There is, on the whole, a great diversity of opinion as to how the European fauna has originated; however, except in Dr. Kobelt's work, no attempt has hitherto been made to collect together all the available information, and to include in the inquiry more than one class of animals. The little work which I venture to bring before the public will not by any means exhaust the subject, nor is our knowledge of the European fauna sufficient to give more than a mere sketch of many of the animal groups mentioned. As we have learned in the introduction, different classes of animals are not all of equal importance in indicating the changes which have taken place in the distribution of land and water. While Dr. Kobelt is of opinion that the land-snails are by far the most important in such an inquiry, Mr. Lydekker believes that mammals afford the safest and truest indications of such changes. Mr. Beddard puts in a claim for earthworms, as even a narrow strait of sea-water forms an insuperable barrier to their dispersion. Dr. Wallace agrees with Mr. Lydekker, and goes so far as to say (p. 74) that "whenever we find that a considerable number of the mammals of two countries exhibit distinct marks of relationship, we may be sure that an actual land-connection, or at all events an approach to within a very few miles of each other, has at one time existed." Besides the groups referred to, I claim that particular attention should be devoted to Amphibia, which, contrary to Wallace, I hold do not possess special facilities for dispersal; and also to spiders and to all wingless animals leading a subterranean life, such as some of the wood-lice, planarian worms and apterous beetles.