A Monograph on the Sub-class Cirripedia Part 26

_Capitulum_ with fourteen valves, consisting of a pair of scuta and of terga, a carina, (which five valves are much larger than the others,) a rostrum, sub-rostrum, sub-carina, and three pair of small latera. All the valves are covered by membrane, as are the calcareous scales on the peduncle; and this membrane everywhere is densely clothed with spines.

The upper valves are not very thick; they stand rather close together.

The eight valves of the lower whorl are more solid, and are placed far apart; they are small, tending to become rudimentary. None of the valves are added to at their upper ends, in which respect this species differs remarkably from the others of the genus, and approaches in character to Pollicipes.

_Scuta_, with a deep hollow for the adductor muscle, triangular, with the basal margin elongated, and protuberant.

_Terga_, large, flat, triangular, basal point blunt, with the carinal margin slightly hollowed out, and the scutal margin protuberant. Apex solid.

_Carina_, rather longer than the terga, straight, gradually widening from the upper to the basal end, deeply concave. In young specimens the upper part is slightly bowed inwards. Apex solid.

_Sub-carina_, with the inner surface crescent-shaped; the umbo points transversely outwards; in width it exceeds the largest of the latera.

_Rostrum_, triangular, internally (fig. 8 _a_) concave; basal margin slightly hollowed out, and deeply notched; rather less in width than the carina; short, with the umbo pointing upwards and outwards. In young specimens the apex curves a little inwards.

_Sub-rostrum_, with the inner surface transversely elongated (fig. 8 _b_), slightly crescent-shaped, about two thirds as wide as the rostrum.

The apex points transversely outwards.

_Latera_, three pair; the middle pair apparently corresponds with the upper latera of the other species of the genus. The two other pair of latera, together with the rostrum and sub-carina, form a whorl. The sub-rostrum lies by itself, a little beneath this whorl. The latera are smaller than the rostrum or the sub-carina. They are placed far distant from each other; their inner surfaces are triangular; their umbones point upwards; the rostral pair is smaller than the other two pair, which are of equal size. The exact position of the rostral latus differed on the two sides of the specimen examined; apparently its normal position is at the baso-lateral angle of the scuta.

_Peduncle_, wide at the summit, longer than the capitulum; calcified scales small, not arranged very regularly; flattened, spindle-shaped, rather far separated from each other; imbedded in membrane, so that even their summits are rarely uncovered. The surface of the membrane is thickly clothed with spines, which are strong, thick, yellow, pointed, and furnished with large tubuli running to the underlying corium. These spines are arranged in groups of from three or four, to five or six.

Besides these larger spines, the whole surface is villose with very minute colourless spines, not above 1/20th of the length of the larger ones. The surface of attachment is broad. This species, not being symmetrically attached to a coralline, the peduncle does not curve, as in most of the other species, towards the rostrum.

The capitulum is above half an inch in length.

_Mouth._--The labrum is much produced downwards, but yet the mouth is not very far distant from the adductor muscle: the upper part is bullate, forming a small overhanging point, and in longitudinal diameter equals the rest of the mouth. _Palpi_ blunt.

_Mandibles_ with four teeth, strong, short, thick, the second tooth much smaller than the others; inferior angle broad, pectinated.

_Maxillae_ with a long, rather sinuous edge, which, near the inferior angle, has a narrow projecting point, bearing rather finer spines; there is, also, apparently, a very minute tuft of small spines close under the two large upper spines: there are, altogether, about twenty pair of spines, without counting the smaller ones.

_Outer Maxillae_, with the inner edge slightly concave, continuously covered with bristles; exteriorly, with a prominence covered with longer bristles. Olfactory orifices prominent, protected by a slight punctured swelling between the bases of the first pair of cirri.

_Cirri._--Prosoma moderately developed; first pair of cirri rather far removed from the second pair. The segments of the three posterior pair are not elongated, short, slightly protuberant in front, bearing four or five pairs of strong spines; a little below each pair, there is an intermediate tuft of very fine straight bristles, of which the upper tuft is the largest; on the lateral upper rims there are some short, strong spines; dorsal tufts rather small and thick; spines all more or less serrated, especially on the broad basal segments of the three anterior cirri. Pedicels of the cirri not particularly protuberant in front. First cirrus with rami, slightly unequal in length; not short; basal segments much thicker and more protuberant than the upper segments. Second cirrus; anterior ramus with six or seven basal segments highly protuberant, and crowded with spines; posterior ramus with about six segments, similarly characterised. Third cirrus with the anterior ramus having six, and the posterior ramus five segments, also similarly characterised.

_Caudal Appendages_ absent, there being only a slight swelling on each side of the a.n.u.s.

The _oesophagus_ runs parallel to the labrum, and enters obliquely the summit of the stomach, which is dest.i.tute of caeca: the biliary envelope is longitudinally plicated.

