142 HALF HOURS WITH INSECTS. LPackard. 



remained there for ten minutes by the watch, and then 

 darted up again, leaving an air bubble in its wake, which 

 rose to the top afterwards. It carries down with it a broad 

 silvery streak along the side of the bo(l3\ 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 tliin membrane, from the surface of 

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

 thorax, 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 edge of 

 the prothorax a space appears in front of and behind the 

 prothorax, by which tlie air passes into the breathing holes 

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

 maining in these two cracks. Two minute spiracles may be 

 detected in deep pits, one on each side, just above the inser- 

 tion of the legs, and from which the trachcce arise, each one 

 dividing into three irregular short branches, as may be seen 

 by detaching the segment and holding it up to tlie light. 



So much for tliose insects which simply rise to tlic surface 

 and take in air without any special modification of the spir- 

 acles. We now come to a second group of adult insects 

 which, by a change in the number, position and form of the 

 spiracles, are provided with a special respiratory contrivance. 

 A striking example is seen in Ranatra, the water stick bug. 

 The end of this creature's body terminates in two thin tubes 

 nearly as long as the insect itself, at the end of which are 

 two spiracles, each connecting with a trachea. These lono- 

 appendages, which are simply elongated spiracles, it thrusts 

 out of the water, takes in its supply of air, and then goes 

 on in its deliberate ramble. The Nepa of Europe has much 

 shorter respirator3' tubes than Ranatra, while those of Belos- 

 toma scarcely project beyond the body, though in B. annec- 



14 



