ABDOMEN. 291 



bees, it appears to be affixed by its entire breadth; and, 

 second, those in which the connecting piece is elongated into 

 a peduncle, and the base of the abdomen itself is narrow. This 

 is the case with many exotic wasps, sand-wasps (Ammo- 

 phila), &c. In the latter division the abdomen is said to be 

 pedunculated or petiolated. The peduncle itself is liable to 

 great variation. Thus, in some ants, it consists of two knots 

 (petiolus binodosus) ; in others only of one. Sometimes it is 

 disproportionately long ; at other times it is saucer-shaped, 

 bell-shaped, &c. 



Of the shape of the entire abdomen little in general can 

 be said. It is, however, more generally triangular, ovate, 

 or quadrate, with the posterior angles rounded off; gene- 

 rally, too, the upper surface is more or less depressed; 

 sometimes it is very short, at others disproportionately 

 long; sometimes wider than the thorax, but more com- 

 monly narrowed. The extremity of the abdomen is generally 

 pierced by the anal aperture. The terminal segment is very 

 variable in its form, being formed with reference to the 

 coupling of the insects, or to facilitate the deposition of the 

 eggs in appropriate situations. Sometimes, also, it is organ- 

 ized in a manner to become an instrument of defence or of- 

 fence. The various organs to be noticed below form part of 

 this segment. It still remains for me to notice the motions 

 of this part of the body. Unlike the thoracic segments, 

 which, from bearing the organs of locomotion, are neces- 

 sarily required to be as firm as possible, and are not, conse- 

 quently, capable of much distinct motion, the abdominal seg- 

 ments being destitute of such organs, and having important 

 functions to perforn, are, on the contrary, gifted with a con- 

 siderable but variable degree of motion. Thus, in those 

 species which have the extremity of this part of the body 

 furnished with offensive or defensive instruments, it is capa- 

 ble of very considerable movements in every direction. This 

 is the more noticeable in insects which have a very much 



