The carapace folds itself together, so that the little animal acquires
the aspect of a bivalve shell, the foremost limbs become transformed
into very peculiar adherent feet ("prehensile antennae," Darwin), and
the two following pairs are cast off; like the frontal horns. On the
abdomen six pairs of powerful biramose natatory feet with long setae
have been formed beneath the Nauplius-skin, and behind these are two
short, setigerous caudal appendages (Figure 58).

The pupae of the Cirripedia (Figure 57), which are likewise astomatous,
agree completely in all these parts with those of the Rhizocephala, even
to the minutest details of the segmentation and bristling of the
natatory feet;* they are especially distinguished from them by the
possession of a pair of composite eyes. (* Compare the figure given by
Darwin (Balanidae Plate 30 Figure 5) of the first natatory foot of the
pupa of Lepas australis, with that of Lernaeodiscus Porcellanae
published in the 'Archiv fur Naturgeschichte' (1863 Taf 3 Figure 5). The
sole distinction, that in the latter there are only 3 setae at the end
of the outer branch, whilst in the Cirripedia there are 4 on the first
and 5 on the following natatory feet, may be due to an error on my
part.) Sometimes also traces of the frontal horns seem to persist.* (*
Darwin describes as "acoustic orifices" small apertures in the shell of
the pupae of the Cirripedia, which, frequently surrounded by a border,
are situated, in Lepas pectinata, upon short, horn-like processes. I
feel scarcely any hesitation in regarding the apertures as those of the
"shell-glands," and the horn-like processes as remains of the frontal
horns.)

As the Cirripedia and Rhizocephala now in general resemble each other
far more than in their Nauplius-state, this is also the case with the