542 J. T. WILSON AND J. P. HILL. 
factor may have some influence in the case of the antemolar 
teeth, seeing that the first formation of the dental lamina 
itself progresses from before backwards. But the significantly 
early differentiation of the enamel-organ of dp. 3, which we 
have shown to occur in the case of Perameles, obviously 
cannot be explained either by position in the jaw or by future 
size of the tooth. It will be remembered that dp. 3 in 
Parameles is the smallest of all the (functional) 
teeth in that animal. And yet it is differentiated from 
the dental lamina before any of the enamel-germs of the adult 
dentition have taken origin. Leche has been misled in the 
case of dp. 3 through the accident of its large size in Didel- 
phys. Had he been conversant with the facts of develop- 
ment as we have ascertained them in Perameles, he could 
not have rested satisfied with his suggested explanation. 
The relatively early differentiation of the adult canine 
Anlage, to which Leche refers in Didelphys in order to 
illustrate the law that future size influences period of differen- 
tiation, is not to be remarked in Perameles in our, for this 
purpose, most critical Stage 111.1 On the other hand, it is a 
fortunate circumstance that just in this stage we possess a 
perfect example of the differentiation, in connection with the 
canine Anlage of an enamel-organ which is truly synchronous 
with the enamel-organ of dp. 38, and which cannot, in our 
judgment, be regarded as other than that of a genuine canine 
“milk” tooth. This fact will, however, be more fully dis- 
cussed in the sequel. 
The fact, to which Leche several times refers, that in some- 
what later stages of Didelphys (e. g. his Stage C) dp. 3 is 
less advanced than, e. g., the second premolar (p. 2), is of no 
avail in diminishing the importance of the fact of its early 
appearance. 
So also in Perameles we have found that dp. 8 in its 
1 In our Stage 11 the common canine Anlage is certainly very large, but it 
is yet in an indifferent phase. In the lower jaw it may be seen that an 
enamel-organ is in process of differentiation from its labial surface, but it is 
not that of <, but of d:. 
