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From this point of view the process, which, in its superficial aspect, is epigenesis, appears in essence, to be evolution, in the modified sense adopted in Bonnet's later writings; and development is merely the expansion of a potential organism or "original preformation" according to fixed laws. II. The Evolution of the Sum of Living Beings.
The epigenesis of a spiritual body lies outside his horizon. The volitionist finds all the value of life in the moral nature. For him the good will persists when all else is resolved into nothingness. Character alone, he says, survives the shock of death. All these limited views of survival are symptoms of monophysite ways of thinking.
To these modern preformationists are opposed the modern upholders of epigenesis or gradual differentiation, who attempt to elaborate a mechanical theory of development. And with the contrast between these two schools there is necessarily associated the discussion as to the inheritance or non-inheritance of acquired characters.
And, especially, how do they set to work to build up their organ? Here the whole riddle of the theory of epigenesis, which Weismann wished to do away with as a mystery, is repeated a thousand times and made more difficult.
But we cannot leave M. Flourens without calling our readers' attention to his wonderful tenth chapter, "De la Preexistence des Germes et de l'Epigenese," which opens thus: "Spontaneous generation is only a chimera. This point established, two hypotheses remain: that of 'pre-existence' and that of 'epigenesis'. The one of these hypotheses has as little foundation as the other."
Lewes, they talk of the 'specific shape' assumed by an 'organic plasma' being 'always dependent on the polarity of its molecules, 'or due to the operation of immanent properties; or declare that, in the process of organic evolution, 'each stage determines its successor, 'consensus of the whole impressing a peculiar direction on the development of parts, and the law of Epigenesis necessitating a serial development, insomuch that, 'every part being the effect of a pre-existing, and in turn the cause of a succeeding part, the reason why, when a crab loses its claw, the member is reproduced, is that the group of cells remaining at the stump 'is the necessary condition of the genesis' of precisely that new group which the reproductive process imperatively requires to follow next in order, this second group equally the necessary condition for genesis of the one required third, the third for the fourth, and so on; and that the reason why the thorns of a blackberry admit of somewhat close comparison with the hooks and spines of certain crustaceæ, is that portions of the integument of both plant and crawfish 'tend under similar external forces to develop' into similar forms?
But we cannot leave M. Flourens without calling our readers' attention to his wonderful tenth chapter, "De la Preexistence des Germes et de l'Epigenese," which opens thus: "Spontaneous generation is only a chimaera. This point established, two hypotheses remain: that of pre-existence and that of epigenesis. The one of these hypotheses has as little foundation as the other."
But the work is also significant in its espousal of epigenesis, and, supported as his argument was by observation and logic, it became the prime formulation of that concept of development during the seventeenth and eighteenth centuries.
His statement of epigenetic development is clear: In the egg ... there is no distinct part or prepared matter present, from which the fetus is formed ... an animal which is created by epigenesis attracts, prepares, elaborates, and makes use of the material, all at the same time; the processes of formation and growth are simultaneous ... all its parts are not fashioned simultaneously, but emerge in their due succession and order ... Those parts, I say, are not made similar by any successive union of dissimilar and heterogeneous elements, but spring out of a similar material through the process of generation, have their different elements assigned to them by the same process, and are made dissimilar ... all its parts are formed, nourished, and augmented out of the same material.
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