( olo ) 



between Sumatra aud Java (about 3« per cent, of the total nnmber), and that 

 between Sambawa and Timor (33 per cent, of the total nnmber), and is not mnch 

 inferior to the amount of discrepancy between the lesser Sunda Islands and 

 Australia (65 per cent.), the lesser Sunda Islands can be considered as a faunistic 

 district in opposition to the greater Sunda Islands and Australia ; and it is very 

 interesting to note that almost the same amount of numerical discrepancy must in 

 the case of the lesser Sunda Islands and Java be accounted for by biological 

 factors, while in the case of the lesser Sunda Islands and Australia the only 

 acceptable explanation is the assumption of the existence of a geological barrier 

 between Australia and Timor at the time when the lesser Snnda Islands became 

 populated by Papilios. 



Turning now our attention to the second (|uestion proposed above to be 

 discussed, we note that the characters of tlie fortj'-seven specifically or subspecifically 

 different representative forms of Papilio occurring ou the lesser Sunda Islands are 

 such that forty-one of the forms are not found (as such) outside the group of islands, 

 and hence are " peculiar " to the group. As these forty-one forms are so distributed 

 that every island has some of its own and otiiers in common with other islands of 

 the group, while not a single form is identical on all the islands and at the same 

 time distinguished by some peculiarity from the representative occurring on Java, 

 Borneo, or in Australia, each island is in fact a small faunistic district, and the 

 question arises whether the faunistic peculiarity exhibited by each island is not due, 

 instead of to differences in the biological conditions existing on each island, to 

 the mechanical separation of the islands by arms of sea, aud hence finally woulil 

 have to be referred to the action of geological factors. In the introduction we have 

 endeavoured to show on a priori grounds that mechanical geographical separation 

 as such cannot give rise to a new form ; let us now consider the a posteriori reasons 

 which speak against the origin of forms by mechanical isolation. 



The widely distributed Papilio surpedon has on the lesser Sunda Islands 

 developed into three subspecies, one inhabiting Adonara, Sambawa, and Lombok — 

 specimens from the latter island come very close to tliose from Java — a second 

 found on Sumba, and a third occurring on Timor and Wetter. The external char- 

 acters of the Timor form are such that it agrees in the shape of the hindwing best 

 with the representative from Ceylon, in the breadth of the band of the forewing with 

 the Austrnlian form, and in the special shape of the anterior portion of the band 

 with montiroliis from Celebes, while it bears also great affinities to the forms from 

 Sumba and Adonara. Setting apart all the reasons brought forward against the 

 theory of isolation in the introduction, and conceding, for the sake of argument, that 

 geographical isolation of aberrational sjiecimens could lead to the origin of a new 

 form of animal without the help of any biological factor, the combination of difterent 

 affinities in the wing-characters of the Timorese, Sumbanese, or Adonaranese 

 sarpedon forms might be thought due to the first specimens immigrated into each 

 island having accidentally possessed the respective combination of characters. As 

 a combination of characters such as exhibited by P. sarpedon timorensis is not found 

 even in a less obvious degree in any specimen of sarpedon from the larger Sunda 

 Islands and Australia wo have seen, and therefore must be very rare, it is certainly 

 scarcely probable that just such specimens wliich ha<l that combination of characters 

 should have hai)])ened to be the first to come to Timor ; and this applies to all those 

 localised forms, not only of the lesser Sunda Islands, l)nt also of all other districts, 

 the characters of which point iu diiferent directions. The improbability, however, 



