cenogenesis

The most important phenomena to be included under the general heading of cenogenesis are, first, the occurrence of food-yolk, and second, those anomalies of development which are classed by Haeckel as heterochronies and heterotopies.

Form and Function A Contribution to the History of Animal Morphology

In this evolutionary appreciation of the facts of embryology we must, of course, take particular care to distinguish sharply and clearly between the primitive, palingenetic (or ancestral) evolutionary processes and those due to cenogenesis.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

When, on the other hand, it has been altered by cenogenesis, or disturbance of development, we find a limitation of the law, which increases in proportion to the introduction of new features by adaptation (cf. Chapter 1.1).

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

By cenogenesis we understand those embryonic processes which we cannot directly correlate with corresponding evolutionary processes, but must regard as modifications or falsifications of them.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

Thus the apparent exceptions to the law can always be traced to cenogenesis.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

For my part, I regard it as the first condition for forming any just idea of the evolutionary process, and I believe that we must, in accordance with it, divide embryology into two sections -- palingenesis, or the science of recapitulated forms; and cenogenesis, or the science of supervening structures.

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876

But without the biogenetic law, without the distinction between palingenesis and cenogenesis, and without the theory of evolution on which we base it, it is quite impossible to understand the facts of organic development; without them we cannot cast the faintest gleam of explanation over this marvellous field of phenomena.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

Hence in the embryology of the higher animals, especially, palingenesis is much restricted by cenogenesis; it is to-day, as a rule, only a faded and much altered picture of the original evolution of the animal's ancestors.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

Such inference becomes more or less precarious when there has been cenogenesis, or disturbance of development, owing to fresh adaptations.

The Evolution of Man — Volume 2 Ernst Heinrich Philipp August Haeckel 1876

In view of these facts, we may now give the following more precise expression to our chief law of biogeny: The evolution of the foetus (or ontogenesis) is a condensed and abbreviated recapitulation of the evolution of the stem (or phylogenesis); and this recapitulation is the more complete in proportion as the original development (or palingenesis) is preserved by a constant heredity; on the other hand, it becomes less complete in proportion as a varying adaptation to new conditions increases the disturbing factors in the development (or cenogenesis).

The Evolution of Man — Volume 1 Ernst Heinrich Philipp August Haeckel 1876