2 COLLECTION OF WATER INSECTS 



compass and put away in the fishing-bag until 

 wanted. The net will be found of great use for 

 the collection of spinners of the EPHEMERID^: 

 and many of the caddis-flies. 



When collecting duns, I seek an eddy, or a 

 spot where the set of the stream carries the 

 flies in under the bank, and then lift them 

 off the water on the rim of my landing-net. 



Two tubes may be carried in the waistcoat 

 pocket, each 2 inches in length by J inch in 

 diameter, the one containing collecting fluid, 

 and the other a few lumps of cyanide of potas- 

 sium embedded at the bottom of the tube in 

 plaster of Paris. In another pocket may be 

 placed a pair of magnifying glasses, one giving 

 a magnification of about ten, and the other of 

 about twenty diameters. This comprises the 

 entire field outfit. 



The collecting fluid is made up of one part of 

 alcohol to two parts of 2 per cent, formalin 

 solution (described below), a few crystals of 

 menthol being dissolved in the mixture, which 

 should then be filtered. 



On returning to my headquarters, I transfer 

 the insects in the collecting fluid to tubes or 

 glass-stoppered bottles containing a 2 per cent, 

 solution of formalin, made by taking one part 

 of commercial formalin, which is a 40 per cent, 

 solution of formic aldehyde, and adding to it 

 nineteen parts of water. If insects are left too 

 long in collecting fluid, the alcohol contained 

 therein is apt to destroy the colour. 



The flies collected in the cyanide tube I set 



