Chapter C: VIRGATA, var. OLFERSII (3)

_Ova_, spherical, 5/400ths of an inch in diameter, united as usual into two ovigerous lamellæ. The ovigerous fræna are extraordinarily small, and might be very easily overlooked; their length, in a full-sized specimen, was only 7/400ths of an inch, and they projected only 2/400ths from the inner surface of the sack. The glands on their margin, to which the lamellæ adhere, are pointed oval, with an extremely short footstalk, and that rather thick; the entire length of gland and footstalk, being only 2/3000ths of an inch. The larvæ, in their first stage of development, offer the usual characters, and closely resemble those of Scalpellum; the probosciformed mouth, however, is remarkably prominent, and the limbs unusually thick.

_Affinities._--This species most closely resembles _I. Cumingii_, and cannot be distinguished externally, except by the absence of the blue colour on the marginal and interior portions of the valves; and this can hardly be ascertained without separating and cleaning them, owing to the blueness of the underlying corium. Internally some slight differences may be perceived in the form of the valves. Considering these so slight differences, it is highly remarkable that this species should be hermaphrodite, whilst _I. Cumingii_ is unisexual. There is a greater, though still slight, difference in the included animal’s body; the palpi in _I. quadrivalvis_ are blunter, the mandibles smoother, the olfactory orifices darker-coloured; the rami of the first cirrus more unequal, the spines more numerous on the segments of the posterior cirri, and lastly and most conspicuously, the caudal appendages are very much longer relatively to the length of the sixth cirrus, than in _Ibla Cumingii_.

COMPLEMENTAL MALE.

I have examined one specimen of the hermaphrodite _I. quadrivalvis_, preserved in spirits from Kangaroo Island, and one dry from Adelaide, both places in South Australia, and four from an unknown locality, purchased from Mr. Sowerby; and within five out of these six specimens, males were attached. In one of them, two males of different ages were included, one adhering to the peduncle of the other: in _I. Cumingii_, also, it may be remembered, there was a case of two males parasitic on one female. I may add that I opened another quite young specimen, from Adelaide, not counted with the above, and it was without a male. The males in the five specimens were attached low down, at the rostral end, almost in a horizontal position, stretching across the bottom of the sack; one of them, however, was placed considerably on one side. One individual which I measured, was 16/100ths of an inch in length, and 5/100ths in width in the widest part, namely, about half down the peduncle. I may state, for the sake of comparison, that the hermaphrodite to which this individual was attached, was, including the peduncle and capitulum, one inch in length, that is, six times as long as the male, and one fifth of an inch in width, that is, four times as wide. The above measurements show that the male of this species is rather more than twice as large as that of _I. Cumingii_. In consequence of this greater size, I dissected, with the utmost care, the one specimen which was excellently preserved in spirits, and found every part, with a few exceptions, so exactly the same as in the male of _I. Cumingii_, only larger and more conspicuous, that it will be sufficient to indicate the few points of difference.

The most conspicuous difference is, that the oblique fold separating the thorax and peduncle is more plainly developed, projecting at the point corresponding to _h_ in fig. 1, Pl. V, 8/1000ths of an inch; in the middle the fold is notched; it can be traced more easily than in _I. Cumingii_, running beneath and parallel to the basal edge of the mouth, to the ventral margin of the body. In the mouth there is hardly any difference; the maxillæ, however, have two notches even plainer than in the hermaphrodite _I. quadrivalvis_, or than in the male _I. Cumingii_, but the depth of such notches is always a variable character; there are also more spines on the edge in the male of the present species, than in _I. Cumingii_. Both mandibles and maxillæ in the male _I. quadrivalvis_, are larger than in the male _I. Cumingii_, to a greater degree than the larger proportional size of the body in the former will account for; and this, likewise, is the case with these same organs in the hermaphrodite _I. quadrivalvis_ compared with the female _I. Cumingii_. The tubular olfactory orifices are situated in the same peculiar position as in the hermaphrodite, and as in both sexes of _I. Cumingii_: they are 1/500th of an inch in diameter, and about as thick as one of the lower segments in the rami of the sixth cirrus.

The thorax, as in the male of _I. Cumingii_, is quite rudimentary, and serves as a mere flap to protect the mouth. In the three specimens carefully examined, the posterior cirri had each only one ramus, whilst the anterior cirri generally had two: in one specimen, one of the rami in the anterior cirrus was formed of five segments, and the other ramus of three segments, both rami being supported on a uni-articulated pedicel; but on the opposite side of the same individual, the anterior cirrus was represented by a mere knob. The longer ramus of the anterior cirrus, in the best-developed individual, barely exceeded in length the mandibles measured along the line of the teeth! In one specimen between the bases of the posterior cirri, there were two perfectly distinct caudal appendages; these, like the cirri, are in a quite rudimentary condition; one was 5/1000ths of an inch in length, and consisted of three segments, the upper edges of which had short spines; the other was shorter, uni-articulated, but spinose. In a second specimen, these appendages were quite aborted. Close under them, on the inside or towards the mouth, (that is, in the normal position,) there was a rudimentary but quite distinct penis, with the apex projecting freely, and with the sides distinguishable from the ventral surface of the thorax, for the length of 1/1000th of an inch: the corium lining this little penis made the terminal orifice plainly visible. The vesiculæ seminales lie in the usual position, and are conspicuous; they are slightly tortuous, with their ends blunt: in the specimen so well preserved in spirits, they were filled with a mass of spermatozoa, perfectly distinct; and the whole cavity of the body was lined with globular and pear-shaped testes. Assuredly there was no vestige of ovarian tubes. From the greater size and excellent preservation of this specimen, which rendered the examination of the generative system so easy, I was able to examine the contents of the stomach, in which I found the delicate epithelial coat, separated as usual, and containing cellular matter, on which the animal had preyed, but the nature of which I was unable to make out. The anus was much plainer than in the male of _I. Cumingii_. I saw the eye distinctly. I could not distinguish the orifices of the acoustic (?) sacks; and I think I should have seen them, if they had existed.

