_'02 



Pill IF. W. A. I1KUDMAN OX THE ABUNDANCE 



They form a conspicuous feature of the plankton for a few weeks in March 

 and April, and constitute, no doubt, an important food-matter at this time 

 when there are comparatively few Copepoda available. 



Mytilus. 



Probably the edible mussel (Mytilus edulis) is the most abundant mollusc 

 in the seas of North-West Europe, and it is certainly the most generally 

 useful to man, both directly as a food and as a fisherman's bait and also in- 

 directly as the food of marketable fishes. Although mussel " beds," " scars," 

 or "scalps," as the}' are variously called, are regularly worked over by the 



Fig. 4. — Mussel '• spat'' on sea-weeds, magnified. 



fishermen, they cannot be regarded as in any sense artificial. The mussels 

 have settled down and grown upon them naturally. It is only very rarely 

 that any transplanting takes place, and there is nothing in this country 

 comparable with the artificial "bouchot" system of mussel culture which 

 takes place in the bay of Aiguillon on the west coast-of France. 



In a mussel bed (fig. 3) not only are the mussels so closely placed as to 

 be touching their neighbours all round, so as in some cases to cause distortion 

 and prevent proper growth, but they are even piled on the top of one another, 

 it may be several layers deep, the interstices below being filled up with mud 

 and the byssus fibres of the molluscs in the layers above. 



At the time when the mussel '"spat" is settling down from the free- 

 swimming larval condition, sea-weeds, zoophytes, rocks, and other objects 



