A man deposits seed in a womb and goes away, and then another cause takes it, and labours on it and makes a child. What a thing from such a material! Again, the child passes food down through the throat, and then another cause takes it and makes perception and motion, and in fine life and strength and other things; how many and how strange I Observe then the things which are produced in such a hidden way, and see the power just as we see the power which carries things downwards and upwards, not with the eyes, but still no less plainly.