ior end,
on the sternal surface, there are two minute orifices, in _L. australis_
.002 in diameter, sometimes having a distinct border round them; the
membrane of the carapace on the inside is prolonged upwards and inwards
in two short funnel-shaped tubes, lodged in closed sacks of the corium:
within these sacks on each side a delicate bag is suspended, and hangs
in the mouth of the above funnel; at the upper end a large nerve could
be distinctly seen to enter the bag: I cannot doubt that this is a
sense-organ; from its position and from the animal not feeding (as we
shall presently see), I conclude that it is an acoustic organ.

_Antennae._--These are large and conspicuous; they are attached very
obliquely on the sternal surface, a little way from the anterior end of
the carapace, beyond which, when exserted, they extend;[9] they can (at
least in Ibla) be retracted within the carapace. They consist of three
segments: the first or basal one is much larger than the others, and
apparently always has a single spine on the outer distal margin. The
second segment consists either of a large, thin, circular, sucking disc,
or is hoof-like (Tab. V, figs. 5, 10, 11, 12); in all cases it is
furnished with one or more spines, (seven very long ones in Lepas,) on
the exterior-hinder margin. The third and ultimate segment is small; it
is articulated on the upper surface of the disc, and is directed
rectangularly outwards; it is sometimes notched, and even shows traces
of being bifid; it bears about seven spines at the end; some of these
spines are hooked, others simple, and in _Lepas_ and _Conchoderma_, two
or three are very long, highly flexible, and plumose, a double row of
excessively fine hairs being articulated on them. I can hardly doubt
that these latter spines, (within which the purple corium could be seen
to enter a little way,) floating laterally outwards, serve as feelers.
The antennae, at first, are well furnished with muscles. They serve, in
Lepas, according to Mr. King, and in Balanus, according to Mr. Bate, and
as I saw myself in another unnamed order, for the purpose of walking,
one limb being stretched out before the other; but their main function
is to attach the larva for its final metamorphosis into a Cirripede. The
disc can adhere even to so smooth a surface as a glass tumbler.[10] The
attachment is at first manifestly voluntary, but soon becomes
involuntary and permanent, being effected by special and most remarka