ZooL.— Vol. III.] KELLOGG— NET-WINGED MIDGES. 205 



somewhat diagonally clear through the body-cavity to the 

 dorsal walls, to which they are attached. The muscles do 

 not rise directly from the "stopper," but are fastened to it 

 by strong, short tendons. The manner of the sucker's 

 functioning can now be understood. With the rim resting 

 on a smooth surface, the rock bed of the stream, and the 

 "stopper" well down in the neck of the air-cavity of the 

 sucker, the lifting muscles may be contracted, the "stopper" 

 raised (the folds at the neck give chance for a considerable 

 movement of the "stopper"), and a partial vacuum formed 

 with the sucker. What muscles are used when the insect 

 desires to loosen the hold of a sucker is not so evident. 

 Probably the contraction of certain dorso-ventral muscles 

 which lie lateral of the muscles which lift the "stopper" 

 serves to force the "stopper" down by flattening the body 

 dorso-ventrally. So firmly can the larvae hold to the rock 

 bed by means of these suckers that one often tears a larva 

 in two in attempting to remove it. 



hnaginal Mouth-farts (PI. XXII, figs. 9, 10 and 11). In 

 the imago the structural conditions of special interest are 

 those presented by the mouth-parts and the eyes. The 

 following account, with the figures of the mouth-parts of 

 Bibioce^hala doanei Kellogg, is taken from Psyche, Vol. IX, 

 1900, pp. 39-41 : 



The mouth-parts of the female consist of the following 

 well developed, independent, and easily distinguishable 

 parts shown in PI. XXII, fig. 9, in sitti to reveal the relative 

 size and natural position with regard to each other; a 

 labrum-epipharynx (/. (2^), a pair of mandibles (md), a pair 

 of maxilla (mx), a labium (//) and a hypopharynx (hyp). 



The labrum-epipharynx is elongate, slender, and pointed, 

 and bears numerous taste-pits (?) on its lower (inner) 

 surface, which is concave. 



The mandibles are long, slender, well chitinized, and each 

 is sharply, finely, and conspicuously serrate along the distal 

 half of the inner margin. The mandibles are articulated 

 with the head-capsule, wholly distinct from the other 

 mouth -parts. 



