IO INTRODUCTION. 
with my own studies, particularly because the phenomena of distribution are similar 
and because these snails are close relatives of the Partule of Polynesia. No snails 
were obtained in Tonga or Fiji, as the islands of these groups in which Partule are 
reported to occur are small and relatively inaccessible. In all of the places visited, 
however, the exploration and detailed study of each additional group, island, and 
island-region established results which by contrast or similarity brought into clearer 
relief many features of great importance which had been previously noted elsewhere. 
The initial journey was made under the auspices of the American Museum of 
Natural History; those of 1907 and 1908 were under the auspices of the Carnegie 
Institution of Washington, as well as that of 1909, when the writer had become an 
officer of the American Museum. To the friends of scientific research and of the 
American Museum who made it possible for the work to be begun, to the President 
and Trustees of the American Museum, and to the President and Trustees of the 
Carnegie Institution of Washington, these memoirs are offered as a partial and inade- 
quate acknowledgment of the writer’s indebtedness for the several opportunities 
afforded him for carrying on the investigations herein and hereafter described. 
Since 1899 the writer has been engaged in laboratory researches upon the 
problems of variation, correlation, and selection in the case of certain saturnid 
moths, the quantitative results remaining unpublished in the main on account of 
their bulk and laborious statistical analysis; but the qualitative results were of 
such a nature that it seemed desirable to supplement them by an investigation 
which would determine the role played by environment as a whole in the differen- 
tiation of species and varieties existing under entirely natural conditions. Directed 
by an interest in the general subject of molluscan distribution, and specifically by 
the brilliant and suggestive research of Mayer upon the Partule of Tahiti, as well 
as by Mayer’s personal advice, the writer undertook the close and detailed study 
in the field of that genus of terrestrial pulmonates. It may be stated at this junc- 
ture that no region could possibly be more favorable than Polynesia for the study 
of the problems in question; the writer cordially indorses the opinion of Mayer 
that the volcanic and other islands of the South Seas offer a field that in almost 
every respect attains the ideal of the biologist—a fact that will receive due enlarge- 
ment and emphasis beyond. 
Three primary subdivisions of the investigation were made at the outset. The 
first was a study of the problem of isolation and environmental influences as “con- 
ditions” or “factors” of biological differentiation. These have been variously 
estimated in the writings of naturalists from Darwin, Wagner, Murray, Wallace, 
Gulick, and Romanes to Allen, Jordan, Ortmann, and others, who have dealt with 
various groups of animals, and who have accorded to the “environment” almost all 
degrees of efficiency from omnipotence to impotence. In pursuance of this purpose 
it was planned to collect the snails as extensively as possible from all the valleys of 
the islands, thus to extend the observations of Mayer in Tahiti, and to make a 
complete survey of the whole group for comparison with the earlier observations 
of Garrett, who of all systematists concerned with the fauna of Polynesia has given 
the fullest and most circumstantial account of the distribution in his time of Par- 
