hegner] GALL INSECTS AND INSECT GALLS 205 



4. These young transform into adults of the spring generation 

 the last of May. 



5 . The gall-flies of this spring generation lay eggs in the veins 

 of white oak leaves. 



6. The larva? that hatch from these eggs cause the formation 

 of oak hedgehog galls, and transform into adults of the autumn 

 generation in November. 



Fig. 5. Huckleberry Melon Gall 



Underside rounded, truncated at apex and concave in the middle, with 

 a small nipple. Around the top is usually an acute ridge which surrounds 

 the concave depression, and at the sides near the top are short ribs which 

 are sometimes nearly obliterated. Represented by a cup-shaped impression 

 on upper side of leaf. On under side of leaf of hackleberry. (After Beuten- 

 muller) . 



The oak hedgehog galls contain not alone the gall-maker but 

 also inquilines and parasites, just as in the willow-cone gall. Nine 

 species of these were found by Triggerson. 



Very little is really known about the life-histories of gall insects 

 and there is plenty of opportunity for original investigations in 

 this field. The two described above are sufficient to indicate the 

 various stages a single species may pass through during its yearly 

 cycle, and we may now turn our attention to some more general 

 phases of the subject. 



The Forms of Insect Galls 



Insect galls are of many different forms and sizes. Some are 

 regular and spherical, with smooth surfaces (Figure 4) ; others 

 are very much misshapen, with hard, woody, horn-like pro- 

 tuberances through which the imprisoned insects escape. The 

 larger number of leaf galls are mere "warts" or excrescences, some 



