Pedicels of Cirri.—The pedicel of the first pair is very short; that of the second is the longest; those of the posterior cirri decreasing in length. Upper segments short; lower segments in the second, third and fourth cirri, irregularly and rather thickly clothed with bristles, but in the fifth and sixth cirri, there is a regular double row of main spines, with some minute intermediate ones: hence there is a difference, both in the rami and in the pedicels, between the fourth cirrus and the fifth and sixth, and this is a unique case. On the dorsal surface of the pedicel of the second cirrus, there is a tuft of much feathered fine spines.

Caudal Appendages.—Each consists of eight much tapering, very thin segments, furnished with a few short simple spines round their upper margins, and with a longer tuft on the terminal short segment; basal segments twice as thick as the middle ones. In length, these caudal appendages equal the pedicels of the sixth pair of cirri, and are a very little shorter than the rudimentary rami of these same cirri.

General Remarks.—Having examined this species first in the genus, I fully anticipated that the very remarkable character of the inner rami of the fifth and sixth cirri being rudimentary, and serving the same function (if any) with the caudal appendages, would have been generic; but this is not the case, for Alepas cornuta cannot be separated from A. minuta without violating a clear natural affinity.

4. ALEPAS TUBULOSA.

Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, fig. 5, 1834.

A. apertura parva prominente et tubulosa: scutis et prominentiis secundum marginem carinalem, nullis.

Orifice small, tubular, protuberant; capitulum without horny scuta or projections along the carinal margin.

Animal unknown.

New Zealand, Tolaga Bay. Attached to a living Palinurus.

I have given the above brief character from the plate, and imperfect description in the voyage of the Astrolabe. The small and distinctly tubular orifice, and the smooth carinated edge of the globose capitulum, appear sufficiently to distinguish this species from A. cornuta. The colour is stated to have been white with violet tints. Length, two (French) lines.

ANELASMA. Gen. Nov. Pl. IV.

ALEPAS. Loven. Ofversigt of Kongl. Vetenskaps-Akad. Foerdhandlinger: Forsta Argangen. Stockholm, 1844, p. 192, Tab. 3.

Capitulum sine valvis: apertura ampla: pedunculus fimbriatus, sub-globosus, infossus.

Capitulum without valves; aperture large; peduncle fimbriated, sub-globular, imbedded.

Cirri without spines; outer maxillae and palpi rudimentary, spineless; mandibles minute, with several small teeth irregularly placed; maxillae minute, with very minute irregularly scattered spines. No caudal appendages.

* * * * *

I owe to the great kindness of Professor Steenstrup, an examination of this very curious cirripede, well described and figured by Loven, who considered it an Alepas. It lives parasitic, with its peduncle imbedded in the skin of sharks, in the North Sea. According to the principles of classification which I have followed, this cirripede cannot possibly remain in Alepas, and must form a new genus; for some time, indeed, I thought that a new family or sub-family ought to have been instituted for its reception; but when I considered that its highly peculiar characters are all negative, as the non-articular, non-spinose structure of the cirri, and that no new or greatly modified functional organ is present, I concluded that it might properly remain amongst the Lepadidae. We shall, moreover, hereafter see that the male of Ibla, which, of course, must remain in the same family with the female, is, in some analogous respects, even more abnormal than Anelasma.

1. ANELASMA SQUALICOLA. Pl. IV, figs. 1-7.

ALEPAS SQUALICOLA. Loven, ut supra.

North Sea. Parasitic on Squalus.

Capitulum, destitute of valves; oval, much flattened; the double membrane composing it, thin, highly flexible, coloured externally and internally, by the underlying corium, of a blackish purple; aperture, extremely large, extending from the upper end of the capitulum, to close above the peduncle, gaping, and not protecting (in the dead condition) the cirri and mouth.

The Peduncle is about half as long as the capitulum, but, according to Loven, this part varies in length; it is a little narrower than the capitulum; colourless, from being imbedded in the shark's skin; sub-globular; basal end almost hemispherical. Total length of animal 1.3; diameter of peduncle .4 of an inch.

The external membrane of the capitulum is not nearly so thick as is usual in other Cirripedes, and is, therefore, unusually flexible. The internal membrane, on the other hand, is very much thicker than is usual, being only a little thinner than the outside coat; this circumstance, as well as the similarity in colour on both sides, is evidently due to the remarkable openness of the sack, and consequent exposure of its inside. The inner membrane, when viewed under a high power, is seen to be covered with the minutest spines; the external membrane is structureless, except that there are a few rows of very minute beads of hard chitine, like those which occur on the capitulum of Conchoderma aurita. Loven, however, states that there are imbedded in the outer membrane, scattered, minute, dendritic, calcareous particles. Of these, I could see no trace. There is a very thin muscular layer between the two coats, all round the capitulum, and this layer becomes rather thicker round the base, near the peduncle. The adductor muscle, occupying its usual place close below the mouth, is thinner than in any other Cirripede of the same size seen by me; nor does it end so abruptly at each extremity, as is usual: where attached to the outer coat, no impression is left. It is a singular fact, that in this Cirripede alone, the fibres of the adductor, and of the muscles of the cirri, and of the trophi of the mouth, are destitute of transverse striae; but it is not singular, that the muscles surrounding the capitulum should, also, be destitute of striae, for this is the case with the muscles which, running up from the peduncle, surround the capitulum in Alepas, and partly surround it in Conchoderma. It must not be inferred from the absence of transverse striae in the muscular fibres of the adductor and of the cirri and trophi, that they are involuntary, but only that they are in an embryonic condition, for I find in the natatory larva, that all the muscles, with the exception of some connected with the eyes, are similarly destitute, and yet perform voluntary movements.[46]

[46] Dr. C. Schmidt in his Contribution to the comparative Anatomy of the Invertebrate animals, &c., (translated in Taylor's Scientific Memoirs, vol. v, p. 1,) says that in young Crustacea, "we find plain primitive fibres, which subsequently acquire the transversely striated aspect."

