Fertilization 1 1 5 



very brief period of five to twelve hours. During this interval 

 the cow may copulate but estrum is not well marked. In the 

 bitch the discharge appears during estrum and continues for some 

 days without usually being very profuse. 



Fertilization. 



Fertilization is the successful union of the male generative cell 

 or spermatozoon with the female egg or ovum, by which the re- 

 sulting cell acquires the power of segmentation and is enabled to 

 develop into an embryo. 



According to Marshall and other embryologists, fertilization 

 in the rabbit occurs in from eight to twelve hours after copula- 

 tion. This interval is not due to the time required for the mi- 

 gration of the spermatozoa from the posterior portion of the. 

 genital canal to and through the oviduct, but to the fact that the 

 ova are not discharged from the ovary until eight to twelve hours 

 after copulation. In the rabbit, the spermatozoa are found to 

 travel the length of the uterus and oviducts in from fifteen 

 minutes to two hours and, in the ordinary course of events, are 

 already in the pavillion of the tube, awaiting the discharge of 

 the ova. The doe rabbit copulateg with the buck immediately 

 after giving birth to young, the interval between estrual periods 

 being the same as the duration of pregnancy. 



We are not aware that any exact observations have been made 

 in our larger domestic animals demonstrating the length of time 

 elapsing between copulation and fertilization. In spaying cows, 

 we have regularly observed that one which is in estrum has ripe 

 ovisacs, which generally rupture the moment the ovary is 

 grasped. If the cow has been in estrum on the previous day, 

 we have found the Graafian foUicle freshly ruptured. This 

 would indicate to us that in the cow, as in the rabbit, ovulation 

 occurs late in the estrual period or just at its close so that, under 

 normal conditions, copulation would precede ovulation and hence 

 that, in the cow, as in the rabbit, ovulation and fertihzation 

 occur some hours after the act of coition. In the rabbit, fertili- 

 zation usually takes. place immediately after the eggs enter the 

 oviduct, which is probably the general rule in mammaha. 



If eggs be taken from the upper portion of the oviduct, sperm- 

 atozoa will usually be found imbedded in the zona radiata or 



