248 BIOLOGY: GENERAL AND MEDICAL 



spermatozoa give rise to females and male eggs 

 fertilized by no sex spermatozoa give rise to 

 males. 



In accounting for the conditions of partheno- 

 genesis, it is assumed that females are of two 

 kinds as the result of fertilization by different 

 kinds of spermatozoa, and that their maturation 

 processes differ so that they may give rise to 

 either males or females. These views accord with 

 certain observations made by Doncaster upon the 

 maturation phenomena of insects. 

 From these brief outlines of the theoretical aspects of 

 the problem, it will appear that the matter of sex deter- 

 mination is by no means clear, and that there are diffi- 

 culties in the way. of solving it. 



The theories most concordant with modern scientific 

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

 the Mendelian theory. These are not discordant the- 

 ories, 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., 1906. 



C. E. McCLUNG: The Biological Bulletin, 1902, iii, 43. 



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

 Heredity of Sex," 1909. 



The Encyclopedia Britannica: Article on Sex. 



T. H. MORGAN: "Experimental Zoology." The Biological Bulletin, 

 1902, iii, 56. 



L. DONCASTER: "Determination of Sex," Cambridge University 

 Press, 1914. 



