On what does disappearance after disuse depend, if not on the Lamarckian principle?--Panmixia--Romanes--Fluctuations in the determinant-system of the germ-plasm due to unequal nutrition--Persistence of germinal variations in a definite direction--The disappearance of non-functioning parts--Preponderance of minus germinal variations--Law of the retrogression of useless parts--Variation in an upward direction--Artificial selection--Influence of the multiplicity of ids and of sexual reproduction--Personal selection depends on the removal of certain id-variants--Range of influence of germinal selection--Self-regulation of the germ-plasm, which is striving towards stability--Ascending variation-tendencies may persist to excess--Origin of secondary sexual characters--Significance of purely morphological characters--The markings of butterflies. Now that we have recognized that the assumption of a transmission of functional modifications is not justifiable, let us discuss some of the many phenomena to explain which many people believe the Lamarckian principle to be indispensable, and let us inquire whether we are in a position to give any other explanation of these. How has it come about that the effects of use and disuse _appear_ to be inherited? Can we find a sufficient explanation in the principle of selection, and in the natural selection of Darwin and Wallace? The answer to these two questions will be most quickly found if we begin by seeking for an explanation of the disappearance of a part when it ceases to be exercised. That this cannot lie in the Lamarckian principle we have already learnt from the fact that passively functioning parts, such as superfluous wing-veins, also disappear, and that the loss of the wings and degeneration of the ovaries has taken place in worker ants, which can transmit nothing because they do not reproduce.