ANNELIDES. 87 



It is true, that the body of the Clymene, a genus furnished with feet, 

 is terminated posteriorly by a sort of concave membranous disk, in 



the centre of which the anus opens ; but it is ascertained that that 

 disk, though dilatable, cannot execute the office of a sucker. 



10. Anus. — The anus is inclined to the dorsal surface and looks 

 upwards. Dr. WilHams says — " There exist other minor families of 

 Annelids in which the terminal outlet of the alimentary system is 

 not seated at the extreme end of the body, but at a point, at the side, 

 more or less removed backwards from the head, resembling intimately 

 the pattern on which that of the Sipunculidse is formed*." 



The Annelides rapacia are the most complicated in organization 

 of any of their class. As the ordinal name implies, they are a wan- 

 dering tribe, and the locomotive apparatus is so much developed, 

 that the species are enabled to creep with considerable quickness, 

 and even to swim with facility. Some of them, as certain Amphi- 

 nomesy appear to be truly pelagian, and are only met with in the high 

 seas ; but the great majority dwell between tide-marks on the shore, 

 where they find refuge and concealment under stones, or among 

 corallines and sea-weeds. A small number burrow in the sand 

 {Nephthys, Arenicola, &c.), in which they form a sort of sheath by a 

 glairy secretion from the skin ; and a few are truly tubicolous ; but 

 these furrows are not indispensable, and can be occasionally aban- 

 doned without inconvenience. The greater number of the Order are 

 provided with special organs of sense considerably developed ; and 

 they have organs of defence in the shape of bristles of curious 

 structure. All of them are inhabitants of the sea or its shore, and 

 only a very few trespass on tidal rivers, not fearing the influence of 

 brackish water. None of them are parasites. Some species may 

 frequently be observed watching in patient solitude, and ready to 

 launch upon weaker worms, moUusks, or other animals on which 

 they prey ; but none offers us any instance of the singular instinctive 

 contrivances which surprise us in the study of insects. Several of 

 * Rep. Brit. Assoc. 1851, p. 220. 



