Perhaps the most powerful of all agents in the transportal of species by accidental means is man. But his actions may be accidental as well as intentional. We have therefore to distinguish between the animals disseminated all over the world by pure chance, and those which have been introduced into new countries purposely. Invertebrates, such as snails, centipedes, woodlice, beetles, and cockroaches, are constantly being unintentionally carried with vegetables, fruit, trees, and with timber from one country to another. Earthworms are sometimes transported in the balls of earth in which the roots of trees are enveloped. As regards molluscs, Mr. Kew believes (p. 178) that during the last three centuries at least, human agency has influenced their disposal more than all other causes taken together. A large number of species of invertebrates in America are said to owe their existence in that country to accidental introduction by man. In most cases, however, no particular reason can be assigned why they should have been thus introduced, and as a matter of fact there are always individual differences of opinion as to the precise number of such. Certain it is, that though the number of supposed introductions from Europe to America is very large, those which have been carried from America to Europe is exceedingly small. In fact, I remember only two instances of accidental animal importations from America which have firmly established themselves in Europe, viz., a small fresh-water mollusc, _Planorbis dilatatus_, and the much-dreaded vine-pest, _Phylloxera vastatrix_. As a rule the animals die out very shortly after their arrival on foreign soil. Many instances, nevertheless, are on record, especially in the case of molluscs, where snails thus transported have not only survived but are apparently in a flourishing condition and spreading. _Helix aspersa_, for example, our large garden snail, has been naturalised in many foreign countries by French and Portuguese sailors, who had taken them on board their ships as food.