CHAPTER II 



THE PHYSICAL BASIS OF INHERITANCE 



" Gebt mir Materie, und ich will daraus eine Welt schaffen." — Kant. 



" We may regard the nucleus of the cell as the principal organ of 

 inheritance " (a prophecy proved true). — Haeckel, Generelle Morpho- 

 logic 1866, vol. i. p. 288. 



" The cell is not only the seat of vital activity, but is also the vehicle 

 of hereditary transmission ; and the life of successive generations of 

 living beings shows no breach of continuity, but forms a continuous vital 

 stream in which, as Virchow said, rules an ' eternal law of continuity.' " — 

 Wilson, 1900, p. 76. 



§ i. What is true in the Great Majority of Cases. 



§ 2. Diverse Modes of Reproduction. 



§ 3. The Hereditary Relation in Unicellular Organisms. 



§ 4. The Hereditary Relation in the Asexual Multiplica- 

 tion of Multicellular Organisms. 



§ 5. Nature and Origin of the Germ-cells. 



§ 6. Maturation of the Germ-cells. 



§ 7. Amphimixis and the Dual Nature of Inheritance 

 in Sexual Reproduction. 



§ 8. Inheritance in Parthenogenesis. 



§ 9. Wherein the Physical Basis precisely consists. 



§ 1. What is true in the Great Majority of Cases 



The Inheritance is usually carried by the Germ-cells.— 



What was for so long quite hidden from inquiring minds, or but 

 dimly discerned by a few, is now one of the most marvellous of 

 biological commonplaces — that the individual life of the great 

 majority of plants and animals begins in the union of two minute 

 elements — the sperm-cell and the egg-cell. These microscopic 

 individualities unite to form a new individuality, a potential 

 offspring, which will by-and-by develop into a creature like to, 

 and yet different from its parents. If we mean by inheritance 



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