_Prehensile Antennæ._--I examined these in the larvæ presently to be mentioned, and therefore they were in better condition than in the mature animal when cemented. Their total length, measured along the outside, from the basal articulation to the end of the disc, is 32/6000ths or 33/6000ths of an inch--that is, one third longer than in _I. Cumingii_; whilst the hoof-like disc itself is 8/6000ths, or only 1/6000th of an inch longer than this same part in _I. Cumingii_: the apex of the disc is downy, or bears some excessively minute spines. The ultimate segment has its end irregularly rounded, with the spines obscurely divided into two groups, the outer group consisting of two or three longer and thinner spines, and the inner group of, as I believe, five rather shorter spines: the longer spines equal in length the whole ultimate segment. I could not perceive that they were plumose, as in many other genera. A single, rather thicker and long spine, pointing backwards, is attached to the under side of the disc, nearly opposite to the point where the ultimate segment is articulated on the upper convex surface. Another single, curved spine is attached on the outer side of the basal segment, near its distal end.

_Development of the Male._--In the specimen before alluded to, which included two males, one of these was only the 30/1000ths of an inch in length, and therefore between one fifth and one sixth of the size of the mature male. It had, probably, undergone only one exuviation since its metamorphosis, for the larva is nearly as long, namely, 25/1000ths of an inch. In this young male, the mouth formed one third of the entire length: it was attached, not as in every other case to the sack of the hermaphrodite, but low down to the peduncle of the other male.

In the sack with these two males, there were certainly four, I believe five, larvæ, which in every main point of structure resembled the larvæ of other pedunculated Cirripedes. From the peculiar form of their prehensile antennæ, differing in no respect, except in the proportional lengths of the segments, from the same organ in the male _I. Cumingii_, I can feel no doubt that these were the larvæ of the male _I. quadrivalvis_;--for a moment’s reflection will show how excessively improbable it is, that several larvæ of some other Cirripede, and that a Cirripede intimately allied to the parasitic male Ibla, should have forced themselves, without any apparent object, into the sack of the hermaphrodite Ibla. The larvæ, though not yet attached, were on the point of attachment, so that the single eye of the mature animal could be distinctly seen, lying near to the two great compound eyes of the larva. We have also just seen, that one male quite recently here had undergone its metamorphosis. The larvæ are 25/1000ths of an inch in length, and rather more than 10/1000ths in width in the widest part: they are boat-shaped, the dorsal edge forming the keel of the boat; the anterior end is only a little blunter than the posterior end; the quasi-bivalve carapace is smooth. All the essential points of structure in the larvæ of other Cirripedes at this stage, could be distinctly here seen,--such as the two compound eyes, with the apodemes to which they are attached, and the two oblong sternal plates whence the apodemes spring,--the adductor muscle,--the six natatory legs, with long plumose spines,--the abdomen, with its three small segments and the caudal appendages,--the prehensile antennæ already described,--and, lastly, the two little (auditory?) sacks at the antero-sternal edges of the carapace, but not so near the anterior extremity as in Lepas. The four or five larvæ, after having undergone in the open sea the several preparatory metamorphoses common to the class, must have voluntarily entered the sack of the hermaphrodite: ultimately would they, on finding two males already attached there, have retired, and sought another individual less well provided; or would they all have remained, and so formed a polyandrous establishment, such as we shall presently see occurs sometimes in Scalpellum? This must remain quite uncertain.

In this same hermaphrodite specimen of _I. quadrivalvis_, the two ovigerous lamellæ contained some hundreds of larvæ in the first stage of development, which were liberated from their enveloping membranes by a touch of a needle: they were about the 16/1000ths of an inch in length, and presented all the usual characters of larvæ at this period. What a truly wonderful assemblage of beings of the same species, but how marvellously unlike in appearance, did this individual hermaphrodite present! We have the numerous, almost globular larvæ, with lateral horns to their carapaces, with their three pair of legs, single eye, probosciformed mouth and long tail:--we have the somewhat larger larvæ in the last stage of development, much compressed, boat-formed, with their two great compound eyes, curious prehensile antennæ, closed rudimentary mouth and six natatory legs so different from those in the first stage:--we have the two attached males, with their bodies reduced almost to a mouth placed on the summit of a peduncle, with a minute, apparently single eye shining through the integuments, without any carapace or capitulum, and with the thorax as well as the legs or cirri rudimentary and functionless:--lastly, we have the hermaphrodite, with all its complicated organisation, its thorax supporting six pairs of multi-articulated two-armed cirri, and its well-developed capitulum furnished with horny valves, surrounding this wonderful assemblage of beings. Unquestionably, without a rigid examination, these four forms would have been ranked in different families, if not orders, of the articulated kingdom.

