ne
connecting the two terga in the female, and there subjected to much
movement. I may here remark, that this fold, in its office of slightly
protecting the thorax and in its position, evidently represents the
capitulum with its valves, enclosing the whole body of the female. The
outer tunic is lined by corium, mottled with purple, and within this
there are two layers of striae-less muscles, transverse and longitudinal,
as in all pedunculated Cirripedes. The corium extends some way into the
imbedded portion of the peduncle, and consequently, the outer tunic
there continues to be added to layer under layer, and as it cannot be
periodically moulted, it becomes much thicker than in the upper free
part of the animal: the corium, however, does not extend to the extreme
point, so that in it growth of all kind ceases.

_Antennae._--The peduncle terminates (Pl. V, fig. 1 _e_) in the two
usual, larval, prehensile antennae, which it is very difficult to see
distinctly; they are tolerably well represented in fig. 5, greatly
magnified. Their extreme length, measured from the basal articulation to
the tip of the hoof-like disc, is 22/6000ths of an inch, the disc itself
being 7/6000ths of an inch. The disc is slightly narrower than the long
basal segment, from which it is divided by a broad conspicuous
articulation; its lower surface is flat and its upper convex, altogether
resembling in shape a mule's hoof; its apex is fuzzy with the finest
down; it bears a narrow ultimate segment, thrown, as usual, on one side;
this segment supports on its rounded irregular summit, at least five, I
believe, judging from the structure of the same part in the male larva
of _Ibla quadrivalvis_, six or seven spines, longer than the segment
itself: one long spine arises from the under side of the disc, near the
base of the ultimate segment, and points backward: there is also a
single curved spine on the outside, near the distal end of the basal
segment. These organs were imbedded in a heart-shaped ball or cylinder
of brown, transparent, finely laminated cement, and thus attached to the
fibrous tissue of the female. The two cement-ducts (fig. 1 _f_) were
very plain, each about 1/6000th of an inch in diameter, containing the
usual inner chord of opaque cellular matter. I traced them at the one
end into the prehensile antennae as far as the disc; and at the other, up
the peduncle for about one fourth of its length, where I lost them, and
could not discover