Forest entomology . Fig. 275.—Wing 0/Aphis sambuci, with third vein twice forked. number of rings or somites is variable. On the sixth segment manygenera have two important tubes or appendages; called cornicles,. Fig. 276. — Wing of Schizoneura ulnii, ivith third vein once forked. which serve for the exudation of a liquid substance known as honeydew ; others have none.

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