The granular matter, after rotating for some time at the pylorus (a provision for prevent ing its too rapid escape from the stomach), passes into the intestine, where it accumulates in little pellets that distend the parietes of the tube, and it is possible that it may' here be still further acted upon by these parietes which have a spotted appearance.
By the contraction of the intestine the little pellets of excrementitious matter are carried rapidly upwards to the anal orifice, which is seen to open and the little pellet to be tilted over its edge, when it is immediately whirled away from the sight in the current produced by the ciliated tentacles, and the orifice of the tube again contracts.
The general character of the alimentary canal appears to be similar in all the cilio brachiate polypes, but in many genera the gizzard does not exist.
The anatomy of the animals inhabiting the cells of Flustrce and Escharce differs in some particulars from that of Bowerbankia. In these, the crown of ciliated tentacula is in serted into the extremity of a kind of pro boscis, Which is itself enclosed in a cylin drical retractile sheath. From the mar gin of the opening of the cell arises a membrane equalling in length the contracted tentacles, and serving to enclose them when the aninial retires into its abode. The ten tacula when thus retracted, as was the case in Bowerbankia, are not bent upon them selves, but are perfectly straight and united into a fasciculus, the length of which, however, is much less than that of the same organs when expanded.
By the opposite extremity to that which is derived from the margin of the cell, the ten tacular sheath unites with a tolerably capa cious tube, the walls of which are exceedingly soft and delicate, and near the point of their union we may perceive a fasciculus of fibres running downwards to be inserted upon the lateral walls of the cell. These fibres appear to be striated transversely, and are evidently muscular ; their use cannot be doubted. When the animal wishes to expand itself, the mem branous sheath above referred to becomes rolled outward, everting itself like the finger of a glove as the tentacles advance. The muscular faseiculi are thus placed between the everted sheath and the alimentary canal, and by their contraction they must necessarily retract the whole within the cell.
The first portion of the alimentary canal (fig. 58,0 is inflated, and much wider than the rest ; it forms a kind of chamber, in which the water set in motion by the cilia of the tentacles ap pears to circulate freely. The walls of this chamber are exceedingly delicate ; the soft membrane forming them is puckered, and ap pears traversed by many longitudinal canals united by minute transverse vessels ; this appearance, however, may be deceptive.
Beneath the first enlargement, the digestive apparatus becomes narrower, but immediately expands again, and offers at this point a cer tain number of' filiform appendages (c), which appear to be free and floating in the interior of the cell. To the second cavity succeeds a nar row canal opening into a third dilatation, gene rally of a spherical form (d). From the last named viscus issues a kind of intestine, which soon bends upon itself and becomes attached to an organ of a soft and membranous tex ture, having the appearance of a cmcum, and which seems to be continuous superiorly with the digestive tube. The latter continues its progress towards the upper part of the cell, and ultimately terrninates by a distinct anal aperture upon the upper aspect of the ten tacular sheath. The operculutn which closes the cell in Flustrae and Escharm is moved by two muscular fasciculi inserted into the in ternal face of this valve by the intermedium of two filaments analogous to tendons ; by their inferior extremity these muscles are attached to the walls of the cell, and when, by its own elasticity, the operculum is turned back, and the mouth of the cell thus opened, they by their contraction can close it like a door.
Reproduction. — The first mode of repro duction observed in the Ciliobrachiate polypes is by a process of gemmation from the com mon stock or creeping stem upon which the animals grow. This is easily witnessed, as the gemmm are met with in every progressive stage of development upon the same specimen, as represented infig. 65.