MYTILHLE. 345 



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 supplies 

 the branchiae ' at the same time. The stomach consists of a white 

 membrane, thin, like opaline, and presenting itself in longitudinal 

 folds ; the liver is granulous, composed of greenish grains more or 

 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 of 

 the mantle near 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 tongue, 

 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. The 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 a 

 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 the 

 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 some 

 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 no 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 of 

 the bys?us ; then, withdrawing the foot suddenly, and hauling on the 

 thread, the animal and shell are moved forward. Every time it repeats 

 this motion it seems to attach an additional hair, so that at the end of 

 the four and twenty hours it has used many inches in length of 

 cordage. In the byssus of some mussels we find as many as a hundred 



