COLOURING OF CHRYSOPHANUS PIILCEAP, 8.37 



explained; and that is that one of the most distinguished of living 

 biologists has simultaneous!}^ arrived at results similar to mine, with 

 the same insect. His experiments indeed have been more compre- 

 hensive than mine, for he has tried them both on the dark form of 

 Southern Europe and on the ordinary form of Central Europe. I 

 refer to Prof. Weismann who, in his work, ' The Germ Plasm,' pub- 

 lished in May last, describes the results of his experiments as fol- 

 lows : — " Caterpillars were raised from the eggs of the German form 

 of G. phlcsas, and the pupse were then exposed to a much liigher 

 temperature till the emergence of the butterfly. The result was 

 that many of the butterflies were slightly dusted with black, but 

 none of them resembled the darkest forms of the southern 

 variety eleus. I then made the contrary experiment, by sub- 

 jecting caterpillars which had just entered the pupal stage, and 

 had been raised from the spring generation of the Neapolitan 

 form, to a very low temperature. Many butterflies were thus 

 obtained which were not so black as those which had emerged 

 from pupse kept at a higher temperature." Prof. Weismann adds 

 that *' both experiments prove the correctness of the old 

 assumption of lepidopterists, that the action of heat on a single 

 generation is capable of giving the German form a blackish 

 tint " ; so that the results now established by experiment appear 

 to be in accordance with the previous opinion among Conti- 

 tinental lepidopterists. I mention this, not as attacliing cardinal 

 importance to prevailing impressions where means exist, but 

 have not been taken, to subject them to exact investigation, but 

 as perhaps not without interest to English lepidopterists, some 

 of whom are, I believe, under a different impression, perhaps 

 accounted for by the fact that in England the summer tempe- 

 rature, being considerably below that of Central Europe, is not 

 high enough to bring out the duskier colouring. I think I may 

 say, in conclusion, that unless something admitting of greater 

 accuracy than field observations do, is brought to bear on this 

 matter, the conclusions arrived at by actual experiment, in 

 Germany and England, must be considered as established. I 

 have gone into the matter rather more fully than was necessary 

 for the immediate purpose of my communication, because it 

 seemed to me that it might be made an opportunity for directing 

 attention and observation to a subject of much wider interest, 

 vi2., the means for correlating the results of observation in the 

 laboratory with those of observation under natural conditions. 

 The chief interest of the former is perhaps their bearing on the 

 latter ; but to compare them effectually, the essential limitations 

 proper to each of the two kinds of observation have to be 

 recognised. 



Brighton, 5tli November, 1893* 



