148 INSECT LIFE. 



nished with strong, toothed mandibles (it is some- 

 times necessary to cut away the upper lip in order 

 to see them well), and the caudal end of the body is 

 furnished with two large setas. The number and 

 position of the tufts of tracheal gills differ in different 

 species. 



The nymphs of stone-flies are carnivorous. 

 THE NYMPHS OF MAY-FLIES (Field and School 

 Work}.- -These are also found beneath stones in the 

 beds of rapidly flowing streams, but they also oc- 

 cur in many other situations. Some live in the 

 banks of streams, where they excavate burrows for 

 shelter; others live in slowly moving waters and 

 conceal themselves by covering the body with mud ; 

 and still others swim among water plants. But in 

 regions where there are rapidly flowing streams, 

 those that live under stones will be most easily 

 found. 



As a rule, the body is not flattened to so great an 

 extent as with the nymphs of stone-flies ; the tracheal 

 gills are usually more or less platelike in form, al- 

 though sometimes they are threadlike and 

 tufted ; and the tarsi end in a single claw. 

 Fig. 117 represents one of our most com- 

 mon species. 



Study the structure of a nymph, and 

 compare it with that of the nymph of a 

 stone-fly. 



FIG. 117. Preserve specimens in alcohol, and put 

 Nymph of them in your collection with the adult Mav- 



a May- fly. J -> 



flies (see page 101). 



THE CADDICE-WORMS (Field and School Work).- 

 When the writer was a lad, before he had heard of 



