempt is made in the latter country to arrive at a 

 quantitative as distinguished from a qualitative result. 



The questions that Hensen attempts to answer are, 1, 

 What does the sea contain at a given time in the shape 

 of living organisms in the plankton ? and, 2, How does 

 this material vary from season to season and from year 

 to year? 



It may be pointed out that the results obtained by the 

 German investigators are largely due to the liberal atti- 

 tude taken by their Government with regard to subsi- 

 dising scientific investigation of problems connected with 

 the Sea-Fisheries. It is to be hoped that the Irish Sea 

 may be subsequently investigated in like manner. A 

 comparison with the results already obtained for the North 

 and Baltic Seas could not fail to be of interest and to 

 yield important results. 



In the preparation of this paper, which is, of course, 

 largely a compilation from the literature already published 

 in German (a list of the more important works is appended), 

 I have received much assistance from Professor Brandt, 

 to whom my best thanks are due both for the assistance 

 given me and for permission to photograph the apparatus 

 at present in use in the Zoological Institute at Kiel. In 

 addition, I have to thank Professor Vanhofren and Dr. 

 Apstein for their unfailing readiness to assist me in 

 matters of difficulty. 



Of the figures, numbers 2, 3 and G are taken, by per- 

 mission, from Dr. Apstein's " Siisswasser Plankton " (5). 

 Figs. 8 and 9 are from Prof. Brandt's work on " Die 

 Fauna der Ostsee " (7). Fig. 10 is from Prof. Heusen's 



* The numbers in parentheses refer to the list of papers at the end (p. 341). 



