Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/458

Rh 438 P L Y Z A iu this way. The Chilostoina include a largo series of genera arranged iu the sections Cellulariua, Flustrina, Esehariiia, aud FIG. 13. A. Ctenoocium of Crisia ebnrnea, Lin., one of the Cyclostoma ; g, g, tubular zooecia with circular terminal mouths; x, occt iuin, being a zooccium modified to serve as a brood-chamber. B. Diagram of a single polypide of one of the Chilostoma in a state of expansion, in order to show the position and action of the operculum. , operculum, a plate of thickened cuticle hinged or jointed to 6, the main area of dense cuticle of the antitentacular region known as the zocecium ; c, the soft-walled portion of the polypide in expansion. C. The same zocecium with the polypide invaginated (telescoped) and the opei culuin a shut down over the mouth of the zoceeium. D. Operculum detached, and seen fiom its inner face, to show the occlusor muscles d d. Celleporina. For the systematic description of the highly complex and very varied colonial skeletons or ccencecia of the Gyranokenia, FIG. U.Kinetoikitt* (Xaretia) ryathut (from Sir Wyville Thomson). The poly- pides and zooeeia are allied to lluijula, but the zoarium as a whole is remarkable for its definite shape, consisting of a number of slightly brant-hud gracefully bending moment* supported like the leaves of a palm on a long trsiiisinrcift walk. (See busk, in Huart. Journ. Micr. iki., 1881, for further details.) the reader i.-, referred to the works of Busk (9), Hincks (10), Sniitt ,11), aud Heller (12). See also Elders (13) on Hypophorella. Sub-class 2. Entoprocta, Nitsche. Eupolyzoa in which the anal aperture lies close to the mouth within the tentacular area or lophophore. Lopho- pliore sunk within a shallow basin formed by the inversion of the broad truncated extremity of the cup-shaped body. Tentacular crown not further introversible, the individual tentacles (as in the Pterobranchia and unlike the Ecto- procta) capable of being flexed and partially rolled up so as to overhang the mouth (see fig. IT), B and C). Body- cavity (cuelom) almost completely obliterated. The anti- tentacular region of the polypide s body is drawn out to form a stalk similar to the gymnocaulus of the Pterobran chia. The extremity of this stalk is provided with a cement gland in the young condition which persists in the adult of some species (Loxosoma neapolitamim, fig. 1G, shs). Cuticular investment (zocecium) of the polypides feebly developed. A pair of small nephridia are present. The Entoprocta consist of the marine genera Pedi- cellina (fig. 15), Loxosoma (fig. 16), and probably the FIG. 15. A. Two polypides and buds of J edicel/ina betyicit, Van B. (after Van Beneden); greatly magnified, a, the polypide-stalk of a fully developed polypide ;, that of a less mature individual ; ft, a bud. All are connected by a common stalk or stolon. B. and C. Two views of the body of the polypide of Pedicellina (after Allman). a, cuticle; b, body-wall; c, permanently in troverted anterior region of the body ; tl, margin of the tentacular cup or calyx thus foimed; e, mouth; /, pharynx; y, stomach; h, intestine; j, anus; i; epistome or prse-oral lobe ; /, nerve-ganglion ; ;/(, gonad ;, retractor muscle of the lophophore ; o, lophophore. insufficiently known freshwater American genus Urnatella of Leidy. To these must be added Busk s new genus Ascopodaria, as yet undescribed, based on a specimen dredged by the &quot; Challenger,&quot; showing a number of Pedi- cellina-like polypides, carried as an umbel on a common stalk of very peculiar structure. Pedicellina is found at tached to alg;e, shells, zoophytes, &amp;lt;fcc., and to the integu ment of some Grephyraean worms (Sipunculus punctatus) and Annelids (Aphrodite) ; Loxosoma occurs on various worms, Arc. Whilst the buds of Pedicellina remain connected so as to constitute a colony, those produced by Loxosoma are continually detached, so that the polypide is solitary. Further, the cup-like body of Pedicellina is deciduous, and frequently falls from the stalk and is replaced by new growth. There is less distinction between body and stalk in Loxosoma, and the former does not become detached. Apparently a very important feature in the structure of the Entoprocta is the absence of a body-cavity. This is, however, more apparent than real. The Entoprocta are true Coelomata, but the coelom is partially obliterated by the growth of mesoblastic tissue. The nephridia presum ably lie in a space which, small as it is, represents the ca-lom. See Manner (18) for details.