OF INSECTS. 
321 
XENOS PECKII. 
Plate XXXIII. Fig. 2. 
Linn. Trans. Vol. xi. PL 8 , fig. 8. 
Body brownish black ; antennse 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 1 lines. 
Larva and pupa found in Polistes fucata, 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 
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