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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 Nymphæa 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.
Genus V. PLUMATELLA, Lamarck, 1816.
Name.--A diminutive noun, formed from pluma, a feather, in allusion to its plume-like crown of tentacles.
When Vaucher, 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 laria, 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 cænæcium 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 cænæcium. 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
* See above, p. 86.
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.—Cænæcium 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, Linnæus. Pl. V.
Specific character.-Cænæcium irregularly branched, cells sub-claviform, destitute of furrow and keel. Tentacula about sixty; margin of calyx distinctly festooned. Statoblasts broad.
Variation a.-Cænæcium 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 B.-Cænæcium 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 Naturæ,” published in 1758, we find Linnæus 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 aquæ dulcis plantis in Nymphæa, &c., minuta.”
The figures here referred to are Trembley's “Polype à Panache,” as copied by Bæck in · Acta Suecica,' Rösel's figures of his “ Federbusch-Polyp,” and Schäffer's figures of his
Corallenartiger Kamm-Polyp.” a reference so discordant as to render it very difficult to determine the animal Linnæus had in view in his Tubipora repens. Linnæus's short description, however, plainly excludes the “Polype à Panache;" and that the original of the Tubipora repens was really Schäffer's animal seems confirmed by the “Fauna Suecica,' published in 1761, where Tubipora repens is also given, but with Schäffer's animal quoted as the only synonym.
In the twelfth edition of the Systema Naturæ,' published in 1767, Tubipora repens is altogether omitted ; but in this edition a new species is introduced under the name of Tubuloria campanulata, with the following short diagnosis:
“ T. reptans tubis campanulatis.”
The animal thus defined is without any doubt the “Polype à Panache” of Trembley, though to the real synonyms of the “Polype à Panache" there is added “Schäffer, tab. 1, fig. 9.” The Tubularia campanulata is intended to replace the Hydra campanulata of the tenth edition, which however, as there described, is certainly an imaginary species, founded on the fifth and sixth figures of Bæck’s plate in the · Acta Suecica,' which are evidently drawn from some animal very imperfectly observed, though most probably intended for the “
“Polype à Panache.”
In 1773 we find O. F. Müller giving the name of Tubularia repens to a polyzoon which he found in the fresh waters in Denmark, and which he viewed as identical with Schäffer's
Kamm-polyp.” If Müller be correct in this view—and there is certainly every reason to think he is—the true synonyms of the Tubularia repens of Müller will be Tubipora repens, Linnæus, and “ Corallenartiger Kamm-polyp,” Schäffer.
It is evident that Linnæus had a very imperfect idea of his Tubipora repens, but we are now happily no longer left in doubt as to the nature of the anima) in question; for though both Schäffer's and Linnæus's descriptions are very meager, Müller’s, on the contrary, is full and perspicuous, though unfortunately not accompanied by an original figure; so that we are compelled to have recourse to the figures of Schäffer, to which Müller refers us, and which, though very imperfect, would seem sufficient for the purposes of identification; one represents a small portion of the cænæcium of the natual size creeping spirally round the stem of some aquatic plant; the other is a portion magnified, with three poly pides in three different states of exsertion.
From this time we find writers relying almost exclusively on the description of Müller, and after some notices of minor importance by different authors, we find the name given by Müller introduced into the "Systema Naturæ’ by Gmelin, who in his edition of this great work, published in 1789, makes mention of the Tubularia repens with Müller's diagnosis.
In 1804 a new element of confusion was introduced into the synonymy of this species by Vaucher, who mentions the occurrence of Tubularia repens, and adds incidentally, that its ova are elongated : this naturalist accompanies his notice with a figure, which, however, in no respect agrees with Müller’s description; and I have no hesitation in considering the animal which Vaucher, under the belief that it was the same as that described by Müller, calls Tubularia repens, to be quite distinct from this species; it comes nearer to Plumatella emarginata of the present monograph; and indeed, were it possible from Vaucher's data to form any opinion of value on this subject, I should not be disinclined to view it as identical with the latter, though the description and figures of Vaucher are so very imperfect as to
render it impossible to decide with satisfaction on his species. The T. lucifuga of Vaucher on the other hand, comes much nearer to the true Tubularia repens, and is probably identical with it, for the number of tentacula which he ascribes to the species is evidently the result of having observed the polypide in a very partially exserted state, and therefore goes for nothing in the description.
We next find Müller's Tubularia repens enumerated by Turton in his edition of the Systema Naturæ,' 1806. In 1816 we have Lamarck substituting the generic name of Plumatella for that of Tubularia, as applied to the fresh-water Polyzoa, and describing, under the name of Plumatella repens, an animal for which he adduces Schäffer's figure, but which he characterises from the erroneous description and figures of Vaucher; the P. repens of Lamarck, therefore, while it must be viewed as synonymous with Vaucher’s Tubularia repens, can find no place in the synonymy of the true Tubularia repens of Müller. Lamouroux, first in 1816 (Pol. Flex.), and afterwards in 1821 (Exp. Méth.), substitutes the name of Naisa repens for Tubularia repens, employing Müller's diagnosis, though referring to Vaucher, and in the latter work reproducing his figure. De Blainville, in 1834, enumerates without any diagnosis Plumatella repens, quoting as synonyms the Tubularia repens both of Gmelin (Syst. Nat.) and Vaucher. Gervais, in “Ann. Franç. et Etrang. d’Anat.,' 1839, enumerates also without description the Plumatella repens, quoting among his synonyms not only Schäffer and Müller, but also Vaucher. The Plumatella repens of Johnston (Brit. Zooph. edit. 1 and 2, 1838 and 1847) is the true animal of Schäffer and Müller. Lastly, Van Beneden (Recherches sur les Bryozoaires fluviatiles, 1848) describes, under the name of Plumatella repens, a Polyzoon which I cannot safely refer to the original Tubularia repens ; Müller's character, “Tubuli basi angustati apice crassiores,” does not at all agree with it, while the elongated ova approach it to Vaucher’s Tubularia repens, and to the Plumatella emarginata of this monograph and of my Synopsis, published in the ‘Annals and Magazine of Natural History,' 1844, from which, however, it is separated by the absence of a furrow. The Plumatella campanulata, on the contrary, of Van Beneden is doubtless identical with the true Tubularia repens of the Danish naturalist, and with the animal here described under the name of Plumatella repens
While the “Corallenartiger Kamm-polyp” of Schäffer thus formed the basis of the various synonyms now enumerated, the animal described by Rösel (Insecten Belustigung, 1755) under the name of “Federbusch-polyp,” was made the basis of another series of synonyms. This Polyzoon was first systematically named by Pallas, who described it in his Elenchus,' published in 1766, giving to it the name of Tubularia gelatinosa. We afterwards find Blumenbach (Handbuch der Naturg. 1777) describing it under the name of Tubularia campanulata, with the following diagnosis, which is evidently formed from the incorrect account given by Rösel :
“ T. crista lunata orificiis vaginæ annulatis corpore intra vaginam abscondito.”
Next comes Gmelin (Syst. Nat.' 1789), who also describes it, employing both the name and diagnosis of Blumenbach. We have already seen that the Tubularia campanulata of the ‘Systema Naturæ,' 1767, was a totally different animal, namely the “ Polype à Panache” of Trembley. Rösel's animal is next described in Dr. Turton's edition of the ‘Systema Naturæ,' 1806, under the name of Tubularia reptans, the Tubularia campanulata of this edition being the same as that of the edition of 1767. From this time forwards, the specific nam campa