ARTIFICIAL PRODUCTION OF CALCAREOUS FORMATIONS. 119 



veloped, which are, for the most part, found in organic 

 nature. The most frequently occurring form affected by- 

 calcium carbonate, in combination with albumen, gelatine, or 

 the other organic substances above mentioned, we will 

 christen Calcospherites (Fig 1). 



When the calcospherites are formed in the midst of the 



Fig. 1. 



liquid, and the surrounding parts are perfectly tranquil, 

 they are perfectly spherical. The dimensions they attain 

 may vary from -^^TToth to J^th of a millimetre ; they become 

 larger in proportion as their formation takes place with 

 greater tranquillity and slowness. The calcospherites often 

 contain a nucleus, and all those which attain a certain size 

 are seen to be formed of concentric layers and very fine 

 radiating fibres. Similar calcosj^herites, of spheroidal shape, 

 are met with in nature, in the Ibrm of different concretions 

 developed in the bile, the urine, and the saliva of certain 

 animals. What is called " brain sand" of the pineal gland 

 and of the choroid plexus is made up of calcospherites ; the 

 otoliths of certain molluscs, worms, and fishes, are calco- 

 spherites ; finally, pearls are calcospherites, which in the 

 course of time have attained remarkable dimensions. 



If the state of equilibrium in the surrounding fluid is not 

 perfect the calcospherites undergo, in the course of their de- 

 velopment, transformations, in consequence of which their 

 form is more or less modified. Under these conditions they 

 may become ellipsoidal, oval, or lenticular bodies. One very 

 remarkable form is that Avhich we have distinguished by the 

 name conostat (Fig. 2). It is characterised by the presence 

 of a cup- or goblet-shaped enlargement, which becomes filled 

 with air; and by this, as by a sort of hydrostatic apparatus, 

 the hemispherical calcospherite is preserved floating-. 



The most remakable of all the conditions, which assist in 

 determining the shape of the calcospherites, consists in the 



