200 DOCTRINE OF EVOLUTION 



strate evolution, there are certain general aspects of the 

 subject to be considered so as to clear the ground, as it 

 were, for further progress. When the several organic sys- 

 tems of the human body were compared with those of 

 the apes and of lower animals, their evolution was proved 

 as far as the purely physical and material character- 

 istics were concerned. But we know that there is no 

 part of any one of these systems which has not its own 

 particular function, even though this may be a rela- 

 tively passive one; while furthermore, science does 

 not know of any physiological activity without some 

 organ or tissue or cell as its material basis. Therefore 

 the evolution of an organic system in material respects 

 involves its functional or dynamic evolution as an insep- 

 arable correlate; the two proceed in unity, and they 

 cannot be regarded as entirely distinct without violat- 

 ing common-sense. 



The fin of a fish is used as an organ of locomotion in 

 water ; from some such organ have evolved the walking 

 limbs of amphibia and reptiles, constructed for pro- 

 gression upon land. Among the mammalia the fore 

 limbs have become structurally adapted so as to be such 

 diverse organs of locomotion as the stilt-like leg of a 

 horse, the flipper of a seal, the whale's paddle, and the 

 bat's wing, while among the birds the wing may change 

 into a flipper like that of the penguin, or become reduced 

 to a vestige as in Apteryx. We may focus our attention 

 upon the material likenesses and differences in such a 

 series of locomotory organs, but an inevitable accom- 

 paniment of their physical changes in the transforma- 

 tion of species has been an evolution in the functional 

 matter of locomotion. The most complex and dif- 



