The goat embryo re-acted the process of the system evolution, which passed through pronephros, mesonephros and metanephros.
山羊胚胎重新反应了系统进化的过程，该过程通过前肾，中肾和后肾。
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The idea here is that - while Earth formed slowly from planetary embryos colliding - Mars is itself a solitary planetary embryo that formed very early in the history of our solar system.
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.