30 FORMATION OF SHELLS OF ANIMALS, ETC., 
arrangement of the same molecules in fine lines, of an 
imperfectly crystalline structure, extending as radii from 
the centre of each calculus to its circumference. These 
radiating lines are not equally distinct in all calculi of the 
same composition. They are, for the most part, best seen 
in those of the largest size, especially when broken into 
fragments, which, in consequence of these calculi splitting 
up from the centre to the circumference, are wedge-shaped. 
These fragments require polarized light for their exami- 
nation. This singular transformation of a condition of 
carbonate of lime, which, when im small pieces, was per- 
fectly globular and appeared to be completely homo- 
genous, into an imperfectly crystalline structure after 
these same particles had become incorporated into large 
spherical masses, will require now to be considered, and 
the cause of the change from the globular mto the crys- 
talline form explained. Now, as these changes are due 
to the same arrangement of the molecules of carbonate 
of lime as takes place in the production of true crystals, 
they cannot be explamed intelligibly until the causes 
producing the ordinary crystalline forms are fully con- 
sidered ; hence the further consideration of the structure 
of spherical calculi must of necessity be interrupted by 
some observations upon the nature and cause of ordinary 
crystallization. As crystalline forms occur in a great 
many organized structures, the explanation of the causes 
leading to their production must be considered as belong- 
ing to the physiology of tissues, and therefore as demand- 
ing the same consideration as the other constituent forms 
of these tissues. Any part, to be studied properly, must 
be considered in its totality, and not in reference to par- 
ticular structures only. It has been observed, at the 
beginning of this paper, that, when the carbonate of lime 
