122 



SEA-SHORE LIFE 



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Fig. So; AMERICAN OYSTER. 



of the body, as two sheets on each side, near the mid-dorsal line, 

 and which lie free in the space between the mantle and the body 



of the oyster. The digestive tract is 

 much coiled and twisted, and the mouth 

 of the oyster is placed close to the 

 hinge at the narrow apex of the shell, 

 where it is surrounded by curtain-like 

 lips. 



There is a well developed stomach 

 which often contains a glistening, gela- 

 tinous, rod called the "crystalline style." 

 The function of this is unknown, al- 

 though it may possibly represent stored 

 up nutrient material. 



The large green-colored liver sur- 

 rounds the stomach into which it 

 empties, while the reproductive organs 

 siirround the coiled intestine, and are very large during the 

 warmer months when the oysters are spawning. 



A full-grown female oyster will produce about 9,000,000 eggs, 

 each being about one-five-hundredth of an inch in diameter. The 

 eggs are cast out into the water through the oviducts which open 

 into the gill cavity on both sides of the body below the adductor 

 muscle. They then develop into little free-swimming larvas which 

 swim rapidly through the water by means of their hair-like cilia. 

 The shells then appear upon the sides of the body, and when about 

 one-eighth of an inch wide the creature settles to the bottom with 

 its left side down, and there remains throughout life. 



The true heart of the oyster is bulb-like in shape, and lies 

 within a delicate translucent sac close to the inner side of the great 

 adductor muscle. It pulsates slowly, and pumps blood from the 

 gills to other parts of the body. Growth is rapid at first, for 

 under favorable conditions the little oyster, or "spat," as it is 

 called, may become an inch across its shell in seven weeks, and 

 two inches in three months. 



The oysters feed upon a great variety of minute organisms, 

 such as simple unicellular plants and animals, and small marine 

 larvfe. The gills are covered with waving cilia, which create a 



