294 Darwin, and after Darwin. 



through more than at most a very few further percentages of its 

 original size. But, after this point has been reached, the now 

 total absence of selection, either for or against the organ, will 

 sooner or later entail this further and most important consequence, 

 a failure of heredity as regards the organ. So long as the 

 organ was of use, its efficiency was constantly maintained by 

 the presence of selection which is merely another way of saying 

 that selection was constantly maintaining the force of heredity as 

 regards that organ. But as soon as the organ ceased to be of 

 use, selection ceased to maintain the force of heredity ; and thus, 

 sooner or later, that force began to waver or fade. Now it is 

 this wavering or fading of the force of heredity, thus originally 

 due to the cessation of selection, that in turn co-operates with 

 the still continued cessation of selection in reducing the structure 

 below the level where its reduction was left by the actual reversal 

 of selection. So that from that level downwards the cessation 

 of selection, and the consequent failing of heredity, act and react 

 in their common work of causing obsolescence. In the case of 

 newly added characters, the force of heredity will be less than 

 in that of more anciently added characters ; and thus we can 

 understand the long endurance of 'vestiges' characteristic 

 of the higher taxonomic divisions, as compared with those 

 characteristic of the lower. But in all cases, if time enough be 

 allowed under the cessation of selection, the force of heredity 

 will eventually fall to zero, when the hitherto obsolescent structure 

 will finally become obsolete. In cases of newly added and 

 comparatively trivial characters, with regard to which reversal 

 of selection is not likely to take place (e.g. slight differences of 

 colour between allied species), cessation of selection is likely to 

 be very soon assisted by a failure in the force of heredity ; seeing 

 that such newly added characters will not be so strongly 

 inherited as are the more ancient characters distinctive of higher 

 taxonomic groups. 



" Let us now turn to Weismann's view of degeneration. First 

 of all, he has omitted to perceive that ' panmixia ' alone (if un- 

 assisted either by reversed selection or an inherent diminishing 

 of the force of heredity) cannot reduce a functionless organ 

 to the condition of a rudiment. Therefore he everywhere 

 represents panmixia (or the mere cessation of selection) as of 



