descendants. This morphological phenomenon is a common result of two distinct processes:

Progenesis (Giard, 1887—"generation before [the ancestral time]"): paedomorphosis produced by an acceleration of maturation.

Neoteny (Kollmann, 1885—"retention of young features"): paedomorphosis produced by a retardation of somatic development.

Thus, in this second category of heterochrony, de Beer mixed an aspect of acceleration with one of retardation. The problems of a taxonomy of results are again evident.

7. "A character which is present or makes its appearance in the adult stage of an ancestor may in the ontogeny of a descendant appear in the late adult stage, i.e. too late, resulting in the reduction of the character to a vestige by retardation" (1930, pp. 37–38—Fig. 29D). Here, de Beer merely presents the other side of neoteny (just as he recorded the obverse of deviation in the separate category of reduction). If youthful characters are retarded, then previously adult characters must be gradually "pushed off" the end of ontogeny and eliminated. "Retardation of structures to vestiges is therefore the other side of the picture presented by the phenomenon of neoteny" (p. 75).

8. "A character which is present or makes its appearance in the adult stage of an ancestor may in the ontogeny of a descendant appear in the same stage, which is no longer adult, the new adult stage being relatively delayed, resulting in 'overstepping' the previous ontogenies or hypermorphosis" (1930, pp. 37–38—Fig. 29F). I argued previously that this prolongation of ontogeny results from the retardation of maturation. De Beer (1930, p. 77) agrees: "This additional development or hypermorphosis, may then be expected in cases where the rate of development of the reproductive glands is delayed relatively to that of the body characters."

De Beer's four admissible categories of heterochrony reduce to two processes with a common basis: acceleration and retardation. These processes affect reproductive organs and somatic features differently. We simplify de Beer's complexities by distinguishing true heterochrony from the introduction of new features, and by focusing on processes instead of results. I summarize my reduction of de Beer's categories of heterochrony in Table 3.

A Historical Paradox:
The Supposed Dominance of Recapitulation

My argument has arrived at the following point: Parallels between ontogeny and phylogeny are produced by heterochrony. Heterochrony proceeds by acceleration or retardation. We have no a