Fertilization 55 



pavilion of the oviduct involves a period of brief duration, 

 probably varying in different species. Marshall estimates 

 that in the rabbit, the migration of the spermatozoa requires 

 but fifteen minutes to two hours. Copulation occurs eight 

 or more hours prior to ovulation so that the spermatozoa 

 ordinarily arrive at the pavilion of the tube six or more 

 hours prior to ovulation and lie in wait preparatory to im- 

 mediate fertilization. According to clinical observations in 

 cows, ovulation occurs at approximately eight to twelve 

 hours after the cessation of estrum. Ovulation is apparently 

 hastened (and estrum abbreviated) by copulation. The in- 

 fluence of copulation upon ovulation in higher animals ap- 

 pears somewhat analogous to insemination in the frog, 

 where the sexual embrace of the male apparently favors the 

 ovulation. It appears from available data that the sper- 

 matozoa of the bull traverse the twenty to twenty-five or 

 more inches of the genital tube (cervix, uterus, and ovi- 

 ducts) in two or three hours and are present in the pavilion 

 of the oviduct some time prior to ovulation. In this manner 

 the single ovum meets at once many spermatozoa so that 

 its prompt fertilization is luxuriantly provided for. 



9. Fertilization 



Fertilization, fecundation, or conception follows when a 

 healthy female copulates naturally with a healthy male. 

 Since copulation, in those animals in which the sequence is 

 known, precedes ovulation, spermatozoa have already mi- 

 grated through the genital tube and have reached the pa- 

 vilion of the oviduct, where they await the discharge of the 

 ovum. One spermatozoon penetrates each egg and traverses 

 the zona radiata to the nucleus. The nucleus of the sper- 

 matozoon fuses with that of the ovum. A beginning has 

 been made for the development of a new individual. The 

 animal has conceived. 



10. The Migration of the Fertilized Ovum 



After the ovum has been fertilized in the pavilion of the 

 oviduct, it must traverse the length of the tube, reach a 



