168 



ELEMENTARY STUDIES IN INSECT LIFE 



interesting insects in the matter of their life his- 

 tory. The adult has an ephemeral life, lasting for a 

 day or so at most. The females of some species drop 

 their eggs upon the surface of the water, and others drop 



their eggs beneath the 

 surface on stones. The 

 young nymph not at 

 all like its parent 

 hatches and lives in the 

 water, feeding upon 

 water plants or minute 

 insects for from one to 

 three years according to 

 the species. They come 

 forth at maturity, and 

 can be found in great 

 numbers in the warm 

 summer evenings around 

 the electric lights or 

 upon the trunks of trees 

 in the vicinity of water. Catch one of these adult 

 forms and note the delicacy of its body. Examine its 

 mouth-parts, and note that they are extremely rudi- 

 mentary or even wanting, a condition brought about by 

 disuse, since the life of the adult has become of such 

 short duration that the necessity for taking food is no 

 longer urgent. These insects are exceptional in their 

 life history, since they molt once after having reached 

 the winged stage. 



Stone-Flies. 1 - - In structure of wings these insects 

 resemble the May-flies. The net-work of the veins 



'Family. Perlidce. 



FIG. 128. A May-fly. From a photograph. 

 Enlarged. 



