yolk blastopore

例句：

1. 1. The embryonic stage of the chicken is characterized by the presence of a yolk sac.
   鸡的胚胎阶段特征是存在一个卵黄囊。
2. 2.During the development of the fetus, the yolk sac gradually shrinks and eventually disappears.
   在胎儿发育过程中，卵黄囊逐渐缩小并最终消失。
3. 3.In some species, the yolk sac continues to function as an organ until the chick hatches.
   在某些物种中，卵黄囊继续作为一个器官直到小鸡孵化。