aristotle says, that seed is that thing which contains in itself a power of moving, whereby it is enabled to produce a being like unto that from whence it was emitted. pythagoras, that seed is the sediment of that which nourisheth us, the froth of the purest blood, of the same nature of the blood and marrow of our bodies. alcmaeon, that it is part of the brain. plato, that it is the deflux of the spinal marrow. epicurus, that it is a fragment torn from the body and soul. democritus, that it proceeds from all the parts of the body, and chiefly from the principal parts, as the tissues and muscles.