718 



Marsupials would have lost in their latest pli^'logenetic-al evolution. 



Lechk, who also assigned a definite significance to the free l)order 

 of the dental lamina, therefore gave anotiier explanation which from 

 this point of view was more plausible, namely tiiat it should not 

 be considered as ihe last trace of a lost dental series but as the 

 first indication of a new one. Lkchk's opinion found no adherents 

 and so Ihc free border of the dental lamiiui was assumed l)y a group 

 of investigators, following Kükenthal, to prove liiat the Marsupials 

 must have lost a dental series. And once arrived at this point of 

 view these authors were now obliged to identify this series, being 

 the most inwardly situated, with the permanent set of teeth of Ihe 

 Monodelphif.n mammals and the middle series, which in Marsupials 

 develops into the functionating dentition, could then oidy be identified 

 with the milk-dentition of the higher mammals.') 



Now the difficulty arose how to explain the outer row of small 

 teeth which in Marsupialian embryos evolve and partially develop, 

 but are afterwards reduced. This led Kükenthal to introduce into 

 literature the conception of a prelacteal dental series, a dentition 

 which would precede the milk-teetii. 



The rea.soii why Kükenthal attached so much importance to the 

 thickened border of the dental lamina is not very evident, the less 

 so as it created such a fundamental difference in the dental evolu- 

 tion between Didelphian and Monodelphian mammals. In both groups 

 the Anlage of two series of tooth-germs is found, an outer and an 

 inner one. But instead of identifying these two, the inner row of 

 the Didelphian mammals is identified f)y him with the outer row 

 of the Monodelphiaiis, while the inner row of these latter is met 

 with in Marsupials as a simple thickening of the border of the dental 

 lamina in which never a trace of real dental evolution has been 

 observed, and the outer row is referred to a hypothetical dental 

 series which is supposed to have functionated in the hypothetical 

 ancestors of the mammals. Now this interpretation seems rather 

 strained and moreover it must a priori be highly improbable that 

 the dental series which in the Monodelphian mammals has such a 

 preponderating significance as a permanent dentition would have 

 disappeared in the more primitive Didelphian mammals without 

 leaving a trace, even in the embryo. Placing our:?elves for a moment 

 on Kükenthal's viewpoint that there have originally been three 



') Tfie opinion that from this tliickened edge of the dental lamina the only 

 tooth having a predecessor (\'^) would originate, is wrong. This particular tooth 

 belongs to the series of the other functionating teeth and its Anlage is exactly 

 the same but only starts a little later than the other teeth. 



