Note 57 — Chapter IV · ORGANS AND CHARACTERS OF VARIATION.

Although, in our ignorance of their real nature, we cannot cite them as actually analogous to these separate phases in certain members of the Insecta, yet we are forcibly reminded by the latter of the distinct states which many of the Terrestrial Mollusca present (frequently in equal proportions) in the same localities. Thus, most of the Pupæ have at least two abruptly-marked forms,—a larger and smaller one. Many of the Helices also exhibit this tendency in an eminent degree: I have indeed been shown specimens by Sir Charles Lyell of the Helix hirsuta, Say, from North America, one state of which is considerably more than double the dimensions of the other; and I believe it is a well-known fact that intermediate links have not yet been observed to connect the extremes. May not therefore the gigantic H. Lowei and Bowdichiana, which are now extinct in the Madeira Islands, have been but forms of the H. Portosanctana and punctulata, respectively,—co-existent with them, though more sensitive to the great diminutions of altitude and area which were consequent on the breaking-up of a once continuous land? If such be the case, however, it is certain that they were far commoner at an early period than their smaller colleagues (which, now, in their proper districts, absolutely teem),—seeing that the latter are extremely rare in the fossil deposits, whilst they themselves literally abound.