7J9 



series of teeth, we should expect that where the so-called prelacteal 

 dental series is still visible as a number of small but fully developed 

 teeth, also something would be seen of that inner row, since it is 

 this latter which develops so powerfully in the Monodelphiaii mam- 

 mals. And especially since according to Kükenthal one of the teeth 

 of this inner row does not become rudimentary, but develops fully.') 

 So while one element of this inner row attains its full development, 

 the development of all the other would always have been completely 

 checked. This is exactly opposite to what is observed in the outer 

 one of the supposed tiiree rows, which also does not produce fully 

 developed teeth, but the elements of which do ofleii appear as well- 

 shaped little teeth that are reduced after having formed. 



This difference in development between the outer and inner row 

 with Didelpliian mammals could in my opinion only be explained 

 by assuming that the inner row were checked in its development 

 long before the outer one. But in this case the ancestral forms of 

 IMarsupials would have pos.sessed not three but only two dental series, 

 which would however not have agreed with the two series of tiie 

 Monodclphian mammals. 



The preponderant and absolutely unjustilied significance assigned 

 by KtJKKNTHAL, ROSE and Dkpendorf to the thickening of the border 

 of the dental lamina of Marsupials has complicated the problems of 

 dentition in no small measure. Wilson and Hill already showed 

 this in 1897 by pointing out in particular that in this thickened 

 lamina not the least traces of local tiiickening can be observed which 

 would indicate a commencing Anlage of any tooth. According to 

 them the free border of the dental lamina simply originates by 

 emancipation of the tooth-germs of the teethband. 



So Kükenthal postulated already three dental series for the 

 Marsupials: a prelacteal, a lacteal and a permanent one. But the 

 complications of this problem of dentition were not at an end yet. 

 For also at the lingual side of the Anlage of the molars the so-called 

 free teethband border was observed. 



Now KtJKKNTHAL aiid other authors are of opinion that the molars 

 originate by fusion of the Anlage of teeth of both series, namely 

 of elements of the lacteal and of the permanent dentition. By this 

 hypothesis one was obliged to iissign to the free teethband border 

 lingualiy of the molars a different meaning from tiiat lingually of 

 the more frontally situated teeth. 



With these latter it was an indication of the lost series of per- 



1) II has been reinaiked above that this opiniou is erroneous. 



