83 



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

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

 whether an allantois was developed at a subsequent period of the 

 growth of the embryo, dissected very young mammary foetuses of 

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

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

 vessels, he stated that " it would 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 a uterine foetus 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 foetus, was a sac of considerable 

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

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

 uterus by being disposed in innumerable folds and wrinkles. 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. The foetus was further ad- 

 vanced than the one previously described in the Philosophical Trans- 

 actions. The digits on the hinder extremities were distinctly formed. 

 The umbilical chord extended nearly three lines from the abdo- 

 minal surface of the foetus ; the amnios was reflected from this point, 

 to form the usual immediately investing tunic of the foetus ; and, 

 beyond the point of reflection, the chord divided into a very 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 pyriform 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 consequently 

 was equally free from attachment to the parietes of the uterus in 

 which the foetus 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 circumstances which enabled that embryologist 

 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 



* Emlryogenie comparee, p. 1J8. 



