> [Freud] had to return to check his results later in the year, he chanced upon a pair of furrowed organs, hidden away in the abdominal cavity, which he identified as the much-sought-after testes of a male. With the two sexes now clearly distinguished, definitive evidence of sexual reproduction had been found; and, after more than 2,000 years, Aristotle’s theory of spontaneous generation could at last be laid to rest.