FRESH-WATER RHIZOPODS. 109 



more, the operations, although still very simple, require a special 

 apparatus. The following is my method when far out in a small 

 boat on the Lake of Geneva. 



At the end of a long fishing-line I attach a long, rectangular 

 tin receptacle 14 cm. (5| in.) long and 6 to 7 cm. (2| to 2| in.) 

 wide, fastened to the line by a metal loop (not by hempen cords, 

 which easily twist round one another). In front and about a 

 metre from the receptacle is a weight, a lump of lead weighing 

 about 500 grm. (1 lb.). 



I allow the whole to drop to the bottom, then I begin to row 

 very slowly — at the rate of hardly half a metre per second (about 

 one mile an hour) — so that the lump of lead drags on the 

 bottom, and does not leave it. 



After a minute I slowly withdraw my apparatus, and I 

 generally find it more or less full of mud, mixed with large 

 strips of brown organic felt, which have been torn from the 

 upper surface of the mud, and almost alone contain the 

 rhizopods. 



On returning home I turn the whole into a large jar, and 

 allow it to stand ; the water clears very slowly, and after two 

 or three days there is formed on the surface of the mud a fine 

 felted coating of a lovely golden brown, formed for the most 

 part of beautiful deep-water diatoms, but in which rhizopods 

 are also fairly plentiful.* 



This system of collecting, as one can see, is again pretty 

 simple : even too simple perhaps some will say, for in being 

 raised from the bottom to the surface of the lake the receptacle 

 may lose a good part of its contents. But in reality it loses 

 little, and the material which remains at the bottom of the 

 receptacle is often more abundant than is desirable, for too large 

 a gathering is sometimes troublesome.t 



* In order to obtain large species like Difflugia lebes, D. pyri/ormis, etc., 

 one may employ this equally useful method. Put the collection into a fairly 

 tall cylindrical jar and decant several times, first every minute and then 

 more rapidly. After about thirty decantations all the fine mud has gone, 

 and there remains an extremely rich residue, in which may be found a good 

 number of large rhizopods, crustaceans, small worms, etc. 



f For very special gatherings, where it is intended to make a clear 

 distinction between the organisms of the bottom and those which are 

 pelagic, the system of a constantly open receptacle is certainly defective 

 (less, however, than one would think, for in rising to the surface a 

 receptacle with a water-tight bottom drives back the water before it, 



