328 



MARSUPIALIA. 



Fig. 143; 



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 Chaeropus, 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 foetus 

 of an Opossum : he could not discern equal 

 traces of the nipples: that of the pouch is 



* Annales d'Anatomie et de Physiologic, 1839, 

 p. 237. 



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 capa- 

 cious pouch is situated nearer the posterior thaa 

 the anterior boundary of that receptacle. 



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 unguiculate quadrupeds, 

 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 PLACENTALIA and IM- 

 PLACENTALIA does not rest upon the appro- 

 priateness of the terms, but upon the esta- 

 blishment, by a long series of anatomical re- 

 searches, of a primary division of the Mam- 

 miferous class, which before was a mere hy- 

 pothesis. 



Many acute and sound-thinking naturalists 

 refused their assent to the views of Cuvier and 

 De Blainville, which, as they were supported 

 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 distributing the Mar- 

 supial genera, according to the affinities appa- 

 rently indicated by their dental and locomotive 

 systems,amongthedifTerentorders 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 Ptiascolumys, " What is there of im- 



