BY MOLECULAR COALESCENCE. 101 
sufficiently transparent to admit of being seen by trans- 
mitted light, without the necessity of any kind of manipu- 
lation which can at all injure their structure, or alter 
their natural appearance. The earlier the stage of calci- 
fication, the more complete and spherical will be the forms 
of the carbonate of lime, and the more satisfactory the 
indications of molecular coalescence. If the piece of 
membrane examined has its surface entirely covered with 
caleareous matter, it will not show the earliest stages of 
coalescence, and therefore will only furnish imperfect 
evidence of this fact. The mdications of this process are 
best displayed on those portions of calcifymg membrane 
which are situated over the mterlaminar cavities before 
alluded to, separating these spaces from the general cavity 
or hollow of the valve. In such situations the coalescing 
particles being placed on a membrane intervening between 
two spaces will be almost as little mterfered with in their 
process of coalescence by the pressure of the adjacent 
parts, as if they were on the slide of glass, as in the arti- 
ficial process ; and hence the globular particles formed on 
membranes so situated, ought to be as perfect as those 
produced by that process. And such is the case. I have 
in my possession specimens of these globules in every 
stage of coalescence, distinguishable from the artificial 
formation only by the membranous tissue which forms 
_ their bed. Partially calcified membrane, like the above, 
is most easily obtained by keeping oysters which have 
those caverns on their shells from the contact of water, 
until the branchize become dry, when the calcifying mem- 
brane, becoming slightly discoloured and hardened, can 
be both more easily distinguished and more readily sepa- 
rated from the contiguous parts of the shell. (These 
globules are not to be confounded with crystals which 
