WITH CALCAREOUS MATTER. 79 



bioplasm can he detected in the fully formed deBtine 

 or enamel of the adult, at an early period of develop- 

 ment these tissues -were represented by masses of bio- 

 plasm only. • 



Additional interest attaches to the consideration 

 of the structure and growth of the enamel and dentine 

 on account of the different and conflicting views en- 

 tertaiaed concerning their nature — some holding that 

 enamel corresponds to the epithelial textures we have 

 been considering, while it is maintained that the den- 

 tine is more nearly related to bone and the connective 

 tissues. According to this view, the neutral line 

 between the two represents the position of the base- 

 ment membrane in an ordinary mucous membrane. 

 Huxley, on the other hand, and for reasons which 

 seem to me insufficient and unsatisfactory, holds that 

 both enamel and dentine are dermal tissues, and 

 situated beneath basement membrane. Lastly, the 

 position of the vessels as regards the dentine, the 

 manner or growth of both tissues, and the fact of their 

 origin in a collection of unquestionable epithelial cells, 

 have forced me to conclude that both enamel and den- 

 tine are more nearly allied to epithelium than to any 

 other tissues of the body, and that both are developed on 

 the surface of basement memhrane. The tooth grows 

 in a manner so like a horn and a hair that it is difficult 

 to believe that is is not closely related to these epider- 

 mic appendages, while there are not wanting instances 

 in which an eminence covered with an epithelial tex- 

 ture seems to take the place of a tooth. Hair and 

 teeth are sometimes abnormally developed, and Mr. 

 Darwin has remarked that the teeth of hairless dogs 

 are defective, and that over-hairy men have abnormal 

 teeth. My own conclusion upon this matter, after 

 examining with great care the tooth at a very early 

 period of development is, that the masses of bioplasm 

 concerned in the formation of the enamel and dentine 

 are embedded in epithelium and are arranged in two 



