280 



FOOT-NOTES TO EVOLUTION. 



It is true that all advance in one structure implies 

 degradation of some other. This is the so-called " law 

 of compensation." The specialization 

 of the human hand, for example, has been 

 at the cost of the human foot. The 

 power to live by his wits has taken from man something 

 of the strength and spryness of his apelike ancestors. 



Law of 

 compensation 



FIG. 20. Sacculina attach- FIG. 21. Sacculina ; FIG. 22. Saccu- 

 ing itself to the crab. an early stage, lina after absorp- 



(After Lang.) (After Lang.) tion of the limbs. 



(After Lang.) 



Any organ tends to degenerate when its highest func- 

 tion loses importance or is replaced by some other. To 

 have one's food cooked means the reduction of the 

 lower jaw and its muscles. For a bird to trust to its 

 wings means the decline of the strength of its feet. 

 Reduction of unused parts is a universal rule in organic 

 development. Decline in all parts is the essential mean- 

 ing of degeneration. 



In the current discussions of the day the word de- 



