EXTERNAL ANATOMY OF INSECTS. 705 



movement is very limited ; whilst in the Hymenoptera 

 they are so many little hoops, which inosculate in each 

 other as the tubes of a telescope, one third only of 

 their extent often appearing uncovered a . We see the 

 reason of this structure when we consider the calls they 

 have for greater powers of movement in this part in lay- 

 ing their eggs, and annoying their enemies and assail- 

 ants ; and also in the Staphyliiiidte to enable them to 

 turn up their abdomen like a scorpion, both as a posture 

 of attack, and to fold their wings : in all cases, however, 

 as far as my observation goes, these animals, when they 

 want to lengthen this part, can disengage the rings from 

 almost all inosculation, so that no impediment remains 

 to any movement. 



The articulation of the dorsal and ventral segments 

 with each other is next to be considered. In lulus 

 and some Centroti the ring appears to be formed of 

 a single piece, with scarcely any trace of the existence of 

 any such division; it is however almost universal, and is 

 of three descriptions; in the first the dorsal segments are 

 united to the ventral at the lateral margin or edge of the 

 abdomen; in the second it is above this margin, and in the 

 third below it. You will find that in Fulgora and many 

 other Homopterous Hemiptera these segments unite at 

 the margin, as they do likewise in Cimex lectularius be- 

 longing to the other Hemipterous section ; but in the 

 rest of the Heteropterous tribes, the ventral segments 

 turn upwards, and their union with the dorsal is in the 

 back of the abdomen ; in these the Hemelytra and wings 

 only cover the dorsal segments, leaving the edge, formed 



a Anatom Com par. i. 451. 

 VOL. III. f 2 Z 



