1. Male and Female adult animals make haploid gametes by meiosis. 2. An egg and a sperm fuse, producing a zygote. 3. This zygote divides by mitosis, forming a blastula (an early embryonic stage, which is a hollow ball of cells). 5. One side of the blastula folds inward, forming a stage called gastrula. 6. The internal sac formed by gastrulation becomes the digestive tract, lined by a cell layer called the endoderm, ectoderm, and mesoderm. 7. After the gastrula stage, many animals develop into adults but some animals (like the sea star) develop into a larva. 8. Then metamorphis