730 



3 and 6 which develop fnlh', belong to the same series and are 

 entirely equivalent to the riidimeiitarj little teeth 1, 2, 4, 5. and 8. 

 Tooth 7 will presently be separately dealt with. Bearing in mind 

 that by the adherents of Kükknthai/s theory these rndiinentary little 

 teeth are adduced as a proof for the assumed prelacteal dentition, 

 the importance of the mentioned fact becomes evident. If we accept 

 Kükenth.\l's theory teeth 8 and 6 must be considered as |)relacteal 

 teeth reaching development. This consequence however no adiierent 

 of this theory has until now had the courage to accept. The view- 

 point of this paper is much simpler and more natural, the teeth 

 1 — 8 are exostichicai (milk-teeth of the Monodelphians) and among 

 these 3 and 6 attain development and push themselves in between 

 the elements of the endostichical teeth, as with the reptilianlike 

 ancestral forms also the remaining teeth of this series would have done. 

 The point of view of this paper leads in its consequences to 

 somewhat radical conclusions as to the I'elation of the incisors of 

 the Marsupials to those of the Monodelphian mammals. For if the 

 functionating incisors of the Marsupials are derived from the two 

 dental series and so foim a haraastichical row, they must not be 

 identified with the incisors of either set of teeth of the Monodelphians, 

 but with both. In other words the incisors of a poiyprotodontian 

 Marsupial are identical with the incisors of both the milk-set and the 

 permanent set of the Monodelphians. By this conclusion it seems to me 

 that an existing difticulty in the comparison of the incisors of Monodel- 

 phian and Didelphian mammals is solved in a simple manner. The 

 largest number of incisors of the Monodelphian mammals is three, in 

 the permanent and milk-set together six. With the Marsupials five 

 develop at the utmost, although the Anlage of six is present. As 

 well in the permanent as in the milk-dentition at least three would 

 accordingly be lost with the Didelphians. But no trace of them has 

 ever been detected. And so there always remained an unbridged 

 gap between the two groups of mammals. In my opinion this gap 

 does not exist. The highest number of incisors, evolved with Marsu- 

 pials, was stated to be six. ') Woodward has found this number in 

 Petrogale. Of these six only three develop with Petrogale, namely 

 2, 4 and 6, while J, 3 and 5 become rudimentary. It is clear that 

 here we have development of the incisors of the endostichical series 

 only, while the exostichicai teeth do not develop. The three teeth 

 that become rudimentary must be identitied with the three milk- 



1) The total number of rudimentary and developing teeth may occasionally be 

 larger than six in the domain of the incisors, e. g with Dasyurus, but this is 

 the result of a complication which will be explained in the foüowiüg communication. 



