In 1784, Spallanzani established the need of interaction between the female's ovum and male's sperm to form a zygote in frogs. In 1827, Karl Ernst von Baer observed a therian mammalian egg for the first time. Oscar Hertwig (1876), in Germany, described the fusion of nuclei of spermatozoa and of ova from sea urchin.
In 1784, Spallanzani established the need of interaction between the female's ovum and male's sperm to form a zygote in frogs. In 1827, Karl Ernst von Baer observed a therian mammalian egg for the first time. Oscar Hertwig (1876), in Germany, described the fu.sion of nuclei of spermatozoa and of ova from sea urchin