proof, insusceptible of refutation. The argument for it is chiefly this: Life exists on a globe once lifeless. How did life begin? If not through spontaneous generation, how did it come? Must it not have been by the operation of those laws and forces which through all time change lifeless into living matter? Very likely, but we do not know. We know nothing whatever of such laws and forces, and we gain nothing by veiling our ignorance under a philosophical necessity.

Moreover, if spontaneous generation occurs as a resultant of any forces, like forces would produce it again. We have never known it to occur. Should it occur, the organisms thus produced would have no bonds of blood relationship with those already in existence. With these they should show no homology, as they could have no inheritance in common. But all known organisms have common homologies. The factors of organic evolution are essentially the same for all. The unity of life amid all its diversity seems to point to origin from a common stock. If not from one stock, the lines of division between one and another are hidden from us. The study of embryology breaks down the time-honoured branch lines of vertebrates, articulates, molluscs, and radiates. The groups of animals are more numerous, more complex, and more intertangled than Cuvier and Agassiz thought. The number of primary branches of animals or plants is uncertain, their boundaries undefined.

If spontaneous generation exists, it is a factor in evolution. If it is a factor, our explanation of the meaning and nature of homology must be fundamentally changed. But it may be that it should be changed. We can not show that spontaneous generation does not exist. All we know is that we have no means of recognising it. If there is now spontaneous generation of

protoplasm, it can not take the form of any creature we know. An organism fresh from the mint of creation would be too small for us to see with any microscope. It would be too simple for us to trace by any instrumentality now in our possession. It could contain but a few molecules, and a molecule in a drop of water is as small as an orange beside the sun. Such a race of creatures, spontaneously generated, without concessions to environment, would grow hoary with the centuries before it came to our notice. Its descendants would have belonged for ages to the unnumbered hosts of microbes before we should be aware of its creation.

Evolution not a creed.

Evolution is not a creed or a body of doctrine to be believed on authority. There is no saving grace in being an evolutionist. There are many who take this name and have no interest in finding out what it means or in making any application of its principles to the affairs of life. For one who cares not to master its ideas there is no power in the word. Evolution is not a panacea or a medicine to be applied to social or personal ills. It is simply an expression of the teaching of enlightened common sense as to the order of changes in life. If its principles are mastered a knowledge of evolution is an aid in the conduct of life, as knowledge of gravitation is essential in the building of machinery.

There is nothing "occult " in the science of evolution. It is not the product of philosophic meditation or of speculative philosophy. It is based on hard facts, and with hard facts it must deal.

It seems to me that it is not true that "Evolution is a new religion, the religion of the future." There are many definitions of religion, but evolution does not fit any of them. It is no more a religion than gravitation is. One may imagine that some enthusiastic follower of

Evolution not a religion.

Newton may, for the first time, have seen the majestic order of the solar system, may have felt how futile was the old notion of guiding angels, one for each planet to hold it up in space. He may have received his first clear vision of the simple relations of the planets, each forever falling toward the sun and toward one another, each one by the same force forever preserved from collision. Such a man might have exclaimed, "Great is gravitation; it is the new religion, the religion of the future! In such manner, men trained in dead traditions, once brought to a clear insight of the noble simplicity and adequacy of the theory of evolution, may have exclaimed, "Great is evolution; it is the new religion, the religion of the future!"

But evolution is religion in the same sense that every truth of the physical universe must be religion. That which is true is the truest thing in the world, and the recognition of the infinite soundness at the heart of the universe is an inseparable part of any worthy religion.

But, whether religion or not, the truths of evolution must be their own witness. They can be neither strengthened nor controverted by any authority which may speak in the name of philosophy or of theology or of re"Roma locuta est; causa finita est"

Science its own witness.

ligion or of reason. is not a dictum which science can regard. Her causes are never finished. No power on earth can give before

hand the answer to her questions. Her only court of appeal is the experience of man.

III.

THE ELEMENTS OF ORGANIC EVOLUTION.

ALL the laws of life, whatever their nature, are valid throughout the organic world. They control the life. processes of man, those of the lower animals, and those of "our brother organisms, the plants." They extend to each in its degree. The fact that the laws of heredity, for example, extend unchanged in essence from one extreme of organic life to another is most vital to our understanding of the nature of life. For such homology as this, for any fact of homology whatsoever, we have found but one cause, the influence of common descent.

There are many elements or factors which enter into the processes of organic evolution, and they stand in varied relations to one another. It is not possible to make a classification of them in which there shall not be inequality and overlapping of elements. For the purpose of our present discussion we may group these forces and factors under eight principal heads.

I. Heredity. This is the "law of persistence in a series of organisms." Throughout Nature each creature tends to reproduce its own qualities and those of its ancestors. "Like begets like." Creatures resemble their ancestors. The germ cell specialized for purposes of reproduction is capable in its development "of repeating the whole with the precision of a work of art." Heredity is the great conservative force of evolution.

Its influence is shown in the persistence of type, in the existence of broad homologies among living forms, in the possibility of natural systems of classification in any group, in the retention of vestigial organs, in the early development and subsequent obliteration of outworn structures once useful to the race or type.

The physical basis of heredity has been in recent years the subject of many elaborate investigations. The complete homology of the germ cell with the one-celled animals, or protozoa, is now generally recognised, and there is large reason to believe that in the bands and loops of the nucleus of the germ cell is found the visible vehicle by which hereditary tendencies are transmitted.

II. Irritability.-All living beings are affected by their environment. Living matter must always respond in some degree to every external stimulus. All living beings are moved by or react from every phase of their surroundings. The nervous system and its associated sense organs are directly related to the conditions of life. They are concessions made to the environment. The power of motion, whatever it may be, requires the guidance obtained from the impressions made by external things. In all animals this knowledge, whatever its degree of completeness, tends to work itself out in action. In plants the same thing is in some degree The essential difference is that, having no power of locomotion, the plant is without a general sensorium. The parts that move-growing rootlets, tips of branches, and the like-have sensibility and power of motion in the same series of cells. The animal, a colony of cells which move as a whole, has a specialized nervous system which guides the whole.

true.

As a rule, the environment does not act directly on the individual. Its influence is felt chiefly in modifying its action, in increasing, diminishing, or changing its