_Concluding Remarks._--If the creature which I have considered as the male of _Ibla Cumingii_ be really so, and the evidence formerly given seems to me amply conclusive, then the animal just described, from its close affinity in every point of structure with the former, assuredly is the male of _Ibla quadrivalvis_. But feeling strongly how improbable it is, that an additional or complemental male should be associated with an hermaphrodite, I will make a few remarks on the only possible hypothesis, if my view be rejected,--namely, that the two parasites considered by me to be exclusively males, are not so, but are independent hermaphrodite Cirripedes, the female organs and ova (which, if present, would have been nearly mature, judging from the presence of spermatozoa in both species) having been overlooked by me in every specimen: and again, that in the animal described as the female _I. Cumingii_, I have, though minutely dissecting several specimens, and finding far smaller parts, such as the organs of sense and nervous system, entirely overlooked all the conspicuous male organs, though when I came to _I. quadrivalvis_, and naturally expected to find it likewise exclusively female, a single glance showed me the great probosciformed penis, and by the simplest dissection the vesiculæ seminales and testes were exhibited. Such an oversight is scarcely credible; but even if assumed, we have to believe in the extraordinary circumstance of the two parasites being species of an independent genus, not only the very next in alliance to the animals to which they are attached, but in certain most important points, namely, the organs of the mouth, actually deserving a place in the very same genus. Moreover, the two parasites differ from each other, not only in about the same slight degree, but in a corresponding manner, as do the two Iblas to which they are attached; thus the mouths of _Ibla quadrivalvis_ and _I. Cumingii_ are closely similar, (the difference being barely of specific value,) so are the mouths of the two parasites; but the parts are larger in the hermaphrodite _I. quadrivalvis_, than in _I. Cumingii_, so are they in the parasites. Again, the most conspicuous character in _I. quadrivalvis_, is the number of segments in the caudal appendages, far exceeding those in the other species of Ibla, as well as of every other pedunculated Cirripede, and the parasite of this species has articulated spinose appendages, far larger than the barely visible, non-articulated pair in _I. Cumingii_.

Considering the whole case, there seems no room to doubt the justness of the conclusion arrived at, under the former as well as under the present species, namely, that these little parasites are the males of the two species of Ibla to which they are attached;--wonderful though the fact be, that in one case, the male should pair with an hermaphrodite already provided with efficient male organs. It is to bring this fact prominently forward, that I have called such males, Complemental Males; as they seem to form the complement to the male organs in the hermaphrodite. We look in vain for any, as yet known, analogous facts in the animal kingdom. In the genus Scalpellum, however, next in alliance to Ibla, in which, consequently, if anywhere, we might expect to find such facts, they occur; and until these are fully considered, I hope the conclusions here arrived at, will not be summarily rejected. Although the existence of Hermaphrodites and Males within the limits of the same species, is a new fact amongst animals, it is far from rare in the Vegetable Kingdom: the male flowers, moreover, are sometimes in a rudimentary condition compared to the hermaphrodite flowers, exactly in the same manner as are the male Iblas. If the final cause of the existence of these Complemental Males be asked, no certain answer can be given; the vesiculæ seminales in the hermaphrodite of _Ibla quadrivalvis_, appeared to be of small diameter; but on the other hand, the ova to be impregnated are fewer than in most Cirripedes. No explanation, as we have seen, can be given of the much simpler case of the mere separation of the sexes in _Ibla Cumingii_: nor can any explanation, I believe, be given of the much more varied arrangement of the parts of fructification in plants of the Linnean class, Polygamia.

_Genus_--SCALPELLUM. Pls. V, VI.

SCALPELLUM. _Leach._ Journ. de Physique, t. lxxxv, July, 1817.

LEPAS. _Linn._ Systema Naturæ, 1767.

POLLICIPES. _Lamarck._ Animaux sans Vertebres, 1818.

POLYLEPAS. _De Blainville._ Dict. des Sc. Nat., 1824.

SMILIUM (pars generis). _Leach._ Zoolog. Journal, vol. 2, July,
1825.

CALANTICA (pars generis). _J. E. Gray._ Annals of Philosophy, vol.
x, (new series,) Aug. 1825.

THALIELLA (pars generis). _J. E. Gray._ Proc. Zoolog. Soc., 1848.

ANATIFA. _Quoy_ et _Gaimard_. Voyage de l’Astrolabe, 1826-34.

XIPHIDIUM (pars generis). _Dixon._ Geology of Suffolk, 1850.

(_Herm. et Foem._) _Valvis 12 ad 15: lateribus verticilli inferioris quatuor vel sex, lineis incrementi plerumque convergentibus: sub-rostrum rarissime adest: pedunculo squamifero, rarissime nudo._

(Herm. and Fem.) Valves 12 to 15 in number: latera of the lower whorl, four or six, with their lines of growth generally directed towards each other: sub-rostrum very rarely present: peduncle squamiferous, most rarely naked.

Filamentary appendages, none: labrum, with the upper part highly bullate: trophi, various: olfactory orifices, more or less prominent: caudal appendages, uniarticulate and spinose, or none.

_Males_, parasitic at or near the orifice of the sack of the female or of the hermaphrodite: thorax enclosed within a capitulum, furnished with three or four rudimentary valves, or with six perfect valves: peduncle either short and distinct, or confounded with the capitulum: sometimes mouth and stomach absent, and cirri non-prehensile; sometimes mouth and cirri normal.

Generally attached to horny corallines, in the warmer temperate
seas over the whole world.

