184 Professor Owen's Reply 



have the Academy to believe, that the difference between us 

 is one of words, and not of things. I am much mistaken, how- 

 ever, if any one of the learned Academicians, how different 

 soever his studies may be from the subject of animal physio- 

 logy, will need to be informed that an ovum is something more 

 than a foetus and its vesicular appendages, and that it is a 

 great deal more than an uterine foetus alone. 



The marsupial embryo, like every other embryo, is deve- 

 loped within a chorion, which incloses and conceals it, so far 

 as observation has yet extended, at every stage of its deve- 

 lopement. I found it necessary to lay open this exterior sac, 

 in order to expose the foetus, when I discovered, in 1834, its 

 first-developed appendage ; namely, the umbilical sac. I 

 found it equally necessary to lay open the chorion, in order 

 to expose its contents, when I discovered, in June, 1837, the 

 second-developed vesicular appendage of the foetus, namely, 

 the allantois. The embryologist must pardon me, if, in re- 

 ply to M. Coste's assertion, that I am contending for words 

 instead of things,* I make the trite observation, that the cho- 

 rion is no part of the embryo, that it is not developed by or 

 from the embryo, but that it pre-exists to the first rudiments 

 of the embryo, and, together with the embryo and its vesicular 

 appendages, forms an essential constituent of the ovum. 



It is of importance only to M. Coste, that it should be be- 

 lieved that an ovum in general is as complete without a cho- 

 rion as with one ; and that in the kangaroo in particular, if a 

 chorion can be said to exist at all in the ovum, it exists in a 

 state of fusion with the umbilical vesicle, or that the two mem- 

 branes are confounded together ; — a proposition which is es- 

 sential to his claim of having discovered the allantois, since 

 the only opportunity which he ever enjoyed of seeing the al- 

 lantois of the kangaroo, was after it had been exposed by the 

 removal of the chorion, and when the true ovum had been 

 reduced, by previous dissection, to the condition of a foetus 

 and its vesicular appendages. This I hope to prove to the 

 satisfaction of the Academy, and of the commission ap- 

 pointed to report upon the merits of M. Coste's Memoir, by 



* In reference to my letter which M. Coste states to relate "au sujet d'un 

 produit uterin de kangaroo, qu'il designe sons le nom de foetus et ses ap- 

 pendices vesiculeux, et que j'ai considere comme un ceuf," M. Coste ob- 

 serves in his note printed in the'Comptes Rendus de l'Academie,' "Comme 

 sur ce point la discussion parait porter plutot sur les mots que sur les choses, 

 et comme d'ailleurs je suis parfaitement enmesure de repondre a toutesles 

 assertions de M. Owen, je demande a l'Academie la permission de soumet- 

 tre a son jugement le Memoire ci-joint, dans lequel elle trouvera, j'espere, 

 les moyens de decider la question, et dans le fond, et dans la forme." 



