DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGV. 321 



seen the membrana granulosa to pass above the discus proligerus. On the immature 

 ovulum [ovum] of the Cow, on the contrary, I have recognised no more than a conti- 

 nuous lamina, which I consider as the membrana granulosa. From all that has been 

 said, I think I may conclude that the ovula [ova] of the Mammalia, those at least 

 which are approaching maturity, are plunged into a couch, formed of a thick emi- 

 nence, the cumulus, and of a flat disc, and that the latter may or may not be primi- 

 tively isolated from the membrana granulosa; development predominating some- 

 times on the part of the disc, sometimes on the part of the cumulus, examples of 

 which are offered (respectively) by the Bitoli and Cow-j~." See Plate VII. fig. 62. and 

 Plate VIII. fig. 80.J. 



63. This description appears to be accurate in a few particulars, but for the most 

 part it does not accord with my observations. I have naturally felt some hesitation 

 in stating this, not only from its being opposed to the opinion of so experienced and, 

 generally speaking, so accurate an observer, but because those who have succeeded 

 Baer in these researches appear to have adopted entirety his description of this struc- 

 ture. In now offering a different account of it, I would express my belief that should 

 this prove more accurate, it will have been rather due to my examination of the ovum 

 when situated in the centre (as well as near the surface) of the Graafian vesicle, than 

 to imperfect observation on the part of those eminent observers. But I must first 

 describe a structure which, to my surprise, has not been hitherto observed, though 

 visible in those situations in which the ovum has been usually examined. 



The Tunica granulosa. 



64. On the rupture of a Graafian vesicle under the compressor, the ovum escapes, 

 and with it a mass of the peculiar granules I have at some length described (8.). 

 This mass of granules, as hitherto obtained, has presented the appearance of a lace- 

 rated structure, and been regarded simply as a portion of the "disc" of Baer§. I 

 find, however, that if the mass thus escaping be attentively examined, those granules 

 that immediately surround the ovum appear to be in a state of denser aggregation 

 than the rest, from which they are to be distinguished therefore by a circumscribing 

 line. If the granules thus circumscribed be viewed at different distances, they are 

 seen to invest the whole surface of the ovum, forming a tunic, which is perfectly 

 spherical in form (Plate VI. figs. 42. to A7.g^.). I have frequently obtained the ovum 

 invested by no other granules than those of this tunic ; that is, this tunic has been 

 freed from the other granules, which on the bursting of a Graafian vesicle generally 

 escape adherent to it ; the fact being, that all that properly belongs to the ovum of 

 the mass of granules in which it is found imbedded in the Graafian vesicle is this 



t Coramentaire, &c., p. 40. 



X Lettre, &c., figs. ix. and xii. of Baer. These figures I have introduced for the purpose of contrasting 

 them with my own drawings. , 



§ This lacerated structure is the " zona granulosa" of Bernhardt, Symbolae, &c., figs. i. vii. xviii. xxi. xxiii. 

 See also (in the present memoir) Plate VIII. fig. 72. gK, which is taken from that author. 



MDCCCXXXVIII. 2 T 



