34 THE SKIN OF INSECTS. 



THE ABDOMEN IN INSECTS. 



WE are obliged to use this very objectionable term 

 for the third and last division of the body, which is 

 more or less closely united to the corselet. The ab- 

 domen may be described to be that part of the body 

 which succeeds the corselet, consisting in most cases 

 of a certain number of rings, without any jointed 

 members for locomotion, and uniformly enclosing a 

 portion, sometimes a very small one, of the intestines. 



It is formed by a series of very short hollow 

 cylinders or rings, united with each other by a joint, 

 by a membrane, and sometimes by an intimate junc- 

 tion, the exact line of which is not obvious. Some- 

 times the rings slide into one another like the tubes of 

 a telescope. 



Each of these cylinders is called a ring or seg- 

 ment ( 1 ), and is sometimes composed of a single piece, 

 sometimes of two half cylinders, whose two borders 

 usually come into contact. In other cases they do not 

 touch at this point, but remain free, and one more or 

 less overlaps the other, as in bees. 



Each ring is virtually composed of two principal 

 portions, which, when they can be distinguished, (this 

 is not always possible) take the name of arches ( 2 ). The 

 upper, is called the arch of the back( 3 ); the under, 

 the arch of the belly ( 4 ). 



In the flea, the bed bug, and other insects without 

 wings, as well as in grubs and caterpillars, where the 

 joining of the corselet with the abdomen is not so 

 obvious, the latter may always be known by the legs 

 never being jointed with it. 



When the back of the abdomen is covered, as in 



(1) In Latin, Segmentum. (2) In Latin, Arcus. 

 (3) In Latin, Arcus tergi. (4) In Latin, Arcus ventris. 



