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P. jugalis is a small species and occurs, rather abundantly in the sluggish waters of the Chelmer Canal, attached to the petioles and under surface of the leaves of Nymphaea aloa. It is throughout closely adherent to the surface on which it grows, and is very remarkable by its mode of development in two distinct groups of branches, which are united to one another by a simple connecting tube, from which they extend in two opposite directions. The ectocyst is brown, becoming lighter towards the extremities of the branches, and finally extending as a delicate transparent and colourless membrane to the margin of the orifice; this transparent portion being, as in other furrowed species, withdrawn into the more opaque portion of the tube during extreme retraction. Most of the branches are intersected near their origin by very distinct septa, which are visible through the walls of the tube. I could find no statoblasts in any of the specimens I examined.
In its peculiar mode of development in two groups of tubes, P. jusalis presents a striking resemblance to Alcyonella flabellum ; from the latter animal, however, it is at once distinguished by its narrow, widely diverging branches never contracting the slightest adhesion to one another.
I have as yet met with this species in but one locality, though its striking physiognomy could scarcely allow of its being overlooked.
The Plumatella nitida, Leidy (“Proc. Acad. Nat. Sci. of Philadelphia, vol. v., p. 321), I cannot think entitled to rank as a distinct species. With the exception of the number of tentacula, which are described as being only forty-two, there is no character in which P. nitida does not entirely agree with P. repens, and this character by itself can scarcely be considered of sufficient importance to separate the two forms.
Genus VI. FREDERICELLA, Gervais, 1838. Name.—In honour of Frederick Cuvier.
In 1774 Blumenbach gave the name of Tubularia sultana to a little fresh-water Polyzoon which he found in the neighbourhood of Göttingen, and which differed from all the then known fresh-water species in having the tentacula disposed in a circle instead of forming a crescent. This circular disposition of the tentacula, which at once distinguishes Blumenbach's animal from all the other fresh-water species except Paludicella, was properly considered by M. Gervais to be of sufficient importance to cause the Tubularia sultana to take the rank of a distinct genus, and he has accordingly assumed it as the type of his genus Fredericella.
Though the tentacular crown, however, may at first appear quite similar in its form to that of Paludicella, a careful examination will detect in the lophophore a deviation from the orbicular condition presented by this part in the latter, and the bi-laterality of the lophophore in Fredericella is still further maintained by the presence of the epistome, which is altogether absent in Paludicella. The epistome and calyciform membrane are, indeed, as well developed in Fredericella as in the species with crescentic lophophores, while Paludicella, the only genus with a truly orbicular lophophore, is also the only one in which the epistome and membrane are absent. The whole structure, moreover, of Fredericella is quite in accordance with that of the species with crescentic lophophores, and differs in many important particulars from the structure of Paludicella, so that notwithstanding the circular disposition of the tentacula the true affinities of the genus are with Plumatella rather than Paludicella
Generic character.—Coenoecium confervoid, composed of a membrano-corneous branched tube, with the branches distinct from one another and terminated by the orifices. Lophophore nearly circular; tentacular crown campanulate. Statoblasts bean-shaped, destitute of annulus and spines.
Species unica.” F. sultana, Blumenbach. Pl. IX. Specific character.—The same as that of the genus.
SYNoNYMs.-1777. Tubularia sultana. Blumenbach, Handbuch der Naturgeschichte. (Original figure.) 1789. Tubularia sultana. Gmelin, Linn. Syst. Nat., p. 3835.
* In my Synopsis of Fresh-water Zoophytes, published in the ‘Annals of Natural History,’ 1844, I have described as a distinct species, with the specific name dilatata, a Fredericella in which the branches become dilated towards the extremities; subsequent investigations, however, have led me to look upon the F. dilatata of that publication as a merely accidental variation of F. sultana, and the
species must accordingly be suppressed.
1806. Tubularia sultana. Turton, Linn. Syst. Nat, vol. iv, p. 669.
}Allman, Ann. Nat. Hist., vol. xiii, p. 331.
Iconography.—The original figures are those of Blumenbach, Van Beneden (Bul. Ac. Brux.), Van Beneden (Mém. de l'Acad. Brux.), Gervais, and Hancock. There is also an original figure apparently referable to this species, though unaccompanied by a name, illustrating a paper by Mr. Varley in the ‘Lond. Phys. Journal, No. 2, 1844.
HABITAT.-On submerged stones and the stems and leaves of aquatic plants, in still water and moderately rapid rivulets. Preferring the shade.
Localities.—British : Generally distributed through England, Ireland, and Scotland; abundant in the Regent Canal, London; in the Grand Canal, Dublin; and in the Union Canal, Edinburgh. G. J. A.—Northumberland Lakes. Mr. Hancock.