I have felt much doubt in limiting this genus: the six recent species which it contains, differ more from each other than do the species in the previous genera. Mr. Gray has proposed or adopted generic names for four of the species, and a fifth certainly has equal claims to this same rank. These genera have been founded almost exclusively on the number of the valves; and oddly enough, the numbers have generally been given wrongly, namely, in Scalpellum, Calantica, Thaliella, and Xiphidium. Scalpellum blends through _S. villosum_ into Pollicipes; and this latter genus has an equal right with Scalpellum, to be divided into sub-genera, three in number. Hence, no less than eight genera might be made out of the twelve recent species of Scalpellum and Pollicipes, and their formation, in some degree, be justified; but, in my opinion, this inordinate multiplication of genera destroys the main advantages of classification. At one time, I even thought that it would be best to follow Lamarck, and keep the twelve recent species in one genus; but considering the number of fossil species, I believe the more prudent course has been followed, in retaining the two genera Scalpellum and Pollicipes; more especially as I can hardly doubt, that several other species will be hereafter discovered.

Having so lately described in the Memoirs of the Palæontographical Society, the fossil species, I will not here further allude to them, than to state, that out of the fifteen species therein described, _S. magnum_ comes very close to the recent _S. vulgare_, and that several Eocene and Cretaceous species, such as _S. quadratum_, _S. fossula_, and _S. maximum_, are allied to _S. rutilum_ and _S. ornatum_. _Scalpellum villosum_, a recent species, has stronger claims than any other species to be generically separated; and its habits, in not being attached to horny corallines, are also different, but the identity of its Complemental Male with that of _S. Peronii_, and its numerous points of resemblance in structure with the other species, have determined me not to separate it. _Scalpellum Peronii_, _villosum_, and _rostratum_, in having a sub-carina,--in the rostrum being pretty well developed,--and in the Complemental Male being pedunculated, and furnished with a functional mouth and prehensile cirri, may be separated from _S. vulgare_, _ornatum_ and _rutilum_; but even between these two little groups, _S. rostratum_ is in some respects intermediate, namely, in having three pairs of latera, and more especially in the rudimentary condition of the valves of its Complemental Male, and in the position in which the male is attached to the hermaphrodite. The three species in the second little group, namely, _S. vulgare_, _S. ornatum_, and _S. rutilum_, are more nearly allied to each other in all their characters, especially in the characters drawn from their Males, than are the other three species. _S. ornatum_ and _S. rutilum_ are considerably nearer to each other than any other two of the species. Upon the whole I conclude that the six species must be thrown either into five or into four genera (the first three species making one genus), or all into one genus, and this latter has appeared to me the preferable course. The separation even of Scalpellum and Pollicipes, as already stated, is hardly natural. The fact of these genera having existed from a remote epoch, and having given rise during successive periods to many species now extinct, is probably the cause that the few remaining species are so much more distinct from each other, than is common in the other genera of Lepadidæ. Whenever the structure of the whole capitulum in the fossil species is well known, and as soon as more species, recent and fossil, shall have been discovered, then probably the genus Scalpellum will have to be divided into several smaller genera.

_Description._--The _Capitulum_ is much compressed, and generally produced upwards; it is formed of from twelve to fifteen valves, which are rather thin, and with the exception of _S. ornatum_, almost entirely covered by membrane, bearing spines: the valves are seldom locked very closely together. A sub-rostrum exists only in _S. villosum_, which species leads on to Pollicipes; in _S. vulgare_ the rostrum is rudimentary and hidden. The scuta, terga and carina, are much larger than the other valves: these five valves seem to differ essentially from the others in being at first developed under the form of the so-called primordial valves: the other valves commence by a small indistinct brown spot, very different from the hexagonal tissue of the primordial valves: I saw this very clearly in young specimens of _S. vulgare_. At first, the scuta, terga and carina, grow exclusively downwards (and permanently so in most fossil species), and therefore the growth of the scuta and carina is in an absolutely opposite direction to what it is in Lepas, Pæcilasma and Dichelaspis. After a short period the scuta are added to at their upper ends; the portion thus added, stands at a rather lower level, and projects in a rather different direction from the first-formed part of the valve, giving to it, in some respects, the appearance of having been broken and mended. This structure is common to _S. vulgare_, _S. rostratum_ and _S. Peronii_. The upper Latera (except in _S. villosum_) grow in the same manner, namely, at first exclusively downwards, and then both upwards and downwards. The rostral and carinal latera (with the same exception of _S. villosum_) have their umbones seated laterally, at opposite ends of the capitulum,--the umbones of the rostral latera being close to the rostrum, and those of the carinal pair close to the carina, and consequently their chief growth is directed towards each other. The carina in all the species, except _S. villosum_, is either bowed or angularly bent; in the latter case the lower half is parallel to the peduncle, and the upper half, extending far up between the terga, is parallel to their longer axes. In some of the species the carina is added to almost equally at both ends; in _S. ornatum_ it grows but little at the upper end, and to a varying degree in different individuals according to their age; in _S. rutilum_ the umbo is at the apex, and there is consequently no upward growth; lastly, in _S. villosum_ the carina widening much from the apex to the basal margin, grows exclusively downwards, and a portion of the apex projects freely,--characters all common to the carina in the genus Pollicipes. The upper latera occur in all the species; in the lower whorl there are either two or three pair of latera, in the former case the infra-median pair being absent. The latera differ considerably in shape in the different species.

The _Peduncle_ is generally rather short, and, with the exception of _S. Peronii_, is covered with calcified scales. These scales are generally small, and placed symmetrically in close whorls, in an imbricated order, with each scale corresponding to the interspace between two scales in the whorls above and below. In _S. ornatum_, the scales are so wide, transversely, that there are only four in each whorl. In _S. villosum_, the scales are spindle-shaped and arranged somewhat irregularly in transverse rows, not very near to each other. New calcareous scales originate only round the top of the peduncle, and they continue to grow only in the few upper whorls; and as the peduncle itself continues to increase in diameter by the formation of new inner membranous layers and the disintegration of the old outer layers, the calcareous scales come in the lower part of the peduncle to stand further and further apart. In the earliest stage of growth there are no calcareous scales on the peduncle in _S. vulgare_; they first appear under the carina. Spines are articulated in great numbers on the surface of the peduncle in _S. vulgare_, _S. Peronii_, and _S. villosum_, and very short ones on that of _S. rostratum_.

