166 



NATURAL HISTORY OF ARTHROPODS. 



Fig. 241. — Case 

 of Helicopsyche 

 glabra. 



eastern States. Tlie case is like a Ifelix or Valuata shell, usually very regular in form, 

 though the umbilicus varies in size. It is composed of fine grains of sand so arranged 

 that the outer surface is smooth. It is closed during the pupal stage by a dense, silken, 

 concave, suborbicular oi^erculum, with concentric lines, rounded on one 

 side, and but slightly convex on the other, with a slightly curved slit 

 for the passage of water situated on the less convex side, each side 

 of the slit being provided with slender straight teeth which nearly 

 touch each other, thus forming an imperfect grate. The larva does not 

 spin a cocoon, but after spinning its operculum lies in its case with its 

 head just behind it. Though the body of the larva is curved it is not spirally so, as 

 would be inferred from the shape of its case. It is a quarter of an inch long. The 

 adult or imago of the species of this genus is not very dissimilar to other small caddis 

 flies. 



The larvae of the Phryganeidae are, in general, cylindrical, and bear a general 

 resemblance to caterpillars, except that they possess only six pairs of feet — the 

 thoracic ones. Living constantly in the water and never leaving it, they breathe by 

 so-called gills, by which they are enabled to extract the 

 air from the water. The gills are long, slender filaments 

 containing an air-tube or trachea, which bi-anches off 

 from the main tube. The larvaj are mostly carnivorous, 

 living on Entomostraca, so far as we have observed, 

 though they may at times eat decaying vegetable matter. 

 When about to pupate they close up the mouth of the 

 case with a grating, or, as in the cases of Helicopsyche, 

 by a dense, silken lid with a single slit, and in some instances spin a slight, thin, silken 

 cocoon, within which the pupa state is passed. Our large Neuronia semifasciata 

 transforms to a pupa in the spring, the larva passing the winter in its case. Most of 

 the smaller caddis flies appear in July. 



A. S. Packaed, Je. 



Fio. 242. — Neuronia semifasciata. 



