protoplasm, or at least without traceable lineaments of the future embryo. It was a single cell, apparently essentially like any other cell, a single one of the units of structure of which living organisms are made.

Thence arose the theory of upbuilding or epigenesis (πí, upon, yéveris, birth) of organisms, by the addition of cell upon cell, to the original germ or egg. Each egg cell by segmentation divides into two daughter cells, and these, through the influence of heredity, naturally arrange themselves so that a new organism is formed similar to the parent organism. It was recognized that the form was predetermined by the ancestry, but no longer that the embryo was literally released from encasement within the structure of the egg. The evolution of the individual is thus conceived as the realization of an hereditary tendency.

But "hereditary tendency" is again a metaphorical expression. In biology, we know no "influence" or "tendency" which is not localized somewhere. Any act or modification of an act is a function of some particular organ. To account for the likeness involved in the facts of heredity, we must expect to find some form of organic mechanism.

Such mechanism must exist within the germ cell itself, and its existence as the "physical basis of heredity" is now well established. In a later chapter we shall discuss the nature of this physical basis, the structures within the nucleus of the germ cell which control or preside over the development of the individual. From our knowledge of the operation of the cell in heredity we recognize the facts of epigenesis, and with these a theory of individual evolution, much more subtle than the old theory of encasement.

We may therefore still imagine the maturing of the individual organ as a process of evolution, or unrolling, of the hereditary plan as hidden in the structure of its cells. We may also speak of the same process as a development. To envelop is to make snug. Development is its opposite. To develop is to make free or independent.

From the evolution of the individual it is natural to extend the use of the word evolution or the word development to the changes which characterize the history of a species or other group of animals or plants, a process which has also been called transformism or transmutation. This word transmutation describes the process more literally than either evolution or

development. That species do change their structure with time or with space is a matter of common scientific observation. With the lapse of time, generation following generation, directive influences combine to modify the line of descent. With the separation of individuals by barriers of land and water and varying climate, differing lines of descent are brought into existence. The fact of descent with modification large or small is a matter of common knowledge in the biology of to-day, verified in the hundreds of thousands of species of organisms now known and classified. To call this transmutation of species is but to state the fact. To call it evolution is to suggest a theory that all these changes are but the unrolling of the plan—a movement toward some predetermined end. That this is true we have no means of knowing, and the results as they appear to us seem to be determined by proximate causes alone. Among these proximate causes are differences in structure and in degrees of adaptability among individuals, the operation of the rule of the survival of the best adapted, the inheritance by individuals of the traits of the immediate ancestry, and the effects of climatic changes, and of migrations hampered and unhampered by the presence of physical barriers. The effects of influences like these are considered by most writers as the essential elements in "organic evolution." But a few writers give external influences a secondary place, confining the term. evolution solely to the results of causes resident within the individual.

Speaking broadly we find as a fact that transmutation of species through the geologic ages has been accompanied by increasing divergence of type, by the increased specialization of certain forms, and by the closer and closer adaptation to conditions of life on the part of the forms most highly specialized, the more perfect adaptation and the more elaborate specialization being associated with the greatest variety or variation in environment. Accepting for this process the name of organic evolution, Herbert Spencer has deduced from it the general law that as life endures generation after generation, its character, as shown in structure and function, undergoes constant differentiation and specialization. In this view, the transmutation of species is not merely an observed process, but a primitive necessity involved in the very organization of life itself.

A process of orderly mutation is observed not only in living things but in inanimate objects as well. The features of the surface of the earth pass through a slow process of unrollingfrom primitive chaos to the diversified earth of to-day. Manifestly we cannot imagine a homogeneous earth which could forever retain its homogeneous condition. At least our universe and our earth have not done so. A cooling earth must lose its perfect rotundity, its surface must become diversified, its relation to the sun must cause its equator to differ from its poles. A single homogeneous form of life on this earth could. not remain uniform because it would be thrown under varying conditions. It could not be the same under the tropical sun as under the arctic cold, and the individuals adapted to either would tend to reproduce individuals likewise adapted. There must, then, exist in all things a "tendency " to become specialized and differentiated. In accordance with this tendency, it is conceived that nebulous masses have been concentrated into planets and the generalized creatures of geologic time have been succeeded by variant and specialized forms, their lineal descendants.