Foreign : In a small lake called the Roth See, near the town of Lucerne; in Lago di Mezzola, Northern Italy; in the Canal du Midi, near Toulouse. G. J. A.—Germany. Blumenbach.-Near Paris. Gervais-Belgium. Dumortier and P’an Beneden.
F sultana is one of the most widely distributed of the fresh-water Polyzoa ; I have met with it abundantly in England, Scotland, and Ireland. It occurs in rather confused tufts attached to submerged plants, stones, &c. The coenoecium is partly free, partly adherent, the adherent portion frequently extending over several inches, and sending off numerous free subdivided branches of an inch or more in height. The ectocyst is brown, membranocorneous, opaque, with a slightly prominent keel running along each branch, but without any slit-like furrow. At the origin of the branches there is frequently found a more or less perfect septum. The tentacula are about twenty-four in number, constituting when the polypide is exserted a campanulate crown of great elegance. The statoblasts are somewhat kidney-shaped or bean-shaped, with the annulus obsolete. They are small and seem to be but sparingly produced, a circumstance in which this animal differs strikingly from several species of Alcyonella and Plumatella, in which the tubes at the proper season are constantly found loaded with statoblasts in the greatest profusion. The close resemblance of the bushy coenoecium of this species to that of Plumatella fruticosa has been already mentioned, indeed I have no doubt of the one having been frequently mistaken for the other. I have met with F. Sultana during the whole of the spring, summer, and autumn months, both in standing water and rivers, generally avoiding direct exposure to the daylight, though not so decidedly a lover of obscurity as several other species of fresh-water Polyzoa. The tentacular plume is even to the naked eye an object of extreme elegance, and we can easily participate in the feelings which must have actuated Blumenbach when he bestowed on this little animal the imperial designation it has since borne. It can be kept alive and healthy in a phial of pure water, and when undisturbed the polypides will readily issue from their cells and display their plumy crowns. A large branch thus studded with the campanulate crests of the polypides is an object which in elegance can hardly be surpassed, and with these strange, sentient flowers instantly retreating on the approach of danger, and when all is once more quiet again coming forward in their beauty, presents a spectacle not easily forgotten.
Genus VIII. PALUDICELLA, Gervais, 1836. Name.—A diminutive noun, formed from palus, standing water.
In the number of the ‘Symbolae Physicae,’ published in 1831, Ehrenberg described under the name of Alcyonella articulata, a fresh-water Polyzoon which he discovered in the neighbourhood of Berlin. M. Gervais shortly afterwards, having discovered near Paris an animal which agreed with Ehrenberg's description, saw the necessity of separating it from Alcyonella and placing it in a distinct genus, which he named Paludicella. About the same time Ehrenberg's animal was detected in the neighbourhood of Louvain by M. Van Beneden, and in Lough Erne, in Ireland, by Mr. William Thompson, of Belfast, who was thus the first to add this interesting Polyzoon to the Fauna of the British Isles.
Paludicella is one of the best marked of all the genera of fresh-water Polyzoa; its perfectly orbicular lophophore, with the absence of epistome and calyx, and its strikingly articulated coenoecium, formed of regular claviform cells, all separated from one another by complete septa, together with several peculiarities in its internal structure already described, remove it by a well-marked interval from the other genera of the present monograph, and approximate it to certain marine representations of the class. The genus consists as yet of but a single species.
Generic character.—Coenoecium membrano-corneous, branched; branches composed of a series of claviform cells placed end to end and separated from one another by complete septa; orifices tubular, lateral, placed near the wide extremity of each cell. Lophophore orbicular, no epistome or calyx. Statoblasts not observed.
Species unica. Paludicella Ehrenbergi, Van Beneden. Pl. X. Specific character.—The same as those of the genus.
SYNoNYMs.—1831. Alcyonella articulata. Ehrenberg, Symb. Phys. Evert., Dec. 1, Pol., fol. a. 1832. Alcyonella diaphana. Nordmann, Mikrograph. Beiträge, vol. ii., p. 75. 1836. Paludicella articulata. Gervais, Comptes Rend. 1837. Paludicella. Gervais, Ann. Sc. Nat., 2d series, tom. vii, p. 80. 1839. Paludicella articulata. Gervais, Ann. Franç. et Etrang. d’Anat, tom. iii, p. 75. 1839. Paludicella. Van Beneden, Bull. Ac. Brux., tom. vi, 2d part, p. 278, fig. 1. (Original figure.) 1840. Paludicelle articulée. Gervais, Dict. Sc. Nat., Suppl., vol. i., pl. 1, Pol. Fluv., fig. 6. (Original figure.) 1842. Paludicella articulata. Allman, On the Muscular Syst. of Palud., &c., Roy. Irish Acad., No. 38, with a plate. (Original figure.)