514 MR. D. G. ELLIOT ON THE GENUS PTILOPUS. [May 7, 



have but little in common with the members of Ptilopus, the 

 peculiarly notched first primary and bare face easily distinguishing 

 them. 



Geographical Distribution. 



Probably no group in ornithology exhibits to a greater degree the 

 effects upon the coloration of plumage arising from the physical 

 causes incidental to an insular life than the one here considered as 

 composing the genus Ptilopus. Some of these birds that have 

 evidently had a common origin exhibit greater or less variations 

 from each other, according to the position of their various habitats, 

 sometimes of sufficient importance to constitute their possessors dis- 

 tinct species, at others only of that trivial kind that would at 

 best but cause them to rank merely as varieties, the lapse of time 

 during which the individuals have dwelt in their separate localities 

 not having been sufficiently great, or the physical causes of climate, 

 food, and soil not powerful enough to modify essentially their 

 appearance from the typical form. It is therefore not surprising 

 that we find some species inhabiting one island only, others dwelling 

 upon several, though perhaps separated by miles of sea, while again 

 in other localities uncertain forms are observed not changed suffi- 

 ciently to authorize the bestowal upon them of a separate distinctive 

 rank, but yet differing enough to show that a departure from the 

 type and towards a distinctive independent form has been com- 

 menced, and will continue (unless the race should become exter- 

 minated) until the variety eventually blooms into a separate species 

 possessing characters not found elsewhere. It is not to be supposed 

 that the continents of which the islands of the Pacific and those 

 of the Eastern Archipelago are the sole remains, were broken up 

 simultaneously or always suddenly throughout their length and 

 breadth ; but more probably the casualty happened at various periods 

 and sometimes gradually. Therefore we may not be surprised at 

 the apparently strange phenomenon that one species should inhabit 

 various islands, between which are others containing totally distinct 

 forms of the same genus. This may have been brought about 

 in two probable ways. A species may have been widely dispersed 

 over the continent ; and when portions of this had disappeared 

 beneath the waves, the fragments that remained above water at 

 the outset were all occupied by the same species : but physical 

 effects at intermediate points were of a different character from 

 those at the extremes ; and in course of time the birds dwelling on 

 the intervening islands departed entirely from their types, while 

 those most widely separated retained their original characters. Or 

 it may, on the other hand, have been that on the breaking-up of the 

 continent a district inhabited by a strictly local species (but one 

 surrounded by a more widely disseminated and distinct species) had 

 not been entirely submerged ; and this, all other circumstances being 

 equal, would explain the fact that a distinct form should intrude itself 

 on an island lying between others inhabited by a different one, the 

 species with the greater range having been preserved at the extremes 



