POETAL MEMBRANES OF OPOSSUM AND OTHER MARSUPIALS. 473 



Observations upon the Foetal Membranes of the 

 Opossum and other Marsupials. 



By 



Henry F. Osboru, Scl>., 



Assistant Professor of Natural Science, Princeton, U.S.A. 



With Plate XXXIII. 



In 1834 and 1837 Professor Owen published in the ' Philo- 

 sophical Transactions' and the 'Proceedings of the Zoological 

 Society' descriptions of the foetal membrane of the kangaroo. 

 Quite recently his observations have been confirmed by Pro- 

 fessor Chapman/ of Philadelphia. They are given in full in 

 the ' Comparative Anatomy of the Vertebrates,' and are to be 

 found, in abstract, in Balfour's ' Comparative Embryology/ 

 vol. ii. It is surprising that no additions have been made to 

 our knowledge of these forms during the long period interven- 

 ing between Owen's observation and the present time, even 

 when one is aware of the extreme difficulty of obtaining females 

 during the period of gestation. 



Professor Owen established the following as the distinctive 

 features of the Marsupial foetal membranes : (1) A. large sub- 

 zonal membrane with folds fitting into the uterine furrows, 

 but not adhering to the uterus and without villi. 

 (2) A large and vascular yolk-sac partly flattened out over the 

 inner surface of the subzonal membrane, and supplied by an 

 artery and two veins. (3) An allantois of comparatively small 

 size, not attached to the subzonal membrane, with a blood 

 » ' Proc. Acad. Nat. Sciences of Pliila.,' 1881. 



