specimens examined. It is naked. The prehensile antennæ were not in a
good state of preservation: the disc is narrower than the basal segment,
and only slightly pointed, in which important respect it differs from
the same part in the foregoing species; at its distal end, rather on the
inner side, there are two or three spines, apparently in place of the
excessively minute hairs, which are found at the same spot in some or in
all the other species of Scalpellum, and in Ibla: similar strong spines
occur in Pollicipes. Unfortunately, for the sake of comparison, I was
not able to find the prehensile antennæ in the hermaphrodite _S.
villosum_.
_Mouth._--Labrum bullate, with teeth on the crest. _Palpi_ blunt,
spinose.
_Mandibles_, with three teeth; inferior point rather strongly
pectinated.
_Maxillæ_, with a considerable notch under the upper pair of large
spines; inferior part of the edge not prominent.
_Outer Maxillæ_, with the spines on the inner edge arranged into two
groups. Olfactory orifices tubular and prominent, with some long
bristles near their bases. In the mandibles having only three teeth, in
the maxillæ being notched and in the lower part not being prominent,
and, lastly, in the bristles on the inner face of the outer maxillæ
being arranged in two groups, these several organs differ from those in
the hermaphrodite.
_Cirri._--First pair short, with only three or four segments in each
ramus: second cirrus, with the basal segments not very thickly clothed
with spines: sixth cirrus with seven segments, not protuberant in front,
each bearing four pairs of spines, without intermediate tufts.
_Caudal appendages_, none. This is an interesting fact, considering that
these organs are likewise absent in the hermaphrodite _S. villosum_,--an
absence highly remarkable, and confined to the genus Conchoderma and the
one species of Anelasma.
_Penis_ thick, not tapering, rather exceeding in length the pedicel of
the sixth cirrus, square at the end, and furnished with some spines. In
one specimen, I believe I distinguished the vesiculæ seminales: if so,
they contained only pulpy matter, and not spermatozoa. There were no
ovarian tubes within the peduncle, which was lined by the usual muscles;
I traced the two delicate cement-ducts, running from within the antennæ
close up to the animal’s body. Hence in this case, as in that of _S.
Peronii_, I dare positively affirm that ovarian tubes do not occur; for
it is out of the question that I could have traced the cement-ducts,
and, at the same time, overlooked the far larger and more conspicuous
ovarian tubes, into which, moreover, the ducts, had they existed, would
have run. Consequently, these parasites are not females; but judging
from the probosciformed penis, and from the presence, as I believe, of
vesiculæ seminales, they are males.
The complemental males of the present species, and of _S. Peronii_, so
closely resemble each other, that what I have stated regarding the
affinities of the latter, are here quite applicable. It is singular how
much more alike the parts of the mouth and the cirri of these two
complemental males are, than the corresponding parts in the two
hermaphrodites: this no doubt is due to the two males having been
arrested in their development, at a corresponding early period of
growth. Several of the characters, by which the hermaphrodite _S.
villosum_ so closely approaches, and almost blends into the genus
Pollicipes,--such as the thicker cirri, with the intermediate tufts of
bristles, the small second tooth of the mandibles, and the little
brush-like prominence on the maxillæ,--are not in the least apparent in
the complemental male.
SUMMARY ON THE NATURE AND RELATIONS OF THE MALES AND COMPLEMENTAL MALES,
IN IBLA AND SCALPELLUM.
