110 FORMATION OF SHELLS OF ANIMALS, ETC., 
formed artificially were treated in like manner; but this 
basis being a constituent of the smallest as well as of the 
largest particles, and being formed simultaneously, and in 
combination with the carbonate of lime, must be so blended 
with the earthy matter of the latter, as to be present in 
every part of their substance; hence the two materials— 
the earthy matter and the animal basis—being thus incor- 
porated in every globule large enough to be looked upon 
as a true cell, would in no way agree with the idea of a 
hollow body with a membranous exterior, and with an 
internal cavity either completely or incompletely filled 
with carbonate of lime, which, from the descriptions given 
of these cells in the works of those who have written upon 
the shell-tissues, is evidently the idea generally enter- 
tained of these globular bodies. And what is still more 
remarkable, these so-called cells are believed to possess 
an inherent vital power of forming others exactly like them. 
And, thirdly, when the carbonate of lime is precipitated 
on a membrane which is not homogeneous, but is marked 
out into squares or parallelograms or other figures, still 
the marking has no influence on the earthy matter formed 
upon its surface. Sometimes, however, it seems to follow 
these markings, and then has the appearance of being 
contained in cells ; yet such a circumstance is completely 
accidental, as any one may convince himself who will 
examine such appearances without any bias; when it will, 
at once, be apparent, that the earthy matter is deposited, 
and extends itself irregularly, and without any limitation, 
by such markings, or without in the least corresponding 
to them. I may just notice here, that although the curvili- 
near contour may not be regarded by histologists as essential 
to organic cells, yet, that the tendency of the vital force is 
always to produce that form. Hence in the descriptive and 
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