114 FORMATION OF SHELLS OF ANIMALS, ETC., 
globule, anatomically and physiologically, like the one in 
which it is contained. I have frequently seen pathologists, 
in examining morbid products, point out cells with their 
cell-germs extending through several generations ; but to 
me the matter has always appeared to be entirely specula- 
tive, and perfectly gratuitous. Lastly, if the exterior layer of 
each of these globules had been a cell constructed according 
to the cell-theory, for the purpose of secreting the carbonate _ 
of lime contained within it, the question might be asked 
how it happens that, with the microscope, aided by the 
polariscope, all the carbonate can be seen when perfect 
globules are being acted upon byacid, gradually to disappear 
from their interior, and to leave the part which it had 
before occupied demonstrable, whilst, by the same means, 
no deposition of carbonate into the interior of similar 
bodies can ever be shown? whilst if it had been deposited 
in previously formed cells, the fact of its deposition ought 
to have been as demonstrable as that of its removal. The 
only answer this question admits of is, that cells or 
globules so constructed have only a hypothetical existence, 
and that there are in fact no such globules apart from their 
earthy constituent; but that in all stages of their develop- 
ment, the earthy component and animal basis are always 
found together, which being possessed of a property of 
coalescence, as shown by experiment, pass through a 
succession of coalescences, until they result in the forma- 
tion of the globular bodies in question. The hard tissue 
next to be considered is bone. 
ON THE STRUCTURE AND FORMATION OF BONE.: 
Of all the tissues which have been described in the 
preceding pages, the calcified tendons in crustaceans come 
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