Figure 98. — Prismatic layer of the new growth of shell at the edge of the mantle. Four to five days old. Photomicrograph 



of an unstained whole mount. 



probably a transfer agent involved in tiie mobiliza- 

 tion of calcium. The localization of tliis enzyme 

 along the border of the mantle and in the surface 

 epithelium of the oyster, shown by tlie Gomori 

 technique (fig. 80), confirms tlie opinion of 

 Manigault and of Bevelander that tlie phosphatase 

 plays an active role in the calcification of oyster 

 shells. 



During the last decade consideraT)le advance 

 was made in studies of the metabolic aspects of 

 shell formation. Hammen and Wilbur (1959) 

 paid particular attention to carbon dio.xide con- 

 version to shell carbonate and to the secretion of 

 conchiolin matri.x in whicli the calcium carboiuite 

 crystals are deposited by Mie oyster (C. inrgiriica). 

 Tlie work of Jodrey and Wilbur (1955) on high 

 activity of the enzyme oxalocetic decarboliylase 

 in the mantle tissue of this species suggested that 

 tlie deposition of carbonate may be related to 

 decarboxylation reactions of tlie mantle. Experi- 



mental work conducted by Hammen and Wilbur 

 at the Duke University Marine Laboratory at 

 Beaufort, N.C., corroborated this hypothesis. 

 Living oysters and isolated shells were placed for 

 12 hours in sea water containing 240 microcuries 

 of NaHC'^Oa per liter. The radioactivity of the 

 shell surface was determined near the posterior 

 margin of the right valve and corresponding cor- 

 rection was made for self absorption on the surface. 

 By incubating pieces of oyster tissues in NaHC'^Os 

 it was found that C" is incorporated into organic 

 acids of the mantle. More than 90 percent of the 

 radioactivity occurs in succinic and smaller 

 amounts in fumaric and malic acids. The initial 

 step in the process is the fixation of carbon dioxide 

 by propionic acid resulting in the formation of 

 succinic acid. Botii acids were found in relatively 

 iiigii concentrations in the shell forming tissues 

 of the oyster. The fact that in these experiments 

 labeled amino acids were found in the radioactive 



THE MANTLE 



99 



