xvir 



case with those of P. Megaera L. and J. Astf.rie L. This might be expressed 

 thus : P. Egeria L. : J. Erigone Cram. = P. Megaera L. : J. Asterie L. 

 The lavanese butterflies like the European ones live also in the same regions, 

 onlv J. Erigone Cram, does not seek the shade so much as P. Egeria. L., 

 but on the other hand it is a curious fact, that while P. Megaera L. in 

 Germany bears the popular denomination of Maticr/uchs, in England it is called 

 Wall-butter lly on account of its preference to fly upon walls that are brightly 

 illuminated and scorched by the sun, on Java I have repeatedly seen J. Asterie L. 

 flying upon white-washed walls on which the sun was shining brilliantly. Surely 

 a proof that similarity in development is not confined to colour alone. From 

 the above we may doubtless infer that where once the same process of evolutional 

 change has set in, this process when no disturbing influences modify its 

 course, can bring about in different animals a striking similitude of form and 

 hence also of colour. However the study of the nature of biological evolution 

 also teaches, that the course of such a process may be modified through the 

 operation of disturbing influences, and consequendy it may be regarded as not 

 improbable that such influences can also cause evolutional changes and give 

 a certain direction to them. Now, if such an influence begins to operate in 

 that manner on different species, it is not unlikely that the said conformity 

 in form or colour will result from it. Now it is also known that prolonged 

 periods of ifislasy may temporarily impede the course of an evolutionary process, 

 but that this condition may also sometimes suddenly come to an end, in which 

 case the interrupted process again goes on. This may also warrant the supposition 

 that by the rise of new influences forcibly operating on an organism in a state 

 of cpistasy, this may also be modified to such an extent that the cause of the 

 cpistasy is removed, and consequently the said state ceases and the development 

 again proceeds, but, into a new direction by the aforesaid new influence. The 

 cause, forsooth, of the action of ifisiasy must probably be of a correlative nature 

 and lie in the incompatibility of other requirements of such an organism with 

 a determinate direction of development. If, now, this occurs in more than one 

 species, i.e. if the same influence begins to act upon several species being in 

 such a state, then surely, — and all the more, if those species already have in 

 general a very close affinity to each other — the further development will doubtless 

 be the same, and so cause a striking likeness in form and as the pigmental 

 colour is nothing else but a kind of form, thus in so far also in colour. 



The influences in question may, no doubt, be of various kinds. In the above 

 named example of two species of larvae both living in the kernels of fruits, but 

 in no wise closely allied, the very peculiar life in the dark, which for some 

 reason or other they have adopted, and which is very different from the life 



III 



