392 SCOTT. [Vol. V. 



extremely scanty, and indeed what direct evidence there is, tells 

 against it. Thus Galton's researches have brought out the law 

 of "regression to mediocrity," by virtue of which the succeeding 

 generations of a population resemble each other. " In each gen- 

 eration, individuals are found to be tall and short, heavy and 

 light, strong and weak, dark and pale ; and the proportions of 

 those who present these several characteristics in their various 

 degrees, tend to be constant " (No. 20, p. 1 16). Galton's results, 

 which are too long to quote and cannot very well be abridged, 

 tell strongly against attributing any importance to panmixia as 

 a factor in transformation. Lloyd Morgan, following the same 

 line of reasoning, points out that panmixia " can only affect a 

 reduction from the 'survival-mean ' to the ' birth-mean'" (p. 191). 

 " Unless, therefore, some cause be shown why the negative 

 variations should be prepotent over the positive variations, we 

 must, I think, allow that unaided panmixia cannot affect any 

 great amount of reduction " (p. 193). Lankester does not admit 

 that panmixia can explain the reduction of parts, unless assisted 

 by the principle of economy of growth (No. 31, p. 559). But 

 the importance of this principle may be easily overrated. In the 

 admirably thorough investigations of Tornier (No. 54) upon the 

 calcaneo-astragalar joint, it is shown how closely the develop- 

 ment and reduction of facets follows the manner in which the 

 foot is used, and the consequent mechanical necessities. Now, 

 it is incredible that economy of growth should demand the re- 

 duction of these minute facets, when such rudiments as the 

 splint-bones of the horse or the pelvis of the whale are allowed 

 to persist in the organism. Nor is it easy to see how the prin- 

 ciple of economy can apply to domesticated animals, and still 

 more to internal parasites which have such a superabundance of 

 nutriment, and yet the latter are precisely the forms in which 

 reduction of parts has proceeded to the greatest extremes. 

 Among domesticated animals and plants we find that those parts 

 which are not subject to selection are (aside from the effects of 

 correlation and the direct action of the environment, such as too 

 much or too little of certain foods, water, etc.) remarkably con- 

 stant, which by Weismann's theory they should not be. 



Another class of facts, which are very difficult to explain from 

 the standpoint of panmixia, is furnished by certain larvae. In 

 another paper (No. 50) I have examined the development of 



