178 THE MICROSCOPE. Dec. 



angled tanks of glass which are used for making certain 

 electrical piles. 



I prefer that kind of tank to the cylindrical ones, be- 

 cause they facilitate observation. Many organisms 

 adhering on the inner side develope there more uniformly 

 and light strikes them in a more equal manner. 



To commence these aquariums, after rinsing them well 

 they should be filled three-quarters full with fountain 

 or river water as pure as possible. The gatherings made 

 in a pond or any pool whatever may consist of the 

 washings of floating leaves of potamogeton, of neuphar, 

 of stems of typhlina, of scirpus or of any other aquatic 

 plants of that kind ; or, of a certain quantity of water 

 from the pond or the pool itself. This should be taken 

 in a spot where many organisms have been seen in sus- 

 pension. Even a small portion of these floating masses 

 which are frequently found at the surface of water may 

 be taken. Oftentimes, these contain quite a number of 

 different things. Then, in each vase, should be placed 

 one or two stems of a small aquatic plant, such as Nitella, 

 Elodea canadensis, Callitriche aquatica, Ceratophyllum 

 demersum, Pilularia globulifera, some Lemnia and one 

 or two small-sized mollusks, 6 or 8 millimetres long. 



The orifice of the vases must be covered with a simple 

 pasteboard of the form of a box-cover wide enough to 

 let the air go in without admitting the dust. The aqua- 

 riums thus prepared are then placed in a lighted place but 

 well out of the sun's rays. About every fifteen days, a 

 little water is added in order to offset evaporation. That 

 is very important. The water is added slowly and 

 dropped on the side of the glass, so as not to disturb the 

 water of the aquarium. 



During all the year, even in winter, the presence of 

 living and numerous organisms will be noticed, but it is 

 especially from August to November when the surprises 

 will quickly succeed each other. 



