31 '2 DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 



The Ovisac of Birds ('^ Chorion' of Authors) compared with the Ovisac of Mammals. 



27. The ovarian calyx of the Bird, if deprived of its peritoneal investment, and 

 what there is of the parenchyma'}^ of the ovary, would, I apprehend, present a structure 

 analogous to the Graafian vesicle of Mammals, that is, a structure consisting of an 

 ovisac that has acquired a proper (and in the later stages a highly vascular) covering. 

 Yet the ovisac of Birds has been mistaken for a vesicle corresponding to the chorion 

 of Mammals, and accordingly it has been called the "chorion." The impropriety of 

 this designation will appear evident if the vesicle in question be followed through its 

 several stages of formation, which I do not find to have been hitherto attempted. 

 For this purpose I need not do more than refer to the several figures. 



28. Plate V. fig. 22. Ovisacs of the Pigeon, ^"' to-^jV'"- Germinal vesicle (c) in the 

 centre, surrounded by oil-like globules (*), the incipient yelk. Compare with fig. 15. 

 from the Hog. 



29. Plate V. fig. 23. Ovisac of the Common Fowl,vVWith similar contents. Com- 

 pare with fig. 15. from the Hog. 



30. Plate V. fig. 24. Ovisac of the common Fowl, Vr'"- Yelk {d) just formed, but 

 the membrana vitelli not yet visible. 



31. Plate V. fig. 25, Ovisac of the common Fowl, -v'". Membrana vitelli (e) now 

 seen. Compare with fig. 16. from the Hog. 



32. Plate V. fig. 26. Ovisac of the common Fowl in a stage much more advanced ; 

 g, peculiar granules (8.). The yelk {d) has become in some degree opake. The 

 ovisac has now a proper covering or tunic, and presents by this addition a structure 

 (capsule) (A i) analogous to the Graafian vesicle of Mammals. The quantity of yelk in 

 Birds is very large ; hence that portion of the ovary which contains the structure now 

 descril)ed (as analogous to the Graafian vesicle of Mammals) becomes pendent, and 

 now the united coverings of the yelk-ball, viz. the ovisac, its proper tunic, the paren- 

 chyma of the ovary, and the peritoneal investment, are together called the calyx, which 

 is connected with the ovary by a pedicle;}:. 



33. Plate VIII. fig. 76. Ovisac of the Pigeon, with its vascular covering or tunic. 

 The yelk has escaped, and large granules, essentially the same as those in the ovisac 

 of Mammalia (8.), are seen slowly passing out. 



t This term is here intended to include the " capsula propria" of authors, for the same reason as that which 

 influenced Baer in declining to admit any distinction, except a difference in density, between his stroma and 

 the so-called " tunica albuginea" in the ovary of Mammals. 



X When a minute incipient capsule is crushed under the microscope, the yelk is observed to escape into the 

 pedicle. If the ideal section (Plate VI. fig. 38^.) be referred to, it will be seen that the yelk, in taking this 

 direction, ruptures the parietes of its containing cavity at a point where it meets with the least resistance. It 

 ruptures, not the whole thickness of the capsule, but its internal membrane only, formerly the ovisac. (In this 

 instance (Plate V. fig, 26.) the yelk is seen to have subsequently ruptured also the pedicle itself, and appears 

 escaping through the opening.) 



