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Alcyonella fungosa presents itself in the form of brown fungoid masses of very variable size and shape, attached to the surface of different fixed objects, as stones, pieces of wood, fresh-water shells, &c. The masses frequently acquire a considerable size, weighing upwards of a pound. They are often irregularly lobed, and when they grow upon the surface of a cylindrical body, as a twig on the stem of some aquatic plant, usually surround it so as to assume a somewhat spindle-shaped figure, gradually diminishing in thickness from the centre towards the extremities. They are fond of attaching themselves to the branches of trees which dip into the water, and then constantly exhibit lobed, pear-shaped masses pendant from the extremities of the sprays. When a living specimen is examined in the water, its whole surface seems covered with a whitish down, which a slight examination shows to be occasioned by the protrusion of innumerable polypides. When removed from the water, the polypides shrink back into their cells, and the surface then seems covered with a gelatinous investment, caused by the soft, papilla-like, extremities of the tubes. These extremities contract no adhesion to one another, like the rest of the tubes, and the ectocyst, as it passes over them, becomes very delicate and transparent; in dead specimens they shrivel up and disappear, and then the surface of the mass presents a multitude of closely applied hexagonal or pentagonal orifices. The whole production now assumes the appearance of a spongy, honeycomb-like mass, and this has not unfrequently been mistaken for a fresh-water sponge. A vertical section shows it to be composed of a vast number of tough, membrano-corneous-branched tubes, closely adherent to one another, and each opening on the surface by one of the angular orifices, just mentioned. Imperfect transverse septa may be seen at the origin of many of the branches. The tubes, towards the end of summer, are loaded with mature statoblasts, which, on the rupture of the coenoecium, escape in great numbers into the surrounding water. The colour of the living mass varies somewhat with the nature of the food and the state of depletion at the time, the contents of the stomach being visible through the transparent portion of the tubes. When the stomach is not filled with food, so as to impart an adventitious colour to the mass, the latter is generally of a light-brown, or gray, upon the surface, and of a darker brown in section. It is in perfection during the summer and autumn; in winter, nothing is to be found of it but the empty and decaying coenoecium. A. fungosa is a widely distributed Polyzoon, having been found in Russia, France, Prussia, Belgium, and the British Isles. It is curious enough that, though it is common in England and Scotland, it has never yet been found in Ireland, where all the other British genera are abundant. It prefers stagnant and slowly running waters. Some of the largest specimens I have seen were in the Chelmar, a sluggish river in the county of Essex, which has been widened and deepened into a canal, for the purposes of inland navigation.
2. Alcyonella Benedeni, Allman. Pl. IV, figs. 5–11.
Specific character.—Coenoecium fungoid; formed of numerous branched vertical tubes, which are emarginate at the orifice, and furnished with a furrow. (Free) Statoblasts elongated.
SYNoNY.M.–1850. Alcyonella Benedeni. Allman, British Association Report.
Iconography.—No published figure.
HABITAT.-Stagnant waters. Same as that of A. fungosa.
Locality.—Chelmar Canal, Essex. G. J. A.
The present well-marked species I have great pleasure in dedicating to M. Van Beneden, a naturalist who has not only done more than any one else in the particular department to which this monograph is devoted, but who has enriched our knowledge of the lower animals generally, by contributions numerous and valuable. A. Benedeni occurs in spongy masses attached to twigs, and other fixed bodies, and resembling A. fungosa in their general appearance. They would seem, however, never to attain to so large a size as the latter, the largest specimens I have seen, measuring about three inches in length, and an inch in thickness at the thickest part. The tubes are closely adherent to one another until within a short distance of their terminations, when they become free. The ectocyst is dark brown, becoming rather abruptly lighter in the vicinity of the orifices, where the peculiar characteristic furrow commences by a triangular notch-like space, and then passing down as a narrow slit-like line, is finally lost where the adhesion of the tubes begins. When withdrawn from the water, the tubes seem terminated by a little papilliform body, formed by the endocyst, over which the ectocyst is continued as a very delicate, transparent, and colourless membrane. In extreme retraction, the papilliform terminations are entirely withdrawn into the remainder of the tube. The statoblasts are of two kinds—free, and adherent. The free statoblasts are narrowly elliptical, approaching to bean-shaped; the disc is brown, minutely mamillated; the annulus is dull yellow, widely overlapping the disc, especially on the more convex side. These statoblasts are found in immense numbers towards the end of summer, lying quite free in the interior of the tubes, and, on the rupture of the latter, escape, and instantly rise to the surface of the water. Besides these bodies, others much less numerous are also found in the present species, but are always attached to the inner walls of the tubes. They are broadly elliptical, enclosed in a pergamentaceous shell, like the free statoblasts, but with a very narrow margin.” Of their real import we are ignorant. I have met with A. Benedeni only in one locality, namely, the River Chelmar, in Essex, where it existed in abundance, along with A. fungosa and the following species:
