88 4 



FRESH-WATER BIOLOGY 



perfected, and regressive development of gills, external armor, and 

 feeding apparatus occurs, but the change of form and of proportions 

 of the body is slight. 



The nymphs of stoneflies are, so far as known, carnivorous: 

 they feed on the nymphs of Mayflies, on the larvae of caddisflies 



FIG. 1355. Pteronarcys dorsata, adult female. FIG. 1356. Pteronarcys dorsata, grown nymph. 



and small diptera and perhaps on the young of other stoneflies. 

 They are themselves the food of the trout and of other fishes that 

 frequent swift waters. Hudson has demonstrated the importance 

 of stoneflies as fish food in the mountain streams of New Zealand. 

 Adults and nymphs are equally serviceable for bait in all our 

 mountain streams. 



While no keys to the genera of the nymphs of stoneflies have yet 

 been published, if the adults are known, the nymphs may be 

 readily determined by comparison, for the wing venation is fully 



