40 Dr Martin Barry's liesearclies in Embryology. 



and the absence of anything like a " zona pellucida," — that 

 made me hesitate to consider the mulberry-like revolving body 

 as the essential part of an ovum ; for, as regarded that mul- 

 berry-like body, I stated the resemblance it bore to an ovum 

 to be perfect. There certainly were not wanting inducements 

 that would have made it very agreeable to one who had shewn 

 ihat cleavage of the yelk takes place in the ovum of the Mam- 

 malia* could he have extended from the ovum of some of the 

 lower animals to that of the highest class, the remarkable 

 phenomenon of rotation also. But I contented myself with 

 the remark : " It remains to be discovered whether the mul- 

 berry-like structure with its germ in the ovum of Mammalia 

 also performs rotatory motions." f 



Among the objections anticipated by Keber as likely to be 

 raised by others against his view, that these vesicles are ova, 

 is the fact that their membrane is fibrous, — a fibrous structure 

 never having been discovered in the " zona pellucida." Now 

 this objection I have just met by my statement that the mem- 

 brane in question is not the " zona pellucida," but the ovisac. 

 For there can be no doubt that a multitude of particles I 

 figured as dividing and subdividing to enter into the formation 

 of the ovisac (before the existence of what could be denomi- 

 nated membrane), and leaving remarkable centres which also 

 I delineated, Were the elements of fibre. \ 



Another objection that might be raised against Keber's 

 view has reference to size ; an objection fully provided for by 

 my idea that the vesicle in question is not the vitellary mem- 

 brane but the ovisac. 



Keber observed, that in the membrane of one of the vesicles 

 containing a revolving body there had been formed an orifice ; 

 and this by an arrangement of the fibres too regular to admit 

 of the supposition that the orifice was accidental. This ori- 

 fice I believe to exist before the expulsion of the ovum from 

 the ovary ; an opinion founded on the following observation 



* Phil. Trans. 1839, Plate 6. f Phil. Trans. 1839, p. 357. 



X See especially in the Phil. Trans, for 1841, Plate 25, figs. 164 to 173. 

 And see a paper of mine in this Journal for October 1853, " On Animal and 

 Vegetable Fibre." 