3. Alcyonella flabellum, Van Beneden. Pl. IV, figs. 1–4.
Specific character.—Coenoecium flabelliform, composed of branched prostrate tubes, furnished with a furrow. Statoblasts broad.
SyNoNYMs.–1848. Alcyonella flabellum. Van Beneden, Recherches sur les Bryozoaires fluv. de Belg., p. 19; Mém. de l'Acad. Roy. de Belg., 1848. (Original figures.) 1850. Alcyonella flabellum. Allman, Proc. Roy. Irish Acad., vol. iv, p. 470.
* Wide supra, p. 40.
Iconography.—The original figures of Van Beneden.
HABITAT.-Stagnant and slowly running waters, adhering to the submerged stems of aquatic plants.
Localities.—British : Chelmar Canal, Essex. G. J. A.—Reading. Mr. Bowerbank. Foreign : Belgium. Van Beneden.
This species was first characterised by M. Van Beneden, who discovered it in Belgium, and described it in the “Memoirs of the Royal Academy of Belgium,' for the year 1848. In September, 1849, I received from Mr. Bowerbank a living specimen, obtained in the neighbourhood of Reading; it was attached to a decayed twig, along with A. fungosa, and had developed itself in the form of two flabelliform masses, attached to one another by a short simple tube, as figured by Van Beneden. In July of the following year, I met with the same species in the River Chelmar, attached to the petioles and under surface of the leaves of Nymphaea alba.
A. flabellum is a small, but very pretty Polyzoon, and rendered very striking by its mode of growth in two flabelliform fasciculi of tubes, each fasciculus closely adherent by one face to the surface of the body on which it is developed. The largest specimens I have met with measure about half an inch in their longest direction. The ectocyst is dark brown, becoming abruptly lighter towards the orifices; the furrow, commencing wide in the vicinity of the orifices, extends as a narrow transparent line along the free surface of the tubes, giving them the appearance of being slit along one side.
The polypides have about forty tentacula, and the margin of the calyciform membrane is distinctly festooned.
I have not observed the statoblasts, as these bodies were not present in any of the specimens I examined; they are, however, figured and described by Van Beneden as broadly elliptical.
Name.—A diminutive noun, formed from pluma, a feather, in allusion to its plume-like crown of tentacles.
When Waucher, in 1804, added, under the name of Tubularia lucifuga, a supposed new species of fresh-water Polyzoa to those previously known, all these animals, with the exception of the Alcyonium fluviatile of Bruguière, and the Kleiner Federbusch Polyp of Rösel, for which Cuvier had constituted a genus under the name of Cristatella, were placed in the genus Tubularia, along with numerous marine polypes of a totally different organization. The unzoological nature of this association was apparent to Bosc, who, in 1804, pointed out the necessity of viewing the so-called Tubularias of fresh water as a distinct generic group, of which he gave the characteristics, but which he neglected to name, and it was reserved for Lamarck, by naming Bosc's genus, to confer on it a fixed and definite place in our systems. The name of Plumatella was that which Lamark gave to this group, but as it included the “Polype à Panache,” a polyzoon whose organization does not admit of a generic association with the others, it has since been found necessary to restrict the genus Plumatella as established by Bosc and Lamarck, and to constitute a separate genus for the “Polype à Panache.”
