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. INTRODUCTION. ==Biology a New Science==.--In recent years biology has been spoken of as a new science. Thirty years ago departments of biology were practically unknown in educational institutions. To-day none of our higher institutions of learning considers itself equipped without such a department. This seems to be somewhat strange. Biology is simply the study of living things; and living nature has been studied as long as mankind has studied anything. Even Aristotle, four hundred years before Christ, classified living things. From this foundation down through the centuries living phenomena have received constant attention. Recent centuries have paid more attention to living things than to any other objects in nature. Linnaeus erected his systems of classification before modern chemistry came into existence; the systematic study of zoology antedated that of physics; and long before geology had been conceived in its modern form, the animal and vegetable kingdoms had been comprehended in a scientific system. How, then, can biology be called a new science When it is older than all the others?