Contents 



XI 



CHAPTER XXIII 



The Life-cycle of Some Hy.menopterous Insects. Bees 

 Other Hymenoptera 



PAGE 



351 

 356 



EXPERIMENTAL STUDY OF THE DETERMINATION 



OF SEX 



CHAPTER XXIV 



Introduction : The Different Kinds of Sexual Individuals . . 363 



Dioecious Species, composed of Unisexual Individuals .... 365 



Monoecious Species, composed of Bisexual or Hermaphrodite Individuals 368 



Parthenogenetic Species 372 



CHAPTER XXV 



External Factors of Sex Determination 376 



Influence of Food .......... 376 



Supposed Influence of Nourishment in determining Sex in Man and 



other Mammals . 384 



Geddes's and Thomson's Theory of Sex . . ... 387 



CHAPTER XXVI 



Internal Factors of Sex Determination 

 Age of Parents 

 Condition of the Germ-cells 

 Vigor of the Parents 

 Effects of Inbreeding . 

 Size of the Egg 

 Ratio of Nucleus to Cytoplasm 

 The Extrusion of the Polar Bodies, and the Analogous Process in the 



Sperm-cells 



The Formation of Male and Female Producing Spermatozoa 



391 

 391 

 393 

 393 

 394 

 394 

 396 



397 

 401 



CHAPTER XXVII 



The Internal Factors of Sex Determination {Confimied) . . 407 



The Origin of Gynandromorphs 407 



The Sex of Multiple Embryos 410 



The Sex of Human Twins and Double Monsters 41 1 



Two Recent Theories of Sex Determination based on the Assumption 



of Male and Female Eggs 4^3 



The Reduction Process in Parthenogenetic Eggs 415 



Influence of the Cytoplasm . . . . . . . . .417 



