Video: Embryotic and fetal development 

Watch the video of embryotic and fetal development and study the following things:

a) How is the egg fertilized (15 seconds into the video)?
b) How does the embryo evolve: 2-cell, 4-cell, etc. (30-55 s)?
c) How is the blastocyst formed (1 min)?
d) How does the third stage, the gastrula, display three layers of different coloured cells? How do they begin to differentiate into tissues and organs?