74 Observations on Cynipidae. 



springing from an axillary one. It is spherical, varying 

 in diameter from 1-4 cm. When fresh it is of a pale 

 colour often beautifully tinted with rose, resembling 

 an apple. At first its tissue is soft and sappy, but at 

 maturity it becomes hard and woody within, while its 

 periphery changes to a loose spongy mass ; in the 

 woody kernel lie countless larva chambers. (Fig. 17^.) 

 The gall matures in June, and the flies emerge in July. 

 Owing to the great abundance of the gall, the flies can 

 be reared in large quantities without difficulty, although 

 the galls are much interfered with by parasites, 

 particularly by the larva of one of the Curciilionidae, 

 Balaninus villostis. I have frequently found this rather 

 rare beetle in the gall of the Teras terminalis. It 

 hollows out a perpendicular channel with its long thin 

 proboscis, lays an ^g^, and pushes it down into the 

 end of the passage. Afterwards, when the larva 

 escapes from the ^^^^, it eats its way through the gall 

 in various directions ; as it happens that several eggs 

 are usually laid in a gall, the gall is so completely 

 wormed through by the grubs, that often not a single 

 larva chamber remains undisturbed. 



Fly. Size 3 mm. long ; of a uniform yellow colour ; 

 abdomen darker, especially on the dorsum ; the males 

 are paler in colour, and are winged ; the females are 

 wingless or with rudimentary wings only. 



Experimental breeding. I made my first experiments 

 in July, 1876. I put a large number of flies on one 

 of the little oaks under a covering, and observed them 

 for several days indoors. When the flies began to lay 

 their eggs, I was at first surprised to find that they 



