( vii ) 



experiments upon seasonally dimorphic species, and every 

 entomologist who has bred the spring and summer genera- 

 tions of S. illunaria knows that the two forms approach each 

 other so closely in some individuals that unless actually 

 labelled at the time it would be difficult to say to which 

 generation they belonged. From these considerations it 

 appeared to him that S. illustraria, although a species well 

 worthy of being bred and studied, was perhaps not so well 

 adapted for the proposed inquiry as some other species in 

 which the phenomena of heredity were not so complicated. 

 In attacking scientific problems where large numbers of facts 

 had to be registered it was always desirable to eliminate, as 

 far as possible, all disturbing influences, and to begin with 

 the simplest attainable cases. Whether such a simplification 

 of the results was possible in the case of a seasonally 

 dimorphic species, it was for Mr. Galton to determine ; but, 

 since the only object in selecting S. illustraria was that, 

 being double-brooded, it would be possible to get through 

 two generations annually, he would suggest that some 

 digoneutic non-seasonally dimorphic species should in the 

 first place be experimented upon, and he would mention the 

 very common Rumia cratagata as a very good moth for the 

 purpose. In concluding Prof. Meldola said that he did not 

 in any way wish to discourage the proposed experiments with 

 P. illustraria. He thought that many points of the highest 

 possible importance to the theory of heredity, some of which 

 he had alluded to in his previous remarks, could be cleared 

 up by the projected investigation ; and he trusted that 

 Mr. Merrifield would carry on the work, bearing those points 

 in view. All he contended for was that for Mr. Galton's 

 particular purpose this or any other seasonally dimorphic 

 species was not likely to yield such satisfactory results as the 

 species suggested by him. 



Mr. W. F. Kirby pointed out a difficulty which might arise 

 in making these experiments on account of the general 

 diminution of size in specimens bred in confinement ; and he 

 cited Li par is dispar as an instance of the gradual diminution 

 in size of a species when bred in confinement for several 

 generations. He remarked that prior to the extinction of the 



