578 J. T. WILSON AND J. P. HILL. 
tions as inevitably arise in consequence of the discovery by 
one of us (H., 30) of a true allantoic placenta in Perameles. 
It is obvious that this discovery admits of only a limited 
number of alternative explanations. It implies either (@) that 
an allantoic placenta has been quite independently evolved 
within the limits of the Metatherian and Eutherian groups, 
thus affording a quite remarkable instance of parallelism in 
development ;! or (4) that the Eutheria have inherited their 
allantoic placenta actually from polyprotodont marsupial 
ancestors closely allied to the modern Peramelida; or (c) 
that both the Metatheria and the Eutheria have sprung 
from an earlier mammalian proto-placental stock. 
If the latter alternative were adopted (and we believe that it 
alone will in the end commend itself to the judgment of 
morphologists), then we should be in a position to define the 
common mammalian ancestors of the Metatheria and Eu- 
theria as both placental and diphyodont. 
The much-debated question as to whether or not this early 
mammalian stem was also marsupial in its organisation may, 
in view of developmental researches upon the mammary organs 
during recent years, admit of a not unsatisfactory reply. For 
the researches of Gegenbaur (86), Klaatsch (82), and others 
appear to have established the fact of the possession of rudi- 
ments of ‘‘mammary pouches” (“ Mammartaschen”’) by 
embryo Kutherians. Such mammary pouches (to be distin- 
guished from a true Marsupium) are, in ruminants, accord- 
ing to Klaatsch, converted into the tubular teat-cavity.? Bonnet 
expresses Klaatsch’s view in this connection as follows :—“ Wo 
aber die Mammartasche unverdndert bestehen bleibt, wie bei 
den Wiederkaiiern und den Equiden macht er den Anschluss 
dieser Formen an ganz niedere Zustande, die gar kein Mar- 
supium ausgebildet haben, wahrscheinlich ” (81, p. 628). 
1 But in such case Perameles, contrary to all previous belief, would 
exhibit a more advanced or specialised condition than any other known 
Marsupial. 
2 The contrary opinions of Rein, though accepted by Minot in his ‘ Human 
Embryology,’ have been subjected to severe criticism by Klaatsch, and the 
views of the latter observer have been adopted by Bonnet (31). 
