XVI. FERTILIZATION IN PLANTS AND UNICELLULAR ORGANISMS AND ITS IMMEDIATE SIGNIFICANCE 312 XVII. THE GERM-PLASM THEORY 345 XVIII. THE GERM-PLASM THEORY (_continued_) 373 XIX. THE GERM-PLASM THEORY (_continued_) 392 LIST OF ILLUSTRATIONS FIGURE PAGE 1. Group of various races of domestic pigeons 35 2. Longitudinally striped caterpillar of a Satyrid 67 3. Full-grown caterpillar of the Eyed Hawk-moth (_Smerinthus ocellatus_) 67 4. Full-grown caterpillar of the Elephant Hawk-moth (_Chærocampa elpenor_) 68 5. The Eyed Hawk-moth in its 'terrifying attitude' 69 6. Under surface of the wings of _Caligo_ 70 7. Caterpillar of a North American _Darapsa_ 71 8. Caterpillar of the Buckthorn Hawk-moth (_Deilephila hippophaës_) 73 9. _Hebomoja glaucippe_, from India; under surface 76 10. _Xylina vetusta_, in flight and at rest 77 11. _Tropidoderus childreni_, in flying pose 79 12. _Notodonta camelina_, in flight and at rest 80 13. _Kallima paralecta_, from India, right under side of the butterfly at rest 83, 357 14. _Cœnophlebia archidona_, from Bolivia, in its resting attitude 85 15. _Cærois chorinæus_, from the lower Amazon, in its resting attitude 86 16. _Phyllodes ornata_, from Assam 87 17. Caterpillar of _Selenia tetralunaria_, seated on a birch twig 90, 360 18. Upper surfaces of _Acræa egina_, _Papilio ridleyanus_, and _Pseudacræa boisduvalii_ 102 19. Barbed bristles of _Opuntia rafinesquii_ 123 20. Vertical section through a piece of a leaf of the Stinging-nettle (_Urtica dioica_) 123 21. A piece of a twig of Barberry (_Berberis vulgaris_) 124 22. Tragacanth (_Astragalus tragacantha_) 125 23. Bladderwort (_Utricularia grafiana_) 133 24. Pitcher of _Nepenthes villosa_ 134 25. Butterwort (_Pinguicula vulgaris_) 136 26. The Sundew (_Drosera rotundifolia_) 137 27. A leaf of the Sundew 137 28. Leaf of Venus Fly-trap 138