BIRTH, GROWTH AND REPRODUCTION OF OYSTERS. Iig 



oyster becomes reproductive may be easily fixed, and it 

 will no doubt be found to vary in different localities. At 

 some places it becomes saleable chiefly, however, for 

 fattening in the course of two years ; at other places, it 

 is three or four years before it becomes a saleable commo- 

 dity ; but on the average, it will be quite safe to assume 

 that at four years the oyster is both. ripe for sale and able 

 for the reproduction of its kind.* 



" Let us hope that the breeders will take care to have 

 at least one brood from each batch before they offer any 

 for sale. Oyster farmers should keep before them the 

 folly of the salmon-fishers, who kill their grilse i.e., the 

 virgin fish before they have an opportunity of perpetu- 

 ating their race. 



" When the free larva of the oyster settles down into 

 the fixed state, the left lobe of the mantle stretches beyond 

 its valve, and applying itself to the surface of the stone or 

 shell to which the valve is to adhere, secretes shelly matter, 

 which serves to cement the valve to its support. As the 

 animal grows, the mantle deposits new layers of shell over 

 its whole surface, so that the larval shell-valves become 

 separated from the mantle by the new layers which crop 

 out beyond their margins, and acquire the characteristic 

 prismatic and nacreous structure. The summits of the 

 outer faces of the umbones thus correspond with the 

 places of the larval valves, which soon cease to be dis- 

 cernible. After a time, the body becomes convex on the 

 left side and flat on the right ; the successively added new 



* S. P, Woodward in his "Manual of Mollusca," asserts that 

 oysters reared in artificial grounds do not attain their full growth in less 

 than five or seven years, whilst the sea oysters, namely those found in 

 natural oyster beds, which usually occur in water several fathoms deep, 

 are full grown in four years, p. 254. 



