22 FORMATION OF SHELLS OF ANIMALS, ETC., 
the ultimate effect of gravity achieved. As there were, 
before the figure had attained the spherical form, two 
ellipses, so now there will be two spheres, one contained 
within the other. (See fig. 2, c.) 
The complete coalescence of two such spherules as that 
last described would result in the production of one 
spherule with more than two concentric zones. Hence 
the careful inspection of specimens exhibiting these different 
stages of coalescence brings to view numerous examples of 
calculi with concentric laminz (as shown in figs. 2 and 3). 
Such specimens can easily be prepared, and they occur 
abundantly as organic products, showing that the existence 
of rings or concentric laminze in organic bodies is not 
necessarily the effect of successive depositions on its surface 
as believed by physiologists and pathologists. (See 
Kolliker’s ‘ Manual of Histology,’ p. 458.) 
Now as these calculi are composed of only one material, 
it is mexplicable on known general principles that in such 
a body as the one just described, consisting of an elliptical 
portion contained within an irregularly spherical one, both 
without doubt in accurate apposition, the one should be so 
easily distinguished by the microscope from the other. 
For if this particle had been everywhere of the same 
density, and if every part of it had possessed the same 
index of refraction, that is, if it had been like two pieces 
of any homogeneous substance, as glass, with these forms 
accurately jomed by Canada balsam, one part could not 
have been thus easily distinguished from the other. But 
this difficulty, on the further investigation of this subject, 
will be removed, when it is demonstrated that the different 
parts of these globules, formed as they have been shown to 
be under the influence of gravity, vary in their density 
according to the degree of attraction exerted upon their 
