MELANOCHROISM IN BRITISH LEPIDOPTERA. 145 



dential address to the Fellows of the Entomological Society of London, 

 in 1890, and not mine at all. I am credited with it, it is quoted at length, 

 my views have been changed according to Mr. Kobson (because, I suppose, 

 Lord Walsingham made this statement), and my ideas are ridiculed. 

 Why ? Because Mr. Robson really does not pay eitough attention to 

 the subject he attempts to criticise, and mixes up the ideas of different 

 people, in this marvellous fashion. Surely this is sufficient to lead 

 thoughtful entomologists to put Mr. Robson's criticism down as a most 

 valuable one, which should be relegated to a work entitled Fairy Tales 

 for the Ignorant. Surely a subject which needs the greatest care, and a 

 rather large amount of general scientific knowledge, should be handled 

 by one who shows the first, and possesses the other. 



With regard to my remarks as to the supposed effect of the actinic 

 rays of the sun, the statement that I should not be inclined " to give the 

 action of the sunlight the short shrift 1 gave it in a previous paragraph," 

 does not bear in any sense the construction Mr. Robson puts on it. I 

 attempted to collect and criticise the various views put forward to 

 account for the phenomenon. The suggestions of Lord Walsingham 

 presented this view in a new light, and I was quite willing to discuss 

 the matter, although i:)reviously it had not appeared to me to be of 

 sufficient gi-avity to be worth discussion. I decided in my criticism 

 against the probability of it having any value, and Messrs. Poulton and 

 Merrifield have since conducted experiments tending to strengthen the 

 position I took up. 



Mr. Robson then goes off at a tangent, and criticises the possibility 

 of moisture producing dark varieties. Here, again, he fails in ele- 

 mentary principles. I would again repeat that (1) Moisture may so 

 affect larvaa that they are physically changed to suit an environment ^ 

 direct action (in supposed area towards melanism) ; (2) Moisture may 

 •so darken objects as to increase the power of "natural selection" = 

 indirect action (in supposed area towards melanism). Here is a com- 

 pound action of moisture, the units of which Mr. Robson fails to dis- 

 criminate. 



Mr. Robson's further remarks, in which he refers to " an inclination 

 to retreat from the very decided views," &c., are really a product of his 

 own imagination. Unfortunately, he views his science from a very 

 narrow standpoint, hedged on both sides most carefully to prevent 

 Avandering. Observation has taught me that Nature has no such 

 method in any of her moods. Variation is her great point, and the 

 means by which this is brought about are various. To give my readers 

 a distinct idea of what I consider one potent and active force, I dis- 

 ■cussed the action of moisture at length, because it is that force which 

 most intimately concerns Bi'itish lepidopterists. At the same time, I 

 went into such other side views that Nature takes — temperature, 

 heredity, environment, natural selection, etc. — partly to show that 

 I knew such existed, but more particularly because it is impossible 

 to discuss one view without considering others. These are the 

 symptoms of mental aben-ation, I suppose, to which Mr. Robson casually 

 refers on every other page. 



Mr. Robson quotes Dr. Chapman as saying that he considered 

 melanism to be " a western rather than a northern form of variation ; 

 to be associated with wet weather rather than a cold climate ; and it 

 has certainly been most common of recent years, which may be 



