STRUCTURE OF INSECTS. 325 



the viscera subseiTient to nutrition, respiration, 

 and reproduction. The number of these abdo- 

 minal segments is very various in different ge- 

 nera of insects. Sometimes there appear to be 

 but three or four ; while, in other cases, there 

 are twelve, or even a greater number. In the 

 Calosoma (Fig. 150, b), the abdomen has six 

 complete, followed by three imperfect segments. 

 Not being intended to carry any of the organs 

 of progressive motion, they retain the form of 

 simple hoops, which is the primitive type of 

 the segments of annulose animals. Each seg- 

 ment has a ligamentous connexion with the next, 

 which is often so close, as hardly to admit of any 

 motion between them; but in other instances it 

 is more lax, and allows of the abdomen being- 

 flexible. In the former case, which is the con- 

 struction in all the Coleoptera, or beetles, the 

 rings have an imbricated arrangement ; that is, 

 each overlaps the next, often to the extent of 

 two-thirds of its breadth : so that they present a 

 succession of spheroidal hoops, capable of being 

 drawn out, to a certain extent, like the tubes of 

 a telescope. This very artificial construction is 

 manifestly designed to allow of a great variety of 

 movements, determined by the position of the 

 muscles they enclose : for since the surfaces 

 which receive, as well as those which are re- 

 ceived, are segments of spheroids, this structure 



