TUBE-BUILDING. 297 



each pair of hooks. The base of the crown is always 

 concealed in the mouth of the tube, but it springs from 

 a narrow frilled membrane of pure white. The body is 

 destitute of a thoracic shield, or conspicuous collar. 

 The tube is largely composed of soft homogeneous mud, 

 usually of a pale purplish hue, of about the thickness of 

 the shelly tube of 8. tubularia. 



The process of building the mud tubes of the Sabellse 

 is a very interesting one. It is performed, according to my 

 own observations, 1 mainly by means of the gill-filaments 

 and their pinna! grooves. The filaments are bent-over, 

 till the inner or grooved face cornes in contact with the 

 soft mud on which the animal is lying, when the sensi- 

 tive pinnae close on a minute portion of the mud, taking 

 it up in a pellet, which is then fashioned by the form 

 of the groove ; the filament is now erected, and the 

 pellet, passing down the groove to the bottom by means 

 of the cilia, is delivered to the care of two delicate 

 moveable organs, like leaves or flaps, which place it on 

 the edge of the tube, and then shape and mould it, 

 smoothing both surfaces. Doubtless, either from these 

 organs, or from some other part of the circumjacent 

 region, the glutinous secretion is at the same time 

 poured out, which consolidates the mud, and forms the 

 true basis of the tube. 



1 Intellectual Observer, vol. iii. p. 77. 



