{244}_Protodrilus_ and _Polygordius_ are distinctly Annelidan in character. _Protodrilus_[297] is found in the mud of the "Pantano," an inlet of the sea near Messina; whilst of _Polygordius_[298] one species at least occurs on our shores, and several others in the Mediterranean and elsewhere. The worms are cylindrical, with many segments, but these segments are only indistinctly marked externally—by girdles of cilia in _Protodrilus_, or by faint grooves in _Polygordius_; but there are none of the characteristic Chaetopod bristles or chaetae. The small prostomium which overhangs the mouth is provided with a pair of ciliated pits, and carries a pair of tentacles, serving as sensory organs, which, in _Protodrilus_, are also respiratory. The anus is surrounded by glandular papillae in _Polygordius_, by means of which the animal can fix itself; these are represented in _Protodrilus_ by a couple of processes. The nervous system lies entirely in the epidermis. The body-cavity is regularly segmented by transverse septa passing from the body-wall to the intestinal wall. The foregut presents a slight eversible portion in _Polygordius_, whilst in _Protodrilus_ it has a peculiar U-shaped muscular diverticulum on its ventral surface, corresponding with the similar apparatus in _Dinophilus_; it is capable of eversion, and aids the worm in burrowing, as well as in seizing and swallowing the mud. The vascular system is represented by a dorsal and a ventral vessel, neither of which, however, is contractile. In _Protodrilus_ the dorsal vessel divides into two branches in the first segment, each of which passes to the tip of the tentacle, and returning, joins its fellow to form the ventral vessel. In some species of _Polygordius_ there is a pair of vessels connecting the dorsal and ventral vessels in every segment, but no vessel to the tentacle. The blood is colourless in some species of _Polygordius_, but may be yellow (_P. neapolitanus_), red (_P. lacteus_), or green (_P. erythrophthalmus_). Paired nephridia, with distinct funnels, occur regularly throughout the body.