WORMS, ROTIFERS, LEECHES, POLYZOA 87 



presenting a very animated sight. It is a sabelliform worm and 

 hermaphrodite. 



Another interesting tube-builder is a worm that is sometimes 

 called the Shell-binder (Terebella conchilega), which builds a won- 

 derful tube that looks almost like a miniature tree, with its trunk 

 and stunted branches coated with sand, tiny pieces of shell, and 

 very small pebbles. The worm has a large number of long and 

 slender tentacles, which it uses for the capture of prey and for 

 collecting the particles of sand in the process of building its tube. 

 Each tentacle has a groove along one side, and particles of sand 

 or food are conveyed along this furrow to the mouth. Every sand 

 grain used in the construction of the tube is in this way conveyed 

 to the mouth, where it is coated with some natural secretion, and 

 then worked into place by means of the worm's lips at the edge 

 of the tube. 



The pinkish, rounded, shelly tube of the Serpula Worm (Serpula 

 vermicularis) is often to be found adhering to an old whelk shell, 

 or on a rock in some tidal pool. It is about 3 inches long, tapers 

 regularly backwards, and is marked on its dorsal surface with a 

 more or less distinct keel, while the worm is only about I inch 

 n length. It is a very beautiful little creature, with graceful 

 and richly coloured branchiae, consisting of most elegant comb- 

 like filaments arranged in two rows, one on each side of the mouth. 

 These filaments bear numerous cilia, the movements of which 

 set up currents in the water, and in this way particles of food are 

 caught and carried down to the mouth. Occupying a position 

 nearly central to the surrounding comb-like filaments is a long, 

 slender stalk, terminating in a conical, bright-hued organ, the 

 operculum, which acts as a stopper, most effectually closing the 

 entrance of the tube when the worm retires within its shelter. 

 When alarmed, the Serpula withdraws within its tube with light- 

 ning-like rapidity, its swift retreat being accomplished by a most 

 remarkable mechanism consisting of a series of bands provided 

 with a multitude of microscopic hooks which engage in the lining 

 of the tube. Gosse, who made a careful study of Serpula, gives 

 the following description of these organs : " This yellow line, which 

 cannot be appreciated by the unassisted eye, is a muscular ribbon, 

 on which stand up edgewise a multitude of what I will call combs, 

 or rather sub-triangular plates. The edge of each plate is cut 