Although in the dead state, the aperture of the capitulum seems to be always gaping, yet I have little doubt, that the living animal can fold the flexible membrane, like a mantle, round its thorax and cirri, and thus protect, though feebly compared with most Cirripedes, these organs. I suspect that the mouth is always exposed.

Peduncle.—The membrane of the peduncle is thin; the whole surface is sparingly and quite irregularly studded with minute, much-branched filaments (Pl. IV, fig. 3, highly magnified); these are occasionally as much as l/5th of an inch in length; the degree of branching varies much, but is generally highly complex; the ordinary diameter of the branches is about 1/200th of an inch; their tips are rounded, and even a little enlarged, and frequently torn off, as if they had been attached to or buried in the flesh of the shark, in which the whole peduncle is imbedded. These filaments are formed of, and are continuous with the external transparent membrane of the peduncle, and they contain, up to the tips of every sub-branch, a hollow thread of corium, prolonged from the layer internally coating the whole peduncle. In all other Lepadidae, the peduncle increases in length, chiefly at the summit where joined to the capitulum, and in diameter, throughout nearly its whole length, except close to the base; but, owing to the constant disintegration of the outer surface, the old outside coat does not split in defined lines, like the membrane of the capitulum. In Anelasma, however, owing to the imbedded position of the peduncle, the old outer coats are preserved, the lines in which they have split during continued growth being thus exhibited: those in the uppermost part almost symmetrically surround the peduncle, showing that here, as in other Lepadidae, has been one regular line of growth; but in the lower part the lines are extremely irregular; and what is almost unique, it appears that the blunt basal end is constantly increasing in length and breadth, and, apparently, at a greater rate than any other part. I judge of this latter fact, from the whole bottom of the peduncle being covered with numerous curved, or nearly circular, lines of natural splitting, the nature of which can be best understood by examining the much-enlarged drawing (Pl. IV, fig. 3) of a small portion (taken by chance) of the membrane of the base, seen from the outside, and bearing some of the simplest branched filaments: other branches, as may be seen, have been cut off. This manner of growth explains the broad, blunt basal termination of the peduncle, so unlike that in other Lepadidae. New membrane is formed, not continuously as in other cases, under the whole surface of the old membrane, but in irregular patches; thus the portion marked (a) runs under (b), but not under the little circles (c, c), for these are the last-formed portions and underlie the membrane (a) and (b). I do not understand how the splitting of the old membrane is effected; but no doubt it is by the same process by which the membrane of the capitulum in other genera, as in Scalpellum, splits symmetrically between the several valves. In the branched filaments it is particularly difficult to understand their growth, for it is not possible, after examining them, to doubt that they continue to increase, and send off sub-branches, which it would appear probable, penetrate the shark's flesh like roots. I may remark that one, or more commonly two or three branched filaments stand nearly in the centre of each circular line of exuviation or splitting. The branched filaments first commence as mere little pustules, and these appear to be most numerous at the bottom of the peduncle.

The final cause of the downward growth of the bottom of the peduncle, is obviously to allow of the animal burying itself in the shark's body, in the same way as Coronula and Tubicinella become imbedded by the downward growth of their parietes in the skin of Cetacea. The only other genus of Lepadidae, in which the growth of the peduncle is at all analogous, is Lithotrya, in this genus, however, the animal burrows mechanically into soft rock or shells.

I looked in vain for cement, or for the cement-glands, (but the specimen was in an extremely unfavorable state for finding the latter) or for the prehensile antennae of the larva. No doubt this Cirripede at first becomes attached in the same way as others, but after early life, I suspect it is retained in its place, by being so deeply imbedded in the shark's body, and perhaps by the root-like branched filaments. The irregular growth and splitting of the membrane at the base of the peduncle, where the prehensile antennae of the larva must originally have been situated, would account for not finding them.

The inside of the peduncle (fig. 2 g) was gorged, in the specimen examined by me, with immature ova. The innermost muscular layer consists of longitudinal bundles of unusual size, but placed rather far apart from each other; these do not extend to the very base of the peduncle, and at the upper end they curve inwards, almost to the middle of the under side of the diaphragm, separating the peduncle and capitulum. Outside these longitudinal muscles, there are delicate transverse ones, but apparently there are no oblique muscles in the upper part of the peduncle, as in other Lepadidae; near the bottom, the transverse muscles form a thicker layer with many of the bundles running in oblique lines.

Mouth.—uLoven has not described this part quite accurately, owing to his not having used high enough magnifying powers. He states that the trophi are soft and functionless, which is far from the case. The whole mouth (fig. 2 d), is unusually small; it is, to a certain extent, probosciformed, and being curved a little downwards, projects slightly over the adductor muscle, to which it is closely placed. The labrum does not project more beyond the general surface of the body, than in many other Cirripedes, but the probosciformed structure is caused by the elongation of the surface fronting the thorax. The summit of the mouth stands above the level of the top of the pedicels of the first pair of cirri. The labrum is slightly hollowed out in the middle of its upper margin; it can scarcely be called bullate, in which it differs from all other Lepadidae; on the other hand, the outer and inner folds of the labrum are not so close together as in Balanus. On each upper corner, there is, as usual, a small rounded prominence, close to which there is a second slight, rounded, spineless swelling; these latter represent the quite rudimentary Palpi.

The Mandibles (figs. 4, 5) are more highly developed than the other trophi; they are, however, very minute, the toothed edge being only about 16/1000th of an inch in length, measured in its longest direction; the edge is unusually thick, with the teeth placed rather on one side; this organ, when viewed on the labrum side (fig. 5), shows two large teeth placed low down, with the inferior angle pectinated and broadly truncated; but when viewed on the other or maxillae side (fig. 4), several large and small teeth, placed alternately and irregularly in pairs, are seen extending along the whole edge. The mandibles are furnished, as usual, with three principal sets of muscles attached to the basal fold of the mouth.

