So you'd think–no yolk, no yolk sac.

所以你会认为我们不需要卵黄，也不需要卵黄囊。

Humans make an empty yolk sac, and it disappears halfway through pregnancy.

人类在孕期会产生一个空卵黄囊，但是中途就消失了。

Inside a chicken egg, the growing embryo produces something called a yolk sac.

在鸡蛋里面，成长的胚胎产生一种名为卵黄囊的东西。

Each egg contains one embryo and a yolk sac which the embryo feeds off and helps it develop inside the egg.

每枚卵中含有一个胚胎和一个卵黄囊，胚胎从卵黄囊中汲取营养，从而得以在卵中发育。

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.

第二种亚型是卵黄囊瘤，也称为内胚层窦瘤，是由分化为卵黄囊的生殖细胞组成。

The four major types of germ cell tumors are: fetal teratomas, both mature cystic and immature teratomas; yolk sac tumors, or endodermal sinus tumor, choriocarcinoma or placental tissue tumors and finally dysgerminomas or oocyte tumors.

4种卵巢细胞癌如下：畸胎瘤，包括成熟囊性畸胎瘤和未成熟畸胎瘤；卵黄囊瘤，又叫内胚窦瘤；绒毛膜癌，又叫胎盘组织肿瘤；最后是无性细胞瘤，又叫卵母细胞瘤。