83 



the ovo -viviparous reptiles, with the exception of there being no trace 

 of the existence of an allantois. Mr. Owen, iu order to determine 

 vvhether an allantois was developed at a subseąuent period of the 

 growth of the embryo, dissected very young mammary fcEtuses of 

 different marsupial aninials, as the Kangaroo, Phalangista, and Pe- 

 taurus ; and finding in them the remains of a urachus and umbilical 

 vessels, he stated that " it \vould appear that an allantois and um- 

 bilical vessels are developed at a later period of gestation, but pro- 

 bably not to a greater extent than to serve as a receptacle of urine." 

 (Phil. Trans., 1834, p. 342.) 



The examination of auterine fcetus of a Kangaroo kindly placed at 

 Mr. Owen's disposal by Dr. Shearman, and exhibited on this occasion 

 to the Society, has proved the accuracy of this prevision. The chorion, 

 which enveloped and concealed the fcetus, was a sac of considerable 

 capacity,exceeding probably by ten times the bulk of the fcetus and 

 its immediate appendages, and adapted to the smaller cavity of the 

 uterus by being disposed in innumerable folds and ^vrinkles. It did 

 not adhere at any part of its circumference to the uterus, but pre- 

 sented a most interesting modification not observed in the previous 

 dissection of the Kangaroo's impregnated uterus, viz., that it was in 

 part organized by the extension of the omphalo-mesenteric vessels 

 upon it from the adherent umbilical sac. ITie fcetus was further ad- 

 vanced than the one previously described in the Philosophical Trans- 

 actions. The digits on the hinder extremities were distinctUf^formed. 

 The umbilical chord extended nearly three lines from the abdo- 

 minal surface of the fcetus ; the amnios \vas reflected from this point, 

 to form the usual immediately investing tunie of the fcetus ; and, 

 beyond the point of reflection, the chord di^dded into a verjr large 

 superior vascular sac, organized by the omphalo-mesenteric vessels, 

 corresponding in all respects with the vitelline sac described and 

 figured in Mr. Owen's first paper ; but below the neck of this sac 

 there extended a second pyriiorm sac, about one-sixth the size 

 of the vitelline sac, having numerous ramifications of the umbilical 

 vessels, and constituting a true allantois. This sac was suspended 

 freely from the end of the umbilical chord : it had no connexion, at 

 any part of its circumference, with the chorion, and conseąuently 

 was eąually free from attachment to the parietės of the uterus in 

 which the fcetus was developed*. 



* The following note has been communicated by Mr. Owen to be ap- 

 pended as a postscript to the above remarks. " Having been anticipated 

 in the description of my preparation, so far as relates to the allantois, 

 by M. Coste, I here subjoin, by permission of the Committee of Publi- 

 cation, a statement of the clrcumstances which enabled that embrj'ologist 

 to announce the discovery of the allantois to the Academy of Sciences. 

 In a recent work on Embryogeny, M. Coste • has stated that the Marsupiata 

 differ from other Mammalia in the absence of an allantois, — a statement 

 which appears to have arisen from a misconception of my memoir in the 

 Philosophical Transactions for 1834, in which, although the allantois was 



* Embryogenie eomparee, p. U S. 



