84. FORMATION OF SHELLS OF ANIMALS, ETC., 
the cavity of the claw, could have no communication with 
this cavity analogous to that of the fibres of dentine with 
the cavity of a tooth. As the development progresses, 
the globules loose their bright and structureless character, 
and begin to present laminze and radiating lines, just as 
the artificial calculi do. The lines, as stated of disin- 
tegrating globules, being most distinct when the globules 
are suffering disintegration, will be seen best in the layers 
remote from the cavity of the claw, that is, nearer to the 
surface, where the softer component of shell is in excess, 
These lines are the radii first of small circles, then, after 
the smaller globules have coalesced, they become so 
arranged in respect to the globule resulting from this 
coalescence as to be the radii diverging from its centre ; 
and so they continue, as the coalescence advances, to 
become progressively the radu of larger and larger circles, 
until at length, when this process is completed, they 
remain as the radii of a circle, whose centre is that of the 
part around which all the now completely coalesced 
portions of globular carbonite are situated. This, 
through the tendency of these lines, will be interfered with 
in a variety of ways and by a diversity of mechanical 
causes, So as to prevent the figure in any part of a shell 
from ever becoming perfectly circular; hence these lines 
will remain as the radii of a complex curvilinear form, 
whose elements are too complicated ever to admit of being 
mathematically determined. See fig. 5 a, which represents 
a vertical section of calcefying crab-shell. The lines in these 
shells, as im the case of those of the laminated artificial 
calculi, are generally continued uninterruptedly from one 
layer to another, so that they can be traced from the super- 
ficial surface of the claw to the deep one; but it must be 
observed that their distinctness diminishes towards its 
