CHAPTER II 

 SECTION 2 



THE INTERNAL ORGANS 

 THE MUSCLES 



THE muscles serve to move the appendages on the body, and the 

 joints of the appendages on one another; they also bring about move- 

 ments of one segment on its neighbours, and of the separate plates of 

 the exo-skeleton of each segment on one another, when these are not 

 fused together. They always arise from the internal surface of the exo- 

 skeleton, and the joint over which they act may be, as in the legs, a 

 more or less definite articulation formed by a moulding of contiguous 

 parts of the chitinous wall, or it may be merely a space in which the 

 exo-skeleton is represented only by a flexible membrane, such as exists 

 between the segments of the abdomen. 



The peculiarities of the structure of insect muscle have been frequently 

 described, and need not be dealt with here, as they do not concern 

 the parasitologist. There is one physiological feature, however, which 

 is of great importance in relation to the mechanism of feeding and 

 of flight, namely, the capacity which insect muscle possesses for a 

 very high degree of rapidity of contraction. It is stated by Marie 

 that the wing of the fly can make 330 contractions per second, a 

 rate which is probably not equalled by any other creatures, and it is 

 this capacity which enables it, with a comparatively small wing area, 

 to support a weight which must be relatively enormous. Similarly, 

 it is the capacity of the muscles for rapid action which enables the 

 mouth appendages of the blood-sucking forms, with a comparatively 

 small armature and a limited excursion, to act as an extremely rapid 

 and effective piercing apparatus. 



The muscles of the mouth appendages have already been sufficiently 

 described in connection with the parts on which they act. The 

 antennae and palps also possess small muscles, which 



, , .. . , , Arrangement of 



are able to produce a limited amount ot movement Muscles 



of the joints upon one another, and of the whole 



