Definition of "gastrula" [‖Gas•tru•la]

• An embryo at the stage following the blastula, consisting of a hollow, two-layered sac of ectoderm and endoderm surrounding an archenteron that communicates with the exterior through the blastopore. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The embryo in its period of most active morphogenetic movements is usually called a gastrula, but as all agree this word has no morphologic meaning anymore."
• "The young amphioxus has, at this stage, which is called the gastrula stage, a curious parallelism with such a lowly form as the"
• "This stage is called the gastrula stage; ar. is the cavity of the gastrula, the archenteron; b.p. is its opening or blastopore."