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.

原肠胚形成过程中，由上胚层细胞增殖产生的一部分细胞在上、下胚层之间形成的第三层细胞。通常形成骨骼、肌肉、结缔组织、心脏、造血系统、肾脏和其它器官。

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However, if germ free animals were colonized early in life, these effects could be reversed.

FORBES: Thinking With Your Gut. Literally.

But the cells from the first divisions retain the ability to form entire new embryos themselves. (This is how identical twins form.) Germ-line manipulation would require taking some of these early-embryonic cells apart in order to discover what the genetic lottery had delivered to them (a process that would destroy the cells in question).

ECONOMIST: A survey of the human genome