LIST OF ILLUSTRATIONS 



FIG. PAGE 



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



2. — Fertilization of the egg of JVerejs 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 



lo. — An albino male guinea-pig Facing 34 



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



an albino gainea-pig Facing 34 



ijf 



