CHAPTER IV. 



The Piercing Apparatus. — The Method of Ovipositing. — The 

 Object and Function of the Egg-stalk. 



Gall formation, as we have seen, is a complicated 

 process, and necessitates the possession of a very 

 elaborate apparatus to ensure the deposition of each 

 egg in exactly the right spot for gall growth. We 

 consequently find that the gall-fly is furnished with 

 a peculiarly constructed piercing apparatus, of which 

 it is necessary that a short description should now 

 be given. 



The terebra itself consists of three pieces, for the 

 nomenclature of which we, in Germany, follow Krae- 

 pelin ^ ; they are a ridged seta ^, and two serrated 

 spiculae ^. The two spiculae are similar to each other, 

 and the seta is also clearly derived from two symmetrical 

 halves united into one piece. The seta occupies half 

 the area of a tranverse section of the terebra, and the 

 two spiculae together occupy the other half. The 

 terebra is attached to two peculiarly formed chitinous 

 plates which in repose are quite concealed within the 



^ Kraepelin, ' Zeitschrift fur wissenschaftliche Zoologie,' vol. xxiii. 

 Part II. 1872. 

 ^ Schienenrinne. ' Stechborsten. 



