to M. Arauo. 95 



dissected several weeks before his visit to London ; and the 

 external investing membrane, or chorion, removed. I need 

 not observe that the dissection of a mammiferous ovum, and 

 the consequent detection of the sacs appended to the embryo 

 imply, that the chorion should be previously entire. Now, 

 this external membrane of the ovum in question, was not ex- 

 hibited to M. Coste, nor has he ever seen it. 



The modifications which I detected in the chorion of the 

 ovum in question, as compared with that which I had previ- 

 ously dissected and described,* afforded the additional fact, 

 of chief importance in the history of marsupial develope- 

 ment ;t but this fact I did not feel myself called upon to com- 

 municate or demonstrate to M. Coste, as it had not, at that 

 time, been published. 



With respect to the allantois, as its presence afforded 

 merely a confirmation of my previous statements, founded on 

 dissections, the results of which were published in the Phi- 

 losophical Transactions for 1834, I had no hesitation in af- 

 fording M. Coste the means of obtaining ocular demonstration 

 of the fact ; and I was chiefly induced to place before him 

 the foetus of the kangaroo, with the appended allantois, be- 

 cause I found that in his work on * Embriogenie,' p. 118, he 

 states that the allantois is not developed in the Marsupiata, 

 a statement which is in accordance with the figure of the dis- 

 sected embryo, (pi. ix), which is copied from my paper, but 

 which is in direct opposition to my text, where the evidences 

 of the existence of an allantois in the more mature marsupial 

 foetus, are fully described.]: 



In order to gratify M. Coste's praiseworthy desire to ob- 

 tain full evidence respecting the nature of the membranous 

 sacs, appended to the foetus of the kangaroo, I permitted him 

 to dissect the foetus, and, with the assistance which I was 

 happy to afford him, the same connections of the vessels of 

 the umbilical sac with those of the foetus were demonstrated, 

 as are described and delineated in my memoir of 1834 ; and 

 the urachus, which is described and figured in the same me- 

 moir, was found to be connected with the smaller sac, or al- 



* Phil. Trans. 1834. Coste, Embriogenie Comparee, pi. ix. 



f Proceedings of the Zoological Society, 1837, p. 83. 



% In the Philos. Trans. 1834, I state (p. 338), that " I have detected the 

 remains of a urachus, and of umbilical arteries, in a mammary foetus of a 

 kangaroo about a fortnight old ; and of a urachus in a very small mammary 

 foetus of a Petaurus, and Phalangista" (These preparations I also exhibit- 

 ed to M. Coste), and from them I inferred, (p. 342), " that an allantois and 

 umbilical vessels are developed at a later period of gestation, than the uter- 

 ine foetus here described, had arrived at." 



