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The Descent of Man

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tial character, for it is developed only during<br />

the summer; the young in their immature state,<br />

and the adults in their winter dress, being grey<br />

and black. With many kinds <strong>of</strong> gulls (Larus),<br />

the head and neck become pure white during<br />

the summer, being grey or mottled during the<br />

winter and in the young state. On the other<br />

hand, with the smaller gulls, or sea-mews (Gavia),<br />

and with some terns (Sterna), exactly the<br />

reverse occurs; for the heads <strong>of</strong> the young birds<br />

during the first year, and <strong>of</strong> the adults during<br />

the winter, are either pure white, or much paler<br />

coloured than during the breeding-season. <strong>The</strong>se<br />

latter cases <strong>of</strong>fer another instance <strong>of</strong> the capricious<br />

manner in which sexual selection appears<br />

<strong>of</strong>ten to have acted. (53. On Larus, Gavia,<br />

and Sterna, see Macgillivray, 'History <strong>of</strong> British<br />

Birds,' vol. v. pp. 515, 584, 626. On the Anser<br />

hyperboreus, Audubon, 'Ornithological Biography,'<br />

vol. iv. p. 562. On the Anastomus, Mr.<br />

Blyth, in 'Ibis,' 1867, p. 173.)

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