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Updated: June 9, 2025
In his excellent work, On the structure of the Heart in the Amphibia , Carl Rabl has shown how easily these curious cenogenetic facts can be explained by the secondary adaptation of the embryonic structure to the great extension of the food-yelk. The embryology of all the other parts of the vascular system also gives us abundant and valuable data for the purposes of phylogeny.
In this we have throughout taken strict account of the distinction between palingenetic and cenogenetic phenomena. Such inference becomes more or less precarious when there has been cenogenesis, or disturbance of development, owing to fresh adaptations. We cannot understand embryonic development unless we appreciate this very important distinction.
It is the most important source of all for special phylogeny; but it has great defects, and often fails us. We must, above all, clearly distinguish between palingenetic and cenogenetic phenomena. We must never forget that the laws of curtailed and disturbed heredity often make the original course of development almost unrecognisable.
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