ANATOMY AND PHYSIOLOGY. 129 
or, if possible, even to a greater degree than, every 
other structure are adapted to the special requirements 
of the insect, and an exact knowledge of the muscular 
system of the wasp might scarcely apply beyond the 
particular family. 
Within this expanding case are inclosed the diges- 
tive and reproductive organs, the centre of the circu- 
lation, and, if not the most important, at least the 
most obvious portion of the nervous and the respira- 
tory systems. Now, it may seem sometimes as if we 
had quite lost sight of the proper subject of these 
pages while tracmg the anatomy of these different 
organs on other insects more suitable for the purpose 
than wasps. But here, as with regard to the muscles, 
if we learned no more than the structure of wasps 
could teach us, we should know very little about the 
matter. We shall find indeed that, with all the aid 
that comparative entomology can give us, the limits 
of our knowledge on many points will still be very 
narrow. It will be necessary to examine each of 
these systems separately. And first, of the respiratory 
system. 
The first object of respiration is, of course, the 
oxygenation of the blood. The general principle is 
the same in insects as in the higher animals. Air is 
pumped in and out alternately, the same passages 
serving for the entrance of the pure element, and for 
its discharge from the body loaded with effete matters. 
But insects differ from the higher animals in having — 
many passages by which the air is drawn in and out, 
many pairs of lungs, instead of only one. They 
differ, as we shall see further on, in the way in which 
K 
