The Galapagos Islands lie 1,000 kilometres distant from the coast of South America, and they too harbour twenty-one endemic species of land-birds, among them a duck, a buzzard, and about a dozen different but nearly related mocking-birds, each of which is found in only one or two of the fifteen islands. The group of islands also possesses peculiar reptiles, and they take their name from the gigantic land-tortoises, sometimes 400 kilogrammes in weight, which in Tertiary times inhabited also the continent of South America, but are now found in the Galapagos Islands only. The islands also possess endemic lizards of the genus _Tropidurus_, and although the lizards can no more have been transported across the ocean than the tortoises, but corroborate the conclusion drawn from geological data, that the islands were still connected with the mainland in Tertiary times, the occurrence of a particular species of _Tropidurus_ upon almost every one of the fifteen islands testifies anew to the mysterious influence of isolation, for most of these islands are quite isolated regions for the different species of lizard, even more than for the mocking-birds, which have also split up into a series of species. We are thus led to the hypothesis, which was first introduced into the Evolution Theory by Darwin, that the prevention of constant crossing of an isolated colony with the others of the same species from the original habitat favours the origin of new endemic species, and his conclusion is confirmed when we learn that islands like the Galapagos group possess twenty-one endemic land-birds, but only two endemic sea-birds out of eleven, for the latter traverse great stretches of sea, and crossings with others of the same species on the neighbouring continental coasts will often take place. The Bermuda Islands also afford a proof that the development of endemic species is prevented by regular crossing with other members of the species from the original habitat, for although they are 1,200 kilometres distant from the continent of North America--that is, further than the Galapagos Islands from South America--they possess no endemic species of bird, and we may undoubtedly associate this with the fact that the migratory birds from the continent visit the Bermudas every year. Madeira also confirms our conclusion, for only one of the ninety-nine species of bird occurring there can be regarded as endemic, and it has often been observed that birds from the neighbouring African mainland (only 240 kilometres distant) are driven across to Madeira. Terrestrial snails, on the other hand, will seldom be carried to Madeira by birds, and accordingly we find there an extraordinary number of endemic terrestrial snails, namely, 109 species.