OVULATION AND FERTILISATION. 351 



the buck immediately after giving birth to young ; and at a 

 period, estimated by different observers at from eight to twelve 

 hours after impregnation, the ova are liberated from the ripe 

 follicles. 



At each period of ovulation, from three to nine ova are as a 

 rule discharged from each ovary ; the several ova being set free, 

 not absolutely at the same moment, but within a veiy short 

 time of one another. 



Although ovulation, or the discharge of ova from the ovaries, 

 usually occurs a few hours after impregnation, and is probably 

 stimulated by this, it should be regarded as an essentially inde- 

 pendent act, a point of view that will be more fully considered 

 in the next chapter. 



5. Fertilisation. 



Fertilisation appears to occur in the rabbit, as a rule, from 

 eight to twelve hours after copulation , the interval being due, 

 not to the time taken by the spermatozoa to travel up the uterus 

 and oviduct, for this is effected, according to Hensen, in from a 

 quarter of an hour to two hours ; but to the fact that the dis- 

 charge of ova from the ovary does not take place until eight to 

 twelve hours after copulation. 



The act of fertilisation is effected, as a rule, directly after the 

 eggs enter the oviduct : and, in eggs taken from the upper part 

 of the oviduct, spermatozoa may be seen in considerable numbers 

 imbedded in the zona radiata, or lying in the space between the 

 vitelline membrane and the egg, formed by the shrinking of the 

 latter. 



The details of the process of fertilisation have not been accu- 

 rately determined in the rabbit. Fusion of a spermatozoon with 

 the female pronucleus has been seen by Van Beneden ; and there 

 is no reason for supposing the process to differ from what is 

 known to occur in other animals. 



THE EARLY STAGES OF DEVELOPMENT. 



It will be convenient to deal, in the present section, with the 

 mges undergone by the egg up to the end of the seventh day. 

 Ang the first three days the egg is travelling down the ovi- 

 duct, and passing through the stages of segmentation ; at the end 



