SERPULA. 285 



pula, 1 a general favourite in our aquaria, easily and 

 abundantly procured, and readily maintained in health 

 and beauty for a considerable period. I need scarcely 

 describe the general appearance of an object so com- 

 monly kept, and so frequently gazed upon. Many tubes 

 are usually found growing together, adhering to the 

 same shell, bit of broken pottery, or small stone; all 

 much intertwined, and mutually adherent, so that it is 

 practically hopeless to attempt to isolate one. Yet by 

 studying many specimens we are able to ascertain that 

 each individual is at first a very slender tube of white 

 calcareous shell, not thicker than sewing-cotton; 2 this 

 rapidly increases both in thickness and in length, soon 

 rising from its support, to which it at first adhered by 

 the lime deposited in a soft state, and continuing the 

 rest of its growth free, in a direction forming various 

 angles with the ground line, and most irregularly twined 

 and contorted. For the final" half of its length, or there- 

 about, the tube attains a diameter of one-fourth of an 

 inch, the walls being sufficiently thick to be solid, yet 

 leaving an ample cavity for the residence of the industri- 

 ous mechanic, who thus skilfully builds up his own house. 

 If we carefully break, by a moderated blow with a 

 hammer, the shelly tube, so as not to crush the tenant, 



1 Serpula contortuplicata, a mass of which forms the subject of Plate 

 xxxii., mingled with S. triquetra. 



2 Some in this infant state are seen in Plate xxxm. 



