effected, were not able to reproduce whole series of vibrations, which at an earlier date required the constant and continous participation of consciousness ... if it were not able to reproduce them the more quickly and easily in proportion to the frequency of the repetitions" (1870, in Butler, 1880, p. 81). I doubt that a more charmingly simple explanation for the universality of acceleration has ever been offered: ontogeny is continually condensed because each generation practices it one more time. But it is a minute waltz without a lower limit; the correlation of evolutionary duration and speed of ontogenetic development is perfect, linear and inverse:

As a complicated perception may arise by means of a rapid and superficial reproduction of long and laboriously practiced brain processes, so a germ in the course of its development hurries through a series of phases, hinting at them only. Often and long foreshadowed in theories of varied characters, this conception has only now found correct expression from a naturalist of our own time.34 For truth hides herself under many disguises from those who seek her, but in the end stands unveiled before the eyes of him whom she has chosen. (Hering, 1870, in Butler, 1880, p. 81)

Recapitulation and Darwinism

Although recapitulation quickly became the common property of all evolutionists, it achieved greatest popularity among Lamarckian thinkers. Its two necessary principles—terminal addition and condensation—received easy explanations within theories supporting the inheritance of acquired characters. Moreover, the two principles usually received a common explanation from Lamarckians—for both heritability and developmental rate of an acquired character increased as the producing stimulus became more intense and operated more frequently.

Most Darwinians, although they supported recapitulation as a guide to the tracing of lineages, had no such convenient explanation. They were constrained to identify natural selection as the efficient cause of structures added terminally, but why did terminal addition occur so much more frequently than interpolation within an ontogeny? The principle of condensation presented additional difficulties. One could reap the advantages of simplified causation by trying to link it with natural selection, but these arguments, advanced by F. Miiller, Balfour, Neumayr, and Wiirtemberger, were weak and unpopular. Alternately, one could argue that structures are added by natural selection but shunted back by another process. But this version of condensation not only seemed to require an unknown principle of development—what Weismann (1881, p. 277) called "the in-