BY MOLECULAR COALESCENCE. 109 
these pre-existing cells’ ought to be visible under the 
microscope; and the carbonate of lime afterwards de- 
posited in their cavities ought to be apparent when 
examined by the polariscope, especially as the deposition 
must be somewhat gradual, and the means of detecting 
it by this imstrument are most delicate and certain. 
However, notwithstanding these facilities, and having the 
aid of all that is necessary for microscopic examination, 
I have not been able to see anything which gives the least 
countenance to such a view, or which, in any way, agrees 
with the appearances said to present themselves in this 
class of tissues. In the first place, the membrane on which 
the carbonate of lime is precipitated is in most cases as 
devoid of marking of any kind, and as transparent, as a 
film of glass. This is especially the case in the oyster- 
shell, and many parts of the membranous layers of the 
erab-shell, where it forms septa between the cavities con- 
taining the muscles, so that thismembrane, in these cases, 
cannot be regarded as consisting of cells for the secretion 
and retention of the earthy matter. ‘Secondly, when this 
membrane is beginning to be ealcified, and only very 
partially covered with minute particles of earthy matter, 
nothing can be detected, either upon, or within it, so re- 
lated to these particles, as to answer in any way to the 
description of a cell with these particles: contained in its 
cavity. All that can be seen are minute particles joining 
together to form larger ones, and, these again joining to 
form particles still larger, until they acquire the size and 
form of distinct globules; but still, during the whole of 
this process, nothing like a membranous cell ever makes 
its appearance. It is true, that if these particles of 
earthy matter are acted upon by hydrochloric acid, an 
animal basis is left, the same as if a similar compound 
