Investigation of the Origin of Insular Races of Land Mollusca in the Scilly Isles

Abstract

THE study of insular species of animals has for a long time been regarded as an important adjunct to evolutionary research, and the rôle of insular segregation as a factor in specific divergence has been stressed by numerous workers. It has of later years been held that one of the best ways of studying the effects of such isolation is the intensive survey of small groups of islands of tolerably recent formation, in which the divergence can be seen at its earliest stages and perhaps correlated with any incipient ecological divergence that may be manifest in the islands in question. Surveys of this kind have been made from time to time, but the result of such work seems as yet unsatisfactory for several reasons (e.g. insufficiency of material, lack of information as to the forms found on the adjacent mainland, and deficiency in ecological data). As a consequence an attempt has been set on foot in the present year to tackle the problem afresh, more particularly by means of intensive collecting and ecological study and in particular by detailed comparison of insular and mainland forms obtained from similar habitats. It is not claimed that more positive results will be obtained at once by these means than by the distinguished researches of previous workers; but it is hoped that a better approach to the problem may be provided. Thanks to financial assistance from the Government Grant Committee of the Royal Society and the Godman Exploration Fund of the Natural History Museum, a short reconnaissance was made last July in the Scilly Islands and west Cornwall for the purpose of studying the land mol-lusca of these areas.