DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 429 
the dentition in this order. But in part also it is due to the 
fact that the more or less peculiar characteristics of the denti- 
tion in the Metatheria (and, a fortiori, in the Proto- 
theria) have, on account of the usually accepted zoological 
position of the group, been approached with a quite special 
interest, as likely to afford important clues to the phylogenesis 
of the teeth in Mammalia generally. A consideration of the 
literature of this branch of the subject might indeed suggest 
that something like unanimity has been attained upon several 
important matters, e.g. the serial homology of the deciduous 
premolar of Marsupials with the more anterior premolars. As 
will appear in the sequel, however, it is the opinion of the 
present writers that, even on the points referred to, the dis- 
cussion is very far from being finally or satisfactorily con- 
cluded. As regards several other weighty questions, no 
pretence of agreement is made by various investigators; and 
in not a few instances the accounts of what are obviously 
identical phenomena reveal actual discrepancies of observation, 
as well as very diverse interpretations of those facts in regard 
to which their observations do coincide. It has accordingly 
appeared to the authors highly desirable that the body of fact 
and observation available for the construction of adequate 
hypotheses concerning the marsupial dentition should be 
further supplemented from the developmental side ; and, being 
comparatively favorably placed for obtaining suitable ma- 
terial, they have been induced to undertake the task of, at 
least, providing further reliable records of observations upon 
tooth development in Marsupials. With this object the poly- 
protodont genus Perameles was chosen in the first instance, 
and P. nasuta has throughout furnished the major part of 
our material, and formed the basis of most of the descriptive 
part of this paper. Other forms, however, have been examined 
with reference to particular points, e.g. Dasyurus viver- 
rinus, Phascologale cristicauda, Trichosurus vulpe- 
cula, and Macropus ruficollis. 
Perameles was specially chosen as our type for study and 
description as representing a fairly generalised marsupial type 
