328 
Female Didelphys dorsigera, with young and pouch. 
In the Kangaroos and Potoroos, which have 
the shortest uteri and longest vaginal tubes and 
cul-de-sac, the marsupial pouch is wide and 
deep. It is composed of a duplicature of the 
integument, of which the external fold is sup- 
ported by longitudinal fasciculi of the panni- 
culus carnosus converging below to be im- 
planted in the symphysis pubis. The mouth 
of the sac is closed by a strong cutaneous 
sphincter muscle. The interior of the pouch 
is almost naked: a few hairs grow around the 
nipple: it is lubricated by a brown sebaceous 
secretion. The mouth of the pouch is directed 
forwards in most Marsupials: the reversed 
position in the Perameles and Cheropus, where 
the mouth is directed towards the vulva, has 
been already noticed. M. Laurent* has made 
the interesting observation of the presence of a 
rudimental pouch in the male mammary feetus 
of an Opossum: he could not discern equal 
traces of the nipples: that of the pouch is 
* Annales d’Anatomie et de Physiologie, 1839, 
p- 237. 
MARSUPIALIA. 
soon obliterated, as the scrotum increases in 
size. 
In the male Thylacine the rudimental mar- 
supium is retained, in the form of a broad 
triangular depression or shallow inverted fold 
of the abdominal integument, from the middle 
of which the peduncle of the scrotum is con- 
tinued. In the female the orifice of the 
cious pouch is situated nearer the ior than 
the anterior boundary of that receptacle. 4 
A few observations on the claims of the Mar- 
supialia to be regarded as a natural group of ani- 
mals may not inappropriately conclude this ar- 
ticle. Cuvier, in 1816, first separated the mar- 
supial from the other unguicu + 
to form a distinct group, which he describes as 
forming, with the Monotremes, a small collateral 
chain, all the genera of which, while they are 
connected together by the peculiarities of the 
generative system, at the same time correspond 
in their dentition and diet, some to the Car- 
nivora, others to the Rodentia, and a third 
tribe to the Edentata. M. de Blainville, in 
the tables of the Animal Kingdom which he 
published in the same year, 1816, constituted 
a distinct sub-class of Cuvier’s “ small col- 
lateral chain” of mammals, and gave to the 
sub-class the name of Didelphes in antithesis 
to that of Monodelphes, by which he distin- 
guished the Placental Mammalia. 
The class or sub-class ‘ Implacentalia,’ of 
which the Marsupialia form one order, also in- 
cludes a second order, the Monotremata, which 
can only be termed ‘ Didelphes’ in the sense 
in which the word is applicable to many of 
M. de Blainville’s ‘ Monodelphes,’ i. e, in re- 
ference to their having two distinct uterine 
tubes. But the merit of the primary division 
of the Mammalia into Pracentatia and Im- 
PLACENTALIA does not rest upon the appro- 
reer of the terms, but upon the esta- 
lishment, by a long series of anatomical re- 
searches, of a primary division of the Mam- 
miferous class, which before was a mere hy- 
pothesis. str 
Many acute and sound-thinking naturalists 
refused their assent to the views of Cuvier and 
De Blainville, which, as they were sw 
by a knowledge of the conformity of organiza- 
tion of only the generative system in the Mar- 
supials, were unquestionably defective in the 
evidence essential to enforce conviction. The 
best arguments for returning to the older views 
of classification, and for — the Mar- 
supial genera, according to the affinities aj 
rently indicated by their dental and praate: 
systems, among the different orders of the Placen- 
tal Mammalia, have been advanced by Mr. Ben- 
nett, the accomplished author of the Gardens 
and Menagerie of the Zoological Society de- 
lineated, (vol. i. p. 265); and these have been 
repeated with approbation, and adopted by 
later systematists, as by Mr. Swainson. 
The discovery of the true affinities of the 
Marsupialia could only flow from an insight 
into their whole organization, and the question 
which Mr. Bennett proposes with reference to 
the genus Phascolomys, “ What is there of im- 
ee 
