Retrogression \Re`tro*gres"sion\, n. [Cf. F. r['e]trogression.
See {Retrograde}, and cf. {Digression}.]
1. The act of retrograding, or going backward;
retrogradation.
[1913 Webster]
2. (Biol.) Backward development; a passing from a higher to a
lower state of organization or structure, as when an
animal, approaching maturity, becomes less highly
organized than would be expected from its earlier stages
or known relationship. Called also {retrograde
development}, and {regressive metamorphism}.
[1913 Webster]