DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 317 



The foregoing Table shows that in the ovary of Mammalia, the chorion is super- 

 added; and as I shall demonstrate in a future communication (what others, and 

 particularly Coste and R. Wagner, have conjectured) that this membrane is really 

 the chorion of ova met with in the uterus -(-, it may be said that not merely a yelk- 

 ball, but an ovum is expelled from the ovary of Mammals J. 



53. The chorion, as it exists in the ovary, is soft, very thick, and remarkably trans- 

 parent. It closely invests the membrana vitelli, so as in nearly all instances to con- 

 ceal the separate existence of this very delicate membrane (49.). When first formed, 

 the inner portion of the substance of the chorion is probably in a fluid state, as is evi- 

 dent from Plate VIII. fig. 70./., in which instance slight pressure at one side forced 

 a part of the substance of this membrane to the side opposite §. (In this figure the 

 inner circle (e) is probably the proper membrane of the yelk (49.).) Subsequently 

 the chorion acquires more consistence ; for if it be ruptured no collapse takes place 

 even after the escape of its contents, and the membrane continues throughout of 

 equal and undiminished thickness ||. I find^ as already said (51.), that just before the 

 ovum leaves the ovary this membrane begins to be attenuated by imbibition of fluid 

 into its interior, and consequent distention. This imbibition of fluid and distention 

 may be produced by maceration (Plate VIII. fig. 72.). 



54. The great thickness and transparency of the chorion, as it exists in the ovary, 

 long prevented its real nature from being ascertained, and appear to have been the 

 means of misleading several excellent observers. 



55. Von Baer, for instance, after describing the yelk as " une sphere creuse a paroi 

 epaisse," says it is separated " par un intervalle transparent d'une autre sphere creuse 

 a paroi mince^." The "intervalle transparent" of Professor Baer is obviously the 

 transparent substance of the chorion, and his " paroi mince" the external surface of 

 this thick membrane. It appears to have been this supposed "paroi mince" that Baer 

 considered as subsequently forming the "membrane corticale" of ova in the uterus. 



t The membrane here denominated the true chorion is considered by Coste as the " membrane vitelline" 

 (Embryogenie Comparee, p. 80.)- This author, however, as above said, is correct in supposing this membrane 

 to become the chorion in the uterus. 



I On the other hand, there is a structure formed in the ovary of Birds, and some other Vertebrata, which 

 (though it has been described) I do not find existing ante coitum, in the ovary of Mammals. This is the in- 

 cipient " germinal membrane" (" blastoderma"), to be considered in a future paper. 



§ Professor Krause supposes the membrana vitelli to be surrounded by a pellucid fluid, which is circum- 

 scribed by an extremely delicate membrane (Muller's Archiv, 1837, Heft I. S. 27, 28; see also the descrip- 

 tion of these parts in Krause's admirable work, " Handbuch der menschlichen Anatomic, Band i. S. 557, 558."). 

 The Professor's description I find very accurate, as applied to the chorion in an early state ; such, for instance, 

 as that which I have figured in Plate VIII. fig. 70, above referred to ; or possibly it may be applicable to the 

 permanent condition of this membrane in certain animals. I have never met with this state, however, except 

 in ova newly formed. 



II Bernhardt has thus demonstrated the nature of this membrane (Symbolse, &c. fig. xx.) ; and a figure by 

 R. Wagner (Beitrage, &c.. Tab. i. fig. 2.) shows it in a manner still more satisfactory. 



^ Commentaire, pp. 39, 40. 



