CHAPTER III 

 THE INSECT: ITS INTERNAL STRUCTURE 



Few of th(> internal structures of insects are of any fi;reat importance 

 from the standpoint of control methods, but some knowledge of them 

 and their arrangement is desirable. 



Digestive Organs (Fig. 22). — The alimentary canal extends from the 

 mouth through about the center of the body to the anus at the hinder 

 end. In those insects whose food is most concentrated (Fig. 23), it is 

 in its simplest form and is but little if any longer than the body. In 

 those which feed on less concentrated food (Fig. 24), the necessity for a 

 greater digestive and absorptive surface has resulted in an increase 

 of its length and the accommodation of this within the body by the 

 production of loops and coils. 



Fig. 22. — Diagrammatic longitudinal section of an insect to show the arrangement of the 

 internal organs. {After Berlese.) 



In the embryo the alimentary canal forms as three separate sections 

 which connect later. One of these is an ingrowth from the surface where 

 the mouth is to be; another and similar ingrowth occurs where the anus 

 fonns; and a third forming earlier than the other two, arises as two 

 masses of cells, one near each end of the embryo, wliich move inward 

 and toward each other, unite, and surround the yolk. Later, when this 

 has been absorbed, a space is left with which the two ingrowths already 

 mentioned connect, the hollow centers of all three joining to form the 

 tube through which the food travels. The ingrowth from the mouth is 

 usually called the fore-intestine, the central portion the mid-intestine, 

 and the ingrowth from the anus the hind-intestine. The first and last 



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