Menstrual Cycles

(i) It occurs in primates (monkeys, apes and human beings) only.

(ii) This cycle consists of menstrual phase, proliferative phase and the secretory phase.

(iii) Blood flows in this cycle.

(iv) The broken endometrium is passed out during menstruation.

(v) Sex urge is not increased during menstruation.

(vi) Female does not permit copulation during menstrual phase of the cycle.

Oestrus Cycles

(i) It occurs in non-primates such as cows, sheep, rats, deer, dogs, tiger, etc.

(ii) It consists of a short period of oestrus or heat.

(iii) Blood does not flow in this cycle.

(iv) The broken endometrium is reabsorbed.

(v) Sex urge is increased during oestrus period.

(vi) Female permits copulation only during oestrus period.