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Though sometimes a period of cessation may occur, all animal forms, and 

 consequently also the butterflies, are subject to evolutional alteration and there- 

 fore it is obvious that when such a process is taking place, every influence 

 that is particularly favourable to the bodily development in general, will hasten 

 the progress of this evolutional process ; indeed this is very obvious in the 

 process which I indicate as that of the colour-evolution. 



In the second of the works above-mentioned, I have made known in this 

 respect the results of a comparison of 97 specimens of Cyllo Leda l., caught 

 in Java at different times, and such especially with a view to the ringled spots 

 on the underside of the wings. These spots are or different size and develop- 

 ment, but the proportion between them in this respect is constant ; the same 

 spot is always in every individual insect the largest or the smallest ; a proof 

 that their development is not capricious, but is regulated by a general cause. 

 In the appearance of those spots in the different, individual insects there is on 

 the contrar)^ a considerable difference and such of a gradual nature. In some 

 butterflies all those spots have been reduced to tiny dots ; in others this is 

 only the case with the smaller spots while the larger ones have remained 

 ringled spots; at last in the most advanced insects all those dots have become 

 ocellar spots, of which some are very strongly developed and in this way have' 

 become black eye-spots, white centred and set in a clear tawny ring, which is 

 again surrounded by a thin black line. A gradually advancing process of 

 evolutional alteration shows itself unmistakably, but has proceeded in one 

 individual more than in another. It is obvious that the progress of this process 

 is connected with the greater or lesser humidity which prevailed during the 

 time that the caterpillar lived and thus with the greater or smaller nutritiveness 

 of the plant which served it as food. Therefore the most developed ocellar 

 spots are found on butterflies of the rainy season and specimens with only dots 

 by preference in the driest season. But between those there are various 

 transition forms. These are partly caused by the fact already mentioned that 

 the showers are not alwaj-s equally heavy or equally long, as well as by the 

 showers during the dry season ; I possess such butterflies with rather well- 

 developed ocellar spots, the caterpillars of which must, however, have lived in 

 the dry season. But this does not explain how also in the middle of the season 

 of the heaviest rains, in which so many individuals with particularly well-developed 

 ocellar spots occur, there are also found some that have only dots, so that 

 the form which most strongly marks the dry season is found at the same time 

 and at the same place as the one which most clearly shows the type of the 

 rainy season. The reason of this may easily be understood, however, when 

 we know that it is caused b)- a process of evolutional change and not directly 



