150 MICROSCOPIC ANATOMY OF THE TEETH 



nucleus shows a delicate nuclear network and one or more 

 nucleoli, and as Leon Williams says, ' it seems almost a fore- 

 gone conclusion that these cells must be renewed, or at least 

 that the necessary increase in number during the progress 

 of enamel development must come from cell division ' , but 

 the actual process of cell division in the ameloblasts had not, 

 however, been observed. 1 



t 



FIG. 84. Developing tooth of Macro pus cut without decalcifica- 

 tion. a. Ameloblasts ; t. Tomes' processes ; e. enamel ; 8. stratum 

 intermedium. ( x 700. ) 



Mi 1 . Thornton Carter has, however, lately described 

 mitosis in the ameloblast cells and in those of the stratum 

 intermedium of marsupials at the stage immediately pre- 

 ceding the formation of a thin layer of dentine over the 

 pulp, but was unable to detect it in later stages. He divides 

 the life-cycle of the ameloblasts in marsupials into fourteen 

 different stages (5 a). 



As first pointed out by C. S. Tomes, sometimes during 

 active deposition of the enamel the nucleus is crescentic in 

 form (26 d), and the fine fibrillar elements of the cell body 



1 For the description of amitosis in the late stage? of the enamel organ 

 cells see under ' Nasmyth's Membrane ', p. 333. 



