XIV 



also to be discussed presentl}', but already published in the Tijdschyift voor 

 Enfomo/ogif, it appeared to me that the presumably somewhat abnormal condition 

 produced in this animal by this nursing, however carefully conducted, had 

 caused sometimes a noticeable retardation in its colour development and had 

 thus produced a form, no longer existing in Java but still living normally else- 

 where, being doubdess more ancient phylogenetically than its forms occurring 

 in Java at the present day. Cold and heat, withholding oxygen, specially 

 nourishing food, more or less scanty supplies, and, as we shall see also, abnor- 

 mally strong illumination or darkness, therefore, may all act in a similar manner. 

 The different evolutionary processes of change, including that of colour evolution 

 may in their course be influenced by such stimuli and acquire a slower or more 

 rapid development. 



Nevertheless, as I have already stated, the prevalent ignorance retains this atti- 

 tude and one finds repeatedly, especially in Germany, the influence of cold and heat 

 — alleged to have been proved by these experiments with butterflies — adduced 

 on all occasions. I have even met with it in the domain of ethnology. Prof. 

 Dr. Standfuss regarded the change thus brought about in these butterflies as 

 newly acquired characters ; when he succeeded in inducing them to pair and 

 in raising in this manner a second generation, corresponding in colour to the 

 parents, he saw in this a proof of the heridity of the acquired characters! 

 These butterflies, however, had simply, as regards their colour evolution, reverted 

 to an older stage of development. Being at this stage they naturally produced — 

 in like manner as their ancestors had done while at that stage — a progeny 

 which corresponded to it. This contained indeed ample proof of the fact that 

 they had by no means acquired new characters by the experiment but had 

 simply reverted to an earlier stage of development. 



The direction assumed by these processes must, therefore, also be governed 

 by such stimuli, even though their nature is as yet unknown to us. That 

 specific directions of this nature do exist, observation teaches us ; the fact also 

 emerges that where they occur they are not restricted to definite genera but 

 make their appearance in animals otherwise different but living in the same 

 district, sometimes, indeed, in whole genera, but also in a few species or even 

 in one or other of the sexes of these. Where whole genera have assumed 

 such a specific direction it sometimes appears, as is the case with the more 

 ancient American Danaidae, that these are the very ones, if local influences 

 are assumed to operate here, which have been exposed to them during the 

 greatest period ; where, however, only a few species or sexes have assumed a 

 specific direction, this points unmistakably to a difference in susceptibility which 

 has not yet been developed equally in all individuals. In those butterflies, 



