(i) When implantation has occurred in uterus of mother, the inner lining of the uterus thickens and is richly supplied with the blood vessels to provide nourishment to the growing embryo.
(ii) If the egg is not fertilised, it lives for one day. Since, the thickened uterus lining is no more required, it slowly breaks down and comes out of the vagina as blood and mucous known as menstruation which lasts for about two to eight days.
