01 n. A primeval larval form; a double-walled sac from which, according to the hypothesis of Haeckel, man and all other animals, that in the firs…
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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 Gastræa theory of Haeckel. See Gastrula.(Biol.) See: Gastrula