196 THE MECHANICAL FUNCTIONS. 



The rings which encircle the body are connected lateral- 

 ly by a looser and more flexible portion of integument, and 

 also by layers of muscular fibres, curiously collected into 

 bands. The muscular flesh of insects, and other animals of 

 this class, differs much from that of the larger animals, being 

 soft and gelatinous in its texture, though endowed with a 

 high degree of irritability, and contracting with great force. 

 The fibres composing each band are all parallel to one ano- 

 ther, and have seldom any tendinous attachments; being ge- 

 nerally inserted directly on the parts they are destined to 

 move. Thus, the adjacent margins of the rings of worms, 

 (as shown in the diagram. Fig. 131,) are connected together 

 by these muscular bands, which pass transversely from the 

 one to the other, immediately under the skin, and parallel 

 to the axis of the body. There are generally four distinct 

 bands provided; two running along the back, and two along 

 the lower part of the body. 



The effects which result from the action of these muscles 

 are such as might easily be anticipated. The lower set must, 

 when contracting, bring the rings nearer to one another at 

 that lower part; and when the whole series occupying that 

 situation are exerted in concert, they will raise the body in 

 the form of an arch. An opposite curvature will be pro- 

 duced by the contraction of the uj^per bands; whereby the 

 back will be bent downwards, and both ends of the body 

 raised. In proportion as the two bands, situated on each side, 

 act in concert, while the others are relaxed, the body will 

 be bent laterally towards that side. When all the four mus- 

 cular bands contract together equally, their joint effect will 

 be to bring the rings near to each other, and to contract the 

 length of the worm; the skin being at the same time wrink- 

 led and swelled out between the rings. 



Other muscular bands, attached to the rings, pass from the 

 one to the other in more oblique directions. By means of 

 these muscles the rings may be made to recede at some 

 points, while they approach at others; so that the body may 

 be either twisted laterally on its axis, or wholly elongated, 

 according as the actions of these oblique muscles are partial- 

 ly or generally exerted. 



