Note C — PREFATORY NOTE.

Hence, according to Nägeli, every cell of the organism has idioplasm of identical structure. This at once suggests the objection, how can the idioplasm, for instance, of a pollen grain be the same as that of a leaf? Identical idioplasms should always produce identical structures. Nägeli attempts to explain this difficulty by attributing the different results to different "conditions of tension and movement," i.e., a dynamical difference between the idioplasms of the different parts of the organism. (Abstammungslehre, p. 53.)

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.