Chapter 18

_Peduncle._--The main part of the animal, as may be seen in the drawing, consists of the peduncle, of which the imbedded portion tapers more or less suddenly in a very variable manner, and is of variable length,--in one specimen being one fourth of the entire length, and in another consisting of a mere minute blunt point. The free upper part of the animal is bent in various directions, in relation to the imbedded portion. The latter passes obliquely through the chitine membrane and corium, lining the sack of the female, and running along amidst the underlying muscles and inosculating fibrous tissue, is attached to them by cement at the extremity. The peduncle is often, but not in the individual represented, much constricted at the point where it passes through the skin of the female, and generally at several other points, especially towards the extremity (see fig. 1); the stages of its deeper and deeper imbedment being thus marked. The constrictions are, I believe, simply due to the continued growth of the male, whilst the hole through the membrane of the female does not yield. The imbedment, which is considerable only when the lower part of the peduncle is almost parallel to the coats of the sack, seems caused by the growth and repeated exuviations of the female; I believe, that the larva attaches itself to the chitine tunic of the sack, and that the cement, by some unknown means, affects the underlying corium, so that this particular portion of the tunic is not moulted with the adjoining integuments, and that the growth of the surrounding parts subsequently causes this portion to be buried deeper and deeper: it is, I believe, in the same way as the end of the peduncle in _Conchoderma aurita_, sometimes becomes imbedded in the skin of the whale to which it is attached.

The outer tunic of the peduncle is thin and structureless: in the fold (fig. 1 _h_) under the cirri, there is a central triangular gusset of still thinner membrane, corresponding in position to the membrane connecting the two terga in the female, and there subjected to much movement. I may here remark, that this fold, in its office of slightly protecting the thorax and in its position, evidently represents the capitulum with its valves, enclosing the whole body of the female. The outer tunic is lined by corium, mottled with purple, and within this there are two layers of striæ-less muscles, transverse and longitudinal, as in all pedunculated Cirripedes. The corium extends some way into the imbedded portion of the peduncle, and consequently, the outer tunic there continues to be added to layer under layer, and as it cannot be periodically moulted, it becomes much thicker than in the upper free part of the animal: the corium, however, does not extend to the extreme point, so that in it growth of all kind ceases.

_Antennæ._--The peduncle terminates (Pl. V, fig. 1 _e_) in the two usual, larval, prehensile antennæ, which it is very difficult to see distinctly; they are tolerably well represented in fig. 5, greatly magnified. Their extreme length, measured from the basal articulation to the tip of the hoof-like disc, is 22/6000ths of an inch, the disc itself being 7/6000ths of an inch. The disc is slightly narrower than the long basal segment, from which it is divided by a broad conspicuous articulation; its lower surface is flat and its upper convex, altogether resembling in shape a mule’s hoof; its apex is fuzzy with the finest down; it bears a narrow ultimate segment, thrown, as usual, on one side; this segment supports on its rounded irregular summit, at least five, I believe, judging from the structure of the same part in the male larva of _Ibla quadrivalvis_, six or seven spines, longer than the segment itself: one long spine arises from the under side of the disc, near the base of the ultimate segment, and points backward: there is also a single curved spine on the outside, near the distal end of the basal segment. These organs were imbedded in a heart-shaped ball or cylinder of brown, transparent, finely laminated cement, and thus attached to the fibrous tissue of the female. The two cement-ducts (fig. 1 _f_) were very plain, each about 1/6000th of an inch in diameter, containing the usual inner chord of opaque cellular matter. I traced them at the one end into the prehensile antennæ as far as the disc; and at the other, up the peduncle for about one fourth of its length, where I lost them, and could not discover with certainty any cement glands. I may, however, here mention, that I found in the lower half of the peduncle, numerous, yellowish, transparent, excessively minute, pyramidal bodies, with step-formed sides; of these two or three often cohered by their bases like crystals; I have never seen anything like these in other Cirripedes, but it has occurred to me that they may possibly be connected with the formation of the cement: for in the last larval condition of Lepas, the cement-ducts run up to the gut-formed ovaria, filled at this period with yellowish, grape-like, cellular masses, without the intervention of cement glands, and I can imagine that similar masses, not being developed into functional ovaria, might give rise to the yellow pyramidal bodies.

