together, but above the basal fold separating the mouth from the body,
there are, in all the genera, a pair of orifices (Pl. X, fig. 16); these
are sometimes seated on a slight prominence, as in Lithotrya, or on the
summit of flattened tubes (Pl. X, fig. 17), projecting upwards and
towards each other, as in Ibla, Scalpellum, and Pollicipes. In Ibla
these tubular projections rise from almost between the outer and inner
maxillæ. It is impossible to behold these organs, and doubt that they
are of high functional importance to the animal. The orifice leads into
a deep sack lined by pulpy corium, and closed at the bottom. The outer
integument is inflected inwards, (hence periodically moulted,) and
becoming of excessive tenuity, runs to near the bottom of the sack,
where it ends in an open tube: so excessively thin is this inflected
membrane, that, until examining Anelasma, I was not quite certain that I
was right in believing that the outer integument did not extend over the
whole bottom. I several times saw a nerve of considerable size entering
and blending into a pulpy layer at the bottom of the sack of corium; but
I failed in tracing to which of the three pair of nerves, springing from
the front end of the infra-oesophageal ganglion, it joined. I can hardly
avoid concluding, that this _closed_ sack, with its naked bottom, is an
organ of sense; and, considering that the outer maxillæ serve to carry
the prey entangled by the cirri towards the maxillæ and mandibles, the
position seems so admirably adapted for an olfactory organ, whereby the
animal could at once perceive the nature of any floating object thus
caught, that I have ventured provisionally to designate the two orifices
and sacks as olfactory.
_Acoustic_ (?) _Organs._--A little way beneath the basal articulation of
the first cirrus (Pl. IX, fig. 4 _d_, and Pl. IV, fig. 2 _e_), on each
side, there may be seen a slight swelling, and on the under side of
this, a transverse slit-like orifice, 1/20th of an inch in length in
Conchoderma, but often only half that size. In Ibla this orifice is
seated lower down (Pl. IV, fig. 8 _a´_, _e_), between the bases of the
first and second cirri, which are here far apart: in _Alepas cornuta_ it
is placed rather nearer to the adductor scutorum muscle, namely, beneath
the mandibles. The orifice leads into a rather deep and wide meatus; the
external integument is turned in for a short distance, widening a
little, and then ends abruptly. The meatus, enlarging upwards, is lined
by thick pulpy corium, and is closed at the upper end; from its summit
is suspended a flattened sack of singular and different shapes in the
different genera. This, the so-called acoustic sack of _Conchoderma
virgata_, is figured Pl. IX, fig. 6. The deep and wide notch faces
towards the posterior end of the animal; the inferior lobe, thus almost
cut off, is flattened in a different plane from the upper part; the lobe
is lodged in a little pouch of corresponding form, leading from the open
meatus in which the upper part is included. In _Conchoderma aurita_, the
top of the acoustic sack is narrower and more constricted, the whole
more rounded, and the lobe more turned down. In _Lepas fascicularis_ the
notch is not so deep or wide, and the lobe larger. In _Ibla Cumingii_
the sack is of the shape of a vase, with one corner folded over. In
_Scalpellum vulgare_ it is small, oval, with the lower end much pushed
in, and furnished with a little crest. Lastly, in _Pollicipes mitella_
it is simply oval. In all cases the sack is empty, or contains only a
little pulpy matter: it consists of brownish, thick, and remarkably
elastic tissue, formed, apparently, of transverse little pillars,
becoming fibrous on the outside, and with their inner ends appearing
like hyaline points. The mouth of the acoustic sack (removed in the
drawing) is closed by a tender diaphragm, through which I saw what I
believe was a moderately-sized nerve enter; I have not yet succeeded in
tracing this nerve. The first pair of cirri seem, to a certain extent,
to serve as antennæ, and therefore the position of an acoustic organ at
their bases, is analogous to what takes place in crustacea; but there
are not here any otolites, or the siliceous particles and hairs, as
described by Dr. Farre, in that class. Nevertheless, the sack is so
highly elastic, and its suspension in a meatus freely open to the water,
seems so well adapted for an acoustic organ, that I have provisionally
thus called it. In the larva, as I have shown, a pouch, certainly
serving for some sense, I believe for hearing, is seated in quite a
different position at the anterior end of the carapace. I may mention
that I found sessile Cirripedes very sensitive of vibrations in objects
adjoining them, though not, apparently, of noises in the air or water.
