Centimeters 



Figure 72. — Oyster viewed from the right side. Portion of the right mantle and the wall of the epibranchial chamber 

 cut off to expose the gills and their water tubes, the cloaca, and the lower part of the gonad, ad.m.t. — adductor 

 muscle, translucent part; ad.m.w. — adductor muscle, white (opaque) part; an. — anus; bl.v.- — blood vessels of the 

 mantle; cl. — cloaca (the arrow indicates the direction of the outgoing current of water) ; cp.a. — circumpallial artery; 

 cp.n. — circumpallial nerve; ep.br. ch. — epibranchial chamber of the gills; f. — fusion of gills and mantle; g. — gills; 

 gd. — gonoducts; py.p. — pyloric process; q.m. — rudimentary Quenstedt's muscle; t. — tentacles; ur.v. — opening of the 

 urinogenital vestibule ; v.g. — visceral ganglion ; w.t. — water tubes of the gills. Drawn from a preserved specimen. 



through the mantle and gills. The alkalinity of 

 the shell liquor retained in the mantle cavity 

 therefore decreases with time as the oyster remains 

 closed. Although liquor may become slightly 

 acid, excessive acidity is stopped by the buffering 

 action of calcium carbonate dissolved from the 

 shell. 



The ability of the oyster to retain shell liquor 

 is a useful adaptation to life in the intertidal zone 

 permitting the animal to survive many days of 



exposure to air. It is equally useful to those 

 oysters which live below tlie low water mark and 

 are never exposed to air. By closing their shells 

 tightly and by retaining some sea water they are 

 able to survive unfavorable conditions caused by 

 floods or by tlie temporary presence of toxic or 

 irritating substances in the water. 



The color of the surface of the mantle facing tlie 

 shell is variable. Lean oysters devoid of glycogen 

 are usually of a dull grayish color whereas "fat" 



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FISH AND WILDLIFE SERVICE 



