TOOTH-GERMS IN A WALLABY, 941 



tip of the large tooth, and thei'e is no doubt that the exact mor- 

 phological localisation of the vestige in relation to the large incisor 

 is a matter of difficulty. On the whole, therefore, we are in closer 

 agreement with Woodward's conclusions than with those of any 

 other writer. 



The close approximation which we have found between the 

 representatives of these fovir anterior incisors is of considerable 

 interest when we remember the condition of the lower incisors in 

 Didelphys. 



Canines. — These teeth call for no further observations. 



Maxillary teeth.- — ^The fourth true maxillary tooth of the upper 

 jaw, as has already been stated, has a well-marked " concenti'ic 

 epithelial body " lying superficially to it. The importance of 

 these structures as representing the last ti'ace of a tooth vestige 

 has been frequently insisted upon by one of vts (H.W. M.T.) 

 (7, 8), and the more recent researches of Wilson & Hill (10) seem 

 to have placed the matter beyond doubt. So long as the present 

 distinction as to whether or not there are predecessors is the ci'i- 

 terion of distinction between premolars and molars, confusion is 

 bound to result. Embryology often reveals the presence of these 

 vestiges which bi'eaks down this conception of a trne molar tooth. 

 It would in our opinion be better to call all post-canine teeth 

 maxillary teeth. Until such a. suggestion is adopted we must 

 regard the fourth tooth of the series as a premolar ( pm. 4 ). 

 The relationship of this tooth to the one immediately behind it 

 suggests that the fifth tooth, i. e. m\ is the deciduous tooth which 

 is replaced by pm'', a suggestion strongly vu-ged by one of us in a 

 previous paper (8). 



It seems to be tolerably certain that the 2nd maxillary tooth 

 will not be able to develop further, thus confirming the opinion of 

 Oldfield Thomas that pm^ is the missing premolar. 



The same interpretation holds good for the lower teeth. 



To which dentition do the teeth of Marsupials belong "^i 



No very decided answei' to this question cru be obtained fi^om 

 the material examined. Traces of a successional dentition are 

 scanty, while those of a deciduous series are somewhat more 

 abvindant and more distinct. One of us (H. W. M. T.) has in 

 more than one paper (6, 7) previously ui^ged, upon general grounds, 

 the view that the permanent dentition of the marsupials is the 

 permanent dentition of the Eutheria and that both the deciduous 

 and successional pm* belong to one and the same dentition. This 

 conclusion has been independently arrived at by Wilson & Hill 

 (10) and adopted by 0. S. Tomes (9). The joint authors of the 

 present paper are in agreement upon this subject, and we have 

 found nothing in the material which we have examined to cause 

 us to doubt the correctness of this view. 



iSToTE. — I would desire to express my gratitude to the Odonto- 

 logical Society of Great Britain, for a grant in aid of lesearches 



