Ife forms. J. Mol. Evol. 28:98?12. 34. Chatton, E. 1937. Titres et travaux scientifiques (1906?937) de Edouard Chatton. E. Sottano, Sete, France. 35. Clark, C. G., and A. J. Roger. 1995. Direct evidence for secondary loss of mitochondria in Entamoeba histolytica. Proc. Natl. Acad. Sci. USA 92: 6518?521. 36. Cohan, F. M. 1994. Genetic exchange and evolutionary divergence in prokaryotes. Science 264