252 FOREST ENTOMOLOGY. 



short-beaked Chennes lives on smooth bark, on which the sHghtest 

 tap would yield the necessary juice. 



The antennae 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 larvse 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. 246) the cubitus or post-costal 

 nervure gradually expands into a semi -coriaceous stigma, whence 

 proceed the veins of the wing. Fig. 246 is a camera-lucida sketch of 

 the wing of Aplii>i samlmci, and may be considered as a very good 

 examjDle of a typical wing. 



The following is an explanation of the characters : — 



a. Cubitus or post-costal nervure. 1. Costal cell. 



h. Posterior marginal. 2. Basal cell. 



c. Costal nervure. 3. First discoidal. 



d. Cubital nervure. 4. Second discoidal. 



e. First furcal. 5. Infra-marginal. 

 /. Second furcal. 6. Marginal. 



g. Second oblique. 7. Second cubital. 



h. First oblique. 8. First cubital. 



i. Insertions. 9. Stigma. 



k. Apical marginal. 



/. Stigmatic. 

 p. Ilooklet. 



The above is adapted from Buckton's jNIonograph, 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 ApMdince and Laclmince (fig. 246) ; once forked 

 in the tribe Schizoneurime (fig. 247) ; and not forked in the tribe 

 Pempliigi7i(e (fig. 248), and also in Chermesmce (fig. 249). In the 

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

 oblique veins only. The Avings 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. 



