ON CONCEPTION. 585
Whenever B is actually in existence, C also is actually in existence (i. e. moving in some way).
"Whenever A is actually in existence, B is also in actual ex- istence.
Therefore whenever A is in actual existence, C is also in actual existence.
Natural and artificial generation take place after the same manner. 1 Both are instituted for the sake of something fur- ther, and by a kind of providence both direct themselves to a proposed end; both too are first moved by some " form" con- ceived without matter, and are the products of this conception. The brain is the organ of one kind of conception (for in the soul, the organ of which is the brain, art, without the inter- vention of matter, is the "reason" or first cause of the work), the uterus or ovum of the other.
The "conception," therefore, of the uterus or the ovum resem- bles, at least in some sort, the conception of the brain itself, and in a similar way does the " end" inhere in both. For the " species" or " form" of the chick is in the uterus or ovum without the intervention of matter, just as the " reason" of his work is in the artist, e. g. the "reason" of the house in the brain of the builder.
But since the phrase " to be in" is perhaps equivocal, and things are said to be coexistent in various senses, I affirm, further, and say, that the "species" and immaterial "form" of the future chick are, in some sort, the cause of the impregna- tion or fecundation of the uterus, because after intercourse no corporeal substance can be found within that organ.
But how this immaterial cause, this first principle, exists alike in the uterus and brain, or how the conceptions of the brain and uterus, answering to art and nature, resemble or dif- fer from each other, and in what way the thing which fecundates (viz. the internal efficient cause whereby the animal is gene- rated) exists alike in the male and his semen and in the woman and her uterus in the egg also, the mixed work of both sexes andwherein their differences consist,! shall subsequently attempt to explain when I treat generally of the generation of animals (as well of those creatures which are produced by metamor-
1 Arist. cle Part. Aniiu. lib. i, cap. 1.
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