48 THE EGGS OF MAMMALS 



body is given off and the second polar spindle formed at or 

 shortly after 8 hours post coitum (Figure 18). The follicle 

 enlarges during this period also, the first signs of follicular 

 development being evident at two hours after copulation. 

 An exactly similar sequence of events occurs when prolan 

 (pregnancy urine extract) or anterior pituitary extracts are 

 injected. 





-# 



^mf9 ^^^ 



Fig. 17. Ovum from follicle of ral)l)it don taken 4 hours after copulation. 

 Formation of metaphase plate and dissolution of nuclear membrane. (From 

 the Journal of Experimental Medicine.) 



It has been definitely established that prolan and anterior 

 pituitary hormones cause ovulation when injected into the 

 rabbit (Bellerby, 1929; Friedman, 1929). The ovulation 

 occurring after copulation occurs because of the increased 

 level of pituitary hormones secreted into the blood. This 

 level is increased by nervous stimulation of the pituitary 

 consequent on the orgasm. It has been shown by Deansley, 

 Fee and Parkes (1930) that hypophysectomy within one 

 hour of copulation prevents ovulation in the rabbit (see also 

 Smith and White, 1931), and McPhail fl933) has demon- 



