122 THE AMERICAN MUSEUM JOURNAL 
of the state of Mississippi there is an extensive fishery of the paddlefish 
(Polyodon folium) which is in charge of Mr. J. E. McGehee, a friend of 
the Museum, who put at its service his launches, fishermen and nets. 
There was thus offered an unusual opportunity for securing the desired 
collection, which was further improved by the fact that during the present 
spring a lake, Moon Lake, was to be fished, which had not been netted 
before. The collecting party consisted of Dr. L. Hussakof and Mr. 
Dwight Franklin. ‘They report excellent success in collecting speci- 
mens and in obtaining casts and color studies which will ultimately be 
used in the preparation of habitat groups. 
A FOURTH JOURNEY TO THE SOUTH SEAS 
URING the years 1906 to 1908, inclusive, I made three voyages to 
Tahiti and the other islands of the Society group, under the au- 
spices of the American Museum and of the Carnegie Institution 
of Washington. ‘The purpose was the investigation of the land-snails of 
these islands, and each year the results proved so unexpectedly satisfac- 
tory that further explorations were found desirable and were accordingly 
planned and carried out. My fourth journey, that of 1909, extended 
over about 15,000 miles of the Pacific Ocean and involved travels in 
seven groups of islands (the Society, Cook, New Zealand, Tongan, 
Samoan, Fijian and Hawaiian) while some of the Paumotus were seen 
in passing. My route is shown in the chart on page 125. The investi- 
gation of the land-snails of the Polynesian region was undertaken on 
account of the unusually favorable conditions for the study of certain 
evolutionary results and processes. Every biologist is familiar with 
Gulick’s famous writings of the last quarter of the nineteenth century, 
in which he demonstrates that the Achatinellid land-snails of the Hawai- 
ian Islands vary from valley to valley and from island to island of the 
group. As descendants of a common ancestral stock the different valley 
colonies and island types are the products of divergent evolution in corre- 
lation with their greater or lesser degrees of isolation. ‘The efficiency of 
differing environmental conditions as actual factors in the process of 
species differentiation has been variously estimated by writers like 
tomanes, Jordan, Allen, Wallace and others, who have dealt with 
