12 INTRODUCTION. 
have been established for species previously considered as separate. The study of 
the relations between young snails and their parents is of the highest importance in 
establishing these facts. 
(4) The abundant material, taken in connection with the results of Garrett, 
gives astonishingly clear evidence of a recent origin of some types, while it is possible 
also to determine their parentage and rate of dispersal, when this has occurred, as 
well as the fixity of the new characteristics. 
(5) Mutation has been demonstrated in numerous instances, and in many 
species belonging to several islands, so that it can not be regarded as a unique process. 
(6) The originative influence of the “environment” seems to be little or 
nothing. Isolation proves to be a “condition” and not a “factor” in differentiation 
of forms belonging to this genus. 
(7) A result with a wider scientific bearing is established by the intercomparison 
of the snail populations of islands of the same group and of the species of different 
groups. The evidence tends to prove that the dominant geological process in South 
Pacific regions has been one of subsidence, which has progressively isolated various 
mountain ranges previously connected, so that they have become separate island- 
masses, which in their turn have been subsequently converted into the disconnected 
islands of the several groups. Here and there the reverse process of uplifting has 
caused many islands to rise above the surface of the ocean, but such uplifts are 
relatively rare and they seem to be the secondary results of the dominant process 
of subsidence. It is obvious that this complex subject is one that can be discussed 
with profit only after the detailed biological results have been presented in full. 
