DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES, 545 
found that phenomena in the way of shedding or absorption of 
rudimentary teeth actually do occur, such as might naturally 
be interpreted by Owen as cases of ordinary, if precocious, 
tooth-succession. 
As yet, however, we can only deal with the one undoubted 
manifestation of tooth-change admittedly occurring in Marsu- 
pials. Is such tooth-change to be regarded as the survival of 
an originally more complete succession? With the single ex- 
ception of Professor Leche all the recent authorities would 
seem to adopt the affirmative answer to this question, thus 
taking their stand upon the primitive diphyodontism of Marsu- 
pials, and inferentially of mammals generally. We have 
already seen how Mr. Oldfield Thomas (8) definitely, if rather 
reluctantly, gave in his adherence to this theory as a conse- 
quence of Kukenthal’s researches. Any hesitation he exhibits 
is confessedly due to the difficulty he finds in explaining upon 
this hypothesis the striking fact that Triconodon already in 
Mesozoic times exhibited just the same fulness (or meagre- 
ness) of tooth-change which to-day characterises the marsupial 
group. But after all it does not appear that the peculiar fact 
mentioned (even if Triconodon is admitted as really of 
marsupial organisation, as seems probable) is easier of explana- 
tion on any alternative hypothesis. Surely itis just as difficult 
to account for the fact that a new acquisition of milk-teeth 
(as supposed by the older Flower-Thomas hypothesis) should 
have stopped short with Triconodon in the marsupial group, 
as to believe that the process of degeneration (supposed by the 
newer hypothesis) should have been suspended as far back as 
the Mesozoic age. For any secondary condition capable of 
accounting for the former suspension, such as the peculiar 
nutritional conditions of Marsupials, may without much diffi- 
culty be applied so as to account for the latter. 
Leche has more recently come forward as an advocate of the 
alternative hypothesis that the tooth-change in the case of 
the last premolar is not the remnant of a more complete change, 
but the first appearance of a new dentition foreign to the 
primitive marsupial organisation. His theory, however, is 