In a group of specimens, I could not touch one even most delicately
with a needle, without all the adjoining ones instantly withdrawing
their cirri; it made no difference if the one touched had its operculum
already closed and motionless.
_Reproductive System_,--_Male Organs._--All the Cirripedia which I have
hitherto examined, with the exception of certain species of Ibla and
Scalpellum, are hermaphrodite or bisexual.[17] I shall so fully describe
the sexual relations of the several species of these two genera, under
their respective headings, and at the end of the genus of Scalpellum,
that I will not here give even an abstract of the grounds on which my
firm belief is based, that the masculine power of certain hermaphrodite
species of Ibla and Scalpellum, is rendered more efficient by certain
parasitic males, which, from their not pairing, as in all hitherto known
cases, with females, but with hermaphrodites, I have designated
_Complemental Males_.
[17] I am compelled to differ greatly from the account given by
Prof. Steenstrup of the reproductive system in the Cirripedia, in
his ‘Untersuchungen über das Vorkommen des Hermaphroditismus, ch.
v, 1846;--a translation of which I have seen, owing to the great
kindness of Mr. Busk. Mr. Goodsir has described (‘Edin. New Phil.
Journal,’ July 1843,) what he considers the male of Balanus; but
I have seen this same parasitic creature charged with ova,
including larvæ! From the resemblance of the larvæ to the little
crustacean described by Mr. Goodsir, in the same paper, as a
distinct parasite, I believe the latter to be the male of his
so-called male Balanus, and that all belong to the same species,
allied to Bopyrus. This genus, as is well known, is parasitic on
other crustacea; and it is a rather interesting fact thus to
find, that this new parasite which is allied to Bopyrus, in
structure, is likewise allied to it in habits, living attached to
Cirripedia, a sub-class of the crustacea.
The male organs have been well described by M. Martin St. Ange, whose
observations have since been confirmed by R. Wagner.[18] The testes are
small, often leaden-coloured, either pear or finger-shaped, or branched
like club-moss,--these several forms sometimes occurring in the same
individual; they coat the stomach, enter the pedicels, and even the
basal segments of the rami of the cirri, and in some genera occupy
certain swellings on the thorax and prosoma, and in others the
filamentary appendages: the testes seen in the apex in one of these
appendages in Conchoderma, is represented in Pl. IX, fig. 5. The two
vesiculæ seminales are very large; they lie along the abdominal surface
of the thorax, and generally (but not in some species of Scalpellum)
enter the prosoma, where their broad ends are often reflexed; here the
branched vessels leading from the testes enter. The membrane of the
vesiculæ seminales is formed of circular fibres; and is, I presume,
contractile, for I have seen the spermatozoa expelled with force from
the cut end of a living specimen. The two canals leading from the
vesiculæ generally unite in a single duct at the base of the penis; but
in _Conchoderma aurita_, half-way up it. The probosciformed penis,
except in certain species of Scalpellum, is very long; it is capable of
the most varied movements; it is generally hairy, especially at the end;
it is supported on a straight unarticulated basis, which in _Ibla
quadrivalvis_ alone (Pl. IV, fig. 9 _a_), is of considerable length; in
this species, the upper part is seen to be as plainly articulated as one
of the cirri; in Alepas, the articulations are somewhat less plain, and
in the other genera, the organ can be said only to be finely ringed, but
these rings no doubt are in fact obscure articulations. In the females
of _Ibla Cumingii_ and _Scalpellum ornatum_, there is, of course, no
penis.
