have been cut off. This manner of growth
explains the broad, blunt basal termination of the peduncle, so unlike
that in other Lepadidae. New membrane is formed, not continuously as in
other cases, under the whole surface of the old membrane, but in
irregular patches; thus the portion marked (_a_) runs under (_b_), but
not under the little circles (_c_, _c_), for these are the last-formed
portions and underlie the membrane (_a_) and (_b_). I do not understand
how the splitting of the old membrane is effected; but no doubt it is by
the same process by which the membrane of the capitulum in other genera,
as in Scalpellum, splits symmetrically between the several valves. In
the branched filaments it is particularly difficult to understand their
growth, for it is not possible, after examining them, to doubt that they
continue to increase, and send off sub-branches, which it would appear
probable, penetrate the shark's flesh like roots. I may remark that one,
or more commonly two or three branched filaments stand nearly in the
centre of each circular line of exuviation or splitting. The branched
filaments first commence as mere little pustules, and these appear to be
most numerous at the bottom of the peduncle.

The final cause of the downward growth of the bottom of the peduncle, is
obviously to allow of the animal burying itself in the shark's body, in
the same way as Coronula and Tubicinella become imbedded by the downward
growth of their parietes in the skin of Cetacea. The only other genus of
Lepadidae, in which the growth of the peduncle is at all analogous, is
Lithotrya, in this genus, however, the animal burrows mechanically into
soft rock or shells.

I looked in vain for cement, or for the cement-glands, (but the specimen
was in an extremely unfavorable state for finding the latter) or for the
prehensile antennae of the larva. No doubt this Cirripede at first
becomes attached in the same way as others, but after early life, I
suspect it is retained in its place, by being so deeply imbedded in the
shark's body, and perhaps by the root-like branched filaments. The
irregular growth and splitting of the membrane at the base of the
peduncle, where the prehensile antennae of the larva must originally have
been situated, would account for not finding them.

The inside of the peduncle (fig. 2 _g_) was gorged, in the specimen
examined by me, with immature ova. The innermost muscular layer consists
of longitudinal bundles of