BROOK LIFE. 



147 



stone. In our common forms there is a tuft of hair- 

 like tracheal gills just behind the base of each leg, 

 and the more mature individuals have conspicuous 

 wing-pads (Fig. 1 16). These general characteristics 

 will enable the pupil to recognize 

 these insects. Specimens should 

 be collected and taken to school 

 for a more careful study of their 

 structure. Look also for empty 

 nymph skins ; these will be found 

 clinging to stones and other ob- 

 jects on the shores of the stream, 

 where they were left when the 

 adults emerged. 



Pin the empty nymph skins 

 and preserve the nymphs in al- 

 cohol. Put both in your collec- 

 tion with the adult stone-flies (see 

 page 103). 



In the study of the structure 

 of these insects note the follow- 

 ing : The nymphs resemble the adults to a consid- 

 erable degree, except that they lack wings. The 

 order Plecopiera, or stone-flies, is a good example 

 of those orders, the members of which undergo an 

 incomplete metamorphosis. The body is greatly 

 flattened ; in this way the insect is well fitted for 

 creeping under stones. The legs are flattened and 

 fringed with hairs, fitting the insect for swimming as 

 well as for creeping. The tarsi are each furnished 

 with two claws. The organs of special sense are well 

 developed, there being large compound eyes, three 

 simple eyes, and long antennae. The mouth is fur- 



FlG. 116. — Nymph of 

 stone-fly. 