[18] In ‘Müller’s Archiv,’ 1834, p. 467. I have already several
times referred to M. Martin St. Ange’s excellent Memoir, read
before the Academy of Sciences, and subsequently, in 1835,
published separately.
_Female Organs._--M. Martin St. Ange has described how the peduncle[19]
is gorged with an inextricable mass of branching ovarian tubes, filled
with granular matter and immature ova. In Conchoderma and Alepas, the
ovarian tubes run up in a single plane (Pl. IX, fig. 3,) between the two
folds of corium round the sack. Here the development of the ova can be
well followed: a minute point first branches out from one of the tubes;
its head then enlarges, like the bud of a tulip on a footstalk; becomes
globular; shows traces of dividing, and at last splits into three, four,
or five egg-shaped balls, which finally separate as perfect ova. Within
the peduncle, the ovarian tubes branch out in all directions, and within
the footstalks of the branches (differently from what takes place round
the sack), ova are developed, as well as at their ends. Close together,
along the rostral (_i. e._, ventral) edge of the peduncle, two nearly
straight, main ovarian tubes or ducts may be detected, which do not give
out any branches till about half way down the peduncle, where they
subdivide into branches, which inosculate together, and give rise to the
mass filling the peduncle, and sometimes, as we have just seen, sending
up branches round the sack. These two main unbranched ovarian ducts,
followed up the peduncle, are seen to enter the body of the Cirripede
(close along side the great double peduncular nerves), and then
separating, they sweep in a large curve along each flank of the prosoma,
under the superficial muscles, towards the bases of the first pair of
cirri; and then rising up, they run into two glandular masses. These
latter rest on the upper edge of the stomach, and touch the cæca where
such exist; they were thought by Cuvier to be salivary glands. They are
of an orange colour, and form two, parallel, gut-formed masses, having,
in Conchoderma, a great flexure, and generally dividing at the end near
the mouth into a few blunt branches. I was not able to ascertain whether
the two main ducts, coming from the peduncle, expanded to envelope them,
or what the precise connection was. The state of these two masses varied
much; sometimes they were hollow, with only their walls spotted with a
few cellular little masses; at other times they contained or rather were
formed of, more or less globular or finger-shaped aggregations of pulpy
matter; and lastly, the whole consisted of separate pointed little
balls, each with a large inner cell, and this again with two or three
included granules. These so closely resembled, in general appearance
and size, the ovigerms with their germinal vesicles and spots, which I
have often seen at the first commencement of the formation of the ova in
the ovarian tubes in the peduncle, that I cannot doubt that such is
their nature. Hence I conclude, that these two gut-formed masses are the
true ovaria. I may add, that several times I have seen in the two long,
unbranched ducts, connecting the true ovaria and the ovarian tubes in
the peduncle, pellets of orange-coloured cellular matter (_i. e._,
ovigerms) forming at short intervals little enlargements in the ducts,
and apparently travelling into the peduncle.
[19] I may here mention, that in all sessile Cirripedes, the
ovarian branching tubes lie between the calcareous or membranous
basis and the inner basal lining of the sack, and to a certain
height upwards round the sack: the true ovaria and the two ducts
occupy the same position as in the Lepadidæ.
The structure here described is quite conformable with that which we
have seen in the larva; in the latter, two gut-formed masses of equal
thickness extended from the cæca of the stomach to within the future
peduncle, where the cement-ducts entered them, and where, after a short
period, they were seen to expand into a mass of ovarian tubes. In the
mature Cirripede, the cement-ducts can still be found united to the
ovarian tubes in the middle of peduncle; and the cause of the wide
separation of the true ovaria and ovarian tubes, can be simply accounted
for by the internal, almost complete intersection of the animal, which
takes place during the last metamorphosis.
