DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 523 
PART III. 
Discussion oF GENERAL PROBLEMS OF THE MARSUPIAL 
DENTITION IN THE LIGHT OF THE FOREGOING OBSER- 
VATIONS. 
Our own conclusions may, perhaps, be most conveniently 
introduced in the course of a discussion of the views of pre- 
vious writers—already partly outlined in the introductory 
portion of this paper. And in order to focus the discussion, 
and to set forth its issues more clearly and definitely, we have 
thought it useful to formulate certain leading questions, and 
to define the attitude which has been assumed towards these 
by other observers whose views are related to our own either 
by way of agreement or contrast. In the formulation of these 
questions we have pretty closely followed the lines, and even 
in part the language, of writers who, like Thomas, Schwalbe, 
and Leche, have so greatly advanced the intelligent discussion 
of the subject of mammalian dentition. 
I. “Do the existing teeth of Marsupials in front of 
the last premolar correspond to those of the milk or 
of the successional dentition of higher mammals?” 
It will presently appear that the discussion of this question 
involves a consideration of those criteria which may enable us 
to determine a given embryonic structure as the germ of a 
successional tooth. 
II. How are we to explain the single tooth-change 
or succession (i.e. in the case of the last premolar), 
hitherto almost universally recognised as the sole 
instance of tooth-change among Marsupials? 
III. To which dentition belong the molars of Mar- 
supials and of mammals generally? and— 
IV. What is the nature of that generally admitted 
process of evolution by which multicuspidate teeth 
have been derived from a primitively simple uni- 
cuspidate type? 
