The genesis of sperm and eggs, then, must require first halving the number of chromosomes, twenty-three each, and then restoring them back to forty-six upon fertilization. This variant of cell division—reduction, followed by restoration—was observed in sea urchins by Theodor Boveri and Oscar Hertwig in the mid-1870s. In 1883, Belgian zoologist Édouard van Beneden also observed meiosis in worms, confirming the commonality of the process in more complex organisms.
