32 BRITISH OAK GALLS. 



often secures the perpetuation of the species more 

 effectually than sexual reproduction. Individuals who 

 lay their eggs in winter are unhindered l)y the require- 

 ments of fertilisation, and the ability to reproduce 

 independently is an advantage to them during the 

 period of frosts and snow. It is not confined to 

 winter species. Cjjnips Knllari and others possess no 

 male ; all the imagines are perfect female forms. 