Had the question been, whether the parasites which I have now described,
were simply the males of the Cirripedes to which they are attached, the
present summary and discussion would perhaps have been superfluous; but
it is so novel a fact, that there should exist in the animal kingdom
hermaphrodites, aided in their sexual functions by independent and, as I
have called them, Complemental males, that a brief consideration of the
evidence already advanced, and of some fresh points, will not be
useless. These parasites are confined to the allied genera Ibla and
Scalpellum; but they do not occur in Pollicipes,--a genus still more
closely allied to Scalpellum; and it deserves notice, that their
presence is only occasional in those species of Scalpellum which come
nearest to Pollicipes. In the genera Ibla and Scalpellum, the facts
present a singular parallelism; in both we have the simpler case of a
female, with one or more males of an abnormal structure attached to her;
and in both the far more extraordinary case of an hermaphrodite, with
similarly attached Complemental males. In the two species of Ibla, the
complemental and ordinary males resemble each other, as closely as do
the corresponding hermaphrodite and female forms; so it is with two
sets of the species of Scalpellum. But the males of Ibla and the males
of Scalpellum certainly present no special relations to each other, as
might have been expected, had they been distinct parasites independent
of the animals to which they are attached, and considering that they are
all Cirripedes having the same most unusual habits. On the contrary, it
is certain that the animals which I consider to be the males and
complemental males of the two species of Ibla, if classed by their own
characters, would, from the reasons formerly assigned, form a new genus,
nearer to Ibla than to the parasites of Scalpellum: so, again, the
assumed males of the three latter species of Scalpellum would form two
new genera, both of which would be more closely allied to Scalpellum,
than to the parasites of Ibla. With respect to the parasites of the
first three species of Scalpellum, they are in such an extraordinarily
modified and embryonic condition, that they can hardly be compared with
other Cirripedes; but certainly they do not approach the parasites of
Ibla, more closely than the parasites of Scalpellum; and in the one
important character of the antennæ, they are identical both with the
parasitic and ordinary forms of Scalpellum. That two sets of parasites
having closely similar habits, and belonging to the same sub-class,
should be more closely related in their whole organisation to the
animals to which they are respectively attached, than to each other,
would, if the parasites were really distinct and independent creatures,
be a most singular phenomenon; but on the view that they differ only
sexually from the Cirripedes on which they are parasitic, this
relationship is obviously what might have been expected.
The two species of Ibla differ extremely little from each other, and so,
as above remarked, do the two males. In Scalpellum the species differ
more from each other, and so do the males. In this latter genus the
species may be divided into two groups, the first containing _S.
vulgare_, _S. ornatum_ and _S. rutilum_, characterised by not having a
sub-carina, by the rostrum being small, by the constant presence of four
pair of latera, and by the peculiar shape of the carinal latera; the
second group is characterised by having a sub-carina and a large
rostrum, and may be subdivided into two little groups; viz., _S.
rostratum_ having four pairs of latera, and _S. Peronii_ and _villosum_
having only three pairs of latera: now the males, if classed by
themselves, would inevitably be divided in exactly the same manner,
namely, into two main groups,--the one including the closely similar,
sack-formed males of _S. vulgare_, _ornatum_, and _rutilum_, the other
the pedunculated males of _S. rostratum_, _Peronii_, and _villosum_; but
this latter group would have to be subdivided into two little
sub-groups, the one containing the three-valved male of _S. rostratum_,
and the other the six-valved males of _S. Peronii_ and _S. villosum_. It
should not, however, be overlooked, that the two main groups of
parasites differ from each other, far more than do the two corresponding
groups of species to which they are attached; and, on the other hand,
that the parasitic males of _S. Peronii_ and _S. villosum_ resemble each
other more closely, than do the two hermaphrodite forms;--but it is very
difficult to weigh the value of the differences in the different parts
of species.
Besides these general, there are some closer relations between the
parasites and the animals to which they are attached; thus the most
conspicuous internal character by which _Ibla quadrivalvis_ is
distinguished from _I. Cumingii_, is the length of the caudal appendages
and the greater size of the parts of the mouth; in the parasites, we
have exactly corresponding differences. Out of the six species of
Scalpellum in their ordinary state, _S. ornatum_ is alone quite
destitute of spines on the membrane connecting the valves; and had it
not been for this circumstance, I should even have used the presence of
spines as a generic character; on the other hand, _S. villosum_, in
accordance with its specific name, has larger and more conspicuous
spines than any other species. In the parasites we have an exactly
parallel case; the parasite of _S. ornatum_ being the only one without
spines, and the spines on the parasite of _S. villosum_ being much the
largest! This latter species is highly singular in having no caudal
appendages, and the parasite is destitute of these same organs, though
present inn the parasites of _S. rostratum_ and _S. Peronii_. Again, _S.
villosum_ approaches, in all its characters, very closely to the genus
Pollicipes, and the parasite in having prehensile antennæ, with the disc
but little pointed, and with spines at the further end, departs from
Scalpellum and approaches Pollicipes! Will any one believe that these
several parallel differences, between the Cirripedial parasites and the
Cirripedes to which they are attached, are accidental, and without
signification? yet, this must be admitted, if my view of their male sex
and mature be rejected.
