the general theory of Evolution, relates to the manner, or methods, or means by which living organisms are developed, or evolved, from one another; namely, the inherent susceptibility and tendency to variation according to conditions of environment; the preservation and perfection of organs best suited to the needs of the individual in its struggle for existence; the perpetuation of the more favorably organized beings, and the destruction of those less gifted to survive; the operation of natural selection, in which sexual selection is an important factor; and the general proposition that at any given time any given organism represents the result of the foregoing factors, acting in opposition to the hereditary tendency to adhere to the type, or 'breed true'

The Lamarckian Theory of Evolution." The portion of the theory of Development [Evolution] which maintains the common descent of all species of animals and plants from the simplest common original forms might, therefore, in honor of its eminent founder, and with full justice, be called Lamarckian; on the other hand, the theory of Selection, or breeding, might be justly called Darwinism, being that portion of the theory of Development [Evolution] which shows us in what way, and why, the different species of organisms have developed from those simplest primary forms." *

Phylogenetic Evolution. We may quote again from the Century Dictionary the definition of Phylogenetic Evolution: "It is the name for that form of the doctrine of Evolution which insists upon the direct derivation of all forms of life from other antecedent forms, in no other way than as, in ontogeny, offspring are derived from parents, and consequently grades all actual affinities according to propinquity, or remoteness of genetic succession. It presumes, as a rule, such derivation or descent, with modification, is from the more simple to the more complex forms, from low to high in organization, and from the more generalized to the more specialized in structure and function; but it also recognizes retrograde development, degeneration or degradation."

The law of Evolution is put in a terse form by Huxley, who

*Haeckel, "Hist. of Creation," etc., vol. 1. p. 150.

expands the Latin phrase of Harvey "omne vivum ex ovo" into "omnum vivum ex vivo," and carries the evolution idea still further in the phrase " omnis cellule cellula."

The Fact of Evolution Established Beyond Controversy; the Real Nature of Evolution to be Learned only by a Study of the History of Organisms. The followers of Cuvier, with their "immutability of species," recognized the principle of “development" in the sense above defined, but they believed that the metamorphoses, which are called evolution, are the results. of independent originating force, or they discarded the belief altogether. The more modern school, represented by the idea of the "mutability of species," fully accepts both development and evolution as established facts in the order of nature. This principle of evolution is so far-reaching in its application, and so dominates the speculations of our times, that typical illustrations of it as exhibited in the history of organisms are worthy of special study in order that these applications to other things may be correctly made, for only by understanding precisely what evolution is in nature can one apply the term correctly in discussing the philosophical application of it to other things.

What is an Individual?—When we push the analysis of organic nature farther, we meet the question, What is the individual? A very superficial consideration of the problem shows us that the organic individual is not merely the sum of the matter constituting the body of the individual at any particular time. The matter of the individual is not made in the course of the growth, but it is only organized. The matter in the case is the food, which before was not a part of the individual. So that it is true to say that an organic individual develops, but the matter it uses is not in any sense characteristic of the individual, nor is the particular structure of the cells or tissues, for this is common to other individuals, but cach individual differs from others in the mode and purpose of its activities, and in the results of such activities as expressed in its morphological characters.

In other words, the organic individual is what it is in each. case, not by virtue of the chemical or physical materials of which it is composed, but by virtue of the form, structure, and

activity of the whole as constructed. Thus the likeness in form and function, which leads to the classification of organisms as of the same species, does not arise by virtue of likeness of the matter involved in its construction, but by virtue of likeness of the agency by which the particular construction is brought about. To put this proposition in concrete form, a particular cat has the form and function it possesses, not by virtue of any qualities inherent in the bones or muscles or tissues of which it is composed, or in the cells or in the ultimate chemical elements of which it is composed, but its individual characteristics are altogether determined by the fact that it developed from a cat which was its mother.

Descent is the explanation of the particular characteristics of each individual. In dealing with such characteristics, we are dealing with the phenomena of life which are continuous, so far as our experience tells, and depend for their expression not alone upon the immediate surroundings of the individuals, but upon pre-existing living organic individuals, its ancestors.

CHAPTER IX.

WHAT IS AN ORGANISM?—THE CHARACTERISTICS OF THE INDIVIDUAL AND ITS MODE OF DEVELOPMENT.

Mutability of Organisms a Foundation Principle of all Evolution. In an analysis of the meaning of evolution, it is essential to remember, at the outset, that the evolution takes place only in respect of mutable things. The species is said to be mutable, but it is the organic species as contrasted with everything else. The mutability, therefore, is respecting organisms only. I have shown how the organic "species," which one school of naturalists calls "mutable," is in one sense a mere abstract idea but in another it stands for an aggregate of real existing individual organisms. Such an earnest advocate of mutability of species as Oskar Schmidt says, "The retention of species is, moreover, scientifically justifiable and necessary, if only the determining impulses be taken into account and the definition reduced to harmony with reality;" and the definition he gives is, "While we regard species as absolutely mutable, and only relatively stable, we will term it, with Haeckel, the sum of all cycles of reproduction which, under similar conditions of existence, exhibit similar forms."'"*

Morphological Similarity the Characteristic of Species.-The essential notion in species is similarity of form. The fact recorded in the term species is the occurrence in nature of numerous organisms of almost identical form and structureindividuals which seem, in general, to live and grow separately, but are also organically associated together. In order to explain this community of form among the individuals of the same species, we must examine into the laws by which

"The Doctrine of Descent and Darwinism," p. 103, New York, 1878.

the individual attains its form, and to this end we must analyze the characteristics of an organism.

The Definition of an Organism.-Organism may be defined in two ways: we may point to a concrete example and say, "That cat is an organism," and then take away all those characteristics which are peculiar to the particular example, as its hair, its limbs, its eyes, its teeth, in fact, all its special organs and parts, and come down to a fully abstract definition of an organism, of which the cat is a concrete example; or we may take the philosophical definition, and with Kant define the organism to be "that whose every part is at once the means and end of all the rest." For our purposes it is better to combine the two methods, and say, An organism is a living being whose every part is at once the means and end of all the rest; for it should be insisted that, whatever its full meaning may be, living is an essential quality of any organism that either develops or evolves, and the idea of organism includes the necessary relationship of the parts to each other and to the whole.

Living and Performance of Physiological Functions are Essential Parts of the Definition of an Organism. "Under one aspect," says Huxley, "the result of the search after the rationale of animal structure thus set apart is Teleology, or the doctrine of adaptation to purpose; under another aspect it is Physiology."

Inversely, then, a dead animal is not an organism. It is only a mass of organic matter which some organism has constructed. So much are we engaged in handling dead animals and plants that we are apt to overlook this important distinction. Too often the modern naturalist conceives of the organism as only an aggregate of matter having a definite form and structure of parts, as a house might be defined as a building made of mortar and bricks.

A Zoological Specimen in the Museum as much a Vestige of Organism as a Fossil. The animals we see in the zoological museums and dissect in the laboratories are as much remains or vestiges of organisms as are fossils; growth and structure

Thomas Henry Huxley, "An Introduction to the study of Zoology illustrated by the Crayfish," p. 47, New York, 1884.