swiftness to a distance of 660 geographical miles. As this Helix has a thick calcareous operculum, I removed it, and when it had formed a new membranous one, I again immersed it for fourteen days in sea-water, and again it recovered and crawled away. Baron Aucapitaine has since tried similar experiments: he placed one hundred land-shells, belonging to ten species, in a box pierced with holes, and immersed it for a fortnight in the sea. Out of the hundred shells, twenty-seven recovered. The presence of an operculum seems to have been of importance, as out of twelve specimens of Cyclostoma elegans which it thus furnished, eleven revived. It is remarkable, seeing how well the Helix pomatia resisted with me the salt-water, that not one of fifty-four specimens belonging to four other species of Helix tried by Aucapitaine, recovered. It is, however, not at all probable that land-shells have often been thus transported; the feet of birds offer a more probable method."

We have here positive evidence that such shells as Helix pomatia and Cyclostoma elegans might easily be transported to an island from the mainland. The former occurs in France, Holland, and England, and the latter all along western continental Europe and England. And yet neither of these species inhabits the Canary Islands, Madeira, or Ireland, none of which are at too great a distance from Europe to be within easy reach for a floating object. The fact that Cyclostoma elegans does not live in Ireland is of particular interest in connection with the floating-theory just quoted, as on all sides of Ireland dead specimens have been picked up on the shore, showing that marine currents carry specimens and have thus transported them for countless centuries. Nevertheless the species has not established itself in Ireland. If such a fate meets a land-shell of the type of Cyclostoma elegans, it may be asked, with some justification, what chance slugs or the smaller non-operculated species would have to reach an island like Ireland alive from the mainland, and to colonise it successfully.

Both slugs and their eggs are killed by a short immersion in sea-water, as I have proved experimentally. I have also subjected slugs, in the act of crawling on twigs, to an artificial spray of sea-water. This seemed to irritate their tender skins to such an extent that they curled themselves up, released their hold on the twig and let themselves drop to the ground. If we supposed, therefore, that a slug had successfully reached the sea, transported on a tree-trunk, the moisture would tend to lure it forth from its hiding-place under the bark, whilst the mere spray would prove fatal to its existence. Those species of snails and slugs which lead an underground existence, rarely venturing above ground, such as Testacella and Coecilianella, would have even less chance of being accidentally carried to some distant island.

The suggestion advanced by Darwin (p. 353), that young snails just hatched might sometimes adhere to the feet of birds roosting on the ground and thus be transported, appears to me so extremely improbable as to be scarcely worth serious consideration. Indeed, as Darwin himself acknowledged later on, it does not help us very much to suggest possible modes of transport. What we require is direct evidence. How far we are, however, from obtaining it, may be inferred from Mr. Kew's remark (p. 119), that "we have little or no actual evidence of precise modes of dispersal even for short distances on land."

A very curious statement was made by a well-known French conchologist, the late M. Bourguignat, with regard to introductions of mollusca. Whether he had any actual facts collected in support of it, I cannot say, but he maintained that species accidentally transported, with the exception of those under maritime influence, can only be acclimatised from north to south, and not from south to north—from east to west, but not from west to east (p. 353).

The whole theory of the accidental or abnormal dispersal of mollusca appears to have been originated by Darwin, in order to account for their presence on so-called Oceanic islands. His views were strongly supported by Wallace, who defines these islands (p. 243) as those which are of volcanic or coralline formation usually far from continents, entirely without indigenous land mammals or amphibians, but with a fair number of birds and insects, and usually with some reptiles.

I do not wish it to be understood that I am in any way undervaluing the great works of these distinguished naturalists. Darwin's views have had more influence in advancing Zoology than those of any man, and his fame is unassailable. Nevertheless, I feel that his theories regarding the origin of the faunas of oceanic islands require revision.

The formerly prevalent belief of the permanence of ocean basins has been shaken by the utterances of some of the greatest geologists of our day, whilst many positively assert that what is now deep sea of more than 1000 fathoms was dry land within comparatively recent geological epochs. Thus the Azores are classed by Darwin and Wallace among the oceanic islands—that is to say, among such as have received their fauna and flora by flotsam and jetsam. But Professor Neumayr believes, on geological grounds, that the Old and New Worlds were connected by a land-bridge during Tertiary times right across the Atlantic, and that the Canary Islands, Madeira, and Azores (p. 547) are the last remnants of this continent. This meets with the entire approbation of Dr. von Ihering, who has recently re-investigated the subject from a faunistic point of view (p. 135). Take another instance of one of Wallace's most typical oceanic islands, the Galapagos Group. Their fauna and flora have recently been most thoroughly re-explored by an American expedition, the result of which, according to Dr. Baur, goes to show that these islands must have formed part of the mainland of South America at no distant date. The fauna and flora are therefore to be regarded as having reached them in the normal mode, viz., by migration on land. According to Mr. Beddard (p. 138), it is difficult to see how earthworms could be transported across the sea. Floating tree-trunks have been observed far out at sea, but unless the water remained absolutely calm during the long period necessary for the drifting by currents so that no splashing occurred, the worms would probably be killed. Yet earthworms do occur on oceanic islands. It is indeed quite possible that our views with regard to the origin of the remainder of the Pacific Islands may change very materially, and once more revert to what Dr. Gould expressed nearly fifty years ago in the following words: "From a consideration of the land-shells on the Pacific Islands, it seems possible to draw some fair inferences as to the relations of the lands which once occupied the area of the Pacific Ocean, and whose mountain peaks evidently now indicate or constitute the islands with which it is now studded." Indeed Dr. von Ihering goes so far as to positively state that in his opinion the Polynesian Islands are not volcanic eruptions of the sea floor, which being without life were successively peopled from Australia and the neighbouring islands, but the remains of a great Pacific continent, which was in early mesozoic times connected with other continental land masses (a, p. 425).

Before coming to a decision on the part played by flotsam and jetsam in the constitution of an island fauna, those who have studied the problem on the spot should, however, have a voice in the matter. And though, from my experience in northern latitudes, I feel sure that island faunas there are but slightly affected by occasional