310 ENTOMOLOGICAL NEWS. [J an 



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 chitiu (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, WM-S.), 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, .). 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 u stopper " 

 well down in the neck of the air cavity of the sucker, the lift- 

 ing 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-veutral 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. 



The larvae breathe by means of small tufts of short, thick, 

 cylindrical, tracheal gills (Fig.l, </.). There is a pair of these 

 gill tufts on the ventral aspect of each of the first to fifth 

 abdominal segments. Each tuft consists of five or six short 

 branches springing from a common short basal stem. On the 

 sixth (last) abdominal segment there is no tuft of slender, 

 branching gills, as in the other segments ; but there are two 



