INTRODUCTION. 9 
proper place, when speaking of the various types of winged 
insects. 
In the perfect insect (of which we have been speaking in the 
preceding pages) the. abdomen does not carry either the wings 
or the legs. It is formed of nine segments, which are without 
appendages, with the exception of the posterior ones, which often 
earry small organs differing much in form and function. These 
are saws, probes, forceps, stings, augers, &c. We will speak later 
of these different organs in their proper places. 
With vertebrate animals, which have an interior skeleton suited 
to furnish points of resistance for their various movements, the 
skin is a more or less soft covering, uniformly diffused over the 
exterior of the body, and intended only to protect them against 
external injury. In insects the points of resistance are changed 
from the interior to the exterior. The skin changes in nature to 
fit it to this purpose. It becomes hard, and presents between 
the segments only membranous intervals, which allow the hard 
parts to move in all directions. 
We are examining a perfect insect; we have glanced at its 
skeleton and the different appendages which spring from it. The 
principal organs which are contained in the body remain to be 
examined. 
We will first study the digestive apparatus. This apparatus 
consists of a lengthened tubular organ, swollen at certain points, 
forming more or less numerous circumvolutions, and provided with 
two distinct orifices. This alimentary canal is always situated 
in the median line of the body, traversing its whole length, in 
juxtaposition to the nervous ganglia.* 
In its most complicated form the alimentary canal is composed 
of an esophagus, or gullet, of a crop, of a gizzard, of a chylific 
ventricle, a small intestine, a large intestine, divers appendages, 
salivary, biliary, and urinary glands. The csophagus is a duct 
often not thicker than a hair, in many species enlarged into a 
pouch, which is called the crop because it occupies the same 
position, and performs analogous functions with that organ in 
birds. It is enough to say that the food remains there some time 
before passing on to the other parts of the intestinal canal, and 
* Ganglion—a mass, literally a knot, of nervous matter.—E. W. J. 
