( X ) 



freezing point, or considerably above 100° F. — the eifects in 

 appearance produced by such cold and heat were very similar. 

 Prof. Standfuss and Dr. E. Fischer had both, he believed, 

 suggested that as regards these different temperatures the 

 one brought out past atavistic features, the other developed 

 future anticipatory ones. That was a point on which he 

 could form no opinion, so he must be content with the word 

 " shock," without being able to enter on the question of the 

 rationale of its operation. 



He could not refrain from thanking Col. Manders for hia 

 paper and for its judicial tone, recording observations, which, 

 from their impartial character would be of so much assistance 

 to all in arriving at due conclusions on the probable explana- 

 tion of the facts observed. 



Dr. Chapman congratulated Col. Manders on his success in 

 carrying out a valuable and difficult experiment. He said 

 that in interpreting the result as showing that dorippus is the 

 ancestral form, we overlooked certain considerations, or 

 hypotheses, that, though unprovable, like mimicry itself as 

 Prof. Poulton had just told us, still similarly enabled us to 

 form a connected picture of otherwise isolated and even con- 

 tradictory phenomena. The hypothesis, as applied to chrysippus, 

 pictured it and dorippus as having in their past history (no 

 matter which be the older form) frequently crossed with each 

 other, and as subjected to alternative conditions either by 

 migration or by change of climate, so that at the present day 

 an individual, say of chrysippus, had ancestors that were often 

 pure ckrysippus, often pure dorippus, and though it may be 

 in an area where dorippus does not occur, it still possesses, 

 inherited in its tissues, the materials for pi'oducing under a 

 suitable change of environment the race dorippus, deeply 

 recessive though the dorippiis inheritance may be — recessive 

 of course not in any strictly Mendelian sense. 



This view of the relation of dimorphic forms to each other 

 seemed to afford the only possible explanation (not of why, 

 but) of how melanic races appear in a very few years, on a 

 change of conditions. A. betularia, when apparently a pure 

 race, had probably had in its ancestry very many, not only 

 crosses with douhledayaria, but actual changes from betularia 



