the reason of it, and is apparently very much surprised by it, his observations 

 convinced him that these changes are not merely arbitrary, or caused by 

 casual influences, but follow fixed rules. As a matter of fact this is so, and 

 that because they are neither more nor less than phenomena that appear in the 

 course of an evolutionary process moving steadily in a definite direction. And 

 hereby Dr. Couvoisier practically acknowledges the principle, which I have 

 always insisted upon, that the great variety of colouring and marking which 

 are shown on the wings of the Lepidoptera, are regulated in their genesis and 

 modification by definite rules, and are nothing but manifestations of natural 

 evolutionary processes. 



Furthermore two other observations by Dr. Courvoisier agree equally 

 well with my views, thereby lending them a firm support. On the strength 

 of his observations he considers that it may be regarded as a fixed rule that 

 while in other respects the difference between the various species correspond 

 to the peculiarities of each of them, the aberrations here referred to by him 

 occur in exactly the same manner in all species, without the peculiarities of 

 the species exercising any influence upon it. He does not know how to explain 

 this, but the fact is perfectly correct; the reason being that changes observed 

 by him, are not aberrations at all, but independent evolutionary phenomena, 

 which occur in the same way in every species which possesses the susceptibility 

 to it. I have repeatedly pointed this out ; it is the constancy of these changes 

 which proves their evolutionary character. 



Moreover Dr. Courvoisier points out quite rightly that it is therefore 

 misleading to give such names to the aberrations as give the impression that 

 they belong to special districts, and are therefore of a local nature ; while as 

 a matter of fact they have not in the least that character. Quite true, and 

 the same is frequently the case in the fabrication of sub-species, which are 

 also often based merely upon differences of an evolutionary kind. 



The course of the evolution of colour in the Rhopalocera I have treated 

 so often in my former introductions that it may well be considered superfluous 

 to discourse upon it in general terms here. There are, however, some points 

 with regard to it, which still require some discussion. 



The pigmental colours which are subject to colour-evolution, red, orange 

 and yellow in various shades, and white, are all found on the wings of 

 Lycaenidae ; red, of course, as the oldest colour and therefore most affected 

 by the fading process, only occasionally, as in all Lepidoptera, and white, the 

 most advanced stage of this evolution, the most frequently. They moreover 

 occur in such transitional forms as indubitably prove the existence of this 



