IX 



from each other, display a remarkable similarity in this respect, which serves 

 to show that a great similarity may occur between species even when they 

 do not inhabit the same district, so that there is no question of its being due 

 to mimicry. A study of the above mentioned process is sufficient to enable 

 us to recognise the evolutionary character of the changes of form, and demon- 

 strates that all these differences of colouring are caused by such processes of 

 change, developing at very different periods in different ways, regulated by 

 the susceptibility of the individuals, and subject to all manners of disturbances, 

 but still always proceeding in one definite direction, and as concerns the kind 

 of change and the desired object to be obtained always retaining the same 

 character. For although this distinct tendency cannot always be demonstrated 

 yet this is so frequently the case, that we are justified in assuming that it must 

 always exist, even when it cannot be traced. 



I will now proceed to demonstrate this again, by the study of what the 

 Lycaenidae show us in this respect. Before doing so I consider it advisable 

 to devote somewhat more attention to the very important observations made 

 by Prof. Dr. Courvoisier of Bale, which I have already mentioned on p. XII 

 of the introduction to the Pieridae, and on p. liii of that to my third 

 monograph. In various essays, to be found amongst other places in the 

 '' Zeitschri/t fiir ivissemchaftlichc Iiisektenbio/ogie" , igoy, and in the " Detihchc 

 Entomolooische Zcitschrift Iris" igi2. Dr. Courvoisier has published his obser- 

 vations concerning what he calls " aberations" in the markings of Lycaenidae. 

 Starting from the usual dogmatic point of view, he has taken infinite pains, to 

 fit his observations systematically into the conventional frame of genera, species, 

 variations and aberrations, as well as to think out a corresponding system of 

 nomenclature to distinguish them by. I cannot follow him along this road. 

 Changes in such small patches of colour upon the underside of the secondaries I 

 am well aquainted with, also in the Satyridae, and I have discussed them 

 on p. LIII of the introduction to my third monograph ; how they extend them- 

 selves in this way can be clearly seen for instance in the drawings of Dcbis 

 Dyrta Felder (plate XVII, 47^, 47^) and D. Europa. F. (plate XVII, 48a, 48^). 

 But looked at from my point of view these are not aberrations, but merely 

 different stages in a process of evolution, which require neither a systematic 

 arrangement, nor a special nomenclature. Thus, although I cannot share the 

 opinion of my learned friend as to the nature of these patches, yet both his 

 observations in themselves, and his view of them are of great value to me. 

 In very important points these views entirely agree with what I think may be 

 inferred from my own observations. 



In the first place, although Dr. Courvoisier is quite unable to explain 



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