DEVELOPMENT AND SUOOESSION OF TEETH IN PERAMELES, 493 
we cannot regard as conclusive. For, according to Mr. Wood- 
ward’s statement and figures, the enamel-organ of dp2 (his dp*) 
at the stage referred to has not yet differentiated itself as an 
organ distinct from the dental lamina. The whole lamina in 
the dp* region appears as if converted into the enamel-organ, 
as is commonly the case in the earlier stages of tooth develop- 
ment. This phase of development is, however, only a passing 
one. By-and-by the separation of the enamel-organ from the 
lamina which gives it birth is indicated, and the resulting 
appearance of a residual lamina or “ Hrsatzleiste” we 
regard as the first condition of the appearance of a succes- 
sional tooth. 
This first condition is as yet absent in the early stage of 
Petrogale under notice. Mr. Woodward in effect maintains 
that in its absence we must forthwith accept the presence of 
an enlargement of the lamina in front as the true Anlage of 
p* (his p*). We hold, on the contrary, that until we are in 
a position to trace the fate of the residual lamina, which will 
assuredly manifest itself by the lingual side of dp, it is pre- 
mature to decide upon what constitutes the earliest germ of 
p® (“pt”). If the evolution of the swelling figured by 
Woodward can be clearly traced up to the formation of the 
enamel-organ of p= (“p+”), without suspicion of a confusion 
with the subsequent evolution of a true “Ersatzleiste” of 
dp2, then Mr. Woodward’s case for Petrogale will have been 
made out. 
We therefore insist that it is necessary to have recourse to 
somewhat later stages for corroboration, or otherwise, of Wood- 
ward’s view. And what is the result of such a reference? We 
shall quote Mr. Woodward’s own words. “In a slightly older 
embryo the same condition was observed, but owing to the de- 
velopment of the third and fourth premolars, especially of the 
latter, they somewhat overlap the lamina connecting the two, 
and it in consequence becomes displaced to the inner side of 
these structures. So much does the fourth premolar grow 
forward with age that it appears as if this lamina was 
a downgrowth from the inner side of the enamel- 