_Mouth._--The mouth is well developed; it is represented as seen vertically from above, in Pl. V, fig. 2, magnified about 60 times; the positions of the cirri and the outline of the thorax are accurately shown by dotted lines; a lateral view is given in fig. 1. In the specimen figured, the longitudinal diameter of the mouth, including the labrum, was 5/400th of an inch. The muscles of the several trophi have transverse striæ, and are the strongest and most conspicuous of any in the body. The labrum is largely bullate, with its summit slightly concave; the trophi are arranged in a remarkable manner, in a semicircular line, so as to be opposed to the labrum rather than to each other: there are no teeth or spines on the crest of the labrum, which overhangs the oesophageal cavity.

The _Palpi_ (fig. 2 _b_ and fig. 3) are very small, dark purple, bluntly pointed, with a few small bristles at the point; they do not extend beyond the knob at each corner of the labrum, which is here present, as in all other Lepadidæ; they are much smaller than in the female, though of a similar shape, and consequently, their points are much further apart: within their bases, the lateral muscles of the mandibles are, as usual, attached; they are represented in fig. 3, as seen from the inside, with the eye on a level with the concave summit of the labrum. The rudimentary condition of the palpi is connected, as remarked under the _Anelasma squalicola_, with the absence of efficient cirri.

The _Mandibles_ (fig. 7) are well developed; they so closely resemble those of the female that it is superfluous to describe them: they are, however, smoother, without any trace of the teeth being pectinated, and with the inferior point smaller: measured in their longer direction, they are 7/2000th of an inch in length, and, therefore, a little less than one third of the size of those of the female. These organs have the usual muscles well developed, and the usual articulations.

The _Maxillæ_ (fig. 8) have a rather rudimentary appearance; yet they have the same size relatively to the mandibles, as in the female, the spinose edge being 3/2000ths of an inch in length. These organs resemble, to a certain extent, those of the female, differing from them in being less prominent,--in the outline being more rounded, with the notches even less distinct,--and in the spines being fewer. The apodeme is short and broad.

The _Outer Maxillæ_ (fig. 6) are pointed, with a small tuft of bristles at the apex; they are much less hairy than in the female, but have nearly the same unusual shape. Outside their bases, and between them and the inner maxillæ, the two well-developed, tubular, flattened, square-topped, olfactory orifices, project in exactly the same remarkable position as in the female; these are not represented in fig. 2, though sometimes they can be very distinctly seen, when the mouth is viewed from vertically above.

