D. J. SC0UEF1ELD ON FRESH-WATER BIOLOGICAL STATIONS. 131 



ditions of existence in the lakes, ponds, and streams in which the 

 fishes live are required before a rational method of fish-culture 

 can be devised. With this end in view several observation and 

 experiment stations have been founded. The work done in these 

 is essentially biological, although limited, as far as possible, to 

 the particular problems connected with the rearing of market- 

 able fishes. There are two such stations in Germanv, one of 

 which, the Miiggelsee Station, is to be made into a " Reichsanstalt 

 fur das Fischereiwesen," at a cost of 150,000 marks, and with a 

 grant from the State of 25,000 to 30,000 marks per annum. 



The growing importance of the subject of a pure water supply 

 for great towns can also be considered to have had some influence 

 on the study of fresh-water biology in recent years, although it 

 has only been in a comparatively few instances that adequate 

 provision for biological work in this connection has been made. 

 Nevertheless, the investigations already carried out, especially in 

 the United States — e.g. by Whipple in the technical station of the 

 Boston Waterworks — have been of a very instructive character, 

 and have led to some important improvements in the methods of 

 research. It is very probable that in the near future many other 

 large waterworks will find it advantageous, if not absolutely 

 necessary, to maintain laboratories for attacking the special 

 biological problems with which they are from time to time 

 confronted. 



The last factor that need be referred to in relation to the 

 progress of fresh-water biology and of the demand for fresh- 

 water stations is the introduction of the quantitative method of 

 investigating the plankton — i.e. the w-hole assemblage of minute 

 organisms living permanently in the open waters of the sea and 

 lakes. Prof. Hensen, of Kiel, first showed how, by means of a 

 special net drawn vertically from a known depth at a definite 

 speed, comparable samples of the plankton could be collected and 

 treated statistically. Apstein, in 1891, applied the method to the 

 study of lakes, and brought to light a whole series of new facts in 

 connection w T ith the fresh-water plankton organisms. Although 

 his investigations were not made with the advantages afforded 

 by a biological station, he fully acknowledged how much easier 

 and how much more satisfactory it would be to do such work at 

 a special station situated by the side of a lake. And it is, more- 

 over, perfectly evident that to get full, regular, and continuous 



