48 



TRANSFORMATIONS OF INSECTS. 



do not always have spiracles, but they often breathe like fishes, 

 by branchiae or gills. 



The imago or adult insect, which is produced by metamor- 

 phosis from the water larva and nymph, becomes an air breather 

 — and spiracles are developed in its sides exactly in the places 

 where the gills were attached during its fish-like life. In the 

 larvae of the May flies the branchiae are formed of expansions of 

 the skin, which are very delicate, thin, and variously folded and 

 fringed, and they are attached in pairs to the first seven seg- 



THE AQUATIC LARVA AND NYMPH OF THE CADDIS FLY {Phryganea flavicornis). 



ments of the abdomen. The tracheae are included in the folds 

 and are continued into the body of the larva, and they transmit 

 the purified air to it; but the gills disappear during metamorphosis. 

 Some packets of filaments of thin tissue derived from the 

 skin occupy the same position in the larvae and nymphs of caddis 

 flies, and have the same function and fate as the branchiae of the 

 May fly larvae. These branchire are not found in all aquatic larvae, 

 for many which do not become metamorphosed eventually into 

 winged insects still continue to breathe air, although they live 

 in the water. Such larvae come to the surface to breathe every 

 now and then, and they, do so by the means of their swimming 



