n of the
larval integuments, and when calcification commences, the first layer of
shell is deposited under, and then round these primordial valves. The
latter, in well preserved old specimens, may often be detected on the
umbones of the scuta, terga, and carina, but not on the umbones of any
other valves.

The _mouth_ seems one of the earliest parts developed: in the youngest
larva dissected, I could make out at least points corresponding with
each organ; and, at the period when the young Cirripede could be
dissected out of its larval envelopes, their general details were quite
plain. The labrum, however, had not become bullate. The mouth, as we
have seen, is formed under the rudimentary mouth of the larva, and at
the same relative spot occupied by the probosciformed mouth of the larva
in the second stage. Thus far, in the young Cirripede and larva, there
has been no great change in the relative positions of the parts: the
rudimentary eyes, however, of the former are developed posteriorly to
(or above, as applied to a Cirripede,) the cast-off compound eyes of the
larva; but the position of the mouth, of the antennae, and of the several
coloured marks in the corium, prove to demonstration, the correspondence
in both of part to part. The case is rather different with what follows.

The _Cirri_ are developed at first of considerable length, so that the
young animal may soon provide itself with food; in _Lepas australis_
they are of great length, the sixth pair consisting of seventeen or
eighteen obscure segments. The extreme tips of the twenty-four rami of
the six pair of cirri, are formed within the twenty-four, corresponding,
little, bi-segmental rami of the six pair of natatory legs; but as the
cirri are many times longer than these legs, they occupy in a bundle
the whole thorax of the larva; no part whatever of the thorax of the
Cirripede is formed within the thorax of the larva, but (together with
the pedicels of the anterior cirri) within the cephalic cavity. As a
consequence of this, the longitudinal axis of the thorax of the young
Cirripede lies almost transversely to the longitudinal axis of the
larva; and the Cirripede, from this transverse position of its thorax,
comes to be, as it were, internally, almost cut in twain, and the sack
thus produced. As soon as the young Cirripede is free and can move
itself, the cirri are curled up, and the thorax is advanced towards the
orifice of the capitulum, its longitudinal