On the Generations of Animals 729b1
"How is it that the male contributes to generation, and how is the seed from the male a cause of what is produced? Is it by being present within and by being immediately a part of the body that is being produced, mingling with the matter from the female? Or does the body of the seed not participate, but only the capability and movement that is in it? For it is the latter that is the agent, while that which becomes constituted and takes the shape is the remainder of the female residue. This is evident both according to reason and on the facts. For, considering it generally, we do not see on thing being produced out of agent and patient in the sense that the agent is present with the product, nor indeed (to generalize) out of mover and moved. But now the female qua female is the patient, while the male qua male is the agent and is that from which comes the beginning of movement. So that if we take the extremes of each, whereby the one is agent and mover while the other is patient and moved, the one thing being produced is not out of those except in he way that the bed is out of the carpenter and wood or sphere out of the wax and the form. Clearly then it is not necesssary that something should come away from the male; and if something does come away, it does not follow that ht offspring is made out if as out of something present within, but only as out of mover and form, in the way that the cured invalid is the product of the medical art."