PROGRESS IN THE STUDY OF VARIATION. 67 



lections from places where the intermediates might be 

 expected to shade off into the northern form. 



It is certainly likely that there may here prove to be a 

 true case of continuity, but so far this is not quite clear, 

 either from the wild specimens or from those that have 

 been reared by crossing. The cross between the northern 

 and southern types usually produces the intermediate, 

 agreeing exactly with Breton specimens, but on recrossing 

 these with the southern form my evidence inclines, but by 

 no means certainly, towards the conclusion that there is 

 not complete blending between the two. I anticipate, on 

 the whole, that fuller investigation will show that there is 

 complete or almost complete continuity. The abrupt change 

 on passing from Poitiers to Tours is, however, scarcely 

 consistent with this anticipation. 



The insect is very local, and probably wanders hardly 

 at all. It is therefore a good subject for this inquiry. The 

 west side of France is most suitable ground for the investi- 

 gation, for here there are no mountain ranges or other 

 barriers. 



In mountainous parts of the country the true egeria is 

 always replaced by paler forms. Such forms are found, 

 for example, at Chambery, and these are not strikingly 

 different from those of Brittany, though on the whole in- 

 clining to the fulvous type, while from Doubs M. Oberthur 

 has sent me specimens precisely like English ones. 



Cases which might repay statistical study in this country 

 are, amongst others, those of the varieties of Polyommatus 

 agestis and the two forms of Fidonia piniaria. The latter 

 is very probably a case of discontinuity. In examining it 

 difficulty may arise, as Mr. Fletcher has pointed out to me, 

 from the possibility that with the recent plantation of the 

 Scotch Fir in many parts of the country artificial introduc- 

 tions may have taken place. I should be grateful for the 

 loan of series of specimens or for accurate records of the 

 occurrence of these forms. 



The illustrations here given will suffice to show lines on 

 which the objective study of the origin of species may, as it 

 seems to me, be profitably pursued. Until work of this 



