vi CONTENTS. 



PAGE 



II. Over five hundred theories suggested -*■ 



Theological. 



Metaphysical. 



Statistical and hypothetical. 



Experimental. (Chap. IV.) 



III. Theory of male and female ova requires analysis. 



IV. Theory of "polyspermy," or multiple fertilization, 



dismissed. 

 V. The theory of age of elements allowed. Thury, 



Hensen, &c. 

 VI. Theory of parental age of secondary moment. Hofacker 

 and Sadler. 



VII. Theoriesof" comparative vigor," &c, require analysis. . 



VIII. Theory of Starkweather, — many factors combined under 



"superiority." 



IX. Darwin's position. 



X. Diising's synthetic treatment, and theory of self-regu- 

 lation of numbers. 



XL The sexes of twins. 



CHAPTER IV. 



The Determination of Sex (Constructive Treatment) - - 36-4S 



I. Nutrition as a factor determining sex. Favorable 



nutrition tends to females. 



(a) Yung's tadpoles. 



(b) Cases of bees. 



(c) Von Siebold's observations. 



(d) Case of aphides. 



(e) Caterpillars. 

 (/) Crustaceans. 

 (g) Mammals. 



(//) Human species. 

 (/) Plants. 



II. Temperature as a factor. Favorable conditions tend to 



females. 



III. Summary of factors : — 



(a) Nutrition, age, &c, of parents affecting — 



(b) Condition of sex-cells, followed by — 



(c) Environment of embryo. 



IV. General conclusion : — Anabolic conditions favor pro- 



duction of females, katabolic conditions males. 



V. Hence corroboration of conclusion of Chap. II., that 

 females were preponderatingly anabolic, males 

 katabolic. 

 VI. Note on Weismann's theory of heredity. 



