DEVELOPMENT OF TEETH IN HATTEKIA PUNCTATA. 201 



suppression of tooth replacement, or whether it has only 

 been concomitant with it, I do not venture to decide. 



Summary and Conclusions. 



1. The first dentition of Hatteria consists of a 

 set of minute teeth, about thirty-six in number, 

 which originate immediately below the epidermis, 

 labial to the dental lamina. They subsequently pass 

 into the epidermis, and are shed about the time of hatching. 

 The period of their best developraeut is about the fifth month 

 of incubation. They are never functional, and form no con- 

 nection with the bone. The anterior end of each palatine 

 dentigerous region is first indicated by the development of 

 one of these teeth, formed before the dental lamina. Amongst 

 other reptiles Crocodilus porosus and Iguana tuber- 

 culata possess a somewhat similar, though less extensive, 

 f unctiouless dentition, the members of which closely resemble 

 the first teeth of some Selachians as regards place of origin. 



2. The dental lamina arises as in other Vertebrates, and 

 its position is at first indicated externally by a dental furrow. 



3. At an early stage (R) the dental laminae and the enamel 

 organs (of the future functional teeth of the newly-hatched 

 animal) in all the main tooth-bearing regions, become in- 

 volved in epidermal ingrowths, which much obscure the 

 primary relationships of the parts. In each case there is a 

 lingual and a labial ingrowth, and the former carries wath it 

 the dental lamina, which is thus for a long period indis- 

 tinguishable as an independent structure. Towards the end 

 of incubation the lingual ingrowth is mainly converted into 

 a glandular groove; the side attached to the base of the 

 tooth, however, i-emains in the condition of a stratified epithe- 

 lium, and may project as an epithelial ridge beyond the 

 deepest part of the groove ; it is from the cells of this portion 

 that the enamel organs of the successional teeth are deve- 

 loped in the young animal. The labial ingrowths (labio- 

 dental strands) of the premaxillas, maxilla3, and mandible, 



