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Updated: May 17, 2025
In the great class of the Crustacea, forms wonderfully distinct from each other, namely, suctorial parasites, cirripedes, entomostraca, and even the malacostraca, appear at first as larvae under the nauplius-form; and as these larvae live and feed in the open sea, and are not adapted for any peculiar habits of life, and from other reasons assigned by Fritz Muller, it is probable that at some very remote period an independent adult animal, resembling the Nauplius, existed, and subsequently produced, along several divergent lines of descent, the above-named great Crustacean groups.
It is true, that we long ago knew that the Cyclopes of our fresh waters were excluded in the Nauplius-form, and that we were acquainted with some others of their young states; we had learnt, through Nordmann, that the same earliest form belonged to several parasitic Crustacea, which had previously passed, almost universally, as worms; but the connecting intermediate forms which would have permitted us to refer the regions of the body and the limbs of the larvae to those of the adult animal, were wanting.
In these also the brood bursts out in the Nauplius-form, and speedily strips off its earliest larva-skin which is distinguished by no peculiarities worth noticing. A pair of similar filaments spring, in the larvae of the Cirripedia and Rhizocephala, directly from the brain. Nauplius of Sacculina purpurea, shortly before the second moult, magnified 180 diam.
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