OP INSECTS. 32: 



XENOS PECKII. 

 PLATE XXXIII. Fig. 2. 



Linn. Trans. Vol. xi. PI. 8, fig. 8. 



BODY brownish black ; antennae pale fuscous, almost 

 diaphanous, sprinkled with minute white points. 

 Wings ashy white, the anterior margin and nervures 

 deep black, legs dull cinereous, tarsi dusky, extremity 

 of the abdomen pale reddish. Length 1^ lines. 



Larva and pupa found in Polistesfucata, an Ame- 

 rican insect. 



ORDER IX. DIPTERA. 



THIS extensive order admits of a very brief and precise 

 definition. The possession of only a pair of mem- 

 branous wings, and a mouth formed for sucking, 

 affords obvious characters for distinguishing it from all 

 others. It is to the former peculiarity that the name 

 refers, being derived from dig, twice, with the usual 

 addition. Another marked singularity is to be found 

 in the presence of two clubbed moveable bodies, 

 termed balancers or halteres, projecting from each 

 side of the thorax, and placed a little behind the 

 wings. 



The sucker attached to the mouth is composed 

 of several slender pieces, from two to six in number, 

 which are enclosed in, or rest upon, a fleshy pro- 

 boscis or sheath, which gives support to them when 

 employed, and also serves to pierce the cuticle of 

 plants or animals, on the juice of which the insects 

 live. When these pieces are six in number, they 