The Maxillae (fig. 7) are still smaller than the mandibles; the spinose edge being only the 1/100th of an inch in length; the edge, instead of being square, and furnished with a double row of long spines, as in all other Cirripedes, is rounded, thick, club-shaped, and with the side facing the mandibles, thinly and irregularly strewed with short, thick, very minute spines; there is a large broad apodeme (a), in the usual place, but it is much more transparent and flexible than common: there are also the usual muscles. In other cirripedes, the mandibles alone seem to force the prey down the oesophagus; but here, the mandibles and maxillae equally stand over the orifice, and their adjoining spinose faces and edges, seem excellently adapted to force, by their united action, any minute living creature down the passage.

The Outer Maxillae are almost in as rudimentary a condition as the palpi; they are quite spineless; viewed externally, they appear like two smooth, blunt, very minute projecting points; but viewed internally, the membrane forming the supra-oesophageal hollow seems to be united actually to their tips, so that they do not project at all. I was surprised to find that the longitudinal muscles going to these organs were developed, in proportion to the other muscles, quite as fully as in ordinary cirripedes: hence, these two little outer maxillae, no doubt, serve as an under lip, and possess the usual backward and forward movement.

The surface of the probosciformed mouth facing the first pair of cirri, has a deep central longitudinal fold, and rather more than half-way down, a transverse fold; just above this latter fold, and therefore quite below the outer maxillae themselves, the two olfactory orifices are seated; these are unusually large, and the sack into which they lead, is most unusually large and deep. In this Cirripede, I was first enabled to observe that the membrane lining the sack is tubular, and open at the bottom.

Cirri.—There are, as usual, six pair, and not of very small size; they have a shapeless and rudimentary appearance; they are coloured, like the rest of the body, blackish purple: they are quite spineless, and not articulated, but their anterior faces are either obscurely or very plainly lobed, so that in some (for instance in the third pair, Pl. IV, fig. 6), nine or ten prominent steps could be counted, manifestly representing so many segments. The rami are equal in length in the first pair, and slightly unequal in the second and third pair; these two latter are longer than either the first or three posterior pair. There is a small interspace as usual between the first and second pair of cirri. Internally, the cirri are occupied, even up to their tips, by delicate striae-less muscles. The external membrane of the thorax and limbs, when examined under a very high power, is seen to be covered with minute toothed scales, as in most Cirripedes.

The thorax is articulated as usual: the posterior part, however, is smaller, and tapers more suddenly than in other species, and this corresponds with the smaller size and more rudimentary condition, of the three posterior pair of cirri, compared with the anterior pair. The prosoma is hardly at all developed. The orifice (Pl. IV, fig. 2 e) of the acoustic (?) sack, beneath the first cirrus, is unusually large.

There are no filamentary appendages.

Alimentary Canal.—The membrane lining the oesophagus is unusually thin: it is furnished with the ordinary constrictor muscles, and others radiating from them like spokes of a wheel. The stomach is lined by unusually prominent biliary folds, which in the duodenum are transverse, sending forth, however, short folds at right angles; and these latter, in the proper stomach, become so much developed that the folds appear longitudinal. The rectum extends inwards, about as far as the base of the fourth pair of cirri, but is very short, owing to the little development of the three posterior segments of the thorax. The anus is seated in its usual place, at the dorsal basis of the penis, and is hidden by loose folds of skin; but there are no distinct caudal appendages. The stomach, in the specimen examined, was quite empty.

Reproductive Organ.—The penis (fig. 2, c) is thick, short (about twice as long as the sixth cirrus), constricted at the base, ringed, spineless, with the terminal aperture large; internally it is well furnished with muscles. The two vesiculae seminales, appeared to be unusually small; and one was much smaller than the other; they do not (I believe) become united into a common tube, till near the apex of the penis. They were empty; and, I presume, from the state of the ova, that their contents had lately been discharged. The whole thorax was filled with a white, fibrous and cellular mass, consisting perhaps of the testes in their undeveloped state. The individual dissected by me, appeared to have been defective in its last act of reproduction, for there were only two or three ova attached to the fraenum on one side, and not very many on the other. The ova are much less elongated than is usual; they are of a remarkable size, namely 22/1000ths of an inch in their longer diameter; the membrane by which they are united into a pair of lamellae is remarkably strong; the fraenum (Pl. IV, fig. 2 f) on each side is large, strong, with rounded edges, pale coloured and hence conspicuous; on the side nearest the body, the whole surface is covered with club-shaped glands, having very short footstalks, and being in total length 5/6000ths of an inch; these glands secrete a reticulated layer of gut-formed fibres, attached to the ovigerous lamellae. In the specimen described by Loven, the lamellae (fig. 1, and fig. 2, b, b) appear to have been very large: and in that examined by myself, the peduncle was gorged with immature ova, showing that the female reproductive powers were ample, though at the foregoing period, only a few eggs had been formed.

Habits.—According to Loven, this species lives imbedded in the skin of Squalus maximus and spinax, in the North Sea: I suspect that it is not closely compressed in its cavity, otherwise, I do not see the use of the two layers of muscles round the whole peduncle; it probably adheres to the sides of the cavity by the tips of the branched, root-like filaments; owing to the flexible nature of the capitulum, this Cirripede can offer little resistance to the water, and, therefore, is little likely to be torn out of its cavity. I have no doubt that it can fold the membrane of the capitulum, like a cloak, round its thorax and cirri; but it certainly can offer far less resistance, than other Cirripedes, to any enemy. This creature must obtain its food, and considering its productiveness much food must be required, in a manner quite different from nearly every other member of its Order. As the whole of the peduncle is imbedded, and as the mouth is probosciformed, with the labrum a little curled over the adductor muscle, I conclude that this Cirripede can reach minute animals crawling by on the surface of the shark's body.

