ITS BRISTLES. 287 



The protrusion of the fore parts, which takes place 

 in a much more leisurely manner, is performed by quite 

 another set of instruments, formed on a totally different 

 principle. Their action is a pushing or shoving. The 

 instruments for effecting this are the fine but strong 

 bristles which run through the feet. Each bristle is 

 composed of a strong rigid unyielding shaft, having an 

 expanded shoulder drawn out into a point. On one side 

 of this pointed shoulder may be remarked a double row 

 of fine teeth, admirably calculated to catch against any 

 roughnesses of the surface with which they come into 

 contact, against which they then push with the force 

 of the proper muscles. Acting diagonally backwards, 

 from the two sides of the animal, the result of the com- 

 bination of the forces is that the animal itself is pushed 

 forwards, and so protruded from the mouth of the tube. 

 The feet on the hinder portion of the body are, accord- 

 ing to Dr. Williams, 1 modified in structure with express 

 reference to the duties of mopping, sweeping, scraping, 

 and wiping the inferior closed end of the habitation. 

 I think, however, he has forgotten that this end, formed 

 by the animal in its infant state, must now be very much 

 too strait to be reached by any portion of the body, or 

 by any of its organs. 



Dwelling in a tubular house, the Serpula would find 



1 Brit. Annelida, in Rep. Brit. Assoc., 1851. 



