Biological Survey — Erie-Niagara Watershed 



61 



joarticular station or depth, a 50-liter sample of water was pumped 

 into a galvanized iron can made for this purpose. From the pet- 

 cock at the bottom of the can, the water sample was allowed to run 

 through No. 20 silk strainer with bucket. The organisms retained 

 in the bucket were then washed into a 4: oz. bottle and enough 

 formaldehjTle added to preserve. 



Pump arrangement for net plankton 



To obtain a sample of the organisms that were so small as to go 

 tlirough the meshes of the No. 20 silk strainer a one-liter sample 

 of water Avas collected immediateh' after the 50-liter sample had 

 been taken. To this 1-liter sample w^as then added sufficient 

 formaldehyde to preserve until it could be centrifuged in the 

 laboratory. 



In addition to the above quantitative collections, at each station 

 qualitative collections were made by towing a No. 20 silk bolting 

 cloth net, one foot in diameter, for 5 minutes at the surface and one 

 also at the bottom. The depth at which the bottom net was strain- 

 ing was determined from the angle and length of line out. These 

 townet collections were preserved with formaldehyde and used in 

 the laboratory for identification and as a supplement to the quan- 

 titative catches. 



Laboratory Method. — The organisms strained from the 50-liter 

 water samples were brought into the laboratory in the 4 oz. bottles. 

 The excess water was siphoned off with a bent glass tube over the 



