ixj OF SPHERULITES OR CALCOSPHERITES 657 



zoologists./ But it is now admitted that even in specimens of a single species, 

 from one and the same locality, the spicules may vary immensely in shape 

 and size: and Professor S. J. Hickson declared that after many years of 

 laborious work in striving to determine species of these animal colonies, he 

 felt "'quite convinced that we have been engaged in a more or less fruitless 

 task*." 



The formation of a tooth is a phenomenon of the same order. That is to 

 say, '"calcification in both dentine and enamel is in great part a physical 

 phenomenon; the actual deposit in both tissues occurs in the form of calco- 

 spherites, and the process in mammalian tissue is identical in every point with 



Fig^ 298. Additional illustrations of alcyonarian spicules: Eunicea. After Studer. 



the same process occurrmg m lower organisms!." The ossification of bone, 

 we may be sure, is in the same sense and to the same extent a physical 

 phenomenon. 



The typical structure of a calcospherite is no other than that of 

 a pearl, nor does it differ essentially from tha^ of the otohth of a 

 mollusc or of a bony fish. (The otoliths of the elasmobranch fishes, 

 like those of reptiles and birds, are not developed after this fashion, 

 but are true crystals of calc-spar.) 



The effect of surface-tension is manifest throughout these pheno- 

 mena. It is by surface-tension that ultra-microscopic particles are 

 brought together in the first floccular precipitate or coagulum; by 



* Mem. Manchester Lit. and Phil. Soc. lx, p. II, 1916. 



t J. H. Mummery. On calcification in enamel and dentine, Phil. Trans. (B), 

 rev, pp. 95-111. 1914. 



