Morula develops in the upper section of the oviduct, known as the isthmus.
A diploid zygote is formed when the haploid nuclei of the sperm and the ovum fuse together.
By mitotic division known as cleavage, the zygote divides rapidly as it passes across the isthmus of the oviduct, producing 2,4,8,16 daughter cells known as blastomeres.