430 J. T. WILSON AND J. P. HILL. 
which has not hitherto been made the subject of any complete 
or extended investigation, though several authors (Rése [1], 
Woodward [2], and Leche [3] ) have made reference to obser- 
vations made by them on isolated individual stages of its 
development. 
The series of specimens at our disposal has been a fairly 
complete and satisfactory one, and in its collection we are 
indebted to the following HERLESET for material generously 
placed at our disposal : 
The Trustees of the Australian Museum, Sydney; Pro- 
fessor W. A. Haswell, University of Sydney; Professor W. 
Baldwin Spencer, University of Melbourne; Messrs. C. W. 
De Vis, Brisbane Museum; A. G. Hamilton, George Masters, 
A. M. lea, and Dr. R. Broom. 
Review of Past and Present Opinion.—Whilst we 
have disclaimed any attempt after historical completeness, we 
nevertheless deem it expedient, or even imperative, before 
attempting to set forth our own observations, to make such 
reference to past and present views as may be necessary to pro- 
vide a basis for the future discussion of our own observations. 
In 1867 the law of the succession of the teeth in the Mar- 
supialia was definitely formulated by Flower (4). 
This author claimed to show by means of his own researches 
and those of others that, wherever a tooth-change can’ be 
shown to occur in marsupial animals, such tooth-change in- 
volves only one tooth—the last of the premolar series. 
This view being accepted, the question naturally arose— 
“to which set of teeth in non-marsupial Mammals do the 
non-changing antemolar teeth of Marsupials correspond ? ” 
Flower concluded that they answered to the permanent or 
successional teeth of higher Mammalia, and that thus only 
one true milk-tooth was present in any Marsupial. This in- 
terpretation, taken along with the more primitive character of 
the marsupial organisation in other respects, led him to suggest 
that “ the milk or deciduous teeth may rather be a set super- 
added to supply the temporary needs of Mammals of more 
complex dental organisation ” (4, p. 639). 
