The animal kingdom thus occupied a very important place, and the chief who could count his camels and horses by the hundred was the one who received the greatest honors, and could hold easy dominion over his less wealthy neighbors.

Very early, too, we find that men learned to put a different and greater value on animals than that granted by the mere power of possession, for in many countries they were worshipped as gods, and received divine honors; and even those which were not actually regarded as deities, were in many cases held sacred, from the great reverence which was paid to life.

Thus many animals not used for food, such as cats, dogs, crocodiles, and serpents, were looked upon as sacred to certain divinities, and it was considered an ominous sign to kill one of these, even by accident, while he who should so disregard custom as to be willfully guilty of the death of one was regarded with the greatest horror.

In Egypt this superstition arose largely from the popular belief that the soul of man after death entered the body of some animal as a punishment for the sins committed in life, and the study of medicine was hindered by the abhorrence attached to one who dared to aid his studies by the dissection of a dead animal; but in many cases, as in India to-day, the dislike to slay an animal, needlessly, arose from the awe and mystery which were attached to life, which the mystics of all European and Asiatic nations invested with the utmost sacredness.

For many centuries man was content to know that certain animals could be put to certain uses, and were called by certain names, and let his interest cease at that point.

But later, when Greek civilization and learning had combined to invest all knowledge with priceless value, the animal kingdom began to be looked upon as an interesting study, and Aristotle, whose genius left no branch of knowledge unimproved, may be said to have founded the science of zoölogy when he incorporated among his other works an account of all the animals known to the ancients, and made some attempt at classification and description.

In this work Aristotle sums up such a vast number of statements in regard to the resemblances and differences of animals, their anatomy and the functions of the various organs, that the modern naturalists have only had to follow the way he marked out to arrive at some of the most interesting discoveries in Zoology.

It is supposed that Aristotle was assisted in his zoölogical studies by the great number of strange animals that Alexander the Great had sent to him from Asia and Africa, for this monarch was justly proud of the genius of the famous philosopher, and took pleasure in affording him every opportunity for displaying it.

Aristotle placed the backboned animals first in his order of classification, and distinguished between these and the white-blooded animals, which have no backbone, and are divided into rings or segments.

Although the student who now reads the works of Aristotle will find many statements that are absurd and false, they do not detract from the genius of the man who first conceived the possibility of arranging the different families of the animal kingdom so that they might be intelligently studied, and it has been suggested by an eminent modern authority that the errors in Aristotle's treatise may have arisen from the fact that the students who listened to his lectures incorrectly reported his notes, and that it is these notes which form the greater part of what is now known as Aristotle's treatise on animals.

Hippocrates, who died ten years before the birth of Aristotle, had taught that the practice of medicine could not be properly followed without a knowledge of the structure of the human body, and his studies in zoölogy first led to the foundation of the art of healing upon scientific principles. Many of his descriptions of the symptoms and developments of fevers and other diseases are found accurate to-day, and although his theories have for the greater part fallen into disuse, he will ever be remembered as one of the world's most progressive thinkers, whose work it was to destroy the superstition that all disease resulted from the anger of some offended deity, and to found instead a belief based upon reason and experiment.

Aristotle's influence on thought was shown by the fact that when the great library of Alexandria was founded, there were gardens, menageries, and dissecting rooms especially devoted to the study of zoölogy; and if the results of that period of investigation had not been lost it is probably that many of the modern discoveries in zoölogy would be but the finding again of well-known truths.

After the decline of the Greeks the Arabs became prominent as cultivators of literature, the arts and science. Taking for their motto: "He dies not who gives his life to science," these careful students stored up the priceless treasures of Greek learning, and at time when the nations of Europe were sunk in ignorance and superstition, kept alive the spirit of scientific inquiry and preserved for posterity much of the wisdom of the ancient world.

About the middle of the sixteenth century the study of zoölogy received a fresh impetus from the works of Gesner, a Swiss physician and professor of Natural History at the University of Zurich.

Gesner published a valuable work on animals in which he received the old authorities, contributed many important facts in regard to living species, and gave illustrations of many fossils.

The link between the past and present was formed by the work of Gesner, for modern zoölogy dates from that time; and although nearly a century passed before the appearance of another eminent naturalist, yet the work went slowly on, and the interest in zoölogy kept steadily increasing, so that by the end of the seventeenth century it was possible to indicate a very decided advance in that study.

Harvey had discovered the circulation of the blood, and given the world the benefit of his wonderful anatomical discoveries which revolutionized the study of medicine; Ray had published his classification of the animal kingdom, the scientific merit of which has won him renown; and the use of the microscope had led to the knowledge of those minute forms of animal life which had hitherto escaped observation, and to an acquaintance with the anatomy of insects.

Thus the beginning of the eighteenth century found the world in a state of expectancy in regard to the natural sciences, and the work of Réaumur, who was born early in the century, gave evidence that the time was fruitful in original thinkers.

Réaumur's labors were confined almost entirely to zoölogy, though his experiments in chemistry, wherein he discovered the art of tinning iron, and made several contributions toward the manufacture of iron and steel and porcelain, were of great service in the mechanic's arts.

His work in zoölogy consisted of a most exhaustive study of insects. He describes their habits and anatomy, and was the first zoölogist to bring their instincts into notice. The work was published in six volumes, and has been a valuable source of information to succeeding entomologists.

Linnĉus' work on zoölogy was of great value, as his method of classification enabled students to easily place any animal in its proper order and family, and Buffon, another zoölogist of the eighteenth century, gave to the world a popular illustrated work on the animal kingdom which will ever be remembered as being the inspiration of more than one eminent naturalist.

Buffon's work was not distinguished for the careful exactness which belongs to other writers, but his glowing descriptions, and animated style gave his volumes a peculiar value. Zoölogy from that time ceased to be regarded as the province of the learned, for Buffon had shown that it could be a source of amusement and instruction to the most unscientific; and we have only to call up the picture of Linnĉus and Cuvier sitting in a college library and poring over the fascinating pages of this author to realize the important influence exercised by Buffon in the history of zoölogy.