114 



SABELLA. 



(Plate XXII. Fig. 5.) 



Shell tubular, formed of sandy and calcareous 

 particles agglutinated and inserted in a membra- 

 naceous sheath. 



The best claim which the Sabella could assert 

 to be ranked among Testacea is, that the cement 

 with which the fragments of organised and siliceous 

 matter are fastened to the mould is really calca- 

 reous, and not an animal gluten only. By immers- 

 ing a portion of the shell in muriatic acid the cal- 

 careous particles will be dissolved, and many, if not 

 all the indissoluble fragments will be precipitated, 

 leaving the membranaceous sheath entire, and im- 

 pressed with the forms of the substances which were 

 attached to its exterior surface. Still, some will be 

 found to adhere and resist the action of the acid : it 

 is therefore difficult to affinn whether they have been 

 fastened by a gelatinous secretion, or by a cal- 

 careous one. In either case, the fibre of the animal 

 membrane growing round a slight projection in the 

 siliceous pebble might be a sufficient bond. 



