142 
HALF HOURS WITH INSECTS. 
[PACKARD. 
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 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 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 
protliorax, by which the 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 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. 
So much for those insects which simply rise to the 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 respiratory tubes than Ranatra, while those of Belos- 
toma scarcely project beyond the body, though in B. annec - 
14 
