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The Descent of Man

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service to them, and from the females <strong>of</strong> other<br />

species moulting twice yet retaining the same<br />

colours throughout the year, we may conclude<br />

that the habit <strong>of</strong> annually moulting twice has<br />

not been acquired in order that the male should<br />

assume an ornamental character during the<br />

breeding-season; but that the double moult,<br />

having been originally acquired for some distinct<br />

purpose, has subsequently been taken<br />

advantage <strong>of</strong> in certain cases for gaining a nuptial<br />

plumage.<br />

It appears at first sight a surprising circumstance<br />

that some closely- allied species should regularly<br />

undergo a double annual moult, and others<br />

only a single one. <strong>The</strong> ptarmigan, for instance,<br />

moults twice or even thrice in the year,<br />

and the blackcock only once: some <strong>of</strong> the<br />

splendidly coloured honey-suckers (Nectariniae)<br />

<strong>of</strong> India and some sub-genera <strong>of</strong> obscurely<br />

coloured pipits (Anthus) have a double,<br />

whilst others have only a single annual moult.

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