(i) When implantation has occurred in ** of mother, the inner lining of the ** 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 ** lining is no more required, it slowly breaks down and comes out of the ** as blood and mucous known as menstruation which lasts for about two to eight days.