_Thorax and Cirri._--The thorax is in a rudimentary condition: I did not observe the usual articulations. The whole, as seen from vertically above, is of small size, compared with the mouth; the outline is accurately shown by dotted lines in Tab. 5, fig. 2, together with the positions of the two pair of cirri, the caudal appendages, and anus. The posterior end of the thorax does not rise to the level of the summit of the mouth; and the thorax seems of no service, excepting perhaps as a sort of outer lip to protect the mouth. The cirri are in an extreme state of abortion, and evidently functionless; they are lined with purplish corium, without the vestige of a muscle; they are usually distorted and bent in different directions; they vary in size, and even those on opposite sides of the same individual, sometimes do not correspond, and do not arise from exactly corresponding points of the thorax. There are always two pair of cirri, which, as I conclude from the position of the excretory orifices, answer to the fifth and sixth pair in other Cirripedes. Each cirrus (fig. 4) usually carries only one ramus, placed on a large basal segment, evidently corresponding to the pedicel of a normal cirrus. The posterior are larger than the anterior cirri, which latter spring from points a little lower down on the thorax. In the posterior cirrus figured, the great basal articulation or pedicel, almost equals in length, and much exceeds in thickness, the four segments of the ramus; these segments are furnished on their upper dorsal edges with little brushes of spines, but have not even a trace of the normally larger and far more important anterior spines. In one specimen, the anterior cirrus had a large pedicel, carrying three segments, like those of the posterior pair; but in another specimen, one of the three segments showed traces of being divided into two, thus making four imperfect segments; whilst on the corresponding side of this same individual there were only two ill-formed segments, with their few spines differently arranged. Again, in a third specimen, the great basal segment of the anterior cirrus on one side, bore, exteriorly to the usual ramus, a single segment furnished with bristles, and evidently representing a second ramus; thus showing that the great basal segment certainly answers to a pedicel. I may here add, that on the integuments of these cirri, I observed with a high power, the serrated scale-like appearance common in other Cirripedes. Directly between the bases of the sixth cirrus, there is a very minute papillus, which, under the highest power, can be seen to consist of two closely approximate, flattened points; these, I have no doubt, are the caudal appendages in an extremely rudimentary condition, for I traced the vesiculæ seminales to this exact spot: close outside these rudimentary points, on a slight swelling, is the anus. It will presently be seen that in the male of the closely allied _Ibla quadrivalvis_, the nature of these caudal appendages admits of no doubt, for in this species they consist of more than one segment, are spinose, and close under them towards the mouth, there is a perfectly distinct papillus, representing the usual probosciformed penis.

_Alimentary Canal._--The oesophagus is very narrow, and of remarkable length; from the orifice under the mandibles, it first runs back (in this respect not well represented in Pl. V, fig. 1,) under the bullate labrum, and then straight down the peduncle, where it terminates in the usual bell-shaped expansion, entering one side of the small globular stomach; the latter, at its lower end, is slightly constricted, and then is rather abruptly upturned. The rectum is of unparalleled length, and extremely narrow; it can be best detected after the dissolution by caustic potash of the softer parts, when its inner coat of chitine can be seen to be continuous, in the ordinary manner, with the outer integuments of the thorax. The anus, as already stated, is seated on a slight swelling, and consists of a small longitudinal slit (_f_, fig. 2), placed close outside the two very minute caudal appendages.

_Organ of Sight._--In all the specimens, a little below the fold separating the mouth from the peduncle, and near the abdominal (or rostral) edge, a black ball (_c_, fig. 1), about 1/1000th of an inch in diameter, is conspicuous. When dissected out, it is somewhat conical in form, and appears to consist of an outer coat, with a layer of pigment-cells of a dark purple colour, surrounding a transparent, rather hard lens, apparently leaving a circular orifice at the summit, and forming a short tube at the base, surrounding what I believe to be a nerve. I was not able to perceive that this eye consisted of two eyes united, which the analogy of other Cirripedes makes me suppose probable, although in the ordinary and hermaphrodite _Ibla quadrivalvis_, the eye also appeared single. It is seated under the two transparent muscular layers, close upon the upper end of the stomach, and this is the exact position, as stated in the introductory discussion (p. 49), in which the eyes of pedunculated Cirripedes are commonly situated.

_Generative System._--Within the muscular layer all round the upper part of the peduncle, and surrounding the stomach, there are numerous, little, rather irregular globular balls, with brown granular centres, so closely resembling the testes in other Cirripedes, though of smaller size, that I cannot doubt that this is their nature: they were much plainer, larger, and more numerous in some specimens than in others. The vesiculæ seminales can seldom be made distinctly out; but having cut one specimen transversely across the thorax, they were as plain as could be desired, lying parallel and close to each other above the rectum, (the animal being in the position as drawn,) and therefore in their normal situation. Each had a diameter four times as great as that of the rectum. In this individual the contents seemed (whether from decomposition or state of development, or from my not having used high enough power, I know not,) merely pulpy; but I have since found, in another specimen, masses of the most distinct spermatozoa, with the usual little knots on them, associated with numerous cells, about as large as and resembling those which I have examined in living Cirripedes, and from which I have every reason to believe the spermatozoa are developed. The vesiculæ seminales unite and terminate under the two extremely minute caudal appendages, and here I think I saw an orifice; but there is certainly no projecting, probosciformed penis.

