244 THE MECHANICAL FUNCTIONS. 



In general, the first of the segments into which 

 the body is divided, contains the principal organs 

 of sense, and is sufficiently distinct from those 

 wliich follow to entitle it to the appellation of the 

 head; while the lengthened prolongation of the 

 opposite extremity, when such a form is present, 

 may be denominated the tail. 



The rings which encircle the body are connected 

 laterally 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 another, and have seldom 

 any tendinous attachments ; being generally in- 

 serted directly on the parts they are destined to 

 move. Thus the adjacent margins of the rings of 

 worms (as shown in the diagiam, Fig. 131) are 

 connected together by muscular bands of this des- 

 cription, passing 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 eft'ects which result from the action of these 

 muscles are such as might easily be anticipated. 

 The lower set, when they contract, bring the rings 

 nearer to one another at that lower part ; and when 

 the whole series occupying that situation are 

 exerted in concert, they raise the body in the form 

 of an arch. An opposite curvature will be produced 



