116 FORMATION OF SHELLS OF ANIMALS, ETC., 
obtaining the globular form of the carbonate of lime, it 
does not, like this compound, assume that form, or lose 
its crystalline character, but its crystals congregate into 
globular masses ; if, however, a small quantity of carbo- 
nate of lime be formed together with it, then the phos- 
phate of lime, combining with this carbonate, forms a 
globular coalescing compound, like that of the globular 
carbonate of lime. This compound is not quite so homo- 
geneous as that of the unmixed globular carbonate, but 
its optical and physical properties are very similar. This 
combination can be produced by introducing into the same 
bottle a small quantity of phosphate of soda, and muriate 
of lime, dissolved in separate portions of white of egg, 
and allowing them to mix gradually, when a phosphate 
and carbonate of lime will be formed. The carbonic acid 
is furnished by the alkaline carbonate contaimed in the 
white of egg, which is quite sufficient to prevent the 
crystalline arrangement of a considerable quantity of the 
phosphate of lime. This effect of a small quantity of 
carbonate of lime is also beautifully seen in the change 
which it produces on the form of the crystals of triple 
phosphate, forming with that substance the largest and 
most perfect spherical calcul. (See page 36). Having 
now determined by experiment this important fact, which, — 
being connected with the chemical composition of bone, 
stands at the head of this imquiry. I shall next give the 
results of a careful examination of the appearances pre- 
sented by bone in its very earliest stage of development, 
as seen in the ossifyimg tendons of birds, and in some 
parts of the lower animals. The structure of the osseous 
tissue has been too exclusively studied by means of thin 
sections. These are not only useful, but for some purposes 
indispensable, still they give no idea whatever of the 
