Organisation is due to internal causes. Structural characters crystallise out, as it were. “Orthogenesis,” or the definitely determined tendency of evolution to advance in a few directions, is a law for the whole of the animate world. In active response to the stimuli and influences of the environment the organism expresses itself in “organic growth” without any relation to utility. Butterflies in particular, and especially their markings and coloration, are taken as illustrations. In the Darwinian theory of “mimicry” these played a brilliant part. The great resemblance [pg 175] to leaves, to dried twigs, or to well-protected species which are secure from enemies, was regarded as the most convincing proof of the operation of natural selection. But Eimer shows that markings, striping, spots, the development of pattern, and the alleged or real resemblances to leaves, are really subject to definite laws of growth, in obedience to which they gradually appear, developing according to their own internal laws, varying and progressing altogether by internal necessity, and without any reference to advantage or disadvantage, In association with this orthogenesis, Eimer recognises halmatogenesis, correlation and “genepistasis” (coming to a standstill at a fixed and definite stage), and these seem to him to make the Darwinian theory utterly impossible. The text and the illustrations of the book show how, in the sequence of evolution (according to Eimer's laws of transformation), the groupings of stripes, bands, and eye-spots must have appeared on the butterfly's wing, how convex or concave curvings of the contour must have come about at certain points, so that the form of a “leaf” and the lines of its venation resulted, how the eye-spots must have been moulded and shunted, so that they produced the effect of rust or other spots on withered leaves. Particular interest attaches to the detailed arguments against the idea that the butterfly must receive some advantage from its “mimicry.” Even the Darwinians have to admit that in a whole series of cases the advantage is not obvious. They talk with some embarrassment of “pseudomimicry.” [pg 176] Some butterflies that are supposed to be protected have the protective markings on the underside, so that these are actually hidden when the insects are flying from pursuing birds. Many of the leaf-like butterflies are not wood-butterflies at all, but meadow species,47 and so Eimer's arguments continue.

A specially energetic fellow-worker on Eimer's line is W. Haacke, a zoologist of Jena, author of “Gestaltung und Vererbung,” and “Die SchÖpfung des Menschen und seiner Ideale.”48 In the first of these works Haacke combats, energetically and with much detail, Weismann's “preformation theory,” and defends “epigenesis,” for which he endeavours to construct graphic diagrams, his aim being to make a foundation for the inheritance of acquired characters, definitely directed evolution, saltatory, symmetrical, and correlated variation.

The principles of the new school are very widespread to-day, but we cannot here follow their development in the works of individual investigators, such as Reinke, R. Hertwig, O. Hertwig, Wiesner, Hamann, Dreyer, Wolff, Goette, Kassowitz, v. Wettstein, Korschinsky, and others.49