from the capitulum; it is much compressed; it is composed of unusually
thin and delicate membrane, transversely wrinkled and thickly clothed
with long cylindrical horns or spines of chitine. These horns (fig. 8
_c´_) are not the analogues of the spines which are articulated on the
external membranes of many Pedunculated and Sessile Cirripedes, but of
the calcified scales on the peduncle of Scalpellum and Pollicipes; for
they pass through the membrane (the underlying corium being marked by
their bases) and are persistent, being added to, like the valves, during
each successive period of growth. Their bases are concave, so that a
section of the layers of growth exhibits a series of pointed cones, one
within another. Each spine is nearly cylindrical, irregularly curled,
and nodose or slightly enlarged at intervals: the apex smooth and
pointed; the exterior surface longitudinally and finely ribbed, like the
valves. The spines increase irregularly in size from the bottom to the
top of the peduncle, those at the carinal and rostral ends being
generally the longest; they point upwards and hide the bases of the
valves. They are not arranged symmetrically, and new ones are formed
over all parts of the peduncle. They are formed of the same substance as
the valves, and do not contain any calcareous matter. These horns are
yellowish, generally ringed with pale and dark blueish brown, which on
pressure becomes slightly opalescent with pale blue and fiery red:
sometimes only the upper horns are thus ringed, and in rare instances
all are simply yellowish. The muscles of the peduncle run up to the
bases of the four valves.
_Surface of Attachment._--The cement appears to proceed from only two
points. In some specimens, a considerable length of one side of the
peduncle was fastened to the surface of attachment, the horns or spines
being enveloped in the cement. The prehensile antennæ of the larva will
presently be described under the male.
The _length_ of an average specimen, including the peduncle and valves,
is about half an inch, and the width across the widest part one fifth of
an inch. Mr. Cuming has one specimen an inch in length, but this is
owing to the peduncle being unusually tapering. In a specimen kept some
years in spirits, the cirri, trophi, caudal appendages, and corium under
the membrane between the scuta, were all dark purple; the sack and
corium of peduncle clouded with purple, and the prosoma pale-coloured.
The _Body_ (Pl. IV, fig. 8 _a´_) is small compared with the capitulum
and peduncle; it is much flattened; the prosoma is of a very peculiar
shape, being square, the sides of equal length, and, in an average-sized
specimen, 75/1000th of an inch long. The peculiar shape arises from the
great distance between the first and second cirrus--from the mouth being
far removed from the adductor scutorum muscle--and lastly, from the
lower part of the prosoma being not at all protuberant. The thorax which
supports the cirri is also unusually small, plainly articulated, and
separated from the prosoma by a deep fold. The thin membrane of the
prosoma is studded with some fine, pointed hairs, about 3/400ths in
length, and articulated on little circular discs.
_Mouth_, placed at a considerable distance from the adductor, and
directed in an unusual manner towards the ventral surface of the thorax:
the trophi are arranged, in a curved line, facing the thorax (see Pl. V,
fig. 2, for this part in the male), and therefore less laterally than is
usual.
_Labrum_ (Pl. IV, fig. 8 _a´_ opposite _c_) highly bullate; the upper
part produced into a blunt point: on its crest there are no teeth.
_Palpi_ (fig. 8 _a´_ opposite _d_) small, blunt and rounded at their
ends; inner margins slightly concave.
_Mandibles_ (Pl. X, fig. 4), with three teeth, of which the first is
much larger than the second and third, and distant from them: inferior
angle produced and pectinated; upper edges of the second and third teeth
finely pectinated.
_Maxillæ_ (Pl. X, fig. 11) small, slightly but distinctly indented by
two notches, supporting, besides the three upper great spines, three
pairs of moderately long spines and some finer ones: apodeme short,
thick.
_Outer Maxillæ_, unusually pointed, with the inner bristles not very
numerous, continuously arranged; externally, the bristles are longer.
Olfactory orifices, tubular, projecting, flattened, square on the
summit, smooth: they point upwards and obliquely towards each other:
they arise more laterally than in the other genera, namely outside the
bases of the outer maxillæ, and between them and the inner maxillæ.
Between the bases of the first pair of cirri, there is a conical
prominence, clothed with bristles and coloured purple: it projects
nearly as high as the top of the lower segment of the pedicel of the
first cirrus: it lies over the infra-oesophageal ganglion, and serves, I
suspect, to fill up a little interval between the outer maxillæ.
