IV 



based simply on the venation of the wings, has been postulated some time or 

 other, does not, therefore, actually exist. 



As regards the group of Danaidae, this is of purely tropical origin ; the 

 few species which occur outside the tropics have, indeed, both in the old and 

 the new world, spread to the north and the south but their home is, never- 

 theless, in the tropics ; the tendency of spreading outside their centre of origin 

 is, indeed, not at all rare in this group ; one of the greatest migrators amongst 

 the Rhopalocera — Danais, (or Anosia) Plexippus, L. — even belongs to it. 

 The tropical origin at times manifests itself very stronghly in such colonisers. 

 Daxais Chrysippus, L. has spread, not only over Africa, and a part of Asia 

 as well as over nearly the whole of the Malayo-Australian faunal region, but 

 has also established itself in the extreme south of Europe, in Greece ; but, 

 whereas, in the tropics it occurs annually in several generations, in Greece it 

 has only one and occurs there in the imago state only in August, i. e. the 

 warmest season of the summer. In the tropics the Danaidae are, however, 

 numerous in the Malayo-AustraUan as well as in the Ethiopian and the Neo- 

 tropical regions ; evidently, therefore, the Danaidae must have originated under 

 a tropical climate in the southern hemisphere and must have spread east and 

 west by means of former land connections ; an adaptation to life in the northern 

 and southern non-tropical districts, however, has occurred in only a few species. 

 A ver)' ancient separation has, presumably, led to the independent existence of 

 the group now found over the whole of South America where, during a very long 

 period, it has, evidently, developed independently to such an extent that at 

 present it is scarcely considered to belong to the same family but has been 

 raised to a separate group under the title of Neotropidae. Nevertheless, some 

 features of the most ancient Danaidae appear to have been better preserved in 

 this group than is the case with its allies in the old world, for in the Malay 

 Archipelago some small butterflies occur possessing these same features and 

 which for that reason have to be classed with the group Neotropidae although 

 their home is situate in the region of the Danaidae proper. This can scarcely 

 be explained otherwise than by regarding them as relics of the original form 

 which have experienced little or no change and therefore agree to that extent 

 with the group separated at a remote age and now restricted to South America, 

 in which likewise some of the original features have been retained. In America, 

 on the other hand, Danaidae are found in the genera Lycorea and Ituna, 

 which must have arrived at a more recent period when the peculiar type of 

 Danaidae had already become developed in the old world, by land connections then 



