CHAPTER III 

 THE INTERNAL ANATOMY OF INSECTS 



Before making a more detailed study of the internal anatomy of 

 insects, it is well to take a glance at the relative positions of the differ- 

 ent systems of organs within the body of insects and other arthropods. 



One of the most striking features in the structure of these animals 

 is that the body-wall ser\^es as a skeleton, being hard, and giving sup- 

 port to the other organs of the body. This skeleton may be repre- 

 sented, therefore, as a hollow cylinder. We have now to consider the 

 arrangement and the general form of the organs contained in this 

 cylinder. 



The accompanying diagram (Fig. 105), which represents a vertical, 

 longitudinal section of the body, will enable the student to gain an 



Fig. 105. — Diagram showing the relations of the internal organs; 

 a, alimentary canal; A, heart; w, muscle; n, nervous system; 

 r, reproductive organs. 



idea of the relative positions of some of the more important organs. 

 The parts shown in the diagram are as follows: The body-wall, or 

 skeleton; this is made up of a series of overlapping segments; that 

 part of it between the segments is not hardened with chitin, thus 

 remaining flexible and allowing for the movements of the body. Just 

 within the body-wall, and attached to it, are represented a few of the 

 muscles (m) ; it will be seen that these muscles are so arranged that the 

 contraction of those on the lower side of the body would bend it down, 

 while the contraction of those on the opposite side would act in the 

 opposite direction, other muscles not shown in the figure provide 

 for movements in other directions. The alimentary canal (a) occupies 

 the centre of the body, and extends from one end to the other. The 

 heart (/z) is a tube open at both ends, and lying between the alimentary 

 canal and the muscles of the back. The central part of the nervous 

 system (w) is a series of small masses of nervous matter connected by 



(94) 