_Cirri_ long, little curved: the first pair (Pl. IV, fig. 8 _a´_) is
situated at an extraordinary distance from the second; hence its basal
articulation is on a level with the upper articulation of the pedicel of
the second cirrus. In the three posterior cirri, the segments are
laterally very flat, with their anterior surfaces not protuberant; each
supports three pairs of thin, non-serrated bristles, of which the second
pair is much shorter than the upper, and the lowest pair minute; between
each pair there is a minute, rectangulary projecting bristle; dorsal
tufts consist of two or three spines, of which one is longer than the
others. The two bristles forming each pair, are not of equal length; for
in the rami of each cirrus, the inner row of bristles is much shorter
than the outer; and this seems to be connected with the flatness of the
whole animal, and the consequent little power of divergence in the rami
of the cirri. The first cirrus is rather short, with the rami unequal in
length by about two segments: the anterior ramus is shorter and thicker
than the other: segments numerous, each clothed with several rows of
bristles. The second cirrus has the anterior ramus thicker and more
thickly clothed with spines than the posterior ramus; this latter is
rather more thickly clothed with spines than are the three posterior
cirri; the third cirrus is in all these respects characterised like the
second cirrus, but in a lesser degree. The pedicels of the second and
third cirri are thickly and irregularly clothed with spines; in the
three posterior pairs, the spines are placed in two regular rows, with
some minute intermediate spines.
_Caudal Appendages_ (Pl. IV, fig. 8 _a´_, _f_), multiarticulate, thin,
tapering, in one specimen equalling, in another just exceeding, in
length the pedicels of the sixth cirrus. In the latter specimen there
were thirteen segments, of which the basal segments were broader and
shorter than the upper; these latter are slightly constricted round the
middle, so that they resemble, in a small degree, an hour-glass. Their
upper margins are surrounded by rings of bristles; the terminal segment
being surmounted by one or two very fine bristles much longer than the
others. The two appendages are closely approximate; each arises from a
narrow elongated slip, attached to the side of the pedicel of the sixth
cirrus.
_Nervous system._--I examined the upper part of the nervous chord, in
order to ascertain whether the infra-oesophagean ganglion, which is of a
globulo-oblong shape, was far separated from the second ganglion; and
this I found to be the case, in accordance with the distance of the
first cirrus from the second. I may here remark, that in _S.
quadrivalvis_ I discovered the eye, which, though in all probability
really double, appeared to be single; it was situated near to the
supra-oesophageal ganglion; and this ganglion was situated near to the
adductor scutorum muscle, and at a considerable distance from the
labrum. The aperture leading into the acoustic (?) sack, is situated
much lower down than is usual (Pl. IV, fig. 8 _a´_), namely, at the
length of the pedicel of the first cirrus beneath its basal
articulation.
_Generative system._--The specimens here described, of which I examined
six, are exclusively female; they have no trace of the external,
probosciformed penis, or of the two great vesiculæ seminales, or of the
testes: on the other hand, the ovarian tubes within the peduncle are
developed in the usual manner, and owing to the large size of the ova,
are of large diameter, and hence very distinct: I detected, also, the
true ovaria at the upper edge of the stomach.
MALE. Plate V, figs. 1-8.
Of the above-described _Ibla Cumingii_ I dissected six specimens, four
from the Philippine Archipelago,[47] and two from the Burmah Empire, and
none of them, as we have just seen, possessed the probosciformed penis,
the vesiculæ seminales, or the testes, so conspicuous in other
Cirripedes; on the other hand, all were furnished with the usual
branching ovarian tubes and sometimes with ova, and consequently were
unquestionably of the female sex. Within each of these specimens there
was attached within the sack, in a nearly central line, at the rostral
end, (Pl. IV, fig. 8 _a´_, _h_, magnified five times,) a flattened,
purplish, worm-like little body, projecting about the 1/20th of an inch:
in one of the six individuals, there was a second similar little
creature attached at the carinal end of the sack. Before giving the
reasons which I think conclusively prove that these little animals are
the Males of the ordinary form of the _Ibla Cumingii_, it will be
convenient to describe their structure in detail.
[47] I am deeply indebted to the liberality and kindness of Mr.
Cuming, in allowing me to cut up four specimens of this new
species; and to Dr. Gould, of Boston, U. S., for the examination
of the Burmese specimens.
The whole consists of a long, much flattened peduncle, separated from
the mouth and thorax by an oblique fold, (Pl. V, fig. 1 _h_, _b_), which
is conspicuous on the dorsal margin under the cirri, and can be traced
with difficulty to the ventral margin. The thorax, itself rudimentary,
and supporting rudimentary cirri, is in some individuals, as in the one
represented (fig. 1, _magnified 32 times_), covered by, or received in
the oblique fold _h_, just mentioned: in other individuals the thorax is
drawn out, and then the fold shows merely as a notch on the dorsal
margin, and the basal articulations of the cirri stand some little way
above it. The basal edge of the large, well-developed month can be
traced all round, and on the ventral margin (_b_), is generally marked
by a slight notch. The dimensions and proportions vary much: the longest
specimen, including the imbedded portion, was 8/100th, and the shortest
barely 5/100ths of an inch in length; the width of the widest portion
varied from 1 to 2/100ths of an inch: the specimen figured (Pl. IV, fig.
