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FOUNDATIONS OF BIOLOGY 



'architectural necessity,' let us say, for the four-chambered 

 heart to arise from a two- and three-chambered condition 

 and undoubtedly if this were the only example of 'ontogeny 

 repeating phylogeny' the conclusion might be justified. 

 But when one considers the widespread general correspond- 



FIG. 191. Embryos in corresponding stages of development. A, Fish (Shark) ; 

 B, Bird; C, Man. g, gill slits. (From Scott.) 



ence of the developmental stages in higher forms with con- 

 ditions as they exist in the adults of lower forms, the facts 

 almost overwhelmingly force us to go further and conclude 

 that the similarity has its basis in inheritance, in actual 

 blood relationship between the higher and lower forms, in 

 descent with modification evolution. 



