abdominal.

I feel much confidence, that the homologies here given are correct. The
cause of their having been generally overlooked arises, I believe, from
the peculiar manner, already described, in which the animal, during its
last metamorphosis, is internally almost intersected: even for some
little time after discovering that the larval antennae were always
embedded in the centre of the surface of attachment, I did not perceive,
that this was the anterior end of the whole animal. The accompanying
woodcut gives at a glance, a view of the homologies of the external
parts: the upper figure (from Milne Edwards) is a Stomapod Crustacean,
Leucifer of Vaughan Thompson, and the abdomen, which we know becomes in
Cirripedes, after the metamorphosis, rudimentary, and therefore does not
fairly enter into the comparison, is given only in faint lines: the
lower figure is a mature Lepas, with the antennae and eyes, which are
actually present in the larva, retained and supposed to have gone on
growing. All that we externally see of a Cirripede, whether pedunculated
or sessile, is the three anterior segments of the head of a Crustacean,
with its anterior end permanently cemented to a surface of attachment,
and with its posterior end projecting vertically from it.

[Illustration: [_m._--Mouth.]]

CAPITULUM.

I will now proceed to a general description of the different parts and
organs in the Lepadidae. The Capitulum is usually much flattened, but
sometimes broadly oval in section. It is generally formed of five or
more valves, connected together by very narrow or broad strips of
membrane; sometimes the valves are rudimental or absent, when the whole
consists of membrane. When the valves are numerous, and they
occasionally exceed a hundred in number, they are arranged in whorls,
with each valve generally so placed as to cover the interval between the
two valves above. Of all the valves, the scuta are the most persistent;
then come the terga, and then the carina; the rostrum and latera occur
only in Scalpellum and Pollicipes, and in a rudimentary condition in
Lithotrya, and, perhaps, in the fossil genus Loricula. The valves are
formed sometimes of chitine (as in Ibla and Alepas), but usually of
shell, which varies from transparency to entire opacity. The shell is
generally white, occasionally reddish or purple; exteriorly, the valves
are covered by more or less persistent, generally yellow, strong
membrane. The scuta and terga are