y them. That cross impregnation may and sometimes
does take place, I infer from the singular case of an individual, in a
group of Balani, in which the penis had been cut off, and had healed
without any perforation; notwithstanding which fact, larvae were included
in the ova.

_Exuviation; Rate of Growth; Size._--I have had occasion repeatedly to
allude to the exuviation of the Lepadidae: with the exception of the
genus Lithotrya,[20] in which the calcareous scales on the peduncle,
together with the membrane connecting them, is cast off, neither the
valves nor the membrane uniting them, nor that forming the peduncle with
its scales and styles, are moulted; but the surface gradually
disintegrates and is removed, perhaps sometimes in flakes, whilst new
and larger layers are formed beneath. In Scalpellum, I ascertained that
the new membrane, connecting together the newly-formed calcified rims
under the valves of the capitulum, was formed as a fold, with the
articulated spines which it bears, all adpressed in certain definite
directions. This fold of new membrane, when the old membrane splits and
yields, of course expands, and thus the size of the capitulum is
increased. In the peduncle, lines of splitting can seldom be perceived,
except, indeed, in the sub-globular, embedded, downward-growing peduncle
of Anelasma, as described under that genus. I do not understand what
determines the complicated lines of splitting of the old membrane
between the several valves of the capitulum,--without it be simply, that
along these lines alone, the old membrane is not strengthened by the new
membrane being closely applied under it, the new being formed, as we
have just said, in a fold, in order to allow of increase in size.
Although, as I believe, there is strictly no exuviation in the outer
membranes of mature Lepadidae, it seems that narrow strips of membrane
are cast off from between the valves, for the few first moults, after
the final metamorphosis of the larva. I may here remark that, in most
sessile Cirripedes, the outside membrane connecting the operculum and
shell, is regularly moulted.

[20] The external integuments being moulted in Crustacea, but not
in the Cirripedia, may appear, at first, an important difference:
but we here see that non-exuviation is not universal amongst the
Lepadidae, and, on the other hand, according to M. Joly, ('Annales
des Sciences Naturelles,' 2d series, Zoolog.), there is one true