192 INTERNAL ANATOMY OF INSECTS. 



rises and falls ; it bends in various directions ; and its 

 segments can often be lengthened or retracted. Besides 

 all this, its spiracles open and shut, and its reproductive 

 and other anal organs have their appropriate motions. 

 In numerous Coleoptera, however, and some Hemiptera, 

 the upper-side of the abdomen is almost the only part 

 that is moveable, especially near the trunk ; the under- 

 side, having its first segments soldered together, is only 

 capable of motion near the tail a . The muscles that pro- 

 duce the various motions of this part must be entitled to 

 all the denominations stated above 5 . I have on a former 

 occasion explained to you how, in insects that have a 

 petiolate abdomen, that part is elevated and depressed . 

 In those with a sessile one the base is attached to the 

 metaphragm by strong ligaments , and the muscles that 

 move the first piece act from one segment to another. 

 The partial movements of the segments of this part, 

 where they have place, are produced by muscular fibres 

 which extend from the whole anterior margin of one to 

 the whole posterior one of that which precedes it. If 

 those, for example, of the back contract, the abdomen 

 becoming shorter above, bends upwards; and if those 

 of the sides or belly, it bends sideways or downwards 6 : 

 this is a beautiful as well as simple contrivance. 



The alternate rush of air from the abdomen into the 

 alitrunk, and from the atmosphere into the abdomen, is 

 attended by the constriction or expansion of that part 



Chabrier Sur Ic Vol dcs Ins. c. i. Addend. 298. 

 See above, p. 178 . 

 VOL. III. p. 700. 

 Chabr. ubi siqw. c. i. 422. 

 Cuv. Anat. Comp. i. 451. 



