Whether wind eggs are generated from a superfluity of sperm.
Further one inquires whether wind eggs are generated from a superfluity of sperm.
1. And it seems so. In every work of nature there is something superfluous. But an animal's generation is a work of nature. Therefore, something superfluous remains behind. But nature is not lazy and it therefore can create something from this superfluity. It can generate some kind of egg from what is left behind after the generation of true eggs, but this is only a wind egg. Therefore, etc.
2. In addition, that superfluity (that is, the residue from generation) is more digested than is the residue remaining from nourishment. But an egg can be formed from that. Therefore, one can be formed even more readily from the residue remaining from generation. But the one generated from this residue is not a true egg. Therefore, a wind egg is generated from the residual sperm after the generation of a true egg.
The Philosopher says the opposite.
One must reply that wind eggs are not generated from residual sperm after generation, for wind eggs are found in many birds that never produce sperm. This would not be so if wind eggs were generated from the residue of the sperm left after generation. But when female birds desire coition and take pleasure in it, they emit the menses at the opening of the womb, and although the male's sperm does not make contact with this semen, it is still received into the womb, and the female's nature works on it as far as she can. Therefore, she can form an egg from the menses. But because the agent power consists in the male's sperm and the male's sperm does not make contact with the egg or its matter, this egg is not suited for generation and does not have the power for generating something itself.
1. On to the arguments. To the first, one must reply that something can be left behind after the formation of a fetus or a true egg, but this residue is not the material for a wind egg but instead is suited for the generation of a true egg.
2. And one must reply in the same manner to the second argument.
Whether in a wind egg the white has to be distinguished from the yellow.
Further one inquires whether in a wind egg the white has to be distinguished from the yellow.
1. It seems not. The white is to the yellow just as the sperm is to the menses. But females do not always menstruate [ mundificant], as is said in the fifteenth book of this work. Therefore, since the female's power alone generates a wind egg, there will be no white in a wind egg.
2. In addition, the more perfect a power is, the greater differentiation there is. But a woman's power is stronger than a female bird's. Therefore, since the woman's power cannot so distinguish her own menses so that it may resemble the parts of a true fetus, therefore neither will a bird's power distinguish the parts of a wind egg so that it resembles a true egg.
The Philosopher says the opposite, and it is evident to the senses.
One must reply that there is a distinction between the white and the yellow in a wind egg. This is that, just as in a woman, a part of the menses at least is double, one of which results in the material part of the fetus and the other in its nourishment. The first part is more digested than the second because the second will be digested further before it is suited for conversion. The same holds true for a wind egg: there is something that results in the material part of the fetus if there is an approximately analogous agent, and there is something that results in nourishment. The first one is the egg white and the second is the yellow. Therefore, since there is a potent power operating with sufficient heat in a [female] bird's semen, it can distinguish these two in a wind egg without union with a male.
1. On to the arguments. To the first, one must reply that the white is not to the yellow just as the sperm is to the menses, but it is rather more the relationship which the more digested part of the menses has to the less digested.
2. To the second argument one must reply that it occurs analogously in birds and in women, because, just as the female bird's power can distinguish parts of the egg, so the woman's power can, in some manner, distinguish the parts of the menses. But just as an animal cannot be formed from a wind egg, so neither can a human being be formed from a woman's menses by her power alone.