GROUNDS AND CONSEQUENCES OF EVOLUTION. 337 



brate is divided by a septum into two ventricles. In the 

 alligator the rudiment of a septum exists, as if either it 

 were in a stage of development from the condition of the 

 fish, or else of disappearance from the condition of the 

 mammal or bird. The splint-bones of the horse's foot 

 are, beyond all question, the rudiments of additional dig- 

 its, either digits in process of development, in the course 

 of generations, or digits in process of disappearance. So 

 the bird has a rudimentary thumb attached to the angle 

 of its wing. Of the same nature is the stumpy caudal 

 extremity of the bird's spinal column, the styloid pro- 

 longation of that of the frog, or even the os coccygis of 

 the human subject. Here, as in many other instances, are 

 structures which are rudimental, and perform no function, 

 or only a greatly modified function, in the economy of the 

 animal; while they are manifestly the same morphological 

 elements or combinations as in other animals execute 

 important and often essential functions. What do they 

 mean? On the hypothesis of independent specific crea- 

 tions, it is necessary to suppose the Creator has introduced 

 again and again certain parts which are functionally use- 

 less. On the principle that structures are adapted to 

 ends, how are structures without an end to be brought 

 under the rule of special creation? But now, if the 

 theory of common genetic descent is admissible, all mys- 

 tery vanishes. With progressive changes in the physical 

 surroundings and necessities of the line of generations, 

 some structures became more important, more exercised, 

 and more developed, while others became less important, 

 less exercised, and less developed; and some finally shrank 

 to mere non-functional rudiments of their former selves. 

 Thus the world of contemporaneous existence affords 

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