T. F. GOREAU 283 



GOREAU: Yes. If we assume the hypothetical scheme of calcifica- 

 tion which I published some years ago, then the removal of CO- 

 from the system would tend to drive the equilibrium to the right and 

 increase the rate of CaCO.; formation. 



MUSCATINE: This differs from the scheme of Wilbur and Jod- 

 rey who found that calcification in their oyster mantle preparations 

 was increased about five fold if a source of COo such as oxaloace- 

 tate was added to the external medium. 



GOREAU: Oxaloacetate is an intermediate in the Krebs cycle. Any 

 increase in the rate of this cycle may have rather non-specific effects, 

 and changes in calcification rates would tell us little. Nevertheless, 

 it's a very interesting possibility and we are planning work along 

 similar lines. Unfortunately, as Wainwright mentioned, there are 

 certain small difficulties in running such experiments. 



MARTIN: In mammals, the accretion of bone substance is not a 

 one-way affair, but as accretion goes on, elimination and dissolu- 

 tion of bone material also goes on. I wonder if these views contri- 

 bute any insight into the problem. 



GOREAU: Yes. This is a very important point. Bone and coral 

 differ in at least one fundamental way. Bone is mesodermal and 

 remains at all times part of the internal medium of the body. At 

 least 2(y/c of the bone mineral is exchangeable with calcium and 

 phosphate dissolved in the body fluids. In addition, mammalian bone 

 is vascularized and full of cells. The corallum, on the other hand, is 

 an ectodermal mineral deposit which lies outside the body of the 

 coral polyp. We have evidence that once the CaCO;^ is deposited 

 there, it undergoes little or no further exchange with the environ- 

 ment or with the coral; that is, it seems to be essentially isolated as 

 long as it is covered by a layer of living tissue. 



LOO MIS: Dr. Goreau has shown that the rate of calcification at 

 the end of a coral branch is something like tenfold what it is at a 

 shoulder. I find this position effect fascinating since the two en- 

 vironments appear identical at first glance. 



Another point is that CO^. plays a double role: (a) it is part of 

 the calcium carbonate which is part of the corallum, and (b) it 



