737 



A view, entire!}' agreeing witli the principle developed in this 

 paper, lias already been held by Winge in regard to the large 

 number of molars of Myrmecobins. This author is namelj' of opinion 

 that tliis large number n)ust be explained by the non-expulsion of 

 milk-teeth. So also for this author the dentition of Myrmecobius at 

 any rate consists of a mixture of milk-teeth — exostichical teeth 

 in my nomenclature — a,nd "permanent" i. e. endostichical teeth. 

 Also according to Winge the dentition of the mentioned Marsupial 

 is consequently hamastichical. 



Finally in this relation the results may be mentioned of Leche's 

 investigation of the dentition of Erinaceus whicli consists of elements 

 of the milk-set and of the permanent set. Whether this hamasti- 

 chism is a secondary acquisition or the direct continuation of the 

 original phylogenetic condition does not matter. However, this 

 phenomenon is certainly remarkable in a form which has remained 

 so primitive as Erinaceus. That besides hamastichism, be it to a 

 limited extent, may also re-appear in other Monodelphian manmiais, 

 is proved by the dentition of the catarrhine Primates, in which the 

 first molar is an element of the milk-set, become permanent. 



If we now return once more to our starting-point and contpare 

 the here developed theory of the constitution of the marsupialian 

 dentition with the two existing theories, it appears to stand between 

 these two. While according to the older investigators the functionat- 

 ing dentition of the Marsupials corresponds with the permanent 

 dentition of the Monodel[)hians, according to the more recent workers 

 with the milk-dentitioii, it is in my opinion built up (+f elements of 

 both, although in a very disproportional mixture. It is an aniso- 

 crasic , hamastichical dentilion, betraying by its hamastichism its 

 nearer relation to the dentition of the Reptiles and certainly also 

 of the most primitive Mammals, and by its anisocrasy its progres- 

 sive character as compared with that of the Reptiles. 



In this communication I have endeavoured to prove that the 

 Marsupialian dentilion in its evolution and constitution still shows 

 relationship to that of the Reptiles, in a following one it will be 

 shown that also in the development and structure of the Marsupialian 

 tooth there exist points of agreement with the Reptilian teeth. 



