DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 525 
determine which of these may legitimately be utilised in 
arriving at such a decision. 
(1) The Criteria of Serial Tooth Homology as set 
forth by Leche. 
We propose first of all to summarise Leche’s treatment of 
this fundamental problem. After reviewing his position the 
extent of our agreement and difference with him will become 
apparent in the course of discussion. 
In the first place Leche discusses (a) the significance of 
the occurrence of epithelial downgrowths of the 
dental lamina lingually to developing enamel-organs. 
That the presence of swollen epithelial downgrowths in- 
ternal to the enamel-organs of mammalian teeth was sufficient 
to stamp the latter as belonging to the milk dentition, no one 
apparently, until Leche, had thought of questioning. 
Woodward (2), indeed, is somewhat guarded in his language 
when he writes, “If these various and often minute down- 
growths of the dental lamina are to be interpreted as repre- 
senting rudiments of teeth, as seems probable from comparison 
with known rudiments of the first or second dentition in other 
mammals,” &c.; but, nevertheless, he appears to accept in 
their entirety those dentitional theories which depend wholly 
upon the determination in question. 
Leche, however, enters fully into the question of the validity 
of the assumption that Kiikenthal’s swollen downgrowths 
actually represent successional enamel-germs; and his con- 
clusions are by no means decisive in favour of that assumption. 
The following passages will serve to illustrate his attitude :— 
‘“Da, wie bereits erwahnt, die Differenzirung des Schmelz- 
keimes ausschliesslich oder doch vorzugsweise an der labialen 
Flache der Schmelzleiste erfolgt, so ist auch von vorneherein 
zu erwarten, dass das tiefe Ende der Schmelzleiste lingualwarts 
vom Schmelzkeim auftritt. Ist also jene ‘ Knospe,’ welche 
von demselben verdichteten Mesodermgewebe welches das 
Zahnsackchen bildet, umgeben ist (figs. 9, 10), nichts anderes 
