Crampton, The Principles of Geographical Distribution etc. 645 



upon the Partulae of Tahiti, I initiated and prosecuted during 

 four years the studies upon various species of this genus of ter- 

 restrial molluscs, and the general qualitative results it is now 

 my privilege to present. 



It maj' be recalled in a purely formal manner that the 

 problems of geographical distribution involve a wide series of 

 factors quite diverse in nature; among these are geological, cli- 

 matological and topographical conditions which stand in sharp 

 contrast to the heterogeneric and homogeneric biological influences 

 affecting the lives of organisms. All of these various factors parti- 

 cipate in the production of a particular status quo ofa 

 given species, and they must be accorded their proper respective 

 values for the determination of specific organic qualities as well 

 as of specific organic situations. 



The Field of Investigation. During four journeys 

 undertaken in 1906, 1907, 1908 and 1909, explorations were 

 carried on in the Society, Cook, Tonga, Fiji, Samoan and 

 Hawaiian Islands. The field studies were made complete as far 

 as the Society Islands were concerned for this group is of the 

 greatest interest because it is the headquarters of the genus in- 

 vestigated. 



The Material of Investigation. The organic 

 forms selected for study were terrestrial pulmonate snails belonging 

 to the genus Partula Fer. This genus occurs only in the South 

 Pacific Ocean, mainly in Polynesia, although some species are 

 recorded from Melanesia. These animals are of particular in- 

 terest because, as Garrett and Mayer have shown, their 

 discontinuous distribution resembles that of the classic Achatinel- 

 lidae of the Hawaiian Islands. Furthermore, they are viviparous, 

 thus providing abundant data for the determination of inheritance ; 

 while finally they exhibit indubitable evidences of mutation. In 

 the Society Islands more than two hundred Valleys of the seven 

 largest islands havebeen explored and more than one hundred 

 thousand adult individuals have been collected for the purposes 

 of the present study. 



The principles of geographical distribu- 

 tion o f Partula. Under the present limitations of time and 

 space it is impossible to give the füll evidences for the results 

 presendet herein. The general principles will be stated together 

 with characteristic data illustrating the whole series of facts in 

 hand. 



A. When a comparison is made of the various species of 

 Partula inhabiting the island groups of Polynesia it appears that 

 each group possesses peculiar species with one single exception 

 Furthermore, the Partulae of any group resemble most closely 

 the species of a neighboring Cluster of islands. In general the 

 relations everywhere in Polynesia are identical, — that is, the 



