362 
THE OCEAN - WORLD. 
the byssus large. In Lythodemus the byssus is rudimentary ; the 
muscles are retractile, equal, and two pairs only. In Anio, Cardium, 
and Hyria, the foot is large and not byssiferous. 
The animal, as described by M. Chenu, is elongate, oval, the lobes 
ot the mantle simple or fringed, divided at the edge into two leave s > 
the interior being very short, bearing a fringe of small, cylindrical 
and movable fillets ; the exterior leaf is united to the shell very near the 
edge. The opening by which water and food are introduced suppl' eS 
the branchiae at the same time. The stomach consists of a whit® 
membrane, thin, like opaline, and presenting itself in longitudinal 
folds; the liver is granulous, composed of greenish grains more °r 
less deep, contained in the meshes of a whitish tissue forming a 
thickish bed, which surrounds the stomach, the intestines taking the 
direction of the median and dorsal line, and beneath the heart are 
received and terminate in a small appendage, floating in the cavity ot 
the mantle near to the hinge. The foot is, perhaps, the remarkable 
organ of the mussel : it is small, semi-lunar when not in motion, but 
capable of great elongation, resembling thus a sort of conical tong ue » 
having a longitudinal furrow on its side. It is put in motion by 
several pairs of muscles, all of which penetrate and are interlaced with 
the tissue : behind it is the silky byssus. The mouth is large, and 
furnished with two pairs of soft palpi, which are pointed and fixed by 
their summit. Abdominal masses emanate, and on each side a pair of 
nearly equal branchiae. Two additional muscles, one anterior and 
small, the other posterior, large, and rounded. At the base of the 
foot is a gland which furnishes a viscous secretion; this viscous 
liquid is organized and moulded in the groove of the foot, and forms » 
thread, and originates the byssus ; it is a bundle of hairs, mane, or 
thread, which holds on to its shell. 
The byssus plays an important part in the organization of th e 
mussel. While the oyster remains eternally riveted to its rock, until 
torn from it by violence, the mussel moves about, and in this motion 
the byssus is an active agent. The mussel attaches its byssus to som e 
fixed object, and drawing upon it, as upon a line, the shell is displaced- 
The house is drawn onwards ; the animal is in motion. It takes great 
strides, but a fraction of an inch satisfies its desires ; it is, however, an 
advance upon the oyster, and a lesson in mechanics. The mussel 
stretches out its foot, and, at the point chosen, it hooks on a hair °1 
