320 



The Two-winged Flics 



immature stages of one moth-lly species, Pericoma calijonika, which is, so 

 far, the only North American member of this family whose life-history is 

 known. The larvae (Fig. 446), which are little slug-like creatures, one- 

 tenth of an inch long, cling by a row of eight suckers on their ventral side 

 to stones in or on the margin of the stream, where they are constantly 



Fig. 444. Fig. 445. 



Fig. 444. — Diagram of wine; of Dixn sp., showing venation. 

 Fig. 445. — .\ moth-fly, Pericoma calijornica. (Much enlarged.) 



wetted by the da.shing water. When ready to pupate the larva; crawl a little 

 higher on the stones, where only the spray will reach them, and, fi.xing them- 

 selves to the rock face by a gummy exudation, change to small flatti.sh, 

 turtle-backed pupa? (Fig. 446), each with a pair of club- or trumpet-shaped 

 respiratory horns on the back of the prothora.x. They look indeed much 

 like dwarf net-winged midge pupas. After ^v. Sfm!'^''- 



aljout three weeks the adults is.sue and fly \ i lA'V- \( ' '^J 



mxL 



«iX- 



FiG. 446. • Fig. 447. 



Fig. 446. — Larva, ventral surface (at left), and pupa, dorsal surface (at righll. of the 

 moth-fly, Perkoma calijornica; also enlarged prothoracic respiratory tutx- of pupa. 

 (Much enlarged.) 



Fig. 447. — Mouth-parts of moth-fly, Psychoda sp. //)., labrum; ni.v., ma.xilla; m.x.p., 

 maxillary palpus; mx.l., maxillary lobe; //., labium; pg., paraglossa; hyp., hypo- 

 pharynx. 



u]) into the overhanging foliage, where they spend most of their time 

 resting on the under side of the leaves. 



The largest family of nematocerous flies in point of number of species, 



