20 Tattersall & Coward, Fauna of Rostheme Mere, 



bacteria act. We believe, therefore, that the excess of 

 organic matter in solution in the water of Rostherne Mere 

 is derived from two sources, the peaty water from the small 

 northerly basin, and the abundance of decaying animal 

 matter with which the bottom of the mere must be 

 covered. 



We have entered at some length on the discussion of 

 the chemical composition of the water, because it seems 

 possible that later on we shall find that it has an important 

 bearing on the nature of the plankton of the lake. We 

 do not propose to discuss that question at present. 



Methods of Investigation. 



Our methods of investigation of the fauna have been 

 as follows. One of us (T. A. C.) has had the mere under 

 frequent observation for upwards of thirty years, and 

 within the last ten years his visits have been more or less 

 regular, with the object of observing the vertebrate fauna. 



For eighteen months, from May, 1912, to November, 

 191 3, approximately fortnightly visits were made to the 

 mere for the especial purpose of collecting the plankton. 

 At the same time a little dredging and shore collecting 

 were done and these are still being carried on. In making 

 our collections of the plankton, we used three nets, two for 

 surface hauls and a Nansen net, kindly lent by the Lanca- 

 shire and Western Sea Fisheries Committee, for vertical 

 hauls. The latter were made in the deep water of the 

 mere, at depths varying from 85 to 95 feet, with the object 

 of making a quantitative examination of the plankton by 

 the counting methods. The two nets used for surface 

 hauls were a coarse one made of muslin, and a fine one 

 made of Muller's gauze, No. 20. They were towed at the 

 surface of the water in the centre of the mere, the fine net 

 for five minutes and the coarse one for ten minutes. 