_Attachment._--All the species, except _S. villosum_, are attached to horny corallines: the singular means of attachment in _S. vulgare_ will be described under that species, and is probably common to several of the other species. The larva in most, or in all cases, when it proceeds to attach itself, clings head downwards to the branch, and hence the capitulum comes to be placed upwards, with its orifice fronting the branch and the carina outwards. The sucking disc of the prehensile antennæ of the larva, in the five species examined, was a little pointed, and in shape resembled the hinder hoof of a mule: this may perhaps be accounted for by the narrowness of the branches of the corallines, to which it has to adhere: a large circular disc, as in Lepas, would have been worse than useless: the ultimate segment in most or all the species, has on its inner side (the segment being supposed to be extended straight forward) a notch or step, bearing, I believe, two spines.

_Size and Colour._--Some of the species attain a medium size, others are small. The valves are generally clouded red or pink, but sometimes white.

_Mouth._--The various parts vary far more than in any genus hitherto described. The labrum is highly bullate, with the upper part forming a rounded overhanging projection, and with the lower part much produced, so that the mouth is placed far from the adductor scutorum muscle, and consequently the orifice is directed more towards the ventral surface of the thorax than in most other Cirripedes: on the crest of the labrum there are some very small teeth in several of the species, but not in all. The mandibles have either three or four main teeth, generally with either one or two small teeth intermediate between the first and second large teeth, and in the case of _S. Peronii_, with small teeth between all the larger ones. The maxillæ have their edges furnished with many spines, and are either straight or have the inferior part prominent and step-formed. The outer maxillæ have the spines on their inner edges either continuous or divided into two groups, of which latter structure we have not hitherto had any very well characterised example. The olfactory orifices are either highly or moderately protuberant.

In most of the species the prosoma is little developed, and the first cirrus is placed far from the second. The _Cirri_ are generally but little curled, and have elongated segments, with long, generally serrated spines: the first cirrus varies in proportional length; the second and third cirri have both their rami more thickly clothed with spines than are the three posterior cirri, the spines being generally arranged in three or four longitudinal rows: the cirri, however, of _S. villosum_ in all respects resemble closely the cirri of _Pollicipes sertus_ and _P. spinosus_.

The _Caudal Appendages_ are uniarticulate, small, and clothed with spines: in _S. villosum_, however, differently from in all other allied forms, there are no appendages.

The _Stomach_, in those species which I opened, is destitute of cæca. There are no filamentary appendages.

_Generative System._ The ova are nearly spherical, and remarkably large, as was stated to be the case in the introductory discussion, in which the larva of _S. vulgare_, in the first stage of development, was described: the ovigerous fræna are small. The testes are large, but the vesiculæ seminales in some of the species extraordinarily small. _Scalpellum ornatum_, and perhaps _S. rutilum_, are unisexual; the other species are hermaphrodite, but most or at least some of the individuals, are furnished with Complemental Males. These latter are fully described under each species, so I will here only remark, that _S. ornatum_, which alone (excepting perhaps _S. rutilum_) is unisexual, has less claim than the other species to be generically separated: we have seen also, in Ibla, that similar sexual differences occur in two most closely allied species. It is very singular how much more some of the Males and Complemental Males in Scalpellum differ from each other, than do the female and hermaphrodite forms; this seems due to the different stages of embryonic development at which the males have been arrested. In the males, however, of _S. rostratum_, _S. Peronii_, and _S. villosum_, compared one with another, but not with the males of the other species, the parts of the mouth and apparently the cirri, resemble each other more closely, than do the same organs in the hermaphrodites. At the end of this genus I shall give a summary on the highly remarkable sexual relations both in Scalpellum and Ibla.

_Distribution._--The species seem distributed over the whole
world, but as far as we can trust our present scanty materials,
are most common in the warmer temperate regions. The _S.
vulgare_ ranges from the Norwegian seas to Naples. Most of the
species are inhabitants of deep water.

_Affinities._--In the preliminary remarks, we have seen how this genus blends into Pollicipes; and under the head of Oxynaspis, I have shown its close affinity to that genus. If, indeed, we take _Pollicipes spinosus_, and destroy all but six of the already minute and almost rudimentary latera, we shall, as far as the capitulum is concerned, convert it into a Scalpellum, closely similar to _S. villosum_. If we take any species of Scalpellum, (excepting _S. villosum_ and _S. rutilum_,) and destroy all the valves, but the scuta, terga and carina, we shall convert it into an Oxynaspis. Lastly, I have shown under Ibla, that in several most remarkable peculiarities of structure, there is a manifest affinity between Scalpellum and that genus.

_Geological History._--Full details on this subject have been given in the Memoirs of the Palæontographical Society. I will here only state, that the oldest known form of Scalpellum occurs in the Lower Green Sand.

[=T= SUB-CARINÂ NULLÂ.]

1. SCALPELLUM VULGARE. Pl. V, fig. 15.

SCALPELLUM VULGARE. _Leach._ Encyclop. Brit. Suppl., vol. iii,
1824.

LEPAS SCALPELLUM. _Linn._ Systema Naturæ, 1767.

---- _Poli._ Test. utriusque Siciliæ, Pl. vi., fig. 16. 1795.

