140 The Naturalist of Cumbrae. 



eight days, during that time adding more fibres till it 

 had twenty-one, the lowermost now appearing circu- 

 larly below the shell, and the upper ones circularly 

 above it. It was now, apparently, a permanent fix- 

 ture, at least within the limits of its moorings ; by 

 drawing the byssus towards the beak, or the base, it 

 could move the ends of the shell alternately up and 

 down. The movements were at times frequent. 



" On the tenth day after mounting the side of the 

 jar it detached itself, and fixed upon another place a 

 little farther round, by four new fibres, leaving the old 

 byssus hanging to the glass. This is an interesting 

 microscopic object, somewhat palmate, dividing into 

 numerous filaments, and is attached to the animal by 

 a small peduncle, which nature has given the creature 

 power to sever when a change is required. 



" I was desirous to see the actual process of fixing 

 the fibres, and began to watch with more care. It 

 had now six fibres ; and, with the hope that it would 

 require to produce more, I cut three, leaving only 

 three, by which it supported itself and went through 

 its usual movements with apparent ease ; the only 

 perceptible effect was a slight jerk down at the 

 severance of each fibre. The fewness and fineness of 

 the filaments, and the delicacy of the attachment, 

 looked very inadequate for the suspension of the 

 animal ; but they proved to be strong enough and 

 something to spare, as one of its neighbours, the 

 hermit crab (Pagurus Bernhardus], mounted occa- 

 sionally on the top of the inoffensive mussel without 

 the least appearance of giving pain or oppression, 

 although the crab used no precaution in taking light 



