Abdominal Cavity and Uterus. 327 



3. In Mammalia the ovisac does not continue long in 

 the ovary after the expulsion of the fecundated ovum. A 

 few hours after the Rabbit's ovum has been discharged, if 

 lateral pressure be applied, the ovisac escapes from the thick 

 vascular mass which has no connection with it. Of an ovisac 

 thus removed with its large aperture, I gave a drawing.* 

 Soon after, the ovisac is no longer met with in the ovary. 

 There is now seen protruded from the centre of what was 

 formerly the Graafian follicle, a mammillary process, noticed 

 by several observers, very accurately figured by De Graaf, 

 apparently mistaken by Cruikshank for the ovum, and not 

 inappropriately compared to a sort of hernia by Coste. This 

 mammillary process consists solely of an inverted portion 

 of the vascular spongy substance which previously consti- 

 tuted the covering'of the ovisac. In the Rabbit the 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-t For the vesicle described by Dr Pockels as re- 

 maining in the incipient corpus luteum eight days and more 

 after the expulsion of the ovum in the Sheep and Goat, was 

 evidently my ovisac. 



4. The ovisac therefore can take no part in the formation 

 of the corpus luteum. J 



The large and sometimes elliptical aperture in the ovisac, 

 which I figured,§ is obviously for the purpose not only of ad- 

 mitting the fecundating element, but also for the passage 

 through it of the fecundated ovum. (Such an aperture is 

 not required where, as in the case of the wnfecundated ovum, 

 the latter continues in its ovisac — the ovisac escaping with 

 its ovum ; though it is by no means improbable that such 

 an aperture may be intimated even here.) 



We have thus seen a vesicle — my ovisac — to exist in the 

 ovary, — to be unconnected with its vascular covering, — to 

 have a fibrous structure, — and, either with the ovum or after 

 it, to be expelled from the ovary. This is in Mammalia, 



* Phil. Trans. 1839, PL V., fig. 98. t lb., 1839, p. 318. 



I lb., p. 350, § 261. § lb., PI. V., fig. 98. 



