DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 575 
latter is by no means regarded, at least by Kiikenthal, as in- 
consistent with the doctrine of phylogenetic concrescence of 
dental germs. Replying to Hoffmann, he observes, “ Der 
Backzahn eines heutigen Saugers is ein so complicirtes plas- 
tisches Gebilde, welches im Laufe seiner Stammesgeschichte 
einer solchen Summe von Verinderungen unterworfen worden 
ist, dass ich nie daran gedacht habe, dass seine Entwickelung 
uns tiber die ersten Stammesgeschichtlichen Vorgange, die in 
die Uebergangsperiode von Reptilien zu Saugern fallen, wiirde 
Aufschluss geben kénnen, und ich habe schon friiher.... 
die wenig glickliche Idee Rése’s, dass die Ausbildung einzelner 
kegelf6rmigen Schmelz- und Dentinkappen an der spitze von 
Backenzahnanlagen fiir die Verschmelzung spricht, als nicht 
beweiskraftig zuriickgewiesen” (27, p. 658). 
Certainly the crude theory here disclaimed will not stand 
even a very superficial criticism. But the differentiation of 
the molar dental lamina in Marsupials does not in the least 
suggest the occurrence of a fusion-process of any kind. And 
we are in a position to add that even the teeth of Ornitho- 
rhynchus! are to be found, at a stage considerably anterior to 
that described by Poulton (25), still in the condition of quite 
simple deeply-cupped enamel-organs, from which the advanc- 
ing complication of form shown in Poulton’s figures, and well 
known in the fully developed teeth, is derived by differentiation 
in the way of mere inequality of growth. 
There can be no doubt that the advocates of the fusion- 
hypothesis, instead of being aided by ontogenetic considera- 
tions, will have to face the fact—perhaps not necessarily fatal, 
but at least disconcerting—that, in a series of comparatively 
primitive mammalian forms, the cusp-development of a compli- 
cated molar can be traced out as a mere growth-differentiation 
of a primitively smooth and simple bowl-shaped enamel-organ, 
just as, according to Osborn (84, p. 206), we can be “in at 
the birth of every successive cusp” in phylogenetic develop- 
ment. 
1 We hope ere long to make our observations in this direction the subject 
of a special paper. 
