DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 435 
Rose has also pushed boldly into the realm of theory, and 
has presented hypotheses to account not only for the more 
divergent types of mammalian dentition, but for the derivation 
of the latter from that of polyphyodont and homodont 
ancestors. We cannot avoid the feeling that in his views ~ 
upon these matters the quantity of theorising is somewhat 
disproportionate to the extent of the basis of fact and ob- 
servation. His schematic representation (29), for example, 
of the mode of derivation of the human dentition from a lowly 
reptilian-like type appears to us to be a rather striking 
instance of a highly ingenious but a somewhat uncritical 
exercise of the scientific imagination. 
Rose’s contributions to our knowledge of tooth development 
are, however, both extensive and of very great interest and 
importance, and his interpretations are, as a rule, entitled to 
the utmost respect. 
As regards the mammalian dentition, Rése is a powerful 
advocate (a) of the primitive diphyodontism of the mam- 
malian stock, (0) of the doctrine that the multituberculate 
teeth of the heterodont dentition originated by a process of 
fusion of several individually distinct and simple conical 
members of a homodont dentition. 
In these views Rose has, of course, had many predecessors, 
Kikenthal among others, but Rose’s attempts to further estab- 
lish the validity of these propositions deserve special recognition. 
As regards the marsupial dentition in particular, Rése’s 
general conclusions may be thus summed up :—That dentition, 
like that of mammals generally, was originally diphyodont: 
** Allein die Thatsache, dass hinter allen Zahnen zeitweilig eine 
zusammenhingende, bandférmige Zahnleiste verlauft, beweist 
uns, dass die Beuteltiere von diphyodonten Saéugern und 
weiterhin von polyphyodonten reptilienihnlichen Vertebraten 
abstammen” (34, p. 508). And again: ‘Das Milchgebiss 
der Siugetiere ist nicht eine Neuerwerbung, sondern eine 
phyletische Vererbung und ist entstanden durch zusammen- 
draugen mehreren reptilienahnlichen Zahnserien in eine 
Einzige” (ib., p.509). Thus it is held that during phylogeny 
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