one, not even in the brightest days of Haeckel's triumph, surpassed Hyatt in the exaltation of recapitulation.

Lamarckism and the Memory Analogy

Although Lamarckians30 easily identified the processes that could produce recapitulation, their attempts to explain how these processes operated were surrounded by self-acknowledged frustration and defeat. They avoided the issue assiduously, and contented themselves with displaying the processes and making causal appeals to the mystery of heredity. This frustration merely reflected a more general problem of evolutionary biology before the early years of this century —ignorance of the mechanisms of inheritance. Among the numerous theories posed between Mendel's original work and its rediscovery, one was both attractive to Lamarckians and particularly conducive to an explanation of recapitulation: the analogy of memory and heredity. The general form of the argument was simple and acceptable to all adherents: the acquisition of a character is like learning; since characters so acquired are inherited in proportion to the intensity of their producing stimuli, inheritance is like memory (learning is retained through memory; memory is enhanced by constant repetition over long periods; actions invoked at first by conscious thought become automatic when repeated often enough). Instincts are the unconscious remembrance of things learned so strongly, impressed so indelibly into memory, that the germ cells themselves are affected and pass the trait to future generations. If behavior can be first learned and then inherited as instinct, then morphological features might be acquired and inherited in an analogous way. Thus, ontogeny is the sequential unfolding of characters in the order of their phyletic acquisition: it is the organism's memory of its past history. As Samuel Butler wrote:

The small, structureless, impregnate ovum from which we have each one of us sprung, has a potential recollection of all that has happened to each one of its ancestors prior to the period at which any such ancestor has issued from the bodies of its progenitors—provided, that is to say, a sufficiently deep, or sufficiently often-repeated, impression has been made to admit of its being remembered at all.31 (1877, p. 297)

But what is the physical ground of memory, indeed of all inheritance, if thoughts and things follow the same laws of transmission? What is impressed upon the germ cells to allow them to reproduce a sequence of acquired characters in the proper order? This question divided adherents to the general view: some spoke of vibrations and wave motions (Hering, 1870, in Butler, 1880; Haeckel, 1876), others