These images show the 2-fold eversion in an early "gastrula" stage, at a stage between the creation of the first and second double curves, and finally almost at the halfway stage.
Images extracted from a video by John M. Sullivan, George Francis and Stuart Levy / Copyright 1998, University of Illinois
The embryo of most of animals belongs to the triploblastic type, made from three fundamental “leafs”: ectoderm, mesoderm and endoderm. At the beginning of the life of the embryo, after 5-7 days, blastula is constituted by endoderm on its inner surface, ectoderm on its outer surface and mesoderm in between. By successive invaginations of the blastula, the three derms will shape the body. The ectoderm will become the skin (not all of it), sensorial organs, and the nervous system; the mesoderm will produce the bones muscles, blood, heart, vascular system, excretion organs and a part of the skin; the endoderm, intestinal mucous and varied digestive glands like the liver. This construction of the body (at the opposite of the insects, shut up in their shells made of endoderm) gives a predisposition for the sensibility to the exterior. René Thom is even talking of alienation to the outer world: “Intelligence is the ability to identify to something else, to others. The human nervous system is an organ of alienation. It allows to be something else than oneself.*”
According to R. Thom, this ternary constitution of the body has to be linked to the ternary constitution of the language itself: the endoderm becoming the subject (S), the mesoderm the verb (V), and the ectoderm the object (O).
“SVO like in the sentence: “The cat eats the mouse”. Like the mesoderm built the bones and the muscles, its identification with the grammatical category of the verb is plain. On the other hand, a certain ambiguity remains about the correspondence between subject-object and ectoderm-endoderm. In the sentence “The cat eats the mouse”, we must, by understanding all action like a predation, make of the endoderm the subject: because at the end the intestinal mucous, of endodermic origin, will assimilate the prey after the digestion. The assimilation objet (prey)-ectoderm, justifies itself by the fact that the ectoderm (…) builds the nervous tissue; and the nervous system, for the vertebrate, is an organ that simulates the state of the exterior world and who contains, at the states of engrams, the shapes of the preys.*”
*Extracts from morphogenèse and imaginaire, René Thom, 1978, CIRCE
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