ODONATA 129 



morphosis is incomplete. The nymphs, like those of the 

 dragon-fly, are aquatic. They are provided with gills. Those 

 who advocatt' the aquatic ancestry of insects believe that the 

 spiracles are the openings left when the gills were lost, but certain 

 species of stone-flies retain their gills — though shrivelled and 

 probably functionless — and have wholly independent spiracles.^ 



A B 



Fig. 99. — A, Stone-fly. B, A nymph ot a stone-fly. (Comstock.) 



The larvse of stone-flies are flat and cling closely to the surface 

 of stones in the swiftest portion of the stream. They cannot 

 live in stagnant or foul water. Their resemblance to a fossil 

 is almost perfect. This resemblance is their protection from 

 their enemies, the fishes. These larval stone-flies are good bait 

 for trout. 



ORDER IV. ODON'ATA 



Dragon-flies. — To this order again belongs^ a single family,' 

 the Libellu'lidoB, or dragon-flies (Fig. 100). They have many 

 common names, as " mule-killers," " snake-doctors," and 

 " devil's darning-needles," but, in spite of these terrifying names, 

 they are all perfectly harmless to man. 



' Kellogg, p. 72. 



^ Kellogg includes the damsel flies. 



3 Comstock, p. 90. 



