EXTERNAL ANATOMY OF INSECTS. 701 
in different genera: thus, in the bee it is triangular, with 
the vertex reversed ; and in the wasp the upper one is cir- 
cular, and the lower one transversely oblong ; but in all, 
the apertures of the trunk correspond with those of the 
abdomen. In Evania, in which the minute abdomen is 
inserted in the upper side of the metathorax, there is 
scarcely any trace of this structure. With regard to the 
articulation of the pedicle itself with the lower orifice of 
the trunk, it appears simply suspended, with little or no 
inosculation. I may observe under this head, that though 
the abdomen in almost all insects is wholly clear of the 
cavity of the trunk, yet in Gonyleptes it appears almost 
retracted within it *. 
il. Composition. I shall next consider the segments 
into which the abdomen is usually divided, their num- 
ber, and other circumstances connected with them. In 
the Pupipara, Acarina, Phalangide, and Araneide, the 
part we are considering is not divided into segments, 
though in some instances, as in Gonyleptes and the can- 
criform spiders, they are represented by folds ; but in 
the great majority of insects it consists of several dorsal 
and ventral pieces or segments, forming by their union 
the annuli or rings into which it appears divided. The 
number of these abdominal segments varies in different 
insects; I have noticed more than ¢wenty such variations, 
and probably there are many more. Before I give you 
them in detail, I must first observe that the dorsal and 
ventral segments, though sometimes they correspond in 
number, yet very often do not, the dorsal most com- 
monly exceeding the ventral by a segment; in a few 
* Prate XV. Fic, 11, Linn, Trans. xii. t, xxii. f. 16. 
