THE ANATOMY OF IX SECTS. 



CHAPTER II. 



THE ANATOMY OF INSECTS. 



Tin: subject of insect anatomy is separated into two divisions: 

 one, treating of the structure of the body-wall or skeleton ; the other, 

 of the internal organs. The former is termed external anatomy : the 

 latter, internal anatomv. 



THE EXTERNAL ANATOMY OF INSECTS.* 



The relative positions of the more important parts of the body of 



in be easily comprehended by recalling what has been said, 



in the Introductory Chapter, regarding the type of structure pre- 



by the Arthropoda. In this branch of the Animal Kingdom, 



which includes insects, the body is an elongated cylinder composed 



of many rings (Fig. 14). A cross-section of the body shows it to be 



FIG. 14. Diagram of structure of Arthropoda. 



a tube within which are the various viscera, muscles, alimentary 



canal, heart, nervous system, reproductive organs, etc. The tubular 



body-wall, being hardened and furnishing support to the softer or- 



the skeleton. This hardening of the body-wall is due to the 



n in it of some hard substance. In insects the substance 



horny, and is termed chit inc. 



Between certain rings or segments of the body the body-wall 



remain- soft and flexible. In this way provision is made for the 



>us motions of the body. The ring-like nature of ti enta 



is b< in larv.e. and in the caudal part of adult In the 



cephalic part of adult insects it is less obvioi. 



\Vli tncnt of the body 19 examined, the liar.: 



portion is not found to be a continuous ring. In:: made 



il portions more or less movable upon each other. Such 

 rdcned portion of the body-wall is termed a 



* See Tabular Review at the end of this pan of this chapter for an explanation of the 

 lettering of the illustrations. 