Having dissected the six specimens with the utmost care, and having scrupulously examined the ovaria in other Cirripedes during their early stages of development, even before the exuviation of the larval locomotive organs, and in specimens of smaller size than the male Ibla, I am prepared to assert that there are no ovaria, and that these little creatures are exclusively males. It should be borne in mind, that in some of the specimens there were perfect spermatozoa in the vesiculæ seminales (as likewise in some of the males of _I. quadrivalvis_), and, therefore, if these individuals had been hermaphrodites, their ova would have been, at this period, well developed, and ready for impregnation: in this state it is almost impossible that they could have been overlooked. Moreover, it is probable that such ova would not have been very small, for the larvæ whence the parasitic males are derived, attain (as might have been inferred from the known dimensions of their prehensile antennæ, and as we shall show actually is the case in _I. quadrivalvis_,) the size common amongst ordinary Cirripedia.

_Concluding Remarks._--That these animals are true Cirripedes, though having so different an external appearance from others of the class, admits of not the least doubt. The prehensile antennæ, enveloped in cement and including the two cement-ducts, would have been amply sufficient, without other parts--for instance, the mouth, by itself perfectly characteristic with each organ, together with the whole alimentary canal, constructed on the normal plan,--to have proved that they were Cirripedia. Under the head of the closely-allied _Ibla quadrivalvis_, we shall, moreover, see that the males are developed from larvæ, having every point of structure--the peculiar quasi-bivalve shell, the two compound eyes, the six natatory legs, &c.,--characteristic of the Order. But in some respects, the males are in an embryonic condition, though unquestionably mature, as shown by the spermatozoa;--thus, in the thorax and mouth opening throughout their whole width into the cavity of the peduncle, that is, homologically into the anterior part of the head, and in the viscera being there lodged instead of in the thorax and prosoma, there is a manifest resemblance to the larva in its last stage of development: the absence of a probosciformed penis, the spineless peduncle, the food being obtained without the aid of cirri, and the length of the rectum, are likewise embryonic characters. Not only are these males, as just remarked, Cirripedia; but they manifestly belong to the Pedunculated Family. If a specimen had been brought to me to class, without relation to its sexual characters, I should have placed it, without any hesitation, next to the genus Ibla; if the mouth alone had been brought, I should assuredly have placed it actually in the genus Ibla: for let it be observed how nearly all the parts resemble those of _Ibla Cumingii_, excepting only in size and in being less hairy. The trophi are arranged in the same peculiar position as in the female; the labrum is largely bullate, without teeth on the crest; the palpi, though relatively smaller, are of the same shape; so are the mandibles; the maxillæ are more rounded and less prominent, but have the same exact size relatively to the mandibles; the outer maxillæ have the same, quite peculiar pointed outline, and the olfactory orifices are tubular, and hold the same unusual position. It is most rare to find so close a resemblance in the parts of the mouth, except in very closely allied genera, and often species of the same natural genus differ more. Again, in the long oesophagus and constricted stomach there is a resemblance to Ibla. In the male of _Ibla quadrivalvis_, the caudal appendages are multi-articulate; now, this is a character confined to four genera, namely, Ibla, Alepas, Pollicipes, and Lithotrya. I may add, that large tubular olfactory orifices are confined to the same genera, together with Scalpellum. Lastly, it particularly deserves notice, that the prehensile antennæ, in having a hoof-like and pointed disc, with a single spine on the heel, much more closely resemble these organs in Scalpellum, certainly the nearest ally of Ibla, than in any other genus; they differ from the antennæ in Scalpellum, only in the ultimate segment not having a notch on one side. These organs, unfortunately for the sake of comparison, were not found in the female and ordinary form of Ibla. The full importance of the above generic resemblance in the antennæ, will hereafter be more clearly seen, when their classificatory value is shown in the final discussion on the sexual relations of Ibla and Scalpellum.