There are no _Filamentary Appendages_.

_Testes_ large, branched like a stag's horns, attached in a sheet to the ventral surface of the stomach: the vesiculae seminales enter the prosoma, and have their reflexed ends not very blunt. The _p.e.n.i.s_ is rather narrow, with the terminal half plainly ringed, and bearing tufts of fine bristles arranged in circles, one tuft below the other; on the basal half there are only a few scattered minute bristles.

_Affinities._--In the downward growth of all the valves, in the presence of a sub-rostrum, in the shape of the scuta, carina, and more especially of the triangular latera, in the form of the peduncle, with its irregularly-scattered calcified scales, in the shape of the animal's body, in the structure both of the mandibles and maxillae, in the arrangement of the spines, both on the anterior and posterior cirri, _Scalpellum villosum_ most closely resembles, or rather is identical with, Pollicipes. Had it not been for the formation of the valves forming the capitulum, and from the presence of Complemental Males, I should have placed this species alongside of _Pollicipes spinosus_ and _sertus_. In not having caudal appendages, _S. villosum_ differs from all the species of Scalpellum and Pollicipes; but this organ is variable to an unusual degree in Pollicipes.

COMPLEMENTAL MALE. Pl. VI, fig. 4.

From the kindness of Professor Owen, Mr. Gray, and Mr. c.u.ming, I have been enabled to examine six specimens of this species; and on two of them I found Complemental males. They were attached in the same position as in _S. Peronii_; namely, beneath the adductor muscle, in the fold between the scuta, so as to be protected by the latter when closed. This parasite is six-valved, and has a close general resemblance with that of _S. Peronii_, but differs in very many points of detail. It is represented of the natural size at _a_ fig. 4. The capitulum is 43/1000ths of an inch, measured across the scuta and terga; and the same measured from the base of the carina to the top of the capitulum; hence it is broader, by a quarter of the above measurement, and considerably higher than the male of _S. Peronii_. From the capitulum being higher, that is, not so much truncated, the orifice is placed more obliquely.

The membrane connecting the valves is finely villose, and is besides furnished with spines, conspicuously thicker and longer than those on the male _S. Peronii_. The scuta and terga are much more elongated, a scutum being here 35/1000ths of an inch in length. The carina descends only just below the basal points of the terga, instead of far below them. The rostrum is a little broader and more arched than the carina; it is 2/1000ths in length, and therefore more than two thirds of the length of the carina, the latter being 28/1000ths of an inch from the apex to the basal margin. The primordial valves, with the usual hexagonal tissue, are seated on the tips of the scuta, terga, and carina, but not on the rostrum; so that these valves follow the same law of development, as in the ordinary and hermaphrodite form of Scalpellum.

The scuta (_a_, fig. 4, greatly enlarged), the terga (_b_), and carina (_c_) of the male, resemble the same valves in the hermaphrodite, much more closely than do these valves in the male and hermaphrodite _S.

Peronii_. The rostrum has not its basal margin hollowed out, and is very much larger relatively to the carina, than in the hermaphrodite. The large relative size of the rostrum in the complemental male both of this species and of _S. Peronii_, is a remarkable character, which I can in no way account for.

The peduncle is narrow and short, but in a different degree in the two specimens examined. It is naked. The prehensile antennae 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 antennae 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.

_Maxillae_, with a considerable notch under the upper pair of large spines; inferior part of the edge not prominent.

_Outer Maxillae_, 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 maxillae being notched and in the lower part not being prominent, and, lastly, in the bristles on the inner face of the outer maxillae 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.

_p.e.n.i.s_ 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 vesiculae 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 antennae 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 p.e.n.i.s, and from the presence, as I believe, of vesiculae 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 maxillae,--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 s.e.xual 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 cla.s.sed by their own characters, would, from the reasons formerly a.s.signed, form a new genus, nearer to Ibla than to the parasites of Scalpellum: so, again, the a.s.sumed 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 antennae, 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-cla.s.s, 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 s.e.xually from the Cirripedes on which they are parasitic, this relations.h.i.+p 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 cla.s.sed 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. c.u.mingii_, 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 dest.i.tute of spines on the membrane connecting the valves; and had it not been for this circ.u.mstance, 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 dest.i.tute 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 antennae, 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 s.e.x 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 antennae. I observed the antennae 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 antennae 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 antennae 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 antennae 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 antennae in the Lepadidae, 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 antennae might, _a priori_, have been deemed of high importance for cla.s.sification. They are, moreover, embryonic in their nature; and embryonic parts, as is well known, possess the highest cla.s.sificatory 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 antennae 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 s.e.xual 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 cla.s.s 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 ANTENNae, in the Lepadidae, 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.