28o PHYSIOLOGY OF THE INVERTEBRATA. 



lime next the shell, which is decomposable even by the carbonic 

 anhydride of the air or of the water, but of retaining the 

 phosphoric acid and returning it to the organs which require 

 it for the process of cell formation. In proof of this he gives 

 the following analysis of the ash of the secreting layer of the 

 mantle : 



II. 

 14-91 



3-45 



I. 

 Calcium phosphate . . . . . 14 '85 

 Calcium carbonate, sodium phosphate,) 



2.71 

 sodium chloride, and calcium sulphate/ 



showing how large a proportion of the lime salts must, in 

 this secreting layer, be in the form of phosphates. As 

 further proof he gives analysis of the mucus which is found 

 between the shell and the mantle, in which he finds much 

 albuminate (basic) of lime, a small proportion of carbonic 

 anhydride, but not a trace of phosphate. In the delicate 

 membran,e in which the lime is deposited we have an analo- 

 gous membrane to that of egg-shell membrane (of birds), 

 separated from the secreting layer of cells by a fluid containing 

 albumin, carbonic anhydride, and lime salts, in whatever way 

 combined, and deposited in the structureless membrane. 

 According to analysis of the ash, the lime salts present are 

 in the following proportion : 



AnoAonta. Selix^ 



Calcium carbonate . . . 99-45 •■• 99.06 

 Calcium phosphate . . . 0.55 ... 0.94 



So that Schmidt was able to trace the transition stages 

 through the excess of phosphate in the mantle, the albu- 

 minate in the intermediate bathing mucus, and the carbonate 

 in the shell." 



Irvine and Woodhead believe that the carbonic anhydride 

 in this case was the result of metabolic processes going on 

 in the mantle, and that the carbonate of lime formed was 

 gradually passed on in this condition from the lime-mucous 

 solution (if present in that condition) into the membrane 

 again by dialysis. 



