OYSTER 



banks' at depth- of 3 to 20 fathoms, and are 

 strangely fastidious an to locality. They have 

 many enemies liesidcs tin- dmlger, such an the 

 lit'.li- siMiiigi-s (Clione), whirh U>re in the shell-; 

 marine worms, anil sea-snails (P.I;. Piirpnra and : 

 Murex ), which aUo effect an entrance ; I>e8ides ! 

 starfishes, which -wallow little one- intact, or, em- 

 bracing larger specimens, insert their arms when 

 the shells gape. Although these passive animals 

 hare no eyes or ears they can detect the shadow of 

 an approaching boat ; the mantle-fringe and some 

 other parts are undoubtedly sensitive ; and some 

 enthusiasts have even inferred 'intelligence' from 

 the fact that in the 'oyster-schools ' mid elsewhere 

 the molluscs learn to keep their shells shut when the 

 tide retires or when they are transported by mil ! 



Life-hittory There are many interesting facts 

 connected with the life history of the oyster. Thus, 

 O. tdu'.it u hermaphrodite, In-ing first an egg-laying 

 female, afterwards a stierm-producing male, while 

 O. Hii'jii/'itx and the American O. virpinica have 



. . 



the sexes separate. Maturity is sometimes rapidly 

 atuine-il, but usually not until the third or 

 fourth year of life, and the maximum fertility is 

 lietween the fourth anil seventh year. The repro- 

 ductive season generally lupins in May, and con- 

 tinue* till the beginning of autumn, but ite limits 

 are extended or lessened by the conditions of tem- 

 perature. When the oyster becomes 'sick,' 'milky,' 

 or 'out of season,' the mantle-cavity and the inter- 

 spaces between the gills are packed with developing 

 eggs, which fishermen call ' white,' and at a later 

 stage 'black spat.' Buckland likened this black 

 rpat to fine slate-pencil dust, and the emergence of 

 Hi'- young from the mother to a puff of smoke from 

 a railway-engine. He computed the numlier of 

 developing eggs in an oyster at from 276,000 to 

 829,000; and Professor Mohius, the greatest Ger- 

 man authority on oysters, calculates that 1000 

 full-grown patents produce 440 million embryos 

 annually. 



These embryos are only aliout T r,th of an inch in 

 length, and about two millions of them might be 

 packed into a cubic inch, but the numl>crs which 

 rise from an oyster-bank are so immense that the 

 water seems to Ira clouded. They are very unlike 

 the adults in habit, for they swim actively for some 

 days by means of a protrnsible ciliated cushion or 

 velum. The valves of the shell are transparent 

 ami symmetrical ; the gills, palps, and some other 

 adult structures have yet to be developed. In the 

 American oyster, the eggs are set adrift at an early 

 sta^e, fertilisation and the whole of development 

 taking place onteide the shelter of the parent. In 

 either case the mortality is enormous ; multitudes 

 are washed away to unsuitable localities, and multi- 

 tudes are devoured by hungry animals ; in fact 

 Mobius computes that out of 440 million embryos 

 only 421 individuals reach maturity. 



Those that survive become weighted by their 



C wing shells, draw in their ciliated velum' for the 

 ; time, and sink to the bottom as a ' fall of spat.' 

 They settle on stone*, shells, or other 'culch,' and 

 often nowaday* on chalked tiles or on floating 

 collectors which arc placed for the purpose of 

 receiving them. Moored by their left shells, they 

 grow rapidly, from ,' th of an inch when first 

 attached, till at the end of six to eight months they 

 are like threepenny pieces, and are known as 

 ' brood. ' ' The diameter of an oyster at two years 

 is about two inches, another inch is added in the 

 third year, after which the growth U much less 

 rapid/ 



Uifftrtnt Kindt. Oysters are represented by 

 several widely distributed species e-g. the Euro- 

 pean 0. eiliitit and 0. anyulata, the American 

 0. cirginica with several varieties, two others 

 from the western coasts (0. eonchophila and 0. 



