During fetal development, the entire body derives from three layers, called germ layers, the ectoderm, mesoderm, and endoderm.

胚胎发育过程由三个胚层组成，：外胚层、中胚层与内胚层。

Under the microscope, they form Schiller-Duval bodies which are rings of cells around a central blood vessel.

显微镜下，他们形成Schiller-Duval小体，即恶性内胚层细围血管呈放射状排列。

But that was not true of human hypoblast or extra-embryonic mesenchyme cells, both of which behaved more like monkey cells.

但内胚层或胚外间充质细中人类细为却都更像猴子细。

The layer of cells, the endoderm, is thin, like the ectoderm, allowing nutrients to be directly absorbed into the surrounding cells.

细内胚层很薄，像外胚层一样，可以让营养物质直接被周围细吸收。

The second subtype is a yolk sac tumor, also called an endodermal sinus tumor, and it's made of germ cells that differentiate into yolk sac tissue.

第二种亚型卵黄囊瘤，也称为内胚层窦瘤，由化为卵黄囊生殖细组成。