PREFACE vii 



with eternal snow, offers exceptional opportunities 

 for the study of the vertical distribution of animals. 

 The hot, steaming forests of the valleys and foothills 

 and the sweltering bushland of the coast districts, 

 are zoologically very different from the mountains, 

 where the climate is cold and chilly mists envelope the 

 landscape. At the medium and higher altitudes, 

 from three or four thousand feet upwards, many of 

 the lowland species are replaced by others which 

 do not exist at lower elevations. One of the most 

 surprising discoveries in these mountains is the 

 large number of species of the butterfly-genus Delias, 

 species with such brilliant colouring that one would 

 associate them with a hot climate rather than with 

 a cold Alpine district. These Delias are repre- 

 sented by different varieties and even distinct species 

 in the various mountain ranges of New Guinea, 

 testifying to the great age of the island. Only one 

 or two of the species have near allies in Australia, 

 while the islands around New Guinea have nothing 

 which resembles the mountain species. The low- 

 land species of Lepidoptera and other groups of 

 animals, on the other hand, are generally of wider 

 distribution. 



This contrast between the species of the high and 

 low altitudes of New Guinea will readily explain 

 itself when the geological history of the island is 

 better known. The explanation will probably be 

 as follows : 



