After a few more divisions, the cells rearrange into a three-layered ball called
a gastrula. The innermost layer of the gastrula is endoderm (literally “inner
skin”), the middle is mesoderm (“middle skin”), and the outermost is ectoderm
(“outer skin”). Each layer is composed of a batch of cells, so from the
gastrula stage onward, what cells turn into depends on which layer they start
out in. In other words, the cells are no longer totipotent; they have specific
functions.
a gastrula. The innermost layer of the gastrula is endoderm (literally “inner
skin”), the middle is mesoderm (“middle skin”), and the outermost is ectoderm
(“outer skin”). Each layer is composed of a batch of cells, so from the
gastrula stage onward, what cells turn into depends on which layer they start
out in. In other words, the cells are no longer totipotent; they have specific
functions.
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