Chapter 3, Lesson 3 is composed of three videos.

PART 1

PART 2.1

PART 2.2  

This is the movie shown in Part 1, Slide 8:

This movie is taken from Swinstead et al., 2016, Cell 165, 1–13, April 21, 2016 

http://dx.doi.org/10.1016/j.cell.2016.02.067