The ova, when excluded, remain in the sack of the animal until the larvæ
are hatched; they are very numerous, and generally form two concave,
nearly circular, leaves, which I have called after Steenstrup and other
authors, the _ovigerous lamellæ_ (Pl. IV, fig. 2 _b_). These lamellæ lie
low down on each side of the sack: in _Conchoderma virgata_, however,
there is often only a single lamella, forming a deeply concave cup: in
_C. aurita_ there are generally on each side four lamellæ, one under the
other. The ova lie in a layer from two to four deep; and all are held
together by a most delicate transparent membrane, which separately
enfolds each ovum: this membrane is often thicker and stronger round the
margins of the lamellæ, where they are united, in a peculiar manner,
presently to be described, to a fold of skin, on each side of the sack:
these two folds, I have called the _ovigerous fræna_ (Pl. IV, fig. 2
_f_).
M. Martin St. Ange, describes an orifice under the carina, by which he
supposes the ova to enter the sack; this, after repeated and most
careful examinations, I venture to affirm does not exist; on the
contrary, I have every reason to believe that the ova enter the sack in
the following curious manner. Immediately before one of the periods of
exuviation, the ova burst forth from the the ovarian tubes in the
peduncle and round the sack, and, carried along the open circulatory
channels, are collected (by means unknown to me) beneath the
chitine-tunic of the sack, in the corium, which is at this period
remarkably spongy and full of cavities. The corium then forms or rather
(as I believe) resolves itself into the very delicate membrane
separately enveloping each ovum, and uniting them together into two
lamellæ; the corium having thus far retreated, then forms under the
lamellæ the chitine-tunic of the sack, which will of course be of larger
size than the last-formed one, now immediately to be moulted with the
other integuments of the body. As soon as this exuviation is effected,
the tender ova, united into two lamellæ, and adhering, as yet, to the
bottom of the sack, are exposed: as the membranes harden, the lamellæ
become detached from the bottom of the sack, and are attached to the
ovigerous fræna. To demonstrate this view, an individual should have
been found, with both the old and new chitine tunic of the sack, and
with the lamellæ lying between them; this, I believe, I have seen, but
it was before I understood the full importance of the fact: a great
number of specimens would have to be examined in order to succeed again,
for the changes connected with exuviation supervene very quickly. I
have, however, several times found the ova so loose under the sack, as
to be detached with a touch from the ovarian tubes; and I have twice
carefully examined specimens, which had just moulted, as shown by even
the mandibles being flexible, in which the lamellæ had not become united
to the fræna, but still adhered to the newly-formed chitine tunic of
the sack; in these, the ova were so tender, that they broke into pieces
rather than be separated from the membrane of the lamella, itself hardly
perfectly developed, for pulpy cellular matter adhered outside some of
the ova. These and other facts are quite inexplicable on any other view
than that advanced.
As the lamellæ are formed without organic union with the parent, they
would be liable to be washed out of the widely open sack of the
Lepadidæ, if they had not been specially attached to the _fræna_. These
fræna consist of a pair of more or less semicircular folds of skin,
depending inside the sack, on each side of the point of attachment of
the body. The fræna are often of considerable size, but in Ibla, they
are very minute; they are formed of chitine tunic with underlying
corium, like the rest of the sack; on their crests, there is a row, or a
set of circular groups, or a broad surface, covered, either with minute,
pointed, bead-like bodies mounted on long hair-like footstalks, or with
staff-formed bodies on very short footstalks. I measured some of the
bead-like bodies, in _Lepas anserifera_, and they were 1/2000th of an
inch in diameter, and the footstalks three or four times as long as the
elongated heads. These heads, of whatever shape they may be, have an
opaque, and, I believe, glandular centre; I could not make out with
certainty an aperture at their ends, but, I believe, such exists, and
they seem to secrete a substance, which hardens into a strong membrane,
serving to unite the crest of the frænum to the edges of the lamellæ. In
one case, this bit of membrane seemed formed of a woven mass of threads.
