APHIDID^. 



253 



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

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



Fig. 2i6.— Whig 0/ Aphis sanibuei, vUh third vrin twice JVirknl. 



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

 genera have t^yo important tubes or appendages, called cornicles, 



Fig. 247. — Wind 0/ Schizoneura ulmi, with third vci)i once forl-cd. 



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

 dew " : others have none. 



Fig. 2-iS.— Wing o/Pemphigu.s pallidas, 

 with third vein stroA<jht. . 



Fig. 249. — 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 



