If you watch carefully you can see the salamander embryo changing shape - becoming a bit more egg-shaped intead of round. And you can also notice, near the end,

If you watch carefully you can see the salamander embryo changing shape - becoming a bit more egg-shaped intead of round. And you can also notice, near the end, the deposit of algae on the side, before they enter the egg. I'm pretty sure that's what it is meant to demonstrate.