VI 



manner it is evidently carried off at times by air currents to which it can offer 

 no resistance and thus travels occasionally eastwards across the whole width of 

 the Atlantic Ocean to the western coasts of Europe and North Africa ; it has 

 thus even been observed once to arrive amongst the dunes of Holland across 

 England and the North Sea. That these are no intentional migrations may 

 be inferred from the fact that all these individuals perish and are unable to 

 propagate the species since the food required by the larva does not exist in 

 Europe. To the westward, however, across the Pacific Ocean, in regions 

 producing the requisite food, it has spread in this manner to Australia and as 

 far as China, while other species, such as Danais Chrysippus L., inhabit so 

 extended an area, from Australia to Africa, Asia, and even South Europe, that 

 in that case also it must be attributed to an abnormal distribution. Danais 

 LiMxiACE Cram, likewise occupies a very extensive area, from the east of the 

 Malayo-Australian Archipelago as far as Africa, and the latter continent cannot be 

 its home on account of its form which is entirely of the Malayo-Australian type; it 

 must, therefore, have migrated thither. Over palaearctic western Asia and outside 

 the tropical part of Australia some species of Danais have likewise spread. 



A striking difference is also to be observed in this family with regard to 

 the manner in which the process of colour evolution operates, especially the 

 diffusion and recession of black, giving rise to definite groups each character- 

 ized by a special colour pattern. After the occurrence of the remotest severance, 

 which gave rise to the separate existence of the Neotropidae, the Danaidae of 

 the old world followed a course of development of their own in which, however, 

 the process of colour mutation has moved on various lines, evidently under 

 special influences entirely unknown to us, and has produced, in this manner, 

 several groups. A portion of these (Lycorea Doubl., Itura Doubl.), as has 

 been stated, arrived subsequently in South America, has adopted, the same as 

 has occurred in the case of the Neotropidae, both the special " South American " 

 form of wing and the manner in which the process of colour evolution operates 

 there. In the Danaidae of the old world this process has moved on no less 

 than three different lines. In the genus Amauris, found in Africa, a peculiar 

 distribution of black occurs side by side with a fading of the original colour 

 to a complete white, which must doubtless be ascribed to local influences since 

 the same phenomenon occurs in African Rhopeilocera of other families, giving 

 rise to the alleged mimicr)- of species of Amauris, by female forms by Papilio 

 Dardanus Brown. In the Indo-Australian region, presumably in the western 

 part, in tracts between Madagascar and India, now covered by the Indian 

 Ocean — in Madagascar and the groups of islands to the north some forms 

 of EuPLOEA are still to be found — two lines in the process of colour evolution 



