X CONTENTS. 



CHAPTER III. 



I'AGE 



The Determination of Sex (Hypotheses and Obser- 

 vations) .-.-.-- 32-40 



§ I. The period at which sex is settled. Ploss, Sutton, 



Laulanie, &c. 

 § 2. Over five hundred theories suggested — 

 Theological. 

 Metaphysical. 



Statistical and hypothetical. 

 • Experimental. (Chap. IV.) 

 § 3. Theory of male and female ova requires analysis. 

 § 4. Theory of " polyspermy," or multiple fertilisation, 



dismissed. 

 § 5. The theory of age of elements allowed. Thury, 



Hensen, &c. 

 § 6. Theory of parental age of secondary moment. Hofacker 



and Sadler. 

 § 7. Theories of " comparative vigour," &c., require analysis. 

 § 8. Theory of Starkweather, — many factors combined under 



" superiority." 

 § 9. Darwin's position. 

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

 lation of numbers. 

 § II. The sexes of twins. 



CHAPTER IV. 



The Determination of Sex (Constructive Treatment) - 41-54 



§ I. Nutrition as a factor determining sex. Favourable 

 nutrition tends to females. 

 (a.) Yung's tadpoles. 

 (/a) Cases of bees, 

 (f.) Von vSiebold's observations. 

 {(/.) Case of aphides. 

 (e.) Caterpillars. 

 (/. ) Crustaceans. 

 {g.) Mammals. 

 {A.) Human species. 

 {i.) Plants. 

 § 2. Temperature as a factor. P'avourable conditions tend to 



females. 

 § 3. Summary of factors : — 



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

 (d.) Condition of sex cells, followed by — 

 [c.) Environment of embryo. 

 § 4. General conclusion : — Anabolic conditions favour pro- 

 duction of females, katabolic conditions males. 

 § 5. Hence corroboration of conclusion of Chap. II., that 

 females were preponderatingly anabolic, males 

 katabolic. 

 § 6. Note on Weismann's theory of heredity. 



