725 



3 



Fig- i- 

 system. It is easily perceived that for each of the above described 

 points of ditFereiice between the reptilian and nionodelphian dentitions 

 this question must he put and answered separately. Now there are 

 three possibilities : a. it behaves like the reptilian dentition, h. like 

 that of the Monodelphian inaniinals, and r. it occupies an intermediate 

 position and has points in common with both, so that it is no longer 

 a reptilian dentition but not yet in every respect that of a Monodel- 

 phian mammal. The answer, based on an investigation of a fair 

 number of young ones of several marsupial groups is given as suc- 

 cinctly as possible in the following table. 



i Anlage of Anlage of \ Shape of | Form of ; Tooth- 

 the dentition tine teeth the teeth ! the dentition j change 



Kept lies 



Monodelphian 

 mammals 



Marsupials 



Distichical stoicheomeric monomeric hamastichical : merobolic 

 I ' (isocrasic) | 



Distichical symphyomer. dimeric or chorisstichical j stichobolic 

 I j trimeric i (complete) 



Distichical symphyomer. monomeric hamastichical stichobolic 

 ;0r stoicheom. or dimeric (anisocrasic) '(very incomp. 



This table shows that according to my investigations the Marsu- 

 pials agree with the Reptiles and the remaining mammals oidy in 

 regard to the Atdage of their dentition, since also with (hem it is 

 evolved in two rows : an exostichal and an endostichical one, but 

 that foi' the rest the Marsupials form in every respect a transition 

 between Reptiles and Monodelphian mammals. 



This will be shown successively for each of the ontogenelical 

 and morphological properties of the dentition and the teeth. In this 

 first communication only the dentition as a whole will be dealt with, 

 in a following one the teeth as elements of the dentition will be 

 studied more closely. 



Concerning the dentition it will therefore be attempted to show 



