398 OSTRACE^E ; OYSTERS. 



the ligament which unites the valves is of small size. On 

 separating the valves, the four rows of gills are observed, form- 

 ing what is called the beard, at a J ; ttle distance from the fringed 

 edge of the mantle. The adductor muscle is situated at about 

 the centre of the body ; and the heart lies between it and the 

 mass of the viscera, and is easily to be distinguished by the 

 brown colour of its auricle. The mouth is to be found beneath 

 a kind of hood, formed by the union of the two edges of the 

 mantle near the hinge. The ovaries are of very large size at 

 breeding time ; and one individual produces, according to Poli, 

 1,200,000 eggs. These eggs appear to be generally developed 

 within the valves of the parent ; so that the young Oysters may 

 be often seen swimming slowly in the fluid surrounding the gills, 

 or attached to these organs. According to Leeuwenhoek, each of 

 these is about 1 -120th of an inch in length ; so that two millions 

 of them closely packed together would not occupy above a cubic 

 inch. He reckoned from 3000 to 4000 to exist in one Oyster at 

 the same time. The principal breeding time of the common 

 Oyster is in April and May, when they cast forth their young 

 in little masses like drops of grease, formed of several united 

 together by an adhesive fluid, upon rocks, stones, or other hard 

 substances that happen to be near ; and to these the spats, 

 as they are termed by fishermen, immediately adhere, soon 

 forming a thin shelly covering. Very commonly they adhere to 

 adult shells ; and thus are formed the large masses termed banks. 

 Their growth is very rapid. In three months they are larger 

 than a shilling ; and at the end of the first year they have a 

 diameter of two inches. When they are about a year and a half 

 old, they are reckoned fit for the table ; and they are then taken 

 by dredges, and stored in pits, where they undergo changes in 

 their condition, which render them more fit for the market. 

 When removed altogether from their native element, they very 

 commonly open their shells, and lose the water retained between 

 them, which occasions their speedy death ; but if placed in 

 situations which the tide occasionally reaches, they learn to keep 

 their shells closed in the intervals. Although no special organs 

 of sensation can be detected in them, except the tentacula around 



