314 Miscellaneous. 



MISCELLANEOUS. 



Remarks on the Habits of the Comtnon Mussel. 

 By David Robertson, Esq, 



I HAVE been much interested in watching the habits of a common 

 Mussel {Mytilus edulis), which has afforded me many hours of plea- 

 sant amusement. It had been in my keeping for three months. I had 

 taken little notice of it, till finding that it had removed from the 

 bottom, and attached itself about two inches up the side of the jar, 

 I became curious to know how it had got up. I observed that the 

 fibres of the byssus were fixed at various heights ; that the lowermost 

 were fully an inch from the bottom ; that by their apparent contrac- 

 tion it could raise itself nearly an inch ; and that from this position 

 other fibres could and had been fixed higher up ; hence the ascent. 

 It remained in this position for eight days, during that time adding 

 more fibres till it had twenty-one, the lowermost now appearing cir- 

 cularly below the shell, and the upper ones circularly above it. It 

 was now apparently a permanent fixture, 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 hang- 

 ing to the glass ; this is an interesting microscopic object, some- 

 what 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 appa- 

 rent 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 their 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 {Pa- 

 gurus Bernhardus), mounted occasionally 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 steps in ascend- 

 ing, nor seemed in any way doubtful of the stability of his footing. 

 I watched all day patiently — but no more fibres ; after dark, I made 

 my observations only occasionally and by candle-light, the gas being 

 too distant for minute inspection. Returning on one of these visits, 

 after an absence of an hour, I found four new fibres affixed. This 

 was a great disappointment, to lose, by this short absence, a sight I 

 had so much wished to see. Next day there were no more new 

 fibres ; and, as it had seven, it might not be in much want of more. 

 To reduce it again to the necessity of making a new supply, I cut 

 four, leaving three, and I again set to watch with renewed zeal. 



