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There were, I believe, perfect Insects before larvae and pupae; but, on the contrary, Nauplii and Zoeae far earlier than perfect Prawns. In contradistinction to the INHERITED metamorphosis of the Prawns, we may call that of the Coleoptera, Lepidoptera, etc. an ACQUIRED metamorphosis.* In favour of this view we have:
All this is wanting in the young Rhizocephala. The Nauplii of the Cirripedia have to undergo several moults whilst in that form; the Nauplii of the Rhizocephala, being astomatous, cannot of course live long as Nauplii, and in the course of only a few days they become transformed into equally astomatous "pupae," as Darwin calls them.
He shook his head hopelessly, turned, and went downstairs. He lit the dining-room lamp, got out a cigar, and began pacing the room, ejaculating. Now and then he would argue with himself. "Invisible!" he said. "Is there such a thing as an invisible animal? ... In the sea, yes. Thousands millions. All the larvae, all the little nauplii and tornarias, all the microscopic things, the jelly-fish.
It may, however, be remarked, that the different curvature of the embryo in the Amphipoda and Isopoda is so far instructive, as it proves that their present mode of development was adopted only after the separation of these orders, and that, in the primitive stock of the Edriophthalma, the embryos were, if not Nauplii, at least short enough in the body to find room in the egg in an extended position, like the larvae of Achtheres enclosed by the Nauplius-skin.
Notwithstanding their agreement in this important peculiarity, the Nauplii of these two orders present material differences in many other particulars. The young Cirripedes have a mouth, stomach, intestine, and anus, and their two posterior pairs of limbs are beset with multifarious teeth, setae, and hooks, which certainly assist in the inception of nourishment.
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