Organic Evolution. 



197 



to hold good in the history of the individual. They believe 

 that, in the race, the continued functional activity of an 

 organ is necessary for the maintenance of the integrity 

 and perfection of its structure, and that, if not so exercised, 

 the organ will inevitably tend to dwindle to embryonic 

 proportions and to degenerate. The healthy, functionally 

 valuable tissue passes at last into the condition of 

 degenerate, comparatively useless tissue. The force of 

 heredity will long lead to the production in the embryo 

 of the structure which, in the ancestral days of healthy 

 exercise, was to be of service to the organism. At this 

 stage of life the conditions have not changed. The 

 degeneration sets in at that period when the ancestral use 1 

 is persistently denied. There is no reason why " disuse " 

 should in all cases remove all remnants of a structure ; 

 but if the presence of the degenerate tissue is a source of 

 danger to the organism which possesses it, that organism 

 will be eliminated, and those (1) which possess it in an 

 inert, harmless form, or (2) in which it is absent, will 

 survive. Thus natural selection (which will fall under Mr. 

 Eomanes's reversed selection) will step in will in some 

 cases reduce the organ to a harmless and degenerate 

 rudiment, and in others remove the last vestiges of the 

 organ. 



On the whole, even taking into consideration the effects 

 of panmixia, of reversed selection, and of the principle of 

 economy, the reduction of organs is difficult to explain, 

 unless we call into play " disuse " as a co-operating factor. 



Sexual Selection, or Preferential Mating. 



It is well known that, in addition to and apart from 

 the primary sexual differences in animals, there are certain 

 secondary characters by which the males, or occasionally 

 the females, are conspicuous. The antlers of stags, the 

 tail of the peacock, the splendid plumes of the male bird of 

 paradise, the horns or pouches of lizards, the brilliant 

 frilled crest of the newt, the gay colours of male stickle- 



