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exhibited by a certain furm is dne to the form having come under the inflnence of 

 the biological factors of the respective- district at an earlier period than another 

 form which shows a less high degree of divergency, unless the sensitiveness of the 

 forms has been tested by experiment. And again, the higher or lesser degree of 

 geographical isolation, though often corresponding to the greater or lesser diversity 

 of the isolated forms, is a factor the actual influence of which it is in a given 

 case scarcely possible to estimate rightly. The great diversity of the representative 

 of Pripilio peranfhus on the island of 8nmba compared with the lesser diversity 

 between the representatives inhabiting Java, Sambawa, Timor, Kalao and Djampea, 

 Celebes, etc. ; the high degree of specialisation of the representative of Papilio 

 memnon ou Timor compared with the lesser degree of divergency of the forms 

 occurring on Sumba, iSambawa, Lombok, Java, etc.; the absence of a difference 

 between some Lombok and Java forms of Papilio which on the other lesser Sunda 

 Islands have developed divergently, compared with the presence of a difference in 

 other Lombok forms ; the great similarity between the specimens of Papilio sarpedoii 

 found in the area extending from N.W. India to Lombok, the gradual transition to 

 the more divergent Adonara form, and the obvions divergency in the pattern and 

 shape of the wings and the sexual armature (of the t?) of the forms inhabiting 

 Sumba, Timor, and \\'etter respectively, compared with the great diversity of so 

 many forms in N. India, Sumatra, Java, Lombok, Sambawa, and Adonara ; the 

 identity of the Malayan form of Papilio aristeus on the Philijiitines, Borneo, the 

 lesser Sunda Islands, and the island of Djampea, comj)ared with the great diversity 

 exhibited in the same area by Papilio memnon and other species, and so on, are 

 phenomena which seem to us most readily explainable by the surmise that the 

 diverse species are sensitive in a different degree to the external biological factors ; 

 while the surprisingly great divergency of so many Celebensian Papilios must be attri- 

 buted to a high intensity of the biological factors on that islanil and to a high degree 

 of geographical isolation. However, it does not appear to us very probable that the 

 narrow sea between Celebes and Borneo i.s a sufficiently effective barrier to prevent 

 passive migration * of the wides2)read and common low-land Papilios of Borneo, 

 such as P. ayamemnon, sarpedon, polytes, etc., from Borneo to Celebes; and the 

 same could be said of 'New Guinea, New Britain, and other islands. In fact the 

 absence of intergraduate specimens between two representative forms in localities 

 which are geographically close together — the intergradations may occur in other 

 localities — makes it manifest to us that, as the effect of the biological factors would 

 in these cases be annihilated, or at least much les.sened, b}' specimens of the old 

 stock coming into the country in consequence of the insufficiency of the geographical 

 barrier, there must lie another factor active to assist the external biological factors 

 to such a degree that the migration of fresh individuals, if it does not take place 

 very often, is not able to prevent divergent development. Now, recalling to mind 

 the kind of variation in the scent-organs found to exist in a certain moth, as men- 

 tioned ou p. 43.T, it is evident that where such a variation takes place in the 

 geographical forms of a species the difference in the organs of smell and scent must 

 be of great influence as preventing (to a certain extent) intercrossing between racial 



* Passive migration by means of hurrieaaes seems to occur often among birds, as the records of foreign 

 birds found in England prove ; in the case of Lepidoptera the power of resistance is certainly slighter, but 

 the effect of migration in respect to intercrossing with specimens of the same species in the new locality 

 will often be annihilated in consequence of the ncw-comern having too much suffered to tie fit for 

 propagation. 



