articulated on the edge of the
organ, and stand in a double row. At a point corresponding with the
upper articulation of the mandibles, a long, thin, narrow, rigid
apodeme, projects inwards (fig. 10), and running down nearly parallel
to the thin, outer, flexible membrane of the mouth, is attached to the
corium, and thus serves as a support to the whole organ. This apodeme is
embedded in muscles (Pl. X, fig. 10); there are other large muscles
attached to the inner side of the organ, and again others running
laterally towards the mandibles. The apodeme, of course, is moulted with
the integuments of the mouth. The _Outer Maxillae_ (Pl. X, figs. 16, 17)
serve as a lower lip; they are thicker than the other trophi; they have
their inner surfaces clothed with spines, sometimes divided into an
upper and lower group, and occasionally separated by a deep notch: there
are often long bristles outside. They are furnished with at least two
muscles; in sessile Cirripedes I have seen that they are capable of a
rapid to and fro movement, and I have no doubt that their function is to
brush any small creature, caught by the cirri, towards the maxillae,
which are well adapted to aid in securing the prey, and to hand it over
to the mandibles, by them to be forced down the oesophagus. On the
exterior face of the outer maxillae, above a trace of an upper
articulation, either two small orifices or two large tubular projections
can always be discovered; and these, as will presently be mentioned, I
believe to be olfactory organs.

_Cirri._--The five posterior pair are seated close to each other and
equidistant; the first pair is generally seated at a little distance,
and sometimes at a considerable distance from the second pair. The first
pair is the shortest; the others, proceeding backwards, increase
gradually in length. The rami of each pair are either equal in length or
slightly unequal: those of the first pair are oftenest unequal. The
number of segments in the posterior cirri is sometimes very great; in
one species of Alepas, there were above sixty segments in one ramus, the
other ramus being in this unique case (Pl. X, fig. 28) small and
rudimentary. The pedicels consist of two segments, a lower, longer, and
upper short one (fig. 18, _c_, _d_.) In the usual arrangement of the
spines on the segments of the three posterior pair of cirri, there are
(figs. 26, 27) from three to six pair of long spines on the anterior
face, with generally som