POLLICIPES SCALPELLUM. _Lamarck._ An. sans Vertebres, 1818.

POLYLEPAS VULGARE. _De Blainville._ Dict. Sc. Nat., Plate, fig. 4.
1824.

SCALPELLUM LÆVE, var. _Leach._ Zoolog. Journal, vol. ii, p. 215,
1825.

---- SICILIÆ, var. _Chenu._ Illust. Conch. Pl. iv, fig. 9.

SCALPELLUM VULGARE, (et var.) _Brown._ Illust. of Conch., 1844,
Pl. li., figs. 7 to 20.

_S. (Herm.) valvis 14, si rostrum pæne rudimentale includatur: lateribus superioribus inæqualiter ovatis._

(Herm.) Capitulum with 14 valves, including the rudimentary rostrum: upper latera irregularly oval.

Mandibles, with four or five teeth: maxillæ, with the edge straight, bearing numerous spines.

COMPLEMENTAL MALE flask-formed, with four rudimentary valves; no mouth; cirri not prehensile; attached to the occludent margin of the scutum, near the umbo.

Great Britain, Ireland, France, Norway, Naples. Attached to
horny corallines, at from twenty to thirty, sometimes even to
fifty fathoms in depth, according to Forbes and MacAndrew.

HERMAPHRODITE.

_Description._--Capitulum much flattened with the apex produced, of a pale brown colour, sometimes faintly tinted purple, composed of 14 valves, of which the rostrum is rudimentary and barely visible externally; valves thin, white, translucent, smooth, slightly marked by the lines of growth, separated from each other by rather wide interspaces of colourless membrane, which is thickly clothed by small, articulated spines of unequal length. The valves, excepting sometimes their umbones, are also covered with membrane, bearing spines, placed in rows parallel to the lines of growth; the spines are particularly numerous round the orifice of the sack.

_Scuta_ slightly convex, thrice as long as broad; upper part much acuminated; occludent margin almost straight; basal margin nearly at right angles to the occludent margin; the tergal margin is separated from the lateral margin by an angle more or less prominent; a slight curved ridge runs from the umbo to this angle, and this deserves especial notice, inasmuch as it indicates the outline which the valve assumed in its earliest growth, and which is permanently retained in most of the older fossil species. Along the occludent margin, there is a trace of a ledge, developed in a variable degree, and which is noticed only on account of the plainly visible ledge along this same margin, in the allied genus Oxynaspis. The umbo, or centre of calcification, is seated close to the occludent margin, and at about one fourth of the length of the valve from the apex. Internally, (fig. 15, _a´_, Pl. V,) the part above the umbo is flat; and beneath this upper part, there is a large rounded hollow (_d_) for the adductor muscle: a fold or indentation (_a_) running downwards from the umbo, extends in a very oblique line across the occludent margin. This fold is of high interest as giving lodgment to the Complemental Males, and will hereafter often be referred to.

_Terga_, triangular, flat; occludent margin, very slightly arched.

_Carina_ much bent, with the umbo placed at barely one third of the entire length of the valve from the apex. Two very slight ridges can be perceived, one on each side, running from the umbo to the basal margin, and separating the roof from the parietes of the valve; these ridges are of great use in distinguishing the fossil carinæ of Scalpellum, from the carinæ of Pollicipes. The part above the umbo is formed by the upward production of a marginal slip along each side of the valve, which slips in the fossil species (C in the woodcut, fig. 1, given in the Introduction,) I have designated as the intra-parietes. The lower part of the valve gradually widens from the umbo downwards; internally, the whole is deeply concave, and continuously curved. The angle varies at which the upper and lower portions externally meet each other; but is never less than 135°. The upper part of the carina runs up between the terga for three-quarters of their length; the basal margin does not extend down low enough to pass between the carinal latera.

_Rostrum_, (fig. 15 _b´_, seen externally, and highly magnified,) minute, almost hidden by the enveloping membrane and by the small prominent umbones of the rostral latera; in area equalling about one fourth of the rostral latera; externally pyramidal, with the upper side rather longer than the lower; internally slightly concave, square, with the upper margin and sometimes with the lower margin, slightly hollowed out. Umbo of growth nearly central.

_Upper Latera_, flat, irregularly oval, with an almost rectangular shoulder under the basal angle of the terga; in area, about one third larger than the largest valve of the lower whorl; the exact degree of elongation of the oval figure varies a little. Umbo seated a little above the central point.

_Lower Whorl_,--_Rostral Latera_, nearly twice as long as broad, lying under the basal margins of the scuta: umbo seated over the rostrum; opposite end, towards which the valve widens either sensibly or but little, is either square or rounded; in area, less than any of the other valves, excepting the rostrum; in breadth, equalling either half or one third of the height of the infra-median latera; growth, directed chiefly towards the infra-median latera. The freely-projecting umbo is about one sixth part of the entire length of the valve.

_Infra-median Latera_, rather larger than the carinal latera; their shape varies from elongated pentagonal with the angles rounded, to oval, with the longer axis directed upwards. The umbo is seated a little above the middle of the basal margin, so that there is some little growth downwards, but the main growth is upwards. The upper point generally stands a little above that of the carinal latera.

_Carinal Latera_, flat, less in area than the infra-median latera; basal margin nearly straight; carinal margin slightly hollowed out, terminal margin arched and protuberant. The umbones of the two valves almost touch each other under the middle of the carina; main growth towards the infra-median latera and upwards; umbones projecting not above one fifth of the entire length of the valve.