The universal formula of the process of evolution is compactly stated by Herbert Spencer in these famous words:

"Evolution is a continuous change from indefinite incoherent homogeneity to a definite coherent heterogeneity of structure and function, through successive differentiations and integrations. In its physical aspect evolution is further an integration of matter with concomitant dissipation of motion."

This formula applies more or less to all forms of orderly change, that is, change due to a persistent cause, a continuous force. Thus solar systems are conceivably formed from nebulæ. Thus continents and mountain chains, islands and river basins are shaped. Thus organisms are derived from parent organisms. Thus all the variant chemical elements may have been (hypothetically) derived through influences as yet not even imagined, from the unknown and probably unknowable primitive element, protyl. The general movement is from the simple to the complex, from the homogeneous to the heterogeneous, from the inexperienced to the experienced, from the undivided to the divided, from the inchoate to the integrated. Whatever

happens in time or is encountered in space promotes evolution. But the kind of evolution thus produced is very different in different kinds of objects.

Biological evolution and cosmic evolution are not the same. From the biological side a certain objection must be made to this philosophical theory of universal or cosmic evolution. In organic and inorganic evolution there is much in common so far as conditions and results are concerned; but these likenesses belong to the realm of analogy, not of homology. They are not true identities because not arising from like causes. The evolution of the face of the earth forces parallel changes in organic life, but the causes of change in the two cases are in no respect the same. The forces or processes by which mountains are built or continents established have no homology with the forces or processes which transformed the progeny of reptiles into mammals or birds. Tendencies in organic development are not mystic purposes, but actual functions of actual organs. Tendencies in inorganic nature are due to the interrelations of mass and force, whatever may be the final meanings attached to these terms or to the terms matter and energy. It is not clear that science has been really advanced through the conception of the essential unity of organic evolution and cosmic evolution. The relatively little the two groups of processes have in common has been overemphasized as compared with their fundamental differences. The laws which govern living matter are in a large extent peculiar to the process of living. Processes which are functions of organs cannot exist where there are no organs. The traits of protoplasm are shown only in the presence of protoplasm. For this reason we may well separate the evolution of astronomy, the evolution of dynamic geology and of physical geography, as well as the purely hypothetical evolution of chemistry, from the observed phenomena of the evolution of life. To regard cosmic evolution and organic evolution as identical or as phases of one process is to obscure facts by verbiage. There are essential elements in each not shared by the other or which are at least not identical when measured in terms of human experience. It is not clear that any force whatever or any sequence of events in the evolution of life is homologous with any force or sequence in the evolution of stars and planets. The unity of forces may be a philosophical necessity. A philosophical necessity or corner in logic is un

known to science. We can recognize no logical necessity until we are in possession of all the facts. No ultimate fact is yet known to science.

For reasons indicated above the term evolution is not wholly acceptable as the name of a branch of science. The term bionomics is a better designation of the changing of organisms influenced through unchanging laws. It is a name broader and more definite than the term organic evolution, it is more euphonious than any phrase meaning life adaptation, it involves and suggests no theory as to the origin of the phenomena it describes.

It is a matter of common observation that organisms change from day to day, and that day by day some alteration in their environment is produced. It is a conclusion from scientific investigation that these changes are greater than they appear. Not only do they affect the individual animal or plant, but they affect all groups of living things, classes or races or species. No character is permanent, no trait of life without change; and as the living organism and groups of organisms are undergoing alteration, so does change take place in the objects of the physical world about them. "Nothing endures," says Huxley, "save the flow of energy and the rational order that pervades it." The structures and objects change their forms and relations, and to forms and relations once abandoned they never return; but the methods of change are, so far as we can see, immutable. The laws of life, the laws of death, and the laws of matter never change. If the invisible forces which rule all visible things are themselves subject to modification and evolution we have not detected it. If these vary, their aberrations are so fine as to defy human observation and computation. In the control of the universe we find no trace of "variableness nor shadow of turning."

But the objects we know do not endure. Only the shortness of human life allows us to speak of species or even of individuals as permanent entities. The mountain chain is no more nearly eternal than the drift of sand. It endures beyond the period of human observation; it antedates and outlasts human history.. So may the species of animal or plant outlast and antedate the lifetime of one man. Its changes are slight even in the lifetime of the race. Thus the species, through the persistence of its type among its changing individuals, has come to be regarded