CLASS ACEPHALA. 



37 



FIG. 51. 



The Pearl-oyster, the shells of which sometimes meas- 

 ure twelve inches in diameter, is found in nearly all 

 tropical seas. Its exterior 

 is uncouth, but the irides- 

 cent lining is one of the 

 most beautiful creations of 

 nature. If any irritating- 

 substance, as a grain of 

 sand, should inconvenience 

 the oyster, the animal at 

 once deposits around it 

 layer upon layer of this 

 nacre, thus forming a 

 pearl.* 



Mel e dg'n na mar gar i fife ra, with lead 

 images covered with Mother-of-pearl. 



care, the beating of this organ may be distinctly seen. The dark liver is large 

 and secretes a deep yellow bile in large quantity. The mouth is provided with 

 palps by which food is selected and carried inside. The eggs are yellowish, and 

 a single oyster may contain two millions, which, lying in the folds of the mantle, 

 look like thick cream. When the proper time arrives, they are ejected into the 

 water in a milky cloud. Each little oyster, though not larger than the point of a 

 pin a whole troop being able to swim freely about in a drop of water has a per- 

 fect shell, and is provided with a fleshy pad for attaching itself to any object at 

 hand. Crustaceans, worms, and enemies of all kinds, with a natural liking for 

 raw oysters, flock in to the feast, and a few score only of the millions escape. 

 The survivors anchor themselves to some smooth surface and grow rapidly. In a 

 month, they will be as large as a pea. If we examine a shell, we can see the 

 layers overlapping each other like shingles, each one indicating a season's growth, 

 and the series showing the oyster's age. In three or four years, a marketable 

 size will be reached. The little red crab often found sharing the oyster's home, 

 is the Pinnotheres ostreum (Pin no the' res oVtrg um). The female is generally seen, as 

 the male is scarce. The latter has its back ornamented with a white figure, 

 very like an anchor. At the discovery of America the oyster was abundant upon 

 the Atlantic coast. Immense mounds of shells lie along the shore, from Maine 

 to Florida. They antedate the time of the Indian, and are so large that in 

 Florida, during the late war, some were used as forts. See Lockwood's "Natural 

 History of an Oyster," in Popular Science Monthly, November, 1875. 



* Taking advantage of this, the Chinese have long been in the habit of pro- 

 ducing pearls artificially by slipping metal images under the mantle and then 

 releasing the animals. In six months, the figures are found overlaid with a pearly 

 secretion. Sometimes, however, the crafty Celestials paste these images upon the 

 interior of a dead shell and then paint it over with a mixture of powdered 

 " mother-of-pearl," in exact imitation of the genuine. 



