i893.] THE BRITISH NATURALIST. 157 



$r ; 



the fact that his book was built up as it were in successive sections : 

 internal evidence of this and the consequent lack of cohesion and 

 unity are very distinct. Mr. Tutt's own opinion, indeed, seems to 

 have become modified in the course of its expression. Thus, on page 

 26, reference is made to certain experiments of Mr. Merrifield with 

 Ennomos auiimmavia , and Mr. Tutt says that he believes the difference in 

 imagines, differently treated as larvae, to have been " due to the 

 difference of the Wet and moist conditions to which the larvae were 

 subjected." Now this, if it mean anything, means that Mr. Tutt 

 believes dampness to have had some direct physiological influence on 

 these larvae, the inference being that melanism in an imago, might be 

 induced by subjecting its larva to humid conditions. 



Now I am sure Mr. Tutt never appreciated how wide a chasm 

 separates such a humidity theory as this, from that which it is the 

 whole purpose and burden of his book to explain and justify, a 

 humidity theory of melanism, perfected by natural selection, and such 

 as I have expressed above. But in this explanation of the differentia- 

 tion of E. autumnaria by humidity, it is clear that overboard must go 

 humidity, natural selection, derivative advantage, protective re- 

 semblance, every principle except the novel and purely unsupported 

 one, that certain larvae are compelled by some unknown necessity in their 

 organism, to respond to the physical application of humidity by the 

 production of melanic imagines. 



Again, Mr. Tutt at the commencement of his essay (pp. 17-24) 

 expounds very fully and with many admirable instances protective 

 resemblance effected by natural selection (and here the term is very 

 accurately employed) as one of the principal reasons for the existence 

 of melanism ; but near the close (p. 60) he sums up thus : " Having 

 now considered this subject from man}' points, I think we may safely 

 assume that the general cause of melanism is to be sought for in 

 meteorological influence, and that this cause must act in some way 

 on the larva.'" 1 Could anything be more inconsistant ? Here we have 

 seven pages devoted to demonstrating how melanism has arisen 

 through the advantage acruing to the imago from assimilative colora- 

 tion, and eight lines t; safely assuming" that melanism has arisen 

 through purely physiological influences brought to bear on the larva. 



These are instances of the want of homogeniety in the general 

 course of Mr. Tutt's argument. Now let us see into what a fallacy he 

 has been led by his want of clear discrimmination of the cases under 

 discussion. Let us take what seems to be his earlier and certainly 

 best supported view, viz. : that this humidity acts, in the way most 

 other natural influences act, by natural selection and the survival of 

 the fittest, and that melanism generally is due to such influences. 

 1. The italics are mine. 



