286 Dr. W. Kikenthal on the 
thus laying the foundation of the theory that the milk-den- 
tition has been secondarily acquired by the Mammalia, and 
occurs in Mar supials only in a single case (the third premolar). 
Although Flower’s deduction was by no means generally 
accepted, the conception of the Marsupial dentition as 
belonging to the permanent or, to speak more correctly, the 
second series of teeth, was universally adopted. Thus it is 
supposed by Winge ze who otherwise in opposition to Flower 
regards tooth- change as an old arrangement, inherited from 
the lower Vertebrates, that the milk-dentition in the Marsu- 
pials has been lost, w ith the exception of one milk-tooth, the 
precursor of the third premolar. A higher grade would 
therefore have to be assigned to the dentition of Marsupials 
than to that of the majority of Mammals. “ But if, con- 
trary to all probability, it should appear that the Marsupial 
teeth in question have never had precursors in the course of 
either ontogeny or phylogeny, they would correspond to the 
milk-teeth in other Mammals; but they would be milk-teeth 
developed to such an extent that m respect of their form ce. 
they would have to be compared with the teeth of the second 
series in other Mammals.” 
Our knowledge of the dentition of Marsupials received a 
further and very material advance in consequence of Oldfield 
‘Thomas’s paper t, in which the homologies of the various 
teeth are determined and the typical Marsupial dentition 
stated as consisting of 5 incisors, 1 canine, 4 premolars, and 
4 molars. . Reduction set in, and gave rise to the dentition of 
the various Marsupials; that of Diédelphys arose in conse- 
quence of the loss of the second premolar. The third pre- 
molar, which is provided with a precursor, should therefore 
really be termed the fourth premolar. Thomas follows 
Flower in regarding the milk-dentition as having been secon- 
darily acquired within the Mammalian class, and consistently 
follows out this idea. He himself points out that, besides 
other things, the possible discovery of the rudiments of a 
successor in the case of Marsupial teeth which exhibit no 
tooth-change would be fatal to his theory. 
It was this consideration which guided me in my own inves- 
tigations, If in the course of development rudiments of second 
* Herluf Winge, “Om Pattedyrenes Tandskifte, isaer med Hensyn til 
Taendernes Former,” Vidensk. Meddel. fra den naturh, Foren. in Kjoben- 
havn, 1882, p. 52. 
+ Oldfield Thomas, “ On the Homologies and Succession of the Teeth 
in the Dasyuride, with an Attempt to trace the History of the Evolution 
of Mammalian Teetb in general,” Philosophical Transactions of the Royal 
Society (London, 1887), 
