HEXAPODA. 67 



cles, through which honey dew is excreted : these are com. 

 monly called honey-tubes ; they are also termed cornicles, 

 nectaries, or siphuncles. 



THE INTERNAL ANATOMY OF INSECTS. 



(For advanced students.} 



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 contained in this cylinder. For the details of the 

 structure of th . internal organs the student is referred to more special 

 works. 



The accompanying diagram (Fig. 80), which represents a vertical, 

 longitudinal section of the body, will enable the student 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 



FIG. 80. Diagram showing the relation of the internal organs. 



(y) ; this is made up of a series of overlapping segments ; that part of it 

 between the segments is thinner, and is not hardened with chitine. 

 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. The alimentary canal (a) occu- 

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

 The heart (A) is a tube open at both ends, and lying between the 

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

 the nervous system () is a series of small masses of nervous mat 

 connected by two longitudinal cords: one of these masses, 

 lies in the head above the alimentary canal ; the others are situated. 



