Experimental approaches to developmental biology Search 2. A zygote undergoes cell divisions to become a blastula. The blastula undergoes cell movements to become a gastrula.
Specialized structures develop as the embryo matures.
It's like organization among workers at a factory. If you just throw 1000 workers together at the bread-baking factory, without assigning any specific tasks, little bread will ever get made. To illustrate this I want to describe how some whole embryos receive instructions from their environments, in order to make certain decisions. They received a special signal while embryos that altered the fate of their head tissues. In some species, the gender of the embryo depends on environmental signals.