in that form of biological speculation which is held here to be the soundest.[39] [38] From the Greek. {Πλαστος from verb Πλαττειν to mould. {διηθειν to strain through. [39] The twin metaphor here chosen for the name of a complex natural process should be cleared a little of a certain obscurity of meaning. A mould is familiar to all in domestic and industrial matters, but there are two sides to the metaphorical conception. A plastic object may be moulded by the hand of man as in his ruder, but more laborious days, or it may be pressed into an artificial mould that he has made by means of his hands and tools. One of these we know in the rude pottery made by prehistoric man and the vessel of the potter described by Jeremiah the prophet. We know also those machine-made moulds, so accurate as to be fitted for the coinage of a nation and able to puzzle a clever coiner who tries to copy them. We know the rough hewing of the stone by the sculptor which follows his moulding of the clay. And in Sacred Writ we read of a double process when the Hebrews not content with their object of worship took the golden ear-rings of their women and Aaron “received them at their hand and fashioned it with a graving tool, after he had made it a _molten calf_.” But as no conception of a mould in biological matters, which connotes the rigid accuracy of the coiner’s mould, can represent the truth, the rougher and freer meaning of the term is here employed. A similar double meaning is implicit in the metaphor of the sieve, considered as a human utensil. I believe we owe this idea of a sieve to Professor Thomson, but am not sure on this point. But I have not been able to find any definition as to the way in which the sieve of natural selection is held to act. A sieve is of course for sifting substances, and the size of the mesh is adapted by us for the purpose we have in view. We may want a sieve to hold back for us the fit or good and allow the unfit or bad to pass through, for example wheat and chaff, or we may employ it to separate sand for our purposes from fine gravel. The former is of course the most common of the purposes for which a sieve is used. So here the comparison of personal selection with the action of a sieve agrees with this aspect of a sieve, the fit being retained and the unfit allowed to pass through, thus agreeing with that view of Spencer’s of the survival of the fittest which is held by most authorities to be more accurate than Darwin’s Natural Selection. So the banns between Lamarck and Darwin are published, not for the first time of asking, and who shall say that there is cause or just impediment why these two should not be joined together in holy matrimony?