34 



THE STUDY OF INSECTS 



them in working out the classification of the group to which the species 

 belongs. 



The cells of the wing are designated by applying to each the number 

 or the abbreviation of the name of the vein that forms its cephalic (front) 

 margin. In Figure 06 the veins are designated by letters at the margin 

 of the figure; the cells by letters within the figure. When a cell is 

 divided by a cross- vein the parts are numbered, as in the case of cell M 2 

 in Figure 66. 



The Abdomen and its Appendages 



The abdomen is the third or caudal region of the body. Its segments 

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

 The number of segments of which it appears to be composed varies 

 greatly. In the cuckoo-flies {Chrysididaz) there are usually only three or 

 four visible, while in many other insects nine appear. Except in the 

 lowest order of insects (Thysanura) the abdomen of the adult bears no 

 locomotory appendages. But many larvas have fleshy appendages which 

 aid in locomotion: these are termed prolegs. In the adult the end of the 

 body in many families is furnished with jointed filaments — the cerci, and 

 caudal setce. Frequently also the body is furnished in the male with 

 organs for clasping — the claspers; and in the female with saws, piercers, 

 or borers — the ovipositor. In the female of certain insects there is a 

 sting, a modified ovipositor, which is used as an organ of defence; and 

 the abdomen of plant-lice and certain other insects bears a pair of tubes 

 or tubercles, through which a wax-like material is excreted: these are 

 termed cornicles, or siphuncles; see page 115. 



The Internal Anatomy of Insects 



As has been shown in the preceding pages, the body-wall serves as a 

 skeleton, being hard, and giving support to the other organs of the body. 

 This skeleton may be represented, therefore, as a hollow cylinder. We 

 have now to consider the arrangement and the general form of the organs 



Fig. 67. — Diagram showing the relation of the internal organs. 



contained in this cylinder. For the details of the structure of the internal 

 organs the student is referred to more special works. 



The accompanying diagram (Fig. 67), which represents a vertical, 

 longitudinal section of the body, will enable one to gain an idea of the 

 relative position of some of the more important organs. The parts shown 

 in the diagram are as follows: the body-wall, or skeleton (s); this is 

 made up of a series of overlapping segments; that part of it between the 

 segments is thinner, and is not hardened, thus remaining flexible and 

 allowing for the movements of the body. Just within the body-wall, 



