INSECTS IN GENERAX,. 



sect's body, called si)iiacles. The spiracles or breatliiiig- pores can be 

 easily seen along the sides of all caterpillars which are not too densely 

 covered with hairs. In the perfect or winged state of insects the 

 branches of the air tnbes are dilated into a great number of little ves- 

 sicles or air bladders, which render their bodies lighter, and thus facili- 

 tate their flight. 



In some aquatic larvte the trachea3 project from the body in the form 

 of little tufts, analogous to the gills of fishes. The aquatic beetles are 

 under the necessity of rising to the surface, at intervals, for air, in a 

 manner similar to that of the aquatic mammalia, the whales and the 

 doljihins. 



THE DIGESTIVE OR NUTRITIVE SYSTEM. 



fFi-. 2.1 



The digestive apparatus of insects, 

 like that of other animals, consists of 

 an elongated tube called the aliment- 

 ary canal, extending through the body, 

 j and having a number of enlargements 

 in its course, and in many insects pre- 

 :^^ seiits a particular resemblance to the 

 digestive apparatus of birds. First, 

 1 there is a short, straight oesophagus 

 or gullet ; this expands into a much 

 larger cavity, resembling the crop ; 

 then follows a smaller muscular part, 

 analogous to the gizzard ; and next, a 

 much larger and longer cavity, which 

 is the true digestive stomach; this be- 

 comes contracted into the intestinal 

 canal, which sometimes runs nearly 

 straight through the body, and in other cases is more or less convolu- 

 ted; the intestine enlarges again before it reaches the end of the body 

 into what is known as the large intestine or colon. As in other ani- 

 mals, the alimentary canal is much longer and more capacious in the 

 herbivorous than in the carnivorous kinds. As a general rule the canal 

 is much more capacious in the larva than in the imago state. 



In Fig. 2, 0, represents the digestive organs of one of the carnivo- 

 rous beetles, Cicindela aonpestris; a the commencement of the oesopha- 

 gus or gullet; c the crop; d the gizzard ; e the stomach or i)rincipal di- 

 gestive cavity; / the commencement of the small intestine ; h the large 

 intestine; both of these parts are unusually short in this tribe of in- 

 sects; m m the convoluted vessels which are supposed to represent the 

 liver of the higher animals. 



Digestive organs of iiihocls, uxplaiucd in 

 the text. 



