PAGES 



SUMMARY OF CHAPTERS 



INTRODUCTION 



PART I 



THE THEORY OP DESCENT 

 CHAPTER I 



The Factors of EvoLUTioif 



Importance of Darwin's work for biology and sociology — The four 

 factors at the basis of the theory of descent — Variability, 

 heredity, excessive fecundity, selection — Struggle for existence, 

 indirect as weU as direct — Importance of conflict — Three 

 degrees in the biological value of progeny - . . . 1-10 



CHAPTER II 

 The Mechanism of Heredity 



1. The two great groups of organic beings, miicellulars and multi- 



cellulars — Intermediary forms — Growth of the division of 

 labour : reproductive and somatic cells ; sexual differentiation. 



2. Experiments of Hertwig on the egg of the sea-urchin — 



Mechanism of fecundation — Cellular division, or karyokinesis — 

 Highly complex nature of cellular nucleus— Fundamental impor- 

 tance of the chromosomes — Result of karyokinesis : equal 

 division of chromatic substance, and equal repartition of the 

 chromosomes between the two daughter-cells — ^The germ-plasm — 

 Equal biogenetic value of nucleus in the egg and in the spermato- 

 zoon : experiment of Boveri — Conjugation of Noctiluca — 

 Maturation of the germ-cells — Bole of the chromosomes during 

 the process of maturation — Amphimixis — Adaptation of the 

 egg and the spermatozoon to amphimixis — ^The meaning of 

 amphimixis — ^Experiments of Maupas on infusorians — Experi- 

 ments of Weismann on Cypris reptans — ^Regression of centro- 



