717 



lacteal would be the functionating dentition with Marsupials, of the 

 permanent one only a single tooth (the last premolar) would develop 

 and of the prelacteal one small teeth would be evolved but never 

 reach full development and always be reduced. 



How did the investigators between 1890 and 1900 arrive at this 

 view? Embryological investigalion of the development of the Mar-' 

 supialian dentition sliowed I hat also with this group of vertebrates 

 two dental series were undoubtedly evolved. And the topographical 

 relation of the tooth-germs of either series was exactly similar to 

 that which is found in the Anlage of the dentition of the Monodel- 

 phian mammals, viz. the germs of one series lie buccally of those 

 of (he other series and alternate with them. Now it appeared, how- 

 ever, that otherwise than with the Monodelphian mammals, the teeth 

 of the buccal or outer set become rudimentary, while the germs of 

 the inner set develop into the functionating dentition. At first sight 

 this would seem to con firm the view of the older anatomists that 

 the functionating dentition of the Marsupials corresponds with the 

 second or [)ermanent set of the Monodelphians, for also this latter 

 develops from the inner series of tooth-germs. If Kükenthal had only 

 given this obvious inter|)retation to his observations, as e.g. Wilson and 

 Hill') did in 1897, much confusion and contradiction in odoiitological 

 literature would have been avoided. But Kükknthal was led astray 

 by a histological phenomenon to which he attributed a paramount 

 and in my opinion erroneous significance. He saw namely that the 

 free border of the dental lamina, after the germs of the inner series 

 had evolved, became slightly thickened. This phenomenon drew his 

 particular aliention and he attributed so great a significance to it that 

 it becan)e the basis for his theory. He saw namely in this thickening 

 the indication of still another dental series, so that three sets of 

 teeth would evolve with Marsupials, an outer one, of whicli the 

 teeth show a rudimentary development and are afterwards reduced, 

 a middle one, the teeth of which form the functionating dentition, 

 and an inner one which however only appears as a thickening of 

 the free border of the dental lamina and of which only a single 

 tooth would develop — the only successional tooth of Marsupials. 

 I wish to point out at once, however, that no investigator has ever 

 observed in this slightly thickened free border of the dental lamina 

 anything that ])oints to even a beginning of dental development. 

 Now this should raise our doubt whether in this thickening we may 

 see a phenomenon, actually pointing to a dental series which the 



') Development and succession of teeth in Perameles. Quat. Journ. of microsc* 

 Sc. Vol. XXXIX. 1897. 



