THE ANATOMY OF IX SECTS. 



CHAPTER II. 



THE ANATOMY OF INSECTS. 



The 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 anatomy. 



The External Anatomy of Insects * 



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

 insects can be easily comprehended by recalling what has been said, 

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

 sented 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- 

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

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

 thus deposited is horny, and is termed chitine. 



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

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

 various motions of the body. The ring-like nature of the segments 

 is best seen in larvae, and in the caudal part of adult insects. In the 

 cephalic part of adult insects it is less obvious. 



When a single segment of the body is examined, the hardened 

 portion is not found to be a continuous ring, but is seen to be made 

 up of several portions more or less movable upon each other. Such 

 a hardened portion of the body-wall is termed a scleritc. 



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

 lettering of the illustrations. 



