HYMENOPTERA. 



619 



gif i-c'a), is most common on the red oak, but it occurs also 

 on the black oak. In this gall the space between the kernel 

 and the outer layer is quite densely filled with a porous 

 mass, which suggests the name spongy. 



The Larger Empty Oak-apple, Holcaspis inanis (Hol- 

 cas'pis i-na'nis). — There are two oak-apples which are very 

 similar in structure, and which may be termed the empty 

 oak-apples. In these the space between the central kernel 



Fig. 746. — Gall of Amphibolips coccinece. 



and the outer shell contains only a few, very slender, silky 

 filaments, which hold the kernel in place. The larger of 

 these two galls measures an inch or more in diameter, and 

 is found on the scarlet oak and the red oak. 



The Smaller Empty Oak-apple, Holcaspis centricola (H. 

 cen-tric'o-la), is found on the post-oak, and measures three 

 fourths of an inch or less in diameter. It also differs from 

 the preceding in that the outer shell is mottled. 



The Bullet-gall, Holcaspis globulus (H. glob'u-lus). — One 

 of the most common galls on our oaks in the Northeastern 



