XXX 



is very large, it becomes evident, to what the great variety of colouring amongst 

 these butterflies is due; and that casual or capricious, such as meteorological, 

 influences can only play a very insignificant part in it. 



In this Vi'ay I believe that the origin, and at the same time the nature 

 of the wealth of colour in the Lepidoptera, which is especially remarkable in 

 the Lycaenidae, becomes intelligible. It is true that the application of my 

 theory is not complete, in the first place because I have been obliged to 

 confine myself to the Lycaenidae of a part of the Indo-Malayan fauna, and a 

 similar treatment of this family over the whole world will greatly supplement 

 and improve our knowledge of the subject, and further because more minute 

 investigations, even in the confined circle in which I moved, may also do this 

 to a considerable extent. But I have made at least an attempt to elucidate 

 the subject by observations and conclusions drawn from them, that is upon 

 scientific lines, instead of using the current phraseology. In my opinion, in 

 the face of these, it is now impossible for a serious student of nature, who is 

 not obsessed by conventions, not to acknowledge what I have maintained for 

 years, that the variety in colour amongst the Lepidoptera is caused by 

 evolutionary processes, which I have called those of colour evolution. Not 

 that we can expect this to happen at once: superstition and error are not 

 easily overcome upon any subject. My investigation of this subject has led 

 to other most important conclusions. It has enabled me te see, that the 

 evolutionary pressure towards change takes place in a manner which, I believe, was 

 hitherto unknown, or at any rate very little generally understood, and the conclusion 

 cannot be ignored, that this must also be the case with regard to all other 

 evolutionary change. 



My views apply to all manner of false prevalent theories, such as those 

 concerning the nature of the so-called seasonal variations, those ccncerning the 

 sexual significance of the difference in colour in so-called sexual dimorphism, 

 and others. The phenomena in question demonstrate very clearly, what I have 

 already pointed out in my first introduction (p. xi), that the preasure towards 

 evolutionary change, does not, as is generally believed, act upon at whole 

 organism of a particular species as such, but that only special organs or other 

 physiological units in such a group are altered by it. At the same time, as 

 this may take place with several such units simultaneously, or because these 

 separate changes, through correlatine action, may stimulate a similar pressure 

 in other such units, a change of such importance in a group of organisms may 

 be brought forth. ^) 



') When the above was ready for press I noticed an article by Henry Fairfield Osborn 

 {Columbia University) in Nature of Nov. ii"' igi^ from which I give the following extract: 



