Oil the Dcniition o/'Di.lclplijs. 28/5 



formation from reptile-lilcc progenitors, a number of .simple, 

 conical reptile-teeth came together to form each mammalian 

 molar? Palaeontology is in favour of my view; the oldest 

 known mammals, e. g. Triconodon from the Upper Jura, 

 exhibit molars of the typical structure requisite for our idea, 

 each consisting of three similar conical tooth-segments, lying 

 one behind the other and fused together. The admirable 

 papers of Cope, Osborn, Sclilosser, and others have shown 

 that from the triconodont, that is the tricuspid type, the 

 molars of all mammals may be derived. 



A multitude of questions as to the specialization of the 

 teeth within the various orders, the teeth with continuous 

 growth, the formation of roots, &c., still remain to be 

 answered; I shall make the attempt to do this in a detailed 

 account of my investigations. 



Jena, June 5, 1891. 



XLIV. — The Dentition of Didelphys : a Contribution to the 

 Embryology of the Dentition of Marsupials *. By W. 

 KiiKENTHALf. 



In the case of Didelphys the dental formula 4 [ ^ 4 is very 



generally accepted. The tooth- change is limited to one 

 tooth, the last premolar, as was first discovered by Gervais 

 and Flower to be the case in Marsupials. By this discovery 

 the older view that in Marsupials the whole of the teeth are 

 replaced with the exception of the four molars was finally 

 overthrown. The question, however, now arose as to how 

 the dentition of Marsupials was to be regarded, i. e. whether 

 it corresponds to the milk-dentition or to the permanent series 

 of other Mammals. While Owen was rather inclined to 

 adopt the former view, the latter was maintained by Flower, 



* Translated from a separate impression from the ' Anatomischer 

 Anzeiger,' vi. Jalirgaug (1891), nos. 23 and 2-J, pp. 608-666. 



t In a paper which was recently published in this periodical, entitled 

 " Eiuige Bemerkungeu iiber die Saugetierbezahnung " (Anat. Auz. 

 1891, p. 369 \yide supra, " Observations on the Dentition of Mammals," 

 pp. 279-285]), I have already alluded to the chief result of my investiga- 

 tions, which formed the subject of an address delivered on the 30th of 

 May of the present year in the Aula of our University. But, in con.^e- 

 quence of the delay which has arisen in the setting-up of my detailed 

 statements owing "to the compositors' strike, lam now induced to give 

 herewith a somewhat closer prr of of my assertions, at^cast as regards the 

 Marsupials. 



