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 by 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. Cynips Kollavi and others possess no 
male; all the imagines are perfect female forms. 
