xrr 



least, does not seem to be anv more in a period of increase, but of decrease. 

 The increase of the blaci: always takes place in such a manner, that though 

 among the specimens of the same species all kinds of variations occur according 

 to their more or less advanced stage in this evolutionary change, this process 

 always follows the same course among the individual insects of the same species 

 or even among a whole genus. This also proves without any doubt that a 

 certain evolutional process which proceeds in a fixed direction, must be the 

 cause. How strongly this may be the case in such alterations, unmistakably 

 proving that there can be no question of external influences, but that the 

 cause must be of an evolutionar}^ nature by which a fixed direction in this 

 change arises which answers to it, also became obvious to me by examining 

 the extremely important collection of Lycaenidae of Prof. Dr. L. G. Coi'rvoisier 

 at Basle ; the spots on the under-side of these butterflies also show in their 

 so-called varieties, everywhere the same fixed way of changing. Therefore 

 we often see among polymorphic butterflies the same forms in many islands 

 of the Indian archipelago, because the same direction or several such directions 

 are working in the evolutional process of alteration which causes those forms 

 and make it take the same course, though, as sometimes happens, local influences 

 may affect and hinder it at the same time. For there are also local influences 

 which affect the colour and the form of the Lepidoptera ; whenever this is the 

 case, I shall mention it. 



All those who have in this way got acquainted with the phenomenon of 

 the colour-evolution, especially with regard to the black, will understand that 

 the explanation given by Dr. Frederick A. Dixey in his essay: On tJic 

 Phylogeiiy of the Pierinae, as illustrated by theiy Wing-markings and Geographical 

 Distribtdion (Trans of Ent. Soc. of London 1894), of some colour-phenomena 

 caused by it among the Pieridae, cannot be scientifically accepted, just as 

 little as his Phylogenesis of this family which is concluded from what, in reality, 

 is only a supposition. 



The colour-evolution reveals itself in changes of physiological nature which, 

 if possible, follow the same direction, but which also follow different directions, 

 if such be required by the circumstances; consequently sometimes showing a 

 great difference, though always tending to the same end. Evidently these 

 changes are governed by the same leading element of evolution, but the nature 

 of this element is entirely unknown to us. As it only attains its end some- 

 times after many thousands of years and as during all that time the existence 

 of the being which is subject to it remains uninjured, we cannot think of any 

 necessity for this existence and therefore neither of reasons of utility or fitness. 

 So we can only see in it a phenomenon of that motivity which characterizes 