It must be borne in mind that the mouth, as in all Cirripedes, has the power of independent movement, and that the mandibles and maxillae are here beautifully adapted to catch and force down any small living creature into the muscular oesophagus; the rudimentary outer maxillae, moreover, no doubt have the power of scraping, like a lip, anything towards these prehensile organs. It will hereafter be seen, that the male of Ibla Cumingii, in which the cirri are quite rudimentary, obtains its food in a somewhat analogous manner, though in this case the whole peduncle moves, and not merely a probosciformed mouth: it deserves attention, that in the male Ibla and in Anelasma, in neither of which the cirri are prehensile, the palpi are rudimentary and useless. I am tempted to believe, that the largely developed olfactory sacks, and perhaps, likewise, acoustic (?) sacks, in Anelasma, replace, by giving notice of the proximity of prey, the loss of tactile cirri. It should be remembered that all Cirripedes subsist on animals which happen to swim or float within reach of the cirri; but here it is only those which happen to crawl within reach of the probosciformed mouth. It would, however, be rash to assert that the cirri in Anelasma, considering their muscular though feeble structure, may not be of some slight use, when thrown over the prey, in preventing its escape.

Professor Steenstrup informs me that, from late observations, it appears that this animal always adheres to the shark's body in pairs. I regret extremely that I have not been able to examine a pair: that the individual examined by me was bisexual, I can hardly doubt, though the male organs certainly were feebly developed; it appears probable, that the individual described by Loven was likewise bisexual: but after the facts presently to be revealed regarding the sexes in Ibla and Scalpellum, it is quite possible that the male and female organs may be developed in inverse degrees in different and adjoining individuals.

The genus Anelasma is, I think, properly placed between Alepas and Ibla. In several of its characters, such as the absence of calcareous valves, the broad blunt end of the peduncle, the spineless cirri, the small size of the trophi, and more especially the absence of transverse striae in those muscles, which in mature cirripedes are thus furnished, we see that this genus is in some degree in an embryonic condition.

Genus—IBLA. Pls. IV, V.

IBLA. Leach. Zoolog. Journal. vol. ii, July, 1825.

ANATIFA. Cuvier. Mem, pour servir, ... Mollusques, Art. Anatifa, 1817.

TETRALASMIS. Cuvier. Regne Animal, 1830.

(Foem. et Herm.) Valvae 4, corneae: pedunculus spinis corneis, persistentibus vestitus.

(Fem. and Herm.) Valves four, horny: peduncle clothed with persistent, horny spines.

Body partly lodged within the peduncle; mandibles with three teeth; maxillae with two obscure notches; outer maxillae pointed; olfactory orifices prominent; caudal appendages multiarticulate.

Male and Complemented Male, parasitic within the sack of the female or hermaphrodite; mouth and thorax seated on a long tapering peduncle, but not enclosed within a capitulum; mouth with normal trophi, but palpi small and almost rudimental; cirri rudimental, reduced to two pairs; penis reduced to a pore; caudal appendages rudimentary.

Attached to fixed littoral objects: Eastern Hemisphere.

General Remarks.—As there are only two species as yet known, and as these resemble each other in every respect most closely, a generic description would be a useless repetition of the full details given under Ibla Cumingii. I have taken this latter species as the type, from having, owing to the kindness of Mr. Cuming, better and more numerous specimens. Ibla and Lithotrya are the only two recent genera in which the body of the animal is lodged within the peduncle; but there is no distinction of any importance, though useful for classification, between the capitulum and peduncle; and these two parts, as we have seen, tend to blend together in some species of Conchoderma and Alepas. The entire absence of calcareous matter in the valves and spines of the peduncle, at first appears very remarkable; but we have seen a similar fact in Alepas, and there is an approach to it in some varieties of Conchoderma aurita and C. virgata. In all four valves of Ibla, the umbones, or centres of growth, are at their upper points. The horny spines on the peduncle, are the analogues of the calcareous scales in Scalpellum and Pollicipes; and in this latter genus, two of the species have their scales, almost cylindrical, placed irregularly, with new ones forming over all parts of the surface, and not exclusively at the summit,—in which several respects there is an agreement with Ibla. The shape of the body (i. e. thorax and prosoma, Pl. IV, fig. 8 a') is peculiar; but it is only a slight exaggeration of what we have seen in several genera, and shall meet again in some species of Scalpellum. The presence of hairs on the outer membrane of the prosoma is a peculiarity confined to this genus amongst the Lepadidae, though observed in the sessile genus, Chthamalus. The caudal appendages in the I. quadrivalvis attain a greater length than in any other species of the family, being four times the length of the pedicels of the sixth cirrus. A far more important peculiarity is the fact of the oesophagus, in both species, running over or exteriorly to the adductor scutorum muscle, instead of, as in every other species, close under this muscle. I took great pains in ascertaining the truth of this singular anomaly: the course of the oesophagus is approximately represented in Pl. IV, fig. 8 a' by faint dotted lines. The stomach has no caeca; the biliary folds are longitudinal; there is a marked constriction at the line corresponding with the junction of the thorax and prosoma. There are no filamentary appendages.

The generative system gives the chief interest to this genus. We here first meet with Males and Females distinct; and, within the limits of this same restricted genus, the far more wonderful fact of hermaphrodites, whose masculine efficiency is aided by one or two Complemental Males. The complemental and simple males closely resemble each other, as do the female and hermaphrodite forms; but under the two following species I enter into such full and minute details on these remarkable facts, that I will not here dilate on them. I may add that, at the end of the genus Scalpellum, I give a summary of the facts, and discuss the whole question. The penis (Pl. IV, fig. 9 a) in the hermaphrodite, I. quadrivalvis, is singular, from the length of its unarticulated support, and from the distinctness of the segments in the articulated portion.

As ovigerous fraena occur in the usual place in I. quadrivalvis, though much smaller than in any other species, I have no doubt that they occur in I. Cumingii, although I failed in observing them. The glands on the margin, in I. quadrivalvis, are singular, from not being borne on a long, hair-like footstalk.

