Gastraa
Gastraa , noun
[New Latin, from Greek {not transcribed}, {not transcribed}, the stomach.]
(Biology) 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 Gastraa theory of Haeckel. See Gastrula.
Also: Gastraea