I can recognise in the
Cirripede, on evidence as good as can generally be obtained, all with
the exception of the four terminal abdominal segments; these do not
occur in any species known to me, in any stage of its development. If
that part of the larva in front of the mouth, bearing the eyes, the
prehensile antennae, and in an earlier stage two pair of antennae, be
formed, as is admitted in all other Crustacea, of three segments, then
beyond a doubt, from the absolute correspondence of every part, and even
every coloured mark, the peduncle of the Lepadidae is likewise thus
formed. The peduncle being filled by the branching ovarian tubes is no
objection to this view, for I am informed on the high authority of Mr.
J. D. Dana,[12] that this is the case with the cephalo-thorax in some
true Crustaceans, for instance, in Sapphirina. To proceed, the mouth,
formed of mandibles, maxillae, and outer maxillae, correspond with the
fourth, fifth, and sixth segments of the archetype Crustacean.
Posteriorly to the mouth, we come, in the larva, to a rather wide
interspace without any apparent articulation or organ, and then to the
thorax, formed of six segments, bearing the six pair of limbs, of which
the first pair differs slightly from the others. The thorax is succeeded
by three small segments, differently shaped, with the posterior one
alone bearing appendages; these segments, I cannot doubt, from their
appearance alone, and from their apparent function of steering the body,
are abdominal segments. If this latter view be correct, the thoracic
segments are the six posterior ones of the normal seven segments, and
there must be two segments missing between the outer maxillae and first
thoracic pair of legs, which latter on this view springs from the ninth
segment. Now, in a very singular Cirripede, already alluded to under the
name of Proteolepas, the two missing segments are present, the mouth
being actually succeeded by eight segments, and these by the three usual
abdominal segments,--every segment in the body being as distinct as in
an Annelid: hence in Proteolepas, adding the three segments for the
mouth and three for the carapace, we have altogether seventeen
segments, which, as I stated, is the full number ever observed in any
Cirripede, the four missing ones being abdominal, and, I presume, the
four terminal segments. That the cavity in which the thorax is lodged,
in the larva and therefore in the mature Cirripede, is simply fo