_Peduncle_, much flattened, rarely as long as the capitulum, with the upper end nearly as wide as it; the lower end is either blunt, or tapers to a very fine point. The calcareous scales are transversely elongated, and are about four times as wide as high; their internal surfaces are slightly concave, and their external, convex; the two ends are pointed. Viewed internally, the scales approach in shape to rhomboids. There are, in a medium-sized specimen, about twenty scales in each whorl, their tips overlapping each other: the whorls are placed not very near each other and at rather unequal distances, except round the uppermost part, where, being in process of formation, they are packed closely together. The membrane uniting the scales, supports numerous transverse rows of articulated spines, varying from 1/100th to 1/500th of an inch in length, and each furnished with a long sinuous tubulus, 1/10,000th of an inch in diameter, running through the membrane to the underlying corium.

_Attachment._--Specimens are attached to various horny corallines, and occasionally to the peduncles of each other.[51] In both cases, supposing the coralline to be erect, the capitulum is placed upwards, with its orifice towards the branch to which it is attached, and consequently with its carina outwards. Where several are crowded in a group, their peduncles often become twisted and their positions irregular, with their orifices facing in any direction. This uniform position is simply the consequence of the larva attaching itself head-downwards, and from the position of the prehensile antennæ, necessarily with its sternal surface parallel and close to the branch of the coralline; hence the dorsal surface, which afterwards is converted into the carina, faces outwards. The peduncle, as already stated, often tapers, at its basal extremity, to a sharp point. In very young specimens, for instance in one with a capitulum only 1/20th of an inch in length, the method of attachment is the same as in Lepas and many other genera, namely, by cement proceeding exclusively from the antennæ of the larva; but in older and full-grown specimens, instead of the whole bottom of the peduncle becoming flattened and broadly attached, which would be here impossible, the cement is poured out through a straight row of orifices along the rostral edge, thus causing, by an excellent adaptation, a narrow margin to adhere firmly to the thin and cylindrical branches of the coralline. These orifices are represented, magnified seven times, in Pl. IX, fig. 7, in which the lower attached portion of the peduncle is split open and exhibited; they are circular, and stand at regular intervals, in a straight line; the higher orifices are larger, but further apart from each other than the lower ones; in one full-grown specimen, I counted ten of these orifices in a length of exactly a quarter of an inch. At each period of growth, the corium recedes a little from the attached portion of the peduncle; of which portion, the greater part is thus left empty and as incapable of further growth, as are the larval antennæ at the extreme point: in the specimen figured, the corium extended a little below the upper orifice. The prehensile antennæ, however, I must remark, do not strictly rise from the extreme point of the peduncle, but at a little distance from it, on the rostral surface; this simply ensues from the antennæ in the larva, being situated on the sternal surface, close to, but not actually on the front of the head. The two cement glands are seated high up on the sides of the peduncle, and remote from each other; they are small, unusually globular and transparent. The two cement-ducts (fig. 7 _a_ _a_) proceeding from them, are 3/2000ths of an inch in diameter, and run in a zig-zag line; at the point where they pass through the corium to enter the lower attached portion of the peduncle, they become closely approximated, and partially imbedded in the membrane of the peduncle. Together they run along the rostral edge, giving out through each orifice a little disc of brownish cement, and finally they enter the larval antennæ. The peduncle, just above the attached portion, where still lined by corium, no doubt increases in diameter at each period of growth, and must, I presume, become pressed against the almost parallel branch of the coralline. The corium, at this same period, shrinks, or is absorbed, and the two cement-ducts come in contact with, and adhere to, the inner surface of the outer membrane of the peduncle; and then, by a process which I do not understand in this or any other Cirripede, apertures are formed both in the ducts and through the membrane, so that the cement passes through, firmly fastening the outer surface of the peduncle with its calcareous scales and spines, to the coralline.

[51] Mr. Peach, (Transact. Brit. Assoc., 1845, p. 65,) states
that this is sometimes the case in Cornwall; and I have seen a
similar instance in a fine group from Naples.

The structure of the larval prehensile antennæ will be most conveniently described when we come to the Complemental male; and figures (10-12, Pl. V) will be given.

_Size and Colours._--Montagu states (‘Test. Brit.,’ p. 18) that British specimens rarely have a capitulum .62 of an inch in length; I have, however, seen an Irish specimen, .7 long; and several specimens, from the Bay of Naples, .8 long, and including the peduncle, 1.3 in length. The valves in all the specimens are white, and the membrane connecting them either nearly white, or dirty pale yellowish, or purplish-brown. Within the sack the corium under the valves is tinted pale purple, and two very faint bands of the same colour can generally be distinguished running down the two sides of the peduncle. Body, coloured yellowish-white, with the upper segments of the pedicels of the cirri, tinted in front with purple.

_Body_, much flattened, the prosoma is very little developed; the mouth placed far from the adductor muscle, and is directed in a remarkable manner towards the ventral surface of the thorax: the first pair of cirri stands far separated from the second pair.

_Mouth._--Labrum with the upper part highly bullate, forming an overhanging projection equalling the longitudinal axis of the mouth; basal margin much produced; crest with a row of bead-like teeth.

_Palpi_ rather small, with their external margin straight, and internal margin oblique: the bristles on the two palpi just meet each other.

_Mandibles_, with five or six teeth, with the second, (or second and third, when there are six teeth,) smaller than the others; in two specimens, there were five teeth on one side and six on the other; inferior angle rather broad and strongly pectinated.

_Maxillæ_ with the edge nearly straight, without any notch, but with the inferior portion very slightly projecting; there are twelve or thirteen pairs of unequal spines, of which some of the middle ones are rather longer than the others, and almost as long as the two upper great spines.

