To the first question I answer, if what I have said on the subject of the penetration of the internal mould by organic molecules, in nutrition or expansion, be well understood, it will easily be conceived that these molecules, not being able any longer to penetrate those parts they did before, they will be necessitated to take a different road, and consequently arrive at some part, as the testicles or seminal vessels; for to explain the animal economy, and the different movements of the human body, solely by mechanical principles, is the same as if a man would give an account of a picture by shutting his eyes and feeling on it; for it is evident that neither the circulation of the blood, nor the motion of the muscles, nor the animal functions, can be explained by impulsion, nor other common laws of mechanics: it is as evident that nutrition, expansion, and reproduction, is made by other laws, why therefore not admit of acting and penetrating powers on the masses of bodies, since we have examples of it in gravity, in magnetical attractions, and in chemical affinities? And as we are now convinced by facts, and the multitude of constant and uniform observations, that there exists in nature powers which do not act by the mode of impulsion, why should we not make use of those powers as mechanical principles? Why should we exclude them from the explanations of effects, which we are convinced they produce? Why should we be confined to employ only the power of impulsion? Is not this like judging of a picture by the touch, and explaining the phenomena of the mass by those of the surface, and the penetrating power by superficial action? Is not this making use of one sense instead of another; and, on the whole, is it not confining the faculty of reasoning on a small number of mechanical principles, totally inadequate to follow the various productions of nature. But those penetrating powers being once admitted, is it not natural to suppose that the most analogous particles will unite and bind themselves intimately together; that each part of the body will appropriate the most agreeable to itself, and that from the superfluity of all these particles there will be formed a seminal fluid, which will contain all the organic molecules necessary to form a small organized body, perfectly like that from which this fluid is extracted? A power like that which was necessary to make them penetrate into each part, and produce expansion, may be sufficient to collect them in an organized form, like that of the body in which they originated.