32 Animal Life by the Sea-shore. 



as large as the common species, but mrt valued for food, has 

 the shell of an orange or dark brown colour, quite unlike the 

 bluish-black of its ally. The shells of mussels are often covered 

 with barnacles, hydroids or weeds. 



The most valuable of all our molluscs, the Oyster (Osirea 

 cdulis), is anotlier permanently fixed bivah'e, but, unlike the 

 mussel, it spins no tlireads, attachment being bj' one of the 

 valves of the shell, which are unequal in size, the right being 

 flat, and functioning as a kind of lid. In accordance with the 

 lack of locomotory power, the foot is very much reduced, 

 vestigial in fact, and to the reduction of this tough muscular 

 organ the universal popularitj' of the OA'ster as an article of 

 food is in great part due. The gills form a fringed frill, popu- 

 larly known as the beard. Our British oyster is hermaphro- 

 dite, while other edible species, such as the American and 

 Portuguese oysters, have the sexes distinct. The breeding 

 season extends from May to August, according to individuals, 

 when a large number of minute eggs are pniduced ; but instead 

 of being immediatelj' discharged tire)- first spend some time 

 within cavities above the gills. When in tins condition 03'sters 

 are said to be sick, and are not fit fm- consumption. Cases of 

 poisoning through eating oysters during the period of repro- 

 duction are not infrequent, and this fully justifies the popular 

 notion that one should abstain from this delicacy during those 

 four months in the year the names (jf which are without an 

 " r." After a few weeks the 3'oung oysters escape from the 

 parent as tini,' swimming lar\';e, which, after a few hours' 

 freedom, iix themselves to s(une suitable support, rapid gro\\'th 

 following. Natural oyster-beds are now no longer abundant round 

 our coasts, and occur in fairly deep water, where the fry or 

 " spats " are collected and transferred to artificial oyster-beds 

 or parks. What are called " nati\-e " (_iysters are such as have 

 been reared in or near tlu: Thames estuary, although they may 

 have developed from sjiats (obtained elsewhere. The Colchester 

 beds are among the lew natural settlements on the East Coast. 



The oyster is only one of man}' bi\falves in ^\'luch the two 

 halves of the shell differ in size and shape. We meet \\-ith 

 another case in the Scallops or Fan-shells (Pecten), in which the 

 dissimilarity of the t\\'() vah-es is \-ery pronounced. Peclcii 

 Diaximns is the species of the greatest commercial importance, 

 from its large size, occasionally as much as eight inches in 

 diameter. Althougli usually resting on the deeper right valve, 

 scallops sometimes displa\- considerable acti^'ity, and swim 

 vigorously through ra]U(ll\' opening and closing the shell by 



