Arthropods and vertebrates share some broad features of general organization - elongated, bilaterally symmetrical bodies, with sensory organs up front, excretory structures in the back, and some form of segmentation along the major axis. But the geometry of major internal organs could hardly be more different... Arthropods concentrate their nervous system on their ventral (belly) side as two major cords running along the bottom surface of the animal. The mouth also opens on the ventral side, with the esophagus passing between the two nerve cords, and the stomach and remainder of the digestive tube running along the body above the nerve cords. In vertebrates, and with maximal contrast, the central nervous system runs along the dorsal (top) surface as a single tube culminating in a bulbous brain at the front end. The entire digestive system then runs along the body axis below the nerve cord.
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"Brotherhood by Inversion", p. 321Stephen Jay Gould
» Stephen Jay Gould - all quotes »
Geoffrey also recognized that the opposite orientations of gut and nervous system posed a problem for his claim that insects and vertebrates represent different versions of the same archetypal animal - and he proposed the first account of the inversion theory to resolve this threat to unification. ...Geoffroy pursued the... aim of establishing a "unity of type" that could generate both arthropods and vertebrates from the same basic blueprint. ...The single grand design includes a gut in the middle and the main nerve cords somewhere on the periphery.
Stephen Jay Gould
How ironic. In order to avoid the "nutty" theory of inversion, Gaskell invented the even odder notion of stomachs turning into brains with new guts forming below. No wonder then, that later biologists cast a plague on both speculative houses and opted instead for the obvious alternative: arthropods and vertebrates do not share the same anatomical plan at all, but rather represent two separate evolutionary developments of similar complexity from a much simpler common ancestor that grew neither a discrete gut nor a central nerve cord.
Stephen Jay Gould
Evolution embodies information in every part of every organism. ... This information doesn't have to be copied into the brain at all. It doesn't have to be "represented" in "data structures" in the nervous system. It can be exploited by the nervous system, however, which is designed to rely on, or exploit, the information in the hormonal systems just as it is designed to rely on, or exploit, the information embodied in your limbs and eyes. So there is wisdom, particularly about preferences, embodied in the rest of the body. By using the old bodily systems as a sort of sounding board, or reactive audience, or critic, the central nervous system can be guided - sometimes nudged, sometimes slammed - into wise policies. Put it to the vote of the body, in effect. ...
Daniel C. Dennett
That's where the truth lies, right down here in the gut. Do you know you have more nerve endings in your gut than you have in your head? You can look it up. I know some of you are going to say "I did look it up, and that's not true." That's 'cause you looked it up in a book. Next time, look it up in your gut. I did. My gut tells me that's how our nervous system works.
Stephen Colbert
In France, Étienne Geoffroy Saint-Hilaire attempted to portray the skeleton of vertebrates as a set of modifications upon an archetypal vertebra. In the 1820's, Geoffroy extended his ambitious plan to include annelids and arthropods under that same rubric. ...Vertebrates support their soft parts with an internal skeleton, but insects must live within their vertebrae (a reality, not a metaphor, for Geoffroy). This comparison led to... the claim that a vertebrate rib must represent the same organ as an arthropod leg - and that insects must therefore walk on their own ribs!
Stephen Jay Gould
Gould, Stephen Jay
Govorov, Leonid
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