Here, then, we have a pedunculated Cirripede _very much_ nearer in all its essential characters to Ibla than to any other genus, and exclusively of the male sex; and this Cirripede in six specimens, from two distant localities, adhered to an Ibla exclusively of the female sex. May we not, then, safely conclude that these parasites are the males of the _Ibla Cumingii_? Considering that, in the same class with the Cirripedia, there is a whole family of crustaceans, the Lerneidæ, in which the males, compared with the females to which they cling, differ as much in appearance as in Ibla, and are even relatively smaller, I should not have added another remark, had there not been under the head of the following species, and of the next genus Scalpellum, a class of allied facts to be advanced, which in some respects support the view here taken, but in others are so remarkable and so hard to be believed, that I will call attention to the alternative, if the above view be rejected. The ordinary _Ibla Cumingii_ must have a male, for that it is not an hermaphrodite can hardly be questioned, seeing how easy it always is to detect the male organs of generation; and we must consequently believe in the visits of a locomotive male, though the existence of a locomotive Cirripede is improbable in the highest degree. Again, as the little animal, considered by me to be the male of _I. Cumingii_, is exclusively a male, (for there were no traces of ova or ovaria, though the spermatozoa were perfect,) we must believe in a locomotive Cirripede of the opposite sex, though the existence in any class of a female visiting a fixed male is unknown:[48] in short, we should have hypothetically to make two locomotive Cirripedes, which, in all probability, would differ as much from their fixed opposite sexes, as does the Cirripede, considered by me to be the male of _I. Cumingii_, from the ordinary form. This being the case, I conclude that the evidence is amply sufficient to prove that the little parasitic Cirripede here described, is the male of _Ibla Cumingii_.

[48] It deserves notice, that in the class Crustacea, both in the Lerneidæ and in the Cirripedia, the males more closely resemble the larvæ, than do the females; whereas amongst insects, as in the case of the glow-worm in Coleoptera, and of certain nocturnal Lepidoptera, it is the female which retains an embryonic character, being worm-like or caterpillar-like, without wings. But in all these cases, the male is more locomotive than the female.

If we look for analogies to the facts here given, we shall find them in the Lerneidæ already alluded to, but in these the males are not permanently attached to the females, only cling, I believe, to them voluntarily. The extraordinary case of the Hectocotyle, originally described as a worm parasitic on certain Cephalopoda, but now shown by Kölliker to be the male of the species to which it is attached, is perhaps more strictly parallel. So again in the entozoic worm, the _Heteroura androphora_ the sexes cohere, but are essentially distinct: “this singular species, however,” according to Professor Owen,[49] “offers the transitional grade to that still more extraordinary Entozoon, the _Syngamus trachealis_, in which the male is organically blended by its caudal extremity with the female, immediately anterior to the slit-shaped aperture of the vulva. By this union a kind of hermaphroditism is produced; but the male apparatus is furnished with its own peculiar nutrient system; and an individual animal is constituted distinct in every respect, save in its terminal confluence with the body of the female. This condition of animal life, which was conceived by Hunter as within the circle of physiological possibilities, has hitherto been exemplified only in the single species of Entozoon, the discovery of the true nature of which, is due to the sagacity and patient research of Dr. C. Th. Von Siebold.” In Ibla, the males and females are not organically united, but only permanently and immovably attached to each other. We have in this genus the additional singularity of occasionally two males parasitic on one female.

[49] Cyclopædia of Anatomy and Physiology, p. 142.