STUDIES ON SHELL FORMATION. III. MEASUREMENT OF CALCIUM DEPOSITION IN SHELL AND CALCIUM TURNOVER IN MANTLE TISSUE USING THE MANTLE-SHELL PREPARATION AND Ca45 ,

Abstract

1. A study of calcium turnover and calcium deposition by the oyster mantle in the absence of other soft tissues has been carried out using mantle-shell preparations of Crassostrea virginica. 2. The mantle of the mantle-shell preparation is able to deposit calcium from the sea water in shell. At least part of the calcium deposited as shell substance does not require the participation of digestive and circulatory systems. 3. The rate of deposition in the mantle-shell preparation was about one-ninth that of the whole oyster under the conditions of the experiment, but the distribution of newly deposited calcium was similar in both. 4. The greater portion of the calcium in the mantle appears to be inert, since the specific activity of the mantle calcium could not be increased beyond a small percentage of the specific activity of the sea water calcium. A small fraction (2.4 per cent) was renewed every 24 minutes, the turnover rate being 0.6 micrograms of calcium per minute per gm. of mantle. 5. The calcium turnover rate in the mantle edge is approximately twice as rapid as in the mantle interior but since the latter is renewing a calcium reservoir which is only about one-half as great as the former, the turnover time for the renewing fraction is the same in each. 6. Since the amount of calcium being renewed in the mantle is very nearly the same as the amount being deposited on the shell, it would seem that in the mantle-shell preparation at least, the fraction of rapid turnover brings about the formation of shell.