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?

There must be some reason why this, the oldest of all, has been recently called a new science, and some explanation of the fact that it has only recently advanced to form a distinct department in our educational system.  The reason is not difficult to find.  Biology is a new science, not because the objects it studies are new, but because it has adopted a new relation to those objects and is studying them from a new standpoint.  Animals and plants have been studied long enough, but not as we now study them.  Perhaps the new attitude adopted toward living nature may be tersely expressed by saying that in the past it has been studied as at rest, while to-day it is studied as in motion.  The older zoologists and botanists confined themselves largely to the study of animals and plants simply as so many museum specimens to be arranged on shelves with appropriate names.  The modern biologist is studying these same objects as intensely active beings and as parts of an ever-changing history.  To the student of natural history fifty years ago, animals and plants were objects to be classified; to the biologist of to-day, they are objects to be explained.