THE BRITISH NATURALIST. 



159 



his argument, and I quite admit the western half of these islands to be 

 more humid than the eastern. 



Another point I refer to as of greater import. Mr. Tutt appears 

 to quite misunderstand the meaning of Professor Weissman's and, 

 I think also of Mr. Merrifield's experiments on the effect of tempera- 

 ture on larvae and pupae. Mr. Tutt assumes that these are held to 

 prove that the application of cold induces melanic variation (see p. 24), 

 and he dissents from such a conclusion. They appear to me to do 

 necessarily nothing of the kind. 1 The idea suggested by those experi- 

 ments seems to be somewhat as follows :— Every form in its normal 

 perfected condition as we know it now, is the result by evolution of 

 a vast series of antecedent forms. — That series we call the phyllogeny 

 of the species — but each individual roughly recapitulates in its own 

 development an abstract of the whole series of that phyllogeny — this 

 we call the outogeny of the individual. Now, the application of cold 

 is supposed to arrest the normal outogenetic development at some pen- 

 ultimate point, and the resultant imago appears in a form more or less 

 approximated to some antecedent stage of the phyllogeny. Thus the 

 pupae which should have given the butterfly A.pvorsa, on the application 

 of cold resulted in something much nearer A . levana, because levana is the 

 antecedent, but the levana pupae could never be made to approximate 

 to pvovsa, because that form was not included in their outogeny. The 

 inference therefore is, that were melanic forms present recently, in the 

 phyllogenetic series of any species, then it might be possible that the 

 application of cold might arrest development at a point below the 

 present normal, and produce instead such an archaic, melanic form. 

 Such, as briefly as I can express it, seems to be the philosophy of the 

 great German biologist's experiments, but it is evident that is it a mere 

 distortion of their meaning to say, that they seek simply to prove that 

 cold applied to larvae or pupae induces melanism in the imagines — it 

 can only induce it if the melanism was there pre-existent in some 

 former stage of the species' development. 



I have dwelt on these points at some length, as they illustrate 

 what careful accuracy is necessary in the examination of biological 

 ; problems. Mr. Tutt's long essay furnishes other examples of the want 

 of this quality on which it would be easy to dilate. 



I have purposely refrained from any comment on the opinions 

 expressed by Dr. Chapman, Mr. Cockerell, and others, in the long 

 quotations which Mr. Tutt prints from the letters of these entomolo- 

 gists, as it seems hardly fair to criticize mere selected extracts from 

 iprivate letters, as the settled and deliberate opinions of the writers as 

 to the causes of melanism. 



1. See " Studies in the Theory of Descent," Dr. Weissman, English edition, 1882. 



