22 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



conveys the ideas of progress, development, im- 

 provement, of increasing differentiation, and of the 

 progressive co-ordination of the functions or organs 

 thus differentiated. 



Degenerative evolution, on the other hand, con- 

 veys the ideas of decline, of decay, and of de- 

 generation, such as the atrophy of the organs of 

 locomotion in Sacculina, the degeneration of the 

 leaves of parasitic plants, or the dissolution of 

 corporate bodies in a declining state. 



We propose to show, however, that these two 

 ideas, which at first sight seem contradictory and 

 mutually exclusive, are found, on a strict examina- 

 tion of the facts, to interpenetrate and complete 

 each other. Degeneration and progress will appear 

 as the two sides of one whole, or as two aspects of 

 the same evolution, and it will be seen that all 

 progress must necessarily be attended by degenera- 

 tion. 



CHAPTER I 



IN THE EVOLUTION OF ORGANS ALL MODIFICATION IS 

 NECESSARILY ATTENDED BY DEGENERATION 



Section I. Preliminary Considerations 



IN order to effect the demonstration which is the 

 object of this chapter, only the phylogenetic modifi- 

 cations of organs will be discussed, setting aside 