_Outer Maxillæ._--On the inner margin the bristles are divided into two separate tufts; exteriorly, near the base, there is a distinct rounded swelling with bristles. The olfactory orifices are highly protuberant, approximate, flattened, scarcely tapering towards their upper ends.

_Cirri._--The five posterior pair are elongated, very little curled, with short pedicels; their segments are long, not at all protuberant in front, bearing five or six pairs of long, slightly serrated spines, with a very minute tuft of bristles between each pair, and with some short lateral spines on the inner side of each segment; on the fourth pair of cirri, these lateral spines are considerably developed; dorsal tufts consist of fine spines, with one much longer than the others. _First pair_ short, separated by a wide interval from the second; rami unequal in length, by between two and four segments; longer ramus having nine segments, scarcely half as long as the rami of the second cirrus; shorter ramus with seven segments; in the same individual there were twenty segments in the sixth cirrus. The segments in the shorter ramus of the first cirrus are oblong in a transverse direction, and may be compared to a set of shields placed transversely and strung together; in the longer ramus the segments are longitudinally oblong; in both they are thickly covered with spines. _Second cirrus_; the anterior ramus is a little broader than the posterior ramus, with the segments bearing about five rows of bristles; fifteen segments in the shorter ramus. _Third pair_, with the two rami equal in thickness, and with the segments differing very little from those of the posterior cirri, excepting that the serrated spines in the external lateral rows are rather larger. The fourth pair is remarkable by having, on the inner side of the upper edge of each segment, a little tuft of minute smooth spines, flattened, and a little enlarged near their ends, so as to be spear-shaped; I could not see these singular spines on the other cirri. The lower segments of the pedicels of all the cirri, excepting the sixth pair, are remarkable from having their inner edges, in the middle, produced into a considerable, abrupt, rounded projection, irregularly covered with spines.

_Caudal Appendages_, (Pl. X, fig. 21,) very small, flattened, of nearly the same width throughout; in a medium-sized specimen, only 1/100th of an inch in length; each bears from ten to twenty small bristles placed distantly from each other, of which those on the rounded apex are the longest.

_Generative System._--The penis is remarkably acuminated; the vesiculæ seminales are unusually small, and enter only for a short distance into the prosoma; the testes are large. The ovarian tubes are of large diameter; the ova are nearly spherical and large, namely, 9/400ths of an inch in diameter; they are not numerous, and lie in single layers in the two lamellæ. The ovigerous fræna are well developed, and lie under the scuta; one I measured was 5/100ths of an inch in length and 2/100ths in width; the margin is obliquely truncated and slightly sinuous. This species breeds late in the autumn, and even in mid-winter; I have examined a specimen from Cornwall with ova containing larvæ, taken on the 26th of October; again, in another specimen from Belfast, sent to me by Mr. Thompson, taken in January, there were ova in the lamellæ, and therefore no doubt impregnated; and on February the 12th I received from Mr. Peach, from Cornwall, specimens so very young that they must have become attached during the first days of the month.

_Varieties._--The specimens from near Naples, (which I owe to the kindness of the Rev. F. W. Hope,) are somewhat larger, and differ slightly from those of Britain: they form, I imagine, the _S. Siciliæ_ of Chenu. After carefully examining them internally and externally, I think it is quite impossible to consider them specifically distinct, for although in several specimens, the valves were placed a little further apart from each other,--the upper latera a little more elongated,--the carinal latera rather narrower in their upper half,--the infra-median latera rather more rounded,--and, lastly, in the scuta, the tergal margin extended almost in the same line with the lateral margin; nevertheless in other specimens, I could perceive no difference whatever. It is, however, remarkable that in several full-grown Neapolitan specimens there were no Complemental males, whereas I have never seen a single full-grown British specimen without such being present. In some specimens in the British Museum, without any given locality, I have observed considerable variation in the breadth of the carinal and rostral latera.

COMPLEMENTAL MALE. Pl. V, figs. 9-14.

When first dissecting _Scalpellum vulgare_, I was surprised at the almost constant presence of one or more very minute parasites, on the margins of both scuta, close to the umbones: these are represented, but rendered darker and therefore more conspicuous than in nature, in the drawing, Pl. V, fig. 15, which is three times the natural size. I carelessly dissected one or two specimens, and concluded that they belonged to some new class or order amongst the Articulata; but did not at that time even conjecture, that they were Cirripedes. Many months afterwards, when I had seen in Ibla, that an hermaphrodite could have a complemental male, I remembered that I had been surprised at the small size of the vesiculæ seminales in the hermaphrodite _S. vulgare_, so that I resolved to look with care at these parasites; on doing so, I soon discovered that they were Cirripedes, for I found that they adhered by cement, and were furnished with prehensile antennæ, which latter, I observed with astonishment, agreed in every minute character, and in size, with those of _S. vulgare_: the importance of this agreement will not at present be fully appreciated. I also found, that these parasites were destitute of a mouth and stomach; that consequently they were short-lived, but that they reached maturity; and that all were males. Subsequently the five other species of the genus Scalpellum were found to present more or less closely analogous phenomena. These facts, together with those given under Ibla (and had it not been for this latter genus, I never probably should have even struck on the right track in my investigation,) appear sufficient to justify me, in provisionally considering the truly wonderful parasites of the several species of Scalpellum, as Males and Complemental Males. When these parasites are fully described, will be the proper time to discuss and weigh the evidence on their sexual relations and nature. I will now describe the parasite of _S. vulgare_.