again during the evolutionary change — perhaps even after hundreds of years — in the 

 existence of the same species or of the same genus, is undeniably evident from 

 the comparison of the different stadia of development. It sometimes proceeds 

 in a very peculiar manner, showing clearly that it advances according to certain 

 rules. Sometimes we only see a lot of black scales spread in such a way 

 among the light coloured ones that f. i. the yellow of some species of Colias 

 and of the well-known marblings on the under-side of the hind-wings of 

 EucHLOE (Antocharis) Cardamines l. which have been taken for mimicr)', 

 look like green. Another time such black scales cover more or less closely the 

 lighter ones and cause what is called an irroration of black scales. But not 

 seldom also does the black entirely cover the other colours on smaller or 

 larger parts of the wings or even their whole surface. And in that case also we 

 see the black spread so much in the same manner or in the same direction, 

 that this may only be explained by the circumstance that this process does 

 not take place by occasional influences, but is the outcome of fixed factors, 

 which govern the evolutionary change, though they are not always the same 

 in all the species. 



From the study of a polymorphic species this process may readily be known. 

 Especially in the African Pap. Dardanus Brown ^) the different stadia of the 

 evolutional increase of the black on the fore-wings are very obvious, provided 

 that one has the disposal of a sufficient material for study to compare its numer- 

 ous evolutional forms. In the o" form of this species which is distinguished as 

 Antinorii Ch. Oberth., there is nothing of it to be seen yet; in other d" forms 

 as TiBULLUS Kirby and HuMBLOrr Ch. Oberth., a black stripe which stretches 

 itself on the upper-side from the basis of the fore-wings along the costal margin, 

 may distinctly be discerned; in the 9 of the form Humbloti Ch. Oberth., 

 this stripe is still stronger developed, and in the 9 of the form Meriones 

 Felder as well as in that 9 form of Antinorii Ch. Oberth., which resembles 

 the d form, this stripe is bent on the middle of the wing into a broad hook 

 which, growing broader and broader, extends all across the wing in the 9 forms 

 HiPPOCOON F., Tkophonius Westw. and Niobe Aur., till at last in the 9 forms 

 Cenea Stoll and Echerioides Trim., the black covers the entire wing with 

 the exception of a few small spots. So, notwithstanding the variation occurring 

 in each form, we see the black gradually extend itself across the wing in such 



') It has been tried to explain several forms of this butterfly by mimicry ; in this way, most 

 forms, however, remain unexplained. I consider the mimicry theory a mistake, but to those who 

 still attach value to it, I must recommend the perusal of a study by Guy A. K. Marshall, F. Z. S., 

 a convinced partisan of this theory, which is to be found on jiage i2i of Part I of the Trans- 

 actions of the Entom. Soc. of London, iqoS. 



