In Darwin's time animal breeding was so far advanced that he got his ideas of selection by nature in evolution from the artificial selection practiced by animal breeders. A glance at the pictures will give some idea of the changes that have taken place in the form of some animals since man began to breed them a few thousand years ago. [Illustration: The four-toed ancestor of the present horse, restored from a study of its fossil skeleton. (After Knight in American Museum of Natural History.)] Some Domesticated Animals.--Our domesticated dogs are descended from a number of wolflike forms in various parts of the world. All the present races of cats, on the other hand, seem to be traced back to Egypt. Modern horses are first noted in Europe and Asia, but far older forms flourished on the earth in former geologic periods. It is interesting to note that America was the original home of the horse, although at the time of the earliest explorers the horse was unknown here, the wild horse of the Western plains having arisen from horses introduced by the Spaniards. Long ages ago, the first ancestors of the horse were probably little animals about the size of a fox. The earliest horse we have knowledge of had four toes on the fore and three toes on the hind foot. Thousands of years later we find a larger horse, the size of a sheep, with a three-toed foot. By gradual changes, caused by the tendency of the animals to vary and by the action of the surroundings upon the animal in preserving these variations, there was eventually produced our present horse, an animal with legs adapted for rapid locomotion, with feet particularly fitted for the life in open fields, and with teeth which serve well to seize and grind herbage. Knowledge of this sort was also used by Darwin to show that constant changes in the form of animals have been taking place since life began on the earth. The horse, which for some reason disappeared in this country, continued to exist in Europe, and man, emerging from his early savage condition, began to make use of the animal. We know the horse was domesticated in early Biblical times, and that he soon became one of man's most valued servants. In more recent times, man has begun to change the horse by breeding for certain desired characteristics. In this manner have been established and improved the various types of horses familiar to us as draft horses, coach horses, hackneys, and the trotters. It is needless to say that all the various domesticated animals have been tremendously changed in a similar manner since civilized man has come to live on the earth. When we realize the very great amount of money invested in domesticated animals; that there are over 60,000,000 each of sheep, cattle, and swine and over 20,000,000 horses owned in this country, then we may see how very important a part the domestic animals play in our lives.