292 



FOREST ENTOMOLOGY. 



The abdomen is composed of several rings, and is capable of much 

 distension, this being dependent on the amount of food taken. The 



Fig. 275. Wing of Aphis sambuci, with third vein twice forked. 



number of rings or somites is variable. On the sixth segment many 

 genera have two important tubes or appendages ; called cornicles, 



Fig. 276. Wing o/Scliizoneura ulmi, with third vein once forked. 



which serve for the exudation of a liquid substance known as "honey 

 dew " ; others have none. 



Fig. 277. Wing o/ Pemphigus pallidus, 

 loith third vein straight. 



Fig. 278. Wing o/Chermes abietis, 

 with third vein straight. 



The honey-dew itself is a substance which has given rise to a good 

 deal of interesting thought and speculation. It is of a saccharine 

 nature, and is consequently sought after by other insects, more 



