The amnion and chorion consist of which type of composition?

Which one of the following is derived from the ectoderm?

Identify the structure shown in the process of human embryonic development.

The diagram shows one of the human embryonic developmental stages. What do $A$ and $B$ indicate?

The first sign of the growing foetus may be noticed by listening to the heart sound carefully through the stethoscope. The embryo's heart is formed . . . . . . .

If after ovulation no pregnancy results,the corpus luteum