luritln)~M of them edible, while the Ca]>e of 

 Good HO|K>, Australia, Japan, Ac. arc not without 

 their share. They vary considerably in -!/': tli"-e 

 from .'Uoti inches are common, but Sir.l. E. Tennont 

 found one in (Vslon measuring u little over 11 

 inches in length. American oysters are often 

 very large. The bank- of oysters sometimes form 

 important marine and shore deposits witness the 

 banks of long, narrow ' raccimn ' oysters off the 

 coast of Georgia and other parts of N'ort h America, 

 which are said to form natural breakwaters. The 

 race is an ancient one, for oysters appear in the 

 Carboniferous strata, and two related forms 

 Grypha-a and Exogyra with thick heavy shells, 

 are common fossils. The name i* sometimes ex- 

 tended to other bivalves, such as the false oyster 

 Anomia (one valve of which is perforated by a tag 

 of attaching byssus), the pearl-oyster Melcagrina 

 (see PEAKL), and the thorny oyster Spondylus. 



Edibility. The accumulations of oyster-shells in 

 the ' kitchen-middens ' of Neolithic ages show that 

 the appreciation of oysters is no modern taste. 

 To I toman palates the oyster was precious, and the 

 praises of its appetising flavour (qrata itigltivies) 

 were often sounded. Those of liiitnpia* (Rich- 

 liorough, in Kent) were earlv known to the epi- 

 cures and highly esteemed. When eaten alive or 

 half-alive in the usual fashion, they arc not only 

 pleasant, but nutritions and readily digested, nor 

 can any evil effects (such as parasites) lie traced to 

 moderate indulgence in these dainties. ' The points 

 of an oyster are," Frank Buckland says, ' first the 

 shape, which to be perfect should resemble very 

 much the petal of a rose-leaf. Next , the thickness 

 of the shell ; a first-class thoroughbred native 

 should have a shell of the tenuity of thin china or 

 a Japanese tea-cup. It should also have an almost 

 metallic ring, ana a peculiar opalescent lustre on 

 the inner side ; the hollow for the animal of the 

 oyster should l>e as much like an egg-cup as possible. 

 I.a-iK . the flesh itself should be white and firm, 

 and nut-like in taste. It is by taking the average 

 proportion of meat to shell that oysters should be 

 critically judged. The oysters at the head of the 

 list are of course "natives" (oysters artificially 

 reared ) ; the proportion of a well-fed native is one- 

 fourth meat." 



Oysters and Disease. Many coses of enteric ill- 

 ness and death having been of late referred to the 

 eating of oysters, the Local Government Board 

 made searching inquiry into the conditions of 

 oyster culture and storage along the coasts of 

 England and Wales, and ran led on bacteriological 

 investigations as to the power of the oyster to 

 absorb, retain, and transmit the typhoid bacillus 

 and the cholera vibrio. It appears from a report 

 in 1894-90 that oysters contaminated by sewage, 

 &c., can and do transmit disease; and that in 

 many localities the conditions of culture and stor- 

 age do expose oysters to the serious risk of such 

 contamination. 



Demand. Some years ago 500 millions were sold 

 annually in London, at a cost of 100,000 ; but the 

 supply has decreased, and the price increased. The 

 total British expenditure in oysters has since been 

 calculated at 2,000,000, for aliout 240 million 

 oysters. In Paris the annual consumption is 

 said to lie over 100 millions, which cost, it is 

 said, 1,654,350 francs in 1853, and 4,500,000 in 

 1890. In the United States the business employs 

 60,000 persons and 5000 vessels ; some 25 million 

 bu-hels are sold for 815,500,000. In New York 

 state alone the capital invested now exceeds 

 86,000.000. Oysters are sent from Baltimore, 

 New York, and other principal markets in car- 

 loads to the west to Milwaukee, Chicago, St 

 Louis, anil even San Francisco. The great beds 

 occur in Long Island Sound and Chesapeake Bay ; 



