DEVELOPMENT OF MARSUPIALIA. 721 



allantois depends freely from the end of the umbilical cord, and 

 has no connection at any part of its circumference with the 

 adjoining membrane. Its office, as in the Batrachia, is apparently 

 limited to that of a receptacle of urine. The vitellicle or 'um- 

 bilical vesicle ' presented the same large proportionate size and 

 vascular structure as in the first described foetus. The chorion 

 which enveloped this foetus and its appended sacs was adapted to 

 the cavity of the uterus by being disposed in innumerable folds 

 and wrinkles. It did not adhere at any part of its surface to the 

 uterus, but presented a modification not present in the chorion of 

 the earlier foetus, in being partially organised by the extension of 

 the omphalo-mesenteric vessels upon it from the adherent vitel- 

 licle. The digits of the hind legs were distinctly formed in this 

 embryo. 



In some smaller kinds of Kangaroo an ovum from each ovary 

 may be impregnated, and two embryos be simultaneously deve- 

 loped. 1 



Rengger gives the following account of the generation of a 

 species of Opossum (Didelphis Azarcz)'. ' The foetuses are deve- 

 loped in the cornua uteri, and not in the lateral canals. Some 

 days after impregnation they have the form of small round gela- 

 tinous corpuscles, which do not appear, even when examined with 

 a lens, to have any communication with the mother, but a red 

 line indicates the first commencement of development. Towards 

 the end of gestation, when the foetuses have attained the length 

 of six lines, they are seen to be enveloped in a membrane and 

 provided with an umbilical cord, which is united to the uterus ' 

 (chorion ?) ' by the medium of many filaments. The head, the 

 four extremities, and tail are recognisable with the naked eye, 



CJ / 



but those foetuses which are nearest the Fallopian tubes are 

 generally least advanced. In gestation they make the circuit of 

 the lateral canals, in which they are found to be deprived of their 

 foetal envelopes, and to have no communication with the parent 

 by means of the umbilical cord ; whilst one foetus was found in 

 this situation, two others were still in the body of the uterus ' 

 (vaginal cul-de-sac ?), f from which the umbilical cords were 

 not yet detached. At this period a slight enlargement of the 



1 Two have not been found in the same uterus. Mr. Collie, Surgeon, E.N., states, 

 ' I have just now procured gravid uteri (of the Macropus Brttnii) in which two foetuses 

 seem to be arrived at, or very near to, the termination of the period of gestation. 

 One of them, which was aboxit one-half larger than the body of the common wasp, has 

 protruded through an opening inadvertently made in the uterus, and is distinctly seen 

 through its transparent membranes and the liquor amnii. 1 ' Zoological Journal, vol. 

 v. p. 240. 



VOL. I IT. 3 A 



