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 hesitation in saying that natural selection is unable to offer a satisfactory explanation in a considerable 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 therefore—to argue thus is merely to affirm an intrinsically improbable dogma in the presence of a great and consistent array of opposing facts.” Men of science not infrequently charge the clergy with adhering to dogma in face of opposing facts; it seems to us that many of the apostles of science are in this respect worse offenders than the most orthodox of Churchmen. The example of the mollusca of the Sandwich Islands is by no means a solitary one. D. Dewar cited some interesting cases in a paper recently read before the Royal Society of Arts (p. 103 of vol. lvii. of the Society’s Journal):