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The development of the Zoea-brood to the sexually mature animal was traced by Spence Bate in Carcinus maenas. He proved that the metamorphosis is a perfectly gradual one, and that no sharply separated stages of development, like the caterpillar and pupa of the Lepidoptera, could be defined in it. The development of the Palinuridiae seems to be very peculiar.
"Once in the year," says Troschel's 'Handbuch der Zoologie, "they migrate in great crowds to the sea in order to deposit their eggs, and afterwards return much exhausted towards their dwelling places, which are reached only by a few." The most important peculiarities which distinguish this Zoea-brood from the adult animal, are as follows:
Full number of limbs not produced in the egg. Zoea-brood. Ord. 6. Ametabola. Full number of limbs produced in the egg. This sample may suffice. The farther we go into details in this direction, the more brilliantly, as may easily be imagined, does the naturalness of such an arrangement as this force itself upon us.
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