286 Dr. Barry's Remarks on the Article " Ovum.^ 



ovum of birds, but to the vesicle of 

 Purkinje. The discovery, in 1834, 

 of the germinal vesicle in the mam- 

 miferous ovum, of the existence of 

 which von Baer had no distinct 

 knowledge, induced Valentin and 

 others to maintain that the essential 

 parts of the ovum are the same in 

 the bird and the mammifer. But it 

 may be doubted whether physiolo- 

 gists may not have proceeded further 

 than they were wai-ranted by obser- 

 vation in regarding the vitelline 

 membrane and large corpuscles of 

 the yellow yolk of birds as essentially 

 eoiTcsponding parts with the zona 

 pellucida and the smaller granular 

 yolk of the mammifer." 



" The minutely granular yolk [of 

 the Bird], in which the cicatricula 

 originates, and the germinal vesicle 

 together are the true representatives 

 of the small ovum of the mammifer.'* 

 In conclusion it is remarked : " This 

 substance by itself constitutes the 

 whole yolk of mammalia; but in 

 birds it probably remains as a part, 

 if not the whole, of the proligerous 

 disc (afterwards cicatricula)*." 



ova of the animals just mentioned 

 which corresponds to the ' yelk-ball ' 

 in Mammalia. Is not the * discus 

 vitellinus ' in the ovarian ovum of 

 the Bird the seat of similar divisions? 

 If so, it will perhaps appear that the 

 so-called * yelk-ball ' in the marami- 

 ferous ovum coiTcsponds more par- 

 ticularly to the ' discus vitellinus * 

 (with its germinal vesicle) in the 

 ovum of the Bird .... If the con- 

 tents of the ovarian vesicle of Baer 

 correspond to no more than the 

 * discus vitellinus ' in the ovarian 

 ovum of Birds and other animals, 

 the former will not appear to be 

 relatively so minute as hitherto sup- 

 posed. As to the difference in form 

 of these two objects, perhaps a 

 globular form of the substance com • 

 posing the ' discus vitellinus ' would 

 have been incompatible with its 

 position under the vitellary mem- 

 brane and with the presence around 

 it — in the ovum of the Bird for 

 instance — of a large quantity of true 

 yelk, provided for a future purpose ; 

 while no such provision being re- 

 quired in the ovum of the mammal, 

 the substance corresponding, as I 

 suppose, to the * discus vitellinus ' 

 of other animals fills the vitellary 

 membrane (/), and is therefore glo- 

 bular in formf." 



" In the theoretical deductions '' made from his observations, 

 Prof. Allen Thomson remarks that the German author " has not 

 been equally successful/' The paper of Dr. H. Meckel I have 

 not seen, and became aware of its existence through the article 

 '* Ovum '' published in June of the present year : but, judging 

 from the following, quoted by Prof. A. T. from the said paper, 

 I too am of the opinion that in theoretical deductions its author 



* Article " Ovum," I. c. pp. 76 and 79- 



t Researches in Embryology, Second Series, Phil. Trans. 1839, 



{»p. 369, 370. I added at the same time in a note (p. 370) : " If the ana- 

 ogy in question really exists, the * discus vitellinus ' is obviously a nucleus 

 destined to undergo changes like those occurring in the so-called ' yelk-ball * 

 of the Mammalia. The round white spot called the * cicatricula ' in the 

 Bird's laid egg may possibly con-espond to my layer of ' cells,' plate 6. 

 figs. 1 1 1-1 13, lining the vitellary membrane (/) in the uterine ovum of the 

 IVlammal ; while my * mulberr}'-like object,' in the same figures, may 

 perhaps be represented in the Bird's laid egg by the stmcture which lies 

 under the * cicatricula,' and has been denominated Keimhiigel, cumulus 

 proligerus," &c. 



