MOLLUSCA 47 



tions were published by Brooks in his book, "The Oyster," in which 

 he described in a popular yet scientific way, the natural history of the 

 American oyster, and showed the necessity of conserving the supply by 

 proper cultivation just as is done with most other natural food prod- 

 ucts. The food of the oyster consists of microscopic organisms living 

 in the salt or brackish water in which the oyster thrives best. They 

 are carried into the mantle chamber, Fig. 29, by the cilia cover- 

 ing the organs of that region and enter the mouth of the animal. 

 Among these organisms, of course, may be disease germs, if the water 

 be polluted with sewage, as will be noted below. It requires three or 

 four years, depending on the food supply, etc., for the oyster to reach 

 maturity. 



In the European oyster the eggs are fertilized and begin their de- 

 velopment in the gill tubes of the female, while in the American form it 

 was found by Brooks that the eggs are fertilized outside of the female, 

 in the surrounding water. Since an average Maryland oyster will 

 lay the incredible number of 16,000,000 eggs per year, it is evident that 

 the struggle for existence must be terrific or the sea would soon be filled 

 with oysters. If the egg should happen to be fertilized, it segments 

 and develops into a tiny ciliated larva which swims to the surface, where 

 it may be killed by a heavy rain. After living for a time at the surface, 

 if it escape its many perils, it sinks to the botUta, loses its cilia, devel- 

 ops a tiny shell, and attaches itself to some solid object, if such be 

 found, and is known as a "spat; " if no solid object be present the young 

 oyster will perish, but if it succeed in becoming "set" it will proceed to 

 develop into the mature oyster. 



Oyster Culture. Brooks found that by mixing eggs and sperm from 

 "ripe" oysters in salt water the eggs could be easily fertilized in un- 

 limited numbers; but, for some reason, these artificially fertilized 

 eggs when they develop to the spat stage will not set, so that this stage 

 of oyster culture is not practicable. What may be done is to allow the 

 spat to form in the natural way and then collect it by placing various 

 kinds of hard objects in the water at the breeding season; if placed 

 in the water too long before the spat are ready to set these solid objects, 

 known collectively as "cultch," may become covered with mud or 

 other sediment and thus prevent the spat from setting. Various sub- 

 stances are used as cultch: tiles; a bunch of twigs (bamboo in Japan) 

 tied together and sunk to the bottom with a stone; crushed rock; scrap 



