190 



ENTOMOLOGY 



FIG. 230. 



Branchial respiration, however, is the prevalent type among: 

 aquatic nymphs and is perhaps the most important of their 

 adaptive characteristics. Thin-walled and extensive out- 

 growths of the integument, containing tracheal branches or, 

 rarely, only blood, enable these forms to obtain air from the 

 water. May fly nymphs (Figs. 19, A ; 169), with their ample 

 waving gills, offer familiar examples of branchial respiration. 

 Tracheal gills are very diverse in form and situation, occurring 

 in a few species of May fly nymphs on the 

 thorax or head, though commonly re- 

 stricted to the sides of the abdomen, 

 where they occur in pairs or in paired 

 /clusters (Fig. 19, A). Caudal gills are 

 found in agrionid nymphs (Fig. 170). 

 The aquatic caterpillars of Paraponyx 

 (Fig. 171) are unique among Lepidop- 

 tera in having gills, which are filamentous 

 in this instance. 



Caddis worms, enclosed in their cases, 

 maintain a current of water by means 

 of undulatory movements of the body, 

 and the larvae and pup'se of most black flies 

 (Simuliidae, Fig. 230) secure a continuous 

 supply of fresh air simply by fastening 

 themselves to rocks in swiftly flowing streams. 



Rectal respiration is highly developed in odonate and ephe- 

 merid nymphs. In these, the rectum is lined with thousands 

 of tracheal branches, which are bathed by water drawn in from 

 behind, and then expelled. 



All these kinds of respiration cutaneous,, branchial^ and 

 rectal occur in young ephemerid nymphs; while m6squito 

 larvae have in addition spiracular respiration. 



With the arrival of imaginal life, tracheal gills disappear, 

 except in Perlidae, and even in these insects the gills are of 

 little if any use. 



Marine Insects.- Except along the shore, the sea is almost 



Simulium; A, larva; B, 

 pupa, showing respira- 

 tory filaments. 



