138 Dr Barry's Researches in Embryology. 



exceeds the number of those which actually discharge them. 

 Ova of the rabbit, which are destined to be developed, are, 

 in most instances, discharged from the ovary in the course of 

 nine or ten hours post coitum; and they are all discharged 

 about the same time. 



There is no condition of the ovum uniform in all respects 

 which can be pointed out as the particular state in which it is 

 discharged from the ovary ; but its condition is in several re- 

 spects very different from that of the mature ovum ante coitum. 

 Among the changes occuiTing in the ovum before it leaves the 

 ovary, are the following, viz. the germinal spot, previously on the 

 inner surface, passes to the centre of the germinal vesicle ; the 

 germinal vesicle, previously at the surface, returns to the centre 

 of the yolk ; and the membrane investing the yelk, previously 

 extremely thin, suddenly thickens. Such changes render it 

 highly probable that the ovary is the usual seat of impregna- 

 tion. The author considers this view as being not incom- 

 patible with the doctrine that contact between the seminal 

 fluid and the ovum is essential to impregnation, since he has 

 found, in the course of his researches, that spermatozoa pene- 

 trate as far as to the surface of the ovary. The retinacula 

 and tunica granulosa are the parts acted upon by the vis a 

 tergo, which expels the ovum from the ovary. These parts 

 are discharged with the ovum, render its escape gradual, pro- 

 bably facilitate its passage into the Fallopian tube, and appear 

 to be the bearers of fluid for the immediate imbibition of the 

 ovum. After the discharge of the ovum from the ovary, the 

 ovisac is obtainable free from the vascular covering, which, 

 together with the ovisac, had constituted the Graafian vesicle. 

 It is the vascular covering of the ovisac which becomes the 

 corpus luteum. Many ova, both mature and immature, dis- 

 appear at this time by absorption. In some animals minute 

 ovisacs are found in the infundibulum, the dischai'ge of which 

 from the ovary appears referable to the rupture of large Graa- 

 fian vesicles, in the parietes or neighbom'hood of which those 

 ovisacs had been situated. 



The diameter of the rabbit's ovum, when it leaves the ovary, 

 does not generally exceed the 135th part of an inch, and in 

 some instances it is still smaller. The ovmn enters the uterus 



