224 GENERAL BIOLOGY 



same way. On the other hand, when the likeness is super- 

 ficial only, and not fundamental; when it is likeness in 

 function or in superficial appearance, it is called analogy. 

 Thus the wing of a bird and the wing of a butterfly are 



LOUIS AGASSIZ 



(1807-1873) 



A great teacher of zoology, who did much to promote the 

 development of science in North America. 



analogous organs, for though agreeing in form and function 

 they are totally different in structure, and have no com- 

 ponent parts that we can recognize as identical. 



Homology is .therefore, the ordinary criterion by which we 

 judge of the relationship of organisms. In the neck of 



