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ing to my view move complicated than would have been the case 

 according to the two above mentioned excahxtion tlieories. Two pheno- 

 mena may be distinguished in this process of development, namely 

 progressive development of one of the elements : Jii, loses its character 

 of temporary element and becomes persistent, and the second pheno- 

 menon is the reduction of two other elements. These two elements 

 are at the extremity of eacli of the two tooth series, P, at tiie end 

 of the series of replacing teeth, y]/, of the end of the series of 

 the teeth of the first generation. Contrary to the two above mentioned 

 excalation hy])otheses 1 might distingnish the one defended by me 

 as the hypothesis of the terminal retluction. 1 shall try to show 

 the correctness of my opinion. 



If I lei m^ of the Platyrrhines become a persistent tooth, no 

 new principle is introduced into odontologie. For it is kwown to us 

 from othei- groups of animals that milk teeth may become persistent 

 teeth; I remind the reader of the Marsupialia, where but for some 

 exceptions the whole set of milk teeth has become a set of persistent 

 teeth except a single tooth. Furthermore to Erinacaeus, where according 

 to the investigations of Leche the so called persistent set of teeth 

 consists partly of milk teeth partly of |)ermanent teeth. So my 

 opinion is nothing more than a new example of the tendency also 

 observed elsewhere of a diphyodont set of teeth to pass into a 

 monophyodont. So against the principle as such (here can be no 

 objection. 



As a tirst argument for the correctness of my opinion I state the 

 morphology of the milk molars in platyrrhines, 1 had the opportunity 

 of stiulying them from Hapale, Chrysothrix, Cebus, Mycetes, Pithecia 

 and Ateles. Without going into details it must only be mentioned here 

 that 7»3 of the platyrrhines dilfcrs a great deal l)olh in the comjjo- 

 silion of its crown and in the number of its fangs from ///, or tn 

 and shows much resemblance lo M^ of these apes. 



It is of much importance with this that v», is functionally a 

 higher developed tooth than its deciduous tooth J\, so that means 

 that at the moment that m^ is replaced by Pj, the set of teeth 

 becomes to a certain degree functionally inferior. So if »?,, becomes 

 persistent, this means a gain for the mechanism of the set of teeth. 

 This does not hold true for ni^ and m^, the replacing F^ and I\ 

 are functionally higher developed. 



A second motive is derived from the development of the set of 

 teeth of the catarrhine Primates, in particular that of man. So according 

 to my opinion our tirst molar has passed from a milk tooth into 

 a persistent tooth in a relatively recent stadium, with the Platyr- 



