The blastopore is found in which of the following developmental stages?

Which of the following embryos exhibits a parasitic mode of nutrition?

Which part of the ovary acts as an endocrine gland after ovulation?

Ovulation does not occur during pregnancy in the human female because

$A$: If fertilization occurs,the corpus luteum is rescued from regression by human chorionic gonadotropin $(hCG)$,which is produced by the placenta.
$R$: In the first trimester,the corpus luteum,stimulated by $hCG$,is responsible for the production of progesterone.

The lens of the eye is derived from which germ layer?