256 COOK 



alone would be limited to comparatively few generations, and 

 would dispose of superficial and recently acquired characters 

 only, an inference apparently supported by the persistence of 

 many rudimentary organs. 



The extreme constancy of vestigial characters confirms the a 

 ■priori expectation that selection would have little to do with 

 them except to eliminate ; but differences, nevertheless, occur, 

 of which progressive modification without selective influence 

 must necessarily be predicated. 



Weismann's panmixia was intended to represent a view 

 diametrically opposite to that of Darwin, approaching the 

 question of reduction from the side of heredity only, and laid 

 emphasis on the opinion that, selection being discontinued, indis- 

 criminate crossing without reference to the character previously 

 at a premium would result ultimately in the reduction of the 

 selectively developed parts. But even if it be admitted that a 

 reduced average would be attained within specific limits or 

 where intercrossing is possible, panmixia remains entirely inad- 

 equate to explain the progressive elimination of wings, legs, 

 eyes or other important parts of the body, unless it be extended, 

 as in the previous case, to an organic law of economy, a prop- 

 osition logically quite distinct from panmixia. It is of inci- 

 dental interest to note that both Darwin and Weismann have thus 

 tacitly admitted a law of organic motion in the direction of the 

 simplification of organisms, and that this proposition is again 

 the exact opposite of that of Nageli whose " Vervollkommungs- 

 jirincij)'''' works from the simple to the complex. 



The phenomena of degeneration may appear to militate 

 against the idea of a spontaneous organic motion. The belief 

 has been that though organisms are in a sense elastic, in that one 

 or more characters can be far drawn out by selection, they tend 

 more or less promptly to return to what might be viewed as the 

 previous condition of rest or equilibrium. Especially would this 

 be the case where selection has been very acute and has accen- 

 tuated one character at the expense of the total efficiency of the 

 organism with reference to conditions other than that which has 

 determined the special selection. The removal of the latter 

 would then involve the loss of the advantage gained by selec- 



