Contents xl 
CHAPTER XXIII 
PAGE 
THE LIFE-CYCLE OF SOME HyMENopTEROUsS INSECTS. BEES . : + 351 
Other Hymenoptera. if A . : : 7 F ‘ » 356 
EXPERIMENTAL STUDY OF THE DETERMINATION 
OF SEX 
CHAPTER XXIV 
INTRODUCTION: THE DIFFERENT KINDS OF SEXUAL INDIVIDUALS . - 363 
Dicecious Species, composed of Unisexual Individuals . ‘ , 365 
Moneecious Species, composed of Bisexual or Hermaphrodite Tnidividwela 368 
Parthenogenetic Species. 3 a . ri ‘ : a . 372 
CHAPTER XXV 
EXTERNAL Facrors OF SEX DETERMINATION . : . . . - 376 
Influence of Food 3 < . . 376 
Supposed Influence of Noutebinent in paving Sex in Nits rl 
other Mammals . . 5 . ‘ . » 384 
Geddes’s and Thomson’s Theory of Sex ‘ . $ 7 e . 387 
CHAPTER XXVI 
INTERNAL Factors OF SEX DETERMINATION . ‘ : 5 - + 391 
: Age of Parents . . . 2 " . a ‘ . é - 391 
Condition of the Germ-cells . : 5 . i : : - 393 
Vigor of the Parents . ‘ : . . . ‘ . . - 393 
Effects of Inbreeding . ‘ ‘ : . . ‘ . . » 394 
Size of the Egg . : : ri ; - ‘i ‘ F - 304 
Ratio of Nucleus to Gitopiacun ‘ "i 396 
The Extrusion of the Polar Bodies, and the canalopaie eae in the 
Sperm-cells . ‘ é . + 397 
The Formation of Male and Female Producing Sperttakodon . . 401 
CHAPTER XXVII 
THE INTERNAL FAcToRS OF SEX DETERMINATION (Continued) . - 407 
The Origin of Gynandromorphs . 7 . : : . 3 + 407 
The Sex of Multiple Embryos. . . . : - 410 
The Sex of Human Twins and Double ‘Monsters é . 411 
Two Recent Theories of Sex Determination based on the Assninpon 
of Male and Female Eggs . F F . : + 413 
The Reduction Process in Parthenogenetic Ege P . : » 415 
Influence of the Cytoplasm . é 7 : fs . . F . 417 
