50 CHARLES S. TOMES. 



ciated with implantation in a socket, though it may be in a 

 very incomplete one. 



To sum up the results of the foregoing observations : 



1. x\ll tooth-germs whatever consist of at least two parts — 

 an enamel organ and a dentine pulp ; a capsiile may or may 

 not be present. 



2. The first step recognisable is invariably the ingrowth 

 of epithelium, i.e. an enamel germ. 



3. Enamel germs of successional teeth in mammals, rep- 

 tiles, batrachia, and elasraobranch fish are derived from 

 the necks of the enamel organs of their predecessors ; the - 

 respective dentine pulps originating independently, the 

 enamel germs constitute the sole connection between dental 

 germs of various ages. 



4. In all the osseous fish examined by me the several 

 enamel germs originate de novo from the oral epithelium; 

 this may, perhaps, be the case in some other creatures, but 

 I have never seen it. 



5. The enamel organ, invariably present, consists primarily 

 of external and internal layers of epithelium ; the former atro- 

 phies, the latter groAvs largely if the tooth is to be capped with 

 enamel ; otherwise it also atrophies, but at a later period. 



6. The stellate tissue of the mammalian enamel organ is 

 obviously non-essential; indeed, it is probably a retrograde 

 metamorphosis. 



7. Dentine pulps originate independently of each other, 

 at points in the submucous connective tissue apparently de- 

 termined by the position attained by the ingrowing enamel 

 germs ; in structure they are singularly uniform in all animals. 



8. There is no example of a dentine pulp originating as a 

 free papilla upon the surface ; on the other hand, as in the 

 snake, the process often takes place at a great depth below 

 the surface. 



9. The terms " papillary," '' follicular," and " eruptive 

 stage" should be quite abandoned, as tending to perpetuate 

 a somewhat mistaken hypothesis. 



10. Enamel is obviously a metamorphosed epithelium;^ 

 dentine belongs to the submucous connective tissue ; the 

 homologies of cementum have yet to be determined ; but the 

 basement membrane known as membrana prefoimativa has 

 probably no significance in the process, if indeed it has any 

 existence. 



1 This is particularly obvious in Fisli aud Amphibia, aud Hertwig has 

 given figures of developiug placoid scales in which the rete Malpighi, but 

 little specialised into an enamel organ, appears to become calcified into 

 enamel. 



