In these titles we see the decisive advance beyond Johannes Müller. As Goethe had already declared, morphology as such can be formed into a real and profound science. It will then not confine itself pedantically to a registration of forms. It will compare them with each other, and seek the hidden law in the straggling phenomena. It will mark out broad lines that will enable the human mind to grasp its objects in all their fulness. Johannes Müller had only been able to confirm that in the narrower sphere of biology. This was the nerve that gave vitality to zoology and botany, and made them a province of the mind in the higher sense. But the question now was: which laws were detected, and in which category of thought were they to be found? Müller had the theory, but was weak on the practical side. There were the “forms” of animals and plants. What was it that really connected them? What was the reality that corresponded to the philosophic craving of the intelligence? Müller’s next school, the generation immediately preceding Haeckel, that of Du Bois-Reymond, Virchow, and many others, had apparently indicated the solution. They had replaced Müller’s vague general conception of the laws of morphology and life, which was undermined by older influences, by a single great demand. We want to grasp nature as a unity. At one point in nature we have reached deep and apparently fundamental factors—in physics and chemistry and their plain natural laws or forces. Now let us try, starting from the idea of unity and from the plainest of all philosophical principles, that of proceeding from the known to the unknown, to reduce the forms and phenomena of life to these natural laws of chemistry and physics. Let us find out whether the whole form-world of the animals and plants—in other words, the whole province of morphology in the narrower sense—can be traced to the same natural laws that we have in chemical and physical phenomena. The globe is the object of chemistry and physics. Shall these few green or other-coloured things that lie at the limit of the air, water, and rocks, a small minority in nature, the things we call animals and plants, alone in the whole world be exempt from the action of these laws? It is immaterial that Müller’s best pupils, Du Bois in his later years and Virchow at an early date, departed more or less from this consistent position of theirs into philosophic and other sidepaths. The younger generation, to which Haeckel belongs, that only came into direct touch with Müller in his last years, heard no other gospel. What further advance was to be made? In chemistry and physics they had before them the deep stratum that yielded good mechanical laws. The first stage of physiology after Müller, as we find it, for instance, under Du Bois-Reymond, yielded some good indications for the organic. But was the whole of morphology to be remodelled? Was the vast labyrinth of the thousands and thousands of