148 Comparative Classification of Cynipidae. 



a two-year cycle, a species in which the greater part of 

 the individuals complete their evolution in one year. 



It may perhaps be taken as an indication that at some 

 former time, when conditions of climate were different, 

 a long larval stage was the rule, but that little by little 

 it has diminished, in some already to its full extent, in 

 some only partially, and in others as yet not at all. 

 We must also admit the same view to hold good with 

 regard to the species which have no alternate generation ; 

 with a certain number of individuals the cycle has become 

 annual, with others it is still biennial. 



