142 MICROSCOPIC ANATOMY OF THE TEETH 



shell can be very distinctly followed in thin ground sections 

 (fig. 82). 



In all these organisms, in Crustacea, Mollusca, and Brachio- 

 poda, there is a distinctly visible delicate fibrillar basis 

 substance which appears to serve as a support to the deposited 

 material secreted by the animal, and in which calcification 

 takes place. This is a clear, apparently structureless, 

 substance, and does not seem in any way to determine the 

 actual arrangement of the particles. It is not a con- 





FIG. 81. Calcospherites in the carapace of the Prawn. ( x 100.) 



nective tissue, and shows no connexion with cells. It is 

 evident in all these examples that the shell is ultimately 

 formed by the fusion of the calcospherites. 



The view held by Bower bank (3) and Carpenter (4} 

 with regard to the formation of shell in the Mollusca was 

 that ' shell is an organic formation growing by interstitial 

 deposit in the same manner as in the teeth and bones of the 

 higher animals '. This view, which accorded with the 

 opinion held at the time, that enamel and dentine were 

 formed by actual deposit in the formative cells, supposed 

 that the same thing occurred in the Mollusca, and that in 



