THE KINSHIP OF LIFE. 



33 



degenerate forms. So it is with cave animals, as well as 

 with most organisms of the deep sea or the far North. 

 All forms which are withdrawn from open competition 

 to a solitary and secluded life lose one by one the ad- 

 vantages which competition has gained for them, and 

 are known as degenerate types. What is true of the 

 lower animals is likewise true of man. The highest 

 type of manhood, of human powers and human virtues, 

 will come from victory in the struggle for existence and 

 not from withdrawal from the struggle. Easy living 

 always brings degeneration. The sheltered life is the 

 source of weakness. The desire to get something for 

 nothing is the bane of human society. 



Parallel with the case of general degeneration of 

 type is that of the degeneration of individual parts of the 



organism. An organ well developed in 

 Vestigial organs. ... 



one group of animals or plants may in 



some other be reduced to an imperfect organ or rudi- 

 ment so small or incomplete as not to perform its nor- 

 mal function, or, indeed, to serve any purpose whatever. 

 Such rudimentary or functionless structures may be 

 found in the body of any of the higher animals and in 

 most or all of the higher plants. The appendix vermi- 

 formis and the unused muscles of the ears in man are 

 examples. Such are also the atrophied lung, pelvis, and 

 limbs of the snake, the "thumb" of the bird, the splint 

 bone of the horse, and the like, without mentioning less 

 familiar internal organs. By the theory of descent we 

 may understand how much structures may be retained 

 by the action of the law of heredity, while their reduc- 

 tion may be the result of long-continued disuse, or the 

 growth and selection of other organs at the expense of 

 these which are no longer needed. 



Among a multitude of examples I need refer espe- 

 cially to but one a recent discovery in homology. 



