14 THE OYSTEK A^TD THE OYSTEP. TIsTDUSTRY. 



Once secured, the swimming organ disappears and the oyster never 

 wanders again of its own volition. 



GROWTH. 



The shell is secreted by the mantle, the membrane lining the shell. 

 Horny material is first deposited over the outer sm-face of the mantle 

 and to this is added lime, forming the familiar hard shell. As the 

 mantle increases in size with the general growth of the rest of the 

 body, and as it can be extended somewhat from between the edges 

 of the valves, new shell material is added to the inner surface of the 

 valve and to the outer edge. This makes each valve thick in the 

 central portion, sloping to a condition of extreme thinness at the 

 edges. The outer edges of the valves of a rapidly growing oyster 

 are so thin and knifelike that care must be exercised in handling 

 them to avoid cutting the fingers. 



The rate of growth of oysters varies widely, depending on tem- 

 perature, density and food content of the water, season of the year, 

 and other factors. Its growth is more rapid in the warmer southern 

 waters than in the colder northern. In Long Island Sound about 

 four years are required for an oyster to reach a length of 4 to 5 inches, 

 or marketable size. In southern waters that size is reached in two 

 years. Oysters if left undistm^bed may attain a length of 8 to 10 

 inches or more. While the exact age which an oyster may reach 

 can not be definitely stated, oysters have been found which appeared 

 from the number of layers in the shell to be at least 15 years of age. 



Oysters which have unrestricted space for growth acquire the normal 

 shape shown in Plates I, XX, and XXI. When crowded together, 

 the shape becomes modified, even greatly distorted at times. Often 

 numerous set will fasten upon a relatively small piece of cultch, and 

 as growth proceeds a crowded cluster of oysters will result. If 

 broken apart by pressure of growth or by artificial means, their 

 shape will improve. 



The crowding of oysters reaches its climax upon the "raccoon '' oyster beds. Rac- 

 coon oysters are usually found in localities where the bottom is soft and the only 

 firm place which offers itself for the attachment of the spat is upon the shells of its 

 ancestors. Temperature and other conditions are favorable, growth is rapid, the young 

 oysters are crowded into the most irregular shajjes, the shells are long, thin, and sharp- 

 edged, and eventually the mass of young is so dense that it crowds out and smothers 

 the preceding generations which produced it and offered means for its attachment. 

 Oysters crowded in this excessive manner are poor-flavored, as well as ill-shaped, 

 but both defects are corrected if they be broken apart, as may be readily done, and 

 planted elsewhere." 



FACTORS OF ENVIRONMENT.* 

 TEMPERATURE OF WATER. 



The fact that the oyster is found from Cape Cod to Mexico shows 

 that it can become adapted to livmg in waters of considerable differ- 

 ence of temperature and in certain regions may withstand wide 

 changes during the course of the seasons. In Long Island Sound 



aMoore, H. F. (1897, p. 275.) 



b The outline of this section, " Factors of Environment," and of the one following, "Natural Beds," and 

 the details of certain topics therein, specifically stated in each such case, are substantially as prepared by 

 Dr. n. F. Moore, Deputy Commissioner of Fisheries, for an uncompleted revision of his "Oysters and 

 Methods of Oyster Culture" (1897). 



