Between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus.
Entre 1876 e 1878 Oscar Hertwig publicou varios estudos sobre a fecundación de ovos de ourizo de mar, mostrando que o núcleo do espermatozoide entraba no oocito fusionándose co seu núcleo.