']6 Observations on Cynipidae. 



shown by the fact that in Teras terminalis some flies 

 presei've the habit of pricking buds Hke their mother 

 flies. Here the great resemblance of the two flies, 

 in spite of their different development and manner of 

 life, is striking \ Since Biorhiza aptera is wingless, it 

 need cause no surprise that the Teras terminalis 

 generation is also deficient in wings, for we must 

 remember that although the males are always provided 

 with perfect wings, yet the females are either wingless 

 or have short rudimentary wings only. Are these 

 rudiments to be considered as organs in the process 

 of development or of degeneration ? I believe that 

 the decision must depend on whether the possession 

 of perfect wings would be more advantageous than 

 the present rudimentary ones. It must be apparent 

 to anyone who watches the flies while pricking, that 

 perfect wings could be of no great use to them. The 

 fly does not need wings to reach the place where it 

 is to lay its ^g^, as it has only to creep down the trunk 

 to get at the roots ; but having done this it has in 

 addition to penetrate the ground, which it accomplishes 

 by pushing its way backwards with the aid of its abdo- 

 men. In the act of burrowing, wings could only be 

 a hindrance, therefore the apterous condition is a decided 

 advantage to the fly. 



There is a curious phenomenon in the propagation of 

 Teras terminalis which deserves notice. It appears that 

 while some galls produce both sexes, some yield only 



[^ Another point of resemblance is found in both generations 

 possessing a disagreeable bug-like smell, which is probably defensive 

 in character, as it persists after ovipositing is over.] 



