236 BIOLOGY: GENERAL AND MEDICAL 



The theories most concordant with modern scientific 

 information are Wilson's theory of the z-element and the 

 Mendelian theory. These are not discordant theories, and 

 both may contain the truth; the former is a qualitative, 

 the latter a quantitative demonstration of what may take 

 place. 



REFERENCES. 



O. HERTWIG: "Text-book of the Embryology of Man and Mam- 

 mals." Translated by E. L. Mark, N. Y. 



JOHN C. HEISLER: "A Text-book of Embryology," Phila. 



L. P. McMuRRicn: "The Development of the Human Body/' 

 Philadelphia, 1904. 



C. S. MINOT: "A Laboratory Text-book of Embryology," Phila., 

 1903. 



A. M. MARSHALL: "The Frog, " etc., N. Y M 1906. 



E. B. WILSON: "Recent Researches on the Determination and 

 Heredity of Sex." 1909 



The Encyclopedia Britannica: Article on Sex. 



T. H. MORGAN: "Experimental Zoology." 



