78 INTRODUCTION TO EVOLUTION 



of embryonic development. Both species inherited the pattern. But each 

 species proceeded to evolve in its own way; thus eventually each came to 

 differ from the ancestor and from the other species. Consequently the later 

 portions of the embryonic developments of the two species differ, even 

 while both retain certain features of the pattern of early embryonic devel- 

 opment inherited from the common ancestor. Evidently, then, recapitula- 

 tion will occur in only those portions of embryonic development which two 

 species share in common. The human embryo, for example, is never a fish 

 or a fish embryo, yet it follows a course of development similar to that of 

 a fish embryo up to a point representing the stage at which the line leading 

 eventually to man diverged from the line leading eventually to modern 

 fishes. 



Embryonic rudiments and reversions add confirmatory evidence of inher- 

 itance of embryonic patterns from common ancestry. 



References and Suggested Readings 



Arey, L. B. Developmental Anatomy, 6th ed. Philadelphia: W. B. Saunders Co., 

 1954. 



Barth, L. G. Embryology, rev. ed. New York: Henry Holt & Co., 1953. 



de Beer, G. R. "The evolution of the Metazoa." In J. Huxley, A. C. Hardy, and 

 E. B. Ford (eds.). Evolution as a Process. London: Allen & Unwin, 1954. 

 Pp. 24-33. 



de Beer, G. R. Embryos and Ancestors, 3rd ed. Oxford: Oxford University 

 Press, 1958. 



Boyden, A. A. "Comparative evolution with special reference to primitive mech- 

 anisms." Evolution, 1 (1953), 21-30. 



Coghill, G. E. Anatomy and the Problem of Behaviour. Cambridge: Cambridge 

 University Press, 1929. 



Corner, G. W. Ourselves Unborn. New Haven: Yale University Press, 1944. 



Gilbert, M. S. Biography of the Unborn. Baltimore: The Williams & Wilkins 

 Co., 1939. 



Hadzi, J. "An attempt to reconstruct the system of animal classification." Sys- 

 tematic Zoology, 2 (1953), 145-154. 



Marcus, E. "On the evolution of the animal phyla." Quarterly Review of Biol- 

 ogy, ^7> (1958), 24-58. 



Romer, A. S. Man and the Vertebrates, 3rd ed. Chicago: Chicago University 

 Press, 1941. (Note particularly Chap. 20.) 



Smith, H. M. "Paleogenesis the modern successor to the biogenetic law." Turtox 

 News, 34 (1956)^ 178-181, 212-216. Chicago: General Biological Supply 

 House. 