Affinities.—Ibla, though externally very different in appearance from Scalpellum, is more nearly related to that genus than to any other; in both genera some species have the sexes separate, the imperfect males being parasitic on the female, and other species are bisexual or hermaphrodite, but aided by parasitic complemental males. In Scalpellum, again, the oesophagus pursues a sinuous course, resembling that in Ibla, though it does not pass exteriorly to the adductor scutorum muscle. The disc of the prehensile antennae of the larva, in both genera, has an unusual oblong form, like a mule's hoof; there is also an affinity between the two genera in the size and form of the ova, in the prominent orifices of the olfactory cavities, and in the peduncle not being naked; though, in these two latter respects, in the structure of the cirri, and in the multiarticulate caudal appendages, there is an equal affinity to Pollicipes and Lithotrya. I have already shown that Alepas is likewise related to Ibla.

1. IBLA CUMINGII. Pl. IV, fig. 8.

I. (foem.) valvarum marginibus lateralibus, et superficie interiore, caeruleis: pedunculi spinis plerumque annulis caeruleo-fuscis.

Fem.—Valves coloured, along the lateral margins and on the upper interior surface, blue: spines on the peduncle, generally ringed with blueish-brown.

Caudal appendages barely exceeding in length the pedicels of the sixth cirrus: rami of the first cirrus unequal in length by about two segments.

Male,—with scarcely a vestige of a capitulum: maxillae with fewer spines than in the female.

Hab.—Philippine Archipelago, Island of Guimavas; invariably attached to the peduncle of Pollicipes mitella, in groups of two or three together; Mus. Cuming. Tavoy, British Burmah Empire; Mus. A. Gould of Boston.

FEMALE.

The capitulum is formed of four valves, but is hardly distinct from the peduncle. The latter includes, in its wide upper part, the animal's body. The valves, namely, a pair of scuta and terga, are composed of an extremely hard, horny substance, or properly chitine, and do not contain any calcareous matter; they are extremely flat or thin, and both pairs project freely, like curved horns, to a considerable height above the sack enclosing the body: the terga project about twice as much as the scuta, and their flat apices generally diverge a little. The tips of the valves are frequently broken off; their surfaces are plainly marked or ribbed by the layers of growth, which are wide apart. The bases of the valves externally are hidden by the long spines of the peduncle.

Scuta.—These are shorter and broader than the terga; their internal (Pl. IV, fig. 8 b') growing or corium-covered surfaces are slightly concave, triangular, with the basal margin longer than the other margins and slightly excised in the middle: there is no depression for the strong adductor muscle: the internal surface of the free horn-like portion, has a small central fold (formed by an oblique crest) running from the summit of the triangular growing surface to the tip of the valve: in perfect specimens, the growing and the free horn-like portions (the latter represented much too long in fig. 8 a' and b') are about equal in length: the basal portion of one side of the scutum overlaps the tergum.

Terga.—The internal glowing surface (fig. 8 b') is almost diamond-shaped, and less in area than the sputa: external surface rounded; internal surface of the free horn-like portion, slightly concave.

Colour and Structure of Valves.—The external surfaces of the scuta and terga are yellow along the middle, plainly marked by zones of growth, and finely ribbed longitudinally: the internal surfaces and sides of the horns of the two valves, are coloured fine blue or purple; in the terga, however, the internal surface is mottled with yellow. In some specimens, especially in one from Tavoy, each zone of growth was only very narrowly edged with blue. When a thin layer is removed from one of the valves, the dark blue or rather purple appears by transmitted light a beautiful pale blue; and it is a very singular fact, that this blue portion is permanently turned by very gentle into a fiery red; the same singular effect is produced by muriatic and acetic acids. This blue part is much harder than the yellow; the latter exhibits, under a high power, a folded structure, and is penetrated by a few tubuli, whereas the harder blue portion has a cellular or scaled appearance. The spines of the peduncle exhibit, in a smaller degree, similar phenomena.

Peduncle.—This, as already remarked, cannot be distinctly separated from the capitulum; it is much compressed; it is composed of unusually thin and delicate membrane, transversely wrinkled and thickly clothed with long cylindrical horns or spines of chitine. These horns (fig. 8 c') are not the analogues of the spines which are articulated on the external membranes of many Pedunculated and Sessile Cirripedes, but of the calcified scales on the peduncle of Scalpellum and Pollicipes; for they pass through the membrane (the underlying corium being marked by their bases) and are persistent, being added to, like the valves, during each successive period of growth. Their bases are concave, so that a section of the layers of growth exhibits a series of pointed cones, one within another. Each spine is nearly cylindrical, irregularly curled, and nodose or slightly enlarged at intervals: the apex smooth and pointed; the exterior surface longitudinally and finely ribbed, like the valves. The spines increase irregularly in size from the bottom to the top of the peduncle, those at the carinal and rostral ends being generally the longest; they point upwards and hide the bases of the valves. They are not arranged symmetrically, and new ones are formed over all parts of the peduncle. They are formed of the same substance as the valves, and do not contain any calcareous matter. These horns are yellowish, generally ringed with pale and dark blueish brown, which on pressure becomes slightly opalescent with pale blue and fiery red: sometimes only the upper horns are thus ringed, and in rare instances all are simply yellowish. The muscles of the peduncle run up to the bases of the four valves.

Surface of Attachment.—The cement appears to proceed from only two points. In some specimens, a considerable length of one side of the peduncle was fastened to the surface of attachment, the horns or spines being enveloped in the cement. The prehensile antennae of the larva will presently be described under the male.

The length of an average specimen, including the peduncle and valves, is about half an inch, and the width across the widest part one fifth of an inch. Mr. Cuming has one specimen an inch in length, but this is owing to the peduncle being unusually tapering. In a specimen kept some years in spirits, the cirri, trophi, caudal appendages, and corium under the membrane between the scuta, were all dark purple; the sack and corium of peduncle clouded with purple, and the prosoma pale-coloured.

