724 



ot a single product, containing potentially a larger number of eleinentaiy 

 teeth, a number of dental generations. A whole dental family of 

 the Reptiles has as it were been condensed in a mammalian tooth. 

 This dental Anlage will therefore be distinguished as "symphyomeric". 



So the mammalian tooth is not identical witii a reptilian one, but 

 represents all the generations which come forth from one matrix of 

 the teeth-band, i. e. a reptilian dental family. In most cases two, 

 sometimes three such generations can be recognised on the relief of 

 the mammalian teeth, they are accoi'ding to their structure diraeric 

 or trimeric. 



The re}(liliaii teeth on the other hand are always monü??imc, each 

 tooth corresponds to a single generation only, these generations 

 succeeding each other sometimes more sometimes less rapidly. In 

 contradistinction to the symphyomeric dental Anlage of Mammals 

 the dentition of Reptiles must therefore be iiidivated as stoicheomeric. 



Summarising the main points of the above comparison between 

 the dentitions of Reptiles and Monodelphian mammals, we have 

 what follows. The Anlage of the dentition is in both groups distich- 

 ical, the Anlage of the teeth with Monodelphian mammals sym- 

 phyomeric, with Reptiles stoicheomeric, the shape of the teeth with 

 the Mammals dimeric, seldom tri- or polymeric, with the Reptiles 

 monomeric, the functionating dentition with the Monodelphian mam- 

 mals chorisstichical, with the Reptiles isocrasic hamastichical, the 

 tooth-change with the Mammals stichobolic, with the Reptiles merobolic. 

 Comparing this characterisation of the dentitions of the vertebrate 

 groups with the generally accepted one, that the dentition of Reptiles 

 is polyphyodontical, the teeth simple, with the Mammals the dentition 

 diphyodontical and the teeth partly composite, it would appear as 

 if I had made the difference between the two forms of dentition 

 larger. But this is not so much the case as it seems. The essential 

 difference is that by me the relation between the so-called polyphy- 

 odontism of the Reptiles and the diphyodontism of the Mammals is 

 rejected in principle, since the tooth-change is an entirely different pheno- 

 menon in these two groups. Directly related to this is the difference 

 in structure of the functionating dentition on which I ha\ e laid stress. 



The differences described above are schematically represented in 

 fig. 1. Scheme A refers to the Reptiles, the exostichieal teeth are 

 dotted, the arrows show the mechanism of the tooth-change. Scheme B 

 refers to the Monodelphian mammals. The dots and arrows have the 

 same meaning as in A. 



Basing ourselves on what precedes w'e may answer the question 

 what place the dentition of the Didelphian mammals occupies in the 



