LECTUEE XXV 

 GERMINAL SELECTION 



On what does disappearance after disuse depend, if not on the Lamarckian principle? 

 —Panmixia— Eomanes— 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 varia- 

 tions — 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 trans- 

 mission 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, whicli 

 can transmit nothing because they do not reproduce. 



We might be inclined to regard tJiis gradual disappearance and 

 ultimate elimination of a disused organ as a direct gain, on tlie 

 ground that the economy of material and space thus effected may be 

 of decided advantage to the individual animal and thereby also for tlie 

 maintenance of the species, and that those animals would have an 

 advantage in the struggle for existence in wliich the superfluous 

 organ was reduced to the smallest expression. But tliat would be 

 far from supplying us with a sufficient explanation of the phenome- 

 non ; the individual variations in the size of an organ wliich is in 



5 

 II. I 



