126 



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 organized and siliceous 

 matter are fastened to the mould, is really calca- 

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

 mersing a portion of the shell in muriatic acid the 

 calcareous particles will be dissolved, and many if 

 not all the indissoluble fragments will be precipi- 

 tated, leaving the membranaceous sheath entire, 

 and impressed 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 affirm whether 

 they have been fastened by a gelatinous secretion, 

 or by a calcareous one. In either case the fibre 



