702 EXTERNAL ANATOMY OF INSECTS. 



Formicidce, Scoliadce, &c, instead of a separate orifice, 

 the part I call the pulley is merely an upper sinus of the 

 large orifice that receives the pedicle of the abdomen. 

 The shape of these orifices, both of the trunk and abdo- 

 men, varies in different genera : thus, in the bee it is tri- 

 angular, with the vertex reversed ; and in the wasp the 

 upper one is circular, and the lower one transversely ob- 

 long ; 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 me- 

 tathorax, 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 sus- 

 pended, 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 

 some Phalangidce {Gonyleptes K.) it appears almost re- 

 tracted within it a . 



iii. 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 Hippoboscidce, AcaridcE, Phalangidce, and Araneidce, 

 the part we are considering is not divided into segments, 

 though in some instances, as in Gonyleptes and the can- 

 criform Epeir<e h , 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 



a Plate XV. Fig. 11. Linn. Trans, xii. t. xxii. /. 16. 

 b Surely these Epeirce, of so different a habit from the rest, form 

 a distinct genus? 



