Cirripedes, vision
seems confined to the perception of the shadow of an object passing
between them and the light; they instantly perceived a hand passed
quickly at the distance of several feet between a candle and the basin
in which they were placed.

As the infra-oesophageal ganglion sends nerves to the trophi and to the
first pair of cirri, it must correspond to the segments, from the fourth
to the ninth inclusive, of the archetype crustacean. The state of the
supra-oesophageal and ophthalmic ganglia appears to me very interesting:
I do not believe that in any _mature_ ordinary crustacean, the first or
ophthalmic ganglion can be shown to be distinct from the two succeeding
ganglia, or to be itself composed of a pair laterally distinct. The
ganglia, corresponding with the second and third segments of the body,
which should normally support two pair of antennae, are in the Lepadidae
united together; but laterally they are generally distinct in outline,
and are actually separate in Alepas: the supra-oesophageal ganglion
shows also its double nature, by giving rise to a pair of large double
nerves, evidently corresponding with the two pair of antennular nerves
in ordinary crustaceans. The embryonic condition of the whole
supra-oesophageal portion of the nervous system in the Lepadidae,
corresponds with the rudimentary state of the only organ of sense
supplied by it, namely, the eye, which in size and general appearance
has retrograded to the state in which it was in, during the first stage
of development of the larva;--I have used the term embryonic, because,
in the embryos of ordinary crustacea, all the ganglia are at first
longitudinally distinct, and laterally quite separate. The conclusion at
which we before arrived from studying the metamorphoses, namely, that
the whole peduncle and capitulum consisted of the first three segments
of the head, is beautifully supported by the structure of the nervous
system, in which these parts are seen to be supplied with nerves
exclusively from the supra-oesophageal ganglion: now in ordinary
crustacea the supra-oesophageal ganglion sends nerves to the eyes and
the two pair of antennae corresponding, as is known by embryological
dissections, to the first three segments of the body. Moreover, it is
asserted that the carapace which covers the thorax in crustacea, is not
formed by the development of the first segment; and this, likewise, may
be inferred to be the case with the peduncl