456 DR. H. W. MAEETT TIMS OK THE 



the Marsupials being supposed to be the milk series ; and this 

 conclusion was based on the fact that Kiikenthal had discovered 

 strong swellings of the dental lamina on the lingual side of these 

 teeth in Dldelphys (9). 



In the absence of any evidence of four dentitions being repre- 

 sented in any one part of the jaw of any animal, it seems to me 

 to be only reasonable to infer that the three dentitions of the 

 Marsupials are the same as those represented in the Seal, Man, 

 Hedgehog, and Dog ; and, consequently, I would regard Leche's 

 Pre-milk dentition as the vestigial remains of the milk series and 

 the functional set as belonging to the true permanent series, 

 thus reverting to the view long ago held by Flower and Oldfield 

 Thomas. The formerly vexed question as to which is the super- 

 added dentition, the Milk or Permanent, is no longer a serious 

 one, as the three dentitions are an inheritance from polyphyodont 

 ancestors. 



The next question arises, to which dentition do pm.^ and the 

 true molars belong ? since they are functional in one series only. 

 If sections of an animal three days old be examined, in the region 

 of the first premolar tootli, three downgrowths of the dental 

 lamina are to be seen, and it is from the central one of these 

 that the tooth develops (27). Regarding these three down- 

 growths as representing the same three dentitions found in the 

 outer incisor region, I would consider this first premolar tooth 

 as belonging to the Permanent or Successional series. This con- 

 clusion is, I think, in harmony with that of the majority of 

 observers ; but there are some who prefer to regard it as a delayed 

 milk-tooth. This tooth is replaced in one or two animals only, 

 namely, the Indian Taper (19), the Hvrax (3), occasionally the 

 Pig(12) and lihinoceros, and the extinct Palseotherium (4). la 

 these cases the two teeth may be of the milk and permanent, 'or 

 of the permanent and post-permanent series. I am not as yet 

 in a position to say anything definite upon this point, though, 

 from the appearances of the dental lamina in the Dog and in the 

 Pig, I incline to the latter view. 



"With regard to the true molar teeth opposing views have also 

 been held, namely, that they are permanent teeth, or that they 

 are delayed milk-teeth. HoflFmann (6) has recently concluded 

 that the Ungulate molars belong to the milk series ; and Leche 

 (10), though admitting that this is by no means settled, is 

 inclined to the same opinion. 



