This second module is very short, only 5 lessons. These lessons didn’t quite fit with the themes of any of the other modules, so I made embryology its own module. I also guessed that this topic would be the one that students and teachers would be most likely to skip if pressed for time. I thought perhaps making it a bonus freebie might encourage it use. I didn’t want to wait and put this topic at the end, as knowing a bit about embryology can enhance our study of tissues and organs. If you are pressed for time and need to skip this unit for now, you can always come back later when you have time.