The Body (Pl. IV, fig. 8 a') is small compared with the capitulum and peduncle; it is much flattened; the prosoma is of a very peculiar shape, being square, the sides of equal length, and, in an average-sized specimen, 75/1000th of an inch long. The peculiar shape arises from the great distance between the first and second cirrus—from the mouth being far removed from the adductor scutorum muscle—and lastly, from the lower part of the prosoma being not at all protuberant. The thorax which supports the cirri is also unusually small, plainly articulated, and separated from the prosoma by a deep fold. The thin membrane of the prosoma is studded with some fine, pointed hairs, about 3/400ths in length, and articulated on little circular discs.

Mouth, placed at a considerable distance from the adductor, and directed in an unusual manner towards the ventral surface of the thorax: the trophi are arranged, in a curved line, facing the thorax (see Pl. V, fig. 2, for this part in the male), and therefore less laterally than is usual.

Labrum (Pl. IV, fig. 8 a' opposite c) highly bullate; the upper part produced into a blunt point: on its crest there are no teeth.

Palpi (fig. 8 a' opposite d) small, blunt and rounded at their ends; inner margins slightly concave.

Mandibles (Pl. X, fig. 4), with three teeth, of which the first is much larger than the second and third, and distant from them: inferior angle produced and pectinated; upper edges of the second and third teeth finely pectinated.

Maxillae (Pl. X, fig. 11) small, slightly but distinctly indented by two notches, supporting, besides the three upper great spines, three pairs of moderately long spines and some finer ones: apodeme short, thick.

Outer Maxillae, unusually pointed, with the inner bristles not very numerous, continuously arranged; externally, the bristles are longer. Olfactory orifices, tubular, projecting, flattened, square on the summit, smooth: they point upwards and obliquely towards each other: they arise more laterally than in the other genera, namely outside the bases of the outer maxillae, and between them and the inner maxillae.

Between the bases of the first pair of cirri, there is a conical prominence, clothed with bristles and coloured purple: it projects nearly as high as the top of the lower segment of the pedicel of the first cirrus: it lies over the infra-oesophageal ganglion, and serves, I suspect, to fill up a little interval between the outer maxillae.

Cirri long, little curved: the first pair (Pl. IV, fig. 8 a') is situated at an extraordinary distance from the second; hence its basal articulation is on a level with the upper articulation of the pedicel of the second cirrus. In the three posterior cirri, the segments are laterally very flat, with their anterior surfaces not protuberant; each supports three pairs of thin, non-serrated bristles, of which the second pair is much shorter than the upper, and the lowest pair minute; between each pair there is a minute, rectangulary projecting bristle; dorsal tufts consist of two or three spines, of which one is longer than the others. The two bristles forming each pair, are not of equal length; for in the rami of each cirrus, the inner row of bristles is much shorter than the outer; and this seems to be connected with the flatness of the whole animal, and the consequent little power of divergence in the rami of the cirri. The first cirrus is rather short, with the rami unequal in length by about two segments: the anterior ramus is shorter and thicker than the other: segments numerous, each clothed with several rows of bristles. The second cirrus has the anterior ramus thicker and more thickly clothed with spines than the posterior ramus; this latter is rather more thickly clothed with spines than are the three posterior cirri; the third cirrus is in all these respects characterised like the second cirrus, but in a lesser degree. The pedicels of the second and third cirri are thickly and irregularly clothed with spines; in the three posterior pairs, the spines are placed in two regular rows, with some minute intermediate spines.

Caudal Appendages (Pl. IV, fig. 8 a', f), multiarticulate, thin, tapering, in one specimen equalling, in another just exceeding, in length the pedicels of the sixth cirrus. In the latter specimen there were thirteen segments, of which the basal segments were broader and shorter than the upper; these latter are slightly constricted round the middle, so that they resemble, in a small degree, an hour-glass. Their upper margins are surrounded by rings of bristles; the terminal segment being surmounted by one or two very fine bristles much longer than the others. The two appendages are closely approximate; each arises from a narrow elongated slip, attached to the side of the pedicel of the sixth cirrus.

Nervous system.—I examined the upper part of the nervous chord, in order to ascertain whether the infra-oesophagean ganglion, which is of a globulo-oblong shape, was far separated from the second ganglion; and this I found to be the case, in accordance with the distance of the first cirrus from the second. I may here remark, that in S. quadrivalvis I discovered the eye, which, though in all probability really double, appeared to be single; it was situated near to the supra-oesophageal ganglion; and this ganglion was situated near to the adductor scutorum muscle, and at a considerable distance from the labrum. The aperture leading into the acoustic (?) sack, is situated much lower down than is usual (Pl. IV, fig. 8 a'), namely, at the length of the pedicel of the first cirrus beneath its basal articulation.

Generative system.—The specimens here described, of which I examined six, are exclusively female; they have no trace of the external, probosciformed penis, or of the two great vesiculae seminales, or of the testes: on the other hand, the ovarian tubes within the peduncle are developed in the usual manner, and owing to the large size of the ova, are of large diameter, and hence very distinct: I detected, also, the true ovaria at the upper edge of the stomach.

MALE. Plate V, figs. 1-8.

Of the above-described Ibla Cumingii I dissected six specimens, four from the Philippine Archipelago,[47] and two from the Burmah Empire, and none of them, as we have just seen, possessed the probosciformed penis, the vesiculae seminales, or the testes, so conspicuous in other Cirripedes; on the other hand, all were furnished with the usual branching ovarian tubes and sometimes with ova, and consequently were unquestionably of the female sex. Within each of these specimens there was attached within the sack, in a nearly central line, at the rostral end, (Pl. IV, fig. 8 a', h, magnified five times,) a flattened, purplish, worm-like little body, projecting about the 1/20th of an inch: in one of the six individuals, there was a second similar little creature attached at the carinal end of the sack. Before giving the reasons which I think conclusively prove that these little animals are the Males of the ordinary form of the Ibla Cumingii, it will be convenient to describe their structure in detail.

