METAZOA INSECTA. 453 



organs form a proboscis which is adapted for probing 

 flowers and obtaining the sweet nectar. 



The cases of caddis-flies are exceedingly varied and 

 ingenious little objects. Leptocerus (PI. 1149, % l ) 

 builds a straight tube of sand. Limnephilus vittatus 

 Fabr. has a slightly curved tube of the same substance 

 (fig. 2), while Helicopsyche makes the young or nepionic 

 part of its case straight, while the older or ephebic portion 

 (fig. 3 ; PI. 1150, fig. 2) is coiled like a snail shell. Fritz 

 Miiller x says, that " when preserved in adult specimens 

 the oldest portion [in reality the young shell] peeps out 

 from the top of the heliciform case like a little chimney." 



The body of the caddis-fly is not spiral like that of the 

 snail but symmetrical like that of other Trichopterous 

 larvae, as shown in PI. 1150, fig. i. When ready to 

 transform, the larva (fig. 2, in its case) spins an oper- 

 culum (fig. 3) which has concentric lines like many of 

 the opercula of Gastropods, but unlike the latter this oper- 

 culum has a slit for the admission of water. 



Some caddis-flies, like Setodcs tineiformis, do not select 

 foreign substances for their cases, but spin them entirely 

 of a secretion from their own bodies, popularly known as 

 "silk." 



The caddis-fly larvae already described are free-moving 

 and live in comparatively still water, but there are others 

 living in swift flowing streams that attach their habitations 

 to stones and the like. One of the most ingenious of this 

 group is Hydropsyche (PI. 1151). It builds its case of 

 sand or of bits of plants, fastening it to a stone so that 

 the latter forms the lower part of the case (PL 1152). 

 Close to the opening of the case it erects a vertical frame- 

 work across which it stretches a net. The food brought 

 down by the current is caught by the net and the larva 

 can eat its meal without wholly leaving its house (see 

 PI. 1152). 



1 Trans. Ent. Soc. London, 1879, p. 132. 



