ACCELERATION A speeding up of development in ontogeny (relative to
any criterion of standardization), so that a feature appears earlier in the
ontogeny of a descendant than it did in an ancestor.
ADULTATION Jagersten's term for the appearance, by acceleration, of
adult ancestral characters in the larvae of descendants. A variety of reca-
ADULT VARIATION De Beer's term for the introduction of new features
in the adult stage during evolution.
ALLOMETRY Change of shape correlated with increase or decrease in
size. The change in size may reflect ontogeny, phylogeny, or merely the
static differences among related animals (adults of all mammals, for ex-
ALLOMORPHOSIS Allometry based on the comparison of related individ-
uals, rather than upon ontogeny. Systematic change of shape among suc-
cessive adults of a phyletic sequence, for example, is allomorphosis.
ALTRICIAL A mode of vertebrate ontogeny characterized by large litters,
rapid development, short gestations, and the birth of relatively undevel-
oped, helpless young.
ANABOLY Severtzov's term for evolution by addition of a new feature to
the end of the embryonic period of morphogenesis and before the subse-
quent period in which growth proceeds in geometric similarity.
ANALOGY A similarity between two organisms due to independent evolu-
tion of the similar feature by each—for example, the wings of a bat and a
butterfly. See homology.
*I include all terms for processes and results of the relation of ontogeny and phy-,
logeny, but not, for the most part, names of organisms or parts of the body.