Here also we find again the same pyriform
shape of the unsegmented body, the same number and structure of the
feet, the same position of the median eye (which, however, is wanting in
Sacculina purpurea, and according to Darwin in some species of Lepas),
and the same position of the "buccal hood," as in the Nauplii of the
Prawns and Copepoda. From the latter the Nauplii of the Cirripedia and
Rhizocephala are distinguished by the possession of a dorsal shield or
carapace, which sometimes (Sacculina purpurea) projects far beyond the
body all round; and they are distinguished not only from other Nauplii,
but as far as I know from all other Crustacea, by the circumstance that
structures which are elsewhere combined with the two anterior limbs
(antennae), here occur separated from them.
The anterior antennae of the Copepoda, Cladocera, Phyllopoda (Leydig,
Claus), Ostracoda (at least the Cypridinae), Diastylidae, Edriophthalma,
and Podophthalma, with few exceptions relating to terrestrial animals or
parasites, bear peculiar filaments which I have already repeatedly
mentioned as "olfactory filaments." A pair of similar filaments spring,
in the larvae of the Cirripedia and Rhizocephala, directly from the
brain.
(FIGURE 56. Nauplius of Sacculina purpurea, shortly before the second
moult, magnified 180 diam. We may recognise in the first pair of feet
the future adherent feet, and in the abdomen six pairs of natatory feet
with long setae.
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