62 PROBLEMS OF EVOLUTION 



species of butterfly will disappear from the earth. Now the 

 colour of butterflies is in the scales that clothe 

 the wings and body, and these scales are dead 

 structures. They cannot be exercised ; even if 

 they could, it is difficult to imagine that their 

 colours could be altered by such means. On the 

 other hand, the bird's sharpness of sight may im- 

 prove with practice, and, according to Lamarckians, 

 such sharpsightedness may be transmitted to sub- 

 sequent generations. Here, then, we should have 

 birds that have Lamarckian principles to help on 

 their evolution, preying upon butterflies whose 

 progress in protective coloration must be on 

 Weismannite or Nee-Darwinian principles. 



In one and the same organism we might find 

 the same incongruity of rival systems. Birds 

 improve their flight muscles by practice. Many 

 of the best flyers can be seen enjoying them- 

 selves in the air, systematic, if unconscious, 

 assiduity, beyond that of- any gymnast, leading 

 them towards the goal of perfection, towards 

 perfect development and co-adaptation of many 

 muscles, perfect knowledge of gusts of wind 

 and how to deal with them, perfection at every 

 acrobatic feat that the practical needs of life may 

 call upon them to perform. If Lamarck was 

 right, how rapidly such a species must acquire 

 and co-ordinate all the muscles that flight re- 

 quires ! How slow, on the other hand, must be 

 the improvement of dead structures, such as 

 feathers, for which no exercise is possible ! 

 FIG Primary And Y et ^e adaptation of the feathers to the 

 wing feather of needs of .flight is as perfect as the adaptation of 



heron. The outer . ,-,-, . , 



web is narrow. the muscles. To give the wmg its rounded 



concavity beneath and make it impervious to air, 



the outer webs of the great flight feathers have been much 



reduced in width. The air acting mainly on the broader 



