FAMILY APIIIDJD.E 



121 



benefit of the lioney dew wliich is extruded from the anal 

 opening. There is no \er,>' definite glandular struetm-e eon- 

 nected with the nectar tubes or cornicles but a liquid does 

 come from them and its function is interpreted in various 

 ways, one being that it serves the insect in defence against 

 predaceous or parasitic enemies. 



Fig. 74. — Pea aphis (Macrosiphum pisi): a, winged female; b, same 

 from side, with wings folded in natural position, as when feeding; c, apterous 

 female; d, nymph in last stage; e, third joint of antenna of winged form; 

 a and d, much enlarged; e, more highly magnified. (From Chittenden, 

 Div. Ent., U. S. Dept. Ag.) 



The classification of the Aphididse is based largely on the 

 structure of the winged forms, and it is very desirable that 

 the winged form of a species be obtained in attempting its 

 identification. 



Other characters of special value are found in the antenna^ 



