170 mr. w. h. hudson on the [Mar. 3, 



the two kinds of divergence, essentially different in origin, may be di- 

 stinguished 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 vari- 

 ation ; for not one circumstance in the history of the genus could in- 

 cline 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. Iu 

 the following instances we have, I think, examples of these two kinds 

 of divergence. 



All the wild Pigeons of La 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 incon- 

 gruous. Such a habit can only be due to the special conditions in 

 which the bird is placed — that is, to the shelterless plains with nu- 

 merous burrows in which alone it can find security from persecution. 

 One of the common Pampas butterflies, the Pyrantels 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. 

 On 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 Pyrantels 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. 



