310 ENTOMOLOGICAL NEWS. [Jan 



is coated with chitin, so as to be thick and strong, although 

 still flexible. At its base the skin is almost free from chitin, 

 thrown into fine folds, and bent in toward the interior of the 

 body and then out again. Here it is greatly thickened by a 

 circular, lens-shaped deposit of chitin (Fig. 1, st.), which is 

 slightly larger than the inner neck of the sucker, which it 

 closes internally. The neck of the sucker is the apparent cen- 

 tral opening and the lens-shaped thickening is the bell-shaped 

 structure, which closes this opening internally, as seen in 

 looking at the sucker from the under or external side. The 

 structure of the sucker is all plainly shown in Fig. 1, B, and 

 can be much more readily understood from an inspection of 

 the figure than from reading this description. Attached to 

 the inner face of the lens-shaped " stopper " of the sucker are 

 two great muscles (Fig. 1, mus.), which run dorsally and 

 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 (Fig. 1, t.). 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 lift- 

 ing muscles may l>e contmcteil, the ''stopper" raised (the 

 folds at the neck give chance for a considerable movement of 

 the "stopper"; and a partial vacuuu) formed with the sucker. 

 "What muficleft are used when the insect desires to loosen the 

 hold of a sucker is not so evident. Probably the contraction 

 of certain dorHo-ventral muscles which lie latenil of the 

 miiw;l(!H which lift the "stopper" serves to force the "stopper" 

 down by flattening the Ijody <lorHo-ventrally. So firmly can 

 the lar\'n' hold to the ro<'k-l>e<l by mcaiiH of Wwnv suckoi*s that 

 one often tears a larva in two in :iii«iiipting to remove it. 



The lar\'i» breathe by iii< n ill tufts of short, thick, 



<?ylindn<3il, trachwilgilJM (I'n;. I, //. i. TIumt is a ]>air of these 

 gill tufts on the vcntnil aspiH't of each of the iii'st to fifth 

 atKloiiiinal MegtnentH. I'^u-h tuft consirttH of five or six short 

 branchi'H Mpringliig from a common short Iwisal strm. On the 

 sixth (hist; alHloniinal segment there is no tuft of slender, 

 branching gills, as In the other M'gments; bnt there are two 



