to M. Coste' s Memoir. 187 



observations and mistaken analogy which seduced him into 

 the error of supposing the mammiferous chorion to be the ana- 

 logue of the vitelline membrane of the oviparous ovum, are 

 fully appreciated by all of his contemporaries, whose opinions 

 on this subject possess any value in the physiological world. 



With the same taste which pervades the whole of his work 

 on Embryogenie, M. Coste observes, (p. 288), with respect to 

 the chorion, "cette membrane, que, dans ces demiers temps 

 encore un savant tres haut place a ete conduit, nous ne sa- 

 vons trop pour quelle raison, mais sans doute en V absence de 

 toute idee d'analogie, a considerer comme le representant de 

 la coque de l'ceuf des ovipares," &c. In this paragraph M.= 

 Coste spoke more truths than he intended, in confessing his 

 ignorance of the reasons which induced the distinguished sa- 

 van to whom he thus pertly alludes, to regard the mammife- 

 rous chorion as the analogue of the cortical membrane of the 

 ovipara. I shall leave M. Coste in the state of ignorance in 

 which he confesses himself to be on this point, and merely 

 observe that the correctness of the opinion at which he sneers, 

 has been established by the late excellent researches of 

 Krause, (in Midler's 'Archiven'), and of Wharton Jones, (in 

 the Philos. Trans, for 1837). And the Academy will permit 

 me to state that prior to the discoveries of these acute observ- 

 ers, I had shewn the fallacy of M. Coste' s dogma, that the 

 chorion of the mammiferous ovum is the analogue of the vitel- 

 line membrane, by demonstrating the co-existence of the cho- 

 rion and the vitelline membrane in the ovum of the Qrnitho* 

 rhynchus ; Philos. Trans. 1834. With the structure of this 

 ovum, the ova of the Batrachia present a close analogy, being 

 inclosed by both a vitelline membrane and an external gela- 

 tinous chorion : and in the Triton, Mr. Jones has observed, 

 that when the embryo has attained a certain size, but still at 

 an early period, the vitelline membrane is ruptured, and the 

 embryo, with its amnios, and umbilical sac, is then immedi- 

 ately invested by the chorion. It is, I apprehend, in this 

 curious phenomenon of the destruction of the vitelline mem- 

 brane, that we have the key to the true analogies and rela- 

 tions of the mammiferous chorion. 



I pass over other general questions in oology in which M. 

 Coste conceives that I entertain erroneous opinions. My de- 

 fence of these views, like the remarks I have just offered, would 

 demonstrate how much M. Coste has to learn, before he will 

 be able to teach all the known history of any single branch 

 of comparative embryogeny. I beg the Academy to believe 

 that I omit to notice these points only because I am desirous 

 to proceed to the allegations and arguments of M. Coste, 



q3 



