﻿HABITS AND STRUCTURE OF INSECTS. 



105 



it may be that the larva, by its presence there, causes the 

 unnatural growth of the leaf, resulting in a wart or tumor, 

 and sometimes in a large round nut. It is believed, however, 

 that the adult insect, in depositing the egg, also stings the 

 leaf, and, poisoning it at the same time, induces the ab- 

 normal growth of the leaf. Within this the larva feeds, 



Fig. 102. — Gall-Nft on Oak-Leaf. 

 (Copied from Harris's "Insects injurious to Vegetation, 1 ' third edition.) 



and changes into the pupa state, and finally into the perfect 

 insect, when it gnaws its w T ay out. 



In the autumn the pupils will find the gall-nuts abun- 

 dantly in the woods. Let them collect a number of these, 

 and, on carefully cutting them open, they will find within a 

 tiny oval case, and upon opening this they will discover 

 snugly stowed away a little, polished black fly having four 

 wings. The creature when liberated is ready to fly away. 



