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obtained by our ex-President, Mr. Merrifield. So far they 

 show, as many similar investigations by other naturalists 

 have done, that it is possible by varying the external con- 

 ditions to which a butterfly is exposed in its earlier stages, to 

 induce a well-marked alteration in its final aspect. This is 

 the first and obvious conclusion to be derived from these 

 experiments. But Weismann, as I need hardly remind you, 

 was not content to stop at this point. The fact was un- 

 deniable that warmth tended to produce in the northern form 

 of the species an approach towards the darkened aspect of 

 the southern race ; and conversely, refrigeration brought 

 about in the latter a tendency towards the familiar golden-red 

 of German or English specimens. From this the further 

 inference seemed clear that the difference in aspect of the 

 two geographical races was a direct result of the temperature 

 conditions to which they were respectively exposed during 

 the course of their normal life-history. But it was further 

 to be remarked that in neither series of experiments was the 

 transformation complete. In each instance several members 

 of the brood appeared to be unaffected, and in none did the 

 artificially-produced lightening or darkening reach the same 

 pitch of intensity as in the local races corresponding to the 

 respective conditions of temperature. The most probable 

 interpretation of this result seemed to be that, in Weismann's 

 words, the difference between the two geographical races 

 originated in consequence of " a gradual cumulative effect of 

 the climate, the slight effects of one summer or winter having 

 been transmitted and added to from generation to generation." 

 At this point we may imagine the neo-Lamarckian asking, 

 " What further proof can be required of the possibility of the 

 transmission of acquired characters 1 " It is admitted, he 

 would say, that the difference between the northern C. -phlaeas 

 and the southern var. eleus is in some way or other the result 

 of climatic conditions. It has also been shown that these 

 conditions are only partially operative for a single generation. 

 The effect is therefore cumulative. It has not been suggested 

 in this case that the change is an adaptation ; no reason has 

 been alleged why in the one instance the lighter and in the 

 other the darker coloration should have been selected as being 



