MOLLUSCA — MUSCLE. 765 



THE MUSCLE, 



As is well known, consists of two equal shells, joined at the back by a strong 

 muscular ligament that answers all the purposes of a hinge. By the elastic 

 contraction of this, the animal can open its shells, at pleasure, about a quar- 

 ter of an inch from each other. The fish is fixed to either shell by four 

 tendons, by means of which it shuts them close, and keeps its body firm 

 from being crushed by any shock against the walls of its own habitation. 

 It is furnished, like all other animals of this kind, with vital organs, though 

 these are situated in a very extraordinary manner. It has a mouth furnish- 

 ed with two fleshy lips ; its intestines begin at the bottom of the mouth, 

 pass through the brain, and make a number of circumvolutions through the 

 liver ; on leaving this organ, they go on straight into the heart, which they 

 penetrate, and end in the anus; near which the lungs are placed, and 

 through which it breathes, like those of the snail kind; and in this manner 

 its languid circulation is carried on. 



The multitude of these animals in some places is very great ; but from 

 their defenceless state, the number of their destroyers is in equal pro- 

 portion. 



But notwithstanding the number of this creature's animated enemies, it 

 seems still more fearful of the agitations of the element in which it resides; 

 for if dashed against rocks, or thrown far on the beach, it is destroyed with- 

 out a power of redress. In order to guard against these, which are to this 

 animal the commonest and the most fatal accidents, although it has a power 

 of slow motion, which we shall presently describe, yet it endeavors to be- 

 come stationary, and to attach itself to any fixed object it happens to be 

 near. For this purpose it is furnished with a very singular capacity of bind- 

 ing itself by a number of threads to whatever object it approaches; and 

 these Reaumur supposed it to spin artificially, as spiders their webs, which 

 they fasten against a wall. Of this, however, later philosophers have found 

 very great reason to doubt. It is, therefore, supposed that these threads, 

 which are usually called the beard of the muscle, are the natural growth of 

 the animal's body, and by no means produced at pleasure. 



Its instrument of motion, by which it contrives to reach the object it 

 wants to bind itself to, is that muscular substance resembling a tongue, 

 which is found long in proportion to the size of the muscle. In some, it is 

 two inches long; in others, not a third part of these dimensions. This the 

 animal has the power of thrusting out of its shell ; and with this, it is capa« 

 ble of making a slight furrow in the sand at the bottom. By means of this 

 furrow, it can erect itself upon the edge of its shell ; and thus continuing to 



I Mytilus. Shell longitudinal, equivalve, rea;ular, pointed at the hase, and adhering by 

 a byssus : beaks almost straight, terminal, and pointed ; hinge lateral, generally without 

 teeth; ligament marginal, subinterior; muscular impressiou elongated, clavate sub- 

 lateral. 



