ASSUMPTION UNDERLYING ALL EVIDENCES OF EVOLUTION 65 



point of anatomical relations and embryonic derivation, entirely differ- 

 ent. The resemblances which are so obvious superficially are examples 

 of analogy, not of homology, and are the result of molding unlike 

 materials into a semblance of likeness in adaptation to a common en- 

 vironment. Analogous structures, while not considered as evidences 

 of kinship, are strong evidences of descent with modification, for their 

 very existence implies that they have been changed from a former 

 condition to one in which they are adapted to a new medium. To 

 illustrate this point, call to mind that both the ichythyosaur and the 

 porpoise (Fig, 42, 5 and C) belong to groups that are fundamentally 

 terrestrial air-breathing vertebrates, and that whatever they have that 

 is fishlike must be interpreted as adaptive modifications for aquatic 

 life. This type of conception and the way in which it bears witness for 

 organic evolution is well brought out in the next chapter by George 

 John Romanes, a chapter that for a generation has been considered a 

 classic. A few of the statements in this chapter would, in all probabil- 

 ity, be somewhat altered if the author were to rewrite it in the light 

 of newer knowledge, but on the whole the statements made would 

 still have the support of the most critical of modern anatomists. 





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