DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 315 



siderable this portion of the calyx may appear, yet for the sake of analogy the distinc- 

 tion is not unworthy of being made-f*. 



The proper Membrane of the Velk in Mammals. 



49. Several distinguished authors have not described this membrane J. And in 

 fact it is not easy to demonstrate the separate existence of such a membrane in the 

 class Mammalia generally, at those periods in the formation of the ovum when the 

 latter is usually examined. On the other hand, a very accurate observer, Krause, 

 has figured it in the Goat§, and appears to have often seen it in other Mammals. 

 My friend Professor Rudolph Wagner pointed it out to me in the Cat; and he seems 

 convinced from analogy that its existence must be general in the class Mammalia, 

 but does not appear to have discerned it in any other instance ||. I have since met 

 with and figured it in early stages of the ovum of the same animal (the Cat), and I 

 believe also in the Hog (Plate V. figs. 1/. and 16. e. ; Plate VIII. fig. 70. e.). In later 

 stages, ante coitum, I have sought this membrane in vain as a distinct structure*[[ ; but 

 I think it not improbable that the well-marked line generally regarded as representing 

 the internal surface of the thick chorion, may be partly due to the proper membrane 

 of the yelk, as is obviously the case in Plate V. fig. 17- e. andy. 



50. It appears to me that the existence of a proper membrane of the yelk in the 

 ovary throughout the class Mammalia, may be inferred from what we know of the 

 effect observed to be produced on ova by maceration ; when the thick chorion, im- 

 bibing fluid into its interior, becomes distended beyond the size of the yelk-ball, but 

 the latter retains its form, which certainly would not be the case were not the yelk 

 circumscribed by a proper membrane (Plate VIII. fig. 72./*. and d.W). 



51.1 have observed a very interesting fact connected with the proper membrane 

 of the yelk post coitum not hitherto made known, which not only adds probability 

 to the supposition that this membrane has a previous existence, but also accords in 

 some degree with a change known to take place in Birds. I find that in the Rabbit, 



t ProfessorR.WAGNERinhisexaminationof ova of the Frog, finding his "chorion" (ovisac) to disappear, makes 

 the following inquiry : " 1st sie nun mit der Dotterhaut verschmolzen oder hat sie, was wahrscheinlicher ist, 

 sich an die gefassreiche Kelch-membran angelegt und bildet sie nur die innere Lamelle derselben?" (Beitrage, 

 &c., S. 76.) This inquiry, made by one of the most accurate of observers, bespeaks, I think, the perception, 

 in a single instance, of something that was very near the truth. 



X Among these are Coste (Embryogenie Compar^e, p. 80.) andT. W. Jones (London and Edinburgh Phil, 

 Mag., No. 39, Sept. 1835, p. 210.). 



§ MiJLLER's Archiv, 1837, Heft I. Taf. I. figs. 4, 5, 6. 



II Beitrage, &c., S. 20. 



% Since the above was written, an examination of the ovum of the Goat enables me to attest the accuracy 

 of Professor Krause in his representation of the membrana viteUi in this animal, in which it is exceedingly 

 distinct. I did not however, in any instance find the membrana vitelli surrounded by a fluid as described by 

 Krause (53. Note), but by the perfectly formed and consistent chorion. 



ft I borrow this figure from the excellent Thesis of Bernhardt (Symbolse, &c., fig. xxiii, p. 45.), but am 

 compelled to offer an explanation of several of its parts different from that given by the author. This is de- 

 ferred, however, until after the description of the chorion (56. Note). See also the Description of the Plates. 



2 s 2 



