germ-layer

基本解释

Mesoderm --- The middle germ layer in the early embryo; the source of cells that go on to make bones, muscles, connective tissue, heart, hematopoietic system, kidney, and other organs.
原腸胚形成過程中，由上胚層細胞增殖産生的一部分細胞在上、下胚層之間形成的第三層細胞。通常形成骨骼、肌肉、結締組織、心髒、造血系統、腎髒和其它器官。
Germ layer --- One of three distinct layers of cells that arise in the inner cell mass, the ectoderm, mesoderm, and endoderm, each of which develops into a distinctly different tissue in the embryo.
胚胎發育到原腸胚時的細胞層，分爲內胚層、中胚層、外胚層，各胚層將發育成一定的組織器官。

any of the three layers of cells formed during gastrulation &rarrsee ectoderm , mesoderm , endoderm