But as soon as karyogamy or nuclear fusion was associated with mere plastogamy, complete amphimixis could never be lost again, because it alone made it possible that there should be harmonious transformation and adaptation in organisms which were becoming ever more complex; the primary effect of the mingling would be more and more transcended, since, without amphimixis, transmutation with harmonious adaptation in all directions would be less and less possible as organisms became more complex in structure. I have already referred to the manifold details in the structure and development of the lowest organisms which make this conclusion appear luminous to us, but we can also infer the necessity for an unceasingly active selection, from a quite different set of facts, namely, from what we know of rudimentary organs in Man. We may regard Mankind as a species which has its local races and sub-races, but which is fixed in its essential characters, and only fluctuates hither and thither in individual variation in each sub-race, just like any other modern mammal, such as the marmot or the hare. Nevertheless we know that Man, as regards certain fairly numerous parts, is continually and persistently varying in a definite direction. Wiedersheim, in his book _On the Structure of Man_[23], enumerates a long series of parts and organs of the human body, which are in process of gradual degeneration, and of which it may be predicted that they will disappear from the human structure since they have lost functional significance. Among these dwindling structures are the two last ribs, the eleventh and twelfth, while the thirteenth has already disappeared, and only occurs exceptionally as a small vestige in the adult human being of to-day. The series includes also the seventh cervical rib, the _os centrale_ of the wrist, the wisdom teeth, and the vermiform appendix of the intestine. The last is much larger in many mammals, and represents an important part of the digestive apparatus, but in Man it has dwindled to an unimportant appendage, which is a source of danger when foreign bodies (cherry stones and such like) lodge in it and set up inflammation. The variations in its length warrant us in concluding that it is still in process of degeneration; its average length is about 8½ cm., but it varies from 2 cm. to 23 cm. in length, and in about 25 per cent. of cases a partial or entire closing up of its opening into the intestine may be observed. [23] _Ueber den Bau des Menschen_, 2nd ed., Freiburg-i.-Br., 1893. Trans. London, 1896.