One more, and the most important special relation between the parasites
and the cirripedes to which they are attached, remains to be noticed,
namely that of their prehensile larval antennæ. I observed the antennæ
more or less perfectly in the males of all, and except in _S. villosum_,
in all the species, though so utterly different in general appearance
and structure, I found the peculiar, pointed, hoof-like discs, which are
confined, I believe, to the genera Ibla and Scalpellum. In the
hermaphrodite forms of Scalpellum, I was enabled to examine the antennæ
only in two species, _S. vulgare_ and _S. Peronii_, (belonging,
fortunately, to the two most distinct sections of the genus,) and after
the most careful measurements of every part, I can affirm that, in _S.
vulgare_, the antennæ of the male and of the hermaphrodite are
identical; but that they differ slightly in the proportional lengths of
their segments, and in no other respect, from these same organs in _S.
Peronii_,--in which again the antennæ of the male and of the
hermaphrodite are identical. The importance of this agreement will be
more fully appreciated, if the reader will consider the following table,
in which the generic and specific differences of the antennæ in the
Lepadidæ, as far as known to me, are given. These organs are of high
functional importance; they serve the larva for crawling, and being
furnished with long, sometimes plumose spines, they serve apparently as
organs of touch; and lastly, they are indispensable as a means of
permanent attachment, being adapted to the different objects, to which
the larva adheres. Hence the antennæ might, _à priori_, have been deemed
of high importance for classification. They are, moreover, embryonic in
their nature; and embryonic parts, as is well known, possess the highest
classificatory value. From these considerations, and looking to the
actual facts as exhibited in the following table, the improbability that
the parasites of _S. vulgare_ and _S. Peronii_, so utterly different in
external structure and habits one from the other, and from the
Cirripedes to which they are attached, should yet have absolutely
similar prehensile antennæ with these Cirripedes, appears to me, on the
supposition of the parasites being really independent creatures, and
not, as I fully believe, merely in a different state of sexual
development, insurmountably great.
The parasites of _S. vulgare_ take advantage of a pre-existing fold on
the edge of the scutum, where the chitine border is thicker; and in this
respect there is nothing different from what would naturally happen with
an independent parasite; but in _S. ornatum_ the case is very different,
for here the two scuta are specially modified, _before the attachment of
the parasites_, in a manner which it is impossible to believe can be of
any service to the species itself, irrespectively of the lodgment thus
afforded for the males. So again in _S. rutilum_, the shape of the
scutum seems adapted for the reception of the male, in a manner which
must be attributed to its own growth, and not to the pressure or
attachment of a foreign body. Now there is a strong and manifest
improbability in an animal being specially modified to favour the
parasitism of another, though there are innumerable instances in which
parasites take advantage of pre-existing structures in the animals to
which they are attached. On the other hand, there is no greater
improbability in the female being modified for the attachment of the
male, in a class in which all the individuals are attached to some
object, than in the mutual organs of copulation being adapted to each
other throughout the animal kingdom.
Generic Characters of the larval prehensile ANTENNÆ, in the Lepadidæ,
as far as known from their imperfect state of preservation, and the
number of species examined.
|Name of Species.
| |Length of, from end of disc to the further margin of the
| |oblique basal articulation: Scale, fractions of the 1/6000ths
| |of an inch.
| | |Length of, from end of disc to the inner margin of the
| | |basal articulation. Scale same.
| | | |Width of basal segment, in widest part. Scale same.
| | | | |Disc, length of. Scale same.
| | | | | |Disc, width of. Scale same.
| | | | | | |Ultimate segment, length of. Scale
| | | | | | |same.
| | | | | | | |Ultimate segment, width of.
| | | | | | | |Scale, fractions of the
| | | | | | | |1/20,000ths of an inch.
