from
The Collaborative International Dictionary of English v.0.48
Metazoa \Met`a*zo"a\, n. pl. [NL., fr. Gr. ? after + zo^,on an
animal.] (Zool.)
Those animals in which the protoplasmic mass, constituting
the egg, is converted into a multitude of cells, which are
metamorphosed into the tissues of the body. A central cavity
is commonly developed, and the cells around it are at first
arranged in two layers, -- the ectoderm and endoderm. The
group comprises nearly all animals except the Protozoa.
[1913 Webster]