320 DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGV. 



PART II. 



On a granulous Tunic of the Ovum of Mammalia not hitherto described ; on the manner 

 of origin of the " Membrana Granulosa''^ of Authors ; on the different situations of 

 the Ovum in the Graafian Vesicle at certain periods ante coitum, not hitherto ob-' 

 served ; and on certain structures by means of which the Ovum is made to occupy 

 those several situations. 



61. Professor Baer has described and figured the "ovulum" (ovum) of Mammalia 

 as situated in a mass of granules at or near to the periphery of the vesicle of Graaf 

 (Plate VII. fig. 62.), and the following is the substance of the description he has given. 



The "Disc"" ofProfessor Baer. 



62. This accumulation of granules, according to Baer, is not globular but discoid-j-, 

 thicker at the central part J, and surrounding the "ovulum" like the frame of a lens 

 its glass, but probably extended so as completely to inclose the under surface of the 

 "ovulum"'5i in addition to its sides. The lateral portion of this mass of granules 

 Von Baer calls the disc (" discus proligerus")\\, and the central thickened part he 

 calls the "cumulus strati proligeri\\." This description is intended to apply to this 

 part in the Mammalia generally ; but Von Baer describes the form of the " cumulus" 

 as varying in different animals, and in the same animal at different periods, perhaps 

 according to its degree of maturity. Thus it is very inconsiderable in the Dog, re- 

 quiring the greatest attention to discern that the disc is thickened at its middle : and 

 here Von Baer compares the granulous accumulation to a plate used at table, as seen 

 on its lower surface. In the Cow he has seen the " cumulus" cylindrical or globular. 

 This convex middle part is also very considerable in other animals ; in the human 

 female it has the appearance of a depressed hemisphere ; and in the Hog it pre- 

 sented very varied forms ^, the cause of which differences Baer was not able to ex- 

 plain-j-'f-. In the Cow he saw a plane granulous substance, very distinct from the 

 eminence ("cumulus"), extending itself at the surface of the fluid of the Graafian 

 vesicle ; but whether this was situated internal to the cumulus, or formed a part of 

 it destined to be detached, he considered extremely difficult to decideJJ. He adds, 

 " when we examine an ovulum of the Sow or Cow under the microscope, we there 

 see commonly adherent a portion more or less considerable of a flat disc. In the Sow 

 I have seen this little membrane bounded by a circular border ; I believe that 

 I have sometimes obtained it entire. In the Dog the disc is always limited by a 

 circular border, but in this animal the membrana granulosa is too small to admit of 

 being well examined. In the ovary of the human female I think I have distinctly 



t Lettre, &c., p. 15. + L. c, p. 16. § L. c, p. 16. 



II He gives it this name from the supposition of its analogy with the granules surrounding the germinal 

 vesicle of Birds. 



% L. c, p. 16. tt Commentaire, &c., p. 40. ++ Commentaire, &c., p. 40. 



