n. - In embryonic development, a vesicle filled with fluid,
formed from the morula by the divergence of its cells in such a manner
as to give rise to a central space, around which the cells arrange
themselves as an envelope; an embryonic form intermediate between the
morula and gastrula. Sometimes used as synonymous with gastrula.
n. - The very young, free-swimming larva of the coelenterates.
It usually has a flattened oval or oblong form, and is entirely covered
with cilia.