190 Professor Owens Reply 



veloppement etant deja assez avance, et l 1 aspect general de cet 

 oeuf etant le meme que celui qu'offrent les rongeurs &c. nous en 

 avons conclu que la membrane vitelline, ou chorion, etait con- 

 fondue avec la vesiculeombilicale:"p. 15. M. Coste will pardon 

 me if I doubt that he drew his conclusion from the premises 

 which he here assigns. He knows well what the general as- 

 pect, and even what the general conditions of the ovum of a 

 rodent are, for he has figured the ovum of the rabbit in his work 

 on Embryogeny. Now let any one compare these figures with 

 the sketch by M. Coste of what he calls the ovum of the kan- 

 garoo, or the figure of the real ovum of the kangaroo, in which 

 the chorion is truly represented, and which figure M. Coste 

 has borrowed from me, to form the 9th plate of his treatise of 

 Embryogeny. I cannot think so poorly of M. Coste's pow- 

 ers of comparison, as to suppose he could see a resemblance 

 in ova, the conditions of which are so totally different. 



The commission, M. Coste however adds, will judge if he 

 has been deceived by this comparison. 



If I mistake not there will be one honourable Academician 

 to whom, in conjunction with the immortal Cuvier, science is 

 indebted for many just and excellent observations on the ova 

 of the Mammalia, and who will be peculiarly able to form a 

 true judgment of the comparison suggested by M. Coste. M. 

 Dutrochet will not require to be informed that in the Roden- 

 tia, there is an early and active determination of the blood 

 and organizing forces to the exterior of the ovum, for the pur- 

 pose of developing a large cylindrical placenta, and of pro- 

 ducing an adhesion of the ovum to the parietes of the uterus, 

 by an interlacement of innumerable foetal and maternal capil- 

 laries. While, on the contrary, in the Marsupialia, no pla- 

 centa is developed, and no adhesion, by interlacing capillaries 

 or otherwise, ever takes place, so far as experience has hither- 

 to informed us, between the exterior surface of the ovum and 

 the internal surface of the womb. Now no two conditions of 

 an ovum could be expected to affect more differently the re- 

 lations of the chorion to the umbilical sac and allantois, that 

 are those of the rodent and marsupial. Yet M. Coste asserts 

 that it was his knowledge of the structure of the ovum of the 

 Rodentia which led him to describe inductively the chorionoi 

 the kangaroo. Had he not made this assertion, I should 

 certainly have thought that he had been induced to hazard 

 his brief but comprehensive description of that part, with a 

 view to persuade the Academy that he had dissected an ovum 

 that had never been dissected before. 



I have next to notice the criticisms of M. Coste on my de- 

 scription of the ovum of the kangaroo dissected in 1834; — 



