This idea of differences of structure being due to dynamic rather than to material causes plays a considerable part in Nägeli's theory, but is the point on which he speaks with least certainty—in fact with a noticeable hesitation. He does not clearly explain the phrase "conditions of tension and movement," nor does he give a convincing explanation of the known phenomena as results of the action of dynamic influence.
Nägeli is not the only one who posits dynamic rather than material differences as to the basis of diversities of structure. More recently, Cope has built up a system of evolution founded largely on this idea.—Trans.
[D] This assertion is a direct corollary from the structure of the determinants and the idioplasm. If the idioplasm of the fertilizing cell were to pass through the membrane about the ovum by osmosis, its organized structure would be lost.—Trans.
[E] In order to explain adaptations Nägeli assumes that external influences, if acting at the same point in a given manner for a long time, may induce slight adaptive variations which are perpetuated and increased. On the important subject of adaptation in general Nägeli is almost diametrically opposed to Darwin and Weismann. Nägeli assigns to the principle of utility a very limited sphere; Weismann regards adaptation as all-powerful. According to Nägeli, the organic world would have become much what it is, if natural selection and adaptation had performed no part in the operations of nature. He aptly says, that natural selection prunes the phylogenetic tree, but does not cause new branches to grow. He allows that the principle of selection is well suited to explain the adaptation of organisms to their environment and the suitableness and physiological peculiarities of their structure, but he asserts that in the definiteness of variation of plants and in their progressive differentiation there is evidence of a higher and controlling perfecting principle.—Trans.
[F] Nägeli, like Weismann, arrives at the conclusion that acquired characters are not inherited. He was not content, however, to rest the generalization upon purely speculative grounds, but undertook the experimental demonstration. After seventeen years of work by himself and son, especially upon several species of Hieracium, he satisfied himself that his theory was true to the facts. We all know now how far he fell short of settling the question.—Trans.
[G] The distinctions which Nägeli here erects are, of course, purely arbitrary, and his definitions are suitable for use only in his own thesis.—Trans.
[H] It is interesting to compare this statement with Weismann's recent theory of Germinal Selection.—Trans.
[I] Nägeli's idioplasm corresponds in many respects, though by no means in all, to Weismann's germ-plasm. Weismann's idea of continuity or "immortality," which has been so widely noticed, is set forth with equal clearness, though with less emphasis, by Nägeli.
[J] For a fuller discussion of the notion of these hypothetical units of organic existence, see Weismann's Germinal Selection, (Open Court Publishing Co., Chicago, 1896), especially the foot note, page 230.