[47] I am deeply indebted to the liberality and kindness of Mr. Cuming, in allowing me to cut up four specimens of this new species; and to Dr. Gould, of Boston, U. S., for the examination of the Burmese specimens.

The whole consists of a long, much flattened peduncle, separated from the mouth and thorax by an oblique fold, (Pl. V, fig. 1 h, b), which is conspicuous on the dorsal margin under the cirri, and can be traced with difficulty to the ventral margin. The thorax, itself rudimentary, and supporting rudimentary cirri, is in some individuals, as in the one represented (fig. 1, magnified 32 times), covered by, or received in the oblique fold h, just mentioned: in other individuals the thorax is drawn out, and then the fold shows merely as a notch on the dorsal margin, and the basal articulations of the cirri stand some little way above it. The basal edge of the large, well-developed month can be traced all round, and on the ventral margin (b), is generally marked by a slight notch. The dimensions and proportions vary much: the longest specimen, including the imbedded portion, was 8/100th, and the shortest barely 5/100ths of an inch in length; the width of the widest portion varied from 1 to 2/100ths of an inch: the specimen figured (Pl. IV, fig. 8 a', and Pl. V, fig. 1,) is a broad, short individual. Generally, the middle of the peduncle is rather wider than the upper part.

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

The outer tunic of the peduncle is thin and structureless: in the fold (fig. 1 h) under the cirri, there is a central triangular gusset of still thinner membrane, corresponding in position to the membrane connecting the two terga in the female, and there subjected to much movement. I may here remark, that this fold, in its office of slightly protecting the thorax and in its position, evidently represents the capitulum with its valves, enclosing the whole body of the female. The outer tunic is lined by corium, mottled with purple, and within this there are two layers of striae-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.

Antennae.—The peduncle terminates (Pl. V, fig. 1 e) in the two usual, larval, prehensile antennae, 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 antennae 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 striae, 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 Lepadidae; 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 Maxillae (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 Maxillae (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 maxillae, 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 vesiculae 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 vesiculae 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 vesiculae 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 vesiculae 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 larvae whence the parasitic males are derived, attain (as might have been inferred from the known dimensions of their prehensile antennae, 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 antennae, 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 larvae, 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 maxillae are more rounded and less prominent, but have the same exact size relatively to the mandibles; the outer maxillae 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 antennae, 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 antennae 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 antennae, 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 Lerneidae, 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 Lerneidae and in the Cirripedia, the males more closely resemble the larvae, 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 Lerneidae 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 Koelliker 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] Cyclopaedia of Anatomy and Physiology, p. 142.

I have used the term parasitic, which perhaps ought strictly to be confined to cases where one creature derives its nutriment from another, inasmuch as the male is invariably and permanently attached to and imbedded in the female,—from its being protected by her capitulum, so that its own capitulum is not developed—and from its feeding on minute animals infesting her sack. The male Ibla must seize its prey, guided probably by its well-developed olfactory organs, through the movement of its long, flexible body, furnished with muscles, and with the mouth seated on the summit. We have already seen one instance of a Cirripede, the Anelasma, obtaining its food without the aid of cirri, by means of its probosciformed, flexible mouth. The eye can serve only to announce to the male when the female opens her valves, allowing occasionally some minute prey to enter. In ordinary Cirripedes the penis is long, articulated, and capable of varied movements, I presume for the purpose of impregnating each separate ovum: the male Ibla has no such organ; and no doubt the whole body, furnished like the penis with longitudinal and transverse muscles, serves the same purpose! I may remark, that it seems surprising that so small a male should secrete sufficient semen to impregnate the ova of the female, but the ova are not nearly so numerous in Ibla as in most genera of Cirripedes; and the smallness of the males in some parasitic Crustacea has already been alluded to. The male must always be younger than the female, for the latter must first grow large enough for the larva of the male to crawl into her sack. Whether the male lives as long as the female I know not, but he certainly lives for a considerable period and increases in size, as shown by the depth to which the end of the peduncle is imbedded. Moreover we shall see, under the next species, that the male is metamorphosed from a larva, not one sixth of its own size.

In the male Ibla, abortion has been carried to an extraordinary and, I should think, almost unparalleled extent. Of the twenty-one segments believed to be normally present in every Crustacean, or of the seventeen known to be present in Cirripedes, the three anterior segments are here well developed, forming the peduncle: the mouth consists as usual of three small segments: the succeeding eight segments are represented by the rudimentary and functionless thorax, supporting only two pair of distorted, rudimentary and functionless cirri: the seven segments of the abdomen have disappeared, with the exception of the excessively minute caudal appendages; so that, of the twenty-one normal segments, fifteen are more or less aborted. The state of the cirri is curious, and may be compared to that of the anthers in a semi-double flower; for they are not simply rudimentary in size and function, but they are monstrous, and generally do not even correspond on opposite sides of the same individual. As males in other classes of the animal kingdom often retain some female characters, so here (though the case is not strictly analogous[50]) the male possesses the cementing apparatus, which homologically is part of an ovarian tube modified.

[50] Certain plants offer a closer, though not perfect, analogy. Thus, in the florets of some compositous flowers, the pistil, besides its proper female functional end, serves to brush the pollen off the anthers; while, in the florets of some other compositae (see the account of Silphium in 'Ch. K. Sprengel Das entdeckte Geheimniss der Natur'), the pistil is functionless for its proper end, the flower being exclusively male, but its style is developed, and still serves as a brush. So in the male Ibla, part of the ovaria, in a modified condition, is still present, and serves as a cementing apparatus.

