At the anterior extremity of this disc an invagination arises to form the oesophagus (fig. 129 A, _oe_); and not long afterwards a posterior invagination to form the rectum (fig. 129 B, _an.i_). The oral disc and the oesophagus are richly ciliated. The oesophagus first, and afterwards the rectum unite with the archenteron (fig. 130), the walls of which soon become differentiated into a stomach and intestine, and on the upper wall of the former the hepatic cells become especially conspicuous (fig. 130). During the completion of the alimentary canal a number of important structures is formed. The disc in which the oral and anal apertures are situated becomes converted into a true vestibule. On its floor, between the mouth and the anus, there arises a marked prominence with a tuft of cilia (fig. 130 B), which persists in the adult. [FIG. 129. TWO STAGES IN THE DEVELOPMENT OF PEDICELLINA. (After Hatschek.) _oe._ oesophagus; _ae._ archenteron; _an.i._ anal invagination; _f._ fold of epiblast; _f.g._ ciliated disc; _x._ problematical body derived from hypoblast (probably a bud).] This prominence is perhaps equivalent to the epistome of the Phylactolæmata and the disc-like organ of Rhabdopleura, which Lankester has compared to the molluscan foot[120]. [120] Lankester. "Remarks on the Affinities of Rhabdopleura." _Quart. J. of Micro. Science_, Vol. XIV. 1874. Very shortly after the first formation of the vestibule there appears at the opposite end of the larva a thickening of the epiblast, which soon becomes invaginated, and forms an eversible pit (fig. 129 A and B, _f.g._). Round its mouth there is formed a ring of stiff cilia (fig. 130, _f.g._). This organ is very possibly equivalent to the cement gland described by Kowalevsky in the adult Loxosoma. I shall speak of it as the ciliated disc. The epiblast cells early secrete a cuticle. The two mesoblast cells soon increase by division, and occupy the space between the alimentary canal and the body wall. They do not become divided into a splanchnic and somatic layer; but give rise to the interstitial connective tissue and muscles. From the mesoblast there is also formed, according to Hatschek, a pair of ciliated excretory canals, in the space between the mouth and anus (fig. 130 B, _nph._). The development of the nervous system has not been observed. At a comparatively late stage in the development there is formed round the edge of the vestibule a ring of long cilia (fig. 130 B, _m._). [FIG. 130. TWO STAGES IN THE DEVELOPMENT OF PEDICELLINA. (After Hatschek.) _v._ vestibule; _m._ mouth; _l._ liver; _hg._ hind-gut; _a._ anus; _an.i._ anal invagination; _nph._ duct of kidney; _fg._ ciliated disc; _x._ dorsal organ (probably bud).]