BROOK INSECTS 65 



flies (fig. 38), moth-like flying insects, with four wings covered 

 with hairs, among which are y 



distributed many flattened scale- 

 like hairs. The antennae are very 

 long and thread-like, and the in- 

 sects may be found fluttering among 

 the foliage or alight upon it, at 

 the brook's margin. 



Collect and put into the school- 

 room aquarium a number of those 

 caddis worms (in their cases) which 

 you find in the quiet places of the brook. These may live in the 

 aquarium and an opportunity thus had to observe their habits 

 more closely and also, perhaps, to observe the manner of their 

 transformation into winged adults. The caddis worm or young 

 caddis-fly does not transform directly into the winged form as 

 does the young stone-fly or May-fly. When ready to transform it 

 closes the opening of the case by spinning a silken sheet across 

 it or filling it with a stone, The opening is not absolutely closed, 

 but space is left for the ingress of water which carries oxygen to the 

 insect within. Thus enclosed, the caddis worm changes to a 

 pupa, that is, to a stage in which the insect lies quiescent, taking 

 no food, while it is undergoing the great structural changes neces- 

 sary for the development of the caddis-fly from the caddis worm. 

 The occurrence of this change to a pupa (pupation, the changing 

 is called) can be recognized by noticing the closed-up condition 

 of the case. Such closed cases may be found in the brook, and 

 perhaps in the aquarium. Open one of these closed cases and 

 examine the pupal caddis-fly within. Note how the legs and the 

 developing wings of the caddis-fly are folded against the body. 

 Can you find any tracheal gills on the pupa? Can the pupa 

 move ? It can only wriggle a little. This wriggling or bending of 

 the body is necessary to keep going some sort of a current of 



