OP INSECTS. 1 95 



t is to retain that portion of the central canal in its 

 ilace. The brief enumeration now given refers to 

 nasticating insects alone; it will readily be understood 

 ;hat the muscles are greatly modified in sucking insects, 

 since in these the parts of the mouth have undergone 

 m important change. 



Muscles of the Thorax. The muscular system of 

 ;he thorax has for its office to unite the component 

 segments of that portion of the body,, and to furnish 

 i motive apparatus for the organs of locomotion, the 

 ^vings and legs. They differ somewhat according as 

 ;he prothorax is free or connate with the succeeding 

 jegments. In the former case, (as among the Cole- 

 >ptera, for example,) the principal mass of the muscles 

 s concentrated in the prothorax, and they are almost 

 wholly employed in effecting its free movements, there 

 oeing no wings to be supplied. In general, four pairs 

 jan be detected, which have their posterior attachment 

 n the mesothorax, and an orbicular one accompanies 

 >ach spiracle. The mesothorax, in the kind of insects 

 >f which we now speak, is provided with three pairs 

 )f muscles, all of which have greater or less influence 

 >n the motions of the anterior wings. A like number, 

 ind acting mediately in a similar manner, is found in 

 ;he metathorax ; the largest, which occupies the upper 

 Dart, assisting to depress the posterior wings, the 

 second, placed at its side, to draw them backwards, 

 ind the third to elevate them. Besides these principal 

 muscles, numerous others of smaller size occur in the 

 metathorax, consolidating the various pieces of which 

 it is composed, and also acting for other purposes. 



