l66 FIRST LESSONS IN ZOOLOGY 



dragged b\' the slowly walking caddis- worm. Pull a 

 worm iVom its case and examine it. How does it hold 

 itself so lirml)' in the case.^ What is the case for.^ Why 

 is the head and front part of the body so much harder 

 than the rest.' How does the caddis- worm breathe.' 



Not all of the caddis-worms live in cases, and some 

 which make cases do not remain in them all of the time, 

 so that )'oii ma)' sometimes find them crawling about on 

 the stones. Some of these make tinv nets of silk stretched 

 between two near-b)' stones. These nets are "usually 

 funnel-shaped, opening up-stream, and in the center of 

 them there is a portion composed of threads of silk ex- 

 tending in two directions at right angles to each other, 

 so as to form meshes of surprising regularity'. It is as if 

 a spider had stretched a small web in the water where 

 the current is swiftest. " In these nets are caught bits of 

 organic matter which serve as food for the insects. The 

 caddis-worms wliich build these nets li\'e in rude cases, 

 on the under sides of stones, composed of an inner silken 

 tube partly covered with little pebbles. 



All these creatures are the young, or larv,-e, of caddis- 

 flies, which, ^\■hen adult, are moth-like flying insects, 

 with four wings covered with hairs, among which are 

 distributed many flattened scale-like ones; the antennte 

 are very long and thread-like. The insects may be 

 found fluttering among the foliage, or alight upon it, at 

 the brook's margin. Caddis-flies have a complete meta- 

 morphosis. When read}' to pupate the caddis-worm 

 closes the opening of its case b)' spinning a silken sheet 

 across it or filling it with a stone. The opening is of 

 course not absolutely closed, space being left for the 

 ingress of water which carries ox3'gcn to the pupa within. 

 This lies quietl)- in its case until read)' to emerge as the 

 winged caddis-ll)-, when it crawls out of its case, up on some 

 plant stem in- stick and there moults the ])upal cuticle. 



