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. 
Fic. 20.—Sacculina attach- Fic. 21.—Sacculina; Fic. 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: 
