marginal ring depression 边缘环形坳陷
Proliferation of cells in a ring around the feather germ creates a cylindrical depression, the follicle, at its base.
环绕羽芽有一圈细胞不断增生，在基部形成圆柱状凹陷，称为毛囊。
The scientists determined that the depression was a volcanic vent, and the bright ring around it was pyroclastic, remnants of lava that had been spewed outward, much like a volcanic fountain on Earth.
科学家确定凹陷处是一个火山口，并且在它附近明亮的圆环是火山碎屑岩，是火山喷发出岩浆的残余，很象地球上的火山喷口。
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