Gas*trae"a (?), n. [NL., from Gr. , , the stomach.] Biol.
A primeval larval form; a double-walled sac from which, according to the hypothesis of Haeckel, man and all other animals, that in the first stages of their individual evolution pass through a two-layered structural stage, or gastrula form, must have descended. This idea constitutes the Gastraea theory of Haeckel. See Gastrula.
© Webster 1913.