INDUSTRIAL PROGRESS DURING THE YEAR 1876. clxv 



hairs cling to the sides of the body, revealing very distinctly the 

 breathing-holes. Some air occasionally penetrates under the elytra, 

 and remains there most of the time. Often the whole under side of 

 the body between the pairs of legs is a continuous bubble, like a 

 mass of quicksilver or molten lead. The Notonecta often rises for a 

 new supply of air before the old is exhausted. 



Anotlier water-bug, the Corixa^ is less tame, and does not come to 

 the surface nearly as often as Notonecta. It receives its supply of air 

 in an instant, and darts down to the bottom. It does not swim in 

 an inverted position. It takes in the air so suddenly that it is im- 

 possible without patient observation to see the mode, which has not 

 been described. It rises to the surface in a horizontal position, and 

 no sooner is the surface reached than it darts to the bottom, and in 

 one instance remained there for ten minutes, and then darted up 

 again, leaving an air bubble in its wake, which rose to the top after- 

 ward. It carries down with it a broad, silvery streak along the 

 side of the body. The air is really introduced under the head and 

 front thorax. The head is large and very movable, as well as the 

 prothorax. It slides back and forth on a thin membrane, from the 

 surface of which it can be raised. So with the hinder edge of the 

 l^rothorax, which rides over the membranous hind thorax, which it 

 nearly conceals. When the Corixa rises to the surface it floats in a 

 horizontal position, the hind edge of the head and the prothorax 

 rising slightly above the surface. Now slightly raising the back of 

 the head and the hind edges of the prothorax, a space appears in 

 front of and behind the prothorax, by which the air passes into the 

 breathing-holes beneath. This is proved by the small bubbles of air 

 remaining in these two cracks. Two minute spiracles may be de- 

 tected in deep pits, one on each side, just above the insertion of the 

 legs, and from which the tracheae arise, each one dividing into three 

 irregular short branches, as may be seen by detaching the segment 

 and holding it up to the light. 



