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The Descent of Man

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that as soon as he saw its happy sense <strong>of</strong> security,<br />

he felt sure that it was uneatable. After several<br />

trials he succeeded in tempting a young<br />

duck to snatch up a young one, but it was instantly<br />

rejected; and the duck "went about jerking<br />

its head, as if trying to throw <strong>of</strong>f some<br />

unpleasant taste."<br />

With respect to sexual differences <strong>of</strong> colour, Dr.<br />

Gunther does not know <strong>of</strong> any striking instance<br />

either with frogs or toads; yet he can <strong>of</strong>ten distinguish<br />

the male from the female by the tints<br />

<strong>of</strong> the former being a little more intense. Nor<br />

does he know <strong>of</strong> any striking difference in external<br />

structure between the sexes, excepting<br />

the prominences which become developed during<br />

the breeding-season on the front legs <strong>of</strong> the<br />

male, by which he is enabled to hold the female.<br />

(47. <strong>The</strong> male alone <strong>of</strong> the Bufo sikimmensis<br />

(Dr. Anderson, 'Proc. Zoolog. Soc.' 1871, p. 204)<br />

has two plate-like callosities on the thorax and<br />

certain rugosities on the fingers, which perhaps

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