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laid on this point is on account of the circumstance that while teeth 

 a and h will later develop into the first and second incisors, tooth 

 3 produces ihe third incisor. Now it follows from what precedes 

 that with Perameles ihe functionating incisors do not all originate 

 from a single dental series, but partly from the endostichos (= 

 permanent set of the Monodelphian mammals), partly from the 

 exostichos (== milk-set of the same mammalian group). 



As to Ihe dental Anlage of tooth 6, (his will produce the last 

 premolar, the onlj too*h which, as we know, is rei)laced in the 

 marsupialian dentition and which in all respects behaves as a milk- 

 tooth. To this I shall return later. As to the manner of Anlage 

 and the relation between the tooth germ and the teeth-band there 

 is not the slightest difference between tooth 3 and 6. This is 

 acknowledged as well by Wilson and Hill as by Depkndokf, although 

 this latter without any reason and quite erroneously sim[)ly considers 

 this as a secondary state. This \iew was forced ujion the author 

 since otherwise he would according to his system necessai'ily have 

 arrived at the conclusion that tooth 3 and 6 belonged to the so- 

 called prelacteal dental series, while a complete development of 

 teeth of this series may not be assumed by adherents of a prelacteal 

 dental series. This is a very striking instance how strongly the 

 idea of a "prelacteal dentition" spoils objectivity in judging the 

 facts. WiisoN and Hill, who like myself consider the row 1 — 8 

 in fig. 2 as the row of the milk-set, accordingly state ex[)ressly that 

 tooth 6 at its first appearance is evolved from the buccal wall of 

 the teeth-band and not terminally, (curiously enough liowever they 

 do not state this for tooth 3 and 7, although their drawings clearly 

 show such an Anlage at any rate for tooth 3, as will appear from 

 figure 6, here reproduced. Very peculiar is Dkpendokf's reasoning 

 concerning the remarkable situation of tooth 3. "Wiirde der Kiefer", 

 he says on p. 255, "spater nicht an Lange zunehmen. so hiitten 

 wir im Bereiche der Incisivi von Perameles ebenfalls einen Zahn- 

 wechsel zu erwarten, in der Art, vvie er wirklich bei den Diprot- 

 odontiern in der Pramolarenreihe vor sich geht" (If the jaw did 

 not later increase in length we should have to expect in the region 

 of the incisors of Perameles a tooth-change as it actually occurs 

 with the Diprotodontians in the premolar series). So he grains 

 indirectly that the Ardage of the developing tooth 3 in regard to 

 that of tooth /; and c agrees entirely with the relation of a toolh- 

 germ of the milk-set to that of the permanent teeth. 



For the genetical significance of the teeth constituting the deniition 

 of Perameles it is impiu'tant euiphatically to point out that the teeth 



47* 