8 _a´_, and Pl. V, fig. 1,) is a broad, short individual. Generally, the
middle of the peduncle is rather wider than the upper part.
_Peduncle._--The main part of the animal, as may be seen in the drawing,
consists of the peduncle, of which the imbedded portion tapers more or
less suddenly in a very variable manner, and is of variable length,--in
one specimen being one fourth of the entire length, and in another
consisting of a mere minute blunt point. The free upper part of the
animal is bent in various directions, in relation to the imbedded
portion. The latter passes obliquely through the chitine membrane and
corium, lining the sack of the female, and running along amidst the
underlying muscles and inosculating fibrous tissue, is attached to them
by cement at the extremity. The peduncle is often, but not in the
individual represented, much constricted at the point where it passes
through the skin of the female, and generally at several other points,
especially towards the extremity (see fig. 1); the stages of its deeper
and deeper imbedment being thus marked. The constrictions are, I
believe, simply due to the continued growth of the male, whilst the hole
through the membrane of the female does not yield. The imbedment, which
is considerable only when the lower part of the peduncle is almost
parallel to the coats of the sack, seems caused by the growth and
repeated exuviations of the female; I believe, that the larva attaches
itself to the chitine tunic of the sack, and that the cement, by some
unknown means, affects the underlying corium, so that this particular
portion of the tunic is not moulted with the adjoining integuments, and
that the growth of the surrounding parts subsequently causes this
portion to be buried deeper and deeper: it is, I believe, in the same
way as the end of the peduncle in _Conchoderma aurita_, sometimes
becomes imbedded in the skin of the whale to which it is attached.
The outer tunic of the peduncle is thin and structureless: in the fold
(fig. 1 _h_) under the cirri, there is a central triangular gusset of
still thinner membrane, corresponding in position to the membrane
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 striæ-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.
_Antennæ._--The peduncle terminates (Pl. V, fig. 1 _e_) in the two
usual, larval, prehensile antennæ, 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 antennæ 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 with certainty any cement glands. I may, however,
here mention, that I found in the lower half of the peduncle, numerous,
yellowish, transparent, excessively minute, pyramidal bodies, with
step-formed sides; of these two or three often cohered by their bases
like crystals; I have never seen anything like these in other
Cirripedes, but it has occurred to me that they may possibly be
connected with the formation of the cement: for in the last larval
condition of Lepas, the cement-ducts run up to the gut-formed ovaria,
filled at this period with yellowish, grape-like, cellular masses,
without the intervention of cement glands, and I can imagine that
similar masses, not being developed into functional ovaria, might give
rise to the yellow pyramidal bodies.
_Mouth._--The mouth is well developed; it is represented as seen
vertically from above, in Pl. V, fig. 2, magnified about 60 times; the
positions of the cirri and the outline of the thorax are accurately
shown by dotted lines; a lateral view is given in fig. 1. In the
specimen figured, the longitudinal diameter of the mouth, including the
labrum, was 5/400th of an inch. The muscles of the several trophi have
transverse striæ, and are the strongest and most conspicuous of any in
the body. The labrum is largely bullate, with its summit slightly
concave; the trophi are arranged in a remarkable manner, in a
semicircular line, so as to be opposed to the labrum rather than to each
other: there are no teeth or spines on the crest of the labrum, which
overhangs the oesophageal cavity.
The _Palpi_ (fig. 2 _b_ and fig. 3) are very small, dark purple, bluntly
pointed, with a few small bristles at the point; they do not extend
beyond the knob at each corner of the labrum, which is here present, as
in all other Lepadidæ; they are much smaller than in the female, though
of a similar shape, and consequently, their points are much further
apart: within their bases, the lateral muscles of the mandibles are, as
usual, attached; they are represented in fig. 3, as seen from the
inside, with the eye on a level with the concave summit of the labrum.
The rudimentary condition of the palpi is connected, as remarked under
the _Anelasma squalicola_, with the absence of efficient cirri.
The _Mandibles_ (fig. 7) are well developed; they so closely resemble
those of the female that it is superfluous to describe them: they are,
however, smoother, without any trace of the teeth being pectinated, and
with the inferior point smaller: measured in their longer direction,
they are 7/2000th of an inch in length, and, therefore, a little less
than one third of the size of those of the female. These organs have the
usual muscles well developed, and the usual articulations.
The _Maxillæ_ (fig. 8) have a rather rudimentary appearance; yet they
have the same size relatively to the mandibles, as in the female, the
spinose edge being 3/2000ths of an inch in length. These organs
resemble, to a certain extent, those of the female, differing from them
in being less prominent,--in the outline being more rounded, with the
notches even less distinct,--and in the spines being fewer. The apodeme
is short and broad.
