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 

 carry small organs differing much in form and function. These 

 are saws, probes, forceps, stings, augers, &e. 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 membraneous 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, the nervous ganglia.* 



In its most complicated form the alimentary canal is composed 

 of an oesophagus, 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 oesophagus 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 

 undergoes a certain amount of preparation. It is in the gizzard, 

 * Ganglion, a collection of nerves. ED. 



