ON THE QUESTION OF AN ARBOREAL ANCESTRY 
OF THE MARSUPIALIA, AND THE INTER- 
RELATIONSHIPS OF THE MAM- 
MALIAN SUBCLASSES. 
A REVIEW OF CERTAIN PHASES OF PRESENT AND PAST OPINION. 
B. ARTHUR BENSLEY. 
RECENT researches have seemed to indicate that the theory, 
proposed by Huxley, of a genetic succession of the former repre- 
sentatives of the Monotremata, Marsupialia, and Placentalia, 
is untenable, and have thus reopened the most fundamental 
question of mammalian zoólogy, as to the interrelationships 
of the primary subclasses and the possibility of a di- or 
polyphyletic origin. 
The recent publication by Dollo (99) of the results of his 
studies on the foot structure of the Marsupialia, which he 
interprets as confirming the growing idea of a placental origin 
of the group, renders this an opportune time to review and 
comment upon certain features of the evidence which has 
lately been produced in opposition to Huxley's theory. 
I. Tue EVIDENCE OF AN ARBOREAL ANCESTRY OF THE MAR- 
SUPIALIA AND ITS BEARING AS INTERPRETED BY DOLLO. 
The question of arboreal ancestry is of considerable impor- 
tance in determining the relationships of the Marsupialia, and 
Dollo’s results may accordingly be reviewed in some detail. 
On page 191 of his paper we find the problem involved set 
forth as follows: 
“Car si cette étude démontre que les ancétres immédiats des 
Marsupiaux étaient arboricoles, il sera prouvé, du méme coup, 
que ces Mammiféres ne peuvent représenter la souche des 
Placentaires. 
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