Some needles fixed in handles will also be necessary. These may be bought, or made by fixing ordinary needles of requisite sizes into the handles sold for small brushes. The needles must be kept free from rust, and should always be carefully wiped after use. A good plan to keep them clean is to stick them in a gallipot in which has been melted a mixture of lard and paraffin in equal proportions. Small dissecting-knives are useful, but all the work described here may be done with an ordinary pocket-knife in good trim. [Illustration: FIG. 12.--Three forms of Dipping-tube. Method of using it.] The best preservative for our purpose is formalin, which is sold in a forty per cent. solution. This should be treated as absolute, and a five per cent. solution made. This will really be a two per cent. solution, and is sufficiently strong for general use. The most profitable use we can make of specimens is to watch their habits while living, and to break them up and learn as much as we can about their structure when they are dead. For us to make a collection of specimens in tubes would be a waste of material. [Illustration: FIG. 13.--Mounted Needles.] Little need be said about collecting. The objects treated of are so plentiful that no great skill, nor any wealth of appliances, is needed to secure an ample supply. The following remarks on the methods employed at the Illinois State Laboratory for the capture of aquatic insects and larvae are, however, worth quoting:-- ‘Insects in vegetation, and on or in the bottom, were taken by means of a dip-net--a net of about equal depth and width attached to a strong semicircular ring, firmly fixed to a long handle, the straight side of the ring being opposite the point of attachment. For the larger and more active forms, a coarser net was used, and for smaller forms one made of finer net proved most durable and satisfactory. To collect from the mud of the bottom, the water immediately over it was violently stirred and then swept with the net. The surface layer of mud was also scooped up in the fine dip-net, and then allowed to wash through, leaving the coarser contents in the net. Insects on the bottom in deep water were secured by using a dredge, and washing its contents through net sieves. The aquatic vegetation, when free from mud, was violently washed in a large pan, many smaller forms being thus dislodged and coming to the surface. Insects occurring in open water were taken in drawing an ordinary towing-net[6].’ Here we have, so to speak, the general principles of collecting. It will be easy to adapt them to particular cases.