CLASS LAMELLIBRANCHIATA : ORDER ASIPHCWATA. 253 



Fig. U2U. 



Meleagnna margaritiftra, with lead images covered with pearl nacre. 



The Aviculidse (little-bird) include the pearl-makers. 

 These gems are caused by the effort of the animaJ 



Fiq. 



the shell and* used in bringing inside animalcules and the spores of algae for food. The 



lime for building the shell is secreted by the 



mantle. The plaited frills on the mantle 



are the gills. The heart, shaped like an 



old-fashioned purse, has an auricle and 



ventricle, and circulates a limpid colorless 



blood. If the shell be opened with care, the 



beating of this organ may be distinctly seen. 



The black liver is large and secretes a deep 



yellow bile in large quantity. The mouth is 



provided with tentacles by which food is 



selected and carried inside. The oyster 



wants brains and eyes, and has no sense 



except that of touch, which is located in 



the tentacles. The eggs are yellowish, and 



a single oyster may contain two millions, 



lying in the folds of the mantle and looking 



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 perfect shell, and is provided 



with a fleshy pad for attaching itself to any Ostrea edulis, Common Oyster, in shell, 



object at hand. Crustaceans, worms and upper valve removed, a. Upper portion 



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 rough 



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 



of mantle covering the month with its 

 four lips; b, c. The mantle; d. The 

 breathing organs ; e. Portion of th6 

 lobes of the mantle, between which is 

 the extremity of the intestinal canal; 

 f. Part of the heart; g. Adductor 



