282 Veterinary Obstetrics 



va.z.Y have travelled some distance along the oviduct toward the 

 uterus. 



In the typical fertilization of the ovum in tTie rabbit, where 

 the spermatozoa have already reached the anterior end of the 

 oviduct when the Graafian follicle ruptures, the ovum undergoes 

 segmentation or division during its passage toward the uterus. 

 According to Van Beneden, the segmentation of the ovum begins 

 ID or 12 hours after fertilization or 18-24 hours after copulation 

 and continues for the next two days or until about the end of 

 the third day, at which time the ovum reaches the uterus and 

 its segmentation has been completed. At this time it is about 

 the same size as the original ovum or possibly somewhat smaller, 

 but has acquired, during its passage through the oviduct, a layer 

 of albumen on its exterior, which increases the total size very 

 considerably. 



Fig. 22. A rabit's ovum from the middle of the length of the oviduct, 

 about 22 hours after copulation, showing division of the ovum into two 

 cells. X 200. Marshall after Bischoff. 



CB, Blastomere, or segmentation cell, MO, Spermatozoon imbedded in the 

 zona radiata. N, Nucleus. Z, Zona radiata. 



The length of the time required for the passage of the ovum 

 from the ovary to the uterus has not been determined for most 

 animals, but, reasoning from other data in embryology, it 

 would appear possible that, in the larger animals, it may require 

 a longer period of time for travelling through the tube than in 

 small ones like the rabbit. If we are to judge of the time re- 

 quired for the passage of the ovum through the oviduct by the 

 appearance of estrum and menstruation, we would be led to assume 

 that, in the cow, it is quite as rapid as in the rabbit. Some 



