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1·Primordial germ cells came from pole cells and moved in two masses to the laterodorsal abdomen of embryo, and then were enveloped by mesoderm to form germinal ridge.

原始生殖细胞来自极细胞，分两团移至胚胎腹部侧背面，被中胚层细胞包裹，形成生殖脊。