ANCÈTRES DES MARSUPIAUX. 189 
I. — Cependant, tout récemment, plusieurs naturalistes autorisés (!) sont 
arrivés à la conclusion que les Marsupiaux ne forment nullement le passage des 
Monotrèmes aux Placentaires, mais qu’ils représentent un rameau latéral de 
ceux-ci, spécialisé de très curieuse manière. 
NT. — En effet, comme cela semble résulter des recherches de M. J. P. 
Hrz À), professeur à l'Université de Sidney. les Marsupiaux qui n’ont pas de 
2 Ÿ 2 Ï 
placenta l’ont perdu, et ceux qui en ont encore un sont en voie de le perdre. 
IV. — Ce n’est pas qu’on ne se fût point aperçu antérieurement (*) de la haute 
spécialisation des Marsupiaux à bien des égards. Mais on croyait que l’absence 
de placenta (seule constatée jusqu'alors) était un caractère primitif préservé ; 
en d’autres termes, que les Marsupiaux n’avaient pas encore atteint le stade 
(t) « Thus, in our view, it is unnecessary to trace the placental ancestry of Eutheria back into 
the marsupial group....... We therefore fall back upon the view that the Metatheria and Eutheria 
are the divergent branches of acommon ancestral stock, which was not only diphyodont but also 
placental. » J. P. Hizz. The Placentation of Perameles. Quart. Jour. Micr. Soc. 1897, vol. 40, 
p. 436. 
« Prof. Osborn said that in order to clear the ground for a successful attack upon the difficult 
problem of the origin ofmammals is was necessary to reject the hypothesis, brilliantly formulated 
by Huxley in 1880, of a genetic succession between Monotreme, Marsupial and Placental types, 
since this could not be supported by either palæontology or comparative anatomy ....... There 
was abundant evidence that many of the small mammals of the Middle and Upper Jurassic were 
not Marsupials, but insectivorous Placentals, fulfilling all the conditions required for the ancestry 
of the living Insectivora and the Creodonta, and, through the latter, of all the higher existing 
types of mammals, including man. » The International Congress, etc., p. 427. 
«Prof-AHubrecht..-"-"" referred to Prof. Hills discovery of a definite deciduous placenta in 
Perameles, and to the less complete placenta of Phascolarctos, and concluded by expressing his 
doubts as to the intermediate position occupied by the Marsupials between the Monotremes and the 
Placental mammals. » The International Congress, etc., p. 427. 
(2) « The occurrence there of a true allantoic placenta, and its absence in the majority of members 
of the order, do no doubt, at first sight, suggest that in this group we must find the first begin- 
nings of the organ. But we believe that the explanation is to be found in the fact that marsupials 
are, after all, a markedly specialised group, and that in it conditions have obtained producing 
placental disappearance, just as conditions (probably identical in character) have determined the 
degeneration of other early nutritional arrangements, i. e. the milk-teeth. » J. P. Hirz. The Placen- 
tation, etc., p. 436. 
(3) « However this may be, the characters of the existing Marsupialia leave no doubt on my 
mind that they are greatly modified members of the metatherial type ; and I suspect that most, if 
not all, of the Australian forms are of comparatively late origin. » T. H. Huxrex. Ox the Appli- 
cation, etc., p. 656. 
