154 Royal Society :-— 
The principal facts which my observations enable me to state 
are :— 
That there is no such thing as a “dental groove” or “dental 
fissure” in the Batrachia and Sauria, but that the whole process 
takes place beneath an unbroken surface of epithelium. 
That there is no such thing as a stage of “free papillw,” and 
consequently no sinking of papille into the gum and subsequent 
encapsulation of the same. 
Instead of being formed in a “ dental groove” the teeth are de- 
veloped in a region which may be termed the area of tooth-develop- 
ment, varying in form and extent in different Reptilia, but agreeing 
in all in possessing the following characters :— 
It is bounded on the one side by the teeth in place and the 
parapet of bone which carries them, and on the other, or inner, 
side by an exceedingly sharply defined boundary, consisting of 
dense connective tissue. At the surface, near where the functional 
tooth projects above the oral epithelium, it is narrow, but it expands 
as it passes more deeply below the surface. Within this area are 
developing tooth-sacs of different ages, the interspaces being 
occupied by a loose areolar tissue, differing in appearance from 
that which is seen outside the area, and appearing to be derived 
from portions of older tooth-sacs, which have not been entirely 
used up in the formation of the teeth. 
The individual tooth-sacs are formed thus: an inflection of the 
cells of the oral epithelium, in section like a tubular gland, passes 
down along the inner side of the area above defined, until it 
reaches nearly to the level of the floor of the area. The depth to 
which it penetrates is considerable in many forms, e. g. in the 
Lizards, in which, therefore, this double layer of epithelial cells 
appears a mere line. 
At the bottom of this inflection of epithelial cells the adjacent 
tissue assumes the form of a small eminence (without at first any 
visible structural alteration), while the epithelial process takes the 
shape of a bell-like cap over the eminence. 
This epithelial inflection then goes to form the enamel-organ ; 
the eminence becomes the dentine-organ. 
Thus the enamel-germ is the first thing recognizable, and the 
presence of this ingrowth of epithelial cells seems to determine 
the formation of a dentine-organ at that particular spot which 
lies beneath its termination. 
The enamel-organs, after they are fully formed, retain a con- 
nexion with epithelial cells, external to the ovoid or spherical tooth- 
sacs, at their summits; and the enamel-organs of successive teeth 
appear to be derived from the necks of those of their predecessors 
rather than from fresh inflections from the surface of the oral 
epithelium, though I am not sure that this is, in all instances, the 
case. 
The tooth-sae of the newt is entirely cellular, and has no special 
investment or capsule ; under pressure it breaks up and nothing 
but cells remain, as was noted by Dr. Lionel Beale. 
