这个词是什么意思？
A post-MORULA preimplantation mammalian embryo that develops from a 32-cell stage into a fluid-filled hollow ball of over a hundred cells. A blastocyst has two distinctive tissues. The outer layer of trophoblasts gives rise to extra-embryonic tissues. The inner cell mass gives rise to the embryonic disc and eventual embryo proper.
中文名称索引；定义为 MeSH 英文原文，尚未逐条译审。MESH:D001755 · MeSH 2026。
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