MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS. 353 



pouchj I found both the true uteri of three times the diameter of the same in an un- 

 impregnated specimen ; but the vaginee were unaltered in size, indicating that the 

 situation in which gestation takes place in this species is the same as in the Kan- 

 garoo. The vaginae, after receiving the uteri, descend close together half way 

 towards the commencement of the urethro-sexual passage, but do not communicate 

 together in this part of their course. From the upper part of these culs de sac they 

 are continued upwards and outwards, forming a curve like the handles of a vase, 

 then descend, converge, and terminate close together, as in the preceding example. 



In Dasyurus viverrinus and Didelphys virginiana, the mesial culs de sac of the 

 vaginae descend to the urethro-sexual passage, and are connected to, but do not 

 communicate with it. The septum dividing them from each other is complete, being 

 composed of two layers, which can be separated from each other, and which result, 

 indeed, from the apposition and mutual adhesion of the vaginae at this part. In 

 order to reach the common passage, each tube is continued outwards from the upper 

 end of the cul de sac, and forming the usual curve, terminates parallel to the orifice 

 of the urethra. The vaginae in the Dasyures are smaller in proportion to the uteri 

 than in the Virginian Opossum, but of a similar form. 



In another species, the Didelphys Opossum of Linn^us, it would appear from the 

 description and figures of Daubenton^'*^, that the septum of the mesial culs de sac of 

 the vaginae was imperfect ; but it is doubtful whether this intercommunication was 

 not the result of parturition, or of an accidental rupture in the specimen examined. 

 If it should prove to be a specific difference of structure, it is an approximation to 

 the type of the female organs as they exist in the Phalangers, the Wombat, and the 

 Kangaroo. 



In the latter animal the vaginae preponderate in size greatly over the uteri ; and 

 the septum of the descending cul de sac being always more or less incomplete, a 

 single cavity is thus formed, into which both uteri open ; but however imperfect 

 the septum may be, it always intervenes and preserves its original relations to the 

 uterine orifices. 



The foetus has been conjectured to pass into the urethro-sexual cavity by a direct 

 aperture formed after impregnation at the lower blind end of the cul de sac, but I 

 have not been able to discover any trace of such a foramen in two kangaroos which 

 had borne young ; and besides, I find that this part of the vagina is not continuous 

 by means of its proper tissue with the urethro-sexual passage, but is connected to it 

 by cellular membrane only ; and this structure is agreeable to what is presented in 

 the simpler forms of the marsupial uterus, as in Didelphys dorsigera, and the Petauri, 

 in which the culs de sac do not even come into contact with the urethro-sexual 

 passage. The evidence of M. Rengger on the development of the young and the 

 parturition of the Didelphys Azarce is also directly opposed to the theory of a tempo- 

 rary orifice in the mesial cul de sac. 



* BuFFON, Hist. Nat., torn. x. 



