Ovulation 49 



3. Ovulation 



At about the close of estrum, in those animals where the 

 phenomena have been studied, as in the cow, the distended 

 ovisac ruptures and discharges the ovum. Prior to the rup- 

 ture of the ovisac, preparation for the detachment of the 

 ovum from the enveloping and supporting cells of the dis- 

 cus proligerus has been made by the formation of numerous 

 vacuoles in the mound, as shown in Fig. 24. The attachment 

 of the ovum is rendered exceedingly frail, subject to de- 

 tachment upon the slightest disturbance. The ovum is ap- 

 parently maintained in situ chiefly, if not wholly, by the 



Corona vadiata 



Fig. 24— Section of ovary of cow with a nearly ripe ovum in 



an ovisac, 5x7 mm., showing vacuoles in the 



cumulus preparatory to ovulation. 



sustaining pressure of the follicular liquid. When the ovi- 

 sac ruptures, the ovum, the follicular fluid, and some of the 

 granular cells of the discus proligerus in which the ovum 

 was embedded are discharged into the pavilion of the ovi- 

 duct, which is at this epoch erected and closely applied to 

 the ovary at that point where the ovisac is about to rupture. 

 Here, if successful copulation has occurred, spermatozoa are 

 already present, meet the ovum and a single spermatozoon 

 fuses with each, to constitute fertilization. 



The precise period at which ovulation occurs, as related 

 to estrum, has not been determined for all domestic animals. 

 In the rabbit, which has given birth to young, copulation 



