1888 - 89 .] Mr Irvine & Dr Woodhead on Carbonate of Lime. 341 
it to the organs which require it for the process of cell forma- 
tion. 
In proof of this he gives the following analysis of the ash of the 
secreting layer of the mantle : — 
Phosphate of Lime, . . . * 14*85 14*91 
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 acid, but not a trace of the phos- 
phate. In the delicate membrane in which the lime is deposited 
we have an analogous membrane to that of the egg-shell membrane 
separated from the secreting layer of cells by a fluid containing 
albumen, carbonic acid, and lime salts in whatever way combined, 
and deposited in this structureless membrane. According to analysis 
of the ash, the lime salts present are in the following proportion : — 
So that Schmidt was able to trace the transition stages through 
the excess of phosphate in the mantle ; the albuminate in the 
intermediate bathing mucus, and the carbonate, in the shell. 
We should be inclined to argue that the carbonic acid 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 condi- 
tion) into the membrane again by dialysis. As the process of 
shell-formation must necessarily go on slowly, it is not at all 
astonishing that such a small proportion of carbonic acid should be 
found in the mucous material. It is used up as it is formed in laying 
down the carbonate of lime in the shell. In the same way, as 
before pointed out, there are albumen and phosphate of lime 
in the oviduct of the hen, although the egg-shell is composed 
almost entirely of carbonate. 
Anodonta. Helix. 
Carbonate of Lime, . 
Phosphate of Lime, . 
99*45 99*06 
0*55 0*94 
