Dr Martin Barry's Researches in Embryology. 41 



spot nor the spermatozoon really disappears, •* but that both 

 enter into the formation of the nuclei of the new organism."* 

 And he finally says : " Through observation alone can it be 

 decided, whether the nuclei arising out of the spermatozoon 

 and the germinal spot unite to pass into the embryonic cells." \ 

 That such union is what takes place in the mammiferous 

 ovum I think was shewn by my own observations in 1840, 

 when it was recorded that, before the cleavage of the yelk 

 begins, the hyaline centre of the germinal spot is determin- 

 ately held by the retinacula, up to a certain time, as near as 

 possible to the surface of the ovary ; that an orifice is formed 

 in the " zona pellucida," at the part where this centre lies ; 

 that on one or two occasions I saw this centre of the germi- 

 nal spot, apparently without any covering from the germinal 

 vesicle,^ actually protruded into the orifice in the " zona 

 pellucida," as if to meet the fecundating element ; and that 

 subsequently the germinal spot passes to the centre of the 

 germinal vesicle, and the germinal vesicle to the centre of 

 the ovum. I added, that the germinal vesicle, which by de- 

 terminate pressure at the periphery became lenticular, now 

 resumes the spherical form, and that an orifice in the " zona 

 pellucida" is no longer seen. Such alterations suggest the 

 probability of some sudden and important change having been 

 effected in the condition of the ovum. The nature of the al- 

 terations is such as to induce the belief, that the ovum has 

 undergone fecundation ; the mysterious hyaline centre or nu- 

 cleolus of the germinal spot having received the fecundating 

 element of the seminal fluid, and having thus been the point 

 of fecundation. And farther, from an observation I published 

 at the same time, it is to be inferred that the fecundating 

 element is the pellucid substance (nucleolus) contained in the 

 head-like extremity of the spermatozoon, a direct union taking 

 place in the mammiferous ovum between this substance and 

 the hyaline nucleolus of the germinal spot. I have already 

 stated why I think such direct union between the spermato- 



* Keber, loc. cit., p. 56. f Keber, loc. cit., p. 111. 



J I have since recorded the fact, that an orifice is sometimes seen at the cor- 

 responding part in other cells. Phil. Trans. 1841, Part ii., p. 204, Plates 17 to 

 19. 