Except in the condition of the dermal system, the structure of Plumatella differs in no essential point from that of Alcyonella. This system, however, in the coalescence of the tubes into a common mass in Alcyonella, while they remain totally distinct in Plumatella, presents us with a difference which I believe to be of sufficient importance to justify us in placing the two forms in separate generic groups.”
The coenoecium in Plumatella consists essentially of a linear, more or less branched series of tubular cells of membrano-corneous consistence, each springing from its predecessor, and constituting a short ramulus, which is terminated by the orifice destined for the egress of the polypides. In some species the cells are nearly cylindrical, in others they are claviform, and when the latter figure occurs, especially in connection with short cells, a more or less moniliform, or concatenated appearance is presented by the coenoecium. In most of the species, perhaps in all, transverse septa or diaphragms occur near the origin of certain cells when complete, separating the cavities of these cells from those of the neighbouring ones. They, however, are very frequently incomplete, admitting of a free communication between neighbouring cells, and in many cells are even totally absent. In some species they occur at distant and irregular intervals, and may be easily overlooked, while in others (P. coralloides) they exist with almost as much regularity and completeness as in Paludicella. The first instance in which I became aware of the existence of these septa was in Plumatella coralloides, where they occur with singular regularity and distinctness. So striking, indeed, was the character thus presented, that I thought it of sufficient importance to entitle this species to the rank of a distinct genus. Further investigation, however, rendered apparent the presence of similar septa in other species, but occurring frequently at such distant intervals in the tubes, and with so much irregularity, as to deprive this character of that importance which one
would feel at first inclined to attribute to it. Indeed, the tendency to the formation of transverse septa would seem to occur generally throughout Alcyonella, Plumatella, and Fredericella, while in Paludicella these septa acquire their maximum in development and constancy, and become thus one of the most striking features of the Polyzoon. In drawing out the diagnoses of the species of Plumatella, I have availed myself of the same class of characters as those which were used for a similar purpose in Alcyonella, namely, the general habit of the animal, the presence or absence of the furrow in the ectocyst, and the shape of the statoblasts. The number of the tentacula also, and the more or less plicated or festooned condition of the edge of the calyciform membrane are generally introduced into the specific character. It must be recollected, however, that unless the difference in the number of tentacula amounts to ten or fifteen, it can scarcely be relied on as a specific character, and the condition of the calyx, though perhaps really of sufficient constancy to form a good character, is often very difficult to determine. These last two characters can in general, therefore, only be considered as of secondary value, and merely adjuvant to the former.
Generic character.—Coenoecium confervoid, branched, composed of a series of membranocorneous tubular cells, each of which constitutes a short ramulus with a terminal orifice; branches distinct from one another. Lophophore crescentic. Statoblasts elliptical, with an annulus, but without marginal spines.
Number of known species twelve, of which nine are British.
1. Plumatella repens, Linnaeus. Pl. W.
Specific character.—Coenoecium irregularly branched, cells sub-claviform, destitute of furrow and keel. Tentacula about sixty; margin of calyx distinctly festooned. Statoblasts broad.
Variation a...—Coenoecium closely adherent, creeping along the surface of various submerged bodies, to which the branches are attached in their entire length. (Pl. V, figs. 1, 2.)
Variation 3.-Coenoecium attached only towards the origin, branches soon becoming free. (Pl. V, figs. 3, 4.)
It is scarcely possible to conceive of a species burdened with a more discordant and perplexing synonymy than that which encumbers the history of P. repens. In order to reduce this chaos to some sort of order, the first step is, of course, the determination of the exact animal which the original founder of the name had in view in his description. In the tenth edition of the ‘Systema Naturae,” published in 1758, we find Linnaeus introducing an animal under the name of Tubipora repens, and placing it amongst his Lithophyta with the following diagnosis: “T. corallio repente filiformi dichotomo: tubis flexilibus cylindricis distantibus erectis. “Habitat in aquae dulcis plantis in Nymphaea, &c., minuta.” The figures here referred to are Trembley’s “Polype à Panache," as copied by Baeck in • Acta Suecica, Rösel's figures of his “ Federbusch-Polyp,” and Schäffer's figures of his