History of Monsters | Ulisse Aldrovandi, Page 32
...just as a plant combined from an olive tree and a grapevine, which would produce both wine and oil, does not exist; similarly, an animal integrated from a human and a bull is not found. This opinion is bolstered by another assertion from the same Philosopher, for in his *History of Animals* he taught that animals of different species do not produce offspring when they mate unless their gestation periods are the same and their body sizes do not differ significantly.
Galen also demonstrates with strong arguments that the procreation of Centaurs is absurd; he believes that the substances of a human and a horse can in no way be mixed. Justinian holds this same opinion