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The Descent of Man

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sub-families, the males on first emergence from<br />

the pupal state, are coloured exactly like the<br />

females; but that their bodies in a short time<br />

assume a conspicuous milky-blue tint, owing to<br />

the exudation <strong>of</strong> a kind <strong>of</strong> oil, soluble in ether<br />

and alcohol. Mr. MacLachlan believes that in<br />

the male <strong>of</strong> Libellula depressa this change <strong>of</strong><br />

colour does not occur until nearly a fortnight<br />

after the metamorphosis, when the sexes are<br />

ready to pair.<br />

Certain species <strong>of</strong> Neurothemis present, according<br />

to Brauer (53. See abstract in the 'Zoological<br />

Record' for 1867, p. 450.), a curious case <strong>of</strong><br />

dimorphism, some <strong>of</strong> the females having ordinary<br />

wings, whilst others have them "very richly<br />

netted, as in the males <strong>of</strong> the same species."<br />

Brauer "explains the phenomenon on Darwinian<br />

principles by the supposition that the close<br />

netting <strong>of</strong> the veins is a secondary sexual character<br />

in the males, which has been abruptly<br />

transferred to some <strong>of</strong> the females, instead <strong>of</strong>,

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