Embryo Adaptation

or cenogenesis, the adaptation of embryos or larvae in the course of evolution to the environmental conditions in which they develop. Embryo adaptations, arising and ending in the process of embryonic or larval development, are not preserved in the adult organism.

The term “embryo adaptation” was proposed in 1937 by B. S. Matveev as a substitute for “cenogenesis” because the latter term was applied by various authors to any disturbance of palingenesis (that is, the repetition of the stages of phylogenesis in the process of embryogenesis) as well as to embryo adaptation proper. The two terms are used interchangeably in the modern literature. Some examples of embryo adaptation are the placenta in mammals, the fin fold in amphibian larvae, and the fat drop in the pelagic eggs of certain fishes.