Entomology of tJie Illinois River. 159 



^ series of 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. 



A whole world of minute insect life largely passes 

 through these nets, which would clog up badly were 

 they made of finer material, and a set of wire sieves was 

 therefore used, the lowest one of very fine brass wire 

 gauze, through which the mud or sand of the bottom 

 and margins was sifted, the washing in the fine sieve be- 

 ing diluted and examined ; or the bottom of the sieve 

 was held slightly below the surface in a large vessel of 

 clear water, and the contents gently stirred and closely 

 examined. These fine washings from mud or thick vege- 

 tation are often well worth saving in bulk. The minute 

 life of weedy waters may be well collected by means of a 

 Birge net, which is a small, deep, fine net, the opening 

 guarded by a coarse wire gauze cone, its apex outward, 

 w'hich parts the vegetation as the net is drawn through 

 it. The contents are removed by unscrewing a small cap 

 from a short tube inserted at the narrow bottom of 

 the net. 



Preserving. — Methods of preservation have very greatly 

 improved of recent years, but much remains to be done 

 before all kinds of material can be satisfactorily pre- 

 served. The best results with most larvae of any size 

 were obtained by heating them in water, not too rap- 

 idly, to about 200° Fahr., and setting aside till cool. A 

 small percentage of acetic acid will prevent the collapsing; 

 of very soft larva?. The principal trouble with this method 

 arises from the expansion of the air within, but a slight 

 inflation, especially in the crane-fly larvae (Tipulidse), 

 is desirable, as it fills out the anal prominence and its 

 soft appendages. This method is not suitable for pupae 

 generally, nor for ephemerid nor perlid larvae with their 

 flat gills. As a general preservative for material so pre- 

 pared and for other large insects, we have depended 



