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The Descent of Man

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projection, and the teeth grow into regular<br />

fangs, <strong>of</strong>ten more than half an inch in length.<br />

With the European salmon, according to Mr.<br />

Lloyd (9. 'Scandinavian Adventures,' vol. i.<br />

1854, pp. 100, 104.), the temporary hook-like<br />

structure serves to strengthen and protect the<br />

jaws, when one male charges another with<br />

wonderful violence; but the greatly developed<br />

teeth <strong>of</strong> the male American salmon may be<br />

compared with the tusks <strong>of</strong> many male mammals,<br />

and they indicate an <strong>of</strong>fensive rather than<br />

a protective purpose.<br />

<strong>The</strong> salmon is not the only fish in which the<br />

teeth differ in the two sexes; as this is the case<br />

with many rays. In the thornback (Raia clavata)<br />

the adult male has sharp, pointed teeth, directed<br />

backwards, whilst those <strong>of</strong> the female are<br />

broad and flat, and form a pavement; so that<br />

these teeth differ in the two sexes <strong>of</strong> the same<br />

species more than is usual in distinct genera <strong>of</strong><br />

the same family. <strong>The</strong> teeth <strong>of</strong> the male become

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