174 



PHYSIOLOGY OF FARM ANIMALS 



[CH. 



material. The second division results in the formation of the mature 

 ovum and the second polar body (the latter consisting like the 

 first polar of nuclear material). The two polar bodies are extruded 

 when the ovum is in the tube; sometimes the first polar body 

 divides into two equal halves so that altogether there are three 

 polar bodies; all of these die and disappear, the mature ovum 

 with the reduced number of chromosomes alone remaining. The 

 normal number is restored by the union with a spermatozoon, 

 this process usually occurring in the Fallopian tube. 



v5;?\»cfe«iW#,,.r^«llf 



W t>/ 



.# 



.*C^ 



ID 

 ©PR© ■ 







Fig. 86. Section through edge of mucous membrane of dog during early 

 recuperation (from Marshall), bl. v. blood vessel, ep. epithelium 

 in process of renewal, pig. pigment, pol. polymorph leucocyte. 



During oestrus the mucous membrane of the uterus becomes 

 recuperated and external bleeding from the vaginal opening 

 ceases. 



Oestrus in the ])itch is followed either by pregnancy or by 

 pseudo-pregnancy according to whether or not the ovum or ova 

 become fertilised as a consequence of coitus. Under both con- 

 ditions the uterus undergoes growth changes which relate chiefly 

 to the blood vessels and glands in the mucosa. These increase in 

 size, the whole organ assuming a histological appearance indicative 

 of great activity. The secretion coming from the glands is a 



