FAM. 3. _Arenicolidae._—Here belongs the common "lug-worm" _Arenicola marina_ L., which occurs all round our coasts between tide-marks, and is so generally used as bait in fishing. The worm, which measures 5 to 8 inches, is of a dark tint, usually brownish-green. It burrows to a depth of some 18 inches or 2 feet, and throws up a considerable quantity of "castings" or "sand-ropes," which are noticeable on every shore consisting of mud or muddy sand. The body of the worm is cylindrical, thicker anteriorly; the segments are indistinct, owing to the secondary groovings and furrows on the skin. The prostomium is in the adult fused with the peristomium; this and the second segment are achaetous. Then follow twenty chaetigerous segments with dorsal bundles of capillary chaetae and ventral rows of short crotchets. The hinder region of the body is achaetous and narrower than the rest, forming a "tail." There are twelve (sometimes thirteen) pairs of arborescent red gills on segments 9 to 20 (21). Internally there are {334}only four complete septa, and six pairs of nephridia, which are of large size: the fore-gut is eversible. Atlantic and Mediterranean. A second and smaller species, _A. ecaudata_ Jnstn., occurs on our southern coasts; it is readily distinguished by the absence of a "tail," the chaetae and gills being continued to the end of the body. FAM. 4. _Scalibregmidae._—Prostomium ill-marked, fringed with small processes. Parapodia represented by slight papillae; two bundles of chaetae; usually cirriform lobes above and below them. _Lipobranchius jeffreysii_ M‘I. has a grub-like body pointed at each end; forms tubes of mud. Firth of Clyde and elsewhere in North Sea. _Sclerocheilus_ Gr. in old oyster shells. Channel, Mediterranean. _Eumenia crassa_ Oerst. has gills on first six segments. North Sea. _Scalibregma inflata_ Rthke. has arborescent gills on segments 4 to 7. The anterior part of the body is dilated. North Sea. FAM. 5. _Chlorhaemidae._—The family derives its name from the green colour of the blood, due to chlorocruorin. The representatives are comparatively short worms, with capillary chaetae on all the segments, the limits of which are not evident. The prostomium carries a pair of long grooved yellowish processes, which are perhaps palps, and several green tentacles, acting as "gills," arranged in a transverse series above the mouth (Fig. 134, F, p. 262). The peristomium is achaetous; the whole "head" can be withdrawn into the body. The chaetae of the anterior segments are especially long, and directed forwards so as to form a "cage" for the head. The body-wall is covered with longer or shorter papillae. Internally, the chief points of interest are the presence of only two septa (_Trophonia_) or only one septum (_Siphonostoma_), situated somewhere in front of the middle of the body, and forming a great backwardly-directed pouch, which contains a part of the looped intestine, and the nephridia, of which there are only two or four.