from a cooler climate, and have not been able to don a tropical garb; or perhaps they belong to a far-back age, when the vegetable kingdom also was less rich in colouring than it is at present, and the birds were in harmony with it. This, indeed, seems still to be the character of the Galapagos plants, which Darwin says have "a wretched, weedy appearance," without gay flowers, though later visitors have expressed a more favourable opinion. These plants are in themselves very remarkable, for they are largely peculiar species, and are in many cases confined to particular islands, having apparently been unable to cross from one island to another, though in some way able to reach the group. The explanation is that they resemble North American plants, and came to the Galapagos at a time when a wide strait separated North and South America, allowing the equatorial current to pass through, and drift plants to the Galapagos, where they have been imprisoned ever since. This was probably in Miocene times, and when we know more of the Miocene flora of the southern part of North America we may hope to recover some of the ancestors of the Galapagos plants. In the meantime their probable origin and antiquity, as stated by Wallace, render unnecessary any hypothesis of modification. Before leaving this subject, it is proper to observe that on the continents themselves there are many remarkable cases of isolation of species, which help us better to understand the conditions of insular areas. The "variable hare" of the Scottish highlands, and of the extreme north of Europe, appears again in the Alps, the Pyrenees, and the Caucasus, being in these mountains separated by a thousand miles of apparently impassable country from its northern haunts. It no doubt extended itself over the intervening plains at a time when Europe was colder than at present. Another curious case is that of the marsh-tit of Europe. This little bird is found throughout south-western Europe. It reappears in China, but is not known anywhere between. In Siberia and northern Europe there is, however, a species or distinct race which connects these isolated patches. In this case, if the Siberian species is truly distinct, we have a remarkable case of isolation and of the permanence of identical characters for a long time; for in that case this bird must be a survivor of the Pliocene or Miocene time. On the other hand, if, as is perhaps more likely, the marsh-tit is only a local variety of the Siberian species, we have an illustration of the local recurrence of this form when the conditions are favourable, even though separated by a great space and long time.