INVERTEBRATE ANIMALS. 61 



dant on Fuci ; and in Serjmla, the meandering tubes of 

 which frequently almost cover the valves of marine 

 shells ; or it may be formed of grains of sand and frag- 

 ments of shells, as in Terehella ; or it may be of a 

 leathery consistence, made up of mud strengthened by 

 a glutinous secretion, as in Sabella, which at Hilbre 

 may be seen rendering the deeper tide-pools gay as a 

 border of flowers. In Serpula, one of the plumes carries 

 a little calcareous lid closing the mouth of the tube 

 when the animal retires. 



II. Order Errantia. In the free Annelides the 

 gills are arranged in tufts along the back or sides of the 

 body. In the Sea-mouse, Aphrodite, the back is pro- 

 tected by scales concealing the gills, the scales being 

 themselves hidden by bundles of flexible bristles glitter- 

 ing like spicular iron ore, and displaying all the 

 colours of the rainbow. The Lob-worm, Arenicola, 

 burrows in the wet sand, and is much used by fishermen 

 for bait. In the Sand-worms, Nereides, the anterior 

 extremity is sometimes furnished with eyes, and a 

 mouth with jaws and feelers, and thus makes a nearer 

 approach to a true head than is found in any other of 

 the Vermes. Eunice gigantea attains a length of four 

 feet, and has as many as four hundred segments. The 

 tracts and burrows of the free Annelides on the ancient 

 sea-bottoms are found in rocks of almost all ages from 

 the Cambrian upwards. The tubes of the Tuhicola occur 

 as early as the Silurian period. The little Microconchus 

 was found by the writer in the Middle Coal-measures at 

 Eavenhead. 



