in A NECESSITY OF THOUGHT 163 



true, it becomes an absolute necessity of 

 thought that there must have been, in 

 the history of organic life, a whole series 

 of special organs appearing from time to 

 time as rudiments, and then, after a 

 period of functional activity, disappear- 

 ing again as vestiges. The course of 

 organic life has certainly been, on the 

 whole, one of progress from lower to 

 higher organisations, and if it be true 

 that all these changes have come about 

 with infinitesimal slowness or even if 

 they have been occasionally rapid there 

 must have been always as many structures 

 in course of preparation for future use, 

 as there were other structures in course 

 of extinction because they were ceasing 

 to be of any use whatever. 



It is curious to observe that Dar- 

 winians, generally, never seem to per- 

 ceive this necessity at all. When they 

 see a rudimentary organ in any animal 



