Identify $X$ from the figure.

In mammals,eggs are microlecithal and isolecithal because these are

Which of the following is $NOT$ a secondary sexual characteristic in females?

Which of the following statements are correct regarding the female reproductive cycle?
$A$. In non-primate mammals,cyclical changes during reproduction are called the oestrus cycle.
$B$. The first menstrual cycle begins at puberty and is called menopause.
$C$. Lack of menstruation may be indicative of pregnancy.
$D$. Cyclic menstruation extends between menarche and menopause.
Choose the most appropriate answer from the options given below.

Give differences between:
$(A)$ Spermatogenesis and Oogenesis
$(B)$ Embryo development and Foetus development

Which two events in the life cycle maintain the same (constant) number of chromosomes?