LEPAS: disc large, thin, almost _circular_, slightly elongated, with
several long spines on the hinder margin; end segment with three very
long, plumose spines on the upper _exterior_ angle.[61]
|_L. anatifera_ (?)
| |62
| | |--
| | | |20
| | | | |23
| | | | | |22
| | | | | | |--
| | | | | | | |--
|_L. australis_,
| |111
| | |--
| | | |40
| | | | |42
| | | | | |39
| | | | | | |18
| | | | | | | |30
|_L. pectinata_,
| |51
| | |--
| | | |23
| | | | |16
| | | | | |14
| | | | | | |9
| | | | | | | |16
|_L. fascicularis_,
| |60
| | |40
| | | |22
| | | | |16
| | | | | |15
| | | | | | |--
| | | | | | | |--
DICHELASPIS: disc _small_, thin, circular, with several spines on the
hinder margin; end segment, with two long spines on the upper _exterior_
angle.
|_D. Warwickii_,
| |54
| | |--
| | | |11
| | | | |7-8
| | | | | |7-8
| | | | | | |6
| | | | | | | |13-14
CONCHODERMA: disc large, thin, _transversely_ elongated, with several
long spines on the hinder margin; end segment, with two excessively
long, plumose spines on the upper _exterior_ corner.
|_C. virgata_,
| |82
| | |40
| | | |28
| | | | |25
| | | | | |35
| | | | | | |12
| | | | | | | |26
|_C. aurita._
| |--
| | |--
| | | |--
| | | | |28
| | | | | |40
| | | | | | |11
| | | | | | | |26
ALEPAS: disc small, slightly elongated, with two or more spines on the
hinder margin; end segment, with two long spines on the upper _inner_
corner, and four shorter ones on the exterior corner.
|_A. cornuta_,
| |60
| | |--
| | | |24
| | | | |14
| | | | | |12
| | | | | | |8
| | | | | | | |20
IBLA (parasitic males of): disc, _hoof-like_, _pointed_, elongated, with
a single spine on the hinder margin; end segment, with four short spines
on the upper exterior corner.
|_I. Cumingii_,
| |22
| | |--
| | | |7-8
| | | | |7
| | | | | |--
| | | | | | |3-4
| | | | | | | |7-8
|_I. quadrivalvis_,
| |32-33
| | |--
| | | |10
| | | | |8
| | | | | |5
| | | | | | |4
| | | | | | | |8
SCALPELLUM: disc _hoof-like_, generally _pointed_ and elongated, with a
single spine on the hinder margin; end segment, with a notch on the
inner[61] side, bearing two spines, longer than on the exterior corner.
|_S. vulgare_,
| |39
| | |19
| | | |10
| | | | |10-11
| | | | | |5-6
| | | | | | |6
| | | | | | | |7
|_S. ornatum_,
| |36
| | |21
| | | |10
| | | | |12
| | | | | |--
| | | | | | |--
| | | | | | | |--
|_S. Peronii_,
| |30
| | |19
| | | |--
| | | | |9
| | | | | |6
| | | | | | |5
| | | | | | | |10
POLLICIPES: disc small, _hoof-like_, not pointed, with a single spine on
the hinder margin; end segment, as in _Scalpellum_.
|_P. cornucopia_,
| |20
| | |--
| | | |6
| | | | |6
| | | | | |6
| | | | | | |6
| | | | | | | |8
[61] In the diameter of the disc, the thin membranous border,
which is present in the first three genera, is included; but I
have some doubts, whether this border be not the first rim of
cementing tissue, as all the specimens, of which measurements are
here given, had been removed after attachment. In using the terms
inner and outer sides of the end segment, it is supposed, that
this segment is stretched straight forwards, instead of being
bent rectangularly outwards, as in its natural position; and then
there can be no doubt which is the inner and outer sides.
