TRICHOPTERA. 371 



case previous to assuming the pupa state. This grating 

 hardens in the water, and becomes indissohible ; strong 

 threads crossing each other forming a small thickish circular 

 plate of bro^^^l silk, which becomes as hard as gum, and fits 

 exactly into the opening. De Geer has described and 

 figured several of these cases thus grated at one end ; and 

 Reaumur has ascertained that the holes left in the grating 

 were for the pm-pose of breathing, by admitting a current of 

 fresh water, effected evidently by the spiracles of the pupa ; 

 and he actually saw the grate-work in alternate motion, 

 from convex to concave, as the water passed out and in. 

 When, therefore, the time arrives for the insect to quit its 

 watery abode, and assume the winged state, it is endowed 

 with powers of motion far greater than are possessed by any 

 other incomplete pupa, so that it is enabled not only, in the 

 first place, to cut through the grating of silk, bvit afterwards 

 to creep out of its case, and ascend into the air, where it 

 throws off its outer skin, and appears as a caddice-fly (fig. c). 

 The species are found flying, chiefly after sunset, about 

 streams, ponds, &c. They are of a small or moderate size, 

 and generally of obscure pale brownish colom's. They 

 greatly resemble each other in general appearance, although 

 sufficient characters are to be found in the nerves of the 

 wings, the form of these organs, colours, &c. The admirable 

 work of M. Pictet upon these insects has made us acquainted 

 with the characters and habits of very numerous species. 



ORDER VIII. — HYMENOPTERA. 



This order is distinguished by having four membranous 

 wings, furnished with various veins, forming cells, but not 

 assuming the appearance of net-work, the posterior pair 

 being smaller than the anterior ; the mouth composed of a 

 pair of upper and lower jaws, and two lips, the lower of 



