XIIl] 



FEMALE GENERATIVE ORGANS 



173 



the uterus for the reception of a fertilised ovum, for at this 

 period the superficial tissues of the mucous membrane undergo a 

 process of partial renewal. The prooestrum corresponds to men- 

 struation in women, but its manifestations are less pronounced. 

 Oestrus is the period of desire and sexual intercourse is 

 ordinarily restricted to this jDeriod. In the bitch it lasts for about 

 a week. OYiilation or the rujDture of the Graafian follicles and 

 the discharge of the ova occurs during this period. The final 

 maturation of the ova commences just prior to ovulation and is 

 completed in the Fallopian tube. The process is similar to that 



pol. 



ex. b. 



Fig. 85. Section througli prooestrous uterine mucous membrane of dog showing 

 extravasated blood (ex. b.), pol. polymorph leucocyte, sec. cells showing 

 secretory activity (from Marshall). 



\\hich occurs in spermatogenesis (see p. 153) and results in the 

 nuclear material of the mature ovum being reduced to one half 

 of what it was previously, that is to say, the number of chromo- 

 somes is one half that of the normal number which is character- 

 istic of the cells of the body for the species in question (in the 

 horse 26, and in man 24). 



The maturation of the ovum differs from the corresponding 

 process in the spermatozoon in the unequal division of the cell. In 

 the first division (which is the reduction division, the chromosomes 

 not splitting longitudinally as they do in all other cell divisions) 

 the first jjolar body is extruded. This consists of half the nuclear 



