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Heterochrony and the Parallel
of Ontogeny and Phylogeny

Acceleration and Retardation

Confusion in and after Haeckel's Wake

A nice dilemma we have here,
That calls for all our wit:
And at this stage, it don't appear
That we can settle it.

W. S. Gilbert, Trial by Jury

Ernst Haeckel might have borrowed a line from his nation's adversary, Louis XV, and exclaimed: "Après moi le déluge." Once recapitulation had lost its universal status and become but one mode among many, numerous authors tried to elaborate more complete taxonomies of the relationship between ontogeny and phylogeny. These new schemes proliferated under so many criteria of such diverse standing that an almost anarchic confusion soon arose. There is no way that I can bring order to the next few pages. I wish only to record the confusion of these complex schemes as a prelude to my subsequent attempt at resolution and simplification.

The elaborations proceeded from each of Haeckel's laws. Some authors expanded the law of terminal addition; as a basis for classification they used the stage of ontogeny at which new features arise in evolution (traits might also be deleted, and this too could occur at any stage). Many elaborate classifications were based entirely upon the addition and subtraction of characters at various times. Franz (1927), for example, distinguished four "biometabolic modes": (1) prolongation,

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