12 slides

1 - Sea urchin, unfertilized eggs
2 - Sea urchin, fertilized eggs
3 - Sea urchin, two cells
4 - Sea urchin, four cells
5 - Sea urchin, eight cells
6 - Sea urchin, sixteen cells
7 - Sea urchin, thirty-two cells
8 - Sea urchin, morula
9 - Sea urchin, blastula
10 - Sea urchin, blastula, beginning gastrulation
11 - Sea urchin, blastula, progressive gastrulation
12 - Sea urchin, pluteus larva