APHIDID.E. 291 



short-beaked Chermes lives on smooth bark, on which the slightest 

 tap would yield the necessary juice. 



The antenna? are from three- to seven-jointed, and form good points 

 for classification. They are very variable in length according to 

 genera, and are also variable in the larvae as compared with perfect 

 insects of the same species. Hence it is essential in the discrimin- 

 ation of genera to know that we are dealing with adults. 



The wings are thin, and of a beautiful transparent iridescent colour, 

 folded ridge-wise over the body, but possessing poor powers of flight. 

 In the wing of a typical aphis (fig. 275) the cubitus or post-costal 

 nervure gradually expands into a semi- coriaceous stigma, whence 

 proceed the veins of the wing. Fig. 275 is a camera-lucida sketch of 

 the wing of Aphis sambuci, and may be considered as a very good 

 example of a typical wing. 



The following is an explanation of the characters : 



p. Hooklet. 



The above is adapted from Buckton's Monograph, but in that work 

 the wings of Siphonophora are used as a typical case. 



The third vein, counting from the body of the insect, is twice 

 forked in the tribes of Aphidince and Lachnince (fig. 275) ; once forked 

 in the tribe ScMzoneurince (fig. 276) ; and not forked in the tribe 

 Pempihigince (fig. 277), and also in CJierniesince (fig. 278). In the 

 lower wing of the typical aphis the post-costal vein gives off two 

 oblique veins only. The wings are carried vertically when at rest, 

 with the costal vein downwards. In the foregoing sketches we have 

 typical wings represented, and the student would do well to study 

 the wing venation of the family, more especially as it is not infrequent 

 to find different venation on each side in some forms. 



