Although the tentacles may be correctly described as organs used in capturing prey, they do not themselves seize it but waft it by means of the currents set up by their cilia to the mouth, into which it is swept by the currents produced by the cilia lining the pharynx. The tentacles are also able in some species to interlace themselves in order to prevent the escape of prey. Apparently they have the power of rejecting unsuitable food, for they may often be observed to bend backwards and forwards and thrust particles that have approached them away, and if the water contains anything of a noxious nature in solution the lophophore is immediately retracted, unless it has been completely paralysed. In the phylactolæmata the peculiar organ known as the epistome is capable of closing the mouth completely, and probably acts as an additional safeguard in preventing the ingestion of anything of an injurious nature. In many genera and larger groups the food commonly passes down the pharynx into the stomach without interruption, although it is probable that in all species the oesophagus can be closed off from the stomach by a valve at its base. In some forms, however, a "gizzard" is interposed between the oesophagus and the stomach. This gizzard has not the same function in all cases, for whereas in some forms (_e. g._, in _Bowerbankia_) it is lined with horny projections and is a powerful crushing organ, in others (_e. g._, in _Hislopia_ or _Victorella_) it acts as an antechamber in which food can be preserved without being crushed until it is required for digestion, or rough indigestible particles can be retained which would injure the delicate walls of the stomach. Digestion takes place mainly in the stomach, the walls of which are of a glandular nature. The excreta are formed into oval masses in the rectum and are extruded from the anus in this condition. Although the gross non-nutritious parts of the food are passed _per anum_, the waste products of the vital processes are not eliminated so easily, and a remarkable process known as the formation of brown bodies frequently takes place. This process cannot be described more clearly and succinctly than by quoting Dr. Harmer's description of it from pp. 471 and 472 of vol. ii. of the Cambridge Natural History, a volume to which I have been much indebted in the preparation of this introduction. The description is based very largely on Dr. Harmer's own observations[AW]. [Footnote AW: Q. J. Micr. Sci. xxxiii, p. 123 (1892).]