LIST OF ILLUSTRATIONS 



FIG. PAGE 



1. Egg and sperm of the sea-urchin, Toxopneustes 9 



2. Fertilization of the egg of Nereis 12 



3. Egg of a mouse previous to maturation Facing 14 



4. Maturation and fertilization of the egg of 



a mouse . Facing 14 



5. Diagrams showing the essential facts of 



chromosome reduction in the development 



of the sperm-cells 17 



6. An ordinary fern 21 



7. The prothallus of a fern 23 



8. Diagram showing the chromosome number in 



the spermatogenesis of ordinary animals 



and of the wasp 24 



9. Diagram showing the relation of the body to 



the germ-cells in heredity 29 



10. A young, black guinea-pig Facing 30 



11. An albino female guinea-pig Facing 30 



12. An albino male guinea-pig Facing 30 



13. Pictures of three living guinea-pigs and of the 



preserved skins of three others . . . Facing 32 



14. A black, female guinea-pig, and her young 



Facing 34 



15. An albino male guinea-pig Facing 34 



16. Two of the grown-up young of a black and of 



an albino guinea-pig Facing 34 



ix 