It should be observed that the evidence in this summary is of a
cumulative nature. If we think it highly, or in some degree
probable,--from the ordinary form of _Ibla Cumingii_ having been shown
on good evidence to be exclusively female,--from the absence of ova and
ovaria in the assumed males of both species of Ibla, at the period when
their vesiculæ seminales were gorged with spermatozoa,--from the close
general resemblance between the parts of the mouth in the parasites and
in the Iblas to which they are attached,--from the differences between
the two parasites being strictly analogous to the differences between
the two species of Ibla,--from the generic character of their prehensile
antennæ,--and from other such points,--if from these several
considerations, we admit that these parasites really are the males of
the two species to which they adhere, then in some degree the occurrence
of parasitic males in the allied genus Scalpellum is rendered more
probable. So the absolute similarity in the antennæ of the males and
hermaphrodites both in _S. vulgare_ and _S. Peronii_; and such relations
as that of the relative villosity of the several species in this same
genus, all in return strengthen the case in Ibla. Again, the six-valved
parasites of _S. Peronii_ and _S. villosum_ are so closely similar, that
their nature, whatever it may be, must be the same; hence we may add up
the evidence derived from the identity of the antennæ in the parasite
and hermaphrodite _S. Peronii_, with that from the antennæ in the male
_S. villosum_, approaching in character to Pollicipes, to which genus
the hermaphrodite is so closely allied; and to this evidence, again, may
be added the singular coincident absence of caudal appendages in the
male and hermaphrodite _S. villosum_. If these two six-valved parasites
be received as the complemental males of their respective species, no
one, probably, will doubt regarding the nature of the parasite of _S.
rostratum_, in which the direct evidence is the weakest; but even in
this case, the particular point of attachment, and the state of
development of the valves, form a link connecting in some degree, the
parasites of the first three species with the last two species of
Scalpellum, in accordance with the affinities of the hermaphrodites.
When first examining the parasites of _S. rostratum_, _S. Peronii_, and
_S. villosum_, before the weight of the cumulative evidence had struck
me, and noting their apparent state of immaturity, it occurred to me
that possibly they were the young of their respective species, in their
normal state of development, attached to old individuals, as may often
be seen in Lepas; this, however, would be a surprising fact, considering
that _S. rostratum_ and _S. Peronii_ are ordinarily attached, in a
certain definite position, to horny corallines, and considering that the
exact points of attachment in these three parasites, (of which I have
seen no other instance amongst common Cirripedes,) namely, between the
scuta, would inevitably cause their early destruction, either directly
or indirectly, by their living supports being destroyed. Nevertheless, I
carefully examined a young specimen of _S. rostratum_ only thrice as
large as the parasite; and not having very young specimens of _S.
Peronii_ and _villosum_, I procured the young of closely-allied forms,
namely, of _S. vulgare_, (with a capitulum only 4/100th of an inch in
length,) and of _Pollicipes polymerus_, (with a capitulum of less size
than that of one of the parasites,) and there was not the least sign of
anything abnormal in the development of the valves. In _S. vulgare_, at
a period when the calcified scuta could have been only 1/100th of an
inch in length, (and therefore considerably less than the scuta in the
parasites,) the upper latera must have been as much as 4/1000ths of an
inch in length, and the valves of the lower whorl certainly
distinguishable.
To sum up the evidence on the sex of the parasites, I was not able to
discover a vestige of ova or ovaria in the two male Iblas; and I can
venture to affirm positively, that the parasites of _S. Peronii_ and _S.
villosum_ are not female. On the other hand, in the two male Iblas, I
was enabled to demonstrate all the male organs, and I most distinctly
saw spermatozoa. In the parasitic complemental male of _S. vulgare_, I
also most plainly saw spermatozoa. In the parasites of _S. rostratum_,
_S. Peronii_, and _S. villosum_, the external male organs were present.
I may here just allude to the facts given in detail under Ibla, showing
that it was hardly possible that I could be mistaken regarding the
exclusively female sex of the ordinary form of _I. Cumingii_, seeing how
immediately I perceived all the male organs in the hermaphrodite _I.
quadrivalvis_; and as the parasite contained spermatozoa and no ova, the
only possible way to escape from the conclusion that it was the male and
_I. Cumingii_ the female of the same species, was to invent two
hypothetical creatures, of opposite sexes to the Ibla and its parasite,
and which, though Cirripedes, would have to be locomotive! I insisted
upon this alternative, because if the parasite of _I. Cumingii_ be the
male of that species, then unquestionably we have in _I. quadrivalvis_ a
male, complemental to an hermaphrodite,--a conclusion, as we have seen,
hardly to be avoided in the genus Scalpellum, even if we trust
exclusively to the facts therein exhibited.