These little glandular bodies, with the membrane formed by them, are
cast off at each exuviation, and new glands formed on the crest of the
frænum underneath. In some species of Pollicipes, (viz., _P. cornucopia_
and _elegans_,) the fræna, though present and large, are functionless
and destitute of the glands: I believe, they exist in this same
functionless condition, and in rather a different position in the
sessile Cirripedes, and that in this family they serve as Branchiæ.
The above-described method by which Cirripedia lay their eggs, namely,
united together in a common membrane, placed between their old outer and
new inner integuments, and the manner in which the lamellæ, when thus
formed, are retained for a time fastened to the fræna, and are then cast
off, appears to me very curious. In some of the lower Crustacea, it is
known, that the ova escape by rupturing the ovisacs formed by the
protruded ovarian tubes, and this is the nearest analogy with which I am
acquainted. The ova are impregnated (as I infer from the state of the
vesiculæ seminales), when first brought into the sack, and whilst the
membrane of the lamellæ is very tender: the long probosciformed penis
seems well adapted for this end. In the male of _Ibla Cumingii_, which
has not a probosciformed penis, the whole flexible body, probably,
performs the function of the penis: in _Scalpellum ornatum_, however,
the spermatozoa must be brought in by the action of the cirri, or of the
currents produced by 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, larvæ were included
in the ova.
_Exuviation; Rate of Growth; Size._--I have had occasion repeatedly to
allude to the exuviation of the Lepadidæ: 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 Lepadidæ, 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
Lepadidæ, and, on the other hand, according to M. Joly, (‘Annales
des Sciences Naturelles,’ 2d series, Zoolog.), there is one true
crustacean, the _Isaura cycladoides_, which has a persistent
bivalve shell.
The delicate tunic lining the sack, (a mere duplicature of that thick
one, forming the outside of the capitulum, and generally transformed
into valves,) and the integuments of the whole body, are regularly
moulted. With these integuments, the membrane lining the oesophagus, the
rectum, and the deep olfactory pouches, and the horny apodemes of the
maxillæ, are all cast together. I have seen a specimen of Lepas, in
which, from some morbid adhesion, the old membrane lining one of the
olfactory pouches had not been moulted, but remained projecting from the
orifice as a brown shrivelled scroll. The new spines on the cirri (and
on the maxillæ) are formed within the old ones; but as they have to be a
little longer than the latter, and as they cannot enter these up to
their very points, their basal portions are not thus included, but are
formed, running obliquely across the segments of the cirri; and what is
curious, these same basal portions are turned inside out, like the
fingers of a glove when hastily drawn off. After the exuviation of the
old spines, the new spines have their inverted basal portions drawn out
from within the segments, and turned outside in, so as to assume their
proper positions.
All Cirripedia grow rapidly: the yawl of H. M. S. _Beagle_ was lowered
into the water, at the Galapagos Archipelago, on the 15th of September,
and, after an interval of exactly thirty-three days, was hauled in: I
found on her bottom, a specimen of _Conchoderma virgata_ with the
capitulum and peduncle, each half an inch in length, and the former
7/20ths in width: this is half the size of the largest specimen I have
seen of this species: several other individuals, not half the size of
the above, contained numerous ova in their lamellæ, ready to burst
forth. Supposing the larva of the largest specimen became attached the
first day the boat was put into the water, we have the metamorphosis, an
increase of length from about .05, the size of the larva, to an whole
inch, and the laying of probably several sets of eggs, all effected in
thirty-three days. From this rapid growth, repeated exuviations must be
requisite. Mr. W. Thompson, of Belfast, kept twenty specimens of
_Balanus balanoides_, a form of much slower growth, alive, and on the
twelfth day he found the twenty-first integument, showing that all had
moulted once, and one individual twice within this period. I may here
add, that the pedunculated Cirripedes never attain so large a bulk as
the sessile; _Lepas anatifera_ is sometimes sixteen inches in length,
but of this, the far greater portion consists of the peduncle.
_Pollicipes mitella_ is the most massive kind; I have seen a specimen
with a capitulum 2.3 of an inch in width.