( Ivi ) 



under the loving care of its numerous .adrairors, it has by no 

 means arrived at maturity; on the other hand, no jealous or 

 disparaging critic can at present be justified in putting it 

 down as an "ill weed." 



The only conclusion that I would venture to maintain, in 

 regard to this very wide subject, is that variation of colour 

 in the direction of melanism, melanochroism, or such suf- 

 fusion of markings as can appreciably affect the rapidity of 

 heat-absorption by the wing-surface of any insect, is very 

 generally proportionate to the degree of interference with 

 the direct action of sunlight caused by climatic or other 

 conditions to which the insect is exposed, and that such in- 

 terference may have a more or less immediate, or only a very 

 gradual effect upon the variation of species. We have yet 

 to ascertain how far such effect is assisted by a process of 

 natural selection, and whether such natural selection is 

 exercised for the sake of protective resemblance, or for the 

 advantage derived from an increased power of heat-absorp- 

 tion, or whether it is produced by the direct chemical action 

 of the visible or invisible rays of the solar spectrum. 



I sincerely wish that Mr. Poulton, or Mr. Merrifield, or 

 some of those gentlemen who have time and opportunity for 

 studying this question, would carry out an experiment 

 originally put into my head by Sir John Lubbock, viz., the 

 rearing of some of our variable Geometrulce, such as Gnophns 

 ohscararia, Cidaria russata, or some of the species of Mel- 

 aniiq:>e or Hyhernia, guarding them in the larval and pupal 

 stages by hyposulphide of carbon or bichromate of potash 

 from the action of the ultra-violet rays of the sun, which are 

 supposed by many to have such a strong chemical effect upon 

 the colouring matter in the scales, or on the chlorophyll 

 in the pigment of the larvte. If it were found that under 

 such conditions any appreciable change could be made in the 

 percentage of dark as compared with paler varieties, it would 

 go far to prove that melanic variation cannot be attributed 

 to the direct influence either of cold or' moisture, but rather 

 to the indirect influence of the two combined ; and the facts, 

 so far as they are at present known, point, I think, some- 

 what forcibly to this conclusion. 



