BYSSUS, a long, delicate, lustrous, and silky fasciculus of filaments, by which some of the conchiferous molluscs, for example the Mytilacea, mussels, and Malleacea, hammer oysters, are moored to rocks, etc. It is an assemblage of muscular fibres, dried up in one part of their extent, but still contractile and in a living state at their origin. The tendinous foot of Byssoarca and Tridacna seems to be a step towards the organiza tion of a true byssus. The byssus of the great Pinna of the Mediterranean is in a fleshy sac or sheath at the base of the foot, which is attached towards the middle of the abdominal mass of the animal. In Italy it is manufactured into various articles ; and there are few museums without a glove or a stocking woven out of this substance. The pearl oyster, by a byssus, secures itself to the rocks. The animal's foot is composed of muscular fibres, and is 21- inches long when distended. On the lower side there is a groove lined by a secreting membrane, which is an exact mould for the for mation of the byssus. When the animal desires to attach itself to the rock, its foot is protruded, and, after seeking out a suitable spot with the tip for some minutes, is again retracted into the shell. A strong fibre, of the form of the groove
in the foot, is thus left, attached to the base of the foot at one end, and to the rock at the other. The process is again and again repeated, until a strong cable is formed ; and it was one of the most important results of the careful investigations of Dr. Kelaart in Ceylon, that the power of the animal to cast off its byssus at pleasure was ascer tained. It leaves it behind to make another in a more convenient place. From this ability to shift its berth, it follows that the pearl oyster might safely be taken from its native beds and made to colonize other parts of the sea, and also that it would move of its own accord if the surrounding water should become impure or sandy, or when there is an influx of fresh water. The animal can reform the byssus at pleasure, if in good health and condition.