Usually, only one sperm into the egg to complete fertilization, said such as Qiangchangdongwu, echinoderms, part animal, the hard bone fish, amphibians and no tail mammals.

• 通常，只有一个精子进入卵内完成受精，称单精受精，如腔肠动物、棘皮动物、环节动物、硬骨鱼、无尾两栖类和哺乳类动物。