by it, assumes an essentially different form. For in this case, of course, there is no question of the formation of tissues; the formation of the independent cell that remains independent is determined partly and directly by the influence of the outward conditions of existence, partly by the counteraction exercised by the Plastidules or Micellsthe active, living plasma-molecules of the cell. We may even assume a constant struggle for existence between these latter; and Roux has shown what great importance has to be ascribed to it in regard to change of substance and the nutrition, hence also as regards adaptation and the formation of the elementary organism. However, this molecular selection is just as hypothetical, and as little demonstrable, as the molecular structure which we have to assume (in some form or another) for the plasma. As an hypothesis it is indispensable, and, moreover, both as regards the independent one-celled Protista and for the dependent tissuecells of the Histones.

The more deeply we have recently penetrated into these elementary relations of organic life, and the more we have become acquainted with their intricate correlations, the more highly we have learnt to appreciate the value of the theory of selection, and the grander appears to us Darwin's philosophical and scientific work. For by founding the theory of selection on the struggle for existence, he not only discovered the most important cause of the formation and transformation of organic forms, but he at the same time gave a conclusive answer to one of the greatest philosophical problems, viz. the question as to how arrangements serving a purpose can arise mechanically without causes acting for a purpose.

An endeavour to answer this difficult fundamental question, in accordance with nature, was made as early as the fifth century before Christ, by Empedocles of Agrigentum, the great Greek philosopher. According to him, the forms of animals and plants that serve a purpose, and as we now know them, originated only gradually, and, moreover, owing to the continual struggle of opposing forces of nature; the present living forms he considered the remains of an immensely large number of extinct forms, and, indeed, because they were most advantageously adapted for that struggle, and hence were the most suitable survivors. Empedocles, on the one hand, lays special emphasis on the fact that the structure of the bodies of living creatures serve a purpose; but, on the other hand, he at the same time points out that we must not set up any "principle of intentional design' in explanation of them, as they have arisen in a purely mechanical way by the interaction of natural forces. Fritz Schultze, therefore, in his account of Greek philosophy, justly says, "To have first conceived the grand thought of a theory of tracing the origin of what is suitable from what is unsuitable, is the brilliant merit of Empedocles, and when we consider that his two fundamental principles, love and hate, are the germinal forms of the modern fundamental forces of attraction and revulsion, we cannot assuredly deny Empedocles, the early investigator of nature, our full admiration."

Hence, as regards the solution of this most important question, Empedocles must be regarded as Darwin's earliest predecessor. For although other philosophers of nature, in classic antiquity, especially Lucretius, recognized the great significance of the question, still it was subsequently alto

gether forgotten. Even Kant-as was shown in a preceding chapter-so little estimated its true value, that he considered it absurd even to hope of ever being able to solve the question: "we must, in fact, deny that man can ever gain further insight into the matter."

But as Charles Darwin, by means of his theory of selection, has actually solved this most weighty fundamental question, he has, I repeat it, become a new Newton, the possibility of whose coming Kant considered himself justified in denying for ever. Short-sighted naturalists have, indeed, declared this comparison exaggerated and ridiculous, but have only shown how little they are capable of estimating the philosophical value of Darwinism. For the problems, as well as the means for answering them, were incomparably simpler in the case of Newton's theory of gravitation than in Darwin's theory of selection. For which reason, also, the natural truth of the former theory is at once evident to every cultivated mind, whereas thorough scientific study is necessary for the full appreciation and understanding of the theory of selection. Both, however, have rendered service of equal value, by having cast out the supernatural idea of purposeness in nature, and the miracles. associated with it, from the domain of our scientific knowledge-Newton from the anorganic domain, and Darwin from the domain of organic nature.

The speculative philosophy of recent times has become more and more convinced of the necessity of retracing its steps from the Icarian cloudland of "pure speculation" to the firmer ground of the empiric knowledge of nature, and especially of comprehending the important biological advances of the last generation. Thus Wundt,

Fritz Schultze, G. H. Schneider, B. von Carneri, Spitzer, and others have of late been zealously endeavouring to form a proper estimate of the philosophical significance of Transformism, and in drawing the most important conclusions from Darwin's theories. And Darwinism also forms the basis of the monistic philosophy of Herbert Spencer, Jacob Moleschott, Ludwig Büchner, and others. Hugo Spitzer, especially, has ably pointed out the value of the theory of selection, and how it has thrown a perfectly new light on "teleology in the conception of the world of organisms." Spitzer's Spitzer's "Contributions to the Theory of Descent and to the Methodology of Natural Science" (1886) is, as yet, the fullest attempt correctly to estimate the philosophical importance of Darwinism. It sets aside the supernatural and dualistic "transcendental idea of purposeness;" it gives us in its place the natural and monistic principle of " teleological mechanism."

CHAPTER XII.

DIVISION OF LABOUR AND DIVERGENCE OF FORMS.

PROGRESS AND RETROGRADATION.

Division of Labour (Ergonomy) and Divergence of Forms (Polymorphism). -Physiological Divergence and Morphological Differentiation both necessarily determined by Selection.-Transition of Varieties into Species. The Idea of Species.-Hybridism.-Personal Divergence and Cellular Divergence.-Differentiation of the Tissues.-Primary and Secondary Tissues.-Siphonophora.-Change of Labour (Metergy).— Convergence. The Law of Progress and Perfectioning.-The Laws of the Development of Mankind.-The Relation between Progress and Divergence.-Centralization as Progress.--Retrogradation.—The Origin of Rudimentary Organs by Non-Use and Habits discontinued.-The Doctrine of Purposelessness, or Dysteleology.

WHEN we contemplate the historical development of the organic world in its entirety, we meet with, in the first place as the most general phenomena, two great laws, the law of Divergence and the law of Progress. The principle of Divergence or Separation teaches us, in the first place, as a fact-based upon our knowledge of petrifactions-that the variety and difference of the living forms on our earth has continually increased from the earliest times up to the present. The second principle, that of Progress or of Perfectioning, teaches us-on the same basis of paleontological records-that this divergence has, upon the whole, been