VIII 



roptera, from which the Lepidoptera have sprung. Each of the three thoracic 

 segments of these insects was originally provided with one pair of legs and 

 one pair of wings; in their descendants living nowadays the wings of the 

 prothoracic segment fail entirely and in many families the legs have also partly 

 been annihilated. Some few remains had already made anatomists suppose 

 the former existence of these wings ; later on this supposition has been entirely 

 confirmed by the finding of fossil remains of Pseudoneuroptera of the Devonian 

 and the carboniferous age. Among these remnants of the said wings were 

 clearly obvious. It was also evident that even in those ancient times the process 

 of atrophy must have been going on for a long time, as it had already far 

 advanced in those species whose remains had been preserved; the difference 

 in size of those remnants also clearly shows that a gradually proceeding extinction 

 must have taken place. This evolutionary change has come to an end now. 

 But with another one, which at present is taking place among the Lepidoptera, 

 this is not at all the case. This process aims at making the prothoracic legs 

 of the Rhopalocera disappear gradually; there is also much difference in its 

 appearance. In some families it already appears distinctly in both sexes, but 

 among the Libytheidae, the Erycinidae and the Lycaenidae it is only developed 

 in the male sex, whereas in the other sex it only begins to appear. And in 

 some families it seems to have not yet begun. Such a gradual difference in 

 its appearance, however, makes it easy for the biologist te recognize it as an 

 evolutional process of change. But little as this process may have advanced, 

 it is already of old date, for, as Scudder has shown concerning the Tertiary 

 Nymphalidae and Libytheidae, the present difference in this respect existed 

 already in these families during the Tertiary age. 



In the same way as I have explained in the above-mentioned essay, I think 

 I may deduce a third similar process to which the Rhopalocera are subject, 

 from the state in which nowadays the hind-wings of many species happen to 

 be. Not only that the appendages of those wings which occur in different 

 ways and are of no use and which therefore can evidently be considered as 

 remnants, are very numerous, but the wings often become narrower, one thing 

 and another altogether more and more reducing the size and with that also the use 

 of those organs, in such a degree that in two species of the genus Difiilon 

 nothing but an insignificant remnant has remained. Here also the great 

 variety in which this change occurs and the gradual extinction of the said wings, 

 which is common to it, indicates to the biologist the gradual progress of 

 a process which is also annihilating in this way these subthoracic wings, 

 as formerly happened with the prothoracic ones. At the same time it seems 

 that, probably by correlative influence, the size of the thoracic wings, and 



