Mollusca of Sandwich Isles 
external appearance when the environment is 
changed, In the one case the peculiarity is not 
inherited ; in the other it is inherited. 
The Wallaceian explanation is, of course, that 
the phenomenon is the result of natural selection. 
There must, say Wallace and his followers, be 
some differences in the environment, differences 
which we poor human beings cannot perceive, 
that have caused the divergence between the 
various isolated sections of the species. In the 
case of some local species this explanation is 
probably the correct one, but we have no hesita- 
tion in saying that natural selection is unable 
to offer a satisfactory explanation in a con- 
siderable number of instances. Take, for 
example, the case of the land mollusca of the 
Sandwich Islands. Mr Gulick worked for fifteen 
years at them, and states that so far as he is able 
to ascertain the environment in the fifteen valleys 
is essentially the same. ‘To argue,’ writes 
Romanes, on p. 17 of vol. iii. of Darwin and 
after Darwin, “that every one of some twenty 
contiguous valleys in the area of the same small 
island must necessarily present such differences 
of environment that all the shells in each are 
differently modified thereby, while in no one 
out of the hundreds of cases of modification in 
minute respects of form and colour can any 
human being suggest an adaptive reason therefor 
—to argue thus is merely to affirm an intrinsic- 
377 
