4S Dv Martin Barry's Researches in Embryology. 



followed by the expulsion of the ovisac.* So that in Mammalia 

 the ovisac appears to escape either with the ovum or after it. I 

 This brings me to conclusions, which 1 venture to offer as 

 perhaps sufficient to supply analogies long sought for by 

 Physiologists in vain, viz. : — 



1. That in the Mammalia the vesicle I described as the 

 foundation of the Graafian follicle, and termed the ovisac, 

 does not remain permanently in the ovary, but is expelled 

 and absorbed. if 



2. That in the Bird the ovum, when escaping from the 

 ovary, is accompanied by the corresponding vesicle, — the ovi- 

 sac, and that the ovisac becomes the shell-membrane of the. 

 Bird's egg ; the Bird's " egg," as we call it, being thus a 

 shelled ovisac, and the contained " yelk," as is known, be- 

 ing the true ovum. 



3. That the expelled and lost ovisac in the Mammalia 

 therefore corresponds to the shell-membrane in the Bird. 



4. That after the formation of the ovum, the albuminous 

 contents of the ovisac in the Mammalia correspond to the al- 

 bumen in the Bird's " egg.^ 



5. That my retinacula in the Mammalia after all find their 

 analogue in the chalazse of the Bird ; and that both have their 

 origin in the granular contents of the ovisac, which, at an 

 early period, are in appearance just the same in both. 



6. That the shell-membrane of the Bird's " egg" is thus 

 a primary cell. 



(We next come to the " zona pellucida' 1 in the ovum of 

 Mammalia, known to correspond to the vitellary membrane 



* In the Rabbit this expulsion of the ovisac seems to take place in three or 

 four days after the fecundated ovum has escaped. In the Sheep and Goat not 

 so soon; for it appears to me to have been this vesicle (my ovisac) that l)r 

 Pockels refers to in these animals, as remaining in the incipient corpus luteum 

 eight days and more after the expulsion of the ovum from the ovary. — (Midler's 

 Archiv, 1836, Heft ii., s. 203.) 



t The ovisac escapes freed from its vascular covering; the latter alone enter- 

 ing into the formation of the co?-pus luteum. " Researches in Embryology, 

 Second Series." Phil. Trans, 1830, § 261, Plate 5, fig. 98. 



I And, therefore, as I formerly shewed, can take no part in the formation 

 of the corpus luteum. 



