Chapter III

THE FACTORS CONCERNED IN THE BUILDING OF THE LIVING MACHINE.

History of the living machine--Evidence for this history--Historical--Embryological--Anatomical--Significance of these sources of history--Forces at work in the building of the living machine--Reproduction--Heredity--Variation--Inheritance of variations--Method of machine building--Migration and isolation--Direct influence of environment--Consciousness--Summary of Nature's power of building machines--The origin of the cell machine--General summary 131

LIST OF ILLUSTRATIONS.

FIGURE PAGE

_Amoeba Polypodia_ in six successive stages of division _Frontispiece_

1. Figure illustrating osmosis 30

2. Figure illustrating osmosis 31

3. Diagram of the intestinal walls 32

4. Diagram of a single villus 33

5. Enlarged figure of four cells in the villus membrane 33

6. A bit of muscle showing blood-vessels 36

7. A bit of bark showing cellular structure 61

8. Successive stages in the division of the developing
egg 63

9. A typical cell 65

10. Cells at a root tip 66

11. Section of a leaf showing cells of different shapes 66

12. Plant cells with thick walls, from a fern 67

13. Section of potato 67

14. Various shaped wood cells from plant tissue 68

15. A bit of cartilage 68

16. Frogs' blood 69

17. A bit of bone 69

18. Connective tissue 70

19. A piece of nerve fibre 70

20. A muscle fibre 71

21. A complex cell, vorticella 71

22. An amoeba 73

23. A cell as it appears to the modern microscope 86

24. A cell cut into pieces, each containing a bit of
nucleus 89

25. A cell cut in pieces, only one of which contains any
nucleus 90

26. Different forms of nucleii 93

27 and 28. Two stages in cell division 96

29 and 30. Stages in cell division 98

31 and 32. Latest stages in cell division 100

33. An egg 103

34 and 35. Stages in the process of fertilization of the
egg 104

36 and 37. Stages in the process of fertilization of the
egg 105

38, 39, and 40. Stages in fertilization of the egg 106

41 and 42. Latest stages in the fertilization of the egg 109

43 and 44. Two stages in the division of the egg 111

45. A group of cells resulting from division, the first step
in machine building 135

46. A later step in machine building, the gastrula 135

47. The arm of a monkey 144

48. The arm of a bird 144

49. The arm of an ancient half-bird, half-reptile animal 144

50. Diagram to illustrate the principle of heredity 156

THE STORY OF THE LIVING MACHINE.