OYSTERS. 363 



The interior surface of the valves is smooth and white, diaphanous 

 or pearly towards the centre, but near the hack an oval or rounded 

 impression may be observed, to which a thick and whitish fleshy body 

 is attached. This is the central muscle which draws the valves 

 together, hermetically closing them upon the animal. This muscle 

 is cut through in the process of opening the oyster. 



The animal has no power of locomotion ; its foot is very small and 

 often wanting, no syphon, but lies with its mouth open, and slightly 

 attached to the shell. The shell itself is always adherent, as if sol- 

 dered to the rock or other submarine body, the point of adherence 

 being near the summit of the lower valve, at the part called the heel. 



Let us suppose the oyster opened by the double dissection of the 

 ligament of the central muscle and of the abductor valves. When 

 displayed before our eyes, we see in the bottom of the shell a flattened, 

 shapeless animal, semi-transparent, greyish, and somewhat oval- 

 shaped. The gastronomist, who seldom sees beyond his nose, thinks 

 that in spite of its culinary merits the oyster belongs to the lowest 

 rank of animal existence ; but he deceives himself, and does not know 

 how complex and delicate is the organization of the humble bivalve. 

 The animal is enveloped in a sort of smooth, thin, contractile tissue 

 called the mantle, which folds round it, presenting two lobes, separated 

 on the greatest part of its circumference, and forming a sort of hood, 

 the summit of which abuts upon the hinge of the bivalve. The edges 

 of this mantle are fringed with very small cilia, which the creature 

 can extend and draw back at pleasure, and which seem to be gifted 

 with a certain amount of sensibility. It is this mantle which secretes 

 and deposits the calcareous matter which forms the shell, each plate of 

 which is an enlargement on the preceding one, until it constitutes a 

 pyramid of thin convex lamellae. 



At the point where the lobes of the mantle meet, near the summit 

 of the valve, is the mouth of the animal, with its thin membranous 

 lips. This organ is large and dilatable, and is accompanied by four 

 flat triangular pieces, by means of which the animal introduces its 

 food into the stomachal cavity* 



A very short gullet is attached to the mouth, which leads to a 

 pear-shaped stomach. After this stomach comes a slender sinuous 

 intestine, which, leading obliquely towards the interior, descends a 

 little, then reascends, passes behind the stomachal cavity, nearly on 



