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Show 1 70 MR. W. H. HUDSON ON THE [Mar. 3, the two kinds of divergence, essentially different in origin, may be distinguished in much the same way as in divergences from type in structure, colour, &c. A horse clothed with hair 6 inches long would afford an instance of divergence arising from the laws of variation ; for not one circumstance in the history of the genus could incline one to believe it an instance of reversion of type *. But the stripes on the dun horses and on mules are attributed to recurrence to an ancestral type, because other species of Equus are striped. In the following instances we have, I think, examples of these two kinds of divergence. All the wild Pigeons of L a Plata (four in number), when feeding, walk upon the ground in a somewhat leisurely manner. The Zenaida maculata of Patagonia, which in its other habits so closely resembles the La-Platan Zenaida when feeding hurries about, snatching up its food with such marvellous rapidity that the most animated motions of other birds that feed on the ground in flocks seem languid in comparison. This lively habit of the Patagonian Pigeon, in which it differs so much from its congeners, is, I believe, due to the conditions of life. The barren soil and scanty vegetation of the region it inhabits requires in an exclusively seed-eating species that goes in large bodies a far greater activity than is necessary in the rich fertile regions further north. When pursued by a bird of prey or by a man on horseback, the Nothura maculosa escapes into the burrows of the Vizcacha or Armadillo. To take refuge in burrows is not, I believe, a habit of any other gallinaceous species, but in every thing (structure, colour, and habits) they all appear to be beautifully adapted to elude their enemies on the exposed surface of the earth ; so that the habit of the Buenos-Ayrean Partridge seems very incongruous. Such a habit can only be due to the special conditions in which the bird is placed-that is, to the shelterless plains with numerous burrows in which alone it can find security from persecution. One of the common Pampas butterflies, the Pyrameis carye, has a remarkable habit: when not feeding, it alights on the bare ground rather than on plants; and immediately on alighting it opens its wings and turns itself rapidly about till placed in such a position that the sun shines directly on the sloping surface of the wings and body. O n cold days, when other species of Lepidoptera sit with closed wings amidst the leaves and appear weak and languid, the P. carye basks with open wings upon the barren ground, and is then just as shy and lively as when the weather is warm. This sun-loving habit is identical in one of our birds, the Cyanocorax pileatus, described in a former paper. Every year many individuals of P. carye survive the winter; and their extreme hardiness is perhaps attributable to the heat-catching habit. Two other Lepidopteres also possess the habit; but it is far less perfect in them, and they never live through the winter. This habit of our Pyrameis and Cyanocorax I am also inclined to attribute to variation induced by the conditions of life. *_The hide of a long-haired variety of the horse was brought by the Tehuelcho Indians to the settlement on the Eio Negro of Patagonia a few years ago. |
