146 Comparative Classification of Cynipidae. 



deposition in the bud, I have never yet been able to 

 imitate them artificially. In spite of all the methods 

 employed I have never succeeded, after many days of 

 observation, in seeing even the commencement of yolk 

 segmentation, although in eggs taken from buds I could 

 always reckon with certainty on seeing this take place 

 after twenty hours. I have already explained the 

 important part which the egg-stalk plays at the outset 

 of embryonic evolution. 



The larval stage presents differences in the two genera- 

 tions, but they only concern the duration of development, 

 which is very variable. The larvae agree perfectly in 

 their structure and organization ; as they all live under 

 similar conditions, no opportunity is offered for any 

 special or varied adaptation to environment. The 

 structure of the mandibles alone differs in some species ; 

 thus the larva of Neuroterus has strongly toothed man- 

 dibles, while that of Spaihegaster has them simple and 

 unindented. It is the character of the galls that regulates 

 these modifications. When the gall substance is hard, 

 as in the Neuroterus galls, the larva is found provided 

 with strong mandibles ; if on the contrary the galls are 

 succulent and their walls soft, as in the Spaihegaster 

 galls, the mandibles of the larva will be found to be 

 simple and less powerful. 



The duration of larval evolution varies much in the 

 two generations. In the summer species the larva 

 increases rapidly, and when full grown passes straight 

 into the pupa state. In the winter species the larval 

 stage is infinitely longer, and presents the following 

 varieties : — 



