— 9 — 



trace the outlines of each segment. We will return to this 

 subject later. 



Abdomen. — The abdomen is the third or caudal region 

 of the body. The segments of which it is composed are 

 more simple, distinct, and ring-like than those of the other 

 regions. 



STRUCTURE OF THE BODY-WAU,. 



Chitine. — In studying the anatomy of insects it is found 

 that in the adult state the greater portion of the body-wall, 

 that part of the insect which corresponds in position to the 

 skin of higher animals, is hard. 



This hardness is due to the deposition of a horny sub- 

 stance, called chitine, in the membrane which constitutes the 

 body -wall. 



Sclerites — The chitine is not evenly distributed through- 

 out this membrane. Pull the head of a locust so as to sepa- 

 rate it from the thorax as far as possible without breaking 

 the insect. Note that the head is joined to the thorax by a 

 soft flexible membrane, in which but little, if any, chitine 

 has been deposited. 



Examine the sides of the thorax with a lens and observe 

 that the body-wall appears to be made up of man}' distinct 

 pieces. The integument is, however, really continuous ; 

 and in each case what appears as a distinct piece is simply a 

 portion of the body-wall in which considerable chitine has 

 been deposited. Such a portion of the body- wall is called a 

 sclerite* 



Sutures. — The sclerites constitute the greater part of the 

 body- wall, the soft membranous portions separating them 

 being in most cases narrow. Usually these narrow portions 

 are mere lines ; they are then called sutures. 



Frequently the sutures become entirely effaced. We are 



* The sclerites are analogous to the centers of ossification in the bones of the 

 higher animals. 



