He discovered fertilization of sea urchins , he recognized the role of the cell nucleus during inheritance and chromosome reduction during meiosis . In 1876 , he found that fertilization includes the penetration of a spermatozoon into an egg cell . He discovered fertilization of sea urchins , he recognized the role of the cell nucleus during inheritance and chromosome reduction during meiosis : in 1876 , he found that fertilization includes the penetration of a spermatozoon into an egg cell .