BUILDERS IN THE SAND. 15 



dwells a worm-tenant which is doing its best to 

 escape into the sand by the lower end of its dwelling- 

 place. 



This is the Terebella, a worm which ranks among 

 the most common of all the architects of the sand. 

 Look at the tube closely (Fig. 5). Its composition 

 is varied enough. It consists of a series of odds and 

 ends in the way of particles, and the heterogeneous 

 materials of the tube account for the rugged appear- 

 ance of the structure. The bulk of this worm's house 

 is built of grains of sand, but you also note how it 

 has seized upon pieces of broken shells, and even 

 minute pebbles as building-stones. These materials 

 are all duly glued together by means of a natural 

 marine cement, which resists the action of the water, 

 and defies the damp to disintegrate the tenement of 

 the Terebella. 



The tuft at the top of the tube, which is modelled 

 in sand, is really the outer investment or covering of 

 the gills and feelers which the head of the worm 

 bears. The gills are plume-like, and the feelers, or 

 tentacles, act as purveyors in the commissariat de- 

 partment. They sweep food-particles into the mouth, 

 and possibly filter from the sea or sand around, the 

 matters necessary for the nutrition of the worm- 

 frame. 



But in our shovelful of sand there are worm- 

 tubes of another description. You now disinter a 

 tube of smoother and more regular aspect than those 

 of the Terebella. This second tube is composed of 

 sand particles alone, cemented together to form a 

 symmetrical structure, which impresses us by contrast 

 with the rougher build of the Terebella's dwelling- 

 place. The smooth tube (Fig. 6) is the abode of 



