those lines represent sites where cells are migrating in and out
and here's an important stage when the three beginning layers of the embryo the
so-called germ layers are formed and i'll come back to that in a few minutes
as development recedes there's more growth and movement themselves
it'll begin the foreman girl too
he returns and appendages start to butt out
you see the head forming in the eye
and then eventually we get a small embryo and some months later of course
this will be born