The individuals in every other genus (with the exception of Scalpellum), in the several families, in the three Orders of Cirripedia, are hermaphrodite or bisexual. Why, then, is Ibla unisexual; yet, becoming, in the most paradoxical manner, from its earliest youth, essentially bisexual? Would food have been deficient, and was the seizure of infusoria by another and differently constructed individual, necessary for the support of the male and female organs? The orifice of the sack of the female is unusually narrow; would the presence of testes and vesiculae seminales have rendered her thorax and prosoma inconveniently thick? Seeing the analogous facts in the six, differently-constructed species of the allied genus Scalpellum, I infer there must be some profounder and more mysterious final cause.

2. IBLA QUADRIVALVIS. Pl. IV, fig. 9.

ANATIFA QUADRIVALVIS. Cuvier. Mem. pour servir ... Mollusq. 1817, Art. Anatifa, Plate, figs. 15, 16.

IBLA CUVIERIANA. J. E. Gray. Annals of Philosophy, vol. x, New Series, Aug. 1825.

—— J. E. Gray. Spicilegia. Zoolog. Tab. iii, fig. 10.

TETRALASMIS HIRSUTUS. Cuvier. Regne Animal, vol. iii, 1830.

ANATIFA HIRSUTA. Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, figae. 7-10, 1834.

I. (Herm.), valvis et pedunculi spinis sub-flavis: basali tergorum angulo, introrsum spectanti, hebete, quia margo carinalis inferior longius quam margo scutalis prominet.

Hermaph.—Valves and spines on the peduncle yellowish: basal angle of the terga, viewed internally, blunt, owing to the lower carinal margin being more protuberant than the scutal margin.

Caudal appendages four times as long as the pedicels of the sixth cirrus: rami of the first cirrus unequal in length by about six segments.

Complemental Male, with a notched crest on the dorsal surface, forming a rudiment of a capitulum: maxillae well furnished with spines.

Kangaroo Island, South Australia (Mus. Brit., given by Cuvier to Leach); Adelaide, South Australia (Mus. Stutchbury); King George's Sound, Voyage of Astrolabe; New South Wales, attached to a mass of the Galeolaria decumbens, (Mus. Hancock).

HERMAPHRODITE.

All the external parts so closely resemble those of I. Cumingii, that it would be superfluous to describe more than the few points of difference. The horny substance of both scuta and terga is uniformly yellow; though in dryed specimens, from the underlying corium being seen through the valves, these generally have a tinge of blue.

The Scuta, viewed internally, are less elongated transversely; they have their basal margins slightly more hollowed out, and the fold on the upper free and horn-like portion rather deeper.

The Terga, viewed internally, have the apex of the growing or corium-covered surface higher relatively to the scuta than in I. Cumingii; and the basal angle is much broader, owing to the lower carinal margin being much more protuberant than the scutal margin. The spines on the peduncle are all yellowish-brown, and are rather longer than in I. Cumingii. I observed in three or four specimens, that the lowest part of the peduncle had become internally filled up with the usual, brown, transparent, laminated cement, cone within cone, so that this lower part was rendered rigid and stick-like; this latter effect, I apprehend, is the object gained by the formation of cement within the peduncle, of which I have not observed any other instance. The entire length of the largest specimen was one inch; some other specimens were only half this size.

The thorax and prosoma are of the same shape as in I. Cumingii, and in the largest specimen, about one tenth of an inch square; the prosoma, as in that species, is hairy. In the Mouth, all the parts are closely similar to those of I. Cumingii, but one third larger; the crest of the labrum is a little roughened with minute points: the palpi are squarer and blunter at their extremities: the mandibles have their second and third teeth nearly equal in size to the first, and they do not appear pectinated: the maxillae have their spinose edge very nearly straight: the outer maxillae are pointed. The olfactory orifices are similarly situated, and of similar shape; they are dark coloured.

Cirri.—These also are similar to those of I. Cumingii; the segments, however, of the three posterior cirri have each four pair of spines, placed very close together in a transverse direction. First cirrus has its two rami unequal in length by about six segments. The anterior rami of the second and third cirri are thicker, and more thickly clothed with spines, than the posterior rami, to perhaps a greater degree than in I. Cumingii. In the posterior cirri, the upper segments of the pedicels are nearly as long as the lower segments.

Caudal Appendages, four times as long as the pedicel of the sixth cirrus, and three fourths of the length of the rami of this same cirrus: segments thirty-two in number, and therefore as many as those forming the sixth cirrus: the upper segments are much thinner and longer than the basal segments; each furnished with a circle of short bristles; whole appendage excessively thin and tapering: the two closely approximate.

Colour.—From some well-preserved dryed specimens in Mr. Stutchbury's possession, it appears that the sack, cirri and trophi, were dark blue, as in I. Cumingii; after being long kept in spirits, these parts become brown.

Generative System.—The penis (Pl. IV, fig. 9 a) is very singular in structure; it is of the ordinary length, but of small diameter; it tapers but little; it consists of a moveable articulated, and a fixed unarticulated portion; this latter is smooth, much flattened, not divided into segments, and projects straight out under the caudal appendages; it is about one third of the length of the entire penis; it corresponds with a part present in all Cirripedes, but here surprisingly elongated. The articulated portion consists of separate segments, twenty in number, quite as distinct as those of the cirri; each one is oblong, being longer by about a third part than broad; each has a few short bristles round its upper margin; the terminal segment has a circular brush of bristles. The vesiculae seminales are easily seen, though they are narrow; they are slightly tortuous; they enter the prosoma, and lie on each side of the stomach; their outer case has a ringed structure, but is not fibrous; the contents in the best specimen consisted of a mass of spermatozoa, which I saw with perfect distinctness. The testes are unusually large and egg-shaped.

Ova, spherical, 5/400ths of an inch in diameter, united as usual into two ovigerous lamellae. The ovigerous fraena 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 lamellae 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 larvae, 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 maxillae, 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 maxillae 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 vesiculae 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.