The _Outer Maxillæ_ (fig. 6) are pointed, with a small tuft of bristles
at the apex; they are much less hairy than in the female, but have
nearly the same unusual shape. Outside their bases, and between them and
the inner maxillæ, the two well-developed, tubular, flattened,
square-topped, olfactory orifices, project in exactly the same
remarkable position as in the female; these are not represented in fig.
2, though sometimes they can be very distinctly seen, when the mouth is
viewed from vertically above.
_Thorax and Cirri._--The thorax is in a rudimentary condition: I did not
observe the usual articulations. The whole, as seen from vertically
above, is of small size, compared with the mouth; the outline is
accurately shown by dotted lines in Tab. 5, fig. 2, together with the
positions of the two pair of cirri, the caudal appendages, and anus. The
posterior end of the thorax does not rise to the level of the summit of
the mouth; and the thorax seems of no service, excepting perhaps as a
sort of outer lip to protect the mouth. The cirri are in an extreme
state of abortion, and evidently functionless; they are lined with
purplish corium, without the vestige of a muscle; they are usually
distorted and bent in different directions; they vary in size, and even
those on opposite sides of the same individual, sometimes do not
correspond, and do not arise from exactly corresponding points of the
thorax. There are always two pair of cirri, which, as I conclude from
the position of the excretory orifices, answer to the fifth and sixth
pair in other Cirripedes. Each cirrus (fig. 4) usually carries only one
ramus, placed on a large basal segment, evidently corresponding to the
pedicel of a normal cirrus. The posterior are larger than the anterior
cirri, which latter spring from points a little lower down on the
thorax. In the posterior cirrus figured, the great basal articulation
or pedicel, almost equals in length, and much exceeds in thickness, the
four segments of the ramus; these segments are furnished on their upper
dorsal edges with little brushes of spines, but have not even a trace of
the normally larger and far more important anterior spines. In one
specimen, the anterior cirrus had a large pedicel, carrying three
segments, like those of the posterior pair; but in another specimen, one
of the three segments showed traces of being divided into two, thus
making four imperfect segments; whilst on the corresponding side of this
same individual there were only two ill-formed segments, with their few
spines differently arranged. Again, in a third specimen, the great basal
segment of the anterior cirrus on one side, bore, exteriorly to the
usual ramus, a single segment furnished with bristles, and evidently
representing a second ramus; thus showing that the great basal segment
certainly answers to a pedicel. I may here add, that on the integuments
of these cirri, I observed with a high power, the serrated scale-like
appearance common in other Cirripedes. Directly between the bases of the
sixth cirrus, there is a very minute papillus, which, under the highest
power, can be seen to consist of two closely approximate, flattened
points; these, I have no doubt, are the caudal appendages in an
extremely rudimentary condition, for I traced the vesiculæ seminales to
this exact spot: close outside these rudimentary points, on a slight
swelling, is the anus. It will presently be seen that in the male of the
closely allied _Ibla quadrivalvis_, the nature of these caudal
appendages admits of no doubt, for in this species they consist of more
than one segment, are spinose, and close under them towards the mouth,
there is a perfectly distinct papillus, representing the usual
probosciformed penis.
_Alimentary Canal._--The oesophagus is very narrow, and of remarkable
length; from the orifice under the mandibles, it first runs back (in
this respect not well represented in Pl. V, fig. 1,) under the bullate
labrum, and then straight down the peduncle, where it terminates in the
usual bell-shaped expansion, entering one side of the small globular
stomach; the latter, at its lower end, is slightly constricted, and then
is rather abruptly upturned. The rectum is of unparalleled length, and
extremely narrow; it can be best detected after the dissolution by
caustic potash of the softer parts, when its inner coat of chitine can
be seen to be continuous, in the ordinary manner, with the outer
integuments of the thorax. The anus, as already stated, is seated on a
slight swelling, and consists of a small longitudinal slit (_f_, fig.
2), placed close outside the two very minute caudal appendages.
_Organ of Sight._--In all the specimens, a little below the fold
separating the mouth from the peduncle, and near the abdominal (or
rostral) edge, a black ball (_c_, fig. 1), about 1/1000th of an inch in
diameter, is conspicuous. When dissected out, it is somewhat conical in
form, and appears to consist of an outer coat, with a layer of
pigment-cells of a dark purple colour, surrounding a transparent, rather
hard lens, apparently leaving a circular orifice at the summit, and
forming a short tube at the base, surrounding what I believe to be a
nerve. I was not able to perceive that this eye consisted of two eyes
united, which the analogy of other Cirripedes makes me suppose probable,
although in the ordinary and hermaphrodite _Ibla quadrivalvis_, the eye
also appeared single. It is seated under the two transparent muscular
layers, close upon the upper end of the stomach, and this is the exact
position, as stated in the introductory discussion (p. 49), in which the
eyes of pedunculated Cirripedes are commonly situated.