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the adaptation of an organism occurring in the fetal or larval stage but not retained in the adult form. Examples of cenogénesis are the placenta of mammals (which provides for the respiration, nutrition, and excretion of the fetus), the external gills of the larvae of amphibians, the egg teeth of nestlings (which serve for breaking through the shell), the attachment organs of ascidian larvae, and the tail of the cercaría stage of trema-todes. The term “cenogénesis” was introduced in 1866 by E. Haeckel to designate those features that, in violation of palingenesis (the repetition of distant stages of phylogenesis in the fetal development of an individual organism), make it impossible to trace the sequence of the phylogenetic stages of their precursors during the ontogenesis of modern forms. In other words, cenogenetic features violate the biogenetic law. At the end of the 19th century, the term was used for any change in the course of ontogenesis characteristic of precursors (the German scientists E. Mehnert and F. Keibel). The modern understanding of the term developed as a result of the work of A. N. Severtsov, who retained only the meaning of temporary adaptations or embryo-logical adaptations.
REFERENCESLebedkin, S. I. “Biogeneticheskii zakon i teoriia rekapituliatsii.” Za marksistsko-leninskoe estestvoznanie, 1932, [nos.] 3–4.
Severtsov, A. N. Morfologicheskie zakonomernosti evoliutsii. Moscow-Leningrad, 1939.
Ivanova-Kazas, O. M. Sravnilel’naia embriologiia bespozvonochnykh zhivotnykh. Novosibirsk, 1975.
Haeckel, E. Generelle Morphologie der Organismen, vols. 1–2. Berlin, 1866.
A. S. SEVERTSOV