160 Illinois State Laboratory of Natural History. 



chiefly upon 80% alcohol and water. Exporiments with 

 formaline indicate that it will satisfactorily preserve- 

 small and easilj'' penetrated forms. 



Breeding. — For merely rearing insects, the best cage 

 proved to be a wide-mouthed glass vessel varying in 

 size according to the insects to be reared. The mouth 

 may be covered when desirable by a piece of "Swiss"^ 

 or cheese cloth held in place by a rubber band. For 

 most work, cylindrical battery jars five or six inches in 

 diameter and about seven inches deep were very useful. 

 In these, by attending to a few simple rules, one can 

 rear successfully almost any kind of aquatic insects, e.i.- 

 cept such as require running water. Direct sunlight 

 must not fall on the vessels, as it often overheats the- 

 water; and hard water should not be used. We repro- 

 duce so far as possible the natural surroundings where 

 the insect occurred, using ma.terial from the place where 

 it was found. The water need not be changed if no film 

 appears upon its surface and healthy animal and plant 

 life are present; but if a film develops and a foul odor 

 becomes noticeable, actively decaying organic matter i» 

 evidently present. This should be immediately removed, 

 the water being frequently changed for a time. A very 

 little water is often better than a large quantity, and too 

 much vegetation may be a disadvantage. A foothold 

 above water for emerging imagos is desirable. Those 

 forms which leave the water for pupation, such as the lar- 

 vae of beetles, horse-flies and some Neuroptera, (Sialidae), 

 are transferred when full grown to clean damp sand, cov- 

 ered with light, fresh rubbish for shelter and moisture. 

 Beetle larvae will often pu[)ate under chips in such a 

 place; and pupae in pnparia may be placed on damp 

 sand. Pupae will often be killed by suffocation if collect- 

 ed in a bottle of water. Some isolated individuals should 

 be reared to verify results. 



For keeping insects under continual observation and 

 in natural conditions a square box, eight inches each- 

 way, was used, two sides and the bottom of wood, the 



