On its way west in the Pacific the Beagle spent a month at the Galapagos Archipelago, which lies under the equator five or six hundred miles from the mainland. "Most of the organic productions are aboriginal creations, found nowhere else; there is even a difference between the inhabitants of the different islands; yet all show a marked relationship with those of America." Why should the plants and animals of the islands resemble those of the mainland, or the inhabitants of one island differ from those of a neighboring island? Darwin had always held that species were created immutable, and that it was impossible for one species to give rise to another. In the Galapagos Archipelago he found only one species of terrestrial mammal, a new species of mouse, and that only on the most easterly island of the group. On the South American continent there were at least forty species of mice, those east of the Andes being distinct from those on the west coast. Of land-birds he obtained twenty-six kinds, twenty-five of which were to be found nowhere else. Among these, a hawk seemed in structure intermediate between the buzzard and polyborus, as though it had been modified and induced to take over the functions of the South American carrion-hawk. There were three species of mocking-thrush, two of them confined to one island each. There were thirteen species of finches, all peculiar to the archipelago. In the different species of geospiza there is a perfect gradation in the size of the beaks, only to be appreciated by seeing the specimens or their illustrations. Few of the birds were of brilliant coloration. The same was true of the plants and insects. Darwin looked in vain for one brilliant flower. This was in marked contrast to the fauna and flora of the South American tropics. The coloration of the species suggested comparison with that of the plants and animals of Patagonia. Amid brilliant tropical plants brilliant plumage may afford means of concealment, as well as being a factor in the securing of mates.