FABRICATION OF BYSSUS. 473 



is carried to the desired extent, sometimes fully two 

 inches. It is next employed in feeling or testing all 

 the objects within reach, moving backwards and for- 

 wards, or to the right and left, apparently to ascertain 

 the security of the intended holdings. The point of the 

 foot is then settled, and retained for a short time on 

 the chosen spot, when it is again suddenly removed 

 and immediately withdrawn entirely within the shell, 

 leaving behind a thread that reaches from the point 

 selected to the base of the foot. By many repetitions 

 of this operation, carried on patiently day after day 

 (for not above four or five threads are produced in 

 the twenty-four hours), and by attaching the disc-like 

 extremities of the threads to different places, the 

 mussel at last completes its mooring and secures a 

 safe anchorage. 



The machinery whereby the byssus is manufac- 

 tured, or spun, as some people erroneously term it, is 

 very simple. Along the centre of the foot, which is 

 at once distinguishable by its powers of elongation 

 and contraction, and, in the edible mussel, by its 

 deep violet colour, there is an open furrow, capable 

 of being converted, at the will of the animal, into a 

 closed canal, along which the glutinous secretion, 

 whereof the threads are formed, flows. This is fur- 

 nished by a glandular structure, situated near the 

 base of the foot. The glutinous material is thus 

 moulded into the shape of a thread, and speedily 

 hardens into a strong, tenacious filament ; so that, in 

 accordance with the number produced will of course 

 be the strength of the attachment. 



The Pecten is likewise capable of manufacturing 



