CONFORMITY TO TYPE 



261 



and among the lower animals, but whiteness and black- 

 ness of the human skin are not Mendelian. On the 

 other hand, the color of the human eyes appears to be 

 a Mendeiian character. Many spontaneously appearing 

 pathological conditions are Mendelian, as, for example, 

 polydactylism or excessive fingers and toes, hemophilia 

 or bleeder's disease, deaf-mutism, color-blindness, etc. 

 The frequency with which generations are skipped in the 

 heredity of such conditions is fully explained by the laws 

 of dominance and recession. 



DIAGRAM EXPLAINING MENDELIAN PROPORTIONS. 



For purposes of convenience we imagine two organisms, one the 

 female (9), black; the other the male, (<?), white, whose cells have 

 but two chromosomes. 



? Black animal. c? White animal. 



Resting germinal cells. 

 Primary Oocytes. Primary Spermato- 

 cyte. 



Preparation for reduction. 

 Appearance of the chromosomes. 



Conjugation of the chromosomes. 



Heterotype mitosis with reduction of the 

 chromosomes. (Reduction Division.) 



Results of the Reduction Division. 



Ovum and Polar body Secondary sperm- 



atocytes. 



Second Division by Homotype Mitosis. 



Outcome of the Second Division. 

 Ovum and three polar Four spermato- 

 (/) (?) (7) bodies. The ovum zoa all equally 

 alone physiologically physiologically 

 functional. functional. 



FIG. 102. 



FIG. 103. 



