TOOl^H DEVELOPMENT — DASYPUS NOVEMCINCTUS 671 



upon the inside of this mass being able to secrete as actively as 

 those which are ordinarily destined to become odontoblasts. 

 The pulp cavity is always rich in blood vessels. 



I have searched the literature for analogous cases of odonto- 

 blasts secreting dentine upon all sides of themselves and becom- 

 ing inclosed within this secretion. Cases of this sort are appar- 

 rently rare, and the only description which seems to apply was 

 found in Hopewell-Smith's 'Dental Microscopy,' where under 

 the heading of 'patho-histological dentine,' there is the following 

 brief description of so-called 'cellular dentine:' "Cells with nu- 

 clei retained (suddenly caught) in the midst of the deposit." 



Fig. 13 Section through second front tootii at birth showing celluUir dentine 

 and closure of entrance to pulp cavity. Depositions of dentine can also be seen 

 within the pulp cavity. E, enamel; D. dentine. X 560 (reduced h). 



Fig. 14 Section through first front tooth at birth. Some of the enamel organ 

 still remains so that enamel deposition may have still continued. 560 (reducecf |). 



The authors also give an illustration of this 'cellular dentine,' 

 which show an apparently homogeneous substance in which are 

 imbedded round nucleated cells. The figure does not show any 

 cell processes, extending into the dentine, such as I have found, 

 but I believe that this is the same kind of dentine that occurs in 

 the degenerate front teeth of Dasypus. At least the account 

 and figure given by the authors more nearly agree with this 

 dentine than does anything else in the literature. Evidently we 

 have here an example of very degenerate or generalized odonto- 

 blasts which, instead of sending out their secreting processes in 

 one direction only, may extend them in any direction. The 

 secretion thus formed must be very hard, for in sectioning it is 

 frequently torn from the surrounding tissue. 



