196 



ELEMENTARY ZOOLOGY 



by means of gills which do not project from the outside 

 of the body, as do the gills of other aquatic insects, but 

 line the inner wall of the posterior or rectal part of the 



FIG. 58. A dragonfly. Sympetrum FIG. 59. The young (nymph) of the 

 illotum, common in California. dragon-fly, Sympetrum illotum. 

 (From life.) (From Jenkins and Kellogg.) 



alimentary canal. Water enters the canal through the 

 anal opening and bathes these gills, bringing oxygen to 

 them and taking away carbonic acid gas. The aquatic 



FlG. 60. Young (nymph) dragon-fly, showing lower lip folded and ex- 

 tended. (F_rom Jenkins and Kellogg.) 



immature life of the dragon-flies lasts from a few months 

 to two years. When ready to change to adult, the young 

 crawls out of the water and clinging to a rock or plant 

 makes its last molt. 



